Kinematic and Dynamic Response of a Novel Engine Mechanism Design Driven by an Oscillation Arm

applied sciences

Article Kinematic and Dynamic Response of a Novel Engine Mechanism Design Driven by an Oscillation Arm

Călin Itu 1, Maria-Lumini¸taScutaru 1 ,Cătălin Iulian Pruncu 2,3,* and Radu Muntean 1

1 Transilvania University of Bra¸sov, B-dulEroilor, 29, 500036 Bra¸sov, Romania; [email protected] (C.I.); [email protected] (M.-L.S.); [email protected] (R.M.) 2 Mechanical Engineering, School of Engineering, University of Birmingham, Birmingham B15 2TT, UK 3 Mechanical Engineering, Imperial College London, Exhibition Rd., London SW7 2AZ, UK * Correspondence: [email protected]; Tel.: +40-7-4027-8642

Received: 26 February 2020; Accepted: 10 April 2020; Published: 15 April 2020

Abstract: The goal of this paper is to highlight the advantage fulﬁlled by a novel engine mechanism, the concept of which is based on an oscillating arm relative to the classical engine mechanism. Further, the results of this paper demonstrate the beneﬁts of a novel type of mechanism and the major advantages in terms of functioning parameters of an engine. Their performances highly depend on the joint positions of the oscillating arm. The increases in the functional performances rate of success (i.e., piston stroke, volume of the combustion chamber or compression ratio) enable a superior engine power parameter (higher power, torque) and bring some additional improvement on the eco parameters of the engine related to consumption, emission, etc.

Keywords: engine modeling; multibody simulation (MBS); engine dynamics; variable compression ratio (VCR); power; energy; control

1. Introduction

1.1. Background The fleet of vehicles has expanded from year to year and has led to an undesired overall increasing of the exhaust emission and consumption. For this reason, engineers are pushed to improve and optimize the existing constructive solutions of current engines. Furthermore, the increased pressure on the engine manufacturers has imposed implementation in the production stream of some new constructive solutions for the current engine that must accomplish current standard requests imposed by the marketplace. This means an improvement of some parameters or engine characteristics, such as: increased power and torque and lower consumption and emissions, which allow to increase durability and reliability [1–5]. Generally, the efficiency of an engine with internal combustion is evaluated by means of characteristic processes on a cycle or based on some constructive parameters, such as: engine displacement, stroke–bore ratio and compression ratio. Furthermore, the efficiency can be evaluated based on the operational parameters (engine management, forming and controlling mixture air/combustible and ignition timing). One of the most representative concepts developed after year 2000 in order to meet these requirements is an engine constructive solution with satisfactory outcomes based on an oscillatory arm and variable compression ratio (VCR). The promoter of this solution was Dr. Joe Ehrlich who after 11 years of research, implemented it on the Mayflower e3 engine for the first time [6,7]. In this configuration, the compression ratio is a controllable parameter. Therefore, for this engine with internal combustion, the VCR technology [8] could be considered one of the keys that led to

Appl. Sci. 2020, 10, 2733; doi:10.3390/app10082733 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 2733 2 of 15 better performances both for partial loads and for the full loads of engines. This technology is based on a multi-link mechanism that allows to change the top and bottom dead center positions, which enable the compression ratio to be continuously changed [9]. It can provide higher compression ratio, variable valve timing, low friction, reduced throttling losses, boosting and down-sizing [10]. However, most benefits are related to minimal fuel consumption, minimal nitric oxides and particulate matter emissions [11]. To obtain superior performances, a cumulative method is required for improving the design process and final geometry, combustion process parameters [12–15] type of fuel [16] and other environmental parameters. Other researchers have focused on VCR development and they have developed various technological solutions. In this sense, the SAAB has developed two concepts for the gasoline engine with natural aspiration: the engine with variable compression ratio SVC (Saab Variable Compression) and the system to control the combustion process SCC (Saab Combustion Control). Both solutions led to a reduction of consumption by 30%. The SVC system from SAAB allows continuous variation of the compression between 8:1 and 14:1 [17]. Another VCR solution developed by Peugeot is for the MCE-5 VCRi engine [18]; it has added an intermediary element in the form of a special gear. The system can change the compression ratio from 7:1 to 18:1, and the system can even control each cylinder separately, allowing all four cylinders to operate at different compression ratios. Gomecsys offered another VCR solution based on the possibility to rotate the crank axis, changing the position of the eccentric on the big end of the connecting rod. In this type of engine, an eccentric mounted carrier carries the crankshaft bearings that can rotate to raise or lower the pistons to the top dead center (TDC) in the cylinder. The compression ratio can be adjusted by just altering the rotation of the eccentric carrier. This technology saves fuel and overall CO2 emission by 18% [19–23]. Nissan has achieved considerable success in the development of VCR engines over time [24,25]. The VC-Turbo engine from Nissan uses a multi-link system in place of a traditional connecting rod to rotate the crankshaft, and an actuator motor changes the multi-link system endpoint in order to vary the piston reach to transform the compression ratio. This makes it possible to vary the compression ratio continuously as needed within the range of 8:1 (for high load) to 14:1 (for low load). FEV developed a two-stage VCR engine system that has been proven to be a good concept, considering its low cost to manufacture and the benefit if integration into common engine architectures. The system uses a length-adjustable connecting rod with an eccentric piston pin in the small eye; the compression ratio adjustment is performed through a combination of gas and mass forces [26,27]. A potential improvement of fuel consumption is 5–7% depending upon drive cycle and vehicle/powertrain combinations [28]. Furthermore, Ford has extensively worked on the development of VCR engines in the last 20 years and a VCR Engine with varying length of piston and connecting rod was developed in 2003 [29]. The research goal is focused to increase engine performance, in which the research-development process has to search for solutions to minimize the expensive costs, by developing and optimizing the end product. This can be achieved by using modern software through computers that can simulate the real process based on experimental data. The use of computer capabilities helps to reduce the experimental tests which means reducing cost for the test itself besides maintenance [30–32]. There are many domains related to a mechanical system which are analyzed with commercial software in order to reduce the time consuming, providing better/reliable and competitive products on the market. Here, we can name some of these types of domains: MBS (multibody simulation) used for kinematic and dynamic analysis of bodies in motion and FEA (Finite Element Analysis) used for analysis of deformable bodies. There are also other types of analyses developed in the FEA domain: static analysis, vibration analysis, fatigue analysis and CFD (Computed Fluid Dynamics) used for analysis of fluid flows prediction based on some mathematical and numerical methods [33–35]. Recently, these were extended to some novel challenging domains of interest which start to embed/develop numerical simulations accordingly: electromagnetic field or electrical field [36–41]. Numerous commercial software programs have been developed in the last two decades with the goal to cover requests coming from customers or market needs [42–45]. They permit reducing Appl. Sci. 2020, 10, 2733 3 of 15 Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 15 thetime time to obtain to obtain a product a product to its to smaller its smaller time timelimits limits [22,23,46–50]. [22,23,46 –Another50]. Another important important goal of goal using of using these thesesoftware software programs programs developed developed as tools as consists tools consists the possibility the possibility to make to a make very aquick very decision quick decision on the onchoice the choiceof a viable of a design viable designsolution solution from a frommultitude a multitude of proposed of proposed solutions, solutions, based on based different on di virtualfferent virtualanalyses analyses processes. processes. In this paper, we discuss the benefitsbenefits achieved through using the mechanism with an oscillating arm in comparison with with a a classical classical mechanism mechanism of of a aconventional conventional engine. engine. To To validate validate the the success success of ofthe the proposed proposed mechanism, mechanism, we we evaluated evaluated the the kinematic kinematic and and dynamic dynamic parameters parameters such as: piston stroke, compression compression ratio, ratio, torque torque and and power power per per cycle. cycle. To do To so, do the so, analyses the analyses were performed were performed using usinganalytical analytical calculus calculus and multibody and multibody simulation simulation techniques. techniques. The results The gathered results gathered in this survey in this confirm survey confirmthe achievement the achievement of superior of superior engine enginepower powerparameters parameters (power, (power, torque) torque) and an and improvement an improvement of eco of‐ eco-parametersparameters of the of studied the studied engine engine (consumption, (consumption, emission). emission).

