Method for the synchronisation of an internal combustion engine

Abstract: The present invention relates to the synchronisation of an internal combustion four-stroke engine (1) during engine start up. The engine (1) comprises a number of cylinders (11-14) with pistons (I-IV) linked to a crankshaft (36), means (32,33,34) to provide a series of pulses (30) on each cycle of the engine (1), and an engine management system (10) that includes: a memory (44); means (10,29,32) to determine the engine cycle after the engine (1) is cranked; and means (9) to count thereafter the series of pulses (30) until the engine comes to a stop in order to determine the engine cycle of the engine (1) when subsequently stopped so that data representative of the engine cycle may be stored in the memory (44). According to one aspect of the invention, the means (10,29,32) to determine the engine cycle after the engine (1) is cranked is a means to determine the engine cycle during running of the engine. According to another aspect of the invention, the means (10,29,32) to determine the engine cycle after the engine is cranked includes a memory (44) that stores data representative of the engine cycle of the engine before the engine was cranked.

Description: The present invention relates to the synchronisation of an internal combustion four-stroke engine during engine start up. When a fuel injection internal combustion engine is started, it is desirable to supply fuel and, for a gasoline engine, sparks to each cylinder in turn at the correct time in order to optimise performance and engine emissions. There are two common ways of determining the state of the engine cycle, either with a single sensor detecting the rotational position of the camshaft, or with a pair of sensors, one on the camshaft and the other on the crankshaft. The single sensor on the camshaft is relatively expensive, and also has to be timed in to provide the required accuracy. The alternative approach uses cheaper sensors that do not have to be timed in, but the provision of two sensors adds manufacturing cost. Ideally, it would be desirable to use just one sensor, which does not need to be timed in: that is, a crankshaft sensor alone. The crankshaft sensor gives an accurate signal according to the angular position of the crankshaft, but in a four-stroke engine cannot unambiguously determine engine cycle. For example, in a four-cylinder engine, the crank signal cannot discriminate between cylinder pairs 1 and 4, or 2 and 3. Patent documents US 5,425,340 and US 5,613,473 disclose ways of addressing the problem of determining engine cycle when there is just a crankshaft sensor. In both of these disclosures, an engine management system purposely causes a misfire on one or more cylinders. This causes a drop in engine power immediately following the misfire, and a consequent small drop in engine speed, which can be detected from the crankshaft signal. Although this approach is effective in determining engine cycle, the misfiring is noticeable to the driver, who will interpret such misfires upon start up of the engine as an engine fault. Furthermore, such misfires adversely affect the emissions performance of a motor vehicle engine. Although such misfires during cranking of the engine may not affect rated emissions performance in the case where this performance is measured during steady running of the engine, such misfires will affect the rated performance for stricter regulations including the period from when an engine is first started. It is an object of the present invention to provide a more convenient way of synchronising an internal combustion engine upon start up of the engine. According to the invention, there is provided a four-stoke internal combustion engine, comprising a number of cylinders with pistons linked to a crankshaft, means to provide a series of pulses on each cycle of the engine, and an engine management system that includes: a memory; means to determine the engine cycle after the engine is cranked; the engine management system further comprising means to count thereafter the series of pulses until the engine comes to a stop in order to determine the engine cycle of the engine when subsequently stopped so that data representative of the engine cycle may be stored in the memory; characterised in that the amplitude of the series of pulses varies in proportion with rotational speed of the crankshaft, and wherein the means to count the pulses includes predictive means to extrapolate from the falling frequency and amplitude of the pulses, as the engine comes to a stop, the engine cycle for the last pulse, and in which the means to count pulses determines, in addition to the engine cycle, the engine angle of the stopped engine, so that data representative of the stopped engine angle may be stored in the memory. The means to determine the engine cycle after the engine is cranked may include a means to determine the engine cycle during running of the engine, for example some time after cranking of the engine. The