GB2261475A

GB2261475A - Fuel-injection pump for internal combustion engine

Info

Publication number: GB2261475A
Application number: GB9222775A
Authority: GB
Inventors: Helmut Laufer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-11-13
Filing date: 1992-10-30
Publication date: 1993-05-19
Anticipated expiration: 2012-10-30
Also published as: GB9222775D0; DE4137252A1; FR2683595A1; KR930010366A; FR2683595B1; GB2261475B; JPH05215031A; KR100280059B1

Abstract

The fuel-injection pump has a piston (14) reciprocated in cylinder bore (13) by a cam drive (16), thereby to deliver fuel from a working chamber (21) to an injection nozzle (36). To end delivery the working chamber is connected to a lower pressure channel (22) by a solenoid valve (38). During the period following the end of delivery, a relief line (50) with a pressure holding valve (52) is connected to the working chamber in order to maintain a residual pressure therein. The relief line (50) issues from the cylinder bore (13) and is connected by axial and annular grooves (30, 40) to the working chamber (21). The connection between the annular groove (48) and the relief line (50) occurs prior to the pump piston (14) reaching its top dead point and shortly after the valve (38) is closed again so that fuel flows out of the pump working chamber (21) only through the relief line (50). The residual pressure maintained by the pressure holding valve (52) acts to prevent the piston leaving its drive. In a second arrangement, the relief line is connected in series with the solenoid valve. <IMAGE>

Description

-1DESCRIPTION FUEL-INJECTION PUMP FOR INTERNAI COMBUSTION ENGINES

The invention relates to a fuel-injection pump for internal combustion engines.

A fuel-injection pump is known from DE 39 43 245 Al. This fuel-injection pump has a pump working chamber which can be connected to at least one delivery line, the pump working chamber being delimited by a pump piston. The pump piston is driven at least in an axial reciprocal movement by means of a rotating drive shaft and cam drive and produces in this way a fuel-injection pressure in the delivery line. A fuel channel, which is controlled by means of a solenoid valve, is connected to the pump working chamber. The solenoid valve is closed at a predetermined point in time of the delivery stroke of the pump piston and in so doing determines the commencement of the high pressure delivery of the pump piston. In order to terminate the high-pressure delivery of the pump piston, the solenoid valve is opened so that fuel can flow away out of the pump working chamber by way of the fuel channel. The point in time when the solenoid valve closes and opens is determined by a control unit. After the termination -2 of the delivery has been determined by opening the solenoid valve, the solenoid valve is cyclically closed and opened, in order to obtain in the pump working chamber a residual pressure which lies below the fuelinjection pressure. The residual pressure prevents the pump piston as a result of its inertia after the termination of the delivery, from disengaging with the cam drive and that the pump piston is no longer exactly allocated relative to the rotational position of the drive shaft. The solenoid valve must at the same time be rapidly closed and opened, alternately, in order to prevent the residual pressure in the pump working chamber from rising to the level of the fuel-injection pressure, which would lead to an undesired fuel-injection. The frequency with which the solenoid valve can be alternately closed and opened is, however, limited by its inertia, so that it is not possible reliably to avoid a greater residual pressure in the pump working chamber and it is therefore possible for an undesired fuel-injection to occur.

In accordance with the present invention there is provided a fuelinjection pump for an internal combustion engine having a pump working chamber which can be connected to at least one delivery line, a pump piston delimiting the pump working chamber, the pump 1 1 -3piston being driven by means of a rotating drive shaft by way of a cam drive at least in an axial reciprocal movement and a fuel-injection pressure is produced in the pump working chamber by means of the reciprocal movement of the pump piston, a fuel channel which can be connected to the pump working chamber, a solenoid valve which controls the fuel channel, the solenoid valve determining the termination of the fuelinjection by opening the fuel channel during the delivery stroke of the pump piston, and a control unit for controlling the solenoid valve wherein a residual pressure is maintained in the pump working chamber after the termination of the fuel-injection, this residual pressure being less than the fuel-injection pressure and preventing the pump piston from being raised from the cam drive, whereby the pump working chamber is connected to a relief line prior to termination of the fuel-injection which relief line has a pressure holding valve, which opens the relief line when the residual pressure in the pump working chamber is less than the fuel-injection pressure.

