GB2056720A

GB2056720A - Control valve

Info

Publication number: GB2056720A
Application number: GB8026009A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-08-10
Filing date: 1980-08-08
Publication date: 1981-03-18
Also published as: FR2463448B1; FR2463448A1; IT1132365B; GB2056720B; IT8024072A0

Abstract

A control valve for maintaining the viscosity or the temperature of the fluid in an hydraulic installation constant comprises a pilot valve (34) which is influenced by a temperature sensitive expansible element (37). The pilot valve (34) controls a valve member (29) which, together with the pilot valve, brings the temperature of the pressure medium to the desired value by throttling. The pilot valve is connected in series with the main valve member, and the expansible element (37) is arranged in the pilot valve. The expansible element controls a bypass connection from the inlet to the load which can be, for example, a shaft lubrication device (24). The expansible element moves a control pin (42) out of a bore (45) in the pilot valve member to provide a pressure drop to move the pilot valve member towards its seat (32). <IMAGE>

Description

SPECIFICATION Control valve This invention relates to a control valve for maintaining the viscosity or the temperature of the fluid in an hydraulic installation constant. In one proposal an element of expansible material acts directly on the valve member of the control valve and a small quantity of fluid passes through a throttle and flows around the expansible material element. However, with that arrangement, temperature sensing and temperature control is relatively inaccurate. Furthermore, during blocking of the throttle the fluid becomes over-heated.

The control valve in accordance with the invention comprises an element influenced by the temperature of the fluid, and a pilot valve arranged in the valve housing downstream of the control valve member, the pilot valve accommodating the said element and the said element being arranged to control an additional throttle connection from the inlet to the outlet of the control valve.

The element is preferably an element of expansible material controlling a passage in the pilot valve. The element may also be urged against a shoulder on the pilot valve member by a spring loading the pilot valve.

The control valve member is preferably urged into the closed position by a spring. A throttle bore may be provided in the control valve member for the passage of cold fluid at the start of an hydraulic operation.

The element may also influence a piston for actuating a control pin guided in the pilot valve member, the pin controlling a fluid passage around the pilot valve.

The control pin may be frictionally urged against the piston by a spring. A connection, controllable by the control pin, may be provided in the pilot valve member, the connection providing an additional by-pass around the pilot valve, on breakdown of the element.

In an alternative arrangement in accordance with the invention, a safety member is associated with the control pin and which, on breakdown of the element, is arranged to come into play to establish a by-pass connection to the outlet of the control valve, under the influence of over-heating of the fluid resulting from breakdown of the element.

The safety member may be in the form of a shear pin retained in a hollow member which is urged, together with the control member, against the piston by a spring.

Preferably, the pin is of temperature sensitive plastics material, which is retained in a transverse bore in the control valve member and the ends of which are located in recesses in a bush which is arranged in the hollow member which is located inside the pilot valve.

In order that the invention may be well understood and readily carried into effect, two control valves in accordance therewith will now be described with reference to the accompanying drawings in which: Figure 1 is a longitudinal section through one control valve for maintaining constant the viscosity and/or the temperature of fluid passing through it, and provided with one form of safety device against breakdown of the expansible element; Figure 2 is a similar section through another control valve provided with an alternative safety device against breakdown of the expansible element.

Each of the control valves shown in the drawings comprises a housing 10, through which passes a bore 11 one end of which forms an inlet 1 2 to the control valve. A line 13, into which a pump 14 delivers hydraulic fluid, leads to the inlet 1 2 the fluid being withdrawn through a suction line 1 5 from a reservoir 16. A control bush 17, a valve seat member 1 8 and a spacer sleeve 1 9 are arranged one behind the other in the bore 11 and are urged against a shoulder 22 by a hollow screw 20 provided with a bore 21 passing through it.The end of the bore 21 forms the outlet 26 from the valve from which a line 23 leads to the load 24, for example a shaft lubrication device, a return line 25 being provided back to the reservoir 1 6. It is essential that fluid at the same temperature or viscosity always prevails at the load 24.

