WO2014199018A1

WO2014199018A1 - Determination of angular speed in an engine

Info

Publication number: WO2014199018A1
Application number: PCT/FI2014/050475
Authority: WO
Inventors: Fredrik ÖSTMAN; Tom Kaas
Original assignee: Wärtsilä Finland Oy
Priority date: 2013-06-12
Filing date: 2014-06-12
Publication date: 2014-12-18
Also published as: CN105283768A; KR20160019442A; EP3008472A1; KR102206697B1

Abstract

The invention relates to a system for determining an angular speed of a flywheel of an internal combustion engine. At least two measurement points are defined on the flywheel and a measurement unit is configured to receive information from the sensor on detections, when each of the at least two measurement point arrives in detection space of the sensor and points of time of the detections are determined. Furthermore, a time difference of a first detection of a measurement point and a sequential detection of the same measurement point for each of the at least two measurement points and the angular speed of the flywheel in relation to each of the at least two measurement points is calculated at least party by means of the time difference. In this way, speed values are always determined on the basis of a full rotation, so that errors caused by a different or irregular angular spacing of the markers are avoided. The invention also relates to a method for determining the angular speed.

Description

Determination of angular speed in an engine

TECHNICAL FIELD

The invention concerns in general the technical field of measurement arrangement. Especially the invention concerns measurement of angular speed of an engine.

BACKGROUND OF THE INVENTION

In engine systems it is extremely important to measure different parameters relating to the operation of the engine. One area of important parameters to measure is rotation dependent parameters of the engine, such as angular speed of a flywheel of the engine. For example, one type of internal combustion engine comprises four cylinders, each of which accommodates a corresponding piston mechanically coupled to a crankshaft for transmitting the force generated by the combustion inside the cylinder to the crankshaft itself. A flywheel is coupled to the crankshaft for storing the energy from the operation of the engine.

Known methods for measuring the angular speed of the flywheel are based on a use of holes or teeth on the flywheel as a measurement points. The angular speed of the flywheel is measured by measuring the time it takes for the flywheel to rotate a certain number of holes or teeth. Assuming that the holes or teeth are machined in an equidistant manner the rotational angle can be calculated according to

number of measured holes or teeth

rotating angle (deg) = x 360

total number of holes or teeth

When the rotating angle is determined the angular speed of the flywheel, and thus the engine, can be calculated according to

(deg\ rotating angle (deg)

The drawback in determining the angular speed of the flywheel by counting the number of holes or teeth in a period of time during rotation is that distances between holes or teeth in the flywheel may vary. This is due to tolerances in the machining precision of the holes or teeth. In practice, small tolerances in the hole or tooth positions can give rise to considerable errors in the measurement of angular speed, which are called geometric errors.

Fig. 1 illustrates a known solution for determining an angular speed of the flywheel 101 of an engine, such as internal combustion engine. The flywheel ac- cording to the example comprises four holes 103A-103D. The holes 103A- 103C are positioned equidistantly, but the position of the hole 103D deviates from the equidistant position, which is marked with 103D'. The rotational motion of the flywheel is measured with a sensor 105 and a sensor system, which is configured to detect the holes during the rotational motion. Due to the geo- metric error in the position of the hole 103D (referred with Ae in Fig. 1 ) any angular speed measurement based at least partly on the hole 103D produces corresponding error in the speed. The positioning tolerances in each of the holes, or teeth, cause similar unpredictable error for the measurement.

There have been developed methods for compensating the geometric errors in the angular speed measurement. They are typically based on mathematical methods in which a correction factor is defined for the geometric errors of holes or teeth in the flywheel of an engine. When the speed of the flywheel is measured with respect to several holes or teeth, the measurement values are corrected with corresponding correction factors. An example of such a method is disclosed in US201 1029267.

SUMMARY OF THE INVENTION

An objective of the invention is to present a system and a method for determining an angular speed of a flywheel. Another objective of the invention is that the system and the method provide a solution to minimize geometric errors in the angular speed determination.

The objects of the invention are reached by a system and a method as defined by the respective independent claims.