1.2. Objective In general, the processes and phenomena developed in the real mechanical systems are quite complex and are didifficultﬃcult to bebe representedrepresented asas closeclose asas possiblepossible inin thethe virtualvirtual models.models. In fact, they represent an approximation of the realreal systems.systems. A proposal to evaluate the mechanism behavior is done according to the general blocbloc diagramdiagram shownshown inin FigureFigure1 1..

Generated Inertia External motion loading loading

Geometric Kinematic Dynamic Data model model

Output data: Output data: position, velocity, acceleration Load reaction, torque, power

Evaluating of the mechanism

Figure 1. General Bloc diagram to evaluate a mechanism based on a multibody simulation.

As can be viewed from Figure1 1,, in in a a first first stage stage of of thethe analysisanalysis mechanism,mechanism, some some input input data data have have been used to definedefine thethe kinematickinematic modelmodel suchsuch as:as: joint position and constrained motion imposed to generate a complete cycle of motion. In the 2nd stage, the input data used for dynamic MBS analysis were the mass and inertia moments of the element, inertia loading resulting from motion and external loading coming from in-linein‐line cylindercylinder andand in-cylinderin‐cylinder pressures.pressures. The objective of this paper was achieved by performing numerous MBS simulations. The results were used to describes the role of parameters from two didifferentfferent engine mechanism solutions: conventional and VCR. All virtual simulations were carried out with a rigidrigid multibodymultibody techniquetechnique using MSC ADAMS ADAMS software. software. In In the the first first step, step, some some kinematic kinematic simulations simulations were were made made to check to check the thefunctionality functionality of the of mechanism the mechanism and, after and, that, after dynamic that, dynamic analyses analyses were carried were carriedout taking out into taking account into accountexternal externalforces coming forces from coming cylinder from cylinderpressures pressures and inertial and loading inertial from loading kinematic from kinematic motion. Analysis motion. Analysisprocesses processes were performed were performed as per the as general per the methodology general methodology described described in Figure in 1. Figure 1.

2. Simulation Method Appl. Sci. 2020, 10, 2733 4 of 15 Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 15 2. Simulation Method Appl.The Sci. 2020principle, 10, x FOR of functionalityPEER REVIEW of a classical mechanism is known and, for this reason, it will4 not of 15 be detailed.The principle This kind of of functionality mechanism of converts a classical rotating mechanism motion is of known crank into and, a for translation this reason, motion it will of not a The principle of functionality of a classical mechanism is known and, for this reason, it will not piston.be detailed. The overall This kindprinciple of mechanism is shown in converts Figure 2a. rotating motion of crank into a translation motion of be detailed. This kind of mechanism converts rotating motion of crank into a translation motion of a a piston. The overall principle is shown in Figure2a. piston. The overall principle is shown in Figure 2a.

(a) (b)

Figure 2. Kinematic schema( afor) two concept of engine mechanism:(b ()a ) classic; (b) with oscillating arm.

