WO2009153233A1

WO2009153233A1 - Method and system at a vehicle

Info

Publication number: WO2009153233A1
Application number: PCT/EP2009/057332
Authority: WO
Inventors: Ulf Carlsson; Mats JÄRGENSTEDT
Original assignee: Scania Cv Ab (Publ)
Priority date: 2008-06-18
Filing date: 2009-06-15
Publication date: 2009-12-23
Also published as: SE0801424L; SE534427C2

Abstract

The present invention relates to a method for determining the phase of a four-stroke internal combustion engine, the said engine comprising a plurality of cylinders and at least one valve of each of the said cylinders, wherein a first control unit controls fuel injection into the said cylinders and a second control unit controls opening and/or closing of the said valves, wherein the method comprises the step of : by means of the said second control unit, controlling the said valves in a manner such that the first control unit can determine the phase of the four-stroke cycle of the said cylinder by determining a variation of rotation of a shaft of the said engine. The invention also relates to a device and a vehicle.

Description

METHOD AND SYSTEM AT A VEHICLE

Field of the invention

The present invention relates to systems for determining the phase angle of an internal combustion engine, and in particular to a method for determining the phase of an internal combustion engine according to the preamble of claim 1. The invention also relates to a system according to claim 9, a device according to claim 16 and a vehicle according to claim 18.

Background of the invention

Internal combustion engines are often of the four-stroke kind, i.e. the crack shaft turns through an angle of 720° (two revolutions) during one combustion cycle. Each piston consequently completes two cycles during one combustion cycle (i.e. the four strokes which consist of intake-compression- power (combustion) -exhaust) .

The intake of air to be compressed, as well as the let-out of exhaust resulting from the combustion, is, in a conventional internal combustion engine, often controlled by means of valves, wherein opening and closing of these valves are controlled by a cam shaft, which rotate in synchronism with the crank shaft so that the valves are opened and closed at a correct timing in dependence of the location of the pistons in the cylinders.

There also exist solutions in which there are a plurality of air inlet valves and/or exhaust outlet valves for each cylinder, and also solutions wherein there are more than one cam shaft provided with cams for opening and closing the valves . Apart from such engines having cam shaft operated valves, however, there also exist engines wherein the valves, instead of being cam shaft operated, are opened and closed by means of hydraulic and/or electromechanical means.

Regardless of which technology that is used, it is important that it at all times is known in which stroke of the four strokes a piston in a cylinder is present, that is, it must be possible to unambiguously determine which cycle of the two cycles of an individual piston that constitutes the intake/compression and which that constitutes the power/exhaust so that intake of air and let-out of exhaust is synchronised with the fuel injection.

The four stroke cycle begins at the point where the cylinder is at its top dead center (TDC) , and this position represents the phase angle 0° of the 720° (two revolutions) that the crank shaft rotates during a four-stroke cycle.

With regard to engines having cam shaft driven valves, this can be obtained by having a sensor arranged on the cam shaft. The cam shaft rotates with half the speed of the crank shaft, and by knowing the position of the cam shaft it can always be determined whether a cylinder is in, e.g., a compression stroke or an exhaust stroke.

With regard to engines without cam shaft, however, the phase angle (e.g. if the crank shaft is in the first or second revolution of the four-stroke cycle) must be determined in a different manner.

If the valves and the fuel injectors are controlled by a same control unit, this control unit can simply decide, e.g. when the engine is started, that the first stroke is an exhaust stroke to be immediately followed by a compression stroke (or vice versa) , since the control unit operates both the valves and the fuel injectors. It may, however, for various reasons be desirable to have the valve control integrated in a first control unit and the fuel injector control in a second control unit, e.g. to reduce the load on the control unit since this otherwise can have a great number of tasks to perform, e.g. if the control unit is an engine control unit.

However, use of two control units means that both control units must have the same view of which stroke a TDC piston position is about to begin (i.e. intake-compression or power- exhaust) . Consequently, it is necessary that the two control units are "synchronised" to each other.

There are several possible ways of accomplishing this. For example, one control unit could be determined as master control unit and decide which of the two top dead centre positions that is to be interpreted as the start of an intake, and then communicate this message to the other control unit being a slave control unit. The disadvantage of such a solution, however, is that should the information be transmitted on, e.g. a vehicle control system data bus, such data buses are often not suitable for real-time critical data. Therefore, an alternative to this is that the two control units are connected to each other, e.g. using a dedicated signal connection. This, on the other hand, has the disadvantage that apart from imposing extra costs, the extra cable may break or in other ways malfunction.

