Abstract:
An apparatus ( 30 ) and a method for providing an output signal ( 28 ) indicative of a vehicle operating parameter. Preferably, the operating parameter is lateral acceleration of the vehicle. A lateral acceleration sensor ( 36 ) senses lateral acceleration and provides a first signal ( 38 ). A lateral acceleration estimator ( 40 ) estimates lateral acceleration and provides a second signal ( 42 ). The first signal ( 38 ) is passed through filters ( 44, 46 ) to provide first signal portions ( 38 L,  38 H). The second signal ( 42 ) is passed through filters ( 48, 50 ). The first signal ( 38 ) and the filtered second signal ( 42 H) are provided to a fuzzy logic controller ( 56 ) for analysis. The fuzzy logic controller ( 56 ) provides two fuzzy variable values (K 1 , K 2 ) based upon the analysis. The second signal portion ( 38 H) and the filtered second signal ( 42 H) are multiplied by the fuzzy variables, respectively. The results of the two multiplications and the first signal portion ( 38 L) are summed together to provide the output signal ( 28 ). Preferably, the apparatus ( 30 ) is part of an active roll control suspension system ( 10 ) and the output signal ( 28 ) is provided to a controller ( 24 ) for use in controlling force to counteract the chassis roll force.

Description:
TECHNICAL FIELD 
     The present invention is directed to active roll control for a vehicle and is particularly directed to an apparatus and method for improving the dynamic response of an active roll system. 
     BACKGROUND OF THE INVENTION 
     Vehicle suspension systems have as their goal the control of chassis motion during vehicle operation. One operating motion characteristic, which is controlled by known suspension systems, is chassis roll. A vehicle experiences chassis roll during a turning maneuver. During chassis roll, the chassis tilts or “rolls” about the vehicle&#39;s fore-to-aft axis toward an outside direction of the turn. 
     It is known to counteract the roll effect of the chassis by providing an opposing force to the chassis. Several methods are known to apply the opposing force. One method includes applying a chassis lifting force via corner actuators located on the vehicle side that is on the outside of the turn and/or a chassis lowering force via corner actuators located on the vehicle side that is on the inside of the turn. 
     Another known method is to utilize a stabilizer bar that extends laterally across the vehicle. The stabilizer bar, which is also known as a roll-control bar, acts as a torsion spring to apply the opposing force. Further, it is known to vary the opposing force that the stabilizer bar applies to the chassis. One way to vary the opposing force is to utilize and control one or more hydraulic actuators in the connection of the stabilizer bar. An example of such a system is shown in U.S. Pat. No. 5,362,094 to Jensen. 
     To determine the amount of roll-opposing force to be applied to the chassis, such active suspension systems require an indication of lateral acceleration to which the vehicle is subjected during the turning or cornering maneuver. In one known system, an estimated value of lateral acceleration is calculated. The lateral acceleration calculation requires a sensory input from a steerable road wheel angle sensor, a sensory input from a vehicle velocity sensor, and the value of the vehicle wheel base dimension. In one example, the road wheel angle sensor is a steering shaft angle sensor and the vehicle velocity sensor is a drive-train (e.g., transmission) sensor. 
     The accuracy of the calculated estimate is dependent upon the accuracy of the relationship of the road wheel angle sensor and the vehicle velocity sensor to the actual lateral acceleration being experienced by the vehicle. The signals from the road wheel angle sensor and the vehicle velocity sensor may not accurately reflect the actual lateral acceleration experienced due to terrain conditions over which the vehicle is being driven. For example, driving the vehicle on a low traction surface may result in some amount of road wheel slippage. The calculated lateral acceleration, in this wheel slippage example, would not equal the actual lateral acceleration experienced by the vehicle. 
     Other known systems have a physical lateral acceleration sensor mounted to the vehicle and which provides a signal indicative of sensed actual lateral acceleration. However, the signal provided by the lateral acceleration sensor may include high frequency components resulting from road noise. One solution for eradicating such high frequency noise is to digitally low-pass filter the output signal from the acceleration sensor. However, use of a low-pass filter introduces a phase lag into the control system and thereby degrades the system&#39;s performance by reducing the system&#39;s bandwidth and the system&#39;s ability to quickly respond to steering maneuvers. 