Figure 2. Kinematic schema for two concept of engine mechanism: (a) classic; (b) with oscillating arm. InFigure Figure 2. 2b,Kinematic we show schema the kinematic for two concept scheme of engine for the mechanism: case of a mechanism (a) classic; (b with) with an oscillating oscillating arm. arm. The difference between these two types of mechanism concepts consists in how the con‐rod is In Figure 22b,b, wewe showshow thethe kinematickinematic schemescheme forfor the case of a mechanism with an oscillating arm. assembled in the mechanism: for a conventional engine, the con‐rod is directly connected to the The didifferenceﬀerence between between these these two two types types of mechanism of mechanism concepts concepts consists consists in how thein con-rodhow the is con assembled‐rod is crankshaft, and for the engine with oscillating arm, the con‐rod is connected to crankshaft through assembledin the mechanism: in the mechanism: for a conventional for a engine,conventional the con-rod engine, is directly the con connected‐rod is directly to the crankshaft, connected andto the for arm 2. This oscillating arm slides into an axial bearing (5) that is oscillated about D point, and it may crankshaft,the engine with and oscillatingfor the engine arm, with the con-rod oscillating is connected arm, the tocon crankshaft‐rod is connected through to arm crankshaft 2. This oscillating through also change the length of vector OB and the piston stroke. When the engine mechanism is running, arm slides2. This into oscillating an axial arm bearing slides (5) into that an is oscillatedaxial bearing about (5) D that point, is oscillated and it may about also changeD point, the and length it may of the pivot point (D) can be moved in the vertical and horizontal direction and thus, the position of the alsovector change OB and the the length piston of stroke.vector OB When and the the engine piston mechanism stroke. When is running, the engine the mechanism pivot point is (D) running, can be oscillating arm is changed. In this way, we can obtain different values of the compression ratio and themoved pivot in point the vertical (D) can and be moved horizontal in the direction vertical and and thus, horizontal the position direction of the and oscillating thus, the arm position is changed. of the piston stroke. Finally, we can obtain an optimization of the engine working regimes depending also oscillatingIn this way, arm we canis changed. obtain di Inﬀ erentthis way, values we of can the obtain compression different ratio values and of piston the compression stroke. Finally, ratio we and can on the mechanical loading and crank speed. pistonobtain stroke. an optimization Finally, we of thecan engineobtain workingan optimization regimes of depending the engine also working on the regimes mechanical depending loading also and In case of the engine mechanism with oscillating arm, the trajectory of the con‐rod big end oncrank the speed.mechanical loading and crank speed. obtained on a complete crankshaft rotation is an ellipse, unlike the circular trajectory obtained on a In casecase of of the the engine engine mechanism mechanism with with oscillating oscillating arm, arm, the trajectory the trajectory of the con-rodof the con big‐ endrod obtainedbig end conventional engine mechanism (Figure 3). This elliptical trajectory will determine an increase of obtainedon a complete on a crankshaftcomplete crankshaft rotation is anrotation ellipse, is unlikean ellipse, the circular unlike trajectorythe circular obtained trajectory on aobtained conventional on a piston motion time between top dead center and bottom dead center comparison by a conventional conventionalengine mechanism engine (Figure mechanism3). This (Figure elliptical 3). trajectoryThis elliptical will trajectory determine will an increase determine of pistonan increase motion of engine. pistontime between motion toptime dead between center top and dead bottom center dead and center bottom comparison dead center by comparison a conventional by engine.a conventional engine.

(a) (b)

FigureFigure 3. 3. TrajectoryTrajectory of of the the con con( arod) rod big big end end for for a acomplete complete rotation rotation of of (crankb crank) shaft: shaft: (a ()a classic;) classic; (b ()b VCR.) VCR.

Figure 3. Trajectory of the con rod big end for a complete rotation of crank shaft: (a) classic; (b) VCR. Appl. Sci. 2020, 10, x FOR PEER REVIEW 5 of 15

Maintaining the piston closer to the TDC (top dead center) as long as possible will create better Appl. Sci. 2020, 10, 2733 5 of 15 conditions for ignition process at constant volume and an improvement of efficiency. In order to demonstrate the advantages that the oscillating arm mechanism can bring, some scenarioMaintaining analysis has the pistonbeen made. closer As to a the particular TDC (top case, dead we center) started as the long survey as possible from a will classical create engine better conditionswith the following for ignition characteristics: process at constant bore: 82 volume mm, stroke: and an 76 improvement mm, crank speed of eﬃ range:ciency. 1000–6000 rpm. For aIn relevant order tocomparative demonstrate analysis, the advantages the same components that the oscillating were used arm for mechanism the two solutions can bring, analyzed. some scenarioBasically, analysis the element has been that made. makes As the a particulardifference case,between we started the two the solutions survey fromis the a classicaloscillating engine arm, withtogether the followingwith the bearing characteristics: in which bore: it slides. 82 mm, The stroke:input data 76 mm, used crank for kinematic speed range: simulation 1000–6000 is shown rpm. Forin the a relevant Table 1. comparative analysis, the same components were used for the two solutions analyzed. Basically, the element that makes the diﬀerence between the two solutions is the oscillating arm, together with the bearing in which itTable slides. 1. Kinematic The input input data data. used for kinematic simulation is shown in the Table1. Initial Position of Joints

TableConsidering 1. Kinematic in input Mechanism data. [mm]

Joint Initial PositionClassic of Joints Considering inVCR Mechanism [mm] x Classicy x VCR y Joint O x0 0 y0 x0 y O A 00 38 00 038 0 A B 00 165 3843.15 063.5 38 B 0 165 43.15 63.5 C C 0 0207.2 207.2 D 120 80 D −− − − −120 − 80

As cancan be be viewed viewed in in the the Figure Figure4, the 4, pivotthe pivot point point was modiﬁed was modified on the verticalon the vertical direction direction to indicate to howindicate the strokehow the parameter stroke parameter is inﬂuenced is influenced and also and chamber also chamber volume and volume compression and compression ratio. ratio.

Figure 4. Piston stroke influence inﬂuence with modifying the pivot point on vertical direction.

