JP7754036B2 - Predictive detection device for electric vehicles - Google Patents

Description

This invention relates to a device for detecting signs of some kind of problem, such as an abnormality or deterioration, in an electric motor with a power generating function in an electrically powered vehicle such as an electric vehicle (BEV) or a hybrid electric vehicle (HEV).

Patent Document 1 describes a device configured to detect or determine the degree of fatigue of the rotor of a rotating electric motor in an electric vehicle and provide an alert. The device described in Patent Document 1 detects the rotor's rotation speed and the temperature of the rotating electric motor, measures the operating time of the rotating electric motor at a specified temperature, calculates the rotor's degree of fatigue or a parameter related to this based on that operating time, and if the degree of fatigue or parameter exceeds a specified threshold, limits the rotation speed or provides an alert to the driver or other person.

Japanese Patent Application Laid-Open No. 2017-158312

Fatigue and deterioration of generators, motor-generators (hereinafter collectively referred to as electric motors), or their rotors progress as the motor operates, with the higher the motor's temperature, the greater the degree of fatigue and deterioration. The device described in Patent Document 1 detects or determines the degree of fatigue based on the operating time of the rotating electric motor, allowing for detection or determination based on the progression of fatigue and deterioration. Meanwhile, the temperature of an electric motor rises primarily due to heat generation caused by factors such as copper loss and iron loss. Iron loss is affected by the configuration of the core around which the electric wire is wound, and even with the same specifications such as torque, there are individual differences, with some motors being more susceptible to heat generation and others being less susceptible to heat generation. Therefore, if electric motors are cooled uniformly or in a uniform manner, the temperature of electric motors that are more susceptible to heat generation will rise with operating time, accelerating their fatigue and deterioration.

The device described in Patent Document 1 detects or determines the degree of fatigue based on the operating time of the rotating electric machine. However, since the relationship between operating time and the degree of fatigue or deterioration is not constant in electric motors with the individual differences described above, there is a possibility that an electric motor that is already significantly fatigued or has the potential to become significantly fatigued may be determined to have a low degree of fatigue because the operating time is still short. Conversely, an electric motor that does not generate heat easily due to low losses may be determined to have a high degree of fatigue because the operating time is long, even though it has not yet become significantly fatigued or deteriorated. In other words, conventional methods have not taken individual differences into consideration when detecting or determining fatigue or deterioration, and there is still room for improvement in terms of improving the accuracy of determining the degree of fatigue or deterioration or durability of electric motors.

This invention was made in response to the technical issues described above, and aims to provide a device that can accurately detect signs of deterioration or reduced durability in electric motors such as generators and motor-generators in electric vehicles.

To achieve the above object, the present invention provides a warning sign detection device for an electric vehicle that detects signs of deterioration or reduced durability in a power-generating electric motor having a coil with windings held around a core made of laminated electromagnetic steel sheets. The device determines the difference between adjacent maximum and minimum values in the temperature change of the electric motor, which repeatedly appears as maximum and minimum values that fluctuate when the electric motor is driven. The device also divides the difference into multiple categories based on the magnitude of the difference, accumulates the number of times the difference occurs for each of the multiple categories to determine a cumulative value, calculates the ratio of the cumulative value to a predetermined upper limit for each of the multiple categories, calculates the sum of the ratios for each of the multiple categories, and outputs a warning signal if the sum exceeds a predetermined threshold value. The threshold value is a predetermined value based on the deviation between the command torque commanded to the electric motor and the actual torque actually generated by the electric motor in response to the command torque.

When an electric motor is operated, its temperature fluctuates continuously, alternating between maximum and minimum values due to factors such as current and cooling. The device of this invention calculates the difference between the maximum and minimum values, dividing the temperature into multiple categories, and then calculates the cumulative value for each category. In other words, the frequency of temperature changes is calculated by dividing the temperature into multiple categories. The ratio of the cumulative value to a predetermined upper limit is then calculated for each category. The upper limit can be a predetermined value based on, for example, the strength and durability of the electromagnetic steel sheet or the insulating resin applied to its surface. Therefore, the cumulative value can be considered the amount or degree of factors causing deterioration or reduced durability. If the cumulative value exceeds a predetermined threshold, an alarm signal is output. The alarm signal may be a signal to limit the operation of the electric motor or a signal to notify the driver or user of the electric vehicle. Furthermore, because the threshold value is determined based on the deviation of the actual torque from the command torque, the threshold value reflects the individual differences expressed as the deviation, eliminating the variability caused by individual differences in the motor and enabling accurate detection of signs of deterioration, etc.

