High-Pressure Fuel Pump for an Internal Combustion Engine

A high pressure fuel pump for an internal combustion engine with direct fuel injection includes a pump housing, a pressure damper, and a pressure regulating valve. The pressure damper is connected to a pump inlet in a low pressure region via a first bore in the housing, and to a pump outlet in a high pressure region via a second bore in the housing. The pressure regulating valve has a limit pressure, is disposed in the second bore, is configured to open in response to a pressure in the high pressure region being greater than the limit pressure, and is configured to close in response to the pressure in the high pressure region being less than the limit pressure, such that pressure in the high-pressure region is regulated toward a constant value of the limit pressure.

TECHNICAL FIELD

The disclosure relates to a high-pressure fuel pump for an internal combustion engine.

BACKGROUND

High-pressure fuel pumps with direct injection typically have a low-pressure region and a high-pressure region. An electric prefeed pump feeds the fuel from a tank into the low-pressure region, from which the fuel is fed via the high-pressure fuel pump into a fuel collection line (called “common rail”) that communicates with the high-pressure region. The pressure in the common rail is typically regulated by a pressure regulating and/or quantity control valve, and the valves are controlled by a control and/or regulating device, among other ways via an evaluation of signals of a pressure sensor. The pressure regulating valve can also function mechanically.

From German Patent Disclosure DE 103 27 411 A1, a pressure limiting valve is known for a high-pressure fuel pump that has a pressure limiting valve.

SUMMARY

One object of the disclosure is to create and further refine a high-pressure fuel pump for an internal combustion engine of the type defined at the outset, which functions reliably and is compact in construction. Moreover, the high-pressure fuel pump should be economical.

This object is attained by a high-pressure fuel pump for an internal combustion engine according to this disclosure. Characteristics important to the disclosure are also found in the ensuing description and in the drawings; the characteristics may be important for the disclosure both on their own and in various combinations, without this being referred to in each case explicitly. Advantageous refinements are found in the claims.

Because of the design of the high-pressure fuel pump, on the one hand space in the engine region of a motor vehicle is saved, and on the other, by skilled integration of the pressure regulating device with the high-pressure fuel pump, the known external dimensions of the high-pressure fuel pump can be kept unchanged. No additional hydraulic lines are needed. This advantageously leads to a very compact construction of the high-pressure fuel pump. Because controlling the fuel quantity is dispensed with, the high-pressure fuel pump also needs no quantity control valve with an associated end stage and an electrical trigger line. The pressure sensor required for electronic control can also be dispensed with. This makes the pump especially economical and also economizes on engine performance. Since the unneeded quantity of fuel is diverted into the low-pressure region, a pressure limiting function is ensured as well.

When a less pressure-sensitive fuel system is used in an internal combustion engine, such as a constant-pressure system, complicated electronic quantity control of fuel can be dispensed with. On this condition, the pressure regulation in the high-pressure region is then done via a mechanical pressure regulating device, which is integrated with the high-pressure pump. The pressure regulating device is disposed hydraulically between the low-pressure region and the high-pressure region. Once a previously adjustable opening pressure of the pressure regulating device is reached, the unneeded quantity of fuel is returned from the high-pressure region to the low-pressure region. As a result, in engine operation, an at least substantially constant pressure is established on the high-pressure side.

In a first refinement, it is proposed that the mechanical pressure regulating device includes a mechanical pressure regulating valve, in particular a mechanical check valve, for instance subjected to a spring. Mechanical pressure regulating valves are relatively simple in construction, reliable, and thus economical. This is true particularly for check valves. Such a valve is moreover extremely small and therefore can be integrated without problems into the high-pressure fuel pump.

It is especially advantageous if a mechanical throttle restriction is disposed upstream of a valve element of the pressure regulating device, so that adverse effects on the regulating performance in the common rail, especially of single-cylinder fuel pumps are used, from unwanted pressure pulsations of the high-pressure pump are reduced. Wear to the pressure regulating valve is thus reduced as well. The throttle restriction can be embodied as a separate throttle element or other cross-sectional constriction in an inflow conduit on the high-pressure side, a valve body, or a receiving opening in the pump housing.

It is also proposed that the pressure regulating valve is disposed off-center in the pump housing of the high-pressure fuel pump, in a bore, and that optionally a connecting bore from the pressure regulating valve to the high-pressure region is also disposed off-center. The middle, central region in the pump housing is reserved in a known fashion for the actual pumping functions of the high-pressure fuel pump. In the off-center region, however, there is enough room to integrate the pressure regulating function. This makes the high-pressure fuel pump into a very effectively usable, compact device. Moreover, this makes machining of the pump housing easier.

