GB2032062A

GB2032062A - Inching valves

Info

Publication number: GB2032062A
Application number: GB7930705A
Authority: GB
Original assignee: Komatsu Ltd
Current assignee: Komatsu Ltd
Priority date: 1978-09-12
Filing date: 1979-09-05
Publication date: 1980-04-30
Also published as: FR2436271A1; FR2436271B1; GB2032062B; CA1114718A; JPS6336161Y2; JPS5541612U

Abstract

An inching valve for a hydraulic circuit in construction machinery comprises a valve stem in hydraulic balance which makes for precise control and reduces the likelihood of chatter. The valve comprises a spool 10 having a spring chamber 14 at one end and a pressure-receiving chamber 16 at the other. A stem 24 is slidable in the spool 10, and has a step 30 and a load piston 34 thereon. The step 30 engages a spring 32 in the chamber 14. A restriction 20 connects the pressure-receiving chamber 16 to an outlet 7. In operation pressure passes from a modulator valve (not shown) to an inlet 6 past a reduced diameter portion 12 of the spool 10 to the outlet 7 and a clutch (not shown). Balance is achieved through the restriction 20. <IMAGE>

Description

SPECIFICATION Inching valves The invention relates to inching valves suitable for a hydraulic circuit in construction machinery.

The invention provides an inching valve suitable for a hydraulic circuit in construction machinery; which valve comprises a spool having a spring chamber at one end and a pressure-receiving chamber at the other; a stem slidable longitudinally in the spool, having a step contactable with a spring in the spring chamber at an open end of the spring chamber, and a nut retaining a load piston slidably mounted on the stem in the pressure-receiving chamber; the pressure-receiving chamber being connected to a valve outlet through a restriction; and the valve stem being axially balanced between the pressure of the spring and hydraulic pressure on the load piston.

The hydraulic baiance of the valve stem makes for precise inching control, and reduces the likelyhood of valve chatter. The valve itself is of relatively simple construction.

DRAWING The drawing is a cross-section of an inching valve according to the invention.

A valve box 2 has a longitudinal bore hole 4 and four ports 5, 6, 7 and 8 formed therein. The ports 5 and 8 are connected to a reservoir. The port 6 is an inlet port which is connected, for example, to a modulate valve (not shown) while the port 7 is an outlet port connected, for example, to a clutch of a variable speed gear (not shown). Slidably mounted within the bore hole 4 is a spool 10 having a reduced diameter portion 12 at an intermediate part thereof.

The spool 10 has a spring chamber 14 formed at one end thereof and a hydraulic pressure receiving chamber 1 6 formed at the other end thereof. A cylindrical wail 1 8 of the hydraulic pressure-receiving chamber 16 has formed therein a restriction 20 comunicating the port 7 with the hydraulic pressure-receiving chamber 1 6. A plurality of small holes 22 are also formed in the cylindrical wall 1 8.

Slidably inserted within the spool 10 is a valve stem 24 having a large diameter section 26 and a small diameter section 28. A stepped portion 30 is formed between the large diameter section 24 and the small diameter section 26. A compression spring 32 is disposed within the spring chamber 14 with one end being in touch with the stepped portion 30 of the valve stem 24. Thus, the spring 32 normally urges the spool 10 and the valve stem 24 to separate from each other. Disposed within the hydraulic pressure receiving chamber 1 6 is a load piston 34 with its inner surface being in sliding contact with the small diameter section 28 of the valve stem 24 and its outer surface being in sliding contact with the inner surface of the cylindrical wall 1 8.

Right-hand end 35 of the load piston 34 is brought in contact with a washer 36 mounted around the small diameter section 28 of the valve stem 24 when hydraulic fluid is introduced into the hydraulic pressure receiving chamber 1 6. A nut 38 is screw-threaded on the valve stem 24 at right-hand end thereof. A plug 40 having a collar 42 integrally formed therewith is threadably engaged with the valve box 2 at right-hand end thereof to close the bore hole 4. The collar 42 functions as a stopper for the spool 1 0.

A block 44 is fastened by a plurality of bolts 46 to the left-hand end of the valve box 2 to close the bore hole 4.

Pivotally connected at 48 to the valve stem 24 is a link 50 which in turn is pivotable about a pin 52. A rod 54 is provided for interconnecting the link 50 and an inching pedal 56. The inching pedal 56 is pivotable about a pin 58 and is normally urged clockwise by a spring 60.

The link 50 is urged counter-clockwise about the pin 52 by a spring 62, thereby normally pushing the valve stem 24 toward right in the drawing.

In operation, when the inching pedal 56 is not depressed, the inching valve remains as it is shown in the drawing. The inlet port 6 is communicated with the outlet port 7 through the reduced diameter portion 1 2 of the spool 1 0 thus hydraulic pressure remains same in the both ports.

In the state shown, the spool 10 is urged toward right by the spring 32 but is also urged leftward by the hydraulic pressure introduced into the hydraulic pressure receiving chamber 1 6 through the restriction 20 from the outlet port 7 and therefore the spool 10 is hydraulically balanced.

Similarly, the valve stem 24 is urged toward left in the drawing by the spring 32 but is also urged toward right by the hydraulic fiuid pressure in'the hydraulic pressure receiving chamber 1 6 because the rightward movement of the load piston 34 is transmitted to the valve stem 24 through the washer 36 and the nut 38. Thus the valve stem 24 is also hydraulically balanced.

When the inching pedal 56 is depressed the valve stem 24 is pulled toward left through the rod 54 and the link 50, thus the spring force of the spring 32 is weakened. To compensate this the spool 10 is moved toward left thereby blocking the communication between the port 6 and the port 7. Therefore the hydraulic pressure in the port 7 is lowered and the hydraulic pressure in the chamber 16 is also lowered. As a consequence, the spool 10 is moved rightward by the force of the spring 32, allowing communication between the port 6 and the port 7. By repeating these steps the hydraulic pressure in the port 7 is set lower than that of the port 6. In short, the hydraulic pressure in the port 7 is reduced in proportion to the amount of depression of the inching pedal 56.

When the inching pedal 56 is depressed to its stroke end, the spool 10 is moved leftward to a position where the port 7 is communicated with the drain port 8 through the plurality of small holes 22.

As mentioned hereinabove, since the spring force is balanced by the hydraulic pressure introduced into the single hydraulic pressure receiving chamber 16, the inching valve of the present invention can provide a good response to the depression of the inching pedal 56 and hardly produce the so-called chattering problem.

Claims

1. An inching valve suitable for a hydraulic circuit in construction machinery; which valve comprises a spool having a spring chamber at one end and a pressure-receiving chamber at the other; a stem slidable longitudinally in the spool, having a step contactable with a spring in the spring chamber at an open end of the spring chamber, and a nut retaining a load piston slidably mounted on the stem in the pressure-receiving chamber; the pressure-receiving chamber being connected to a valve outlet through a restriction; and the valve stem being axially balanced between the pressure of the spring and hydraulic pressure on the load piston.

2. An inching valve according to claim 1 in which the valve stem is connected at an end remote from the nut to operating means.

3. An inching valve according to claim 1 or claim 2 in which the spool has a reduced diameter portion selectively connecting a valve inlet with the valve outlet.

4. An inching valve according to any preceding claim in which the spring chamber and/or the end of the valve stem nearer the nut is connected to a drain port.

5. An inching valve according to any preceding claim in which the spool has small holes for connecting a valve inlet to the valve outlet when the valve stem is fully actuated.

6. An inching valve as herein described with reference to the drawing.