GB2559472A

GB2559472A - Internal combustion engine control method and apparatus

Info

Publication number: GB2559472A
Application number: GB1720594.9A
Authority: GB
Inventors: Stacey Stephen; Ian Cooper; Saunders Jonathan
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2016-12-14
Filing date: 2017-12-11
Publication date: 2018-08-08
Anticipated expiration: 2037-12-11
Also published as: GB201720594D0; GB2557641A; GB2559472B; GB201621230D0

Abstract

A control unit 1 for controlling an internal combustion engine 2 having at least one cylinder 4 having a piston 5, crankshaft 6, and at least one camshaft 7, 8; The control unit 1 includes at least one processor 15 configured to receive a crankshaft position signal (CRK1, Fig. 2) from a crankshaft position sensor 9 and at least one camshaft position signal (CAM1, CAM2, Fig. 2) from at least one camshaft position sensor 11, 12; A memory 16 is connected to the at least one processor 15; The at least one processor 15 is configured to identify one or more reference engine stop position and, during start-up of the internal combustion engine 2, to determine an absolute engine position in dependence on said one or more reference engine stop position in combination with the crankshaft position signal (CRK1, Fig. 2) and/or the at least one camshaft position signal; an encoder with a distinctive element, and a detector are configured to have an offset of less than 45° when the engine is shut down.

Description

(54) Title of the Invention: Internal combustion engine control method and apparatus Abstract Title: Internal combustion engine start-up control method and apparatus (57) A control unit 1 for controlling an internal combustion engine 2 having at least one cylinder 4 having a piston 5, crankshaft 6, and at least one camshaft 7, 8; The control unit 1 includes at least one processor 15 configured to receive a crankshaft position signal (CRK1, Fig. 2) from a crankshaft position sensor 9 and at least one camshaft position signal (CAM1, CAM2, Fig. 2) from at least one camshaft position sensor 11, 12; A memory 16 is connected to the at least one processor 15; The at least one processor 15 is configured to identify one or more reference engine stop position and, during start-up of the internal combustion engine 2, to determine an absolute engine position in dependence on said one or more reference engine stop position in combination with the crankshaft position signal (CRK1, Fig. 2) and/or the at least one camshaft position signal; an encoder with a distinctive element, and a detector are configured to have an offset of less than 45° when the engine is shut down.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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FIGURES

INTERNAL COMBUSTION ENGINE CONTROL METHOD AND APPARATUS

TECHNICAL FIELD

The present disclosure relates to an internal combustion engine control method and apparatus. In particular, but not exclusively, the present disclosure relates to a control unit for controlling an internal combustion engine. The present disclosure also relates to a vehicle. The present disclosure also relates to a method of controlling an internal combustion engine.

BACKGROUND

An internal combustion engine comprises at least one cylinder having an associated piston, a crankshaft and at least one camshaft. A control unit, such as a powertrain control module (PCM), is provided to control fuelling and ignition of the fuel in said at least one cylinder. The control unit is connected to a crankshaft position sensor; and at least one camshaft position sensor. In order to determine the absolute engine position, for example during start-up of the internal combustion engine, the control unit receives a crankshaft position signal and at least one camshaft position signal while a starter motor rotates the internal combustion engine. The control unit combines these sensor signals to determine the absolute engine position. The control unit may thereby be synchronised with the internal combustion engine. The startup of the internal combustion engine cannot be initiated until synchronisation is complete so the time taken to determine the absolute engine position has a direct influence on how quickly the internal combustion engine may be started. The time to achieve synchronisation is dependent on how quickly edges are detected on the camshaft position sensors and how these relate to the crankshaft position sensor, typically comprising a trigger wheel having a 'missing tooth' pattern. The rotation of the internal combustion engine required to determine a valid absolute engine position may vary due to the form of the trigger wheel pattern used in a typical camshaft position sensor and also the configuration of the trigger wheel pattern in the crankshaft position sensor. The camshaft position sensor may, for example, comprise a trigger wheel having a 140°+40° pattern; and the camshaft position sensor may comprise a 'missing tooth' pattern.

The resulting delay in starting the internal combustion may prove significant when performing an eco-start when rapid starting of the internal combustion engine is required. By eco-start is meant the restarting of a vehicle engine after the vehicle has automatically stopped the engine during the course of a drive cycle to save fuel when conditions permit. For example, a vehicle may be arranged to adopt an eco-stop condition when a driveroperated brake pedal of the vehicle is depressed and the vehicle is stationary. When the driver releases the brake pedal the engine may be restarted and a transmission of the vehicle may be re-engaged. That is, release of the brake pedal by the driver triggers the engine to be restarted, the driveline to be closed and torque to be transmitted to the drive wheels. However, restarting the engine from an eco-stop condition should not cause nuisance to the driver and there should be no appreciable delay in the reapplication of torque to the drive wheels. As a result, there is a requirement for an engine to be started rapidly during eco-start. In the context of the present application, an eco-stop/start functionality may also be provided when a vehicle is moving, for example, in a hybrid vehicle in which the internal combustion engine may be stopped and re-started as required when the vehicle is not stationary.

