JP4333572B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

BACKGROUND ART An electric power steering device for a vehicle applies auxiliary steering torque to a vehicle steering system by a rotational force of a motor. When the control means of this electric power steering device is stopped (for example, when the ignition switch is turned off), the rotation of the motor is stopped and the auxiliary steering torque is rapidly reduced, which greatly affects the steering feeling. give. Therefore, even when the control means of the electric power steering device is stopped, the auxiliary steering torque to be applied is calculated based on a predetermined table so that the auxiliary steering torque does not rapidly decrease, and is applied. It has been proposed to rewrite the table according to the transition of the auxiliary steering torque to be performed (see Patent Document 1 below).
JP 2003-312511 A

  By the way, when a driver continuously performs stationary operation in a vehicle equipped with an electric power steering device, a large current flows through the motor because the rotational force required for the motor is large. If the state in which a large current flows through the motor is continued, the motor generates heat, and the motor coil, brush, and the like may reach a heat-resistant allowable temperature. In order to avoid such a situation, the electric power steering apparatus described in Patent Document 1 stores the motor temperature and the maximum current value corresponding to the motor temperature in the table in association with each other and is detected by the sensor. By selecting and controlling the maximum current value based on the motor temperature, the heat resistant allowable temperature is prevented.

  On the other hand, from the viewpoint of vehicle manufacturing cost reduction and structure simplification, it is required to reduce sensors as much as possible. Therefore, the motor temperature is estimated and calculated from the current flowing through the motor. In this estimation calculation, calculation logic is set on the assumption that the motor is constantly exposed to the maximum temperature. Therefore, even if it is left for a long time in a cold region, it is calculated that the motor is exposed to the maximum temperature, so it is controlled with a margin less than the actual allowable temperature limit. Become.

  Accordingly, an object of the present invention is to provide an electric power steering device that enables control based on a temperature close to the actual motor temperature without using a sensor that directly detects the motor temperature.

  The inventors of the present invention have repeatedly studied focusing on a case where a motor for generating auxiliary steering torque is disposed in a vehicle interior in an electric power steering apparatus that applies auxiliary steering torque to a vehicle steering system. It was. As a result, it has been found that the ambient temperature in the passenger compartment converges to a predetermined temperature after the operation is started. It has also been found that if the ambient temperature in the passenger compartment converges to a predetermined temperature, the steady-state motor temperature also converges to the predetermined temperature in accordance with the predetermined temperature. The present invention is based on these findings.

  An electric power steering device according to the present invention is an electric power steering device that applies an auxiliary steering torque to a vehicle steering system by a motor disposed in a vehicle interior of the vehicle, and the vehicle ignition switch is turned on. Based on the elapsed time calculated by the elapsed time calculating means, the ambient temperature estimating means for estimating the ambient temperature around the motor based on the elapsed time calculated by the elapsed time calculating means, and the elapsed time calculated by the elapsed time calculating means The ambient temperature estimating means estimates the no-load temperature estimating means for estimating the motor no-load temperature when no load is applied to the motor during the elapsed time, and the filter constant for calculating the motor temperature. Constant calculating means for calculating based on the ambient temperature, the calculated filter constant and the motor flowing to the motor Motor temperature estimating means for estimating the temperature of the motor corresponding to the current value based on the current value of the current and the no-load temperature of the motor estimated by the no-load temperature estimating means, and the motor based on the estimated temperature Control means for controlling the current to flow.

  According to the electric power steering device of the present invention, based on the elapsed time from when the ignition switch is turned on, the no-load temperature serving as a base for estimating the temperature of the motor with respect to the current flowing through the motor is estimated. Therefore, the temperature of the motor can be estimated according to the actual usage situation. In addition, since the motor temperature at the current value is estimated based on the filter constant according to the elapsed time and the current value flowing through the motor and the no-load temperature, the motor temperature more accurately reflects the actual usage situation. Estimation is possible.

