Patent Application
20060217859
The present invention relates generally to vehicle dampers, and more particularly to a method for controlling a controllable suspension damper for a vehicle wheel and to a method for differentiating between a wheel event and a body event.
Known controllable suspension dampers for a vehicle wheel include magnetorheological suspension dampers and hydraulic-valve suspension dampers. A known method for controlling a magnetorheological (MR) suspension damper for a vehicle wheel includes obtaining the vertical velocity of the vehicle wheel. The vertical velocity of the vehicle wheel is the velocity of the vehicle wheel in a direction substantially perpendicular to the road surface. The known method uses a band-pass filter designed to favor passing vertical velocity signals having a frequency band (typically 10 to 20 Hertz) within the wheel event range (typically 10 Hertz or greater). An example of a wheel event is a wheel hop occurring when a wheel passes in and out of a disturbance in the road. A wheel event is different from a body event which produces a vertical velocity signal typically in the range of 1 to 3 Hertz. An example of a body event is a when the body of the vehicle moves (pitches, heaves, and then pitches again) after it goes up and over a dip in the road. The magnitude of the band-passed filtered signal remains fairly constant over the wheel event frequencies, but the phase of the filtered signal does not. The filtered signal is used in a calibratable look-up table, based on a predetermined wheel control curve, to obtain the MR damper control current, which is always applied to the MR suspension damper.
What is needed is an improved method for controlling a controllable suspension damper for a vehicle wheel event and an improved method for differentiating between a wheel event and a body event.
A first method of the invention is for differentiating between a wheel event and a body event in a control algorithm for a controllable suspension damper for a vehicle wheel. The first method includes steps a) through d). Step a) includes obtaining an input signal corresponding to the vertical velocity of the vehicle wheel. Step b) includes filtering the input signal with a filter to obtain an output signal. Step c) includes determining the frequency of the input signal using the input and output signals. Step d) includes distinguishing between a wheel event and a body event using the determined frequency.
A second method of the invention is for controlling a controllable suspension damper for a vehicle wheel. The second method includes steps a) through e). Step a) includes obtaining an input signal corresponding to the vertical velocity of the vehicle wheel. Step b) includes filtering the input signal with a filter to obtain an output signal. Step c) includes determining the frequency of the input signal using the input and output signals. Step d) includes applying a vehicle-wheel-event control signal to the controllable suspension damper for at least some determined frequencies greater than a predetermined low value. Step e) includes applying no vehicle-wheel-event control signal to the controllable suspension damper if the determined frequency is below the predetermined low value, wherein the predetermined low value differentiates between a vehicle wheel event and a vehicle body event.
A third method of the invention is for controlling a magnetorheological suspension damper for a vehicle wheel. The third method includes steps a) through e). Step a) includes obtaining an input signal corresponding to the vertical velocity of the vehicle wheel. Step b) includes filtering the input signal with a lead-lag filter to obtain an output signal. Step c) includes determining the frequency of the input signal using the magnitudes of the input and output signals. Step d) includes applying a vehicle-wheel-event control signal to the magnetorheological suspension damper for at least some determined frequencies greater than a predetermined low value. Step e) includes applying no vehicle-wheel-event control signal to the magnetorheological suspension damper if the determined frequency is below the predetermined low value, wherein the predetermined low value differentiates between a vehicle wheel event and a vehicle body event.
Several benefits and advantages are derived from one or more of the methods of the invention. In one example, applying no vehicle-wheel-event control signal to the controllable damper if the determined frequency is below a predetermined low value (such value differentiating between a vehicle wheel event and a vehicle body event) provides a more consistent ride than using the control method of the prior art. In the same or a different example, using a lead-lag filter gives a more consistent phase response over wheel event frequencies providing a more consistent ride than using the band-pass filter of the prior art.
Referring now to
In one construction, the filter 14 is a lead-lag filter 18. In one variation, step c) includes determining the ratio of the magnitude of the output signal 16 to the magnitude of the input signal 12. In one modification, step c) includes using a predetermined (calibratable) look-up table of determined frequencies versus ratios for the filter 14 (such as a lead-lag filter 18). In another construction, not shown, the filter is a band-pass filter, step c) includes determining the phase difference between the output and input signals, and step c) includes using a predetermined look-up table of determined frequencies versus phase differences for the band-pass filter. The use of other filter constructions is left to the artisan.
