EP2812564A1

EP2812564A1 - Diagnosis of starter motor

Info

Publication number: EP2812564A1
Application number: EP13746140.6A
Authority: EP
Inventors: Holger Dreher; Gunnar Ledfelt
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2012-02-07
Filing date: 2013-01-22
Publication date: 2014-12-17
Also published as: SE536801C2; EP2812564A4; SE1250086A1; WO2013119168A1

Abstract

A combustion engine (120) in a vehicle is started by means of an electric starter motor (110) which is diagnosed via measuring means (130, 140), a temperature measurement means (150) and a processor (160). The measuring means (130, 140) are configured to measure technical magnitudes related to the vehicle but representing only a supply voltage (U) to the starter motor and a rotation speed (RPM) of the engine (120). The temperature measurement means (150) is configured to measure at least one temperature (T) related to the vehicle. The processor (160) is configured to determine for the starter motor (110) a status indicator (S) which serves as a measure of the quality of the starter motor's performance. The status indicator (S) is based on the measured technical magnitudes and the at least one temperature (T) related to the vehicle.

Description

DIAGNOSIS OF STARTER MOTOR

BACKGROUN D TO TH E INVENTION AN D PRIOR ART

The present invention relates generally to diagnosis of an electric starter motor for a combustion engine. The invention relates particularly to a system according to the preamble of claim 1 and a method according to the preamble of claim 1 0. It relates also to a computer programme according to claim 1 9 and a computer- readable medium according to claim 20. In principle, all motor vehicles provided with combustion engines depend today on an electric starter motor to enable them to be started. The function of the starter motor is thus vital for the operation of the vehicle. There are various known solutions for verifying this function. For practical reasons it is considered preferable if there is no need for the starter motor to be removed from the vehicle for testing of its function.

Specifications GB 2 003 281 , J P 55057659, US 2009/0309530 and US 7,409,856 describe examples of solutions for investigating the fu nction of an electric starter motor. All of them i nvolve considering a supply voltage to the starter motor, a rotation speed parameter and the current supplied to the starter motor. However, the measurement of cu rrent is relatively complicated to perform. There is also risk of the actual measurement affecting the starter motor's fu nction. Specification KR 1 0081 9334 describes a method in which the only input parameters for the diag nostic fu nction are the battery voltage for the starter motor and a rotation speed generated by the starter motor.

PROBLEMS ASSOC IATE D WITH PRIOR ART The solution according to the last-mentioned specification proposes for an electric starter motor a diagnostic method of exemplary simplicity, but it has been fou nd that consideri ng only the battery voltage and the rotation speed results in insufficient precision i n assessing the starter motor's fu nction in at least certain circumstances.

SUMMARY OF TH E I NVENTION

The object of the present invention is therefore to propose a solution which alleviates the above problems and therefore makes possible a more reliable diagnosis of an electric starter motor with which a motor vehicle is provided.

One aspect of the invention achieves this object by the system described in the introduction which comprises a temperature measurement means configu red to measu re at least one temperatu re related to the vehicle. The processor is here configu red to determine the status indicator on the further basis of the at least one measu red temperatu re.

This system is advantageous in that environment changes (e.g. due to changing seasons and/or geographical conditions) are catered for in the diagnostic method in a natural and appropriate way. The viscosity of the oil in a combustion engine does in fact vary considerably with temperature, with consequent effects upon the rotation speed measured.

In one embodiment of this aspect of the invention, the processor is configured to assign the status indicator a first value if the starter motor's function is deemed acceptable, and a second value if the starter motor is not deemed to be functioning satisfactorily. Specifically, the status indicator is assigned the first value if the measured voltage is above a voltage threshold and the measured rotation speed is above a rotation speed threshold. In other words, a correctly functioning starter motor is expected to result in at least a certain rotation speed of the combustion engine when the starter motor is provided with a certain supply voltage. In another embodiment of this aspect of the invention, the processor is configured to apply in addition an adaptive subcondition on the basis of the at least one measured temperature so that at a relatively high measured temperature a relatively low measured voltage has to be matched by a measured rotation speed to enable the adaptive subcondition to be deemed fulfilled and the status indicator to be consequently assigned the first value. Conversely, at a relatively low measured temperature a relatively high measured supply voltage may be matched by a measured rotation speed which is just above the rotation speed threshold at which the adaptive subcondition is deemed fulfilled and the status indicator is assigned the first value. The effect of temperature on the requirements for the starter motor to function is thus taken relevant account of. The adaptive subcondition is with advantage inversely proportional to the measured temperature.

