EP1374385A1

EP1374385A1 - Method for determining the drive torque of an alternator

Info

Publication number: EP1374385A1
Application number: EP02753743A
Authority: EP
Inventors: Philippe Langry; Olivier Blondel
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2001-03-28
Filing date: 2002-03-28
Publication date: 2004-01-02
Also published as: WO2002078169A1; FR2823028A1; FR2823028B1

Abstract

The invention relates to a method consisting in: a) calculating the current (IR) circulating in the rotor of the alternator (1) taking account of the current rotor temperature; b) recording the rotation speed of the alternator (1); and c) determining the drive torque value using a predetermined relation that is specific to said alternator and linking said drive torque to the values for rotor current (IR) and rotation speed calculated during steps a) and b).

Description

Method for determining the driving torque of an alternator

The present invention relates to a method for determining the driving torque of an alternator, in particular that which in a motor vehicle ensures the production of electrical energy for its on-board network. There is currently a strong tendency to increase the electrical power installed on board motor vehicles, in particular that of various charges necessary for heating which is more and more assured by means of resistors with positive temperature coefficient (PTC resistors). The switching on and off of these large loads on the on-board network considerably varies the drive torque required by the alternator, which is felt at the level of the internal combustion engine driving the vehicle and to which the alternator is also mechanically coupled.

Furthermore, the control computer of such an internal combustion drive engine increasingly needs to know the values of the drive torques required by the accessories surrounding the engine and among these accessories is the alternator.

The need therefore arises in this context to be able to determine with satisfactory precision and at all times the value of the drive torque of such an alternator. From US 5,952,586, a method is known for determining the driving torque requested by an alternator by which the value of this torque is deduced from a relationship between the speeds of an output pulley of the internal combustion engine and d '' a drive pulley mounted on the alternator shaft, the two pulleys being mechanically coupled by a belt. The speed of the alternator pulley is deducted from the current supplied by the alternator. This method has the disadvantage of giving an imprecise result, in particular due to the fact that in the calculation of the torque requested by the alternator, it is necessary involve the elastic properties of the belt coupling the two pulleys to each other.

The object of the invention is to propose a method for determining the torque required by an alternator which does not have these drawbacks of the prior art.

The subject of the invention is therefore a method for determining the driving torque of an alternator of a motor vehicle, this alternator comprising a rotor winding characterized in that it consists: - a) in calculating the current flowing in the alternator rotor taking into account the current rotor temperature;

- b) to note the speed of rotation of the alternator; and - c) determining the value of said drive torque from a predetermined relationship specific to this alternator and relating this drive torque to the calculated values of the rotor current and the speed of rotation, established during steps a ) and B) . Thanks to these characteristics, it becomes possible, with a minimum of hardware and software means, to determine the drive torque of the alternator by taking into account the current rotor operating temperature and by avoiding any implication of parameters relating to the mechanical alternator drive elements in determining the drive torque.

The process according to the invention can also have the following advantageous features: - it consists in extracting the value of said drive torque from a first characteristic table recorded on a test bench and in which the current and speed values corresponding to said predetermined relationship have been previously stored; it consists in determining said rotor current by calculating the quotient of the current voltage delivered to the rotor winding, by the rotor resistance corrected as a function of the current rotor temperature. - the determination of the rotor current is only carried out if the value of the current voltage delivered by the alternator exceeds a predetermined minimum value; in the case where said alternator comprises a rotor current regulator comprising a controlled semiconductor component whose control signal is impulse for determining the value of the rotor current as a function of the duty cycle of this control signal, the method consists in calculating the produces said duty cycle by the current voltage delivered by the alternator to determine said voltage delivered to the rotor winding; it consists in subjecting the value of said duty cycle to a first-order low-pass filtering operation whose cut-off frequency is determined by the quotient of the rotor resistance established at a first predetermined temperature, by the value of the rotor inductance, said rotor resistance at a first predetermined temperature being temperature corrected as a function of said current rotor temperature; said cutoff frequency is established according to the relationship:

v = -! - î - i [1 + 0.0039 ^• fa -T]

2-π-L

in which: F _c = Cutoff frequency

T _x = Said first predetermined temperature R _Tx = Resistance of the rotor winding at temperature T _x 0.0039 = Temperature coefficient of the resistivity of copper T _R = Current temperature of the rotor winding L = Rotor inductance it consists of calculate said rotor current using a relation of the form:

