Abstract:
A hydraulic fan powered in a branch of a vehicle-carried working load hydraulic circuit helps cool hydraulic fluid in a cooler. A switching block has a bypass mode which kicks in whenever sensed hydraulic fluid temperature indicates an overheat condition. The bypass mode shuts off hydraulic fluid to all the working loads of the system, while circulating hydraulic fluid as fast as possible through the cooler and running the cooling fan at a slower rate. After the hydraulic fluid cools below the overheat threshold temperature, a start button must be pressed before the switching block will again power the working loads and run the fan at a higher speed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    The present application claims priority from U.S. Provisional Application No. 61/746,354 entitled PUMP FAN CONTROL CIRCUIT AND BLOCK FOR TRUCK MOUNTABLE HYDRAULIC SYSTEM, filed Dec. 27, 2012, incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to hydraulic systems mounted on trucks or similar vehicles to deliver hydraulic fluid, sometimes referred to as wet kit installations, such as used in tractor/trailers or trucks known as end dumps, side dumps, walking floors, tankers, low boys or similar vehicles. An example is shown in U.S. Pat. No. 7,913,713, incorporated by reference. 
         [0003]    Common problems of such hydraulic systems are evidenced when the hydraulic fluid overheats, which can be indicative of other root causes of the hydraulic overheating on the tractor/trailer. In response to the overheating problem, some hydraulic systems have temperature switches which sense the temperature of the hydraulic fluid and turn the hydraulic system off if the sensed temperature exceeds a threshold value. By turning the hydraulic system off, often an underlying problem can be identified and corrected before a catastrophic overheating failure occurs. However, inoperability of the hydraulic system due to the overheating shut-off typically occurs at an inopportune time and location. 
         [0004]    Hydraulic switching blocks can include one or more pressure relief mechanisms (such as pressure relief valves) that prevent fluid pressure within a portion of the hydraulic circuit from exceeding a threshold pressure value. When the hydraulic circuit powers the cooling fan as well as a working load, a pressure relief valve may be used to reduce the pressure used to drive the cooling fan. When a hydraulic circuit serves more than one device at the same time, the circuit designer may determine that the hydraulic circuit should share the hydraulic fluid on some basis of priority. Depending upon what other working load is being driven, and the cooling fan may or may not be considered a priority usage of the hydraulic fluid. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention involves the realization that overheating of the hydraulic fluid can occur due to a wide range of underlying causes, not all of which call for or require immediate inoperability of the entire system, and the further realization that by turning the hydraulic system off (such as at the power take-off or PTO) the hydraulic system loses its ability to quickly cool the hydraulic fluid. The present invention thus includes a hydraulic system and block which shuts off pressure to the trailer or other hydraulically operated equipment when hydraulic fluid overheats, but which continues circulation of the hydraulic fluid through the cooler and continues use of the hydraulic fluid to run the cooling fan. The block includes all the switching components of the system for easy mounting on a truck. In another aspect, the cooling fan is run at a lower rate after the overheat threshold is surpassed, and oil circulates faster through the cooler. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a first perspective (isometric) view of the hydraulic switching block of a preferred embodiment of the present invention, shown from the bottom to better see the various attached components. 
           [0007]      FIG. 2  is a second perspective (isometric) view of the hydraulic switching block of  FIG. 1 , shown from the top. 
           [0008]      FIG. 3  is a rear view of the hydraulic switching block of  FIGS. 1 and 2 . 
           [0009]      FIG. 4  is a right side view of the hydraulic switching block of  FIGS. 1-3 . 
           [0010]      FIG. 5  is a front view of the hydraulic switching block of  FIGS. 1-4 . 
           [0011]      FIG. 6  is a left side view of the hydraulic switching block of  FIGS. 1-5 . 
           [0012]      FIG. 7  is a top plan view of the hydraulic switching block of  FIGS. 1-6 . 
           [0013]      FIG. 8  is a bottom plan view of the hydraulic switching block of  FIGS. 1-7 . 
           [0014]      FIG. 9  is a hydraulic schematic for the preferred switching block and hydraulic system. 
           [0015]      FIG. 10  is an electrical schematic for the preferred system. 
       
    
    
       [0016]    While the above-identified drawing figures set forth a preferred embodiment, other embodiments of the present invention are also contemplated, some of which are noted in the discussion. In all cases, this disclosure presents the illustrated embodiments of the present invention by way of representation and not limitation. Numerous other minor modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention. The labels “rear”, “right”, “front”, “left”, “top” and “bottom” are merely for reference, as the orientation in which the hydraulic switching block is mounted is not significant to the operation of the invention. 
