Abstract:
A pump assembly and method for an internal combustion engine includes a high-pressure pump for pressurizing oil used to actuate fuel injectors or other devices, a hydraulic inlet throttle valve, a three-way valve for alternatively connecting the inlet throttle valve to output pressure or to the sump and a solenoid responsive to signals from an electronic control module for shifting the three-way valve.

Description:
FIELD OF THE INVENTION 
     The invention relates to pump assemblies and pumping methods for internal combustion engines where the liquid pumped by the assembly is used to actuate hydraulically driven devices, typically fuel injectors, intake and exhaust valves, and engine brakes. 
     DESCRIPTION OF THE PRIOR ART 
     Diesel engines using hydraulically actuated devices including fuel injectors, intake and exhaust valves and engine brakes are well known. The hydraulically actuated devices each include an actuation solenoid, which, in response to a signal opens a valve for an interval to permit high-pressure liquid supplied to the device to extend a piston and actuate the device. 
     U.S. Pat. No. 6,460,510 discloses a pump assembly for a diesel engine with hydraulically actuated fuel injectors including a high-pressure pump for pumping high-pressure engine oil to the injectors, a hydraulic inlet throttle valve for controlling inlet flow of low-pressure engine oil to the pump and a hydraulic circuit for opening and closing the inlet throttle valve in response to signals from an engine control module (ECM) proportional to the difference between measured pump outlet pressure and desired outlet pressure as determined by the ECM. 
     The inlet throttle valve includes a spool and a spring that biases the spool toward a full open position. A piston on the spool forms one wall of a pressure chamber which is connected to an injection pressure regulator (IPR) valve and is also vented to the sump through a restriction. High-pressure output oil is flowed to the chamber by the IPR valve to shift the spool against the spring toward the closed position. The pressure drop across the restriction prevents pressurizing the chamber at full output pressure. Additionally, when the ECM determines the output pressure must be increased, the restriction prevents rapid flow of oil out from the pressure chamber and slows opening movement of the spool. Rapid opening and closing response of the inlet throttle valve to signals to increase or decrease output pressure is desirable. 
     The pump assembly of U.S. Pat. No. 4,460,510 is particularly adapted to controlling the output pressure of oil used to actuate fuel injectors for a diesel engine which is operated primarily at high engine speed, such as an engine in an over-the-road truck. 
     Accordingly, there is a need for an improved pump assembly with a hydraulic inlet throttle valve and method for flowing engine oil to a high-pressure pump for an internal combustion engine where the pump assembly responds rapidly and accurately to ECM signals, particularly when the engine is at low speed or idling and output pressure is low. The pump assembly should be capable of rapidly opening or closing the inlet throttle valve to increase or decrease the flow of low-pressure oil to the pump and rapidly increase or decrease the output pressure. The assembly should improve the stability of the inlet throttle valve by damping the effect of output pressure spikes on the inlet throttle valve. The inlet throttle valve should respond directly to full output pressure when a decrease in output pressure is required and should drain oil directly to the sump, without flow restriction, when increased output pressure is required. Operation of the inlet throttle valve by high output pressure oil should not damage the valve. 
     There is also a need for a pump assembly and method for an internal combustion engine with improved fuel efficiency, particularly when the engine is operating at low speed or idling. 
     SUMMARY OF THE INVENTION 
     The invention comprises a pump assembly and method for actuating a fuel injector, intake or exhaust valve, engine brake or other member in an internal combustion engine. The pump assembly has a high-pressure variable output pump and a hydraulically actuated inlet throttle valve for the pump. The inlet throttle valve has a valving spool that is biased toward an open position by a spring and by inlet pressure. The spool is biased toward a closed position by high-pressure oil from the pump. 
     The pump assembly includes a three-way valve responsive to a signal from the ECM to rapidly open or close the inlet throttle valve. The inlet throttle valve is rapidly closed by oil at full output pressure. The inlet throttle valve is rapidly opened by a spring and inlet pressure while draining oil in the valve directly to the sump. 
