Detents for Locking Movable Elements

This invention relates to detents, for example spool detents in hydraulic control valves.

Hydraulic control valves are known which incorporate a spool shiftable, by means of a manual control lever, from a "neutral" position to one or more of "maximum flow" positions. Usually, in such valves, variable flow control is achieved according to different spool positions intermediate the neutral position and the maximum flow position. Moreover, it is usual in such valves that the spool is constantly urged towards the neutral position by means of a return spring. Where the spool is shiftable from the neutral position in either of mutually opposite directions to two different maximum flow positions, the return spring is called a "centering spring." In some practical applications, it is desirable that the spool may be held at a maximum flow position by means of a releasable detent capable of resisting the return spring. In other applications, such a detent is undesirable. Hitherto proposed arrangements offering a spool detent which is optionally engageable at a maximum flow position suffer the disadvantage that exercise of the option has to be made prior to moving the manual control lever, for example by appropriately setting a separate selector or the like. Thus, with such previous arrangements, it is required to establish in advance whether or not the detent facility is desirable. This requirement detracts from overall flexibility, especially in installations having several control valves, and allows error or lack of foresight to cause inefficient operation or even accidents.

An object of the present invention is to provide a detent for use with a spool-type hydraulic control valve, the detent being optionally engageable at a maximum flow position of the spool and obviating or mitigating the aforesaid disadvantage.

According to one aspect of the present invention, there is provided a detent for use with a spool-type hydraulic control valve, comprising a cage member having means defining a bore, a carrier axially slidable in said bore for attachment to a valve spool, a resiliently depressible element arranged in the carrier and pressing on said bore, means defining a recess in said bore engageable by said depressible element to effect detent, and stop means engageable by the cage member and allowing the cage member to shift within limits defined by the stop means in directions parallel with the axis of said bore.

According to another aspect of the present invention, there is provided a control device having a housing, a control element which is shiftable in the housing between first and second positions, an operating member connected to the control element and operable manually to shift the control element, return spring means continuously biassing the control element towards the first position, the control element being shiftable beyond the second position in a direction away from the first position, second spring means arranged to augment the manual effort required to shift the control element beyond the second position, and releasable detent means for holding the control element at the second position, said detent means including detent elements which are mutually engageable upon movement of the control element beyond the second position, one of said detent elements being shiftable to permit the control element when the detent elements are engaged to shift to the second position.

Further, according to the present invention, there is provided a spool-type hydraulic control valve incorporating a detent as aforesaid.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional elevation showing a detent in accordance with the present invention in combination with a spring-centered manually operable hydraulic control valve of the sliding spool type; and

FIG. 2 is a sectional elevation similar to part of FIG. 1 to a larger scale and shows the valve spool at one extreme of its full range of movement.

In the drawings, a combined spring centre and detent unit is arranged at the left hand end of a spool 1 housed in valve body 2 and operable manually by means of a control lever 3. The unit mechanism is contained within a housing formed by a cap 4 and an extension piece 5 both of which are rigidly attached to the valve body 2 by bolts. The right hand compartment of the unit constitutes the spring centering mechanism where two spring seats 6 are urged apart by a return or centering spring 7 and engage the opposite ends of the right hand compartment and also the end face of the spool and the shoulder of a detent carrier 8 in such a manner that virtually no axial movement of the spool 1 can take place without the centering spring 7 being compressed. A second spring in the form of a nest 9 of disc springs is fitted over the detent carrier 8 and between the spring seats 6. The axial distance between the inner faces of the spring seats 6 less the axial length of the disc spring nest 9 is equal to the distance which the spool 1 travels from its centre position to either maximum flow position.

When the spool 1 is at either maximum flow position, the inherent rigidity of the disc springs of nest 9 is sufficiently high to prevent most accidental over-travel or overstroking of the spool 1 but is not high enough to prevent deliberate overstroking. Therefore, movement of the spool 1 to the left will cause the right hand spring seat 6 to travel towards the left hand seat and this movement will be opposed by the centering spring 7. With normal forces applied to the control lever 3, spool movement will cease when the inner faces of both spring seats 6 abut the disc spring nest 9. In this position, the full rated capacity of hydraulic fluid can pass through the control valve.