It is also proposed that a limit pressure in the high-pressure region is fixed by means of a valve spring and/or a sealing diameter between the valve element and the valve seat of the pressure regulating device. This means that in the design of the pressure regulating device, and optionally upon assembly of the high-pressure fuel pump, the limit pressure can be set precisely. Accordingly, no calibration of the completed high-pressure fuel pump, or even a high-pressure fuel pump already built into a motor vehicle, is needed.

In addition, it is proposed that the pressure regulating device has a cartridge-like valve housing. Thus the pressure regulating device can be manufactured and adjusted as a separate component unit and then fitted into the pump housing and kept between the sleeve and the pump housing, for instance by way of a press fit. Adjusting the function of the pressure regulating valve is simpler, since among other factors, when the opening pressure is hydraulically set, there is no need also to clean the pump housing for further assembly steps. Moreover, if an incorrect setting occurs, it does not mean the rejection of the pump housing as well.

It is also advantageous if the inlet valve is disposed coaxially to the pump piston of the high-pressure fuel pump. This makes it possible to achieve a high delivery rate of fuel from the low-pressure region, which can be even further increased if, between a pressure damper of the high-pressure fuel pump and the inlet valve, the diameter of the corresponding connecting bore is relatively large compared to the opening of the inlet valve.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the embodiments described herein, reference is now made to the drawings and descriptions in the following written specification. No limitation to the scope of the subject matter is intended by the references. This disclosure also includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the described embodiments as would normally occur to one of ordinary skill in the art to which this document pertains.

The construction and general function of the high-pressure fuel pump of the disclosure will be described in its main aspects in conjunction withFIG. 1.FIG. 1is a schematic illustration of a fuel system8for an internal combustion engine (not shown) having a high-pressure fuel pump10. The fuel system, as will also be discussed hereinafter, is subdivided in a low-pressure region12, shown on the left inFIG. 1, and a high-pressure region14, shown on the right. A prefeed pump16disposed in the low-pressure region12pumps fuel from a fuel tank18via a low-pressure line20at a prefeed pressure to an inlet stub22of the high-pressure fuel pump10. In the high-pressure fuel pump10, a filter24and a pressure damper26are disposed in the low-pressure region12. The pressure damper26damps pulsations on the low-pressure side that occur in the high-pressure fuel pump10and ensures a high delivery rate even at high rotary and cam speeds.

Via an inlet valve28, the fuel is aspirated into a work chamber30of the high-pressure fuel pump10. The volume of the work chamber30depends on the position of a pump piston32and a pump cylinder34. During a downward motion of the pump piston32, the work chamber30is increased in size, and as a result fuel is aspirated. During the upward motion of the pump piston32, the fuel is highly compressed and is fed via an outlet valve36and an outlet stub38, belonging to the high-pressure region14, onward via a high-pressure line40into a rail42. Injection valves44are connected to the rail42and inject the fuel directly into the combustion chambers46of the engine.

The pump piston32is driven via a cam48, which is driven by the engine—for instance via a camshaft or crankshaft (not shown). The cam48can also be part of the camshaft or crankshaft.

Sealing off the pump piston32from the cam48is effected via a sealing element50. Piston leakage that occurs in the gap between the pump piston32and the pump cylinder34is returned to the low-pressure region12via a return line52.

Since in normal operation the feed quantity of the pump piston32is greater than the injected fuel quantity, an unneeded quantity of fuel on the high-pressure region14is returned to the low-pressure region12again via a purely mechanically functioning pressure regulating valve54. The pressure in the common rail42thus substantially corresponds to the opening pressure of the pressure regulating valve54.

In the high-pressure region14as well, pulsations occur, especially if single-cylinder pumps are used. These pulsations can adversely affect the pressure regulating function in the rail42. For decoupling, a throttle restriction56is disposed hydraulically upstream of the pressure regulating valve54, and as a result, the pulsations upstream of the pressure regulating valve54and wear of that valve are reduced.

The following drawings show the construction of the high-pressure fuel pump10in perspective or sectional views in greater detail. It should be pointed out that for reasons of simplicity and clarity, not all components are identified by reference numerals in all the figures.

