energies
Article Design and Analysis of a Fully Variable Valve Actuation System
Longxin Jiang 1 , Liang Liu 1,* , Xiaowei Peng 2 and Zhaoping Xu 1 1 School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China; [email protected] (L.J.); [email protected] (Z.X.) 2 Shanghai Space Control Technology Research Institute, Shanghai 201109, China; [email protected] * Correspondence: [email protected]; Tel.: +86-25-84303903
Received: 9 October 2020; Accepted: 1 December 2020; Published: 3 December 2020
Abstract: With the problem of environmental pollution and energy shortage becoming more and more serious, the fuel efficiency of automobile engines has attracted much attention, and variable valve technology is one of the important technologies to solve this problem. A novel fully variable valve actuation (FVVA) system based on a brushless direct current motor (BLDCM) is designed to achieve fully variable valve adjustment. The system uses a crank-moving guide rod mechanism to convert the rotary motion of the BLDCM into the linear motion of the valve. The fully variable valve system can realize real-time continuous adjustment of valve operating parameters through the motion control of BLDCM, including variable valve timing, variable valve opening duration, and variable lift. A BLDCM and a transmission mechanism for the FVVA system is designed in this paper. In order to better analyze the performance of the system, a dynamic model is established. Then, a three closed-loop control method is adopted to realize position control of the valve. Finally, a complete system model is established to verify the theory conclusions. The results show that the system can realize fully variable valve adjustment.
Keywords: fully variable valve actuation; BLDCM; crank-moving guide rod mechanism; motion control
1. Introduction As one of the important components of the engine, the valve train has the advantages of improving engine power, economy, and reducing harmful emissions. It has a wide range of research prospects and application prospects [1]. Traditional valve trains use a fixed mechanical structure to drive the cams. The internal combustion engine can only obtain the best performance under certain operating conditions, not all operating conditions. The variable valve train can realize flexible control of valve parameters. Its advantage is that it can provide a suitable valve opening and closing time or lift under different operating conditions of the engine. It better meets the requirements of engine power, economy, and exhaust emission at different velocities and different loads to improve the overall performance of the engine [2,3]. The variable valve trains are usually divided into cam valve trains and camless valve trains. This includes cam valve trains, such as the VTEC dual camshaft valve timing system developed by Honda. This cam valve train can only achieve extreme adjustment; it cannot meet the requirements of the best performance of the engine under all working conditions. There are many limitations [4–6]. The camless variable valve can be driven by electro-magnetic, electro-hydraulic, or electro-pneumatic actuations. The biggest feature of the electro-magnetic system is the spring system [7,8], which is shown in Figure1a. In this article, it is referred to as an electromechanical camless valve (EMCLV) system. The valve starts in the middle position, and the valve is opened or closed by energizing different coils. This system can realize valve timing, but the valve lift cannot be changed, and the seat speed is difficult to control.
Energies 2020, 13, 6391; doi:10.3390/en13236391 www.mdpi.com/journal/energies Energies 2020, 13, x FOR PEER REVIEW 2 of 17
The biggest feature of the electro-magnetic system is the spring system [7,8], which is shown in Figure 1a. In this article, it is referred to as an electromechanical camless valve (EMCLV) system. The valve starts in the middle position, and the valve is opened or closed by energizing different coils. This system can realize valve timing, but the valve lift cannot be changed, and the seat speed is difficult to control. To solve this problem, an electromagnetic linear actuator valve mechanism is proposed, which is rigidly connected to the valve through the linear actuator and directly drives the valve to achieve variable lift of the valve. The system detects the position of the valve through a linear displacement sensor. However, now, the market does not have a suitable speed sensor to detect the velocity of the valve; therefore, the valve seat velocity is still difficult to control. The electro-hydraulic system [9–11] is quite simple in concept. Due to the elastic characteristics of hydraulic fluid, the system has the characteristics of a liquid spring, which has a certain cushioning effect on the valve seat, and the seating velocity is low. However, the electro-hydraulic system usually uses engine oil as the hydraulic fluid, and its viscosity changes greatly by temperature, so the performance drops sharply at low temperatures. At the same time, it is not easy for hydraulic systems to achieve good energy efficiency, because their kinetic energy cannot be recovered well when the valves decelerate. Moreover, the response speed of the electro-hydraulic system is not high, and the sealing is difficult to solve. The electro-pneumatic system [12] is similar to the electro-hydraulic type, and it replaces the electro-hydraulic driven medium with gas. The inertia of gas motion is small, but the compressibility of gas has become its fatal flaw as a driving medium. In addition, the authors of [13] proposed a new transmission scheme based on motor-driven valves. The crankshaft is not directly connected to the camshaft; instead, the rotary motor directly Energies 2020, 13, 6391 2 of 16 drives the camshaft to drive the rocker arm to control the valve. During the camshaft rotation, the angular velocity of the camshaft is reduced and increased to produce different valve timings. Its Tomechanical solve this problem,complexity an is electromagnetic relatively high, linear and actuatorthe valve valve lift cannot mechanism be adjusted is proposed, continuously, which is rigidlybut the connectedcamshaft tosystem the valve has throughgood performance the linear actuator in terms and of directly seating drives velocity. the valveIn the to literature achieve variable [14], Parlikar lift of theT.A valve. designed The systema disc-shaped detects thecam position with functions of the valve similar through to traditional a linear displacement cams, and made sensor. a non-linear However, now,profile the as market needed. does The not author have modeled a suitable the speed system sensor and todid detect related the experiments velocity of the to change valve; therefore,the valve theaction valve by seat controlling velocity isthe still operation difficult of to control.the motor. It has better flexibility.
