Patent Application
20200055543
The present disclosure relates to a motor drive apparatus and an electric power steering apparatus.
Driving of a motor used in an electric power steering apparatus or the like is controlled by a motor drive apparatus having a control unit. Electronic components included in the control unit may be damaged by the heat generated by drive control of the motor. Damage to the electronic components impairs the performance of the electric power steering apparatus.
A conventional overheat protection apparatus calculates an estimated value of the temperature of a motor and a controller without using a temperature sensor and adjusts an electric current supplied to the motor on the basis of the estimated value to thereby prevent overheating of the motor and the motor peripheral device.
However, the conventional overheat protection device does not take into account changes in the heat release amount over time. Therefore, temperature estimation accuracy may be insufficient. When an error in the estimated value becomes larger, for example, an electric current supplied to the motor may be limited in a state where it is not necessary to prevent overheating, and the assisting power of the electric power steering apparatus may be excessively reduced. This may impair driving comfortability.
A first example embodiment of the present disclosure is a motor drive apparatus that includes a control assembly that controls driving of a motor. The control assembly includes a controller that outputs a drive signal instructing a drive amount of the motor, a drive that supplies electric current, supplied from an external power supply, to the motor based on the drive signal output from the controller, a current detector that detects electric current flowing through the drive, and a first temperature detector that detects a temperature of the drive. The control assembly calculates a heat storage amount stored in the control assembly at a predetermined cycle, and when the calculated heat storage amount is larger than a predetermined threshold, the control assembly outputs the drive signal that instructs a drive amount smaller than the drive amount at the time of calculation. A heat storage amount Qn calculated at the nth time, where n is an integer equal to or greater than 1, by the controller is a value that is obtained by, when Q0 is a predetermined initial value, adding, to a heat storage amount Qn-1 calculated at the n−1th time, an estimated value of a heat generation amount of the motor obtained based on a voltage of the external power supply, the predetermined cycle, and a current value of the electric current detected, and subtracting an estimated value of a heat release amount obtained based on a difference between the temperature detected by the first temperature detector and a predetermined temperature.
The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.
Hereinafter, example embodiments of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the example embodiments described below, but includes any modification thereof within the scope of the technical idea of the present disclosure.
The torque sensor 10 is attached to the steering shaft 92. When the driver operates the steering wheel 91 to rotate the steering shaft 92, the torque sensor 10 detects the torque applied to the steering shaft 92. A torque signal that is a detection signal of the torque sensor 10 is output from the torque sensor 10 to the motor drive apparatus 30. The motor drive apparatus 30 drives the motor 20 on the basis of the torque signal input from the torque sensor 10. The motor drive apparatus 30 may refer to not only the torque signal but also other types of information (for example, vehicle speed).
In the present example embodiment, a three-phase synchronous brushless motor is used as the motor 20. The motor 20 is configured of a three-phase coil of a U phase, a V phase and a W phase. When the motor 20 is driven, electric current is supplied from the motor drive apparatus 30 to each of the U phase, the V phase, and the W phase in the motor 20. When the electric current is supplied, a rotating magnetic field is generated between a stator having a three-phase coil of the U phase, the V phase and the W phase and a rotor having a magnet. As a result, the rotor rotates with respect to the stator of the motor 20.
The motor drive apparatus 30 supplies a driving current to the motor 20 using electric power obtained from the external power supply 40. The driving force generated from the motor 20 is transmitted to the wheels 93 via a gear box 50. Thereby, the steering angle of the wheel 93 changes. Thus, the electric power steering apparatus 1 amplifies the torque of the steering shaft 92 by the motor 20, and changes the steering angle of the wheel 93. Therefore, the driver can operate the steering wheel 91 with a light force.
The power supply unit 31 supplies electric power from the external power supply 40 to the controller 32. The drive 33 is supplied with electric power from the external power supply 40 without going through the power supply unit 31.
The controller 32 receives a torque signal output from the torque sensor 10. As the controller 32, for example, a computer having an arithmetic processing unit such as a CPU, a memory such as a RAM, and a storage unit such as a hard disk drive is used. However, an electric circuit having an arithmetic device such as a microcontroller may be used instead of the computer. The controller 32 calculates the heat storage amount stored in the control assembly using the detection result by the first temperature detector 34, the detection result by the current detector 35, the detection result by the second temperature detector 36, and the like. A specific calculation method will be described later.
The drive 33 includes an inverter circuit and an inverter drive, and supplies an electric current to the motor 20. The inverter circuit includes, for example, a transistor such as a metal oxide semiconductor field effect transistor (MOSFET) as a switching element. In the present example embodiment, since a three-phase synchronous brushless motor is used as the motor 20, the inverter circuit is provided with three pairs of switching elements in parallel. Note that when the motor drive apparatus 30 is used as a multi-system drive system to drive one motor 20 or a plurality of motors 20, the drive 33 includes a plurality of inverter circuits.