Movement of the spool 1 to the right causes the left hand spring seat 6 to be carried by the shoulder on the detent carrier 8 towards the right hand seat 6 in a manner similar to that described above. When the control lever 3 is released from either maximum flow position, the centering spring 7 returns the spool 1 to its normal central or rest position.

The left hand compartment of the unit houses the detent means and contains a floating detent cage 10 carried from one end of the compartment to the other by the friction created between its inside diameter and radially depressible elements in the form of balls 11 held by a tapered thrust pin 12 biassed to the left by a detent spring 13. The centering spring and the detent compartments are separated by a buffer plate 14 which serves as an abutment for the left-hand spring seat 6. The buffer plate 14 and the cap 4 together constitute stop means to limit axial movement of the cage 10.

Movement of the spool 1 to the right causes the detent cage 10 to move to the right until it makes contact with the buffer plate 14. Further movement of the spool 1 to the maximum flow position causes the detent carrier 8, the balls 11 and the detent spring 13 to slide inside the detent cage 10. The maximum flow position, determined by the spring centering mechanism, is reached before the balls 11 can engage a recess or groove 10A in the detent cage 10. Up to this point the detent mechanism is inoperative and has no effect upon the action of the spring centre mechanism.

As increased force on the control lever 3 will cause the disc spring nest 9 to become compressed and permit further travel of the spool 1 beyond the maximum flow position. This movement can be called overtravel and can continue until the balls 11 engage in either groove 10A of the detent cage 10. The energy in the detent spring 13 is released causing the thrust pin 12 to move further into engagement with the balls 11 and also causing the detent cage 10 to shoot over to an extreme position, its movement being arrested by contact either with the cap 4 or the buffer plate 14. If the increased force on the lever 3 is sustained, no further spool movement will take place as the disc springs will become flattened (see FIG. 2). If the force on the lever 3 is removed the spool 1 will travel back until the balls 11 make contact with the sides or ramp of the adjacent groove 10A in the detent cage 10. Inward radial movement of the balls is opposed by the tapered thrust pin 12 and detent spring 13 and is in excess of the force imparted by the centering spring in an axial direction. Thus, the balls 11 remain in the detent cage groove 10A and at this point the spool 1 is at the maximum flow position and the disc spring nest 9 returns to its free state.

As increased force applied to the control lever 3 and in the opposite direction to that previously applied will release the detent hold causing the balls 11 to move radially inwards and the detent spring 13 recompressed, the spool 1 returning to its centre or rest position.

In constructing the unit described above, it is to be noted that there is radial clearance between the cage 10 and the cap 4. Also, the sliding fit of the detent carrier 8 in the bore of the cage 10 must be such as to minimise the possibility of jamming. In the arrangement described, the detent surfaces, namely the surfaces of the balls 11 and the shoulder surfaces of the grooves 10A, are such as to provide a clearly defined axial station at which detent occurs. In the described arrangement, the radius of the balls is equal to the radius of shoulders. More generally, it is preferable that the balls radius be equal to or greater than the shoulder radius.

The amount of spool shift beyond the maximum flow position to engage detent is determined by the axial position of the groove(s) 10A in the cage 10 and by the axial float of the cage 10. The arrangement described above enables the amount of the detent-engaging spool shift to be minimised.

Modifications of the above-described arrangement within the scope of the present invention include eliminating one of the grooves 10A in a unit providing detent facility at one maximum flow position only; replacing the balls 11 by radial plungers or the like; replacing the thrust pin 12 by alternative means adapted to thrust the balls or plunger radially outwards; varying the configuration of the detent surfaces, for example using wedges or other cam surfaces instead of the spherical surfaces of the balls 11, and employing a coil or another type of spring in place of the disc spring nest 9.