GB2320080A

GB2320080A - Fluid control valve

Info

Publication number: GB2320080A
Application number: GB9625450A
Authority: GB
Inventors: Brian James Darling; Roy Wayne Rodammer; Jean Claude Kachel
Original assignee: Delphi Automotive Systems France
Current assignee: Delphi Automotive Systems France
Priority date: 1996-12-07
Filing date: 1996-12-07
Publication date: 1998-06-10
Anticipated expiration: 2016-12-07
Also published as: GB9625450D0; GB2320080B

Abstract

A fluid control valve (10) for a fluid pump (12) comprises a housing (18) having a longitudinal bore (20). An outlet port (16) connects with the bore for delivering pressurised fluid. An inlet port (42) connects with the bore for receiving pressurised fluid. A piston (26) is slidable within the bore to control flow of fluid from the inlet to the outlet. The piston has at least two axially spaced lands (32, 34) engaging surface (36) of the bore, and at least one circumferential groove (44, 46) in each land. Each groove has a first side (48) defining the opening of the groove, a second side (50) defining a radially inner surface, and a third side (52) connecting the first and second sides. The third side is at an obtuse angle to the first side and at an acute angle to the second side. An undercut region (56) in each groove traps any particles in the hydraulic fluid. Grooves (44, 46) retain hydraulic fluid for lubrication.

Description

FLUID CONTROL VALVE Technical Field The present invention relates to a fluid control valve, and in particular to a fluid flow or pressure control valve associated with a fluid pump.

Background of the Invention A control valve is used in association with a fluid pump to control the flow or pressure of fluid leaving the pump. The control valve consists of a piston slidably mounted within the bore of a housing. The piston is biased by a spring and moves against the bias to provide a substantially constant output fluid flow or pressure at an outlet port in the housing. The piston typically has two or more lands which make a sliding engagement with the surface of the bore. One or more circumferentially extending grooves are formed in each land. The grooves trap fluid to provide lubrication between the piston and the bore surface. An example of this known arrangement is shown in US-A-4,570,667. Where the piston and housing are made from steel, the grooves typically have a V-shaped cross-section. Where there is a need to reduce weight, the housing and/or piston are made from aluminium or aluminium alloy. In this latter case, however, there is a risk that particles can be trapped within the V-shaped grooves which can interfere with the relative movement of the piston within the housing.

Summarv of the Invention It is an object of the present invention to overcome the above mentioned problem.

To this end, a fluid control valve in accordance with the present invention for use with a fluid pump comprises a housing having a longitudinally extending bore; an outlet port connecting with the bore for delivering pressurised fluid; an inlet port connecting with the bore for receiving pressurised fluid; and a piston slidable within the bore to control the flow of fluid from the inlet port to the outlet port, the piston having at least two axially spaced lands engaging the surface of the bore, and at least one circumferentially extending groove in each land; wherein each groove has a first side defining the opening of the groove, a second side defining a radially inner surface of the groove, and a third side connecting the first and second sides, the third side being at an obtuse angle to the first side and at an acute angle to the second side.

Each lubricating groove is shaped to form at least one undercut region. The undercut region of each groove traps particles therein. This arrangement substantially prevents the particles from interfering with the movement of the piston.

Brief Description of the Drawings The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view, partially in cross-section, of a fluid control valve in accordance with the present invention mounted on a fluid pump; Figure 2 is a side view of the piston of the fluid control vale of Figure 1; Figure 3 is a cross-sectional view of the area labelled HI in Figure 2; and Figure 4 is a cross-sectional view similar to that of Figure 3 showing an alternative cross-sectional shape for each lubricating groove.

Description of the Preferred Embodlment Referring to Figure 1, the fluid control valve 10 in accordance with the present invention is mounted on a hydraulic fluid pump 12 which provides pressurised hydraulic fluid to the power steering system (not shown) on a motor vehicle. The pump 12 receives fluid from a reservoir (not shown) by way of an inlet port 14, and the assembly of pump and control valve 10 delivers pressurised fluid by way of an outlet port 16.