It is against this backdrop that the present invention has been conceived. At least in certain embodiments, the present invention seeks to overcome or ameliorate at least some of the problems associated with prior art systems.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a control unit, a vehicle and a method as claimed in the appended claims.

According to a further aspect of the present invention there is provided a control unit for controlling an internal combustion engine comprising at least one cylinder having an associated piston, a crankshaft and at least one camshaft, the control unit comprising:

at least one processor configured to receive a crankshaft position signal from a crankshaft position sensor and at least one camshaft position signal from at least one camshaft position sensor; and a memory connected to the at least one processor;

wherein the at least one processor is configured to identify one or more reference engine stop position and, during start-up of the internal combustion engine, to determine an absolute engine position in dependence on said one or more reference engine stop position in combination with the crankshaft position signal and/or the at least one camshaft position signal. The at least one processor is configured to determine the absolute engine position during start-up of the internal combustion engine, typically as the internal combustion engine is rotated by a starter motor or a traction motor. The control unit uses the reference engine stop position to facilitate determination of the absolute engine position. In particular, the control unit may use each reference engine stop position as a candidate start position for the internal combustion engine during a successive start-up procedure. At least in certain embodiments, the rotation of the internal combustion engine required to determine the absolute engine position may be reduced, thereby helping to expedite a start-up procedure. During shut-down, the internal combustion engine is predisposed to stop in certain positions within the engine cycle. These stop position may be dependent on a range of factors, such as cylinder compression forces. The one or more reference engine stop position each correspond to a position within the engine cycle where the internal combustion engine is predisposed to stop.

The reference engine stop position may be defined as a discrete value, for example to define a particular angle within the engine cycle. Alternatively, the reference engine stop position may be defined as an angular range, for example to define an angular range within the engine cycle. The reference engine stop position may, for example, comprise a range less than or equal to 15°, 30°, 45° or 60°.

During start-up of the internal combustion engine, the at least one processor may be configured to determine the absolute engine position by monitoring said crankshaft position signal and/or said at least one camshaft position signal as the internal combustion engine is rotated. The at least one processor may be configured to identify a predefined signal pattern in said crankshaft position signal and/or said at least one camshaft position signal. The predefined signal pattern corresponds to a specific engine position and identification of said predefined signal pattern enables the at least one processor to determine the absolute engine position. The at least one processor may identify the predefined signal pattern in relation to said one or more reference engine stop position.

The at least one processor may be configured to identify said predefined signal pattern in dependence on detection of a change and/or an absence of change in the crankshaft position signal. Alternatively, or in addition, the at least one processor may be configured to identify said predefined signal pattern in dependence on a change and/or an absence in change in said at least one camshaft position signal. It will be understood that the detection of a change and/or the absence of a change can be indicative of position, for example in relation to the edges of a camshaft trigger wheel.

The at least one processor may be configured to identify said predefined signal pattern in dependence on angular rotation of the crankshaft from said one or more reference engine stop position. At least in certain embodiments, the at least one processor may identify the predefined signal pattern based on an angular rotation of the crankshaft from the one or more reference engine stop position, rather than having to measure the angular rotation of the crankshaft between consecutive identifiable signal patterns. The at least one processor may be configured to identify the predefined signal pattern assuming that the internal combustion engine is being rotated from said one or more reference engine stop position.

The one or more reference engine stop position may be predefined. The one or more reference engine stop position may be derived from computer modelling or empirical analysis for a particular type and/or configuration of internal combustion engine.

The at least one processor may actively control shut-down of the internal combustion engine to target a particular engine stop position. The at least one processor may, for example, control fuelling and/or ignition during the shut-down of the internal combustion engine. The at least one processor may be configured to control shut-down of the internal combustion engine to target an engine stop position coincident with or proximal to said one or more reference engine stop position.

The at least one processor may be configured to determine said one or more reference engine stop position during shut-down of the internal combustion engine.

The at least one processor may be configured to control shut-down of the internal combustion engine to target an engine stop position to facilitate start-up of the internal combustion engine. For example, an engine stop position may be targeted to position one or more piston in the internal combustion engine ready for combustion.

According to a still further aspect of the present invention there is provided a vehicle comprising a control unit as described herein.

According to a yet further aspect of the present invention there is provided a method of controlling an internal combustion engine comprising at least one cylinder having an associated piston, a crankshaft and at least one camshaft, the method comprising:

identifying one or more reference engine stop position; and determining an absolute engine position in dependence on said one or more reference engine stop position in combination with a crankshaft position signal and/or at least one camshaft position signal. At least in certain embodiments, the method may reduce the rotation of the internal combustion engine required to determine the absolute engine position. The method may thereby expedite start-up of the internal combustion engine.