In Figures 44 andand5 5,, the the nominalnominal positionposition of the the bearing bearing joints joints that that connected connected the the bearing bearing to tothe theengine engine block block was noted was noted with the with letter the D letter as was D as used was on used the kinematic on the kinematic scheme. scheme.As can be Asviewed can bein viewedFigure 2b, in Figure the mechanism2b, the mechanism is related is relatedto the toglobal the globalcoordinate coordinate system system placed placed in the in axis the axis of the of thecrankshaft. crankshaft. With With respect respect to this to this GCS GCS (Global (Global coordinate coordinate system), system), the the notations notations that that define deﬁne a new position ofof thethe bearingbearing jointjoint DD werewere usedused asas follows:follows:

 FfFf the bearing joint is moved in the opposite direction with respect to GCS axes, the the number number “1” “1” • isis usedused asas aa secondarysecondary subscriptsubscript of thethe letterletter D; thethe ﬁrstfirst subscriptsubscript indicatesindicates thethe axis direction of thethe movementmovement takestakes place;place;  InIn aa similar similar manner, manner, a subscripta subscript number number “2” “2” will will be used be used if the if bearing the bearing joint is joint moved is inmoved the positive in the • directionpositive direction of the GCS of axes.the GCS In the axes. kinematic In the kinematic analysis, analysis, the movable the rangemovable of pivotrange point of pivot has point been consideredhas been considered as +/ 40 mm as +/ on−40 the mm horizontal on the directionhorizontal and direction+/ 25 mm and on +/ the−25 vertical mm on direction. the vertical direction. − − Appl. Sci. 2020, 10, 2733 6 of 15 Appl. Sci. 2020, 10, x FOR PEER REVIEW 6 of 15

Figure 5. PistonPiston stroke stroke influence inﬂuence with modifying the pivot point on horizontal direction.

Table2 2 contains contains an an overview overview of of results results for for all all extreme extreme positions positions of of the the pivot pivot pointpoint (D)(D) indicatedindicated in Figure 44b and and for for the the initial initial position position of of this this point. point. According According to to these these results, results, it it can can be be seen seen thatthat moving point D on the right extreme position will lead to an increasing of stroke and a decrease of compression ratio relative to the initial position. Furthermore, the the lowering lowering of point D from initial position to the extreme down position will lead toto anan increaseincrease ofof strokestroke andand compressioncompression ratio.ratio.

Table 2. Output kinematic parameters for extreme position of pivot point D. Table 2. Output kinematic parameters for extreme position of pivot point D. D Point Clearance Compression Clearance [mm] Stroke [mm] Bore Diameter [mm] Total Volume [L] ExtremePositionD Bore Total ClearanceVolume [L] Ratio (CR) Clearanc Stroke[m Compressio pointinitialExtremePositi 13.78 98.21 82Diamete Volum 0.59Volume 0.07 8.13 Left 9.80e [mm] 94.88 m] 82 0.55 0.05n Ratio 10.68 (CR) & % Righton 21.35 99.42 82r [mm] e 0.64 [L] [L] 0.11 5.66 % & Down 6.18 105.7 82 0.59 0.03 18.1 initial 13.78 % 98.21 82 % Up 21.20 89.1 82 0.580.59 0.07 0.11 8.13 5.2 & & Left 9.80 94.88: Increase; ↘ : Decrese.82 0.55 0.05 10.68 ↗ % & Right 21.35 99.42 ↗ 82 0.64 0.11 5.66 ↘ AccordingDown to Figure4,6.18 moving the105.7 pivot ↗ point in82 the upward0.59 direction 0.03 will reduce the18.1 piston ↗ stroke andUp will increase the21.20 chamber volume89.1 ↘ when the piston82 is close0.58 to the TDC. 0.11 Furthermore, 5.2 moving ↘ the pivot point in a horizontal direction, the piston stroke is also reduced (Figure5). The stroke evolution on a complete crank angle rotation for diﬀerent positions of the pivot point Appl. Sci.According 2020, 10, x FOR to Figure PEER REVIEW 4, moving the pivot point in the upward direction will reduce the 7piston of 15 strokecan be viewedand will on increase the both the graphs chamber from volume Figure6 .when the piston is close to the TDC. Furthermore, moving the pivot point in a horizontal direction, the piston stroke is also reduced (Figure 5). D to left D to right D to down D to up The stroke evolution on a complete crank angle rotation for different positions of the pivot point can be viewed onD initial the both graphsclasic from Figure 6. D initial clasic In120 Figure 6a, we see the increase of the piston stroke120 moving the pivot point to the right side. Furthermore,100 the increase of the piston stroke can be obtained100 based on moving the pivot point in the upward80 direction (Figure 6b). It can be seen that the moving80 point to the vertical direction has a greater 60influence compared to that against moving in the horizontal60 direction. To40 have better comparative information regarding the40 two solutions, a graph with the stroke 20 20 obtainedStroke [mm] for the classic solution was overlaid on Figure 6.Stroke [mm] It can be viewed that the stroke for the VCR 0 0 solution (with point D in a nominal position) is increased by25%. ‐20 ‐20 An improvement0 90 from 180 the kinematic 270 viewpoint 360 will have0 an influence 90 on 180 the ratio 270 compression 360 and chamber volume and could also lead to improving the burning process on a complete cycle and Crank angle [deg] Crank angle [deg] consumption. (a) (b)

FigureFigure 6. 6. PistonPiston stroke evolutionevolution during during complete complete rotation rotation of crankshaftof crankshaft when when the pivotthe pivot point point is moved is movedin: (a) in: horizontal (a) horizontal direction direction (b) vertical (b) direction. vertical direction.

OtherIn Figure kinematic6a, we parameters see the increase analyzed of the as pistona comparison stroke movingcan be viewed the pivot in Figure point to 7. theThis right is about side. velocityFurthermore, and acceleration the increase of the of thepiston. piston stroke can be obtained based on moving the pivot point in theRegarding upward the direction mechanism (Figure configurations6b). It can be analyzed, seen that it thecan movingbe viewed point from to the the graphs vertical that direction higher valueshas a greaterare obtained inﬂuence using compared the VCR tosolution that against in comparison moving in to thethe horizontalclassic solution. direction. More exactly, using the VCR solution, absolute maximum values obtained for velocity and acceleration piston are higher by25% with respect to the conventional solution, considering a crankshaft speed rotation with a constant value of 6000 rpm. In these conditions, from a dynamical viewpoint, the inertia loading that is proportional with acceleration could induce a slightly increasing effect that will influence the loading evolution in all joints of the mechanism. For this reason, some dynamic analyses were made to have a know‐how about some important parameters such as load reactions, torque or power.

clasic VCR clasic VCR

40 20000

30 ] 2 10000 20 10 0 0 ‐10 ‐10000

Velocity [m/s] ‐20 ‐20000

‐30 Acceleration [m/s ‐40 ‐30000 0 200 400 600 800 0 200 400 600 800 Crank angle [deg] Crank angle [deg] (a) (b) Figure 7. Kinematic parameters evolution on a complete cycle rotation crankshaft: (a) piston velocity; (b) piston acceleration.