This has the advantage that the residual pressure in the pump working chamber is kept reliably below the fuel-injection pressure by means of the pressure holding valve and that the solenoid valve does not require any special requirements with respect to the -4valve dynamics in order to be sufficient.

Preferably, the fuel channel serves as the relief line and the solenoid valve is arranged between the pump working chamber and the pressure holding valve. Thereby, no additional costs are required for the relief channel.

Preferably, the pump working chamber is filled with fuel by way of the fuel channel during the intake stroke of the pump piston and a non-return valve which opens towards the pump working chamber is arranged parallel to the pressure holding valve. Thereby it is possible to fill the pump working chamber by way of the fuel channel during the intake stroke of the pump piston.

By way of example only specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:Fig. 1 is a longitudinal sectional view of a uel-injection pump constructed in accordance with a first embodiment of the present invention; Fig. 2a is a graph illustrating the stroke of the pump piston in dependence upon the angle of rotation of the drive shaft of the pump of Fig. 1; Fig. 2b is a graph corresponding to Fig. 2a illustrating the control of the solenoid valve; Fig. 2c is a graph corresponding to Fig. 2a -5illustrating the pressure in the pump working chamber; Fig. 3 is a longitudinal sectional view of the fuel-injection pump constructed in accordance with a second embodiment of the present invention; Fig. 4a is a graph illustrating the stroke of the pump piston in dependence upon the angle of rotation of the drive shaft of the pump of Fig. 3; Fig. 4b is a graph corresponding to that of Fig. 4a of the control of the solenoid valve; and Fig. 4c is a graph corresponding to that of Fig. 4a of the pressure in the pump working chamber.

Referring to Fig. 1 the fuel-injection pump for internal combustion engines, has a pump housing 10 in which a cylinder liner 12 is arranged and a pump piston 14, which simultaneously acts as a distributor, performs a simultaneous reciprocal axial and rotating movement in a cylinder bore 13 in the cylinder liner 12. The pump piston 14 is driven by means of a drive shaft 17 by way of a cam drive 16, the drive shaft rotating synchronously to the rotational speed of the internal combustion engine driven by the fuelinjection pump.

The cam drive 16 is only schematically illustrated in Fig. 1 and has in the known manner a claw coupling in order to connect the pump piston 14 to the drive shaft 17 in a positive rotary manner.

-6Moreover, the cam drive 16 has a front cam disc 18 which is connected to the pump piston 14 and is pressed by way of a compression spring (not illustrated) against a roller 20 held in a roller ring. The roller ring is held in the pump housing 10. A pump working chamber 21 is delimited by means of the front side of the pump piston 14 and the cylinder liner 12. The pump working chamber can be connected to an internal chamber 24 of the fuel-injection pump by way of a fuel channel 22. Fuel is delivered from a reservoir 28 into the internal chamber 24 by means of a feed pump 26 driven by means of the drive shaft 17.

The pump piston 14 has a longitudinal groove 30 which issues from its front side and during a corresponding rotational movement of the pump piston the said longitudinal groove produces a connection of the pump working chamber 21 to one of the several delivery lines 32. A delivery valve 33 is arranged in each of the delivery lines 32 and opens the delivery line 32 when a predetermined pressure is achieved. The delivery lines 32 lead by way of the cylinder liner 12, the pump housing 10 and fuel-injection lines 34 to fuel-injection nozzles 36 on the internal combustion engine.

A fuel channel 22 which has a solenoid valve 38 issues from the pump working chamber 21 to the internal -7chamber 24. The solenoid valve 38 has a valve closure member 40, which cooperates with a valve seat 42 which can be un the cylinder liner 12 or on a valve body. The valve member 40 is actuated by a solenoid 44 which is controlled by a control unit 46. The solenoid valve 38 is controlled by means of the control unit 46 in dependence upon operating parameters of the internal combustion engine, such as for example load, rotational speed, temperature etc. The points in time when the solenoid valve 38 opens and closes are controlled by the control unit 46 and determine the commencement and the termination of the high pressure delivery of fuel by means of the pump piston 14. The solenoid valve 38 is open if there is no fuel flow and is closed by means of a flow of fuel.

