Fluid-pressure and analogous brake systems – Pulsation neutralizers
Reexamination Certificate
1999-11-09
2002-02-19
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Pulsation neutralizers
C188S351000, C138S031000
Reexamination Certificate
active
06347841
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for regulating pressure in the hydraulic brake system for a vehicle via a brake master cylinder, and, more particularly, to an apparatus for regulating pressure in a hydraulic brake system, the apparatus causing the brake lining and brake shoe to approach each other, such that initial brake response time is reduced, braking efficiency is improved, the slip rate between the vehicle tires and the road is minimized, stopping distance is shortened, and the fluid in the brake master cylinder flows into the apparatus such that the pressure of the brake master cylinder is prevented from rapidly rising during emergency or other urgent application of the brakes.
BACKGROUND
As described in
FIG. 1
, in a typical vehicle hydraulic brake system, when the driver applies the brake pedal
1
, hydraulic pressure rises in the master cylinder
3
, which is typically a tandem master cylinder, and pressure is thereby transmitted to the wheel cylinder
7
through hydraulic line P. The brake shoe
9
is moveable so as to frictionally contact the brake drum
13
via pressure transmitted to the wheel cylinder
7
, producing a braking force.
The master cylinder
3
comprises a piston
4
, a piston cup
5
, a check valve V and a return spring S. A reservoir tank
10
is typically located in close proximity to and communicates with the master cylinder
3
, so as to provide a supply of brake fluid. In front of the piston
4
(to the left as viewed in
FIG. 1
) is located a rubber piston cup
5
to maintain the hydraulic pressure. In the rear (to the right as viewed in
FIG. 1
) of the piston
4
is located a piston packing
6
to prevent the leakage of brake fluid. If the pressure in the master cylinder
3
is sufficient to activate a check valve V, the check valve V opens and transmits pressure from the master cylinder to the wheel cylinder
7
.
If driver releases the brake pedal
1
, the piston
4
returns by virtue of return spring S. Upon such return, if the fluid pressure in the master cylinder
3
is sufficiently reduced, this pressure causes the check valve V to close, preventing return of brake fluid to the master cylinder
3
. At the front of the piston cup
5
(to the left as viewed in FIG.
1
), the pressure drops temporarily during return, and fluid flows into the master cylinder
3
via hole H, which is formed in the piston
4
and about the circumference of the piston cup
5
, as described further with respect to FIG.
2
. The availability of this flow ensures that the return of the piston
4
is not prevented or impaired due to low pressure in the master cylinder
3
.
As the piston
4
returns, brake fluid is able to return to the reservoir tank
10
through the relief port
11
and the inlet port
12
. The check valve V remains closed until the pressure in the master cylinder
3
reaches the set-pressure.
Improving the handling of an automobile requires both good acceleration and good deceleration, in turn necessitating a hydraulic brake system having superior characteristics. Such superior characteristics are especially important with respect to safety.
The brake system for a typical vehicle provides a great deal of stopping force, which is utilized to stop the revolution of the vehicle's tires. However, this force can completely stop the vehicle's tire rotation without stopping the vehicle, resulting to slippage of the tires on the road (wheel lock). Such slippage occurs when the slippage force on the tires is less than the braking force. This slippage force is calculated by multiplying the frictional coefficient between the tire and the road by the weight applied to the road via the tire.
Namely, frictional coefficient &mgr;, is extremely low on slippery road surfaces, as occur with the presence of ice or snow, while &mgr; is much higher on, for example, dry concrete roads. In general, varying by motor vehicle model and road surface, the slip rate has a maximum, from which it quickly drops off.
The formula for the slip rate is expressible as follows:
Y
-
W
S
×
100
=
v
where:
V−W=the velocity of wheel;
S=the rate of slip; and
V=the velocity of vehicle.
In other words, when the driver applies the brake, it is advisable to maintain the wheels in a state such that the braking force is maximized and just less than the force that causes wheel lock. Safety is reduced and the rate of vehicle deceleration is reduced, resulting in longer stopping distances, when wheel revolution stops and wheel lock occurs.
To help achieve this condition in existing vehicles, hydraulic pressure in the brake system is typically reduced for the rear wheels relative to the front wheels, which prevents handling instability that would otherwise be caused by premature locking of the rear wheels. In existing vehicles, appropriate hydraulic pressure to maintain this condition is achieved through use of the following valves, which are installed on certain portions of tandem brake master cylinders to improve the braking efficiency:
Check valve—this valve improves braking efficiency by preventing return of pressure to the tandem brake master cylinder below a certain predetermined pressure, leaving any remaining pressure in the brake hydraulic lines. As a result, air osmosis is prevented and initial response time is shortened.
P valve (proportioning valve)—this valve is used to control the increase of hydraulic pressure and the triggering pressure point for activation of the brakes. This valve reduces the hydraulic pressure increase rate for the rear wheels as the brake force transmitted from the piston increases.
G valve—this valve controls the pressure of hydraulic fluid transmitted to the rear wheels. The G valve, which uses a ball valve that moves in accordance with a decrease in velocity of the vehicle, causing transfer of pressure among an outlet portion and an inlet portion, resulting in variation in the effective piston area applying the braking pressure.
Load sensing proportioning valve—this valve is used to control the hydraulic pressure to the rear wheels, with the opening position of the valve simultaneously varying in relation to the car weight.
Metering valve—this valve is used to decrease the abrupt hydraulic pressure of the front disk brake in low hydraulic pressure situations by decreasing the hydraulic pressure transmitted to the front wheels until the hydraulic pressure transmitted to the rear wheels becomes higher than the tension of return spring of the rear brake shoe. With this feature, brake pad life is prolonged.
In addition, an anti-lock brake device is used to prevent wheel lock from occurring when, for example, a car is braked on a road with low friction. The anti-lock brake device decreases the stopping distance and helps with control of the car by maintaining the vehicle's direction and enabling steering control by keeping the wheels at the ideal slip rate.
However, in the prior art, the method for controlling hydraulic pressure to obtain the proper braking force, except with regard to the anti-lock device, depends on the driver recognizing the need to provide the correct brake pedal effort and to know to apply the brakes in sufficient time. In an emergency, if a driver applies the brakes strongly (to increase the brake force), wheel lock can occur based on the abrupt pedal stroke and resultant increase in hydraulic brake pressure. The prior art addresses this problem with the use of valves that provide measured decrease of braking pressure and thereby enhance braking safety. However, even with these systems, if the hydraulic pressure increases abruptly in the tandem brake master cylinder, which is the starting point for building hydraulic pressure, wheel lock—the so-called “skid state”—can occur. In this event, stopping distance increases and braking safety decreases abruptly.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for regulating pressure in the hydraulic brake system that causes the brake lining and brake shoe to approach each o
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