US 3522999 A
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3 Sheets-Sheet 1 Filed Nov. 8, 1968 6 Aviva/ d lcrefrarxer 5/4r/er J #1 W5 0 M 1 i m y 2% a 4...6 i 5 Hi} w i h\\ 4 M 0 5 Z 5 2 2 1970 c' E. LILES 3,522,999
PUMP UNLOADING VALVE Filed Nov. 8, 1968 3 Sheets-Sheet 2 ,vrramvevp United States Patent 3,522,999 PUMP UNLOADING VAL E Clarence E. Liles, Los Angeles, Calif., assignor to White lbllpitor Corporation, Cleveland, Ohio, a corporation of Filed Nov. 8, 1968, Ser. No. 774,309 Int. Cl. F04b 17/00, 49/00; F04d 15/00 US. Cl. 417282 Claims ABSTRACT OF THE DISCLOSURE In an arrangement wherein a starter cranks an internal combustion engine to a given starting speed below the idling speed of the engine and the engine drives a pressure-compensated pump to maintain a given normal pressure in a hydraulic system, a bypass valve for diverting the discharge of the pump to the low pressure side of the system is initially held open by spring pressure and is responsive to the rate of fluid flow therethrough to close only after the engine is accelerated past its starting speed thereby avoiding imposing the burden of the fully loaded pump on the starter.
BACKGROUND OF THE INVENTION In a typical hydraulic system on a truck or tractor wherein a positive displacement pump coupled to the engine is pressure compensated to maintain a given normal operating pressure in the hydraulic system, a starter cranks the engine to a given starting speed and then the engine accelerates to a higher idling speed.
A typical starter that is not burdened with the drag torque of the pump is readily capable of overcoming the drag torque of the engine to accelerate the engine to its starting speed, which is typically 80 to 100 r.p.m., where upon the engine power accelerates the engine to an idling speed which may be in the range of 600-800 rpm. The added drag torque of a positive displacement pump, however, is beyond the capability of a typical starter because the pump has full displacement as it starts to rotate and as system leakage is overcome the system pressure rises proportionately with flow until it overcomes the pressure compensator to stroke the pump to a lower displacement. Peak torque occurs when the pump is at maximumdisplacement and at maximum overshoot pressure just prior to stroking the pump to lower displacement with compensator action. Thus the first few revolutions of the pump brings the hydraulic system up to a normal operating pressure in the range of 2000-3000 p.s.i. with consequent immediate abrupt rising of the pump drag to a peak before the starter brings the engine to its starting speed. To handle the combined initial drag torque of the pump and engine the starter must be excessively larger than a typical starter.
One solution to this problem has been the provision of a bypass valve to connect the pump outlet to the lower pressure side of the system in preparation for starting the engine and is subsequently closed after the engine is well started. If the opreator fails to open the bypass valve, however, the pump load necessarily stalls the starter and if subsequently the operator fails to close the valve, the hydraulic system fails to function.
A further problem arises when the hydraulic fluid is cold and highly viscous because of low environmental temperature. In such an event, the operator should delay closing the bypass valve until the continuous bypass recirculation of the hydraulic fluid heats it to a normal temperature range.
Here again the burden is on the operator to keep the bypass valve open long enough for the desired rise in temperature of the hydraulic fluid without wasting time and power by holding the bypass valve open longer than necessary.
The object of the present invention is to provide solutions for both of these problems.
SUMMARY OF THE INVENTION The invention takes advantage of the fact that the velocity of the fluid flow through a positive displacement hydraulic pump rises progressively with the progressively increasing speed of the pump as the engine speed progressively increases up to the starting speed of the engine and beyond to the idling speed of the engine, the velocity of fluid flow through the pump being correlated with the speed of the engine.
Accordingly the bypass valve is constructed to inherently sense the rising flow velocity and to close in response to rise of the flow velocity to a magnitude that corresponds to an engine speed above the starting speed of the engine and preferably corresponding to an engine speed that is intermediate the starting speed and the idling speed of the engine.
The bypass valve is further constructed to sense a substantial drop in the operating pressure of the system after the valve closes and to open in response to a drop in pressure that is well below the normal pressure fluctuations of the system. Consequently when the engine is shut down at the end of an operating period, hydraulic leakage lowers the system pressure with resultant automatic opening of the bypass valve in preparation for a new period of op eration.
