Land vehicles – Suspension modification enacted during travel – Lateral and longitudinal vehicle attitude control
Utility Patent
1998-10-05
2001-01-02
Johnson, Brian L. (Department: 3611)
Land vehicles
Suspension modification enacted during travel
Lateral and longitudinal vehicle attitude control
C280S005514, C280S006160, C701S037000, C701S038000, C701S039000
Utility Patent
active
06168171
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a vehicle height adjust control apparatus and method for controlling an actuator while the differential motion between the front and rear wheels is limited and, more particularly, to a vehicle height adjust control apparatus for a vehicle having a drive force distributing device that enables distribution of the drive force to the front and rear wheels while the differential between the front and rear wheels is limited.
2. Description of Related Art
Four-wheel drive vehicles suitable for driving off road or on snow-covered roads or the like are well known wherein the drive force from the transmission is transmitted to the front and rear wheels, as disclosed in, for example, Japanese Patent Application Laid-Open Nos. HEI 2-3508 and HEI 5-58133. Such vehicles typically employ a switching device to simply change between the transmission of the drive force from the transmission only to the rear wheels (or the front wheels) and the transmission thereof to the front and rear wheels, or a differential device having a differential motion limiting function to continuously change the ratio between the drive forces distributed to the front wheels and the rear wheels.
There is another well known technology wherein actuators for changing the vehicle height is provided between the vehicle body and a plurality of wheels so as to change the vehicle height stepwise in accordance with the selection made by a driver, or so as to always maintain a target vehicle height at each wheel position despite changes in the load, or so as to change the vehicle height at each wheel position in accordance with the driving condition of the vehicle, as described in, for example, Japanese Patent Application Laid-Open No. SHO 60-261714 and HEI 2-151515.
However, in such a four-wheel drive vehicle, tight-cornering braking may occur if the vehicle turns in accordance with the operation of the steering wheel while the differential motion between the front and rear wheels is limited so that the revolution speed of the front wheels and the revolution speed of the rear wheels are approximately equal to each other (in particular, while the front and rear wheels are interlocked for equal revolution speeds). Tight-cornering braking occurs due to the inhibition of differential motions between the front and rear wheels. In tight-cornering braking, the wheel base changes due to deformation of bushes and the like, instead of differential motions of the front and rear wheels. Along with wheel base changes during the tight-cornering braking, the vehicle height also changes; for example, the vehicle height at the inner wheel side increases while the vehicle height at the outer wheel side decreases. If an operation is performed to increase the vehicle height in such a condition, the change in the wheel base caused by the change in the vehicle height must be absorbed by a suspension apparatus because of the equal revolution setting on the front and rear wheels. Therefore, considerably great forces are needed to change the vehicle height. When the turning of the vehicle ends, the thus-changed vehicle height needs be re-adjusted. Moreover, during vehicle height adjustment at the end of the turning, a sudden vehicle height change may occur. This is undesirable in view of the driving stability of the vehicle. Furthermore, in this event, unnecessary driving of the actuators for changing the vehicle height inevitably occurs, which is unfavorable in view of the durability of the actuators.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to eliminate the need to re-adjust the height of a vehicle after the vehicle comes out of a turning or cornering state and avoid a sudden vehicle height change after the end of turning so that good vehicle driving will be secured and so that the drive force needed to operate actuators and the frequency of operation thereof will be reduced and therefore the durability or service life of the actuators will be increased, by limiting the vehicle height adjustment when occurrence of the tight-cornering braking is expected.
According to one aspect of the invention, there is provided a vehicle height adjust control apparatus including an actuator capable of changing a vehicle height, a vehicle height detection device that detects a vehicle height, an adjustment control device for adjusting and controlling the vehicle height so that the vehicle height detected by the vehicle height detection device becomes substantially equal to a target vehicle height, by controlling the actuator, and a steering angle detection device that detects a steering angle of a steering wheel. The vehicle height adjustment control by the adjustment control device is limited if the steering angle detected by the steering angle detection device is greater than a predetermined steering angle. A plurality of actuators as described above may be provided between a vehicle body and a plurality of wheels, so as to detect the vehicle heights at the corresponding wheel positions. A plurality of vehicle height detectors may also be provided to detect actual vehicle heights at a plurality of positions.
According to another aspect of the invention, there is provided a vehicle height adjust control apparatus similar to the apparatus described above, wherein the steering angle detection device is replaced by a differential limitation detection device that detects a wheel differential-limited state. The vehicle height adjustment control by the adjustment control device is limited if the wheel differential-limited state is detected by the differential limitation detection device. The differential limitation detection device may detect a state where differential motions between front and rear wheels in a drive force distributor device.
According to still another aspect of the invention, a vehicle height adjust control apparatus similar to the apparatus described above has one or both of a steering angle detection device and a differential limitation detection device. If the steering angle detected by the steering angle detection device is greater than a predetermined steering angle and the wheel differential-limited state is detected by the differential limitation detection device, the vehicle height adjustment control is limited.
The adjustment control device may integrate a deviation of the detected actual vehicle height from a target vehicle height when the deviation exceeds a predetermined threshold, and may start control of the actuator so as to adjust the vehicle height to the target vehicle height, when the integral reaches a predetermined value. The vehicle height adjustment control may be limited by switching the threshold to an increased value.
Furthermore, the vehicle height adjustment control may be limited by stopping the control of the actuator.
In a vehicle height adjust control apparatus according to the invention, a condition where the tight-cornering braking is likely to occur is detected on the basis of the steering angle and/or detection of a differential-limited state. In such a condition, the vehicle height adjustment is limited. Therefore, unnecessary or unfavorable vehicle height changes will be eliminated in a condition that the vehicle height changes due to the tight-cornering braking, in a condition that, due to the tight-cornering braking, great forces will be needed to change the vehicle height, or the like. Consequently, the invention eliminates the need to re-adjust the vehicle height and avoids a sudden vehicle height change after an event of the tight-cornering braking, and avoids a vehicle height change that requires a great force during an event of the tight-cornering braking. As a result, good driving stability of the vehicle is maintained, and the durability or service life of the actuators and the like is increased.
REFERENCES:
patent: 4593920 (1986-06-01), Natsume et al.
patent: 4693493 (1987-09-01), Ikemoto et al.
patent: 4787644 (1988-11-01), Yokote et al.
patent: 4803630 (1989-02-01), Takizawa et al.
patent
Sato Atushi
Shono Shoichi
Johnson Brian L.
Oliff & Berridg,e PLC
Shriver J. Allen
Toyota Jidosha & Kabushiki Kaisha
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