WO2004067966A1

WO2004067966A1 - Pump system with variable restriction

Info

Publication number: WO2004067966A1
Application number: PCT/US2003/002043
Authority: WO
Inventors: Richard F. Teerman
Original assignee: Robert Bosch Gmbh
Priority date: 2003-01-24
Filing date: 2003-01-24
Publication date: 2004-08-12
Also published as: AU2003209344A1

Abstract

A pumping system for a fuel injection system includes a pump body defining a pumping chamber (16), a high pressure outlet, a high pressure fluid line (18) connecting the pumping plunger to the outlet and a variable valve restriction arrangement (15) along the fluid line.

Description

PUMP SYSTEM WITH VARIABLE RESTRICTION

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to pump systems for fuel injection systems.

Description of the Related Art

Engine exhaust emission regulations are becoming increasingly restrictive. One way to meet emission standards is to precisely control the quantity and timing of the fuel injected into the combustion chamber to match the engine cycle. For certain engine operating conditions, effective injection rate shaping may result in reduced levels of particulates and oxides of nitrogen in the engine exhaust.

Some existing rate shaping techniques attempt to control injection rates by making various modifications to the injector nozzle assembly. A newer rate shaping technique utilizes a separate control valve to provide more precise rate shaping than with modified injector nozzle assemblies. An example of such a control valve is disclosed in U.S. Patent No. 6,276,610 to Spoolstra et al.

Although one or more of these existing rate shaping techniques have been employed in many applications that have been commercially successful, a known side effect of fuel injection is the generation of noise. Noise can arise from a number of sources, including cavitation in the high-pressure fuel lines and vibration of mechanical linkages in the drive system. The selection of certain injection rate shapes can reduce noise. For example, one form of effective rate shaping injects fuel slower during the early phase of the combustion process, minimizing cavitation, and resulting in less engine noise.

It is also known to provide a restriction between the pump and the control valve to enable storing energy by maintaining pressure in the pump during the injection event. In U.S. Patent No. 6,450,778 to Spoolstra et al., a valve and restriction arrangement allows sophisticated control over the quantity and timing of injection and can also reduce the rate of pressure release at the pump plunger after injection. Higher pressure in the pump minimizes vibration of connected mechanical linkages to reduce noise. There remains a need for a simpler and less costly solution for noise reduction in high-pressure fuel injection systems. SUMMARY OF THE INVENTION

According to the invention, a fuel injection pump system has a pump body defining a pumping chamber; a plunger disposed in the pumping chamber for pressurizing fuel in response to movement from a drive system; an outlet to an injector; means to control an injection event at the injector; and a fluid line connecting the pumping chamber to the outlet. The invention is characterized by a variable valve restriction arrangement in the fluid line wherein fuel flow from the pumping chamber is significantly restricted during an injection event to reduce noise by maintaining pressure in the pumping chamber and maintaining force on the drive system. Preferably, the variable valve restriction arrangement comprises a pin on the plunger located and configured to be received within the fluid line during a stroke of the plunger.

In one aspect of the invention, the pin is disposed on the end of the plunger. In another aspect, the pin is received in the fluid line as the plunger approaches the end of its stroke. The fuel injection pump system can be incorporated into a unit pump or it can be incorporated into a unit injector.

DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram of the invention. Fig. 2 is a side elevation in cross section of a unit pump in accord with the invention.

Fig. 3 is a side elevation in cross section of a unit injector in accord with the invention.

Fig. 4 is a chart comparing pumping chamber pressure over an injection cycle in cam degrees with and without the invention.

Fig. 5 is a chart comparing upper nozzle chamber pressure over an injection cycle in cam degrees with and without the invention.

Fig. 6 is a chart showing the amount of restriction over an injection cycle in cam degrees with the invention. Fig. 7 is a chart showing cam velocity versus cam angle over the injection cycle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pump system for a fuel injection system is generally indicated schematically at 10, in FIG. 1. An engine driven cam 12 is part of a drive system that drives a plunger 14. The drive system may include some linkages (not shown) that are common in some fuel injection systems. The pumping chamber 16 of plunger 14 is connected to an injector via a high pressure fluid line 18. The pump system may be a unit pump connected via a high pressure fluid line to an injector, or alternatively, may be a unit injector. Further, it is appreciated that although an embodiment of the present invention is broadly illustrated in FIG. 1, the exemplary implementation in FIG. 2 is included for illustration purposes. That is, there are many different ways to implement the present invention in accordance with the schematic illustration in FIG. 1.

