NL2001772C2

NL2001772C2 - Dual fuel e.g. gasoline, injection system for internal combustion engine of motor vehicle, has high pressure pump for pressurizing fuels, and injector injecting pressurized fuels into combustion chamber of engine

Info

Publication number: NL2001772C2
Application number: NL2001772A
Authority: NL
Inventors: Thomas Van Veen
Original assignee: Teleflex Gfi Europ B V
Priority date: 2008-07-07
Filing date: 2008-07-07
Publication date: 2010-01-11

Abstract

The system has a gasoline pump (1) for pumping liquid fuel e.g. gasoline, and a fuel pump (4) for pumping liquefied petroleum gas (LPG), respectively. A supply duct (26) supplies the liquid fuel from a gasoline tank (40) to the fuel pump, where the supply duct comprises a supply duct junction (33) connected to an outlet of the pump (1), to provide the LPG supplied by the fuel pump into the duct. A high pressure pump (12) downstream the gasoline pump pressurizes the fuel, and an injector (16) injects the pressurized fuels into a combustion chamber of an internal combustion engine.

Description

P29460NL00/HSE

Title: Dual fuel injection system and motor vehicle comprising such injection system

The invention relates to a dual fuel injection system for an internal combustion engine, preferably a direct injection internal combustion engine, and to a motor vehicle comprising such injection system.

Traditionally, use has been made of separate injectors for different fuels in a same 5 internal combustion engine. As an example, motor vehicles equipped with a liquid petrol gas (LPG) injection system were supplied with separate injection valves for the LPG fuel, in addition to gasoline injection valves.

Recent developments in fuel injection include the application of direct gasoline injection systems. Here, gasoline is injected directly into a combustion chamber of the internal 10 combustion engine. Improvements in fuel economy may be achieved thereby. Injection of LPG and gasoline via the same injection valves has been disclosed in DE101 46 051. Here, a high pressure pump provides a low pressure fuel or a medium pressure fuel to an injection rail. Injection valves inject the pressurized fuel. In order to supply the low pressure (gasoline) or medium pressure (LPG) fuel from respective reservoirs to the high pressure pump, two 15 serially connected pumps are provided in the gasoline supply line from the gasoline reservoir, while a single pump is provided in the LPG supply line from the gasoline reservoir.

A disadvantage of this configuration may be found in its complexity. As an example, next to the high pressure pump, a total of 3 additional fuel pumps is required The invention aims at improving such an injection system.

20 According to an aspect of the invention, the injection system comprises - a first fuel pump for pumping a first fuel, - a second fuel pump for pumping at least a second fuel, - a supply duct for supplying the second fuel to the second fuel pump, the supply duct comprising a junction connected to an outlet of the first fuel pump, to join the first fuel 25 supplied by the first fuel pump into the supply duct, - a high pressure pump, downstream of the second fuel pump, for pressurizing the first and/or second fuel, and - an injector for injecting the pressurized first and/or second fuel into a combustion chamber of the internal combustion engine.

30 Operating the first respectively the second fuel pump (possibly in combination with a closing of suitably positioned valves) will supply the first respectively the second fuel to the high pressure pump. Operating the first fuel pump will supply the first fuel to the junction, into the supply duct, and via the second fuel pump to the high pressure pump. Operating the second pump, will supply the second fuel from the supply duct to the high pressure pump.

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The second fuel pump may however not only be applied to pressurize the second fuel, but also to increase a pressure of the first fuel by the series connection of the first and second fuel pumps that has been created. In case the first fuel is a liquid fuel (at ambient temperature and atmospheric pressure), such as gasoline, while the second fuel is a fuel which needs to 5 be held at a pressure in order to maintain it in liquid state at ambient temperature, such as LPG, the first and second fuel pumps can be operated simultaneously in order to force a remainder of second fuel out of the high pressure pump by the first fuel, when a supply of the second fuel has been switched off. Thereby, second fuel vapor in the high pressure pump, injection valves etc, may be prevented without requiring an additional pump in order to further 10 pressurize the first fuel.

