Land vehicles – Wheeled – Running gear
Patent
1985-12-05
1987-06-09
Love, John J.
Land vehicles
Wheeled
Running gear
180236, 180141, B62D 700
Patent
active
046715231
DESCRIPTION:
BRIEF SUMMARY
The invention involves a steering mechanism for a motor vehicle with steerable front wheels and steerable rear wheels and more particularly to rear wheel steering means responsive to front wheel steering torque.
Steering devices of this type are identified for example by publications DE-OS Nos. 31 24 821 and 31 33 985. The steering angle and the speed of the motor vehicle are tracked, among others, as vehicle specific parameters and used to derive the degree of turning of the rear wheels. In addition, the lateral acceleration and the yaw angle of the vehicle can be factored into the calculation.
The intention of these measures is to obtain increased stability in curves, a faster response of the motor vehicle's steering in curve maneuvers, and finally greater maneuverability for parking. The steering of the rear wheels can result in either positive or negative indications; in other words, the rear wheels can either be steered in the same sense as the front wheels or in the opposite sense against the front wheels. In this case, the first-mentioned measure (positive indication) works against oversteering the vehicle when driving through fast curves. The latter measure (negative indication) serves particularly to diminish the turning radius and to provide rapid entry into sharp curves.
The handling of relatively high performance passenger cars is extremely problematic in terms of stability at the front and rear wheels. Steering and handling devices for the rear wheels, and particularly the necessary sensors, pose significant challenges. For this reason, implementation of such devices is in practice extremely expensive. In addition, the dynamic effects of road conditions have not been adequately factored in, so that even small slippage between the road and tire could cause instability due to the rear wheel steering device.
The objective of the invention, therefore, is to create a more simple device of this type which also takes into account actual road conditions.
This objective is fulfilled according to the invention by providing means for steering the rear wheels dependent on the steering angle of the front wheels and the steering torque developed on the front wheels. It turns out that the torque exerted by the vehicle operator on the steering of the front wheels has a relevant effect on the handling of the rear wheels. Note that the steering torque is affected by a number of driving specific parameters, such as the speed of the vehicle, the friction of the road surface, the curve radius, etc.
For example, only a small steering torque can be developed on a road surface covered with smooth snow. In addition, the torque is kept small by the generally cautious response of the driver under such slippery road conditions. Similar considerations apply when the vehicle is driven at high speed. In this case, according to the invention, a very small or even no turning degree is imparted to the rear wheels.
On the other hand, the steering torque increases almost immediately when, for example, a sudden obstacle in the road causes an extreme steering reaction on the front wheels. Through a corresponding turning of the rear wheels, an increased bypass impulse is created (the vehicle moves out of the way faster). If the steering torque then decreases, the turning degree of the rear wheels is again more or less adjusted according to the steering angle of the front wheels.
If, during parking of the vehicle, a large steering torgue is developed, then a relatively strong turning of the rear wheels also occurs. A large torque can be developed even on smooth road surfaces when the front wheels reach their end turning point thus causing internal resistance.
The steering torque can be obtained by measuring the force transmitted from the steering wheel to the steering gear, for example, within the steering column. Devices for this are common in the application of power steering mechanisms.
According to the invention, steering of the rear wheels is eliminated by very small steering torques. Thereby, unproblematical tracking of the ve
REFERENCES:
patent: 3856102 (1974-12-01), Queen
patent: 4263979 (1981-04-01), Sturgill
patent: 4406472 (1983-09-01), Furukawa
Audi AG
Love John J.
Rice Kenneth R.
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