FigureFigure 1. 1.The The electromechanical electromechanical camless camless valve valve system: system: (a(a)) Solenoid Solenoid controlled controlled ( b(b)) Motor Motor controlled controlled
The electro-hydraulic system [9–11] is quite simple in concept. Due to the elastic characteristics of hydraulic fluid, the system has the characteristics of a liquid spring, which has a certain cushioning e ffect on the valve seat, and the seating velocity is low. However, the electro-hydraulic system usually uses engine oil as the hydraulic fluid, and its viscosity changes greatly by temperature, so the performance drops sharply at low temperatures. At the same time, it is not easy for hydraulic systems to achieve good energy efficiency, because their kinetic energy cannot be recovered well when the valves decelerate. Moreover, the response speed of the electro-hydraulic system is not high, and the sealing is difficult to solve. The electro-pneumatic system [12] is similar to the electro-hydraulic type, and it replaces the electro-hydraulic driven medium with gas. The inertia of gas motion is small, but the compressibility of gas has become its fatal flaw as a driving medium. In addition, the authors of [13] proposed a new transmission scheme based on motor-driven valves. The crankshaft is not directly connected to the camshaft; instead, the rotary motor directly drives the camshaft to drive the rocker arm to control the valve. During the camshaft rotation, the angular velocity of the camshaft is reduced and increased to produce different valve timings. Its mechanical complexity is relatively high, and the valve lift cannot be adjusted continuously, but the camshaft system has good performance in terms of seating velocity. In the literature [14], Parlikar T.A designed a disc-shaped cam with functions similar to traditional cams, and made a non-linear profile as needed. The author modeled the system and did related experiments to change the valve action by controlling the operation of the motor. It has better flexibility. The traditional motor-driven valve mechanism adopts a cam and spring structure (see Figure1b), and the system needs to overcome a large spring force when opening or closing the valve, so the energy consumption is high. Its mechanical complexity is high, and the valve lift is not adjustable. However, the motor-driven systems are outstanding in transient time and seating velocity. It will be used as Energies 2020, 13, 6391 3 of 16 the benchmark for this FVVA system. However, unlike it, the FVVA system does not apply to the camshaft system but directly drives the valve through the transmission mechanism, with relatively low mechanical complexity. At the same time, the spring structure is eliminated without having to overcome the larger spring force. Different from the electromagnetic valve drive mechanism, the FVVA system uses a relatively mature rotary encoder to obtain the absolute position of the valve, such as an absolute photoelectric encoder, which can obtain the velocity of the valve through the position. This is advantageous to better control the valve seat velocity. Vibration and noise during engine operation can be reduced by reducing the impact of the valve on the seat. In addition, due to the expansion effect of the valve rod after being heated, the traditional camshaft valve driving system adopts the method of reserving valve clearance to solve the problem. Due to the existence of valve clearance, the valve distribution mechanism will produce a certain impact and noise when working. In order to solve this contradiction, some systems adopt a hydraulic tappet column without valve clearance. However, the hydraulic tappet structure has high machining precision, and cannot be adjusted after wear and tear, and can only be replaced directly, so it is rarely used. In the FVVA system, the valve is directly connected to the transmission mechanism, and the influence of the thermal expansion of the valve rod can be solved by recalibration when the valve is closed. This article aims to propose a novel fully variable valve actuation system based on BLDCM to improve fuel efficiency, including motor design, optimized transmission mechanism design, and control strategy design. First, the overall design scheme according to the system requirements is proposed. Then, the structural design and development are completed based on the scheme. Finally, a complete system model is established to achieve the position of the three closed loop control. The results show that this scheme can realize the full flexible valve adjustment.
2. System Overview
2.1. System Requirements In order to achieve the performance of the traditional valve drive system, the system needs to meet the following basic requirements:
1. In order to ensure adequate intake and exhaust, the FVVA system needs to provide a maximum valve lift of 8 mm in general, and it also needs to have the function of adjusting the valve lift. 2. In order to ensure that the internal combustion engine runs at high load and high velocity, the valves need to be able to move to a specified displacement in a short time. For the FVVA system, the important indicator is the transition time of valve opening or closing. The transition time is defined as the time from 5% to 95% of the valve opening or closing position.
For the calculation of the transition time, the engine is generally operated at the maximum velocity nmax = 6000 r/min. The maximum time tmax allowed for valve opening or closing is defined as follows:
60 103 ∆lϕν 1 tmax = × , (1) 360 · nmax · 2 where the maximum continuous crank angle of the valve ∆ϕν is 288◦, so tmax = 4 ms, and the valve transition time needs to be controlled within 4 ms.
3. During the valve closing process, if the seating velocity exceeds a certain range, it is very likely to cause an impact between the valve seat and the valve with the valve rebound. This will easily cause the valve to fail to close in time and affect the ventilation function. It is generally believed that the maximum allowable valve seat velocity is 0.3 m/s [15,16].
2.2. System Structure As shown in Figure2, the FVVA system is mainly composed of an actuator, a valve control unit, a power drive module, and a signal feedback module. The actuator is composed of a BLDCM and Energies 2020, 13, x FOR PEER REVIEW 4 of 17
2.2. System Structure EnergiesAs2020 shown, 13, 6391 in Figure 2, the FVVA system is mainly composed of an actuator, a valve control4 unit, of 16 a power drive module, and a signal feedback module. The actuator is composed of a BLDCM and a acrank crank moving-guide rodrod mechanism. mechanism. The The BLDCM, BLDCM, as a poweras a power source forsource driving for the driving valve movement,the valve itmovement, is used to it provide is used power.to provide The power. crank moving-guideThe crank moving-guide rod mechanism rod mechanism includes a includes rotating a arm rotating and aarm valve and connector, a valve connector, which is usedwhich to is connect used to theconnect BLDCM the BLDCM and the valve.and the It valve. can transform It can transform the rotary the motionrotary motion of the BLDCM of the BLDCM into the into linear the motion linear motion of the valve. of the valve.
Figure 2. Structure of the FVVA system. Figure 2. Structure of the FVVA system. The electronic variable valve system eliminates the traditional camshaft. The valve timing and The electronic variable valve system eliminates the traditional camshaft. The valve timing and valve lift can be adjusted flexibly according to the working conditions of the engine. In this system, valve lift can be adjusted flexibly according to the working conditions of the engine. In this system, the engine control unit controls the work of the engine. The valve control unit collects the valve timing the engine control unit controls the work of the engine. The valve control unit collects the valve timing and valve lift signals, and the signal feedback module feeds back the running state of the motor to the and valve lift signals, and the signal feedback module feeds back the running state of the motor to valve control unit; then, the valve control unit determines its output through the control algorithm. the valve control unit; then, the valve control unit determines its output through the control The power drive module amplifies the signal to control the velocity and position of the BLDCM. algorithm. The power drive module amplifies the signal to control the velocity and position of the Through the control of the actuator, the control of valve operating parameters can be realized. BLDCM. Through the control of the actuator, the control of valve operating parameters can be 3.realized. Structure Design
