EP1710421A1

EP1710421A1 - Method and system for internal combustion engine

Info

Publication number: EP1710421A1
Application number: EP05102698A
Authority: EP
Inventors: Anna Pernest L; Mats JÄRGENSTEDT
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2005-04-06
Filing date: 2005-04-06
Publication date: 2006-10-11

Abstract

Method for determining where in its operating cycle at least one cylinder of a four-stroke internal combustion engine that has an odd number of cylinders is located. Said at least one cylinder drives a crankshaft on which a flywheel (1), that rotates through two revolutions (i,ii) during every four-stroke operating cycle, is mounted. The method comprises the step of; determining the rotational speed (ω) of the flywheel (1) or a value corresponding thereto as the flywheel (1) rotates through a given rotational angle (α), determining the present phase of the flywheel (1) and then determining whether the present phase of the flywheel (1) corresponds to the phase of the ordinary oscillation of the flywheel (1) during its first revolution (i) or whether it corresponds to the phase of the ordinary oscillation of the flywheel (1) during its second revolution (ii) for determining where in its operating cycle said at least one cylinder is.

Description

Technical field

The present invention concerns a system and method for determining where in its operating cycle or in which cycle position, at least one cylinder of a four-stroke internal combustion engine that has an odd number of cylinders is located. The invention also re-lates to a vehicle, an electronic control unit (ECU), a computer program and a computer program product.

Background art

In internal combustion engines of the four-stroke type the camshaft rotates at half the crankshaft speed, which means that the rotary position of the camshaft at any moment clearly indicates where in its operating cycle a given cylinder i.e. the piston in a cylinder, is located. By studying the rotary position of the camshaft, it is therefore possible to determine whether the position of a cylinder is to be assigned to the first or the second crankshaft revolution in each operating cycle of the cylinder.
By means of camshaft sensors, it is therefore possible to provide an electronic control unit for a fuel injection system with reliable information about the cycle position in a cylinder, so that fuel injection can always take place at the correct time. In an internal combustion engine of the four-stroke type, an operating cycle of two crankshaft revolutions is performed for each cylinder and ignition takes place once in each cylinder every other crankshaft revolution. In cases where this type of engine is provided with fuel injection, it is important that fuel injection and ignition in each cylinder take place when the cylinder is located in the correct position. This is particularly important if fuel injection takes place electrically and is independent on the camshaft, as in so called "Common Rail" systems in which cylinders are located on a single high-pressure rail. However, such camshaft sensors are relatively difficult to install and to make sufficiently robust. In electronic fuel injection systems, the failure of such a camshaft sensor can result in functional problems, as the possibility of determining the cycle position is thus lost.
It has also been found to be difficult to use only flywheel sensors as uncertainty arises about which of two crankshaft revolutions the engine is in at the time. A flywheel, that transmits the output of the engine to an external component such as a clutch or transmission, is mounted on the crankshaft and rotates through two revolutions during each four-stroke cycle while a camshaft rotates through one revolution. This means that when a motor is started a cylinder's position is known but it is not known whether the cylinder is in an exhaust stroke or compression stroke or whether it is in an intake or combustion stroke.
Another problem in this context is that an electronic control unit, for example in connection with being started or after a programming change or the like, has to check the position in which the crankshaft last stopped since the crankshaft may, since the engine stopped, have been rotated as a result of the vehicle having been moved with a gear engaged. If the crankshaft position is not checked the control unit may misinterpret the situation and operate in an incorrect cycle position.
US 6595193 discloses a multiple cylinder four-stroke engine with fuel injection in which an interference oscillation is generated briefly on the flywheel on starting by temporarily varying the fuel supply to different cylinders so that some cylinders receive more fuel and others receive less. After oscillation analysis of the resultant oscillation of the flywheel, phase positions of the superimposed interference oscillation and of the interference oscillation are compared. If predetermined phase positions of the oscillations appear, the engine is considered to be operating in the correct cycle position, but otherwise a control unit is initiated to correct its cycle position so that the correct cycle position of the engine is obtained.
A disadvantage with such a method is that fuel has to be injected into the cylinders in order to determine their positions, which increases emissions on starting and increases the wear and tear on engine components. Furthermore such a method is relatively slow and reliable analysis may take up to 12 seconds at the beginning of a starting operation.

