GB1582435A - Hydraulic control system - Google Patents

Description

(54) HYDRAULIC CONTROL SYSTEM (71) We, KONTAK MANUFACTURING COMPANY LIMITED, a British company, of Belton Park, Londonthorpe Road, Grantham, Lincolnshire, NG3 1 9SJ, Great Britain, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a hydraulic control system having a hydraulic directional control valve operated by a cable assembly.

With the introduction of so-called "Quiet Cab Legislation" governing the manufacture of tractors and the like vehicles (hereinafter referred to as "tractors") it has been found necessary to produce operating mechanisms for hydraulic valves on tractors which enable the valves to be mounted externally of the cab while enabling remote and precise operation from within the cab. The simplest and cheapest method of effecting such operation is by means of a cable assembly.

Hitherto, operating cable assemblies for transmitting motion in mutually opposite directions, that is on a "push-pull" basis, to hydraulic directional control valves and the like, have consisted, basically, of a fixed flexible sheath wherein slides a motiontransmitting flexible cable. Such assemblies are known by the name "Bowden mechan isms".

A disadvantage of previously proposed cable assemblies is that clearance between the inner surface of the sheath and the motion-transmitting cable gives.rise to lost motion in changing from the push mode to the pull mode and vice versa. One previously proposed solution to mitigate this problem is to minimise the aforementioned clearance using components manufactured to close tolerances; and to employ relatively heavy duty components, the sheath and cable diameters being larger than is strictly necessary according to the dictates solely of the magnitude of the forces to be transmitted. Another previously proposed solution is to introduce rolling elements, for example, balls, between the sheath and the cable or inner motion-transmitting member.

Both of these solutions are relatively costly, and both tend to increase the minimum practical bend radius at any place in the assembly.

According to the present invention, there is provided a hydraulic control system comprising a hydraulic directional control valve which includes a control member in the form of a spool having a positive neutral position and which is operated by a cable assembly, said assembly comprising an actuator, a tubular sheath, a flexible motion transmitting operating cable disposed within said sheath, one end of said cable being connected to said actuator and the other end being connected to said spool, first and second flanged collars fitted to said one end and said other end of the cable, respectively, a first spring means located within a first housing adjacent said actuator and acting between said first flanged collar and an inner face of said first housing, and a second spring means located within a second housing adjacent the spool and acting between said second flanged collar and said second housing, said first and second spring means acting in opposite directions to tension said cable and exert balanced forces on said cable when said spool is in the neutral position.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:--- Fig. 1 shows, in partly sectioned side elevation, a hydraulic control system including a directional control valve having an operating mechanism including actuating and actuated devices mutually interconnected by a cable assembly in accordance with the present invention Fig. 2 is a sectional elevation of a detail marked 'A' in Fig. 1; and Fig. 3 is a view corresponding to Fig. 1 of a second embodiment of the invention.

In the drawings, an operating cable assembly including input and output units 10 and 11 respectively interconnects an actuating device in the form of a manually operable operating lever 12, and an actuated device in the form of a two-way hydraulic directional control valve 13 (only part of which is seen in Fig. 1). The units 10 and 11 are interconnected by means of a sheath in the form of a seamless steel tube 14 in which a flexible motion-transmitting multiwire-strand cable 15 is slidable.

The control or operating lever 12 is shown in Fig. 1 in a centre or neutral position and is pivoted on a pivot pin 16 so that it can be moved to either of forward and reverse positions denoted by lines 12A and 12B respectively. The pivot pin 16 extends between two cheeks, one of which is indicated by reference numeral 17, which are formed as extensions of the- left-hand portion of the unit 10. The lower portion of the control lever 12 is cross-slotted; one slot straddling a stepped slider or plunger 18 which is axially slidable in a bore 19 in the unit 10; the other slot 20 engaging a gudgeon pin 21 on the plunger 18 so that operation of the control lever 12 shifts the plunger 18 axially in the unit 10.

The hydraulic control valve 13 is a conventional valve having a valve spool 22 which is shown, in Fig. 1, in a centred or neutral position, and which is axially slidable to select forward and reverse flows in known manner.

The unit 10 has a cylindrical recess or bore 23 the outer end of which is closed by a plug 24 retained by a circlip 25. The middle portion of the plunger 18 carries a flanged sleeve 26 the flanged end of which abuts the wall at the left-hand end of the bore 23. The right-hand end portion of the plunger 18 carries a washer 27 which abuts the inner face of the plug 24 and also a circlip 28 on the plunger 18. An inner centring compression spring 29 extends between the washer 27 and the flanged portion of the sleeve 26; and an outer counterbalance compression spring 30 extends between the inner face of the plug 24 and the flanged portion of the sleeve 26. The sleeve 26 and the washer 27 constitute stops to limit axial movement of the plunger 18, the range of movement being determined by the gap between the washer 27 and the right-hand end face of the sleeve 26. The adjacent end of the sheath tube 14 is received in a recess in the outer face of the plug 24. The plunger 18 is drilled through axially to receive the cable 15 which is secured to the plunger 18, in the manner illustrated in Fig. 2, by means of a compression type fitting consisting of a threaded compresser member 31 and a deformable collar element 32 which grips the cable 15.