3.1.3. Structure Requirement Design Analysis Ideally, after receiving the control command, the actuator should drive the valve with the maximum 3.1. Requirement Analysis current to uniformly accelerate and move at the maximum acceleration. When reaching the midpoint of the targetIdeally, position, after thereceiving valve should the control be driven command, to uniformly the actuator decelerate should with thedrive maximum the valve acceleration with the throughmaximum the current maximum to uniformly reverse current. accelerate When and themove valve at the reaches maximum the target acceleration. position, When the velocity reaching is exactlythe midpoint 0, so that of the the valve target movement position, can the meet valve the should requirements be driven of a quickto uniformly response decelerate and seating with velocity the atmaximum the same acceleration time. The maximum through th valvee maximum lift is required reverse tocurrent. be 8 mm, When and the the valve transition reaches time the is target 4 ms. Accordingposition, the to thevelocity law of is kinematics,exactly 0, so the that acceleration the valve thatmovement the valve can should meet reachthe requirements is 935 m/s2. Therefore,of a quick theresponse maximum and seating acceleration velocity of the at valvethe same should time. be The the maximum design goal valve in the lift design. is required to be 8 mm, and the transitionFigure2 shows time is the 4 ms. structure According of the to FVVA the law system. of kinematics, The BLDCM the isacceleration connected that to the the valve valve through should areach crank-moving is 935 m/s guide2. Therefore, rod mechanism, the maximum which acceleration comprises a of valve the connectorvalve should and be arotating the design arm. goal Through in the thisdesign. mechanism, the rotary motion of the BLDCM can be converted into the linear motion of the valve. The lengthFigure of 2 the shows rotating the structure arm has a of great the influenceFVVA system on the. The performance BLDCM is of connected the drive system.to the valve Determining through thea crank-moving appropriate arm guide length rod provides mechanism, maximum which acceleration comprises and a ensures valve connector the quick response and a rotating of the system. arm. AssumingThrough this that mechanism, the length of the the rotary boom ismotionR and of the th acceleratione BLDCM can of the be BLDCMconverted is α into, the the expression linear motion of the accelerationof the valve. of The the valvelength is: of the rotating arm has a great influence on the performance of the drive system. Determining the appropriate arm lengtha = Rprovidesα. maximum acceleration and ensures the(2) quick response of the system. Assuming that the length of the boom is 𝑅 and the acceleration of the BLDCMAssuming is 𝛼, the the expression motor rotation of the acceleration angle is very of small,the valve the is: linear relationship between the valve displacement and motor rotation angle can be considered, and the relationship between motor torque and acceleration is: 𝑎=𝑅𝛼. (2) h 2i T = J + (m + m1)R α, (3)
Energies 2020, 13, 6391 5 of 16
where J is the moment of inertia of the motor, m is the mass of the valve, m1 is the mass of the valve connector, and the rotating arm is made of an aluminum alloy structure. The moment of inertia is not considered during the design, and the angular acceleration of the motor rotor is:
T α = 2 . (4) J+(m+m1)R
By substituting Formula (4) into Formula (2), the valve acceleration can be obtained:
TR a = 2 . (5) J+(m+m1)R
Taking the derivative of a with respect to R results in:
T[J+(m+m )R2] 2T(m+m )R2 da = 1 − 1 (6) dR 2 2 . [J+(m+m1)R ]
By setting the derivative equal to zero, one finds the rotating arm length that provides maximum acceleration: q R = J . (7) m+m1 Substituting Formula (7) into Formula (5), the maximum valve acceleration is obtained as follows:
a = TmaxR = Tmax max J+(m+m )R2 . (8) 1 2 √J(m+m1)
It can be seen from Formula (8) that the maximum acceleration of the valve movement is related to the maximum torque of the motor, the moment of inertia of the motor, and the quality of the valve and the valve connection. In order to ensure the linear relationship between the valve displacement and the motor rotation angle, the motor rotation angle is required to be limited to 20◦, then the minimum arm length of the corresponding rotating arm is: q R = J xmax , (9) m+m1 ≥ θmax where xmax is the maximum valve displacement and θmax is the maximum angle of motor rotation, then the minimum moment of inertia requirement of the motor is:
2 xmax (m+m1) J 2 . (10) ≥ θmax Therefore, based on the above theoretical analysis, the steps to determine the structural parameters are as follows:
1. According to Formula (10), the minimum moment of inertia of the motor is related to the maximum lift of the valve and the mass of the valve and the valve connector. The motor rotation angle is required to be limited to 20◦. 2. According to Formula (7), in order to ensure that the motor can provide the maximum acceleration of the valve, the arm length can be determined. In the design stage, the inertia of the rotating arm and the mass of the valve connector cannot be calculated, which can be temporarily ignored. It can be verified after the design is finished. 3. According to Formula (8), the drive capacity of the motor is estimated through the motor parameters. It is necessary to ensure that the acceleration of the valve can meet the theoretical requirements. 4. After determining the mechanism parameters, step 2 and step 3 are repeated, considering the moment of inertia of the rotating arm and the mass of the valve connector to ensure that the actuator meets the requirements. Energies 2020, 13, 6391 6 of 16
3.2. Structure Design of the BLDCM According to the previous section, two important standards for motor design are as follows:
1. First, determine the minimum moment of inertia of the motor. In this system, the valve mass is 48 g, the maximum valve lift is 8 mm, and the rotation angle of the motor is limited to less than 20◦. According to Formula (10), the minimum inertia of the motor is 2.54 10 5 kg m2. × − · 2. After determining the arm length, according to Formula (8), the maximum acceleration of the valve is proportional to the maximum torque of the motor, and inversely proportional to the moment of inertia of the motor. It is necessary to ensure that the acceleration capability of the valve meets the theoretical requirements, namely a 935 m/s2. ≥ In the motor design, the maximum torque of the motor is mainly related to factors, such as air gap flux density, current, and coil length. The thickness of different permanent magnets and the air gap will have a great impact on the air gap magnetic flux density. Under the constraints of external dimensions, the thicker the permanent magnet, the smaller the air gap size, and the greater the air gap flux density that can be achieved. However, as the thickness of the permanent magnets of the rotor increases, the rotor inertia will also increase, and the stator yoke will become more and more saturated. The reduction in the size of the air gap will inevitably lead to a reduction in the size of the coil, which will also lead to a drop in electromagnetic force. Therefore, it is necessary to find suitable structural parameters through optimized design to ensure that sufficient acceleration can be provided when the motor moment of inertia meets the requirements. Maxwell can realize the parameterized analysis function, so the maximum acceleration that the valve can reach should be the optimization goal in the motor design. In the range of an outer diameter of 60 mm and length of 60 mm, with a permanent magnet size, stator and rotor inner and outer diameter, and motor length as variables, after a large number of variable parameter calculations, the final solution that can achieve the maximum acceleration is selected. Table1 shows the basic parameters of the BLDCM. Figure3 shows the 2-D flux density distribution of the BLDCM. At this time, the maximum torque that the motor can reach is 5.94 N m, the moment of inertia of the motor is 4.75 10 5 kg m2, and the mass of · × − · the valve is 48 g. According to Formula (8), the maximum acceleration that can be reached is 1967 m/s2, which meets the design index of the motor.
Table 1. Main parameters of the BLDCM.
Name Parameters Outer diameter of the stator 60.8 mm inner diameter of the stator 38 mm Outer diameter of the rotor 37 mm inner diameter of the rotor 28 mm Length of the motor 59 mm The rated voltage 48 V Phase resistance 0.61 Ω Phase inductance 0.57 mH Constant torque 0.198 N m/A · Peak current 30 A The moment of inertia 4.75 10 5 kg m2 × − · Energies 2020, 13, x FOR PEER REVIEW 6 of 17
3. According to Formula (8), the drive capacity of the motor is estimated through the motor parameters. It is necessary to ensure that the acceleration of the valve can meet the theoretical requirements. 4. After determining the mechanism parameters, step 2 and step 3 are repeated, considering the moment of inertia of the rotating arm and the mass of the valve connector to ensure that the actuator meets the requirements.
3.2. Structure Design of the BLDCM According to the previous section, two important standards for motor design are as follows: 1. First, determine the minimum moment of inertia of the motor. In this system, the valve mass is 48 g, the maximum valve lift is 8 mm, and the rotation angle of the motor is limited to less than 20°. According to Formula (10), the minimum inertia of the motor is 2.54 × 10−5 kg·m2. 2. After determining the arm length, according to Formula (8), the maximum acceleration of the valve is proportional to the maximum torque of the motor, and inversely proportional to the moment of inertia of the motor. It is necessary to ensure that the acceleration capability of the valve meets the theoretical requirements, namely a ≥ 935 m/s2.
