KR101280193B1 - Method and Apparatus for Preventing Overheating in Electric Power Steering System - Google Patents

Abstract

The present invention relates to an overheat prevention device of an electric power steering system and a method thereof.

In accordance with an aspect of the present invention, there is provided an apparatus for preventing overheating of an electric power steering system, comprising: a current sensing unit configured to sense a driving current flowing from an electronic controller of the electric power steering system to a motor; A rotation sensing unit sensing a rotation speed of the motor; And obtaining the driving current, obtaining a worst-case temperature change rate by referring to a first temperature change rate map, obtaining a rotation weight by referring to a rotation weight map from the rotation speed, and obtaining a voltage weight by referring to a voltage weight map from the voltage. After that, the weighted temperature change rate is calculated, wherein the worst-case temperature change rate changes according to the rotation weight value, the heat capacity remaining from the weighted temperature change rate to the threshold temperature of the ECU is calculated, and when the heat capacity reaches a specific value, The present invention provides an overheat prevention device and a method of an electric power steering system including a heat capacity control unit for controlling a driving current in a direction of lowering a driving force of a motor.

EPS, Overheating Protection, Power Steering

Description

Overheating prevention device of electric power steering system and its method {Method and Apparatus for Preventing Overheating in Electric Power Steering System}

Embodiments of the present invention relate to overheat protection devices and methods of electric power steering systems. More specifically, the present invention relates to an overheat prevention device for an electric power steering system and a method thereof for controlling the drive current in consideration of the rotational speed and the input voltage of the motor so as not to overheat the electronic control device for driving the motor in the electric power steering system. will be.

An electric power steering system (EPS) hereinafter detects when the driver applies torque by moving the steering wheel and generates steering auxiliary torque in a direction to steer.

The heavier the weight of a vehicle employing EPS, the greater the driving force it needs to support to give the driver a lighter steering. For greater driving force, greater driving force is required for EPS motors and electronic control units (ECUs).

However, a large driving force requires more current in the EPS motor and the ECU, and inevitably a lot of heat can be generated in the EPS motor and the ECU.

Conventionally, in order to protect the EPS motor and the ECU from the heat generated in this case, the current flowing to the EPS motor is limited, in which case the driver feels a heavy steering feeling during low speed driving. Therefore, EPS must generate driving force for as long as possible while protecting the EPS motor and ECU from overheating.

However, since the conventional method controls assuming that the most heat is generated among the various operating conditions of the ECU and the EPS motor, the steering feeling of the driver becomes heavier by limiting the driving current of the motor before assisting the steering force sufficiently. There was a problem.

Embodiment according to the present invention controls the drive current in consideration of the rotational speed and the input voltage of the motor so that the electronic control device for driving the motor in the electric power steering system does not overheat.

Another embodiment according to the present invention, in the overheat prevention device of the electric power steering system, the current sensing unit for detecting a drive current flowing from the electronic control unit (Electronic Control Unit (ECU)) of the electric power steering system to the motor; A rotation sensing unit sensing a rotation speed of the motor; And obtaining a worst-case temperature change rate with reference to a first temperature change rate map from the driving current, and obtaining a rotation weight value with reference to a rotation weight map from the rotation speed, wherein the worst-case temperature change rate is a value that changes according to the rotation weight value. A heat capacity control unit for calculating a weighted temperature change rate, calculating a heat capacity remaining from the weighted temperature change rate to a limit temperature of the ECU, and controlling the driving current to reduce the driving force of the motor when the heat capacity reaches a specific value. Provided is an overheat prevention device for an electric power steering system.

Here, the weighted temperature change rate may be calculated according to the formula (weighted temperature change rate = a x (worst condition temperature change rate) x rotation weight value) (where a is a proportionality constant).

Here, the overheat prevention device further includes a voltage sensing unit for sensing an input voltage input to the electronic control device, wherein the heat capacity control unit obtains the driving current and refers to a first temperature change rate map to show a worst-case temperature change rate. Obtain a rotation weight from the rotation speed with reference to the rotation weight map and obtain a voltage weight from the input voltage with reference to the voltage weight map, and then the worst condition temperature change rate is determined according to the voltage weight and the rotation weight. The change in the weighted temperature change rate, which is a variable value, may be calculated, and the heat capacity remaining from the weighted temperature change rate to the limit temperature of the ECU may be calculated to control the driving current to reduce the driving force when the heat capacity reaches a specific value.

 In this case, the weighted temperature change rate may be calculated according to the formula (weighted temperature change rate = a x (worst condition temperature change rate) x rotation weight value x voltage weight value) (where a is a proportionality constant).

