Abstract:
A method and system for controlling a vehicle suspension system comprise determining a relative velocity between a wheel and a corresponding corner of the vehicle, and determining responsive to the relative velocity a raw wheel demand force. The method and system also comprise determining a relative position between the wheel and the corresponding corner of a vehicle body, determining a scale factor responsive to the relative position of the wheel, modifying the raw wheel demand force as a function of the scale factor to determine a scaled wheel demand force, and controlling the vehicle suspension system responsive to the scaled wheel demand force.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a variable force suspension system. 
     BACKGROUND OF THE INVENTION 
     Known variable force suspension systems include variable force shock absorbers and/or struts that provide suspension-damping forces at a magnitude controllable in response to commands provided by a suspension system controller. Some systems provide control between two damping states and others provide continuously variable control of damping force. 
     In a known manner of control of a variable force suspension, the demand force for each variable force damper is determined responsive to a set of gains, the wheel vertical velocity and the body heave, roll and pitch velocities. An example system determines the body demand force as follows: DF b =G h H′+G r R′+G p P′, where DF b  is the demand force, G h  is the heave gain, G r  is the roll gain, G p  is the pitch gain, G w  is the wheel velocity gain, H′ is the body heave velocity, R′ is the body roll velocity, and P′ is the body pitch velocity. A control signal representing the determined body demand force is output to control the variable force damper responsive to the demand force. Example systems are described in U.S. Pat. Nos. 5,235,529; 5,096,219; 5,071,157; 5,062,657; 5,062,658; 5,570,289; 5,606,503; 5,579,229; 5,559,700; 5,510,988; and 5,570,288. 
     Modules are typically used by variable force damper systems for identifying and controlling different aspects of automotive control. The modules typically use specialized algorithms designed for interpreting the automobile&#39;s input forces for a preferred control signal. In addition to the body control module described above, wheel and handling modules are also typically included in a complete suspension control system. One module known in the art commands individual damper outputs to a minimum damping state whenever the applicable desired force and damper wheel to body velocity signals are opposite in sign (a state in which the given damper is said to be in an “active” quadrant). Within the limits of damper travel for small to medium-sized inputs, this approach provides acceptable vehicle body motion control. However, on larger inputs that cause the limits of damper travel to be tested, the absence of damping in the “active” quadrants can allow very undesirable compression and/or rebound bumpstop impacts. In this context, compression and rebound bumpstops are defined as damper positions at which either full metal to metal impact and/or compression of one or more hard rubber parts occurs. To this end, wheel-to-body relative position-based “electronic bumpstop” algorithms have been used. Adversely, it has typically been difficult for the existing bumpstop algorithms known in the art to satisfactorily improve compression and/or rebound bumpstop impact energy without undesirable side effects on inputs that do not require the bumpstop algorithm use. 
     Therefore, it would be desirable to have an algorithm that would improve upon the above-mentioned situation, and related situations in which system control is released prematurely. Such an algorithm may provide superior gross motion control and reduced compression and/or rebound bumpstop activation during large events. Ideally, the algorithm would provide bumpstop and improved body motion control with minimal, if any, sacrifice in ride comfort and impact isolation. 
     SUMMARY OF THE INVENTION 
     The present invention is a method and system for controlling a vehicle suspension system. The method and system comprise determining a relative velocity between a wheel and a corresponding corner of the vehicle, and determining responsive to the relative velocity a raw wheel demand force. The method and system also comprise determining a relative position between the wheel and the corresponding corner of a vehicle body, determining a scale factor responsive to the relative position of the wheel, modifying the raw wheel demand force as a function of the scale factor to determine a scaled wheel demand force, and controlling the vehicle suspension system responsive to the scaled wheel demand force. 