Disclosure of the invention

The object of the present invention is to provide a method for reliably determining where in its operating cycle at least one cylinder of a four-stroke internal combustion engine which has an odd number of cylinders, i.e. one, three, five, seven etc, is located, where said at least one cylinder drives a crankshaft on which a flywheel, that rotates through two revolutions during every four-stroke operating cycle, is mounted.
This object is fulfilled using a method according to claim 1, namely a method that comprises the step of determining the rotational speed of the flywheel or a value corresponding to the rotational speed of the flywheel as it rotates through a given rotational angle i.e. one or more revolutions or a part thereof. The method also comprises the step of determining the present phase of the flywheel by determining the, or each rotational angle at which the rotational speed of the flywheel reaches a predetermined value, such as its maximum or minimum rotational speed. Alternatively the present phase of the flywheel is determined by determining the number of times the flywheel reaches a predetermined value, such as its maximum or minimum rotational speed as the flywheel rotates through said given rotational angle. The method comprises the further step of determining whether the present phase of the flywheel corresponds to, i.e. is in phase with, the phase of the ordinary oscillation of the flywheel during its first revolution or whether it corresponds to, i.e. is in phase with, the phase of the ordinary oscillation of the flywheel during its second revolution. Since each ordinary oscillation revolution corresponds to a particular half of the cylinder's operating cycle, it is possible to determine whether said at least one cylinder is in a compression stroke or an exhaust stroke, or whether said at least one cylinder is in an intake stroke or a combustion stroke.
It should be noted that fuel does not need to be injected into the cylinders while the position of the cylinders is being ascertained because the movement of each cylinder during each four-stroke operating cycle affects the rotational speed of the flywheel even if no fuel is injected into the cylinder. The linear speed of the piston in the cylinder and consequently the rotational speed of the flywheel decrease during the compression stroke while the fuel/air mixture is being compressed due to the resistance to motion experienced by the piston. During the exhaust stroke there is virtually no resistance to the motion of the piston and therefore no decrease in the speed of the flywheel. The engine therefore merely has to be rotating or be brought to rotate in order for the location of at least one of its cylinders to be determined. However the inventive method may also be used while fuel is injected into said at least one cylinder. The inventive method allows the location of said at least one cylinder of an engine to be determined very quickly.
It should also be noted that the expression "determining the rotational speed of the flywheel or a value corresponding to the rotational speed of the flywheel" is to be interpreted broadly. It is not necessary that an actual rotational speed is determined but it is sufficient to merely determine a change in the rotational speed of the flywheel for example. The rotational speed of the flywheel or said value corresponding to the rotational speed of the flywheel is determined directly from the flywheel or indirectly by determining the rotational speed of some other component, such as the crankshaft on which the flywheel is mounted or a value corresponding thereto. The inventive method is furthermore applicable to any type of engine i.e. both of the Common Rail type and of non Common Rail type.
According to a further embodiment of the invention the method comprises the step of initiating fuel injection or combustion when said at least one cylinder is found to be in the correct position in its operating cycle. Using the inventive method no fuel is ever injected into said at least one cylinder at the wrong time, which minimises emissions when an engine is started.
According to an embodiment of the invention the phase of the flywheel is determined by determining the rotational angle at which the rotational speed of the flywheel first reaches a predetermined value, such as its maximum or minimum value. This means that a flywheel only needs to be rotated through part of one revolution before the phase of the flywheel and consequently the position of said at least one cylinder is ascertained. According to a further embodiment of the invention said given rotational angle through which the flywheel is rotated is $\frac{720 °}{N}$