In addition, according to another embodiment of the present invention, in the overheat prevention device of the electric power steering system, a current sensing unit for detecting a drive current flowing from the electronic control unit (ECU) of the electric power steering system to the motor ; A voltage sensing unit sensing an input voltage input to the electronic controller; And acquiring the driving current, obtaining a worst-case temperature change rate with reference to a first temperature change rate map, and obtaining a voltage weight with reference to a voltage weight map from the input voltage, wherein the worst-case temperature change rate is determined according to the voltage weight value. A heat capacity control unit for calculating the weighted temperature change rate, which is a variable value, and calculating the heat capacity remaining from the weighted temperature change rate to the limit temperature of the ECU to reduce the driving force of the motor when the heat capacity reaches a specific value. It provides an overheating prevention device of the electric power steering system comprising a.

Here, the weighted temperature change rate may be calculated according to the formula (weighted temperature change rate = a x (worst condition temperature change rate) x voltage weight value) (where a is a proportionality constant).

The specific value may be such that a limit capacity of a certain margin is given from the limit temperature.

The first temperature change rate map may be a worst-case temperature change rate value corresponding to the driving current so that a larger worst-case condition change rate corresponds to a larger value of the driving current.

The rotation weight map may be set such that the rotation weight increases with the RPM of the motor and has the largest value at the rated RPM and decreases after the rated RPM of the motor.

The rotation weight may have a linear pattern of increasing or decreasing according to the RPM of the motor.

The voltage weighting map may be set such that the voltage weighting value increases with the input voltage and has the largest value at the rated voltage and decreases after the rated voltage.

The voltage weighting value may be linear in a pattern that increases or decreases according to the input voltage.

The heat capacity can be cumulatively calculated by the formula (heat capacity = conventional heat capacity-(weighted temperature change rate x time)).

In addition, according to another embodiment of the present invention, a method for preventing overheating of an electric power steering system, the method comprising: detecting a driving current flowing from an electronic control unit (ECU) of the electric power steering system to a motor; Sensing an input voltage input to the electronic controller; Sensing a rotational speed of the motor; Obtain the driving current, obtain a worst-case temperature change rate by referring to a first temperature change rate map, obtain a rotation weight by referring to a rotation weight map from the rotation speed, and obtain a voltage weight by referring to a voltage weight map from the input voltage. Calculating a weighted temperature change rate, wherein the worst-case temperature change rate is a value that changes according to the voltage weight value and the rotation weight value; And calculating the heat capacity by acquiring the weighted temperature change rate and controlling the drive current to reduce the driving force of the motor when the heat capacity reaches a specific value. To provide.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In addition, in describing the components of the embodiment of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

1 is a view showing the overheating device of the electric power steering system according to an embodiment of the present invention.

As shown in FIG. 1, the overheating preventing device of the electric power steering system according to an exemplary embodiment of the present invention includes a current sensing unit 102, a heat capacity control unit 104, a voltage sensing unit 106, and a rotation sensing unit 108. ) And a current supply unit 118.

The current sensing unit 102 detects the magnitude of the driving current flowing from the current supply unit 118 of the control object, that is, the electronic control unit (ECU) that controls the motor 116. In the present embodiment, the driving current sensed by the current sensing unit 102 may be an average current sensed for a predetermined time (for example, 1 second) or a current sensed in real time.

In this embodiment, the motor 116 means a motor that provides the driver's steering driving force in the EPS.

As the current detection unit 102, a current sensor for detecting an average current for a predetermined time (for example, for 1 second) or for detecting current continuously in real time may be used.

The heat capacity control unit 104 obtains the driving current to convert the temperature change rate of the ECU and calculates the heat capacity remaining until the limit temperature is reached based on the temperature change rate and the time when the driving current flows. In extracting the temperature change rate of the ECU, specifically, the temperature change rate of the input terminal of the ECU (that is, the EMI choke coil) is extracted. The location at which the rate of temperature change is extracted in the ECU may vary and the present invention is not limited thereto.

In converting the temperature change rate of the ECU, the worst-case temperature change rate, which is the temperature change rate for the worst operating condition when the current is supplied by the ECU, is calculated, and the weighted temperature change rate, which is a value that varies according to the weight of various operating conditions, is calculated.

The temperature affected by the operation of the ECU and the motor under various temperature conditions is defined as the limit temperature, and the time to reach the limit temperature is defined as the allowable time. Here, the rate of temperature change may be determined by the formula according to [Equation 1].

Temperature change rate = (limit temperature-ambient temperature) / time allowed

Among the various operating conditions, the temperature change rate at the shortest time (permissible time) for reaching the limit temperature at which the elements of the ECU and the motor are affected by temperature becomes the worst-case temperature change rate.

The weights used to calculate the temperature change rate (ie, the weighted temperature change rate described below) that may vary under actual operating conditions are weighted considering the battery input voltage input to the ECU and the rotational RPM of the motor controlled by the ECU. Can be used.

On the other hand, the limit temperature is determined for each component of the ECU and the motor. For example, in this embodiment, the limit temperature of the EMI choke coil of the ECU most affected by the rotation of the motor is assumed to be 220 degrees.

