The design and development of an Integrated Propulsion System – Phase 3: the testing bench

The paper presents the testing bench dedicated to the integrated propulsion system (IPS). The IPS consists of a wheel that carries the electric machine and the suspension inside. Its behaviour needs to be tested while being used independently on a test bench and then on road tests. Because no already existing testing bench was available for this kind of testing, a dedicated testing bench was designed and developed. Its main role is to investigate the functional behaviour of the wheel, together with the integrated suspension system behaviour. The tests were made following different scenarios, where different tire dimensions, different environment properties, different road profiles etc. were reproduced.


Introduction
The innovation fits very well with the road vehicles design during the current progress of automotive industry, while simplifying the solutions and reducing the costs are mandatory.Both are conditioned by the research efforts made through virtual and physical testing, while the equipment used for testing define the value of the research results.Consequently, when the system to be tested has higher innovation level, the test benches to be used are difficult to be find.When it becomes impossible to find suitable test benches for new and innovative systems, there is a need to develop dedicated customizable test benches.
The testing bench for an e-wheel with integrated suspension system and the electric machine coupled to the hub is a very complex and highly targeted equipment.Many electronic components, power electronics, control systems are part of this type of testing bench, and their integration goes hand in hand with the adaptability to work together properly.
The testing bench for in-wheel suspension systems must reproduce real-world conditions, including road bumps, potholes and various road surface irregularities.It must have multi-axis testing capability, including vertical displacement, in addition to yaw, pitch/tilt and roll movements.The testing bench must have another crucial capability: to adjust different loading conditions for the evaluation of different types of in-wheel suspension, depending on the types of the vehicles for which it is dedicated.For a more comprehensive evaluation of an e-wheel with integrated suspension system, it is mandatory to allow dynamic testing: to replicate the acceleration and deceleration, braking and regenerative braking, steering behaviors.Different suspension configurations should be tested without limits.
The data logging and analysis systems will collect, store and analyze the information from different transducers, which can be also linked with various simulation software.By integrating a simulation software as part of the testing bench, the virtual testing will enable design refinement before the 1303 (2024) 012011 IOP Publishing doi:10.1088/1757-899X/1303/1/012011 2 manufacturing processes begin, and well in advance of physical testing.In addition, the adaptive testing should use real-time feedback from the transducers used and to adjust the parameters for different scenarios.
The modularity and the flexibility of the testing bench make it easy to reconfigure and adapt to different configurations, sizes and requirements to meet.
The safety represents a top priority for the testing bench.All component parts and all the operation procedures must be provided carefully.The mechanisms of the testing bench must have emergency stop mode, actuated manually or automatically.
This paper tries to cover most of the above-mentioned tasks for developing a testing bench dedicated for an e-wheel with integrated suspension and the electric machine coupled to its hub.

The state of the art
The current literature presents several solutions for different test benches for being used either for ewheels or for suspension systems.The technology of e-wheels is evolving rapidly and when a solution like the in-wheel integrated suspension comes as an addition, the difficulty of finding physically testing solutions increases.
The road vehicles tire stiffness represents an important characteristic for evaluating the e-wheel with integrated suspension system.The force ratios under vertical and horizontal loads on the tire can be investigated by different testing benches.Investigating the tire vertical behavior can be done using testing benches that are also used for testing the suspension systems.The test rig presented in [1] allows to test independently the shock absorber and the spring, or if needed, to test all the suspension system components simultaneously.Testing the tire behavior can also be done independently, this test rig being able to apply a displacement of controlled frequency and amplitude.Special attention must be given to the rim deformation that can influence the measurements.
The industry dedicated to developing testing benches facilities helps testing independently the springs, the shock absorbers and the other components that are part of the suspension system.Testing different suspension system components is possible by using the test rigs from [9] and from [10].The multiple design configurations allow easy adjustment of the system frequency and choosing different types of actuators.The extended features of this already existing testing rig dedicated very well cover the detailed investigation of all the components of the automotive suspension systems.
The dynamic wheel force measurement represents an important task, used to determine the dimensions of a testing bench supporting load bearing or of the springs and dampers.One such technique is presented by [11], where several requirements are applied to maintain the driving dynamics, including not to change the unsprung mass or the stiffness of the wheel.
In [2], a test bench for suspension systems is presented, where its development started from the quarter-car model, where the controller and its functional behavior were preliminary simulated.The different road surfaces were reproduced by a linear motor placed under the wheel of the quarter-car model.The same approach of reproducing the road profile is presented by [4], where the vertical excitation of the wheel is achieved by an electrical linear motor connected to the wheel`s base plate.A testing rig suspension system based on a quarter car is also presented in [6], where the road surface is reproduced by using a second wheel with a cam on its external profile, while the wheel of the quarter car model is considered as follower.The road surface can be reproduced also by using the vertical movement of the suspension system produced by a cam, as being presented in [8], where the test rig includes an induction motor and a gearbox for reducing the axle speed.
In [7], an automotive suspension testing rig is presented as having the characteristics to be used also as an educational, training and research tool.Its design allows investigating the impact of various road surface bumps and humps for both an active and a passive suspension system.In [3], the vehicle wheel load estimation is presented by using the suspension mechanism.The developed virtual model allows to easily understand where the most significant loads are met in relation to the components of the suspension system.The in-wheel electric motor may suffer from common faults, both mechanical and electrical.The operating conditions of an in-wheel electric motor was studied by [5], which developed a dedicated test bench to also simulate the road shocks and the vertical load.
Based on the existing solutions, the testing bench to be developed will be open for different improvements and optimization criteria.