The method may comprise determining the absolute engine position by monitoring said crankshaft position signal and/or said at least one camshaft position signal as the internal combustion engine is rotated.

The method may comprise identifying a predefined signal pattern in said crankshaft position signal and/or said at least one camshaft position signal in relation to said one or more reference engine stop position.

The method may comprise identifying said predefined signal pattern in dependence on detection of a change in the crankshaft position signal and/or a change in said at least one camshaft position signal.

The method may comprise identifying said predefined signal pattern in dependence on angular rotation of the crankshaft from said one or more reference engine stop position.

The one or more reference engine stop position may be predefined. The method may comprise reading said predefined reference engine stop position, for example from a memory device.

The method may comprise controlling shut-down of the internal combustion engine to target an engine stop position coincident with or proximal to said one or more reference engine stop position.

The method may comprise determining said one or more reference engine stop position during shut-down of the internal combustion engine.

The method may comprise controlling shut-down of the internal combustion engine to target an engine stop position to facilitate start-up of the internal combustion engine.

According to a yet further aspect of the present invention there is provided a system comprising: an engine; an encoder synchronised with a cycle of the engine, the encoder having a first direction of rotation during normal operation of the engine and having a distinctive element, the encoder being configured such that the distinctive element stops within a range of angular positions when the engine is shut-down; a detector configured to transmit a signal indicative of the distinctive element of the encoder passing the detector; wherein the position of the detector is offset in the first direction of rotation from the upper limit in the first direction of rotation of the range of angular positions within which the distinctive element of the encoder is configured to stop when the engine is shut down, the offset being less than 45°.

The offset may be less than 15°.

In some but not necessarily all examples, the encoder has a plurality of distinctive elements and the encoder is configured such that one of the plurality of distinctive elements is configured to stop in the range of angular positions when the engine is shut-down.

Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller” or “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a schematic representation of a vehicle incorporating a control unit in accordance with an embodiment of the present invention;

Figure 2A shows a first signal generated by the crankshaft position sensor as the internal combustion engine is rotated;

Figure 2B shows a second signal generated by an inlet camshaft position sensor as the internal combustion engine is rotated;

Figure 2C shows a third signal generated by an exhaust camshaft position sensor as the internal combustion engine is rotated;

Figure 3 shows a first plot showing the rotation of an internal combustion engine required to determine the absolute engine position;

Figure 4 shows a schematic representation of a vehicle engine system; and Figure 5 shows a schematic representation of a vehicle engine system.

DETAILED DESCRIPTION

A control unit 1 for controlling an internal combustion engine 2 of a vehicle 3 according to an embodiment of the present invention will now be described The control unit 1 may form part of a Powertrain Control Module (PCM). In particular, the control unit 1 may be in the form of an Engine Position Module (EPM). As described herein, the control unit 1 is configured to expedite start-up of the internal combustion engine 2 and has particular application in performing an eco-start following automated shut-down of the internal combustion engine 2 in a stop/start mode. However, the control unit 1 is not limited in this respect and may be used during conventional start-up procedures.

In the present embodiment the internal combustion engine 2 has four cylinders 4 arranged in an inline configuration. A piston 5 is disposed in each of the cylinders 4. The cylinders 4 each define a combustion chamber in which fuel is combusted to propel the pistons 5. The internal combustion engine 2 comprises a crankshaft 6, an inlet camshaft 7 and an exhaust camshaft 8. The crankshaft 6 is driven by the pistons 5 which reciprocate within the associated cylinder 4. The inlet camshaft 7 controls an intake valve for regulating intake air into the combustion chamber of each cylinder 4; and the exhaust camshaft 8 controls an exhaust valve for expulsion of exhaust gases from the combustion chamber of each cylinder 4. During operation of the internal combustion engine 2, fuel is injected into the cylinders 4 and combusted to force the pistons 5 down and rotate the crankshaft 6. Each cycle of fuel injection and combustion takes two full revolutions of the crankshaft 6; thus, the crankshaft 6 rotates through 720° during each cycle of the internal combustion engine 2. For a given cylinder 4, the first revolution comprises an intake stroke (piston 5 descending) for taking in air, and a compression stroke (piston 5 ascending) for compressing an air/fuel mixture before ignition. The second revolution starts with an ignition spark and comprises a power stroke (piston 5 descending) for combusting the fuel and forcing the piston downwards, and an exhaust stroke (piston 5 ascending) for expelling exhaust gases. The full cycle (intake, compression, power and exhaust) is continually repeated during operation of the engine. At a given moment during operation of the internal combustion engine 2, two of the cylinders 4 are in the intake or compression strokes and the other two cylinders 4 are in the power or exhaust strokes. The standard firing sequence of the cylinders 4 is one (1), three (3), four (4), two (2), but it will be understood that other sequences, such as one (1), three (3), two (2), four (4) may also be implemented.

