US3448685A - Quick drop valve for bulldozer blade hydraulic controls - Google Patents

Description

June 10, 1969 N. w. KROTH 3,448,685

I QUICK DROP VALVE FOR BULLDOZER BLADE HYDRAULIC CONTROLS Filed Aug. 1, 1967 INVENTOR. NEIL W. KROTH ail M, a, W+M

ATTORNEYS United States Patent 3,448,685 QUICK DROP VALVE FOR BULLDOZER BLADE HYDRAULIC CONTROLS Neil W. Kroth, Joliet, Ill., assignor to Caterpillar Tractor Co., Peoria, 111., a corporation of California Filed Aug. 1, 1967, Ser. No. 657,669 Int. Cl. F151) 11/10, 13/042; G05d 11/02 US. Cl. 91-436 4 Claims ABSTRACT OF THE DISCLOSURE A value associated with a double-acting hydraulic jack controlling elevation of a bulldozer blade and permitting rapid extension of the jack and corresponding rapid descent of the blade to ground level while maintaining adequate hydraulic fluid for driving the blade in further descent to a suitable cutting position. The value has a restricted flow path from the rod end of the jack to drain so that increased fluid pressure acts against a spring loaded spool which communicates the rod end of the jack with the head end of the jack. As the weight of the blade increases its rate of descent toward ground level, a corresponding increased rate of flow of fluid from the rod end of the jack moves a sleeve into closing relation with the fluid flow path through the valve to drain. Thus, a substantial portion of fluid from the rod end of the jack is provided to the head end of the jack.

To increase the operating efiiciency of a bulldozer it is desirable that the operator be able to lower the blade to the ground very rapidly without the time delay inherent in typical float lowering techniques. Accordingly, bulldozer blades are commonly capable of being freely lowered to ground level under the force of gravity. However, when the lowering of the blade is accompanied by extension of the jack which controls blade elevation, lowering of the blade and extension of the jack by gravity normally results in a time lag of operator control over the blade since the hydraulic pump associated with the jack is not of suflicient capacity to fill the head end of the jack at a corresponding rate. This time lag is undesirable since the operator is unable to force the blade below ground level into a suitable cutting position until the head end of the jack is filled with hydraulic fluid. Undesirable vacuum conditions may also occur within the jack.

The present invention provides a quick drop valve, for employment with a hydraulic motor, which substantially eliminates the undesirable time lag discussed above while still permitting rapid operation according to gravity.

Use of the quick drop valve is particularly advantageous when employed with a double-acting hydraulic jack controlling a bulldozer blade since it permits the blade to be rapidly lowered toward ground level at an initial rate determined by the force of gravity. However, as the bulldozer blade approaches ground level and the fluid flow rate from the lower end of the hydraulic jack reaches a preselected level, the quick drop valve directs most of this fluid to the upper end of the jack so that the upper end of the jack is filled with fluid and the operator may immediately force the bulldozer blade into the ground to a suitable cutting position.

Other advantages and features of the present invention will be apparent from the following description and the accompanying drawings, wherein FIG. 1 is a schematic representation of the hydraulic control circuit for a double-acting hydraulic jack controlling elevation of a bulldozer blade and FIG. 2 is a sectional view of a quick drop valve employed within the hydraulic control circuit of FIG. 1 and embodying the present invention.

Referring now to FIG. 1, the bulldozer blade 11 is supported upon conventional push arms 12 while its elevation is controlled by a double acting hydraulic jack 13. The blade is lowered by extension of a rod 14 of the jack while retraction of the rod into the jack serves to raise the blade. The bulldozer operation positions the blade by manipulating a common spool-type control valve 16'which directs the flow of hydraulic fluid from a pump 17 through a conduit 18 to a return conduit 19 and tank 21, or alternately to the jack 13. The control valve is communicated with the head end of the hydraulic jack by a conduit 22 while the rod end of the jack is communicated with the control valve through a conduit 23, a quick drop valve 24 and another conduit 26. The quick drop valve 24 is also communicated with the conduit 22 and thus with the head end of the jack by another conduit 27. When the operator desires to raise the blade, he positions the control valve to direct fluid from the pump through the conduit 26, the quick drop valve and the conduit 23 to the rod end of the hydraulic jack while the head end of the jack is communicated to drain by the conduit 22, the control valve and the conduit 19. To lower the blade, the operator positions the control valve spool to direct fluid to the head end of the jack through the conduit 22 while the rod end of the jack is communicated to drain through the conduit 23, the quick drop valve, the conduit 26, the control valve and the conduit 19.

