Patent Publication Number: US-2004055290-A1

Title: Dual function hydraulic valve and circuit

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates in general to hydraulic circuits and more particularly to hydraulic circuits that are pneumatically controlled from the cab of a truck.  
       BACKGROUND OF THE INVENTION  
       [0002] Trucks and other large vehicles often incorporate pumps for maintaining hydraulic pressure. The truck itself may include a hydraulic circuit, or may be connectable to a trailer having a hydraulic circuit. The hydraulic pressure in this circuit can be maintained by the pump located on the truck to run various hydraulically operated components linked to the circuit.  
       [0003] Different hydraulic components will operate at different pressures. For example, some components may operate at 2,000 psi, while other components operate at 3,000 psi. If a liquid at 2,000 psi is supplied to a high pressure component, then no great harm will typically follow—in all likelihood the high pressure component will simply be inoperative. However, if a 3,000 psi liquid is supplied to a low pressure component, damage to the component is likely.  
       [0004] To address this problem, hydraulic circuits according to the prior art have included separate conduits for high pressure and low pressure components, as well as valves for directing the liquid between these different conduits. While this solution addresses the problem, it greatly increases the amount of piping and valving required to implement a workable hydraulic circuit, and, more importantly, greatly increases installation costs. Accordingly, a hydraulic circuit suitable for mounting on a truck and requiring less valving and piping, is desirable.  
       SUMMARY OF THE INVENTION  
       [0005] An object of one aspect of the present invention is to provide an improved hydraulic circuit.  
       [0006] In accordance with this aspect of the present invention, there is provided hydraulic circuit for supplying fluid at a plurality of different pressures. The circuit comprises (a) a reservoir containing fluid at an upstream pressure level; (b) a pump for receiving a fluid from the reservoir and for raising the fluid pressure of the fluid from the upstream pressure level to a downstream pressure level; (c) a pressure conduit for receiving the fluid from the pump; (d) an adjustable relief valve for receiving fluid at the downstream pressure level from the pump; and, (e) remote control means for remotely adjusting the adjustable relief valve. The adjustable relief valve is (i) connected to a relief conduit and to the pressure conduit, (ii) operable to open to connect the pressure conduit with the relief conduit when the downstream pressure level exceeds an actuation pressure level, (iii) operable to close to isolate the pressure conduit from the relief conduit when the actuation pressure level exceeds or is equal to the downstream pressure level, and (iv) remotely adjustable to change the actuation pressure.  
       [0007] An object of a second aspect of the present invention is to provide an improved hydraulic pump.  
       [0008] In accordance with the second aspect of the present invention, there is provided, in a pump for providing a pressurized liquid to a hydraulic circuit, an adjustable relief valve. The hydraulic circuit includes a pressure conduit for receiving pressurized liquid from the pump and a relief conduit for receiving pressurized liquid from the pump when the relief valve is open. The adjustable relief valve includes (a) a valve conduit for connecting the relief conduit to the pressure conduit to provide fluid communication therebetween; (b) a conduit blocking element for, when the adjustable relief valve is in a closed position, blocking the valve conduit to impede fluid communication between the pressure conduit and the relief conduit, and for, when the adjustable relief valve is in an open position, permitting the fluid communication between the pressure conduit and the relief conduit; (c) a biasing means for biasing the conduit blocking element to the closed position when the downstream pressure level is less than the actuation pressure, wherein the biasing means is remotely adjustable to change the actuation pressure; and, (d) remote control means for remotely adjusting the biasing means.  
       [0009] An object of a third aspect of the present invention is to provide a method of converting a one pressure hydraulic circuit into a multiple pressure hydraulic circuit.  
