Output filter and method for on/off semi-active suspension control

• US 5,024,460 A
• Filed: 12/26/1989
• Issued: 06/18/1991
• Est. Priority Date: 12/26/1989
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Radcliffe, Scott T., Hanson, Reed D.
• Primary Examiner(s): Rice, Kenneth R.
• Application Number:
  US07/454,309
• Time in Patent Office: 539 Days
• Field of Search: 280/707
• US Class Current: 280/5.519
• CPC Class Codes: B60G 17/018 characterised by the use of a specific signal treatment or control method
• CPC Class Codes: B60G 2400/102 vertical
• CPC Class Codes: B60G 2400/106 longitudinal with regard to vehicle, e.g. braking
• CPC Class Codes: B60G 2400/202 Piston speed; Relative velocity between vehicle body and wheel
• CPC Class Codes: B60G 2400/204 Vehicle speed
• CPC Class Codes: B60G 2400/252 vertical
• CPC Class Codes: B60G 2400/40 Steering conditions
• CPC Class Codes: B60G 2500/102 stepwise
• CPC Class Codes: B60G 2600/02 Retarders, delaying means, dead zones, threshold values, cut-off frequency, timer interruption
• CPC Class Codes: B60G 2600/12 Sampling or average detecting; Addition or substraction
• CPC Class Codes: B60G 2600/14 Differentiating means, i.e. differential control
• CPC Class Codes: B60G 2600/16 Integrating means, i.e. integral control
• CPC Class Codes: B60G 2600/26 Electromagnets; Solenoids
• CPC Class Codes: B60G 2600/604 low pass
• CPC Class Codes: B60G 2600/70 Computer memory; Data storage, e.g. maps for adaptive control
• CPC Class Codes: B60G 2600/74 Analog systems
• CPC Class Codes: B60G 2600/76 Digital systems
• CPC Class Codes: B60G 2600/90 other signal treatment means
• CPC Class Codes: B60G 2800/22 Braking, stopping

Abstract

In a suspension control comprising a damper having a valve switchable at frequencies within a desired activation frequency range between high and low damping modes, an unfiltered damper signal is repeatedly derived from vehicle suspension related variables at a range significantly greater than the desired activation frequency range. An output filter derives a filtered damper signal from each successive binary actuator force signal by (1) resetting a timer each time the unfiltered damper signal changes value, (2) causing the filtered damper signal to be the same value as the unfiltered damper signal while the timer is inactive, and (3) maintaining the filtered damper signal value unchanged while the timer is active. The damper is controlled in response to the filtered damper signal, whereby unnecessary high frequency switching of the valve is reduced but the damper responds without unnecessary delay to signals within the desired activation frequency range.

Claims

1. A suspension control for a vehicle having a body and a road contacting wheel connected by a damper effective to apply a damping force therebetween, the damper including apparatus including a valve switchable in response to a binary filtered damper signal at frequencies within a desired activation frequency range between a first mode of operation characterized by a low damping force, in response to a first value of the filtered damper signal, and a second mode of operation having a high damping force, in response to a second value of the filtered damper signal, the suspension control comprising:

first means effective to repeatedly derive from one or more sensed vehicle suspension related operating variables, at a rate significantly greater than the desired activation frequency range, a binary unfiltered damper signal comprising a first value or a second value;

a timer active for a predetermined time after a reset and otherwise inactive; and

filter apparatus effective to derive the filtered damper signal from each successive unfiltered damper signal by (1) resetting the timer each time the unfiltered damper signal changes value, (2) causing the filtered damper signal to be the same value as the unfiltered damper signal while the timer is inactive, and (3) maintaining the filtered damper signal value unchanged while the timer is active, whereby unnecessary high frequency switching of the valve is reduced but the damper responds without unnecessary delay to signals within the desired activation frequency range.

2. The suspension control of claim 1 in which the first means provides the first value of the unfiltered damper signal when a body/wheel force needed to provide a desired suspension behavior would require active power and the second value thereof at least some times when the body/wheel force needed to provide a desired suspension behavior would cause power to be dissipated.

3. A method for controlling a damper connected to provide a damping force between a body and a road contacting wheel of a vehicle, the damper comprising apparatus including a valve switchable in response to a binary filtered damper signal at frequencies within a desired activation frequency range between a first mode of operation characterized by a low damping force, in response to a first value of the filtered damper signal, and a second mode of operation having a high damping force, in response to a second value of the filtered damper signal, the method comprising the steps:

repeatedly deriving from one or more sensed vehicle suspension related operating variables, at a rate significantly greater than the desired activation frequency range, a binary unfiltered damper signal comprising a first value when a body/wheel force needed to provide a desired suspension behavior would require active power and a second value at least some times when the body/wheel force needed to provide a desired suspension behavior would cause power to be dissipated;

resetting a timer whenever the unfiltered damper signal changes value, the timer being active for a predetermined time after a reset and otherwise inactive;

for each derived unfiltered damper signal, providing the filtered damper signal with the same value as the unfiltered damper signal if the timer is inactive and with a value unchanged from the immediately preceding filtered damper signal if the timer is active, and

applying the filtered damper signal to the damper to determine the damper mode of operation, whereby unnecessary high frequency switching of the valve is reduced but the damper responds without unnecessary delay to signals within the desired activation frequency range.

4. A method for controlling a damper connected to provide a damping force between a body and a road contacting wheel of a vehicle, the damper comprising apparatus including a valve switchable in response to a binary filtered damper signal at frequencies within a desired activation frequency range between a first mode of operation characterized by a low damping force, in response to a first value of the filtered damper signal, and a second mode of operation having a high damping force, in response to a second value of the filtered damper signal, the method being performed in a digital computing apparatus in a programmed cycle repeated at a rate significantly greater than the desired activation frequency range and comprising the steps, in each successive cycle:

deriving from one or more sensed vehicle suspension related operating variables a binary unfiltered damper signal comprising a first value when a body/wheel force needed to provide a desired suspension behavior would require active power and a second value at least some times when the body/wheel force needed to provide a desired suspension behavior would cause power to be dissipated;

providing the filtered damper signal with the same value as the unfiltered damper signal if a count has reached a reference count from an initial count or, alternatively, with a value unchanged from the filtered damper signal of the immediately preceding cycle if the count has not reached the reference count from the initial count;

comparing the unfiltered damper signal with an unfiltered damper signal generated during the immediately preceding cycle and resetting the count at the initial count if the unfiltered damper signal has changed value or, alternatively, incrementally changing the count toward the reference count if the unfiltered damper signal has not changed value;

directing the value of the filtered damper signal to the same value as the unfiltered damper signal if the count became equal to the reference count in the preceding step; and

applying the filtered damper signal to the damper to determine the damper mode of operation.