GB2292184A

GB2292184A - I.c.engine fuel supply and recirculation system

Info

Publication number: GB2292184A
Application number: GB9516058A
Authority: GB
Inventors: Peter Geoffrey Chapman; Michael David Frampton; Gareth Paul Roberts; Raymond Paul Doherty; William Richard Hutchins; Robin Anthony Smith
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1994-08-06
Filing date: 1995-08-04
Publication date: 1996-02-14
Anticipated expiration: 2015-08-04
Also published as: GB2292184B; GB9415950D0; WO1996005423A2; AU3184695A; GB9516058D0; WO1996005423A3

Abstract

Fuel supplied from the tank 11 by the electric motor driven feed pump 14 or an engine driven feed pump to one end of a duct 20 supplying one or more fuel injectors 18, e.g. combined pumps and injectors, is recirculated through the line 34 from the other end of the duct by a pump 33. The pump 33 may be an injector pump, a separate motor driven pump (33A, Fig. 2) or a pumping element (133, 233, 333, Figs. 3 to 6) driven by the feed pump drive. An injector pump 21 operated by returned fuel passing through the line 19 draws fuel from the tank 11 into an auxiliary reservoir 13 with a perforated baffle 24 which prevents flow of air bubbles to the feed pump 14. The pressure in the line 19 is maintained by a regulator 28. A heat exchanger (335, Figs. 5 and 6) with a thermostatically controlled bypass (337), a pressure regulator (328) and a filter and air separator (332) may be provided in the recirculation line (334). <IMAGE>

Description

A FUEL F < ED SYSTEM FOR AN INTERNAL COMBUSTION ENGINE The invention relates to fuel feed systems for internal combustion engines. Typically such a system comprises a fuel tank, a motor driven feed pump operable to draw fuel from the tank and supply fuel to a fuel injection device on the engine through a feed pipe and a return pipe to return unused fuel to the tank. In certain engines, particularly diesel engines with unit injectors (a combined injector pump and injector), there can be a considerable transfer of heat from the engine into the fuel before the fuel is injected into the engine.Whilst it is important not to exceed temperature limits, it is equally important that the temperature of the fuel to each unit injector is fairly constant at any given time, otherwise different cylinders will receive different quantities of fuel and the engine performance and smoothness will deteriorate.

According to the invention there is provided a fuel feed system for an internal combustion engine having a fuel injection device supplied by a feed duct on the engine, the system comprising a fuel tank, a feed pump operable to draw fuel from the tank and supply fuel through a feed pipe to the fuel injection device through a fuel inlet at one end of the feed duct, a fuel outlet at the other end of the feed duct for the return of unused fuel, a recirculation duct connecting the fuel outlet and the feed pipe and a recirculation pump in the recirculation duct to cause fuel to recirculate through the recirculation duct from the fuel outlet to the fuel inlet.

Conveniently the recirculation pump is a venturi pump, the feed pump supplying fuel to the venturi which draws fuel from the recirculation duct. Alternatively, the recirculation pump can be driven by an electric motor, in which case, where the feed pump is also driven by an electric motor, the recirculation pump may comprise a pumping element on the feed pump. Preferably the feed pump delivers fuel to the feed pipe through the electric motor.

The electric motor, the feed pump and the recirculation pump are preferably situated in the fuel tank.

The recirculation pump may be mechanically driven by the engine. Where the feed pump is also mechanically driven by the engine, the recirculation pump may comprise a pumping element on the feed pump.

Preferably a pressure regulator is operable in use to control pressure in the recirculation duct downstream of the injector feed duct. A return pipe may be operable to return some of the fuel from the recirculation duct to the tank, in which case the pressure regulator may be in the return pipe. Alternatively the pressure regulator may be situated upstream of the return pipe.

A thermostat valve, heat exchanger and bypass duct may be operable in use to control the temperature of fuel in the recirculation duct downstream of the injector feed duct, conveniently with the thermostat valve, heat exchanger and bypass duct in the recirculation duct upstream of the recirculation pump and, preferably, downstream of the pressure regulator.