     Connection of the inlet throttle valve to oil at output pressure moves the valve spool in a closing direction responsive to the full output pressure, without pressure reduction due to flow of the oil to the sump through a restriction. The spool moves in an opening direction with direct drain to the sump, without flow through a restriction. In each case, response time for movement of the spool is reduced. 
     The inlet throttle valve includes a soft or hydraulic stop to prevent physical contact between the spool and the valve body when the valve is rapidly closed by flow from a full output pressure oil passage. 
     The three-way valve includes a spool having a valving land which moves across valving openings leading to the pressure chamber in the inlet throttle valve. When the inlet throttle valve is pressure balanced, the land is in a null position, overlies the valving openings and the valving openings are underlapped, permitting limited flow of high-pressure oil past the land and directly to sump. Underlapping damps spikes in output pressure by flowing oil directly to the sump and improves stability of the inlet throttle valve. 
     The pump assembly is designed for stable operation both at high engine speed with output pressure as high as 4,060 PSI and at low or idle engine speed where the output pressure may be as low as 360 PSI. This results in improved fuel economy, particularly in engines that frequently operate at low RPM or at idle. 
     Three embodiment pump assemblies are disclosed. In the first embodiment the three-way valve spool is biased against a spring and is shifted by hydraulic pressure. The hydraulic pressure is determined by flow through a solenoid controlled valve. In the second and third embodiments, the three-way valve spool is biased against a spring by a proportional solenoid. In all embodiments, the ECM sends a current signal to a solenoid that is influenced by the difference between the output pressure of the high-pressure pump and desired output pressure. 
     Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of the hydraulic circuitry of a first embodiment pump assembly; 
     FIG. 2 is a sectional view, partially broken away, of valve components of the pump assembly of FIG. 1; 
     FIG. 3 is a flattened view of an interior cylindrical surface of a valving bore in the assembly; 
     FIG. 4 is a sectional view through an inlet throttle valve; and 
     FIGS. 5 and 6 are diagrams of hydraulic circuitry of second and third embodiment pump assemblies. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First embodiment pump assembly  10  is a component of an internal combustion engine, typically a diesel engine, and provides high-pressure liquid, typically engine oil, for actuating fuel injectors for the engine. The assembly may also provide high-pressure liquid for actuating mechanisms for intake and exhaust valves or for other devices. 
     My U.S. Pat. No. 6,460,510 discloses a diesel engine with a pump assembly for hydraulically actuated fuel injectors which is related to assembly  10 . The disclosure of U.S. Pat. No. 6,460,510 is incorporated herein by reference, in its entirety. 
     The diesel engine includes a low-pressure oil pump  12  which draws oil from sump  14  and flows the oil through low-pressure line  16  to engine bearings and cooling jets. The fuel injectors for the engine (not illustrated) are actuated by high-pressure engine oil supplied by assembly  10  through high-pressure outlet passage  18 . 
     Assembly  10  includes hydraulically actuated inlet throttle valve  20  and variable output high-pressure pump  22 . The pump may be identical to the pump disclosed in U.S. Pat. No. 6,460,510. Pump  22  is rotated by the engine. Branch low-pressure line  24  extends from line  16  to the inlet port of inlet throttle valve  20 . Inlet passage  26  extends from the outlet port of the inlet throttle valve to the inlet port of pump  22 . High-pressure outlet passage  18  is connected to the outlet port of pump  22 . 
     Inlet throttle valve  20  is illustrated in FIG.  4 . Valve  20  includes a body  28 , which may be part of the body of high-pressure pump  22 . Bore or passage  30  extends into body  28  to closed end  32 . Low-pressure line  24  extends to oil inlet port  34  at the open end of bore  30 . Inlet passage  26  extends to oil outlet port  36  which surrounds the bore  30  between the open and closed ends of the bore. 
