US 3465649 A
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Description (OCR text may contain errors)
Sept. 9, 1969 R. G. EGGERS ETAL 3,455,649
DETENT LOCKOUT FOR HYDRAULIC CONTROL VALVES Filed March 29, 1968 2 Sheets-Sheet 1 INVENTORS ROBERT G. EGGERS ARTHUR E GRANT -MWJJ '2 7 i 2 ATTORNEYS Sept. 9, 1969 EGGERS ET AL 3,465,649
DETENT LOCKOUT FOR HYDRAULIC CONTROL VALVES 2 Sheets-Sheet 2 Filed March 29, 1968 Fig-4.
//// anqmm INVENT S ROBE G. EIG RS ARTH FF GRANT m I 4 v 2 W abwl P I AZTORNEYS United States Patent 3,465,649 DETENT LOCKOUT FOR HYDRAULIC CONTROL VALV ES Robert G. Eggers, Eastlake, and Arthur R. Grant, East Cleveland, Ohio, assignors to Towmotor Corporation, Cleveland, Ohio, a corporation of Ohio Filed Mar. 29, 1968, Ser. No. 717,122 Int. Cl. F]: 11/02, 15/26; F1611 /00 US. Cl. 91426 6 Claims ABSTRACT OF THE DISCLOSURE Where a double acting hydraulic motor is employed for raising and lowering of a load, for example, to position the carriage of a forklift truck, it is desirable to provide for multiple speed operation of the motor to increase operating efficiency. However, since the load may vary greatly, it is necessary to provide some means for preventing high speed operation when the load is too heavy. Otherwise, inadvertent high speed operation could result in damage to the lift truck and possibly dangerous working conditions.
A prior art solution for overcoming this problem has been to employ a pressure responsive lockout which prevents positioning of the motor control valve for high speed operation. Placing the lockout in communication with the lower chamber of the motor permits it to be selectively operable according to the load supported by the motor. However, during operation of the motor, particularly while lowering the load, the hydraulic fluid exhibits velocity characteristics due for example to its passage to drain. Velocity of the fluid past the sensing port for the lockout commonly results in a false reduced pressure signal to the lockout. Accordingly, shifting of the control valve for high speed operation of the motor is possible even though the load is substantially greater than may be safely handled at high speeds. This problem has been avoided in the prior art by reducing the pressure responsive level at which the lockout operates. Such a practice is undesirable since it unduly restricts high speed operation of the motor. It is further undesirable since the lockout is commonly employed to limit high speed operation of the motor during both raising and lowering of the load. Thus, operating flexibility is still further decreased.
The present invention provides lockout means for positively establishing a selected load limit above which the motor control valve is locked from high speed operation. This is accomplished by permitting communication of pressure, indicative of the carried load, to the lockout only while the control valve is in its neutral position. The load is then static so that pressure communicated to the lockout is always indicative of the true load.
Preferably the lockout limits only high speed motor operation during lowering of the load while other means are employed for limiting high speed raising operation. Optimum load limits for establishing permissible high speed motor operation may be separately selected for raising and lowering of the load.
In a preferred embodiment of the invention, where pressurized fluid is communicated to the lockout while the control valve is positioned in neutral, a check valve is otherwise operable to prevent variation of the fluid pressure sensed by the lockout, for example, due to fluid leakage.
Other advantages and objects of the present invention are made apparent in the following description having reference to the accompanying drawings wherein:
FIG. 1 is a schematic illustration of a double acting hydraulic motor and its control valve;
FIG. 2 is a sectioned view of the control valve of FIG. 1 including a lockout arrangement according to the present invention;
FIG. 3 is an enlarged view in section of the right end of the control valve of FIG. 2 more clearly illustrating the lockout arrangement; and
FIG. 4 is a fragmentary view in section of a check valve arrangement for normally preventing fluid leakage from the lockout.
Referring now to FIG. 1, a pump 11, driven by an engine 12, draws fluid from a tank 13 and transfers it under pressure through a conduit 14 to a control valve 16. A drain conduit 17 communicates the control valve directly to the tank 13. Conduits 18 and 19 communicate the control valve respectively with a rod end portion 21 and a head end portion 22 of a double acting hydraulic motor or jack 23. The hydraulic jack rod 24 penetrates upwardly from the jack to support a load 26 which may be, for example, the fork lift carriage of a fork lift truck (not shown). A conventional relief valve 27 protects the pump 11 and the control valve from excessive pressures occurring in the conduit 14.