The solenoid valve 38 is open during the intake stroke of the pump piston 14 so that fuel can flow from the internal chamber 24 through the fuel channel 22 into the pump working chamber 21. At a predetermined point in time during the delivery stroke of the pump piston 14, the solenoid valve 38 is closed as a result of the flow of fuel instigated by the control unit, so that the pump working chamber 21 is separate from the internal chamber 24 and high pressure is built up by means of the reciprocal movement of the pump piston 14. In a predetermined -8rotational position of the pump piston 14, the delivery line 32 is connected by way of the longitudinal groove 30 to the pump working chamber 21 and when the fuel-injection pressure is achieved, the delivery valve 33 opens and fuel is supplied to the fuel-injection nozzles 36. At a predetermined point in time during the delivery stroke of the pump piston 14, the solenoid valve 38 is opened again by means of the control unit 46 by interrupting the flow of fuel, so that fuel can return from the pump working chamber 21 by means of the fuel channel 22 into the internal chamber 24 and the high pressure delivery is terminated. The quantity of fuel actually supplied under high pressure by the pump piston 14 is only a part of the maximum possible quantity of fuel by way of the entire delivery stroke of the piston pump. The solenoid valve 38 can, however, also be closed prior to the commencement of the delivery stroke of the pump piston 14, so that the commencement of the delivery stroke of the pump piston is at the same time also the commencement of the fuel- injection and the solenoid valve 38 only determines the termination of the high pressure delivery or rather the termination of the fuel- injection by means of opening the fuel channel 22. For such a case, the change in the point of time of fuel-injection can be controlled by means of an 4 -9additional, e.g. mechanical fuel-injection adjusting device.

In a first embodiment illustrated in Fig. 1, the pump piston 14 has on its periphery an annular groove 48 which is connected to the longitudinal groove 30. A relief line 50 issues radially from the cylinder hole 13 and the relief line is allocated a pressure holding valve 52 which opens even at a lower pressure than the fuel-injection pressure. The arrangement of the relief line 50 and the annular groove 48 is such that they are coordinated with each other in such a way that the connection of the pump working chamber 21 to the relief line 50 is produced prior to the pump piston 14 having reached its top dead point. Fig. 2a illustrates'the stroke of the pump piston 14 by way of the angle of rotation of the drive shaft 17. Shortly after the connection to the relief line 50 has been initiated, the solenoid valve 38 is closed again by means of the control unit 46, so that fuel can flow out of the pump working chamber 21 only by means of the relief line 50. The control of the solenoid valve 38 in dependence upon the angle of rotation of the drive shaft 70 is illustrated in Fig. 2b. In so doing, as illustrated in Fig. 2c, the residual pressure is maintained in the pump working chamber 21 by means of the pressure holding valve 52 and the -10residual pressure slows down the pump piston 14 prior to reaching its top dead point. In this way, the pump piston 14 is prevented from jumping off the roller 20 with its front cam disc 18. The residual pressure can, for example, amount to between 20 and 40 bar. Once the pump piston 14 has reached its top dead point, the solenoid valve 38 is opened again for the subsequent intake stroke.

Figs. 3 and 4 illustrate a second embodiment of a fuel-injection pump. The basic structure of the fuelinjection pump in the second embodiment is the same as that of the first embodiment. The pump working chamber 121 which is delimited by a pump piston 114 in the cylinder bore hole 113 can be connected by way of a connection controlled by means of the solenoid valve 138 to the fuel channel 122 which issues in the internal chamber 124. A pressure holding valve 152 is arranged between the solenoid valve 138 and the fuel channel 122 or in the fuel channel 122 and the pressure holding valve opens the connection of the pump working chamber 121 to the internal chamber 124 when the solenoid valve 138 is opened and when the residual pressure rises above a predetermined value. A return valve 154, which opens in the opposite direction to that of the pressure holding valve 152, i.e. towards the pump working chamber 121, can be z a c -11provided parallel to the pressure holding valve 152.

