Coil temperature estimation

Abstract

Methods for estimation of lost temperature increment after system restart for motor coil temperature estimation in an electric power steering apparatus of a motor vehicle with a power pack including an ECU with a temperature sensor and an electric motor. The methods allow to easily recover the lost heat increment value after restart of the system. Consequently, the estimation of the temperature of the motor coils will start from the correct temperature value. Damage of the motor due to overheat can be prevented. Further a more robust system diagnostics and a more accurate torque signal estimation can be provided.

Claims

1. A method for estimation of lost temperature increment (T.sub.LostIncrement) after system restart for motor coil temperature estimation in an electric power steering apparatus of a motor vehicle with a power pack comprising an ECU with a temperature sensor and an electric motor, said method comprising the steps of: a) storing a given resistance curve of the motor coils; b) storing a measured resistance curve of the ECU; c) measuring a demand voltage vector (U.sub.d,d), a current feedback value I.sub.d,fb based on a demand current vector (I.sub.d,d) and a battery voltage (U.sub.bat) during a special measurement pulse; d) determining the power pack resistance (R.sub.powerpack) based on the parameters measured in step c); e) measuring the temperature of the ECU (T.sub.ECU) with the temperature sensor; f) determining the resistance of the ECU (R.sub.ECU) on basis of the measured temperature in step e) and the stored resistance curve of the ECU; g) subtracting the resistance of the ECU (R.sub.ECU) from the determined power pack resistance (R.sub.powerpack); h) determining the temperature of the motor coils (T.sub.motorcoil) based on the value obtained in step g) and the stored resistance curve of the motor coils; and i) obtaining the lost temperature increment (T.sub.LostIncrement) by subtracting the measured temperature of the ECU (T.sub.ECU) from the determined temperature of the motor coils (T.sub.motorcoil).

2. The method of claim 1, wherein the motor coil resistance curve is given by $T_{\mathrm{motorcoil}}=\frac{\left(\frac{R_{\mathrm{motorcoil}}}{R_0}\right)-1}{{}_{\mathrm{Cu}}}+T_0,$ wherein T.sub.motorcoil is the motor coil temperature, R.sub.motorcoil the resistance of the coil, T.sub.0 the room temperature, .sub.Cu the heat coefficient of the coils' copper and R.sub.0 the resistance of the coil at room temperature.

3. The method of claim 1, wherein the motor coil resistance (R.sub.motorcoil) increases with a gradient of about 39%/100 C.

4. The method of claim 1, wherein the special measurement pulse is of an extent such that the rotor of the motor does not move.

5. The method of claim 1, wherein the special measurement pulse is less than 25 ms.

6. The method of claim 1, including storing the motor coils resistance curve and the ECU resistance curve by polynomial equations.

7. The method of claim 1, including storing the motor coils resistance curve and the ECU resistance curve each by two polynomial equations, one for a first and another for a second part, wherein the first and second part are separated by the minimum of resistance of the ECU resistance curve.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic view of an electric power steering apparatus.

(2) FIG. 2 is a block diagram showing an electrical structure of the electric power steering apparatus.

(3) FIG. 3 is a graph of the calculated resistances plotted against temperature.

DETAILED DESCRIPTION

(4) Although certain example methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. Moreover, those having ordinary skill in the art will understand that reciting a element or an element in the appended claims does not restrict those claims to articles, apparatuses, systems, methods, or the like having only one of that element, even where other elements in the same claim or different claims are preceded by at least one or similar language. Similarly, it should be understood that the steps of any method claims need not necessarily be performed in the order in which they are recited, unless so required by the context of the claims. In addition, all references to one skilled in the art shall be understood to refer to one having ordinary skill in the art.

(5) The present invention relates to an electric power assisted steering system of a motor vehicle.

(6) In some examples, a method for estimation of lost temperature increment after system restart for motor coil temperature may involve an estimation in an electric power assisted steering system of a motor vehicle.

(7) Accordingly, a method for estimation of lost temperature increment in an electric power steering apparatus of a motor vehicle with a power pack comprising an ECU with a temperature sensor and an electric motor, is provided, said method comprises the steps of: a) Storing a given resistance curve of the motor coils; b) Storing a measured resistance curve of the ECU; c) Measuring a demand voltage vector, a current feedback value I.sub.d,fb based on a demand current vector and a battery voltage during a special measurement pulse; d) Determining a power pack resistance based on the parameters measured in step c); e) Measuring the temperature of the ECU with the temperature sensor; f) Determining the resistance of the ECU on basis of the measured temperature in step e) and the stored resistance curve of the ECU; g) Subtracting the resistance of the ECU from the determined power pack resistance; h) Determining the temperature of the motor coils based on the value obtained in step g) and the stored resistance curve of the motor coils; and i) Obtaining the lost temperature increment by subtracting the measured temperature of the ECU from the determined temperature of the motor coils.

