Brakes – Operators – Fluid pressure
Reexamination Certificate
1998-12-14
2001-08-07
Oberleitner, Robert J. (Department: 3613)
Brakes
Operators
Fluid pressure
C303S119100, C303S113100
Reexamination Certificate
active
06269921
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to motor vehicles, more particularly to those of them enjoying anti-lock brake system (ABS) and/or traction control system (ASR, for anti-slip regulation), and still more particularly to a bleed valve in a hydraulic control unit of such a system.
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.
Alternatively, in order to evacuate the low-pressure circuit, a check valve must be installed between the low-pressure circuit and the main circuit. The check valve must be set to a low delta-pressure value for good evacuation, but this can lead to unwanted movement of the valve during normal braking and ultimately to the loss of brake performance.
The reason for that to occur lies in that when the pedal is allowed to return rapidly, normal braking can create a transient partial vacuum in the brake system. The vacuum forms in the brake system when the momentum of the fluid tends to push into the master cylinder when the pedal abruptly stops. The transient vacuum at the HCU can open the check valve, allowing the partial vacuum to become trapped in the low-pressure circuit. Over time, the trapped vacuum tends to pull ambient air into the low-pressure circuit of the HCU. 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 exists in the art to provide a check valve for evacuating the low-pressure circuit without energizing the NC valves and also without subsequent movement during normal braking.
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 hydraulic brake system comprising a check valve for evacuating the low-pressure circuit without energizing the NC valves and also without subsequent movement during normal braking.
These and other objects are attained in the present invention that provides a one-time bleed valve with reset capability for an anti-lock hydraulic control unit. The unit has a body accommodating a low-pressure line and a primary hydraulic pressure circuit connecting a tandem master cylinder to a wheel brake caliper via a normally open electromagnet valve mounted in a recessed part of said body. 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. The bore is in communication on its one end with the primary hydraulic pressure circuit and on another its end with the low-pressure line. Owing to such a structure of the bleed valve, when the piston sits loosely in the bore, an air communication is established between the primary hydraulic pressure circuit and the low-pressure line. Due to 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.
The piston may further comprise an O-ring fitted on an annular groove made on a head portion of the piston.
To facilitate pushing the piston into the bore, the bore is made with a lead-in chamfer.
To limit a travel distance of the piston, the bore is located in a portion of the body that is immediately under the recessed part of the body that accommodates the normally open electromagnet valve.
To provide the bleed valve with a reset capability, an access hole is made between outside of the body and the bore, the hole having an expansion in an area thereof adjoining the outside, the expansion accommodating a seal ball.
Also claimed according to the present invention is a hydraulic brake system for vehicle wheels in a multiple-brake-circuit design. The system comprises a master brake cylinder, hydraulic control unit, wheel brakes and a plurality of brake circuits. Each circuit of this plurality comprises a primary hydraulic pressure circuit and a secondary hydraulic pressure circuit. The primary hydraulic pressure circuit connects the master cylinder with at least one wheel brake for applying hydraulic pressure thereto via a normally open electromagnet valve in the hydraulic control unit. The secondary hydraulic pressure circuit that returns hydraulic pressure from the wheel brake to the master cylinder via a normally closed electromagnet valve in the hydraulic control unit comprises a low-pressure line. The hydraulic control unit includes a body accommodating the primary hydraulic pressure circuit, the normally open electromagnet valve, and the low-pressure line. Each circuit of the plurality of brake circuit also comprises a bleed valve to connect the primary hydraulic pressure circuit and the low-pressure line together. The bleed valve comprises a piston adapted to be sealingly installed into a bore made in the body of the hydraulic control unit, the bore being sized to create a seal when the piston is pushed in
Agnew David L.
Zaviska Dalibor
Continental Teves Inc.
King Bradley
Oberleitner Robert J.
Rader & Fishman & Grauer, PLLC
LandOfFree
One-time bleed valve with reset capability for anti-lock... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with One-time bleed valve with reset capability for anti-lock..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and One-time bleed valve with reset capability for anti-lock... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2484793