According to a first aspect, a system for determining an angular speed of a flywheel of an internal combustion engine is provided. The system comprises at least one sensor and a measurement unit wherein at least two measurement points are defined on the flywheel and wherein the measurement unit is configured to receive information from the sensor on detections, when each of the at least two measurement point arrives in detection space of the sensor during the angular motion of the flywheel; determine points of time of the detections; determine a time difference of a first detection of a measurement point by the sensor and a sequential detection of the same measurement point by the sensor for each of the at least two measurement points; and determine the angu- lar speed of the flywheel in relation to each of the at least two measurement points by dividing 360 degrees with the determined time difference.

The measurement unit may comprises a processor which is configured to identify the measurement point, which is detected by the sensor. The identification may be based on at least one of the following: identity information of the measurement point, measurement value of the detection received from the sensor, sequential measurement values with respect to number of measurement points.

Furthermore, the measurement unit may be configured to couple a time stamp for each of the detections received from the sensor. The time difference may be determined based on the time stamps of sequential detections. The time stamp may be received from at least one of the following: a clock in the measurement unit, external clock signal.

According to a second aspect, a method for determining an angular speed of a flywheel of an internal combustion engine is provided. The method comprises steps of monitoring angular motion of the flywheel; detecting, when each of at least two measurement point arranged on the flywheel arrives in a detection space of the sensor during the angular motion of the flywheel; determining points of time of the detections; determining a time difference of a first detection of a measurement point by the sensor and a sequential detection of the same measurement point by the sensor for each of the at least two measurement points; and determining the angular speed of the flywheel in relation to each of the at least two measurement points by dividing 360 degrees with the determined time difference.

The exemplary embodiments of the invention presented in this patent applica- tion are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following de- scription of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 illustrates a prior art solution for determining an angular speed of the flywheel of an engine, fig. 2 illustrates an example of a system according to the invention, and fig. 3 illustrates an example of a method according to the invention.

DETAILED DESCRIPTION

The inventive idea according to the present invention lies in a novel way of arranging the measurement of angular speed of the flywheel of an engine, or any similar element representing rotational motion and the operation of the engine. The idea is to establish multiple measurement points in the flywheel of the engine and measure the rotational motion of them, within the operation of the engine.

The system according to an example of the invention is illustrated in Fig. 2. The measurement system comprises at least one sensor 203 and a measurement unit 205. The measurement values from the at least one sensor 203 are configured to be read by a processor 207 of the measurement unit 205. The processor is configured to couple a time stamp for each measurement value received from the sensor 203. The time value for the time stamp may be re- ceived from a clock 209 arranged in the measurement unit 205. The measurement values with corresponding time stamp may be stored in a memory 21 1 within the measurement unit 205. Alternatively or in addition, the processor 207 may be configured to determine parameters representing the operation of the engine, such as angular speed of the flywheel 101 , without storing any measurement values in the memory 21 1 . Furthermore, the processor 207 may be configured to store the determined parameters representing the opera- tion of the engine to the memory 21 1 . In its simplest form the measurement value is just an indication of a detection, such as a pulse signal.

The processor 207 as described may comprise a buffer memory into which the measurement values from the sensor 203 are configured to be read and stored at least temporarily. The measurement value according to an example of the invention may comprise information on a detection of predetermined measurement points arranged in the flywheel 101 . In the case of having multiple measurement points 201 A-201 H each of the measurement points may be identified. The identification may be arranged by introducing a marker as an identifier in the measurement point, which is then detected by the sensor. Alternatively, or in addition, the detection may be based on structural implementation of the flywheel 101 , and especially the holes or teeth when used as measurement points, in such a manner that each measurement point is arranged to produce a different measurement value in the sensor, which meas- urement values are analyzed by the processor 207.

According to some example of the invention the number of measurement points 201 A-201 H may be known in the processor 207 when the processor 207 is executing a computer program code into which the information on the number of measurement points is coded. The number of measurement points may e.g. be a parameter for the computer program code, which is inserted by the operator when installing the measurement system. Then, the processor is configured receive the measurement values from the sensor 203 and on the basis of the information on the number of measurement points 201 A-201 H in the implementation, the processor 207 is arranged to combine the measure- ment values from a certain measurement point 201 A-201 H . For example, if there are two measurement points arranged in the flywheel 101 , the processor 207 is configured to and capable of determining the angular speed for the first measurement point from every second measurement values and for the second measurement point from the other every second measurement values re- ceived from the sensor 203. Thus, there is no need to arrange any identification for the measurement points in this kind of arrangement, but arranging the identification of measurement points through sequential, i.e. consecutive, measurement values with respect to the number of measurement points. A counter may be arranged within the measurement unit, e.g. in the processor, which is increased one step each time a detection is done in the sensor. When the counter reaches the maximum value, which equals to the number of measurement points it is restarted. In this manner it is possible to keep on track, which measurement values, such as detection pulses, are from which measurement point.

