Patent Publication Number: US-6712043-B2

Title: Actuating fluid control system

Description:
FIELD OF THE INVENTION 
     This invention relates to control of actuating fluid for use in an intensified fuel injection system for internal combustion engines. More particularly, the present invention controls a variable output pump that provides pressurized actuating fluid to an accumulator. 
     BACKGROUND OF THE INVENTION 
     A prior art hydraulically actuated, intensified injection system (commonly a HEUI injection system)  10  is depicted in prior art FIG.  1  and consists of five major components: 
     Electronic Control Module (ECM)  20   
     Injector Drive Module (IDM)  30   
     High Pressure actuating fluid supply pump  40   
     Rail Pressure Control Valve (RPCV)  50   
     HEUI Injectors  60   
     Electronic Control Module (ECM)  20   
     The ECM  20  is a microprocessor which monitors various sensors  22  from the vehicle and engine as it controls the operation of the entire fuel system  10 . Because the ECM  20  has many more operational inputs than a mechanical governor, it can determine optimum fuel rate and injection timing for almost any condition. Electronic controls such as this are absolutely essential in meeting standards of exhaust emissions and noise. 
     Injector Drive Module (IDM)  30   
     The IDM  30  is communicatively coupled to the ECM  20  and receives commands therefrom. The IDM  30  sends a precisely controlled current pulse to energize the solenoid of each injector. Such energization acts to port high pressure actuating fluid to the intensifier of the respective injector  60 . The timing and duration of the IDM  30  pulse are controlled by the ECM  20 . In essence, the IDM  30  acts like a relay. 
     High Pressure Actuating Fluid Supply Pump  40   
     The high pressure actuating fluid supply pump  40  is a single stage pump and is in the prior art typically a seven piston fixed displacement axial piston pump and is driven by the engine. The high pressure actuating fluid supply pump  40  draws in low pressure actuating fluid (most commonly engine oil, but other actuating fluids could be used as well) from the reservoir  46 , elevates the pressure of the actuating fluid for pressurization of the accumulator or rail  42 . The rail  42  is plumbed to each injector  60 . During normal engine operation, pump output pressure of the high pressure actuating fluid supply pump  40  is controlled by the Rail Pressure Control Valve (RPCV)  50 , which dumps excess flow back to the return circuit  44  to the reservoir  46 . The reservoir  46  is at substantially ambient pressure and may be at the normal pressure of the lubricating oil circulating in the engine of about 50 psi. Pressures for specific engine conditions are determined by the ECM  20 . 
     Rail Pressure Control Valve (RPCV)  50   
     The RPCV  50  is an electrically operated dump valve, which closely controls pump output pressure of the high pressure actuating fluid supply pump  40  by dumping excess flow to the return circuit  44  and to the reservoir  46 . A variable signal current from the ECM  20  to the RPCV  50  determines pump output pressure. Pump pressure can be maintained anywhere between about 450 psi and 4000 psi during normal engine operation. When the actuating fluid is engine lubricating oil, pressure while cranking a cold engine (below 50 degrees F.) is slightly higher because cold oil is thicker and components in the respective injectors  60  move slower. The higher pressure helps the injector  60  to fire faster until the viscosity of the actuating fluid (oil) is reduced. 
     HEUI Injector  60   
     Injectors  60  of this type are known and are representatively described in U.S. Pat. Nos. 5,460,329 and 5,682,858, incorporated herein by reference. The injector  60  includes an intensifier piston and plunger, the actuating fluid acting on the intensifier to pressurize a volume of fuel acted upon by the plunger. The injector  60  uses the hydraulic energy of the pressurized actuating fluid (preferably, lubricating oil) to dramatically increase the pressure of the volume of fuel and thereby to cause injection. Actuating fluid is ported to the intensifier by a valve controlled by a solenoid. The pressure of the incoming actuating fluid from the rail  42  controls the speed of the intensifier piston and plunger movement, and therefore, the rate of injection. The amount of fuel injected is determined by the duration of the pulse from the IDM  30  and how long it keeps the solenoid of the respective injector  60  energized. The intensifier amplifies the pressure of the actuating fluid and elevates the pressure of the fuel acted upon by the plunger from near ambient to about 20,000 psi for each injection event. As long as the solenoid is energized and the valve is off its seat, high pressure actuating fluid continues to push down the intensifier and plunger to continuously pressurize fuel for injection until the intensifier reaches the bottom of its bore. 
     Fuel economy is becoming more and more important. More efficiency in fuel usage is needed. The fuel consumption of the engine varies with engine speed and load. The need for actuating fluid also varies with engine speed and load, a higher volume of actuating fluid being required to develop sufficient high pressure fuel in the injector  60  at higher engine speeds and load. The actuating fluid pump  40  is engine driven and develops the same output at a given engine speed without regard for the volume of actuating fluid needed by the injectors  60 . The volume is selected to ensure that the rail  42  is always fully charged with high pressure actuating fluid at the highest demand for actuating fluid. As noted above, excess actuating fluid is vented by the RPCV  50  to the reservoir  46 . This means some engine power is used unnecessarily at lower to intermediate engine loads to run the actuating fluid pump  40 . As noted above, in the prior art engines, the actuating fluid pump  40  is a one stage actuating fluid pump delivering actuating fluid to the pressurized rail  42 . Under certain engine operating conditions, typically relatively low engine load, the unneeded actuating fluid is dumped to ambient (reservoir  46 ), resulting in energy loss. 
