WO2003002946A1

WO2003002946A1 - Method to determine an angular position of a flywheel

Info

Publication number: WO2003002946A1
Application number: PCT/SE2002/001096
Authority: WO
Inventors: Pär Gustafsson
Original assignee: Abb Ab
Priority date: 2001-06-29
Filing date: 2002-06-06
Publication date: 2003-01-09
Also published as: SE0102374L; SE0102374D0

Abstract

A method and system for determining a relative angular position of a gear tooth on a rotating flywheel 3 of a crankshaft of a combustion engine. A first time Tsli is measured when a gear tooth i passes a first sensor 1 and a second time Ts2i is measured when the gear tooth passes a second sensor 2 in a complete revolution of the flywheel. A reference gear tooth 6 is arranged with means so that it may be identified. The angular position of each gear tooth is calculated relative to the position of the reference gear tooth. The angular position is used to find the angular position of a flywheel on a crankshaft accurately, and used in measurements such as torque, on a crankshaft accurately, and used in measurements such as torque, and/or work output parameters which may be used for engine diagnostic and/or control purposes.

Description

Method to determine an angular position of a flywheel.

TECHNICAL AREA

The present invention concerns the technical area of measurement of position of an object moving along a rotating path. In particular it concerns a method and system to determine the angular position of a gear tooth on a gear wheel, such as for a flywheel fitted to a crankshaft of a combustion engine.

TECHNICAL BACKGROUND

The demand for reduced fuel consumption, together with environmental demands concerning chemical composition of exhaust gases increase the requirement to monitor the operation of combustion engines in very close detail . Misfiring influences exhaust gas chemical composition, fuel consumption, and can also negatively influence the working life of a combustion engine. With the help of continuous measurement misfiring can be detected and action be taken to ensure proper functioning is regained.

With the control of large combustion engines such as for example ships engines, there is a requirement for accurate measurement of the torque in an output shaft . One area of use for continually measuring torque and parameters associated with work output is in very large combustion engines which are operated at relatively low revolutions per minute. Such motors are used for example as ships engines and as stationary engines for driving electrical generators and gas compressors .

A difficulty in the measurement of torque and/or calculation of parameters such as a work output, an IMEP of a cylinder, is to determine accurately the angular position of the crankshaft of the engine (crankshaft angle) . The crankshaft angle is usually obtained by an independent measurement of the angular position of the flywheel (flywheel angle) relative to a known position such as a timing mark, according to known methods.

For instance in EP 742 359 A2, a method and apparatus for controlling the operation of an internal combustion engine is described. In this description the crankshaft angle is measured by a sensor detecting gear teeth on a ring gear fixed to the flywheel of an engine .

In such applications where it is necessary to measure angular position of a crankshaft in a combustion engine it can also often be impossible to use commercially available angle encoders . In particular this applies to larger diesel engines that are used as drives for electricity generation or for ships motors. These motors are exclusively equipped with a flywheel and each flywheel is arranged with gear teeth or a ring gear. It would thus be appropriate if these gear rings could be used to determine the angular position of the crankshaft, because it is already present in the engine .

Unfortunately the precision of manufacturing of these ring gears is not good enough to use the nominal angular position of each gear tooth to measure angular position. To carry out the task of determining, for example, work output, the angular position of each gear tooth must be known with an error less than +/- 0.05 degrees. However every ring gear has different dimensions and therefor must be measured individually in every motor installation and usually without the geometry of the flywheel and sensor installation being 'known in advance.

Moreover, the gear teeth become worn, typically to a varying extent and may also become somewhat damaged during their service life. This means that those measuring systems available on the market would measure inaccurately the angular position of such a gear tooth. SUMMARY OF THE INVENTION.

Embodiments of the present invention aim to address one or several of the above mentioned problems. According to one aspect of the invention a method is provided to determine an angular position of a gear tooth on a flywheel.

To carry the task of determining work output, the angular position of each gear tooth must be known with an error less than +/- 0.05 degrees. Moreover every ring gear has different dimensions and therefor must be measured individually in every motor installation without the geometry of the flywheel and sensor installation being known in advance. The present invention discloses a method to determine the angular position of every gear tooth on a ring gear of a flywheel with the help of an arrangement of two sensors, preferably a type that uses electromagnetic inductance to determine the position of an electrically conducting object.