As it is known, to have a durability for a mechanism, it is desirable to have the internal forces that are as small as possible in the system. Furthermore, to have the best mechanical performance, it is desirable to obtain from these internal forces values of torque and power that are as large as possible, too. Basically, it has to be somewhere between ideal durability and ideal mechanical performance. For this reason, the loads from the joints and bearings must be studied based on dynamic simulations or analytical calculus. Appl. Sci. 2020, 10, x FOR PEER REVIEW 7 of 15

D to left D to right D to down D to up D initial clasic D initial clasic 120 120 100 100 80 80 60 60 40 40 20 20 Stroke [mm] Stroke [mm] 0 0 ‐20 ‐20 0 90 180 270 360 0 90 180 270 360 Crank angle [deg] Crank angle [deg] (a) (b)

Figure 6. Piston stroke evolution during complete rotation of crankshaft when the pivot point is moved in: (a) horizontal direction (b) vertical direction.

Other kinematic parameters analyzed as a comparison can be viewed in Figure 7. This is about velocityAppl. Sci. 2020and, 10acceleration, 2733 of the piston. 7 of 15 Regarding the mechanism configurations analyzed, it can be viewed from the graphs that higher values are obtained using the VCR solution in comparison to the classic solution. More exactly, using To have better comparative information regarding the two solutions, a graph with the stroke the VCR solution, absolute maximum values obtained for velocity and acceleration piston are higher obtained for the classic solution was overlaid on Figure6. It can be viewed that the stroke for the VCR by25% with respect to the conventional solution, considering a crankshaft speed rotation with a solution (with point D in a nominal position) is increased by 25%. constant value of 6000 rpm. An improvement from the kinematic viewpoint will have an inﬂuence on the ratio compression In these conditions, from a dynamical viewpoint, the inertia loading that is proportional with and chamber volume and could also lead to improving the burning process on a complete cycle acceleration could induce a slightly increasing effect that will influence the loading evolution in all and consumption. joints of the mechanism. For this reason, some dynamic analyses were made to have a know‐how Other kinematic parameters analyzed as a comparison can be viewed in Figure7. This is about about some important parameters such as load reactions, torque or power. velocity and acceleration of the piston.

clasic VCR clasic VCR

40 20000

30 ] 2 10000 20 10 0 0 ‐10 ‐10000

Velocity [m/s] ‐20 ‐20000

‐30 Acceleration [m/s ‐40 ‐30000 0 200 400 600 800 0 200 400 600 800 Crank angle [deg] Crank angle [deg] (a) (b) FigureFigure 7. 7. KinematicKinematic parameters parameters evolution evolution on on a a complete complete cycle cycle rotation rotation crankshaft: crankshaft: (a (a) )piston piston velocity; velocity; ((bb)) piston piston acceleration. acceleration.

AsRegarding it is known, the mechanism to have a durability configurations for a analyzed,mechanism, it can it is be desirable viewed fromto have the the graphs internal that forces higher thatvalues are are as small obtained as possible using the in VCR the system. solution Furthermore, in comparison to tohave the the classic best solution. mechanical More performance, exactly, using it isthe desirable VCR solution, to obtain absolute from maximum these internal values forces obtained values for velocity of torque and and acceleration power that piston are are as higherlarge as by possible,25% with too. respect Basically, to the conventional it has to be solution, somewhere considering between a crankshaftideal durability speed rotationand ideal with mechanical a constant performance.value of 6000 rpm.For this reason, the loads from the joints and bearings must be studied based on dynamicIn these simulations conditions, or analytical from a dynamical calculus. viewpoint, the inertia loading that is proportional with acceleration could induce a slightly increasing effect that will influence the loading evolution in all joints of the mechanism. For this reason, some dynamic analyses were made to have a know-how about some important parameters such as load reactions, torque or power. As it is known, to have a durability for a mechanism, it is desirable to have the internal forces that are as small as possible in the system. Furthermore, to have the best mechanical performance, it is desirable to obtain from these internal forces values of torque and power that are as large as possible, too. Basically, it has to be somewhere between ideal durability and ideal mechanical performance. For this reason, the loads from the joints and bearings must be studied based on dynamic simulations or analytical calculus. It is well known that for a classic mechanism, in order to obtain the mechanical torque and internal loading from all joints, it will be necessary to write the equilibrium equations on all bodies from assembly based on the kineto–static methodology used in the Multi Body Dynamic calculus. General equations that can be written for any individual body from an assembly are as follows: P for translational motion: →F = m →a ; • · P for rotational motion: M→ = j →ε . • · In the free body diagrams, the following notations have been used: r- arm length, R—magnitude force, G—weight element, Fi—inertia forces, J—inertia mass moment, Fp—piston force, N—normal force coming from a contact, ω—angular speed, ε—angular acceleration, T—engine torque). Appl. Sci. 2020, 10, x FOR PEER REVIEW 8 of 15

It is well known that for a classic mechanism, in order to obtain the mechanical torque and internal loading from all joints, it will be necessary to write the equilibrium equations on all bodies from assembly based on the kineto–static methodology used in the Multi Body Dynamic calculus. General equations that can be written for any individual body from an assembly are as follows:

 for translational motion: ∑ F m∙a;  for rotational motion: ∑ M J∙ε. In the free body diagrams, the following notations have been used: r‐ arm length, R—magnitude force, G—weight element, Fi—inertia forces, J—inertia mass moment, Fp—piston force, N—normal force coming from a contact, ω—angular speed, ε—angular acceleration, T—engine torque). Appl. Sci. 2020, 10, 2733 8 of 15 As per example for the classic mechanism from Figure 8, the equations can be written as follow:

