GB1586288A

GB1586288A - Fuel injection pumps

Info

Publication number: GB1586288A
Application number: GB4064677A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1976-10-02
Filing date: 1977-09-30
Publication date: 1981-03-18
Also published as: DE2644698C2; JPS5344723A; DE2644698A1; JPS6119828B2

Description

(54) IMPROVEMENTS RELATING TO FUEL INJECTION PUMPS (71) We, ROBERT BOSCH GMBH, a German Company, of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly desscribed in and by the following statement:- The present invention relates to a fuel injection pump for an internal combustion engine.

In certain known fuel injection pumps the adjustment of the commencement of fuel injection is effected by means altering the efficient range of the drive cam available for effective fuel injection, so that the entire available range of the drive cam is considerably widened. In the case of the majority of engines, however, an earlier commencement of injection is required for cold starting and the subsequent warming up or accelerating of the internal combustion engine. On the other hand in order to maintain the pump working chamber well filled at full load and high speed in the case of these known pumps it is desirable to have a connection between the suction chamber and the pump working chamber that is as long as possible. To achieve this result, one solution is to use large control cross-sections.However this requires very accurate control in order to avoid the commencement of fuel delivery to the individual cylinders varying during individual compression strokes. For this reason control of an overflow passage takes place uniformly during all compression strokes after a definite initial stroke. A general adjustment of the commencement of injection can cause the operation of the internal combustion engine to become too rough.

According to the present invention there is provided a fuel injection pump for internal combustion engines comprising at least one pump piston which is arranged to reciprocate and which during its delivery stroke during normal operation blocks an overflow passage from a pump working chamber after an initial part of the stroke movement to thus commence injection and in co-operation with a control member which is actuated by a speed governor for the purposes of altering the injection quantity, opens a spill passage of the pump working chamber to terminate injection, the control member being arranged to, in use, block the overflow passage and spill passage during starting speeds.

A fuel pump constructed in accordance with the present invention has the advantage that the first range of the initial stroke of the drive cam is also utilised for the adjustment of the commencement of injection to an earlier position during the start. Furthermore this additional early adjustment is effected independently of the load- and speeddependent adjustment of injection during normal running.

It is particularly advantageous when the spill passage and the essential portions of the overflow passage are located in the pump piston itself. This limits the number of edges required for control to a minimum and considerably simplifies their manufacture.

The present invention will now be further described by way of example, with reference to the accompanying drawing in which a longitudinal section of part of a fuel injection pump according to the present invention, is illustrated.

The pump comprises a pump piston 4 located inside a housing 1 here shown by a dash-dot line. The piston 4 is slidable in a bore 2 of a cylinder liner 3 which is set into the pump housing 1, and by means that are not shown a reciprocating and simultaneous rotational movement are imparted to the piston. A pump working chamber 6 of the pump is supplied with fuel from a suction chamber 9 by way of longitudinal grooves 7 that are disposed in the peripheral surface of the pump piston and at least one bore 8 that runs through the cylinder liner 3 in the housing 1. Fuel is supplied for as long as the pump piston 4 carries out its suction stroke or until it adopts its bottom dead centre position. The suction chamber 9 is supplied with fuel from a fuel container 12 by way of a feed pump 11.A pressure control valve 13 controls the pressure, in a known manner so as to be speed-dependent, in the suction chamber 9, so that the pressure therein rises with increasing speed.

A spill passage 15 in the pump piston leads from the working chamber 6 and opens by way of an outlet opening 16, into the pump suction chamber 9 in the lower part of the pump piston which projects from the cylinder liner 3. The outlet opening 16 is controlled by a sleeve valve 17 which co-operates with the pump piston. A transverse bore 18 branches off from the spill passage 15 into the part of the pump piston 4 that extends through cylinder liner 3 and opens into a longitudinal distributor groove 19 in the peripheral surface of the pump piston.

During each delivery stroke of the pump piston, after the piston has rotated to shut the bore 8, one of the pressure lines 20, shown by a dotted line, is connected to the pump working chamber 6 by way of the spill passage 15, the transverse bore 18 and the longitudinal distributor groove 19.

The pressure lines 20 all lead by way of a pressure valve that is not shown to the individual injection nozzles of the cylinders of an internal combustion engine that is likewise not shown, and are distributed about the bore 2 according to the number of cylinders to be supplied. During the delivery stroke of the pump piston 4 fuel is thus delivered to the injection nozzles by way of the spill passage 15 for as long as the outlet opening 16 of the spill passage 15 remains closed by the sleeve valve 17.