     SUMMARY OF THE INVENTION 
     The present invention includes an apparatus for providing a weighted signal indicative of acceleration of an object. Means provides a first signal indicative of object acceleration. Means calculates a weighting factor using the first signal. Means multiplies the first signal by the weighting factor to provide the weighted signal. 
     In accordance with another aspect, the present invention includes an apparatus for providing an output signal indicative of a vehicle operating parameter. Sensor means senses the operating parameter and provides a first signal indicative thereof. Estimator means estimates the operating parameter and provides a second signal indicative thereof. Means processes the first and second signals to provide the output signal. The means for processing includes: means for determining first and second weighting factors for the first and second signals, respectively, using at least portions of the first and second signals, means for modifying the first and second signals using the first and second weighting factors to provide first and second modified signals, and means for combining the first and second modified signals to provide the output signal. 
     In accordance with another aspect, the present invention includes an active roll control suspension system for controlling chassis roll of a vehicle. Force application means applies force to the chassis. Control means controls the force application means in response to at least one operating parameter signal indicative of a vehicle condition. Means provides an acceleration signal to the control means as an operating parameter signal. The means for calculating an acceleration signal includes: means for providing a first signal indicative of acceleration, means for providing a weighting factor using the first signal, means for multiplying the first signal by the weighting factor to provide a weighted signal, and means for utilizing the weighted signal as a component to provide the acceleration signal. 
     In accordance with another aspect, the present invention includes an active vehicle suspension system for controlling chassis roll of a vehicle. Force application means applies force to the chassis. Control means controls the force application means in response to at least one operating parameter signal indicative of a vehicle condition. Means provides the operating parameter signal to the control means. The means providing the operating parameter signal includes sensor means for sensing the operating parameter and for providing a first signal indicative thereof. The means for providing includes estimator means for estimating the operating parameter and for providing a second signal indicative thereof. The means for providing also includes means for processing the first and second signals to provide the operating parameter signal. The means for processing includes: means for determining first and second weighting factors for said first and second signals, respectively, using at least portions of the first and second signals, means for modifying the first and second signals using the first and second weighting factors to provide first and second modified signals, and means for combining the first and second modified signals. 
     In accordance with yet another aspect, the present invention includes a vehicle suspension control apparatus having a controllable actuator for controlling at least one suspension characteristic in response to a control signal. Means senses lateral acceleration of the vehicle and provides a sensed lateral acceleration signal indicative thereof. Means estimates lateral acceleration of the vehicle and provides an estimated lateral acceleration signal indicative thereof. Means blends the sensed lateral acceleration signal and the estimated lateral acceleration signal to provide the control signal so that the control signal is initially responsive to the estimated lateral acceleration signal and subsequently responsive to the sensed lateral acceleration signal. 
     In accordance with still a further aspect, the present invention includes a method for providing a weighted signal indicative of acceleration of an object. A first signal indicative of object acceleration is calculated. A weighting factor is provided using the first signal. The first signal is multiplied by the weighting factor to provide the weighted signal. 
     In accordance with yet a still further aspect, the present invention includes a method for providing an output signal indicative of a vehicle operating parameter. The operating parameter is sensed and a signal indicative thereof is provided. The operating parameter is estimated and a second signal indicative thereof is provided. The first and second signals are processed to provide the output signal. Processing the first and second signals includes determining first and second weighting factors for the first and second signals, respectively, using at least portions of the first and second signals. During processing, the first and second signals are modified using the first and second weighting factors to provide first and second modified signals. Also during processing, the first and second modified signals are combined. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from reading the following description with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic illustration of a portion of a vehicle having an active roll control system in accordance with the present invention; 
     FIG. 1A is an enlarged view of a roll-control actuator shown in FIG. 1; 
     FIG. 2 is a schematic illustration of a lateral acceleration apparatus of the system shown in FIG. 1; 
     FIG. 3 is a graphical representation of membership functions of sensed lateral acceleration used by a fuzzy logic controller shown in FIG. 2; 
     FIG. 4 is a graphical representation of membership functions for estimated lateral acceleration used by the fuzzy logic controller shown in FIG. 2; 
     FIGS. 5 and 6 are graphical representations of membership functions for fuzzy variable values used by the fuzzy logic controller shown in FIG. 2; and 
     FIG. 7 is an illustration of the fuzzy base rule for the fuzzy logic controller shown in FIG.  2 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to FIG. 1, a portion of a vehicle  8  that has an active roll control suspension system  10 , in accordance with the present invention, is schematically illustrated. The illustrated portion of the vehicle  8  includes one axial pair of ground-engaging wheel assemblies  11 A and  11 B. Each wheel assembly  11 A,  11 B includes a road wheel which is rotatable about a respective wheel axes  12 A,  12 B. The wheel axes  12 A and  12 B are transverse to the vehicle&#39;s fore-to-aft axis  13 . In the illustrated example, the wheel assemblies  11 A and  11 B are the vehicle&#39;s front pair of wheel assembles. Thus, the road wheels of the wheel assemblies  11 A and  11 B are the steerable wheels of the vehicle  8 . 
