GB2354568A - Pressure regulator - Google Patents

Abstract

A fuel pressure regulator comprises a piston 14 moveable under the influence of the fuel pressure to control the degree by which an opening 17 is obscured. A return passage connects an outlet of a pump 10 to the inlet and the opening 17 is located in the return passage. An additional flow restriction 19 is located in the return passage downstream of the opening 17. Preferably the restriction 19 is variable, the piston 14 being slideable in a sleeve 12 which can have its angular or axial position adjusted to provide the variation of the restriction 19. The sleeve 12 may be located in a bore (21, figure 4) in a housing (22), and have collar (20) cooperating with bore (21) to define the restriction (19).

Description

2354568 PRESSURE REGULATOR This invention relates to a pressure regulator

suitable for use in regulating the outlet pressure of a low pressure, transfer pump of a fuel system for a compression ignition internal combustion engine.

It is known to use, as the transfer pump for use in a fuel system, a vane pump which is arranged to operate at a speed associated with engine speed. The vane pump is provided with a regulator for example as illustrated in Figure 1. The regulator comprises a sleeve 1 within which a piston member 2 is slidable. The piston member is biased by a spring 3 and is moveable under the action of the fuel pressure at the outlet of the transfer pump. The piston member 2 is moveable between a position (illustrated) in which it closes an outlet 4 and a position in which the outlet 4 is open to allow fuel to return to the inlet side of the transfer pump. The degree to which the outlet 4 is opened depends upon the magnitude of the pressure applied to the piston member 2. By appropriate selection of the size of the piston member 2 and the spring 3, the regulator can be set in such a manner that the outlet pressure of the transfer pump as regulated by the pressure regulator is related to the engine and pump speed in a desired manner.

The pressure at the outlet of the transfer pump as modified by the presence of the pressure regulator is used, in some arrangements, to control the operation of arrangements used to adjust the maximum fuelling level of a high pressure fuel pump with which the transfer pump is associated. It has been found that setting of such transfer pumps is difficult as the relationship between the outlet pressure and speed varies from pump to pump as a result of production variations in the pressure regulators.

2 It is an object of the invention to provide a pressure regulator in which the relationship between the outlet pressure and pump speed can be controlled.

According to the present invention there is provided a pressure regulator comprising a piston member moveable under the influence of the fuel pressure applied thereto to control the degree by which an opening is obscured, a return passage which connects an outlet of a pump to the inlet thereof, the opening being located in the return passage, and an additional flow restrictor located in the return passage downstream of the opening.

In such an arrangement, where the fuel pressure applied to the piston member is low and the opening is largely closed by the piston member, the fuel flow rate along the return passage is low and the additional flow restrictor has little effect. When the pressure applied to the piston is higher and fuel is able to flow through the opening at a higher rate, the fuel flow rate along the return passage is increased and the additional flow restrictor restricts the rate of fuel flow along the return passage. As a result, the additional flow restrictor generates a back pressure increasing the pump outlet or transfer pressure. Clearly, the provision of the additional flow restrictor downstream of the opening permits modification and control of the relationship between the outlet pressure and the pump speed.

The magnitude of the restriction formed by the additional flow restrictor is preferably variable, permitting further control of the relationship. Such an arrangement allows adjustments to be made to compensate for production variations.

3 Conveniently, the piston member is slidable within a sleeve, the restriction to fuel flow defined by the additional flow restriction being adjustable by adjusting the angular or axial position of the sleeve.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a sectional view illustrating part of a fuel pump including a typical pressure regulator; Figure 2 is a diagrammatic view illustrating a pressure regulator in accordance with an embodiment of the invention; Figure 3 is a view illustrating the regulator of Figure 2 operating under high speed conditions; Figures 4 and 5 are diagrammatic views illustrating an alternative embodiment; Figure 6 is a diagrammatic sectional view of the embodiment of Figures 4 and 5; Figure 7 is a graph illustrating the relationship between transfer (outlet) pressure and pump speed of the embodiment of Figures 4 to 6 under various settings; and Figure 8 is a view similar to Figure 4 illustrating a further alternative embodiment.

4 Figures 2 and 3 illustrate a pressure regulator for use in regulating the outlet pressure of a transfer pump 10 which is used to supply fuel to an inlet of a high pressure fuel pump, for example in the form of a rotary distributor pump or a high pressure fuel pump for supplying fuel to a common rail of a common rail fuel system. The transfer pump 10 is arranged to draw fuel from a fuel tank 11, supplying the fuel at a relatively low fuel pressure to the high pressure fuel pump.