Table 1 is a table showing an example of the motor applied current and allowable time when the motor rotor is fixed, Table 2 is a table showing an example of the motor applied current and allowable time when the motor rotor rotates at the rated RPM.

Current (A)
(When fixing the rotor)
Permissible time (ambient temperature: 85 ℃)
Permissible time (ambient temperature: 25 ℃)
120
120 seconds
320 seconds
80
400 seconds
Continuous electricity
60
1200 sec
"
40
Continuous electricity
"

As shown in Table 1, the allowable time is 120 seconds (ambient temperature: 85 ℃) when the drive current of 120A flows in the fixed rotor of the motor, and the temperature change rate is (( Limit temperature-ambient temperature) / hour = (220-85) / 120 = 1.125 ° C / sec).

Also, if the drive current of 120A flows to the motor when the ambient temperature is 25 ℃, the allowable time is 320 seconds, and if the limit temperature is 220 ℃, the temperature change rate is ((220-25) / 320 = 0.61 ℃ / Seconds).

Table 1 shows an example in which the driving current is 80A, 60A, and 40A when the ambient temperature is 25 ° C, but does not reach the limit temperature even though the driving current flows continuously.

Current (A)
(At rated RPM rotation)
Permissible time (ambient temperature: 85 ℃)
Permissible time (ambient temperature: 25 ℃)
120
90 seconds
160 seconds

As shown in Table 2, when 120A drive current flows in the motor rotating at the rated RPM, the allowable time is 90 seconds (when the ambient temperature is 85 ℃) and the limit temperature is assumed to be 220 ℃. The rate of change of temperature is ((limit temperature-ambient temperature) / hour = (220-85) / 90 = 1.5 ° C / sec).

In addition, when the ambient temperature is 25 ℃ temperature change rate is ((220-25) / 160 = 1.2 ℃ / second).

Therefore, when looking at Table 1 and Table 2, the worst-case temperature change rate is 1.5 ℃ / second when the drive current is 120A.

However, the temperature change rate under normal operating conditions (for example, the operating condition where the ambient temperature is not 85 ° C. or the motor rotation speed is not the rated rpm, etc.) is the worst case temperature change rate set under the worst condition in the above manner. Is smaller than.

Therefore, when only the worst-case temperature change rate is adopted in the present invention, in the case of general operating conditions other than the worst-case condition, the actual temperature change rate is smaller than the worst-case temperature change rate. Give weight.

2 is a graph showing an input current vs. a first temperature change rate map of a motor.

The first temperature change rate map shows the worst-case temperature change rate according to the change of the drive current. The first temperature change rate map may be set such that a larger worst-case condition change rate corresponds to a larger value of the drive current. In this embodiment, the case where the ECU battery voltage is 11V, the ambient temperature is 85 ° C. and the motor rotates at the rated rpm is the worst operating condition, and FIG. 2 shows the temperature change rate in this case.

As shown in FIG. 2, the worst-case temperature change rate of the corresponding drive current condition can be obtained by using a graph between the drive current applied to the motor and the worst-case temperature change rate, and the first temperature change rate map corresponds to the worst-case temperature corresponding to the drive current. The rate of change value may be set to increase linearly.

In the present invention, the weighted temperature change rate can be obtained by considering the voltage weight value considering the battery voltage of the ECU and the rotation weight value considering the rpm of the motor to the worst-case temperature change rate obtained in the graph of FIG. 2.

The weighted temperature change rate in consideration of such a weight can be obtained by, for example, [Equation 2].

Weight change rate = a x (worst case temperature change rate) x rotation weight value x voltage weight value (where a is proportional constant)

If only the rotational RPM of the motor is additionally considered, the weighted temperature change rate can be obtained from the equation (3).

Weighted temperature change rate = a x (worst condition temperature change rate) x rotational weight value (where a is proportional constant)

If only the battery voltage of the ECU is considered additionally, the weighted temperature change rate can be obtained from the equation.

Weighted temperature change rate = a x (worst case temperature change rate) x voltage weight value (where a is proportional constant)

In [Equation 2], [Equation 3] and [Equation 4], a is a proportional constant, and in the following description, when a formula for obtaining the weighted temperature change rate is described, a is assumed to be 1 and the indication of a is omitted. do.

On the other hand, in calculating the weight, whether to consider only the battery voltage of the ECU, only the rotation RPM of the motor, or both, may vary depending on the embodiment. If only the battery voltage of the ECU is considered, the rotation sensing unit 108 may be omitted from the components shown in FIG. 1, and if only the rotational RPM of the motor is considered, the voltage sensing unit 106 may be omitted. ) Can be omitted.

3 is a graph showing an example of the ECU current consumption according to the RPM of the motor.

As shown in FIG. 3, in the case of a motor having a peak current of 120 A and a rated rpm of 1200 rpm, the ECU consumption current increases until the ECU input battery current reaches the rated rpm, and then decreases after the rated rpm. Seems. Since the temperature of the ECU increases by the current consumption of the ECU, the speed of the motor is given as a weight factor.

