Fluid-pressure and analogous brake systems – Speed-controlled – Sensing jerk – acceleration – or deceleration
Reexamination Certificate
1999-07-15
2001-07-03
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Sensing jerk, acceleration, or deceleration
36
Reexamination Certificate
active
06254204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for measuring longitudinal acceleration of vehicles, and more particularly, to such a longitudinal acceleration measuring device that is immune to static and dynamic errors.
2. Description of the Prior Art
A device for measuring longitudinal acceleration of a vehicle is well known and widely used in the art of automobiles, particularly in the art of the modern vehicle stability control using the microcomputers. Examples of those vehicle stability controls are shown in U.S. Pat. No. 5,702,165, U.S. Pat. No. 5,704,695 and U.S. Pat. No. 5,839,798. Those vehicle stability controls employ microcomputers to make vehicle stability calculations during the driving of the vehicles based upon various input signals in which the longitudinal acceleration of the vehicle is included.
As a matter of principle, a sensor for measuring longitudinal acceleration of a vehicle is operable with a pendulum adapted to shift forward or rearward relative to a housing which suspends the pendulum to be so swingable in response to an inertial force applied thereto according to a deceleration or an acceleration of the vehicle. Although a longitudinal acceleration sensor is generally one of the most important parameter sensors in most of the vehicle stability controls, errors in the measuring operations of the longitudinal acceleration sensors were cared for in none of those prior art controls. Nevertheless, the sensors for measuring the longitudinal acceleration of vehicles are inherently bound with static and dynamic errors which should be called external errors, because they are not such errors that will occur in the measuring device itself but they occur in a phase of the pertinent physical phenomenon transmitting to the sensor as a longitudinal acceleration. The static error is due to a longitudinal inclination of the road surface on which the vehicle is driven, while the dynamic error is mostly due to a temporal longitudinal oscillation of the vehicle caused by a small convex or concave deformation of the road surface.
SUMMARY OF THE INVENTION
In view of the above-mentioned particular situations of the longitudinal acceleration measurement in vehicles, particularly automobiles, it is a primary object of the present invention to provide a device for measuring longitudinal acceleration of a vehicle improved to be immune to such static and dynamic errors as described above.
According to the present invention, the above-mentioned primary object is accomplished by a device for measuring longitudinal acceleration of a vehicle having wheels, comprising:
first means for detecting wheel speed of at least one of the wheels to generate a first signal indicating the wheel speed;
second means for detecting longitudinal acceleration of the vehicle to generate a second signal indicating the longitudinal acceleration;
third means for differentiating the first signal by time to generate a third signal indicating change rate of the wheel speed;
fourth means for filtering the second signal to remove low frequency components thereof therefrom to generate a fourth signal;
fifth means for filtering the third signal to remove high frequency components thereof therefrom to generate a fifth signal; and
sixth means for composing the fourth and fifth signals together to generate a sixth signal indicating the longitudinal acceleration of the vehicle.
The first signal obtained by the first means for detecting the speed of at least one of the wheels of the vehicle to indicate the wheel speed is based upon the rotation speed of the wheel, and therefore, the first signal is sensitive to a small convex or concave deformation of the road surface but not sensitive to a longitudinal inclination of the road surface. Therefore, the third signal indicating the change rate of the wheel speed obtained by the third means for differentiating the first signal by time is sensitive to a small convex or concave deformation of the road surface but not sensitive to a longitudinal inclination of the road surface.
On the other hand, the second signal obtained by the second means for detecting longitudinal acceleration to directly indicate the longitudinal acceleration of the vehicle is not sensitive to a small convex or concave deformation of the road surface but is sensitive to a longitudinal inclination of the road surface.
Therefore, when the fourth signal is obtained from the second signal by the fourth means so that low frequency components are removed from the second signal, the fourth signal is immune to both of a small convex or concave deformation of the road surface and a longitudinal inclination of the road surface. Similarly, when the fifth signal is obtained from the third signal by the fifth means so that high frequency components are removed from the third signal, the fifth signal is immune to both of a small convex or concave deformation of the road surface and a longitudinal inclination of the road surface.
Thus, there are obtained two separate signals each indicating the longitudinal acceleration of the vehicle while being immune to such static and dynamic errors as described above. Therefore, by composing the fourth and fifth signals together, the device for measuring longitudinal acceleration of a vehicle can provide an appropriate magnitude of the longitudinal acceleration, with such a performance that it is immune to the static as well as dynamic errors.
In the above-mentioned device, the sixth means may compose the sixth signal by averaging the magnitudes of the fourth and fifth signals.
The device may further comprise seventh means for detecting a locking condition of at least one of the wheels due to a braking applied by the brake system of the vehicle, and the fifth means may lower a threshold frequency for the filtration above which they remove the high frequency components from the third signal to generate the fifth signal when the seventh means detect the locking condition of the wheel.
In such a modification, the seventh means may detect the locking condition of the one wheel by a slip ratio thereof being larger than a threshold value thereof predetermined therefor.
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Hara Kouichi
Kagawa Kazunori
Kanagawa Akiharu
Oliff & Berridg,e PLC
Schwartz Christopher P.
Toyota Jidosha & Kabushiki Kaisha
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