GB2115755A

GB2115755A - Improvements in fluid flow regulators

Info

Publication number: GB2115755A
Application number: GB08200945A
Authority: GB
Inventors: Anthony William Harrison
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-01-13
Filing date: 1982-01-13
Publication date: 1983-09-14
Also published as: FR2519720A1; GB2115756B; FR2519781B1; GB2115756A; FR2519781A1; GB2115755B

Abstract

A fluid flow regulator for use in a vehicle hydraulic suspension system has a constant restriction (5) connected in series with a variable restriction (9) defined between two relatively movable members (2, 3). Fluid flow through the regulator produces a pressure differential across the constant restriction (5) which controls relative movement of the members (2, 3) to determine the size of the variable restriction (9) such that an increase in the pressure differential causes a reduction in the size of the variable restriction (9). Resilient means (11, 12) is operative to bias a movable one (3) of the relatively movable members (2, 3) against the action of the pressure differential across the constant restriction (5) for each direction of fluid flow through the regulator, so that for each direction of fluid flow, relative movement of the relatively movable members (2, 3) is controlled such that an increase in the pressure differential causes a reduction in the size of the variable restriction (9). <IMAGE>

Description

SPECIFICATION Improvements in fluid flow regulators This invention relates to fluid flow regulators of the kind having a constant restriction connected in series with a variable restriction defined between two relatively movable members, fluid flow through the regulator producing a pressure differential across the constant restriction which controls relative movement of the members to determine the size of the variable restriction such that an increase in the pressure differential causes a reduction in the size of the variable restriction.

Known fluid flow regulators of the kind set forth comprise a movable piston working in a fixed bore, with the piston biassed against the action of the pressure differential across the constant restriction for one direction only of fluid flow through the regulator. Such a regulator can regulate the fluid flow, using the variable restriction, in one direction only and any flow in the opposite direction cannot be so regulated, as the flow will be dependent only on the characteristics of the constant restriction. If it is necessary to control fluid flow in both directions, two oppositely-acting regulators are needed, each with an associated one-way valve to prevent unregulated flow. The construction of a two-way regulator is therefore relatively complex and expensive to produce.

According to one aspect of our invention, a fluid flow regulator of the kind set forth incorporates resilient means which is operative to bias a movable one of the relatively movable members against the action of the pressure differential across the constant restriction for each direction of fluid flow through the regulator.

The regulator is therefore able to regulate fluid flow in each direction using a variable restriction.

The construction of a two-way regulator is therefore simplified, and is cheaper to produce.

Preferably the resilient means comprises two oppositely-acting resilient members, each acting to bias the movable member against the action of the pressure differential for one direction of flow.

The resilient members conveniently comprise compression springs. Such springs may be caged, which ensures that the inactive spring, that is the spring which tends to bias the movable member in the same direction as the action of the pressure differential, does not affect the movable member.

Alternatively, the resilient means may comprise a single resilient member, such as a spring, which works in compression for one direction of fluid flow, and in tension for the other direction.

The resilient means may be arranged to exert different loads in each of the two directions so as to produce a different flow rate in one direction from that in the opposite direction.

The flow rates may also be arranged to differ by selection of a suitable profile for the constant restriction, to provide a different coefficient of discharge (Cd) according to the direction of fluid flow.

The relatively movable members may comprise a movable piston working in a bore, the bore wall comprising a fixed member. The constant restriction is provided in a bore in the piston, and the variable restriction is defined between a radial passage leading to the bore, and an annular recess on the piston which communicates with the piston bore.

In a preferred construction the resilient means comprises springs acting on opposite ends of the piston through abutment members. The abutment member of the inactive spring engages with a step in the bore so that the inactive spring does not affect the piston.

In a second construction the resilient means comprises a single spring attached at one end to the piston and at the other to a fixed member. The spring may be adjustable in length.

A further aspect of our invention relates to vehicle hydraulic suspension systems of the kind in which a vehicle body is supported by hydraulic suspension struts including suspension springs, the length of the struts being adjustable, by displacement of hydraulic fluid into and out of the struts, to raise and lower the vehicle body.