Consequently, there exists a need for an improved method of synchronising two control units, wherein a first control unit controls opening and closing of valves while the other control unit controls injection of fuel, in particular with regard to engines without cam shaft. Summary of the invention

It is an object of the present invention to provide a method that solves the above mentioned problem. This object is achieved by a method according to the characterising portion of claim 1.

The present invention relates to a method for determining the phase of a four-stroke internal combustion engine, the said engine comprising at least one cylinder and at least one valve of the said cylinder, wherein a first control unit controls fuel injection into the said cylinder and a second control unit controls opening and/or closing of the said valve, wherein the method comprises the step of, by means of the said second control unit, controlling the said at least one valve in a manner such that the phase of the four-stroke cycle of the said cylinder can be determined by determining a variation of rotation of a shaft of the said engine.

The present invention has the advantage that by making it possible to detect the phase of the four-stroke cycle simply by observing the variation of rotation of a shaft of the engine, such as the crank shaft (e.g., by measuring on the flywheel) the first control unit can determine the phase without phase information being communicated between the two control units. The present invention is particularly advantageous when used in connection with a diesel engine of a heavy duty vehicle.

Brief description of the drawings

Fig. 1 discloses an exemplary engine in which the present invention advantageously can be utilised.

Fig. 2 discloses a graph of crank shaft variations during a four-stroke cycle. Fig. 3 discloses an exemplary embodiment according to the present invention.

Detailed description of preferred embodiments

As was mentioned above, there exist engines wherein the valves, instead of being cam shaft operated, are opened and closed by means of hydraulic and/or electromechanical means.

As also was mentioned above, it is often preferred to control fuel injection and valves of such an engine using separate control units.

In fig. 1 is shown a cross section of an exemplary engine wherein the valves are controlled using electro-mechanical or hydraulic means according to the present invention. The figure discloses a piston 102 connected to a crank shaft 101. The piston reciprocally moves up and down in a cylinder 103 as a response to a rotation of the crank shaft 101. At the top of the cylinder 103 there are valves 105, 106. Valve 105 can be opened to allow intake of air in the cylinder and the valve 106 can be opened to let out exhaust gas resulting from combustion in the cylinder. A vehicle engine often comprises a plurality of cylinders with associated pistons, e.g. 4, 5, 6, 8, 10, 12, 14, 16. The engine disclosed in fig. 1 can be of any such configuration, although only one cylinder is disclosed.

As was mentioned above, the valves of an internal combustion engine are conventionally operated by means of a cam shaft which is arranged to rotate synchronised with the crank shaft at half the speed of the crank shaft so that the valves open and close at desired points in time with regard to the position of the piston 102. Instead of being operated by a cam shaft, however, the valves 105, 106 of the engine in fig. 1 are operated by electromechanical means and/or hydraulic means. The use of valves being operated electro-mechanically or hydraulically has, for example, the advantage that the valves can be opened and closed to various extents in dependence of the current speed and/or load of the engine. Such configurations also have the advantage that the points in time at which the valves open and close can be adjusted, e.g. on the basis of the current running conditions of the engine.

Fig. 1 also discloses a control unit 110 for controlling the operation of the valves 105, 106 (and corresponding valves of other cylinders of the engine), e.g. by controlling suitable means (not shown) for opening/closing the said valves. Fig. 1 also discloses a control unit 111, which in a conventional manner controls fuel injection nozzles (not shown) that are used to fuel the cylinders for subsequent combustion. The control unit 111 can, for example, be the engine control unit that often is present in a vehicle. The control units 110, 111 constitute part of the vehicle control system. Vehicle control systems in modern vehicles usually consist of a communication bus system consisting of one or more communication busses to interconnect various electronic control units and components located on the vehicle. Consequently, the signals to/from valve controlling means and injection nozzle controllers can, for example, be communicated to/from the control units 110, 111 by means of a suitable communication bus.

As was mentioned above, with regard to an engine without cam shaft, the two control units 110, 111 must agree on the current phase (phase angle) of the crank shaft, that is, in which of the two revolutions of a four-stroke cycle that a cylinder at present is operating. If the valve control unit is of the opinion that an intake is about to occur, while the engine control unit (injector control unit) is of the opinion that combustion is about to occur, the engine will behave poorly.

Usually, it is sufficient to determine the phase for one cylinder, preferably the first cylinder of the engine, since the other cylinders, in general, operate in a fixed relation to the first cylinder. For example, in an eight cylinder engine, the first four cylinders reach the TDC with a ninety degree rotational displacement of the crank shaft. Each of the rest of the cylinders (cylinders 5-8) often operate in pair with one of the cylinders 1-4.

