Fluid-pressure and analogous brake systems – Speed-controlled – Wheel pressure delay compared to reference
Reexamination Certificate
2000-11-29
2002-10-08
Butler, Douglas C. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Wheel pressure delay compared to reference
C303S003000, C303S015000, C303S155000, C303S114100
Reexamination Certificate
active
06460944
ABSTRACT:
This application is based on Japanese Patent Application No. 11-353539 filed Dec. 13, 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 an improvement of a braking system of a type wherein a brake is operated to produce a braking force corresponding to an output of a brake operating device.
2. Discussion of Related Art
JP-A-8-230634 discloses an example of a vehicle braking system of the type indicated above, which is provided with a brake operating device in the form of a vacuum booster, which is one type of a booster. The vacuum booster is arranged to receive an input force from a brake operating member in the form of a brake pedal upon operation of the brake pedal, and boost the received input force on the basis of a negative pressure, so that the boosted input force is transmitted as an output of the vacuum booster to a master cylinder, in order for the master cylinder to pressurize a working fluid. The pressurized fluid is delivered from the master cylinder to a brake cylinder of a wheel brake, so that the wheel brake is activated. The braking system disclosed in the above-identified publication is further adapted such that a pressurized fluid delivered by a pump is supplied to the wheel brake cylinder so that the fluid pressure in the wheel brake cylinder is made higher than that in the master cylinder, whereby the wheel brake generates a braking force larger than that based on the fluid pressure in the master cylinder. The pressurized fluid is delivered from the pump to the wheel brake cylinder when the brake operating member is rapidly operated to apply an abrupt brake to the vehicle, as well as when the wheel brake suffers from a phenomenon so-called “fade” wherein the friction coefficient of a friction member such as a friction pad or brake lining is excessively lowered. A determination that the application of an abrupt brake is required is made when the fluid pressure of the master cylinder detected by a suitable pressure sensor is higher than a predetermined value and when a rate of increase of the fluid pressure of the master cylinder has exceeded a predetermined value. When the requirement for the abrupt brake application is detected, the fluid pressurized by the pump is supplied to the wheel brake cylinder so that the braking force generated by the wheel brake when the brake pedal is abruptly operated is made larger, than when the brake pedal is normally operated.
In the braking system disclosed in the above-identified publication wherein the brake operating device such as a vacuum booster is disposed between the brake operating member and the master cylinder, there is a risk of a delay in the determination that the application of an abrupt brake is required, due to a delay in the operation of the brake operating device. For instance, the vacuum booster includes: a housing; a power piston which is axially sidably received within the housing and which cooperates with the housing to define a low-pressure chamber formed on the front side of the power piston and connected to an air intake system of an engine of the vehicle, and a variable-pressure chamber formed on the rear side of the power piston; an input member operatively connected to the brake operating member; an output member operatively connected to a pressurizing piston of the master cylinder; and a switch valve operable between a retracted position for fluid communication of the variable-pressure chamber with the low-pressure chamber, on the basis of a relative movement of the input and output members, an advanced position for fluid communication of the variable-pressure chamber with the atmosphere, and an intermediate position for inhibiting the fluid communication of the variable-pressure chamber with both of the low-pressure chamber and the atmosphere. In this case, the input force is received by the input member, and the output force is applied from the output member to the pressurizing piston of the master cylinder. The operational delay of the vacuum booster indicated above is a delay of the application of the output force to the pressurizing piston of the master cylinder with respect to the application of the input force to the input member, which delay may take place due to a delayed flow of the atmosphere into the variable-pressure chamber or a relatively low degree of vacuum in the low-pressure chamber (a relatively small difference of the pressure in the low-pressure chamber from the atmospheric pressure). The operational delay tends to increase with an increase in the operating speed of the brake operating member. Accordingly, the detection of the requirement for an abrupt brake application tends to be delayed when the brake operating member is operated at a relatively high speed. That is, a relatively rapid operation of the brake operating member tends to cause a delay in the moment at which is satisfied the above-indicated condition that the fluid pressure of the master cylinder is higher than a predetermined value and that a rate increase of the fluid pressure of he master cylinder has exceeded a predetermined value. There is a similar tendency also where a brake operating device of any other type such as a hydraulic booster is disposed between the brake operating member and the master cylinder, although there is some difference in the degree of the operational delay in the two cases indicated above.
The braking system disclosed in the above-identified publication is not provided with any means for solving the operational delay of the vacuum booster. As discussed above, the brake operating device such as the vacuum booster as the typical example may suffer from the operational delay, which prevents a delay in the increase of the master cylinder pressure concurrently with an increase in the operating force of the brake operating member (hereinafter referred to simply as “brake operating force”, where appropriate). This delay in the increase of the master cylinder pressure with respect to the brake operating force necessarily results in an increase in the required brake operating force. However, the conventional braking system is not provided with any means for dealing with this drawback.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a braking system for an automotive vehicle, which is less likely to suffer from a delay in the detection of a requirement for an abrupt brake application and an insufficient amount of the brake operating force, even in the presence of an operational delay of a brake operating device disposed between the brake operating member and the master cylinder.
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, 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 or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking system for braking a wheel of an automotive vehicle, including a brake for braking said wheel and an operating device operable to produce an output corresponding to an input thereof, for activating the brake according to the output, and wherein the output of the operating device is delayed with respect to the input depending upon an operating condition of the braking system, the braking system comprising:
a brake-operating-force increasing device operable on the basis of a delay of the output of the operating device with respect
Isono Hiroshi
Mizutani Yasuji
Butler Douglas C.
Kramer Devon
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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