Analysis on Steering Performance of Active Steering Bogie According to Steering Angle Control on Curved Section

applied sciences

Article Analysis on Steering Performance of Active Steering Bogie According to Steering Angle Control on Curved Section

Hyunmoo Hur 1,*, Yujeong Shin 1 and Dahoon Ahn 2 1 Advanced Railroad Vehicle Division, Korean Railroad Research Institute, 176 Cheoldobakmulkwan-ro, Uiwang-si, Gyeonggi-do 16105, Korea; [email protected] 2 Department of Mechanical and Automotive Engineering, Kongju National University, 1223-24 Cheonan-daero, Cheonan-si, Chungcheongnam-do 31080, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-31-460-5245

Received: 6 April 2020; Accepted: 23 June 2020; Published: 26 June 2020

Abstract: In this paper, prior to the commercialization of a developed active steering bogie, we want to analyze steering performance experimentally according to steering angle level with the aim of obtaining steering performance data to derive practical design specifications for a steering system. In other words, the maximum steering performance can be obtained by controlling the steering angle at the 100% level of the target steering angle, but it is necessary to establish the practical control range in consideration of the steering system cost increase, size increase, and consumer steering performance requirements and commercialize. The steering control test using the active steering bogie was conducted in the section of the steep curve with a radius of curvature of R300, and steering performance such as bogie angle, wheel lateral force, and derailment coefficient were analyzed according to the steering angle level. As the steering angle level increased, the bogie indicated that it was aligned with the radial steering position, and steering performance such as wheel lateral force and derailment coefficient was improved. The steering control at 100% level of the target steering angle can achieve the highest performance of 83.6% reduction in wheel lateral force, but it can be reduced to about one-half of the conventional bogie at 25% level control and about one-third at 50% level. Considering cost rise by adopting the active steering system, this result can be used as a very important design indicator to compromise steering performance and cost rise issues in the design stage of the steering system from a viewpoint of commercialization. Therefore, it is expected that the results of the steering performance experiment according to the steering angle level in this paper will be used as very useful data for commercialization.

Keywords: active steering bogie; steering angle; steering performance; bogie angle; lateral force; derailment coeﬃcient

1. Introduction When a railway vehicle runs on curved sections, severe wheel wear and noise occur between the wheel and the rail. This is because the railway vehicle is not equipped with a steering device, so it is diﬃcult to run smoothly in the curved section. That is, an attack angle is generated between the wheel and the rail, which causes unnecessary force in the running and lateral direction of the wheel, which causes wheel wear and noise. Research on an active steering bogie began in the early 1990s to solve problems caused by existing railway bogies when running on curved sections. Theoretical studies were carried out, such as the control concept for steering control of an active steering bogie to improve the poor steering performance of conventional railway vehicles [1–5].

Appl. Sci. 2020, 10, 4407; doi:10.3390/app10124407 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 4407 2 of 15

Recently, a railway vehicle with a combination of active steering technology, active suspension and tilting technologies has been commercialized [6]. However, although the rough concept of active steering is described, details such as specifications of the steering system and steering test results are not described. Umehara has performed active steering control tests on the curved section of a factory test line using active steering bogie prototypes equipped with an electro-hydraulic type actuators, and analyzed the reduction of wheel lateral force [7]. Suzuki tested the wheel lateral force reduction according to active steering control in the steep curve of a factory test line for a prototype steering bogie with a pneumatic-type active steering system [8]. In the above two experimental papers, wheel lateral forces generated running on curved sections were measured and wheel lateral force reduction was analyzed in order to analyze the performance of the active steering bogie. To evaluate directly the steering performance of an active steering truck, it is necessary to measure the wear of the wheels and analyze the amount of reduction. However, this requires measuring and analyzing the wear shape of the wheels throughout a long test run, which takes a lot of time and cost. Therefore, in the stage of development, it is efficient to measure the lateral force of the wheel, which directly affects the wheel wear, and analyze the lateral force reduction according to the active steering control. Therefore, the above experimental results analyzed the active steering performance by measuring lateral forces acting on wheels. Meanwhile, Hur proposed the concept of radial steering position control through real-time curve detection [9]. The feasibility of the curve-detecting method, which is a core technology of steering control strategy, has been verified experimentally [10]. The validity of the proposed control concept has been verified through active steering simulation analysis [11]. In addition, a prototype of an electro-mechanical type steering system was manufactured to be installed on an active steering bogie and performance tests were conducted on the steering system. Steering bogies equipped with steering systems were manufactured and steering control tests simulating curve running prior to the test run on the commercial line were conducted [12]. Based on the results of the above study, Hur constructed a test EMU (Electronic Multiple Unit) train equipped with an active steering bogie and conducted steering performance tests according to active steering control on a commercial line, not on a factory line [13]. The test results showed that the wheel lateral force was reduced by up to 86.2% compared to the conventional bogie. This result was the best of the wheel lateral force test results for the active steering bogie reported to date. According to the results of the above study, the concept of radial steaming position control through real-time curvature radius estimation proposed by Hur was proved with simulation and a test run, and steering performance was also proved to be excellent. In this paper, prior to the commercialization of a developed active steering bogie, we want to analyze steering performance experimentally according to the steering angle level with the aim of obtaining steering performance data to derive practical design specifications for steering system. In other words, the maximum steering performance can be obtained by controlling the steering angle at 100% level of the target steering angle, but it is necessary to establish the practical control range in consideration of the steering system cost increase, size increase, and consumer steering performance requirements, and to commercialize this. Therefore, an experimental study using an active steering bogie was conducted to analyze the steering performance according to the steering angle level. The steering control test was performed on a steep curve section with a radius of curvature of 300 m using an active steering bogie prototype for EMU. This study analyzes the bogie angle, wheel lateral force reduction and derailment safety under the steering angle control of the active steering bogie and describes the results. Appl. Sci. 2020, 10, 4407 3 of 15 Appl. Sci. 2020, 10, x 3 of 16 causesAppl.2. Active Sci. unnecessary 2020 Steering, 10, x Control force in Strategy the driving direction and the lateral direction of the wheel, which3 ofis 16a major factor causing wear of the wheels and rails and the generation of noise. When the railway vehicle runs on the curved section, attack angle between the wheel and the rail causesTherefore, unnecessary in order force for in thethe railwaydriving vehicledirection smoot and hlythe runlateral the directioncurve section, of the the wheel, angle which of attack is a are generated as shown in Figure1 due to the lack of steering function of the wheel [ 13]. This causes becomesmajor factor “0” causingif the wheelset wear of is the aligned wheels with and the rails center and ofthe curvature generation as ofshown noise. in Figure 2 using active unnecessary force in the driving direction and the lateral direction of the wheel, which is a major factor steeringTherefore, control intechnology. order for Atthe this railway time, vehiclethis geometri smootchly position run the is calledcurve thesection, radial the steering angle position.of attack causing wear of the wheels and rails and the generation of noise. becomes “0” if the wheelset is aligned with the center of curvature as shown in Figure 2 using active steering control technology. At this time, this geometric position is called the radial steering position.