FIG. 2 is a schematic diagram for explaining a control system of an electric motor and a drive system extending from the electric motor to drive wheels. 2 is a schematic diagram showing a part of the coil and the laminated state of the electromagnetic steel sheets in the core. FIG. FIG. 4 is a diagram illustrating the relationship between an instruction torque and an actual torque. 10 is a diagram conceptually showing an example of a map in which threshold values are determined according to the amount of decrease (deviation) of actual torque from command torque. 10 is a diagram illustrating how the maximum and minimum values of the motor temperature appear and the difference between them; FIG. 10 is a graph illustrating divisions into which temperatures of maximum and minimum values are divided, as well as cumulative values and upper limit values in each division. FIG. 2 is a block diagram illustrating the functional configuration of a controller. 3 is a flowchart illustrating an example of control in the embodiment of the present invention.

Next, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is merely one example of how the present invention may be implemented, and is not intended to limit the scope of the present invention.

The electric vehicle covered by this invention is a vehicle equipped with an electric motor 1, such as an electric vehicle (BEV) powered solely by a motor or a hybrid vehicle (HEV, PHEV) powered by both an internal combustion engine (engine) and a motor. The electric motor 1 may be a generator that generates electricity when driven by an external force such as an engine, or a motor-generator that functions as both a generator and a motor. Figure 1 shows a schematic diagram of an example of a vehicle equipped with an electric motor 1 with power generation capabilities as a drive source. The electric motor 1 is connected to drive wheels 3 via a transmission (T/M) 2. The electric motor 1 receives electric power, outputs drive torque, and generates electricity when rotated by external force transmitted from the drive wheels 3. A permanent magnet synchronous motor or an induction motor can be used. The electric motor 1 also has a coil 6 configured by winding an electric wire 5 around a core 4. Figure 2 shows a schematic of a portion of a coil 6 made of distributed windings of rectangular wire. The core 4 is made of a cylindrical structure made by laminating multiple thin electromagnetic steel sheets 4a, and electric wires (windings) 5 are housed in slots formed on the inner periphery.

The transmission mechanism 2 includes a gear train, a winding transmission mechanism such as a chain or belt, and even a differential mechanism, and is configured to accelerate or decelerate the power output by the electric motor 1 and transmit it to the drive wheels 3. The transmission mechanism 2 may include a transmission that can change the gear ratio, or it may be a transmission mechanism with a fixed gear ratio (gear ratio).

Although not specifically shown, a cooling mechanism is provided to cool the electric motor 1 using fluid (oil) or the like.

The electric motor 1 is connected to a storage battery (BAT) 8 via an inverter (INV) 7. The inverter 7 is controlled by a controller (CONT) 9 to control the rotation speed, power generation, and torque of the electric motor 1. The controller 9 is primarily composed of a microcomputer, and is configured to use input data and pre-stored data to perform calculations according to pre-stored programs and output control command signals to the inverter 7 and other devices. The controller 9 is also configured to detect signs of deterioration or fatigue of the electric motor 1 before it reaches its limit and output a warning signal. To detect such signs, a temperature sensor 10 that detects the temperature of the electric motor 1 inputs a detection signal to the controller 9. If the warning signal is intended to notify the driver or service engineer of the signs, an HMI (Human-Machine-Interface) 11, such as an LCD monitor, is connected to the controller 9.

The following describes the control of warning signs detection by the controller 9. Heat generation and the resulting deterioration of the electric motor 1 will vary depending on the thickness of the electromagnetic steel sheets 4a that make up the core 4 and the way in which the electromagnetic steel sheets 4a are laminated, even if the diameter and axial length of the windings 5 and core 4 are the same. In other words, since there are individual differences between electric motors 1, the controller 9 is configured to reflect these individual differences and detect warning signs of deterioration or reduced durability. These individual differences manifest themselves, for example, as a discrepancy or difference between the command torque and the actual torque.