means to determine the engine cycle after the engine is cranked may also includes a memory that stores data representative of the engine cycle of the engine before the engine was cranked. The means to measure the rotation of the engine may include a sensor that measures the revolution of the crankshaft, said sensor producing as an output the series of pulses on each revolution of the crankshaft. The memory is preferably a non-volatile memory such as an EEPROM or flash memory, and may optionally be integrated with the engine management system. The sensor may be arranged to measure directly the rotation of the crankshaft. For example, the crankshaft may have a toothed wheel, the sensor being arranged to detect the passage of said teeth as the crankshaft rotates. The sensor is preferably a non-contact type of sensor such as a variable reluctance sensor (VRS). Variable reluctance sensors are less expensive and provide an output signal with an amplitude that varies in direct proportion with the crankshaft rotational speed. The predictive means may be an empirically derived algorithm, or a look-up table, constructed according to the measured performance of the sensor arrangement. It is therefore possible to compensate for the variability in pulse amplitude such that the final resting position of the crankshaft may be determined, for example to an accuracy defined by the number of pulses output per revolution of the crankshaft. When the engine is started, the engine management system may use the series of pulses, for example pulses output from the crankshaft sensor, and said data stored in the memory, to synchronise fuel delivery to the cylinders. In the case of a direct or indirect injection engine, the synchronisation may include timing of fuel injection events. Similarly, for a spark ignition engine, the synchronisation may include cylinder spark events. Synchronisation may therefore be achieved rapidly upon start up of the engine, so improving engine performance including emissions performance as the engine is started. Also according to the invention, there is provided a method of synchronising a four-stoke internal combustion engine, the engine comprising a number of cylinders with pistons linked to a crankshaft, means to provide a series of pulses on each cycle of the engine, and an engine management system that includes: a memory; means to determine the engine cycle after the engine is cranked; and means to count the series of pulses; the method comprising the steps of: a) providing a series of pulses on each cycle of the engine; b) supplying the series of pulses to the engine management system; c) determining the engine cycle; d) thereafter counting the series of pulses until the engine comes to a stop in order to determine the engine cycle of the subsequently stopped engine; and then e) storing data representative of the engine cycle of the stopped engine in the memory; characterised in that the amplitude of the series of pulses varies in proportion with the rotational speed of the crankshaft, and wherein: f) the step of counting the pulses includes a predictive step to extrapolate from the falling frequency and amplitude of the pulses, as the engine comes to a stop, the engine cycle for the last pulse; and g) the step of counting the pulses also determines, in addition to the engine cycle, the engine angle of the stopped engine, data representative of the stopped engine angle then being stored in the memory. Step c) may involve determining the engine cycle during running of the engine, for example some time after cranking of the engine. Step c) may also involve storing in memory data representative of the engine cycle of the engine before the engine was cranked. When the engine is to be subsequently started, the data previously stored in memory may be recalled. Then when the engine is cranked, the engine management system can thereafter track or count the series of pulses in order to keep track of the engine cycle. This permits the fuel delivery to the cylinders to be synchronised according to the recalled data and the output from the means to provide a series of pulses. Optionally, in the case where the engine is a spark ignition engine, cylinder spark events may be synchronised according to the recalled data and the means to provide the series of pulses. The invention will now be described in further detail by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic drawing of a four-cylinder four-stroke internal combustion engine according to the invention, with an engine management system that receives an engine speed signal from a sensor that detects the passage of teeth on a crankshaft flywheel; Figure 2 are plots of the signal from the sensor, before and after digitization by the engine management system; Figure 3 is a flow diagram describing the control of the engine by the engine management system; Figures 4A and 4B are respectively plots of the sensor signal and the crankshaft angular velocity during a misfire of a cylinder; Figure 5A is a plot