Recent years have seen an increasing demand for more fuel efficient vehicles. To accommodate that demand, it is anticipated that future vehicles will be smaller, lighter, and run on tyres with lower rolling resistance. Because these vehicles may require stability improvement, we developed a system which uses rear active camber to increase stability. In this paper, we describe a simulation model based on an experimental vehicle which has a rear active camber system installed, and use the model to quantitatively describe the effect of camber. We show that the stability improvement effected by the system results from the use of camber thrust at low lateral acceleration, and roll steer at high lateral acceleration. An active camber control mechanism was designed which allows for two distinct camber angles. For the Lexus HS250h, the system was implemented on the body side joint of the trailing arm double wishbone suspension upper arm. A crank shaft, which can be rotated using a motor, was placed in the joint. As illustrated in a figure, rotating the crank shaft moves the upper arm joint, changing the wheel camber angle. Hence it was possible to implement the system with only a slight modification to the existing suspension. As shown in the figure, the crank shaft has two dead points. When the crank shaft is at one of the two dead points the system is resistant to rotation, even during large lateral force inputs from the wheel, so the camber angle setting can be maintained. By this method a self-locking, a two-state variable camber system has been realised. For the present vehicle, when stationary, there is a compression load on the upper arm due to vehicle weight, which leads to a natural tendency toward negative camber. Hence by taking advantage of the vehicle's weight, negative camber can be added when necessary using little power and within a short time. In addition, since camber can be changed by 3° using a crank radius of 5 mm, even during large loads only a small torque is needed to rotate the crank shaft. The primary benefits of this design are: (1) A separate mechanism for maintaining camber angle is unnecessary; (2) a large gear ratio can be used (since the gear is not used for locking); (3) the motor/gear assembly is situated on the sprung mass, and so is not directly subject to suspension vibrations (improving durability), and does not add to unsprung weight. A simulation model has been constructed, based on an actual experimental vehicle, and the close agreement between simulation and experiment proved the utility of the model. Simulations using the vehicle model proved the effect of an active camber control system. It was shown that for low lateral acceleration the system's effect could be quantitatively explained by the development of camber thrust, while for higher lateral acceleration roll steer provided the dominant effect. Hence it has been shown that, when necessary (for example at high speeds), via a switch to the negative camber condition the system fulfils the aim of utilizing both camber thrust and roll steer for vehicle stability improvement, for all lateral acceleration regimes.


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    Title :

    Development and analysis of an active camber control system for stability improvement


    Contributors:


    Publication date :

    2013


    Size :

    17 Seiten, 18 Bilder, 1 Tabelle, 10 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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