FIG. 2shows the high-pressure fuel pump10in a perspective view. The inlet stub22(low-pressure region12) and the outlet stub38(high-pressure region14) are disposed on a pump housing58. A filter64is integrated with the inlet stub22. The high-pressure fuel pump10further includes an inwardly-indented cap66and a flange plate68for securing the high-pressure fuel pump10, for instance to a cylinder head of the engine. Both parts66and68are solidly connected to the pump housing58. The pump piston32protrudes downward out of the pump housing58. A piston spring70is braced on one end on a spring plate72solidly connected to the pump piston32, and is braced on the other end (not visible) on the pump housing58. The force of the piston spring70is accordingly introduced into the pump piston32via the spring plate72. It is thus ensured that in operation, the pump piston32always follows the contour of the cam.

As can be seen fromFIG. 3, the inlet stub22with the filter64communicates, via a bore74that is eccentric to a longitudinal axis73of the pump housing58, with a receiving chamber (not identified by reference numeral) for the pressure damper26, the receiving chamber being located below the cap66. The receiving chamber in turn can be made to communicate with the pump work chamber30, via two bore segments78and80, which are coaxial with the pump housing58, and via the inlet valve28. The pump piston32is displaceably supported in a cylinder bush82. During an intake phase of the pump piston32, the fuel reaches the pump work chamber30via the bores78and80and the inlet valve28.

As seen fromFIG. 4, the pump work chamber30and the outlet valve36communicate hydraulically with one another via a bore88in the pump housing58. FromFIGS. 5 and 6, it can be seen that the pressure regulating valve54in the pump housing58is disposed eccentrically in a bore90and parallel to the longitudinal axis73. Accordingly, the sectional plane inFIG. 4is not central; instead, it is spaced apart from the longitudinal axis73. On the high-pressure side, the pressure regulating valve54communicates with the outlet valve36via a bore92that is also spaced apart from the longitudinal axis73. On the outlet side, the pressure regulating valve54communicates via the bore90with the receiving chamber for the pressure damper26. The pressure regulating valve54includes a valve seat (not identified by reference numeral) on a valve seat body94having an inflow bore95, and also includes a ball valve body96, a spring guide98, a valve spring100, and a spring holder102.

The valve seat body94is solidly anchored in the bore90, for instance via a press fit. Via the spring guide98, the valve spring100presses the valve body96into the valve seat. InFIG. 5, the valve body is ball-shaped. Depending on the spring force and the sealing diameter between the valve body96and the valve seat body94, a defined opening pressure results. In the upper part ofFIG. 5, the valve spring100is braced on the spring holder102. The spring holder102is in turn solidly anchored in the bore90(for instance via a press fit). Upon the assembly of the pressure regulating valve54, the opening pressure is set by way of the press-fit travel distance of the spring holder102.

The high-pressure fuel pump10functions as follows: Upon a downward motion of the pump piston32(“intake stroke”), fuel is aspirated into the work chamber30via the inlet valve28. Upon an upward motion (“delivery stroke”), the fuel in the work chamber30is compressed and is fed via the outlet valve36into the high-pressure line40. If the pressure in the high-pressure region14exceeds the limit pressure of the pressure regulating valve54, the latter opens because the valve body96lifts from the valve seat, so that fuel can flow away into the receiving chamber of the pressure damper26and thus into the low-pressure region12. If the pressure in the high-pressure region14drops below the limit pressure of the pressure regulating valve54, the latter closes again. In this way, the pressure in the high-pressure region14is kept essentially constant, namely at the limit pressure or opening pressure of the pressure regulating valve54.

FIG. 7shows a variant of the high-pressure fuel pump10. In it, those elements and regions that have equivalent functions to elements and regions that have already been described are identified by the same reference numerals and will not be explained again.

In the alternative variant shown, the pressure regulating valve54is embodied in a cartridge version. The assembly of the pressure regulating valve54and the setting of the opening pressure can be done here outside the pump housing58. The valve seat body94is fitted into a sleeve104and retained, for instance via a press fit. After the valve body96, spring guide98, and valve spring100are put together, the spring holder102is fitted into the sleeve104as well. Once again, the spring force and thus the opening pressure are set by the position of the spring holder102. The spring holder102can, as shown inFIG. 7, be screwed into the sleeve104. As an alternative to the screw-in version, a press fit is also possible. Once the pressure regulating valve54has been installed and set, it is fitted as a component unit into the pump housing58and retained, for instance via a press fit, between the sleeve104and the pump housing58.

In the variant of the high-pressure fuel pump10shown inFIG. 7, a throttle restriction56is also positioned in the bore92. It is also conceivable to dispose the throttle restriction56in the bore90. As an alternative to the throttle restriction56, the inflow bore95can also have a reduced cross section in some regions in the valve seat body94, as a result of which once again a throttling function is achieved.

It will be appreciated that variants of the above-described and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the disclosure.