Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication
Utility Patent
1998-09-08
2001-01-02
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
C701S036000, C701S037000, C701S038000, C701S048000, C303S150000, C280S005508
Utility Patent
active
06169939
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of generating a vehicle lateral acceleration signal for use in an active tilt control system, and more particularly, to a method for generating a virtual lateral acceleration signal using an accelerometer mounted at the vehicle center of gravity.
BACKGROUND OF THE INVENTION
Numerous sensors can be used to provide vehicle information necessary for controlling an active tilt control (ATC) system. The sensor set typically consists of various combinations of the following sensors: steering wheel angle sensors, accelerometers, pressure transducers, suspension height sensors, ATC actuator displacement sensors and vehicle speed sensors. The optimal sensor set should be simple, inexpensive, reliable, have few parts, provide a signal that leads vehicle body roll to allow compensation for hydraulic response time and provide the proper signal under all driving conditions.
An attractive solution that has proven to be successful in vehicle evaluations and in ADAMS simulations is a single accelerometer mounted laterally, forward of the vehicle's sprung-mass center of gravity. Using a lateral accelerometer as the sensor set has several benefits. It is cost effective and allows direct measurement of lateral acceleration, which is more accurate than a lateral acceleration signal synthesized from steering wheel angle and vehicle speed. There are many automotive uses for lateral accelerometers, such as airbag systems, braking systems, etc., which will further drive cost reductions through higher volumes.
Mounting the accelerometer forward of the center of gravity (C.G.) adds lead to the signal by coupling yaw acceleration with lateral acceleration.
FIGS. 1 through 3
provide graphical illustrations of the behavior of a popular sport utility vehicle when driven through an abrupt double lane change. The steering wheel angle was measured in real time on an ATC equipped vehicle going through the maneuver at
50
mph and then used as an input to an ADAMS model of the vehicle.
FIG. 1
illustrates that the steering wheel angle leads the vehicle's body roll angle by roughly 300 msec., which is more than enough time for the hydraulics to react.
FIG. 2
illustrates the relationship between yaw acceleration and steering wheel angle. Yaw acceleration is developed almost instantaneously with steering wheel angle input. By locating the lateral accelerometer forward of the sprung mass center of gravity yaw acceleration is super-imposed on the lateral acceleration measured by the accelerometer (in proportion to the distance of the accelerometer from the center of gravity) giving valuable lead time the signal without requiring the added expense and complexity of using a steering wheel angle sensor.
The relationship is governed by the following equation, neglecting roll acceleration affects:
a
y
=a
cg
+r*a
where a
y
equals lateral acceleration at the accelerometer mounting point; a
cg
equals lateral acceleration at the sprung mass center of gravity; r equals distance from the sprung mass center of gravity to the accelerometer mounting point; and &agr; equals yaw acceleration.
The further forward the lateral accelerometer is moved, the more predominant the yaw acceleration component becomes and the more the measured signal leads roll.
FIG. 3
illustrates the affect of moving the lateral accelerometer forward of the center of gravity by two feet. This configuration is also shown in FIG.
4
. The signal from a center of gravity mounted accelerometer leads the body roll by roughly 60 msec. which is insufficient time to react hydraulically. For such a system, abrupt steering inputs would be reacted by hydraulic forces that are out of phase with body roll, resulting in an unnatural and undesirable feeling to the vehicle occupants.
The signal from the forward mounted accelerometer leads body roll by 140 msec., which is optimal for this particular system and would provide a proper amount of lead time on the control signal to provide a linear roll feel to the vehicle. Proper placement of the lateral accelerometer along the longitudinal vehicle axis is required to achieve the full benefit of lead compensation. If the sensor is placed too far forward of the center of gravity, then control signal integrity is sacrificed by adding too much signal lead and by reducing signal amplitude at the point of peak acceleration. Signal amplitude reduction results from the yaw acceleration component subtracting from the center of gravity acceleration component at the point of peak acceleration as shown in FIG.
3
. If the sensor is not placed far enough forward of the center of gravity, then insufficient lead will be provided by yaw acceleration to compensate for hydraulic, mechanical and electronic system delays.
As shown in
FIG. 4
, the lateral accelerometer
10
is mounted to the vehicle
12
forward from the sprung mass center of gravity
14
.
A problem with such a system is that the vehicle may not have the appropriate structure to support a lateral accelerometer at the desired location. Furthermore, it may be desirable to measure lateral acceleration at various positions on the vehicle in real time.
SUMMARY OF THE INVENTION
The present invention provides a method of synthesizing a virtual accelerometer at any desired vehicle location by using a conveniently mounted lateral accelerometer and vehicle speed signals.
More specifically, the present invention provides a method of generating a vehicle lateral acceleration signal for use in an active tilt control system. A single lateral accelerometer is mounted at a specific mounting point on the vehicle to generate a first lateral acceleration signal. A second lateral acceleration signal is generated representative of vehicle lateral acceleration at a point spaced from the specific mounting point based upon the first lateral acceleration signal for use in the active tilt control system.
Preferably, the specific mounting point of the lateral accelerometer is the sprung mass center of gravity of the vehicle. In this configuration, a virtual accelerometer may be synthesized mathematically in real time at any desired point with respect to the sprung mass center of gravity of the vehicle for optimizing active tilt control system performance.
Accordingly, an object of the present invention is to provide a synthesized lateral acceleration signal at any point on a vehicle with respect to a single lateral accelerometer mounted to the vehicle, thereby optimizing active tilt control system performance.
The above objects and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
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Hermann Steven A.
Raad Joseph Mikhael
Villec George Nicholas
Brown Gregory P.
Cuchlinski Jr. William A.
Ford Global Technologies Inc.
Mancho Ronnie
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