WO1999058838A1

WO1999058838A1 - A four stroke engine

Info

Publication number: WO1999058838A1
Application number: PCT/GB1999/001397
Authority: WO
Inventors: Andrew John Burnard
Original assignee: Rover Group Limited
Priority date: 1998-05-09
Filing date: 1999-05-05
Publication date: 1999-11-18
Also published as: GB9809966D0; GB2337123A; AU3835199A

Abstract

A four stroke engine (12) is disclosed which comprises an odd number of cylinders and is controlled by a controller (14) which derives the compression points of the cylinders within the four stroke cycle. Because there is an odd number of cylinders, the angle of the compression points with respect to the top dead centre (TDC) of number one cylinder is different between the revolutions of a cycle and the controller (14) is able to associate each compression point with its respective cylinder. The invention can be applied to four stroke engines having any odd number of cylinders and eliminates the need for a camshaft transducer in synchronising the camshaft timing with the crankshaft timing.

Description

A Four Stroke Engine

This invention relates to four stroke engines and in particular to: a four

stroke engine having an odd number of cylinders: to a control system for

such an engine; a controller for such a control system; and to a method of

controlling such a four stroke engine.

It is known to provide an engine with a control system which is

arranged to determine the rotational speed and position of its crankshaft.

One such prior art arrangement is disclosed in GB 2065310, and is capable

of indicating the rotational speed of a crankshaft and the top dead centre

(TDC) position of one cylinder on each revolution of the crankshaft.

It is desirable to synchronise the camshaft timing with the crankshaft

timing of a four stroke engine so that, for example, sequential fuel injection

can be performed. This is equally true of both spark and compression

ignition engines.

A known solution to the problem of synchronising the camshaft and

crankshaft timing is the provision of a camshaft transducer and associated

circuitry and signal processing. A prior art arrangement of this type is

disclosed in GB 2223803, but suffers itself from the higher cost, packaging

difficulties and signal processing complexity associated with including an

additional transducer. A system which discriminates between compression and exhaust

strokes without using a separate camshaft sensor is proposed in

US 4,870,587. The method takes advantage of the fact that the rotational

speed of a crankshaft rises after the top dead centre (TDC) position of a

cylinder on its compression stroke but does not rise after TDC on the

exhaust stroke. The method relies on detecting the speed of rotation at

predetermined points of crankshaft rotation before and after TDC, so that

those crankshaft speeds can be compared with predetermined values in

order to determine the stroke of that cylinder.

The system of US 4,870,587 uses a complex transducer target form, in

order to obtain the measurements to perform the complex processing it

employs. The system is, furthermore, described only in relation to engines

having an even number of cylinders.

It is an object of this invention to provide an improved four stroke

engine having an odd number of cylinders: a control system for such an

engine; a controller for such a control system; and to provide a method of

controlling such a four stroke engine.

According to the invention there is provided a four stroke engine

comprising an odd number of cylinders, a crankshaft connected to a piston of

the or each cylinder and a transducer arranged in use to provide a signal - 3 -

indicative of the rotational speed of the crankshaft to a controller, wherein

the signal comprises the substantially instantaneous rotational speed of the

crankshaft over at least part of at least one cycle of the engine and the

controller is arranged to determine the compression point of: the; one; more

than one; or each cylinder from at least one variation in said instantaneous

rotational speed with respect to the angle of rotation of the crankshaft over

said at least part of said at least one cycle.

The controller may be arranged to translate said signal into a

synchronisation signal which relates the timing of a camshaft of said engine

to the timing of said crankshaft.

The engine may comprise multiple cylinders and the controller may be

arranged in use to determine the rotational position of said crankshaft,

whereby the controller may be arranged to determine with which of said

multiple cylinders the or each compression point is associated.

The controller may be arranged to control a fuelling program of said

engine in response to said signal.

The engine may comprise a spark ignition engine and the controller

may be arranged to control an ignition program of said engine in response to

said signal. - 4 -

The transducer may be arranged to derive said signal from: a

measurement of the speed of said crankshaft; a measurement of the torque

of said crankshaft; or from a measurement of an electrical current or voltage

of an electrical machine connected to said engine and the electrical machine

may comprise a starting motor of said engine.