       DETAILED DESCRIPTION 
       [0017]    The preferred embodiment of the invention involves a hydraulic system  10  (shown in full in  FIG. 9 ) executed through a switching block  12  which is mounted on the tractor (not shown) of a tractor-trailer rig (not shown). In the preferred embodiment, the block  14  of the switching block  12  is machined out of 6061 T6 aluminum and anodized gold, but it could be equivalently made out of numerous materials. The aluminum material is lightweight, easy to machine, corrosion-resistive, and cost effective for planned quantities. The various valves, plugs etc. depicted are attached to the block  14 , typically via threaded connections to their respective openings. In the preferred embodiment, labels on the block  14  designate which valve, plug and port on the block  14  is which. The preferred block  14  is about 8¾×5×6 inches. Mounting holes  15  may also be present on the block  14 . A wide variety of other shapes and sizes of blocks could alternatively be used, as appropriate for any specific valves and port sizes. 
         [0018]    The block  14  includes two high pressure inlet ports P 1  and P 2 , for connection to first and second pumps  16 ,  18  (shown in  FIG. 9 ) driven by a PTO  20  off the engine  22  of the vehicle (not shown). The preferred port sizes are shown on hydraulic schematic, and in the preferred embodiment high pressure inlet ports P 1  and P 2  are size 16T ports. 
         [0019]    In the preferred embodiment, each pump  16 ,  18  is rated to provide up to 30 gallons per minute, at a hydraulic pressure up to about 2900 psi. In use, the flow rate output of each pump  16 ,  18  is a function of back pressure on the circuit and engine speed, with higher flow rate outputs at lower back pressures and higher engine speeds. The primary purpose of the hydraulic system  10  is to provide hydraulic power to two different trailer circuits  24 ,  26  (shown in part at the top of the hydraulic schematic of  FIG. 9  each via a working load valve  28 ,  30 ), thereby each powering a working load  32 ,  34  on the trailer such as a hydraulic cylinder (not separately shown) for dumping or for movement of a boom (not shown) or for similar known working hydraulic uses. While the preferred embodiment has the same rated pump flow rate and pressure for each pump  16 ,  18 , pumps rated for other pressures and other pump flow rates could be used, including different values for the two different pumps/hydraulic circuits. 
         [0020]    The hydraulic circuit  10  shown is depicted in  FIG. 9  in its normal or unenergized position, which is a bypass mode. On circuit  1  in bypass mode, oil travels through two branches  36 ,  38  of the circuit  1 . In one branch  36 , oil flows through piloted directional valve PD-1 (#16 piloted 2 position, 3 way ext vent 70 psi valve, PD16-S50-0-N- 70 ; all the listed valves can be commercially obtained from Hydraforce, Inc. of Lincolnshire, Ill.) and then through the 500 psi return valve RV2 (relief PO spool 500 psi valve, RV12-26H-0-N-15-05) to output port Cooler, to be piped exteriorly of the switching block  12  back to the oil cooler  40  and tank  42 . The 500 psi value for return valve RV2 is preferably screw adjustable to any pressure within a range, such as to a value within the range of 500 to 800 psi. 
         [0021]    In a second branch  38  of circuit  1 , oil flows through check valve CV1 (#08 check valve, 4 psi, CV08-20-0-N-4) and the 1000 psi Pressure Reduction valve PR1 (#10 pres reduce/relieve P.O. 1000 psi, PR10-36A-0-N-15/10.00) to output port Fan, to be piped exteriorly to the switching block  12  back to drive the cooling fan  44  and then through the cooler  40  and back to the tank  42 . Thus, the screw adjustment of return valve RV2 controls the fan speed while the switching block  12  is in its by-pass mode, to a lower speed than when the switching block  12  is in operational mode, but the fan  44  still operates. While the fan  44  is operating at this low speed, circuit  1  directs an essentially full flow, driven by pump  16  against a back pressure of only about 500 psi, through either the pressure reduction valve RV2 or the fan  44  and through the cooler  40 . 
         [0022]    On circuit  2  during bypass mode, oil flows immediately through the normally open solenoid valve SVR (#12 solenoid operated relief, 2500 psi, SVRV12-26F-0-N-00/25.00 using a #10 e-coil, 12 VDC, metri-pack, zener solenoid, 4303912) for return to the Cooler port. Additionally, oil can flow through the Circuit  2  output port C 2 , through circuit  2  trailer valve and back to the Return port, and then through the switching block  12  back to the Cooler port, cooler  40  and tank  42 . While the fan  44  is operating at low speed, circuit  2  directs a completely full flow, driven by pump  18  against almost no back pressure other than piping loss, through either the solenoid valve SVR or the circuit  2  trailer valve and through the cooler  40 . In sum, during the normal bypass mode, the cooling fan  44  is driven at about half speed, and the oil in both circuits is cooled by a high flow rate through the cooler  40 . 