With continuing reference to FIG. 1, a variable valve restriction arrangement is generally indicated at 15 in the fluid line 18 just outside the pumping chamber 16. The variable valve restriction arrangement 15 comprises a valve body 17 that is movable between a restricted position and an open position. In the restricted position, the valve body 17 causes fuel flow through the high pressure fluid line 18 to be significantly restricted, thereby increasing pressure in the pumping chamber 16. In the open position, the valve body 17 generally does not restrict fluid flow through the high pressure line. It is appreciated that significantly restricted means that there is a noticeable pressure difference between the pumping chamber 16 and the other side of the variable valve restriction arrangement 15. That is, significantly restricted means restricted sufficiently to maintain sufficient pressure in the pumping chamber 16 to reduce vibration in mechanical components between the variable valve restriction arrangement 15 and the engine driven cam 12. Further, generally unrestricted (when the valve body 17 is in the open position) means that there is no noticeable pressure difference between the pumping chamber 16 and the other side of the variable valve restriction arrangement 15 (e.g., the unit pump outlet or the unit injector needle chamber) so that injection events may occur normally.

With continuing reference to FIG. 1, means are provided to control the injection event in an injector 22. Here, a spill or control valve 20 is disposed to route pressurized fuel from the pumping chamber to the pumping system outlet, which in turn, connects to the injector 22 when the control valve is closed. When the control valve 20 is open, fuel flow from the pumping chamber 16 bypasses the injector 22, "spilling" to a low pressure reservoir 24. It is appreciated that the control valve 20 is preferably positioned between the valve and restriction arrangement 15 and the injector 22. It will also be appreciated that other means are known in the art to control injection events, such as a needle nozzle control valve. The particular manner of injection control is not critical to the invention. In FIG. 2, a unit pump in an exemplary implementation of the invention is generally indicated at 50. The pump 50 includes a pump body 52 defining high pressure pumping chamber 54. A plunger 56 is disposed in the pumping chamber for pressurizing fuel. A high-pressure outlet 58 connects to an injector 110 through a high-pressure line 59, optionally including a check valve. The high-pressure outlet 58 is connected to the pumping chamber 54 by a high-pressure fluid line 60. A control valve 70 selectively routes pressurized fuel from the pumping chamber 54 to the outlet 58 when closed, or when open, provides pressure relief to the pumping chamber through a relief passage 88. A pin 72 extends from the plunger 56 within the pumping chamber 54 and is axially aligned with the longitudinal axis of the high- pressure fluid line 60. The diameter of the pin 72 is less than the diameter of the high-pressure fluid line 60. A fuel annulus 80 allows fuel to be drawn into the pumping chamber 54 through the passage 88 when the control valve 70 is open. O- rings 82 and 84 seal the fuel annulus 80. Another passage 86, extending between an annulus 87 around the pumping chamber 54 and the fuel annulus 80, allows any leakage past the plunger 56 to return to the low pressure fuel source (not shown) by way of the fuel annulus 80.

The plunger 56 has a tail end 92 received in a spring seat 90. A plunger spring 96, compressed between the pump body 52 and the spring seat 90, biases the plunger 56 to a retracted position as shown by solid lines in Fig. 2. The plunger 56 may be driven to an extended position (shown in phantom) by an engine driven cam (not shown). A cam follower assembly 94 receives the spring seat 90 and has a cam roller 98 that is driven by the engine driven cam to urge the plunger 56 to the extended position, compressing fuel in the pumping chamber. As the plunger is continuously driven from the retracted to the extended position, the control valve 70 is controlled to selectively supply fuel at various pressures to outlet 58, and to injector 110.

Simultaneously, as the plunger 56 approaches the extended position, the pin 72 extends into the high-pressure fluid line 60, thereby providing a variable valve restriction arrangement 74 to restrict flow of fuel as it enters the high pressure fluid line from the pumping chamber 54. The extended position of the plunger 56 is shown in phantom at 100.

With continuing reference to FIG. 2, the control valve 70 includes a valve body 112 secured to an armature 114. A stator 116 is energized to close the valve by pulling the armature 114 towards the stator 116. As shown, the control valve 70 is open. When closed, a seating surface 120 is urged into closing contact with a valve seat 122. A spring 118 biases the control valve 70 toward the open position.

The variable valve restriction arrangement 74 is shown in the open position. When closed, the pin 72 extends into the high-pressure fluid line 60. When the variable valve restriction arrangement 74 is closed, pressurized fuel from the pumping chamber 54 is significantly restricted to create a pressure differential between the pumping chamber 54 and the outlet 58. Higher pressure in the pumping chamber 54 maintains pressure on the plunger 56, and its connected components, including the cam follower assembly 94 and drive linkages connected thereto (not shown), which in turn, tends to dampen vibration of the components and consequently reduces noise. When the variable valve restriction arrangement 74 is opened, flow from pumping chamber 54 is generally unrestricted, and fuel may flow through passage 60. When the control valve 70 is open, the fuel flow from the pumping chamber 54 may pass the valve seating surface 120 and return through the passage 88 to the low pressure fuel annulus 80.

In FIG. 3, a unit injector exemplary implementation is generally indicated at 170. The unit injector 170 includes an injector body 172 that defines a pumping chamber 174. A plunger 176 is driven by a cam (not shown) that drives against a plunger holder and spring seat 178. A spring 180 biases the plunger to a retracted position as shown.

