Field of the Invention The present invention is directed to a high pressure fuel pump of the type used with vehicle engines, especially a demand controlled pump for delivering fuel to a common rail fuel injection system.

Background of the Invention Examples of such high pressure fuel pumps and associated fuel supply systems are described in U.S. Patent Nos. 6,637,408, "Common Rail Fuel Supply System With High Pressure Accumulator"; 6,494,182, "Self- Regulating Gasoline Direct Injection System"; 6,694,950, "Hybrid Control Method for Fuel Pump Using Intermittent Recirculation at Low and High Engine Speeds", and 6,422,203, "Variable Output Pump for Gasoline Direct Injection", the disclosures of which are hereby incorporated by reference. At least some of the pumps described in these patents utilize a solenoid controlled valve to selectively redirect pumped fuel to a low pressure sump and thereby bypass the injectors. High speed on/off type solenoid actuated valves are often used to control pump fuel delivery and/or fuel system rail pressure for common rail pumps and rotary distributor type pumps. A common problem or complaint associated with these pump types are audible and hydraulic noise associated with the rapid spilling of high pressure and/or solenoid and valve impact. The hydraulic noise is caused by the sudden spilling of a high pressure into a low pressure. The audible noise is caused by this hydraulic noise as well as mechanical noise when the valve and/or solenoid armature suddenly hits its mechanical stop during opening and/or closing.

Summary of the Invention

According to the present invention, instead of a traditional instantaneous switching on or off of the solenoid which results in a rapid response of the armature and control valve, the power pulse for energizing (or deenergizing) the solenoid is modified to slow the force versus time profile acting on the solenoid valve during the transition between on and off or off and on. This control scheme reduces the hydraulic and mechanical noise by reducing the valve's spill rate and / or impact velocity. Added benefits are reduced component wear and cavitation. Additionally, this control scheme can be switched to a more traditional square wave on/off type at higher speeds and duty cycles (when noise is less of an issue) in order to meet fuel delivery requirements if necessary.

Brief Description of the Figures Figs. 1A is a typical square wave control pulse of positive polarity,

Figs 1 B -1D depict square wave control pulses modified according to various embodiments of the present invention, and Figs. 1 E-1 G depict drive current profiles according to other embodiments of the present invention.

Fig. 2 is a schematic of a typical rail fuel delivery system incorporating an embodiment of the present invention.

Fig. 3 is a schematic of a high pressure radial piston pump incorporating an embodiment of the present invention.

Fig. 4 is a schematic that shows use of an active switching device that can selectively recirculate current in order to slow the decay rate during solenoid de-energizing.

Detailed Description

One illustration of the inventive concept is shown in Figures 1A-1G.

As shown in Figure 1A a typical control pulse 10 is characterized by a positive square wave having a starting or leading edge 11 , a nominal pulse

width 12, and an ending or trailing edge 13. In accord with an embodiment of the present invention, Figure 1 B depicts a period of pulse width modulation (PWM) or PWM burst 14 added to the end of each typical square wave control pulse 12'. This execution would slow the release time of a normally open electrically controlled solenoid actuated valve. The same operating principle applies to a normally closed electrically controlled solenoid actuated valve. PWM burst 14 is triggered by the ending edge 13' of the normal control pulse 12', begins after a specified delay period 15, and continues for a specified number of pulses at a set frequency and duty cycle.

Alternatively, a PWM burst 14' can occur before the normal control pulse 12' as shown in Figure 1C, or PWM bursts 14, 14' can both precede and follow the normal control pulse 12' as shown in Figure 1 D. Alternative embodiments of the present invention include modulation of the pulse count, frequency and duty cycle during the release or closure event. Although positive voltage control pulses are shown, the invention applies equally well to the modification of negative voltage pulses.

It should also be appreciated that typically, a nominal voltage pulse would be in the form of a square wave, the associated current would rise and fall with modest, non-instantaneous slopes, and the associated armature force (motion) of the solenoid valve would likewise exhibit modest rise and fall slopes. The present invention modifies the electronic control pulse relative to nominal, to "soften" the resulting force vs. time profile acting on the armature, e.g, by prolonging or extending the rising or falling slope of the voltage or current control pulse. The nominal control pulse need not be a square wave; whatever the nominal shape, the inventive technique modifies it for softening the driving force on the armature. For example, a nominal pulse can have a liner (non-instantaneous) rise, a constant peak amplitude, followed by linear fall, whereas the modified pulse can be bell- shaped.