In the motor design, the maximum torque of the motor is mainly related to factors, such as air gap flux density, current, and coil length. The thickness of different permanent magnets and the air gap will have a great impact on the air gap magnetic flux density. Under the constraints of external dimensions, the thicker the permanent magnet, the smaller the air gap size, and the greater the air gap flux density that can be achieved. However, as the thickness of the permanent magnets of the rotor increases, the rotor inertia will also increase, and the stator yoke will become more and more saturated. The reduction in the size of the air gap will inevitably lead to a reduction in the size of the coil, which will also lead to a drop in electromagnetic force. Therefore, it is necessary to find suitable structural parameters through optimized design to ensure that sufficient acceleration can be provided when the motor moment of inertia meets the requirements. Maxwell can realize the parameterized analysis function, so the maximum acceleration that the valve can reach should be the optimization goal in the motor design. In the range of an outer diameter of 60 mm and length of 60 mm, with a permanent magnet size, stator and rotor inner and outer diameter, and motor length as variables, after a large number of variable parameter calculations, the final solution that can achieve the maximum acceleration is selected. Table 1 shows the basic parameters of the BLDCM. Figure 3 shows the 2-D flux density distribution of the BLDCM. At this time, the maximum torque that the motor can reach is 5.94 N·m, the moment of inertia of the motor −5 2 Energiesis 4.75 2020 × ,10 13, x kg·mFOR PEER, and REVIEW the mass of the valve is 48 g. According to Formula (8), the maximum7 of 17 2 accelerationEnergies 2020, 13 that, 6391 can be reached is 1967 m/s , which meets the design index of the motor. 7 of 16 Figure 3. 2-D flux density distribution of the BLDCM.
Table 1. Main parameters of the BLDCM.
Name Parameters Outer diameter of the stator 60.8 mm inner diameter of the stator 38 mm Outer diameter of the rotor 37 mm inner diameter of the rotor 28 mm Length of the motor 59 mm The rated voltage 48 V Phase resistance 0.61 Ω Phase inductance 0.57 mH Constant torque 0.198 N·m/A Peak current 30 A The moment of inertia 4.75 × 10−5 kg·m2 Figure 3. 2-D flux density distribution of the BLDCM.
3.3.3.3. Structure Structure Design Design of ofthe the Cr Crank-Movingank-Moving Guide Guide Rod Rod Mechanism Mechanism FigureFigure 44 shows shows the the structure structure diagram diagram of of the the cr crank-movingank-moving guide guide rod rod mechanism. mechanism. The The valve valve and and thethe valve valve connector connector are are connected connected by by the the valve holderholder andand thethe valvevalve lock lock clip. clip. The The valve valve holder holder and and the thevalve valve connector connector are are connected connected by threads, by threads, so that so thethat valve the valve lock clip lock and clip the and valve the groove valve groove form a relativelyform a relativelyfirm clamping-type firm clamping-type fit. It can ensurefit. It can that ensure the valve that connector the valve can connector drive the can valve drive to move the valve quickly. to move Due to quickly.the relative Due slidingto the relative of the rotating sliding arm of the and rotating the valve arm connector, and the valve the rotating connector, arm andthe therotating valve arm connector and theneed valve to useconnector materials need with to lessuse materials friction to with reduce less wear friction and to tear. reduce At the wear same and time, tear. in At order the tosame reduce time, the inquality, order to the reduce method the shown quality, in Figurethe method4 is adopted. shown in The Figure material 4 is ofadopted. the shaft The sleeve material is graphite of the copper, shaft sleevethe material is graphite of the copper, hole sleeve the ismaterial titanium of alloy, the hole and thesleeve rotating is titanium arm and alloy, valve and connecting the rotating parts are arm made and of valvealuminum connecting alloy withparts a are relatively made lowof aluminum density. As alloy mentioned with a in relatively the previous low section, density. the As motor mentioned parameters in thewere previous determined, section, combined the motor with parameters Formula (7); were when determined, R = 31.5 mm, combined it can provide with the Formula maximum (7); accelerationwhen R = 31.5of themm, valve. it can provide the maximum acceleration of the valve.
FigureFigure 4. 4.TheThe crank-moving crank-moving guide guide rod rod mechanism. mechanism. 3.4. Actuator Design Verification 3.4. Actuator Design Verification BasedBased on on the the analysis analysis in in the the previous previous section, section, in in order order to increase the valvevalve accelerationacceleration asas much much as aspossible, possible, the the motormotor rotatingrotating shaftshaft adopts a hollow structure, structure, and and the the end end of of the the transmission transmission shaft shaft adoptsadopts a aD-shaped D-shaped structure structure for for connecting connecting with with the the crank crank moving moving guide guide rod rod mechanism. mechanism. The The valve valve positionposition signal signal is iscollected collected by by a a14-bit 14-bit photoelect photoelectricric encoder encoder and and connected connected to tothe the motor motor drive drive shaft. shaft.
Energies 2020, 13, 6391 8 of 16
Considering the moment of inertia of the arm sleeve and the mass of the valve connection, the total moment of inertia of the rotating part at this time is 6.8 10 5 kg m2, and the mass of the moving part × − · is 62.6 g. At this time, the initial boom arm length when the maximum acceleration of the valve can be provided is corrected to R = 33 mm. Compared with the initial design arm length change, it can ignore the inertia and mass changes caused by the arm length change. The structural parameters of the actuator at this time are shown in Table2. According to Formula (8), the maximum acceleration that the valve can reach at this time is 1440 m/s2, and it meets the design requirements.
Table 2. Main parameters of the actuator. Energies 2020, 13, x FOR PEER REVIEW 8 of 17 Name Moment of Inertia (kg m2) Name Mass (g) · 5 Considering the momentRotor of inertia of the4.75 arm10 sleev− e and the massValve of the valve connection, 48 the total × 5 moment of inertia Shaftof the rotating part at1.06 this time10− is 6.8 × 10−5Valve kg·m connector2, and the mass 9of the moving part × 5 is 62.6 g. At thisRotating time, the arm initial boom 0.37arm length10− when the maximumHole sleeve acceleration 2.5 of the valve can × 5 Shaft sleeve 0.27 10− Valve lock clip 1.2 be provided is corrected to R = 33 mm. Compared× 5 with the initial design arm length change, it can Encoder 0.35 10− Valve holder 1.9 ignore the inertia and mass changes caused× by 5the arm length change. The structural parameters of Total 6.8 10− Total 62.6 the actuator at this time are shown in Table× 2. According to Formula (8), the maximum acceleration that the valve can reach at this time is 1440 m/s2, and it meets the design requirements. According to thethe aboveabove analysisanalysis andand design,design, thethe developmentdevelopment of thethe variablevariable valvevalve actuatoractuator based on BLDCMBLDCM hashas beenbeen completed.completed. The main componentscomponents are shown in the Figure5 5,, wherewhere thethe valvevalve andand thethe valvevalve locklock clipsclips usedused areare existingexisting products.products.
Figure 5. The main components of the actuator.