A control valve member 29 is sealingly slidingly guided in the bore 28 in the control bush 1 7. It is substantially cup-shaped and has a central throttle 30 which faces the inlet 1 2. The control valve member 29 is urged against the shoulder 22 by a spring 31. The end of the spring 31 remote from the control valve member 29 engages the valve seat member 1 8 on which is formed a valve seat 32 for the valve member 33 of a pilot valve 34. The valve member 33 has a blind bore 35 from which transverse bores 38 lead outwards. An element 37 containing expansible material is located against a shoulder 36 at the open end of the blind bore 35. It is urged against the shoulder 36 by a spring 39 which is located in the bore 21 in the hollow screw 20.The spring 39 acts on the expansible material element through a spring plate 40 and simultaneously urges the valve member 33 onto its shoulder 32.

In the control valve of Fig. 1, the expansible element 37 has a piston 41 against which a control pin 42 engages frictionally. The transmission of force is achieved by a spring 43 which always urges the control pin 42 against the piston 41 through a spring plate 44. Coaxially with the bore 35 in the valve member 33, a bore 45 is provided in which the control pin 42 is guided. On one side, it is flattened so that between it and the wall of the bore there is a gap 46. However, this flattening does not extend over the entire length of the control pin 42 which has a flange 47 at its end which fills the entire cross-section of the bore 45. A plurality of transverse bores 49 formed in the valve member 33 issue into the bore 45. The bores 49 issue behind the seat 32 when it is engaged by the valve member 33.

In the vicinity of the shoulder 22 in the bore 28, an annular groove 50 is formed from which transverse bores 51 proceed and which issue into an annular chamber 52 which extends almost up to the end of the spacer sleeve 19. The annular chamber is formed by a bore 52' extending concentrically with respect to the bore 11 and the parts 17 to 19.

Likewise, at the end of the spacer sleeve, a plurality of transverse bores 53 are formed which issue from the annular chamber 52 into a chamber referenced 54 in which is arranged the expansible element 37. The space behind the control valve member 29 is referenced 55.

Hydraulic fluid delivered by the pump 14 enters the inlet 1 2 into the valve housing 10 and influences the valve member 33 of the pilot valve 34 through the throttle bore 30 in the control valve member 29. At the start of operations, the fluid is cold so that the piston 41 of the expansible material element 37 is retracted and the flange 47 closes the bore 45. With a further increase in pressure, the valve member 33 is raised from its seat 32 against the force of the pre-tensioned spring 39 and fluid flows through the throttle bore 30 and the pilot valve 34 to the outlet 26 and to the load 24. Then, due to the pressure drop at the throttle 30, the valve member 29 is pushed towards the pilot valve 34 against the force of the spring 31 so that communication from the inlet 1 2 to the annular groove 50 is established.From here, fluid arrives through the annular chamber 52 and the transverse bores 53 in the chamber 54 and spreads over the expansible element 37 therein. On reaching the desired maximum operating temperature for the fluid, the piston 41 of the expansible element 37 extends and displaces the control pin 42. After moving a certain distance, the flange 47 leaves the bore 45 whereby a by-pass connection is provided, that is to say, fluid can then arrive through the gap 46 into the interior of the valve member 33 and from whence it flows through the transverse bores 38 into the chamber 54.

With an increase in temperature of the fluid, the valve member 33 is again urged onto its seat 32 by the spring 39 due to the reduction in the pressure drop at the pilot valve 34. The piston 41 is extended still further out of the expansible element 37, and acts further on the control pin 42. Thus, the by-pass is opened still further until the temperature of the fluid has been stabilised. The pressure drop between the inlet 1 2 and the outlet 26 is then controlled by the by-pass opening of the flange 47 with respect to the bore 45, in accordance with the temperature of the fluid. Temperature fluctuations occurring during operation are thus smoothed out.