     In the prior art fuel injection system  10 , pressurized actuating fluid (engine lubricating oil) is used to control the injected fuel quantity by using pressure amplification in the injectors  60 . As noted above, a pressure source pumps actuating fluid to a pressure rail  42  (accumulator) where pressure is regulated according to the engine load and speed requirement. The pressure regulation is done via the pressure-regulating valve  50  that dumps excess pressurized actuating fluid to ambient in order to maintain the desired pressure in the rail  42 . Although it is desirable to minimize the damped flow for efficiency purposes, the required demand must be maintained in order to assure stability of desired rail pressure. 
     In order to achieve a more efficient system, the delivery of the pump  40  must be controlled depending on the engine requirement. A continuous supply of actuating fluid to the rail is needed in order to maintain the desired rail pressure at any engine condition. Further, the engine power used to drive the actuating fluid pump should more nearly reflect the actuating fluid needed in the rail for the present engine operating condition. 
     SUMMARY OF THE INVENTION 
     The actuating fluid control system of the present invention is capable of meeting the aforementioned needs. By matching the power consumption of the actuating fluid pump to the engine needs, the engine fuel consumption is reduced, especially at lower engine load conditions. Further, a continuous supply of actuating fluid is supplied to the rail. 
     The pressure dynamics quality in the pressure rail  42  is a key player in such systems. The impact of transient flow discontinuity in the rail  42  has to be minimized. Dumping flow from a single actuating fluid pump as done in the past created objectionable high pressure fluctuations which were a significant source of transient flow discontinuity in the rail  42 . Hence, a continuous steady flow from a pump stage to the rail  42  as provided for in the present invention has a stabilizing effect in the rail  42 . Further, a proportional flow control valve as used in the present invention allows a smooth controllable pressure transition when transitioning from venting actuating fluid to supplying make up actuating fluid to the rail. 
     The multi-stage pumping system of the present invention, comprising a variable output pump, preferably two de-coupled pumps, is able to select the required flow rate according to the engine load and speed via a specific control strategy. This results in reducing the power used for driving the pump over the total range of engine operating conditions, power to the pump equaling fluid pressure times flow rate. 
     Depending on the engine need, by controlling actuating fluid pump delivery, the power lost in friction in the actuating fluid pump is ultimately reduced. A variable output or multi-stage actuating fluid pump system able to switch from one delivery quantity to another, according to the engine need, reduces the power consumption and, correspondingly, the fuel consumption. The switching strategy of the present invention is implemented via a three-way, two-position flow control valve connected to a low pressure pump. The flow control valve operates on and off to dump actuating fluid to ambient (no power consumption mode) or pump the actuating fluid to the rail (power consumption mode). The flow control valve is driven by a proportional solenoid. An injection pressure-regulating (IPR) valve, or RPCV, is incorporated for rail pressure regulation. A high-pressure pump is pumping actuating fluid continuously to the rail during engine operation, while a low-pressure actuating fluid pump is operated on and off, as noted above. The continuous flow from high-pressure pump is used to drive the system at loads ranging from zero to 50% load and acts to minimize rail pressure fluctuations while the low pressure pump is dumped to ambient. 
     The variable output or multi-stage pump of the present invention increases the overall efficiency of the engine by reducing the fuel consumption by 3 to 5%. The risk of noise and vibration due to pressure instabilities resulting from flow discontinuity and pressure spikes in the rail is reduced since the high flow pump pumps actuating fluid continuously during engine operation to insure stability of the system. Furthermore, a simple flow control strategy of the present invention can be implemented without major changes in the existing fuel system. 
     The present invention is a control system for controlling the flow of an actuating fluid to an accumulator, the accumulator serving the fuel injectors of an internal combustion engine, and includes a controller being in communication with a plurality of engine related sensors. A variable output pump is in fluid communication with a source of actuating fluid and has at least two selectable output conditions, the pump being operably coupled to the controller, the controller acting to selectively port a portion of the actuating fluid to the accumulator in a first pump output condition and to vent the portion of the actuating fluid to a reservoir in a second pump output condition. The present invention is further a fuel injection system and a method of control. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is schematic representation of a prior art fuel injection system; 
     FIG. 2 is schematic representation of the actuating fluid control system of the present invention; 
     FIG. 3 is schematic representation of the actuating fluid control system of the present invention; 
     FIG. 4 is a graphic representation of fuel system actuating fluid demand as a percentage of pump capacity for the smaller pump at various engine speed and load conditions; 
     FIG. 5 is a graphic representation of fuel system actuating fluid demand as a percentage of pump capacity for both pumps at various engine speed and load conditions; 
     FIG. 6 is a graphic representation of fuel system actuating fluid demand as a percentage of pump capacity for the larger pump at various engine speed and load conditions; and 
     FIG. 7 is a graphic representation of actuating fluid pump control strategy at various engine speed and load conditions. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The actuating fluid control system of the present invention is shown generally at  100  as depicted in FIGS. 2 and 3. Referring to FIG. 2, actuating fluid flows from reservoir  46  to variable output pump  102  where power is added via shaft  104  to pressurize the actuating fluid. Shaft  104  is operably coupled to the engine and rotatably driven thereby with a relationship to engine rpm. In a preferred embodiment, the variable output pump  102  has a relatively large stage pump  106  and a relatively small stage pump  108 . A common shaft  104  may serve both stages  106 ,  108 , as depicted in FIG.  3 . Pressurized fluid flow from the large stage pump  106  flows into the accumulator  42  under all engine operating conditions. This supplies a constant source of actuating fluid to the rail  42  from a relatively larger pumping source to minimize the pressure fluctuations in the rail  42  and stabilize the conditions in the rail  42 . Such stability acts to enhance the performance of the respective injectors  60 . 