A crankshaft position sensor 9 is provided for determining the (angular) position of the crankshaft 6. The crankshaft position sensor 9 comprises a crankshaft trigger wheel 10 arranged to rotate with the crankshaft 6. The crankshaft trigger wheel 10 comprises a plurality of radially extending teeth (not shown) having an equal spacing around the circumference of the trigger wheel. Other types of crankshaft trigger wheel 10 may be used. One or more of the teeth are omitted to form a gap (a ‘missing tooth gap’) in the crankshaft trigger wheel 10 to enable detection of a crankshaft reference position. The crankshaft reference position define an angular orientation of the crankshaft in a cycle (i.e. the position between 0° and 360°). Tt will be understood that two reference positions are identified in each 720° cycle. In the present embodiment, each tooth extends over 3° and is offset from the next tooth by 3°, with two teeth omitted to form the missing tooth gap. The rotation of the crankshaft trigger wheel 10 is measured by detecting the presence/absence of the teeth, for example using a Hall Effect sensor, a reluctance sensor or an optical sensor. As the internal combustion engine 2 is rotated the crankshaft position sensor 9 outputs a crankshaft position signal CRK1 to the control unit 1. The crankshaft position signal CRK1 and the engine position (between 0° and 720° inclusive) are shown in Figure 2A. A first camshaft sensor 11 is provided for determining the (angular) position of the inlet camshaft 7; and a second camshaft sensor 12 is provided for determining the (angular) position of the exhaust camshaft 8. The first and second camshaft sensors 11, 12 comprise respective first and second camshaft trigger wheels 13, 14. The first and second camshaft trigger wheels 13, 14 have first and second wheel patterns, for example comprising alternating 140° projections and 40° gaps. The first and second camshaft sensors 11,12 may, for example, comprise a Hall Effect sensor, a reluctance sensor or an optical sensor. As the internal combustion engine 2 is rotated the first and second camshaft sensors 11,12 output respective first and second camshaft position signals CAM1, CAM2 to the control unit 1 generated in dependence on the profiles of the first and second camshaft trigger wheels 13, 14. The first and second camshaft position signals CAM1, CAM2 are shown in Figures 2B and 2C respectively. The first and second camshaft position signals CAM1, CAM2 each comprise rising and falling edges generated in dependence on said first and second wheel patterns.

The control unit 1 is operative to control fuelling and ignition in the cylinders 4 in dependence on the position of the internal combustion engine 2. To ensure accurate fuelling and ignition control, the control unit 1 is synchronised with the internal combustion engine 2. The synchronisation process comprises determining an absolute engine position which represents the actual state of the internal combustion engine 2 in terms of the crankshaft angle (between 0°and 720° inclusive) within an operating cycle. During start-up, the control unit 1 references the crankshaft position signal CRK1 and the first and second camshaft position signals CAM1, CAM2 as the internal combustion engine 2 is rotated by a starter motor (not shown) or a traction motor (not shown). As described herein, the control unit 1 monitors the position of the crankshaft 6, the inlet camshaft 7 and the exhaust camshaft 8 as the internal combustion engine 2 is rotated in order to determine an absolute engine position for synchronisation. The rotation of the internal combustion engine 2 required to synchronise the control unit 1 introduces a delay into the start-up procedure which affects the total time taken to start the internal combustion engine 2.

The control unit 1 comprises a processor 15 connected to a memory device 16. The processor 15 is configured to implement a set of non-transitory computational instructions stored on said memory device 16. When executed, the computational instructions cause the processor to implement an engine control strategy for controlling operation of the internal combustion engine 2. The processor 15 is configured to determine the absolute engine position. As the internal combustion engine 2 is rotated, the processor 15 monitors the crankshaft position signal CRK1, the first camshaft position signal CAM1 and the second camshaft position signal CAM2 to identify predefined signal patterns. Each predefined signal pattern is unique and comprises a known combination of rising and falling edges in the first and second camshaft position signals CAM1, CAM2. The rising and falling edges in the first and second camshaft position signals CAM1, CAM2 may occur concurrently or at a known angular spacing (as determined in dependence on the crankshaft position signal CRK1) within each predefined signal pattern. The predefined signal patterns each relate to a unique engine position and by identifying one of said predefined signal patterns the processor 15 can determine the absolute engine position. The control unit 1 uses the absolute engine position to control fuelling and ignition in the cylinders 4 of the internal combustion engine 2. The control unit 1 may optionally also use the absolute engine position to control intake valve lift. As such, the absolute engine position is required for starting the internal combustion engine 2. In order to expedite starting of the internal combustion engine 2, it is advantageous to reduce the angular rotation of the internal combustion engine 2 required to determine the absolute engine position. This has particular application when performing an eco-start, for example to re-start the internal combustion engine 2 following an automated shut-down.