A suspension system of this kind may be used on buses to lower the body when the bus is stationary to facilitate the entry and exit of passengers, and then to raise the body before the bus moves off. In such a system two or more struts are operated from a common supply of fluid.

It is important to ensure that the attitude of the body is stable when it is being lowered or raised, which means that the rate of adjustment of the length of all the struts must be controlled, and must be independent of the loading on the struts.

If the rate is not controlled, fluid tends to displace more quickly into a lightly loaded strut than into a heavily loaded one, when the body is being raised, and more quickly out of a heavily loaded strut than out of a lightly loaded one during a lowering operation. Clearly, this would alter the attitude of the body during adjustment.

According to the further aspect of the invention, a vehicle hydraulic suspension system of the kind set forth has at least two hydraulic struts operated from a common supply of hydraulic fluid, and each strut has an associated control member, located between the supply and the strut, and movable through a limited distance in order to control displacement of fluid into and out of the associated strut, movement of each control member being responsive to the pressure differential across the control member, and the system incorporates synchronising means for synchronising operation of the control members to provide an equal rate of adjustment of the length of all the struts.

Thus the provision of the synchronising means ensures that the attitude of the body is stable during adjustment of the length of the struts.

Conveniently the pressure of the fluid in the supply is increased in order to raise the body, and is decreased in order to lower the body. The supply is normally at a relatively high pressure to keep the body in its raised position.

Preferably each control member comprises a displacement piston which is able to move freely between opposite ends of an associated bore, and is exposed on one side to the pressure of the supply, and on the other side to the fluid in the associated strut.

The synchronising means comprises two-way fluid flow regulators, with one regulator being located between each control member and its associated strut. Conveniently, the regulator comprises the regulator according to the first aspect of our invention. With such a regulator when the body is to be lowered, for example, the strut with the most load has the greatest pressure differential across its control member and across the constant restriction of its regulator, so that the fluid flow into the strut through the regulator is the most restricted, thus ensuring that the rate of adjustment of the struts is equal.

Alternatively, the synchronising means comprises a mechanical connection between the control members, which ensures that they move at the same rate to control the rate of adjustment.

Embodiments of each aspect of our invention are shown in the accompanying drawings, in which: Figure 1 is a longitudinal section through a fluid flow regulator; Figure 2 shows the regulator of Figure 1 in a different mode of operation: Figure 3 shows a fourth fluid flow regulator; and Figure 4 shows a schematic representation of vehicle hydraulic suspension system.

The regulator shown in Figures 1 and 2 comprises a housing 1 provided with a stepped bore 2, in which a piston 3 works. The piston 3 and the wall of the bore 2 comprise the relatively movable members of the regulator. The piston 3 has a bore 4, which forms a constant restriction 5 at one end. When fluid flows through the bore 4 and through the constant restriction 5 a pressure drop occurs across the constant restriction 5, and the pressure differential acting on the piston 3 controls the movement of the piston 3 in the bore 2. Radial passages 6 lead from the piston bore 4 to an annular recess 7 on the piston 3. The annular recess 7, together with a passage 8 in the housing 1 leading to the bore 2 defines a variable restriction 9 between one edge of the recess 7 and a corresponding oppositely facing wall of the passage 8.A further passage 10in the housing 1 leads from the bore 2, so that fluid flow into and out of the regulator is by the passages 8 and 1 0.

The piston 3 is biassed against the action of the pressure differential for each direction of fluid flow by resilient means comprising first and second compression springs 11 and 1 2 respectively. Each spring 11, 12 is caged, and abuts at its outer end against the housing 1, and its inner end against an annular abutment ring 13, 14. Each spring is able to act on the piston 3 through a respective abutment ring 13, 14, against the action of the pressure differential on the piston 3 for one direction of fluid flow. Thus each spring 11, 12 is active for one direction of fluid flow only, as can be seen in Figures 1 and 2, spring 11 being active in Figure 1, and spring 12 in Figure 2.For the other direction of fluid flow the spring is inactive, and does not affect the piston 3 as the annular ring 1 3 or 14 abuts a step 15 or 16 in the bore 2.