In other words, if the electromagnetic steel sheets 4a are thin, eddy current loss can be reduced, but the number of electromagnetic steel sheets 4a increases, which increases the amount of insulating resin covering the surfaces of the electromagnetic steel sheets 4a, affecting the output torque. Conversely, if the electromagnetic steel sheets 4a are thick, eddy current loss increases, but the fewer electromagnetic steel sheets 4a, the less insulating resin is required, which is advantageous in maintaining torque. In this way, depending on the configuration of the core 4 made up of a large number of electromagnetic steel sheets 4a, the actual torque may differ from the torque assumed in the design (specification torque).

To explain this graphically, Figure 3 shows the relationship between command torque and actual torque. Command torque is the torque that is expected to be output when a certain current is applied, according to the design (specifications), and actual torque is the actual torque of electric motor 1. When electric motor 1 is operated to achieve a certain command torque, if the actual torque matches or nearly matches the command torque, then the individual (electric motor) is operating as expected in the design (or as expected in the specifications) (let's call it Motor A), and the relationship between the command torque and actual torque is shown by the solid line in Figure 3. In contrast, for example, in the case of an individual (let's call it Motor B) where the iron loss in coil 6 is greater than the loss expected in the design, the actual torque will be smaller than the command torque, and the relationship between the actual torque and command torque will be shown by the dashed line in Figure 3.

On the other hand, deterioration or a decrease in durability of the electric motor 1 progresses as the temperature repeatedly rises due to heat generation. Therefore, the above-mentioned electric motor B is more susceptible to deterioration or has a lower tolerance for commanded torque than electric motor A. Therefore, the threshold value for determining deterioration or signs of deterioration is set smaller the greater the difference (deviation) between the commanded torque and the actual torque, i.e., for an individual (electric motor) that has greater losses and is more likely to generate heat than a motor that meets the specifications. This is schematically shown in Figure 4. For an individual (electric motor) with low iron loss due to thin electromagnetic steel sheets 4a, the thinness of the electromagnetic steel sheets 4a results in a larger layer of insulating resin, which is thought to make the resin more susceptible to sagging. Therefore, the threshold value is set to more easily detect deterioration or signs of deterioration. This threshold value can be determined in advance through experiments, simulations, etc., and stored in controller 9.

On the other hand, deterioration or reduced durability of the electric motor 1 due to factors such as wear of the insulating resin or electromagnetic steel sheet 4a occurs according to the temperature of the electric motor 1 and the amount of change in that temperature. Therefore, the controller 9 detects the temperature and change in the electric motor 1. An example of changes in the electric motor temperature is shown schematically in Figure 5, in which the temperature of the electric motor 1 repeatedly rises and falls depending on the required torque, with maximum and minimum values appearing repeatedly. Differences between adjacent minimum and maximum values in time, such as the difference between the maximum value P1 and the next minimum value p1 of the changing electric motor temperature, the difference between minimum value p1 and the next maximum value P2, and the difference between that maximum value P2 and the next minimum value, are detected.

The greater the temperature difference, the greater the impact (i.e., damage) on the motor 1. Therefore, the detected temperature difference is divided into appropriately set temperature ranges. Figure 6 shows these divisions, with temperature differences T1 to T2 (>T1) being Division A, T2 to T3 (>T2) being Division B, T3 to T4 (>T3) being Division C, T4 to T5 (>T4) being Division D, and T5 to T6 (>T5) being Division E (similar below). For each division, the temperature differences that fall within that temperature range are accumulated to determine the number of occurrences (frequency) H2, H3, H4, H5, H6, etc. Additionally, upper limit values G2, G3, G4, G5, G6, etc. are set for each division. These upper limit values represent the number of occurrences (frequency) at which the magnetic steel sheet 4a and its insulating resin reach their limit when a temperature change occurs within the respective division, and can be determined in advance during design.

The controller 9 calculates these temperature differences, allocates them to each category, calculates the frequency for each category, and then calculates the ratio (Hn/Gn) of the frequency (i.e., cumulative value) in each category to the upper limit value. It then calculates the sum of these ratios (= H2/G2 + H3/G3... + Hn/Gn).

The aforementioned threshold value is a threshold value for this total value, and when the total value reaches that threshold value, the controller 9 outputs an alarm signal. The alarm signal is a signal that indicates to the outside world signs of deterioration or reduced durability, such as progressive deterioration or reduced durability, or the arrival of any of these specified states, and can be a signal to limit the operation of the electric motor 1, a signal to display an indication of the signs on the HMI 11 shown in Figure 1, or even a signal to sound an alarm from a speaker (not shown) attached to the HMI 10.