The injection system may further comprise a first fuel reservoir (e/g/ fuel tank) for holding the first fuel, and a second fuel reservoir (e.g. fuel tank) for holding the second fuel. The first fuel reservoir may be connected to an inlet of the first fuel pump. The second fuel reservoir may be connected to the supply duct. Furthermore, the injection system may 15 comprise a control device, such as a microcontroller, microprocessor, analogue or digital switching circuit etc. to control the first and/or second fuel pumps. The first and/or second fuel may comprise any fuel such as but not limited to gasoline, diesel, ethanol, compressed natural gas (CNG), LPG, biogas, etc. Also, mixtures of such fuels may be provided. In an embodiment, the first fuel may comprise a fuel which is in liquid state at room temperature 20 and atmospheric pressure, such as gasoline, while the second fuel may comprise a fuel which is to be held in liquid form at room temperature by a pressurizing thereof, such as LPG. The first and second pumps may be mechanically or electrically driven and may be located in or adjoining the respective fuel reservoir, or separately there from. The high pressure pump may be arranged to supply to fuel at any suitable injection pressure, for example in a 25 pressure range of tens to hundreds of bar (e.g. 30 to 150 or 30 to 200 bar), although higher pressures in an order of magnitude of thousands of bar are possible too.

In order to operate the first and second fuel pumps, the control device being arranged to: operate the first pump to supply the first fuel, and operate the second pump to supply the second fuel. Upon the above described transition from the first fuel to the second fuel, the 30 control device may further be arranged to operate the first and second fuel pumps simultaneously at a transition from the second fuel to the first fuel, to pressurize first fuel so as to propel a remainder of second fuel in or towards the high pressure pump.

A one-way valve may be provided between the outlet of the first fuel pump and the junction, which may prevent the second fuel from flowing into the first fuel pump when not in 35 operation A bypass may be provided in parallel to the second fuel pump to bypass the second fuel pump, in order to allow the second fuel pump to be switched off. In such bypass, a oneway valve is placed to prevent fuel to flow from an outlet of the pump back to an inlet thereof.

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This bypass may allow operation of the injection system with the first fuel, when a remainder of the second fuel has been forced out of the high pressure pump and out of a supply duct towards the high pressure pump, while only operating the first fuel pump, thereby saving power consumption and reducing a flow resistance.

5 The control device may further be arranged to operate the first fuel pump upon a deactivation command, to flush at least the high pressure pump (and possibly a supply duct towards it and/or a high pressure injection rail) with the first fuel. Thereby, it may be prevented that second fuel is retained in those parts, which may cause starting problems as a reduced pressure upon switching of the injection system may evoke vapor of the second fuel 10 in the mentioned parts. The first fuel pump may be operated for a predetermined time, e.g. until the mentioned parts are flushed with the first fuel.

Commonly, the high pressure pump is driven mechanically be the internal combustion engine. As a consequence, the high pressure pump stops when the engine is switched off. As a consequence, a remainder of the second fuel may, despite flushing by the first fuel, be left 15 in the pump. Therefore, one-way valves, e.g. in combination with a shut off valve, may be provided at an inlet and an outlet of the high pressure pump, so as to retain fuel (which may comprise a remainder of the second fuel) in the high pressure pump in a non operating state, at a sufficiently high pressure so as to prevent vaporization thereof.

Different types of fuel may have different requirements as to a desired ratio of fuel and 20 air, and may have different caloric value per volume unit. Therefore, different settings of a motor management system of the internal combustion engine may be desired for the different types of fuel, e.g. a different fuel - air ratio. It is not uncommon that dual fuel injection systems are based on mono fuel (mostly gasoline) solutions, such as found in gasoline cars. Thereto, it is desirable to change as little as possible of the original mono fuel system.

25 Thereto, a sensitivity of a pressure sensor for sensing a fuel pressure behind the high pressure pump may be adapted substantially proportionally to a combustion value of the first and second fuels. Thereby, a simple solution may be provided to allow an existing (mono fuel based) motor management system to operate in a bi fuel solution, as a sensitivity of the sensor may be altered depending on the type of fuel. A simple way to adapt the sensitivity 30 may be to alter (e.g. amplify, attenuate) an analogue electrical output signal of the sensor: As an example, depending on a measured pressure and engine load, an (e.g. attenuated) pressure signal may be provided to the existing gasoline motor management system. The engine load can be measured by any suitable signal such as engine speed, throttle valve position, etc. As a result, the existing motor management system may regulate the output 35 pressure of the high pressure pump in line with the change in the sensor output signal, so as to increase of decrease the pressure, when making use of the other fuel, e.g. LPG or CNG, which may provide that the injection valves of the engine- given the changed pressure- inject a more suitable amount of the fuel, so as to take account of the desired fuel air ratio of that 4 type of fuel. A fine tuning may then be provided by a lambda sensor based control of the internal combustion engine, possibly in combination with a control of a time during which the injection valves are opened.