I U ^ -RCO-PF-filré

^R R _Tx • [l +0.0039 - (T _R -T _X )] in which:

I _R = Rotor current

U _a i _t ⁼ Current voltage delivered by

1 alternator RCO_DF_filtered = Filtered duty cycle T _x = First predetermined temperature

R _τx = _Rotor resistance at temperature

T _x 0.0039 = Temperature coefficient of the resistivity of copper T _R = Current temperature of the rotor winding if the voltage applied to

The rotor winding of the alternator is temperature compensated with a predetermined compensation constant, it consists in determining the current rotor temperature according to the relationship: in which:

T _R = Current rotor temperature

T _y = Second predetermined temperature of the alternator U _a ι _t _τy = Voltage supplied by the alternator at temperature T _y U _a ι _t = Current voltage supplied by

1 alternator K _c = Temperature compensation constant of the regulation voltage _0. = Correlation coefficient between the rotor temperature Tr and the temperature of said regulator the method consists in limiting the rate of variation of the rotor temperature to a predetermined major value ; the rotor current calculation is performed only if the current rotor temperature exceeds a predetermined rate of change; it consists in extracting the value of the current rotor temperature from a second characteristic table previously recorded on a test bench and in which the values of said current rotor temperature are stored as a function of the voltage delivered by the alternator. Other characteristics and advantages of the present invention will become apparent during the description which follows, given solely by way of example and made with reference to the appended drawings in which: FIG. 1 is a diagram showing the evolution of the torque drive C _e of an alternator depending on the rotor current I _R for two rotational speeds Vi and V of this alternator; Figure 2 is a simplified diagram showing as an example of application of the invention, an electrical installation of a motor vehicle powered by an alternator whose drive torque is determined according to the method of the invention; FIG. 3 is a diagram showing an example of a control signal of a semiconductor component inserted in the excitation circuit of an alternator to control the rotor current I _{R thereof} ; and FIG. 4 is a flow chart illustrating the operations executed during the implementation of the method according to the invention. The invention is based on the observation that the torque necessary for driving an alternator can be evaluated with a very good approximation from its rotational speed and the current flowing in its rotor, provided that due account is taken of phenomena of magnetic saturation and rotor temperature.

FIG. 1 illustrates this finding which has been confirmed by numerous measurements made by the Applicant on commercially available alternators for applications in the field of motor vehicles. It can be seen that the relationship between the driving torque C _e and the current I _R flowing in the rotor follows at least approximately a linear law for the different speeds of rotation, for example the speeds Vi and V ₂ , and that each corresponding curve has a linear domain 1 and a saturation domain s.

According to the invention, the beam of curves of the drive torque as a function of the rotor current corresponding to the alternator considered is noted beforehand for an alternator or a type of alternator. considered and the corresponding values are stored in a first table of characteristics TC1 (see FIGS. 2 and 4).

To extract the torque values from the characteristic table TC1, it is necessary to know the rotational speed V of the alternator and the current I _R which flows in its rotor, the value of the torque being calculated at regular intervals to be refreshed periodically with a predetermined period which can be 10 ms for example. Such a periodicity is sufficient in the environment of an internal combustion engine of a motor vehicle.

The rotational speed V of the alternator can be easily measured, for example by a suitable sensor specially provided on the alternator. However, in the case of application in a motor vehicle, the value of the alternator speed is directly available from the engine control computer which can deduce it from the engine speed, ci having a constant relationship with this speed of the alternator.

We will now describe a preferred embodiment of obtaining the other value determining the torque of the alternator, namely the value of the rotor current I _R. In order to facilitate understanding of the description, reference will first be made to FIG. 2 which represents a very simplified diagram of an electrical installation of a motor vehicle, equipped with an alternator 1 to which the determination method is applied of drive torque according to the invention. This example concerns, without limitation, the electrical installation of a motor vehicle.

The alternator 1 comprises a stator winding 2, of the three-phase type for example, and a rotor excitation winding 3. The stator winding 2 is connected to a rectifier bridge 4 which supplies DC voltage to a battery 5 and, via an ignition key 6, to an on-board network 7 of the motor vehicle. The power supply for the rotor winding 3 is taken from the + pole of the battery 6 and sent to the winding 3 via a controlled semiconductor component 8. The latter is part of a regulator 9. The assembly which has just been described is classic in automotive technology. This set also includes a computing device 10 responsible for implementing the method according to the invention. This calculation device 10 can be integrated into the on-board computer (not shown) of the vehicle responsible in particular for controlling its internal combustion engine. It includes in particular the characteristic table TC1 which has already been discussed above.