The pressure regulator comprises a sleeve 12 having a bore 13 formed therein within which a piston member 14 is slidable. The piston member 14 is biased by a spring 15, for example in the forrn of a helical compression spring, away from a blind end of the bore 13, the spring 15 being located between the piston member 14 and the blind end of the bore 13. In order to prevent the piston member 14 becoming hydraulically locked within the sleeve 12, an opening 16 is provided whereby the interior of the part of the bore 13 within which the spring 15 is located is vented, through a suitable passage, to the fuel reservoir 11. If desired, the dimensions of the opening 16 may be selected to act as a viscosity compensator, restricting fuel flow to and from the bore under conditions where the fuel is relatively viscous but forming a smaller restriction to flow when the viscosity reduces.

The piston member 14 includes a surface 14a exposed to the fuel pressure at the outlet of the transfer pump 10. The fuel pressure acting upon this surface urges the piston member 14 against the action of the spring 15, and it will appreciated that the position occupied by the piston member 14 is dependent upon the magnitude of the load applied to the piston member 14 by the spring 15, by the fuel pressure within the bore 13 and upon the magnitude of the outlet pressure of the transfer pump 10.

The sleeve 12 is provided with an opening 17 positioned such that, depending upon the position occupied by the piston member 14, which depends upon the fuel pressure applied thereto, the opening 17 is either obscured by the piston member 14, partially obscured by the piston member 14 or fully open. The opening 17 opens into a chamber 18 which communicates through a restriction 19 with a passage which comniunicates with the ftiel reservoir 11. It will be appreciated that the parts of the sleeve 12, opening 17, chamber 18 and restriction 19 through which fuel flows, in use, define part of a return passage whereby some fuel is able to return from the outlet of the pump 10 to the inlet thereof or the fuel reservoir 11 which communicates with the inlet of the transfer pump 10. In use, as the pump outlet pressure rises, the piston member moves to allow ftiel to flow along the return passage at an increased rate, and as the pump outlet pressure falls, the piston member moves to reduce the fuel flow rate along the return passage. It will be appreciated, therefore, that the piston member is moveable to regulate the outlet pressure of the pump.

It will be appreciated that the arrangement described with reference to Figure 2 differs from the conventional arrangement primarily in that a restriction 19 is located downstream of the opening 17. The provision of the restriction 19 has little effect upon the operation of the pressure regulator where the transfer pump 10 is operating at relatively low speeds. This is because under such conditions, the outlet pressure of the transfer pump 10 is relatively low, thus the piston member 14 occupies a position in which the opening 17 is largely obscured by the piston member 14. In such conditions, the rate at which fuel flows along the return passage is relatively small, and the restriction 19 is of sufficient dimensions that the restriction 19 does not significantly restrict the rate at which fuel is flowing along the return passage. The fuel pressure drop 6 across the restriction 19 will not be great, and so the regulator will operate largely as if the restriction 19 were not present.

When the transfer pump 10 operates at higher speeds, the fuel pressure at the outlet thereof increases, moving the piston member 14 from the position illustrated in Figure 2 towards the position illustrated in Figure 3. In this position, the opening 17 is only obscured by the piston member 14 by a small amount, and fuel flows through the opening 17 at a higher rate. The rate at which fuel flows through the opening 17 is higher than the rate at which fuel is able to flow through the restriction 19 for a given fuel pressure. As a result, the fuel pressure drop across the restriction 19 rises, the fuel pressure within the chamber 18 and upstream of the pressure regulator increases and the outlet pressure of the transfer pump 10 as regulated by the pressure regulator, and known as the transfer pressure, is increased.

Clearly, by modifying the magnitude of the restriction to flow formed by the restriction 19, the relationship between the transfer pressure of the pump and the pump operating speed can be modified.

Figures 4, 5 and 6 illustrate a modification to the arrangement illustrated in Figures 2 and 3 in which the magnitude of the restriction to fuel flow formed by the restriction 19 can be varied. In the arrangement of Figures 4, 5 and 6, the sleeve 12 is provided with a radially outwardly extending flange or collar 20, the sleeve 12 being located within a bore 21 formed in a housing 22 such that the collar 20 forms a substantially fluid tight seal within the bore 21. The sleeve 12 is sealed at its lower end to the bore 21 through a seal arrangement 23, and thus the sleeve 12 and bore 21 together define the 7 chamber 18 to which fuel flows through the opening 17 provided in the sleeve 12.

As illustrated in Figure 6, the collar 20 is provided with two or more flats or other deformations 24 whereby, depending upon the angular orientation of the sleeve 12 within the bore 21, the magnitude of a restriction 19 defined between the flats 24 and an opening 25 formed in the housing 22 controls the rate at which fuel is able to escape from the chamber 18 for a given fuel pressure, the fuel escaping through the restriction 19 being returned to the fuel reservoir I I or inlet to the transfer pump 10. At least two flats are provided, one of the flats 24 being positioned to ensure that the opening 25 is at least partially open over the full range of angular positions which can be occupied by the sleeve 12. Figure 4 illustrates the sleeve 12 in an angular position in which the collar 20 and opening 25 together form a large restriction to fuel flow, and for a given fuel pressure fuel is only able to escape from the chamber 18 at a low rate. In such circumstances, where the transfer pump is operating at a low speed, as illustrated, the restriction to fuel flow has relatively little effect as described hereiribefore. Where the transfer pump 10 is operating at higher speeds, as the rate at which fuel is able to escape from the chamber 18 is throttled, thus a significant pressure drop occurs across the restriction 19 and the transfer pressure rises.

