Low inertia hub dyno or axle-mounted dynamometer


Test bench system architecture


The Low inertia hub dyno or axle-mounted dynamometer consists of the mobile low-inertia AC dynamometer, dynamometer inverter, battery simulator, electrical control cabinet, measurement sensors, vehicle windward cooling system, traffic real-life simulation system, master computer and other components.


Low inertia hub dyno or axle-mounted dynamometer


The dynamometer can perform speed and torque control to simulate the road load. Load simulation methods include: constant torque control, calculated road spectrum simulation, actual road spectrum import and user-defined load spectrum. The power analyzer measures the current, voltage and power of each energy consumption unit of the tested vehicle, analyzes the energy flow of the vehicle under different operating conditions and draws the energy spectrum of the entire vehicle.

The dynamometer adopts a low-inertia dynamometer which has extremely high dynamic characteristics and can simulate fast-changing working conditions and simulate different road models. By integrating into the traffic scene simulation system, real vehicle actions under different road conditions can be truly reproduced including the driver’s operating comfort. The system can also be transformed into a powertrain test system, and the battery simulator can be connected to the powertrain drive to test the powertrain.

The Low inertia hub dyno or axle-mounted dynamometer adopts a flexible design. Each dynamometer adopts the movable method. The dynamometer and the vehicle hub adopt a quick connection structure, so that user can quickly complete the connection between the vehicle and the dynamometer. The dynamometer tray bracket is supported by universal wheels which can be moved easily. At the same time, it can also simulate the actual steering function.


Low inertia hub dyno or axle-mounted dynamometer


The flange shaft connected to the vehicle wheel hub adopts the hollow structure, which reduces the moment of inertia of the shaft system to the greatest extent and improves the dynamic response capability of the dynamometer system. A transitional connection flange is designed between the flange and the vehicle wheel hub, and the flange also adopts a weight reduction design to reduce the moment of inertia.


Low inertia axle-mounted dynamometer or hub dyno


Axle-mounted dynamometer specifications


ModelRated power (kW)Rated torque (Nm)Max. speed (rpm)Inertia (kgm2)


Function of axle-mounted dynamometer


The Low inertia hub dyno or axle-mounted dynamometer is a flexible test system with a very high degree of freedom. User can combine tests at will, and can test four-wheel drive and two-wheel drive vehicles, or separately test electric drive powertrains. The shaft-coupled dynamometer adopts a very low inertia motor and uses real-time Ethernet communication control. It has a very high dynamic response speed and can complete the dynamic alternating working condition test of the load. The axle-mounted dynamometer system has the following functions:


  • Vehicle durability test
  • Vehicle energy flow test
  • Vehicle energy consumption test
  • Vehicle acceleration test
  • Vehicle road simulation test
  • Vehicle braking performance test
  • Universal characteristics test of the whole vehicle
  • Driver in the loop test
  • Vehicle fault detection
  • Development and calibration of vehicle control strategy
  • Vehicle consistency test
  • Vehicle braking energy recovery test
  • Powertrain efficiency test
  • Powertrain speed and torque characteristic test
  • Powertrain temperature rise test
  • Powertrain controller control strategy development verification test
  • Powertrain braking regenerative energy feedback test
  • Powertrain external characteristic test
  • Powertrain development and optimization test
  • Powertrain performance test and calibration test
  • Efficiency map test
  • Accelerated response test
  • Torque response test
  • Endurance test of steady-state cyclic loading

Technical description of vehicle energy flow test system


The driving range test of pure electric vehicles adopts China working condition GB/T 18386 “Electric vehicles – Energy consumption and range – Test procedures” which the working conditions are similar as the test of European NEDC working conditions, and will be introduced high and low temperature test procedures.

Vehicle energy flow test:


  • Energy transfer path

    Based on the specific vehicle configuration, working conditions and working mode, the flow of energy from the power source to the wheel ends is generated, transferred or converted.


  • Energy transfer efficiency and loss

    In the energy transmission path, there are systems and components that have losses, and the corresponding energy consumption forms are quantified energy consumption distributions for energy consumption systems and components.


Data from EPA:

Charge loss16%16%16%
Accompany loss2.5%4%1.5%
Drive loss16%18%14%
Accessory power loss0% – 4%0% – 6%0% – 2%
Energy to the wheel60% – 65%55% – 62%66% – 68%
Brake recovery17%32%6%
Idle speed loss0%0%0%
Total111.5% – 120.5%125% – 138%103.5% – 107.5%


The key points of the vehicle energy flow test are the accuracy of the measurement and the synchronization of the measurement of different energy-consuming components, as well as the authenticity of the vehicle condition simulation.

