GB2441145A

GB2441145A - Laser ignition system for an internal combustion engine

Info

Publication number: GB2441145A
Application number: GB0616636A
Authority: GB
Inventors: Andrew David Scarisbrick; Roy Clissold
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-08-22
Filing date: 2006-08-22
Publication date: 2008-02-27
Anticipated expiration: 2026-08-22
Also published as: GB2441145B; DE102007033809A1; DE102007033809B4; GB0616636D0

Abstract

The laser ignition system comprises a light guide 22 leading to an i.c. engine combustion chamber to introduce a pulse of laser light into the combustion chamber to ignite the charge. Additionally, less powerful pulses of laser light are introduced into the combustion chamber to be reflected from the piston 12 back to a sensor 30 to permit the position and/or the velocity of the piston crown to be determined. Both top dead centre (TDC) and bottom dead centre (TDC) piston positions may be determined. The additional pulses may be transmitted by the same light guide 22, the returning pulses being reflected by a beam splitter 28 to a sensor 30. Alternatively, a second light guide may be provided leading directly to the sensor 30 avoiding the need for a beam splitter; both light guides may be attached to a common connector to fit in place of the conventional spark plug. The data relating to piston speed and position may be used to sense detonation, misfire and burn rate.

Description

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LASER IGNITION SYSTEM

The present invention relates to a laser ignition system.

It has previously been proposed to use a pulse of laser light to ignite the charge in an internal combustion engine, in place of the conventional spark. Hitherto, the timing of the laser pulse was determined using a crankshaft position sensor operating on the principle of electro-magnetically detecting a missing tooth on a wheel rotating in synchronism with the crankshaft.

Aside from the issue of additional cost, such a conventional sensor has the disadvantage of requiring at least one full revolution of the engine before it can ascertain the position of top dead centre.

With a view to mitigating these disadvantages, the present invention provides a laser ignition system for an internal combustion engine, comprising a light guide leading to an engine combustion chamber, first means coupled to the light guide for introducing a pulse of laser light into the combustion chamber in order to ignite the charge, and second means coupled to the light guide for additionally introducing pulses of laser light into the combustion chamber to permit the position and/or the velocity of the piston crown to be determined.

The present invention is based upon the realization that in a laser ignition system it is possible to dispense with a conventional crankshaft position sensor and to rely on laser measurement to determine the position of the crankshaft. This technique enables the position of the crown of the piston to be determined with greater accuracy and can operate even when the engine is stationary.

As a laser source and the light guide are already present in an laser ignition system, the invention can be implemented using only additional processing.

Systems using a laser light to measure position are of course well-known and need not be described within the present context. In U52008/083826, this technique has been applied to measuring the position of the piston in cylinder.

The principle used in measuring distance is based on io measuring the time between instant of transmission of a pulse and the instant of detection of its reflection.

The laser light reflected from the piston crown may be detected using the same light guide as is used for introducing the laser light into the combustion chamber but it is alternatively possible to employ a second light guide leading to a sensor. The use of a second light guide avoids the need to incorporate a beam splitter in the first light guide.

The use of an in-cylinder laser to measure the position of the piston crown offers the additional advantage that it can determine both the bottom dead centre (BDC) and the top dead centre (TDC) positions of the piston. Measurement of both EDO And TDC positions enables the system to determine the crankshaft angle for all positions of the piston between these two limits. Furthermore, the measurement can be carried out separately on each of the cylinders to allow more accurate control of the ignition timing.

A still further advantage of the use of an in-cylinder laser is that it can measure not only the position of the piston crown but also its speed of movement. This measurement technique is also known and relies on the fact that there will be a Doppler shift in the frequency of the reflected light. As taught by JP8121230 this information can be used to determine accurately when the piston reaches the TDO and BDC positions. Such precise determination of the piston velocity would enable the detection of misfire and detonation and calculation of the burn rate.

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a schematic diagram of a laser ignition systom in accordance with the present invention.

The single figure in the drawing shows a cylinder 10 having a piston 12 connected by a connecting rod 14 to a crankshaft (not shown) . The combustion chamber above the piston 12 has an inlet valve 16, an exhaust valve 18 and a lens 20 position centrally between the two valves 16 and 18.

The lens 20 is connected by way of a light guide 22 to a laser source 26. A beam splitter 24 is arranged in the light guide 28 to divert radiation reflected from the piston to a further light guide 28 that leads to an optical sensor 30.

A processing unit 32 receives signals from the sensor and operates the laser source 26 to produce ignition pulses correctly timed in relation to the angle of rotation of the engine crankshaft.

The engine operates in the same manner as a conventional spark ignition engines except that a pulse of laser light is used to ignite the charge. The pulse is generated by the laser source 26 and transmitted to the combustion chamber by the light guide 22.

In order to detect the position of the engine camshaft, pulses of laser light of lesser power are generated by the laser source 26 and transmitted by the same light guide 22 into the combustion chamber. The light reflected from the crown of the piston 12 passes back down the light guide 22 to the beam splitter 24 which may, for example, be a partly silvered mirror. The reflected light passes through the light guide 28 to the sensor 30 where its time of arrival and its frequency are analysed in order to determine the position and the speed of the piston 12. This information is passed on to the processing unit 32 to enable it to set the time the ignition pulses generated by the laser source 26 to coincide with the correct position of the piston.

Aside from the advantage of obviating the need for a conventional crankshaft position sensor, and the invention provides a more accurate information on the position of the piston and can furthermore provide this information even before one complete revolution of the engine has been performed. This helps to speed start-up which in turn reduces hydrocarbon emissions during engine start-up.

While it should suffice to detect the position of only one of the piston is of a multi-cylinder engine, it is alternatively possible to provide laser position sensing in all the cylinders.

A further advantage of the invention is that the data relating to the speed and position of the piston can be used to sense detonation and misfire.

Although the invention has been described by reference to an embodiment that employs a beam splitter to separate the transmitted light from the reflected light, it would be old relatively possible to provide a second light guide in the combustion chamber. In this case the first light guide, connected to the laser source 26, provides both the ignition pulses and the pulses used for determining piston position and speed whereas the second light guide leads directly to the sensor 30, permitting the beam splitter 24 to be omitted altogether. Both of the light guides can be attached to a common connector to fit in the place that would normally be occupied by a spark plug of the engine.

Claims

CLAIMS

1. A laser ignition system for an internal combustion engine, comprising a light guide leading to an engine combustion chamber, first means coupled to the light guide for introducing a pulse of laser light into the combustion chamber in order to ignite the charge, and second means coupled to the light guide for additionally introducing pulses of laser light into the combustion chamber to permit :0 the position and/or the velocity of the piston crown to be determined.

2. A laser ignition system as claimed in claim 1, wherein the light guide includes a beam splitter and serves additionally to direct light reflected from the piston crown to a sensor.

3. A laser ignition system as claimed in claim 1, wherein a second light guide is provided to direct light reflected from the piston crown to a sensor.

4. A multi-cylinder internal combustion engine having a laser ignition as claimed in any preceding claim, wherein the crankshaft angle is determined by sensing the position of only one of the pistons.

4. A multi-cylinder internal combustion engine having a laser ignition as claimed in any of claims 1 to 3, wherein the crankshaft angle is determined by sensing the position of two or more pistons.

5. A laser ignition system constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.