As per example for the classic mechanismRo  RA from G1 Figure Fi1 8, the equations can be written as follow: Body 1:   r x R k  r x R k  T k  J  o o 1 A 1 1 1  Ro + RA + G1 = Fi1 Body 1 :   rox Ro k + r1x RA k + T1k = J1ε1  RA  RB  G2  Fi2 (1) Body 2:  R + R + G = F (1)  A B 2 i2 Body 2 : −r2 x RA k  r3 x RB k  J 2 2  r2x RA k + r3x RB k = J2ε2 − Body 3 : RB + NB + Fp + G2 = Fi3 Body 3:− RB  N B  Fp  G2  Fi3 where by “x” we have notednoted thethe crosscross productproduct andand withwith k kthe the unit unit vector vector of theof the Oz Oz axis. axis.

Figure 8. Free body diagram for the classical mechanism.

As can be viewed from the system of EquationEquation (1), thethe torquetorque TT11 can be obtained. Based Based on on it, it, and knowing the speed of crank, it is possible to evaluate thethe powerpower ofof anan engine.engine. The torque TT11 obtained fromfrom thethe systemsystem of of Equation Equation (1) (1) is is called called the the total total torque torque of of engine engine and and is inis in fact fact a cumulativea cumulative eff effectect that that comes comes from from two two sources: sources: pressure pressure inside inside cylinders cylinders and and inertia. inertia. If it is desired to findfind out the motor torque given only by the inertia eeffect,ffect, in the equations of system (1) the term Fp isis considered considered equal to to zero. Furthermore, Furthermore, if if we want want to to find find out out the the contribution contribution of the pressure in a cylinder on the total torque T1,, all terms terms from from right side of equations from system (1) will be equal toto zero. Furthermore, in a similar manner, for the mechanism engine with oscillating arm (VCR (VCR solution) solution) we will write the equations on allall bodiesbodies fromfrom systemsystem andand thethe torquetorque willwill bebe determined.determined. For the mechanism with an oscillating arm from Figure9 9,, the the equilibrium equilibrium equations equations written written on on each body are shown in the system of Equation (2).(2).    Ro + RA + G1 = Fi1 Body 1 :   rox Ro k + r1x RA k + T1k = J1ε1    RA + RB + G2 + ND = Fi2 Body 2 :  −  r2x RA k + r3x RB k + r4x ND k = J2ε2 −  (2)   RB + RC + G3 = Fi3 Body 3 :  −  r5x RB k + r6x RC k = J3ε3 − Body 4 : R + N + Fp + G = F − C C 4 i4 Body 5 : ND + RE = 0 − Appl. Sci. 2020, 10, x FOR PEER REVIEW 9 of 15

Ro  RA  G1  Fi1 Body 1:  ro x Ro k  r1 x RA k  T1k  J11

 RA  RB  G2  N D  Fi2 Body 2:   r x R k  r x R k  r x N k  J   2 A 3 B 4 D 2 2 (2)  RB  RC  G3  Fi3 Body 3:   r x R k  r x R k  J   5 B 6 C 3 3

Body 4:  RC  NC  Fp  G4  Fi4

Appl. Sci. 2020, 10, 2733 Body 5:  ND  RE  0 9 of 15

FigureFigure 9. 9. FreeFree body body diagram diagram for for the the mechanism mechanism with with oscillating oscillating arm—VCR. arm—VCR.

TheThe input used to solve the system of Equations (1) and (2) was: the geometrical system with jointjoint position, position, crankshaft crankshaft speed speed and and pressure pressure from from cylinders, cylinders, as can as canbe viewed be viewed in Figure in Figure 10 for 10 three for importantthree important crank crankspeeds: speeds: idle speed, idle speed,nominal nominal speed and speed a speed and a close speed to close the maximum to the maximum torque. torque.Figure 10aFigure shows 10a showsthe in‐cylinder the in-cylinder pressure pressure evolution evolution in terms in terms of crank of crank speed. speed. Furthermore, Furthermore, in Figure in Figure 10b, 10web, showwe show the theevolution evolution of in of‐cylinder in-cylinder pressure pressure on on a complete a complete cycle cycle only only for for the the three three crank crank speeds mentioned.mentioned. The in-cylinderin‐cylinder pressurepressure was was converted converted into into the the force force pressure pressure taking taking into into account account the areathe areaof the of piston the piston head head (force (force gas pressure gas pressure is obtained is obtained from multiplyingfrom multiplying pressure pressure with the with area the of area piston of pistonhead). head). Details Details of input of datainput are data presented are presented in Table in3 .Table 3.

Appl. Sci. 2020, 10, x FOR PEER REVIEW 10 of 15

Table 3. Dynamic input data.

Classic VCR Element Mass Inertia Moment Mass Inertia Moment [kg] [kg∙mm2] [kg] [kg∙mm2] 1—crank 16.5 24,560 16.5 24,560 2—con‐rod 0.3 1185 0.3 1185 3—piston 0.354 387.5 0.354 387.5 4—oscillation arm − − 1.55 13,400 Appl. Sci. 10 2020, , 27335—pivot − − 0.275 100 10 of 15

100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 20 30 10 20

In‐cylinder pressure [bar] 0

In‐cylinder pressure [bar] 10 0 200 400 600 800 0 Crank angle [deg] 500 1500 2500 3500 4500 5500 6500 Crank speed [rpm] 1000 rpm 3500 rpm 6000 rpm (a) (b)

(c)