The invention also provides a control system for an engine according to

the invention and a controller for a control system according to the

invention.

The invention also provides a method of determining the compression

point of: the; one; more than one; or each cylinder of a four stroke engine

comprising an odd number of cylinders, the method including the steps of:

a) determining a signal indicative of the speed at which a crankshaft of

the engine is rotating in use over at least part of at least one cycle of the

engine; and

b) determining the or each compression point from at least one

variation in said speed with respect to the angle of rotation of the

crankshaft over said at least part of said at least one cycle. The method may include translating said signal into a synchronisation

signal which relates the timing of a camshaft of said engine to the timing of

said crankshaft.

The engine may comprise multiple cylinders and the method may

include arranging the controller to determine in use the rotational position

of said crankshaft, whereby the controller determines with which of said

multiple cylinders the or each compression point is associated.

The method may include controlling a fuelling program of said engine

in response to said signal.

The engine may comprise a spark ignition engine and the method may

include controlling an ignition program of said engine in response to said

signal.

The method may include determining said signal by: measuring the

rotational speed of said crankshaft; by measuring the torque of said

crankshaft; or by measuring an electrical current or voltage of an electrical

machine connected to said engine.

The invention will now be described by way of example with reference

to the accompanying drawings, in which: Figure 1 shows a vehicle including an engine according to the invention;

Figure 2 is a schematic diagram of a control system associated with the

engine of Figure 1; and

Figure 3 is a timing diagram of the top dead centre positions of the

cylinders of the engine of Figure 1 over one cycle.

Referring to the figures, a vehicle 10 includes a four stroke compression

ignition engine 12 having five cylinders and a firing order of 1,2,4,5,3. A

controller 14 controls a set of five individual electrically actuated fuel

injectors 16, associated one with each cylinder of the engine 12.

The engine 12 includes a crankshaft 18 having mounted thereon an

encoder disc 20. The encoder disc 20 rotates with the crankshaft 18 and

comprises a series of targets 22 equally spaced about its circumference, with

one target missing at a point 24 equivalent to the top dead centre (TDC)

position of number one cylinder.

A transducer 26 is associated with the encoder disc 20 and is arranged

to detect the targets 22 as they pass it and to provide a signal to the

controller 14. The signal is indicative of the rate at which the targets 22 are - 7 -

passing the transducer 26 and is therefore also indicative of the speed at

which the crankshaft 18 is rotating.

The missing target at the TDC point 24 is indicative of the start and

finish of each revolution and confirms the crankshaft position at one point

during each revolution. The controller 14 derives the position of the

crankshaft 18 at other points in the revolution by interpolation from the

TDC point 24 and the crankshaft speed.

As each cylinder approaches its respective compression point (TDC) on

its compression stroke, the crankshaft speed decreases. As each cylinder

passes beyond TDC, the crankshaft speed increases. These changes in

crankshaft speed are detected by the controller 14 using the signal from the

transducer 26, and the controller 14 can therefore determine all the

compression points in the cycle.

Each cycle comprises two successive revolutions of the crankshaft 18

and the controller 14 can define each point in each cycle in terms of

crankshaft angle over 720° . The controller 14 can therefore calculate the

position of each compression point in any cycle with respect to the start and

finish of that cycle. The crankshaft angle between successive compression points within

each cycle is equal throughout the cycle and is determined in accordance

with the following equation:

Angle = 720° / (Number of cylinders in the engine).

It can be seen that, for an engine having an even number of cylinders,

the distribution of compression points throughout each revolution of the

cycle is identical. It is therefore difficult with such an engine to distinguish

between the revolutions within a cycle so as to associate the compression

points accurately with their respective cylinders without including a

camshaft transducer.

For the five cylinder engine 12 of this invention, the compression points

are spaced apart over the cycle by 144° of crankshaft rotation. From Figure

3 it can be seen that the compression points occur at different crankshaft

angles with respect to the TDC point 24 of cylinder number one during each

revolution of the cycle.

Thus the controller 14 determines in which revolution of the cycle the

engine 12 is operating and at which angle in that revolution the

compression points occur. The controller 14 can therefore synchronise the camshaft timing with the crankshaft timing using information derived only

from the crankshaft 18.

