Pumps – Expansible chamber type – Having separate noncyclic valve
Reexamination Certificate
1998-09-04
2001-10-09
Dolinar, Andrew M. (Department: 3747)
Pumps
Expansible chamber type
Having separate noncyclic valve
C091S446000
Reexamination Certificate
active
06299418
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oil pump apparatus for supplying operating fluid to a power-assisting portion of a power steering apparatus of vehicles and the like. More particularly, the present invention relates to improvements of a bypass passage located between an inlet side of the pump mechanism portion and a flow control valve.
2. Description of the Prior Art
Oil pump apparatuses have been proposed for a power steering apparatus of vehicles and the like. In general, the conventional oil pump apparatus mainly consists of a pump mechanism portion and a flow control valve. The pump mechanism portion supplies operating fluid (i.e., oil) to a power-assisting portion of the power steering apparatus. The flow control valve maintains a flow rate of the operating fluid supplied to the power-assisting portion constant by draining part of the operating fluid to an inlet side of the pump mechanism portion as excess operating fluid.
An example of the oil pump apparatus is shown in a Japanese Utility Model No. 05-19594. As shown in
FIG. 1
, this oil pump apparatus includes a bypass hole
30
and a bypass passage
20
connecting with each other. The bypass hole
30
connects with the flow control valve
31
and the bypass passage
20
connects with the inlet side of the pump mechanism portion. The excess operating fluid is drained through the bypass hole
30
and the bypass passage
20
.
The oil pump apparatus also includes an opening
150
of a reservoir passage connecting to a reservoir. The opening
150
is located in the connecting portion between the bypass hole
30
and the bypass passage
20
.
In the conventional oil pump apparatus, a cross-sectional area of the bypass passage
20
widens in a side of the opening
150
of a reservoir passage, i.e., the center axis of the bypass passage
20
is placed offset from the center axis of the bypass hole
30
(shown by an eccentric distance d). In the configuration, since strong fluid stream (shown by arrows A) of the excess operating fluid is drained with causing negative pressure, the operating fluid is effectively led from the reservoir to the inlet side of the pump mechanism portion. As a result, enhanced is suction efficiency of the operating fluid supplied from the opening
150
of a reservoir passage, i.e., supercharging effect. Therefore, a width of the bypass passage
20
is designed to be as wide as possible in the side of the opening
150
in order to include almost of all area of the opening
150
.
After gathering in the bypass passage
20
, the excess operating fluid drained from the flow control valve
31
and the operating fluid sucked by the jet, i.e., strong stream A, of the excess operating fluid are led to an inlet port of the pump mechanism portion.
As described above, when the excess operating fluid is drained from the bypass hole
30
to the bypass passage
20
, the stream of the excess operating fluid spouts with high pressure as the jet A. The jet A dashes against an inner surface of the bypass passage
20
near the bypass hole
30
, so as to possibly cause cavitation damages, i.e., erosion. In addition, since the cavitation removes tiny broken pieces from the inner surface of the bypass passage
20
, the tiny broken pieces enter in the pump mechanism portion, so as to deteriorate quality of the pump mechanism portion.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved oil pump apparatus capable of decreasing cavitation damages and erosion of its bypass passage and bypass hole.
Another object of the present invention is to provide an improved oil pump apparatus whose stream of excess operating fluid reaches an inner surface of the bypass passage after the pressure of the stream is weakened.
Briefly, these and other objects of this invention as hereinafter will become more readily apparent as having been attained broadly by an oil pump apparatus, including a pump mechanism portion for discharging operating fluid, a valve receiving bore formed in a housing, a flow control valve arranged in the valve receiving bore, and a bypass passage.
The valve receiving bore is connected to a supply passage for leading the operating fluid discharged from the pump mechanism portion and connected to a bypass hole for draining excess operating fluid to a reservoir. The flow control valve has a bypass spool for regulating an opening area of the bypass hole in order to control a flow rate of the operating fluid by draining excess operating fluid. The bypass passage is connected to the bypass hole, having a space radially extending from an edge of the bypass hole in a fluid stream direction of the excess operating fluid spouting from the opening area of the bypass hole.
In the oil pump apparatus, when the pump mechanism portion is driven, the operating fluid is supplied to the flow control valve in the valve receiving bore through the supply passage. The flow control valve maintains the flow rate of the operating fluid a determined rate by draining the excess operating fluid through the opening of the bypass hole defined by the bypass spool.
When the excess operating fluid is drained from the bypass hole to the bypass passage, the excess operating fluid spouts from the opening area of the bypass hole, contacting with the inner surface of the bypass passage. When fluid stream of the excess operating fluid reaches the inner surface of the bypass passage, the pressure of the excess operating fluid has been weaken sufficiently. The reason is that fluid stream of the excess operating fluid is diffused by the long span of the bypass passage extended from the edged of the bypass hole. Since the total area receiving the fluid stream of the excess operating fluid is widen by the diffusion of the excess operating fluid, decreased is pressure acting on a unit area of the inner surface of the bypass passage. Therefore, the energy of the fluid stream of the excess operating fluid is decreased by the widen cross-sectional area of the bypass passage. As a result, the inner surface of the bypass passage is protected from cavitation damages and erosion, so as that the quality of the oil pump apparatus is enhanced.
The effect of the protection for the bypass passage especially effective in the case of that the housing is made of materials which is comparatively easily eroded such as aluminum and aluminum alloy.
In preferable construction, the space of the bypass passage further radially extends in a direction toward an opening of a reservoir passage connecting to a reservoir, so as that the bypass passage includes almost of all area of the opening of the reservoir passage.
In this case, the oil pump apparatus is capable of decreasing suction resistance when the operating fluid is inhaled from the reservoir to the pump mechanism portion through the opening of the reservoir passage, since widen is a space in vicinity of the opening of the reservoir passage for discharging the operating fluid. Therefore, the operating fluid is smoothly supplied to the pump mechanism portion even when the operating fluid becomes to have high viscosity such as under low-temperature condition.
In another preferable construction, a width of the bypass passage in a direction perpendicular to the fluid stream direction of the excess operating fluid is approximately the same as a diameter of the bypass hole.
In this case, though a cross-sectional area of the bypass passage is increased, size of the housing of the oil pump apparatus is maintained small.
REFERENCES:
patent: 4917139 (1990-04-01), Narumi et al.
patent: 5822988 (1998-10-01), Kato
Fujiwara Hidetoshi
Honaga Susumu
Yamamori Motoyasu
Castro Arnold
Dolinar Andrew M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyoda Koki Kabushiki Kaisha
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