The computing device 10 receives several input signals.

First of all, the regulator 9 of the excitation winding 3 supplies it with a signal DF for controlling the controlled semiconductor component 8. This signal is shown in supplemented form in FIG. 3. It can be seen that it acts of an impulse signal on the cyclic ratio T _on / T of which the regulator 9 can act, T being the duration of the period of the signal DF and T _on the duration of the interval during which the signal is active to return the component 8 driver. The calculation device 10 produces from this signal DF a signal RC0_DF representative of the instantaneous average voltage applied to the winding 2 according to the relationship:

RCO DF = - ^ - 100 (1) T

The calculation device 10 also receives the voltage

U _bat prevailing at the terminals of the battery 5, as well as a speed value V as already described above.

FIG. 4 illustrates the progress of the determination method according to the invention. The functional block Bl symbolizes the operation of calculating the signal RCO_DF from the signal DF according to the relation (1) given above.

The B2 functional block symbolizes a first order filtering operation performed on the RC0_DF signal. This operation is desirable to take into account the range of variation of the resistance and inductance of the winding 2 as a function of the temperature. Preferably, the filtering executed during operation B2 is of the low-pass type and has a cut-off frequency of the form:

_T7 _R _I , - [l + 0.0039- (T _R -T _x )]

(2:

2-π-L in which:

F _c = Cutoff frequency

T _x = First predetermined temperature

(it is 20 ° C for example)

R _Tx = Resistance of the rotor winding at temperature T _x

0.0039 = Temperature coefficient of copper resistivity

T _R = Temperature of the rotor winding

L = Rotor inductance recorded on a test bench for each type of alternator, a single value being sufficient for the entire operating range of the alternator. It can be seen that the implementation of the calculation of the cut-off frequency F _c of the filtering operation requires knowledge of the rotor temperature T _R occurring during the operation of the alternator. This rotor temperature T _R is not directly available.

It should also be known that alternators used in motor vehicles can be cooled either by air only, or by both water and air. In the first case, the rotor temperature T _R is essentially influenced: by the rotor losses which themselves depend on the current I _R , the latter varying in turn as a function of the stator current I _s ; - by the temperature of the cooling air; by the flow of this cooling air which depends on the speed of rotation V of the alternator.

In the second case, in addition to these parameters acting on the rotor temperature also the temperature of the cooling water which in the case of a motor vehicle is generally that circulating in the internal combustion engine to cool it.

Taking all these parameters into account presents considerable difficulties and makes determining the rotor temperature complex. The invention proposes to circumvent these difficulties in the following manner.

The alternator 1 being equipped with the regulator 9, this must be compensated in temperature in particular to correct the regulation voltage with a view to optimally maintaining the charge of the battery 6. It has been found that the temperature of the regulator 9 has a close correlation with the rotor temperature T _R within the precision limits compatible with a correct implementation of the method according to the invention. The temperature of regulator 9 can be estimated by the relation: U * = U ^ - | τ _rt -T _y ) .K _c ] (3) in which:

U _a ιt = Regulated voltage delivered by

1 alternator T _γ = Second predetermined temperature

(it can be equal to 23 ° C, for example) Uaitjry = Regulated voltage delivered by

1 alternator at temperature T _y

(it can be 14.55 Volts, for example) T _ΘSt = Estimated temperature of the regulator chip 9 K _c = Temperature compensation _constant of the regulation voltage (it can be equal to

0.01 for example) Due to the correlation between the temperature T _es t of the regulator chip 9 and the rotor temperature T _R , it comes from equation (3):

in which:

T _R = Current rotor temperature oc = Correlation coefficient between the rotor temperature T _R and the temperature of the regulator 9 Preferably, the line represented by the relation 4 can be stored in a table of characteristics TC2 (figure 2 and 4) noted on test bench. Referring again to FIG. 4, the method supplies the temperature T _R in the following manner on the basis of the calculation elements which have just been exposed.