In yet another embodiment of this aspect of the invention, the processor is configured to assign to the status indicator a third value which represents it being impossible to determine the starter motor's function if the measured supply voltage is below the voltage threshold. If the supply voltage is too low, it is in fact not possible to draw any conclusions about whether the engine not starting is due to the starter motor being faulty or whether the fault is due to some other cause, e.g. insufficient battery voltage.

In a further embodiment of this aspect of the invention, the measuring means are configured to measure the technical magnitudes over a measuring period and the processor is configured to average the measured technical magnitudes over that period. The processor is also configured to determine the status indicator on the basis of an average supply voltage to the starter motor over the measuring period and an average engine speed over the same period. With advantage, the temperature measurement means is also configured to measure the at least one temperature over a measuring period and the processor is configured to average the measured temperature over the same period. The processor is here configured to utilise this averaged temperature in determining the status indicator. Taking average values thus into account is advantageous in that the momentary values for supply voltage, rotation speed and temperature may be temporarily misleading as regards the actual conditions. It may also be advantageous to take into account other parameters, e.g. a lowest measured supply voltage to the starter motor during a compression cycle.

A further embodiment of this aspect of the invention considers the possibility that the engine may be of at least two possible different types. The processor is here configured to determine the status indicator on the further basis of the vehicle's engine type. The various engine types are supposed to be associated with different requirements for the starter motor's function and it is therefore possible on the basis of information about the respective engine type for suitable parameters and threshold values to be chosen for diagnosis of the starter motor.

Another aspect of the invention achieves the object by the method described in the introduction whereby at least one temperature related to the vehicle is measured and the status indicator is determined on the further basis of the at least one measured temperature. The advantages of this method, as also those of its preferred embodiments, are indicated by the above discussion of the system proposed.

A further aspect of the invention achieves the object by a computer programme directly downloadable to the internal memory of a computer and comprising software for controlling the steps of the method proposed above when said programme is run on a computer. The computer may itself be represented by a control unit on board the vehicle, a diagnostic unit connected thereto, a surfboard, a smartphone etc.

Yet another aspect of the invention achieves the object by a computer-readable medium which has stored on it a programme adapted to enabling a computer to control the steps of the method proposed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained in more detail on the basis of embodiments described as examples with reference to the attached drawings.

Figure 1 is a schematic diagram of a proposed system,

Figures 2a-b are graphs illustrating how the status indicator may be assigned according to embodiments of the invention, and Figure 3 is a flowchart illustrating the general method according to the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

We refer initially to Figure 1 which is a schematic diagram of a system according to the invention for diagnosis of an electric starter motor 110. The starter motor is supposed to be part of a vehicle equipped with a combustion engine 120 which the starter motor is configured for starting. The starter motor is itself powered with advantage by a battery 135.

The proposed system comprises measuring means 130 and 140, temperature measurement means 150 and a processor 160.

The measuring means 130 and 140 are configured to measure technical magnitudes related to the vehicle but representing only a supply voltage U to the starter motor 110 and a rotation speed RPM of the engine 120. The following description discusses throughout this rotation speed RPM. When the starter motor and the engine are connected together (e.g. via a so-called Bendix coupling) there is of course a relation between their respective rotation speeds, so a measured rotation speed of the starter motor may readily be treated as a proposed rotation speed RPM of the engine. The temperature measu rement means 1 50 is configu red to measure at least one temperature T related to the vehicle. This at least one temperatu re may for example refer to an ambient temperatu re pertaining to the vehicle, an oil temperature in the engine, a cooling water temperature, an engine block temperatu re, a starter motor temperatu re and/or a battery temperatu re. It is advantageous to register more than one temperatu re in that this makes it possible to assess whether the vehicle is started cold (all temperatures substantially equal) , warm (oil temperature in engi ne and cooling water temperature considerably hig her than ambient temperatu re) or in a semi- warm state (cooling water temperatu re considerably hig her than ambient temperatu re but oil temperature in engine relatively low). The processor 1 60 is configu red to use the measu red technical mag nitudes U and RPM and the temperature T as a basis for determining for the starter motor a status indicator S which serves as a measure of the quality of its performance.