The tank may comprise a main reservoir, an auxiliary reservoir in which is situated a supply inlet for the feed pump and a top-up pump which in use is driven by the flow of fuel returned to the auxiliary reservoir to draw fuel from the main reservoir to the auxiliary reservoir and maintain the level of fuel in the auxiliary reservoir above that in the main reservoir, in which case the top-up pump conveniently comprises a venturi pump, fuel returning to the auxiliary reservoir drawing fuel through the venturi from the main reservoir. The top-up pump may be driven by fuel in the return pipe or by fuel diverted from the flow delivered to the feed pipe by the feed pump A separator baffle may divide the auxiliary reservoir into a supply zone where the supply inlet is situated and mixing zone into which the top-up pump can discharge fuel.

This is particularly suitable for Diesel fuel which is much more viscous than petrol or gasoline.

Conveniently a filter/separator is in the feed pipe and may incorporate a vent pipe connected to the fuel tank.

Preferably a vent valve allows gases or vapours to return to the tank through the vent pipe but prevents the flow of fuel returning to the tank through the vent pipe.

Other aspects of the invention will be apparent from the following description and with reference to the accompanying drawings of which: Fig. 1 is a diagrammatic elevation of a fuel feed system for an internal combustion engine according to the invention; Fig. 2 is a view based on Fig. 1 and showing a modification to the system shown in Fig. 1; Fig. 3 is a diagrammatic elevation similar to Fig. 1 showing a first modified fuel feed system according to the invention; Fig. 4 is a diagrammatic elevation similar to Fig. 1 showing a second modified fuel feed system according to the invention; Fig. 5 is a diagrammatic elevation showing a third modified fuel feed system according to the invention; and Fig. 6 is a view based on Fig. 5 and showing two modifications to the system shown in Fig. 5; In Fig. 1 a fuel tank 11 comprises a main reservoir 12 and an auxiliary reservoir 13.An electric motor driven feed pump 14 in the auxiliary reservoir 13 is operable to draw fuel from the tank 11 through a supply inlet 15 in the auxiliary reservoir. A strainer 16 is provided to prevent dwrt and debris entering the feed pump 14.

The feed pump 14 can supply fuel to a fuel injection device on an engine 17. As shown in Fig. 1 the fuel injection device comprises five unit injectors 18 which are supplied by an injector feed duct or fuel rail 20 on the engine 17. The unit injectors 18 each combine a jerk type pump and injector as a single unit. Whilst the use of unit injectors on diesel engines is well known, in this case the fuel rail 20 is a longitudinal drilling in the cylinder head of the engine 17 and has an inlet 20A at one end and an outlet 20B at the other end.

Return flow from the injectors 18 is delivered back to the fuel tank through a return pipe 19. The return pipe 19 is connected to a top-up pump 21 situated in the auxiliary reservoir 13. The top-up pump 21 is a venturi pump in which flow from the return pipe 19 enters a venturi which creates a depression which draws fuel from the main reservoir 12 through a strainer 22 and delivers it to the auxiliary tank through an outlet 23. In this way the topup pump 21 is driven by the flow of fuel in the return pipe 19 and the level of fuel in the auxiliary reservoir 13 can rise above that in the main reservoir 12. This helps to ensure that the supply inlet 15 can receive fuel even when the level of fuel in the main reservoir 12 is very low or is fluctuating due to vehicle cornering or braking etc.

A separator baffle 24 divides the auxiliary reservoir 13 into a supply zone 25 where the supply inlet 15 is situated and a mixing zone 26 into which the top-up pump can discharge fuel. The baffle 24 comprises a perforated plate which helps to allow any entrained air to escape in the mixing zone 26 and helps to mix the hot fuel returned by the engine with the cooler fuel from the main tank 12. A non-return valve 27 prevents fuel returning from the auxiliary tank 13 to the main tank 12.