To make the bypass valve responsive to rise in flow therethrough, the bypass valve is designed to create a pressure differential varying with the flow velocity and urging the valve to close in opposition to the valve spring. When the flow velocity climbs to a predetermined magnitude, the pressure differential across the valve overcomes the resistance of the valve spring to close the valve and thereafter the normal static pressure diiferential across the closed bypass valve keeps the bypass valve closed. When the system pressure drops to a predetermined relatively low value after the engine is shut down, however, the spring extends to open the valve.
Automatic delay of the closing of the bypass valve when the hydraulic fluid is initially relatively cold is accomplished by means that senses the temperature of the hydraulic fluid and holds the valve open until hydraulic fluid warms up. Such a thermally responsive delay means may comprise a valve latch or detent controlled by a suitable bimetallic element in the valve.
The presently preferred embodiment of the bypass valve has a spring-pressed valve member in the form of a differential piston with a flow passage so arranged through a portion of the valve member that the flow through passage is cut off by the seating of the valve member. The flow passage through the portion of the valve member serves as a fixed orifice to create drop in pressure across the valve member and when the valve member is in an open position the valve member and cooperating valve seat form a second variable orifice that is in series with the fixed orifice and creates additional pressure drop across the valve member. Once the valve member starts to move towards its closed position the consequent progressive contraction of the variable orifice results in an exponential rise of the combined pressure drop to cause the valve to shut with a snap action.
The features and advantages of the invention may be understood from the following detailed description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative FIG. 1 is a diagram showing how a bypass valve is connected across the hydraulic system of a truck or tractor;
FIG. 2 is an enlarged sectional view showing how the bypass valve may be incorporated into the structure of the hydraulic pump;
FIG. 2a is an enlarged fragmentary section along the line 2a-2a of FIG. 2 showing the thermal delay means;
FIGS. 3 and 3a are diagrams identifying the factors that determine the various dimensions of the valve and the design of the valve spring;
FIG. 4 is a diagram showing how the spring force and the pressure differential across the valve member increases as the valve member moves to its seated position;
FIG. 5 is a diagram showing the drag torque curves of the engine and hydraulic pump in the absence of the bypass valve;
FIG. 6 is a similar diagram showing how the bypass valve delays the peak of the drag torque of the pump until the engine is accelerated past its starting speed; and
FIG. 7 is a similar diagram showing how the thermal time delay means functions when the hydraulic fluid is cold to delay the peak of the drag torque of the pump to provide time for the hydraulic fluid to rise to a normal temperature range.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION FIG. 1 shows diagrammatically how a starter is mechanically coupled to an engine and the engine in turn is mechanically coupled to a pump of a hydraulic system of a tractor or truck. A bypass valve 10 of the construction taught by the present invention is connected across the high and low pressure sides of the hydraulic system as shown. FIG. 2 shows the construction of the bypass valve.
FIG. 2 shows how the bypass valve 10 may be incorporated into the structure of a pressure-compensated radial-piston hydraulic pump. FIG. 2 shows in cross section the high pressure manifold 12 in the cylinder block 14 of the pump and further shows an inclined bore 15 that communicates with the low pressure intake manifold (not shown) of the pump. The pump may be pressure-compen sated by variably restricting the intake flow of the pump in response to pressure changes in the high pressure manifold 12.
The cylinder block 14 of the pump is suitably bored, counterbored and tapped to receive the body 16 of the bypass valve and to engage an external screw thread 18 of the body. The valve body 16 is provided with a hexagonal end portion 20 which may be tightened by a wrench to place a circumferential O-ring 22 under effective sealing pressure.
The inlet end of the valve body 16 is open to the high pressure of the output manifold 12 and the opposite end of the valve body provides an axial outlet passage 24 of reduced diameter, the outlet passage forming a valve seat 25 which preferably is chamfered as shown.