The angular rotation of the internal combustion engine 2 required to determine the absolute engine position for a given starting angular position X (measured in degrees) of the internal combustion engine 2 is shown in a first plot 100 shown in Figure 3. The possible starting angular positions X of the internal combustion engine 2 (ranging from 0° through to 720°) are shown on the X-axis; and the required angular rotation of the internal combustion engine 2 to determine the absolute engine position is shown on the Y-axis. The first plot 100 thereby represents the required angular rotation of the internal combustion engine 2 for any given starting angular position X. As the absolute engine position is required to synchronise the control unit 1, the first plot 100 provides an indication of the time required to perform synchronisation for a given starting angular position X of the internal combustion engine 2. The starting angular positions X of the internal combustion engine 2 are measured relative to the missing teeth gap (0°) formed in the crankshaft trigger wheel 10. In the present embodiment, the top dead centre (TDC) of the piston 5 in the cylinder 4 is at seventy-two degrees (72°) from the missing teeth gap. The first plot 100 shows the required angular rotation of the internal combustion engine 2 to determine the absolute engine position for three configurations of the first and second camshaft sensors 11, 12. Also illustrated in the first plot 100 are engine stop sectors (labelled S1-4) where the internal combustion engine 2 is predisposed to stop, for example due to compression forces within one or more of the cylinders 4. In the illustrated arrangement, there are four of said engine stop sectors (labelled as S1-4). The engine stop sectors S1-4 each extend over an angular range of approximately 45° in the present embodiment. The engine stop sectors S1-4 can be predetermined for a particular internal combustion engine 2. It will be understood that the angular extent and/or location of the engine stop sectors S1-4 may vary depending on the type and/or configuration of the internal combustion engine 2. A reference engine stop position (labelled as STP1-4) is predefined in each engine stop sector S1-4.

The processor 15 is configured to determine the absolute engine position in dependence on said one or more reference engine stop position STP1-4 in combination with one or more of: the crankshaft position signal CRK1, the first camshaft position signal CAM1 and the second camshaft position signal CAM2. The processor 15 monitors the crankshaft signal CRK1, the first camshaft position signal CAM1 and the second camshaft position signal CAM2 to identify predefined signal patterns as the internal combustion engine 2 is rotated. The predefined signal patterns occur when the crankshaft 6, the inlet camshaft 7 and the exhaust camshaft 8 are disposed in an identifiable known angular position. The predefined signal patterns thereby enable the absolute engine position to be determined. The predefined signal patterns comprise rising and/or falling edges in the first camshaft position signal CAM1 and/or the second camshaft position signal CAM2. The rising and/or falling edges may occur simultaneously or may be offset by a predetermined angular extent, as determined with reference to the crankshaft position signal CRK1. The predefined signal patterns may also comprise a change in the crankshaft position signal CRK1 as the missing tooth gap is detected.

The processor 15 uses the reference engine stop positions STP1-4 as additional parameters for identification of said predefined signal patterns. The processor 15 is configured to use each reference engine stop position STP1-4 as a potential (candidate) starting position for the engine during start-up. The processor 15 monitors the crankshaft position signal CRK1, the first camshaft position signal CAM1 and the second camshaft position signal CAM2 to detect one of said predefined signal patterns relative to each of the reference engine stop positions STP. As the internal combustion engine 2 is rotated, the processor 15 can be configured to identify one of said predefined signal patterns at predetermined angular positions relative to each said reference engine stop position STP1-4. The processor 15 initially seeks to identify the predefined signal patterns using all of the reference engine stop positions STP1-4 and, as the internal combustion engine 2 rotates, the candidate predefined signal patterns are reduced until one unique match is found which is indicative of the absolute engine position. The engine stop position can be used to determine which of the matches is most likely to be correct, and therefore achieve synchronisation earlier than would be possible by waiting for further engine rotation to find one unique match.

At least in certain operating scenarios, the processor 15 may utilise the reference engine stop positions STP1-4 to determine the absolute engine position with reduced rotation of the internal combustion engine 2. It will be understood that the processor 15 continues to monitor the first camshaft position signal CAM1 and/or the second camshaft position signal CAM2 to identify a unique signal pattern in the event that none of the predefined signal patterns are identified in relation to said reference engine stop positions STP. The internal combustion engine 2 will not always stop precisely at one of said predefined reference engine stop position STP1-4 and the processor 15 may be configured to identify the predefined signal pattern within a predetermined range, for example ±10°. The start-up procedure of the internal combustion engine 2 is conventional once the absolute engine position has been determined. Similarly, the operation of the control unit 1 to control fuelling and ignition is conventional after synchronisation is complete.

