1. Field of the invention
The present invention relates to a rear wheel suspension controller for a vehicle, particularly to a rear wheel suspension controller which is effective against a sporadic shock caused by a protrusion or a sinking of a road surface on which an automobile is running.
2. Prior art
Conventionally, the spring constant, damping force, bush characteristic or stabilizer characteristic of each of various suspension components provided between a body of a vehicle and its wheels is altered under control depending on conditions of a road surface or running conditions of the vehicle in order to prevent the vehicle from being shocked or vibrated and keep the controllability and the stability of the vehicle good. For example, altering the spring constant of the air spring of a suspension depending on conditions of the road surface, altering the damping force of a shock absorber, and simply making the characteristic of a bush or a stabilizer variable were proposed in published unexamined Japanese patent applications No. sho 59-23712 and No. sho 59-26638, in those No. sho 58-30542 and No. sho 59-23712, and in Japanese utility model application No. sho 58-26605 and published unexamined Japanese utility model application No. sho 59-129613, respectively. In such control, when it is detected by a vehicle height sensor that the vehicle is running on a rough road or when it is detected by a brake sensor or an accelerator sensor that the front of the vehicle has gone up or down, the characteristic of each suspension of the vehicle is altered to maintain a good controllability and stability of the vehicle running on the rough road, or to prevent the front of the vehicle from going up or down further. However, under the above-mentioned conventional control, the vehicle is not judged to be running on a rough road, until a large turbulence is continuously detected by the vehicle height sensor. When the vehicle is judged to be running on a rough road, the spring constants of the suspensions for all the wheels of the vehicle or the damping forces of the shock absorbers for all the wheels are increased to produce a desired effect. If the vehicle passes over a joint of road patches or its sporadic protrusion or sinking, the vehicle usually receives only one shock and resumes running on a flat part of the road again, so that the characteristic of each suspension is not altered. For that reason, passengers of the vehicle are not protected from an unpleasant shock due to such sporadic protrusion or sinking, which is different from the case that the vehicle is running on a rough road having continuous protrusions or sinkings. In some cases of passing over such sporadic protrusion or sinking, the controllability and the stability of the vehicle deteriorate as well.