The regulator is shown in two of its operative positions in Figures 1 and 2. In Figure 1 fluid flows into the regulator through passage 8, through the variable restriction 9, then through the constant restriction 5 and flows out through passage 10.

Fluid flow through the constant restriction 5 creates a pressure drop across the restriction, with the pressure on the upstream side being greater than that on the downstream side of the restriction 5. The pressure differential acts on the piston 3 to move it against the action of the active spring 11, thus varying the size of the variable restriction 9. Clearly, the greater the pressure differential across the constant restriction 5, the smaller the size of the variable restriction 9 becomes. The spring 12 is inactive, as the annular ring 14 is in abutment with the step 1 6 in the bore 2.

In Figure 2 the fluid flow is in the opposite direction, and the operation of the regulator is similar to that of Figure 1, with the spring 12 being active to bias the piston 3 against the action of the pressure differential to control the size of the variable restriction 9, and the spring 11 being inactive.

The embodiment described above uses caged springs but in a modification, any other type of resilient means could be used, such as uncaged springs. However, two requirements affecting the resilient means must be taken into account, and these requirements mean that the use of caged springs has some advantages.

Firstly, it is desirable to minimise the lostmotion in the travel of the piston which occurs when the direction of fluid flow is reversed, that is the distance the piston travels between a position in which the variable orifice is just fully open for one direction of the fluid flow, and a similar position for the other direction of fluid flow.

Secondly, it is desirable to maintain a uniform flow of fluid through the regulator. If uncaged springs are used, a high spring rate is necessary to minimise the lost-motion in the piston travel, but a low spring rate is necessary to maintain uniform flow. Thus if uncaged springs are used the spring rate has to be a compromise with respect to these two requirements. However, if caged springs are used the first requirement can be met by the provision of the abutments for the springs (such as 15, 16 in Figures 1 and 2), which ensures that the lost-motion is minimised, while the spring rates can be chosen to ensure uniform fluid flow.

Thus the use of caged springs, as in the embodiment of Figures 1 and 2, has the advantage that the regulator operates efficiently, and also gives freedom from the effect of manufacturing tolerances.

The regulator shown in Figure 3 is a modification of that shown in Figures 1 and 2, and corresponding reference numerals have been applied to corresponding parts.

Thus the regulator of Figure 3 has a housing 1, provided with a bore 2 in which a piston 3 works.

The passages 8 and 10 are similar to those of Figure 1, as are the constant restriction 5 and the variable restriction 9.

The resilient means which biasses the piston against the action of the pressure differential for each direction of fluid flow comprises a single spring 17, which acts both in compression and tension. The ends 18, 1 9 of the spring 1 7 are of reduced diameter and pitch, and each end has a projection part 20, 21 respectively. The end 18 is mounted on a threaded extension 22 of the piston 3, and the end 19 is mounted on a threaded extension 23 of a plug member 2 which is screwed into one end of the bore 2. Normaliy the ends 18, 1 9 of the spring 17 grip their respective extensions 22, 23, in order that forces can be transmitted between the piston 3 and the spring 1 7 in both directions in operation.However, the length of the spring 1 7 can be adjusted by rotating the extensions 22, 23. The piston 3 is provided with slots 25 on the end opposite the extension 22 which can be used to assist in the adjusting operation.

The operation of the regulator of Figure 3 is similar to that of Figures 1 and 2. The length of the spring 1 7 is adjusted initially to ensure that the inoperative position of the piston 3 is correct, as shown in Figure 3.

In operation, when fluid flows into the regulator through the passage 8, the pressure differential across the constant restriction 5 acts to move the piston 3 towards the passage 10. The spring 17 acts in tension against the action of the pressure differential to regulate the size of the variable restriction 9. With fluid flow in the opposite direction the spring 1 7 acts in compression on the piston 3 against the action of the pressure differential.

Figure 4 is a schematic representation of a vehicle hydraulic suspension system incorporating the two-way fluid flow regulators of Figures 1 and 2 or Figure 3.

