JP2008018860A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering control device capable of suppressing the impairment of steering feeling by reducing an influence of activation operation resistance exerted on a steering mechanical part at low speed operation immediately after a vehicle is started in a low temperature state. <P>SOLUTION: The electric power steering device is provided with a motor 20 for giving assist force to the steering mechanical part; and a control unit 30 for controlling the motor 20 based on an assist map 33 for storing a control instruction value of the motor 20 varied according to a steering torque signal T and a vehicle speed signal V. The device is provided with a temperature sensor for detecting a temperature of the steering mechanical part. The control unit 30 performs compensation for the activation operation resistance based on the detection result of the temperature sensor 7 at the low speed operation immediately after the vehicle is activated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that assists a steering operation of a steering wheel by an assist force of a motor.

  An electric power steering device used in a conventional vehicle detects a steering torque input by a steering wheel with a torque sensor, obtains an auxiliary torque corresponding to the steering torque by a motor, and applies the auxiliary torque to the steering device. The steering force of the steering device input by the steering person is reduced. In addition, the steering torque is greatest when the vehicle is stopped, and the steering torque has a characteristic of decreasing as the vehicle speed increases. Therefore, as shown in FIG. 5, based on a preset assist map, the change characteristic between the steering torque (steering torque signal TA) and the current command value (steering assist command value I) supplied to the motor is set to the vehicle speed. It is known to improve the steering feeling and stabilize the vehicle behavior by changing it accordingly.

  However, the conventional assist map is set on the assumption of a specific use environment. Therefore, the desired assist map is changed depending on the change in the use environment of the vehicle, particularly the change in the temperature characteristics of the steering mechanism such as the reduction gear and the pinion rack mechanism and the motor. When the control is performed based on the assist map, the steering feeling may be impaired.

  As a countermeasure, a plurality of pre-stored control parameters (offset and gain) are selected according to the change in the external environment and calculated based on the assist map so that the steering feeling does not change due to the change in the external environment. There exists a thing which corrects an electric current command value (for example, patent documents 1).

  Also, there is one that detects the motor temperature, corrects the current command value supplied to the motor according to the motor temperature, and corrects the output torque of the motor so as not to change due to temperature change (for example, Patent Document 2).

Japanese Patent Laid-Open No. 2001-138938 (FIGS. 1, 3, and 5) Japanese Patent No. 3643941 (FIG. 3)

  Here, for example, in a low-speed driving immediately after the vehicle is started in a low temperature state in a winter period or an early morning parking lot, a lubricant such as a grease for lubricating the steering mechanism or the steering mechanism In addition, it is known that the starting operation resistance in a rotating contact portion of a sealing device or the like is large.

  For example, the relationship between the lubricating oil for lubricating the steering mechanism and the ambient temperature in the engine room will be described with reference to FIG. As shown in FIG. 6, the relationship increases as the ambient temperature decreases. In particular, when the ambient temperature becomes −30 degrees or less, the lubricant gradually loses its viscosity and solidifies, and the performance deteriorates rapidly. Therefore, the starting operation resistance increases rapidly. FIG. 6 shows a lubricant, a grease base oil, a synthetic oil excellent in low-temperature performance, such as synthetic hydrocarbon oil, ester oil, mineral oil, lithium soap as a thickener, urea compound, etc. The case where a general lubricant is used is shown.

  However, both Patent Document 1 and Patent Document 2 assume a normal running state in which the temperature of the vehicle rises and the starting operation resistance does not become a problem, and low speed driving immediately after starting the vehicle in a low temperature state It does not take into account the starting operating resistance at the time.

  Furthermore, in Patent Document 1, there is no detailed description about correction of the change characteristic in the low temperature state, and there is a possibility that the steering feeling is impaired in the operation in the low temperature state. Moreover, in patent document 2, it is not the structure which correct | amends a change characteristic in a low-temperature state.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce the influence of the starting operation resistance at the time of low speed driving immediately after starting the vehicle in a low temperature state, and to reduce the steering feeling. It is an object of the present invention to provide an electric power steering apparatus that can suppress the above-described problem.

The above object of the present invention can be achieved by the following constitution.
(1) a motor that applies assist force to the steering mechanism;
In an electric power steering apparatus comprising: a steering control drive device that controls the motor based on an assist map that stores a control command value of the motor that changes according to a steering torque and a vehicle speed;
Temperature detecting means for detecting a temperature related to the steering mechanism, and
The electric power steering apparatus according to claim 1, wherein the steering control driving apparatus performs compensation for the starting operation resistance based on a detection result of the temperature detecting means during low-speed driving immediately after starting the vehicle.

(2) In the electric power steering device according to (1),
The electric power steering device according to claim 1, wherein the steering control drive device performs the compensation by changing the assist map based on a detection result of the temperature detection means.