The control valve 16 is of a type having a central neutral position, indicated schematically at 28 where the conduit 19 is blocked so that fluid in the lower motor portion 22 supports the load. The pump inlet conduit 14 and the conduit 18 are in communication with each other and are further communicated to drain through the conduit 17 The valve also has low speed and high speed positions, indicated respectively and schematically at 29 and 31, for raising the load 26 by means of the motor 23. In the low speed raising position 29, the pump conduit 14 is communicated to the lower or head end of the jack through conduit 19 while the upper or red end 21 of the jack and the conduit 18- are in communication with drain through the conduit 17. In the high speed raising position 31, the pump conduit 14 and the rod and head ends of the motor are in common communication and are blocked from drain. Because of the differential cross sectional areas of the rod end and head end of the motor, fluid under pressure from the pump passes into the head end of the motor causing it to raise the load. Additional fluid from the rod end of the motor is also transferred to the head end of the motor so that the load is raised at a substantially increased rate. The control valve also has low speed and high speed positions, schematically illustrated respectively at 32 and 33, for lowering of the load 26 supported by the motor. It is to be noted that from its neutral position, the control valve must first be shifted into its low speed lowering position 32 before being shifted into its high speed lowering position 33. In its low speed lowering position 32, the head end of the motor is in restricted communication with the drain conduit 17. The amount of restriction is selected to determine the low speed lowering rate for the load. The pump conduit 14 is in communication with the conduit 18 and in somewhat restricted communication with the drain conduit 17. The slight restriction to drain maintains a low fluid pressure in the conduit 18 so that the rod end of the motor remains filled with hydraulic fluid. In the high speed lowering position 33, the head end 22 of the motor and the conduit 19 are in substantially free communication with the drain conduit 17 and the pump conduit 14 is in communication with the conduit 18 and the head end 21 of the motor to permit powering down of the load 26.
Having reference to FIG. 2, the control valve has a housing 36 defining an axial bore 37 with a control spool 38 disposed for longitudinal motion in the bore. Fluid from the pump or conduit 14 (see FIG. 1) enters a high pressure port 39 in the control valve housing and passes freely into portions 41, 42 and 43 which are in separate communication with the spool bore. Chamber 44- of the control valve is in communication with the upper rod portion of the motor 23 (see FIG. 1) and chamber 46 is similarly in communication with the head end of the motor through conduit 19. Drain passage 47 is in communication with the control spool bore at each end of the valve housing and with a central annular recess 48 about the spool *bore by means of a passage 49. The drain passage 47 is also in communication with the conduit 17 Shown in FIG. 1. A relief valve 51 normally prevents fluid communication from the chamber 44 into the drain passage 47 but is set to relieve fluid thereacross when pressure in the chamber 44 exceeds a preselected level.
When the valve spool is in its low speed lowering position 32 (see FIG. 1), the control spool 38 is shifted rightwardly so that a notched land 52 meters fluid from the valve chamber 46 into the drain passage 47 and determines the rate at which the load is lowered. Pump fluid from the high pressure port 39 is blocked from the drain passage 49 and passes to drain past the chamber 44 at a rate somewhat restricted by another land 53 on the spool. The slight restriction on the passage of pump fluid to drain maintains a low fluid pressure in the chamber 44 so that the rod end of the motor (see FIG. 1) remains filled with fluid during lowering of the load. As the spool is shifted further rightwardly to its high speed lowering position 33 (FIG. 1), the land 52 permits unrestricted communication of the chamber 46 with the drain passage 47. The land 53 closes the drain passage 47 so that pump fluid from the high pressure port 39 passes only into the chamber 44 and then to the rod end of the motor of FIG. 1.
As pointed out above, it is necessary to prevent accidental or inadvertent shifting of the control spool for high speed lowering operation according to the amount of the load 26 (see FIG. 1). Referring now to FIG. 2 and particularly FIG. 3, lockout means 56 are provided in a rightward extension 57 of the control spool situated in a housing extension 58. An elongated annular recess 59 is formed about the spool extension 57 by a member 61. Detent balls 62 are carried in the spool extension 57 to be forced into locking engagement with the recess 59 and limit longitudinal motion of the spool according to operation of a piston 63 which is also carried in the spool extension. The cambered piston 63 is normally urged leftwardly by means of a spring 64 which exerts a constant leftward force upon the piston regardless of spool position. However, suflicient fluid pressure in a piston chamber 66 at the left end of the piston overcomes the spring 64 and urges the piston rightwardly. Rightward shifting of the piston forces the balls 62 outwardly so that longitudinal motion of the spool is limited by the length of the recess 59. The piston chamber 66 is communicated through the spool by means of a port 67.
To condition the pressure sensitive piston 63 for response to the load being supported by the motor 23, a fluid passage 68 is formed by the valve housing to be in communication with the valve chamber 46 and the spool bore generally adjacent the piston chamber 66. When the spool is in its neutral position as shown in FIGS. 2 and 3, the passage 68 is aligned with the port 67 for the piston chamber 66. When the spool is in its neutral position, the piston chamber is in communication with the lower or head end 22 of the motor 23 (see FIG. 1) so that fluid pressure in the piston chamber 66 is generally in direct proportion to the load 26 being sup ported by the motor. As the control spool is shifted rightwardly into its low speed lowering position 32, the port 67 passes out of register with the passage 68 to positively fix the pressure level in the piston chamber 66. Thus, operation of the piston 63 is no longer responsive to pressure variations in the chamber 46. With the control valve in its low speed lowering position 32, the detent balls 62 are aligned with the rightward end of the recess 59. At this point, pressure in the piston chamber 66 determines whether the piston will force the balls outwardly to prevent further rightward motion of the spool. The strength of the spring 64 is selected so that a predetermined pressure, indicative of a selected load level, is necessary in chamber 46 and in piston chamber 66 to force the piston 63 rightwardly and operate the lockout arrangement. If the load is sufliciently heavy, pressure in chamber 46 overcomes the spring. The pressure in the chamber 66 remains constant when the control spool is in other than its neutral position. The rightwardly shifted position of the piston 63 and extension of the detent balls into recess 59 are fixed by the constant pressure in chamber 66. Shifting of the spool into its high speed lowering position is thus prevented until the spool is again shifted to neutral and pressure in chamber 66 is reduced in response to a reduced load.