     The features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiment, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a variable force damper system for a motor vehicle; 
     FIG. 2 is a block diagram of one embodiment of a continuously variable real-time damping control module algorithm in accordance with the invention; 
     FIG. 3 is a block diagram of one embodiment of an automatic control module algorithm imbedded in the continuously variable real-time damping control module algorithm of FIG. 1; and 
     FIG. 4 is a block diagram of one embodiment of a bumpstop control algorithm imbedded in the automatic control module algorithm of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows an example apparatus for implementation of this invention generally comprising a vehicle body  10  supported by four wheels  11  and by four suspensions including springs of a known type (not shown). Each suspension includes a variable-force real time controllable damper  12  connected to exert a vertical force between wheel  11  and body  10  at that suspension point. Although many such suspension arrangements are known and appropriate to this invention, actuator  12  of this embodiment comprises an electrically controllable, variable force damper in parallel with a weight bearing coil spring in a parallel shock absorber/spring or McPherson strut arrangement. A description of a variable force damper suitable for use as actuator  12  is the continuously variable damper described in U.S. Pat. No. 5,282,645, the disclosure of which is hereby incorporated by reference. 
     Each corner of the vehicle includes a linear position sensor  13  that provides an output signal indicative of the relative distance between the vehicle wheel and the suspended vehicle body at that corner of the vehicle. Suitable position sensors  13  can be easily constructed by those skilled in the art. The outputs of the position sensors  13  may be differentiated to produce relative body-wheel vertical velocity signals for each corner of the vehicle and may be used to determine the body modal velocities of body heave velocity, body roll velocity and body pitch velocity. 
     An example position sensor  13  includes a rotary resistive device mounted to the vehicle body and a link pivotably coupled between both the vehicle wheel and a pivot arm on the rotary resistive device such that the rotary resistive device provides an impedance output that varies with the relative position between the wheel  11  and the corner of the body  10 . Each position sensor  13  may further include an internal circuit board with a buffer circuit for buffering the output signal of the rotary resistive device and providing the buffered signal to a controller  15 . Suitable position sensors  13  can be easily constructed by those skilled in the art. Any alternative type of position sensor, including transformer type sensors, may be used as position sensor  13 . 
     The outputs of relative position sensors  13  are provided to the controller  15 , which processes the signals to determine the states of vehicle body  10  and wheels  11  and generates an output actuator control signal for each variable actuator  12 . These signals are applied from controller  15  through suitable output apparatus to control actuators  12  in real time. Input signals for the determination of the output actuator control signals may also be provided to microcomputer to provide anticipation of vehicle pitch (lift/dive)  17  or by a vehicle speed sensor  18  and a steering wheel angular position sensor  19  to provide anticipation of vehicle roll. Obtaining such signals is easily achieved through the use of known types of sensors available to those skilled in the art. 
     FIG. 2 shows one embodiment of a continuously variable real-time damping (CVRTD) control module algorithm  100 . It should be appreciated, however, that the present invention is also applicable in a magneto-restrictive (MR) CVRTD. Sensor (also called vehicle sensor) and vehicle inputs  105  may include measured vehicle variables and preset constants, which flow to and from individual modules altering the input conditions through multiple processes. Vehicle inputs can be any static or variable input that is not provided by a sensor. The resultant signals provide distinct damping system commands at output  110 . CVRTD is one embodiment of a variable force damping system and is used throughout the detailed description of the invention, but it should be appreciated that alternate damping systems may also be used. In the CVRTD control module algorithm  100 , information is processed through internal modules providing analog signal conditioning  120 , an automatic control algorithm  130 , discrete signal conditioning  140 , and an automatic control algorithm override module  160 . It is in the automatic control algorithm  130  of this embodiment that the present invention resides. 