Table 3 is a table showing an example of weights when the rotor is fixed and the rated RPM of the motor.

Condition
Motor rotor fixing
Motor Rated RPM Rotation
Ambient temperature
25 ℃
85 ℃
25 ℃
85 ℃
Maximum current allowable time
320 s
120 s
160s
90 s
Safety time (70%)
224s
84s
112s
63 s
Rotation Weight (Fm)
0.5
0.5
One
0.8

In Table 3, the ambient temperature refers to the chamber temperature when testing the motor and ECU in the chamber. Therefore, in a real situation, the temperature in the vehicle in which the motor and the ECU are operating may correspond.

In this embodiment, in the rotational state of the motor, the temperature of the ECU rises faster than when the motor rotor is fixed due to the large current flowing in the ECU. When the motor is rotated at 25 ° C, the weight of the motor is given as 1, but in the fixed state of the motor, the weight is 0.5 so that the temperature change rate can be differentiated from that of the motor.

That is, when calculating the heat capacity using the weighted temperature change rate multiplied by the temperature change rate multiplied by 0.5, the heat capacity is calculated by the weighted temperature change rate lowered by the weight considering the motor rotor fixing. In this embodiment, the heat capacity means the temperature remaining until the temperature of the ECU reaches the limit temperature. The heat capacity may be set with a margin of heat capacity of a certain size (or a ratio) from the limit temperature.

On the other hand, the maximum current allowance time in Table 3 means the time when an abnormality starts to occur in the ECU when the peak current flows in the motor, and the safety time set to 70% can be set when there is a certain margin at the maximum current allowance time. It means time to be. In this way, the ratio of setting the safety time may be used as the ratio of setting the heat capacity margin.

The rotation detector 108 detects a rotation RPM of the motor 116, and the voltage detector 106 detects an input voltage of a battery input to the ECU.

The heat capacity controller 104 obtains the driving current, obtains the worst-case temperature change rate by referring to the first temperature change rate map, obtains the rotation weight by referring to the rotation weight map from the rotational speed, and references the voltage weight map from the ECU input voltage. After acquiring the voltage weighting value, the weighted temperature change rate is calculated by calculating the worst-case temperature change rate according to the voltage weight value and the rotational weight value, and calculating the heat capacity remaining from the weighted temperature change rate to the limit temperature of the ECU. When the limit capacity is reached, the driving current is controlled to reduce the driving force for the motor 116.

Here, the weighted temperature change rate is the formula of (weighted temperature change rate = ax (worst condition temperature change rate) x rotational weight value x voltage weighting value) (where a is a proportional constant, where a is assumed to be 1) Can be calculated according to.

Table 4 is a table showing an example of the rotation weight value (Fm) according to the rotational speed (RPM) of the motor.

Motor RPM
0
1200
1400
2200

Rotation Weight (Fm)


0.5
1.0 (at 25 ° C)


0.5
0.8 (at 85 ° C)

As shown in Table 4, when the motor is fixed, the rotation weight value is 0.5, the rotation weight value is 1.0 (at 25 ° C) at 1200 to 1400 rpm near the rated RPM of the motor, and the rotation weight value is 0.5 at 2200 rpm. Can be.

4 is a graph illustrating a rotation weight map.

The heat capacity controller 104 obtains the rotation weight value by referring to the rotation weight map using the sensed rotation RPM.

In FIG. 4, the rotation weight may be set such that the rotation weight increases (linearly or nonlinearly) up to the rated rpm and then decreases (linearly or non-linearly) after the rated rpm.

As shown in FIG. 4, when the ambient temperature is 25 degrees, the motor has a rotational weight of 0.5 when the RPM is 0 and increases linearly as the RPM increases, and then has a rotational weight of 1 at the rated RPM of 1200 RPM. Until now, the rotational weight decreases linearly. The rotation weight map of FIG. 4 is merely an example, and the shape of the graph may be a non-linear graph.

5 is a graph showing the ECU current consumption according to the ECU battery voltage.

As shown in FIG. 5, when the ECU battery voltage is 11V, the ECU current consumption has a maximum value (when fixing the rotor: 100A and when the motor rotates: 50A), and the ECU consumption current decreases as the battery voltage moves away from 11V. (Linearly or nonlinearly), you can put a voltage weight (Fb) that reflects this in the rate of temperature change.

Meanwhile, the voltage detector 106 detects the battery voltage and the heat capacity controller 104 calculates the voltage weight value using the sensed battery voltage.

Table 5 shows an example of the voltage weight value (Fb) according to the ECU battery voltage.

Battery voltage (V)
10
11
15
Voltage weighting value (Fb)
0.9
1.0
0.8

As shown in Table 5, when the battery voltage is 10V, the voltage weighting value is 0.9, and when the battery voltage is 11V, the table set to have 1.0 and 15 when the battery weight is 0.8 may be used.