Therefore, as shown in FIG. 7, the controller 9 in this embodiment of the present invention has the following functional configuration. It includes a temperature difference detection unit 9a that detects the temperature difference between the aforementioned maximum (minimum) value of the motor temperature when the motor 1 is operating and the adjacent minimum (maximum) value. This temperature difference can be determined from data obtained by the temperature sensor 10. It includes a division unit 9b that allocates the temperature difference to each of the aforementioned categories, and an accumulation value calculation unit 9c that calculates the accumulation value Hn by accumulating the number of occurrences of the temperature differences allocated to each category. Each category is assigned a pre-assigned upper limit value Gn, and it includes a ratio calculation unit 9d that calculates the ratio Hn/Gn between the upper limit values Gn and Gn. It also includes a sum calculation unit 9e that calculates the sum of the ratios Hn/Gn obtained for each category. Meanwhile, the controller 9 has the pre-assigned threshold values for each individual motor 1 input. It also includes a comparison unit 9f that compares the sum with the pre-assigned threshold values. Furthermore, it is equipped with an alarm output unit 9g that outputs the aforementioned alarm signal if the comparison result of the comparison unit 9f shows that the sum exceeds the threshold value.

An example of the control by the controller 9 described above will be explained with reference to the flowchart in Figure 8. The control shown in Figure 8 is executed each time the electric motor 1 is operated. First, the temperature difference between the aforementioned maximum (minimum) and minimum (maximum) values of the temperature of the electric motor 1 is detected (step S1). Next, the temperature differences detected sequentially are sorted into the aforementioned divisions A, B, C, etc. according to their magnitude (step S2), and the cumulative value Hn for each division is calculated (step S3).

It is determined whether the cumulative value Hn for each category is smaller than the upper limit Gn set for that category (Step S4). If the determination in Step S4 is affirmative, it means that the electromagnetic steel sheet 4a or the insulating resin on its surface has not been heated to a degree that would cause it to deteriorate. In this case, the aforementioned ratio Hn/Gn is calculated (Step S5), and the sum of these ratios Hn/Gn is calculated (Step S6). It is then determined whether this sum is greater than or equal to a threshold value (Step S7).

If the answer to step S7 is affirmative, this indicates that deterioration or a decrease in durability of the electric motor 1 is progressing, and an alarm signal is output (step S8). Conversely, if the answer to step S7 is negative, i.e., if the sum has not reached the threshold value, the process returns to continue the above-described control. Note that if the answer to step S4 is negative because the cumulative value Hn in any category has reached the upper limit value Gn set for that category, the process proceeds to step S8 described above and an alarm signal is output.

Therefore, in the above-described control, the threshold value used to determine whether to output an alarm signal is a value that corresponds to the deviation between the command torque and the actual torque, and is a value that reflects individual differences. Therefore, signs of deterioration or reduced durability of the electric motor 1 can be detected accurately and precisely, taking individual differences into account.

1 Electric motor 2 Transmission mechanism (T/M)
3 Drive wheel 4 Core 4a Electromagnetic steel plate 5 Electric wire (winding)
6 Coil 7 Inverter (INV)
8 Storage battery (BAT)
9 Controller (CONT)
9a Temperature difference detection unit 9b Division unit 9c Accumulation value calculation unit 9d Ratio calculation unit 9e Total value calculation unit 9f Comparison unit 9g Alarm output unit 10 Temperature sensor 11 HMI

Claims (1)

A symptom detection device for an electric vehicle that detects a symptom of deterioration or a decrease in durability of an electric motor having a power generating function and a coil in which a winding is held on a core made of laminated electromagnetic steel sheets,
a temperature change of the electric motor, which changes high and low as the electric motor is driven, and in which maximum and minimum values repeatedly appear, the difference between the maximum and minimum values adjacent to each other is determined, and the difference is divided into a plurality of groups according to the magnitude of the difference;
accumulating the number of times the difference occurs for each of the plurality of sections to obtain a cumulative value;
calculating a ratio of the cumulative value to an upper limit value that is preset for each of the plurality of categories,
A sum of the ratios for each of the plurality of categories is calculated,
When the sum exceeds a predetermined threshold value, an alarm signal is output.
The threshold value is a predetermined value based on the deviation between an instruction torque instructed to the electric motor and an actual torque actually generated by the electric motor in response to the instruction of the instruction torque.