Figure 1. Wheelset alignment of a conventional railway vehicle when running on curved section. Figure 1. Wheelset alignment of a conventional railway vehicle when running on curved section. Therefore, in order for the railway vehicle smoothly run the curve section, the angle of attack becomes “0” if the wheelset is aligned with the center of curvature as shown in Figure2 using active Figure 1. Wheelset alignment of a conventional railway vehicle when running on curved section. steering control technology. At this time, this geometric position is called the radial steering position.

Figure 2. Wheelset alignment of a railway vehicle with active steering technology when running on curved section. Figure 2. Wheelset alignment of a railway vehicle with active steering technology when running on Figure 2. Wheelset alignment of a railway vehicle with active steering technology when running on curved section. Figurecurved section.3 shows the geometrical relationship between the body and the bogies, assuming the vehicleFigure is in3 showsthe radial the steering geometrical position relationship in the curve between section. the body In Figure and the3, the bogies, angle assuming (2δ) formed the betweenvehicleFigure is two in the3 wheelsetsshows radial the steering is geometrical called position the steeringrelationship in the curve angle, section.between and the In the angle Figure body (3θ, )and theat which angle the bogies, (2 theδ) formedbogie assuming is between rotated the withvehicletwo wheelsetsrespect is in tothe isthe calledradial vehicle thesteering body steering isposition called angle, the andin bogiethe the curve angleangle. section. (θ ) at which In Figure the bogie 3, the is rotated angle with(2δ) formed respect betweento theWhen vehicle two the wheelsets body bogie is and called is wheelset called the bogie the are steering angle. aligned angle, with theand radial the angle steering (θ) at position, which thethe bogiebogie isangles rotated of thewith front Whenrespect and the to rear bogiethe bogies vehicle and wheelsetare body the issame. arecalled aligned At the this bogie with time theangle., from radial the steering geometric position, relationship the bogie of Figure angles 3, of the targetfrontWhen and values rear the for bogies bogie wheelset areand the wheelsetsteering same. Atangleare this aligned and time, bogie with from angle the geometricradial for the steering idea relationshipl wheelset position, ofsteering the Figure bogie 3in, the theangles targetcurve of sectionthe front of and radius rear R bogies are derived are the as same. shown At in this Equations time, from (1) andthe geometric(2) [14,15]. relationship of Figure 3, the target values for wheelset steering angle and bogie angle for the ideal wheelset steering in the curve 2 = 2/ (1) section of radius R are derived as shown in Equations (1) and (2) [14,15].

2=/ = 2/ (2)(1)

=/ (2) Appl. Sci. 2020, 10, 4407 4 of 15 values for wheelset steering angle and bogie angle for the ideal wheelset steering in the curve section of radius R are derived as shown in Equations (1) and (2) [14,15].

2δ = 2d/R (1) Appl. Sci. 2020, 10, x 4 of 16 θ = L/R (2) where, where, 2δ: steering angle(rad) R:2δ :radius steering of curve(m) angle(rad) R: radius of curve(m) 2d: wheel base(m) 2d: wheel base(m) L: semi-spacing of distance between bogie centers(m) θ:: bogie bogie angle angle between between body body and and bogie(rad) bogie(rad)