As stated above, there exist ways in which the phase angle of the crank shaft can be communicated between the two control units. These methods, however, may not, e.g., for the above reasons, be fully reliable, which is why the determination of the phase angle is addressed by the present invention.

According to the present invention, both control units 110, 111, when the vehicle is to be started, can independently assume a phase, which consequently means that there is a possibility that they assume different phases. This phase is then verified by means of the present invention. According to the invention, the valves are operated by the control unit 110 in a manner such that the control unit 111 can detect the phase set by the valve control unit 110 simply by observing the rotational behaviour of the crank shaft 101.

An exemplary method according to the present invention is disclosed in fig. 3. The method starts in step 301, wherein it is determined, e.g. by the control unit 111, if phase determination is required, e.g. if the vehicle engine is about to start (it is, of course, also possible to perform the said determination also in other situations, e.g. after certain periods of time or if there is any indication that the determination for some reason may be preferable to perform) . This can, for example, be triggered by the control unit receiving a message on a vehicle communication bus that the starter engine is about to be activated (e.g. following a request by a driver) . If phase detection is required, the method continues to step 302, wherein the crank shaft motion is monitored by the control unit 111. This can, for example, be accomplished in a conventional manner, e.g. by detecting teeth of a flywheel, wherein one tooth has been removed in order to allow identification of the TDC. The flywheel is fixed to the crank shaft and comprises, in general, a plurality of teeth which allows that the crank shaft speed variations, even within a single crank shaft revolution, can be determined with high accuracy using a suitable sensor detecting the passing teeth.

According to the present invention, the phase is detected by detecting a pattern in the rotational variation of the crank shaft and in one exemplary embodiment, this is accomplished, e.g., by, at the first revolution or revolutions of the crank shaft that are caused by the starter motor, the valve control unit operating the valves of cylinder 1 in a conventional manner, that is, opening and closing the valves 105, 106 as if the engine is being started, while the valves of all other cylinders are kept closed. This has as a result that in the intake-compression phase, cylinder 1 will take in air in a conventional manner and perform a compression in a conventional manner. This compression, however, will, due to the pressure build-up, impose a detectable retardation of the crank shaft. Conversely, the combustion-exhaust phase will present little resistance to piston movement since the exhaust valve (or valves) will be open.

This is further exemplified in fig. 2 in which an exemplary crankshaft characteristic of a four stroke cycle when valves are operated according to the above and when being rotated by the starter motor by n rpm is disclosed. For reasons of simplicity, it is assumed that the curve starts off with the piston at TDC. During the intake, the crankshaft speed will remain substantially constant, i.e. n rpm. During the compression step, however, the crank shaft is retarded by the increasing cylinder pressure, and by the end of the compression step, the crank shaft speed has reduced to n2 rpm. In the power stroke, the piston is no longer subject to the increased counter-pressure, with the result that the crank shaft speed, although no combustion is actually taking place (in the exemplary embodiment, the control unit 111 do not start fuel injection until the phase has been determined. In an alternative embodiment, however, the control unit is allowed to operate fuel injection according to its assumed phase, in which case the characteristic of fig. 2 can be different if there is also a combustion) , returns to substantially n rpm (actually, although not being disclosed in the figure, the speed will reach a higher speed than n rpm due to the energy stored in the compressed air. The speed would exceed n rpm by an even further amount had there actually been a combustion) , where it remains until the next compression (not shown) .

Following the step of detecting the crank shaft (i.e. flywheel) variations, (or, alternatively, simultaneously with the step of detecting the variations) , the phase of the four- stroke cycle is determined. This can, for example, be accomplished by detecting the deviation in rotational speed of the crank shaft shown in fig. 2, or simply by comparing the rotational speed of the crank shaft at TDC=I and TDC=2 in fig. 2, which immediately will reveal that TDC = 1 is to be interpreted as 0° of the 720° cycle, since the crank shaft rotational speed will be lower at 360° (owing to the preceding compression) .

Consequently, the control unit 111, or any appropriate control unit for that matter, can detect the retardation of the crank shaft that depend on the compression and thereby establish that the TDC immediately following the compression

(retardation) is in the 360° position of the 720° cycle.

The method then continues to step 304, wherein it is determined if the determined phase is the same as the assumed phase. If so, the method returns to step 301, and if not, the process continues to step 305, wherein the assumed phase is adjusted in accordance with the determined phase.