     Only the single pair of wheel assemblies and associated suspension components are shown for the purposes of brevity and clarity. Specifically, the suspension components for the rear pair of wheel assemblies have similar structure and similar function as the suspension components for the front pair of wheel assemblies. 
     The wheel assemblies  11 A and  11 B are attached to the vehicle&#39;s chassis  14  (shown as fragments to permit clearer view of the present invention) via control arms  15 A and  15 B, respectively. Each control arm  15 A,  15 B has a pivot connection at each end to permit vertical relative movement between the respective wheel assembly  11 A,  11 B and the vehicle chassis  14  (see FIG.  1 A). The chassis  14  is also connected to the control arms/wheel assemblies via spring assemblies (not shown) and shock absorber assemblies (not shown), which also permit vertical relative movement between the wheel assemblies  11 A,  11 B and the chassis. Thus, the relationship between the chassis  14  and each wheel assembly  11 A,  11 B is that of a sprung mass and an unsprung mass. 
     The system  10  (FIG. 1) includes a stabilizer bar  16  that extends transverse to the fore-to-aft axis  13  of the vehicle  8 . The stabilizer bar  16  is also known as a roll control bar. The stabilizer bar  16  is rotationally mounted (e.g., via mounting brackets  17 ) to the chassis  14 . Rotation of the stabilizer bar  16  relative to the chassis  14  is concurrent with swinging movements of the ends of the stabilizer bar. 
     One end (not visible in the Figures) of the stabilizer bar  16  is connected to the left (as viewed in FIG. 1) control arm  15 A. The other end of the stabilizer bar  16  is connected to an upper (as viewed in FIG. 1) end of a hydraulic actuator  19  (see FIG.  1 A). The other or lower end of the actuator  19  is connected to the right (as viewed in FIG. 1) control arm  15 B. 
     The actuator  19  is a double acting hydraulic actuator having a closed working cylinder mounting a reciprocating piston, as is known in the art. A pump  20  is a source of pressurized fluid for the actuator  19  and a reservoir  21  is a receptacle for fluid returning from the actuator  19 . The flow of hydraulic fluid is through hydraulic lines  22 . A valve system  23  controls the flow of hydraulic fluid between the pump/reservoir and the actuator  19 , to cause or resist telescoping of the actuator. 
     The person of skill in the art will appreciate that the vehicle&#39;s other wheel assemblies (i.e., the rear pair of wheel assemblies, not shown) have a similar suspension structure arrangement. Specifically, the rear stabilizer bar (not shown) is similarly connected to the rear actuator (not shown). The valve system  23  is connected to control the flow of hydraulic fluid to the rear actuator in concert with the front actuator  19  (e.g., the front and rear actuators are connected in parallel). 
     During operation of the vehicle  8 , turning/cornering of the vehicle urges the chassis  14  to roll about its fore-to-aft axis  13  due to the lateral acceleration experienced by the vehicle. The chassis roll is represented in FIG. 1 by the double-headed arrow. Chassis roll is normally manifested at the vehicle corners by compression of the outside corners (i.e., the chassis and the wheel assembly move closer together) and expansion of inside corners (i.e., the chassis and the wheel assembly move apart). 