The proposed design and the applied technologies
The main component for the test bench is the system to be tested and validated, which is the e-wheel that integrates the suspension system and has the electric machine coupled to its hub.The e-wheel dimensions represent one of the applied limitations before starting the test bench design.The test bench must allow to test different e-wheel sizes (especially the diameter).Therefore, it was designed from the beginning to be configurable.The proposed solution for the test bench is based on combining different already developed solutions with new approaches for achieving the current e-wheel needs.The test bench development consists of the definition the 3D design (figure 1) and its validation, followed by the manufacturing processes for each of the components, in addition to choosing the appropriate systems that are part of it.
The frame for the test bench was designed to be made of rectangular tubes, on which an electric motor (figure 2) is fixed.Along with the electric motor, a reduction gearbox (figure 2) was needed to ensure the rotary velocity below 1400 rotations/minute.The electric motor has its own controller, which regulates its rotary velocity.The output shaft of the electric motor reducer is coupled to an axial radial/ thrust bearing containing two bearings.The axial radial/ thrust bearing supports the e-wheel with its integrated suspension.Another radial axial/ thrust bearing, like the first one, is mounted to the frame parallel to the first one.This second axial radial/ thrust bearing drives an upper cam that simulates the road profile.This second axial radial bearing is fixed to the frame by means of oval holes that allow the upper cam wheel to be mounted so that it exerts on the e-wheel a force equivalent to the weight of the car distributed on the rear wheel.

The prototype
The prototype of the test bench (figure 3) was built with respect to the e-wheel characteristics in terms of size, testing approach and costs.Each component was built, manufactured or purchased.The dimensions from figure 3 correspond to testing the 14 inches e-wheel.

Figure 3. The test bench dimensions for the 14 inches e-wheel
The manufacturing processes consist of several operations, both technological and control operations.The main technological operations include the mechanical processing, the welding, the assembly of the mechanical components, the assembly of the electrical and electronic components, the configuration step.
The frame was built from rectangular tubes (figure 4.a), that were cut based on the established dimensions, then being welded or assembled by screws and nuts, with respect to the design, and prepared to be finally painted.The electric motor and its reducing gearbox (figure 2) were purchased.They were mounted to the frame, using a dedicated metal support (figure 4.d).and an axial radial bearing (figure 4.c).Another metal support was manufactured for the second axial radial bearing that is needed for the upper wheel.Two linchpins (figure 4.b) were also manufactured for making possible the mounting of the e-wheel to the metal support and of the second wheel with the cam that simulates the road profile (figure 4.e).
Before the final assembly of the test bench, the dimensional control of each component was carried out.In addition, a variable wheel load force adjustment was set, while several cams have been made to simulate various road profiles.The assembly for the testing bench includes the e-wheel with its integrated suspension system, the upper wheel that simulates the road profile, the electric motor that drives the e-wheel, together with its reducing gearbox and controller (figure 5).

The testing scenarios and the obtained results
The dynamic test bench (figure 6.a) has the role to investigate the behavior for the e-wheel with integrated suspension.The position for the upper wheel allows to choose between various heights that are coming from the road, easily simulating the road profile.A three-axis displacement transducer was used to measure the electromechanical parameters of the e-wheel.First testing scenario consists of measuring the oscillation on the vertical axis relative to the road for a road profile with height irregularities of maximum ten millimeters (10 mm) (table 1, figure 6.b).For the second testing scenario, the road profile height irregularities were increased to 15 mm (table 2, figure 6.c), while for the third testing scenario they were increased to 20 mm (table 3, figure 6.d).The system was tested for five hours continuously for each road profile and no damage to the component parts was found.During the testing scenarios, certain sounds were met which are mainly due to the rectangular profile chosen for the road profile, which is considered the most unfavourable in terms of mechanical demands.The wheel displacement along vertical axis for each of the various road profiles are within acceptable limits, the shock of bumps being easily dissipated by the integrated tire-suspension assembly.The temperatures of the most important components of the e-wheel reached values within acceptable limits, which indicates the absence of unwanted frictional contacts.

Conclusions
The test bench development stages included the definition for the final design by virtual modeling and validation.The development stages also included the manufacturing operations for the frame, the metallic support, the linchpins, the axles for mounting the wheels, the upper wheel together with the cam.To ensure the enough clearance for the e-wheel, the frame was configured to allow different tire IOP Publishing doi:10.1088/1757-899X/1303/1/0120118 dimensions and easily modify the distance between the mounting axis that correspond to the e-wheel and to the upper cam wheel.Several cam sizes were developed for simulating various road profiles.A variable load force adjustment was created.The drive system and the controller were set for operation, while the data collection was achieved using the mobile phone application of the transducer.
The resulted test bench allows testing the wheel with integrated suspension simulating the entire load and speed range.In addition to the functional behavior tests for the e-wheel with integrated suspension system, another important test consisted of the endurance test of the mechanical elements of the e-wheel, which are directly related to the functional safety of the system.

Figure 4 .Figure 5 .
Figure 4.The manufacturing processes for: (a) the frame, (b) the linchpins, (c) the axial radial bearing, (d) the metal support, (e) the upper wheel with the cam

Figure 6 .
Figure 6.The test bench under operation (a) and the oscillation on the vertical axis relative to the road for a rod profile of: (b) 10 mm, (c) 15 mm, (d) 20 mm

Table 1 .
The displacement of the wheel on the vertical axis relative to the road profile of 10 mm

Table 2 .
The displacement of the wheel on the vertical axis relative to the road profile of 15 mm

Table 3 .
The displacement of the wheel on the vertical axis relative to the road profile of 20 mm