The system of Figure 4 is adapted to support a vehicle body (not shown), and has four hydraulic suspension struts 26, 27, 28, 29, each of which includes a gas or steel spring (not shown) for use in normal suspension operation. The length of each strut is adjustable, by displacing hydraulic fluid into and out of the struts, to raise and lower the vehicle body. The lengths of the struts 26, 27, 28,29 is adjusted from a common supply of fluid 30. Each strut is connected to the supply 30 through an associated control member 31,32,33, 34 each of which comprises a displacement piston 25 which has limited movement in a cylinder 36, the movement being controlled by the pressure differential across it. A synchronising means 37 is provided, in the form of a two-way fluid regulator 38 located between each strut and its associated control member.The synchronising means 37 ensures that the rate of adjustment is the same for each strut, independent of the loads on the struts.

The synch ronising means 37 thus equalises the rate of adjustment of the struts, in order to maintain the body in a stable attitude during the raising and lowering operations. If the rates were not equalised, fluid would tend to displace more quickly into a lightly loaded strut than into a more heavily loaded one, but less quickly out of the lightly loaded strut than out of the more heavily loaded one. Clearly, this would alter the attitude of the body during adjustment. Preferably each fluid flow regulator 38 comprises that shown in Figures 1 and 2.

A system such as this is suitable for use on a bus. When the bus is moving the body is in a raised postion, but it can be lowered when the bus is stationary to facilitate the entry and exit of the passengers.

Thus in operation, the pressure of the fluid in the supply 30 is higher than that in the struts 26, 27, 28, 29, so that each displacement piston 35 abuts the right hand end of its cylinder 36.

When the body is to be lowered, requiring fluid to be displaced from the struts, the pressure of the fluid in the supply 30 is reduced rapidly, to a value below the pressure of the fluid in the struts. This reverses the pressure differential across the displacement pistons 35 so that they move leftwardly, allowing fluid to be displaced from the struts, through the regulators 38. The regulators 38 act to ensure that the rate of adjustment is the same for all the struts. Thus if one strut, say 26, is more heavily loaded than the others, the pressure differential between the supply 30 and that strut 26 will be greater than that for the other struts.Fluid tends therefore, to be displaced more quickly from the strut 26 than from the others, but the regulator restricts the fluid flow, ensuring that the rate of adjustment will be the same as for the other struts, irrespective of their individual loading.

Similarly, when the body is to be raised, the pressure of the supply 30 is increased rapidly again, which operates the displacement pistons 35 to displace the fluid into the struts through the regulators 38, which act to synchronise the rate of adjustment of the length of the struts.

Using the two-way fluid flow regulators 38 means that the construction of the system is relatively simple.

In a modification (not shown), the synchronising means comprises a mechanical interconnection between the displacement pistons 35 to ensure that they move at the same rate, which thus means that the rate of adjustment of all the struts is the same.

The system shown in the drawing has four struts, but clearly any suitable number of struts, above the minimum of two, could be operated from the fluid supply 30. The struts may have equal effective areas, or they may have different effective areas corresponding to the weight distribution of the vehicle. In the latter case the areas or the strokes of the displacement pistons may be altered to accommodate the different volumes of fluid which are displaced during adjustment. The suspension struts may also be of the self-levelling type, which include means for automatically maintaining the attitude of the body, regardless of changes in load on the body.

Claims

1. A fluid flow regulator of the kind set forth, incorporating resilient means operative to bias a movable one of the relatively movable members against the action of the pressure differential across the constant restriction of each direction of fluid flow through the regulator.

2. A fluid flow regulator as claimed in claim 1, in which the resilient means comprise two oppositely-acting resilient members, each acting to bias the movable member against the action of the pressure differential for one direction of flow.

3. A fluid flow regulator as claimed in claim 2, in which the resilient members comprise compression springs.

4. A fluid flow regulator as claimed in claim 3, in which the springs are caged, to ensure that the inactive spring, that is the spring which tends to bias the movable member in the same direction as the action of the pressure differential, does not affect the movable member.

5. A fluid flow regulator as claimed in claim 1, in which the resilient means comprises a single resilient member. which works in compression for one direction of fluid flow, and in tension for the other direction.