     The stabilizer bar  16  acts to transfer the roll-induced force bearing on the stabilizer bar into a roll-resisting force acting on the chassis, as will be appreciated by a person skilled in the art. Specifically, the force delivered to one end of the stabilizer bar  16  due the chassis roll action causes the stabilizer bar to rotate at the chassis mounting brackets  17 . Rotation of the stabilizer bar  16  causes the stabilizer bar to apply a force to the chassis  14  for resisting chassis roll. The rotation movement of the stabilizer bar  16  is dependent upon the amount of force applied by the actuator  19 . Specifically, the actuator  19  can increase or decrease the roll damping or reduce roll gain dependent upon the flow of hydraulic fluid provided by the valve system  23 . 
     A controller  24  of the suspension system  10  controls the valve system  23 . The controller  24  provides a control signal  26  to the valve system  23  that is based upon determinations made within the controller. Specifically, the controller  24  monitors a compensated lateral acceleration signal  28  provided by a lateral acceleration apparatus  30  in accordance with the present invention and uses the information contained with the signal  28  to determine control of the valve system  23  (i.e., the compensated lateral acceleration signal  28  is used to determine a roll control command). The controller  24  controls the value system  23  and causes the actuator  19  to apply a variable force to the end of the stabilizer bar  16  to offset the roll force during the turning/cornering of the vehicle  8 . The chassis  14  is thus inhibited from rolling about the for-to-aft axis  13  (e.g., the chassis is kept level). 
     The lateral acceleration apparatus  30  (FIG. 2) of the present invention includes a lateral acceleration sensor  36 , which provides a sensed lateral acceleration signal  38 , and a lateral acceleration estimator  40 , which provides an estimated lateral acceleration signal  42 . The lateral acceleration sensor  36  has any suitable structure for sensing lateral acceleration experienced by the vehicle  8 , such as an accelerometer having an axis of sensitivity extending substantially perpendicular (i.e., lateral) to the fore-to-aft axis  13  of the vehicle  8 . In the illustrated example, the lateral acceleration sensor  36  is located on the fore-to-aft axis  13 . 
     In a preferred embodiment, the sensed lateral acceleration signal  38  has both a magnitude component and a frequency component. Specifically, the signal  38  has a voltage magnitude value, which varies as a function of the magnitude of the sensed acceleration, and a frequency value, which varies as a function of the frequency of the sensed acceleration. 
     The lateral acceleration estimator  40  has any suitable structure for estimating lateral acceleration (i.e., structure that does not directly sense lateral acceleration). For example, the lateral acceleration estimator  40  includes a steerable road wheel angle sensor  41  and a vehicle forward velocity sensor  43 . The angle sensing function of the road wheel angle sensor  41  is schematically shown in FIG. 1 as dash line extending to the wheel assembly  11 A and senses the steering angle schematically represented by the angle A. The person of skill in the art will recognize that any suitable sensor may be used to sense the angle of the road wheels. For example, a steering shaft sensor may be used to sense the steering angle, which is, in turn, indicative of the angle of the road wheels. 
     The person of skill will recognize that the vehicle velocity sensor  43  may be any suitable sensor for sensing the velocity of the vehicle  8 . For example, a transmission sensor may be used to sense the speed of a transmission drive-train member, which is, in turn, indicative of the velocity of the vehicle  8 . 
     Sensory input from the road wheel angle sensor  41  and the vehicle forward velocity sensor  43  are utilized, along with other vehicle data such as wheel base length, by the estimator  40  to estimate a lateral acceleration value. An algorithm is used to determine the estimated lateral acceleration value. For example, any known algorithm for calculation of an estimated lateral acceleration value from road wheel angle, vehicle velocity, and wheelbase length can be used. The estimated acceleration value is provided as the estimated lateral acceleration signal  42 . In a preferred embodiment, the estimated lateral acceleration signal  42  has a voltage magnitude component and a frequency component indicative of the estimated value. 
     Hereinafter, the lateral acceleration is referred to simply as acceleration. Accordingly, the compensated lateral acceleration signal  28  is referred to as the compensated acceleration signal  28 . Similarly, the sensed lateral acceleration signal  38  is referred to simply as the sensed acceleration signal  38 , and the estimated lateral acceleration signal  42  is referred to as the estimated acceleration signal  42 . 