Table 5 is just an example, and similarly to the shape of the graph shown in FIG. 4, the voltage weight increases (linearly or nonlinearly) until the battery voltage is 11V, and the voltage weight decreases again after 11V. Linear or nonlinear).

6 is a graph illustrating a voltage weight map.

The voltage weighting map can be set so that the voltage weighting value increases with the ECU's input voltage and has the highest value at the rated voltage (assuming 11V here) and decreases after the rated voltage.

As shown in FIG. 6, when the battery voltage is 10V, the voltage weighting value is 0.9 and the voltage weight increases linearly as the battery voltage is increased, and when the battery voltage is 11V, the voltage weighting value is linearly up to 15V again. It shows a decreasing form. The voltage weight map of FIG. 6 is merely an example, and the shape of the graph may be a non-linear graph in accordance with an embodiment.

On the other hand, the heat capacity control unit 104 may calculate the heat capacity of the ECU using the combined weight value considering both the rotation weight value and the battery weight value.

In this case, the total weight may be set to a value multiplied by the rotation weight and the battery weight as illustrated in [Equation 5].

Total weight = rotational weight x battery weight

The rate at which the heat capacity changes depends on the value of the combined weight. If the motor current is 120A, the battery voltage is 11V, and the motor rotation speed is 1200rpm, the total weight (ambient temperature is 25 ° C) becomes (total weight = rotation weight x battery weight = 1.0 x 1.0 = 1.0). Therefore, the weighted temperature change rate at this time becomes -1.5 (weighted temperature change rate = temperature change rate x overall weight = -1.5 x 1.0 = -1.5).

If the motor current is 120A, the battery voltage is 11V, and the rotor of the motor is fixed (motor speed: 0 rpm), the total weight (ambient temperature is 25 ℃) is (total weight = rotation weight x battery weight = 0.5 x 1.0 = 0.5). Therefore, the weighted temperature change rate at this time becomes -0.75 (weighted temperature change rate = temperature change rate x composite weight = -1.5 x 0.5 = -0.75).

7 is a graph showing the rate of change of the current-weighted temperature according to the total weight.

As shown in FIG. 7, the slope of the current-weighted temperature change rate varies according to the total weight. Therefore, the rate at which the heat capacity of the ECU (more specifically, the heat capacity of the ECU input terminals) changes over time.

The heat capacity control unit 104 calculates the weighted temperature change rate according to the formula of (weighted temperature change rate = (worst condition temperature change rate) x rotational weight value x voltage weighting value) and calculates the temperature remaining until the limit temperature of the ECU, that is, the heat capacity. do.

For example, if the total weight value (= rotational weight value x voltage weighting value) is 1 and the current flows at 120 A, the worst-case temperature change rate is 1.5, so the weighted temperature change rate is (weighted temperature change rate = (worst-condition temperature change rate) x rotation. The weight x voltage weighting value) is 1.5.

In this case, the heat capacity may be calculated by the equation [Equation 6].

Heat capacity = limit temperature-ambient temperature

Therefore, the heat capacity is 135 ° C by (heat capacity = limit temperature-ambient temperature = 220-85 = 135 ° C).

Meanwhile, in [Equation 6], the ambient temperature means a temperature at which the driving of the motor starts, and can be assumed to be 85 ° C., which is the worst condition.

In this case, the driving reduction time can be calculated by the equation (7).

Time to reach limit temperature = rate of change of heat capacity / weighted temperature

That is, when 90 seconds pass by the formula of (heat capacity / weighted temperature change rate = 135 / 1.5 = 90 seconds), the limit temperature is reached and the driving force of the motor is reduced.

On the other hand, the heat capacity control unit 104 may reduce the driving force of the motor when the heat capacity is 0, that is, when the temperature of the ECU reaches the limit temperature (that is, in this case, the limit capacity becomes 0), By giving a certain percentage of margin, for example, it can be controlled to reduce the driving force of the motor when the heat capacity remains 10 (in this case, the limit capacity is 10).

However, if the total weight value (= rotation weight value x voltage weight value) is 0.5 and the current flows at 120 A, the worst-case temperature change rate is 1.5, so the weighted temperature change rate is (weighted temperature change rate = (worst-condition temperature change rate) x rotation weight value x 0.75 according to the formula of voltage weighting (heat capacity = limit temperature-ambient temperature = 220-85 = 135). In this case, the limit temperature is reached after 180 seconds by the formula (heat capacity / weighted temperature change rate = 135 / 0.75 = 180 seconds).

On the other hand, the remaining heat capacity can be calculated cumulatively by the formula (8).

Heat capacity = conventional heat capacity-(weighted temperature change rate x time)

If the conventional heat capacity was 135, if 100 seconds passed after the current flowed under the above conditions, the heat capacity became (previous heat capacity-(weighted temperature change rate x time) = 135-0.75 * 100 = 60).