Figure 5 illustrates the situation where the angular position of the sleeve 12 has been modified, the sleeve 12 being rotated in the direction of the arrow illustrated in Figure 6 to reduce the magnitude of the restriction to fuel flow formed by the restriction 19 defined between the collar 20 and the opening 25. As a result of the restriction to fuel flow reducing as the sleeve 12 is moved from the position illustrated in Figure 4 to that illustrated in Figure 5, 8 the magnitude of the back pressure formed by the restriction 19 reduces under high transfer pump operating speed conditions, thus the transfer pressure falls. Figure 7 illustrates this effect. In Figure 7, when the sleeve 12 occupies the 30' position, the restriction to fuel flow formed between the collar 20 and the opening 25 is high, thus a large back pressure is formed so that when the transfer pump 10 is operating at high speeds, the transfer pressure is relatively high. As the sleeve 12 is moved towards the 0' position, the magnitude of the restriction to fuel flow falls, and as a consequence the back pressure and the transfer pressure also fall. Regardless as to the angular setting of the sleeve 12, as the pump operating speed falls, so the transfer pressure falls, and the effect of the presence of the restriction 19 is reduced.

Although in the description hereinbefore the variable restriction to fuel flow is achieved by modifying the angular position of a sleeve, it will be appreciated that other types of variable fuel flow restriction could be used and the invention covers the use of all such arrangements located downstream of the opening formed in the sleeve. One possibility is described with reference to Figure 8.

Figure 8 illustrates an arrangement in which the magnitude of the restriction to fuel flow of the restriction 19 is governed by the axial position of the sleeve 12. Where the sleeve 12 occupies the position illustrated, a controlled clearance 19a formed between a collar 20 and the bore within which the sleeve 12 defines the restriction 19, and the restriction to flow formed by the restriction 19 is relatively large. If the sleeve 12 is moved in an upward direction in the orientation illustrated, then the controlled clearance 19a will be defined between the collar 20 and a part 2 1 a of the bore 21 of generally 9 conical form. The further the sleeve 12 is lifted, the smaller the restriction to fuel flow becomes, and the transfer pressure is modified accordingly. The sleeve 12 is conveniently in screw threaded engagement within the bore, the axial position of the sleeve 12 being adjusted by rotating the sleeve 12.

Claims (10)

1. A fuel pressure regulator comprising:

a piston member moveable under the influence of the fuel pressure applied thereto to control the degree by which an opening is obscured; a return passage which connects an outlet of a pump to the inlet thereof, the opening being located in the return passage; and an additional flow restrictor located in the return passage downstream of the opening.

2. A fuel pressure regulator according to claim I wherein the additional flow restrictor is arranged to provide a restriction of variable magnitude.

3. A fuel pressure regulator according to claim 1 or claim 2 wherein the piston member is slidable within a sleeve, the additional flow restrictor being adjustable by adjusting the angular position of the sleeve.

4. A fuel pressure regulator according to claim 3 wherein the sleeve is located within a bore formed in a housing such that the sleeve and bore together define at least a part of the return passage, and the angular orientation of the sleeve within the bore is adjustable to vary the magnitude of the additional flow restriction.

11

5. A fuel pressure regulator according to claim 4 wherein the sleeve is provided with a radially outwardly extending collar, provided with one or more deformations, the additional flow restrictor being defined in part by the deformations.

6. A fuel pressure regulator according to claim 1 or claim 2 wherein the piston member is slidable within a sleeve, the additional flow restrictor being adjustable by adjusting the axial position of the sleeve.

7. A fuel pressure regulator according to claim 6 wherein wherein the sleeve is located within a bore formed in a housing such that the sleeve and bore together define at least a part of the return passage, the axial position of the sleeve being adjustable to vary the magnitude of the additional flow restriction.

8. A fuel pressure regulator according to claim 7 wherein the sleeve is provided with a radially outwardly extending collar, a clearance between the collar and the bore defining the additional flow restrictor.

9. A fuel pressure regulator according to claims 6, 7 or 8 wherein the sleeve is in screw threaded engagement within the bore, the axial position of the sleeve being adjusted by rotating the sleeve.

10. A fuel pressure regulator substantially as herein described with reference to the drawings of Figures 2,3,4,5,6,7 and 8.