     Hollow, cylindrical valving spool  38  has a close sliding fit in the bore permitting movement of the spool along the bore. Outer spool end  40  is open and inner piston end  42  is closed to form a piston. Cylindrical wall  44  extends between ends  40  and  42 . Spring  46  is confined between retainer sleeve  48  at the open end of the bore and the piston end  42  of the spool to bias the spool toward closed end  32  of the bore. Locating post  50  extends inwardly from the closed end of, the spool to prevent the spool end from bottoming on the end of the bore and to define a hydraulic chamber  52  between piston end  42  and bore end  32 . Chamber port  54  permits flow of oil into and from chamber  52 . 
     A number of flow openings  56  extend through cylindrical wall  44 . When the spool is in the full open position as shown in FIG. 4 the openings provide a large flow area communicating ports  34  and  36  for maximum flow of low-pressure oil to pump  22 . High-pressure oil flowed into chamber  52 , moves the spool away from closed end  32 , against spring  46  and the inlet pressure of pump  12 , and moves the flow openings past the oil outlet port to reduce the flow area through the inlet throttle valve and correspondingly reduce the volume of oil flowed to high-pressure pump  22 . 
     Drain port  58  extends through body  28  to bore  30 . When the spool is in the full open position, as shown in FIG. 4, wall  44  overlies port  58  and the piston end  42  is between the port and bore closed end  32 . As oil in chamber  52  moves the spool away from the full open position the piston uncovers port  58  prior to engagement of the spool outer end  40  against retainer  48 . When the piston uncovers the drain port the high-pressure oil in chamber  52  is flowed directly to sump  14  to stop closing movement of the spool and prevent contact between the spool end  40  and retainer  48 . In this way, rapid movement of the spool toward the closed position by the high-pressure oil in chamber  52  is automatically slowed and stopped to prevent mechanical engagement between the spool and retainer. The drain port  58  forms a hydraulic stop, rather than mechanical stop, to cushion closing movement of the spool and prevent damage to the inlet throttle valve because of mechanical engagement between the spool and the retainer. 
     Port  34  opens into the interior of spool  38  so that the pressure of inlet oil in line  24  cooperates with spring  46  to bias the spool toward the open position. When chamber  52  is connected to the sump the inlet oil pressure and the spring rapidly open the valve. The flow area of the inlet throttle valve, and consequently the volume of low-pressure inlet oil flowed through passage  26  to pump  22 , is determined by the position of spool  38  in bore  30 . 
     Regulator valve  60  includes pilot relief valve  62  and main stage, three-way valve  64 . High-pressure branch passage or line  66  extends from passage  18  through opening  68  of valve  60  to restriction  70 . Passage or line  72  extends from the restriction to one end of pilot relief valve  62 . Passage or line  74  extends from line  72  to the inlet port of valve  62  and to one end of main stage three-way valve  64 . The other end of valve  64  is connected to line  66 . 
     Valve  64  includes a high-pressure inlet port  76  connected to line  66 , a drain port  78  connected to sump  14  through line  80  and a work port  82  connected directly to hydraulic chamber  52  in inlet throttle valve  20  through line  84 . Drain port  58  in inlet throttle valve  20  is connected to sump  14  through lines  59  and  80 . 
     Valve  64  has a valving spool  86  ,moveable between first and second positions shown in FIG.  1  and an intermediate null position shown in FIG.  2 . In the first position work port  82  is connected to drain port  78  to vent hydraulic or pressure chamber  52  in inlet throttle valve  20  directly to the sump and inlet port  76  is closed. In the second position drain port  78  is closed and the inlet port  76  is connected to work port  82  to flow high-pressure oil from passage  18  directly to the pressure chamber in the inlet throttle valve. The full output pressure acts on the inlet throttle valve spool to shift the spool toward the closed position against spring  46  and inlet pressure. 