Therefore, the smaller the total weight is, the longer the time for reaching the limit temperature can be supplied for a longer time without dropping the driving current flowing from the current supply unit 118 to the motor 116.

On the other hand, the cumulative calculation of heat capacity means that the heat capacity can be calculated in real time (or at every timing), and the heat capacity is calculated using the weighted temperature change rate calculated by considering variables such as the magnitude of current, battery voltage, and rotation speed. By calculating the reduction in heat capacity and accumulating it, the current heat capacity can be calculated.

The graph of the weighted temperature change rate of FIG. 7 may be linear or nonlinear and may vary according to embodiments.

FIG. 8 is a graph illustrating a point in time at which the heat capacity controller 104 lowers the driving force of the motor 116 according to the magnitude of the current.

The time point at which the heat capacity becomes zero by the heat capacity control unit 104 is a time to lower the driving force of the motor 116.

As shown in FIG. 8, when the current is 120A, the driving force of the motor 116 is lowered after 90 seconds, and when the current is 90A, the driving force of the motor 116 is lowered after 135 seconds.

The heat capacity control unit 104 calculates the heat capacity and limits the driving current of the motor 116 when the size reaches the limit capacity.

In FIG. 8, if the driving current of the motor 116 is lowered to 40 A or less, the temperature of the ECU current input terminal will not increase any more, so that the heat capacity does not decrease over time.

Therefore, as shown in FIG. 8, as the current decreases, the weighted temperature change rate becomes smaller, and thus the weighted temperature change rate becomes 0 at the time when the current reaches 40A. Therefore, the shape of the graph forms a graph shape having an infinite time value at the point where the current is 40A. Done.

9 is a graph illustrating a time point at which the heat capacity controller 104 lowers the driving force of the motor 116 according to the total weight value.

As shown in FIG. 9, when the total weights are different, the timing for lowering the driving force of the motor 116 is different. All the conditions other than the overall weight of 0.5 are the same as the graph of Fig. 8, the time to lower the driving force of the motor is 180 seconds later.

On the other hand, when the voltage sensing unit 106 is excluded from the components of the embodiment of the present invention of Figure 1 (general weight = rotational weight), the heat capacity control unit 104 is the first temperature change rate map from the drive current After acquiring the worst-case temperature change rate by reference and obtaining the rotation weight value by referring to the rotation weight map from the rotational speed of the motor 116, calculating the weighted temperature change rate, which is the value at which the worst-case temperature change rate changes according to the rotation weight value, The heat capacity remaining from the rate of change to the limit temperature of the ECU is calculated to control the drive current to reduce the driving force of the motor 116 when the heat capacity reaches the limit capacity.

In this case, the weighted temperature change rate may be calculated according to the formula (weighted temperature change rate = (worst-case temperature change rate) * rotation weight value).

In addition, when the rotation sensing unit 108 is excluded from the components of the exemplary embodiment of FIG. 1, the total capacity control unit 104 obtains the driving current of the motor 116 since the total capacity value = voltage weighting value is obtained. After acquiring the worst-case temperature change rate by referring to the first temperature change rate map and obtaining the voltage weight by referring to the voltage weight map from the input voltage of the ECU, calculating the weighted temperature change rate, which is the value at which the worst-case temperature change rate changes according to the voltage weight value. Then, the heat current remaining from the weighted temperature change rate to the limit temperature of the ECU is calculated to control the driving current to reduce the driving force of the motor 116 when the heat capacity reaches the limit capacity.

At this time, the weighted temperature change rate can be calculated according to the formula (weighted temperature change rate = (worst-case temperature change rate) * voltage weighting value).

10 is a flowchart illustrating a method for preventing overheating of an electric power steering system according to an embodiment of the present invention.

As shown in FIG. 10, the method for preventing overheating of an electric power steering system according to an embodiment of the present invention includes a driving current sensing step S1002, a voltage sensing step S1004, a rotational speed sensing step S1006, and a calculating step S1008. ) And a driving current control step (S1010).

A method of preventing overheating of an electric power steering system according to an embodiment of the present invention will be described with reference to FIGS. 1 to 10.

In the driving current detection step S1002, the driving current flowing from the electronic control unit (ECU) of the electric power steering system to the motor is detected.

In the voltage sensing step S1004, a voltage input to the electronic controller is sensed.

In the rotation speed detecting step S1006, the rotation speed of the motor 116 is detected.

Here, the driving current detection step S1002, the voltage detection step S1004, and the rotational speed detection step S1006 are steps before calculating the heat capacity, and the order may be changed between them.

In the calculation step S1008, the driving current of the motor 116 is obtained, the worst-case temperature change rate is obtained by referring to the first temperature change rate map, and the rotation weight is obtained by referring to the rotation weight map from the rotation speed of the motor 116. After acquiring the voltage weight value by referring to the voltage weight map from the voltage of the ECU, calculate the weighted temperature change rate according to the formula (weighted temperature change rate = (worst condition temperature change rate) * rotation weight value * voltage weight value).