Figure 3. Radial steering position. Figure 3. Radial steering position. When a railway vehicle is run on a curved section as above, it can ideally pass through the curve if When a railway vehicle is run on a curved section as above, it can ideally pass through the curve it is located in a radial steering position. In other words, if steering control is performed by calculating if it is located in a radial steering position. In other words, if steering control is performed by the target steering angle by applying Equation (1), the railway vehicle will be located in the radial calculating the target steering angle by applying Equation (1), the railway vehicle will be located in steering position. In order to apply Equation (1), information on the radius of the curved section the radial steering position. In order to apply Equation (1), information on the radius of the curved passing through is required. Previously, a method of pre-input of the curve information according section passing through is required. Previously, a method of pre-input of the curve information to the position into the controller was applied, but it was inefficient. In this paper, the method of according to the position into the controller was applied, but it was inefficient. In this paper, the estimating the radius of curvature in real time developed by the author was used, and this method of method of estimating the radius of curvature in real time developed by the author was used, and this estimating the radius of curvature was experimentally verified [10]. method of estimating the radius of curvature was experimentally verified [10]. 3. Steering Control Test on the Curved Section 3. Steering Control Test on the Curved Section 3.1. Active Steering Bogie 3.1. Active Steering Bogie To analyze the steering performance according to the steering angle in the curve section, the test run wasTo analyze carried the out steering using the performance active steering according bogie to prototype. the steering An angle active in the steering curve bogie section, prototype the test runwas was developed carried forout subwayusing the EMU active trains steering running bogie on prototype. urban railway An active areas steering [14,15]. bogie Figure prototype4 shows was the developedconfiguration for ofsubway the active EMU steering trains bogierunning and on Figure urban5 showsrailway the areas active [14,15]. steering Figure bogie 4 prototypeshows the configurationinstalled on the of test the train. active steering bogie and Figure 5 shows the active steering bogie prototype installed on the test train. An active steering bogie adopts a radial steering position control strategy based on real-time curvature radius estimation [9–11]. The active steering system of the bogie is composed of a sensor unit, a control unit and a driving unit [14]. The sensor unit estimates the radius of curvature of the curve in real time, the controller calculates the target steering angle for active steering, and the steering driving unit conducts steering the wheelset according to the controller command. Appl. Sci. 2020, 10, x 5 of 16 Appl. Sci. 2020, 10, x 5 of 16 The minimum radius of the curved section that can be detected by the active steering bogie is The minimum radius of the curved section that can be detected by the active steering bogie is R80 with a radius of curvature of 80 m and the maximum controllable steering angle is 0.5 degrees. R80 with a radius of curvature of 80 m and the maximum controllable steering angle is 0.5 degrees. In other words, steering control is possible up to R250, a radius of curve of 250 m, the smallest curve In other words, steering control is possible up to R250, a radius of curve of 250 m, the smallest curve on commercial lines. on commercial lines. The steering driving unit is adopting an electro-mechanical type actuator, with a maximum The steering driving unit is adopting an electro-mechanical type actuator, with a maximum steering thrust force of more than 50,000 N. Table 1 shows the specifications of the active steering steering thrust force of more than 50,000 N. Table 1 shows the specifications of the active steering Appl.system Sci. of2020 the, 10 active, 4407 steering bogie 5 of 15 system of the active steering bogie

Figure 4. Configuration of the active steering bogie. Figure 4. ConfigurationConﬁguration of the active steering bogie.

Figure 5. Prototype of the active steering bogie. Figure 5. Prototype of the active steering bogie. Figure 5. Prototype of the active steering bogie. An active steering bogie adopts a radial steering position control strategy based on real-time Table 1. Specifications of the active steering system. curvature radius estimationTable [9–11 1.]. Specifications The active steeringof the active system steering of thesystem. bogie is composed of a sensor unit, a control unit and a driving unitCategory [14]. Specification Category Specification The sensor unit estimatesDetectable the radius curve of curvature radius of the curve min in 80 real m time, the controller calculates Detectable curve radius min 80 m the target steering angle for activeSteering steering, angle and the steering driving 0.5 degrees unit conducts steering the wheelset Steering angle 0.5 degrees according to the controller command.Supply voltage three phase 380 VAC Supply voltage three phase 380 VAC The minimum radiusMaximum of the current curved section(per vehicle) that can be detected 16 A by the active steering bogie is Maximum current (per vehicle) 16 A R80 with a radius of curvatureThrust force(per of 80 m anddriving the maximumunit) controllable above 50,000 steering N angle is 0.5 degrees. Thrust force(per driving unit) above 50,000 N In other words, steering control is possible up to R250, a radius of curve of 250 m, the smallest curve on commercialThe steering lines. controller is mounted on the body to perform steering control of the front and rear The steering controller is mounted on the body to perform steering control of the front and rear steeringThe bogies. steering The driving control unit algorithm is adopting of the an steerin electro-mechanicalg controller is type shown actuator, in the withblock a diagram maximum in steering bogies. The control algorithm of the steering controller is shown in the block diagram in Figuresteering 6. thrustThe controller force of morefor steering than 50,000 estimates N. Tablethe ra1 diusshows of curvature the speciﬁcations through ofthe the signal active detected steering in Figure 6. The controller for steering estimates the radius of curvature through the signal detected in realsystem time of from the active the curvature steering bogie sensor and calculates the target steering angle. Figure 7 shows the real time from the curvature sensor and calculates the target steering angle. Figure 7 shows the mechanism by which the drive unit works to achieve the target steering angle. This control method mechanism by which the driveTable unit 1. Speciﬁcations works to achieve of the active the target steering steering system. angle. This control method

Category Speciﬁcation Detectable curve radius min 80 m Steering angle 0.5 degrees Supply voltage three phase 380 VAC Maximum current (per vehicle) 16 A Thrust force(per driving unit) above 50,000 N Appl. Sci. 2020, 10, 4407 6 of 15

Appl. Sci. 2020, 10, x 6 of 16 The steering controller is mounted on the body to perform steering control of the front and rear has beensteering experimentally bogies. The verified control algorithmthrough a of test the run steering using controller a test train is shown equipped in the block with diagram an active in steering bogie [15].Figure 6. The controller for steering estimates the radius of curvature through the signal detected in real time from the curvature sensor and calculates the target steering angle. Figure7 shows the Appl. Sci. 2020, 10, x 6 of 16 mechanism by which the drive unit works to achieve the target steering angle. This control method hashas been been experimentally experimentally verified veriﬁed through through a a test test run run using using a a test test train train equipped equipped with with an an active active steering steering bogiebogie [15]. [15].