     Spring  88  and the pressure of oil in line  74  downstream of restriction  70 , bias spool  86  toward the first position, as indicated in FIG.  1 . High-pressure fluid in line  66  biases the spool toward the second position. Both ends of the spool have the same area so that when there is no pressure drop across restriction  70 , spring  88  holds the spool in the first position, chamber  52  is vented to sump and the inlet throttle valve is open. When the pressure in line  74  is reduced by opening valve  62  to flow fluid in line  74  to sump, there is a pressure drop across restriction  70  and the pressure in line  66  shifts spool  86  toward the second position. 
     Pilot relief valve  62  includes solenoid  90  which is actuated by a current signal from the ECM. The valve includes a spool or pin  92  that is acted upon by the pressure of oil in line  72  to open the valve. The solenoid, in response to the signal from the ECM, biases the spool toward a closed position as illustrated. 
     The regulator valve  60  includes inlet opening  68  in line  28 , drain opening  94  in drain line  80  leading to sump  14 , and work opening  96  in line  84  leading to the inlet throttle valve  20 . 
     Assembly  10  includes a conventional high-pressure mechanical relief valve  98  that opens in response to transient over pressure in passage  18  to flow high-pressure oil directly to sump  14  and reduce the over-pressure. The assembly also includes a conventional makeup check valve  100 . Valve  100  permits flow of makeup oil into the high-pressure passage when the engine is shut off and cools. 
     FIG. 2 is a sectional view through regulator valve  60 . The valve has a body  102  housing valves  62  and  64 . Body  102  has a stepped cylindrical recess  104  extending into one side of the body with the port end  106  of the recess communicating with inlet port  76 . Radial passage  108  extends from the recess to work port  82  and radial passage  110  extends from the recess to drain port  78 . Hollow, generally cylindrical body  112  is threaded into recess  104 . 
     Solenoid  90  is mounted on the outer end of body  102 , outside of body  112 . The solenoid includes coil  114 , which surrounds armature  115 . The armature engages rod  116  which is slideably mounted in solenoid insert  118 . 
     Valve insert  120  is mounted in recess  104  in body  102  and defines a cylindrical valving bore  122  extending from the port end  106  of the recess  104  to cap  124  confined between inserts  118  and  120 . The cap closes the end of bore  122  adjacent the solenoid. A small diameter valving passage  126  extends through cap  124  to communicate bore  122  with chamber  128  formed in solenoid insert  118 . Passage  130  communicates chamber  128  with cylindrical chamber  132  surrounding insert  120  and in flow communication with passage  110  leading to drain port  78 . 
     Cap  124  slideably supports spool or pin  92  of valve  62 . The pin is held between rod  116  and one end of valving passage  126 . The pin is larger than passage  126 . Energization of solenoid  90  by a current signal from the ECM biases the armature  115  against rod  116  and the rod against pin  92  to bias the pin toward the cap. The pressure of the oil in valving passage  122  biases the pin in the opposite direction. 
     Hollow cylindrical valve spool  86  is slideably fitted in bore  122  and includes an open end adjacent cap  124  and piston  134  adjacent port end  106 . Restriction or bleed opening  70  extends through piston  134  to the interior of the spool. The spool is located in bore  122  between cap  124  and the inner end of cylindrical stop  136  fitted in the end of bore  122  adjacent port  76 . Spring  88  is confined between cap  124  and an interior step in spool  86  to bias the spool toward stop  136 . 
     Narrow, cylindrical valving land  138  extends around the end of spool  86  at piston  134 . Land  138  extends from the piston to a circumferential recess  140  formed in the spool and has a close sliding fit in bore  122 . One or more openings  142  extend through insert  120  to communicate recess  140  with chamber  132  at all times. 
     Four like, small diameter cylindrical valving passages  144   a ,  144   b ,  144   c  and  144   d  extend through insert  120  and open into bore  122  a short distance outwardly from stop  136 . Passages  144  open into chamber  146  and passage  108  leading to work port  82 . The passages  144  are spaced apart  90  degrees from each other around the wall of bore  122  and are spaced axially or offset a short distance along the bore as illustrated in FIG.  3 . Flow passages  144   a  and  144   c  are diametrically opposed and in line with each other in bore  122 . Likewise, passages  144   b  and  144   d  are diametrically opposed and in line with each other. Passages  144   a  and  144   c  are axially offset from passages  144   b  and  144   d  in bore  122 . 