The sleeve valve is displaced on the pump piston 4 by a speed regulator (not illustrated) depending on load and speed by way of an intermediate lever 23 which is pivotable about an axle 26 and has a head 24 which engages in a recess 25 in sleeve valve 17. A downward displacement of the sleeve valve 17 thus results in the outlet opening 16 of the longitudinal passage 15 during the delivery stroke of the pump piston 4, being opened increasingly earlier and the pump working chamber 6 being thereby unloaded and no more fuel being fed under pressure into the pressure lines 20. The spill passage 15 thus acts partly as a fuel shut-off passage and partly as a fuel delivery passage. The lower the sleeve valve 17 is adjusted the smaller the injection quantity that is delivered to the internal combustion engine.In the uppermost position of the sleeve valve the outlet opening 16 is no longer opened during the delivery stroke of the pump piston 4 so that the entire amount of fuel that can be delivered by the pump piston becomes injected. This position of the sleeve valve corresponds to the position during starting of the internal com bustion engine.

In the pump piston 4 there is also an over flow passage 28 with two openings 29 and 30 that terminate in the peripheral surface of the piston. The opening 29 is disposed in the region of the cylinder liner 3 and is constantly overlapped by an annular groove 31 disposed in the cylinder liner 3. The second opening 30 by way of contrast is controlled by the sleeve valve 17 and is thus located within the suction chamber 9, opening 30 being above the level of the outlet opening 16. Whilst the internal combustion engine is operating normally a part of the opening 30 is always kept open by the sleeve valve 17. If on the other hand, the sleeve valve is again displaced downwards during starting, then this opening is also blocked at the commencement of the compression stroke.From the spill passage 15 a further radial bore 32 branches off, which likewise terminates in the peripheral surface of the piston 4 in the region of the cylinder liner 3 and whose opening cooperates with the annular groove 31. The co-ordination of this annular groove 31 and the radial bore 32 is such that after an initial stroke hv of the pump piston 4 the bore 32 is separated from the annular groove 31.

By means of this control of the initial stroke movement hv which is naturally equal for all compression strokes, the actual fuel delivery to the internal combustion engine is not effected until the moment at which the bore 32 is separated from the annular groove 31. Thus this actual commencement of delivery is controlled not depending on the rota- tional movement of the pump piston but on the stroke movement so that tolerances in the control can be controlled much better and furthermore the process of filling the pump working chamber 6 can be improved by enlarging the filling grooves 7.

In order to achieve a control that is largely independent of disadvantageous throttle effects a transverse groove 33 is disposed in the peripheral surface of the pump piston and is constantly connected to the radial bore 32 and co-operates with the annular groove 31 to effect a rectangular slit control.

During the initial stroke movement hv of the pump piston fuel flows from the pump working chamber 6 into the suction chamber 9 by way of the overflow passage which comprises the following sections, the radial bore 32, the grooves 31 and 33, the radial bore 29, the passage 28 and the radial bore 30. As the radial bore 32 terminates in the transverse groove 33 the radial bore 30 terminates also in a transverse groove 34, which is then controlled by an end face 35 of the sleeve valve 17.

If at starting speeds the sleeve valve 17 is moved upwards from the full load position illustrated by the stroke ws then during the initial stroke movement hv of the pump piston the overflow passage is not opened.

Opening of the groove 34 does not take place until during a further portion of the stroke of the pump piston and after however the grooves 33 and 31 have already been separated from each other. This thus causes the quantity which flows away i.e. overflows, during the initial stroke movement at normal operation to be injected with the rest of the fuel. This effects an adjustment towards and "early" setting or advance of the commencement of injection with advantageous utilisation of the control of the initial stroke movement hv.

The fuel injection pump in accordance with the invention operates in the following manner: As long as the sleeve valve 17 adopts the position illustrated in the drawing for full load or a position for a smaller injection quantity, during the initial stroke movement hv a certain quantity that corresponds to the initial stroke movement can flow away to the suction chamber 9 through the overflow passage 32, 33, 31, 29, 28, 30 and 34. At this range of load the required adjustment of the commencement of injection is effected by way of the cam drive in a manner well known in the art. For normal operation commencement of fuel injection that is constant with respect to the delivery stroke is achieved by the control of the initial stroke hv.As soon, however, as the sleeve valve 17 is moved upwards into the starting position (illustrated by dotted lines) by means of the intermediate lever 23 and after traversing the distance ws the overflow passage remains blocked during the initial stroke movement hv by the sleeve valve 17. Hereby the distance s between the end face 35 of the sleeve valve 17 and the upper limiting control edge of the groove 34 is larger than hr, i.e.

not until the grooves 33 and 31 are separated from one another, is the groove 34 opened to the suction chamber 9 by the leading edge of the end face 35.

Hence the injection into the internal combustion engine commences from the beginning of the delivery stroke of the pump piston, which results in an additional adjustment of the commencement of injection towards an "early" setting.