A pressure regulator 28 is in the return pipe 19 to maintain pressure of the returned fuel at the engine above the pressure of fuel returned to the top-up pump 21 thereby reducing pressure at the venturi of the top-up pump.

Fuel supplied by the feed pump 14 is delivered to the injectors 18 through a feed pipe 31, a filter/separator 32 and a recirculation pump 33 by way of a feed/recirculation pipe 30 connecting the recirculation pump to the fuel rail inlet 20A. A recirculation duct 34 connects the return pipe 19 and the feed pipe 31, the recirculation pump 33 causing fuel to recirculate from the outlet 20B of the fuel rail 20 to the inlet 20A. In Fig. 1 the recirculation pump 33 is a venturi pump, the feed pump delivering fuel to the venturi where the reduced pressure draws fuel from the recirculation duct 34.

A fine filter 35 is provided upstream of the fuel rail 20 to catch any debris that may be circulated through the recirculation duct 34. Alternatively a fine filter 35A is positioned in the recirculation duct 34 itself.

The recirculation pump 33 and duct 34 allow the fuel flow in the injector rail 20 to be much higher than would otherwise be achieved. The higher flow ensures that the fuel at the outlet 20B of the fuel rail 20 is only a few degrees higher in temperature than that at the inlet 20A.

However, the filter/separator 32 can be of a size which is sufficient only for the flow in the feed pipe 31 and is thus comparable to that used in a conventional fuel feed system.

Fuel circulates in the recirculation duct 34 even when the engine 17 is not under load, since flow in the return pipe 19 is made up by flow in the feed pipe 31 and the venturi of the recirculation pump 33. The venturi of the feed pump 21 may be of a size which allows it to act as a restrictor orifice to control the flow rate in the return pipe 19. Alternatively or additionally a separate restrictor may be used.

In the modification shown in Fig. 2 the recirculation pump 33A is an electric motor driven pump which directly replaces the venturi type recirculation pump 33.

Alternatively the pump 33A may be mechanically driven by the engine.

In the first modified system shown in Fig. 3 items which are the same as or similar to those in Fig. 1 have the same reference with the addition of 100. The recirculation pump takes the form of an additional pump element 133 on the feed pump 114, driven by the same electric motor 136 which is submerged in the fuel for cooling and lubrication. The pressure regulator 128 is in a T connection 137 in the recirculation duct 134 upstream of the recirculation pump 133 and is arranged with a deflector 138 to deflect any air bubbles into the pressure regulator and hence into the return pipe 119.

Operation of the first modified system is essentially the same as that described for the system shown in Fig. 1, the recirculation pump element 133 circulating fuel in the recirculation duct 134 while the engine is running.

In the second modified system shown in Fig. 4 items which are the same as or similar to those in Fig. 1 have the same reference with the addition of 200. The system is generally as described above in relation to Fig. 3 except that fuel delivered from the feed pump 214 through the feed pipe 231 and the filter/separator 232 is ducted to the inlet of the recirculation pump 233 which also takes the form of an additional pump element 233 on the feed pump 214, driven by the same electric motor 236 but which may also be a separate electric motor driven pump or one driven directly by the engine. Alternatively, a pump with two pump elements for the feed pump and the recirculation pump may be driven mechanically by the engine.

Operation of the second modified system is essentially the same as that described for the system shown in Fig. 1, the recirculation pump element 233 circulating fuel in the recirculation duct 234 while the engine is running.

In the third modified system shown in Fig. 4 items which are the same as or similar to those in Fig. 1 have the same reference with the addition of 300. The system is generally as described above in relation to Fig. 4 except for the differences which will be described and others apparent from the drawing.

The top-up pump venturi 321 uses flow diverted from the feed pump flow in the feed pipe 331 instead of flow in the return pipe connected to the recirculation duct as shown in Figs. 1 to 4. This avoids the direct return of hot fuel from the recirculation duct to the fuel tank.

