Fluid-pressure and analogous brake systems – With pump – Pressure control
Reexamination Certificate
2000-11-21
2002-10-15
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
With pump
Pressure control
C303S116200, C303S015000, C303S115400, C303S116100
Reexamination Certificate
active
06464307
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an improved automotive hydraulic pressure brake system in which brake fluid pressure is ordinarily supplied from a pump as a main pressure source, but additional fluid pressure is supplied from a master cylinder when it is necessary to increase brake pressure at a rapid pace, such as for quick brake, at low temperature causing high brake fluid viscosity and upon pump performance degradation.
To optimally control the behavior of the vehicle, vehicle brake systems are increasing which can control the braking effect electrically. For example, the brake system disclosed in Japanese patent 2590825 has, besides a master cylinder for generating fluid pressure when a brake pedal is depressed, a fluid pressure source comprising a pump and an accumulator for supplying fluid pressure to the wheel cylinders in proportion to or independently of how much the brake pedal is depressed. But since such a system needs a bulky accumulator, it is difficult to mount the entire system in an engine room.
Devices for generating brake fluid with a pump only in increasing the wheel cylinder pressure by electronic control are proposed in Japanese patent publications 9-20229 and 10-67311. With these devices, if the passage between the master cylinder and the wheel cylinders is shut off, the entire amount of brake fluid necessary for braking has to be provided by the pump, so that a pump having a large capacity is needed. Also, a delay in the pressure rise during a rapid pressure increase will be a problem, and a longer braking distance will result.
A brake system has been proposed which solves this problem.
FIG. 7
is a basic circuit diagram of such a brake system. As shown, in lines connecting the master cylinder
1
to wheel cylinders
2
A,
2
B (letters A, B are sometimes omitted hereinbelow), an electromagnetic on-off valve
3
and a stroke simulator
4
are provided. This brake system further includes control valves (comprising pressure-increasing on-off valves
5
A,
5
B and pressure-reducing on-off valves
6
A,
6
B in this example) for controlling the wheel cylinder pressure based on command from an electronic control unit (ECU, not shown), an on-off valve
9
provided in a return line extending from the discharge port of a pump
7
(a hydraulic pump in this example) to a reservoir
8
, a bypass
10
connecting the master cylinder
1
to the suction port of the pump
7
, an on-off valve
11
provided in the bypass
10
, and a check valve
12
provided in the return line to check a fluid flow from the bypass
10
to the reservoir
8
. The on-off valves
5
and
6
, which are used for antilock control, are not essential elements in this arrangement.
This brake system is also provided with fluid pressure sensors
13
A,
13
B, a relief valve
14
for preventing overpressure, a silencing throttle
15
and a silencer
16
. Relief valve
14
, throttle
15
and silencer
16
are used in this arrangement but are not essential elements.
The stroke simulator
4
has its back-pressure chamber
4
b
connected to the reservoir
8
to keep the chamber wet. It has a main chamber
4
a.
In the arrangement of
FIG. 7
, in a normal state (i.e. while the electric control unit is functioning normally), brake fluid pressure is supplied by the pump
7
. When it becomes necessary to rapidly increase brake pressure and to compensate for decrease in viscosity of brake fluid due to temperature drop, fluid pressure is supplied to the wheel cylinders
2
both from the pump
7
and the master cylinder
1
.
Fluid pressure can be supplied from the master cylinder by opening the on-off valve
3
. But when it is repeatedly opened and closed, pulsation occurs in the brake lines. It also occurs while the pump
7
is activated. Such pulsation is transmitted to the brake pedal, thus impairing the brake feeling. If the on-off valve
3
is kept open, the brake pedal will kick back when the wheel cylinder pressure exceeds the master cylinder pressure (that is, fluid pressure produced in the master cylinder).
To solve these problems, the brake system of
FIG. 7
has the bypass
10
provided with the on-off valve
11
to supply fluid pressure from the master cylinder
1
via the pump
7
. But this modification posed another problem. That is, since the on-off valve
11
has to be opened in order to rapidly increase pressure, the check valve
12
is closed, so that fluid cannot be supplied to the pump
7
from the reservoir
8
. Thus, a large amount of fluid has to be supplied from the master cylinder. This significantly increases the stroke of the brake pedal
17
compared with when the on-off valve
11
is closed for increase in the brake pressure at a moderate rate.
Further, while the valve
11
is open for rapid pressure increase, the pump sucks fluid discontinuously from the master cylinder. Pulsation in the brake lines is thus directly transferred to the brake pedal. Although the throttle
15
provided at the discharge side of the pump will suppress pulsation and noise, it makes it difficult to increase fluid pressure at a rapid rate.
An object of this invention is to provide a hydraulic pressure brake system that can eliminate a delay in the pressure rise during a rapid pressure increase and worsening of the pedal feeling, and in which the responsiveness is improved by increasing the suction efficiency of the pump during a rapid pressure increase or at a low temperature.
SUMMARY OF THE INVENTION
According to the invention, there is provided an automotive hydraulic pressure brake system comprising a master cylinder for producing fluid pressure corresponding to a force applied to a brake pedal, a reservoir, wheel cylinders, a power pump having an inlet port connected to the reservoir, an on-off valve provided in a fluid line connecting the master cylinder to the wheel cylinders, the on-off valve being closed to supply brake fluid pressure to the wheel cylinders from the pump while an electric control unit of the system is functioning normally, characterised in that a bypass communicating the master cylinder to the wheel brake cylinders while bypassing the on-off valve is provided, and a check valve or a relief valve for allowing only a fluid flow from the master cylinder toward the wheel brake cylinders, and a shut-off valve are provided in the bypass. (This is a first embodiment.)
Also, with the system of
FIG. 7
, the fluid discharged from the back-pressure chamber of the stroke simulator is returned to the reservoir without being utilized effectively.
According to the invention, there is also provided an automotive fluid pressure brake system comprising a master cylinder for producing fluid pressure corresponding to a force applied to a brake pedal, a reservoir, wheel cylinders, a power pump having an inlet port connected to the reservoir, an on-off valve provided in a fluid line connecting the master cylinder to the wheel cylinders, a stroke simulator having a main chamber communicating with a line connecting the master cylinder to the on-off valve and a back-pressure chamber communicating with the reservoir, the on-off valve being closed to supply brake fluid pressure to the wheel brake cylinders from the pump while an electric control unit of the system is functioning normally, characterized in that a throttle is provided in a circuit connecting the back-pressure chamber of the stroke simulator to the reservoir, that the system further comprises a first suction passage extending from a circuit between the throttle and the back-pressure chamber to the suction port of the pump, and a second suction passage communicating the reservoir with the first suction passage, and a check valve provided in the second suction passage to allow only a fluid flow from the reservoir toward the pump. (This is a second embodiment.)
If a bypass having a check valve or a relief valve and a shut-off valve provided in the system of the first embodiment is added to the system of the second embodiment, it will be a more preferable system (this system is a third embodiment).
If as in the system of
FIG.
Burch Melody M.
Graham Matthew C.
Greenblum & Bernstein P.L.C.
Sumitomo (SEI) Brake Systems, Inc.
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