In the driving current control step (S1010), the weight capacity change rate is obtained to calculate the heat capacity, and when the heat capacity reaches the limit capacity, the drive current is controlled in a direction of dropping the driving force of the motor 116.

FIG. 11A is a graph illustrating waveform patterns of an applied current of a motor, and FIG. 11B is a graph illustrating waveform patterns of a motor. Figure 12a is a graph showing the motor applied current before the improvement according to the present invention in an environment of 25 ° C ambient, Figure 13b is a graph showing the motor applied current after the improvement, Figure 13a is a graph showing the improvement before the present invention in an environment of 75 degrees ambient temperature It is a graph which shows the motor applied current, and FIG. 13B is a graph which shows the motor applied current after improvement.

As shown in FIG. 11, it can be seen that as the applied current to the motor 116 increases or decreases, the rotation RPM of the motor 116 also increases or decreases accordingly.

12 and 13 are graphs comparing the number of steering wheel lock-to-lock turns until the driving force of the motor drops. The test mode is the result of the steering angular velocity of about 90 degrees / sec. Handled to the lock position to the left and then stopped at the lock position for 1 second and then reversed to steer.

The results in FIGS. 12 and 13 are based on the case where the input voltage is 13 V after normal startup.

As shown in FIG. 12, when the number of lock-to-turn turns is 20, the driving force of the motor decreases when the lock-to-lock turn is 20. However, in the graph after the improvement of FIG. As a result, it can be seen that the motor driving force is delayed and lowered.

Similarly in FIG. 13, before the improvement of FIG. 13A, the driving force of the motor decreases when the number of lock-to-lock turns is 20, but after the improvement of FIG. 13B, the driving force of the motor decreases when the number of lock-to-turn turns is 32, resulting in a delay in the motor driving force. Able to know.

As described above, according to the exemplary embodiment of the present invention, the driving current is controlled in consideration of the rotational speed and the input voltage of the motor so that the electronic control apparatus for driving the motor is not overheated in the electric power steering system.

Therefore, in this case, the driver has an effect that the driver can be provided with a light steering feeling by the EPS for a longer time during the low speed driving. This can give the driver a greater effect during low speed driving, which requires greater driving force.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. That is, all of the components may operate selectively in combination with one or more of them. In addition, although all of the components may be implemented as one independent hardware, some or all of the components may be selectively combined to perform a part or all of the functions in one or a plurality of hardware. As shown in FIG. Codes and code segments constituting the computer program may be easily inferred by those skilled in the art. Such a computer program may be stored in a computer readable storage medium and read and executed by a computer, thereby implementing embodiments of the present invention. As the storage medium of the computer program, a magnetic recording medium, an optical recording medium, a carrier wave medium, or the like may be included.

In addition, the terms "comprise", "comprise", or "having" described above mean that the corresponding component may be embedded unless otherwise stated, and thus, other components. It should be construed that it may further include other components rather than to exclude them. All terms, including technical and scientific terms, have the same meanings as commonly understood by one of ordinary skill in the art unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a view showing the overheating device of the electric power steering system according to an embodiment of the present invention.

2 is a graph showing an input current vs. a first temperature change rate map of a motor.

3 is a graph showing the ECU current consumption according to the RPM of the motor.

4 is a graph illustrating a rotation weight map.

5 is a graph showing the ECU current consumption according to the ECU battery voltage.

6 is a graph illustrating a voltage weight map.

7 is a graph showing the rate of change of the current-weighted temperature according to the total weight.

FIG. 8 is a graph illustrating a point in time at which the heat capacity controller 104 lowers the driving force of the motor 116 according to the magnitude of the current.

9 is a graph illustrating a time point at which the heat capacity controller 104 lowers the driving force of the motor 116 according to the total weight value.

10 is a flowchart illustrating a method for preventing overheating of an electric power steering system according to an embodiment of the present invention.

FIG. 11A is a graph illustrating waveform patterns of an applied current of a motor, and FIG. 11B is a graph illustrating waveform patterns of a motor.

12A is a graph showing a motor applied current before improvement according to the present invention in an environment of 25 ° C., and FIG. 13B is a graph showing a motor applied current after improvement.

FIG. 13A is a graph showing a motor applied current before improvement according to the present invention in an environment of ambient temperature 75 degrees, and FIG. 13B is a graph showing a motor applied current after improvement.