A heat exchanger 335 is in the recirculation duct 334 upstream of the filter/separator 332 and flow through this is controlled by a thermostat valve 336 which diverts flow through a bypass duct 337 connected in parallel with the heat exchanger when the temperature of fuel entering the thermostat valve is below a given temperature. The pressure regulator 328 is placed upstream of the thermostat valve 336 which helps to reduce the pressure on the heat exchanger 335 and the filter/separator 332. Back pressure of fuel flowing through the thermostat valve 336 and the heat exchanger 335 also helps the operation of the pressure regulator 328.

Although the supply orifice is 319 is depicted diagrammatically in Fig. 4 as being in the wall of the auxiliary reservoir 313, a strainer and non-return valve similar to the strainer 22, 122, 222 and non-return valve 27, 127, 227 would be used in practice. In place of the single longitudinal drilling in the cylinder head depicted in Figs. 1 to 4, the injector fuel rail comprises a feed rail 320C and a return rail 320D, both formed as drillings in the cylinder head.

The filter/separator 332 is in the feed pipe 331 as in Figs. 1 to 4, but has a vent pipe 341 to vent air entrapped by the filter/separator to return to the tank. The connection of the vent pipe 341 to the filter/separator 332 preferably incorporates a flow sensitive vent valve such as a jiggle pin of the type common in engine cooling systems.

This is a normally open valve which has a low resistance to air flow but a higher resistance to the flow of liquid fuel. Hence any air or other gases or vapours are allowed to return to the tank 311 but the vent valve closes as soon as liquid fuel starts to flow.

In Fig. 5 the recirculation pump is upstream of the filter/separator 331 so that the feed/recirculation pipe has two portions 330A and 330B.

Operation of the third modified system is essentially the same as that described for the system shown in Fig. 1, the recirculation pump element 333 circulating fuel in the recirculation duct 334 while the engine is running.

In the fuel feed systems described above with reference to Figs. 1 and 2 the feed pump is a conventional type in which fuel is taken from the tank through an inlet in the lower wall of the pump and is pumped through the motor itself over the motor armature, brushes and commutator.

This helps to cool and lubricate the brushes and allows the motor to be rated for continuous operation over a long period. In the systems described above with reference to Figs. 3 to 5 the feed pump is of the same conventional type but is a two rotor design normally used as a straightforward two stage pump to give higher pressure.

The feed pump 114, 214 or 314 is normally the low pressure pump and is typically an impeller pump and the recirculation pump 133, 233 or 333 is normally the high pressure pump and is typically a two rotor internal gear type, sometimes known as a gerotor. The arrangement shown in Figs. 3 to 5 has the drawback that the fuel circulated over the motor 136, 236 or 336 is hot fuel in the recirculation duct 134, 234 or 334 and the increased temperature has an adverse effect on the service life of the motor.

One of the modifications to the fuel feed system of Fig.

5 shown in Fig 6 is that the outlet from the feed pump 314 is taken by a duct 331A through the motor 336 so that the motor benefits from the relatively cool fuel taken from the auxiliary reservoir 313. The duct 331A may be an external pipe as shown but may also be a passage in the stator of the recirculation pump 333 or an annular passage formed between the stator of the recirculation pump 333 and an outer casing.

The other modification is that the filter/separator 332A is at the junction of the recirculation duct 334 and the feed pipe 331. This puts to the filter/separator 332A the full flow of fuel pumped to the engine 317 through the feed/recirculation pipe 330A and 330B but can allow for better filtration and air venting.

Although described with reference to a diesel engine with unit injectors, the invention may also be applied to diesel engines with separate injector pumps or to petrol/gasoline engines with multi or single point injection.

Claims

1. A fuel feed system for an internal combustion engine having a fuel injection device supplied by a feed duct on the engine, the system comprising a fuel tank, a feed pump operable to draw fuel from the tank and supply fuel through a feed pipe to the fuel injection device through a fuel inlet at one end of the feed duct, a fuel outlet at the other end of the feed duct for the return of unused fuel, a recirculation duct connecting the fuel outlet and the feed pipe and a recirculation pump in the recirculation duct to cause fuel to recirculate through the recirculation duct from the fuel outlet to the fuel inlet.