According to a further aspect of the invention, there is provided a dual fuel injection 5 system, comprising: - a first fuel pump for supplying a first fuel, - a second fuel pump for supplying a second fuel, - a high pressure pump, downstream of the first and second fuel pumps, for pressurizing the first and/or second fuel, and 10 - an injector for injecting the pressurized first and/or second fuel into a combustion chamber of the internal combustion engine, a return duct being provided from the high pressure pump to a reservoir of the second fuel, the return duct for returning an excess of the second fuel back into the reservoir.

The dual fuel injection system according to this aspect of the invention may but not 15 necessarily needs to be combined with all or some of the above described developments. Rather, this aspect of the invention could also be applied to other dual fuel injection systems, such as described in DE101 46 051. By providing a return duct from the high pressure pump instead of in a supply duct towards the high pressure pump, an increased flow of fuel through the high pressure pump may be obtained, as excess fuel supplied by the first and/or second 20 pump but which thus exceeds an amount of fuel injected by the injection valve(s), flows via the high pressure pump to the return duct. Because of this flow, a fuel temperature in the high pressure pump may be reduced, hence reducing a risk of occurrence of fuel vapor. Thereby, a simplification of the system described in DE101 46 051 may be obtained, as cooling of LPG or CNG by a heat exchanger may be omitted. The return duct may provided from e.g. a 25 bypass of the high pressure pump, the bypass being located upstream of a high pressure part of the high pressure pump, allowing a relatively low cost return duct as high pressures therein are obviated and as it prevents interfering in the high pressure part of the system. Alternatively, the return duct may be provided from the high pressure part of the high pressure pump, which may increase a cooling effect.

30 The return duct may be provided with a back pressure valve, so as to regulate a fuel pressure in the return duct.

Further features and advantages of the invention will become clear from the appended drawings, wherein non limiting embodiments are shown, wherein:

Fig. 1 depicts a schematic diagram of an injection system according to an embodiment 35 of the invention;

Fig. 2 depicts a schematic diagram of an injection system according to another embodiment the invention; 5

Fig. 3 depicts a schematic diagram of an injection system according to yet another embodiment of the invention;

Fig. 4 depicts a schematic diagram of an injection system according to a further embodiment of an aspect of the invention; 5 Fig. 5 depicts a schematic diagram of an injection system according to a yet further embodiment of an aspect of the invention.

In the figures, similar or identical items are referred to by similar or identical reference numerals.

Fig. 1 depicts an injection system for direct injection of gasoline and LPG in an internal 10 combustion engine of a motor vehicle. A gasoline (i.e. petrol) tank 40 is provided in which a gasoline pump 1 is housed, the pump having a back pressure valve that will open when the output pressure of pump 1 gets too high, causing fuel to flow back into the tank until the pressure is decreased. Such back pressure valve may be provided in e.g. a so called “returnless” fuel system. Hence, pressure is regulated by valve 14 in combination with valve 15 20.

LPG is held in an LPG tank 41 which is provided with closing valve 8. A supply duct 26 is provided form the LPG tank to the second fuel pump 4. Closing valve 9 is provided in the supply duct. Junction 33 of the supply duct 26 joins a duct from an output of the first fuel pump 1 into the supply duct 26. The supply duct 26 may have any suitable form and 20 dimension, and the first and second fuel pumps may be separate pumps or integrated in respective fuel tanks: The first fuel pump may for example be integrated in the first fuel pump. The second fuel pump may be integrated in for example the second fuel tank. Gasoline and LPG ducts join at junction 33 before being provided to the second fuel pump 4. A bypass duct with one-way valve 22 may be provided to bypass the further pump 4 when not in operation. 25 The second fuel pump 4 transports the LPG or gasoline to a high pressure pump 12 which compresses the fuel so as to reach an injection pressure, the compressed fuel is then guided via duct 29 to an injection rail which is provided with injectors 16. Excess fuel is guided back to the high pressure pump 12 via pressure valve 18 and duct 32. An LPG return duct towards the LPG tank is provided by duct 27 comprising closing valve 19 and pressure regulator 3.

30 The return duct ends in the LPG tank at one way valve 21.

Operating on gasoline, the first fuel pump 1 is operated and fuel flows via the junction 33, via bypass valve 22 to the high pressure pump 12.

Operating on LPG, valves 8, 9 and 19 are opened and the second fuel pump 4 is operated. Pressure regulator 3 in the return duct provides for a resistance, thereby providing 35 a constant pressure to the high pressure pump 12. Excess LPG flows back to the LPG tank, thereby providing a relatively high flow of LPG through the high pressure pump 12, which helps to reduce a fuel temperature of the LPG in the high pressure pump.