of the sensor signal as the engine comes to a stop; and Figure 5B is a plot of the sensor signal after digitization by the engine management system, and raw and corrected counts of threshold crossing of the digitized signal. Figure 1 shows schematically a four-cylinder, four-stroke internal combustion engine 1, having a multipoint injection device by which each of four cylinders 11,12,13,14 is supplied with fuel by an electro-injector 2, which may be a direct or an indirect injector. In this example, the engine 1 is a gasoline engine, and so is also equipped with spark plugs 4. The invention is, however, equally applicable to diesel engines, and to engines having a lesser or greater number of cylinders. The opening sequence and timing of each electro-injector 2 and spark plug 4 is controlled by an electronic engine management system 10, which determines the amount of fuel and timing of fuel and spark events depending on engine operating conditions. This engine control system 10 receives input signals, performs operations and generates output control signals, particularly for the fuel injectors 2 and spark plugs 4. The electronic engine management system 10 conventionally comprises a microprocessor (µP) 9, a random access memory (RAM) 15, a read only memory (ROM) 16, an analog-to-digital converter (A/D) 18 and various input and output interfaces, including a spark plug driver 20 and an injector driver 22. The input signals comprise a driver demand signal (DD) 24, an engine temperature signal (T) 26, an exhaust gas oxygen signal (EGO) 28 from an exhaust gas oxygen sensor 29, and a signal 30 from a variable reluctance sensor (VRS) 32, all of which are digitized by the A/D converter 18 prior to being passed to the microprocessor 9. With reference now also to Figure 2, which shows the VRS signal 30 for an engine running at 6250 rpm, the variable reluctance sensor 32 senses the passage of teeth 33 spaced circumferentially around the periphery of a flywheel 34 on an engine crankshaft 36. The flywheel 34 has a conventional arrangement of teeth referred to herein as 36-1 teeth, wherein thirty-five identical teeth 33 are equally spaced by thirty-four gaps between teeth, and with a one pair of teeth being spaced by a larger gap three times as large as the other gaps. The larger gap corresponds to one missing tooth. The VRS signal 30 therefore comprises a series of pulses for each revolution of the crankshaft, with one missing pulse, generally indicated at 38 in Figure 2. Digitization of the raw VRS signal 30 by the A/D converter 18 yields a digitized VRS signal 40, comprising a series of essentially square waves, with one missing pulse 42 corresponding to the missing pulse 38 in the raw VRS signal 30. The existence of the missing tooth allows the identification of a Top Dead Centre (TDC) position for the engine 1. For example, the falling edge of the last digitized pulse 44 before the missing pulse 42 may be at 90° before TDC. Conventionally, for a four-cylinder four-stroke engine having four corresponding pistons I,II,III,IV, the TDC position for the engine is also the TDC position of pistons I and IV, during one cycle of the engine, and TDC position of pistons II and III during the next cycle of the engine. Figure 1 shows pistons I and IV at the top dead centre position. It should be noted that in the example shown of an in-line four-cylinder four-stroke engine, exhibiting a firing order according to the sequence 1-3-4-2, pistons I and IV (or II and III) pass simultaneously to the TDC position, but with different phases from the engine cycle, one then being in the intake (or compression) phase, and the other being in the power (or exhaust) phase. Each piston passes through two cycles, each consisting of 360° of angle, during the four phases or stokes of the cylinder during the intake/compression and power/exhaust phases. The flywheel 34 turns through an angle of 720° during the two cycles, and the variable reluctance sensor 32 produces two pulses indicating a TDC position of the engine 1. It is therefore not possible from the VRS signal 30 alone to determine which of the two cycles a cylinder is in, even though the VRS signal gives a good measure of angle after one revolution of the flywheel 34. Once the engine cycle is known, however, it is in principle possible to keep track of the engine cycle by counting the series of pulses in the VRS signal 30. The term "counting" as used herein includes any means of keeping track of or distinguishing pulses so that the engine management system can discriminate between the two engine cycles. For example, for a four cylinder engine, the count could cycle repeatedly from one to four, as 1, 2, 3, 4, 1, 2, 3, etc. As will be explained in further detail below, the engine management system 10 therefore comprises means both to determine the engine cycle during running of the engine, and means to count the series of VRS pulses as the engine comes to a stop in order to determine the engine cycle of the stopped engine. Once the engine is