         [0023]    The switching block  12  stays in bypass mode any time the oil temperature sensor  46  (shown in  FIG. 10 ) senses oil temperature above a threshold value, i.e., during all overheat conditions. When the oil is within a standard operating temperature range, an electrical signal can be provided to the electrical circuit to drive both the solenoid valve SV1 (for the first oil circuit, SV10-33-0-N-00) and solenoid valve return SVR (for the second oil circuit) to their other position. For instance, the electrical circuit of  FIG. 10  operates in this way, i.e., so long as the oil temperature is below a threshold value so the temp switch  46  is closed, pressing the “start” button  48  will turn on the light  50 , close both relay-1 and relay-2, and power SVR and SV1. Pressing the “stop” button  52  at any time will return the system  10  to bypass mode. 
         [0024]    Referring back to the hydraulic schematic of  FIG. 9 , when SV1 is energized, SV1 directs oil to switch the piloted directional valve PD-1 to its other position. Circuit  1  now has a primary branch which flows from port P 1 , through piloted directional valve PD1 to circuit port C 1  and to the circuit  1  trailer valve to power the first circuit  24  on the trailer as necessary. Return valve RV1 (relief PO spool 2500 psi valve, RV12-26H-0-N-35/25) has a screw adjustment, such as within a range of 1000-3500 psi and in this case shown at 2500 psi, for limiting the pressure through the first circuit. In the second branch of circuit  1 , oil flows through check valve CV1 to not only power the piloted directional valve PD1, but also through the 1000 psi Pressure Return valve PR1 to drive the fan  44  at full speed. 
         [0025]    In circuit  2 , the other position of solenoid valve return SVR has a screw adjustment, such as within a range of 1000-3000 psi, in this case shown at 2500 psi for limiting the pressure in circuit  2 . When SVR is energized, this 2500 psi pressure is primarily directed to the circuit  2  trailer valve  30 . Oil can also flow through check valve CV2 and through the 1000 psi pressure return valve PR1 to drive the fan  44 . Note that if both the working power valve (circuit  1  trailer valve  28  and the circuit  2  trailer valve  30 ) are in the rest position shown in  FIG. 9 , the pressure on the circuit may decline below 1000 psi with full oil flow through the trailer valves  28 ,  30 . That is, full speed running of the cooling fan  44  is only assured when a) the temperature of the hydraulic fluid remains below the threshold value; and b) either circuit  1  working load  32  or circuit  2  working load  34  presents enough resistance to raise pressure above 1000 psi. 
         [0026]    All of the ports G 1 , G 2 , G 3 , G 4  and G 5  are simply machining ports used for most easily forming the block  14 , and are plugged during normal usage. Temperature port TEMP is also typically plugged, but can be used if desired for a switching block temperature gauge  46  or similar purpose. 
         [0027]    The system  10  includes a temperature sensor  46 , in the temperature port TEMP or elsewhere in the hydraulic system  10 , which senses the temperature of the hydraulic fluid. Whenever an overheat event occurs, the switching block  12  returns to bypass mode, still driving the fan  44  (at low speed) and circulating oil at a very high flowrate (through circuit  1  against a back pressure of 500 psi as controlled by return valve RV2) through the cooler  40  rather than turning off the PTO  20 . In testing of one preferred embodiment, oil exceeded a threshold temperature of about 175° F., kicking the switching block  12  into bypass mode. In bypass mode the oil cooled from 177° F. to about 130° F. in about 5 minutes, much faster than if the PTO  20  had been fully shut down due to the overheat condition. This cool down is also believed to be faster than if the oil had been used to drive the fan  44  at full speed and the commensurately slower flow rate (through circuit  1  against a back pressure of 1000 psi as controlled by pressure reduction valve PR1). 
         [0028]    In one alternative or additional embodiment of the system as shown in the electrical schematic, an oil level gauge  54  can set off a different alarm  56  and shut down sequence than the bypass sequence initiated by temperature sensor  46 . For instance, a low oil condition can first shut off the cruise control (not shown) of the trailer, and then smoothly stop the PTO  20 . 
         [0029]    The electrical circuit shown is primarily embodied in an electrical enclosure box  58  which is mounted in the vicinity of the cooler  40 . In this embodiment, both initial starting and recovery from an overheat condition require a manual pressing of the start button  48 . Requiring the start button  48  to be pressed to exit an overheat event after cool down ensures ensuring that merely returning to operational temperature (without pressing the start button  48 ) does not restart either of the trailer circuits  24 ,  26  and their working loads  32 ,  34  (such as power cylinders on the trailer) at an inopportune or dangerous time. 
         [0030]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. As a particular example, all the specified pressure values detailed herein are merely exemplary of a preferred embodiment, and can be changed or adjusted for a particular use. The important considerations are that an overheating condition result in shutting off hydraulic fluid flow to the trailer circuits  24 ,  26  and their working loads  32 ,  34 , but leave the PTO  20  running to circulate hydraulic fluid through the cooler  40 , and also using the hydraulic fluid to power the fan  44  at a speed which is selected (by the circuit designer and/or adjustment) to be different from the full speed fan rate selected (by the circuit designer and/or adjustment) for cooling during normal working load operation.