In order to expedite the start-up of the internal combustion engine 2, the crankshaft position sensor 9 and/or the first and second camshaft sensors 11,12 may be configured such that unique and valid absolute engine positions can be determined with minimal engine rotation from the predefined reference engine stop position STP1-4. By way of example, the crankshaft trigger wheel 10 and/or the first and second camshaft trigger wheels 13, 14 may be designed and oriented such that a predefined signal pattern is generated at engine positions proximal to one or more of the predefined reference engine stop positions STP1-4 where the internal combustion engine 2 is predisposed to stop. The predefined signal patterns should be generated as the internal combustion engine 2 is rotated from the reference engine stop positions STP1-4. The first and second camshaft trigger wheels 13, 14 may be configured such that predefined signal patterns may be generated when the engine position is equivalent to the reference engine stop positions STP1-4 plus a predetermined angular offset, say an offset of 30°. The first and second camshaft trigger wheels 13, 14 may be adapted such that two or more possible predefined signal patterns are spaced apart from each other as far as possible to make it easier to determine the correct match.

In a further development of the embodiment described herein, the control unit 1 may be configured to control shut-down of the internal combustion engine 2 such that stop position is within one of the engine stop sectors S1-4. A further refinement may be to control shut-down of the internal combustion engine 2 such that the stop position is at a particular location, for example within a particular one of the engine stop sectors S1-4.

Figure 4 illustrates an example of an engine system 20 comprising the control unit 1.

The engine system 20 comprises a rotatable shaft 21 synchronised with an engine cycle. The engine cycle comprises the rotation of the crankshaft 6, in a single direction, over 720°. The rotatable shaft 21 may be rotated over 720° in the same time period or may be rotated at, for example, half the rate, thus rotating over 360° in a first direction of rotation. In some examples, such as the example illustrated in figure 5, the rotatable shaft 21 is the first camshaft 13 as hereinbefore described.

A starter motor 22 rotates the rotatable shaft 21 in the first direction of rotation. During startup, the starter motor output a torque 23 which causes the rotatable shaft 21 to be rotated in the first direction of rotation. In some examples, the starter motor 22 transmits the torque 23 directly to the rotatable shaft 21 and in other examples the torque 23 is transmitted towards the rotatable shaft 21 via intervening components which rotationally couple the output of the starter motor 22 with the rotatable shaft 21. In some examples, these intervening elements comprise the crankshaft 6.

A rotatable encoder element 24 is synchronised with the rotatable shaft 21. In some examples the encoder element 24 comprises a tooth or missing tooth on a trigger wheel such as the crankshaft trigger wheel 10 or the first and second camshaft trigger wheels 13, 14, as hereinbefore described. In some examples the encoder element may be a single tooth or missing tooth, measurably distinct from other encoder elements on the trigger wheel, if any, by virtue of its angular extent around the trigger wheel. In some examples the encoder element may be a sequence of teeth or missing teeth, measurably distinct from other encoder elements on the trigger wheel, if any, by virtue of a unique sequence.

The engine system 20 is configured such that the encoder element 24 stops within a range of angular positions when the engine 2 is shut down.

The engine system 20 comprises a detector 26 which is configured to transmit a signal indicative of the encoder element passing the detector. The detector 26 is located at a detection position 27.

The detector 26 may in some examples comprise one or more of the crankshaft position sensor 9 and first and second camshaft sensors 11, 12 which, as hereinbefore described, respectively output the crankshaft position signal CRK1 and first and second camshaft position signals CAM1, CAM2 to the control unit 1 which identifies a specific unique engine position based on the correspondence of the received signal patterns with predefined signal patterns.

The detection position 27 is offset, in the first direction of rotation, relative to an upper limit in the first direction of rotation of a range of angular positions in which the encoder element 21 is configured stop when the engine 2 is shut down such that, during start-up, the encoder element 24 is rotated in the first direction of rotation, by the action of the starter motor 22, towards the detection position 27.

The offset between the upper limit in the first direction of rotation of the range of angular positions and the detection position 27 is minimised so that the time for the detector 26 to output a signal with a pattern which can be recognised as one of the predefined signal patterns is minimised. The time to synchronise the control unit 1 with the engine 2 is therefore also minimised and control of fuelling and the ignition of fuel in a cylinder 4 can be initiated sooner.

The size of the offset between the upper limit in the first direction of rotation of the range of angular positions the detection position 27 is less than 45°. In some examples the size of the offset is set to be less than 15°.

In some such examples the offset is a function of the uncertainty in the position in which the engine 2 is configured to be stopped. Such uncertainty arises from how precisely engine shut-down can be controlled. Additionally, the engine 2 may be rotated during a time period between being stopped and being required to be restarted, for example as a result of vibrations in the vehicle 3, such that the encoder element 24 moves within the range of angular positions in which it was stopped. Therefore, the exact position of the engine 2 is unknown when the engine 2 is required to be restarted. The size of the offset may therefore be set according to the expected degree of rotation of the engine between being stopped and being required to be restarted.

It will be appreciated that the size of the offset will also be dependent upon the particular specifications and operating conditions of the engine 2, and that however the offset is set, the size of the offset will vary between different engines.