stopped, data representative of the engine cycle, and optionally also the engine angle, are stored in a memory, here a non-volatile electronically erasable programmable read only memory (EEPROM) 44. When the engine is to be restarted, this data is recalled by the microprocessor 9, which together with the series of VRS pulses 30 as the engine starts to turn, allows the microprocessor to fire the engine with correct scheduling of fuel and spark events according to the sequence 1-3-4-2. Figure 3 shows a flow diagram of operation of the engine management system 10 and engine control software running in the microprocessor 9. When an engine is started for the very first time, the engine management system 10 has no record of the engine's resting cycle or angle. This lack of data is represented by a zero value stored in the EEPROM 44. Such a zero value may also be stored in the EEPROM 44 if the engine management system 10, for whatever reason, at some future date was unable to determine the resting cycle of the engine 1. When the driver turns the ignition key (not illustrated), the microprocessor receives a driver demand signal 24 instructing the microprocessor 9 to begin a sequence of operations 50 to start the engine 1. The microprocessor 9 retrieves data from the EEPROM 44, and tests 52 if this is non-zero. If the data is zero 54, then the microprocessor initiates 56 crank and firing of the engine 1 with fuel injection and spark events scheduled on each cycle of the engine for all cylinders 11-14, so that each cylinder receives two fuel injection commands and two spark events during the two cycles that consist of the four-strokes. The engine management system 10 then initiates 58 a procedure whereby the engine cycle is determined, so that each cylinder 11-14 can be supplied just once per two cycles with fuel and a spark event at the correct engine angles. The engine cycle may be determined quickly according to the teaching of US 5,425,340 or US 5,613,473, in which fuel is cut to one of the cylinders 11-14. With reference to Figures 4A and 4B, this will cause a drop in the expected VRS frequency and crankshaft angular velocity during the power stroke for that particular cylinder. Once the engine angle is determined, the microprocessor 9 continues to track or count the VRS pulses in order to keep track of the engine cycle. The microprocessor 9 can then supply 60 the cylinders 11-14 with fuel and spark events just once every two engine cycles at the correct engine angles. The microprocessor tests at intervals if the engine has been switched off 62. If the engine is running 64, then the microprocessor tests 66 the engine to verify that the engine cycle is still correct. Such a test may again be by depriving one cylinder of fuel and measuring the changes in the VRS signal. In general, this. will cause noticeable engine roughness. But such verification need not be rapid, since in all likelihood the engine cycle is still correctly known. The engine management system may therefore initiate a more subtle but slower test, such as running one cylinder rich and then monitoring the signal 28 from the exhaust gas oxygen (EGO) sensor 29, which is conventionally placed in an engine exhaust conduit 68. EGO sensors have a relatively rapid response time of 50-100 ms. If the cycle for a particular cylinder is correctly known, then the response at the EGO sensor 29 will appear at a time delay of approximately 500 ms after injection for that cylinder, for an engine running at about 1000 rpm. The delay is a sum of delays owing to the time taken during the fuel injection, induction stroke, compression stroke, combustion delay, and transport delay of exhaust gasses in the exhaust conduit 68. If the engine cycle is incorrectly known, then the time delay will be shorter by one cycle, or about 60 ms at an engine speed of 1000 rpm. The microprocessor 9 monitors the correlation between the injection time and the delay in the EGO signal response in order to verify that the cycle is correct. If the cycle is incorrect, then the engine management system 10 switches immediately to the correct cycle, and again monitors the EGO signal to verify that this is correct. Optionally, this method of synchronising the engine could be used the first time an engine is started, or whenever the value stored in the EERPROM is zero. As soon as the engine is switched off 70, the microprocessor 9 immediately starts a final count of VRS pulses 30, as illustrated in Figures 5A and 5B. As the engine slows down, the frequency and amplitude of the VRS pulses 30 each decline. The A/D converter 18 has 32 bit resolution and so can distinguish between positive going and negative going sinusoidal VRS pulses between a maximum of ± 20 Volts and a minimum of ± 0.1 Volts. The microprocessor 9 includes a programmable digital signal processor (not shown) which applies a noise filter with a high frequency cut-off that decreases as the expected VRS amplitude 72 drops, in order to help prevent false triggering as the amplitude of the