Fluid-pressure and analogous brake systems – Speed-controlled – Wheel speed versus pseudo vehicle speed
Reexamination Certificate
1999-09-02
2001-10-16
Swann, J. J. (Department: 3611)
Fluid-pressure and analogous brake systems
Speed-controlled
Wheel speed versus pseudo vehicle speed
C303S168000, C303S003000, C303S171000, C701S001000
Reexamination Certificate
active
06302500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for detecting vehicle speed of a vehicle, particularly an ordinary four-wheeled automobile, for the purpose of providing a base of a due slipless rotation speed of the wheels for use in operating the so-called antilock brake system.
2. Description of the Prior Art
The antilock brake system (ABS) is already well known as a brake system of a vehicle such as an automobile which automatically decreases a braking force applied thereby to a wheel or wheels of the vehicle when the braked wheel starts to slip so much as to lose its gripping of the road surface due to an excessive braking force applied thereto.
In order for the antilock brake system to operate at a high appropriateness, it is essential that the vehicle speed, i.e. the running speed of the vehicle body, is correctly measured or estimated to provide the base of a due slipless rotation speed for the respective wheels, so that the slipping or locking condition of each braked wheel is correctly judged from a difference between the due slipless rotation speed and an actual rotation speed of the wheel. Unless the running speed of the vehicle body is directly detected by an expensive high technology device such as a supersonic or laser speed detector, the measurement thereof will have to depend on the measurement of the rotation speed of one or more of the wheels. However, since the rotation speed of each wheel is liable to deviate from such a due slipless rotation speed because of the applications of driving or braking torques thereto and/or irregularities of the road surface, there have been made various contrivances to derive the vehicle speed as correctly as possible from the rotation speeds detected with respect to all or some of the wheels of the vehicle, such as to select the highest or lowest value of them or to calculate a simple or a weighted mean value of some or all of them.
SUMMARY OF THE INVENTION
The inventor has first contemplated that, since the drive wheels of a vehicle such as an automobile are not being driven when the measurement of the vehicle speed for the purpose of operating the ABS is required, there should occur no traction slip in the drive wheels. Moreover since the drive wheels are generally still connected with its power system during such a vehicle speed measurement period, the virtual inertia of rotation of the drive wheels will be relatively large, and, therefore, the rotation speeds detected with respect to at least a pair of drive wheels of a four-wheeled automobile or the like will be effectively usable for estimating the vehicle speed for the above-mentioned purpose.
The inventor has further contemplated that in a front drive or rear drive type four-wheeled automobile, a pair of rear or front driven wheels, each having a relatively small inertia of rotation, will be relatively highly liable to a temporal increase of rotation speed when they roll over a convex or a concave surface of the road. Nevertheless, it will not be appropriate to completely neglect the rotation speeds of the driven wheels in operating the ABS, because in the four-wheeled automobiles the vehicle speed detected based based upon only a front pair of wheels and the vehicle speed deteced based upon only a rear pair of wheels are often so different from one another as to substantially affect a good performance of the ABS due to a turning of the vehicle and/or a change of load distribution between the front and rear wheels.
The present invention is based upon those matters contemplated with respect to the particularities of the conditions concerned with the operation of the ABS and the behaviors of the front or rear drive type four-wheeled vehicles like automobiles, and makes it a principal object to provide a more improved measurement of the vehicle speed for the purpose of operating the ABS of those vehicles.
In order to accomplish such a principal object, the present invention proposes a device for measuring vehicle speed of a vehicle such as an automobile, having a pair of front wheels and a pair of rear wheels, a power system for driving either the front pair or the rear pair of wheels, and an antilock brake system for selectively applying a braking force to the pair of front wheels and the pair of rear wheels with an antilock reducibility of the braking force, the device comprising:
means for detecting rotation speed of each of the front and rear pairs of wheels and generating corresponding first stage electric signals each bearing the detected rotation speed;
means for filtering the first stage electric signals for removing a high frequency component therefrom and generating corresponding filtered second stage electric signals;
means for processing the first and second stage electric signals so as to judge if the rotation speed of any of the first stage electric signals with regard to the driven wheels is larger than the largest of the rotation speeds of the second stage electric signals and identifying such a first stage electric signal or signals to be exceptional; and
means for generating an electric signal indicating a vehicle speed for use in operating the antilock brake system based upon all of the second stage electric signals, excluding one or more thereof corresponding to the exceptional electric signal or signals.
By the device of the above-mentioned construction, when the vehicle is a front or rear drive type vehicle or a four-wheel drive type vehicle operated in a front or rear drive mode, the rotation speeds detected with respect to the four wheels are usually all effectively considered in determining the vehicle speed for use in operating the ABS, whereas if one or both of the pair of driven wheels roll over a convex or a concave portion of a road so as to temporarily increase their rotation speed during the operation of the ABS, the unduly increased rotation speed of the one or both of the driven wheels is excluded only in the meantime from engaging in the determination of the vehicle speed for use in operating the ABS.
In the device of the above-mentioned basic construction, the vehicle speed indication signal generation means may generate the vehicle speed indication signal so as to indicate the vehicle speed to correspond to the largest of the rotation speeds of all the second stage electric signals, excluding the one or more thereof corresponding to the exceptional electric signals or signals.
Since the ABS is operated by judging the braking condition of each wheel based upon a difference between a due slipless rotation speed of the wheel corresponding to the vehicle speed and the actual rotation speed of the wheel, it will be a desirable selection to determine the vehicle speed to correspond to the largest of the rotation speeds available, under the provision that the drive wheels are not in the meantime being driven by the power system, while the rotation speed detected with a driven wheel is excluded if the driven wheel is guessed to have been temporarily accelerated by rolling over a convex or a concave portion of the road surface.
In the device of the above-mentioned construction, the first and second stage electric signals processing means may be constructed to judge if the rotation speed of any of the first stage electric signals with regard to the driven wheels is larger than the largest of the rotation speeds of the second stage electric signals beyond a predetermined allowance to identify the exceptional electric signal or signals.
By such an arrangement, the magnitude of a convex or a concave portion of the road surface to which the device of the present invention is to react is adjusted by an appropriate selection of the magnitude of the allowance.
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patent: 531217
Divine David
Oliff & Berridg,e PLC
Swann J. J.
Toyota Jidosha & Kabushiki Kaisha
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