  According to the present invention, since it is possible to estimate the temperature of the motor reflecting the actual use situation, it is possible to perform control in accordance with the actual motor temperature as much as possible without using a sensor that directly detects the motor temperature. . In particular, when the elapsed time becomes longer, it is possible to assume that the motor temperature is lower.For example, even when stationary driving is performed after a certain amount of steady running, the actual motor temperature is maintained. Accordingly, more auxiliary steering torque can be applied.

  The present invention can be readily understood by considering the following detailed description with reference to the accompanying drawings shown for the embodiments. Subsequently, embodiments of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a block diagram of an electric power steering apparatus according to an embodiment of the present invention. The electric power steering apparatus 10 shown in FIG. 1 is an apparatus that applies an auxiliary steering torque by a motor 20 to a steering system including a steering wheel 30, a reduction gear 31, and a steering shaft 32. In the case of the present embodiment, the motor 20 is disposed in a passenger compartment of a vehicle (not shown) on which the electric power steering device is mounted.

  When the ignition switch 40 is turned on, the electric power supplied from the battery 50 is transmitted as an applied voltage to the motor 20 via the motor drive unit 101 of the electric power steering apparatus 10. The voltage applied to the motor 20 by the motor drive unit 101 is controlled by the assist torque calculation unit 102 (control unit) of the electric power steering apparatus 10. The assist torque calculation unit 102 calculates an assist torque based on the steering torque of the steering system described above, the vehicle speed, and the like, and outputs an instruction signal to the motor drive unit 101 so as to generate the assist torque.

  Subsequently, other components of the electric power steering apparatus 10 will be described. The electric power steering apparatus 10 includes an elapsed time calculation unit 103 (elapsed time calculation unit) and a no-load temperature estimation unit 104 (no-load temperature estimation unit) in addition to the motor driving unit 101 and the assist torque calculation unit 102 described above. An ambient temperature estimation unit 105 (atmosphere temperature estimation unit), a constant calculation unit 106 (constant calculation unit), a motor temperature estimation unit 107 (motor temperature estimation unit), a motor current detection unit 108, and a temperature characteristic storage unit 150 and a constant information storage unit 151. Subsequently, each component will be described.

  The elapsed time calculation unit 103 is a part that calculates the elapsed time from when the ignition switch 40 is turned on. When the ignition switch 40 is turned on, a signal indicating the ignition switch 40 is output from the ignition switch 40 to the elapsed time calculation unit 103. The elapsed time calculation unit 103 starts timing in response to the output of this signal, and integrates the elapsed time since the ignition switch 40 is turned on. The elapsed time calculation unit 103 outputs the accumulated elapsed time to each of the no-load temperature estimation unit 104 and the ambient temperature estimation unit 105.

Based on the elapsed time calculated by the elapsed time calculation unit 103, the no-load temperature estimation unit 104 estimates the no-load temperature T ₀ ° C. of the motor 20 when no load is applied to the motor 20 during the elapsed time. It is a part to do. More specifically, the no-load temperature estimation unit 104 estimates the no-load temperature T ₀ ° C. of the motor 20 according to the elapsed time based on the motor temperature characteristic map stored in the temperature characteristic storage unit 150. The no-load temperature estimation unit 104 outputs the estimated no-load temperature T ₀ ° C. to the motor temperature estimation unit 107.

  Here, the motor temperature characteristic map stored in the temperature characteristic storage unit 150 will be described with reference to FIG. FIG. 2 is a graph for explaining a motor temperature characteristic map. In the graph shown in FIG. 2, the horizontal axis represents the elapsed time since the ignition switch 40 was turned on, and the vertical axis represents the motor temperature. For example, if the steady running is continued without stopping, the motor 20 is substantially in a no-load state, and its temperature gradually approaches a predetermined value. Accordingly, a correlation between the elapsed time and the motor temperature as shown in FIG. 2 is obtained.

  Returning to FIG. 1, the ambient temperature estimation unit 105 is a part that estimates the ambient temperature around the motor 20 based on the elapsed time calculated by the elapsed time calculation unit 103. More specifically, the ambient temperature estimation unit 105 estimates the ambient temperature around the motor 20 according to the elapsed time based on the motor ambient temperature map stored in the temperature characteristic storage unit 150. The ambient temperature estimation unit 105 outputs the estimated ambient temperature to the constant calculation unit 106.