2. A fuel feed system according to claim 1 wherein the recirculation pump is a venturi pump, the feed pump supplying fuel to the venturi which draws fuel from the recirculation duct.

3. A fuel feed system according to claim 1 wherein the recirculation pump is driven by an electric motor.

4. A fuel feed system according to claim 3 wherein the feed pump comprises a pump driven by an electric motor and the recirculation pump comprises a pumping element on the feed pump.

5. A fuel feed system according to claim 4 wherein the feed pump delivers fuel to the feed pipe through the electric motor.

6. A fuel feed system according to claim 4 or claim 5 wherein the electric motor, the feed pump and the recirculation pump are in the fuel tank.

7. A fuel feed system according to claim 1 or claim 2 wherein the recirculation pump is mechanically driven by the engine.

8. A fuel feed system according to claim 7 wherein the feed pump is mechanically driven by the engine and the recirculation pump comprises a pumping element on the feed pump.

9. A fuel feed system according to any preceding claim wherein a pressure regulator is operable in use to control pressure in the recirculation duct downstream of the injector feed duct.

10. A fuel feed system according to any preceding claim wherein a return pipe is operable in use to return some of the fuel from the recirculation duct to the tank.

11. A fuel feed system according to claim 10 when dependent from claim 9 wherein the pressure regulator is in the return pipe.

12. A fuel feed system according to claim 10 when dependent from claim 9 wherein the pressure regulator is upstream of the return pipe.

13. A fuel feed system according to any preceding claim wherein a thermostat valve, heat exchanger and bypass duct are operable in use to control the temperature of fuel in the recirculation duct downstream of the injector feed duct.

14. A fuel feed system according to claim 13 wherein the thermostat valve, heat exchanger and bypass duct are in the recirculation duct upstream of the recirculation pump.

15. A fuel feed system according to claim 13 when dependent on claim 9 wherein the thermostat valve, heat exchanger and bypass duct are in the recirculation duct downstream of the pressure regulator.

16. A fuel feed system according to any preceding claim wherein the tank comprises a main reservoir, an auxiliary reservoir in which is situated a supply inlet for the feed pump and a top-up pump which in use is driven by the flow of fuel returned to the auxiliary reservoir to draw fuel from the main reservoir to the auxiliary reservoir and maintain the level of fuel in the auxiliary reservoir above that in the main reservoir.

17. A fuel feed system according to claim 16 wherein the top-up pump comprises a venturi pump, fuel returning to the auxiliary reservoir drawing fuel through the venturi from the main reservoir.

18. A fuel feed system according to claim 16 or claim 17 when dependent from claim 10 wherein the top-up pump is driven by fuel in the return pipe.

19. A fuel feed system according to claim 16 or claim 17 wherein the top-up pump is driven by fuel diverted from the flow delivered to the feed pipe by the feed pump.

20. A fuel feed system according to any of claims 16 to 19 wherein a separator baffle divides the auxiliary reservoir into a supply zone where the supply orifice is situated and mixing zone into which the top-up pump can discharge fuel.

21. A fuel feed system according to any preceding claim wherein a filter/separator is in the feed pipe.

22. A fuel feed system according to claim 21 wherein the filter/separator incorporates a vent pipe connected to the fuel tank.

23. A fuel feed system according to claim 22 and comprising a vent valve to allow gases or vapours to return to the tank through the vent pipe but prevent the flow of fuel returning to the tank through the vent pipe.

24. A fuel feed system substantially as described herein with reference to Fig. 1, Fig. 1 modified with reference to Fig. 2, Fig. 3, Fig. 4, Fig. 5 or Fig. 5 modified with reference to Fig. 6 of the accompanying drawings.