GB2172339A - Lubrication in a fuel pump - Google Patents

Abstract

A distributor-type fuel injection pump comprises a pump body 1 including an internal lubrication space 5 or 2 to be lubricated with a lubrication oil, a fuel feed pump 34, e.g. of sliding vane type (Figures 3 & 4), disposed in the pump body adjacent to the lubrication space and separated by an oil seal 50a or 50b housed in a sealing chamber 49a, 49b facing to the feed pump, and a pressure release passageway 58 communicating the sealing chamber with the low pressure side of the feed pump. With this construction, the fuel pressure in the sealing chamber is released to the low pressure side of the feed pump through the pressure release passageway 58. As a result, the fuel pressure applied to the oil seal can be maintained low so that the fuel leakage into the lubrication space is minimised. <IMAGE>

Description

SPECIFICATION Distributor-type fuel injection pump The present invention relates to a distributor-type fuel injection pump for a diesel engine.

Bosch pumps or distributor-type fuel injection pumps generally comprise a feed pump disposed in a pump body adjacent to the rear side thereof and a cam chamber defined between the fuel pump and a head portion of the pump body. A drive shaft and a plunger are coupled together within the cam chamber through a cam so that the plunger makes rotational and reciprocating motions simultaneously, in unison with the rotation of the drive shaft.

In general, the cam chamber is utilized as a fuel chamber for receiving a fuel delivered from the fuel pump. The fuel thus received lubricates the cam and other movable components in the cam chamber, however, because of its low viscosity, the fuel gives only an insufficient lubrication which would result in a short service time of the pump.

With the foregoing difficulty in view, it has been a long desire to realize the lubrication of the cam and other compartments in the cam chamber exclusively with a lubrication oil in case high speed and heavy load operation of the pump is intended.

One prior attempt proposed to meet such desire is disclosed in Japanese Patent Laid-open Publication No. 56-154134, wherein a magnetic valve is disposed on the head portion of a fuel injection pump body for controlling the flow of a fuel delivered from a pump working chamber defined between a cylinder and a plunger. The fuel is fed from the outlet of a feed pump to an inlet of the magnetic valve through a bypass passage bypassing the cam chamber. With the magnetic valve thus provided, a governor and a control sleeve are displaced and it becomes possible to introduce a lubrication oil into the cam chamber.

The above-identified Japanese publication does not disclose any seal means for sealing the cam chamber and other spaces to be lubricated from the fuel pump. Even if conventional oil seals were employed as seal means, the fuel would leak in the lubrication spaces because the oil seals are subjected to a high fuel pressure created by the feed pump.

With the foregoing difficulties in view, an object of the present invention is to provide a distributortype fuel injection pump having structural features which prevent fuel from leaking in a space to be lubricated with a lublication oil and thereby im prove the durability of the pump.

The foregoing and other objects of the present invention are attained by a distributor-type fuel injection pump comprising: a pump body having defined therein an internal lublication space to be lubricated with a librication oil; a drive shaft rotat ably mounted on the pump body; a fuel feed pump disposed in the pump body adjacent to the lubrication space and drivingly connected to the drive shaft, the feed pump having a low pressure side; at least one oil seal sealingly mounted around the drive shaft and disposed between the lubrication space and the feed pump for sealingly separating them from one another; a sealing chamber facing to the feed pump and housing therein the oil seal; and a pressure release passageway communicating the sealing chamber with the low pressure side of said the pump.

With this construction, the fuel pressure in the sealing chamber is partially released to the low pressure side of the feed pump through the pressure release passageway. As a result, the fuel pressure applied on the oil seal can be maintained below a value at which the fuel leakage in the lubrication space may occur.

Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiments incorporating the principles of the present invention is shown by way of illustrative example.

Figure 1 is a longitudinal cross-sectional view of a distributor-type fuel injection pump embodying the present invention; Figure 2 is a cross-sectional view taken along line A-A of Figure 1; Figure 3 is an end elevational view of a feed pump of the fuel injection pump shown in Figure 1; and Figure 4 is an enlarged perspactive view of a vane of the feed pump shown in Figure 3.

