Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle diagnosis or maintenance indication
Reexamination Certificate
2000-12-27
2002-08-13
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle diagnosis or maintenance indication
C180S197000, C303S113300, C303S113400
Reexamination Certificate
active
06434456
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to pressure sensors used in hydraulic control systems and in particular to a high reliability pressure sensor utilized in a vehicle brake system with Hydraulic Brake Assist.
Recently, Hydraulic Brake Assist (HBA) has been included on new vehicles. HBA provides maximum braking capability during an emergency braking situation. During a braking cycle, the brake pressure is sensed to determine if an emergency situation has occurred. Alternately, the magnitude of the brake pedal stroke and speed of brake pedal movement can be monitored for an emergency braking situation. Typically, an emergency is identified by a certain pedal-application speed occurring along with a minimum level of brake-pedal force. Thus, a quick, deep stab at the brake pedal actives HBA while a quick shallow stab, as to cancel cruise control, or a slow but deep pedal application, as when slowing for a curve, will not active HBA.
Upon detection of an emergency braking situation, HBA increases brake application pressure to a maximum value and continues to hold the maximum pressure until the vehicle stops or the brake pedal is released, as illustrated in FIG.
1
. In
FIG. 1
, vehicle braking force is plotted as a function of time. The lower curve, which is labeled
4
, is for a brake system without HBA, while the upper curve, which is labeled
6
, is for a brake system that includes HBA. Typically, during an emergency braking situation, the vehicle operator partially lifts his foot from the brake pedal following his initial quick, deep stab. Thus, HBA assures that the brakes remain applied with maximum force.
There are a number of know methods for integrating HBA with a vehicle brake system. One method is completely mechanical and involves modification of the vacuum brake booster to provide HBA. Another method is to include the HBA function in an Anti-lock Brake System (ABS). An ABS is often included in many vehicles to prevent wheel lock up during stops upon low mu road surfaces. Such systems detect excessive slippage of one or more controlled wheels and selectively reduce and reapply the pressure applied to the controlled wheel brakes to reduce the slippage and thereby avoid a potential locking-up of the wheel.
Referring again to the drawings, there is illustrated in
FIG. 2
, a typical brake control system
10
which has HBA included in an Anti-lock Brake System (ABS). The brake control system
10
is intended to be exemplary and it will be appreciated that there are other brake control systems having different architecture than shown. In
FIG. 2
, a brake pedal
12
is mechanically coupled (not shown) to a brake light switch
13
and a dual reservoir master cylinder
14
. The master cylinder
14
is connected to a hydraulic control unit
16
by a pair of hydraulic lines
18
and
20
. The hydraulic control unit
16
includes a plurality of solenoid valves to control the brake pressure applied to the individual wheel brakes. The control unit
16
also typically includes a source of pressurized hydraulic fluid, such as a pump driven by an electric motor. The control unit
16
is connected via hydraulic lines
22
,
24
,
26
and
27
to individual wheel brakes (not shown) for the front wheels
28
and
30
and the rear wheels
32
and
33
. Typically, the brake circuit is diagonally split with one master cylinder reservoir controlling the brakes associated with the left front wheel
30
and right rear wheel
33
and the other master cylinder reservoir controlling the brakes associated with the right front wheel
28
and the left rear wheel
32
.
The brake control system
10
also includes a pair of front wheel speed sensors
34
that generate signals that are proportional to the speed of the front wheels
28
and
30
and a pair of rear wheel speed sensors
36
that generate signals that are proportional to the speed of the rear wheels
32
and
33
. The wheel speed sensors
34
and
36
and the stop light switch
13
are electrically connected to an Electronic Control Unit (ECU)
38
. The control unit
38
includes a microprocessor (not shown), that, under the control of an algorithm, selectively actuates the solenoid valves and pump in the control unit
16
to correct excessive wheel slippage.
The brake control system
10
further includes a pressure sensor
40
that monitors the hydraulic pressure in one of the master cylinder reservoirs. An pressure signal is supplied to the ECU
38
. The microprocessor monitors the pressure signal and responsive thereto, upon detecting an emergency brake application, to actuate HBA.
A typical prior art pressure sensor assembly is illustrated generally at
44
in FIG.
3
. The pressure sensor assembly includes a sensor element
46
that is electrically coupled to an Application Specific Integrated Circuit (ASIC)
47
. Hydraulic pressure is applied to the sensor element
46
. Both the sensor element
46
and the ASIC
47
are typically mounted in a common housing, that is shown schematically by the dashed line labeled
48
in FIG.
3
. The sensor element
46
may include a plurality of strain gauges mounted upon one side of a thin diaphragm. The diaphragm is usually a disc formed from stainless steel. The strain gauges are typically arranged as a conventional half or full bridge circuit, such as, for example, a conventional thin film Wheatstone Bridge. The hydraulic brake fluid in the brake system is in contact with the side of the diaphragm opposite from the strain gauges. When the vehicle brakes are applied, the hydraulic brake fluid is pressurized and causes the diaphragm to deflect from its rest position. As the diaphragm is deflected by the applied pressure, the strain gauges are stretched or compressed, causing a change in the internal resistance of the gauges. The changed resistances result in a voltage appearing across the bridge circuit that is proportional to the magnitude of the pressure. The voltage is conditioned by the ASIC
47
. The ASIC
47
generates an analog or digital pressure signal that is applied to an input port of an ECU microprocessor
49
. The microprocessor
49
is included in the vehicle brake control system
10
.
SUMMARY OF THE INVENTION
This invention relates to a high reliability pressure sensor utilized in a vehicle brake system with Hydraulic Brake Assist.
As explained above, current HBA systems include a pressure sensor to detect an emergency stop condition. However, if the pressure sensor should malfunction or fail, it is possible that a false emergency stop signal may be generated that would trigger the HBA. It is known to improve HBA system reliability by including a second complete pressure sensor to provide a redundant pressure signal to the ECU microprocessor. The ECU microprocessor compares the two signals and, if the signals are different, it is assumed that one of the pressure sensors is malfunctioning and the HBA is disabled. However, the inclusion of two complete pressure sensors is both bulky and expensive. Two pressure sensors also require two ports in the hydraulic control unit which increases the potential for hydraulic fluid leakage. Accordingly, it would be desirable to improve the reliability of the measurement of the brake pressure in a HBA system without requiring two separate pressure sensors.
The present invention contemplates a pressure sensor assembly for a hydraulic control unit that includes a pressure sensor housing adapted to be mounted upon a hydraulic control unit and a pressure sensor diaphragm carried by the housing. First and second pressure sensing elements are mounted upon the pressure sensor diaphragm. A first signal conditioning circuit is connected to the first pressure sensing element and a second signal conditioning circuit is connected to the second pressure sensing element The said first and second signal conditioning circuits are operable to generate first and second pressure signals at output ports. An active electronic device is connected to the output ports of the first and second signal conditioning circuits and is operative to comp
Babala Mike L.
Baron Thomas
Bolitho Marc
Shaya Jeffery E.
Cuchlinski Jr. William A.
Kelsey-Hayes Company
MacMillan Sobanski & Todd LLC
Marc-Coleman Marthe Y.
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