GB2341895A

GB2341895A - Device for dosing fuel into a cylinder of an internal combustion engine

Info

Publication number: GB2341895A
Application number: GB9922199A
Authority: GB
Inventors: Erwin Achleitner
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1998-09-21
Filing date: 1999-09-20
Publication date: 2000-03-29
Also published as: FR2783572A1; GB9922199D0; DE19843175A1

Abstract

A device for dosing fuel comprises a fuel supply device, an injection valve (13), a mixing chamber (14), an air supply device, a mixture injector (15) and a device for adjusting the air pressure in the air supply device as a function of a fuel pressure in the fuel supply device. The mixing chamber is connected to the air supply device. The injection valve (13) is arranged on the mixing chamber in such a way that the fuel is dosed into the mixing chamber. The mixture injector (15) communicates with the mixing chamber (14) and is arranged in the cylinder head (10) of the internal combustion engine in such a way that it doses the mixture in the mixing chamber (14) into the cylinder (4). The adjustment of air pressure means that it is possible to dispense with a return line to the fuel tank; thus no heated fuel flows back to the tank, causing evaporation.

Description

Device for dosing fuel into a cylinder of an internal combustion engine

The invention relates to a device for dosing fuel into a cylinder of an internal combustion engine. A device of this type is described in the publication by R. Houston, G. Cathcart, entitled "Combustion and Emissions Characteristics of Orbital's Combustion Process Applied to Multi-Cylinder Automotive Direct Injected 4-Stroke Engines", Society of Automotive Engineers SAE Paper 980153, Volume SP 136. The known device comprises an injection valve, a mixing chamber and a mixture injector. Arranged between the injection valve and the mixture injector is a mixing chamber in which compressed air is mixed with fuel which is dosed by the injection valve. The mixture injector injects the air-fuel mixture in the mixing chamber into the cylinder of the internal combustion engine in a controlled manner. The device is distinguished as a result of the fact that it renders possible a precise layering of the load, i.e. of the air-fuel mixture, in the cylinder. Thus, a high level of efficiency of the internal combustion engine is achieved.

In the known device, the compressed air is regulated to a permanently preset value of the pressure. The pressure of the fuel in a fuel supply device is regulated in such a way that a predetermined pressure difference is set between the pressure of the fuel and the air. The fuel supply device comprises a fuel pump, a differential-pressure controller close to the engine block of the internal combustion engine, and a return line from the differential-pressure controller towards a fuel tank. Because of the over-pressure required for the regulation, heated fuel flows almost constantly back to the tank during the operation of the internal combustion engine and partially evaporates there.

Embodiments of the invention aim to develop a device for dosing fuel into a cylinder of an internal combustion engine, which device is simple and ensures a precise dosing of fuel According to the invention there is provided a device for dosing fuel into a cylinder of an internal combustion engine, the device having a fuel supply device which is connected to an injection valve, a mixing chamber, which is connected to an air supply device and on which the injection valve is arranged in such a way that the fuel is dosed into the mixing is chamber, and a mixture injector, which communicates with the mixing chamber and is arranged in a cylinder head of an internal combustion engine in such a way that it doses the mixture in the mixing chamber into the cylinder, there being further provided a device for adjusting the air pressure in the air supply device as a function of the fuel pressure in the fuel supply device.

Further preferred features may be found in the attached dependent claims.

In accordance with the invention, in the fuel supply device, it is possible to dispense with a return line to a fuel tank. Thus, no heated fuel flows back to the tank, with the consequence that little fuel evaporates in the fuel tank. By dispensing with the return line, the device becomes more fail-safe.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an internal combustion engine having a device for dosing fuel; and Figure 2 shows a flow chart for controlling the device for dosing fuel.

An internal combustion engine (Figure 1) comprises an intake section 1 having a throttle valve 2 and an engine block 3, which has a cylinder 4 and a crankshaft 5. A piston 7 and a connecting rod 8 are assigned to the cylinder 4. The connecting rod 8 is connected to the piston 7 and the crankshaft 5.

There is provided a cylinder head 10 in which is arranged a valve operating mechanism having at least one intake valve and one discharge valve. Inserted in the cylinder head is furthermore a spark plug 12. An injection valve 13 is arranged on a mixing chamber 14 in such a way that the fuel is dosed into the mixing chamber 14. A mixture injector 15, which communicates is with the mixing chamber 14, is arranged on the cylinder head 10 in such a way that it doses the mixture in the mixing chamber 14 into the cylinder 4.