In an alternative embodiment, the control unit 1 controls engine shut-down such that the encoder element 24 has a target stop position 25 when the engine 2 is shut-down. The encoder element 24 is stopped in the target stop position 25 at a time when the engine 2 is at rest. The target stop position 25 is, in some examples, an orientation about an axis on which the rotatable shaft 21 is rotated.

The detection position 27 is offset, in the first direction of rotation, relative to the target stop position 25 such that, during start-up, the encoder element 24 is rotated from the target stop position 25, in the first direction of rotation, by the action of the starter motor 22, towards the detection position 27.

The offset between the target stop position 25 and the detection position 27 is minimised so that the time for the detector 26 to output a signal with a pattern which can be recognised as one of the predefined signal patterns is minimised. The time to synchronise the control unit 1 with the engine 2 is therefore also minimised and control of fuelling and the ignition of fuel in a cylinder 4 can be initiated sooner.

The size of the offset between the target stop position 25 and the detection position 26 is less than 180°. In some examples the offset is an acute angle. In some examples the size of the offset is set to be less than 10°.

The size of the offset is selected so that the encoder element 24 will be stopped such that the detection position is offset, in the first direction of rotation, relative to the target stop position, said offset being less than 180°. In some such examples the offset is a function of the uncertainty in the reference engine stop position(s). In some examples, the size of the offset may be set larger than, for example, 10° due to the uncertainty in the position in which the engine 2 is controlled to be stopped. Such uncertainty arises from how precisely engine shut-down can be controlled. For example, as hereinbefore described, the engine 2 may be controlled to stop within an engine stop sector S1-4. The angular range of such sectors is, in some examples, approximately 45°. As such the size of the offset may be set at 45°.

Figure 5 illustrates an example of the vehicle engine system 20. As illustrated, in figure 5, the encoder element 24 is one of a plurality of encoder elements 24. Each encoder element 24 corresponds to one of a number of angular positions in which the engine 2 is configured to stop following shut down. As illustrated in figure 5, each of the plurality of encoder elements 24 is measurably distinct, e.g., one is of greater angular extent around the trigger wheel than the others and one comprises a sequence of two teeth. The detection of each of the three encoder elements illustrated in figure 3 yields different signal patterns which can be used by the control unit to determine the unique engine position. The plurality of encoder elements 24 are arranged, on the trigger wheel, such that one of the plurality of encoder elements 24 stops within a range of angular positions whenever the engine 2 is shut-down.

It is to be appreciated that the pattern of encoder elements 24 arranged on the trigger wheel in figure 5 is merely one example and different number of encoder elements, including a just a single encoder element, and different measurable distinctions between the encoder elements 24 are possible.

The control unit 1 may control a lift characteristic of one or more valves 29 in a continuous variable valve lift system 28 so as to manage air charge in at least one cylinder 4 of the engine 2. The air charge is managed so as to effect an engine stop position which causes the encoder element 24 to stop in a target stop position 25. For example, the lift characteristic is modified for an intake valve on a cylinder 4 in which the piston is about to commence the intake stroke so as to resist the downward motion of the piston from the top dead centre position. Alternatively or in addition the lift characteristic is modified for an exhaust valve on a cylinder 4 in which the piston is about to commence the exhaust stroke so as to resist the upwards motion of the piston from the bottom dead centre position.

The control unit 1 is configured to control engine shut-down to stop the engine 2 in any one of a plurality of reference engine stop positions. Particularly in examples where the engine 2 comprise a plurality of cylinders 4, the intake or exhaust valves may be controlled in the manner hereinbefore described on a cylinder by cylinder basis, resulting in a plurality of reference engine stop positions in which the engine 2 can be readily controlled to stop during engine shut-down.

In the example of figure 5, the trigger wheel is the first camshaft trigger wheel 13 and the detector 26 comprises the first camshaft sensor 11. The camshaft 7 and thus the camshaft trigger wheel 13 rotates through one full revolution (360°) over the course of the engine cycle and thus there is no inherent degeneracy in the camshaft position signal CAM1. The camshaft signal CAM1 can be used alone to determine the specific unique engine position with high certainty.

In contrast, a crankshaft 6 completes two full rotations over the course of an engine cycle and thus a unique engine position cannot be obtained solely from the rotation of the crankshaft 6. At best, using the rotation of the crankshaft 6 alone, the engine position can be narrowed down to two possibilities. Since the crankshaft position signal CRK1 provides a very accurate measurement of the engine position, albeit with high uncertainty, in some examples the crankshaft position signal CRK1 is also used in addition to the camshaft position signal CAM1 so as to improve the accuracy of the determine specific unique engine position.