Figure 10. Pressure evolution on a cylinder used as input data in analyses (a) depending on crank Figure 10. Pressure evolution on a cylinder used as input data in analyses(a) depending on crank speed; (b) depending on crank angle for a complete cycle (c) sketch of the engine [13]. speed; (b) depending on crank angle for a complete cycle (c) sketch of the engine [13]. Table 3. Dynamic input data. Taking into account the system of Equations (1) and (2), and using multibody dynamic analyses, the total torque and inertia torque variationClassic on a cylinder have been obtained VCR for a complete cycle Element (two rotation of a crankshaft)Mass [kg] with Inertiarespect Moment to three [kg differentmm2] crankMass [kg] speeds:Inertia idle, Moment maximum [kg mmtorque,2] · · nominal.1—crank The graph evolutions 16.5 of these can be 24,560 viewed in Figures 16.511 and 12. According 24,560 to the graphs from Figures2—con-rod 11 and 12, it 0.3can be seen that the 1185 maximum total torque 0.3 value obtained 1185 for the VCR solution3—piston is higher against 0.354a classical engine mechanism. 387.5 Furthermore, 0.354 the power calculated 387.5 for the 4—oscillation arm 1.55 13,400 input speed used will have a− similar increasing − percent. 5—pivot 0.275 100 − −

Taking into account the system of Equations (1) and (2), and using multibody dynamic analyses, the total torque and inertia torque variation on a cylinder have been obtained for a complete cycle (two rotation of a crankshaft) with respect to three diﬀerent crank speeds: idle, maximum torque, nominal. The graph evolutions of these can be viewed in Figures 11 and 12. According to the graphs from Figures 11 and 12, it can be seen that the maximum total torque value obtained for the VCR solution is higher against a classical engine mechanism. Furthermore, the power calculated for the input speed used will have a similar increasing percent. Appl. Sci. 2020, 10, x FOR PEER REVIEW 11 of 15

From dynamic viewpoint analyses, to have an image about joint loading magnitude that influences the pin wear in time, Figure 11a show the evolution of the joint reaction for a complete cycle on the crank and con‐rod pin when a crankshaft has nominal speed (6000 rpm). As can be viewed, in comparison with classic mechanism, the con‐rod big end on the analyzed VCR solution Appl. Sci. 2020, 10, 2733 11 of 15 has comparable values with the ones from the classic mechanism.

clasic mech VCR

30000 25000 20000 15000 10000 5000

Con‐rod big end force [N] 0 0 200 400 600 800 Crank angle [deg]

(a)

Total torque at 1000 rpm Inertia torque at 1000 rpm

conventional VCR conventional VCR

800 60 40 600 20 400 0 200 ‐20 ‐40 Torque [Nm] Torque [Nm] 0 ‐60 ‐200 ‐80 0 90 180 270 360 450 540 630 720 0 90 180 270 360 450 540 630 720 Crank angle [deg] Crank angle [deg]

(b)

Total torque at 3500 rpm Inertia torque at 3500 rpm

conventional VCR conventional VCR

900 600 600 400 200 300 0 0 ‐200 ‐400 Torque [Nm]

‐300 Torque [Nm] ‐600 ‐600 ‐800 0 90 180 270 360 450 540 630 720 0 90 180 270 360 450 540 630 720 Crank angle [deg] Crank angle [deg]

(c)

Figure 11. Cont. Appl. Sci. 2020, 10, x FOR PEER REVIEW 12 of 15 Appl.Appl. Sci. Sci. 20202020, ,1010, ,x 2733 FOR PEER REVIEW 1212 of of 15 15

Total torque at 6000 rpm Inertia torque at 6000 rpm Total torque at 6000 rpm Inertia torque at 6000 rpm conventional VCR conventional VCR conventional VCR conventional VCR 2000 2000 20001500 2000 15001000 1000 1000 1000 500 0 5000 0 ‐5000 ‐1000 ‐1000‐500 ‐1000 Torque [Nm] ‐1000 Torque [Nm] ‐2000 Torque [Nm] ‐1500 Torque [Nm] ‐2000 ‐1500‐2000 ‐3000 ‐2000 ‐3000 0 90 180 270 360 450 540 630 720 0 90 180 270 360 450 540 630 720 0 90 180 270 360 450 540 630 720 0 90 180 270 360 450 540 630 720 Crank angle [deg] Crank angle [deg] Crank angle [deg] Crank angle [deg]

(d) (d)

Figure 11. (a). Con Con-rod‐rod big end end force force [N], ( b). Torque Torque engine evolution on a complete cycle for a total Figure 11. (a). Con‐rod big end force [N], (b). Torque engine evolution on a complete cycle for a total torque ofof 10001000 rpm, rpm, ( c(c).). Torque Torque engine engine evolution evolution on on a completea complete cycle cycle for for a total a total torque torque of 3500 of 3500 rpm, rpm, (d). torque of 1000 rpm, (c). Torque engine evolution on a complete cycle for a total torque of 3500 rpm, Torque(d). Torque engine engine evolution evolution on a on complete a complete cycle cycle for a for total a total torque torque of 6000 of 6000 rpm. rpm. (d). Torque engine evolution on a complete cycle for a total torque of 6000 rpm.

Power‐clasic Power‐VCR Power‐clasic Power‐VCR Torque‐clasic Torque‐VCR Torque‐clasic Torque‐VCR 200 400 200 400 350 350 150 300 150 300 250 250 100 200 100 200 150 150 Power [kW]

50 100 Torque [N‐m] Power [kW]

50 100 Torque [N‐m] 50 50 0 0 0 0 500 1500 2500 3500 4500 5500 6500 500 1500 2500 3500 4500 5500 6500 Crank speed [rpm] Crank speed [rpm]