     The bore  122  may have a diameter of 0.250 inches with valving passages  144  having diameters of 0.047 inches. The centers of passages  144   a  and  144   c  are axially spaced from the centers of passages  144   b  and  144   d  by a distance  148  of 0.035 inches so that the passages  144  are located within a circumferential band  150  extending around bore  122  and having a width  152  of 0.082 inches. Valving land  138  on spool  86  has a width of 0.076 inches so that when the spool is in the null position shown in FIG. 2, the land overlies passages  144  with an underlap of approximately 0.0015 inches at passages  144   a  and  144   c  and an underlap of 0.0045 inches at passages  144   b  and  144   d . When the spool in the null position, flow through underlapped passages  144   a  and  144   c  equals flow through underlapped passages  144   b  and  144   d . Because the pressure drop across passages  144   a  and  144   c  on the high-pressure side of piston  134  is greater than the pressure drop across passages  144   b  and  144   d  on the low pressure side of piston  134 , passages  144   a  and  144   c  are underlapped less than passages  144   b  and  144   d . The underlaps shown are for a null position at high output pressure. The null position for a reduced output pressure would have a larger underlap at passages  144   a  and  144   c  and a smaller underlap at passages  144   b  and  144   d.    
     The small diameters of passages  144  means that the flow areas through the passages increases and decreases relatively slowly as an edge of the valving land  138  moves across the passages, thus providing relatively gradual increase of high-pressure flow through the passages to the inlet throttle valve  20  during opening. Slow opening of the passages improves the stability of inlet throttle valve. Large passages having a diameter equal to the full width of band  150  would increase and decrease the flow area undesirably rapidly as land  138  moves across the passages. 
     The pressure of oil on the high-pressure side of piston  134  may be as high as 4,060 pounds per square inch. When the valving spool is moved toward cap  124  against spring  88  and partially opens passages  144 , the oil exerts radial pressure on exposed portions of land  138 . Since the diametrically opposed passages  144  are in line with each other, radial forces are balanced. For instance, movement of spool  86  to the right of the position shown in FIG. 2 opens passages  144   a  and  144   c  and the high-pressure oil exerts equal and opposite forces on the portions of the valving land overlying the passages. Thus, there are insignificant radial forces acting on spool  86 , with minimum friction and spool/bore wear. 
     Land  138  underlaps passages  144  and substantially closes the passages when in the null position. In addition, passages  144   a  and  144   c  may be smaller in diameter that passages  144   b  and  144   d  to improve the gradual change of flow area from outlet pressure to work port  82  relative to gradual change of flow area from the work port  82  to sump. If desired, the land may have a width sufficient to completely cover the passages, so that the land completely closes the passages when in the null position. 
     The operation of pump assembly  10  will now be described. 
     Before startup of the engine main stage valve  64  is in the first position indicated in FIG. 1 with spring  88  holding spool  86  against stop  136  and passage  108  is connected to passage  110 . With the hydraulic chamber  52  of the inlet throttle valve connected to the sump through passages  108  and  110 , spring  46  holds the inlet throttle valve spool in the full open position for maximum flow of inlet oil to the high-pressure pump and rapid increase of pressure in outlet passage  18 . 
     When the engine has been started, the pressure in outlet passage  18  is typically less than the desired pressure in the passage so that the ECM sends a high current signal to solenoid  90  to bias pin  92  against passage  126  and close the passage. In the absence of flow through the passage, there is no flow through restriction  70 , no pressure drop across piston  134  and no force exerted on the piston to move spool  86  away from stop  136 . Spring  88  continues to hold spool  86  against the stop. Valving land  138  remains positioned to the left of passages  144  preventing flow of high-pressure outlet oil through the passages and to the inlet throttle valve. The inlet valve stays fully open and pressure in passage  18  rapidly increases. 
