GB2070686A

GB2070686A - Timing control in fuel injection pumping apparatus

Info

Publication number: GB2070686A
Application number: GB8104548A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1980-02-15
Filing date: 1981-02-13
Publication date: 1981-09-09
Also published as: GB2070686B

Abstract

A fuel injection pumping apparatus for supplying fuel to an internal combustion engine includes an angularly adjustable cam whereby the timing of delivery of fuel by the apparatus can be varied. The apparatus includes an electromagnetic valve the setting of which can be varied to adjust a control which is applied to a pistion coupled to the cam. First circuit means 61 is provided to generate a signal which indicates the desired timing of fuel delivery in accordance with the speed of and load on the associated engine and this signal is modified by second circuit means 68 which provides a signal indicative of any discrepancy between the rotary parts of the engine and the apparatus. The resulting signal is compared in a comparison circuit 64 with a signal provided by a transducer 65 which senses the actual position of the cam and the output of the circuit 64 is utilized to control the current flow to the winding 60 of the valve. <IMAGE>

Description

SPECIFICATION Fuel injection pumping apparatus This invention relates to a fuel injection pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a body part, an injection pump mounted in the body part and adapted in use to be driven in timed relationship with the associated engine and means for adjusting in use, the timing of delivery of fuel by the apparatus to the engine.

It is important that the timing of delivery of fuel to an engine should be closely controlled in order to ensure that the engine is operated as efficiently as possible. In practice the timing is varied in accordance with the speed of and the load on the engine. The load on an engine can be represented by a signal which is determined from the amount of fuel supplied by the apparatus to the engine and this together with a speed signal can be fed to a circuit which either works out the required timing of delivery or determines the timing of delivery on the basis of information stored in the circuit. Having determined the required timing of delivery it is necessary to effect adjustment of said means and then to check that delivery is taking place at the desired time.The timing of delivery of fuel can be checked by obtaining a signal indicative of the setting of a part within the apparatus. This signal is utilized as a feed back signal. The operation of the means for adjusting the timing is therefore checked but it will be neces safy to provide further correction for any discrepancies in the mounting of the apparatus on the engine and in the drive mechanism. It should be noted that it is assumed that delivery of fuel takes place at a time having a known relationship to the rotation of the pump drive shaft for each position of the aforesaid part which provides the feedback signal.

According to the invention a fuel injection pumping apparatus for supplying fuel to an internal combustion engine comprises a body part, an injection pump mounted in the body part and adapted in use to be driven in timed relationship with the associated engine, a first transducer for providing a signal indicative of the amount of fuel supplied by the apparatus, means for providing a signal indicative of the speed of operation of the apparatus, first circuit means which receives said signals and on the basis of information stored therein provides a signal representing the desired timing of fuel delivery to the associated engine, a second transducer for providing a signal representative of the timing of delivery of fuel by the apparatus, third and fourth transducers for providing signals representative of the positions of the rotary parts of the associated engine and the apparatus, second circuit means which receives the signals from said third and fourth transducers and provides a signal representative of any discrepancy between the positions of the rotary parts of the apparatus and the associated engine, an adder circuit for adding the signals provided by the first and second circuit means, a comparison circuit which receives the signals from said adder circuit and said second transducer and means controlled by the output of said comparison circuit for adjusting the timing of delivery of fuel by the apparatus to the engine.

In the accompanying drawings: Figure 1 is a sectional side elevation of one example of the apparatus, Figure 2 is a section of part of the apparatus seen in Fig. 1 taken along a different radial plane, Figures 3 and 4 are sections through part of the apparatus seen in Figs. 1 and 2, Figure 5 is a section through part of the apparatus seen in Fig. 1, Figure 6 is a block diagram of a timing control circuit for the example mentioned above, Figure 7 shows in side elevation part of the apparatus of Fig. 1 and Figure 8 is a fluid circuit diagram associated with the part of the apparatus as seen in Fig.

7.

Referring to Fig. 1 of the drawings, the apparatus comprises a body part generally indicated at 10 and which conveniently is formed by a generally cup shaped portion 11 the open end of which is closed by a closure portion 1 2. The body portion 10 is provided with apertured lugs 1 3 whereby in use the apparatus can be secured to the engine with which it is associated.

The body portion 11 mounts a rotary drive shaft 1 4 which in use, is coupled to a drive member of the associated engine so that the drive shaft is rotated in synchronism with the engine. The drive shaft 1 4 extends into the generally cylindrical chamber 1 5 defined by the two body portions and has an enlarged cup shaped portion 1 48 within the chamber.