where N is the number of cylinders in the engine. For an engine comprising three cylinders, said given rotational angle through which the flywheel is rotated is 240° for example and for an engine comprising five cylinders, said given rotational angle through which the flywheel is rotated is 144°.
According to another embodiment of the invention a bandpass filter is used to obtain a signal that shows the rotational speed of the flywheel as it rotates through a given rotational angle.
The present invention also concerns a system for determining where in its operating cycle at least one cylinder of a four-stroke internal combustion engine that has an odd number of cylinders is located, where said at least one cylinder drives a crankshaft on which a flywheel, that rotates through two revolutions during every four-stroke operating cycle, is mounted.
According to an embodiment of the invention the system also comprises means to indicate, by means of a visible or audible signal, to a driver or mechanic for example, that said at least one cylinder is in a particular position in its operating cycle.
The present invention furthermore relates to a computer program and a computer program product. Embodiments of the computer program, computer program product and further embodiments of the system are disclosed in the attached claims.
The present invention also concerns an electronic control unit (ECU) that comprises execution means, a memory and data storage means whereby a computer program according to any of the embodiments of the invention is stored in said data storage means. Finally the present invention even relates to a vehicle that comprises a system according to any of the embodiments of the invention and/or an ECU according to any of the embodiments of the invention.
The method, system, computer program and ECU according to the present invention are intended for use particularly, but not exclusively, to determine when to inject fuel into said at least one cylinder of a four-stroke internal combustion engine that has an odd number of cylinders.
Further advantages as well as advantageous features of the in-vention appear from the following description and the other de-pendent claims.

Brief description of the drawings

Fig 1 is a block diagram of a system according to an embodiment of the invention,
Fig. 2 shows the ordinary speed variation of a flywheel in a four-stroke internal combustion engine with five cylinders, and
Fig. 3 is a flow chart of a method according to an embodiment of the invention.
It should be noted that figure 1 has not been drawn to scale and that the size of certain features has been exaggerated for the sake of clarity.
The following description and drawings are not intended to limit the present invention to the embodiment disclosed. The embodiment disclosed merely exemplifies the principles of the present invention.

Detailed description of an embodiment of the invention

Figure 1 shows a flywheel 1 of a four stroke internal combustion engine (not shown) with fuel injection that is provided with a number of indications 2 in the form of teeth. Other indications such as slots or markings could be used. The indications are distributed around the circumference of the flywheel 1 and are read off by a rotation angle sensor 3 during the rotation of the flywheel 1 so as to determine the rotational position of the flywheel as a function of time. The flywheel 1 is provided with a special indication 4 in a particular position, which tells the sensor 3 that the flywheel has rotated one revolution since the indication 4 last passed. By means of the sensor 3 and the indications 2, 4, the current rotary position of the flywheel can be established and, moreover, oscillations can be read off. A bandpass filter 5 analyses the oscillations obtained in the flywheel 1.
The bandpass filter 5 is contained inside an ECU 6. The ECU 6 evaluates the information from the sensor and controls a fuel injection arrangement 7, by means of which the cylinders are provided with fuel at the correct moment. In the case of a diesel engine, ignition is also obtained at the correct moment. In the case of an Otto engine, the system also includes an ignition system 8 which is controlled by the ECU 6 and by means of which ignition is carried out at the correct time.
Figure 2 shows the ordinary speed variation on the flywheel 1 in an engine with five cylinders with which the present phase of the flywheel 1 is compared. In the case where fuel is injected into the cylinders while their location is being determined, the ordinary ignition pulse-generated speed variation is of the same form as that shown in figure 2.