Figure 6. Block diagram of the active steering control by estimating the radius of the curve. FigureFigure 6. 6. BlockBlock diagram diagram of of the the active active steering steering contro controll by by estimating estimating the the radius radius of of the the curve. curve.

Figure 7. The steering angle produced between the front and rear wheelsets of the bogie. Figure 7. The steering angle produced between the front and rear wheelsets of the bogie. 3.2. Test Curve Section Figure 7. The steering angle produced between the front and rear wheelsets of the bogie. 3.2.The Test Curvesteering Section control test to analyze the steering performance according to the steering angle in 3.2. Testthe Curve curveThe Section steeringsection was control performed test to analyze on the the R300 steering curve performance with a radius according of 300 m to of the the steering commercial angle inline. the Figurecurve section8 shows was the performed curvature onof the R300test section curve withmeasured a radius by ofthe 300 curvature m of the commercialsensor unit mounted line. Figure on8 Thetheshows steering active the steering curvature control bogie oftest the for to test real-time analyze section curve measuredthe steeringdetectio byn. the performanceThe curvature total length sensor according of unit the mountedtest curvedto the on sectionsteering the active is angle in the curve450steering section m and bogie the was length for performed real-time of the curvecircular on detection. thecurve R300 is The250 curve totalm. length with ofa theradius test curved of 300 section m of is the 450 mcommercial and the line. Figure 8length shows of the circularcurvature curve of is the 250 m.test section measured by the curvature sensor unit mounted on the active steering bogie for real-time curve detection. The total length of the test curved section is 450 m and the length of the circular curve is 250 m. Appl.Appl. Sci. Sci.2020 2020, ,10 10,, 4407 x 77 of of 15 16

3.5

2.5

1.5 Curvature(1/km) 1

0.5

0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m) Figure 8. Curvature of the test curve section. Figure 8. Curvature of the test curve section. 3.3. Test Condition for Active Steering Condition 3.3. Test Condition for Active Steering Condition Table2 shows the test conditions for analyzing the steering performance according to the steering angleTable on the 2 curved shows section. the test Passive conditions is the runningfor analyzing condition the of steering the curved performance section of theaccording existing bogieto the notsteering equipped angle with on the activecurved steering section. system. Passive Active is the (25%)running refers condition to the case of the when curved the active section steering of the bogieexisting is run bogie on not the testequipped section with while the controlling active steering to 25% system. of the Active target steering(25%) refers angle. to the case when the active steering bogie is run on the test section while controlling to 25% of the target steering angle. Active (50%) and ActiveTable (75%) 2. Test represent condition when for activesteering steering control control. is conducted at the 50% and 75% levels of the target steering angle, respectively. Active (100%) means that steering control is Case Test Condition conducted completely to 100% level of the target steering angle. Passive No active steering Active (25%) Control to 25% of the target steering angle Table 2. Test condition for active steering control. Active (50%) Control to 50% of the target steering angle ActiveCase (75%) Control to 75%Test ofCondition the target steering angle Active (100%) Control to 100% of the target steering angle Passive No active steering Active (25%) Control to 25% of the target steering angle Active (50%) andActive (50%) (75%) represent Control when to 50% steering of the target control steering is conducted angle at the 50% and 75% levels of the target steeringActive angle, (75%) respectively. Control Activeto 75% (100%)of the target means steering that steering angle control is conducted completely to 100% levelActive of the (100%) target Controlsteering to angle. 100% of the target steering angle

4. Test Results of the Active Steering Control 4. Test Results of the Active Steering Control 4.1. Analysis Method 4.1. Analysis Method In order to analyze the steering performance according to the steering angle on the curved section, In order to analyze the steering performance according to the steering angle on the curved the bogie angle of the front and rear bogies, which are related to the radial steering position of the section, the bogie angle of the front and rear bogies, which are related to the radial steering position bogie, and the lateral force and the derailment coefficient of the wheel, which are dynamic factors, of the bogie, and the lateral force and the derailment coefficient of the wheel, which are dynamic were measured. factors, were measured. To confirm the test conditions for steering angle implementation, steering angle was measured To confirm the test conditions for steering angle implementation, steering angle was measured using a steering angle sensor as shown in Figure9. To measure the bogie angle, which is the rotating using a steering angle sensor as shown in Figure 9. To measure the bogie angle, which is the rotating angle between the body and the bogie, the geometric displacement between the body and the bogie angle between the body and the bogie, the geometric displacement between the body and the bogie was measured and converted into the bogie angle. was measured and converted into the bogie angle. To measure the lateral force and the derailment coefficient of the wheel, a measuring wheelset To measure the lateral force and the derailment coefficient of the wheel, a measuring wheelset was manufactured to measure the lateral and vertical force applied to the wheel and it was installed on was manufactured to measure the lateral and vertical force applied to the wheel and it was installed the active steering bogie [15]. Figure 10 shows the measuring wheelset to measure wheel forces such on the active steering bogie [15]. Figure 10 shows the measuring wheelset to measure wheel forces as wheel lateral force and derailment coefficient. The method of measuring the action force applied to such as wheel lateral force and derailment coefficient. The method of measuring the action force the wheels of a railway vehicle proposed by Ham was used [16]. applied to the wheels of a railway vehicle proposed by Ham was used [16]. Appl. Sci. 2020, 10, 4407 8 of 15 Appl. Sci. 2020, 10, x 8 of 16 Appl. Sci. 2020, 10, x 8 of 16

Figure 9. Steering angle sensor. Figure 9. Steering angle sensor.