As shown in Figure 1, a fuel injection pump embodying the present invention includes a pump body 1 composed of a front or head portion 1a and a rear portion 1 b connected together, the rear portion 1b being elongated and having a tubular portion (not designated) adjacent to the head portion 1a. The rear portion 1b has a central horizintal bore 2 in which a drive shaft 3 is rotatably mounted via a pair of spaced bearings 4a, 4b disposed in the bore 2 at opposite ends thereof. The bearings 4a, 4b in the illustrated embodimebt comprise plain bearings. The drive shaft 3 has one end projecting outwardly from the rear portion 1 b and adapted to be coupled in driven relation with an engine crankshaft (not shown). The other end of the drive shaft 3 extends into the cam chamber 5 defined in the pump body 1.

A plunger barrel 6 is mounted centrally in the head portion 1a and has an axial bore 7 in which a plunger 8 is movably received, the bore 7 and the plunger 8 jointly defining therebetween a pump working chamber 9. The plunger 8 has one end disposed in the cam chamber 5 and connected by a pin 10 to one end face of a cam disc 11. The cam disc 11 is axially movably connected to the other end of the drive shaft 3 by means of a jaw coupling 12. A roller holder 13 is disposed circumferentially around the coupling 12 and secured to the rear portion 1b of the pump body 1. The roller holder 13 retains thereon a plurality of rollers (not shown) held in engagement with cam surface defined on the other end face of the cam disc 11. The cam surface includes circumferentially disposed alternating projections and recesses.The rollers and the cam surface jointly constitute a cam assembly and they are forced against each other by a compression coil spring 15 which is disposed between the head portion 1a and a circular spring retainer 14. The spring retainer 14 is mounted around the plunger 8 adjacent to the end surface thereof. With this construction, when the drive shaft 3 is rotated, rotary motion is transferred through the coupling 12 and the cam disc 11 to the plunger 8. At the same time, reciprocating motion is given to the plunger 8 by the cam assembly and the spring 15. Thus, the plunger 8 makes rotational and reciprocating motions simultaneously, in unison with the rotation of the drive shaft 3.

A magnetic valve 15 includes a valve body 16 threaded to an upper part of the head portion la, and a cover 17 secured to an upper end of the valve body 16 with an armature 18 movably interposed therebetween. An annular stator 20 is fixedly mounted in the valve body 16 in confronting relation to the armature 18, the stator 20 having an exciting coil 19 for energizing the stator 20.

A valve rod 21 extends centrally downwardly from the armature 18 through the stator 20 toward a valve seat 22 defined in the valve body 16. A compression coil spring 23 is disposed between the valve body 16 and the valve rod 21 to urge the latter upwardly away from the valve seat 22. With the magnetic valve 15 thus constructed, when the exciting current is supplied to the coil 19, the stator 20 is energized whereupon the armature 18 and the valve rod 21 are pulled downwardly against the force of the spring 23, thereby bringing a distal end of the valve rod 21 into engagement with the valve seat 22. As a result, flow communication between an inlet 24 (Figure 2) and an outlet 25 is interrupted, the inlet 24 and the outlet 25 being defined in the head portion 1a of the valve body 16.

The outlet 25 of the magnetic valve 15 communicates with the pump working chamber 9 through a fuel intake passage 26 defined in the head portion 1a of the pump body 1. The plunger 8 includes a central longitudinal groove 28 opening at one end to the pump working chamber 9, the other end of the groove 28 communicating with a radial discharge groove 29. The discharge groove 29 is communicatable with a plurality of distributing grooves (not shown) defined in the head portion 1a of the pump body 1, the distributing grooves corresponding in number with the number of the engine cylinders and held in communication with the corresponding delivery portions 30 each having delivery valves (not shown).

A pair of connectors 31a, 31b is threaded to the head portion 1a and the rear portion 1b, respectively, of the valve body 1. The connector 31 a, as shown in Figure 2, communicates with the inlet 24 of the magnetic valve 15 through a connecting passage 32 defined in the head portion 1a of the pump body 1. A connecting pipe 33 extends between the connectors 31a, 31b to connect them together. The connector 31b communicates with a fuel outlet 43 of a feed pump 34.