In order to improve the accuracy of electric energy measurement, it is necessary to configure the high-precision power analyzer and transformer, and use the power analyzer with a high-precision synchronous clock function to synchronously collect and measure the signals of each sensor.

Software system of low inertia hub dyno or axle-mounted dynamometer


The software system mainly includes the following parts:


  • Test management software

    The basic test parameters and related control parameters are set before the test, and the test information file is generated which is called by the test main control software.

    During the test, through the interaction with the real-time control computer, the test process is automatically managed and the specified real-time information is processed.

    After the test is completed, test reports, test record retrieval, data post-processing, etc. are generated.


  • Real-time control software for test bench

    Through the closed-loop control of the sensor information acquisition and interaction with the test management computer, the control parameters solved by the upper layer are obtained and the necessary lower layer calculations are performed. The software realizes the real-time closed-loop control of the speed and torque of the driving and loading motors and the real-time control of other auxiliary facilities.


  • Human-computer interaction processing software

    A unified human-computer interaction interface that integrates the main information on the same machine. The software displays real-time information about the test progress, main test data, the status of the test piece and the test bench.


  • Test data acquisition and post-processing software

    The system provides various mathematical operations of data, including addition, subtraction, multiplication, division, integration, differentiation, maximum value, minimum value, peak value, RMS, average, sum, etc.


All software systems adopt modular design ideas with good flexibility and scalability. The main functional modules of the software are: main program framework module, system control module, data acquisition module, data recording module, data analysis module, data display module, communication module, data playback module, print processing module, sensor calibration module, function setting module, help document module and data post-processing analysis module, etc.


  1. Main test interface

    The vehicle undergoes a formal test after the loss calibration and coasting test. At this time, the simulated load of the dynamometer is similar to the road load of the vehicle.


  1. Calibration of friction loss

    Before user starts to use the device for testing, the device needs an effective friction calibration (the device will only be used if it exceeds a certain speed corresponding to the friction calibration). User can check the calibration status through the dial control page that displays the calibration status.

    User can perform friction calibration regardless of whether the vehicle is equipped or not, but the system cannot distinguish between equipment friction loss and vehicle loss at this time. Therefore, user needs to make a new loss calibration for each new vehicle. It is recommended to do friction calibration where the vehicle is not equipped.

    At the same time, user needs to consider that the friction loss will change with the change of the ambient temperature. Therefore, it is necessary to warm up the device before friction calibration or test and maintain its temperature until the end of the test.


  1. Vehicle loss calibration

    When the vehicle loss calibration is completed, the page will automatically update and display the maximum calibration speed. The friction loss calibration can be analogized to the vehicle loss calibration. The maximum calibration speed displayed is the lower of the friction calibration speed and the vehicle loss calibration speed.


  1. Basic inertia calibration

    The basic inertia calibration is used to calibrate the basic inertia of the test bench, including: the total moment of inertia of each transmission system such as the drum, drive shaft, and motor. The basic inertia calibration is a necessary condition for the correct operation of the test bench.


  1. Sliding test

    During sliding, the system first accelerates the device to above the maximum speed required for sliding, and then enters the road simulation mode to simulate the road environment until the device is below the minimum speed required for sliding. When the specified speed point is passed, the time at that moment will be recorded. The system can accurately calculate the road simulation by calculating the time and average deceleration force for sliding over the specified distance. Users can find this information on the sliding results page.


  1. Road load simulation

    The system can provide various series of dynamometer electromechanical inertia simulation and simulate the road load according to the equation:

    RL = F0 + F1VX + F2Vn + I dv/dt + mg * (Grad/100)

    Among them:

    RLRoad load (road traction)
    F0, F1, F2, nRoad load model coefficient
    F0Friction coefficient independent of speed
    F1Friction coefficient related to speed
    F2Drag coefficient
    nF2 speed index variable (range: 1.2—3.0)
    xF1 speed index variable (range: 0.8-1.2) (if any)
    VDrum surface linear speed
    IElectric simulated inertia


    The parameters F0, F1, F2, n, and x (if any) form the road load model, and they can be obtained in a variety of methods.


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