Although a distributing fuel injection pump was selected as an embodiment of the invention, the invention can be accordingly applied, for example to a series fuel injection pump.

Conventionally this early adjustment during starting is desirable right up to a rate of between 700 and 1000 revolutions per minute of the engine. As however the idling speed normally is lower and the intermediate lever 23 of the speed regulator tends to move back the sleeve valve 17 into its normal position in or before reaching the idling speed, the sleeve valve 17 should be moved back into its normal position by means of a delay mechanism with corresponding shutting off of the starting quantity only after 700 to 1000 revolutions per minute have been reached. It is, however, also conceivable to control this delay by means of a thermostatic member.

WHAT WE CLAIM IS:- 1. A fuel injection pump for internal combustion engines comprising at least one pump piston which is arranged to reciprocate and which during its delivery stroke during normal operation blocks an overflow passage from a pump working chamber after an initial part of the stroke movement to thus commence injection and in co-operation with a control member which is actuated by a speed governor for the purposes of altering the injection quantity, opens a spill passage of the pump working chamber to terminate injection, the control member being arranged to, in use, block the overflow passage and spill passage during starting speeds.

2. A fuel injection pump as claimed in claim 1, in which a sleeve valve disposed about the pump piston and axially adjustable by means of the speed governor serves as the control member, the overflow passage running through the pump piston.

3. A fuel injection pump as claimed in claim 1 or 2, in which the spill passage is constructed as a bore, disposed in the piston and having a predominantly axially extending section with a radially extending section, a further radial bore disposed in the region of the pump cylinder, branching off the axial section as an overflow passage section which is connected during the initial part of the delivery stroke of the pump piston to an annular groove, disposed in the pump cylinder, which groove is constantly connected to a bore that runs in the pump piston and serves as a further overflow section, the opening of said bore being blocked during start speeds by the control member.

4. A fuel injection pump as claimed in any one of the preceding claims, in which the controlled radial bores running in the piston open into transverse grooves which cooperate with corresponding control edges that run at right-angles to the stroke direction.

5. A fuel injection pump for internal combustion engines, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the pump piston and after however the grooves 33 and 31 have already been separated from each other. This thus causes the quantity which flows away i.e. overflows, during the initial stroke movement at normal operation to be injected with the rest of the fuel. This effects an adjustment towards and "early" setting or advance of the commencement of injection with advantageous utilisation of the control of the initial stroke movement hv. The fuel injection pump in accordance with the invention operates in the following manner: As long as the sleeve valve 17 adopts the position illustrated in the drawing for full load or a position for a smaller injection quantity, during the initial stroke movement hv a certain quantity that corresponds to the initial stroke movement can flow away to the suction chamber 9 through the overflow passage 32, 33, 31, 29, 28, 30 and 34. At this range of load the required adjustment of the commencement of injection is effected by way of the cam drive in a manner well known in the art. For normal operation commencement of fuel injection that is constant with respect to the delivery stroke is achieved by the control of the initial stroke hv.As soon, however, as the sleeve valve 17 is moved upwards into the starting position (illustrated by dotted lines) by means of the intermediate lever 23 and after traversing the distance ws the overflow passage remains blocked during the initial stroke movement hv by the sleeve valve 17. Hereby the distance s between the end face 35 of the sleeve valve 17 and the upper limiting control edge of the groove 34 is larger than hr, i.e. not until the grooves 33 and 31 are separated from one another, is the groove 34 opened to the suction chamber 9 by the leading edge of the end face 35. Hence the injection into the internal combustion engine commences from the beginning of the delivery stroke of the pump piston, which results in an additional adjustment of the commencement of injection towards an "early" setting. Although a distributing fuel injection pump was selected as an embodiment of the invention, the invention can be accordingly applied, for example to a series fuel injection pump. Conventionally this early adjustment during starting is desirable right up to a rate of between 700 and 1000 revolutions per minute of the engine. As however the idling speed normally is lower and the intermediate lever 23 of the speed regulator tends to move back the sleeve valve 17 into its normal position in or before reaching the idling speed, the sleeve valve 17 should be moved back into its normal position by means of a delay mechanism with corresponding shutting off of the starting quantity only after 700 to 1000 revolutions per minute have been reached. It is, however, also conceivable to control this delay by means of a thermostatic member. WHAT WE CLAIM IS:-

1. A fuel injection pump for internal combustion engines comprising at least one pump piston which is arranged to reciprocate and which during its delivery stroke during normal operation blocks an overflow passage from a pump working chamber after an initial part of the stroke movement to thus commence injection and in co-operation with a control member which is actuated by a speed governor for the purposes of altering the injection quantity, opens a spill passage of the pump working chamber to terminate injection, the control member being arranged to, in use, block the overflow passage and spill passage during starting speeds.