(8) Preferably, the motor coil resistance curve is given by

(9) $T_{\mathrm{motorcoil}}=\frac{\left(\frac{R_{\mathrm{motorcoil}}}{R_0}\right)-1}{{}_{\mathrm{Cu}}}+T_0,$
wherein T.sub.motorcoil is the motor coil temperature, R.sub.motorcoil the resistance of the coil, T.sub.0 the room temperature, .sub.Cu the heat coefficient of the coils' copper and R.sub.0 the resistance of the coil at room temperature.

(10) In one embodiment, the motor coil resistance increases with about 39%/100 C.

(11) It is advantageous that the special measurement pulse is so short, that the rotor of the motor does not move. Preferably, the special measurement pulse is less than 25 ms. The motion of the rotor and therefore the motor torque generation is further prevented by using the direction of a demand current vector I.sub.d,d and direction of a demand voltage vector U.sub.d,d.

(12) In a preferred embodiment, the motor coil resistance curve and the measured ECU resistance curve are stored by polynomial equations in the ECU software. The resistance curves can be further stored in look-up tables. In a preferred embodiment the proper polynomial equation can be selected.

(13) Favourably, the motor coil resistance curve and the ECU resistance curve are stored each by two polynomial equations, one for a first and one for a second part, wherein the first and second part are separated by the minimum of resistance of ECU resistance curve.

(14) FIG. 1 is a schematic diagram of an electric power steering apparatus 1. A steering wheel 2 is fixed to a steering shaft 3, and the steering shaft 3 is coupled to a rack 4 via a rack-and-pinion mechanism 5. Rotation of the steering shaft 3 accompanying a steering operation is converted into a reciprocating linear motion of the toothed rack 4 by the rack-and-pinion mechanism 5. The linear motion of the rack 4 changes the steering angle of the steered wheels 6. To provide steering assistance, an electric motor 7 mounted to the side of the rack housing drives a ball-screw mechanism 8 via a toothed rubber belt 9.

(15) Electric power assist is provided through a steering controller (ECU) 10 and a power assist actuator 11 comprising the electric motor 7 and a motor controller 12. The steering controller 10 receives signals representative of the vehicle velocity v and the torque T.sub.TS applied to the steering wheel 2 by the vehicle operator. In response to the vehicle velocity v and the operator torque T.sub.TS, the controller 10 determines the target motor torque T.sub.d and provides the signal through to the motor controller 12, where the duty cycles are calculated to produce the phase currents via PWM (pulse-width modulation). The steering controller 10 including a temperature sensor 16 and the electric motor 7 forms a unit referred to as power pack 100. The power pack 100 can comprise further elements like the motor controller 12 or sensing circuits for sensing currents and/or voltages. The power pack 100 is fed with battery voltage U.sub.bat.

(16) FIG. 2 shows a block diagram of the electrical structure of the electric power steering apparatus 1. The steering controller 10 receives signals representative of the vehicle velocity v, the torque T.sub.TS applied to the steering wheel 2 by the vehicle operator and a base temperature T.sub.0 and derives the target motor torque T.sub.d. This torque is fed to the motor controller 12 which determines the voltage input for the PWM and a motor driver 17 generates via the PWM the motor currents I.sub.coils=i.sub.U, i.sub.V, i.sub.W. Hence, the motor 7 generates a torque T which compensates the operator torque T.sub.TS.

(17) An estimator estimates the temperature of the motor coils to adjust if necessary the current flowing through the motor 7 in order to prevent damage of the motor 7. A temperature sensor 16 measures the temperature T.sub.ECU of the ECU 10. The estimator adds to the measured temperature of the ECU T.sub.ECU a heat increment T.sub.Increment.
T.sub.CoilEstimated=T.sub.Increment+T.sub.ECU.

(18) The heat increment is derived as follows

(19) $T_{\mathrm{Increment}}=T_{\mathrm{Increment}\mathrm{Prev}}+\left\{\left(\frac{T_s}{C_{\mathrm{Thermal}}}\right).Math.\left(P-\left(T_{\mathrm{Increment}\mathrm{Prev}}.Math.G_{\mathrm{Thermal}}\right)\right)\right\},$

(20) wherein T.sub.Increment is the value of temperature increment to thermal ground in the actual control cycle, T.sub.IncrementPrev is the value of temperature increment calculated in the previous running cycle, T.sub.S=1/f.sub.S with f.sub.S the running frequency of the estimator, P is the value of calculated dissipated power of motor in the actual control cycle, G.sub.Thermal is the thermal conductance and C.sub.Thermal is the thermal capacity.

(21) After restart of the system the lost heat increment T.sub.LostIncrement needs to be recovered. This is done with the following method. FIG. 3 shows schematically the resistance curves of the motor coils 14, the ECU 15 and the power pack 13 and the calculation of the motor coil temperature T.sub.motorcoil.