Due to the tolerance fit between the spool extension 57 and its bore, fluid pressure in the piston chamber 66 could still vary somewhat because of leakage. A check valve 71 is illustrated in FIG. 4 to prevent such leakage and undesirable pressure variations. Other components in FIG. 4 which are similar to those in FIG. 3 are indicated by primed numerals. The check valve comprises a ball 72 which is urged into closing relation with a circumferential shoulder 73 in the port 67' by a spring 74. Another ball 76 is disposed in an enlarged portion 77 of the passage 68 and is urged against the ball 72 by its spring 78. When the spool is in its neutral position and the passage 68' is in communication with the port 67' (as in FIG. 3), the spring loaded ball 76 unseats the ball 72 and permits substantially free fluid communication thereacross. However, as the spool is shifted away from its neutral position, the ball 76 no longer acts against the ball 72 and it is urged into closing relation with the shoulder 73 by its spring 74 to maintain constant pressure in the piston chamber 66 until the spool is again returned to its neutral position.
The above lockout arrangement may be employed to provide a positive load limit above which the spool cannot be shifted for high speed operation to either raise or lower the load. This is accomplished by extending the annular recess 59 an equal distance in either direction from the position of the balls 62 with the spool in its neutral position (see FIGS. 2 and 3). However for optimum eflicicncy as discussed above, separate limits for high speed raising and lowering operation are desirable. Toward this end, the recess 59 extends an additional distance leftwardly of the balls 62 so that the lockup arrangement 56 is not operative to limit shifting into high speed raising operation. Rather, the load which the motor can raise with the control valve in its high speed raised position 31 (see FIG. 1) is established by means of the relief valve 51 as shown in the control valve in FIG. 2. For high speed raising operation, the control valve communicates the high pressure pump fluid port 39 with both the rod and head ends of the motor by means of the chambers 44 and 46. Thus, selection of the operative pressure level for the relief valve 51 effectively establishes the maximum load which the motor can raise in high speed operation. If that load is exceeded, excess pressure in the control valve is vented to the drain passage 47 across the relief valve 51.
What is claimed is:
1. In a dual speed control valve for a double acting hydraulic motor operating against a load, the valve communicating with a source of fluid under pressure and a fluid drain, the valve having a chamber in communication with a portion of the motor wherein fluid pressure for operating the motor is resisted by the load, the valve including another chamber in communication with a motor portion opposing the first portion and a control spool with a neutral position where it blocks the one chamber from drain for holding the load, a first operative position wherein the one chamber is communicated to drain and a second operative position whereby the one chamber is communicated to drain and the other chamber to the fluid source, the combination comprising:
lockout means associated with the spool and operative in response to increased pressure to prevent shifting of the spool from its first to its second position, and
means for effectively communicating pressure from the one valve chamber to the lockout means only when the spool is in its neutral position.
2. The invention of claim 1 wherein the pressure communicating means is a fluid passage from the one valve chamber, said passage being in communication with the lockout means only when the control 'valve spool is in its neutral position.
3. The invention of claim 2 wherein the lockout means comprises a slidable piston in a piston chamber carried by the spool, detent means operable by the piston to engage another member when the spool is in its low speed lowering position and an inlet port for the piston chamber which communicates with said fluid passage only when the spool is in its neutral position.
4. The invention of claim 3 wherein the piston chamber has a check valve for preventing fluid loss from the piston chamber through its port and means are associated with the fluid passage to open the check valve when the spool is in its neutral position.
5. The invention of claim 3 wherein the valve has relief means communicating fluid above a selected pressure level to drain to limit high speed raising of the load by the motor.
6. The invention of claim 5 wherein the motor is a double acting jack which extends to raise the load and retracts to lower the load, said one valve chamber being in communication with the head end of the jack and the other valve chamber being in communication with the rod end of the jack.
References Cited UNITED STATES PATENTS 2,689,585 9/1954 Presnell 91426 X 3,247,768 4/1966 Tennis 137-62427 X 2,848,014 4/1958 Tennis 137624.27 2,874,720 2/1959 Vahs 137-62427 MARTIN P. SCHWADRON, Primary Examiner I. C. COHEN, Assistant Examiner US. Cl. X.R.