A fuel inlet 182 supplies low-pressure fuel to the unit injector. O-rings 184 and 186 effectively seal the fuel inlet 182 when the unit injector is received in an engine block. A passage 188 connects the fuel inlet 182 to a control valve 194. The control valve 194 operates similarly to the control valve 70 in the unit pump shown in FIG. 2. A high pressure fuel line 196 extends between the pumping chamber 174 and the control valve 194.

The output of the pumping system is passage 192, which passes pressurized fuel to the injector nozzle assembly 200. A lower or needle chamber 202 receives pressurized fuel at a pressure controlled by the control valve 194 as the plunger 176 is reciprocated. Sufficient pressure in the needle chamber 202 causes a needle seating surface 210 of the needle 204 to lift off of a needle seat 212 against the bias of a spring 208, allowing fuel to flow through passage 214 and out the end of the injector through holes 216. A pin 220 extends from the plunger 176 along a longitudinal axis of the high- pressure fuel line 196. The pin 220 has a diameter less than the internal diameter of the high pressure fuel line 196, and is sized and located so that when the plunger 176 approaches its maximum stroke (shown in phantom), the pin will extend into the high pressure fuel line, establishing a variable valve restriction arrangement 222. The result will be a restriction of fuel flow from the pumping chamber 174, maintaining pressure on the plunger 176, the plunger holder and spring seat 178, and the drive linkage with the cam. Consequently, vibration in these components is dampened and noise reduced.

Fig. 4 plots the amount of restriction due to a variable valve restriction arrangement according to the invention versus the cam angle through a single injection cycle. It will be seen that the restriction rapidly increases at 250 as the pin enters the high-pressure fluid line while the plunger approaches the bottom of its stroke. It remains high at 252 while the plunger stays extended until the pin retracts from the high-pressure fluid line at 254 as the plunger retracts toward the end of the cycle.

Fig. 5 shows a plot of the plunger chamber pressure with a variable valve restriction arrangement according to the invention at 260 and without a variable valve restriction arrangement at 262. In plot 260, pressure spikes at 264 as or shortly after the plunger approaches its maximum extension in the pumping chamber. Of course, in accord with the invention, the pin simultaneously enters the high-pressure fluid line, but because fuel continues to spill between the pin and the wall of the high- pressure fluid line, pressure in the pumping chamber will decay at a slower rate 266 than it would if the variable valve restriction arrangement were not present 268. Fig. 6 shows a plot of the needle chamber pressure with the variable valve restriction arrangement according to the invention at 270 and without the variable valve restriction arrangement at 272. In plot 270, pressure spikes at 274 as or shortly after the plunger approaches its maximum extension in the pumping chamber. Of course, in accord with the invention, the pin simultaneously enters the high-pressure fluid line, but because fuel spill from the pumping chamber into the high-pressure fluid line is suddenly restricted, pressure in the needle chamber will decay at a faster rate 276 than it would if the variable valve restriction arrangement were not present 278.

In Fig. 7, cam velocity versus cam angle over a single injection cycle is shown at 280. Point 282 generally coincides with the pressure spikes 264, 274 in the pumping chamber and needle chamber, respectively.

While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.

Claims

CLAIMSWe claim:

1. A fuel injection pump system (10, 50, 170) comprising: a pump body (52, 172) defining a pumping chamber (16, 54, 174); a plunger (14, 56, 176) disposed in the pumping chamber (16, 54, 174) for pressurizing fuel in response to movement from a drive system (12, 98); an outlet (58, 192) to an injector (22, 110, 200); means (20, 70, 194) to control an injection event at the injector (22, 110, 200); and a fluid line (18, 60, 192, 196) connecting the pumping chamber (16, 54, 174) to the outlet (58, 192); characterized by: a variable valve restriction arrangement (15, 74, 222) in the fluid line (18, 60, 192, 196) wherein fuel flow from the pumping chamber (16, 54, 174) is significantly restricted during an injection event to reduce noise by maintaining pressure in the pumping chamber (16, 54, 174) and maintaining force on the drive system (12, 98).

2. A fuel injection pump system (50, 170) according to claim 1 wherein the variable valve restriction arrangement (74, 222) comprises a pin (72, 220) on the plunger (56, 176) located and configured to be received within the fluid line (60, 192, 196) during a stroke of the plunger.

3. A fuel injection pump system (50, 170) according to claim 2 wherein the pin (72, 220) is disposed on the end of the plunger (56, 176).

4. A fuel injection pump system (50, 170) according to claim 2 or 3 wherein the pin (72, 220) is received in the fluid line (60, 196) as the plunger (56, 176) approaches the end of its stroke.

5. A fuel injection pump system according to claims 1-4 wherein the fuel injection pump system is a unit pump.

6. A fuel injection pump system according to claims 1-4 wherein the fuel injection pump system is in a unit injector.