In FIG. 2 a pipe plug 26 seals the outer end of the outlet passage 24 and the outlet passage is in communication with the low pressure bore 15 through a plurality of radial bores 28 from the outlet passage to a surrounding circumferential groove 29 in the cylinder block, the surrounding groove registering with the inclined low pressure bore 15. It is apparent that this arrangement places the intake of the bypass valve in communication with the high pressure manifold 12 of the pump and places the outlet of the bypass valve in communication with the low pressure intake manifold of the pump. It is obvious, however, that in the absence of the inclined bore 15 for communication with the intake manifold of the pump, the pipe plug 26 may be replaced by a pipe connected to the low pressure side of the hydraulic system.
A valve member or valve spool 30 in the form of a differential piston is slidingly mounted in an axial bore 32 of the valve body which bore terminates at the valve seat 25. The upstream end portion 34 of the valve spool completely spans the bore 32 and is closely fitted to provide sealing engagement with the Wall of the bore. The opposite downstream end portion 36 of the valve spool is of reduced diameter and is formed with a conically tapered nose 38 to cooperate with the valve seat 25. A suitable coil spring 40 normally holds the valve spool 30 in open position with the valve spool backed against an inner circumferential snap ring 42.
It is contemplated that the valve spool 30 will be formed with a suitable flow passage therethrough that will be closed by seating of the valve spool. In the construction shown, an axial bore 44 through the upstream end portion 34 of the valve spool intersects a diametrical bore 45 in the reduced downstream end portion 36 of the valve spool and the axial bore is formed with a restriction 46. The flow passage through the valve speed with its restriction 46 functions as a fixed orifice that creates a pressure differential across the valve spool in response to fiuid flow therethrough. It is to be noted that this pressure difierential tends to seat the valve spool in opposition to the force of the spring 40.
It may be noted that the flow passage through the valve spool changes direction with the consequences that the fluid stream therethrough impinges on the far surfaces 48 of the diametrical bore 45. Thus the fluid stream through the valve spool in addition to creating a pressure differential across the valve spool that tends to seat the valve spool additionally creates dynamic pressure against the surface 48 that also tends to seat the valve spool.
When the valve spool is in the open position shown in FIG. 2, the nose 38 of the valve spool and the valve seat 25 cooperate to form a variable orifice that is in series with the fixed orifice and that augments the pressure differential across the valve spool. Preferably the two orifices are shaped and dimensioned for the pressure drop across the fixed orifice to be approximately three times the pressure differential across the variable orifice at the maximum open position of the valve spool but this ratio is not critical.
As the valve spool shifts from its wide open position towards its seated position, the variable orifice is progressively restricted and consequently the pressure drop across the valve spool rises exponentially to cause the valve spool to seat with a snap action. The snap action may be understood by reference to FIG. 4 where it can be seen that the spring force represented by the curve 58 rises linearly at a gradual rate as the valve spool moves towards its seated position whereas the pressure differential on the valve spool created by the fluid flow glarough the valve rises steeply as indicated by the curve As shown in FIG. 2 the means for delaying the closing of the bypass valve in the event that the hydraulic fluid of the system is at an unduly low temperature comprises a tangentially positioned pin 50 in a transverse recess 52 in the wall of the main bore 32 of the valve body. A bowed bimetallic element 54 in the recess responds to a drop in temperature by bowing to force the pin 50 into a circumferential groove 55 in the valve spool 30 as shown in FIG. 2a. At normal operating temperatures of the hydraulic fluid, the bimetallic element 54 permits the pin 50 to retract from the groove 55 to avoid interfering with the normal operation of the valve spool.
FIG. 3 shows diagrammatically the factors that enter into the calculations of the pressure drop and the design of the valve spring 40.
P is the pump discharge pressure P =P minus the pressure drop across orifice 0 P =P minus the pressure drop across orifice O AP1=P1 minus P2 AP2=P2 minus P 3 The area of fixed orifice 0 =A and the variable orifice 0 has a variable cross-sectional area of A in which K is a constant. The variable area A =K h in which K =sin (BF) D is the diameter of the outlet passage 24 which has a cross-sectional area of A The main bore of the valve body has a cross-sectional area A Assuming that the flow rate Q is constant at the time that the pressure diflerential increases to exceed the spring force F thereby to start the closing movement of the valve spool, F =AP A +AP A With the diameter of the main valve bore 32 equal to 0.625 inch, for example, and with the other dimensions of the valve in proportion, the valve spring may be designed in accord with the operating characteristics of the pump together with the selected flow rate at which the bypass valve is to close and the selected drop in system pressure at which the valve spool after the pump is cut oil.