During the operation represented by the functional block B3, the voltage U _bat t_Ecu is preferably recorded on the control computer (not shown) of the internal combustion engine of which it is the supply voltage. It is therefore readily available to the computing device 10. Advantageously, it follows from this supply voltage, the voltage U _has ι _t by increasing the voltage Ubat _t _ _E cu an offset voltage U calibratable _0f f _Ξ and , representing the difference almost constant tension between the two for a type ^'of alternator given. The calculation of the sum Ubatt_reg + U ₀ ff _Se t is symbolized by the functional block B4.

It has been found that the method of determining the drive torque according to the invention gives reliable results only in the absence of the following two operating situations. If the alternator 1 operates with a maximum excitation field (the duty cycle DF of FIG. 3 is then 100%), the voltage U _a ι _t is no longer regulated so that the thermal compensation for the estimate of the current rotor temperature T _R is no longer active. This situation corresponds to the case where the battery operates in "superelevation". This is in fact a theoretical situation because, moreover, the regulation is carried out in such a way that this situation is avoided. However, as a safety measure, the method of the invention performs a test (functional block B5) to check whether the voltage U _a χ _t is greater than a minimum value U _a ι _t __ _n i _n qu. can typically be set at 13.4 Volts for example. As long as this condition is not satisfied, the execution of the process is frozen (functional block Bβ) and the test in B5 continues to be implemented. On the other hand, as long as the above condition is satisfied, during the operation represented by the functional block B7, the method searches in the characteristic table TC2 for the value of the temperature T _R which corresponds to the current regulated voltage U _a i _t of the alternator 1.

Furthermore, preferably, to compensate for fluctuations in the voltage of the network 7, it is advantageous to limit the rate of variation T _R _i _nc of the rotor temperature T _R to a predetermined maximum value _R _i _nc _j _nax . This value corresponds to an increase in the heating of the rotor which can typically be 0.25 ° C. per 10 milliseconds. The corresponding operation is carried out during a test symbolized by the functional block B8. In this block, we examine inequality:

T _R (n)> T _R (nl) + T _{RJnc max} (5)

In other words, it is examined whether the current rotor temperature T _R (n) of the iteration n is higher or not than the sum of the rotor temperature T _R (nl) established during the previous iteration and kept in memory (function block B9).

If the test B8 is answered in the negative, the temperature T _R (n) calculated is used for the rest of the operations. Otherwise, the value for the rotor temperature is set (function block B10):

T _R (n) = T _R (n - 1) + T _R _ _tac _ _MX

This process implemented in the functional blocks B8, 9 and 10 amounts to limiting the rate of change of the rotor temperature to a predetermined increasing value equal to T _R _ _inc _maχ.

The operation corresponding to the functional block B2 results in obtaining the value RC0_DF_filtered, this value then being normalized over a range of 100% during the operation which is symbolized by the functional block B11. The following operation (functional block B12) consists in calculating the current I _R according to the relation:

U _a1t -RCO_DF_ filtered

I .. = „r. „L. „M • ⁽ 7 ⁾

R _Tx • [l + 0.0039 - (T _R - T _X )]

The parameters of this relation (7) are the same as those already defined above. Note however that the value of the resistance R _Tx preferably includes a part due to a parasitic resistance composed in particular of the contact resistance at the level of the rings and. brushes of the alternator 1 and of the resistor R _DS _ _ON φJ-S presents the semiconductor component 8 when it is on. The value of this parasitic resistance can be estimated at 0.25 Ù in the case of most commercial alternators.

During the operation symbolized by the functional block B13, the desired value of the driving torque C _e of the alternator is calculated using the characteristic table TC1 to which the value of the current I is applied. _R which has just been calculated and the current value of the speed of rotation V of the alternator 1. In the application to the alternator of a motor vehicle, the parameters necessary for the execution of the method according to the invention and specific to the type of alternator used, and in particular the. characteristic tables TC1 and TC2 are preferably communicated to the computer 10, at the end of the production line of the vehicle concerned. For example, this data transfer can be carried out by entering data on a CAN bus of the vehicle or by a bidirectional link by which the computer 10 can identify itself and then receive the appropriate data.