The heating of the fluid takes place by throttling at the control valve member 29 or at the pilot valve 34.

Should it happen that the fluid leaks from the expansible element 37, then the control pin 42 is displaced towards the piston 41 so far to the left by the influence of the hydraulic fluid, that a communication exists from the chamber 55 to the transverse bores 49. Hydraulic fluid can then flow out of the chamber 55 to the chamber 54. To the same extent, the control valve member 29 is also displaced further against the force of the spring 31 and allows fluid to flow unthrottled from the supply 1 2 through the annular chamber 52 to the outlet 26. In that way, over-heating of the fluid due to a defective expansible element is excluded.

In the control valve of Fig. 2, the pin 42 frictionally engages the piston 41 of the expansible element 37, as in the arrangement of Fig. 1. The transmitted force is achieved by the spring 43 which acts on a hollow member 44'- which is connected to the control pin 42 by means of a snap ring 45'. At the end facing the piston 41, the control pin 42 has a transverse bore 47 in which is retained a pin 48 of, for example, plastics material, the ends of which penetrate into transverse bores in a small bush 49 which is slidingly arranged on the control pin 42 within the hollow member 44'. A spacer bush 50' is also arranged between the bush 49 and the expansible element 37. A plurality of through transverse bores 52 are located in the lower part of the hollow member 44'.

A bore 55', in which the control pin 42 is guided, is connected coaxially to the bore 35 in the valve member 33. At its lower part, the bore 55' has a plurality of longitudinal grooves 56 which do not however extend completely up to its end so that a flange 57 remains at the end which completely fills the entire cross-section of the bore 55'. A plurality of transverse bores 59 formed passing through the closure member 33 issue into the bore 55' in the vicinity of its end. They issue behind the seat 32 when the valve member 33 engages the seat 32. In the vicinity of the shoulder 22, an annular groove 60 is formed in the bore 28, transverse bores 61 proceeding from the annular groove which issue into an annular chamber 62 which extends almost to the end of the spacer sleeve 1 9.

The annular chamber 62 is formed by a bore 63 extending concentrically with respect to the bore 11 and the parts 17 to 19. A plurality of through transverse bores 64 are likewise formed at the end of the spacer sleeve 1 9 the transverse bores issuing from the annular chamber 62 into a chamber 65 in which is located the expansible element 37.

The space behind the control valve member 29 is referenced 67. Once again, a plurality of through transverse bores 69 are provided in the centre of the sleeve 1 9.

The hydraulic fluid delivered by the pump 14 is forced through the inlet 1 2 into the valve housing 10 and influences the closure member 33 of the pilot valve 34 through the throttle bore 30 in the control valve member 29. At the start of operations, the fluid is cold so that the piston 41 of the expansible element 37 is retracted and the flange 57 on the control pin 42 closes the bore 55'. With a further increase in pressure, the valve member 33 is raised from its seat 32 against the force of the pretensioned spring 39 and fluid flows through the throttle bore 30 and the pilot valve 34 to the outlet 26 and to the load 24.

Due to the pressure drop at the throttle 30, the valve member 29 is then pushed towards the pilot valve 34 against the force of the spring 31 so that communication from the inlet 1 2 to the annular groove 60 is established. From here, the fluid arrives, through the annular chamber 62 and the transverse bores 64, in the chamber 65 and therein spreads over the expansible element 37. On reaching the desired maximum operating temperature for the fluid, the piston 41 of the expansible element 37 is extended and displaces the control pin 42. After a certain distance, the flange 57 leaves the bore 55' whereby a by-pass connection is provided, that is to say, fluid can then arrive also in the interior of the valve member 33 through the longitudinal grooves 56 and likewise flow from there through the transverse bores 59 into the chamber 65.With an increase in temperature of the fluid, the valve member 33 is urged by the spring 39 onto its seat 32 once again, due to the decrease in the pressure drop at the pilot valve 34. The piston 41 is pushed out of the expansible element 37 still further and acts on the control pin 42.