In some implementation of the invention there can be arranged a number of measurement points on the flywheel. As there are developed ways to identify the measurement points, as described above, it is also possible to arrange that some of the measurement points are dropped out from use or added in use during the operation of the measurement system. This can be achieved by determining the measurement points, which are used at the time. In other words, the processor may e.g. be arranged to ignore certain measurement values from the determined measurement points. This kind of adjustable measurement system enables the optimization of computing resources according to need within the measurement unit.

In Fig. 2 it is illustrated that the clock 209 is arranged in the measurement unit 205. Alternatively, or in addition, the clock signal for the creation of the time stamps may be received from an external entity providing clock signal functions.

As described, the sensor 203 may be configured to detect the rotation of a flywheel 101 in the engine. The detection may be based on the holes 201 A-201 H or teeth of the flywheel 101 . Alternatively or in addition, the detection may be based on any other element than the flywheel 101 as long as the element indicates the operation of the engine as required. For example, in some example of the invention a measurement disc may be coupled to a crankshaft of an engine, which thus gives information on the operation of the engine, i.e. speed of the pistons coupled to the crankshaft. Any similar arrangement may be possible. In some implementations of the invention the measurement points, such as identifiers, may be directly arranged on the surface of the crankshaft. Such identifiers may be arranged e.g. with tape markings, or any similar, which can be fastened or marked on the crankshaft, or flywheel. Next the operation of the measurement system is described with an arrangement in which the measurement points are arranged in the holes 201 A-201 H of the flywheel 101 . However, the inventive idea is not limited to such an implementation. The sensor 203 is configured to monitor the rotation of the flywheel 101 and each time the measurement point passes the sensor 203 the processor 207 is configured to detect a change in the measurement value received from the sensor 203. The processor 207 is configured to determine the point of time based on information from the clock 209, when it detects the change in the measurement value. When the processor 207 determines at least two points of time t1 and t2, when the measurement point has passed the sensor 203, it is arranged to determine the angular speed of the flywheel 101 . The angular speed of the flywheel 101 is then

The above described example of the invention is applicable especially in engines in which the revolution speed is not too high. In reality, the sample rate shall be adjusted with an assumed nominal angular speed of the engine in order to avoid aliasing of higher frequency components during the measurement.

According to some example of the invention at least two measurement points are arranged in the flywheel, or a similar element representing rotational motion of the engine. By increasing the number of measurement points, and thus achieving independent measurements, higher sample rate can be enabled. If the determination of the angular speed is based on holes or teeth in the flywheel, the maximum sample rate can be achieved by arranging the independent measurement for every hole or tooth in the flywheel 101 . In other words, the sensor 203 is configured to detect the passings of each of the measure- ment points, i.e. the measurement points arrive in a detection space of the sensor. The determination of the angular speed of each of the measurement points may be based on the knowledge of the number of measurement points or on identification of the measurement point from which the measurement value is received. Furthermore, the identification of the measurement points may be based on an implementation in which each of the measurement points are configured to produce a distinguishable measurement value from each other when detected. The processor 207 is configured to identify the origin of each measurement value, i.e. the measurement point, based on at least one of the mentioned methods. The needed number of samples per a revolution is to be chosen according to need. For example, let's assume that the frequency range of interest in the measured angular speed is from 0 to f_rec Hz. According to Nyquist theory the required sample rate for the frequency range is

In practice, the sample rate is typically chosen higher than required by Nyquist theory, and a rule of thumb is to choose a sample rate fs ⁼ ^> X /n ⁼ 5 x 2 X f_rec = 10 X f_rec . The sample rate at nominal angular speed of the engine is

„ nominal speed . , . nominal speed

^J L^b = 60 x measurement pfoints pfer revolution = ₆₀ x total number of holes on the flywheel _ ^ ^ „

length of measurement segment J rec -

Solving the length of measurement segment, i.e. the mutual distance of two successive measurement points, such as 201 A and 201 B in Fig. 2, is

total number of

r . . nominal speed holes on the flywheel

length of measurement segment = — x ¹

By inserting the following parameters to the equation free = 20 Hz nominal speed = 600 rpm total number of holes on the flywheel = 120, we get that length of measurement segment equals to 6. This means that the value for angular speed is required to be calculated for every sixth hole in order to detect the frequency changes of the angular speed in the required frequency range 0 - f_rec. Thus, according to the invention the number of measurement points can be determined at least party based on the frequency on which the measure- ment is configured to be performed.