     FIG. 3 presents one embodiment for the automatic control algorithm  130 , and illustrates conditioned analog inputs  205 , conditioned discrete inputs  206  and outputs  210  as well as the internal processes required to provide for the outputs  210 . The internal processes for this embodiment of the automatic control algorithm  130  provide the following functionality shown as modules: 
     Body Control Algorithm  230   
     Wheel Control Algorithm  240   
     Stability and Handling Algorithms  250   
     Electronic Bumpstop Algorithm  260   
     Automatic Mode Pulse Width Modulation (PWM) Duty Cycle Determination and Scaling  280   
     The inputs  205 / 206  are a processed and unprocessed subset of the sensor and vehicle inputs  105 . Outputs from the automatic control algorithm  130  consist of an automatic PWM duty cycle  210 . Output  265  from module  260  is used in module  240  to generate output  245 . Additionally the outputs  235 ,  245 , and  255  from respective modules  230 ,  240 , and  250 , and a default PWM duty cycle floor calibration  285  are shown as input variables to the automatic mode PWM duty cycle determination  280 . The output  210  is used by the CVRTD control module algorithm  100  for further processing. The above-mentioned software functional blocks illustrate one embodiment for modular implementation of the automatic control algorithm  130 . The actual implementation may vary from the structure illustrated in FIG.  3 . The body control algorithm  230 , wheel control algorithm  240 , and stability and handling algorithms  250  are all known to the art. 
     In one embodiment of the invention, the suspension damping system may use actuators that are controlled by a PWM (Pulse Width Modulation) signal. However, actuators of another type not based on PWM signals can be substituted in alternative embodiments. Within alternative embodiments, reference to PWM signals may be named “damping command” to designate command signals to alternative actuators. It will be recognized that variable force controls other than those with PWM are equivalent to the PWM controlled signal example set forth herein. 
     FIG. 4 shows the logic of the bumpstop control algorithm. At block  300 , the system first determines whether the position of the damper shows the damper to be is a predefined compression region, which might for instance constitute the last 20% or so of travel. If the damper is in the compression region, the system then determines at block  302  whether the relative velocity of the damper shows the damper to be traveling into further compression. If this determination is negative, i.e. the damper is in rebound, then the system simply returns to the start block. If the determination is positive, however, the system as shown in block  304  then looks up a wheel bumpstop scale factor. In a preferred embodiment, this compression bumpstop area scale factor may simply be a linear function between one and about 300% of the maximum scale factor for positions between the beginning of the compression bumpstop area and perhaps 95% of possible damper travel. Above 95% possible damper travel, the scale factor is set at the 300% level. The wheel PWM is then set equal to the existing wheel PWM times the scale factor, and the algorithm returns to the beginning. 
     If at block  300  the system determines that the damper is not in the compression region, it then determines at block  306  whether the damper is instead in the rebound bumpstop area that might constitute the opposite final 20% or so of the damper travel. If the damper is not in the rebound region, the system returns to the start block. If the damper is in the rebound region, the system as shown in block  308  next determines whether the relative velocity of the damper shows the damper to be traveling into further rebound. If not, the system returns to the beginning. If the damper is traveling further into rebound, the system as shown by block  310  then looks up a wheel bumpstop scale factor. In a preferred embodiment, the rebound bumpstop area scale factor may also be a linear function between one and the maximum scale factor for positions between the onset of the rebound compression area and perhaps 5% of possible damper travel. Below 5% of possible damper travel, the scale factor is set at the maximum. The wheel PWM is then set equal to the existing wheel PWM times the scale factor, and the algorithm returns to the beginning. It should be appreciated, of course, that different curves may be implemented for the front and rear wheels. 
     The scale factors are determined for each corner of the vehicle, and then are output to block  280 , as shown in FIG.  3 . The scaled wheel demand forces are determined by multiplying each raw wheel demand force by the corresponding scale factor, and the resultant scaled wheel demand control outputs are provided on line  210 , which carry the duty cycle commands for the four actuators in the suspension system. The duty cycle commands are converted in a known manner to pulse width modulated signals. 
     When the damper is in a bumpstop region, the block  260  outputs a bumpstop active flag on line  270 . When the bumpstop flag is active, active quadrant moding is disabled in block  280 . 
     The above-described implementations of this invention are example implementation. Moreover, various other improvements and modifications to this invention may occur to those skilled in the art and those improvements and modifications will fall within the scope of this invention as set forth below.