For increased reliability/robustness, the measu ring means 1 30 and 1 40 are configured in one embodiment of the invention to measure the tech nical magnitudes over a measu ring period , e.g. 1 second, du ring which for example ten individual measurements are recorded.

Alternatively, the measu ring period may be adaptively con nected to one or more compression cycles of the engine so that it represents a whole number of compression cycles. The length of a typical compression cycle is about 1 5 ms. As an alternative to pure averaging of the rotation speed RPM, the processor may in such cases be configu red to register a lowest rotation speed du ring a compression cycle. Starting performance has i n fact been fou nd to depend on the rotation speed at its lowest. The processor may fu rther be configu red to average between respective lowest measu red supply voltages U to the starter motor in each of a number of compression cycles. The processor 1 60 may thus be configured to average the measured technical magnitudes over the measuring period and to determine the status indicator S on the basis of an average supply voltage U_avg to the starter motor over the period and an average rotation speed R P M_avg of the engine over the same period.

In a similar way, the temperature measurement means 1 50 is with advantage configured to measure at least one temperatu re T over a measu ring period. If such is the case, the processor is of course configured to average the at least one measured temperatu re T over the measuring period and to use at least one of the at least one averaged temperatu re in determi ning the status indicator S.

It may further be advantageous to respond to changing seasons by adjusting the diagnostic method applied by the processor. A temperatu re adjustment may for example be made in two steps (su mmer/winter) , i n more than two steps (e.g . below -25°C, between -25°C and -20°C, between -20°C and - 1 0°C, between - 1 0°C and ±0°C, between ±0°C and 1 0°C, and over 1 0°C) or continuously on the basis of a defi ned relationship such as R P Mexp = U x P1 /(T + P2) , i n which R P M_exp denotes expected rotation speed , U measu red supply voltage to the starter motor, T a measured temperatu re and P1 and P2 are adjustment parameters. Figure 2a is a first graph illustrating how the status i ndicator S is assigned accordi ng to one embodiment of the invention. It plots on the horizontal axis an average supply voltage U_avg to the engine and on the vertical axis an average rotation speed R P M_avg of the engine. I n this embodi ment of the invention the processor is configu red to assign the status indicator S a first value OK if the starter motor's function is deemed acceptable, and a second value NOT if the starter motor is not deemed to be fu nctioning satisfactorily. The status indicator S is assigned the first value OK if the measured supply voltage U_avg is above a voltage threshold U_th and the measu red rotation speed is at the same time above a rotation speed threshold RPM_th. It is advantageous to calculate the status indicator S continuously by comparing a measured rotation speed RPM with an expected rotation speed and to apply minimum threshold levels (e.g. a first level representing acceptable starter motor fu nction OK and a second level corresponding to unacceptable starter motor fu nction NOT), as for example in the relationship

RPM + N1(T)

S = 80 - U / N2(T) in which RPM denotes a measured rotation speed during an attempted start,

T a measu red temperatu re (e.g. an ambient temperature pertaining to the vehicle) ,

U a measured supply voltage during the attempted start,

N 1 (T) a rotation speed offset at the temperature T, and

N2(T) a rotation speed parameter at the temperatu re T.

In the above relationship, the status i ndicator S = 80 if the starter motor's function is good . S > 70 may thus correspond to acceptable starter motor fu nction OK, but if S < 70 indicates u nacceptable starter motor function NOT, a change of starter motor is advisable.