     As pressure builds in passage  18  the difference between the actual output pressure and the desired output pressure decreases and the ECM signal to solenoid  90  decreases, reducing the force exerted on pin  92  by the solenoid. The reduction of this force, together with the increase of pressure in bore  122  moves pin  92  away from cap  124  sufficiently to permit flow past the pin to passages  130  and  110  and to the sump. High-pressure fluid flows into the spool through restriction  70  in piston  134 . The pressure drop across the piston biases the piston to the right, as shown in FIG. 2, away from stop  136  against the force exerted by spring  88 . As land  138  moves away from stop  136  it gradually closes passages  144 . This occurs until the land is in the null position, the output pressure in passage  18  is equal to the desired pressure and the inlet throttle valve spool  38  has reached a pressure balance position. 
     When the pressure in passage  18  is greater than the desired pressure the ECM signal is decreased, further increasing flow through passage  126  and increasing the pressure on piston  134  to shift spool  86  away from stop  136 . Further movement of the spool moves land  138  past passages  144  to open the passages to flow of high-pressure oil directly from the output passage  18  to hydraulic chamber  52  in the inlet throttle valve, increase the pressure in the chamber and shift the inlet throttle valve spool  38  toward the partially closed position. Venting of the inlet throttle valve to sump is cut off. 
     As the pressure in passage  18  approaches the desired pressure, the signals to solenoid  52  either increase or decrease until the desired pressure is achieved, the inlet throttle valve spool has reached a pressure balance position and land  138  is in the null position shown in FIG. 2 to substantially or fully close passages  112  to the pressure chamber in the inlet throttle valve. 
     When desired output pressure changes, the ECM signal changes and the spools of valves  20  and  64  modulate with spool  86  returning to the null position and inlet throttle valve spool  38  stabilizing at a new equilibrium position. 
     Full output pressure in passage  18  is applied directly to the inlet throttle spool to shift the spool and close the valve. Applying full output pressure to the inlet throttle valve spool is important when the engine is operating at a rotational low speed and the full output pressure is relatively low, yet sufficiently high to rapidly shift the inlet throttle spool  92  against spring  46  and inlet pressure in response to signals received from the ECM. For instance, pump assembly  10  may be mounted on a diesel engine used in a light truck or a passenger vehicle where the rotational speed of the engine is rapidly and frequently increased and decreased through an operating range extending from idle to a high speed maximum and where the output pressure at low speed is considerably less than the output pressure at high speed. Regulator valve  60  utilizes available output pressure to close the inlet throttle valve spool quickly and stably. The hydraulic stop for spool  38  provided by drain port  58  prevents output pressure from moving the spool into contact with stop  136 . Valve  60  allows the inlet throttle valve spring and inlet pressure to shift the spool rapidly to the open position by directly venting the pressure chamber in the valve to the sump. Valve  60  permits rapid response of the inlet throttle valve to changes in the ECM signal over the RPM range of the engine and improves inlet throttle valve stability and fuel economy. 
     At the equilibrium or null position of valve  60 , shown in FIG.  2  and indicated in FIG. 3, land  138  is positioned over and underlaps the four valving passages  144 . Small portions of passages  144   a  and  144   c  on the high-pressure side of land  138  are open and small portions of passages  144   b  and  144   d  on the low-pressure side of land  138  are open. The underlap shown in FIG. 3 is exaggerated for purposes of illustration. The open portions of passages  144   a  and  144   c  may be 0.0015 inches wide and the open portions of passages  144   b  and  144   c  may be 0.0045 inches wide. 
