Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-12-23
2001-02-27
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S168000
Reexamination Certificate
active
06193327
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to anti-lock brake systems and in particular to a spin-and-brake algorithm which includes a test to verify that the vehicle is actually in a spin-and-brake situation.
An Anti-lock Brake System (ABS) is often included as standard or optional equipment on new vehicles. When actuated, the ABS is operative to control the operation of some or all of the vehicle wheel brakes. One type of ABS controls only the vehicle rear wheel brakes. Such a system is referred to as a Rear Wheel Anti-Lock Brake System (RWAL) the following.
A typical prior art RWAL is illustrated generally at
10
in FIG.
1
. As shown in
FIG. 1
, the RWAL
10
is installed on a vehicle having a hydraulic braking system consisting of a brake pedal
12
coupled to operate a dual reservoir master cylinder
14
. When the vehicle operator depresses the brake pedal
12
, the master cylinder
14
supplies hydraulic fluid under pressure from a front reservoir
14
a
through a hydraulic line
16
a
and from a rear reservoir
14
b
through a hydraulic line
16
b
to a conventional combination or proportioning valve
18
. The combination valve
18
includes a first output line
18
a
adapted to supply hydraulic fluid at a first predetermined pressure to actuate a pair of vehicle front wheel brakes
19
a
and
9
b
. The combination valve
18
also includes a second output line
18
b
which supplies hydraulic fluid at a second predetermined pressure to actuate a pair of vehicle rear wheel brakes
20
a
and
20
b.
The RWAL
10
shown in
FIG. 1
utilizes a control valve
21
to selectively control the application of pressure to the rear wheel brakes
20
a
and
20
b
when the system is in an anti-lock braking mode. The control valve
21
includes a normally open solenoid valve
22
connected between the line
18
b
and a line
24
which supplies pressurized brake fluid to the controlled rear wheel brakes
20
a
and
20
b
. During an anti-lock braking cycle, the normally open valve
22
isolates the rear wheel brakes
20
a
and
20
b
from the master cylinder
14
and is commonly referred to as an isolation valve. The isolation valve
22
also can be selectively opened to increase the pressure at the rear wheel brakes
20
a
and
20
b.
The control valve
21
also includes a normally closed solenoid valve
26
, which is connected between the line
24
and a fluid accumulator
28
. The normally closed valve
26
is commonly referred to as a dump valve. The dump valve
26
is selectively opened to reduce the pressure at the rear wheel brakes
20
a
and
20
b
by bleeding brake fluid from the rear wheel brakes to the accumulator
28
. In the RWAL
10
, the master cylinder
14
provides a source of pressurized hydraulic brake fluid during an anti-lock braking cycle, thus eliminating the need for a separate source of pressurized hydraulic fluid, such as a motor driven pump, which is usually included in a four wheel ABS.
The RWAL
10
further includes a computer control module
30
which is electrically connected to a wheel speed sensor
40
. The control module
30
can be mounted directly upon the control valve
21
or located remotely therefrom. The control module
30
includes a RWAL microprocessor (not shown) which is programmed to control the RWAL
10
in accordance with a RWAL control algorithm and parameters permanently stored in a Read Only Memory (ROM). The RWAL microprocessor also can access a Random Access Memory (RAM) for temporary storage and retrieval of data. A detailed description of the RWAL illustrated in
FIG. 1
is included in U.S. Pat. Nos. 4,790,607 and 4,886,322.
During vehicle operation, the microprocessor in the RWAL control module
30
continuously receives speed signals from the wheel speed sensor
40
. The RWAL microprocessor monitors the speed signals for potential rear wheel lock-up conditions. When the vehicle brakes are applied and the RWAL microprocessor senses a first rear wheel speed departure, which is indicative of an impending wheel lock-up condition, the RWAL microprocessor is responsive thereto to close the isolation valve
22
to isolate the rear wheel brakes
20
a
and
20
b
from the master cylinder
14
. The RWAL microprocessor then selectively opens the dump valve
26
to reduce the pressure applied to the rear wheel brakes
20
a
and
20
b
and thereby correct the rear wheel speed departure. Once the wheel speed departure has been corrected and the controlled wheel has spun up to the vehicle speed, the microprocessor opens the isolation valve
22
to initiate a second wheel speed departure.
The operation of the RWAL
10
is illustrated by the graphs shown in FIG.
2
. The upper solid curve labeled
60
represents the velocity of the rear wheels while the dashed curve labeled
61
represents the vehicle velocity. The operation of the isolation valve
22
and the dump valve
26
is illustrated by the curves labeled
62
and
63
, respectively. The lower curve, which is labeled
64
, shows the pressure applied to the controlled rear wheel brakes. During an anti-lock braking cycle, the first and second wheel speed departures are labeled
60
a
and
60
b
, respectively. Following correction of the second wheel speed departure, which occurs at time t
7
, the rear wheel brake pressure is maintained at a constant level P
e
.
With a RWAL system, it is necessary to identify and respond to a situation in which the vehicle operator has used the accelerator to spin the vehicle rear wheels faster than the actual vehicle speed and then steps on the brake pedal. Accordingly, if the brake pedal is depressed and the anti-lock braking mode entered while a rear wheel overspin condition exists, a “spin-and-brake” mode of RWAL operation is entered and a rear wheel overspin condition exists, as shown by the upper curve in FIG.
3
.
FIG. 3
also illustrates the operation of the isolation and dump valves
22
and
26
and the resulting pressure applied to the controlled wheel brakes vs. time.
In the spin-and-brake mode, the RWAL system control algorithm provides two cycles of pressure dumping followed by unlimited reapply until wheel speed departures are forced, as illustrated in FIG.
3
. In
FIG. 3
, the upper curve
80
represents the actual rear wheel speed while the dashed curve
84
represents the actual vehicle speed. During the portion labeled
80
a
, the rear wheel speed is accelerated above the vehicle speed.
The RWAL control algorithm detects conditions which indicate that the vehicle has entered a spin-and-brake mode of operation. For example, if the rear wheel speed is 0.5 g greater than the projected vehicle speed ramp for more than 0.5 seconds, the ABS control algorithm sets a Spin-and-Brake (SPNBRK) flag TRUE. The SPNBRK flag is held TRUE for a relatively long predetermined time period, such as, for example 16 seconds. The long time out period for the SPNBRK flag compensates for the possibility that the rear wheel overspin continues at a nearly constant velocity for several seconds. Once the predetermined time period has elapsed, the SPNBRK flag is cleared. When the SPNBRK flag is TRUE, the control algorithm will enter the spin-and-brake mode upon application of the wheel brakes and entry into the anti-lock brake mode.
In
FIG. 3
, the SPNBRK flag is set TRUE during the portion of the curve labeled
80
a
. When vehicle brakes are applied at time t
a
, the RWAL control algorithm projects a speed ramp
86
and the wheel speed then decreases from the original overspin to actual vehicle speed while brake pressure is kept very low. In most instances, the pressure applied to the controlled rear wheel brakes, B
1
, is very close to zero. However, in order to illustrate the subsequent pressure reductions, B
1
is shown above zero pressure in FIG.
3
.
At tc, a first set of dump pulses
83
a
are generated to deal with a false wheel speed departure which occurs as the rear wheel speed decreases from the original overspin condition to the actual wheel speed. The RWAL control algorithm will then, at time t
d
, enter a “spin-and-brake” reapply mo
Kelsey-Hayes Company
Oberleitner Robert J.
Talavera Melanie
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