To briefly summarize the quick drop valve of the present invention, having reference also to FIG. 2, the quick drop valve 24 has substantially no eflect on fluid flow when the bulldozer blade is being raised, but rather is effective when the operator positions the control valve to lower the bulldozer blade by extension of the hydraulic jack 13. During lowering of the bulldozer blade, a fluid flow path from the rod end of the jack to drain is provided by a passage 28 within the quick drop valve. The passage 28 has a restriction or orifice 29 which does not substantially eflect the rate of flow of fluid through the passage but which creates a pressure differential across the quick drop valve with the conduit 23 representing the high pressure side and the conduit 26 representing the low pressure side thereof. The relatively high pressure hydraulic fluid in the quick drop valve adjacent the conduit 23 acts against a spring-loaded valve 31 and causes it to place the conduit 23 in fluid communication with the conduit 27 and the head end of the jack. As the rate of fluid flow from the rod end of the jack through the conduit 23 and the quick drop valve to drain reaches a level indicating that the blade is approaching ground level, variable valve means 32 respond to that rate of flow by limiting fluid flow into the passage 28 so that a substantial portion of the fluid from the rod end of the jack is directed to the head end of the jack through the quick drop valve and the conduit 27. Thus, the present quick drop valve is doubly advantageous since it initially permits the bulldozer blade to be lowered at a rate substantially determined only by the force of gravity. However, as the bulldozer blade approaches ground level, the fluid from the rod end of the jack is directed to the head end of the jack to assist the pump 17 in filling the head end of the jack with fluid. Thus, the quick drop valve of the present invention permits the operator to immediately force the bulldozer blade below ground level into a suitable cutting position by means of the hydraulic jack.

To describe the quick drop valve in structural detail, it has a central bore 33 with the spring-loaded valve 31 comprising a spool 34 disposed for longitudinal motion in the bore and urged leftwardly into the position illustrated in FIG. 2 by a spring 36. The conduit 23 is communicated directly into the left end of the spool bore 33 while the spool bore is communicated with one end of the passage 28 by means of an annular recess 37. The other end of the passage 28 is in communication with the conduit 26. The spool bore is also in communication with the conduit 27 by means of an annular recess 38 and a passage 39. The spring-loaded spool is recessed at its left end and has radial ports 41 which communicate the recessed left end of the spool with the annular recess 37 when the spool is leftwardly disposed in the bore 33. When the abovenoted differential pressure exists within the quick drop valve, it drives spool 34 rightwardly against the spring 36 so that the ports 41 are in communication with the annular recess 38 as well as the annular recess 37. At this point, the flow path of fluid from the conduit 23 is still substantially through the passage 28 since it represents a free path to drain.

To insure that a substantial portion of the fluid flow from the rod end of the hydraulic jack passes to the head end of the hydraulic jack at least when the blade is approaching ground level, the recessed left end of the spool 34 has a counterbore 42 which is only partially coextensive with the ports 41 in the spool. The variable valve means 32 comprises a sleeve 43 which is slidably disposed in the counterbore 42 for cooperation with the ports 41. When the fluid flow rate from the conduit 23 into the quick drop valve reaches a rate indicating that the bulldozer blade is descending and approaching ground level, the slidable sleeve 43 is carried rightwardly by the fluid flow from the conduit 23 so that it abuts the right end of the counterbore 42. In this position, the sleeve limits fluid flow to the passage 28 by permitting fluid to flow only through that portion of the port 41 which is not coextensive with the counter bore 42. A substantial portion of the fluid flows from the rod end of the jack thus through the annular recess 38, the passage 39, the conduit 27 and the conduit 22 and assists the pump 17 in filling the head end of the hydraulic jack to prevent any time lag in operator control over the bulldozer blade through the jack. The sizing of the components within the quick drop valve is such as to divided fluid flow from conduit 23 between the conduit 27 and the passage 28 at a ratio of, for example, 80 to 20. Some fluid flow is always directed back to drain through the restricted passage 28 in order to maintain the pressure differential necessary to hold the spool 34 in its extreme right position within the spool bore 33 It is also to be noted that when the bulldozer blade is being raised and fluid flow passes through the quick drop valve from the conduit 26 to the conduit 23, the pressure differential resulting within the valve according to the orifice 29 will not effect the position of the spool 34 since the spool is then on the low pressure side of the orifice. Thus, the spool remains in its extreme left position according to interaction with the spring 26.