For example the pump may have an operating speed range of approximately 0-2800 r.p.m. with a capacity for delivering 25 gallons per minute at 2600 rpm. It may be pressure compensated to maintain a normal operating pressure of 2000 p.s.i. in the system with a standby pressure of 2500 p.s.i. and with an inlet pressure of 15 p.s.i. To cause the bypass valve to shut off at three gallons per minute and to cause the valve spool to unseat at 350 p.s.i. after the pump is cut ofl, the specifications for the valve spring are as follows:
Gage: 28 gage Initial loaded length 0.584"
Load at initial loaded length 123+ 1.2 lbs. Final loaded length 0.50
Load at final loaded length 17.2i0.86 lbs. Free length 0.769"
Maximum solid length 0.462
Number of active coils 4.5
Stress at maximum working load 74,000 p.s.i. Stress at minimum working load 52,500 p.s.i. Stress at solid length 87,500 p.s.i.
Spring rate 66.5 lb./ in.
FIG. 5 shows the drag torque of the engine and the drag torque of the pump when operation of the system is initiated without the benefit of the bypass valve 10. It can be seen that in the initial period in which the starter is bringing the engine up to its starting speed, the drag torque of the pump climbs abruptly to a peak that is nearly four times the drag torque of the engine.
FIG. 6 indicates the effect of adding the bypass valve to the system, it being assumed that the hydraulic fluid is at a normal starting temperature. It can be seen in FIG. 6 that the drag torque of the pump is minimal during the time period in which the starter brings the engine up to its starting speed and that the peak drag torque of the pump is delayed until the engine accelerates substantially beyond the starting speed, the peak drag torque of the pump being created by the delayed closing of the bypass valve.
FIG. 7 is similar to FIG. 6 but indicates the result of starting the system with the hydraulic fluid at an unduly low temperature. FIG. 7 shows how the additional time delay provided by the temperature responsive latch for the valve spool provides greater postponement of the peak of the drag torque of the pump, i.e. postponement of the closing of the bypass valve to provide an adequate time interval for the hydraulic fluid to be heated up to normal temperature by continuous bypass recirculation.
My description in specific detail of the presently preferred practice of the invention will suggest various changes, substitutions and other departures from my disclosure.
1. In an arrangement wherein a starter cranks an internal combustion engine to a given starting speed and the engine drives a variable pump to supply fluid to a hydraulic system with the pump pressure-compensated to tend to maintain a given normal operating pressure in the system,
whereby cranking the engine by the starter with initial low pressure in the system results in progressively increasing flow velocity through the pump corresponding with the progressively increasing speed of the pump as the speed of the engine is progressively increased through said starting speed,
the improvement comprising:
a bypass valve having a valve body and a valve member therein, said valve body forming a valve seat and having its inlet connected to its high pressure side of the system and its outlet connected to the low pressure side,
said valve member being movable between an open position for bypass flow to substantially remove the load on the pump and a closed position in said seat to cut oil the bypass flow to load the pump;
means exerting force to bias the valve member to its open position with the magnitude of the biasing force substantially less than the pressure differential across the seated valve member that is created by said normal operating pressure in the system; and
means to sense the rate of fluid flow through the valve when the valve member is in an open position and to move the valve member to closed position in opposi tion to said biasing force when said rate of fluid flow rises to a magnitude corresponding to an engine speed that is at least approximately said starting speed, thereby to substantially avoid imposing actuation of the loaded pump on the starter.
2. An improvement as set forth in claim 1 which includes temperature-responsive means exposed to the temperature of the fluid to prevent seating of the valve member in response to subnormal temperature of the hydraulic fluid and to delay the seating until the temperature of the fluid rises to a predetermined value.