Figure 10. Wheel force measuring wheelset. Figure 10. Wheel force measuring wheelset. Figure 10. Wheel force measuring wheelset. 4.2. Steering Angle 4.2. Steering Angle 4.2. SteeringThe steering Angle control test was performed according to the test conditions in Section 3.3 to analyze The steering control test was performed according to the test conditions in Section 3.3 to analyze the steeringThe steering performance control test according was performed to the steering according angle to onthe the test curved conditions section. in Section Figure 3.311 showsto analyze the the steering performance according to the steering angle on the curved section. Figure 11 shows the steeringthe steering angle performance test results according measured to by the the steering steering an anglegle on sensorthe curved to verify section. that Figure the active 11 shows steering the steering angle test results measured by the steering angle sensor to verify that the active steering controlsteering test angle conditions test results are measured properly implemented.by the steering Table angle3 showssensor theto verify mean valuesthat the for active the steeringsteering controlAppl. Sci. test 2020 conditions, 10, x are properly implemented. Table 3 shows the mean values for the steering9 of 16 anglescontrol when test conditions the steering are bogie properly runs inimplemented. the circular section Table 3 of shows the test the section. mean values for the steering angles when the steering bogie runs in the circular section of the test section. angles when the steering bogie runs in the circular section of the test section. The steering angle of0.7 passive condition with insufficient steering function is 0.029 degrees. This The steering angle of passive Targetcondition steering with angle insufficient steering function is 0.029 degrees. This indicates that the measured value Passiveis very low at 7.3% of the target value, considering that the target indicates that the measured0.6 value is very low at 7.3% of the target value, considering that the target steering angle required to pass the R300Active(25%) curve is 0.4 degrees according to Equation (1). As the steering steering angle required to pass the Active(50%)R300 curve is 0.4 degrees according to Equation (1). As the steering angle implementation level0.5 increasesActive(75%) with active steering control, the steering angle is approximated angle implementation level increasesActive(100%) with active steering control, the steering angle is approximated to the test conditions. That is, in the case of Active (50), it is 0.208 degrees., which is 52% of the target to the test conditions. That0.4 is, in the case of Active (50), it is 0.208 degrees., which is 52% of the target steering angle. In the case of Active (100) which performs 100% steering control, the measured value steering angle. In the case of Active (100) which performs 100% steering control, the measured value is 0.393 degrees., which is0.3 controlled well as 98.3% of the target steering angle. is 0.393 degrees., which is controlled well as 98.3% of the target steering angle. 0.2 Steering angle(deg.) Steering

0.1

0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m) Figure 11. Measured steering angle according to steering control condition. Figure 11. Measured steering angle according to steering control condition.

Table 3. Mean steering angle for the circular section of the test section.

Case Steering Angle (degrees) Ratio to Target Steering Angle (%) Passive 0.029 7.3 Active (25%) 0.131 32.8 Active (50%) 0.208 52.0 Active (75%) 0.295 73.8 Active (100%) 0.393 98.3

4.3. Bogie Angle Figures 12 and 13 show the measured bogie angles generated in the front and rear bogie according to the steering angle test conditions. Figure 14 shows the bogie angle difference between the front and rear bogie. Table 4 shows the mean values for the bogie angles when the steering bogie run the circular section of the test section. In the case of a passive state with insufficient steering function, the bogie angle for the front bogie is 1.404 degrees and that for the rear bogie is 1.055 degrees and the difference is 0.349 degrees, which is very large. This result is due to the lack of steering function and the bogie is not aligned in the radial steering position when running on the curved section. On the other hand, as the steering angle level increases with active steering control, it is shown that the bogie angle for the front bogie decreases and that for the rear bogie tends to increase. In addition, the bogie angle difference is also gradually decreasing. That is, in the case of Active (100) which performs 100% steering control, the bogie angle for the front bogie is 1.242 degrees, that for the rear bogie is 1.228 degrees, and the difference is only 0.014 degrees. This shows that the bogie is aligned in the radial position when running the curved section with active steering control. Appl. Sci. 2020, 10, 4407 9 of 15

Table 3. Mean steering angle for the circular section of the test section.

Case Steering Angle (Degrees) Ratio to Target Steering Angle (%) Passive 0.029 7.3 Active (25%) 0.131 32.8 Active (50%) 0.208 52.0 Active (75%) 0.295 73.8 Active (100%) 0.393 98.3

The steering angle of passive condition with insuﬃcient steering function is 0.029 degrees. This indicates that the measured value is very low at 7.3% of the target value, considering that the target steering angle required to pass the R300 curve is 0.4 degrees according to Equation (1). As the steering angle implementation level increases with active steering control, the steering angle is approximated to the test conditions. That is, in the case of Active (50), it is 0.208 degrees., which is 52% of the target steering angle. In the case of Active (100) which performs 100% steering control, the measured value is 0.393 degrees., which is controlled well as 98.3% of the target steering angle.