VRS signal declines. Digital processing by the microprocessor 9 of the digitised VRS signal 40 allows positive going VRS pulses to be identified and counted 73, as shown in the top row of sequential integers labelled "C" in Figure 5B. In the example presented, the series of VRS pulses 30 in Figure 5A includes a missing pulse 38, and so there is no count in C at this location. A feature of the VRS pulses of the slowing engine is that the time between subsequent zero crossings 74 steadily increases, and so software running in the microprocessor can readily determine that pulse 38 is missing. The microprocessor therefore corrects the count C, labelled as count C' in Figure 5B. The final count of C' is then used by the microprocessor 9 to calculate the correct engine cycle-and optionally engine angle, which is then stored 78 in the EEPROM memory 44. Once an engine stops, it is generally the case that there will be some reverse movement of the flywheel 34 as pistons move to equalise forces gasses in cylinders 11-14. Such reverse movement will result in additional pulses 76 which when identified by the microprocessor result in the corrected count C' being decremented. It is, of course, not necessary to identify all such pulses. For example, if an engine flywheel has 36-1 teeth, then as long as the final count C' is accurate to ±17 teeth, the correct engine cycle can be accurately determined as soon as the engine is cranked and the first missing tooth 38 is detected in the VRS signal 30. As an alternative to detecting individual pulses as the amplitude and frequency drops to zero, the microprocessor 9 could calculate the envelope 72 of the waveform 30, and then either calculate or recall from a look-up table an extrapolated number of counts depending on the rate of decay of the envelope 72. Returning to consider the rest of Figure 3, the next time engine is to be started 50, the microprocessor reads 80 a non-zero value in the EEPROM 44, which is then loaded 82 into the microprocessor 9. When the engine is cranked 84 the microprocessor starts to track or count VRS pulses 30 as soon as these appear, in order to keep track of the engine cycle. The stored data is then used together with the VRS pulses 30 to fire the engine with fuel injection and spark events supplied sequentially for each cylinder 11-14 at the correct times during the four strokes of each cylinder. The engine is then operated as described before, with periodic verification 66 of the correct engine cycle and final count of VRS pulses 73 being stored 78 in the EEPROM 44. Thus, although the initial calibration of engine cycle in step 58 of Figure 3 may cause a noticeable roughness in the engine, once the engine cycle is known this information is stored for future use whenever the engine is re-started. The initial calibration 58 therefore does not normally need to be repeated. The apparatus and method according to the invention thereby permit the engine cycle to be determined in normal operation of the engine without the need to cause intentional misfires of a cylinder, except when an engine is started for the first time. Compared with systems that need to determine engine cycle each time after starting of the engine, the invention also permits an improvement in emission immediately upon start up of the engine. Since known engine management systems are typically equipped with microprocessors in order to handle complex computational and control operations, the changes or additions to be made to carry out the described method of synchronisation can be attained essentially by changes and additions to the existing microprocessor programs.

Claims: A four-stroke internal combustion engine (1), comprising a number of cylinders with pistons (I-IV) linked to a crankshaft (36), means (32,33,34) to provide a series of pulses (30) on each cycle of the engine (1), and an engine management system (10) that includes: a memory (44); means (10,29,32) to determine (58,82) the engine cycle after the engine (1) is cranked; the engine management system (10) further comprising means (9) to count (66) thereafter the series of pulses (30) until the engine (1) comes to a stop in order to determine (73) the engine cycle of the engine (1) when subsequently stopped so that data representative of the engine cycle may be stored (78) in the memory (44); characterised in that the amplitude (72) of the series of pulses (30) varies in proportion with rotational speed of the crankshaft (36), and wherein the means (9) to count the pulses (30) includes predictive means (9) to extrapolate from the falling frequency and amplitude of the pulses (30), as the engine (1) comes to a stop, the engine cycle for the last pulse, and in which the means (9) to count pulses (30) determines, in addition to the engine cycle, the engine angle of the stopped engine (1), so that data representative of the stopped engine angle may be stored in the memory (44). A four-stroke internal combustion engine (1) as claimed in Claim 1, in which the means (10,29,32) to