Claims

1. Method for determining the drive torque (C _e ) of an alternator (1) of a motor vehicle, this alternator comprising a rotor winding (3) characterized in that it consists of: a) calculating the current (I _R ) circulating in the alternator rotor (1) taking into account the current rotor temperature (T _R ); - b) to note the speed of rotation (V) of the alternator (1); and c) determining the value of said driving torque (C _e ) from a predetermined relation specific to this alternator and relating this driving torque (C _e ) to the calculated values of the rotor current (I _R ) and of the speed of rotation (V) established during steps a) and b).

2. Method according to claim 1, characterized in that it consists in extracting the value of said drive torque (C _e ) from a first characteristic table recorded on test bench (TC1) in which the current values and speed corresponding to said predetermined relationship have been previously stored.

3. Method according to any one of claims 1 and 2, characterized in that it consists in determining said rotor current (I _R ) by calculating the quotient of the current voltage (U _a ι _t ) delivered to the rotor winding (3) by the rotor resistance corrected as a function of the current rotor temperature (T _R ).

4. A method according to claim 3, characterized in that the determination of the rotor current (I _R) is only performed if the current voltage value (U _is) delivered by the alternator (1) exceeds a predetermined minimum value (U _have t in) •

5. Method according to claim 4, characterized in that, in the case where said alternator (1) comprises a rotor current regulator (9) comprising a controlled semiconductor component (8) whose control signal is impulse to determine the value of the rotor current as a function of the duty cycle (RCO_DF) of this control signal, the method consists in calculating the product of said duty cycle (RC0_DF) by the current voltage (U _a i _t ) delivered by the alternator in order to determine said voltage delivered to the rotor winding.

6. Method according to claim 5, characterized in that it consists in subjecting the value of said duty cycle (RCO_DF) to a first-order low-pass filtering operation whose cut-off frequency (F _c ) is determined by the quotient of the rotor resistance established at a first predetermined temperature (T _x ), by the value of the rotor inductance (L), said rotor resistance at a first predetermined temperature being corrected in temperature as a function of said current rotor temperature (T _R ) .

7. Method according to claim 6, characterized in that said cut-off frequency is established according to the relation:

R _Tx - [l + 0.0039- (T _R -T _x )] 2-π-L in which:

F _c = Cutoff frequency

T _x = Said first predetermined temperature R _Tx = Resistance of the rotor winding at temperature T _x 0.0039 = Temperature coefficient of the resistivity of copper T _R = Current temperature of the rotor winding = Rotor choke

8. Method according to claim 7, characterized in that it consists in calculating said rotor current using a relation of the form:

U _alt -RCO_DF__ filtered

IR = R _Tx - [l + 0.0039 - (T _R - T _X )] in which:

IR Rotor current

Uait Current voltage delivered by

1 alternator

RCO_DF_filtered Filtered duty cycle T _x First predetermined temperature

RTX Rotor resistance to temperature

T _x

0.0039 Temperature coefficient of copper resistivity

T _R Current temperature of the rotor winding

9. Method according to any one of claims 5 to. characterized in that in the case where the voltage applied to the rotor winding (3) of the alternator (1) is temperature compensated with a predetermined compensation constant (K _c ), it consists in determining the current rotor temperature according to the relationship:

where: T _R = Current rotor temperature

= Second predetermined temperature of the alternator

U _a lt_Ty = Voltage delivered by the alternator at temperature T _y Uait ⁼ Current voltage delivered by the alternator K _c = Temperature compensation constant of the regulation voltage _α = Correlation coefficient between the rotor temperature T _R and the temperature of said regulator (9)

10. Method according to claim 1, characterized in that it consists in limiting the rate of change of the rotor temperature to a predetermined major value

(-1-R_inc_max) •

11. Method according to any one of claims 9 and 10, characterized in that it consists in extracting the value of the current rotor temperature (T _R ) from a second characteristic table (TC2) previously recorded on a test bench and in which are stored the values of said rotor current temperature (T _R) as a function of the voltage (U _is) delivered by the alternator

(1).

12. Calculation device for implementing the method according to any one of claims 5 to 11, this device being able to be integrated into an on-board computer (10) of said vehicle, characterized in that it comprises at least one table characteristic (TC1, TC2) recorded on a test bench in which the values of current (I _R ) and speed (V) responding to said predetermined relationship have been previously stored, and several inputs receiving the following data: the control signals (DF) of said semiconductor component (8) from said regulator (9), the voltage (U _ba tt) across the battery (5) of said vehicle and the speed of rotation (V) of said alternator (1) .