Consequently, the present invention provides a simple yet robust method of synchronising the four-stroke phase of the two (or more, should that be the case) control units, such that the phase of fuel injection can be set to correspond to the operation of the valves by the valve control unit. The present invention also has the advantage that no direct signalling between engine control unit and valve control unit is required, which also has the advantage that no dedicated signal connection between the two control units is necessary.

Preferably, the engine control unit knows which cylinder that has valves working in a normal manner, although in many situations the engine control unit will be able to determine this by noting which position of the crank shaft that corresponds to the TDC of the particular cylinder. As is appreciated by a person skilled in the art, there are various alternative ways in which valve opening and closing can be controlled and which still allows that the phase can be determined. For example, instead of operating the valves of cylinder 1 in a conventional manner, it is, of course, also possible to operate the valves of any cylinder in order to accomplish the phase detection, preferably with the engine control unit knowing which cylinder having its valve working in a conventional manner. It is also contemplated that more complex schemes of operating the valves are used, e.g. by operating valves of more than one cylinder, only one valve of a cylinder, keeping all or part of the valves of the other cylinders open, or opening valves of the other cylinders during their respective compression phase.

The present invention also has the advantage that when starting the engine, the valve control unit and engine control unit can individually set a TDC that is to be considered as the 0° phase, since the engine control unit then immediately can determine if its assumption is correct, and otherwise perform a phase jump to synchronise with the valve control unit .

Claims

1. Method for determining the phase of a four-stroke internal combustion engine, the said engine comprising a plurality of cylinders and at least one valve of each of the said cylinders, wherein a first control unit controls fuel injection into the said cylinders and a second control unit, being different from the said first control unit, controls opening and/or closing of the said valves, characterised in that the method comprises the step of: - by means of the said second control unit, controlling the said valves in a manner such that the first control unit can determine the phase of the four-stroke cycle of the said cylinder by determining a variation of rotation of a shaft of the said engine, said step of controlling the said valves consisting of the step of operating the valve or valves of one cylinder according to normal operation while valves of at least some of the other cylinders are operated in a manner being different from normal operation.

2. Method according to claim 1, characterised in that valves of the said at least some other cylinders are kept closed or open during the said determination of the phase.

3. Method according to any of the preceding claims, characterised in that the determination of the variation of rotation of a shaft of the said engine is a determination of the variation of the rotation of a crank shaft.

4. Method according to any of the preceding claims, characterised in that the said determination of the variation of the rotation of a shaft is determined by measuring a variation of rotation of a flywheel.

5. Method according to any of the preceding claims, characterised in that the said first control unit is an engine control unit.

6. System for determining the phase of a four-stroke internal combustion engine, the said engine comprising a plurality of cylinders and at least one valve of each of the said cylinders, the system comprising a first control unit that is arranged to control fuel injection into the said cylinders and a second control unit, being different from the said first control unit, that is arranged to control opening and/or closing of the said valves, characterised in that the system includes means for:

- by means of the said second control unit, controlling the said valves in a manner such that the first control unit can determine the phase of the four-stroke cycle of the said cylinder by determining a variation of rotation of a shaft of the said engine, said step of controlling the said valves consisting of the step of operating the valve or valves of one cylinder according to normal operation while valves of at least some of the other cylinders are operated in a manner being different from normal operation.

7. System according to claim 6, characterised in that valves of the said at least some other cylinders are kept closed or open during the said determination of the phase.

8. System according to any of the claims 6-7, characterised in that the determination of the variation of rotation of a shaft of the said engine is a determination of the variation of the rotation of a crank shaft.

9. System according to any of the claims 6-8, characterised in that the said determination of the variation of the rotation of a shaft is determined by measuring a variation of rotation of a flywheel .

10. System according to any of the claims 6-9, characterised in that the said first control unit is an engine control unit.

11. Device for use in a system for determining the phase of a four-stroke internal combustion engine, the said engine comprising a plurality of cylinders and at least one valve of each of the said cylinders, the device being arranged to control opening and/or closing of the said valves, characterised in that the device includes means for:

- controlling the said valves in a manner such that the phase of the four-stroke cycle of the said cylinder can be determined by determining a variation of rotation of a shaft of the said engine, said step of controlling the said valves consisting of the step of operating the valve or valves of one cylinder according to normal operation while valves of at least some of the other cylinders are operated in a manner being different from normal operation.

12. Vehicle, characterised in that it comprises a system and/or device according to any of the claims 6-11.