3. In an arrangement wherein a starter cranks an internal combustion engine to a given starting speed and the engine drives a variable pump to supply fluid to a hydraulic system with the pump pressure-compensated to tend to maintain a given normal operating pressure in the system,
whereby cranking the engine by the starter with initial low pressure in the system results in progressively increasing flow velocity through the pump corresponding with the increasing speed of the pump as the speed of the engine is progressively increased through said starting speed,
the improvement comprising:
a bypass valve having a valve body and a valve member therein, said valve body forming a valve seat and having its inlet connected to its high pressure side of the system and its outlet connected to the low pressure side,
said valve member being a differential Valve member with an upstream portion of a given cross-sectional area exposed to the high pressure side of the system and with a downstream portion of smaller cross section shaped and dimensioned to seat in the valve seat to cut off flow through the valve body,
said valve member having a passage therethrough from its upstream end terminating short of said downstream portion whereby flow through the passage is cut ofl when the valve member is seated; and
means biasing the valve member to open position,
said passage through the valve member being shaped and dimensioned to create a pressure differential across the valve member when the valve member is unseated thereby to urge the valve member to seat in opposition to the force of said biasing means, with the pressure differential increasing with increasing velocity of flow through the valve,
said passage through the valve member being shaped and dimensioned and the magnitude of the force of said biasing means being selected to delay the seating of the valve member by said pressure differential as the flow velocity through the passage increases until the flow velocity rises to a magnitude corresponding to an engine speed that is at least above said starting speed thereby to avoid imposing actuation of the loaded pump on the starter,
said force of the biasing means being substantially less than the pressure differential across the seated valve member when the system is at said normal operating pressure whereby the valve member is kept seated by the normal operating pressure and unseats to release the pressure in the system when the system pressure drops substantially below the normal operating pressure after the engine stops.
4. An improvement as set forth in claim 3 which includes temperature-responsive means exposed to the temperature of the fluid to prevent seating of the valve memher in response to subnormal temperature of the hydraulic fluid and to delay the seating until the temperature of the fluid rises to a predetermined value.
5. An improvement as set forth in any of the claims 2 and 4 in which the temperature responsive means comprises:
a latch member movable between a retracted position and an advanced position in engagement with the valve member at an unseated position of the valve member; and
a bimetallic element exposed to the temperature of the hydraulic fluid to move the latch member to its ad vanced position in response to subnormal temperature of the fluid and to permit the latch member to retract in response to higher temperature of the hydraulic fluid.
6. An improvement as set forth in any of claims 3 nd 4 in which said passage through the valve member includes a surface of the valve member in the path of fluid flow to change the direction of flow through the valve member whereby the impingement of the fluid stream on said surface creates dynamic pressure on the surface tending to move the valve member to its closed position with the magnitude of the dynamic pressure rising with the velocity of flow through the passage.
7. An improvement as set forth in any of claims 3 and 4 in which said passage through the valve member constitutes a fixed orifice and the valve member in cooperation with the valve seat forms a second variable orifice in series with the fixed orifice and when the valve memher is at its initial maximum open position, the two orifices are shaped and dimensioned for substantially greater pressure drop at the fixed orifice than at the variable orifice.
'8. An improvement as set forth in any of claims 3 and 4 in which the valve member is slidingly mounted in a bore in said valve body;
in which a portion of the valve member spans said bore; in which the downstream end of the valve member is of smaller cross section than the bore to form therewith an annular space adjacent said seat; in which the passage through the valve member terminates at said annular space; and in which the biasing means is in the forms of a coil spring in said annular space acting in compression between the valve body and the valve member. 9. An improvement as set forth in any of claims 3 and 4 in which said passage through the valve member comprises an axial bore in said upstream portion of the valve member and a transverse bore intersecting the axial bore. 10. An improvement as set forth in any of claims 1, 2, 3 and 4 in which said bypass valve is incorporated in the structure of the pump in communication with the intake and discharge ports of the pump.
References Cited UNITED STATES PATENTS 2,329,401 9/1943 Le Valley 230-29 2,747,598 5/1956 Wooldridge 103-42 X 3,180,266 4/ 1965 Smith 103-41 X 3,253,607 5/1966 Drutchas 103-42 X 3,313,530 4/1967 Bickhaus et a1 103-41 X 3,349,714 10/1967 Grenier 103-41 3,396,663 8/1968 Bratten 103-42 3,415,194 12/1968 Connelly 103-41 WILLIAM L; FREEH, Primary Examiner W. I. KRAUSS, Assistant Examiner U.S. Cl. X.R. 417-292, 299