     Pressurized fluid flow from the small stage pump  108  selectively flows into the accumulator  42  or to the ambient reservoir  46  through a two-position-three-way flow control valve  110  according to the predefined control strategy, as is discussed in greater detail below. A pressure relief valve  112  is used to dampen out any pressure spikes resulting from water hammer effect due to shut off of the flow control valve  110  when a venting of actuating fluid pressure is complete. The pressure relief valve  112  also dumps actuating fluid to the ambient reservoir  46 . A check valve  114  is incorporated to prevent backflow from accumulator  42  to pump  108  or to ambient through the control valve  110 . An injection pressure-regulating (IPR) valve  116  is used to control the desired pressure in the accumulator  42 . 
     In order to control the flow of actuating fluid from the small pump stage  108 , a control strategy has to be defined. As noted above, the large stage pump  106  is not controlled, the output of the large stage pump  106  being always available to the rail  42 . From FIGS. 2 and 3, a two-position three-way valve  110  is used under control of the ECM  20 . The valve  110  is driven by a proportional solenoid, fed by a voltage source, against a pre-loaded spring. When the solenoid is energized, the control valve  110  is on allowing flow to the accumulator  42 . This minimizes the electric power utilized by the actuating fluid control system  100 , requiring such power only when the output of the small stage pump  108  is being made available to the rail  42 . When de-energized, the control valve  110  is off allowing actuating fluid flow to be dumped to ambient. The small stage pump  108  is pumping actuating fluid when actuating fluid is being dumped to ambient, but it is essentially frictionless pumping since the actuating fluid is being pumped directly to the ambient reservoir  46  and offers no resistance to the pumping action of the small stage pump  108 . The power required to effect such pumping is negligible. The position (on/off) of the flow control valve  110  is decided by the ECM  20  as determined by a stored engine load and speed map. A simple hardware change only is implemented in the prior art Engine Control Unit  20  to control the solenoid operation of the control valve  110  of the present invention. 
     In a preferred embodiment of the actuating fluid control system  100  of the present invention, as applied to a certain V 8  configured diesel engine, the actuating fluid required is about 7.2 cc per engine revolution. Of this amount the large pump stage  106  supplies about 4.6 cc per engine revolution or about two-thirds of the actuating fluid required. The small stage pump  108  is capable of making up the remainder. The effect of shifting the small stage pump  108  from supplying actuating fluid to the rail  42  and of dumping the actuating fluid to ambient depending on the conditions in the rail  42  is much less disruptive of rail conditions than in the prior art when the output of the single pump  40  was effectively switched on and off. The fluctuations in the rail  42  caused by shifting the small stage pump  108  on and off are nominal only. The positive effects of actuating fluid control system  100  are both reduction in engine power required and improved stability of injection, a function of stability in the rail  42 . 
     Referring to FIG. 4, it is apparent that the capacity of the small pump would be exceeded by the fuel system demand at all engine speeds greater than 700 rpm, if the engine load is greater than 50 percent. In FIG. 6, the capacity of the large stage pump would never be exceeded, even at 100% load, although it would approach its capacity limit. However, as shown in FIG. 5, in accordance with the invention, with the contribution of actuating fluid from the small stage pump  108  augmenting the output of the large stage pump  106 , even at 100% load, there is a generous amount of unused capacity of the combined pumps, thereby permitting the fuel system demand to be accommodated while maintaining a steady continuous supply of actuating fluid to the rail to insure stability of the system and reduce objectionable high pressure fluctuations in the rail. 
     FIG. 7 illustrates the control strategy for the pump system. During cranking of the engine, a high volume of actuating fluid is required. Accordingly, the output of both pump stages  106 ,  108  is made available to the rail  42 . The cranking stage (during engine start) is generally less than 700 engine rpm. From about 700 rpm to about 3300 engine rpm, only the output of the large stage pump  106  is made available to the rail, when the engine load is less than about 50 percent., and the output of both the small stage pump  108  and the large stage pump  106  is made available to the rail  42  when the engine load is greater than about 50 percent. This map is stored in the ECM  20 .