Other methods of controlling the current decay or current rise, as depicted in Figures 1 E-1G, that fall within the purview of the present invention include direct current control via linear voltage, control of a current chopper driver, and control of current decay by selectively recirculating current during de-energizing, such as through the use of an active switching device.

Figures 2 and 3 illustrate various embodiments of the present invention as incorporated into a common rail fuel supply system and a high- pressure radial piston pump. Figure 2 depicts a fuel supply system having the basic components of: an in-tank (low pressure) supply pump 20, a fuel filter 21 , and a high pressure pump 22, (shown in broken lines for clarity). Pump 22 maintains a high operating pressure in a common rail 23 that is in fluid connection to a plurality of fuel injector nozzles 24. Each fuel injector nozzle 24 is situated to inject fuel according to the timing sequence controlled by the electronic control unit 25. Solenoid valve 26, which incorporates the control scheme of the present invention, is located within the high pressure pump 22. Valve control pulse generator 27 provides the control pulse for solenoid valve 26. The pressure of the rail is monitored by rail pressure sensor 28. Other features of this embodiment of a fuel supply system include pressure relief valve 29, which is fluidly connected to oneway check valve 30.

As shown in Figure 3, a fuel pump having at least one pumping plunger or piston 31 mounted for reciprocation in a respective pumping bore is associated with a pumping chamber whereby fuel at a low inlet pressure is fed to the pumping bore during a charging stroke of the plunger within the bore and the fed fuel is pressurized in the pumping chamber during a discharging stroke of the plunger within the bore. In the embodiment illustrated in Figure 3, a pressurized quantity of fuel from a plurality of pumping chambers is discharged to a common discharge line 32 that is connected to the pump outlet for delivery to the external common rail 24. A

spill control system is provided whereby while the fuel is pressurized in the pumping chamber or discharge line, a solenoid operated binary spill valve 33 opens a spill path to divert some of the pressurized fuel in the pumping chamber or in the discharge line 32, to a low pressure sump, such as the feed line 34 or the pump housing. As a result, the quantity of pressurized fuel that is delivered outside the pump (e.g., enters the common rail) is less than the quantity of fuel fed to the pumping bore or bores during the charging stroke or strokes. The valve then closes the spill path to restore the discharge to the common rail 24. The timing of the energizing and de- energizing of the spill valve 33 is directed by the valve control pulse generator 27 (shown in Figure 2) according to demand control programming such as described in the patents listed above. The improvement in the embodiments depicted in Figures 2 and 3 comprises electronically softening the start and/or end of the energizing and/or de-energizing power pulse and resulting current to the solenoid, such as shown in Figures 1 B thru 1G.

Thus, the discharge from a plurality of pumping chambers can be delivered to a common discharge line that is fluidly connected to the common rail but has a bypass leg in which the control valve is present. In other contexts (not shown), spill controlled distributor type pumps can have a plurality of control valves that operate with a respective plurality of pumping chambers that communicate with a respective plurality of injectors. Depending on the particular configuration, it is possible that one control valve can control the output of each of a plurality of sequentially actuated pumping chambers. The pumping plungers can reciprocate with sequential radially outward pumping, according to which each bore has a respective distinct pumping chamber (as in Fig. 3) or in other types of pumps, the plungers pump radially inwardly into a common volume from which a discharge path leads out of the pump to a discharge fitting or the like.

Figure 4 illustrates an embodiment of a circuit that actively controls recirculation current via a solenoid control module 64, active switch 60, and

a current or voltage sensor 62. Preferably, switch 60 is a FET or other fast switching mode device. A recirculation current control circuit provides the ability to enable or disable the soft spill mode. Moreover, recirculation current control also allows for better management of current decay and armature impact. Finally, it is preferred that the fast switching/recirculating current cycle occurs at least once per pulse modification, and more preferably, the fast switching/recirculating current cycle occurs at least twice. Other techniques for recirculating current are also within the scope of the present invention. These embodiments would also have similar noise control benefits.