If it is desired to operate the control system so that the blade drops completely to ground level under the force of gravity, the sleeve 43 may readily be removed from the quick drop valve and fluid flow from the rod end of the jack to drain through the passage 28 will not be limited even with a high rate of fluid flow through the quick drop valve.

What is claimed is:

1. A quick drop valve in association with a hydraulic control circuit of a double-acting hydraulic motor which is capable of operating under the force of gravity with hydraulic fluid accordingly expelled from a first chamber of the motor while fluid is provided by a pump to a second chamber of the motor, the combination comprising a housing defining a bore in effective communication with the two motor chambers and a conduit having a restrictive orifice for communicating the bore to drain and causing relatively high fluid pressure in the bore when fluid is expelled from the first motor chamber,

a valve spool reciprocably mounted in the bore and normally positioned by a spring to communicate the first motor chamber only with the restricted conduit, the spool being capable of shifting against its spring in response to the relatively high pressure fluid, and

variable valve means eflectively formed as a portion of the valve spool to direct a portion of the fluid from the first motor chamber to the second chamber when the spool is shifted against its spring,

a control valve disposed in the circuit to communicate fluid from a pump with the second motor chamber of the motor by a first conduit, 7

a second conduit communicates the first motor chamber of the motor with the valve bore,

a third conduit communicates the restricted passage with the control valve, and

a fourth conduit communicates the first conduit with the valve bore, the variable valve means being effective to communicate the second conduit with the fourth conduit when the spool is shifted against its spring.

2. A quick drop valve in association with a hydraulic control circuit of a double-acting hydraulic motor which is capable of operating under the force of gravity with hydraulic fluid accordingly expelled from a first chamber of the motor while fluid is provided by a pump to a second chamber of the motor, combination comprising a housing defining a bore in effective communication with the two motor chambers and a conduit having a restrictive orifice for communicating the bore to drain and causing relatively high fluid pressure in the bore when fluid is expelled from the first motor chamber,

a valve spool reciprocably mounted in the bore and normally positioned by a spring to communicate the first motor chamber only with the restricted conduit, the spool being capable of shifting against its spring in response to the relatively high pressure fluid, and

variable valve means effectively formed as a portion of the valve spool to direct a portion of the fluid from the first motor chamber to the second chamber when the spool is shifted against its spring.

the valve bore having a first annular recess in communication with one end of the restricted passage and a second annular recess in communication with with the second motor chamber, the spool having at least one port formed by a tubular portion thereof, the port being in selective communication with the two bore recesses according to the position of the spool within its bore.

3. The combination of claim 2 wherein the variable valve means comprises a slidable sleeve disposed in a counterbore of the tubular portion of said spool, said counterbore permitting said sleeve to be shifted by a preselected rate of fluid flow from the first motor chamber into the valve and block a portion of said port in the tubular portion of the spool.

4. The combination of claim 3 wherein the quick drop valve is effective to permit substantially unimpeded fluid flow from first motor side therethrough the drain except upon operation of said variable valve sleeve,

the tubular portion of the spool comprises a plurality of said ports and the slidable valve sleeve is removable from the quick drop valve.

(References on following page) References Cited 3,241,461

UNITED STATES PATENTS 1/1945 Kehle 91-436 7/1953 Deardorif 9'1-436 10/1961 Ruhl 91-436X 5 137-101 3/1966 Drone 91-436 CARROLL B. DORITY, IR., Primary Examiner.

US. Cl. X.R.

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