The control valve 10 comprises a housing 18 having a longitudinally extending bore 20 formed therein. The bore 20 is open at one end 22, and closed at the other end 24. The outlet port 16 is positioned in the open end 22 of the bore 20. A piston 26 is slidably positioned within the bore 20. A coil spring 28 is positioned within the bore 20 between the piston 26 and the closed end 24 of the bore. A tubular insert 30 is positioned in the bore 20 adjacent the open end 22. The spring 28 acts on the piston 26 to bias the piston towards the open end 22 of the bore 20 and (in the rest position shown in Figure 1) into engagement with the tubular insert 30. The piston 26 has a pair of axially spaced lands 32, 34 which slidingly engage with the surface 36 of the bore 20. The arrangement of the tubular insert 30, piston 26, and bore 20 is such as to define a first annular fluid chamber 38 within the bore 20 around the insert 30, and a second annular fluid chamber 40 within the bore between the lands 32, 34 on the piston 26. The first fluid chamber 38 receives pumped fluid from the pump 12 by way of inlet port 42 in the housing 18. The second fluid chamber 40 is fluidly connected to the fluid reservoir (not shown). The hydraulic fluid provides lubrication between the lands 32, 34 on the piston 26 and the surface 36 of the bore 20. As the fluid pressure increases in the first fluid chamber 38, the piston 26 moves away from the insert 30 against the bias of the spring 28 to allow pressurised fluid to reach the outlet port 16. Movement of the piston 26 compensates for pressure variations in the first chamber 38 to provide a substantially constant output pressure at the outlet port 16, with excess fluid being returned to the fluid reservoir. This arrangement is well known to those skilled in the art, and will not be described in greater detail.

The piston 26 is shown in greater detail in Figures 2 and 3.

Land 32 has a circumferentially extending groove 44 therein. Land 34 has a pair of axially spaced circumferentially extending grooves 46 therein. The grooves 44, 46 retain hydraulic fluid for lubrication between the piston 26 and the surface 36 of the bore 20. Each groove 44, 46 has a cross-sectional shape in the form of a trapezium, as shown in Figure 3. In other words, each groove 44, 46 has a first side 48 which defines the opening to the groove, a second side 50 which defines the radially inner surface of the groove, and third and fourth sides 52, 54 which are both at an obtuse angle to the first side and at an acute angle to the second side. With this arrangement, each groove 44, 46 has a pair of undercut regions 56, 58, and the shape of each groove is such as to remove any particles in the lubricating hydraulic fluid and trap these particles within the undercut regions. Such an arrangement reduces the risk of particles within the hydraulic fluid from interfering with the movement of the piston 26.

In an alternative arrangement, as shown in Figure 4, the fourth side 54' of each groove 44, 46 is perpendicular to the first and second sides 48, 50. With this arrangement, the groove only has a single undercut region 56. As a further alternative, each groove may have the cross-sectional shape of a parallelogram such that each groove has a single undercut region. Other shapes of groove may also be used which provide at least one undercut region within which particles in the hydraulic fluid can be trapped.

The present invention has particular application in fluid control valves 10 in which the housing 18 and/or the piston 26 are formed from aluminium or aluminium alloy.

Claims

1. A fluid control valve for use with a fluid pump comprising a housing having a longitudinally extending bore; an outlet port connecting with the bore for delivering pressurised fluid; an inlet port connecting with the bore for receiving pressurised fluid; and a piston slidable within the bore to control the flow of fluid from the inlet port to the outlet port, the piston having at least two axially spaced lands engaging the surface of the bore, and at least one circumferentially extending groove in each land; wherein each groove has a first side defining the opening of the groove, a second side defining a radially inner surface of the groove, and a third side connecting the first and second sides, the third side being at an obtuse angle to the first side and at an acute angle to the second side.

2. A fluid control valve as claimed in Claim 1, wherein each groove has a cross-sectional shape in the form of a trapezium.

3. A fluid control valve as claimed in Claim 2, wherein the fourth side of each groove is also at an obtuse angle to the first side and at an acute angle to the second side.

4. A fluid control valve as claimed in Claim 1, wherein each groove has a cross-sectional shape in the form of a parallelogram.

5. A fluid control valve substantially as herein described with reference to, and as shown in, the accompanying drawings.