The feed pump 34 is disposed in the pump body 1 adjacent to the cam chamber 5. As best shown in Figure 3, the feed pump 34 is of the sliding-vane rotary type known per se and comprises a circular rotor 35 fixedly coupled with the drive shaft 3 by a woodsruff key 37 fitted in a keyway 36a of the rotor 35 and in a keyseat 36b (Figure 1) of the drive shaft 3. The rotor 35 includes a plurality (four in the illustrated embodiment) of radial slots 38 outwardly opening and circumferentially spaced at equal intervals. Each of the radial slots 38 slidably receives one sliding vane 39. A guide ring 40 is eccentrically disposed around the rotor 35 and guides an outer end of each sliding vane 39 as the latter slides along the inner peripheral surface of the guide ring 40 upon rotation of the drive shaft 3.

The rotor 35, the sliding vanes 39 and the guide ring 40 jointly define therebetween pump working chambers 41. A fuel is trapped between the sliding vanes 39 as the rotor 35 passes a fuel inlet 42 (Figure 1) defined in the rear portion 1b of the pump body 1. Due to the eccentric arrangement of the guide ring 40 with respect to the rotor 35, further rotation of the rotor 35 reduces the volume of each chamber 41 in which the fuel is trapped. Fuel pressure rises until the fuel outlet 43 is reached, when the discharge occurs.

The guide ring 40 is held between the rear portion 1 b and a cover 44. The cover 44 includes a central hole 45 through which the drive shaft 3 extends. The cover 44 also includes an annular projection or ring 46 disposed concentrically with respect to the hole 45 and projecting away from the rotor 35. A washer 48 is disposed between the projection 46 and an annular flange 47 of the drive shaft 33, there being defined between the drive shaft 3, the cover 44 and the washer 48 a first sealing chamber 49a facing to the rotor 35. The rear portion 1b has an annular recess 51 facing at its one end to the rotor 35, the other end of the recess 51 communicating with the bore 2 so that a second sealing chamber 49b is defined between the drive shaft 3, the plain bearing 4a, the rotor 35 and the annular recess 51.A pair of oil seals 50a, 50b is disposed in the respective sealing chambers 49a, 49b to sealingly separate the pump working chambers 41 of the feed pump 34 from lubrication spaces in which a lubrication oil is supplied. The oil seals 50a, 50b are made of a suitable elastic material such as rubber. The first and second sealing chambers 49a, 49 communicate with each other through the keyway 36a of the rotor 35.

In the illustrated embodiment, the lubrication spaces comprise the bore 2 and the cam chamber 5 which are disposed on opposite sides of the feed pump 34. The rear portion 1b of the pump body 1 includes at its upper portion a lubrication oil inlet 52 for receiving therefrom a lubrication oil such as an engine oil. The inlet 52 communicates with the bore 2 between the bearings 4a, 4b through a first oil passageway 54 defined in the rear portion 1b so as to enable the lubrication oil to enter into a space 53 defined between the bore 2, the drive shaft 3 and the bearings 4a, 4b.The drive shaft 3 has a pair of second oil passageways 55a, 55b extending diametrically therethrough and opening at opposite ends to inner peripheral surfaces of the respective bearings 4a, 4b, and a third oil passageway 56 extending axially in the shaft 3 to communicate the second oil passages 55a, 55b with the cam chamber 5. With this construction, the lubrication oil is introduced into the cam chamber 5 through clearances between the drive shaft 3 and the bearings 4a, 4b and through passageways 55a, 55b, 56 defined in the drive shaft 3. The flow of the lubrication oil is choked or limited as the lubrication oil flows through the clearances between the drive shaft 3 and the bearings 4a, 4b. Such choking effect ensures an adequate supply of lubrication oil to the cam chamber 5.An oil overflow port 57 is defined in the cylindrical portion of the rear portion 1b and communicates with the cam chamber 5 at a level slightly below an upper end of the cam chamber 5 for allowing the lubrication oil to flow outwardly through the port 57 into a tank (not shown) when a predetermined oil leven is reached in the cam chamber 5.

According to important features of the present invention, the cover 44 has a pressure release passage 58 opening at its one end to the first sealing chamber 49a and at the other end to the pump working chamber 41 adjacent to the fuel inlet 42.