6. A fluid flow regulator as claimed in claim 5, in which the resilient member comprises a spring.

7. A fluid flow regulator as claimed in any preceding claim, in which the resilient means is arranged to exert different loads in each of the two directions of fluid flow.

8. A fluid flow regulator as claimed in any preceding claim in which the relatively movable members comprise a movable piston working in a bore, the bore wall comprising a fixed member, with the constant restriction being provided in a bore in the piston, and the variable restriction being defined between a radial passage leading to the bore, and an annular recess on the piston which communicates with the piston bore.

9. A fluid flow regulator as claimed in claim 4 and claim 8, in which the springs act on opposite ends of the piston through abutment members, with the abutment member of the inactive spring engaging with a step in the bore.

10. A fluid flow regulator as claimed in claim 6 and claim 8, in which the spring is attached at one end to the piston, and at the other end to a fixed member.

11. A fluid flow regulator as claimed in any preceding claim, in which the regulator is incorporated in a vehicle hydraulic suspension in which a vehicle body is supported by hydraulic suspension struts including suspension springs, the length of the struts being adjustable, by displacement of hydraulic fluid into and out of the struts through the regulator.

12. A vehicle hydraulic suspension system of the kind set forth, having at least two hydraulic struts operated from a common supply of hydraulic fluid, and each strut has an associated control member, located between the supply and the strut, and movable through a limited distance in order to control displacement of fluid into and out of the associated strut, movement of each control member being responsive to the pressure differential across the control member, and the system incorporates synchronising means for synchronising operation of the control members to provide an equal rate of adjustment of the length of all the struts.

13. A vehicle hydraulic suspension system as claimed in claim 12, in which the pressure of the fluid in the supply is increased in order to raise the body, and is decreased in order to lower the body, with the supply is normally at a relatively high pressure to keep the body in its raised position.

14. A fluid flow regulator substantially as herein described with reference to and as illustrated in Figure 3 of the accompanying drawings.

14. A vehicle hydraulic suspension system as claimed in claim 12 or claim 13, in which each control member comprises a displacement piston which is able to move freely between opposite ends of an associated bore, and is exposed on one side to the pressure of the supply, and on the other side to the fluid in the associated strut.

1 5. A vehicle hydraulic suspension as claimed in any of claims 12 to 14, in which the synchronising means comprises two-way fluid flow regulators, with one regulator being located between each control member and its associated strut.

16. A vehicle hydraulic suspension system as claimed in any of claims 12 to 14, in which the synchronising means comprises a mechanical connection between the control members, which ensures that they move at the same rate to control the rate of adjustment.

New claims or amendments to claims filed on 1 7 December, 1982.

Superseded claims 1,8,11,12,13,14,15,16.

New or amended claims:

1. A fluid flow regulator of the kind set forth, incorporating resilient means operative to bias a movable one of the relatively movable members against the action of the pressure differential across the constant restriction for each direction of fluid flow through the regulator, so that for each direction of fluid flow, relative movement of the relatively movable members is controlled such that an increase in the pressure differential causes a reduction in the size of the variable restriction.

8. A fluid flow regulator as claimed in any preceding claim, in which the relatively movable members comprise a movable piston working in a bore in a housing, the bore wall comprising a fixed member, with the constant restriction being provided in a bore in the piston, and the variable restriction being defined between a passage in the housing leading to the bore in the housing, and an annular recess on the piston which communicates with the piston bore.

11. A fluid flow regulator as claimed in claim 10, in which the said one end of the spring is mounted on a threaded extension of the piston and the said other end is mounted on a threaded extension of a plug member which is screwed into one end of the bore in the housing, the extensions being rotatable, thereby enabling the effective length of the spring to be adjusted.

12. A fluid flow regulator as claimed in any preceding claim, in which the regulator is incorporated in a vehicle hydraulic suspension system in which a vehicle body is supported by hydraulic suspension struts including suspension springs, the length of the struts being adjustable, by displacement of hydraulic fluid into and out of the struts through the regulator.

1 3. A fluid flow regulator substantially as herein described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.