The unit 11 consists of a hollow cylindrical housing 33 the right-hand end of which is secured to the body of the valve 33. A cylindrical connector member 34 is slidable axially within the housing 33 and has a threaded stem 35 which is screwed into the end of the valve spool 22. The output end of the cable 15 is anchored to the connector 34 by means of an end nipple 36 and locking pin 37. The sheath tube 15 is fixed to the left-hand end face of the housing 33 by way of a threaded adjuster 38. An operating compression spring 39 extends between the connector 34 and the left-hand inner end face of the housing 33.

The sheath tube 14 is commercially available hydraulic conduit, typically " outside diameter and i" bore, popularly used in vehicle braking systems. Such tubing is relatively inexpensive and is readily bent to desired configurations without kinking.

To install the sheath tube 14 and cable 15 after the actuating and actuated devices are located, a stock length of tubing is bent to the desired path configuration, cut to length as required, fitted with a cable 15 and assembled as illustrated in the drawings. The output end is assembled first, surplus cable 15 being severed adjacent the compressor member 31 after the latter has been tightened.

The springs 30 and 39 maintain the cable 15 always in tension and therefore to a constant path within the sheath tube 14. These two springs also are selected to balance each other in the neutral position. The spring 29 is provided for positive centring.

The stops constituted by the sleeve 26 and the washer 27 isolate the cable 15 from loadings other than loads determined by the springs and by friction in the valve 13; that is, overloading by excessive force applied to the control lever 12 is avoided. Thus, precision of control is not subject to unpredictable cable loadings.

Fig. 3 shows an alternative embodiment of the invention, similar parts being designated by the same reference numerals. In this embodiment the valve 13 is a selector valve so that no provision is made for spring centring of the valve spool 22. Moreover, the unit 11 is partially moulded integrally with the valve body and is provided with an end cap 11A held in position by a circlip 11B, the adjuster 38 being provided at the operating lever 12 end of the cable. The operating lever 12 has three positions as before but is mechanically locked in each position by lifting the lever knob against a spring (not shown) and moving the lever through a gate 45 to the desired position. Release of the knob locks the lever in that position. The pivot pin 16 has mounted thereon a bellcrack 46 arrangement, one side of which is pivotally connected to the cable 15 and the other end of which is acted on by the counterbalance spring 30 which counteracts the load applied by the spring 39 resulting in constant lever loads while maintaining the cable in tension at all times as the lever moves the spool of the selector valve.

WHAT WE CLAIM IS: 1. A hydraulic control system comprising a hydraulic directional control valve which includes a control member in the form of a spool having a positive neutral position and which is operated by a cable assembly, said assembly comprising an actuator, a tubular sheath, a flexible motiontransmitting operating cable disposed within said sheath, one end of said cable being connected to said actuator and the other end being connected to said spool, first and second flanged collars fitted to said one end and said other end of the cable, respectively, a first spring means located within a first housing adjacent said actuator and acting between said first flanged collar and an inner face of said first housing, and a second spring means located within a second housing adjacent the spool and acting between said second flanged collar and said second housing, said first and second spring means acting in opposite directions to tension said cable and exert balanced forces on said cable when said spool is in the neutral position.

2. A system as claimed in claim 1 wherein the assembly further comprises a stop means located in said first housing for limiting movement of the cable in each operating direction.

3. A system as claimed in either claim 1 or claim 2 wherein the assembly further comprises a centering spring for maintaining said spool in the neutral position.

4. A system as claimed in any preceding claim wherein said sheath is formed of wound flexible wire.

5. A hydraulic control system substantially as hereinbefore described with reference to the accompanying drawings. - --

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. in constant lever loads while maintaining the cable in tension at all times as the lever moves the spool of the selector valve. WHAT WE CLAIM IS:

1. A hydraulic control system comprising a hydraulic directional control valve which includes a control member in the form of a spool having a positive neutral position and which is operated by a cable assembly, said assembly comprising an actuator, a tubular sheath, a flexible motiontransmitting operating cable disposed within said sheath, one end of said cable being connected to said actuator and the other end being connected to said spool, first and second flanged collars fitted to said one end and said other end of the cable, respectively, a first spring means located within a first housing adjacent said actuator and acting between said first flanged collar and an inner face of said first housing, and a second spring means located within a second housing adjacent the spool and acting between said second flanged collar and said second housing, said first and second spring means acting in opposite directions to tension said cable and exert balanced forces on said cable when said spool is in the neutral position.

2. A system as claimed in claim 1 wherein the assembly further comprises a stop means located in said first housing for limiting movement of the cable in each operating direction.

3. A system as claimed in either claim 1 or claim 2 wherein the assembly further comprises a centering spring for maintaining said spool in the neutral position.

4. A system as claimed in any preceding claim wherein said sheath is formed of wound flexible wire.

5. A hydraulic control system substantially as hereinbefore described with reference to the accompanying drawings. - --