     When the land  138  is in the null position the uncovered or untapped portions of passages  144   a  and  144   c  communicate with the small area untapped portions of passages  144   b  and  144   d  through chamber  146 . The untapped openings permit limited flow of high-pressure oil at output pressure from passage  18  through the untapped portions of passages  144   a  and  144   c , chamber  146 , untapped portions of passages  144   b  and  144   d , and to sump  14 . The small area underlap bleed passages desensitize inlet throttle valve spool  38  to pressure spikes in outlet passage  18 . The full force of the pressure spike is not transmitted to the inlet throttle valve. The bleed passages communicate port  76  to the sump to dampen pressure oscillation of the inlet throttle valve spool in response to pressure spikes and improve stability of the inlet throttle valve. 
     Regulator valve  60  does not respond to overpressures in passage  18  by dumping high-pressure oil directly to the sump with consequent energy loss when the oil is depressurized. Rather, an overpressure insufficient to open valve  98  shifts main stage valve  64  to flow high-pressure fluid through line  84  to the inlet throttle valve and shift the valve toward the closed position and reduce input to high-pressure pump  22 . Reduced input reduces the volume of oil pumped into passage  18  and reduces output pressure. Underlapping of openings  144  by valving land  138  provides limited direct flow to the sump to reduce instability of the inlet throttle valve. 
     Alternate connection of the inlet throttle valve chamber  52  directly to output pressure or to the sump permits rapid flow of oil into and out of the chamber to move the inlet throttle valve spool rapidly in response to signals from the ECM and reduces the time required to increase or decrease the pressure in the outlet passage  18  to match the desired output pressure as determined by the ECM. Rapid output pressure response is particularly valuable in diesel engines where the speed of the engine may quickly vary from idle, with a low output pressure of about 360 PSI to maximum engine speed with output pressure as great as 4,060 PSI. 
     FIG. 5 illustrates a second embodiment pump assembly  200  which is identical to assembly  10  except that the assembly uses a regulator valve  202  different from regulator valve  60 . Other components of pump assembly  200  are identical to the prior described components of assembly  10  and are identified in FIG. 5 by the same reference numbers used in FIG.  1 . 
     Regulator valve  202  includes a single solenoid three-way valve  204  having inlet port  206 , drain or exhaust port  208  and work port  210 . These ports are respectively connected to regulator valve inlet opening  212 , drain opening  214  and work opening  216 , corresponding to openings  68 ,  94  and  96  of regulator valve  60 . 
     Valve  204  includes a valving spool (not illustrated) having a pressure piston with a cylindrical valving land moveable along a valving bore as in valve  38 . The piston is imperforate. Four cylindrical valving passages open into the bore and are arranged in opposed, spaced pairs, like passages  144  previously described. The valving land is underlapped with regard to the valving passages, as previously described. If desired, the land may completely cover the valving passages. 
     Spring  218  biases the spool toward a first position, previously described, where work port  210  is connected to drain port  208  and the pressure chamber  52  in inlet throttle valve  20  is connected to the sump through lines  84 , valve  204  and line  80 . 
     The valve has a second position, previously described, where the inlet port  206  is connected to work port  210  to flow high-pressure oil from passage  18  directly to the pressure chamber of the inlet throttle valve through line  84 . 
     Valve  204  has a null position, as previously described, with the spool land underlapping or closing the valving passages. The position is the same as indicated in FIG.  3  and previously described. The solenoid force biases the spool against the force of spring  218  to shift the spool in the valve bore relative to the small valving passages like passages  144  described previously. 
     The valve  204  includes a fast acting proportional solenoid  220  having an armature engaging the spool. The solenoid biases the spool toward the second position. The coil of solenoid  220  receives a steady state current signal from the engine ECM to maintain the spool in a null position. Current is increased or decreased proportional to the difference between the desired output pressure in line  18 , as calculated by the ECM, and the actual outlet pressure in line  18 . This signal generates a force biasing the spool toward the second valve position. When the solenoid force is greater than the spring force the spool shifts toward the second position and high-pressure oil from line  18  is flowed directly to the inlet throttle valve to rapidly move the inlet throttle valve toward the closed position. When the solenoid force is less than the spring force the spool shifts toward the first position and the inlet throttle valve opens. 