4.3. Bogie Angle Figures 12 and 13 show the measured bogie angles generated in the front and rear bogie according Appl. Sci. 2020, 10, x 10 of 16 to the steering angle test conditions. Figure 14 shows the bogie angle diﬀerence between the front and rearAppl. bogie. Sci. 2020 Table, 10, x4 shows the mean values for the bogie angles when the steering bogie run the circular10 of 16 section of the test section.2.5 Passive Active(25%) 2.5 Active(50%) 2 Passive Active(75%) Active(25%) Active(100%) Active(50%) 2 1.5 Active(75%) Active(100%)

1.5 1

1 Front bogie angle(deg.) 0.5 Front bogie angle(deg.) 0.5 0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m) 0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m) Figure 12. Measured bogie angle of the front bogie. Figure 12. Measured bogie angle of the front bogie. Figure 12. Measured bogie angle of the front bogie. 2.5 Passive Active(25%) 2.5 Active(50%) 2 Passive Active(75%) Active(25%) Active(100%) Active(50%) 2 1.5 Active(75%) Active(100%)

1.5 1

1 Rear bogie angle(deg.) 0.5 Rear bogie angle(deg.) 0.5 0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m) 0 5650Figure5700 13.5750Measured5800 5850 bogie5900 angle5950 of the6000 rear6050 bogie.6100 6150 Distance(m) Figure 13. Measured bogie angle of the rear bogie.

Figure 13. Measured bogie angle of the rear bogie. 0.6 Passive Active(25%) 0.50.6 Active(50%) Passive Active(75%) Active(25%) 0.40.5 Active(100%) Active(50%) Active(75%) 0.30.4 Active(100%)

0.20.3

0.10.2 Bogie angle difference(deg.) 0.10 Bogie angle difference(deg.) -0.10 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m) -0.1 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Figure 14. Bogie angle difference between Distance(m)front and rear bogies according to steering control

conditions. Figure 14. Bogie angle difference between front and rear bogies according to steering control conditions.

Appl. Sci. 2020, 10, x 10 of 16

2.5 Passive Active(25%) Active(50%) 2 Active(75%) Active(100%)

1.5

1 Front bogie angle(deg.) 0.5

0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m)

Figure 12. Measured bogie angle of the front bogie.

2.5 Passive Active(25%) Active(50%) 2 Active(75%) Active(100%)

1.5

1 Rear bogie angle(deg.) 0.5

0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m)

Appl. Sci. 2020, 10, 4407 Figure 13. Measured bogie angle of the rear bogie. 10 of 15

0.6 Passive Active(25%) 0.5 Active(50%) Active(75%) 0.4 Active(100%)

0.3

0.2

0.1 Bogie angle difference(deg.) 0

-0.1 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m)

FigureFigure 14. 14.Bogie Bogie angle angle diﬀ erencedifference between between front andfront rear and bogies rear according bogies according to steering to control steering conditions. control conditions. Table 4. Mean bogie angle for the circular section of the test section.

Bogie Angle (Degrees) Case Front Rear Diﬀerence Passive 1.404 1.055 0.349 Active (25%) 1.363 1.118 0.244 Active (50%) 1.317 1.151 0.165 Active (75%) 1.278 1.211 0.067 Active (100%) 1.242 1.228 0.014

In the case of a passive state with insufficient steering function, the bogie angle for the front bogie is 1.404 degrees and that for the rear bogie is 1.055 degrees and the difference is 0.349 degrees, which is very large. This result is due to the lack of steering function and the bogie is not aligned in the radial steering position when running on the curved section. On the other hand, as the steering angle level increases with active steering control, it is shown that the bogie angle for the front bogie decreases and that for the rear bogie tends to increase. In addition, the bogie angle difference is also gradually decreasing. That is, in the case of Active (100) which performs 100% steering control, the bogie angle for the front bogie is 1.242 degrees, that for the rear bogie is 1.228 degrees, and the difference is only 0.014 degrees. This shows that the bogie is aligned in the radial position when running the curved section with active steering control.

Table 4. Mean bogie angle for the circular section of the test section.

Bogie Angle (degrees) Case front rear difference Passive 1.404 1.055 0.349 Active (25%) 1.363 1.118 0.244 Active (50%) 1.317 1.151 0.165 Active (75%) 1.278 1.211 0.067 Active (100%) 1.242 1.228 0.014

4.4. Lateral Force of the Wheel Figure 15 is test data obtained by measuring the lateral force generated on the front outer wheel of the test vehicle according to the steering angle test conditions. For lateral force analysis, UIC 518 OR “Testing and approval of railway vehicles from the point of view of their dynamic behaviour— Safety—Track fatigue—Running behaviour”, the world’s railway standard, is applied [17]. When the test standard was applied to calculate the maximum permissible limit of wheel lateral force, the maximum permissible limit was 34 kN, and all measurement results were within the allowable limit. Figure 16 is the result of analyzing the lateral force test data by subdividing 70 m into small sections and arranging them in the cumulative distribution order to extract 99.85% of the values as the representative sections of the small sections. Table 5 shows the mean values of the small section representative values for the analysis results in Figure 15 and the reduction rate for the lateral force of each test case for the passive case. The mean lateral force of the wheel in the passive case with insufficient steering is 14.99 kN. On the other hand, in the active steering control test condition, the wheel lateral force decreases as the steering angle implementation level increases. In the case of Active (25), it is 7.53 kN, which is 49.8% lower than the Passive case. In the case of Active (50) and Active (75), the mean lateral forces were 4.68 kN and 3.20 kN, respectively, decreasing by 68.8% and 78.6%, respectively. In the case of Active (100) with 100% steering control, the mean lateral force is 2.46 kN, which is 83.6% lower than the passive case. Therefore, it was confirmed that the bogie was aligned with the radial position as the steering angle increased to meet the target steering angle as the test train passed through the curved section, Appl.and Sci.the2020 wheel, 10, 4407lateral force was also significantly reduced. 11 of 15

