Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1998-12-23
2001-03-13
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S061000
Reexamination Certificate
active
06199960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to anti-lock brake systems (ABS) and/or traction control systems (ASR, for anti-slip regulation), more particularly to evacuating and filling an ABS unit, and still more particularly to preventing the system from developing air pockets in a low-pressure accumulator area affecting braking performance.
2. Description of the Related Art
ABS (and ASR) is a part of the standard equipment in medium-class and upper-class vehicles. These systems are becoming increasingly included in lower-category and low-cost cars.
ABS and their variations typically comprise a hydraulic control unit (HCU) that houses hydraulic components of the system. The HCU is connected to the vehicle brake system between its master cylinder and calipers of wheel brakes.
A conventional hydraulic brake system, a one-wheel circuit
10
of which is shown in
FIG. 1
, comprises a tandem master cylinder (TMC) common for all wheels (shown is an inlet
12
from TMC), a HCU
14
, and a wheel caliper (shown in
FIG. 1
is an outlet
16
to the wheel caliper). Depicted within dotted lines is a low-pressure portion
18
of the HCU
14
. The portion
18
typically contains a low-pressure accumulator
20
, an input portion
22
of a return pump
24
, and associated lines
26
and
28
. A motor
30
drives the return pump
24
. Depicted in
FIG. 1
are also a return pump outlet valve
32
, a noise damper
34
, and two electromagnet valves: a pressure buildup normally open (NO) valve
36
and a pressure reduction normally closed (NC) valve
38
. The pressure buildup electromagnet NO valve
36
is disposed in a brake line
40
connecting the inlet
12
from TMC to the outlet
16
. A check valve
42
is connected in parallel to the NO valve
36
. The pressure reduction electromagnet NC valve
38
is placed in a return line
44
that eventually, through the return pump
24
reunites with a main brake line
46
.
Prior to filling the system including the circuit
10
with brake fluid, a vacuum is applied at the TMC to remove air from the system. When the vacuum is applied to the HCU, a portion of the unit, namely the low-pressure circuit, is isolated and does not evacuate its air. Any air bubbles still present in the hydraulic medium may bring about such an elasticity of fluid columns formed by the medium that the brake pressures required in wheel brake cylinders are not brought about to the requisite level.
ABS/ASR brake systems have several NC electromagnet valves; the valves of return pumps used in these brake systems are normally closed as well. The problem therefore exists that pockets of air may be present downstream of the NC electromagnet valves, and also downstream of the return pump valves. The air in these pockets may possibly be removed only with difficulty using liquid.
It has been proposed that at least the NC valves be triggered electrically upon evacuation and prior to filling of the system, and thus opened. To do so, special plug connections must be used to supply current to these electromagnet valves. The connections of this kind are expensive and involve operating costs when used, let alone that they are also complicated to manufacture. For many applications, therefore, it is the customer's desire not to energize the NC valves during the evacuation/filling process because of those issues involved.
To avoid the need to electrically energize the valves at the assembly plant, a one-time bleed valve with reset capability for an anti-lock hydraulic control unit has been put forward to address the problem of evacuating the low-pressure circuit. The bleed valve comprises a piston that can be sealingly installed into a bore made in the body of the hydraulic control unit. The bore is sized to create a seal when the piston is pushed into the bore in response to a brake pressure. On one of its ends, the bore is in communication with the primary hydraulic pressure circuit. On another end, it is connected with the low-pressure line. Due to such a structure of the bleed valve, an air communication is established between the primary hydraulic pressure circuit and the low-pressure line when the piston sits loosely in the bore. By virtue of that communication, air can be evacuated from the low-pressure brake circuit when it is exposed to a vacuum applied to the primary hydraulic pressure circuit.
However, all the advantages of such a solution notwithstanding, the placing of the bleed valve into the hydraulic system still may not fully prevent a vacuum from developing over time in the low pressure accumulating area after several normal brake pedal depressions. Specifically, the vacuum can be created upon brake pedal release. The accumulated vacuum may lead to air gaining access into the system and thus to a “soft pedal”. Also, when the HCU subsequently goes into an ABS mode, the trapped air can be pumped into the brake circuit causing reduced brake performance.
Accordingly, a need as yet exists in the art to provide a reliable means for evacuating the low-pressure circuit.
SUMMARY OF THE INVENTION
Therefore, a primary object of the present invention is to provide a hydraulic brake system that would retain all the advantages of the systems in the art, not being subject to their drawbacks discussed in the above.
Another object of the present invention is to provide a method of preventing a vehicle brake system from developing a vacuum in its low-pressure area.
In accordance with the principles of the present invention confined to a vehicle anti-lock brake system of the type including a tandem master cylinder, wheel brakes, and a hydraulic control unit with NO valves connecting the tandem master cylinder with the wheel brakes through primary hydraulic pressure lines, and NC valves that connect the wheel brakes to the tandem master cylinder by low-pressure lines passing through a low-pressure area, the method provides for opening the NC valves periodically when brakes are not applied.
Specifically, the periodical opening of the NC valves is performed each time the ignition is shut off.
Upon periodical opening the NC valves, pressures in the tandem master cylinder and in the low-pressure area are equalized and that eliminates a vacuum trapped in the low-pressure area.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings.
REFERENCES:
patent: 3601452 (1971-08-01), Brunner
patent: 3617098 (1971-11-01), Leiber
patent: 4859005 (1989-08-01), Rey et al.
patent: 5346292 (1994-09-01), Hall
patent: 5882093 (1999-03-01), Enomoto et al.
Continental Teves AG & Co. oHG
Oberleitner Robert J.
Rader & Fishman & Grauer, PLLC
Talavera Melanie
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