(22) Before operation of the estimator the resistance of the power pack R.sub.powerpack 13 at different temperatures over the relevant range is measured. The power pack resistance curve 13 has a turning-point, separating the curve into a cold and warm part, wherein the turning point can be in a range between 0 C. and 15 C. This turning point is the minimum of the resistance curve of the capacitor. The shape of the resistance curve is representing the different temperature dependencies of the materials and electrical parts of the ECU 10. A polynomial formula for each part of the power pack resistance curve 13 is determined based on the demand voltage vector U.sub.d,d and the demand current vector I.sub.d,d expressed in a coordinate system fixed to the electrical angular frequency of the rotating rotor. The electrical angular frequency of the rotating rotor has the same or the opposite direction as the rotor, so the generation of motor torque can be prevented. By using the demand current vector I.sub.d,d and the demand voltage vector U.sub.d,d self-steering can be prevented.

(23) Further the connection between the motor coil resistance and the temperature of the motor coils, given by

(24) $T_{\mathrm{motorcoil}}=\frac{\left(\frac{R_{\mathrm{motorcoil}}}{R_0}\right)-1}{{}_{\mathrm{Cu}}}+T_0,$
is stored,

(25) wherein T.sub.0 is the temperature of the motor coils at the room temperature.

(26) The resistance of the coil R.sub.motorcoil is temperature dependent. The formula depends on the heat coefficient of the coils' copper .sub.Cu. Its value is 39%/100 C. Next the difference between the two curves 13, 14 is calculated resulting in the ECU resistance curve 15. This curve is stored in the parameter file by the help of two polynomial equations, one for the warm part and one for the cold part, wherein the proper polynomial equation can be selected.

(27) During operation of the estimator and after restart of the system the lost increment T.sub.LostIncrement is estimated with the following method;

(28) At first the resistance of the power pack R.sub.powerpack is measured. For that a special measurement pulse is used. The duration of this special measurement pulse is less than 25 ms. During this short time the rotor does not move, no steering assist is provided and the driver will not detect any unusual phenomena, like self-steering of the system. When the power pack 100 is started, the power pack resistance R.sub.powerpack is calculated by measurement of the demand voltage value U.sub.d,d and a current feedback value I.sub.d,fb=I.sub.Powerpack is determined which flows into the powerpack based on the the demand current value I.sub.d,d and the battery voltage U.sub.bat and calculation of the voltage drop U.sub.powerpack by

(29) $U_{\mathrm{powerpack}}=U_D.Math.\left(\frac{2}{3}.Math.U_{\mathrm{bat}}\right)$

(30) and by

(31) $R_{\mathrm{powerpack}}=\frac{U_{\mathrm{powerpack}}}{I_{\mathrm{powerpack}}}.$

(32) A thermal sensor 16, wherein the thermal sensor and the temperature sensor describe the same element, integrated in the ECU 10 measures the temperature of the ECU T.sub.ECU. The proper resistance value of the ECU R.sub.ECU can then be determined by the measured temperature T.sub.ECU and the respective part (cold or warm) of the pre-stored ECU resistance curve. In the next step, the motor coil resistance R.sub.motorcoil is determined by subtracting the ECU resistance value R.sub.ECU from the resistance of the power pack R.sub.powerpack. With the use of the stored motor coil resistance curve 14 and the calculated motor coil resistance R.sub.motorcoil, the motor coil temperature T.sub.motorcoil can be calculated. After that the lost heat increment T.sub.LostIncrement is determined, is which is the difference between the calculated motor coil temperature T.sub.motorcoil and the ECU measured temperature T.sub.ECU,
T.sub.LostIncrement=T.sub.motorcoilT.sub.ECU.

(33) This way the estimator can be restarted not from the base temperature (T.sub.ECU) but with an estimated incremented value T.sub.LostIncrement.

(34) The estimated motor coil temperature T.sub.CoilEstimated is then calculated during system initialization by
T.sub.CoilEstimated=T.sub.LostIncrement+T.sub.ECU.

(35) After that the estimator proceeds with T.sub.Increment, whereas in the first calculation cycle T.sub.LostIncrement is used as T.sub.IncrementPrev,
T.sub.CoilEstimated=T.sub.Increment+T.sub.ECUT.sub.Increment=T.sub.LostIncrement.Math.T.sub.CoilEstimated=T.sub.LostIncrement+T.sub.ECUT.sub.CoilReal

(36) Finally right from the start, the electric motor 7 is operated with the correctly estimated motor coil temperature.

(37) The method according to the present invention allows to easily recover the lost heat increment value after restart of the system. Consequently, the estimation of the temperature of the motor coils will start from the correct temperature value. Damage of the motor due to overheat can be prevented. Further a more robust system diagnostics and a more accurate torque signal estimation can be provided.