25 Passive Active(25%) Active(50%) 20 Active(75%) Active(100%)

10 Lateral force(kN)

0 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Appl. Sci. 2020, 10, x 12 of 16 Distance(m)

Figure 15. Wheel lateral force test data according to steering control test conditions. Figure 15. Wheel lateral force test data according to steering control test conditions. 25 25 Passive Passive Active(25%) Active(50%) 20 20

15 15

10 10 Lateral force(kN) Lateral Lateral force(kN) Lateral

5 5

0 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Section Section

(a) Passive (b) Active(25%)

25 25 Passive Passive Active(75%) Active(100%) 20 20

15 15

10 10 Lateralforce(kN) Lateral force(kN) Lateral

5 5

0 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Section Section

Figure 16. Analysis results for wheel lateral force according to steering control test conditions. Figure 16. Analysis results for wheel lateral force according to steering control test conditions.

Appl. Sci. 2020, 10, x 13 of 16

Table 5. Mean lateral force for the circular section of the test section.

Case Force (kN) Reduction (%) Appl. Sci. 2020, 10, 4407 Passive 14.99 - 12 of 15 Active (25%) 7.53 49.8 Table 5. MeanActive lateral (50%) force for the 4.68 circular section 68.8 of the test section. Active (75%) 3.20 78.6 ActiveCase (100%) Force 2.46 (kN) Reduction 83.6 (%) Passive 14.99 - 4.5. Derailment Coefficient Active (25%) 7.53 49.8 Active (50%) 4.68 68.8 Derailment coefficientActive is a factor (75%) that indicates 3.20 derailment 78.6safety when the vehicle is running and is defined as the ratio Activeof the lateral (100%) force to th 2.46e vertical force acting 83.6 on the wheel. Figure 17 shows the measured derailment coefficient test data of the front outer wheel of the test vehicle according to the steeringThe mean angle lateral test force conditions of the wheel using in the the wheel passive force case measuring with insuffi wheelset.cient steering is 14.99 kN. On the other hand,For the in analysis the active of steering the derailment control test coefficients condition,, the wheelUIC 518 lateral OR forcetest standard decreases used as the for steering wheel anglelateral implementation force analysis was level applied increases. [17]. InFigure the case 18 is of the Active result (25), of analyzing it is 7.53 kN,the derailment which is 49.8% coefficients lower thantest data the Passive by subdividing case. In the 70 casem into of small Active sections (50) and and Active arranging (75), the them mean in the lateral cumulative forces were distribution 4.68 kN andorder 3.20 to kN, extract respectively, 99.85% decreasingof the values by 68.8% as the and repr 78.6%,esentative respectively. sections In of the the case small of Active sections. (100) Here, with 100%according steering to the control, test standard, the mean the lateral allowable force islimit 2.46 of kN, the which derailment is 83.6% coefficient lower than is 0.8 the and passive all thecase. results of theTherefore, analysis itare was within confirmed the tolerance that the limit. bogie was aligned with the radial position as the steering angleTable increased 6 shows to meet the mean the target values steering of the anglesmall assectio then test representative train passed values through for thethe curvedanalysis section, results andin Figure the wheel 18 and lateral the reduction force was rate also for significantly the derailment reduced. coefficient of each test case for the passive case. The mean derailment coefficient of the wheel in a passive case with insufficient steering is 0.537. 4.5.On Derailmentthe other hand, Coeffi cientin the active steering control test condition, the derailment coefficient decreases as the steering angle implementation level increases. In the case of Active (25), the mean derailment Derailment coefficient is a factor that indicates derailment safety when the vehicle is running and coefficient is 0.232, which is 49.3% lower than the Passive case. In the case of Active (50) and Active is defined as the ratio of the lateral force to the vertical force acting on the wheel. Figure 17 shows the (75), the mean derailment coefficients were 0.148 and 0.099, respectively, with 72.5% and 81.6% measured derailment coefficient test data of the front outer wheel of the test vehicle according to the reduction rates. steering angle test conditions using the wheel force measuring wheelset. In the case of active (50) and active (75), the average derailment coefficients were 0.148 and 0.099, For the analysis of the derailment coefficients, the UIC 518 OR test standard used for wheel lateral respectively, decreasing by 72.5% and 81.6%, respectively. In the case of Active (100) with 100% force analysis was applied [17]. Figure 18 is the result of analyzing the derailment coefficients test data steering control, the mean derailment coefficient is 0.074, which is 86.3% lower than the passive case. by subdividing 70 m into small sections and arranging them in the cumulative distribution order to This means that the derailment coefficient is naturally reduced if the wheel lateral force is reduced extract 99.85% of the values as the representative sections of the small sections. Here, according to the because the derailment coefficient is the ratio of the lateral force to the vertical force of the wheel. test standard, the allowable limit of the derailment coefficient is 0.8 and all the results of the analysis Accordingly, it can be seen that the wheel lateral force is reduced by the active steering control and are within the tolerance limit. the derailment coefficient, which is a vehicle running safety evaluation factor, is also significantly Table6 shows the mean values of the small section representative values for the analysis results in reduced. Figure 18 and the reduction rate for the derailment coefficient of each test case for the passive case.

