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US 5,208,751 AGranted
Active four-wheel steering system for motor vehicles
AssigneeDr. Ing. h.c.F. Porsche Aktiengesellschaft
InventorVolker Berkefeld
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AssigneeDr. Ing. h.c.F. Porsche Aktiengesellschaft
InventorVolker Berkefeld
Estimating the term…
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.
An active four-wheel steering system for a motor vehicle having front and rear wheels comprising:
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 (.delta..sub.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 (.delta..sub.H) and the vehicle speed (v) and to generate an output signal representative of lateral acceleration (a.sub.y) when a sideslip angle (.beta.) is reduced to zero according to the relationship ##EQU3## wherein 1 is the wheel base, 1.sub.h is the distance between a center of gravity of the motor vehicle and a rear axle, and C.sub.1 and C.sub.3 are constants, in which (.delta..sub.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 (a.sub.y) 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 (.delta..sub.r) to control the hydraulic control unit according to the relationship
Dependencies are inferred from the claim text.
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From the US filing history. Foreign family members aren’t listed.
Characterised by means varying the ratio between the steering angles of the steered wheels: characterised by computing methods or stabilisation…
Active Steering, Steer-by-Wire: rear-wheel steering; Four-wheel steering
Motor vehicles
Vehicle brake control systems or parts thereof
Term ended 4 May 2010 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
The present invention generally relates to an active four-wheel steering system for motor vehicles, and more particularly to a four-wheel steering system providing improved vehicle handling.
In German Published Unexamined Patent Application (DE-OS) 31 55 618, motor vehicles are disclosed having a four-wheel steering system which comprises steerable front and rear wheels, the rear wheels being controllable as a function of driving condition quantities which are calculated and/or measured and then fed to an electric control unit. For this purpose, the rear wheels are connected with an additional adjusting device for the control of the rear wheels which, corresponding to the actual driving condition quantities, can be adjusted in a certain relationship to the front wheels.
Thus, it is an object of the invention to provide a four-wheel steering system having front wheels actuated by a steering wheel and rear wheels controlled by an electronic control unit as a function of driving conditions, the rear wheels being adjusted with respect to the front wheels in a variable wheel steering angle relationship by means of which an improved vehicle handling is achieved in comparison to vehicles with conventional front-wheel steering systems.
FIG. 1 is a block diagram for a vehicle having a four-wheel steering system in accordance with the teachings of the present invention;
FIG. 2 is a representation of the geometrical relationship of a vehicle during a steady-state driving in a circle;
FIGS. 3A-3B are characteristic-curve diagram concerning the under behavior effect as a function of the lateral acceleration;
The motor vehicle shown schematically in FIG. 1 comprises a steering device 2 for the front wheels 3 which is actuated by means of the steering wheel 1. Another electrohydraulic steering device 4 is provided between the rear wheels 5. This steering device 4 comprises essentially a hydraulic adjusting device consisting of a valve-controlled adjusting cylinder 6, which is connected with the wheels 3 by means of tie rods. A control of the adjusting cylinder 6 for the adjusting of the rear wheels 5 takes place as a function of determined vehicle condition quantities which are fed to an electronic control unit 7, such as a vehicle computer. This computer computes desired values for the steering angle .delta..sub.r rear wheels 5, which are fed to a hydraulic control unit 8, which, by means of a pump, generates the working pressure for the adjusting cylinders 6 required for the adjustment of the rear wheels 5.
In the operating condition of the vehicle, corresponding actual values are measured by a vehicle speed sensor 10 and a steering wheel angle sensor 11 and, as input signals vehicle speed v and steering wheel angle .delta..sub.H (which is known in the art to be related to the front wheel steering angle .delta..sub.r and the steering ratio i expressed as .delta..sub.H =i .multidot..delta..sub.f), are fed to a first function calculation task apparatus 12 of the control unit 7 as best seen in FIG. 5. By means of these measured quantities v and .delta..sub.H, under the condition that, for example, the sideslip angle .beta.=0, the actual lateral acceleration a.sub.y is computed according to equation (8) in the control apparatus. For this calculation, the geometric relationship of a vehicle (FIG. 2) and the understeer behavior of the vehicle (FIG. 3) during steady-state cornering is taken into account according to equations (1) to (5). The lateral acceleration a.sub.y, which was calculated from the above-mentioned equations (1) to (5) in the function calculation task apparatus 12, is entered as an input signal, together with the additional input signal concerning the vehicle speed v, into a second function converter 13 of the control apparatus, in which the rear wheel steering angle .delta..sub.r is programmed and calculated according to equation (9) as a function of the vehicle speed v and the front wheel steering angle .delta..sub.f.
In order to take into account a driving speed change, such as a longitudinal acceleration -a.sub.x or a longitudinal deceleration a.sub.x, the calculated output signal concerning the lateral acceleration a.sub.y, together with an additional signal from the vehicle speed change a.sub.x or -a.sub.x, is fed to a third function calculation task apparatus 14 of the control apparatus 7. As shown in FIG. 5 this input signal a.sub.y, calculated in function 12, and the input signals -a.sub.x or a.sub.x, calculated in the function calculation task apparatus 14, are converted to an output signal additional rear wheel steering angle .delta..sub.r,add., which is added to the output signal .delta..sub.r of the second function calculation task apparatus 13. The sum of these output signals .delta..sub.r and .delta..sub.r,add., as the steering angle signal .delta..sub.r,eff., are fed to the control unit 8 for the control of the hydraulic steering device 6 for the rear wheels 5.