     The sensed acceleration signal  38  and the estimated acceleration signal  42  are analyzed and “blended”, with the end result being the compensated acceleration signal  28 . Specifically, the sensed acceleration signal  38  from the lateral acceleration sensor  36  is provided to a low-pass filter  44 . The output of the low-pass filter  44  is a low frequency portion of the sensed acceleration signal  38 , and is referred to as the low frequency portion  38 L. The sensed acceleration signal  38  from the lateral acceleration sensor  36  is also provided to a non-inverting input of a high-pass filter  46  and the low frequency portion  38 L from the low-pass filter  44  is provided to an inverting input of the high-pass filter  46 . Within the high-pass filter  46 , the low frequency portion  38 L is subtracted from the sensed acceleration signal  38 , and the output from the high-pass filter is referred to as a high frequency portion  38 H of the sensed acceleration signal. 
     The estimated acceleration signal  42  from the lateral acceleration estimator  40  is provided to a non-inverting input of a high-pass filter  48 . An output of the high-pass filter  48  is provided as an input to a low-pass filter  50 . The low-pass filter output  52  is provided to an inverting input of the high-pass filter  48 . Within the high-pass filter  48 , the low-pass filter output  52  is subtracted from the estimated acceleration signal  42  from the lateral acceleration estimator  40 . The output of the high-pass filter  48  is referred to as the filtered estimated acceleration signal  42 H. 
     The sensed acceleration signal  38  from the lateral acceleration sensor  36  and the filtered estimated acceleration signal  42 H from the high-pass filter  48  are also supplied to inputs of a multiplexer  54 . A fuzzy logic controller  56  controls the multiplexer  54 , via a signal  55 , to selectively receive the sensed acceleration signal  38  and the filtered estimated acceleration signal  42 H. The fuzzy logic controller  56  operates on the two input signals  38 ,  42 H to generate two fuzzy variable values K 1  and K 2  using fuzzy logic rules. 
     Specifically, as shown in FIG. 3, the sensed acceleration has two membership functions for which the degree of membership varies dependent upon the magnitude value of the sensed acceleration signal  38 . Similarly as shown in FIG. 4, the estimated acceleration has two membership functions for which the degree of membership varies dependent upon the magnitude value of the filtered estimated acceleration signal  42 H. The fuzzy variable values K 1  and K 2  each have two membership functions (FIGS.  5  and  6 ). The degree of membership for each of the fuzzy variable values K 1 , K 2  is functionally related to the magnitude of the respective fuzzy variable values. 
     The relationship between the sensed acceleration and the estimated acceleration to the two fuzzy variable values K 1  and K 2  will be appreciated by referring to FIG. 7, which illustrates the rule base for the fuzzy logic controller  56 . The rule base includes the following rules: 
     1. If the magnitude value of the sensed acceleration signal  38  is low and the magnitude value of the filtered estimated acceleration signal  42 H is small, then K 1  is low and K 2  is high. 
     2. If the magnitude value of the sensed acceleration signal  38  is high and the magnitude value of the filtered estimated acceleration signal  42 H is small, then K 1  is high and K 2  is low. 
     3. If the magnitude value of the sensed acceleration signal  38  is low and the magnitude value of the filtered estimated acceleration signal  42 H is big, then K 1  is high and K 2  is low. 
     4. If the magnitude value of the sensed acceleration signal  38  is high and the magnitude value of the filtered estimated acceleration signal  42 H is big, then K 1  is high and K 2  is low. 
     The fuzzy logic controller  56  outputs the two fuzzy variable values K 1 , K 2  to a demultiplexer  58 . The first fuzzy variable value K 1  is provided, via the demultiplexer  58 , under control of the fuzzy logic controller  56  via a signal  59 , as a first input to a first multiplier  60 . The high frequency portion  38 H of the sensed acceleration signal  38  from the high-pass filter  46  is provided as a second input to the first multiplier  60 . The first multiplier  60  multiplies the high frequency portion  38 H of the sensed acceleration signal by the first fuzzy variable value K 1 , and provides the result as a first multiplier output. It will be appreciated by a person of ordinary skill in the art that the first fuzzy variable value K 1  is a weighting value and it is used to “weight” the high frequency portion  38 H of the sensed acceleration signal  38 . It will further be appreciated that the first multiplier  60  acts as an amplifier, with the first fuzzy variable K 1 , being used as a gain value. The first multiplier output is referred to as the modified high frequency portion  38 MH of the sensed acceleration signal. 