The inverter drive is an electric circuit for operating the inverter circuit. In the present example embodiment, the inverter drive supplies a PWM drive signal of the pulse width modulation (PWM) system output from the controller 32 and instructing the drive amount of the motor 20, to the six switching elements included in the inverter circuit. The inverter circuit supplies electric current to each of the U phase, the V phase, and the W phase of the motor 20, on the basis of the PWM drive signal supplied from the inverter drive.
The first temperature detector 34 detects the temperature of the drive 33 and outputs the detected temperature to the controller 32. When the drive 33 includes a plurality of inverter circuits, the first temperature detector 34 is disposed for each of the inverter circuits. It is desirable that the first temperature detector 34 be disposed near a location where the heat generating components of the inverter circuit are concentrated, that is, near the center of the circuit, for example. The details will be described with reference to
The second temperature detector 36 detects the temperature of the controller 32 and outputs the detected temperature to the controller 32. When the first temperature detector 34 is arranged for each of the inverter circuits, a single second temperature detector 36 is provided at a position equidistant from the respective first temperature detector 34. The details will be described with reference to
As each of the first temperature detector 34 and the second temperature detector 36, a thermistor whose resistance value varies depending on the detected temperature from the viewpoint of sensitivity, size, and the degree of freedom of resolution. Further, an angle sensor for detecting the rotational position of the rotor of the motor 20 may also serve as the second temperature detector 36. In this case, the motor drive apparatus 30 can be advantageous in terms of device cost and size.
The detected temperatures detected by the first temperature detector 34 and the second temperature detector 36 are used to estimate the heat release amount from the control assembly. By disposing the first temperature detector 34 for each of the inverter circuits and in the vicinity where the heat generating components are concentrated, the estimation accuracy of the heat release amount can be improved. Among the detected temperatures obtained for the respective inverter circuits, the highest temperature is used for estimating the heat release amount. Thereby, the control accuracy of overheat protection can be improved.
In
The drive substrate 300 and the controller substrate 400 are configured with their element surfaces facing each other. The second temperature detector 36 is disposed at a position on the surface of the controller substrate 400 that is equidistant from the respective first temperature detectors 34 disposed on the drive substrate 300. By disposing the first temperature detectors 34 and the second temperature detector 36 in the positional relationship as described above, a difference in the heat release amounts calculated between the inverter circuits is less likely to occur, and the heat release amount can be calculated stably.
In
The current detector 35 detects the electric current flowing through the drive 33. In the present example embodiment, since a three-phase synchronous brushless motor is used as the motor 20, the electric current supplied to each of the U phase, V phase, and W phase of the motor 20 is detected. The current detector 35 outputs a current value of the detected electric current to the controller 32. When the drive 33 includes a plurality of inverter circuits, the current detector 35 detects a current for each of the inverter circuits.
The calculation unit 321 calculates the heat storage amount stored in the control assembly at a predetermined cycle. The predetermined cycle is determined on the basis of, for example, the accuracy required for overheat protection, and is set to 100 milliseconds in the present example embodiment. The heat storage amount Qn calculated at the nth time by the calculation unit 321 is expressed by the following equation (1) where Q0 represents a predetermined initial value, Q+ represents an estimated value of the heat generation amount of the motor at the time of calculation, and Q− represents an estimated value of the heat release amount at the time of calculation. Q0 is zero, for example. If a certain amount of heat storage is already assumed at the time before the calculation is started, a value other than zero can be set as the initial value.
The estimated value Q+ of the heat generation amount of the motor at the time of calculation is obtained by multiplying the square root of the q-axis component and the d-axis component of the current value detected by the current detector 35, the square root of the voltage value of the external power supply 40, and a predetermined period together, for example. The estimated value Q− of the heat release amount at the time of calculation is obtained on the basis of a difference ΔT obtained by subtracting a predetermined temperature from the detected temperature detected by the first temperature detector 34.
The predetermined temperature is a detected temperature detected by the second temperature detector 36 or an ambient temperature of the control assembly measured in advance. Which one is set as the predetermined temperature may be determined depending on the amount of fluctuation of the ambient temperature. For example, when the amount of fluctuation in the ambient temperature is large such as the case where the motor drive apparatus 30 is used in an environment with a severe temperature difference, the estimation accuracy of the heat release amount may be improved if a measured value by the second temperature detector is set as the predetermined temperature. Further, as the predetermined temperature, the calculation unit 321 may set the detection temperature and the ambient temperature to be selectable, and when the second temperature detector 36 fails, for example, the ambient temperature may be selected as the predetermined temperature.
The comparison unit 322 compares the heat storage amount Qn obtained by the calculation unit 321 with a predetermined threshold, and determines whether or not the heat storage amount Qn is larger than the predetermined threshold. The comparison unit 322 outputs the determination result to the drive amount determination unit 323. The comparison unit 322 refers to the first association information stored in the first storage unit 324 and determines the predetermined threshold. The details will be described later.