The internal combustion engine further comprises an exhaust section 16 having a catalytic converter.

A first pipe 17 is led from an intake upstream of the throttle valve in the intake section 1 to a compressor 18, which is driven by a camshaft 20 or even directly or by way of a chain drive by the crankshaft 5. Arranged.in the first pipe 17 is a throttle device 22, which is preferably constructed as a throttle valve. However, an idling filling regulator or another throttle device known to the skilled person can also be provided as a throttle device 22. Preferably, the throttle device 22 is open in the off-circuit state, so as not to impair the flow of air to the compressor if the component fails. A second pipe 23 is led from the exit of the compressor 18 towards a compressed air reservoir 24. The compressed air reservoir 24 is connected by way of a third pipe 25 to the mixing chamber 14.

There is provided a fuel tank 27, in which is arranged a fuel pump 28, which pumps fuel through a fourth pipe 30 towards a compressed fuel reservoir 32.

The compressed fuel reservoir 32 is connected by way of a fifth pipe 33 to the injection valve 13.

A sixth pipe 34 is led from the fuel tank 27 to an active charcoal filter 35 which adsorbs and desorbs fuel. From the active charcoal filter 35, a seventh pipe 37 is led towards a venturi section 40 of the first pipe 17. Arranged in the seventh pipe 37 is a tank vent valve 38.

There is provided a control device 42, to which are assigned sensors which detect different measured variables and ascertain in each case the measured value of the measured variable. The control device 42 ascertains as a function of at least one measured variable one or more actuating signals which each control an actuator. The sensors are a pedal position sensor 45, which detects a pedal position of the accelerator pedal 47, a throttle valve position sensor 48, which detects a degree of opening of the throttle valve 2, an air mass meter 50, which detects an air mass flow, and/or a suction pipe pressure sensor, which detects a suction pipe pressure in the intake section 1, a speed sensor 54, which detects a speed N of the crankshaft 5, and a dif f erential -pressure sensor 55, which detects the differential pressure of the pressure of the fuel in the fourth pipe 30 or in the compressed fuel reservoir 32 and the pressure of the air in the second pipe 23 or the compressed air reservoir 24.

Depending on the embodiment of the invention, there can be any lesser amount of the above-mentioned sensors or additional sensors.

Actuators each comprise an actuating drive and a final control element. The actuating drive is an electromotive drive, an electromagnetic drive or a further drive known to the skilled person. The final -5 control elements are constructed as a throttle valve 2, as an injection valve 13, as a spark plug 12, as a mixture injector 15, as the fuel pump 28 or as the tank vent valve 38. In the following, reference is made to the actuators by means of the associated final control element in each case. The control device 42 is preferably constructed as an electronic engine control.

It can, however, also comprise a plurality of control units which are electrically conductively connected to each other, thus, for example, by way of a bus system.

In the following, the function of the part of the control device that is relevant to the invention is described with the aid of the f low chart (Figure 2) In a step S1, the program is started. In a step S2, the current measured value of the differential-pressure sensor 55 is assigned to an actual value PDIFF AV of the differential pressure. Furthermore, a desired value of a variable representing the load on the internal combustion engine is ascertained. In this connection, there is preferably ascertained a desired value TQI-SP of the torque as a function of the pedal position PV, the speed N and possibly of further operating variables of the internal combustion engine and additionally as a function of torque demands of further functions of the internal combustion engine, such as, for example, an idling speed control, or even torque demands of an electronic automatic transmission control or an anti-slip control. Preferably, the desired values are stored in characteristic diagrams as a function of the above-mentioned variables and are ascertained therefrom, possibly by means of characteristic-diagram interpolation.

In a step S3, a desired value PDIFF SP of the pressure difference is ascertained as a function of the desired value TQI - SP of the torque and the speed N, preferably by way of a characteristic or a characteristic diagram. Alternatively, the desired value PDIFF SP can admittedly also be permanentl-v specified, but the above-mentioned dependency on the desired value TQI - SP of the torque, however, has the advantage that in the case of suitable parameter' sat ion of the characteristic diagram a comparatively small variation of the injection time at the injection valve is necessary, so that an injection valve which is favourable in terms of cost can be used with comparatively low linearity demands between in3ec-ion time and fuel mass.

