GB2344376A

GB2344376A - I.c. engine fuel injection control method with determination of quantity of fuel delivered during pilot injection

Info

Publication number: GB2344376A
Application number: GB9826574A
Authority: GB
Inventors: Benjamin James Bradshaw
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1998-12-04
Filing date: 1998-12-04
Publication date: 2000-06-07
Also published as: GB9826574D0

Abstract

A control method for use in controlling the operation of a fuel system for a compression ignition internal combustion engine comprising the steps of determining the timing of commencement of combustion following the main injection relative to the time at which the main injection commences and using the timing of commencement of combustion relative to the time at which the main injection commences to determine the quantity of fuel delivered during the pilot injection. The invention also relates to a method of balancing the fuel quantities delivered to an engine during pilot injections, the method comprising the steps of determining the quantities of fuel delivered to each cylinder or combustion space of an engine during pilot injection using the control method and modifying the quantity of fuel injected to at least one of the cylinders or combustion spaces until the quantities of fuel delivered during the pilot injections reach a desired level.

Description

CONTROL METHOD This invention relates to a control method for use in controlling the operation of a fuel system for a compression ignition internal combustion engine. In particular, the invention relates to a control method for use in controlling the pilot injection of fuel by a fuel system of the type in which each cylinder or combustion space of the engine is supplie with a pilot injection followed by a main injection, and for use in balancing the quantities of fuel delivered in the pilot injections.

Pilot injection is an important technique for minimizing combustion noise and involves injecting a small amount of fuel before the main injection.

The fuel delivered during the pilot injection burns before fuel is delivered in the main injection, raising the temperature and pressure of the gas within the engine cylinder. As a result, the main injection ignition delay is reduced and the rate of pressure rise during burning of the fuel delivered during the main injection is also restricted.

The quantity of fuel delivered during each pilot injection is usually significantly less than that delivered during the subsequent main injection, for example for a four cylinder passenger vehicle engine operating at 750 rpm against a low load (neutral), the pilot injection quantity is typically 20-25% of the main injection quantity. The manufacture of fuel injectors capable of ensuring that each cylinder of the engine receives the same pilot quantity of fuel places high demands on manufacturing tolerances. It is an object of the invention to provide a control method allowing compensation for differences between individual fuel injectors.

According to a first aspect of the invention there is provided a control method comprising the steps of: determining the timing of commencement of combustion following the main injection relative to the time at which the main injection commences; and using the timing of commencement of combustion relative to the time at which the main injection commences to determine the quantity of fuel delivered during the pilot injection.

The timing of commencement of combustion may be sensed, for example, using a, cylinder pressure sensor, the output signal of which is filtered to permit recognition of the timing of commencement of combustion. It will be appreciated, however, that alternative techniques for sensing the commencement of combustion may be used, for example an engine mounted accelerometer or an optical sensor may be used.

According to another aspect of the invention there is provided a method of balancing the fuel quantities delivered to an engine during pilot injections comprising the steps of: determining the quantities of fuel delivered to each cylinder or combustion space of an engine during pilot injection using the control method of the first aspect; and modifying the quantity of fuel injected to at least one of the cylinders or combustion spaces until the quantities of fuel delivered during the pilot injections reach a desired level.

The desired level may be the same for all of the cylinders or, alternatively, may be selected, using any appropriate technique, to minimise engine speed variations, emissions or engine noise. As a further alternative, the desired level may be chosen to ensure that combustion commences after a predetermined time relative to the commencement of the main injection.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a graph illustrating the effect of varying the pilot injection quantity on the relationship between the in-cylinder pressure and crankshaft position of an engine; and Figure 2 is a diagram illustrating the relationship between the pilot injection quantity and the main injection ignition delay of an engine.

Figure 1 illustrates the relationship between the in-cylinder pressure of a cylinder of a compression ignition internal combustion engine and the crankshaft position. Three traces are shown in Figure 1, the lower trace 10 illustrating the relationship where no fuel is delivered during a pilot injection, the middle trace 11 illustrating the relationship where a pilot injection of volume 0.5 mm3 of fuel is delivered during a pilot injection, the upper trace 12 illustrating the case where the pilot injection quantity is 1.5 mm3. In each case, the pilot injection commences 10 prior to the top-dead-centre position for the cylinder in question. The main injection commences at the top-dead-centre position and consists of a delivery of 4.3 mm3. The engine is operating at a speed of 1,000 rpm against a low constant load.

On each of the three traces 10,11,12 of Figure 1, the position at which combustion of the fuel delivered during the main injection commences is marked. The commencement of combustion can be recognised as the incylinder pressure starts to fall after the top-dead-centre position has been reached, and starts to rise, once more, upon the commencement of combustion. In each case, the ignition delay, that is the delay between the top-dead-centre position at which the main injection commences and the commencement of combustion, is indicated on the graph. It will be appreciated that there is a relationship between the magnitude of the ignition delay and the quantity of fuel delivered during the pilot injection.