     The demultiplexer  58 , under control of the fuzzy logic controller  56  via the signal  59 , provides the second fuzzy variable value K 2  as a first input to a second multiplier  62 . The filtered estimated acceleration signal  42 H is provided to the second multiplier  62  as a second input. The second multiplier  62  multiplies the filtered estimated acceleration signal  42 H by the second fuzzy variable value K 2 , and provides the result as a second multiplier output. It will be appreciated by a person of ordinary skill in the art that the second fuzzy variable value K 2  is a weighting value and it is used to “weight” the filtered estimated acceleration signal  42 H, and further that the second multiplier  62  acts as an amplifier. The second multiplier output is referred to as the modified estimated acceleration signal  42 MH. 
     The modified high frequency portion  38 MH of the sensed acceleration signal  38  and the low frequency portion  38 L of the sensed acceleration signal, and the modified estimated acceleration signal  42 MH are all provided to a summation device  64 . It will be appreciated by a person of ordinary skill in the art that a full “weight” is accorded to the low frequency portion  38 L of the sensed acceleration signal  38 . The summation device  64  adds its three inputs and provides the result as an output that is the compensated acceleration signal  28 . 
     When the value of the first fuzzy variable value K 1  is zero, the contribution to the compensated acceleration signal  28  by the high frequency portion  38 H is zero. Similarly, when the value of the second fuzzy variable value K 2  is zero, the contribution by the filtered estimated acceleration signal  42 H is zero. Accordingly, the compensated acceleration signal  28  is represented by the following equation: 
     
       
         N COMP =(N SEN −N SEN LOW )K 1 +(N EST HIGH )K 2 +N SEN LOW   
       
     
     wherein: 
     N COMP =the compensated acceleration signal  28 ; 
     N SEN =the sensed acceleration signal  38 ; 
     N SEN LOW =the low frequency portion  38 L; 
     N EST HIGH =the filtered estimated acceleration signal  42 H; 
     K 1 =the first fuzzy variable value; and 
     K 2 =the second fuzzy variable value. 
     In a steady-state condition, the compensated acceleration signal  28  has little or no high frequency noise interference associated with the sensed acceleration signal  38  as a result of the low-pass filtering and the full weight given to the low frequency portion  38 L at the summation device  64 . The high-pass filtering of the sensed acceleration signal  38  and the estimated acceleration signal  42  gives phase lead such that the apparatus  30  acts somewhat like an “anticipator” to an input. 
     During a quick steering maneuver, the compensated acceleration signal  28  is initially provided based upon the estimated acceleration signal  42  because of the filtering processes, the fuzzy logic rule base, and the blending process provided by the summation device  64 . If the vehicle stays in the turn (i.e., the sensed lateral acceleration increases), the second fuzzy variable value K 2  goes to zero and the modified estimated acceleration signal  42 MH no longer contributes to the compensated acceleration signal  28 . Thus, when the second fuzzy variable value K 2  is at zero, the compensated acceleration signal  28  is provided entirely based upon the sensed acceleration signal  38 , as provided by the low frequency portion  38 L and the modified high frequency portion  38 MH. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, it will be appreciated by a person of ordinary skill in the art that the present invention is applicable to other types of suspension systems. An example of such a different suspension system is a system that includes a hydraulic actuator at each corner of the vehicle. The compensated lateral acceleration signal would be used to determine control for each of the actuators (i.e., corner control). Another example of a different suspension system is a system that has two actuators for each stabilizer bar. One of the actuators is connected to the first end of the bar and the second actuator is connected to the second end of the bar. 
     Also, it will be appreciated by a person of ordinary skill in the art that as an alternative to maintaining the chassis level, the sufficient force can be applied to the torsion bar to cause the chassis to be tilted toward the inward side of a turn to provide a sensation of “banking” around the turn. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.