It is also advantageous if the processor applies an adaptive subcondition which depends on the at least one measured temperatu re T. This may mean that at a first temperatu re T1 the rotation speed has to exceed the rotation speed threshold RPM_th pro rata to how far the supply voltage U_avg exceeds a first control voltage U_br1 , where U_br1 > U_th. The adaptive subcondition is with advantage inversely proportional to the at least one measured temperature T.

To illustrate this, we refer to Figu re 2b for a second graph showing how the processor assigns the status indicator S. Like Figure 2a, it plots on the horizontal axis an average supply voltage U_avg to the starter motor and on the vertical axis an average rotation speed RPM_avg of the engine.

In Figure 2b a measured temperature T is assumed to have a value T2 > T1 . The adaptive subcondition being inversely proportional to the measu red temperatu re T means that at a hig her temperature T and a given supply voltage U_avg a higher rotation speed RPM_avg is required to enable the starter motor's fu nction to be deemed acceptable (and the status indicator S to be assigned the first value OK) . The slope of the temperature- dependent adaptive subcondition on the g raph in Figure 2b is therefore steeper than in Figure 2a.

To fu rther tig hten the rotation speed requirement at an increased temperature T, a second control voltage U_br2 may at a hig her temperature T2 > T1 be also given a lower value, i.e. U_br2 < U_br1 , where U_br2 > U_th.

The processor 1 60 is therefore with advantage configured to apply the adaptive subcondition on the basis of the measu red temperatu re T so that at a relatively high measured temperature T2 a relatively low measu red supply voltage U_avg has to be matched by a measured rotation speed exceeding the rotation speed threshold RPM_th to enable the adaptive subcondition to be deemed fulfilled and the status indicator S to be assigned the fi rst value OK.

Conversely, at a relatively low measured temperature T2 the processor 1 60 is with advantage configured to assign the status indicator S so that a relatively hig h measured supply voltage U_avg may be matched by a measu red rotation speed which is just above the rotation speed th reshold RPM_th, in which case the adaptive subcondition is deemed fulfilled and the status indicator S is assigned the first value OK.

As mentioned above, if the measured supply voltage U_avg is below the voltage threshold U_th, it is impossible to determine the starter motor's function. In one embodiment of the invention, the processor is therefore configured in such cases to assign the status indicator S a third value UN DEF denoting that the starter motor's function cannot be determined.

One embodiment of the invention considers the possibility that the vehicle's engine 1 20 may be of at least two possible different types. The respective engine types are themselves supposed to be associated with different requirements for the starter motor's function. Different types of engines typically have different starter motors, with consequent need for parameter adjustment, e.g. adjustment for swept volume and number of cylinders. Information about the respective type of engine may be stored on board the vehicle or be provided interactively via data input by a mechanic. I n any case, the processor is configured in this embodiment to determine the status indicator S on the further basis of the vehicle's engine type. On the basis of information about the respective engine type, the processor can set adjusted parameters and threshold values in order to diagnose the starter motor in an appropriate way.

The processor 1 60 is with advantage caused to function as above by means of a computer programme stored in the memory unit M which is part of, or is communicatively connected to, the processor.

To sum up, the general method according to the invention will now be described with reference to the flowchart in Figure 3. As a first step 31 0, a starter motor is supposed activated. This has with advantage been preceded by the fuel injection to the engine being shut off to prevent any risk of its starting during the diagnostic procedure. The starter motor is otherwise deemed to be in a vehicle and to be intended to start a combustion engine with which the vehicle is also provided.

A subsequent step 320 registers a first technical magnitude related to the vehicle in the form of a measured rotation speed of the engine. As described above, this rotation speed is registered over a measuring period which may be synchronised with one or more compression cycles. A step 330 parallel with step 320 registers a second technical magnitude related to the vehicle in the form of the supply voltage to the starter motor. A step 340 parallel with steps 320 and 330 registers at least one temperature related to the vehicle, i.e. a non-technical magnitude. A step 350 then determines a status indicator for the starter motor on the basis of the measured technical magnitudes and the at least one temperature. The status indicator serves as a measure of the quality of the starter motor's performance, e.g. whether it is functioning satisfactorily or not.

