Pumps – With condition responsive pumped fluid control – Pressure responsive relief or bypass valve
Reexamination Certificate
1999-04-27
2001-02-13
Thorpe, Timothy S. (Department: 3746)
Pumps
With condition responsive pumped fluid control
Pressure responsive relief or bypass valve
C417S308000, C417S286000, C417S288000, C137S115260, C137S115130
Reexamination Certificate
active
06186750
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to an oil pump assembly and, more particularly, to an oil pump assembly that includes a pilot pressure relief valve for equalizing the pump discharge pressure and the control valve pilot pressure.
2. Discussion of the Related Art
Vehicles include an oil pump assembly for pumping engine oil through the vehicle engine to lubricate the engine components through various lubrication channels.
FIG. 1
is a cross-sectional view of one type of an oil pump assembly
10
that is used for this purpose in certain vehicles. The assembly
10
includes a metal housing
12
including a pump inlet port
14
connected to an oil source (not shown), a first pump discharge port
16
, a second pump discharge port
18
, and a pilot pressure inlet port
20
. Source oil from the pump inlet
14
is drawn to a first stage pump
24
and a second stage pump
26
. The inlet port
14
is also the low pressure exhaust for the pumps
24
and
26
. The pumps
24
and
26
are rotated by a chain sprocket mounted on the front of a shaft
28
and can be any suitable pump gear configuration, such as a gerotor assembly. Operation of the pump
24
pumps oil to the first discharge port and operation of the pump
26
pumps oil to the second discharge port
18
. The first discharge port
16
is always in fluid communication with the engine
17
. The first and second discharge ports
16
and
18
are sometimes in fluid communication based on the position of the control valve spool. The pilot pressure applied to the pilot pressure inlet port
20
is the pressure of the oil in the engine's lubrication channels.
The pump assembly
10
includes the two pumps
24
and
26
to provide the pump discharge flow at both the discharge ports
16
and
18
so that the total discharge flow can be controlled. As the vehicle speed changes the pump speed changes, and thus the discharge flow changes. Therefore, it is necessary to regulate the discharge pressure during vehicle operation to satisfy the engine's oil pressure limits. To provide this regulation, the pump assembly
10
, with its control valve, selectively adds or removes the second discharge flow at the discharge port
18
and regulates the first discharge flow at the first discharge port
16
. The valve exhaust flows are routed back to the oil source through the pump inlet port
14
. The degree and rate at which the first and second discharge flows are changed is determined by the pressure at the pilot pressure port
20
.
A valve spool
32
positioned within a housing chamber
34
is employed to change the pump discharge flow when the pilot pressure changes during vehicle operation. The chambers
34
are in fluid communication with the first and second discharge ports
16
and
18
and the pump inlet port
14
. A valve spring
36
is positioned within a chamber
37
and a spring land
38
of the valve spool
32
opposite the pilot pressure inlet port
20
, and biases the valve spool
32
towards the pilot pressure inlet port
20
. The valve spool
32
further includes an intermediate land
40
and a pilot pressure land
42
. A narrowed section
44
connects the spring land
38
to the intermediate land
40
, and a narrowed section
46
connects the intermediate land
40
to the pilot pressure land
42
to give the valve spool
32
its general shape as shown.
When the pilot pressure at port
20
is below a certain pressure, the valve spool
32
is in the position shown, and the discharge ports
16
and
18
are in fluid communication to allow the complete discharge flow from both the pumps
24
and
26
to lubricate the engine. Also, the discharge ports
16
and
18
are blocked to the exhaust
14
. When the pilot pressure increases above a certain pressure, it pushes against the pilot pressure land
42
through the port
20
, and the valve spool
32
moves against the bias of the spring
36
. Movement of the land
40
begins closing off the second discharge port
18
from the discharge port
16
to reduce the oil discharge flow and pressure, and also begins opening the discharge port
18
to exhaust through channel
48
. As the pilot pressure continues to increase, the land
40
will eventually completely close the second discharge port
18
so it is not in fluid communication with the first discharge port
16
, and completely open the second discharge port
18
to the exhaust.
If the pilot pressure continues to increase, the valve spool
32
will move far enough against the bias of the spring
36
to cause the spring land
38
to allow the first discharge port
16
to gradually be opened to exhaust through channel
50
. Eventually, the spring land
38
will contact the chamber wall
52
preventing further movement of the valve spool
32
in that direction. If the pilot pressure decreases, the valve spool
32
reverses its direction as just described to increase the oil discharge pressure. Thus, the valve spool
32
allows regulation of the engine oil pressure. Operation of the pump assembly as just described is well known in the art.
A problem exists with the operation of the oil pump assembly
10
described above that causes it to be unstable.
FIG. 2
is a graph with time on the horizontal and pressure on the vertical axis showing a discharge pressure line
54
for the combined first and second discharge pressures and a pilot pressure line
56
for the pilot pressure. As the discharge pressure rises, the pilot pressure also rises with a certain time lag depending on the particular system, because the pilot pressure is taken from a point inside the engine and not the pump discharge in this design. The time lag as being described herein is directly related to the fact that the pilot pressure is the pressure within the lubrication system and not the actual discharge pressure. This lag can be eliminated by sensing the discharge pressure as it leaves the assembly
10
, but certain lubrication system designs benefit from measuring the pilot pressure at this location, as is known in the art.
Once the pilot pressure increases to a certain level, the actuation of the valve spool
32
, as discussed above, causes the discharge pressure to begin to decrease at time
58
. Because of the lag between the change in the discharge pressure and the associated change in the pilot pressure, the pilot pressure does not immediately decrease when the discharge pressure starts decreasing. Once a certain period of time passes, the pilot pressure begins to decrease at time
60
. But, the discharge pressure has been continually decreasing for the period of the time lag. Eventually, the discharge pressure will begin to increase at time
62
because the pilot pressure has been decreasing for some time, but the pilot pressure is still decreasing because of the lag. This process continues through the operation of the assembly
10
. This instability in the operation of the pump assembly
10
causes pressure oscillations and added wear and tear on the pump and engine components, reducing device longevity.
It would be desirable to eliminate the lag of the pilot pressure in the oil pump assembly
10
to decrease the oscillation of the valve spool
32
to allow the pump
10
to operate more smoothly. It is therefore an object of the present invention to provide an improved valve spool for the oil pump assembly
10
.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a valve spool for an oil pump assembly is disclosed that includes a pilot pressure relief valve to provide pilot pressure relief to eliminate the lag between the discharge pressure and the pilot pressure described above, and reduce pump instability. The valve spool operates in response to the pilot pressure to increase or decrease the pump discharge pressure during vehicle operation. The pilot pressure relief valve is positioned within an internal chamber in the valve spool. The chamber within the valve spool is in fluid communication with the discharge pressure at one end and the pilot pressure at the other end. When
Borg-Warner Inc.
Dziegielewski Greg
Thorpe Timothy S.
Tyler Cheryl J.
Warn, Esq. Philip R.
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