With the arrangement in which multiple measurement points are arranged on the flywheel it is possible to increase the sample rate. In such a manner it is possible to achieve a fast update rate of the angular speed of the flywheel and thus enable more sophisticated control methods of the engine. Since the angu- lar speed of the flywheel is determined from two consequential measurement values of a measurement point, the geometrical errors can be eliminated. Fig. 3 illustrates an example of a method according to the invention. In the method, the angular motion of the target, such as a flywheel of an engine, is monitored and measured 301 . The predetermined measurement points are detected 303, when they arrive in the detection space of a sensor. A processor of a measurement unit is configured to determine points of time for each of the mentioned detections 305 and determine an angular speed of the target based on the times of detections. In order to determine the angular speed it is arranged that a time difference of a first detection of a measurement point (201 A-201 H) by the sensor (203) and a sequential detection of the same measurement point (201 A-201 H) by the sensor (203) is determined for each of the measurement points 307 and the angular speed for each of the measurement points is determined 309 by calculating it mathematically. The method steps as disclosed are at least partly performed and/or controlled by a processor within the measurement system. In the description above it is mainly discussed that the measurement points are arranged on the flywheel in the engine. However, any other similar element may be used for the similar purpose, such as crankshaft or measurement disk.

Some advantageous embodiments according to the invention were described above. The invention is not limited to the embodiments described. The in- ventive idea can be applied in numerous ways within the scope defined by the claims attached hereto.

Claims

1 . A system for determining an angular speed of a flywheel of an internal combustion engine, the system comprising - at least one sensor (203)

- a measurement unit (205) wherein at least two measurement points (201 A-201 H) are defined on the flywheel (101 ) and wherein the measurement unit (205) is configured to

- receive information from the sensor (203) on detections, when each of the at least two measurement point (201 A-201 H) arrives in detection space of the sensor (203) during the angular motion of the flywheel (101 ),

- determine points of time of the detections,

- determine a time difference of a first detection of a measurement point (201 A- 201 H) by the sensor (203) and a sequential detection of the same measure- ment point (201 A-201 H) by the sensor (203) for each of the at least two measurement points (201 A-201 H), and

- determine the angular speed of the flywheel (101 ) in relation to each of the at least two measurement points (201 A-201 H) by dividing 360 degrees with the determined time difference.

2. A system as claimed in claim 1 , wherein the measurement unit (205) comprises a processor (207) configured to identify the measurement point (201 A- 201 ), which is detected by the sensor (203).

3. A system as claimed in claim 2, wherein the identification is based on at least one of the following: identity information of the measurement point (201 A- 201 H), measurement value of the detection received from the sensor (203), sequential measurement values with respect to number of measurement points.

4. A system as claimed in any of the preceding claims, wherein the measurement unit (205) is configured to couple a time stamp for each of the detections received from the sensor (203).

5. A system as claimed in claim 4, wherein the time difference is determined based on the time stamps of sequential detections.

6. A system as claimed in claim 4 or 5, wherein the time stamp is received from at least one of the following: a clock (209) in the measurement unit (205), external clock signal.

7. A method for determining an angular speed of a flywheel of an internal combustion engine, the method comprising

- monitoring (301 ) angular motion of the flywheel (101 ),

- detecting (303), when each of at least two measurement point (201 A-201 H) arranged on the flywheel (101 ) arrives in a detection space of the sensor (203) during the angular motion of the flywheel (101 ),

- determining (305) points of time of the detections,

- determining a time difference (307) of a first detection of a measurement point (201 A-201 H) by the sensor (203) and a sequential detection of the same measurement point (201 A-201 H) by the sensor (203) for each of the at least two measurement points (201 A-201 H), and

- determining the angular speed of the flywheel (101 ) in relation to each of the at least two measurement points (201 A-201 H) by dividing 360 degrees with the determined time difference.