In one enablement of the first method, as shown in
A second method of the invention is for controlling a controllable suspension damper 10 for a vehicle wheel. The second method includes steps a) through e). Step a) includes obtaining an input signal 12 corresponding to the vertical velocity of the vehicle wheel. Step b) includes filtering the input signal 12 with a filter 14 to obtain an output signal 16. Step c) includes determining the frequency of the input signal 12 using the input and output signals 12 and 16. Step d) includes applying a vehicle-wheel-event control signal 30 to the controllable suspension damper 10 for at least some determined frequencies greater than a predetermined low value. Step e) includes applying no vehicle-wheel-event control signal to the controllable suspension damper 10 if the determined frequency is below the predetermined low value, wherein the predetermined low value differentiates between a vehicle wheel event and a vehicle body event. It is noted that applying no vehicle-wheel-event control signal is the same as applying a zero vehicle-wheel-event control signal.
In one example of the second method, the predetermined low value corresponds to a predetermined lowest wheel event frequency. In one variation, step d) applies a vehicle-wheel-event control signal 30 to the controllable suspension damper 10 for a range of determined frequencies between the predetermined low value and a predetermined high value, and step e) applies no vehicle-wheel-event control signal to the controllable suspension damper 10 if the determined frequency is above the predetermined high value. In one modification, the predetermined high value corresponds to a predetermined highest wheel event frequency. In one variation, the predetermined low value is 10 Hertz and the predetermined high value is 20 Hertz.
In one application of the second method, step d) includes multiplying the output signal 16 by a scale factor 32 to obtain a scaled output signal 34. In one variation, the scale factor 32 is unity. In a different variation, the scale factor 32 depends on the determined frequency to compensate for frequency-dependent gain changes of the filter 14.
In one implementation of the second method, the vehicle-wheel-event control signal 30 is determined from the scaled output signal 34 and a predetermined wheel control curve (shown as block 36).
In one employment of the second method, the vehicle-wheel-event control signal 30 is an electric current. In one variation, the controllable suspension damper 10 is a magnetorheological damper 38. In a different variation, the controllable suspension damper is a hydraulic-valve suspension damper. Other variations and employments are left to the artisan. In one construction, the filter 14 is a lead-lag filter 18. Other types of filters are left to those skilled in the art.
In one illustration of the second method, the predetermined lowest wheel event frequency corresponds to the natural frequency of the suspension spring (not shown), the controllable suspension damper 10, and the mass of the vehicle wheel (which includes the tire).
In one enablement of the second method, as shown in
A third method of the invention is for controlling a magnetorheological suspension damper 38 for a vehicle wheel. The third method includes steps a) through f). Step a) includes obtaining an input signal 12 corresponding to the vertical velocity of the vehicle wheel. Step b) includes filtering the input signal 12 with a lead-lag filter 18 to obtain an output signal 16. Step c) includes determining the frequency of the input signal 12 using the magnitudes of the input and output signals 12 and 16. Step d) includes applying a vehicle-wheel-event control signal 30 to the magnetorheological suspension damper 38 for at least some determined frequencies greater than a predetermined low value. Step e) includes applying no vehicle-wheel-event control signal to the magnetorheological suspension damper 38 if the determined frequency is below the predetermined low value, wherein the predetermined low value differentiates between a vehicle wheel event and a vehicle body event.
Several benefits and advantages are derived from one or more of the methods of the invention. In one example, applying no vehicle-wheel-event control signal to the controllable damper if the determined frequency is below a predetermined low value (such value differentiating between a vehicle wheel event and a vehicle body event) provides a more consistent ride than using the control method of the prior art. In the same or a different example, using a lead-lag filter gives a more consistent phase response over wheel event frequencies providing a more consistent ride than using the band-pass filter of the prior art.
The foregoing description of several methods of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.