Thus, the by-pass is opened to a greater extent and indeed until the temperature of the fluid has stabilised. The pressure drop between the inlet 1 2 and the outlet 26 is then controlled, in accordance with the temperature of the fluid, by the by-pass opening at the flange 57 with respect to the bore 56. If the temperature of the fluid falls, then the bore 56 becomes closed by the flange 57 and the temperature of the fluid rises again due to the resulting throttling.

If it should happen that the expansible material element breaks down due, for example, to leakage of expansible fluid therefrom, then the throttle effect of the control valve still prevails and the fluid is heated still further. At a predetermined temperature level above the desired level, for example 20 or 30"C, the plastics pin 48 rapidly loses its strength and is broken off by the pressure acting on the control pin 42 from the chamber 67 and is urged towards the piston 41 of the expansible element 37. The piston 41 then enters the expansible element 37, the control pin 42 follows due to the spring 43 and indeed until the flange 57 opens the communication to the transverse bores 59 through the bore 55'.

Thus, a new by-pass connection or neutral circulation is provided from the chamber 67 to the chamber 65 which prevents a further throttling and thus prevents a temperature increase of the fluid.

As long as the expansible element 37 is intact, its piston 41 is extended at an appropriate temperature. Thus, no force acts on the sleeve 49 and on the pin 48 either. Even when the pin 48 then loses its strength as a result of higher temperature, it is not broken off.

In the control valves described above, the temperature of the hydraulic fluid is held constant at a predetermined value. Blocking of the control valves is also avoided so that overheating of the fluid does not occur. The hydraulic fluid is, however, brought to operating temperature rapidly and maintained at or near that temperature.

Both control valves have means safeguarding the temperature and viscosity of the hydraulic fluid, should the expansible element leak or otherwise break down. This is achieved by controlling a by-pass flow through the valve and in Fig. 2 an additional safeguard is provided by a safety member, for example a frangible plastics member, which comes into play under the influence of overheated fluid to provide a further by-pass for fluid through the valve.

Claims

1. A contrdl valve for maintaining the viscosity or the temperature of the fluid in an hydraulic installation constant by throttling the fluid at the control valve member, comprises an element influenced by the temperature of the fluid, and a pilot valve arranged in the valve housing downstream of the control valve member, the pilot valve accommodating the said element and the said element being arranged to control an additional throttle connection from the inlet to the outlet of the control valve.

2. A control valve according to claim 1, in which the element is an element of expansible material controlling a passage in the pilot valve.

3. A control valve according to claim 1 or claim 2, in which a spring, loading the pilot valve, urges the element against a shoulder on the pilot valve member.

4. A control valve according to any one of claims 1 to 3, in which a throttle bore is formed in the control valve member and the control valve member is influenced by a spring.

5. A control valve according to any one of claims 1 to 4, in which the element is arranged to influence a piston for actuating a control pin guided in the pilot valve member and controlling a fluid passage around the pilot valve.

6. A control valve according to claim 5, in which the control pin is frictionally urged against the piston by a spring.

7. A control valve according to claim 5 or claim 6, in which a connection controllable by the control pin is provided in the pilot valve member, the connection providing an addi tional by-pass around the pilot valve, on breakdown of the element.

8. A control valve according to any one of claims 5 to 7, in which a safety member associated with the control pin is arranged to establish a by-pass connection to the outlet of the control valve, under the influence of over heated fluid resulting from breakdown of the element.

9. A control valve according to claim 6 and claim 8, in which the safety member is a shear pin retained in a hollow member which is urged, together with the control member, against the piston by a spring.

10. A control valve according to claim 9, in which the safety member is a pin of temperature sensitive plastics material, which is retained in a transverse bore in the control valve member and the ends of which are located in recesses in a bush which is arranged in the hollow member which is located inside the pilot valve.

11. A control valve substantially as herein described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.