The enlarged portion is provided with a pair of diametrically disposed slots 16. The enlarged portion of the drive shaft is hollow and at its end remote from the smaller diameter portion of the shaft the inner surface is of right cylindrical form and locates about a spigot portion 1 7 defined by the body portion 1 2.

The remainder of the interior surface of the enlarged portion of the drive shaft tapers for a purpose which will be described. Moreover, the drive shaft is provided with a counter bore 18. An oil seal 1 9 is provided at the outer end of the body portion 10 for engagement with the drive shaft 1 4 and a sleeve bearing 20 supports the shaft for rotation, the shaft being given additional support by the spigot 1 7. The shaft is located against axial move ment by thrust surfaces which engage with the end surfaces of the enlarged portion of the shaft.In one case the thrust surface is defined directly by the body portion 1 2 whilst in the other case, the thrust surface is defined by an annular plate 21 which surrounds the drive shaft and which additionally serves as an end closure for a low pressure fuel pump 22. The rotor 22a of the supply pump is carried by the drive shaft 14 and the rotor in turn carries vanes which co-operate with an eccentrically disposed surface on a stator ring 22b which is carried within a body portion 11. The low pressure pump has a fuel inlet 23 connected to a fuel inlet in a housing secured to the body portion 11 and a fuel outlet 24. Moreover, a relief valve 25 is provided to ensure that the output pressure of the pump remains within desired limits, the relief valve being connected between the inlet and the outlet.

Formed in the body portion 1 2 is a cylindrical bore 26 in which is fixed a sleeve 27. The sleeve 27 accommodates an angularly and axially movable distributor member, 28 which projects into the chamber 1 5 and has an enlarged head portion lying within the chamber. Formed in the head portion of the distributor member is a transversely extending bore 29 in which is located a pair of pumping plungers 30. The bore 29 communicates with a blind passage 31 formed in the distributor member and which at its end within the head portions is sealed by means of a plug. As is more clearly shown in Figs. 2, 3 and 4 the passage 31 communicates with a pair of diametrically disposed longitudinal slots 32 formed in the periphery of the distributor member and communicating with the passage 31 by means of a single or a plurality of connecting passages.The passage 31 also communicates with a further longitudinal slot 33 formed in the periphery of the distributor member and this slot communicates in turn with a plurality of outlet ports 34 formed in the sleeve 27 and as seen in Fig. 2, the outlet ports 34 communicate with outlets 35 respectively in the body portion 1 2. Each outlet incorporates a conventional form of delivery valve 36. The slots 32 register in turn with inlet ports 37 formed in the sleeve 27 and communicating with a circumferential groove 38 formed in the periphery of the sleeve. The groove 38 as shown in Fig. 1, communicates with the outlet 24 of the low pressure pump 22 by way of an on/off valve 39 conveniently controlled by an electromagnetic device 40. If desired a single slot 32 may be provided with the number of inlet ports being equal to the number of outlets.

Surrounding the head portion of the distributor member 28 is an annular cam ring 41 on the internal peripheral surface of which are formed pairs of diametrically disposed cam lobes. In the particular example three pairs of lobes are provided since the apparatus is intended to supply fuel to a six cylinder engine. Moreover, the cam ring 41 is angularly movable about the axis of rotation of the distributor member by means of a fluid pressure operable device generally indicated at 42 and connected to the cam ring by way of a radially disposed peg 43. The device 42 and its control will be described in detail later.

Positioned at the outer ends of the plungers are a pair of followers each of which comprises a roller 44 carried in a shoe 45. The followers are retained axially relative to the distributor member by a pair of side plates 46, 47 which are secured to the side faces of the head portion of the distributor member.

Conveniently as shown in Fig. 5, the side plates are of annular form and have a pair of outwardly extending tongues 48, which locate in the slots 1 6 formed in the enlarged portion of the drive shaft. In Fig. 5 the plate 46 is seen, the plates acting to transmit rotary motion to the distributor member from the drive shaft. The shoes 45 are also located within the aforesaid slots 1 6 and the rotary motion is transmitted to the shoes directly by the drive shaft. Moreover, the circumferential side faces of the shoes are provided with circumferentially extending projections 49 the radially outer surfaces of which are tapered to co-operate with the tapered surface formed on the internal surface of the enlarged portion of the drive shaft 14.