0.9 Passive 0.8 Active(25%) Active(50%) 0.7 Active(75%) Active(100%) 0.6

0.5

0.4

0.3 Derailment coefficent 0.2

0.1

0 5650 5700 5750 5800 5850 5900 5950 6000 6050 6100 6150 Distance(m) Figure 17. Derailment coeﬃcient test data according to steering control test conditions. Figure 17. Derailment coefficient test data according to steering control test conditions. Appl. Sci. 2020, 10, x 14 of 16 Appl. Sci. 2020, 10, 4407 13 of 15

1 1 Passive Passive 0.9 Active(25%) 0.9 Active(50%) 0.8 0.8

0.7 0.7

0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3 Derailment coefficient Derailment coefficient Derailment 0.2 0.2

0.1 0.1

0 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Section Section

(a) Passive (b) Active (25%)

1 1 Passive Passive 0.9 Active(75%) 0.9 Active(100%) 0.8 0.8

0.7 0.7

0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3 Derailment coefficient Derailment coefficient Derailment 0.2 0.2

0.1 0.1

0 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Section Section

Figure 18. Analysis results for derailment coeﬃcient according to steering control test conditions. Figure 18. Analysis results for derailment coefficient according to steering control test conditions. Table 6. Mean derailment coeﬃcient for the circular section of the test section.

Table 6. MeanCase derailment coefficient Derailment for Coethe fficircularcient section Reduction of the test (%) section. PassiveCase Derailment 0.537 Coefficient Reduction - (%) ActivePassive (25%) 0.537 0.232 - 56.7 Active (50%) 0.148 72.5 ActiveActive (75%) (25%) 0.232 0.099 56.7 81.6 ActiveActive (100%) (50%) 0.148 0.074 72.5 86.3 Active (75%) 0.099 81.6 The mean derailmentActive coe (100%)fficient of the wheel 0.074 in a passive case 86.3 with insufficient steering is 0.537. On the other hand, in the active steering control test condition, the derailment coefficient 5. Conclusions decreases as the steering angle implementation level increases. In the case of Active (25), the mean derailmentIn this coepaper,fficient a issteering 0.232, whichperformance is 49.3% experiment lower than theaccording Passive case.to steering In the caseangle of Activelevel was (50) conductedand Active with (75), the the aim mean of obtaining derailment steering coefficients perfor weremance 0.148 data and for 0.099, the purpose respectively, of deriving with 72.5% practical and design81.6% reductionspecifications rates. for a steering system prior to the commercialization of an active steering bogie to be Indeveloped. the case of active (50) and active (75), the average derailment coefficients were 0.148 and 0.099,The respectively, test was carried decreasing out in by a 72.5% curved and section 81.6%, wi respectively.th a radius Inof thecurvature case of Activeof R300, (100) and with steering 100% performancesteering control, such the as mean bogie derailment angle, wheel coeffi lateralcient isfo 0.074,rce, and which derailment is 86.3% lowercoefficient than thewere passive analyzed case. This means that the derailment coefficient is naturally reduced if the wheel lateral force is reduced Appl. Sci. 2020, 10, 4407 14 of 15 because the derailment coefficient is the ratio of the lateral force to the vertical force of the wheel. Accordingly, it can be seen that the wheel lateral force is reduced by the active steering control and the derailment coefficient, which is a vehicle running safety evaluation factor, is also significantly reduced.

5. Conclusions In this paper, a steering performance experiment according to steering angle level was conducted with the aim of obtaining steering performance data for the purpose of deriving practical design specifications for a steering system prior to the commercialization of an active steering bogie to be developed. The test was carried out in a curved section with a radius of curvature of R300, and steering performance such as bogie angle, wheel lateral force, and derailment coefficient were analyzed according to the steering angle level of the active steering bogie. Here, the steering angle level was assumed to be 25%, 50%, 75%, and 100% of the target steering angle. As a result of the test, as the steering angle was increased to match the target steering angle, the bogie angle difference between the front and rear bogies was gradually decreased. When steering control was conducted at 100% level, the bogie angles of the front and rear bogie were almost the same, and the difference was only 0.014 degrees. This means that the bogie is aligned in the radial steering position of the curved section by steering control. Wheel lateral force also tended to decrease significantly with increasing steering angle. When steering control was performed at 25%, 50%, 75%, and 100% of the target steering angle, respectively, 49.8%, 68.8%, 78.6%, and 83.6% decreased compared to passive conditions. This means that the steering control at 100% level of the target steering angle can achieve the highest performance of 83.6% reduction in wheel lateral force, but it can be reduced to about one-half of the conventional bogie at 25% level control and about one-third at 50% level. Considering cost rise by adopting the active steering system, this result can be used as a very important design indicator to compromise steering performance and cost rise issues in the design stage of the steering system from a viewpoint of commercialization. Therefore, it is expected that the results of the steering performance experiment according to the steering angle level in this paper will be used as very useful data for commercialization.

Author Contributions: Conceptualization, H.H., D.A.; Methodology, H.H., Y.S. and D.A.; Formal analysis, Y.S., D.A.; Writing—original draft preparation, H.H.; Supervision, H.H., Y.S. and D.A.; Project administration, H.H.; Writing—review and editing, H.H., Y.S. and D.A. All authors have read and agreed to the published version of the manuscript. Funding: This work was supported by a grant from the R&D Program of the Korea Railroad Research Institute (PK2002D1), Republic of Korea. Conﬂicts of Interest: The authors declare no conﬂict of interest

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