  Here, the motor atmosphere temperature map stored in the temperature characteristic storage unit 150 will be described with reference to FIG. FIG. 3 is a graph for explaining a motor atmosphere temperature map. In the graph shown in FIG. 3, the horizontal axis represents the elapsed time since the ignition switch 40 was turned on, and the vertical axis represents the ambient temperature of the motor 20. Since the motor 20 is disposed in the vehicle interior of the vehicle on which the electric power steering device 10 is mounted, the ambient temperature is estimated to be in accordance with the temperature in the vehicle interior. For example, even if the vehicle interior temperature rises to about 65 ° C. after being left under the hot sun, it is estimated that the temperature will be about 25 ° C. after the driver gets on the vehicle for a while. Therefore, a correlation between the elapsed time and the ambient temperature of the motor 20 as shown in FIG. 3 is obtained.

  Returning to FIG. 1, the constant calculation unit 106 is a part that calculates a filter constant for calculating the temperature of the motor 20 based on the ambient temperature estimated by the ambient temperature estimation unit 105. More specifically, the constant calculation unit 106 calculates a filter constant corresponding to the ambient temperature of the motor 20 based on a constant map stored in the constant information storage unit 151. The constant calculation unit 106 outputs the calculated filter constant to the motor temperature estimation unit 107.

  Here, the constant map stored in the constant information storage unit 151 will be described with reference to FIG. FIG. 4 is a graph for explaining the constant map. In the graph shown in FIG. 4, the horizontal axis represents the ambient temperature of the motor 20, and the vertical axis represents the filter constant. As shown in FIG. 4, in this embodiment, three filter constants K1, K2, and K3 are calculated. The basic idea of setting these filter constants is that if the ambient temperature of the motor 20 rises, the motor 20 itself is easily warmed and difficult to cool, and if the ambient temperature of the motor 20 falls, the motor 20 itself becomes difficult to warm and easily cooled. Is based.

  This concept will be described more specifically with reference to FIG. FIG. 5 is a graph showing the heat generation / heat dissipation characteristics of the motor 20 according to the difference in ambient temperature. In the graph shown in FIG. 5, the horizontal axis represents the elapsed time since the ignition switch 40 was turned on, and the vertical axis represents the temperature of the motor 20. The temperature of the motor 20 is considered to be the ambient temperature when the ignition switch 40 is turned on.

It is assumed that when the temperature of the motor 20 is 65 ° C. (that is, when the ambient temperature of the motor 20 is 65 ° C.), the ignition switch 40 is turned on, and the motor 20 is further energized with a current of 65 amperes. The temperature curve in this case is shown by a solid line in FIG. When the maximum current is supplied for t ₁ minutes, the temperature of the motor 20 reaches the allowable heat resistant temperature T _max ° C. If the current flowing through the motor 20 is 0 amperes, the temperature of the motor 20 gradually approaches 65 ° C. as shown in FIG.

  On the other hand, when the temperature of the motor 20 is 25 ° C. (that is, when the ambient temperature of the motor 20 is 30 ° C.), the ignition switch 40 is turned on, and the motor 20 is further energized with a current of 65 amperes. The temperature curve is as indicated by the broken line in FIG. Compared with the temperature curve (solid line in FIG. 5) when the temperature of the motor 20 is 65 ° C., the time for the temperature of the motor 20 to reach the heat-resistant allowable temperature is t2 (> t1). If the current flowing through the motor 20 is 0 amperes, the temperature of the motor 20 gradually approaches 30 ° C. as shown in FIG. The temperature drop of the motor 20 in this case is abrupt compared to the case where the temperature of the motor 20 is 65 ° C.

  Therefore, as described above, when the ambient temperature of the motor 20 rises, the motor 20 itself is easily warmed and difficult to cool, and when the ambient temperature of the motor 20 falls, the motor 20 itself is difficult to warm and easily cooled. The three filter constants K1, K2, and K3 of this embodiment are obtained by fitting based on a temperature curve as shown in FIG.