So as to reduce the time to obtain an accurate determination of the specific unique engine position, one or more further encoder elements (not shown) are also, in some examples, arranged on the crankshaft trigger wheel 10 such that whenever the engine 2 is shut-down, one of the further encoder elements stops in a position which is offset from the detection position of the crankshaft position sensor 9, in the direction opposite to the direction in which the crankshaft will be rotated, by action of the starter motor, during start-up. Thus, during start-up, the time until the further encoder element reaches the detection position of the crankshaft position sensor 9 is minimised.

It will be appreciated that various modifications may be made to the embodiment(s) described herein without departing from the scope of the appended claims.

Claims

CLAIMS:

1. A control unit for controlling an internal combustion engine comprising at least one cylinder having an associated piston, a crankshaft and at least one camshaft, the control unit comprising:

wherein the at least one processor is configured to identify one or more reference engine stop position and, during start-up of the internal combustion engine, to determine an absolute engine position in dependence on said one or more reference engine stop position in combination with the crankshaft position signal and/or the at least one camshaft position signal.

2. A control unit as claimed in claim 1, wherein, during start-up of the internal combustion engine, the at least one processor is configured to determine the absolute engine position by monitoring said crankshaft position signal and/or said at least one camshaft position signal as the internal combustion engine is rotated.

3. A control unit as claimed in claim 2, wherein the at least one processor is configured to identify a predefined signal pattern in said crankshaft position signal and/or said at least one camshaft position signal in relation to said one or more reference engine stop position.

4. A control unit as claimed in claim 3, wherein the at least one processor is configured to identify said predefined signal pattern in dependence on detection of a change and/or an absence of change in the crankshaft position signal; and/or a change and/or an absence of change in said at least one camshaft position signal.

5. A control unit as claimed in claim 4, wherein the at least one processor is configured to identify said predefined signal pattern in dependence on angular rotation of the crankshaft from said one or more reference engine stop position.

6. A control unit as claimed in any one of the preceding claims, wherein the one or more reference engine stop position is predefined.

Ί. A control unit as claimed in any one of the preceding claims, wherein the at least one processor is configured to control shut-down of the internal combustion engine to target an engine stop position coincident with or proximal to said one or more reference engine stop position.

8. A control unit as claimed in any one of claims 1 to 5, wherein the at least one processor is configured to determine said one or more reference engine stop position during shut-down of the internal combustion engine.

9. A control unit as claimed in any one of the preceding claims, wherein the at least one processor is configured to control shut-down of the internal combustion engine to target an engine stop position to facilitate start-up of the internal combustion engine.

10. A vehicle comprising a control unit as claimed in any one of the preceding claims.

11. A method of controlling an internal combustion engine comprising at least one cylinder having an associated piston, a crankshaft and at least one camshaft, the method comprising:

identifying one or more reference engine stop position; and determining an absolute engine position in dependence on said one or more reference engine stop position in combination with a crankshaft position signal and/or at least one camshaft position signal.

12. A method as claimed in claim 11 comprising determining the absolute engine position by monitoring said crankshaft position signal and/or said at least one camshaft position signal as the internal combustion engine is rotated.

13. A method as claimed in claim 12 comprising identifying a predefined signal pattern in said crankshaft position signal and/or said at least one camshaft position signal in relation to said one or more reference engine stop position.

14. A method as claimed in claim 13 comprising identifying said predefined signal pattern in dependence on detection of a change in the crankshaft position signal and/or a change in said at least one camshaft position signal.

15. A method as claimed in claim 14 comprising identifying said predefined signal pattern in dependence on angular rotation of the crankshaft from said one or more reference engine stop position.

16. A method as claimed in any one of claims 11 to 15, wherein the one or more reference engine stop position is predefined.

17. A method as claimed in any one of claims 11 to 16 comprising controlling shutdown of the internal combustion engine to target an engine stop position coincident with or proximal to said one or more reference engine stop position.

18. A method as claimed in any one of claims 11 to 15 comprising determining said one or more reference engine stop position during shut-down of the internal combustion engine.

19. A method as claimed in any one of claims 11 to 18 comprising controlling shutdown of the internal combustion engine to target an engine stop position to facilitate start-up of the internal combustion engine.

20. A system comprising: an engine;

an encoder synchronised with a cycle of the engine, the encoder having a first direction of rotation during normal operation of the engine and having a distinctive element, the encoder being configured such that the distinctive element stops within a range of angular positions when the engine is shut-down;

a detector configured to transmit a signal indicative of the distinctive element of the encoder passing the detector; wherein the position of the detector is offset in the first direction of rotation from the upper limit in the first direction of rotation of the range of angular positions within which the distinctive element of the encoder is configured to stop when the engine is shut down, the offset being less than 45°.

21. A system as claimed in claim 20, wherein the offset is less than 15°.

22. A system as claimed in claim 20 or 21, wherein the encoder has a plurality of distinctive elements and the encoder is configured such that one of the plurality of distinctive elements is configured to stop in the range of angular positions when the engine is shutdown.

Intellectual

Property

Office

Application No: GB1720594.9 Examiner: Bryce D'Souza