The method steps described with reference to Figure 3 may be controlled by means of a programmed computer unit. In addition, although the embodiments of the invention described above with reference to the drawings comprise a computer and processes conducted in a computer, the invention extends to computer programmes, particularly computer programmes on or in a support suited to practical implementation of the invention. The programme may be in the form of source code, object code, a code which is intermediate between source and object code, e.g. in partly compiled form, or in any other form suitable for use in implementing the process according to the invention . The support may be any entity or device capable of carrying the prog ramme. It may for example comprise a storage mediu m such as a flash memory, a ROM (read only memory), e.g . a CD (compact disc) or a semiconductor ROM, E PROM (electrically prog rammable ROM) , EE P ROM (erasable E PROM) , or a mag netic recordi ng mediu m, e.g. a floppy disc or hard disc. It may also be a transmitting support such as an electrical or optical signal which can be conveyed by an electrical or optical cable or via radio or i n some other way. Where the program me takes the form of a sig nal which can be conveyed di rectly by a cable or some other device or means, the support may take the form of such a cable, device or means. Alternatively, it may be an integ rated circuit in which the prog ramme is embedded , in which case the integrated circuit is adapted to conducting , or being used in the conducting of, the respective processes.

The invention is not restricted to the embodiments described with reference to the drawings but may be varied freely within the scope of the claims set out below.

Claims

1. A system for diagnosis of an electric starter motor (110) in a vehicle provided with a combustion engine (120), which engine (120) the starter motor (110) is configured for starting, which system comprises

measuring means (130, 140) configured to measure technical magnitudes related to the vehicle but representing only a supply voltage (U) to the starter motor and a rotation speed (RPM) of the engine, and

a processor (160) configured to use the measured technical magnitudes as a basis for determining for the starter motor (110) a status indicator (S) which serves as a measure of the quality of the starter motor's performance, characterised in that

the system comprises temperature measurement means (150) configured to measure at least one temperature (T) related to the vehicle, which temperature (T) denotes at least one from among an oil temperature in the engine (120), a cooling water temperature for the engine (120), an engine block temperature of the engine (120) and a battery temperature, and

the processor (160) is configured to determine the status indicator (S) on the further basis of the at least one measured temperature (T).

2. The system according to claim 1, in which the at least one temperature (T) further denotes an ambient temperature pertaining to the vehicle.

3. The system according to claim 1 or 2, in which the

processor (160) is configured to

assign the status indicator (S) a first value (OK) if the function of the starter motor (110) is deemed acceptable, and a second value (NOT) if the starter motor is not deemed to be functioning satisfactorily, which status indicator (S) is assigned the first value (OK) if the measured supply voltage (U_avg) is above a voltage threshold (U_th) and the measured rotation speed is above a rotation speed threshold (RPM_th).

4. The system according to claim 3, in which the processor (1 60) is configured to also apply an adaptive subcondition on the basis of the at least one measu red temperature (T) so that

at a relatively high measured temperature (T2) a relatively low measu red supply voltage (U_avg) has to be matched by a measured rotation speed which is above the rotation speed th reshold (RPM_th) to enable the adaptive subcondition to be deemed fulfilled and the status indicator (S) to be assigned the fi rst value (OK) , and

at a relatively low measu red temperatu re (T2) a relatively high measured supply voltage (U_avg) may be matched by a measured rotation speed which is just above the rotation speed th reshold (RPM_th), i n which case the adaptive subcondition is deemed fulfilled and the status indicator (S) is assigned the first value (OK) .

5. The system according to clai m 4, in which the adaptive subcondition is inversely proportional to the at least one measured temperature (T).

6. The system according to any one of clai ms 3 to 5, in which if the measured supply voltage (U_avg) is below the voltage th reshold (U_th) the processor is configu red to assign the status indicator (S) a third value (U N D E F) which denotes that the starter motor's function cannot be determined .

7. The system according to any one of the foregoing claims, in which

the measu ring means (1 30, 1 40) are configured to measure the technical magnitudes over a measuring period , and

the processor (1 60) is configu red to average the measu red technical magnitudes over the measuring period and to

determine the status indicator (S) on the basis of an average measured supply voltage (U_avg) to the starter motor (1 1 0) over the measuring period and an average rotation speed (RPM_avg) of the engine over the same period.

