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Active Suspension

  This study presents an intelligent control strategy for an active MacPherson suspension driven by a pneumatic muscle (PM) actuated system and evaluates its improved control performance on a self developed test-rig. To fulfill the fully-functional test and analysis of active suspension systems, this test-rig comprises three units: 1. an active MacPherson suspension unit, which consists of a PM mechanism and two MacPherson struts, is built to isolate vibration from road disturbances; 2. a road profile generator (RPG) unit, which can produce a vertical force to lift the car-body according to various road profiles; 3. a PC-based control (PBC) unit, which computes, sends and receives signals for both of the active MacPherson suspension and the PC-based control unit. The objective of this study is to improve the MacPherson suspension in terms of the capability of road vibration isolation by using the PM actuation that can actively provide extra compensatory force for MacPherson struts. Then, for motion control of the PM, this study employs an interval type-2 adaptive fuzzy controller to approximate the optimal control law and adopts a self-tuning and fuzzy sliding mode compensator to compensate unmodeled dynamics for the active MacPherson suspension system. Three experiments are conducted to compare the active MacPherson suspension system with the original MacPherson struts through various road profiles on the test-rig. The results show the significant improvement for the proposed active MacPherson suspension system in suppressing the displacement and acceleration of the car-body.








Experimental Results 

  AMSS-PM Unit  


The main components of the AMSS-PM unit are constructed using two MacPherson struts and a PM. This unit also contains a sprung mass which includes a counterweight and an upper support frame to represent a car-body. To measure the displacement and the acceleration of the sprung mass, a linear encoder and an accelerometer are installed on the upper support frame and a linear scale is installed in the plane of the under support frame to measure vertical  displacement. The PM, in parallel with two MacPherson struts, are installed between the vehicle body and the wheel-axle to generate control force to the suspension. A proportional pressure regulator (PPR) regulates air into the PM and the PM produces vertical movement to attenuate external vibration from irregular roads and to maintain the upper support frame in a stable position.

RPG Unit


The RPG unit, consists of a wheel, rollers, an induction motor and a pneumatic cylinder. The induction motor, which is controlled by a frequency converter, rotates the rollers to induce rotation of the wheel. The maximum speed that the wheel can reach is 35 km/hr. A PDCV regulates the flow of air into the cylinder to create vertical displacements to take account of road conditions. The maximum pressure that is provided by the air compressor is 6 bar. To connect the base and the frame for the rollers, the bottom of the pneumatic cylinder is fixed to the base and the rollers bear firmly on the tire. A linear scale which is installed on the support frame is applied to measure the vertical variation in the road profile that is created by the pneumatic cylinder.

 PBC Unit


The PPR is installed inside a control box in the PBC unit. The PBC is implemented on a National Instruments (NI) cRIO-9074 integrated system with an industrial 400 MHz real-time processor, a 64GB memory, a NI-9263 D/A card, a NI-9215 A/D card and a NI-9411 encoder card. The NI-9215 A/D card receives data, including the displacement of the unsprung mass and under support frame, and the acceleration of the sprung mass, from the AMSS-PM unit and the RPG unit. The NI-9411 encoder card receives data for the displacement of the sprung mass and the NI-9263 D/A card sends control signals to the proportional directional control valve (PDCV), the inverter and the PPR. The PM, the pneumatic cylinder and the induction motor are driven according to these signals.


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