Fluid-pressure and analogous brake systems – Speed-controlled – With yaw control
Reexamination Certificate
1999-06-15
2001-05-29
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
With yaw control
C303S113200
Reexamination Certificate
active
06238019
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an automatic brake control system for vehicles, and more particularly to an improved hydraulic circuit structure of a brake control system designed to regulate the braking effort applied to each wheel both in manual and automatic control modes.
2. Background Art
Japanese Patent First Publication No. 8-230634 teaches a brake control system which uses a brake assisting device in a hydraulic circuit extending from a master cylinder to wheel cylinders in order to eliminate the need for a vacuum brake booster and enhance the braking effort applied to each wheel upon urgent braking. This system is also capable of producing the wheel cylinder pressure higher than the master cylinder pressure to shorten the braking distance.
Such a brake control system usually has pumps, one in each hydraulic line, to provide the hydraulic pressure higher than the master cylinder pressure to wheel cylinders. In a case where a vehicle is equipped with two hydraulic lines: one being a front hydraulic line for front right and left wheels and the second being a rear hydraulic line for rear right and left wheels, if a difference in output between pumps disposed in the front and rear hydraulic lines is developed, it will result in a difference in braking effort applied to the front and rear wheels, but do not cause a vehicle body to undergo yawing. However, in a case where a vehicle is equipped with a diagonal hydraulic system (usually used in FF (front engine front drive) vehicles) consisting of a first hydraulic line for front right and rear left wheels and a second hydraulic line for front left and rear right wheels, if a difference in output between pumps disposed in the first and second hydraulic lines is developed, it will cause a vehicle body to yaw, which may result in instability of the braking.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a brake control apparatus which is designed to minimize adverse effects, caused by a difference in electric and/or mechanical performance between two hydraulic brake lines, on a brake assisting operation which applies to each wheel the pressure of brake fluid higher than the master cylinder pressure produced by depression of a brake pedal by a vehicle operator.
It is a further object of the invention to provide a brake control apparatus designed to control instability of a vehicle body with high accuracy.
According to one aspect of the present invention, there is provided a brake control apparatus for a vehicle. The brake control apparatus comprises: (a) a master cylinder producing pressure of a brake fluid when braking the vehicle; (b) a first and a second wheel cylinder receiving the pressure of the brake fluid from the master cylinder pressure to apply braking efforts to a first and a second wheel, respectively; (c) a third and a fourth wheel cylinder receiving the pressure of the brake fluid from the master cylinder to applying braking efforts to a third and a fourth wheel, respectively; (d) a first hydraulic line connecting the master cylinder and the first and second wheel cylinders; (e) a second hydraulic line connecting the master cylinder and the third and fourth wheel cylinders; (f) a first pressure elevation/reduction actuator set disposed between the master cylinder and the first and second wheel cylinders in the first hydraulic line to selectively elevate and reduce the pressure of the brake fluid applied to the first and second wheel cylinders; (g) a second pressure elevation/reduction actuator set disposed between the master cylinder and the third and fourth wheel cylinders in the second hydraulic line to selectively elevate and reduce the pressure of the brake fluid applied to the third and fourth wheel cylinders; (h) a first differential pressure control valve disposed between the master cylinder and the first pressure elevation/reduction actuator set in the first hydraulic line, regulating flow of the brake fluid between a first portion of the first hydraulic line connecting with the master cylinder and a second portion of the first hydraulic line connecting with the first pressure elevation/reduction actuator set to control a difference in pressure of the brake fluid between the first and second portions; (i) a second differential pressure control valve disposed between the master cylinder and the second pressure elevation/reduction actuator set in the second hydraulic line, regulating flow of the brake fluid between a first portion of the second hydraulic line connecting with the master cylinder and a second portion of the second hydraulic line connecting with the second pressure elevation/reduction actuator set to control a difference in pressure of the brake fluid between the first and second portions of the second hydraulic line; (j) a first pump disposed in the first hydraulic line, delivering pressure of the brake fluid to the first and second wheel cylinders and returning an amount of the brake fluid equivalent to a required reduction in pressure of the brake fluid applied to the first and second wheel cylinders to the master cylinder; (k) a second pump disposed in the second hydraulic line, delivering pressure of the brake fluid to the third and fourth wheel cylinders and returning an amount of the brake fluid equivalent to a required reduction in pressure of the brake fluid applied to the third and fourth wheel cylinders to the master cylinder; (l) a first suction branch line connecting the first portion of the first hydraulic line and an inlet of the first pump; (m) a second suction branch line connecting the first portion of the second hydraulic line and an inlet of the second pump; (n) a first discharge branch line connecting an outlet of the first pump and the second portion of the first hydraulic line; (o) a second discharge branch line connecting an outlet of the second pump and the second portion of the second hydraulic line; (p) a connecting line connecting the second portion of the first hydraulic line between the first differential pressure control valve and the first pressure elevation/reduction actuator set and the second portion of the second hydraulic line between the second differential pressure control valve and the second pressure elevation/reduction actuator set; and (q) a fluid pressure difference regulator disposed in the connecting line to regulate a difference between the pressure of the brake fluid in the second portion of the first hydraulic line delivered by the first pump and the pressure of the brake fluid in the second portion of the second hydraulic line delivered by the second pump so as to fall within a given allowable pressure range.
In the preferred mode of the invention, the fluid pressure difference regulator includes a pressure chamber and a piston disposed within the pressure chamber to block fluid communication between the first and second hydraulic lines. The piston is slidable within the pressure chamber so as to eliminate an excess of the pressure difference between the first and second hydraulic lines above the given allowable pressure range.
The fluid pressure difference regulator also includes a spring which has a preselected spring constant and which supports the piston within the pressure chamber.
The spring constant of the spring is set to a value which has the pressure difference between the first and second hydraulic lines fall within the given allowable pressure range.
The pressure chamber of the fluid pressure difference regulator has a volume which allows a desired pressure of the brake fluid to be produced in the second portion of one of the first and second hydraulic lines if the other of the first and second hydraulic lines is failing.
The first pressure elevation/reduction actuator set includes a plurality of pressure elevation control valves which control elevations in pressure of the brake fluid applied to the first and second wheel
Goshima Takahiro
Kiso Takahiro
Morikawa Toshiya
Ohno Sadayuki
Okazaki Koji
Denso Corporation
Pillsbury & Winthrop LLP
Schwartz Christopher P.
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