8. The system according to clai m 7, in which

the temperature measurement means (1 50) is configu red to measure the at least one temperatu re (T) over the measu ring period , and

the processor (1 60) is configu red to average at least one of the at least one measured temperature (T) over the measuring period and to use said at least one of the at least one average temperatu re in determining the status indicator (S) .

9. The system according to any one of the foregoing claims, in which the possibility is assumed of the combustion engine (1 20) being of a certain type from among at least two different possible types, and the processor (1 60) is configu red to

determine the status indicator (S) on the fu rther basis of the vehicle's engine type.

1 0. A method for diagnosis of an electric starter motor (1 1 0) with which a vehicle is provided, which method comprises

measurement of technical magnitudes related to the vehicle but representing only a supply voltage (U) to the starter motor and a rotation speed (RPM) of the engine, and

determining on the basis of the measured tech nical magnitudes a status indicator (S) for the starter motor (1 1 0) which serves as a measu re of the quality of the starter motor's performance, characterised by

measuring at least one temperatu re (T) related to the vehicle, which temperature (T) denotes at least f rom among an oil temperature i n the engine (1 20) , a cooling water temperatu re for the engine (1 20) , an engine block temperatu re of the engi ne (1 20) and a battery temperatu re, and

determining the status indicator (S) on the fu rther basis of the at least one measured temperature (T).

1 1 . The method according to clai m 1 0, in which the at least one temperatu re (T) fu rther denotes an ambient temperatu re pertaining to the vehicle.

1 2. The method according to clai m 1 0 or 1 1 , in which the status indicator (S) may assume a first value (OK) which represents the starter motor's function being acceptable, and a second value (NOT) which represents the starter motor (1 1 0) not functioning satisfactorily, which method comprises assigning the status indicator (S) the first value (OK) if the supply voltage (U_avg) is above a voltage threshold (U_th) and the rotation speed (RPM_avg) is above a rotation speed threshold (RPM_th).

13. The method according to claim 12, comprising applying an adaptive subcondition on the basis of the at least one measured temperature (T) so that:

at a relatively high measured temperature (T2) a relatively low measured supply voltage (U_avg) has to be matched by a measured rotation speed which is above the rotation speed threshold (RPM_th) to enable the adaptive subcondition is to be deemed fulfilled and the status indicator (S) to be assigned the first value (OK), and

at a relatively low measured temperature (T2) a relatively high measured supply voltage (U_avg) may be matched by a measured rotation speed which is just above the rotation speed threshold (RPM_th), in which case the adaptive subcondition is deemed fulfilled and the status indicator (S) is assigned the first value (OK).

14. The method according to claim 13, in which fulfilment of the adaptive subcondition is inversely proportional to the at least one measured temperature (T).

15. The method according to any one of claims 12 to 14, comprising, if the supply voltage is below the voltage threshold (U_th), the status indicator (S) being assigned a third value

(UNDEF) which denotes that the starter motor's function cannot be determined.

16. The method according to any one of claims 10 to 15, comprising

measuring the technical magnitudes over a measuring period,

averaging said respective technical magnitudes (U; RPM) over the measuring period, and

using the averaged technical magnitudes (U_avg; RPM_avg) in determining the status indicator (S).

17. The method according to claim 16, comprising

measuring at least one temperature (T) over the measuring period,

averaging at least one of the at least one temperature (T) over the measuring period, and

using said at least one of the averaged temperature (T) in determining the status indicator (S).

18. The method according to any one of claims 10 to 17, in which the starter motor (110) is configured to start a combustion engine (120) with which the vehicle is provided, which engine (120) is deemed to be of a certain type from among at least two different possible types, which method comprises

determining the status indicator (S) on the further basis of the vehicle's engine type.

19. A computer programme directly downloadable to the internal memory (M) of a computer and comprising programme instructions for controlling the steps according to any one of claims 10 to 18 when said programme is run on the computer.

20. A computer-readable medium (M) which has stored on it a programme which is adapted to enabling a computer to control the steps according to any one of claims 10 to 18.