The fuel pressure in the pump working chamber 41 rises as the rotor 35 approaches the fuel outlet 43.

Such increased fuel pressure is transmitted to the first and second sealing chambers 49a, 49b through the clearances between the rotor 35 and the cover 44 and between the rotor 35 and the rear portion 1b of the pump body 1. In this instance, the fuel is allowed to escape from the sealing chamber 49a through the pressure release passage 58 to the low pressure side of the feed pump 34, thereby lowering the pressure in the sealing chambers 49a, 49b. If not so, the fuel would leak from the sealing chambers 49a, 49b respectively into the cam chamber 5 and the bore 2 through the oil seals 50a, 50b. As described above, the first and second sealing chambers 49a, 49b are held in fluid communication with each other through the keyway 36a so that both sealing chambers 49a, 49b are maintained at the same pressure.

As shown in Figures 3 and 4, each of the sliding vanes 39 has a pressure equalizing grove 59 extending longitudinally in a front face thereof to connect a back pressure chamber 60 defined between the vane 39 and the rotor 35 in each radial slot 38, with the pump working chamber 41 which is ahead of the vane 39. With the pressure equalizing groove 59, it is possible to prevent accidental flow communication between adjacent pump working chambers 41 which would otherwise occur when the vanes 39 are brought out of engagement with the inner peripheral surface of the guide ring 40. More specifically, the vanes 39 are normally urged against the ring's inner peripheral surface by fuel pressure created in the pump working cham bers 60.The back pressure chambers 60 are maintained at a high pressure since the compressed fuel flows from the pump working chambers 41 into the back pressure chambers 60 through the clearances between the rotor 35 and the rear portion 1b and between the rotor 35 and the cover 44.

As described above, the sealing chambers 49a, 49b of the present invention are maintained at a low pressure with the result that the back pressure chambers 60 are also maintained at such low pressure. If the pressure equalizing grooves 59 were omitted, the pressure in the pump working chambers 41 would exceeds the pressure in the back pressure chambers 60, thereby causing the vanes 39 to retract into the respective back pressure chambers 60. With the pressure equalizing chambers 60, the pressure in the back pressure chambers 60 increases with an increase in pressure in the pump working chambers 41 until both chambers 41, 60 have the same pressure value.

The fuel injection pump thus constructed operates as follows: When the drive shaft 3 is rotated, the feed pump 34 is operated. As the volume of the pump working chamber 41 increases, the fuel is drawn into the same chamber 41. Further rotation of the rotor 35 reduces the volume of the chamber 41. Fuel pressure rises until the fuel outlet 34 is reached, when discharge occurs. The discharged fuel flows successively through the connector 31b on the rear portion 1b, the connecting pipe 33, the connector 31 on the head portion 1a and the connecting passage 32 into the inlet 24 of the magnetic valve 15. At the same time, the rotational motion of the drive shaft 3 is transmitted through the coupling 12 and the cam disc 11 to the plunger 8, thereby simultaneously rotating and reciprocating the plunger 8.The fuel pressure in the pump working chamber 9 decreases as the plunger 8 is retracted during the suction stroke. On the contrary, in the compression stroke, the plunger 8 advances to increase the fuel pressure in the pump working chamber 9.

In the suction stroke of the plunger 8, the exciting coil 19 of the magnetic valve 15 is de-energized whereupon the magnetic valve 15 is opened so that the fuel, which has been delivered from the feed pump 34 to the inlet 24 of the magnetic valve 15, is allowed to flow successively through an orifice between the valve rod 21 and the valve seat 22, the outlet 25 of the magnetic valve 15 and the fuel intake passage 26 into the pump working chamber 9. Then the exciting current is supplied to the exciting coil 19 to close the magnetic valve 15, thereby terminating suction of the fuel into the pump working chamber 9. Thus, opening and closing operation of the magnetic valve 15 controls the amount of fuel to be sucked into the pump working chamber 9. Then the plunger 9 begines its compression stroke wherein the fuel in the pump working chamber 9 is pressurized as the plunger 8 advances. The pressurized fuel is delivered through the longitudinal groove 28 and the discharge groove 29 of the plunger 21, and through the nonillustrated delivery grooves to the delivery portions 30 from which the fuel is delivered for injection to the engine cylinders. The fuel injection is termi nated when the exciting coil 19 is de-energized to open the magnetic valve 15 The lublication oil is introduced from the inlet 15 into the rear portion 1b and then flows through the first oil passageway 54 into the oil chamber 53 defined between the bearings 4a, 4b. In the bore 2 the lubrication oil flows in opposite directions along the drive shaft 3 toward the bearings 4a, 4b.