The curve A shows how the speed (ω) of the flywheel 1 varies at normal idling speed during two crankshaft revolutions as different cylinders move. The vertical axis indicates the speed (ω) of the flywheel 1 and the horizontal axis indicates the number of crankshaft degrees (α) from the position in which the first cylinder in the ignition sequence normally ignites, which takes place at 0°.
After the first cylinder has moved through its combustion stroke, the other cylinders move in turn and are normally ignited at a mutual angular distance of 144° according to the ignition sequence of the engine. The second cylinder therefore normally ignites at 144°, the third cylinder at 288°, the fourth at 432° and the fifth at 576°. During the combustion stroke, the speed of the flywheel 1 increases to a peak (ω_max) and then falls before increasing again during the next combustion stroke. The number of compression strokes, or the ignition frequency, in this case is three during the first crankshaft revolution and two during the second, i.e. five compression strokes, or ignitions, per operating cycle.
The vertical line B shows where the second crankshaft revolution (ii) begins at 360°. When the engine is to be started, the sensor 3 does not know with certainty which cycle position a given cylinder is located in, that is to say in which half cycle or in which of two crankshaft revolutions of the operating cycle, (i) or (ii), the flywheel 1 is located at that time.
In order for the ECU 6 to operate correctly it has to operate in the correct half cycle for each cylinder. This problem is solved by determining the present phase of the flywheel 1 and then determining whether the present phase of the flywheel 1 corresponds to the phase of the ordinary oscillation of the flywheel 1 during its first revolution (i) or whether it corresponds to the phase of the ordinary oscillation of the flywheel 1 during its second revolution (ii).
This is done either by determining one or more rotational angles at which the rotational speed of the flywheel 1 reaches a predetermined value, such as its maximum or minimum rotational speed (ω_max, ω_min). For example the speed of the flywheel 1 during its first revolution (i) reaches its first maximum value (ω_max) once the flywheel 1 has rotated through 36° whereas the speed of the flywheel 1 during its second revolution (ii) reaches its first maximum value once the flywheel 1 has rotated through 108°. In order to determine the position of the cylinders it merely has to be determined whether the flywheel first reaches its maximum speed at 36° or 108°.
Alternatively the phase of the flywheel 1 is determined by counting the number of times the flywheel 1 reaches a peak in its speed, i.e. its maximum rotational speed (ω_max), as the flywheel rotates through said given rotational angle and then comparing this number to the number of peaks occurring during the first (i) or second (ii) revolution of the flywheel during ordinary oscillation. In the example shown, the speed of the flywheel 1 reaches a maximum value (ω_max) three times during its first revolution (i) and it reaches a maximum value two times during its second revolution (ii).
Figure 3 shows a flows chart of a method according to an embodiment of the invention. The method comprises the steps of determining the rotational speed (ω) of the flywheel 1 as it rotates through a given rotational angle (α). The present phase of the flywheel is determined and compared to the ordinary oscillation of the flywheel 1 to determine whether it corresponds to the phase of the ordinary oscillation of the flywheel 1 during its first revolution (i) or whether it corresponds to the phase of the ordinary oscillation of the flywheel 1 during its second revolution (ii).
The invention is of course not in any way restricted to the embodiments thereof described above, but many possibili-ties to modifications thereof would be apparent to a man with or-dinary skill in the art without departing from the basic idea of the invention as defined in the appended claims. For example the invention is applicable to an engine where one or more cylinders drive a crankshaft on which a flywheel, that rotates through more than two revolutions during every operating cycle, is mounted as long as there is a difference in the phase of the ordinary oscillation of the flywheel between at least two of its revolutions.

