Active four-wheel steering system for motor vehicles
First Claim
1. An active four-wheel steering system for a motor vehicle having front and rear wheels comprising:
- a) front wheel steering means for setting a front wheel steering angle (δ
f) of the front wheels;
b) rear wheel steering means for setting a rear wheel steering angle (δ
r) of the rear wheels which can be adjusted with respect to the front wheel steering angle (δ
f) in a variable wheel steering angle relationship;
c) steering wheel means for controlling the front wheel steering means to set the front wheel steering angle (δ
f);
d) a steering wheel angle sensor for providing a steering wheel signal representative of a steering wheel angle (δ
H) as set by a position of the steering wheel means;
e) a vehicle speed sensing means for providing a vehicle speed signal representative of a vehicle speed (v);
f) first function calculation task means for receiving the vehicle speed signal and said steering wheel angle signal and for generating a lateral acceleration signal (ay) representative of a lateral acceleration of the vehicle as a function of the vehicle speed and steering angle signals and defined by the relationship ##EQU2## wherein 1 is the wheel base, 1h is the distance between a center of gravity of the motor vehicle and a rear axle, and C1 and C3 are constants;
g) second function calculation task means for receiving the lateral acceleration signal and the vehicle speed signal and for generating a first rear wheel steering angle (δ
r) signal representative of the rear wheel steering angle as a function of the lateral acceleration signal and the vehicle speed signal defined by the relationship
space="preserve" listing-type="equation">δ
.sub.r =-(1.sub.h /v.sup.2 +C.sub.3)·
a.sub.yh) a hydraulic control means for receiving the first rear wheel steering angle signal and for controlling a valve-controlled adjusting means for adjusting the rear wheel steering angle of the rear wheels as a function of the first rear wheel steering angle signal.
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Abstract
An active four-wheel steering system for motor vehicles has steering devices for the front wheels and the rear wheels. These devices operate as a function of driving condition quantities fed to an electronic control unit. A variable wheel steering angle relationship with respect to the front wheels is adjusted, in which case the input signal concerning the steering wheel angle from a steering wheel angle sensor and the additional signal concerning the vehicle speed from a speed sensor is fed to a first function calculation task apparatus of the control unit. This function calculation task apparatus generates a first output signal for the lateral acceleration which, as an input signal, together with the additional input signal of the vehicle speed, is fed to a second function calculation task apparatus. In order to take a driving speed change into account, the output signal concerning the lateral acceleration, together with a signal from the driving speed change, is fed to the third function calculation task apparatus. This input signal, computed in the first function calculation task apparatus, and the input signals concerning the speed change, computed in the third function calculation task apparatus, are converted to an output signal additional rear wheel steering angle, which is overlayed on the output signal rear wheel steering angle. The sum of these output signals, as the steering angle signal, are fed to the control unit for the control of the hydraulic steering device for the rear wheels.
25 Citations
11 Claims
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1. An active four-wheel steering system for a motor vehicle having front and rear wheels comprising:
-
a) front wheel steering means for setting a front wheel steering angle (δ
f) of the front wheels;b) rear wheel steering means for setting a rear wheel steering angle (δ
r) of the rear wheels which can be adjusted with respect to the front wheel steering angle (δ
f) in a variable wheel steering angle relationship;c) steering wheel means for controlling the front wheel steering means to set the front wheel steering angle (δ
f);d) a steering wheel angle sensor for providing a steering wheel signal representative of a steering wheel angle (δ
H) as set by a position of the steering wheel means;e) a vehicle speed sensing means for providing a vehicle speed signal representative of a vehicle speed (v); f) first function calculation task means for receiving the vehicle speed signal and said steering wheel angle signal and for generating a lateral acceleration signal (ay) representative of a lateral acceleration of the vehicle as a function of the vehicle speed and steering angle signals and defined by the relationship ##EQU2## wherein 1 is the wheel base, 1h is the distance between a center of gravity of the motor vehicle and a rear axle, and C1 and C3 are constants; g) second function calculation task means for receiving the lateral acceleration signal and the vehicle speed signal and for generating a first rear wheel steering angle (δ
r) signal representative of the rear wheel steering angle as a function of the lateral acceleration signal and the vehicle speed signal defined by the relationship
space="preserve" listing-type="equation">δ
.sub.r =-(1.sub.h /v.sup.2 +C.sub.3)·
a.sub.yh) a hydraulic control means for receiving the first rear wheel steering angle signal and for controlling a valve-controlled adjusting means for adjusting the rear wheel steering angle of the rear wheels as a function of the first rear wheel steering angle signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An active four=wheel steering system for front wheels and rear wheels of a motor vehicle, having a first apparatus for steering the front wheels actuatable by a steering wheel, a second apparatus for steering the rear wheels comprising a hydraulic control unit with an adjusting device controllable as a function of measured driving condition quantities, including steering wheel angle (δ
-
H) and vehicle speed (v), and an electronic control unit to which the measured driving condition quantities are fed as input signals to vary a wheel steering angle relationship between the rear wheels and the front wheels, wherein a first function calculator task apparatus of the electronic control unit is operative to analyze input signals representative of the measured steering wheel angle (δ
H) and the vehicle speed (v) and to generate an output signal representative of lateral acceleration (ay) when a sideslip angle (β
) is reduced to zero according to the relationship ##EQU3## wherein 1 is the wheel base, 1h is the distance between a center of gravity of the motor vehicle and a rear axle, and C1 and C3 are constants, in which (δ
f) is a front wheel steering angle, and a second function calculator task apparatus of the electronic control unit to which is fed the output signal representative of the lateral acceleration (ay) from the first function calculation task apparatus and the measured vehicle speed (v) is operative to generate an output signal representative of a desired rear wheel steering angle (δ
r) to control the hydraulic control unit according to the relationship
space="preserve" listing-type="equation">δ
.sub.r =-(l.sub.h /V.sub.2 +C.sub.3)·
a.sub.ysuch that the steering angle of the rear wheels can be automatically adjusted with respect to the front wheels in a defined and desired angular relationship. - View Dependent Claims (11)
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H) and vehicle speed (v), and an electronic control unit to which the measured driving condition quantities are fed as input signals to vary a wheel steering angle relationship between the rear wheels and the front wheels, wherein a first function calculator task apparatus of the electronic control unit is operative to analyze input signals representative of the measured steering wheel angle (δ
Specification