Then the lubrication oil passes through learances between the drive shaft 3 and the bearings 4a, 4b during which time fluid-film lubrication is effected.

The lubrication oil flows through the second oil passageway 55a, 55b and then through the third oil passageway 56 into the cam chamber 5 where it lubricates movable parts such as the drive shaft 3, the coupling 12 and the cam disc 11. When the level of the lubrication oil reaches to the overflow port 57, the lubrication oil is allowed to flow outwardly through the port 57 and then to return to the oil tank.

As described above, according to the present invention, the pressure in the sealing chambers 49a, 49b is released through the pressure release passage 58 to the low pressure side of the feed pump 34, thereby lowering the pressure applied on the oil seals 50a, 50b. It is therefore possible to prevent fuel leakage from the sealing chambers 49a, 49b through the oil seals 50a, 50b into the cam chamber 5 and the bore 2. The lubrication oil maintain a suitable viscosity over an extended service time, thereby improveing the durability of the fuel injection pump.As the back pressure chambers 60 are held in communication with the pump working chambers 41 through the pressure equalizing grooves 59, the pressure acting in the back pressure chambers 60 is always maintained above the pressure acting directly on the vanes 39 in a direction to lower the latter, thereby holding the vanes 39 in engagement with the inner peripheal surface of the guide ring 40.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. For example, the lubrication oil may be supplied to one of the bore 2 and the cam chamber 5. Further, the sliding-vane rotary feed pump can be replaced with a gear pump or the like. The pressure release passage 58 may be provided in the rear portion 1b of the pump body 1. It is therefore to be understood that, within the scope of the appended claims, the invention may be practised otherwise than as specifically described.

Claims (5)

1. A distributor-type fuel injection pump comprising: (a) a pump body having defined therein an internal lubrication space to be lubricated with a lubrication oil; (b) a drive shaft rotatably mounted on said pump body; (c) a fuel feed pump disposed in said pump body adjacent to said lubrication space and drivingly connected to said drive shaft, said feed pump having a low pressure side; (d) at least one oil seal sealingly mounted around said drive shaft and disposed between said lubrication space and said feed pump for sealingly separating them from one another; (e) a sealing chamber facing to said feed pump and housing therein said oil seal; and (f) a pressure release passageway communicating said sealing chamber with said low pressure side of said feed pump.

2. A distributor-type fuel injection pump according to claim 1, said feed pump being a slidingvane rotary type and comprising a circular rotor fixedly coupled with said drive shaft and having a plurality of outwardly opening radial slots, sliding vanes slidably received in said radial slots, and a guide ring disposed eccentrically around said rotor for guiding an outer end of each said vane, said rotor, the sliding vanes and said guide ring jointly defining therebetween pump working chambers, said vanes and said rotor jointly defining therebetween back pressure chambers extending in said radial slots, each of said vanes having a pressure equalizing passage communicating one of said pack pressure chambers with one of said pump working chambers which is ahead of said vane.

3. A distributor-type fuel injection pump according to claim 2, including a cover disposed in said pump body at one side of said feed pump for immovably holding said guide ring in said pump body, said cover having a central hole through which said drive shaft loosely extends, and an annular projection extending coaxially with said drive shaft in a direction away from said feed pump, said sealing chamber being defined between said drive shaft and said cover, said oil seal being sealing disposed between said annular ring and said drive shaft, said pressure release passageway being defined in said cover.

4. A distributor-type fuel injection pump according to claim 3, including a further sealing chamber disposed on the other side of said feed pump, said rotor being keyed with said drive shaft and having a keyway, the first-mentioned sealing chamber communicating with the last-mentioned sealing chamber through said keyway.

5. A distributor-type fuel injection pump as described, with reference to, and as shown in, Figures 1 to 4 of the accompanying drawings.