In a step S4, a desired value THR - SP of the degree of opening of the throttle device 22 is ascertained as a function of the desired value PDIFF SP and the actual is value PDIFF - AV of the differential pressure by means of a controller, which has P, PI, PID action or eveT-- another action known to the skilled person, and is corrected as a function of the speed N and a tank venting rate CPR. The desired value PDIFF - SP of the differential pressure can thus be adjusted precisely.

The tank venting rate CPR is ascertained as a function of a degree of loading of the active charcoal fi--zer 35.

In a step ss, an injection time duration TI -'s ascertained as a function of the actual value PD77FJ1W of the differential pressure and the desired value TQI_SP of the torque, preferably from a character-- st Jc diagram.

In a step S6, corresponding actuating signalS fcr adjusting the desired value THR - SP of the degree of opening of the throttle device 22 and for triggering the injection valve 13 for the injection time duration TI are generated. In a step S7, the program is E"hen ended. The program is called up cyclically or as a function of the speed N of the internal combusticn engine during the operation of the internal combustion engine.

As a result of the advantageous ascertaining of the injection time duration TI as a function of the actual value PDIFF - AV of the differential pressure in accordance with step SS, the predetermined fuel mass can be dosed into the cylinder 4 in a precise manner even in the event of short-term deviations of the pressure difference from the desired value PDIFF - SP.

As a result of the arrangement of the throttle device 22 as final control element for adjusting the air pressure in the compressed air reservoir 24, it is ensured that with this adjusting only small losses occur, which losses are basically determined by the drive power of the compressor and are influenced by the is throttle losses. Preferably, there is provided a compressor, the maximum drive power of which is sufficient to be able to adjust the air pressure as necessary despite series scatters of the device for dosing fuel and unfavourable ambient conditions.

As a result of the advantageous arrangement of the throttle valve upstream of the venturi section 40 in which the seventh pipe 37 opens out into the first pipe 17, the tank venting rate can be adjusted simply and precisely by appropriate adjusting of the degree of opening of the throttle device 22.

The provision of the differential-pressure sensor (55) has the advantage that only one pressure sensor has to be provided instead of respective absolute pressure sensors for the air pressure and the fuel pressure. As a result of this, the reliability of the device for dosing fuel is increased.

The first pipe 17, the throttle device 22, the compressor 18, the second pipe 23, the compressed air reservoir 24 and the third, sixth and seventh pipes 25, 34, 37 form together an air supply device. The fuel tank 27, the fuel pump 28, the fourth pipe 30, the compressed fuel reservoir 32 and the fifth pipe 33 form together a fuel supply device.

-g-

Claims

1. A device for dosing fuel into a cylinder of an internal combustion engine, the device having a fuel supply device which is connected to an injection valve, a mixing chamber, which is connected to an air supply device and on which the injection valve is arranged in such a way that the fuel is dosed into the mixing chamber, and a mixture injector, which communicates with the mixing chamber and is arranged in a cylinder head of an internal combustion engine in such a way that it doses the mixture in the mixing chamber into the cylinder, is there being further provided a device for adjusting the air pressure in the air supply device as a function of the fuel pressure in the fuel supply device.

2. A device according to claim 1, wherein the device for adjusting the air pressure is constructed in such a way that the air pressure is adjusted as a function of a variable representing the load on the internal combustion engine.

3. A device according to any of the preceding claims, wher ' ein the device comprises a controller, the controlled and reference variable of which is the pressure difference of the fuel pressure and the air pressure.

4. A device according to claim 3, wherein there is provided a differential-pressure sensor, which detects the pressure difference of the fuel pressure and the air pressure.

5. A device according to any of the preceding claims, wherein there is provided a throttle device in the air supply device, which throttle device is a final control element for adjusting the air pressure.

6. A device according to claim 5, wherein the throttle device is arranged upstream of an opening of a pipe which communicates with an active charcoal filter, which adsorbs and desorbs fuel vapours.

7. A device according to any of the preceding claims, wherein an injection time duration of the fuel is ascertained by the injection valve as a function of the pressure difference and the variable representing the load on the internal combustion engine.

8. A device for dosing fuel into a cylinder of an internal combustion engine, the device being substantially as herein described with reference to the accompanying drawings.