Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-01-19
2004-05-25
Lavinder, Jack (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S115300, C303S012000, C188S356000
Reexamination Certificate
active
06739676
ABSTRACT:
This application is based on Japanese Patent Application No. 10-8383 filed Jan. 20, 1998, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a braking system for an automotive vehicle, which is equipped with a vacuum booster, and more particularly to a vehicle braking system capable of preventing a reduction in braking effect due to reduction in the boosting function of the vacuum booster.
2. Discussion of the Related Art
One example of a known braking system of the type indicated above is disclosed in JP-A-9-30385. This braking system includes (a) a brake operating member, (b) a master cylinder, (c) a vacuum booster for boosting a brake operating force acting on the brake operating member, on the basis of a pressure difference between a pressure in a negative-pressure chamber communicating with a negative-pressure source, and a pressure in a variable-pressure chamber selectively communicating with the negative-pressure chamber and an atmosphere, so that the boosted force is applied to the master cylinder, (d) a wheel brake cylinder connected to the master cylinder through a fluid passage and actuated by a hydraulic pressure applied thereto through the fluid passage, for braking a wheel of an automotive vehicle, and (e) a pressure increasing device actuated when a predetermined condition is satisfied during an operation of the brake operating member, to initiate a pressure increasing operation of increasing a hydraulic pressure in the wheel brake cylinder, with a hydraulic pressure source other than the master cylinder, such that the increased wheel brake cylinder pressure is higher than a hydraulic pressure generated by the master cylinder. The brake operating force or other quantity relating to this force, at which the predetermined condition is satisfied, is referred to as “pressure increase initiating point”.
The known braking system indicated above is adapted such that the brake operating force acting on the brake operating member is boosted by the vacuum booster at a predetermined boosting ratio, until a boosting limit of the vacuum booster is reached, and such that the pressure increasing device initiates the pressure increasing operation when the boosting limit is reached, namely, when the brake operating force or other quantity has increased to the pressure increase initiating point, which is reached when the boosting limit is reached.
In this known braking system, a fact that the boosting limit of the vacuum booster is reached is detected when one of the following three conditions is satisfied: (1) the condition that a pressure switch has detected that the pressure in the variable-pressure chamber has been raised to the atmospheric pressure; (2) the condition that a switch has detected that an input rod of the vacuum booster which is operatively connected to the brake operating member has been brought into abutting contact with an output rod of the vacuum booster which is operatively connected to the master cylinder; and (3) the condition that the actual wheel brake cylinder pressure detected by a pressure sensor has become lower than a nominal value corresponding to the brake operating force detected by a pressure sensor. In the braking system described above wherein the moment at which the boosting limit of the vacuum booster is reached changes with a change in the pressure in the negative-pressure chamber, the pressure increase initiating point changes depending upon the pressure in the negative-pressure chamber. Theoretically, therefore, a change in the pressure in the negative-pressure chamber does not have influences on the braking effect provided by the wheel brake cylinder and on the operating feel of the brake operating member as given to the vehicle operator.
Actually, however, it is difficult to accurately detect that the boosting limit of the vacuum booster has been reached. Accordingly, the known braking system inevitably suffers from a problem that the braking effect and the brake operating feel are influenced by a change in the negative-pressure chamber of the vacuum booster.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a braking system adapted to reduce or prevent influences of a change in the pressure in the negative-pressure chamber of the vacuum booster, on the braking effect and the brake operating feel.
The above object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and refers to or depends from the other mode or modes, where appropriate, so as to indicate possible combinations of elements or features in preferred forms of the invention.
(1) A braking system for braking a wheel of an automotive vehicle, comprising:
a brake operating member;
a master cylinder functioning as a first hydraulic pressure source for generating a hydraulic pressure based on an input force;
a vacuum booster having a negative-pressure chamber connected to a negative pressure source, and a variable-pressure chamber selectively connected to the negative-pressure chamber and an atmosphere, the vacuum booster boosting an operating force of the brake operating member on the basis of a difference between pressures in the negative-pressure and variable-pressure chambers, and transmitted the boosted operating force to the master cylinder, the vacuum booster having a transition point at which a boosting ratio of said vacuum booster is reduced during an increase of the brake operating force before a boosting limit point at which the booster has become inoperable to perform its boosting function is reached, the transition point being kept unchanged irrespective of a change in the pressure in the negative-pressure chamber;
a brake including a wheel brake cylinder which is connected to the master cylinder through a fluid passage and which is activated by a hydraulic pressure supplied thereto through the fluid passage, for braking the wheel; and
a pressure increasing device including a second hydraulic pressure source connected to the fluid passage, the pressure increasing device performing a pressure increasing operation of increasing a hydraulic pressure in the wheel brake cylinder, by using the second hydraulic pressure source, such that the increased hydraulic pressure in the wheel brake cylinder is higher than that generated by the master cylinder, the pressure increasing device initiating the pressure increasing operation when the brake operating force has increased to the transition point.
In the braking system of the present invention constructed as described above, the transition point at which the boosting ratio of the vacuum booster is reduced during an increase of the brake operating force does not change with a change in the pressure in the negative-pressure chamber, while the boosting limit point changes with the pressure in the negative-pressure chamber. When the brake operating force has increased to the transition point, the pressure increasing device initiates its pressure increasing operation. Accordingly, the moment at which the pressure increasing operation of the pressure increasing device is initiated is stabilized. That is, the pressure increase initiating point of the pressure increasing device is stabilized, assuring increased stability of the braking effect and operating feel of the brake operating member.
(2) A braking system according to the above mode (1), wherein the vacuum booster is constructed such that an output of the vacuum booster corresponding to the transition point is smaller than that corresponding to the boosting limit point when the pressure in the negative-pressure chamber is equal to a lower limit of an expected range of variation of the pressure in the negative-pressure chamber.
In the braking system according to the above mode (2) of the invention, the vacuum booster is so constructed that the transition point of the vacuum booster is necessarily reached before the boosting limit point is reached, even if the
Isono Hiroshi
Kondo Koichi
Mizutani Yasuji
Nitta Hirofumi
Onuma Yutaka
King Bradley
Lavinder Jack
Toyota Jidosha & Kabushiki Kaisha
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