According to another aspect of the invention a system is provided for carrying out the method to determine an angular position of a gear tooth on a flywheel.

In another aspect of the invention, a computer program product is provided to carry out the steps of a method according to the invention .

The main advantage of the invention is that the angular position of each tooth on a flywheel can be determined using the invented method without first going to every individual gear tooth on each installed flywheel and physically measuring the position of each gear tooth. That is, it is not necessary to know in advance the dimensions of the gear wheel and the number of gear teeth. According to the invention the angular position of every gear tooth relative to a fixed point of the flywheel is determined during a complete revolution of the flywheel . The relative angular positions of every gear tooth thus determined are then used in the method of the invention to determine the angular position of each tooth at a given point in time during rotation of the flywheel during operation of the motor.

This means that sophisticated engine diagnostics, control and regulation may be more cheaply and efficiently applied to engines, especially engines in larger installations functioning such as ships engines and drives for generators . The invention consequently offers significant environmental benefits in terms of reduced fuel consumption and exhaust emissions for combustion engines. The inventive method has the added advantage that accuracy is not affected by wear or damage to the gear teeth on a flywheel, so that the ability to control an engine accurately throughout it's service life is provided. The invention may be applied very widely to any type of combustion engine motor, and economically retrofitted to existing motors .

BRIEF DESCRIPTION OF THE FIGURES

A more complete understanding of the method and system of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawing wherein:

Figure 1 shows a diagram of a method and system for measuring an angular position on a flywheel according to an embodiment of the invention.

Figure -2 shows a simplified block diagram for a system for carrying out the method according to an embodiment of the present invention .

DESCRIPTION OF EMBODIMENTS

Figure 1 shows in a simplified form a first sensor 1 and a second sensor 2 and a flywheel 3 with a ring gear 4 comprising gear teeth such as 5, 6. Gear tooth 6 is shown as a reference gear tooth which may comprise an indicator mark 8. The diagram does not show all of the gear teeth of the ring gear. A sensor such as any of sensors 1, 2 may be a part of a larger system which is mostly intended for determination of a motors work output.

To carry out the task of determining work output for a combustion engine, the angular position of each gear tooth of the flywheel must be known with an error of less than +/- 0.05 degrees. The method disclosed according to the present invention is to determine the angular position of every gear tooth on a ring gear of a flywheel.

The method is carried out according to the invention with the help of two sensors, 1 and 2 which are arranged close to the ring gear on the flywheel to be measured. The sensors are arranged so that both of the sensors are at the same distance from the flywheel's centre. The radius of the flywheel is R and the sensors are arranged at a distance Δ (Delta) from the crown of the teeth, preferably between 2-20 mm. However, it is not necessary to know R and Δ in advance in order to practice the invention. The distance between the two sensors in the angular direction, , shall be as small as possible and constant. Each sensor 1, 2 detects when a tooth passes and can also recognise a reference gear tooth such as gear tooth 6 on the ring gear 4.

The relative angular position of a gear tooth is calculated according to the following. When the time is measured at which every gear tooth passes each sensor, two time vectors are obtained, Tslx and Ts2i , where indices: si and s2 indicate sensor 1 and sensor 2 respectively and i indicates gear tooth number.

A counter can assume a value between 1 and N+l where N gives the number of gear teeth per revolution and 1 and N+l gives the reference gear tooth or beginning and end of the revolution. Thus it is not necessary to know the number of teeth on the gear wheel in advance in order to practice the invention. To calculate the angular position of every gear tooth we form an expression for angular velocity ω_t of a gear tooth when is passes si and s2 :

where ω,- is the mean angular velocity in the time interval

(T_{s i} -τ_{s i})

We assume that ω_t occurs in the centre of the interval and write that as :

2

We now have two new vectors that describe a point in time and a magnitude of the flywheels angular velocity. A problem is that we still do not have values for JR and for Δ and perhaps not even for d. With known mathematical methods we can fit a function to those vectors that describes the angular velocity (ϋ_t for the points in time Tsli and Ts2i as a function of time 0 (t) . This function is an approximation to the actual angular velocity but a sufficiently close approximation for this purpose. The function Cϋ(t) may be written: ω(i) = ((d/(R + A) *F((l/(T_s2 -T„,));

