Design and Development of Dynamic Test Bench for Electric Wheel Load Sensing Suspension

Abstract

Based on the modular design idea, a new type of dynamic test bench for electric wheel load sensing suspension was designed and developed, including load-bearing platform module, vertical force loading module, electric wheel module, spring mass simulation module, etc., and the test bench has the functions of wheel jump simulation, steering simulation and wheel vertical force and lateral force detection. The finite element simulation results show that the strength of the test bench meets the requirements. The results of the virtual prototype simulation show that the test bench can accurately measure the vertical and lateral forces experienced during the dynamic operation of the wheels.

1 Research Background and Significance

Road test is the most important means for car companies to carry out vehicle performance testing and suspension system testing, which requires a larger site and high cost, and many small and medium-sized car companies do not have the conditions for road testing. In order to meet the needs of small and medium-sized car companies for suspension system testing, many researchers have begun to develop and research suspension test benches for different test objectives. Literature [1, 2] develops an air suspension experimental bench to solve the problem of nonlinear dynamics of air suspension; XUE et al. developed and designed a single-wheel test bench of the anti-lock braking system, which verified the effectiveness of the all-electric ABS algorithm [3]; Literature [4, 5] developed a test bench for suspension performance testing and vehicle performance matching, and studied the dynamic characteristics of suspension components and vehicle characteristic matching; Literature [6, 7] designs an oil and gas suspension test bench to study the electro-hydraulic ratio control of oil and gas suspension; Literature [8, 9] The fatigue life of the suspension system is studied by test bench.

Considering that distributed drive electric vehicles are the most ideal models for autonomous vehicles, and the perception of wheel load can provide the necessary wheel load data for the automatic driving system, there is a lack of research on the test bench for dynamic load measurement of electric wheels, so the dynamic test bench of electric wheel load sensing suspension is developed and designed.

2 The Main Structure and Working Principle of the Test Bench

2.1 The Main Structure of the Test Bench

The overall design of the test bench adopts the modular design idea, as shown in Fig. 1, the main structure of the test bench includes the bearing platform module, the vertical force loading module, the electric wheel module, the spring load mass simulation module, the profile bracket and other structures. The load-bearing platform module is connected to the profile bracket by the vertical guide rails on the front and rear sides, and connected with the vertical force loading module through the horizontal guide rails at the bottom; The electric wheel module is connected to the body simulation board in the spring mass simulation module through the connector, and the wheel is directly pressed on the roller in the load-bearing platform module; The sprung mass simulation module, the vertical force loading module and the profile holder are fixed to the T-slot base.

Fig. 1

Schematic diagram of the structure of the test bench. 1. Hosting platform module, 2. Vertical force loading module, 3. Electric wheel module, 4. Spring-borne mass simulation module, 5. Profile bracket, 6. T-slot base

The structure of the load-bearing platform module is shown in Fig. 2, the four rollers are opened at both ends of the bearing housing bore, the deep groove ball bearings are installed, the bearing inner ring is preloaded through the shaft shoulder of the lock nut to support the roller in the middle of the frame.

Fig. 2

Hosting platform module. 1. Roller, 2. Frame, 3. Lateral force transducers, 4. Internal connectors, 5. External connectors, 6. Seat plate, 7. Lock nut, 8. Guide rail, 9. Slider

Lateral force detection principle: the frame front and rear are connected with the outer connector through two transverse guide rails, to ensure that the frame and the outer connector have a lateral degree of freedom of movement, the inner connector is fixed on the frame, and the tension pressure sensor is connected between the inner and outer connectors, because the outer connector is connected to the profile bracket through a vertical guide rail before and after, ensuring that the bearing platform module only has the freedom of vertical movement, the tension pressure sensor only bears the tensile pressure generated by the lateral movement of the frame, there is no additional torque, and the wheel side declination angle does not exceed 5 [10], the lateral force on the wheel can be measured directly. The seat plate is bolted to the frame.