4. Modeling and Analysis Table 2. Main parameters of the actuator.
4.1. Model for the FVVASystemName Moment of Inertia (kg·m2) Name Mass (g) Rotor 4.75 × 10−5 Valve 48 The system is a mechanical-electrical coupling multi-physics system composed of the BLDCM, Shaft 1.06 × 10−5 Valve connector 9 the crank-moving guide rod mechanism, and the valve. Therefore, mathematical models of the mechanical, Rotating arm 0.37 × 10−5 Hole sleeve 2.5 electrical, and magnetic subsystems are established respectively when modeling [17]. Shaft sleeve 0.27 × 10−5 Valve lock clip 1.2 In the mechanical subsystem, the mechanism can be simplified as shown in Figure6. The forces Encoder 0.35 × 10−5 Valve holder 1.9 received by the moving parts include the driving force Tmag, the mechanical damping force Fc, and the Total 6.8 × 10−5 Total 62.6 gas pressure F0 from the combustion chamber of the internal combustion engine. The mechanical damping force includes the air resistance during operation and the mechanical friction between the 4. Modeling and Analysis system mechanisms. 4.1. Model for the FVVA System The system is a mechanical-electrical coupling multi-physics system composed of the BLDCM, the crank-moving guide rod mechanism, and the valve. Therefore, mathematical models of the mechanical, electrical, and magnetic subsystems are established respectively when modeling [17]. In the mechanical subsystem, the mechanism can be simplified as shown in Figure 6. The forces received by the moving parts include the driving force Tmag, the mechanical damping force Fc, and the gas pressure F0 from the combustion chamber of the internal combustion engine. The mechanical damping force includes the air resistance during operation and the mechanical friction between the system mechanisms.
Energies 2020, 13, 6391 9 of 16 Energies 2020, 13, x FOR PEER REVIEW 9 of 17
FigureFigure 6. 6. DiagramDiagram of of the the dynamical dynamical model. model.
SinceSince the swingswing angle angle of of the the motor motor is very is very small, small, it can beit can assumed be assumed that there that is a linearthere relationshipis a linear relationshipbetween the between valve displacement the valve displacement and the swing and angle theof swing the motor. angle Accordingof the motor. to the According dynamic to model the dynamicdiagram, model the differential diagram, equation the differential of the motion equation process of the in themotion FVVAsystem process in has the the FVVA following system expression has the : following expression: . T m + J v = mag F F (11) 𝐽 R2 𝑇 R c 0, 𝑚 + 𝑣 = −𝐹−−𝐹−, (11) 𝑅 𝑅 where the mechanical damping force is Fc = cv, the electromagnetic driving torque is Tmag. Since only wherevalve motionthe mechanical control anddamping seating force performance is Fc = cv, controlthe electromagnetic are considered driving in this torque article, is the Tmag fully. Since variable only valvevalve motion was not control loaded and into seating the engine performance to run. control This article are considered does not in consider this article,F0, sothe the fully valve variable force valveequation was is:not loaded into the engine to run. This article does not consider F0, so the valve force . T equation is: m + J v = mag cv, (12) R2 R − 𝐽 𝑇 where m is the total mass of the component 𝑚 + 𝑣 moving= −𝑐𝑣, with the valve, including the valve connector, (12) 𝑅 𝑅 the valve lock clamp, the valve holder, and the valve; J is the total moment of inertia of the rotating whereparts followingm is the total the BLDCM, mass of includingthe component the motor moving rotor, with the rotatingthe valve, shaft, including and the the rotating valve arm;connector,v is the thevelocity valve oflock the clamp, valve; andthe valvec is the holder, mechanical and the damping valve; Jcoe is thefficient. total moment of inertia of the rotating parts Infollowing the circuit the subsystem, BLDCM, including the stator the winding motor of rotor, the BLDCM the rotating is a three-phaseshaft, and the Y-shaped rotating connection, arm; v is theand velocity it adopts of athe two-two valve; conductionand c is the mode.mechanical To simplify damping the coefficient. analysis, it can be assumed as follows [18]: In the circuit subsystem, the stator winding of the BLDCM is a three-phase Y-shaped connection, and1. it Theadopts stator a two-two three-phase conduction windings mode. are symmetrical,To simplify the and analysis, the stator it can current be assumed and the as rotor follows magnetic [18]: field are symmetrically distributed.
1.2. TheExcluding stator three-phase the influence windings of eddy are current symmetrical, and hysteresis and the loss. stator current and the rotor magnetic field are symmetrically distributed. 3. Ignore the armature reaction and cogging effect of the motor. 2. Excluding the influence of eddy current and hysteresis loss. 4. Ignore the power loss in the control circuit. 3. Ignore the armature reaction and cogging effect of the motor. 4. IgnoreAt this the time, power the three-phaseloss in the control winding circuit. of the motor is equivalent to a series circuit of resistance and inductance, and the motor balance equation is as follows: At this time, the three-phase winding of the motor is equivalent to a series circuit of resistance and inductance, and the motor balance equation is as difollows: U = ri + L dt + e. (13) 𝑑𝑖 𝑈=𝑟𝑖+𝐿 +𝑒. (13) Thus, the voltage equation of the three-phase𝑑𝑡 winding is:
Thus, the voltage equation of the three-phase winding is: di u r 0 0 i L M 0 0 a e a a dt a − dib ub = 0 r 0 ib + 0 L M 0 + eb , (14) − dt dic uc 0 0 r ic 0 0 L M ec − dt
Energies 2020, 13, x FOR PEER REVIEW 10 of 17
𝑑𝑖 ⎡ ⎤ 𝑑𝑡 𝑢 𝑟00𝑖 𝐿−𝑀 0 ⎢ ⎥ 𝑒 𝑑𝑖 𝑢 = 0𝑟0 𝑖 + 0𝐿−𝑀0 ⎢ ⎥ + 𝑒 , (14) ⎢ 𝑑𝑡 ⎥ 𝑢 00𝑟𝑖 00𝐿−𝑀 𝑒 ⎢𝑑𝑖 ⎥ Energies 2020, 13, 6391 ⎣ 𝑑𝑡 ⎦ 10 of 16 where 𝑟 is the phase winding inductance; 𝐿 is the resistance of the phase; 𝑀 is the mutual whereinductance;r is the 𝑖 phase, 𝑖 , 𝑖 winding are phase inductance; currents;L is𝑢 the, 𝑢 resistance, 𝑢 are phase of the voltages; phase; M isand the 𝑒 mutual , 𝑒 , 𝑒 inductance; are back electromagneticia, ib, ic are phase forces currents; (EMFs).ua, u Accordingb, uc are phase to the voltages; voltage andequation,ea, eb, ethec are equivalent back electromagnetic circuit is shown forces in (EMFs).Figure 7. According to the voltage equation, the equivalent circuit is shown in Figure7.
Figure 7. Equivalent circuit diagram.
