Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2000-01-11
2002-07-02
Lavinder, Jack (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C188S356000
Reexamination Certificate
active
06412881
ABSTRACT:
This application is based on Japanese Patent Applications No. 11-4241 filed Jan. 11, 1999, No. 11-123604 filed Apr. 30, 1999 and No. 11-184816 filed Jun. 30, 1999, the contents of which are 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, and more particularly to a braking system equipped with a booster and a master cylinder.
2. Discussion of the Related Art
JP-A-10-152041 discloses one example of a known braking system of the type indicated above. This braking system includes (a) a brake operating member such as a brake pedal, (b) a booster for boosting an operating force applied to the brake operating member, (c) a master cylinder including a housing, and a pressurizing piston which is substantially fluid-tightly and slidably received in the housing and which has opposite surfaces one of which cooperates with the housing to define a pressurizing chamber in front of said pressurizing piston, the pressurizing piston being advanced by an output force acting on the other of the opposite surfaces thereof, so that a fluid in the pressurizing chamber is pressurized, (d) a brake including a wheel brake cylinder which is connected to the pressurizing chamber of the master cylinder through a fluid passage and which is actuated by the pressurized fluid received from the pressurizing chamber, to apply a brake to a wheel of the vehicle, and (e) a pressure increasing device which is activated, when a predetermined pressure-increase initiating condition is satisfied, for increasing the pressure of the fluid in the wheel brake cylinder.
In this known braking system, the pressure increasing device is disposed in series with the booster, and can be considered to a second booster capable of performing an auxiliary boosting function. In this respect, the pressure increasing device may be designed such that the fluid pressure in the master cylinder is increased at a preset ratio. Where the pressure increasing device is designed according to this design concept, the overall ratio of a braking force produced by the wheel brake cylinder to the brake operating force acting on the brake operating member is expressed by a product of the boosting ratio of the booster and the pressure increasing ratio at which the fluid pressure in the master cylinder is increased by the pressure increasing device.
On the other hand, the operating characteristic or input-output characteristic of the booster tends to vary. This tendency is relatively high where the booster is a vacuum booster which uses a reduced or negative pressure source as a drive power source. The pressure of the negative pressure source available on a motor vehicle is comparatively difficult to accurately control such that the negative pressure is maintained at a predetermined level. For this reason, the operating characteristic of the vacuum booster has a high tendency of change or variation. Further, the operating characteristic of the booster has an influence on the characteristic of change in the fluid pressure in the master cylinder, that is, on the relationship between the brake operating force and the fluid pressure in the master cylinder. Accordingly, a change in the operating characteristic of the booster will result in a variation in the characteristic of change in the fluid pressure in the master cylinder.
Where the pressure increasing device is designed such that the fluid pressure in the master cylinder is increased at a preset ratio, the overall ratio of the braking force produced by the wheel brake cylinder to the brake operating force may deviate from the desired or nominal value to a comparatively large extent, if the characteristic of change in the master cylinder pressure varies with a change in the operating characteristic of the booster. This is because the amount of change in the operating characteristic of the booster is amplified by the predetermined pressure increasing ratio of the pressure increasing device which is connected in series with the booster. Thus, the known braking system has an undesirably high risk of deterioration of the operating feel of the brake operating member due to a change in the operating characteristic of the booster upon activation of the pressure increasing device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a vehicle braking system which is less likely to suffer from the deterioration of the operating feel of the brake operating member due to a change in the operating characteristic of the booster upon activation of the pressure increasing device.
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 depends from the other mode or modes, where appropriate, so as to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features described below, or any combinations of those features.
(1) A braking system for an automotive vehicle having a wheel, comprising: a booster for boosting an operating force acting on a brake operating member; a master cylinder having a housing and including a pressurizing piston which is substantially fluid-tightly and slidably received in the housing and which cooperates with the housing to define a front pressurizing chamber and a rear pressurizing chamber on front and rear sides thereof, the pressurizing piston receiving at a rear end thereof an output force of the booster, a working fluid in the front pressurizing chamber being pressurized by an advancing movement of the pressurizing piston; a fluid passage connected to the front pressurizing chamber of the master cylinder; a brake including a wheel brake cylinder which is connected to the front pressurizing chamber through the fluid passage and which is activated by the fluid pressurized in the front pressurizing chamber, for braking the wheel; and a pressure increasing device activated when a predetermined pressure-increase initiating condition for initiating a pressure increase control is satisfied, to pressurize a fluid in the rear pressurizing chamber, for increasing a pressure of the fluid in the wheel brake cylinder to a value higher than a value before the predetermined pressure-increase initiating condition is satisfied.
In the braking system of the present invention constructed as described above, the pressurizing piston of the master cylinder is adapted to receive both the output force of the booster and a force based on the fluid pressure generated by the pressure increasing device. In the present arrangement, the pressure increasing device and the booster are disposed in parallel with each other, so that a sum of the output force of the booster and the force based on the fluid pressure generated by the pressure increasing device is applied to the wheel brake cylinder. Unlike the conventional braking system, the present braking system is free from a problem that a change in the operating characteristic of the booster is amplified by the pressure increasing device and the amplified change is transferred to the wheel brake cylinder. Thus, the present braking system is less likely to suffer from undesirable deterioration of the operating feel of the brake operating member due to the change in the operating characteristic of the booster.
In the present braking system wherein the electrically controlled pressure increasing device which is primarily controlled electrically and the booster which is primarily controlled mechanically are disposed in parallel with each other, the master cylinder can receive one of the output force of the booster and the force based on the fluid pressure generated by the pressure increasing device, even in the event of a failure of the booster or the pressure increasing device, unless both of the booster and the pressure increasing device simultaneously fail to normally function. Accordingly, the provision of
Kenyon & Kenyon
Lavinder Jack
Nguyen Xuan Lan
Toyota Jidosha & Kabushiki Kaisha
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