The drive amount determination unit 323 determines the drive amount of the motor 20 on the basis of the determination result output from the comparison unit 322. In the case of a determination result that the heat storage amount Qn is larger than the predetermined threshold, the drive amount determination unit 323 determines, as a drive amount of the motor 20, a drive amount smaller than the drive amount of the motor 20 at the time of calculating the heat storage amount Qn, in order to prevent the control assembly from overheating. In the case of the determination result that the heat storage amount Qn is equal to or smaller than the predetermined threshold, the drive amount is not particularly limited.
The first storage unit 324 stores the first association information in which the number of inverter circuits that supply current to the motor 20 among the inverter circuits of the drive (hereinafter referred to as the number of driving inverter circuits) and a threshold of the heat storage amount are associated with each other.
In the first association information, the smaller the number of driving inverter circuits is, the greater the associated threshold is. Thus, it is possible to prevent excessive overheat protection that limits the current supplied to the motor 20 in a state where it is not necessary to prevent overheating. Further, the threshold of the heat storage amount decreases as the temperature of the drive 33 is higher. Thereby, the precision of overheat protection can be improved.
The calculation unit 321 calculates the number of drive inverter circuits on the basis of the detection result by the current detector 35, and outputs the calculated number of driving inverter circuits to the comparison unit 322. The comparison unit 322 refers to the first association information stored in the first storage unit 324, and obtains a threshold of the heat storage amount corresponding to the number of driving inverter circuits output from the calculation unit 321. The comparison unit 322 determines the obtained threshold to be a predetermined threshold to be compared with the heat storage amount Qn.
By storing the first association information in the first storage unit 324 in advance, it is not necessary to calculate a predetermined threshold each time the number of driving inverter circuits varies, and it is possible to perform overheat prevention control stably.
The second storage unit 325 stores second association information in which the difference ΔT obtained by subtracting a predetermined temperature from the temperature detected by the first temperature detector 34 is associated with the heat release amount.
In the second association information, when ΔT is negative, that is, when the temperature of the controller 32 or the ambient temperature is higher than the temperature of the drive 33, the heat release amount corresponding to ΔT is the lowest value (for example, zero). On the other hand, when ΔT is 0° C. or higher, the heat release amount corresponding to ΔT may vary depending on the magnitude of ΔT.
When ΔT is 0° C. or higher, the heat release amount corresponding to ΔT can be obtained as follows. The case of obtaining the heat release amount when ΔT=30° C. will be described as an example. First, the current supplied to the motor 20 is set to zero when ΔT=30° C. for the first time after the driving of the motor 20 is started. Thereafter, the time point at which ΔT=0° C. is measured. The measured time is set as to.
With use of the above equation (1), Q− is calculated such that the time point at which the heat storage amount Qn becomes zero coincides with to. The calculated Q− is the heat release amount corresponding to ΔT=30° C. The second association information can be obtained by performing the above calculation with a plurality of ΔT. The relationship between ΔT and the heat release amount is not only linear but may also be a logarithmic relationship.
As described above, the estimation accuracy can be improved by estimating the heat release amount in consideration of the time variation of the heat release amount. Further, since the heat storage amount can be calculated using the estimated value of the heat release amount with improved accuracy, the accuracy of the overheat protection control can be improved. Furthermore, it is possible to prevent components such as electronic components included in the control assembly from being damaged by the heat.
By storing the second association information in the second storage unit 325 in advance, it is not necessary to calculate the estimated value of the heat release amount each time ΔT is obtained, and it is possible to perform overheat prevention control stably.
Note that as a current detection value and a temperature detection value to be used for calculation of the heat storage amount Qn, not only the values at the time of calculation but also an average value, a median value, and the like of the values detected from the previous (n−1th) time of calculation until the current (nth)) time of calculation may also be used.
As described above, according to the present example embodiment, it is possible to provide a motor drive apparatus that is advantageous in terms of reliability of control for preventing overheating of the control assembly. In addition, the electric power steering apparatus to which the motor drive apparatus of the present example embodiment is applied can be advantageous in terms of driving comfortability.
The motor 20 is not limited to that having three phases. Further, the motor drive apparatus 30 may be applied to devices other than the power steering system. For example, a motor used in other parts of a transportation apparatus such as an automobile may be driven by the motor drive apparatus 30 described above. Further, a motor mounted on an apparatus other than an automobile, such as an industrial robot, may be driven by the motor drive apparatus 30 described above.
While an example embodiment of the present disclosure has been described above, the present disclosure is not limited to such an example embodiment. Various modifications and change can be made within the scope of the spirit of the present disclosure.
The present application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-90199, filed on Apr. 28, 2017, the disclosure of which is incorporated herein in its entirety by reference.
While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-090199 | Apr 2017 | JP | national |
This is a U.S. national stage of PCT Application No. PCT/JP2018/014889, filed on Apr. 9, 2018, and priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is claimed from Japanese Application No. 2017-090199, filed Apr. 28, 2017; the entire contents of each application are hereby incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/014889 | 4/9/2018 | WO | 00 |