As thethe statorstator winding winding of of the the BLDCM BLDCM is ais three-phase a three-phase Y-shaped Y-shaped connection, connection, compared compared with phasewith phasevoltage, voltage, line voltage line voltage is easier is easier to measure. to measure. Therefore, Therefore, line voltageline voltage model model is adopted is adopted here, here, and and the theformula formula is as is follows: as follows: 𝑑𝑖 𝑑𝑖dia dib uab r 0 0 ia ib L M 0 0 ea eb − − ⎡ − dt ⎤− dt − 𝑑𝑡 𝑑𝑡dib dic u𝑢bc = 0 r 0 𝑖 −𝑖ib ic + 0 L M 0 ⎢ ⎥ 𝑒 −𝑒+ eb ec . (15) 𝑟00 − 𝐿−𝑀 − 0 𝑑𝑖 𝑑𝑖dt dt − dic − dia u𝑢ca = 0𝑟00 0 r 𝑖 −𝑖ic i + a 0𝐿−𝑀00 0 L M⎢ − ⎥ + 𝑒 −𝑒 .ec ea (15) − − 𝑑𝑡 𝑑𝑡dt − dt − 𝑢 00𝑟𝑖 −𝑖 00𝐿−𝑀⎢ ⎥ 𝑒 −𝑒 ⎢𝑑𝑖 𝑑𝑖 ⎥ When the motor is running, only two phases of the stator winding − are conducted. If the phase B and ⎣ 𝑑𝑡 𝑑𝑡 ⎦ phase C are conducted, the resulting simplified model is shown in Figure7. Therefore, the relationships betweenWhenib andthe motoric is: is running, only two phases of the stator winding are conducted. If the phase B and phase C are conducted, the resulting isimplified= ic = Imodel, is shown in Figure 7. Therefore, (16)the b − relationships between 𝑖 and 𝑖 is: which also means that: di 𝑖 =−𝑖b = =𝐼,dic = dI . (16)(17) dt − dt dt which also means that: e = ec, so the line voltage becomes: b − 𝑑𝑖 𝑑𝑖 𝑑𝐼 u = =−2rI + 2(L= M.) dI + 2e . (17)(18) bc𝑑𝑡 𝑑𝑡 −𝑑𝑡 dt b 𝑒 =−𝑒 Therefore, , so the line voltage becomes: dI u = u = 2rI + 2(L𝑑𝐼 M) + Keω, (19) 𝑢 bc=2𝑟𝐼+20 (𝐿−𝑀) − +2𝑒dt . (18) 𝑑𝑡 where u0 is the DC bus voltage; Ke is the line back EMF coefficient; and ω = v/R is the velocity of the motor.Therefore, In the magnetic circuit subsystem, the rotor of the𝑑𝐼 BLDCM receives Loren magnetic force in the 𝑢 =𝑢 =2𝑟𝐼+2(𝐿−𝑀) +𝐾 𝜔, (19) magnetic field. It is the main driving force of the valve.𝑑𝑡 Regardless of the influence of the mechanical loss and stray loss of the rotor on the BLDCM, the electromagnetic torque expression of the BLDCM where 𝑢 is the DC bus voltage; 𝐾 is the line back EMF coefficient; and 𝜔=𝑣/𝑅 is the velocity of theis as motor. follows: = Pe = eaia+ebib+ecic In the magnetic circuit subsystem,T magthe rotorω of the BLDCMω , receives Loren magnetic force in (20)the wheremagneticω is field. the electricalIt is the main angular driving velocity force of of BLDCM, the valve. and Regardless when the motorof the influence is running, of only the mechanical two phases of the stator winding are conducted. Therefore, the electromagnetic torque expression of BLDCM can be simplified as: 2eI Tmag = ω = KTI, (21) where KT is the motor torque coefficient, and the motor torque constant depends on the size and material of the motor stator and rotor structure. The torque constant and the back-EMF constant can be obtained through the finite element analysis of the electromagnetic field. Energies 2020, 13, x FOR PEER REVIEW 11 of 17 loss and stray loss of the rotor on the BLDCM, the electromagnetic torque expression of the BLDCM is as follows: 𝑃 𝑒 𝑖 +𝑒 𝑖 +𝑒 𝑖 𝑇 = = , (20) 𝜔 𝜔 where 𝜔 is the electrical angular velocity of BLDCM, and when the motor is running, only two phases of the stator winding are conducted. Therefore, the electromagnetic torque expression of BLDCM can be simplified as: 2𝑒𝐼 𝑇 = =𝐾 𝐼, (21) 𝜔 where 𝐾 is the motor torque coefficient, and the motor torque constant depends on the size and materialEnergies of2020 the, 13 motor, 6391 stator and rotor structure. The torque constant and the back-EMF constant11 of 16 can be obtained through the finite element analysis of the electromagnetic field. Figure 8 shows the relationship between the systems. The voltage 𝑢 is applied to the BLDCM Figure8 shows the relationship between the systems. The voltage u is applied to the BLDCM to to generate current 𝐼 in the coil, and the electromagnetic force 𝑇 is applied to the rotor of the generate current I in the coil, and the electromagnetic force Tmag is applied to the rotor of the BLDCM BLDCMin the in magnetic the magnetic field. field.
Figure 8. Coupling of subsystems of the FVVA system. Figure 8. Coupling of subsystems of the FVVA system. 4.2. Motion Control Algorithm of the FVVASystem 4.2. Motion Control Algorithm of the FVVA System In order to achieve precise controllability of the valve in operation, three closed-loop cascade controlIn order is used to achieve in this research, precise namelycontrollability position of loop, the velocity valve in loop, operation, and current three loop. closed-loop The three arecascade controlconnected is used in in cascade. this research, The control namely block position diagram isloop, shown velocity in Figure loop,9. The and current current loop loop. serves The as three the are connectedregulator in of cascade. current, The the velocity control loop block as thediagram regulator is sh ofown velocity, in Figure and the 9. position The current loop as loop the regulator serves as the of position. The PI control algorithm is adopted for all three loops, which has a low calculation time, regulator of current, the velocity loop as the regulator of velocity, and the position loop as the simple algorithm, and good tracking performance. The tracking error signal is defined as: regulator of position. The PI control algorithm is adopted for all three loops, which has a low calculation time, simple algorithm, and egood(t) = rtracking(t) y(t) .performance. The tracking error (22)signal is − Energiesdefined 2020 as:, 13, x FOR PEER REVIEW 12 of 17 𝑒(𝑡) =𝑟(𝑡) −𝑦(𝑡). (22) The PI control law is as follows: 𝑢(𝑡) =𝐾 𝑒(𝑡) +𝐾 𝑒(𝑡)𝑑𝑡, (23) where 𝑒(𝑡) , 𝑟(𝑡) , 𝑦(𝑡) , 𝐾 , and 𝐾 are the tracking error, reference value, feedback value, proportional, and integral gains of the controller, respectively.
FigureFigure 9. 9.Three-loopThree-loop control control system for for the the FVVA FVVA system. system.
The PI control law is as follows: In this model, the position loop receives the reference position and feedback position, and then outputs the reference velocity by calculating, likewise,R theT velocity loop to receive reference velocity u(t) = Kpe(t) + Ki e(t)dt, (23) and feedback velocity. It then outputs the reference current0 by calculating, the reference current determineswhere e( thet), r (directiont), y(t), K pof, andmotorKi are rotation, the tracking and also error, determines reference value, the direction feedback of value, the movement proportional, of the valve.and The integral current gains loop of the receives controller, the respectively. reference current and feedback current, and then outputs the specified duty ratio, to control the voltage of load on the motor. The driving method of BLDCM is also one of the key steps of system design. This research uses the most commonly used full-bridge drive method for three-phase BLDCM as shown in Figure 10. It mainly consists of a three-phase inverter and an insulated-gate bipolar transistor (IGBT) driver. The effective control is made by using Pulse Width Modulated (PWM). According to the motor rotor position signal, the three-phase winding of the motor is controlled on and off. It adopts the two-by- two conduction mode, that is, according to the position signal, only two phases are turned on at the same time. The torque fluctuation of the motor is small in this case [19]. Table 3 shows the relationship between the BLDCM rotor position and the winding sequence. Through electronic commutation, it can generate a rotating magnetic field to drive the motor rotor to rotate. Here, 1 means the upper bridge arm is on, and 0 means the lower bridge arm is on.