Returning to FIG. 1, the motor temperature estimation unit 107 includes the filter constant calculated by the constant calculation unit 106, the current value I of the current flowing in the motor 20, and the no-load temperature of the motor 20 estimated by the no-load temperature estimation unit 104. This is a part for estimating the temperature T ° C. of the motor 20 relative to the current value I of the current flowing through the motor 20 based on T ₀ .

More specifically, the motor temperature estimation unit 107 first calculates the current square value I ² by squaring the current value I of the motor 20 output from the motor current detection unit 108. Next, the motor temperature estimation unit 107 calculates three constants sum1 (= f (I ² )), sum2 (= g (I ² )), sum3 (= h (I ² )) based on the current square value I ^2. Is calculated. Next, the motor temperature estimation unit 107 multiplies each of the three constants sum1, sum2, and sum3 by the three filter constants K1, K2, and K3 output from the constant calculation unit 106, respectively, to obtain a difference temperature ΔT (= K1 · sum1 + K2). * Sum2 + K3 * sum3) ° C is calculated. Subsequently, the motor temperature estimation unit 107 calculates the temperature T (T ₀ + ΔT) ° C. of the motor 20 by adding the difference temperature ΔT ° C. to the no-load temperature T ₀ ° C. of the no-load temperature estimation unit 104. The motor temperature estimating unit 107 outputs the calculated temperature T ° C. of the motor 20 to the assist torque calculating unit 102.

  The motor current detection unit 108 is a part that detects the current value I of the current flowing through the motor 20 and outputs it to the motor temperature estimation unit 107.

The assist torque calculation unit 102 is a part that controls the current flowing through the motor 20 based on the temperature of the motor 20 estimated by the motor temperature estimation unit 107. More specifically, the assist torque calculation unit 102 calculates the upper limit number of times of stationary based on the difference between the temperature T ° C. of the motor 20 estimated by the motor temperature estimation unit 107 and the allowable heat resistant temperature T _max ° C. . The assist torque calculation unit 102 outputs an instruction signal for controlling the voltage applied to the motor 20 to the motor drive unit 101 within the range of the calculated upper limit number of times.

  Next, the operation of the electric power steering apparatus 10 in the present embodiment will be described. FIG. 6 is a flowchart showing the operation of the electric power steering apparatus 10 in the present embodiment.

  When the ignition switch 40 is turned on, the motor current detection unit 108 detects the current flowing through the motor 20, and outputs the detected current value I to the motor temperature estimation unit 107 (step S01).

The motor temperature estimation unit 107 squares the current value I output from the motor current detection unit 108 and calculates a current square value I ² (step S02). The motor temperature estimation unit 107 calculates three constants sum1 (= f (I ² )), sum2 (= g (I ² )), sum3 (= h (I ² )) based on the current square value I ^2. (Step S03).

  When the ignition switch 40 is turned on, in parallel with the operation of step S01, the elapsed time calculation unit 103 calculates the elapsed time after the ignition switch 40 is turned on, and the no-load temperature estimation unit 104 and the ambient temperature estimation unit It outputs to 105 (step S04).

  The ambient temperature estimation unit 105 estimates the ambient temperature around the motor 20 based on the elapsed time calculated by the elapsed time calculation unit 103 (step S05). The ambient temperature estimation unit 105 outputs the estimated ambient temperature to the constant calculation unit 106.

  The constant calculation unit 106 calculates filter constants K1, K2, and K3 for calculating the temperature of the motor 20 based on the ambient temperature estimated by the ambient temperature estimation unit 105 (step S06). The constant calculation unit 106 outputs the calculated filter constants K1, K2, and K3 to the motor temperature calculation unit 107.

  The motor temperature calculation unit 107 multiplies the three constants sum1, sum2, and sum3 by the three filter constants K1, K2, and K3 output from the constant calculation unit 106, respectively, to obtain a difference temperature ΔT (= K1 · sum1 + K2 · sum2 + K3 · sum3) ° C. is calculated (step S07).