The vertical force loading module structure is shown in Fig. 3, using servo motor to directly drive the ball screw form, different from the test bench in the literature [11], considering to simulate the process of wheel jumping during automobile driving, the lead screw nut and its connecting parts will produce a displacement of 250mm along the direction of the lead screw axis. The ball screw is supported by a fixed end and free at the other, and the fixed end is supported by a pair of angular contact ball bearings arranged back-to-back.

Fig. 3

Vertical force loading module 1. Bracket, 2. Servo motors, 3. Coupling, 4. Bearing end covers, 5. Ball screw pair, 6. Connect the cylinder, 7. Pressure sensors, 8. Connect plate, 9. Guide parts

The connecting plate in the vertical force loading module is connected with the seat plate in the load-bearing platform module through the transverse guide rail, and its direction is consistent with the direction of the transverse guide rail in the load-bearing platform module, so the connecting plate only has the freedom of movement in the vertical direction, because it does not limit the rotational freedom of the lead screw nut, when the lead screw rotates, under the action of friction, the lead screw nut will have a tendency to rotate, and additional torque will be generated on the two pressure sensors, affecting the measurement accuracy and life of the sensor, so two guides are arranged, In order to eliminate the effect of additional torque on the pressure sensor.

The structure of the electric wheel module is shown in Fig. 4, which adopts the form of hub motor integrated MacPherson suspension system, and the wheel is directly driven by the hub motor; The steering of the wheels is realized by pushing the steering knuckle by the electric actuator, the stroke of the electric actuator is 150mm, the running speed is 7mm/s, and the output thrust is 2500N. In addition, different types of suspension can be replaced on the test bench by designing different connectors, and then the performance of different suspension systems can be tested.

Fig. 4

Electric wheel module. 1. Wheels, 2. Hub motor, 3. Steering knuckles, 4. Shock absorber connectors, 5. Spring damping shock absorber, 6. Pusher connection, 7. Electric actuator, 8. Lower control arm

2.2 The Working Principle of the Test Bench

The working principle of the test bench is shown in Fig. 5, with black lines representing motion transfer and red lines representing drives. The working principle is outlined as follows: the hub motor directly drives the wheel to rotate; During the wheel operation, the road surface excitation is input to the servo motor, the servo motor drives the ball screw pair, the movement is transmitted to the bearing platform module, the bearing platform drives the vertical movement of the wheel, simulates the wheel jumping process, the wheel runout is transmitted to the spring-loaded mass simulation module through the suspension system, so that the vehicle weight simulates the vertical movement of the board, simulates the vertical movement of the body, and at the same time, the pressure sensor measures the vertical force of the wheel; After the servo motor is reset, the electric actuator pushes the wheel to deflect a certain angle, simulating the steering movement of the wheel, at this time, there is a certain angle between the wheel speed direction and the roller rotation direction, the wheel is affected by the lateral force, the lateral force is transmitted to the tension pressure sensor through the roller and frame, to achieve the measurement of the lateral force of the wheel, the principle of lateral force generation is shown in Fig. 6, the roller is subjected to the positive pressure F_N applied by the wheel, when the wheel turns, the lateral reaction force F_Y is generated on the roller, The lateral reaction force F_Y can be decomposed into mutually orthogonal components F_YH and F_YV, and when the wheel deflection angle is small, F_Y can be considered approximately equal to F_YH, and F_YH can be directly measured by the tensile pressure sensor of the carrier platform module.

Fig. 5

Test bench experimental schematic

Fig. 6

Schematic of lateral force generation. 1. Roller, 2. Wheel

3 Strength Check of Key Components

3.1 Acquisition of Road Load Spectra

CARSIM as one of the commonly used vehicle simulation software, can more accurately simulate the vehicle in different road conditions during the wheel load, its parametric modeling characteristics can allow users to quickly establish a more accurate vehicle model, a model of full load mass of 1410 kg, the maximum speed of 80 km/h, in order to simulate the bumpy working conditions during the car driving, set in the straight road 6 speed bumps, each speed bump interval of 10 m, through the speed bump speed bump set to 20 km/h; The radius of the curve is set to 12 m, and the speed of the cornering is set to 30 km/h. The CARSIM simulation results are shown in Table 1.