Figure 10. BLDCM control using PWM.
Table 3. The relationship between winding sequence and position.
Electrical Angle Phase A Phase B Phase C 0°–60° 1 0 / 60°–120° 1 / 0 120°–180° / 1 0 180°–240° 0 1 / 240°–300° 0 / 1 300°–360° / 0 1
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Energies 2020, 13, 6391 12 of 16 Figure 9. Three-loop control system for the FVVA system.
In this model, the position loop receives the reference position and feedback position, and then In this model, the position loop receives the reference position and feedback position, and then outputs the reference velocity by calculating, likewise, the velocity loop to receive reference velocity and outputs the reference velocity by calculating, likewise, the velocity loop to receive reference velocity feedback velocity. It then outputs the reference current by calculating, the reference current determines the and feedback velocity. It then outputs the reference current by calculating, the reference current direction of motor rotation, and also determines the direction of the movement of the valve. The current determines the direction of motor rotation, and also determines the direction of the movement of the loop receives the reference current and feedback current, and then outputs the specified duty ratio, valve. The current loop receives the reference current and feedback current, and then outputs the to control the voltage of load on the motor. specified duty ratio, to control the voltage of load on the motor. The driving method of BLDCM is also one of the key steps of system design. This research uses The driving method of BLDCM is also one of the key steps of system design. This research uses the most commonly used full-bridge drive method for three-phase BLDCM as shown in Figure 10. the most commonly used full-bridge drive method for three-phase BLDCM as shown in Figure 10. It It mainly consists of a three-phase inverter and an insulated-gate bipolar transistor (IGBT) driver. mainly consists of a three-phase inverter and an insulated-gate bipolar transistor (IGBT) driver. The The effective control is made by using Pulse Width Modulated (PWM). According to the motor rotor effective control is made by using Pulse Width Modulated (PWM). According to the motor rotor position signal, the three-phase winding of the motor is controlled on and off. It adopts the two-by-two position signal, the three-phase winding of the motor is controlled on and off. It adopts the two-by- conduction mode, that is, according to the position signal, only two phases are turned on at the same time. two conduction mode, that is, according to the position signal, only two phases are turned on at the The torque fluctuation of the motor is small in this case [19]. Table3 shows the relationship between the same time. The torque fluctuation of the motor is small in this case [19]. Table 3 shows the relationship BLDCMbetween rotorthe BLDCM position rotor and theposition winding and sequence. the winding Through sequence. electronic Through commutation, electronic commutation, it can generate it acan rotating generate magnetic a rotating field tomagnetic drive the field motor to drive rotor the to rotate. motor Here, rotor 1to means rotate. the Here, upper 1 bridgemeans armthe upper is on, andbridge 0 means arm is the on, lower and 0 bridge means arm the islower on. bridge arm is on.
FigureFigure 10.10. BLDCMBLDCM controlcontrol usingusing PWM.PWM.
TableTable 3. 3.The The relationshiprelationship betweenbetween windingwinding sequence sequence and and position. position.
ElectricalElectrical Angle Angle PhasePhase A A Phase Phase BB Phase Phase C C
0◦–600°–60°◦ 11 0 / / 60◦60°–120°–120◦ 1 1 / 0 0 120120°–180°◦–180◦ / / 1 0 0 180 –240 0 1 / 180°–240°◦ ◦ 0 1 / 240◦–300◦ 0 / 1 240°–300° 0 / 1 300◦–360◦ / 0 1 300°–360° / 0 1
Figure 11 shows the Simulink model of the FVVAsystem based on Matlab. The model is divided into the three closed-loop control modules, the power drive and motor module, the crank-movement guide rod mechanism module, and valve motion modules. Among them, the output duty cycle is calculated through position, velocity,and current feedback in the three closed-loop control modules. Combined with the commutation command shown in Table3, the specified PWM is output to the power drive and the motor module, thereby outputting the position, velocity, and current signals that need to be fed back. Then, it transmits the torque to the valve through the crank-movement guide rod mechanism, thereby drive valve movement. The precise position control of the valve is ensured by controlling the input of a given position signal. Energies 2020, 13, x FOR PEER REVIEW 13 of 17
Figure 11 shows the Simulink model of the FVVA system based on Matlab. The model is divided into the three closed-loop control modules, the power drive and motor module, the crank-movement guide rod mechanism module, and valve motion modules. Among them, the output duty cycle is calculated through position, velocity, and current feedback in the three closed-loop control modules. Combined with the commutation command shown in Table 3, the specified PWM is output to the power drive and the motor module, thereby outputting the position, velocity, and current signals that need to be fed back. Then, it transmits the torque to the valve through the crank-movement guide rod mechanism, thereby drive valve movement. The precise position control of the valve is ensured Energies 2020, 13, 6391 13 of 16 by controlling the input of a given position signal.
Figure 11. MATLAB/Simulink model of the FVVA system. Figure 11. MATLAB/Simulink model of the FVVA system. 4.3. Results and Discussion 4.3. Results and Discussion The biggest feature of the FVVA system is that the valve operating parameters can be continuously adjustedThe biggest in real time,feature including of the the FVVA variable system valve timing,is that variablethe valve valve operating opening duration,parameters and can variable be continuouslylift. Therefore, adjusted it is necessary in real time, to adjust including the parameters the variable of the valve valve timing, movement variable process valve to opening verify the duration,performance and variable of the FVVA lift. Therefore, system. it is necessary to adjust the parameters of the valve movement processIn to the verify FVVA the system, performance the variable of the parameter FVVA system. adjustment of the valve can be achieved by adjusting the commandIn the toFVVA control system, the opening the variable or closing parameter of the valve. adjustment The parameters of the valve listed can in Tables be achieved1 and2 were by adjustingused for the the command simulation to research. control the Figure opening 12 shows or closin theg valve of the position valve. The curves parameters of the engine listed in under Tables low, 1 andmedium, 2 were and used high for loads. the simulation Among them, research. under Figure low load 12 conditions,shows the valve the given position valve curves lift is 4 of mm, the theengine valve underopening low, duration medium, is 8and ms, high and loads. the maximum Among positionthem, un ofder the low simulation load conditions, result is 3.98 the mmgiven with valve an errorlift is of 4 0.02mm, mm. the valve Under opening medium duration load conditions, is 8 ms, theand given the ma valveximum lift is position 8 mm, the of valvethe simu openinglation duration result is is 3.98 8 ms, mmand with the an maximum error of position0.02 mm. of Under the simulation medium load result conditions, is 7.97 mm the with given an errorvalve of lift 0.03 is 8 mm. mm, Under the valve high openingload conditions, duration theis 8 givenms, and valve the lift maximum is 8 mm, theposition valve of opening the simulation duration result is 16 ms, is 7.97 and mm the maximumwith an errorposition of 0.03 of mm. the simulation Under high result load is conditions, 7.95 mm with thean given error valve of 0.05 lift mm. is 8 mm, It can the be valve seen fromopening the resultsduration that is the16 ms, FVVA and system the maximum can realize position variable of valvethe simulation timing, variable result is opening 7.95 mm duration, with an and error variable of 0.05 lift mm. under It Energies 2020, 13, x FOR PEER REVIEW 14 of 17 candifferent be seen operating from the conditions.results that the FVVA system can realize variable valve timing, variable opening duration, and variable lift under different operating conditions.
