Suspension control apparatus
In a suspension control system a sky-hook command signal (B) obtained from velocity data obtained by integrating a sprung mass acceleration (αu) from a sprung mass acceleration sensor ( 9 u ) and an unsprung mass vibration damping command signal (C) obtained on the basis of an unsprung mass acceleration (αd) detected by an unsprung mass acceleration sensor ( 9 d ) are added together to obtain a control signal (A) for a damping characteristic inverting type shock absorber ( 6 ). The control signal (A) reflects the unsprung mass acceleration (αd) that leads in phase by 90° the piston speed. Accordingly, it is possible to compensate for a response delay due to an actuator ( 11 ), etc.
1. A suspension control system comprising:
a damping characteristic controllable shock absorber provided between a sprung mass member and an unsprung mass member of a vehicle, said shock absorber being arranged such that damping characteristics are adjustable between “soft” and “hard” damping characteristics;
a sprung mass vertical acceleration detecting device that detects a vertical acceleration of the sprung mass member and outputs a sprung mass vertical acceleration signal;
an unsprung mass vertical acceleration detecting device that detects a vertical acceleration of the unsprung mass member and outputs an unsprung mass vertical acceleration signal, said unsprung mass vertical acceleration detecting device being provided on the unsprung mass member; and
a controller that outputs a control signal for controlling said damping characteristic-controllable shock absorber from said sprung mass vertical acceleration signal and said unsprung mass vertical acceleration signal;
wherein said controller comprises:
a sprung mass vibration damping signal computing section that computes a sprung mass vibration damping signal on the basis of said sprung mass vertical acceleration signal;
an unsprung mass vibration damping signal computing section that computes an unsprung mass vibration damping signal on the basis of said unsprung mass vertical acceleration signal; and
a desired damping characteristic control signal computing section that computes said control signal on the basis of said sprung mass vibration damping signal and said unsprung mass vibration damping signal, and
wherein said unsprung mass vibration damping signal computing section computes said unsprung mass vibration damping signal so that said unsprung mass vibration damping signal leads in phase a vertical velocity of the unsprung mass member.
2. A suspension control system according to claim 1 , wherein said unsprung mass vibration damping signal computing section obtains a relative acceleration from said unsprung mass vertical acceleration signal and said sprung mass vertical acceleration signal, and computes an unsprung mass vibration damping signal from said relative acceleration.
3. A suspension control system according to claim 1 , wherein said unsprung mass vibration damping signal computing section has a filter that filters said unsprung mass vertical acceleration signal to pass a signal in the neighborhood of an unsprung mass resonance frequency.
4. A suspension control system according to claim 3 , wherein said filter has an adjustable cut-off frequency.
5. A suspension control system according to claim 4 , wherein said controller further comprises a frequency adjusting section that adjusts said cut-off frequency according to a result of detection by said unsprung mass vertical acceleration detecting device.
6. A suspension control system according to claim 1 , wherein said unsprung mass vibration damping signal computing section has a phase adjusting element that adjusts a phase of a signal.
7. A suspension control system according to claim 1 , wherein said sprung mass vibration damping signal computing section integrates said sprung mass vertical acceleration signal to obtain a signal proportional to an absolute velocity of the sprung mass member.
8. A suspension control system according to claim 1 , wherein said desired damping characteristic control signal computing section computes said control signal by adding together the sprung mass vibration damping signal and the unsprung mass vibration damping signal.
9. A suspension control system according to claim 1 , wherein said desired damping characteristic control signal computing section computes said control signal by selectively outputting either one of the sprung and unsprung mass vibration damping signals.
10. A suspension control system according to claim 1 , wherein said controller is provided with a road surface condition judging device to correct the unsprung mass vibration damping signal according to a result of judgment by said road surface condition judging device.
11. A suspension control system according to claim 10 , wherein the judgment by said road surface condition judging device is made on the basis of a detected signal detected by a sprung mass vertical acceleration detecting device provided for a front wheel side of the vehicle.
12. A suspension control system according to claim 11 , wherein damping characteristics of a damping characteristic inverting type shock absorber provided for a rear wheel side of the vehicle are varied according to a detected signal detected by an unsprung mass vertical acceleration detecting device provided for said front wheel side.
13. A suspension control system according to claim 1 , wherein the unsprung mass vibration damping signal is obtained by multiplying said unsprung mass vertical acceleration signal by a control gain, said control gain being adjustable.
14. A suspension control system according to claim 13 , wherein said controller further comprises a gain adjusting section that adjusts said control gain according to a result of detection by said unsprung mass vertical acceleration detecting device.