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When changing from LPG to gasoline, valves 8 and 9 are closed. The second fuel pump 4 is still operated, causing pressure at junction 33 to lower. The first fuel pump 1 is now operated, while closing valve 20 is closed to maximize output pressure of the first pump 1. As the remaining pressure at 33 is lower than the pressure provided by pump 1, one way valve 6 5 opens, and fuel is provided from the first pump 1 to the second pump 4. The second pump 4, which is still in operation, now pressurizes the gasoline so as to force a remainder of the LPG via the high pressure pump 12 and return duct 27 back into the LPG tank. Then, valve 19 is closed and pump 4 deactivated, while valve 20 is opened. The second fuel pump is now bypassed via valve 22.

10 Operating on LPG requires approximately 30% more fuel to be injected compared with gasoline to take account of differences in combustion ratio requirements. This is achieved in that an output signal of the pressure sensor 15 at the fuel rail is attenuated before being provided to a motor management system or other readout device, which causes an increase in the pressure buildup in the injection rail, as the motor management system or other readout 15 device will counteract by increasing the pressure. If is undesirable to further increase pressure, e.g. because of safety limits, injection times may be prolonged by the motor management system to take account of the lower pressure signal value as perceived by the motor management system. Thereby, more LPG is injected to take the combustion ratio requirements into account. When switching from one fuel to another, the sensitivity of the 20 sensor is adapted with a delay, such delay being based on the time required to inject a remainder of the fuel in the rail upon changeover to the other fuel.

Upon switching off the engine while operating on LPG, a remainder of LPG is forced out of the system by operating the first pump 1 to supply gasoline. By the flow of gasoline, the remaining LPG is propelled towards the high pressure pump and allowed to flow via the high 25 pressure pump 12 and the return duct 27 into the LPG tank, valve 19 being kept open for this purpose. A remainder of LPG in the (non operating) high pressure pump 12 can be retained in the high pressure pump by valves 13 and 13A. Thus, after switching off the engine while driving on LPG, the system will switch to gasoline to remove to LPG out of the fuel lines and high pressure fuel pump. After removing the LPG, valve 19 is closed and together with one 30 way valves 13 and 13A making sure remaining LPG in the high pressure pump cant vaporize because there is no place in the pump for the LPG to expand. In stead of one way valves 6 and shut off valve 9, two shut off valves or a 3-way ball valve may be applied,

Fig. 2 depicts a configuration which is largely identical to that of fig. 1, however the closing valve 20 and pressure regulator valve 14 in the gasoline tank have been replaced by 35 a return duct towards the gasoline tank. Thereto, instead of return duct 27 of fig. 1, a combined return duct 31 is provided which ends in the LPG tank via valve 21 as well as in the fuel tank via a closing valve 28. Operating on gasoline, closing valve 28 is opened, the resulting low fuel pressure in the return duct 31 causing valve 21 to close because of the 7 pressure in the LPG tank. Operating on LPG, closing valve 28 is closed providing a set-up similar to that of fig. 1.

In the configuration according to fig. 2, when changing from LPG to gasoline, when duct 31 has been filled with gasoline, valve 28 is opened and the second fuel pump is 5 switched off.

Fig. 3 depicts a configuration which is largely identical to that of fig. 2, however separate LPG and gasoline return ducts 27 and 24 are provided. This configuration may be used in a vehicle already provided with a gasoline return duct in mono fuel configuration. Operating on LPG, valves 8, 9, and 19 are open, pump 4 operating, and valve 28 is closed.

10 Changing to gasoline, pump 1 is started, and valves 8 and 9 closed. Valve 6 opens as the pressure at 33 lowers while gasoline is provided via duct 25. Having filled the high pressure pump with gasoline, valve 19 is closed and valve 28 opened. The second fuel pump 4 can now be switched off.

Fig. 4 and 5 depict a configuration wherein use is made of an additional fuel pump, 15 resulting in gasoline pumps 1 and 2 and LPG pump 7. Although there configurations do not show all aspects of the invention, they illustrate that the feature of the return duct at the high pressure pump may be applied in other configurations too, thereby achieving same or similar advantages.

In some more detail, in fig. 4, operating on LPG, pump 7 is operated and valves 8, 9, 20 and 19 are open causing LPG to flow to the high pressure pump 12 and via the return duct 27 back to the LPG tank. The flow of LPG through the high pressure pump lowers LPG temperature in this pump, hence decreasing a risk of generation of LPG vapor at the already elevated temperatures in the high pressure pump which is usually mounted near to or forming part of the engine. Switching to gasoline, pump 7 is stopped and valves 8 and 9 closed. Then, 25 pump 2 is operated in addition to pump 1, which may already have been switched on, causing gasoline pressure to open valve 6 and to force a remainder of the LPG via the high pressure pump 12 and the return duct 27 to the LPG tank. Valve 19 can then be closed and operation of pump 2 be stopped. It is remarked that back pressure valve 34 serves to regulate a pressure of pump 2: at a too high pressure, valve 34 will open and allow a flow of the gasoline 30 back to the entry of the pump. When not in operation, pump 2 can be bypassed, e.g. by valve 5.