In use, when fuel is supplied to the bore 29, upon registration of a groove 32 with an inlet passage 37, the plungers 30 are moved outwardly by the fuel pressure and in so doing impart outward movement to the shoes 45 and the rollers 44. The outward movement is limited by the abutment of the tapered surfaces on the shoes and shaft and by moving the distributor member axially the extent of outward movement can be varied.

Thus the amount of fuel supplied to the bore 29 can be controlled and this is turn determines the amount of fuel delivered through an outlet when theplungers 30 are moved inwardly by a pair of cam lobes.

The axial position of the distributor member can be varied mechanically or hydraulically. In the arrangement described the variation is achieved by varying the pressure within a chamber 50 defined by the end of the bore 26 in the body portion 1 2. The end of the bore 26 is closed by a closure member and fuel under pressure is supplied to the chamber 50 by way of a restrited orifice 51 carried by the sleeve 27. The orifice 51 communicates with the outlet 24 of the pump 22. Fuel is allowed to escape from the chamber 50 so that the pressure in the chamber can be controlled, by way of an electromagnetically controlled valve 52. Moreover, the distributor member is biassed by means of a coiled compression spring 53 which is housed within the blind bore 1 8 formed in the drive shaft 14.The spring 53 acts between the drive shaft and the distributor member and urges the distributor member against the action of fuel under pressure in the chamber 50 which acts on the distributor member.

By varying the pressure in the chamber 50 using the valve 52 so the axial position of the distributor member can be varied and therefore the amount.of fuel delivered each time the plungers move inwardly can be varied.

For a given axial setting of the distributor member and ignoring leakage, the amount of fuel delivered by the plungers will remain substantially the same throughout the speed range of the associated engine and an indication of the axial setting of the distributor member, is provided by a position transducer 54 which is carried on the end closure for the bore 26 and may be adjustably mounted thereon for the purpose of calibration. Conveniently the transducer has a part which is carried by the distributor member.

The signal provided by the transducer 54 is representative of the amount of fuel supplied at each injection stroke of the apparatus and is also indicative of the load on the associated engine.

The valve 52 is supplied with current by a circuit which receives a required fuel signal and also the signal from the transducer 54 and the valve is adjusted so that these two signals are equal. The required fuel signal is provided by a governor circuit (not shown) which in turn receives an engine speed signal, a demand signal from the operator e.g. the driver of the vehicle powered by the engine, and also the signal from the transducer and from these signals calculates the required fuel signal, due account being taken of various engine operating parameters for example the maximum allowed engine speed and the maximum amount of fuel which can be supplied to the engine.

Turning now to Figs. 7 and 8 the device 42 which varies the setting of the cam ring is shown in diagrammatic side elevation and it comprises a piston 54 slidable within a cylinder 55. The piston is biassed towards one end of the cylinder 55 by means of a coiled compression spring 56 and the piston is coupled to the cam ring by means of the peg 43.

The spring 56 biasses the piston 54 and the cam ring towards the position in which the delivery of fuel to the associated engine is fully retarded.

In order to advance the timing of delivery, fuel is supplied to the end of the cylinder 55 remote from the spring and conveniently this fuel is derived from the fuel supply pump 22, the fuel flowing by way of a fixed restrictor 57 and a ball check valve 58 to the cylinder 55.

The pressure of fuel supplied to the cylinder is controlled by an electromagnetic valve 59 similar in construction to the valve 52. The valve 59 includes a winding illustrated at 60.

Other forms of fluid circuit can be used which wil! enable the pressure in the cylinder to be varied by varying the current flow in the winding 60 for example, the positions of the restrictor 57 and the valve 59 can be reversed in which case the ball check valve 58 can be omitted. The valve 58 acts to prevent flow of fuel from the cylinder 55 to the rest of the fluid circuits of the apparatus when the rollers 45 engage the cam lobes.

As previously stated the timing of delivery of fuel to an engine should depend upon the speed of the engine and also the load on the associated engine. As shown in Fig. 6 a circuit indicated at 61 receives an engine speed signal from a transducer 62 and the engine load signal as represented by the amount of fuel being supplied to the engine, from the transducer 54. These two signals are supplied to the circuit 61 which is a so called"timing map" that is to say it contains stored information as to the required timing of delivery of fuel for the rage of engine speeds and engine loads which can be expected. The signal is supplied through an adding circuit 63 to a comparison circuit 64. The comparison circuit 64 receives a signal from a transducer 65 which provides a signal representing the timing of delivery of fuel.Any difference between the required timing signal as supplied from the circuit 61 and the timing signal as provided by the transducer 65, produces an output from the circuit 64 which is passed to the winding 60 of the valve 59. An appropriate correction is made in the pressure within the cylinder 55 so as to achieve the correct timing.