Claims

Method for determining where in its operating cycle at least one cylinder of a four-stroke internal combustion engine that has an odd number of cylinders is located, where said at least one cylinder drives a crankshaft on which a flywheel (1), that rotates through two revolutions (i,ii) during every four-stroke operating cycle, is mounted, characterized in that it comprises the steps of;
- determining the rotational speed (ω) of the flywheel (1) or a value corresponding to the rotational speed (ω) of the flywheel (1) as it rotates through a given rotational angle (α),

- determining the present phase of the flywheel (1) by determining the, or each rotational angle (α) at which the rotational speed (ω) of the flywheel (1) reaches a predetermined value, such as its maximum or minimum rotational speed (ω_max , ω_min) or by determining the number of times the flywheel (1) reaches a predetermined value, such as its maximum or minimum rotational speed (ω_max , ω_min) as the flywheel rotates through said given rotational angle (α), and

- determining whether the present phase of the flywheel (1) corresponds to the phase of the ordinary oscillation of the flywheel (1) during its first revolution (i) or whether it corresponds to the phase of the ordinary oscillation of the flywheel (1) during its second revolution (ii) for determining where in its operating cycle said at least one cylinder is.
Method according to claim 1, characterized in that the phase of the flywheel (1) is determined by determining the rotational angle (α) at which the rotational speed (ω) of the flywheel (1) first reaches a predetermined value, such as its maximum or minimum value.
Method according to claim 1 or 2, characterized in that it comprises the step of initiating fuel injection or combustion when said at least one cylinder is found to be in the correct position in its operating cycle.
Method according to any of the preceding claims, characterized in that a bandpass filter (5) is used to obtain a signal that shows the rotational speed (ω) of the flywheel (1) as it rotates through a given rotational angle (α).
Method according to any of the previous claims, characterized in that said given rotational angle (α) through which the flywheel (1) is rotated is 360°.
Method according to any of claims 1-4, characterized in that the four-stroke internal combustion engine comprises N cylinders, where N is an odd number, and said given rotational angle (α) through which the flywheel (1) is rotated is $\frac{720 °}{N}$
System for determining where in its operating cycle at least one cylinder of a four-stroke internal combustion engine that has an odd number of cylinders is located, where said at least one cylinder drives a crankshaft on which a flywheel (1), that rotates through two revolutions (i,ii) during every four-stroke operating cycle, is mounted, characterized in that it comprises means to measure the rotational speed (ω) of the flywheel (1) as it rotates through a given rotational angle (α), means to determine the present phase of the flywheel (1) by determining the, or each rotational angle (α) at which the rotational speed (ω) of the flywheel (1) reaches a predetermined value, such as its maximum or minimum value (ω_max ,ω_max), or by determining the number of times the flywheel (1) reaches a predetermined value, such as its maximum or minimum rotational speed (ω_max ω_min) as the flywheel rotates through said given rotational angle, and means to determine whether the phase of the flywheel (1) corresponds to the phase of the ordinary oscillation of the flywheel (1) during its first revolution (i) or whether it corresponds to the phase of the ordinary oscillation of the flywheel (1) during its second revolution (ii) for determining where in its operating cycle said at least one cylinder is.
System according to claim 7, characterized in that it comprises means to determine the rotational angle (α) at which the rotational speed (ω) of the flywheel (1) first reaches a predetermined value, such as its maximum or minimum value (ω_max, ω_min), and by that the present phase of the flywheel (1).
System according to claim 7 or 8, characterized in that it comprises means to initiate fuel injection or combustion when said at least one cylinder is found to be in the correct position in its operating cycle.
System according to any of claims 7-9, characterized in that it further comprises means to indicate, by means of a visible or audible signal for example, that said at least one cylinder is in a particular position in its operating cycle.
System according to any of claims 7-10, characterized in that it comprises a bandpass filter (5) to obtain the rotational speed (ω) of the flywheel (1) as it rotates through a given rotational angle (α).
Computer program for determining where in its operating cycle at least one cylinder of a four-stroke internal combustion engine with fuel injection which has an odd number of cylinders is located, where said at least one cylinder drives a crankshaft on which a flywheel (1), that rotates through two revolutions during every four-stroke operating cycle, is mounted, characterized by computer readable program code means which when run on a computer connected to the engine causes the computer to:
- determine the rotational speed (ω) of a flywheel (1) as it rotates through a given rotational angle (α) and/or

- determine the present phase of the flywheel (1) by determining the, or each rotational angle (α) at which the rotational speed (ω) of the flywheel (1) reaches a predetermined value, such as its maximum or minimum value (ω_max, ω_min), or determine the number of times the flywheel (1) reaches a predetermined value, such as its maximum or minimum rotational speed (ω_max, ω_min) as the flywheel rotates through said given rotational angle, and/or

- determine whether the phase of a flywheel (1) corresponds to the phase of the ordinary oscillation of the flywheel (1) during its first revolution (i) or whether it corresponds to the phase of the ordinary oscillation of the flywheel (1) during its second revolution (ii), for determining where in its operating cycle said at least one cylinder is.
Computer program according to claim 12, characterized in that it comprises computer readable program code means which when run on a computer causes the computer to determine the rotational angle (α) at which the rotational speed (ω) of a flywheel (1) first reaches a predetermined value, such as its maximum or minimum value (ω_max, ω_max), and by that the present phase of the flywheel (1).
Computer program according to claim 12 or 13, characterized in that it comprises computer readable program code means which when run on a computer causes the computer to initiate fuel injection or combustion when said at least one cylinder is found to be in the correct position in its operating cycle.
Computer program according to any of claims 12-14, characterized in that it comprises computer readable program code means which when run on a computer causes the computer to indicate, by means of a visible or audible signal for example, that said at least one cylinder is in a particular position in its operating cycle.
Computer program product comprising a computer readable medium and a computer program according to any of claims 12-15 stored on the computer readable medium.
Electronic control unit (ECU) (6), characterized in that it comprises execution means, a memory and data storage means whereby a computer program according to any of claims 12-15 is stored in said data storage means.
Vehicle, characterized in that it comprises a system according to any of claims 7-11 and/or an ECU (6) according to claim 17.