Electricity: measuring and testing – Electromechanical switching device
Reexamination Certificate
2001-09-12
2003-06-10
Oda, Christine (Department: 2858)
Electricity: measuring and testing
Electromechanical switching device
C324S207160, C324S389000
Reexamination Certificate
active
06577133
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to solenoid valves utilized in anti-lock brake systems and in particular to measurement of the movement of an armature within a solenoid valve.
An anti-lock brake system (ABS) is often included as standard equipment on new vehicles. When actuated, the ABS is operative to control the operation of some or all of the vehicle wheel brakes. A typical ABS includes a plurality of normally open and normally closed solenoid valves which are mounted within a control valve body and connected to the vehicle hydraulic brake system. Usually, a separate hydraulic source, such as a motor driven pump, is included in the ABS for reapplying hydraulic pressure to the controlled wheel brakes during an ABS braking cycle. The pump is typically included within the control valve body while the pump motor is mounted upon the exterior of the control valve body.
An ABS further includes an electronic control module which has a microprocessor. The control module is electrically coupled to the pump motor, a plurality of solenoid coils associated with the solenoid valves and wheel speed sensors for monitoring the speed and deceleration of the controlled wheels. The control module is typically mounted upon the control valve body to form a compact unit which is often referred to as an ABS electro-hydraulic control unit.
During vehicle operation, the microprocessor in the ABS control module continuously receives speed signals from the wheel speed sensors. The microprocessor monitors the wheel speed signals for a potential wheel lock-up condition. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to actuate the pump motor and selectively operate the solenoid valves in the control unit to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the driver.
As described above, an ABS typically includes a plurality of solenoid valves for controlling the flow of hydraulic fluid to the vehicle wheel brakes. Referring now to the drawings, there is shown generally at
10
a typical cartridge for a normally closed solenoid valve. In an ABS, such normally closed valves are typically referred to as “dump” valves. The valve cartridge
10
includes a generally cylindrical valve body
11
. An inlet port, which includes a stepped bore
12
, extends axially through the valve body
11
. The upper end of the stepped bore
12
is formed into a valve seat
13
. A pair of outlet ports
14
are also formed in the valve body
11
.
A tubular valve sleeve
15
extends axially from the top of the valve body
11
. An axially slidable armature
16
is disposed within the valve sleeve
15
. A valve ball
17
is mounted upon the lower end of the armature
16
. The valve ball
17
co-operates with the valve seat
13
to control the flow of fluid through the valve cartridge
10
. A cylindrical core
18
is secured in the upper end of the valve sleeve
15
. A return spring
19
is disposed between the lower end of the core
18
and the upper end of the armature
16
. The return spring
19
urges the armature
16
in a downward direction in
FIG. 1
to maintain the valve cartridge
10
in a normally closed position. As shown in
FIG. 1
, when the cartridge
10
is in its normally closed position, a small working air gap, which is labeled G
A
, exists between the lower end of the core
18
and the upper end of the armature
16
.
A dump valve also includes an annular flux ring and a solenoid coil (not shown) which slidingly extend axially over the valve sleeve
15
and core
18
. The solenoid coil typically includes insulated magnet wire wound upon a plastic bobbin. A metal cup-shaped flux casing (not shown) encloses the coil and flux ring and is secured to the flux ring by a conventional operation, such as crimping to form a coil assembly. The flux casing and flux ring provide a return path for the magnetic flux when the solenoid valve is actuated. Typically, the coil assembly is attached to a Printed Circuit Board in the ABS control module and is removable from the valve cartridge
10
when the control module is removed for maintenance. When the coil assembly is removed, valve sleeve
15
maintains a sealed hydraulic brake circuit.
During operation, an electric current is passed through the solenoid coil. The resulting magnetic field causes the armature
16
to move in an axial upward direction within the valve sleeve
15
to compress the return spring
19
. As the armature moves, the working air gap G
A
is closed and the valve ball
17
moves away from the valve seat
13
to open the solenoid valve. Upon the interruption of the electric current, the magnetic field collapses and the return spring
19
pushes the armature
16
in a downward axial direction to reset the valve ball
17
upon the valve seat
13
and thereby close the solenoid valve.
As indicated above, an ABS also includes normally open, or isolation, solenoid valves which have a structure similar to the dump valve described above. A cartridge for a typical isolation valve is illustrated in
FIG. 7
, where the working air gap G
A
exists between the lower end of the armature
16
and the upper end of the valve body
11
.
SUMMARY OF THE INVENTION
This invention relates to measurement of the movement of an armature within a go solenoid valve.
As explained above, solenoid valves are important components in anti-lock brake systems. Therefore, it is desirable that such valves are properly assembled. For example, a manufacturer needs to confirm that a return spring has been included within each of the valves. Typically, the valve sleeve is press fit onto the valve body and secured with a laser weld. The axial position of the valve sleeve upon the valve body controls the working air gap between the valve armature and the valve core in a dump valve or the between the valve armature and valve body in an isolation valve. A typical working air gap has a tolerance of 0.004 inches. The size of the working air gap is especially critical in proportional solenoid valves.
It is known to test an assembled solenoid valve by removing the valve from its pallet and turning the valve over to expose a valve port formed through the valve seat. Such ports have a typical diameter of 0.013 inches. A slender test probe is inserted through the valve port and into contact with the valve ball mounted in the end of the valve armature. The test probe is connected to a Linear Variable Differential Transformer (LVDT). The solenoid coil for the valve is energized to axially displace the armature and test probe. The movement of the armature and the test probe, which is a function of the working air gap of the valve, is measured by the LVDT. The coil is then de-energized and the armature movement again measured by the LVDT. The test procedure confirms that the working air gap has the correct size and that a return spring has been included in the valve; however, the test is very time consuming and requires accurate placement of a delicate mechanical component. Accordingly, it would be desirable to provide a simpler method for measuring armature travel within a solenoid valve cartridge to verify correct assembly of the cartridge.
The present invention contemplates an apparatus for testing a solenoid valve cartridge which includes a coil adapted to be placed over the valve cartridge and a circuit for supplying an electric current to the coil. The circuit co-operates with the coil to form a window comparitor. The window comparitor switches the voltage applied to the coil on and off, with the voltage on time being a function of the inductance of the coil. The coil inductance is proportional to the size of the working air gap in the solenoid valve cartridge. Accordingly, the on time for the coil voltage is a functi
Kelsey-Hayes Company
Kerveros James C.
MacMillan Sobanski & Todd LLC
Oda Christine
LandOfFree
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