Description of the Related Art

102: current sensing unit 104: heat capacity control unit

106: voltage detection unit 108: rotation detection unit

116: motor 118: current supply unit

Claims (15)

In the overheat protection device of the electric power steering system, A current sensing unit configured to sense a driving current flowing from the electronic control unit (ECU) of the electric power steering system to the motor; A rotation sensing unit sensing a rotation speed of the motor; And The worst-case temperature change rate is obtained from the driving current with reference to the first temperature change rate map, and the rotational weight value is obtained from the rotational speed with reference to the rotation weight map, and the worst-case temperature change rate is a value that changes according to the rotation weight. A heat capacity control unit which calculates a temperature change rate, calculates a heat capacity remaining from the weighted temperature change rate to a limit temperature of the ECU, and controls the drive current to reduce the driving force of the motor when the heat capacity reaches a specific value Overheat prevention device of the electric power steering system comprising a. The method of claim 1, The weighted temperature change rate is, (Weighted temperature change rate = a x (worst case temperature change rate) x rotation weight value) (where a is proportional constant) Overheat prevention device of the electric power steering system, characterized in that calculated according to the equation. The method of claim 1, The overheat prevention device, Further comprising a voltage sensing unit for sensing the input voltage input to the electronic control device, The heat capacity controller obtains the driving current, obtains a worst-case temperature change rate by referring to a first temperature change rate map, obtains a rotation weight value by referring to a rotation weight map from the rotation speed, and references a voltage weight map from the input voltage. After acquiring the voltage weighting value, the weighted temperature change rate is calculated, wherein the worst-case temperature change rate is a value varying according to the voltage weight value and the rotation weight value, and the heat capacity is calculated by calculating the heat capacity remaining from the weighted temperature change rate to the limit temperature of the ECU. And the drive current is controlled to reduce the drive force when this specific value is reached. The method of claim 3, The weighted temperature change rate is, (Weighted temperature change rate = a x (worst condition temperature change rate) x rotation weight value x voltage weight value) (where a is proportional constant) Overheat prevention device of the electric power steering system, characterized in that calculated according to the equation. In the overheat protection device of the electric power steering system, A current sensing unit configured to sense a driving current flowing from the electronic control unit (ECU) of the electric power steering system to the motor; A voltage sensing unit sensing an input voltage input to the electronic controller; And After obtaining the driving current and obtaining a worst-case temperature change rate with reference to a first temperature change rate map, and obtaining a voltage weight with reference to a voltage weighting map from the input voltage, the worst-case temperature change rate is changed according to the voltage weight value. A heat capacity control unit for calculating the weighted temperature change rate, which is a value, and calculating the heat capacity remaining from the weighted temperature change rate to the limit temperature of the ECU to reduce the driving force of the motor when the heat capacity reaches a specific value. Overheat prevention device of the electric power steering system comprising a. 6. The method of claim 5, The weighted temperature change rate is, (Weighted temperature change rate = a x (worst condition temperature change rate) x voltage weighting value, where a is proportional constant) Overheat prevention device of the electric power steering system, characterized in that calculated according to the equation. 7. The method according to any one of claims 1 to 6, The specific value is a limiting capacity of the electric power steering system, characterized in that the limit capacity of the size given a certain margin from the limit temperature. 7. The method according to any one of claims 1 to 6, The first temperature change rate map is a worst-case temperature change rate value corresponding to the drive current, and the greater the value of the drive current, the greater the worst-case temperature change rate is set so as to correspond to the electric power steering system. 9. The method of claim 8, And wherein the first temperature change rate map is set such that the worst-case temperature change rate value corresponding to the driving current increases linearly. The method according to claim 1 or 3, The rotation weight map is, Wherein the rotation weight increases with the RPM of the motor and has the largest value at the rated RPM and is set to decrease after the rated RPM of the motor. The method of claim 10, The rotation weight is, Overheat prevention device of the electric power steering system, characterized in that the pattern of increasing or decreasing according to the RPM of the motor is linear. The method according to claim 3 or 5, The voltage weight map is, The voltage weighting value increases with the input voltage. The overheat protection device of an electric power steering system, characterized in that it has the largest value at the rated voltage and is set to decrease after the rated voltage. 13. The method of claim 12, The voltage weighting value, The pattern that increases or decreases according to the input voltage is a linear overheating prevention device of the electric power steering system. The method according to any one of claims 1, 3 and 5, The heat capacity is, The overheat prevention device of the electric power steering system, characterized in that the cumulative calculation by the formula (heat capacity = conventional heat capacity-(weighted temperature change rate x time)). In the overheat prevention method of the electric power steering system, Detecting a driving current flowing from the electronic control unit (ECU) of the electric power steering system to the motor; Sensing an input voltage input to the electronic controller; Sensing a rotational speed of the motor; Obtain the driving current, obtain a worst-case temperature change rate by referring to a first temperature change rate map, obtain a rotation weight by referring to a rotation weight map from the rotation speed, and obtain a voltage weight by referring to a voltage weight map from the input voltage. Calculating a weighted temperature change rate, wherein the worst-case temperature change rate is a value that changes according to the voltage weight value and the rotation weight value; And Calculating the heat capacity by obtaining the weighted temperature change rate and controlling the driving current to reduce the driving force of the motor when the heat capacity reaches a specific value; Overheating prevention method of the electric power steering system comprising a.

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