       [0010] In accordance with the third aspect of the present invention, there is provided a method of modifying a hydraulic circuit to operate at multiple pressures. The hydraulic circuit has (a) a reservoir containing fluid in an upstream pressure level; (b) a pump for receiving a fluid from the reservoir and for raising a fluid pressure of the fluid from the upstream pressure level to a downstream pressure level; and, (c) a pressure conduit for receiving the fluid from the pump. The method comprises the steps of incorporating an adjustable relief valve and a remote control means into a hydraulic circuit. The adjustable relief valve is for receiving fluid at the downstream pressure level from the pump. The adjustable relief valve is (i) connected to a relief conduit and to the pressure conduit, (ii) operable to open to connect the pressure conduit with the relief conduit when the downstream pressure level exceeds an actuation pressure level, (iii) operable to close to isolate the pressure conduit from the relief conduit when the actuation pressure level exceeds or is equal to the downstream pressure level, and (iv) remotely adjustable to change the actuation pressure. The remote control means is for remotely adjusting the adjustable relief valve. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] A detailed description of the preferred embodiments is provided herein below with reference to the following drawings in which:  
     [0012]FIG. 1, in a schematic view, illustrates a hydraulic circuit in accordance with the prior art;  
     [0013]FIG. 2, in a sectional view, illustrates a relief valve in accordance with an aspect of the present invention;  
     [0014]FIG. 3, in a front view, illustrates the relief valve of FIG. 2;  
     [0015]FIG. 4, in a schematic view, illustrates a hydraulic circuit incorporating the relief valve of FIG. 2 in accordance with an aspect of the present invention; and,  
     [0016]FIG. 5, in a schematic view, illustrates a valve arrangement in accordance with a further aspect of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED ASPECTS OF THE INVENTION  
     [0017] Referring to FIG. 1, there is illustrated in a schematic view a hydraulic circuit  20  in accordance with the prior art. The hydraulic circuit  20  is supplied with operating liquid from a liquid reservoir  22 . The operating liquid is drawn from the reservoir  22  through supply conduit  26  by pump  30 . Pump  30  is powered by a power takeoff  28  from the truck transmission, and includes an upstream relief valve  32 . Upstream relief valve  32  can be set at a constant pressure of, say, 3,000 psi. When pump  30  raises the liquid received from supply conduit  26  above a pressure of 3,000 psi, upstream relief valve  32  will open until this fluid pressure diminishes to below 3,000 psi. When upstream relief valve  32  is open, a pump return conduit  48  receives liquid from the pump  30  and returns it to the reservoir  22 .  
     [0018] Pressure conduit  36  receives the operating liquid from the pump  30  at a pressure of 3,000 psi. Pressure conduit  36  then conveys the operating liquid to spool valve  40 . Spool valve  40  has a high pressure setting and a low pressure setting. At the high pressure setting, fluid is directed away from downstream relief valve  34  into a high pressure work conduit  46 . High pressure work conduit  46  then operates the hydraulic components that operate at a higher pressure—i.e. at a pressure of 3,000 psi in the present case. After driving the high pressure hydraulic components, the operating liquid returns to the reservoir via high pressure return conduit  44 , return conduit  38  and filter  24 .  
     [0019] In the low pressure setting, spool valve  40  opens fluid communication between pressure conduit  36  and downstream relief valve  34 . Downstream relief valve  34  is set to open at a lower pressure than upstream relief valve  32 —say a pressure of 2,000 psi. Accordingly, operating liquid is bled off by downstream relief valve  34  to return conduit  38  until the pressure of the operating liquid reaches a lower level of 2,000 psi. This lower pressure operating liquid is then supplied to the low pressure work conduit  42 , which supplies the hydraulic components operated at lower pressure. After driving the low pressure hydraulic components, the liquid from the low pressure work conduit  42  returns to the reservoir  22  via return conduit  38  and filter  24 .  
     [0020] Referring to FIGS. 2 and 3, there is illustrated in sectional and front views respectively, a pressure relief valve  58  in accordance with a preferred embodiment of the invention. The pressure relief valve  58  includes a valve ball  60  adapted to be seated against a valve seat  62  to close the valve. The valve ball  60  may be urged into this closed position by a main spring  64 . An adjustment rod  66  is adjustably disposed within a valve body  68  in which the main spring  64  is disposed, in order to set the desired low pressure of, for example, 2,000 psi at which the relief valve  58  opens. Specifically, both the exterior of adjustment rod  66  and the interior of valve body  68  are threaded, such that the adjustment rod  66  may be screwed into or out of the valve body  68 . The rod  66  is locked into position by a lock nut  70 . This low pressure is the lower limit of a range of actuation pressures—pressures at which relief valves open—that may be provided by the relief valve  58 .  
     [0021] While the relief valve  58  is initially set to open at a selected low pressure—2,000 psi in the above example—this—actuation pressure may be changed to a higher pressure of up to, say, 3,000 psi. Specifically, the actuation pressure can be increased by supplying high pressure air to the chamber  72  via inlet  74 . This high pressure air will then urge the piston  76  to the end of its stroke, thereby forcing a piston rod  78  and an end cap  80  to compress the main spring  64 . This compression sets the pressure relief valve to the higher pressure setting of up to 3,000 psi, depending on the extent to which the main spring  64  is compressed. A light spring  82  retains the piston  76  in the position in which the piston rod  78  is in contact with the end cap  80  when the relief valve  58  is at a lower pressure setting.  