Figure 12.12. Engine performance: classic versus VCR. Figure 12. Engine performance: classic versus VCR. FromFurthermore, dynamic in viewpoint the Figure11a–d, analyses, we to havesee the an contribution image about of joint the loading inertia magnitudetorque on the that total influences torque Furthermore, in the Figure11a–d, we see the contribution of the inertia torque on the total torque theengine. pin wear As can in time,be viewed, Figure contribution11a show the of evolution the inertia of the torque joint reactionfrom total for engine a complete torque cycle is significantly on the crank engine. As can be viewed, contribution of the inertia torque from total engine torque is significantly andat higher con-rod speeds. pin when For lower a crankshaft speeds, the has contribution nominal speed of inertia (6000 rpm). is: at idle As canspeed—8%, be viewed, maximum in comparison torque at higher speeds. For lower speeds, the contribution of inertia is: at idle speed—8%, maximum torque withspeed—50%. classic mechanism, the con-rod big end on the analyzed VCR solution has comparable values speed—50%. withBased the ones on from the theperformed classic mechanism. multibody dynamic analyses, Figure 12 shows the characteristic of Based on the performed multibody dynamic analyses, Figure 12 shows the characteristic of powerFurthermore, and torque infor the the Figure two solutions 11a–d, we studied. see the Both contribution maximum of power the inertia values torque and on maximum the total torque power and torque for the two solutions studied. Both maximum power values and maximum torque engine.values obtained As can be have viewed, a percentage contribution increasing of the close inertia to torque 40% for from the VCR total enginesolution. torque is significantly values obtained have a percentage increasing close to 40% for the VCR solution. at higherAnother speeds. important For lower parameter speeds, to the appreciate contribution the ofperformance inertia is: at of idle an engine speed—8%, is the maximum lithic power torque that Another important parameter to appreciate the performance of an engine is the lithic power that speed—50%.means the power divided at engine displacement. To evaluate this parameter for both configurations, means the power divided at engine displacement. To evaluate this parameter for both configurations, it wasBased taken on into the performedaccount that multibody the engine dynamic displacement analyses, Figureobtained 12 showsfor both the solutions characteristic has ofdifferent power it was taken into account that the engine displacement obtained for both solutions has different andvalues torque caused for theby different two solutions strokes. studied. For the Both classic maximum solution, power the stroke values is and lower maximum by25% torque compared values to values caused by different strokes. For the classic solution, the stroke is lower by25% compared to obtainedVCR and have the engine a percentage displacement, increasing too. close Based to 40%on it, for the the lithic VCR power solution. obtained from the calculus for VCR and the engine displacement, too. Based on it, the lithic power obtained from the calculus for VCRAnother is higher important by20% compared parameter to tothe appreciate classic solution. the performance of an engine is the lithic power that VCRmeans is thehigher power by20% divided compared at engine to the displacement. classic solution. To evaluate this parameter for both configurations, it3. wasConclusions taken into account that the engine displacement obtained for both solutions has different values 3. Conclusions caused by different strokes. For the classic solution, the stroke is lower by 25% compared to VCR and Appl. Sci. 2020, 10, 2733 13 of 15 the engine displacement, too. Based on it, the lithic power obtained from the calculus for VCR is higher by 20% compared to the classic solution.

3. Conclusions This review paper aimed to provide a comprehensive overview and a summary of results obtained for a novel solution of a mechanism used for an engine with variable compression ratio compared to a classical mechanism. The overall results were obtained from Multi-Body Simulation technique (MBS) and based on them; it was intended to evaluate kinematic and dynamic parameters from both mechanisms using the considered scenarios. The analytical approaches that are commonly used in the multi-body systems, such as equilibrium equations written only on one body from overall assembly, are reviewed thoroughly. In particular, the paper elaborated on the efficient modifications that can be applied or adopted to a classical engine mechanism. These modifications were applied through synthesizing a novel mechanism using a new configuration of the bodies in assembly thru implementation an oscillation arm between crankshaft and con-rod. Furthermore, possibility to change some kinematic and dynamic parameters from mechanisms through change in the position of the pivot point of oscillation arm was another important novelty. The most important conclusions reached from the literature review are: # From a kinematic point of view, an increase of 25% was obtained for piston stroke on the novelty design mechanism compared to the classical one. This increase is due to the oscillating arm included in the configuration of the mechanism between the crankshaft and con-rod. # Furthermore, the velocity and acceleration of the piston for the novelty mechanism have a similar percent of increase with respect to the piston stroke obtained with a classic mechanism. # The percentage increase of the kinematic parameters also led to the increase of the internal dynamic loads in the mechanism. For example, in the novel mechanism, on the big end of a con-rod, a maximum value of the resulting dynamic load greater than 8% compared to the classical mechanism was obtained. # The dynamic loading reduced to the lever of crankshaft will induce an increase of the torque and also an increase of power. According to the simulations, a major percent of 40% is obtained for the novel mechanism compared to the classic one. # Finally, the lithic power calculated in terms of kinematic and dynamic parameters has a 20% increasing obtain for the novel mechanism comparison to the classic one. Beside the advantageous highlights based on kinematic and dynamic analysis, it can be concluded that from constructive and functional viewpoints, considering the parameters determined from virtual simulation, the engine design with an oscillating arm provides a great advantage in comparison with conventional engine, considering that most parameters obtained from the analyses are accomplished. The mechanism design solution with an oscillating arm can be adopted for most internal combustion engines with two or four-cycle engines, and for any type of engine dimensions. Variable Compression Ratio (VCR) technology offers the largest potential improvement in part-throttle fuel efficiency and CO2 emissions when compared to other competing technologies. Furthermore, VCR technology can offer torque enhancement at low rpm when any boost or auxiliary systems are least effective. A possible obstacle to adoption a VCR solution could be the incompatibility with major components from current production and difficulties of combining VCR and non-VCR manufacturing within existing plants. As environmental pressure on the automobile increases and investment plans for new products are put in place, the justification for VCR will become more evident. Taking into account that large numbers of combustion engines are made every year, the VCR engine with an oscillating arm can represent a very good solution for novel engine design.

Author Contributions: Data curation, C.I.; Formal analysis, M.-L.S.; Project administration, C.I.P.; Writing—original draft, R.M. All authors have read and agreed to the published version of the manuscript. Appl. Sci. 2020, 10, 2733 14 of 15

Funding: This research received no external funding. Acknowledgments: This work was supported in part by the Department of Mechanical Engineering, Transilvania University of Bra¸sov, Romania. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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