F is the mathematical function that is fitted to the function of Cθ(t) . If this function is then integrated for the time interval {tl_/ ti} for the gear tooth i and then divided by the integral of the time interval { ^' tl; tn+l} we obtain an expression for the relative position of each gear tooth in the revolution which is a direct measure of the angular position, φ_t as follows:

where ψι is the relative angular position of the gear tooth d is the distance between the first sensor (1) and the second sensor (2) , R is the radius of the flywheel (3), Δ is the distance from the top (crown) of the gear tooth to the sensors, T_sii is time T at the first sensor (1) for the gear tooth i, T_S2i is time T at the second sensor (2) for the gear tooth i, F is a function derived according to a formula such as ω(t) = ((d/(J?+Δ)*F((l/(r,_2>, -T_sυ));t) .

If we then cancel out the constants R, Δ and d, we obtain the following: f{F((l/(7_v2, -r ,));t)]rft;{tl;t }

<P — J{E((l/(T_ϊ2, -T;_I,));t)}t-t;{tl;tn+l}

where it can be seen that the angular position of a gear tooth, φ_i is found independent of R, Δ and d, that is, the flywheel radius R, the distance to the sensors Δ and the distance d between sensors 1,2. The angular position is determined relative to a reference point, such as gear tooth 6, according to the invention.

In the_. best ,use of the invention .a -sensor .for non-contact measurement of position of an electrically conducting object is used. Preferably the non-contact sensor is of the type described in a Swedish patent application filed on the same date as the application for the present invention and entitled "A method, device and system to determine gear tooth position", by Linder et al . Said application discloses a non-contact sensor which uses electromagnetic induction to determine a position and distance to an electrically conducting object. The method describes that the centre of mass of the gear tooth may be determined, regardless, for example, of tooth wear. The entire said application is hereby incorporated by this reference. . Reference gear tooth 6 may comprise an indicator 8 which may be any identification means including an optical, mechanical, magnetic or physical indicator. Advantageously the indicator means comprises an object or area arranged on the reference gear tooth with different properties of electrical conductivity than the remainder of the reference gear tooth.

Figure 2 shows a block diagram for a system for carrying out the method according to an embodiment of the invention. The system comprises sensors 1, 2, an analogue signal processing unit 9, a includes memory means 10, and a calculation means 11. As noted above, any of sensors 1, 2 may be a part of a larger system which is mostly intended for determination of a motors work output. Thus a part of the larger system, an Engine control and diagnostics 12 component is shown.

Measurements of time such as Tsli and Ts2i described above from sensors 1, 2 are processed as analogue signals at 9, and then sent to a calculation means, for example a processor 11. Signal processing unit 9 processes the signals by, for example, filtering and transforming the analogue signals into a digitally readable form before the sensor measurement values are then communicated to the processor or calculation means 11. The processor 11 calculates the relative angular position of a gear tooth from measurements of the time, using the formulae described in the method. The measurement values, and values derived from them, are further stored in, and/or retrieved from, a memory storage means such as a RAM or FLASH memory 10.

Such a memory storage device 10 may be any commercially available device based on such as a ROM (Read Only Memory) , a Programmable Read Only Memory (PROM) , an Eraseable Programmable Read Only Memory (EPROM) , in a flash memory, or in any other non-volatile or permanent storage. A calculation unit 11 may be any suitable unit such as a microprocessor or processor or a computer. A signal may be generated by the processor 11 and sent to an engine control and diagnostic unit 12 to be used to monitor and control the motor. The signal may be sent from processor 11 to engine control and diagnostic unit 12 via a wired or wireless connection comprising any kind of fieldbus or network suitable for data collection and/or data communication. The signal may be in the form of a data signal encoded according to any suitable protocol transmission protocol including Transmission Control Protocol/Internet Protocol (TCP/IP) and containing data formatted for example with extensible Markup Language (XML) or other Standard ^■ Generalised Markup Language (SGML) derived or Hyper Text Markup Language (HTML) derived meta language.

It is also noted that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention as defined in the appended claims .

Claims

CLAIMS .

1. A method to determine an angular position of a gear tooth on a rotating flywheel (3) of a crankshaft of an internal combustion engine, characterised by: -measuring during a complete revolution of said flywheel a first time (Tsli) when a gear tooth (i) passes a first sensor (1) and a second time (Ts2i) when the gear tooth (i) passes a second sensor (2) for each gear tooth on the wheel, -identifying a reference gear tooth (6), -calculating the angular position of each gear tooth (i) relative to the angular position of the reference gear tooth (6) as a function of measured times (Ts2i, Tsli) .