The controller 14 is arranged to operate the set of injectors 16 to

provide sequential fuel injection in accordance with the synchronisation of

the camshaft and crankshaft timing as described above, without the need

for a camshaft transducer.

This invention can be applied to a single cylinder four stroke engine. It

may also be applied to a spark ignition engine to control either or both of

fuelling and ignition timing.

It is not necessary to measure crankshaft position and / or speed

directly. This information could be derived by measuring crankshaft torque.

It could also be derived by measuring the current in an electrical machine

associated with the engine, such as a starting motor or generator.

Fluctuations in the torque or current used and / or generated could then be

used to derive the compression points.

This invention can therefore be applied to four stroke engines having

any odd number of cylinders and eliminates in many circumstances the

need for a camshaft transducer.

Claims

- 10 - CLAIMS

1. A four stroke engine comprising an odd number of cylinders, a

crankshaft connected to a piston of the or each cylinder and a

transducer arranged in use to provide a signal indicative of the

rotational speed of the crankshaft to a controller, wherein the signal

comprises the substantially instantaneous rotational speed of the

crankshaft over at least part of at least one cycle of the engine and the

controller is arranged to determine the compression point of: the; one;

more than one; or each cylinder from at least one variation in said

instantaneous rotational speed with respect to the angle of rotation of

the crankshaft over said at least part of said at least one cycle.

2. An engine according to Claim 1, wherein the controller is arranged

to translate said signal into a synchronisation signal which relates the

timing of a camshaft of said engine to the timing of said crankshaft.

3. An engine according to Claim 1 or Claim 2, the engine comprising

multiple cylinders, wherein the controller is arranged in use to

determine the rotational position of said crankshaft, whereby the

controller is arranged to determine with which of said multiple

cylinders the or each compression point is associated. - 11 -

4. An engine according to any preceding claim, wherein the controller

is arranged to control a fuelling program of said engine in response to

said signal.

5. An engine according to any preceding claim comprising a spark

ignition engine, wherein the controller is arranged to control an ignition

program of said engine in response to said signal.

6. An engine according to any preceding claim, wherein the transducer

is arranged to derive said signal from a measurement of the speed of

said crankshaft.

7. An engine according to any one of Claims 1 to 5, wherein the

transducer is arranged to derive said signal from a measurement of the

torque of said crankshaft.

8. An engine according to any one of Claims 1 to 5, wherein the

transducer is arranged to derive said signal from a measurement of an

electrical current or voltage of an electrical machine connected to said

engine.

9. An engine according to Claim 8, the electrical machine comprising a

starting motor of said engine. - 12 -

10. An engine substantially as described herein with reference to the

accompanying drawings.

11. A control system for an engine according to any preceding claim.

12. A controller for a control system according to Claim 11.

13. A method of determining the compression point of: the; one; more

than one; or each cylinder of a four stroke engine comprising an odd

number of cylinders, the method including the steps of:

a) determining a signal indicative of the speed at which a crankshaft of

the engine is rotating in use over at least part of at least one cycle of the

engine; and

b) determining the or each compression point from at least one variation

in said speed with respect to the angle of rotation of the crankshaft over

said at least part of said at least one cycle.

14. A method according to Claim 13 including translating said signal

into a synchronisation signal which relates the timing of a camshaft of

said engine to the timing of said crankshaft. - 13 -

15. A method according to Claim 13 or Claim 14, the engine comprising

multiple cylinders, including arranging the controller to determine in

use the rotational position of said crankshaft, whereby the controller

determines with which of said multiple cylinders the or each

compression point is associated.

16. A method according to any one of Claims 13 to 15, including

controlling a fuelling program of said engine in response to said signal.

17. A method according to any one of Claims 13 to 16, the engine

comprising a spark ignition engine, including controlling an ignition

program of said engine in response to said signal.

18. A method according to any one of Claims 13 to 17, including

determining said signal by measuring the rotational speed of said

crankshaft.

19. A method according to any one of Claims 13 to 18, including

determining said signal by measuring the torque of said crankshaft.

20. A method according to any one of Claims 13 to 18, including

determining said signal by measuring an electrical current or voltage of

an electrical machine connected to said engine. - 14 -

21. A method substantially as described herein with reference to the

accompanying drawings.