In fig. 5, provides a variant to the configuration according to fig. 4. A return duct is provided to the LPG tank via valve assembly 23 and duct 27, as well as to the entry of pump 2, namely via valve assembly 23 and duct 24. When changing from LPG to fuel, LPG pump 7 35 is stopped, valves 8 and 9 closed, and pump 2 switched on. LPG flows back to the LPG tank via valve assembly 23 and return duct 27. Then, valve assembly 23 is set to provide a return path for the gasoline via duct 24, thereby preventing pump 2 to overheat caused by too much resistance.

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It is remarked that in the various configurations, temperature sensor 10 and pressure sensor 11 provide data to a control device (not shown) to monitor conditions that are required to maintain the LPG in a liquid state. Should the pressure be below a predetermined pressure threshold, and/or temperature be above a predetermined temperature threshold, thereby 5 risking generation of LPG vapour, the injection system changes to gasoline.

It is further remarked that the pumps and valves in the various embodiments may be controlled by a suitable control device, comprising e.g. a microcontroller unit or programmable logic device (PLD) programmed with suitable software instructions, electronic control circuitry, etc.

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Claims

A dual fuel injection system for an internal combustion engine, comprising: - a first fuel pump for pumping a first fuel, - a second fuel pump for pumping at least a second fuel, a supply channel for supplying the second fuel to the second Fuel pump, wherein the supply channel comprises a connection connected to an outlet of the first fuel pump, to bring together the first fuel supplied by the first fuel pump in the supply channel, - a high-pressure pump, downstream of the second fuel pump, for pressurizing placing the first and / or second fuel, and 10. an injector for injecting the pressurized first and / or second fuel into a combustion chamber of the internal combustion engine.

A dual fuel injection system according to claim 1, wherein a one-way valve is provided between the outlet of the first fuel pump and the connection.

A dual fuel injection system according to claim 1 or 2, wherein a bypass channel 15 comprising a one-way valve is provided in parallel with the second fuel pump to bypass the second fuel pump.

4. A dual fuel injection system according to any of the preceding claims, further comprising a control device for controlling the first and second fuel pumps, the control device being arranged to: drive the first pump to supply the first fuel; driving the second pump to feed the second fuel, and simultaneously driving the first and second pumps at a transition from the second fuel to the first fuel, to pressurize the first fuel to feed a remainder of the second fuel or to propel the high pressure pump.

A dual fuel injection system according to claim 4, wherein the control device is further arranged to drive the first fuel pump in a deactivation command, to flush at least the high pressure pump with the first fuel.

6. Double-fuel injection system according to one of the preceding claims, wherein one-way valves are provided on an inlet and an outlet of the high-pressure pump, to keep fuel in the high-pressure pump in a non-working condition.

A dual fuel injection system according to any one of the preceding claims, wherein a pressure gauge is provided to measure a fuel pressure downstream of the high pressure pump, wherein a sensitivity of the pressure gauge is adjusted substantially proportionally to a combustion value of the first and second fuels. -10-

A dual fuel injection system preferably according to any one of the preceding claims, comprising: - a first fuel pump for supplying a first fuel, - a second fuel pump for supplying a second fuel, 5. a high-pressure pump, downstream of the first and second fuel pumps, for pressurizing the first and / or second fuel, and an injector for injecting the pressurized first and / or second fuel into a combustion chamber of the internal combustion engine, wherein a return channel from the high pressure pump to a reservoir is provided with the second fuel, the return channel returning an excess of the second fuel back into the reservoir.

A dual fuel injection system according to claim 8, wherein the return channel is provided with a by-pass of the high-pressure pump, the by-pass being placed upstream of a high-pressure part of the high-pressure pump.

A dual fuel injection system according to claim 8 or 9, wherein the return channel is provided with a back pressure valve.

A dual fuel injection system according to any of the preceding claims, wherein the first fuel is a liquid fuel, and the second fuel is a fuel that must be kept under pressure to keep it in a liquid state.

A dual fuel injection system according to any of the preceding claims, wherein the first fuel is gasoline and the second fuel is LPG.

A motor vehicle comprising a dual fuel injection system according to any one of the preceding claims.