2. A method according to claim 1, characterised in that the angular position of the gear tooth (i) is calculated using a formula such as :

J{F((l/(7;₂, -7 _M));t) t-t;{tl;t } ^Ψ' ₎ {F((l/(T_s2. -T_sli)); ;{tl;tn + l} where φ. is the angular position of the gear tooth,

T_sii is time T at the first sensor (1) for the gear tooth i, T_S2i is time T at the second sensor (2) for the gear tooth i , F is a function derived according to a formula such as : ω(t) = ((d/(R + A) * F((l/(T_s2 -r ,));t) , and where d is the distance between the first sensor (1) and the second sensor (2) , R is the radius of the flywheel (3),

Δ is the distance from the top (crown) of the gear tooth to the sensors.

3. A method according to claim 1, characterised in that the angular position of the gear tooth (i) is used to determine a value for torque.

4. A method according to any of the previous claims, characterised in that the angular position of the gear tooth (i) is used to calculate a diagnostic variable such as any of the following: Indicated Mean Effective Pressure, heat release, heat

5 release rate, angle of maximum derivative, angle of maximum pressure.

5. A system for determining an angular position of a gear tooth of a flywheel of a crankshaft of an internal combustion engine, said

10 system including a memory means and a calculation means, and said system equipped with a position sensor (1) arranged adjacent to a ring gear of the flywheel, characterised by comprising a second sensor (2) arranged substantially adjacent to the first sensor (1) such that a first time (Tsli) when a gear tooth (i) passes a first

15 sensor (1) and a second time (Ts2i) when the gear tooth (i) passes the second sensor (2) may be measured.

6. A system according to claim 5, characterised in that the calculation means comprises a formula for calculating angular

20 position such as:

where φ_t is the angular position of the gear tooth T_sii is time T at the first sensor (1) for the gear tooth i ?^r T_Ξ2i is time T at the second sensor (2) for the gear tooth i F is a function derived according to a formula such as ω(t) = ((d l(R + A) * F((ll(T_x2J -T_5l,));t) and where d is the distance between the first sensor (1) and the second 30 sensor (2) ,

R is the radius of the flywheel (3),

Δ is the distance from the top (crown) of the gear tooth to the sensors .

7. A system according to claim 5, characterised in that the reference gear tooth (6) is arranged with identifications means (8) .

8. A system according to claim 5, characterised in that the second sensor is arranged at a distance d from the first sensor (1) , each sensor being arranged adjacent a gear tooth of the ring gear at a distance Δ from the periphery of the flywheel .

9. A system according to claim 5, characterised in that at least the first sensor (1) or the second sensor (2) comprises a means to determine the position of an electrically conducting object by means of electromagnetic induction.

10. A system according to claim 7, characterised in that the identifications means (8) is an object or area arranged on the reference gear tooth (6) with electrical conductivity properties different from another part the reference gear tooth.

11. A system according to claim 5, characterised in that said system comprises means to generate a signal comprising a value for the relative angular position of a gear tooth of the flywheel.

12. A computer program product comprising computer program code means which, when run on a computer or processor, will cause the computer or processor to carry out steps of a method according to any of claims 1-4.

13. A computer readable medium on which is stored a computer program product comprising computer code means according to claim 12.

14. Use of a system according to any of claims 5-11 to calculate a relative angular position of each gear tooth on a flywheel on a "crankshaft of an internal combustion engine.

15. Use of a system according to any of claims 5-11 to calculate an relative angular position of a flywheel on a crankshaft of an internal combustion engine.

16. Use of a system according to any of claims 5-11 to calculate a value for an internal combustion engine such as Indicated Mean Effective Pressure, heat release, heat release rate, angle of maximum derivative, angle of maximum pressure.

17. A computer data signal (9) embodied in a data communication comprising information about an angular position of a gear tooth on a rotating flywheel (3) of a crankshaft of an internal combustion engine determined by means of a method according to any of claims 1-4.

18. A computer data signal according to claim 17, characterised in that the information is formatted at least in part according to a standard such as HTML, HTML.