     [0022] Referring to FIG. 4, a hydraulic circuit incorporating a relief valve according to FIGS. 2 and 3 is illustrated. The hydraulic circuit  120  is supplied with operating liquid from a liquid reservoir  122 . The operating liquid is drawn from the reservoir  122  through supply conduit  126  by pump  130 . Pump  130  is powered by a power takeoff  128  from the truck transmission, and includes relief valve  58 . Relief valve  58  can be set at a variety of different pressures within a pressure range determined by the resiliency of main spring  64 .  
     [0023] Say the relief valve  68  is set at a pressure P. Then when pump  130  raises the operating liquid above a pressure of P, the relief valve  58  will open until this fluid pressure diminishes to P. The remaining liquid then travels through work line  136  to power all of the hydraulic components. After driving the hydraulic components, the operating liquid returns to the reservoir  122  via return conduit  138  and filter  124 . Operating liquid tapped by relief valve  58  also returns to the reservoir via pump return conduit  148 , return conduit  138  and filter  124 .  
     [0024] As is apparent from a comparison of FIGS. 1 and 4, incorporating adjustable relief valve  58  into hydraulic circuit  120  permits a number of components to be dispensed with, such as a spool valve, and different low pressure and high pressure work conduits. Adjustable relief valve  58  can be incorporated into the hydraulic circuit at any point upstream of the hydraulic components to be operated, and may be retrofitted into existing hydraulic circuits to enable them to operate at any pressure within a range of different pressures. However, preferably, the adjustable relief valve  58  is incorporated into the pump  130 .  
     [0025] Some hydraulic components may be damaged if they are operated using an operating liquid at too high a pressure. Thus, damage to such components is possible if the hydraulic circuit  120  is switched on when the adjustable relief valve  58  is at too high a pressure setting, as the hydraulic circuit will supply operating liquid to these hydraulic components at too high a pressure.  
     [0026] Referring to FIG. 5, a valve arrangement  160  according to an aspect of the present invention is illustrated. The valve arrangement  160  includes first valve  162  and second valve  172 . Both valves are two-position, three-way pneumatic valves. In valve arrangement  160 , first valve  162  is opened to supply air to engage power takeoff  128 . Power takeoff  128  in turn rotates the hydraulic pump  130  to produce the flow of the operating liquid. First valve  162  also supplies air to second valve  172 , but does not directly supply air to the adjustable relief valve  58 . Specifically, first valve  162  has an open position  164 , and a closed position  166 . In the closed position  166 , air is exhausted from the valve  162  to the atmosphere to allow the piston to return. In the open position  164 , first valve  162  supplies air to first outlet line  168 . First outlet line  168  leads to power takeoff line  168   a , and input line  168   b . Via power takeoff line  168   a , air is supplied to engage the power takeoff  128 . Via inlet line  168   b  air is supplied to second valve  172 .  
     [0027] Second valve  172  includes an open position  174  and a closed position  176 . In the closed position  176 , air is exhausted from the valve  172  to the atmosphere to allow the piston to return. In the open position  174 , second valve  172  supplies air to second valve outlet line  178 . This air is then supplied to inlet  74  of adjustable relief valve  58  to adjust the actuation pressure of adjustable relief valve  58 . However, second valve  172  must be manually changed to the open position by an operator manually depressing valve button  179 . When the work being carried out is finished and the operator disengages the power takeoff circuit via first valve  162 , first valve  162  will no longer supply air to second valve  172 . At this point, second valve  172  will automatically return to the closed position  176 . In closed position  176 , second valve  172  supplies no air to outlet line  178  and valve input  74 , thereby returning the adjustable relief valve  58  to its lower setting. This ensures that the next time the operator uses the hydraulic circuit  120 , adjustable relief valve  58  will be at it lower pressure setting until the operator manually depresses valve button  179  of second valve  172  to supply air to the adjustable pressure relief valve  58 .  
     [0028] In a yet further aspect, the present invention comprises a method of retrofitting an existing hydraulic circuit to operate at multiple pressures. Specifically, an existing hydraulic circuit that operates at only one pressure can be modified to operate at multiple pressures by incorporating the adjustable relief valve  58  into the hydraulic circuit. This adjustable relief valve can be incorporated into the hydraulic circuit at any point upstream of the low pressure hydraulic components—those components that will be damaged by receiving operating liquid at higher pressure.  
     [0029] Other variations and modifications of the invention are possible. For example, the invention may be implemented using relief valves of different configurations, provided that the actuation pressures of these relief valves can be varied. All such modifications or variations are believed to be within the invention as defined by the claims appended hereto.