     In valve  204 , the spool has a central piston carrying the valving land and end pistons spaced to either side of the central piston. The outer ends of the valving bore are connected to sump  14  through passage  80  and are at the same low-pressure. Both ends of the spool have the same area. This assures that the movement of the spool along the valving bore is influenced by spring  218  and solenoid  220  and is not influenced by pressure differentials at the ends of the spool. 
     FIG. 6 illustrates a third embodiment pump assembly  300  which is identical to assembly  200  except that assembly  300  uses a regulator valve  302  different from regulator valve  202 . Other components of pump assembly  300  are identical to the prior described components of assembly  10  and are identified in FIG. 6 by the same reference numbers used in FIG.  1 . 
     Regulator valve  302  includes a single solenoid three-way valve  304  having inlet port  306 , drain or exhaust port  308  and work port  310  like ports  206 ,  208  and  210 . These ports are respectively connected to regulator valve inlet opening  312 , drain opening  314  and work opening  316 , like openings  212 ,  214  and  216 . 
     Valve  304  includes a valving spool (not illustrated) having a pressure piston with a cylindrical valving land moveable along a valve bore, as in valve  204 . The piston is imperforate. Four cylindrical valving passages open into the bore and are arranged in opposed, spaced pairs like passages  144  previously described. The valving land is underlapped with regard to the passages, as also previously described. If desired, the land may completely cover the valving passages. 
     Valve  304  includes a fast acting proportional solenoid  320  which engages the spool. Solenoid  320  is like solenoid  220 , previously described. The solenoid biases the spool toward a first position in which inlet port  306  is closed and work port  310  is connected to drain port  308  so that the spring of the inlet throttle valve  20  holds the inlet throttle valve in a full open position. 
     Spring  318  of valve  304  biases the spool toward a second position where work port  310  is connected to inlet port  306  and drain port  308  is closed. When the spool is in this position high-pressure oil from outlet passage  18  is flowed directly to inlet throttle valve  20  to close the inlet throttle valve and reduce inlet flow to pump  22  to minimum or idle flow. 
     Valve  304  has a null position in which the spool land underlaps or closes the valving passages. This position is the same as indicated in FIG.  3  and previously described. 
     In valve  304  the ends of the valving bore are connected to sump  14  through passage  80  and are at the same low pressure. The spool includes end pistons having the same area and assuring that movement of the spool along the valving bore is influenced by spring  318  and solenoid  320  and is not influenced by pressure differentials at the ends of the spool. 
     The coil of solenoid  320  receives a steady state current signal from the engine ECM to maintain the spool in a null position. Current is increased when the output pressure is lower than desired to shift valve  304  toward the first position and open the inlet throttle valve to increase flow to pump  22  and increase output pressure. Conversely, current is decreased when output pressure is greater than desired to shift valve  304  toward the second position, close valve  20  and increase output pressure. 
     The spool of valve  304  is moved to a null position when the output pressure equals the desired output pressure, as previously described and solenoid  320  holds the spool against the spring with the piston underlapping or closing the passages opening into the valving bore. 
     In the third embodiment of FIG. 6, failure of solenoid  320  allows spring  318  to shift the three-way valve spool to the second position and connect inlet port  306  to work port  310 . High-pressure output oil is supplied directly to the inlet throttle valve, shifting the valve to the closed position and reducing inlet flow to pump  22  to an idle level. Pump assembly  300  facilitates rapid shut down of the engine in the event the solenoid  320  fails. 
     In the embodiment shown in FIG. 6, spring  318  can be replaced by a piston acted upon by outlet pressure from passage  18 . The solenoid force biases the spool against the force of outlet pressure acting on the piston to shift the valve spool in the valve bore relative to the small valving passages like passages  144  described previously. In this case, outlet pressure is proportional to current to solenoid  320 . Current is increased or decreased proportional to the difference between the desired output pressure in line  18 , as calculated by the ECM, and the actual outlet pressure in line  18 . 
     While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.