The solenoid valve 138 is open during the intake stroke of the pump piston 114 so that fuel is drawn into the pump working chamber 121 from the internal chamber 124 by means of the fuel channel 122 and the non- return valve 154. At a predetermined point in time during the delivery stroke of the pump piston 114, the solenoid valve 138 is closed and the pump working chamber 121 is separate from the internal chamber 124 so that a high pressure is built up in the pump working chamber 121. In a predetermined rotational position of the pump piston 114, the pump working chamber 121 is connected to one of the delivery lines 132 and when the fuel-injection pressure is achieved the delivery valve 133 is opened and fuel supplied under high pressure to the fuelinjection nozzles 136 of the internal combustion engine. The solenoid valve 138 is opened again at a predetermined point in time of the delivery stroke of the pump piston 114 so that fuel can flow out of the pump working chamber 121 by way of the pressure holding valve 152 into the internal chamber 124 and the fuel delivery under high pressure is terminated. The non-return valve is in so doing acted upon in the closing direction by means of the residual pressure in the pump working chamber 121 and therefore closed. The -12residual pressure, which is maintained in the pump working chamber 121, slows down the pump piston 114 prior to it reaching its top dead point. No special relief line is required in the second embodiment, since the fuel channel 122 is used as the relief line. Moreover, no special control is required in order to close the solenoid valve 138 again after the termination of the fuel-injection. If the pump working chamber 121 is supplied with fuel during the intake stroke of the pump piston 114 by way of an intake line controlled by the pump piston, then the valve member of the solenoid valve 138 can itself be a pressure holding valve.

The delivery valve'133 serves to separate a pump working chamber 121 from the fuel-injection nozzles 136 of the internal combustion engine in order to ensure that combustion gases cannot flow by way of the fuel-injection nozzles 136 into the pump working chamber 121. The delivery valve 133 has a valve member 156 which is acted upon in the closing direction towards the pump working chamber 121 by means of a spring 158 and rests on a valve seat 160. The valve member 156 can at the same time be designed as a known pressure relief valve and, for example, have a throttle 162 which is constantly open. The delivery valve 133 opens if the fuel-injection -13pressure in the pump working chamber 121 is achieved, in that the valve member 158 is raised from the valve seat 160 against the force of the spring 162. The residual pressure, which is maintained in the pump working chamber 121 by means of the pressure holding valve 152 after the termination of the fuel-injection, rests also against the fuel-injection nozzles 136 by way of the throttle 162 in the valve member 156 of the delivery valve 133 and prevents the combustion gases from opening the fuel-injection nozzles 136 and flowing into the pump working chamber 121. The abovedescribed design of delivery valve can also be used in the fuelinjection pump of the first embodiment.

Claims

-14CLAIMS

1. A fuel-injection pump for an internal combustion engine having a pump working chamber which can be connected to at least one delivery line, a pump piston delimiting the pump working chamber, the pump piston being driven by means of a rotating drive shaft by way of a cam drive at least in an axial reciprocal movement and a fuel-injection pressure is produced in the pump working chamber by means of the reciprocal movement of the pump piston, a fuel channel which can be connected to the pump working chamber, a solenoid valve which controls the fuel channel. the solenoid valve determining the termination of the fuelinjection by opening the fuel channel during the delivery stroke of the pump piston, and a control unit for controlling the solenoid valve wherein a residual pressure is maintained in the pump working chamber after the termination of the fuelinjection, this residual pressure being less than the fuel-injection pressure and preventing the pump piston from being raised from the cam drive, whereby the pump working chamber is connected to a relief line prior to termination of the fuel-injection which relief line has a pressure holding valve, which opens the relief line when the residual pressure in the pump working chamber is less than the fuel-injection pressure.

2. A fuel-injection pump according to claim 1, wherein after the termination of fuel-injection the solenoid valve is again closed, the pump piston is guided in a cylinder bore and a connection of the pump working chamber to the relief line is opened by means of the pump piston in the cylinder bore prior to the pump piston reaching its top dead point.

3. A fuel-injection pump according to claim 2, wherein the connection of the pump working chamber to the relief line is opened prior to the solenoid valve being closed again after the termination of the fuelinjection.

4. A fuel-injection pump according to claim 1, wherein the fuel channel serves as the relief line and the solenoid valve is arranged between the pump working chamber and the pressure holding valve.

5. A fuel-injection pump according to claim 4, wherein the pump working chamber is filled with fuel by way of the fuel channel during the intake stroke of the pump piston and a non-return valve which opens towards the pump working chamber is arranged parallel to the pressure holding valve.

6. A fuel-injection pump according to any one of the preceding claims, wherein a delivery valve, which is open when the fuel-injection pressure is achieved, is arranged in the delivery line and the delivery -16valve has a constantly open throttle.

7. A fuel-injection pump substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

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