In parallel with the operations in steps S05 to S07, the no-load temperature estimation unit 104 is based on the elapsed time calculated by the elapsed time calculation unit 103 and the motor 20 is not loaded during the elapsed time. The no-load temperature T ₀ ° C. of the motor 20 is estimated (step S08). The no-load temperature estimation unit 104 outputs the estimated no-load temperature T ₀ ° C. of the motor 20 to the motor temperature estimation unit 107.

The motor temperature estimation unit 107 calculates the temperature T (T ₀ + ΔT) ° C. of the motor 20 by adding the difference temperature ΔT ° C. to the no-load temperature T ₀ ° C. of the no-load temperature estimation unit 104 (step S09). The motor temperature estimating unit 107 outputs the calculated temperature T ° C. of the motor 20 to the assist torque calculating unit 102.

The assist torque calculation unit 102 calculates the upper limit number of times of stationary based on the difference between the temperature T ° C. of the motor 20 estimated by the motor temperature estimation unit 107 and the allowable heat resistant temperature T _max ° C. The assist torque calculation unit 102 outputs an instruction signal for controlling the voltage applied to the motor 20 to the motor drive unit 101 within the calculated upper limit number of times (step S10).

The effects of the electric power steering apparatus 10 of the present embodiment will be described. Based on the elapsed time from when the ignition switch 40 is turned on, the no-load temperature estimation unit 104 is a base for estimating the no-load temperature T ₀ ° C (the temperature of the motor 20 with respect to the current flowing in the motor 20). Temperature), it is possible to estimate the temperature of the motor 20 according to the actual use situation. Further, based on the filter constants (K1, K2, K3) corresponding to the elapsed time, the current value I flowing in the motor, and the no-load temperature T ₀ ° C., the motor temperature T ° C. at the current value I is estimated. Therefore, it is possible to estimate the temperature of the motor 20 that more reflects actual usage conditions.

It is a block block diagram of the electric power steering device which is embodiment of this invention. It is a graph for demonstrating the motor temperature characteristic map of this embodiment. It is a graph for demonstrating the motor atmosphere temperature map of this embodiment. It is a graph for demonstrating the constant map of this embodiment. It is a graph which shows the heat_generation | fever and heat dissipation characteristic of a motor by the difference in atmospheric temperature. It is a flowchart which shows operation | movement of the electric power steering apparatus which is embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 20 ... Motor, 30 ... Steering wheel, 31 ... Reduction gear, 32 ... Steering shaft, 40 ... Ignition switch, 50 ... Battery, 101 ... Motor drive part, 102 ... Assist torque calculating part, 103 ... Elapsed time calculation unit 104 ... No-load temperature estimation unit 105 ... Atmosphere temperature estimation unit 106 ... Constant calculation unit 107 ... Motor temperature estimation unit 108 ... Motor current detection unit 150 ... Temperature characteristic storage unit 151 Constant information storage unit.

Claims (1)

An electric power steering device that applies an auxiliary steering torque to a vehicle steering system by a motor disposed in a vehicle interior of the vehicle,
An elapsed time calculating means for calculating an elapsed time after the ignition switch of the vehicle is turned on;
Atmosphere temperature estimating means for estimating the ambient temperature around the motor based on the elapsed time calculated by the elapsed time calculating means;
Based on the elapsed time calculated by the elapsed time calculation means, no-load temperature estimation means for estimating the no-load temperature of the motor when no load is applied to the motor during the elapsed time;
Constant calculating means for calculating a filter constant for calculating the temperature of the motor based on the ambient temperature estimated by the ambient temperature estimating means;
The temperature of the motor corresponding to the current value is estimated based on the calculated filter constant and the current value of the current flowing through the motor and the no-load temperature of the motor estimated by the no-load temperature estimating means. Motor temperature estimating means for
Control means for controlling the current flowing through the motor based on the estimated temperature;
An electric power steering apparatus comprising:

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