Where the pilot injection quantity is small, then the ignition delay is of relatively large magnitude, the ignition delay falling as the quantity of fuel delivered during the pilot injection increases. As, in this example, the commencement of pilot injection occurs at a fixed point prior to the topdead-centre position, it will be appreciated that the timing of commencement of combustion of the fuel delivered during the main injection relative to the timing of commencement of the pilot injection also falls as the quantity of fuel delivered during the pilot injection increases.

Figure 2 illustrates the relationship between the magnitude of the main injection ignition delay and the quantity of fuel delivered during the pilot injection for a range of pilot injection quantities. The trace is of step-like form as the ignition delay is measured in 0.5 intervals, and it will be appreciated that if the magnitude of the ignition delay were measured to a greater accuracy, then the trace would form a relative smooth curve.

It will be appreciated from Figures 1 and 2 that as there is a relationship between the quantity of fuel delivered during the pilot injection and the timing of commencement of combustion of the fuel delivered during the main injection relative to the commencement of the main injection, by sensing the timing of commencement of combustion, and after suitable calibration, the timing of commencement of combustion can be used to determine the quantity of fuel which is being delivered during the pilot injection. Hence, by measuring the timing of commencement of combustion, and making corresponding adjustments to the quantity of fuel delivered during the pilot injection, the pilot injection quantities can be balanced. The balancing of the pilot injection quantities may be such as to ensure that equal quantities of fuel are delivered during each pilot injection, or alternatively, the balancing may be used to control the fuel quantities delivered to reduce the levels of particulate emissions produced by the engine or engine noise. Further, it will be appreciated that by varying the quantities of fuel delivered during the pilot injections, the timing of commencement of injection for each cylinder can be balanced.

Thus if, for example, combustion is commencing too quickly, the quantity of fuel delivered during the pilot injection can be reduced to delay the commencement of combustion.

In use, the engine is operated under a range of speed and load conditions, and measurements of the timing of commencement of combustion relative to the quantity of fuel delivered during the pilot injection are taken. This information can then be used during subsequent use of the engine in combination with measurements of the ignition delay to derive information indicative of the quantity of fuel delivered during pilot injections. Appropriate balancing of the quantities of fuel delivered during pilot injection or balancing of the timing of commencement of combustion can then be achieved. During the calibration operation, parameters other than the engine speed and load conditions may be varied, if desired. For example, the temperature of the air with which the engine cylinders are charged, in use, and the air pressure, may be modified.

Although in the description hereinbefore, the timing of commencement of combustion is sensed by monitoring the in-cylinder pressure, it will be appreciated that other techniques for monitoring the timing of commencement of combustion may be used. For example, an optical sensor may be provided to permit detection of the commencement of combustion. Alternatively, an engine mounted accelerometer may be used to monitor engine vibrations, the output of the accelerometer being filtered in such a manner as to permit the detection of the timing of commencement of combustion.

Claims

CLAIMS 1. A control method for use in controlling the operation of a fuel system for a compression ignition internal combustion engine comprising the steps of; determining the timing of commencement of combustion following the main injection relative to the time at which the main injection commences; and using the timing of commencement of combustion relative to the time at which the main injection commences to determine the quantity of fuel delivered during the pilot injection.
2. The method as claimed in Claim 1, wherein the timing of commencement of combustion is sensed using a cylinder pressure sensor.
3. The method as claimed in Claim 2, wherein the cylinder pressure sensor generates an output signal, wherein the output signal is filtered to permit recognition of the timing of commencement of combustion.
4. The method as claimed in Claim 1, wherein the timing of commencement of combustion is sensed using an engine mounted accelerometer.
5. The method as claimed in Claim 1, wherein the timing of commencement of combustion is sensed using an optical sensor.
6. A method of balancing the fuel quantities delivered to an engine during pilot injections comprising the steps of ; determining the quantities of fuel delivered to each cylinder or combustion space of an engine during pilot injection using the control method of any of Claims 1 to 5; and modifying the quantity of fuel injected to at least one of the cylinders or combustion spaces until the quantities of fuel delivered during the pilot injections reach a desired level.
7. The method as claimed in Claim 6, wherein the desired level is the same for all of the cylinders.
8. The method as claimed in Claim 6, wherein the desired level is selected to minimise engine speed variations.
9. The method as claimed in Claim 6, wherein the desired level is selected to minimise emissions.
10. The method as claimed in Claim 6, wherein the desired level is selected to minimise engine noise.
11. The method as claimed in Claim 6, wherein the desired level is selected to ensure that combustion commences after a predetermined time relative to the commencement of the main injection.
12. A control method substantially as hereinbefore described with reference to the accompanying figures.
13. A method of balancing the fuel quantities delivered to an engine during pilot injections substantially as hereinbefore described with reference to the accompanying figures.