Abstract:
Parasitic hydraulic loading on an engine is significantly reduced during cold starts by using an unloader valve to divert the flow of hydraulic fluid from a hydraulic pump to a hydraulic actuator, i.e., load source, recirculating the hydraulic fluid between the hydraulic pump and the unloader valve.

Description:
FIELD OF THE INVENTION 
     This disclosure relates to hydraulic unloading valves and, more particularly, to hydraulic unloading valves suitable for relieving the load form a hydraulic pump, and, thereby, an engine under certain conditions such as, for example, cold starts. 
     BACKGROUND OF THE INVENTION 
     Off road equipment such as diesel powered work vehicles can from time to time experience difficulties making cold starts at cold temperatures such as, for example, temperatures less than 0° C. This can, inter alia, result from a combination of: (1) greater difficulties starting an unloaded engine at cold temperatures; and (2) the contiguous application of parasitic loading (e.g., hydraulic loading) on the engine at startup. As engines become more and more fine tuned to the work requirements of the vehicle, i.e., built and tuned to maximize work efficiency as well as energy efficiency, demanding starting conditions may become a more critical challenge for all. 
     SUMMARY OF THE INVENTION 
     Described herein is an invention that improves the conditions under which cold starts are made by significantly lowering the parasitic loading on the engine. The parasitic loading is lowered by reducing hydraulic loads on the engine via unloading valves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustrative example of a work vehicle on which the invention may be used for cold starts; 
         FIG. 2  is a perspective view of an exemplary hydraulic pump and integrated unloader valve; 
         FIG. 3  is an exemplary view of a hydraulic circuit utilizing the invention; and 
         FIG. 4  illustrates an exemplary flow chart for the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a work vehicle  10 , having a cab  18  and ground engaging means  20 , that may incorporate the invention for the purpose of improving cold starts. In such vehicles there may be many parasitic hydraulic loads, e.g., pumps for hydraulic fans, hydrostatic charge pumps, etc. Parasitic hydraulic loads may be significantly reduced via the use of unloader valves to relieve hydraulic loads in areas where functionality requiring such hydraulic loads may be, at the time, non-essential.  FIG. 2  illustrates an exemplary integrated hydraulic fan pump  100  having a pump portion  110  and an unloader valve portion  120 . While unloading may be accomplished in a non-integrated fashion, such integration may save valuable space via its compactness, increase reliability via reducing the number of exposed and connected parts, and increase efficiency via a reduction in the travel distance of hydraulic oil. 
       FIG. 3 , is an illustration of a system showing an exemplary embodiment of the integrated hydraulic pump  100  operably connected to an engine  160 , which may be, in this embodiment, via a conventional mechanical connection to a transmission  125 ; and a vehicle controller unit (VCU)  140  which may be in electrical communication with a temperature sensor  140   a  located in hydraulic fluid reservoir  150  for detecting the temperature of hydraulic fluid  151  and an engine speed sensor  140   b  which, in this embodiment, may be located within the engine  160 . As illustrated, the integrated hydraulic fan pump  100  may include a pump portion  110  having an inlet  110   a  and an outlet  110   b  and an unloader valve portion  120 . The unloader valve portion  120  may have a closed position  120   a , an open position  120   b , an actuator which is, in this case, a solenoid  120   c , and a biasing device which is, in this embodiment, a spring  120   d . As illustrated, the unloader valve portion  120  may be biased to the closed position  120   a  via the spring  120   d  or other device; it may move to the open position  120   b  upon being energized by an electrical signal from the VCU  140  to its solenoid  120   c  or via some other method. As illustrated, a hydraulic fan  130  having a hydraulic fan motor  131  and fan blades  132  may be powered by pressurized hydraulic fluid  151  from the outlet  110   b . The VCU  140  may continually monitor input from the temperature sensor  140   a  and the engine speed sensor  140   b . Also included in this embodiment is a conventional ignition (not shown) having on and off positions and a conventional starter for the engine. In this embodiment, the engine  160  is started via conventional means. 
     As illustrated, when the unloader valve portion  120  is, by default, in the closed position  120   a , the hydraulic fluid  151  pressurized by the pump portion  110  may flow directly to the hydraulic fan motor  131 , thereby biasing the system, i.e., the integrated hydraulic pump  100  toward conventional vehicle operating conditions, i.e., greater hydraulic loads when the unloader valve portion  120  is not energized. 
     When the ignition is on, the engine  160  is off, i.e., when the engine speed detected by the speed sensor  140   b  is less than a predetermined speed value (300 rpm in this embodiment), and the temperature of the hydraulic fluid, as detected by the temperature sensor  140   a , is less than a predetermined temperature value of, for example, 0° C. as in this embodiment, the VCU  140  signals the unloader valve portion  120  to move to the open position  120   b , thereby allowing hydraulic fluid  151  to flow through the unloader valve portion  120 . This arrangement may keep the inlet  110   a  and outlet  110   b  to the pump portion open but allow a significant amount of hydraulic oil moved by the pump portion  110  to recirculate between the pump portion  110  and the unloader valve portion  120  and, thereby, significantly reduce hydraulic loading from the fan motor  131  as fluids tend to take the path of least resistance which may be, in this case, the path between the pump portion  110  and the unloader valve portion  120 . 
     When the engine  160  has achieved a speed greater than 850 rpm as detected by the engine speed sensor  140   b , or the hydraulic fluid  151  has a temperature greater than or equal to 0° C. as detected by the temperature sensor  140   a , the VCU  140  stops the energizing signal to the unloader valve portion  120  allowing the unloader valve portion  120  to move to the closed position  120 . Once the unloader valve portion  120  is in the closed position  120   b , the hydraulic fluid may cease to recirculate between the pump portion  110  and the unloader valve portion  120  and follow the new path of least resistance, i.e., moving from the pump portion  110  to the hydraulic fan motor  131 . The unloader valve portion  120  may remain in the closed position until the following three conditions are met: (1) the ignition is on; (2) the engine speed is less than 300 rpm; and (3) the detected temperature of the hydraulic fluid  151  is less than 0° C. 
     The actions above are captured in the logic of the program/routine  200  followed by the VCU  140  as illustrated in the flow chart of  FIG. 4 . As illustrated in  FIG. 4 , if the ignition is on at  210  and the engine is off, i.e., the engine speed is less than 300 rpm, at  220 , and the temperature of the hydraulic fluid  151  is less than 0° C. at  230 , unloader valve portion  120  is energized to open at  240 . As illustrated, the unloader valve  120  is energized to remain open until the engine  160  achieves an engine speed greater than the predetermined speed of 850 rpm. Once the engine speed is greater than 850 rpm, the unloader valve portion  120  is de-energized and allowed to close at  260 , i.e., the VCU  140  ceases to energize the unloader valve portion  120 . If, at  220 , the engine speed is greater than or equal to 300 rpm, or at  230 , the temperature of the hydraulic fluid  151  is greater than or equal to 0° C., the unloader valve  120  is set to close. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims. The invention has been described as an integral hydraulic pump and valve arrangement but would work if the pump portion  110  and the unloader valve portion  120  were, not integrated, i.e., physically separated, yet in fluid communication with each other.