The transducer 65 is located in the apparatus and the assumption is made that fuel delivery will occur at a known time in relation to the rotation of the pump for each value of signal from the transducer 65. This arrangement however does not take into account any discrepancies in the mounting of the apparatus or the drive connection, it is to take these into account that the adder circuit 63 is provided and it has an additional input from a comparison circuit 66 which has a reference input 67 and an input from a circuit 68 which in turn receives an engine position signal from a transducer 69 and a signal indicative of the position of the rotary parts of the apparatus from a transducer 70. The signal supplied to the reference input 67 represents the ideal relationship between the signals provided by the transducers 69 and 70.The circuit 68 determines the actual discrepancy between the positions of the rotary parts of the engine and the rotary parts of the apparatus and the output signal is compared with the signal applied to the reference input 67. The error signal is supplied to the adder circuit 63 which algebraically adds the error with its appropriate sign to the required timing signal.

This circuit is therefore able to take into account all the factors mentioned above. It does not take into account any lag which may occur between the delivery of fuel by the apparatus and the actual start of injection of fuel into the engine. This may however be taken into account in the information stored in the circuit 61 or in the value of the signal applied to the reference input 67.

Any necessary adjustment of the datum position of the cam ring i.e. to take into account mounting errors etc., is arranged to occur when the associated engine is operating at a substantially constant speed or at a substantially constant predetermined speed.

The fact that the engine is operating at a constant speed is determined by observing the signals supplied by any one of the transducers 62, 69 or 70. When it is determined that the engine speed is substantially constant then the signal provided by the comparison circuit 66 is supplied to the adder circuit 63. Since the adder circuit 63 must receive a constant signal a sample and hold circuit 71 is dis -posed intermediate the comparison circuit 66 and the adder circuit. The circuit 71 also incorporates a memory section which supplies the continuous signal to the adder circuit and which is updated only when it has been determined that the engine is operating at a substantially constant speed. In order to ensure that the timing is substantially correct when an attempt is made to start the engine, the memory section is of the type or is arranged to hold the signal even when the engine is not in operation.

Claims

1. A fuel injection pumping apparatus for supplying fuel to an internal combustion engine comprising a body part, an injection pump mounted in the body part and adapted in use to be driven in timed relationship with the associated engine, a first transducer for providing a signal indicative of the amount of fuel supplied by the apparatus, means for providing a signal indicative of the speed of operation of the apparatus, first circuit means which receives said signals and on the basis of information stored therein provides a signal representing the desired timing of fuel delivery to the associated engine, a second transducer for providing a signal representative of the timing of delivery of fuel by the apparatus, third and fourth transducers for providing signals representative of the positions of the rotary parts of the associated engine and the apparatus, second circuit means which receives the signals from said third and fourth transducers and provides a signal representative of any discrepancy between the positions of the rotary parts of the apparatus and the associated engine, an adder circuit for adding the signals provided by the first and second cirucit means, a comparison circuit which receives the signals from said adder circuit and second transducer and means controlled by the output of said comparison circuit for adjusting the timing of delivery of fuel by the apparatus to the associated engine.

2. An apparatus according to claim 1 in which said means for adjusting the timing of delivery of fuel includes a fluid pressure oper, able piston which controls the position of a part within the apparatus, said second transducer being responsive to the position of said piston.

3. An apparatus according to claim 2 in which said means for adjusting the timing of delivery of fuel includes an electromagnetic valve having a winding, the electric current flow in which is controlled by the output of the comparison circuit.

4. An apparatus according to claim 1 including a further comparison circuit which receives the signal from said second circuit means and a reference signal, the difference between these signals being supplied to said adder circuit for adding to the signal provided by said first circuit means.

5. An apparatus according to claim 4 including a sample and hold circuit interposed between the output of the further comparison circuit and said adder circuit, said sample and hold circuit including a memory section, whereby a continuous signal is supplied to the adder circuit, said sample and hold circuit being arranged so that the memory section is updated only when the engine is operating at a substantially constant speed.

6. An apparatus according to claim 5 in which the memory section is of the type or is arranged to hold the signal when the apparatus is at rest.

7. An apparatus according to claim 5 in which said constant speed is a predetermined speed.

8. A fuel injection pumping apparatus for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.