Land vehicles – Wheeled – Running gear
Patent
1996-04-30
1998-02-17
Rice, Kenneth R.
Land vehicles
Wheeled
Running gear
280707, B60G 2100
Patent
active
057184461
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a suspension system including a spring and a shock absorber provided between a vehicle body and a vehicle road wheel and, more particularly, to a vehicle suspension system adapted to control the shock absorber to have an optimum damping force characteristic in the presence of vehicle braking.
BACKGROUND OF THE INVENTION
In general, vehicle suspension systems include a plurality of links, a spring for absorbing vibrations transmitted from the road surface to the vehicle body, and a shock absorber for damping the vibrations. Some conventional shock absorbers are of the variable damping force characteristic type having a damping force characteristic controllable according to vehicle operating conditions that are sensed during vehicle operation. For example, Japanese Patent Kokai NO. 4-103420 discloses a vehicle suspension system adapted to control the damping force characteristic of a shock absorber.
In the vehicle suspension system disclosed in the Japanese Patent Kokai, the time rate of change (actual rate of change) of the damping force actually obtained by the shock absorber is calculated. The calculated time rate of change of the damping force is compared with a reference time rate. Normally, a hard damping characteristic is selected to ensure good driving stability. In order to provide a good driving feel to the passenger during vehicle driving on a bad road, the shock absorber damping force characteristic is switched from the hard characteristic to a soft characteristic when the calculated time rate of change of the damping force exceeds the reference time rate. The reference time rate is set at a greater value in the presence of vehicle braking than in the absence of vehicle braking. The reference time rate is increased in response to the operation of an antiskid braking system, that is, in response to the application of urgent braking to the vehicle. This is effective to suppress the vehicle posture changes according to the degree of the vehicle braking.
Although such a conventional system can suppress vehicle posture changes by retaining the shock absorber to have a hard damping force characteristic during the application of braking to the vehicle, the hard damping force characteristic is provided during both of the extension and compression strokes of the shock absorber. For this reason, the following difficulties are associated with the conventional system.
If the shock absorber has a hard damping force characteristic during the application of braking to the vehicle, the contact load (the force under which the tire contacts the road surface) will increase to increase the braking force during its compression stroke, whereas the contact load will decrease to decrease the braking force during its extension stroke. For this reason, the braking distance will increase particularly when the vehicle is running on a bad road causing shock absorber movements. This tendency will be enhanced since the shock absorber is set to have a greater damping force during its extension stroke than during its compression stroke with regard to the direction in which the weight of the vehicle body acts.
FIG. 18 shows variations in the contact load. The dotted curve relates to the contact load variations measured when the ratio TEN/COM (damping coefficient ratio) of the damping force (TEN) provided during its extension stroke with respect to the damping force (COM) provided during its compression stroke is greater than 1.0. The solid curve relates to the contact load variations measured when the damping coefficient ratio is equal to or less than 1.0. As can be seen from FIG. 18, the contact load is smaller in the former case than in the latter case when the vehicle is running on a bad road causing a high frequency road surface input.
FIGS. 19(a), 19(b) and 19(c) show contact loads variations with respect to respective load variation centers at damping coefficient ratios (TEN/COM) of 4.0, 1.5 and 0.8. It can be seen from these figures that the deviation of the load variati
REFERENCES:
patent: 4831532 (1989-05-01), Kondo
patent: 5208749 (1993-05-01), Adachi et al.
patent: 5338058 (1994-08-01), Ohtagaki et al.
Patent Abstracts of Japan, vol. 11, No. 255, Pub. No. JP62061810, Aug. (1987).
Patent Abstracts of Japan, vol. 11, No. 238, Pub. No. JP62050213, Aug. (1987).
Rice Kenneth R.
Unisia Jecs Corporation
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