Development of electronic motor control prototype for vehicle shock absorber

Author: Lucas Paix

Paix, Lucas, 2019 Development of electronic motor control prototype for vehicle shock absorber, Flinders University, College of Science and Engineering

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In all road vehicles, suspension systems act to reduce the effects of road disturbance to improve driving performance and driver comfort. These can be powerful but expensive active systems, cheaper but limited passive systems or the middle-ground semi-active. Different driving conditions require different degrees of control and cost, which must be all considered when deciding what type of suspension to use. Settling the trade-off between cost and performance is typically achieved using passive systems with mechanically adjustable damper strength, as is the case for many dampers made by Supashock. These provide cheap and effective solutions for many cases, but compromise on the flexibility to adjust the damping strength while driving. Addressing this problem can be performed by building an electronic system to control the mechanical damper adjuster on-the-drive through software.

An investigation was performed into the development of an electronic shock absorber controller and demonstration test rig for Supashock. The primary objective was to demonstrate the capability for an electromechanical system to provide accurate control of a variable damper via control of hydraulic oil pressure. This was approached by designing a custom needle-and-seat continuous hydraulic valve which formed the basis of the test rig. The valve was controlled by a motor mechanism and was operated using a custom PCB with appropriate driver circuitry.

The test rig was designed to use the machined aluminium custom valve, 3D printed mounting structures, a stepper motor for actuation and a hall effect sensor for feedback. Overall, a complete prototype was fabricated using a 3D printed test valve, which was demonstrated to provide successful operation of the system mechanical motion. It was measured that the motor could fully sweep the 3D printed valve from open to closed within 0.75 seconds at a maximum speed of 1600 pulses per second. The valve was tested in dry conditions to validate the designs and is awaiting delivery of the machined aluminium valve for further testing against hydraulic pressure.

A custom PCB was designed and fabricated to provide electronic control and measurement of the test rig. This provided capability to drive a stepper motor up to 2.5A and measure the position feedback of the custom valve via a hall effect sensor analog voltage. After overcoming PCB rework requirements, the circuit could successfully demonstrate control of the test rig. The microcontroller provided complete control the stepper motor at desired speed, step count, direction and microstep size, and read the position of the valve via the hall effect sensor voltage.

Additional features of the PCB were tested such as input voltage measurement and motor driver current measurement. This found that the microcontroller successfully calculated the input voltage at 11.6V but could not reliably calculate motor current. When observing the current amplifier output, the voltage contained large noisy spikes which completely obscured any useful information. Further testing has been recommended for this including a low-pass filter to remove the high frequency spikes and analyse for useful information.

The primary outcome of this project successfully provided the development framework for an electronically controlled shock absorber damper. The design focus towards testing flexibility means that these achievements can be easily adapted by Supashock towards any specific shock absorber in a future as desired.

Keywords: Shock Absorber, Electronic, Suspension, motorsport, damper, semi-active

Subject: Engineering thesis

Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: Dr Nasser Asgari