Figure 12. Results of flexible valve motion control. Figure 12. Results of flexible valve motion control. Figure 13 shows the valve movement position and velocity curve when the maximum valve lift Figure 13 shows the valve movement position and velocity curve when the maximum valve lift is 8 mm and the valve opening duration is 16 ms under high load conditions. As shown in the figure, is 8 mm and the valve opening duration is 16 ms under high load conditions. As shown in the figure, the valve movement transition time is about 3.8 ms, and the seating velocity is 0.18 m/s. It meets the the valve movement transition time is about 3.8 ms, and the seating velocity is 0.18 m/s. It meets the design requirements. design requirements.
Figure 13. Position and velocity curve when lift is 8 mm.
Table 4 compares the performance of the FVVA system with the traditional valve drive system and the EMCLV system. It can be seen that compared with the EMCLV system, the FVVA system has a larger seating speed. Even so, on the basis of realizing the variable valve timing of the EMCLV system, the FVVA system can also provide variable valve lift, which brings greater advantages to the internal combustion engine. The three closed loop PID control algorithm used in this paper is relatively simple and is difficult to be integrated into the internal combustion engine electronic control system. In the later stage, the algorithm can be optimized to achieve a lower seating speed and faster response time. Finally, it should be pointed out that the exhaust valve cannot be fitted with this motor, because it does not have enough torque to support the combustion forces.
Table 4. Comparison of performance of the three systems.
Electrical Angle The Traditional Valve Drive System EMCLV FVVA Transition Time (ms) / 3.5 [20] 3.8 Seating Velocity (m/s) 0.3 0.1 0.18 Phase Phase Controllable Variables / During During
Energies 2020, 13, x FOR PEER REVIEW 14 of 17
Figure 12. Results of flexible valve motion control.
Figure 13 shows the valve movement position and velocity curve when the maximum valve lift is 8 mm and the valve opening duration is 16 ms under high load conditions. As shown in the figure, the valve movement transition time is about 3.8 ms, and the seating velocity is 0.18 m/s. It meets the Energies 2020, 13, 6391 14 of 16 design requirements.
FigureFigure 13. 13. PositionPosition and and velocity velocity curve curve when when lift lift is is 8 8mm. mm.
Table4 compares the performance of the FVVA system with the traditional valve drive system Table 4 compares the performance of the FVVA system with the traditional valve drive system and the EMCLV system. It can be seen that compared with the EMCLV system, the FVVA system has and the EMCLV system. It can be seen that compared with the EMCLV system, the FVVA system has a larger seating speed. Even so, on the basis of realizing the variable valve timing of the EMCLV system, a larger seating speed. Even so, on the basis of realizing the variable valve timing of the EMCLV the FVVA system can also provide variable valve lift, which brings greater advantages to the internal system, the FVVA system can also provide variable valve lift, which brings greater advantages to the combustion engine. The three closed loop PID control algorithm used in this paper is relatively simple internal combustion engine. The three closed loop PID control algorithm used in this paper is and is difficult to be integrated into the internal combustion engine electronic control system. In the relatively simple and is difficult to be integrated into the internal combustion engine electronic later stage, the algorithm can be optimized to achieve a lower seating speed and faster response time. control system. In the later stage, the algorithm can be optimized to achieve a lower seating speed and faster response time. Table 4. Comparison of performance of the three systems. Finally, it should be pointed out that the exhaust valve cannot be fitted with this motor, because it does notElectrical have enough Angle torque to The support Traditional the combustion Valve Drive Systemforces. EMCLV FVVA Transition Time (ms) / 3.5 [20] 3.8 Seating Velocity (mTable/s) 4. Comparison of performance 0.3 of the three systems. 0.1 0.18 Phase Phase ControllableElectrical Variables Angle The Traditional/ Valve Drive System During EMCLV FVVADuring Transition Time (ms) / 3.5 [20] 3.8Lift Seating Velocity (m/s) 0.3 0.1 0.18 Phase Phase Finally,Controllable it should Variables be pointed out that the exhaust valve / cannot be fitted with this motor, because it does During During not have enough torque to support the combustion forces.
5. Conclusions This article designed an FVVA system based on BLDCM. The overall design of the system was completed through the demand analysis of the system. The system is simple in structure and control. This design allows rapid recalibration of valves in situations where they are prone to wear and temperature changes, making the system more flexible than conventional valve actuators. The rotary motion of the BLDCM is converted into the linear motion of the valve by using a crank moving guide rod mechanism. It changes the valve lift by increasing or decreasing the BLDCM swing angle when the valve is opened, and it changes the transition time between valve opening or closing by increasing or decreasing the angular velocity of the BLDCM. The simulation results show that the system can provide suitable valve opening and closing time or lift under different operating conditions of the engine. It meets the design requirements. Compared with the traditional camshaft mechanism, the FFVA system can provide a richer valve operation strategy when the engine is running. Depending on the working state of the engine, the valve can be opened and closed at different times with different lift. Although the result of the simulation shows that the design can meet the design requirements very well, as said earlier, the motor cannot provide enough torque to support the combustion forces for the exhaust valve, and the installation of the motor is also an important issue to consider. There are Energies 2020, 13, 6391 15 of 16 inevitable disturbances when the valves work, so we need to optimize the algorithm and structure to get a better variable valve system. The next step in the research is to redesign a smaller BLDCM to fit their mounting sizes, and then test the drive system in an actual internal combustion engine to verify its feasibility. This will provide a better understanding of the disturbances that occur during engine operation.
Author Contributions: Supervision, L.L. and Z.X.; Research—original draft—editing, L.J.; Technical support, X.P. All authors have read and agreed to the published version of the manuscript. Funding: This work was supported by the National Natural Science Foundation of China (Grant No. 51975297 and No. 51875290). Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
FVVA fully variable valve actuation BLDCM brushless direct current motor EMCL electromechanical camless valve PWM pulse width modulated nmax the maximum velocity of the engine The maximum time allowed for valve opening or tmax closing ∆ϕν the maximum continuous crank angle R the length of the boom α the acceleration of the BLDCM a the acceleration of the valve J the moment of inertia of the motor m the mass of the valve m1 the mass of the valve connector xmax the maximum valve displacement θmax the maximum angle of motor rotation Tmag the electromagnetic driving torque c the mechanical damping coefficient F0 the combustion forces v the velocity of the valve r phase winding inductance L resistance of the phase M mutual inductance ia A phase current ib B phase current ic C phase current ua A phase voltage ub B phase voltage uc C phase voltage EMF back ElectroMagnetic Forces ea the EMF generated in A phase eb the EMF generated in B phase ec the EMF generated in C phase ω the electrical angular velocity of BLDCM e(t) the tracking error r(t) the reference value y(t) the feedback value Kp proportional gains of the controller Ki integral gains of the controller Energies 2020, 13, 6391 16 of 16
References
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