determine the engine cycle after the engine is cranked is a means (10,29,32) to determine (58) the engine cycle during running of the engine (1). A four-stroke internal combustion engine (1) as claimed in Claim 1, in which the means (10,29,32) to determine (82) the engine cycle after the engine (1) is cranked includes a memory (44) that stores data representative of the engine cycle of the engine (1) before the engine (1) was cranked. A four-stroke internal combustion engine (1) as claimed in Claim 3, in which the engine management system (10) uses the series of pulses (30) as the engine (1) is started and said data stored in the memory (44) and representative of the engine cycle of the engine (1) before the engine (1) was cranked, to synchronise fuel delivery to the cylinders. A four-stroke internal combustion engine (1) as claimed in Claim 4, in which the engine is a spark ignition engine (1) wherein the engine management system (10) uses said data stored in memory (44) and representative of the engine cycle of the engine (1) before the engine (1) was cranked when the engine (1) is started, also to synchronise cylinder spark events. A four-stroke internal combustion engine (1) as claimed in any preceding claim, in which the means (32,33,34) to provide a series of pulses (30) on each cycle of the engine (1) include a sensor (32) that measures the revolution of the crankshaft (36), said sensor (32) producing as an output the series of pulses (30) on each revolution of the crankshaft (36). A four-stroke internal combustion engine (1) as claimed in Claim 6, in which the crankshaft (36) has a toothed wheel (33,34), the sensor (32) being arranged to detect the passage of said teeth (33) as the crankshaft (36) rotates. A method of synchronising a four-stoke internal combustion engine (1), the engine (1) comprising a number of cylinders (11-14) with pistons (I-IV) linked to a crankshaft (36), means (32,33,34) to provide a series of pulses (30) on each cycle of the engine (1), and an engine management system (10) that includes: a memory (44); means (10,29,32) to determine (58,82) the engine cycle after the engine (1) is cranked; and means (9) to count the series of pulses (30); the method comprising the steps of: a) providing a series of pulses (30) on each cycle of the engine (1); b) supplying the series of pulses (30) to the engine management system (10); c) determining (58,82) the engine cycle; d) thereafter counting (66,73) the series of pulses (30) until the engine (1) comes to a stop in order to determine (73) the engine cycle of the subsequently stopped engine (1); and then e) storing (78) data representative of the engine cycle of the stopped engine (1) in the memory (44); characterised in that the amplitude (72) of the series of pulses (30) varies in proportion with rotational speed of the crankshaft (36), and wherein: f) the step (66,73) of counting the pulses (30) includes a predictive step (9) to extrapolate from the falling frequency and amplitude of the pulses (30), as the engine (1) comes to a stop, the engine cycle for the last pulse; and g) the step (66,73) of counting the pulses (30) also determines (73), in addition to the engine cycle, the engine angle of the stopped engine (1), data representative of the stopped engine angle then being stored (78) in the memory (44). A method of synchronising a four-stroke internal combustion engine (1) as claimed in Claim 8, in which step c) involves determining (58) the engine cycle during running of the engine (1). A method of synchronising a four-stroke internal combustion engine (1) as claimed in Claim 8, in which the step c) involves storing (78) in memory (44) data representative of the engine cycle of the engine (1) before the engine (1) was cranked. A method of synchronising a four-stoke internal combustion engine (1) as claimed in Claim 10, in which the method further comprises: h) recalling (82) from the memory (44) said data representative of the engine cycle of the engine (1) before the engine (1) was cranked; i) cranking (84) the engine (1); and then j) using the series of pulses (30) as the engine (1) is started and said recalled data (44) representative of the engine cycle of the engine (1) before the engine (1) was cranked to synchronise fuel delivery to the cylinders (11-14). A method of synchronising a four-stroke internal combustion engine as claimed in Claim 11, in which the engine is a spark ignition engine and wherein step j) includes using the series of pulses (30) as the engine (1) is started and said recalled data (44) representative of the engine cycle of the engine (1) before the engine (1) was cranked, also to synchronise cylinder spark events.

Inventors: GARRARD MICHAEL ROBERT, MARSHALL RAY CHARLES, GARRARD, MICHAEL ROBERT, MARSHALL, RAY CHARLES
Applicants: FORD MOTOR CO, FORD WERKE AG, GROUPE FORD FRANCE S A, MOTOROLA LTD, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT, GROUPE FORD FRANCE S.A., MOTOROLA LIMITED
Application year: 1999
Main classification: F02D41
IPC codes: F02D41