Table 1 CARSIM simulation results

3.2 Strength Check of Key Components

The bracket in the vertical force loading module as a member to bear all vertical forces, its bottom surface is fixed, the upper four bolt holes apply a total of 7500N force downward, the finite element analysis results are shown in Fig. 7, the maximum stress is 68.6 MPa, much less than the yield stress of Q235, and the strength meets the requirements.

Fig. 7

Stress cloud plot of the bracket

The bearing platform module is directly in contact with the wheel and rotates with the wheel, which is the key component to bear the vertical force of the wheel, and the bearing mounting surface at both ends of the single roller is fixed constraint, and the outer surface in contact with the wheel in the middle is applied along the radial force of 3750N, the finite element analysis results are shown in Fig. 8, the maximum stress is 38.531 MPa, which is much less than the yield stress of Q235, and the strength meets the requirements.

Fig. 8

Stress cloud of a roll

The middle and outer connections of the bearing platform module mainly bear the lateral force, and the 8 bolt mounting holes on the front and rear side plates are fixed and constrained, and the lateral force sensor in the middle is connected to the bolt hole to apply a transverse force of 3000N, and the finite element analysis results are shown in Fig. 9, the maximum stress is 178.36 MPa, which is less than the yield stress of Q235, and the strength meets the requirements.

Fig. 9

Stress cloud of internal connectors

The finite element analysis results show that the strength of the main load-bearing structure meets the requirements, and the strength of the overall structure of the test bench meets the requirements.

4 ADAMS Dynamics Simulation Analysis

4.1 Test Bench Virtual Mockup Model

ADAMS software is a commonly used mechanical system dynamics simulation software, through the construction of the virtual prototype of the mechanical system, the mechanical system structural rationality, drive control and structural force can be analyzed, in the early stage of design optimization and upgrade, the use of ADAMS software to build a virtual prototype of the test bench, as shown in Fig. 10. The drive of the virtual prototype is divided into three parts, including the drive of the hub motor, the drive of the servo motor and the drive of the electric actuator, and the drive control is set in the form of load steps, as follows.

$$ step\left( {time,\;time1,\;data1,\;time2,\;sdata2} \right) $$

(1)

Fig. 10

Test bench virtual mockup model

where time is the independent variable, time1 is the start time, data1 is the increment driven at the start time, time2 is the end time, data2 is the increment driven at the end time, and the drive changes linearly in the time interval.

4.2 Analysis of Simulation Results

The simulation of the vertical load on the wheels in the virtual prototype is shown in Fig. 11a, it shows that the value of the pressure sensor is about 1200N greater than the vertical load at the center of the wheel, because the pressure sensor not only bears the vertical load at the center of the wheel, but also bears the gravity of the wheel, hub motor and the bearing platform, after correcting the value of the pressure sensor, the resulting vertical load simulation is shown in Fig. 11b.

Fig. 11

Vertical load simulation a Vertical load simulation, b Corrected vertical load simulation

The simulation of the wheel lateral load in the virtual prototype is shown in Fig. 12, and the simulation results show that the tension pressure sensor in the load-bearing platform module can accurately measure the side load at the wheel center.

Fig. 12

lateral load simulation

5 Conclusion

In this paper, aiming at the lack of research on 1/4 suspension dynamic test bench and the rapid development of distributed drive technology, this paper designs and develops an electric wheel load sensing suspension dynamic test bench, which can not only test the performance of different types of suspension systems, but also accurately measure the vertical load and lateral load on the wheel. The simulation results show that the test bench has achieved the expected effect, which can effectively solve the problem of high cost of road test for collecting road load spectrum.