(3) In the electric power steering device according to (1) or (2),
The steering control drive device determines that the detection result of the temperature detection means is not more than a predetermined temperature, that the elapsed time since the start of the vehicle is within a predetermined time, and that the vehicle speed is not more than a predetermined speed. The electric power steering apparatus is characterized in that the compensation is carried out at the time.

  According to the present invention, a steering control drive that controls a motor based on an assist map that stores a motor that gives an assist force to the steering mechanism and a control command value of the motor that changes according to the steering torque and the vehicle speed. An electric power steering apparatus comprising temperature detecting means for detecting a temperature related to the steering mechanism, and the steering control drive device detects the temperature detecting means during low-speed driving immediately after starting the vehicle. Based on the results, compensation for the starting operating resistance is performed, so that the influence of the starting operating resistance during low-speed driving immediately after starting the vehicle in a low temperature state can be reduced to suppress a decrease in steering feeling. The steering can be performed as well as during normal driving.

  Moreover, the cost concerning improvement of a lubricant etc. for frictional resistance reduction can be suppressed.

  Hereinafter, embodiments of a control device for an electric power steering apparatus according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an electric power steering apparatus of the present invention. The steering mechanism portion of the electric power steering apparatus is configured such that a column shaft 2 of a steering handle 1 is coupled to a wheel tie rod 6 via a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5, and an engine (not shown) Located in the room. The column shaft 2 is provided with a torque sensor 10 for detecting the steering torque of the steering handle 1, and a motor 20 for assisting the steering force of the steering handle 1 is coupled to the column shaft 2 via the reduction gear 3. ing.

  Electric power is supplied from the battery 14 via the ignition key 11 to the control unit 30 that controls the steering device, which is a steering control drive device. The control unit 30 detects the steering torque signal T detected by the torque sensor 10 and the vehicle speed sensor. The steering assist command value I of the assist command value is calculated based on the vehicle speed signal V detected at 12 and the temperature signal Th detected by the temperature sensor 7, and the motor is calculated based on the calculated steering assist command value I. The assist control is performed by controlling the assist current supplied to the control unit 20.

  The temperature sensor 7 is a thermistor, for example, and is attached to the motor 20 or the control unit 30 in consideration of ease of mounting, and detects the atmospheric temperature of the vehicle from these temperature signals Th. Since the vehicle is exposed to the outside air, the steering mechanism is also at the same level as the ambient temperature in the engine room when the vehicle is activated. The temperature sensor 7 is not limited to the thermistor, and various sensors such as a platinum resistance thermometer, a thermocouple, and a radiation thermometer can be applied. Further, the temperature signal Th may be input to the control unit 30 via a digital communication line such as CAN from a temperature sensor different from the temperature sensor 7 attached to the vehicle.

  The control unit 30 is mainly composed of a CPU, and a program stored in a ROM or the like is read in the CPU to perform the assist control. The steering torque signal T, the vehicle speed signal V, and the temperature signal Th are converted from analog signals to digital signals by an A / D converter (not shown), for example, so that the control unit 30 can perform arithmetic processing. . The speed signal V may be input to the control unit 30 via a digital communication line such as CAN mounted on the vehicle. In addition, the signal is amplified by an amplifier (not shown), and is appropriately filtered by a low-pass filter (not shown).

  FIG. 2 is a block diagram showing a general function of the control unit 30 and an operation procedure of the function. For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function as one function of a program executed by the CPU.

  The control unit 30 includes a phase compensator 31, a steering assist control unit 32, a differential compensator 34, a proportional calculator 35, an integral calculator 36, a subtractor 30a, an adder 30b, a motor drive circuit 37, and a motor current detection circuit 38. It has.

  The steering torque signal T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 to enhance the stability of the steering system, and the phase-compensated steering torque signal TA is input to the steering assist control unit 32. Is done. Similarly, the vehicle speed signal V detected by the vehicle speed sensor 12 and the temperature signal Th detected by the temperature sensor 7 are also input to the steering assist control unit 32.

  The steering assist control unit 32 includes an assist map 33. The steering assist control unit 32 refers to the assist map 33 and, based on the input steering torque signal TA, vehicle speed signal V, and temperature signal Th, the steering that is a control target value of the current supplied to the motor 20. The auxiliary command value I is determined.

  In particular, when the steering assist control unit 32 determines that the steering assist command value I to be supplied to the motor with reference to the assist map 33 is a low-speed driving state immediately after the vehicle starts in a low temperature state, As shown in FIG. 3, the assist curve a shown in the assist map, for example, corresponding to a specific vehicle speed signal V in a normal running state, is added to a gain value G corresponding to the temperature signal Th (where G> 1) is multiplied and changed to calculate the assist curve b. The steering assist control unit 32 determines a steering assist command value I corresponding to the steering torque signal TA based on the assist curve b. Note that the calculation of the gain value G corresponding to the temperature signal Th is performed using a preset conversion table. Thereby, the arithmetic processing can be performed in a short time. Moreover, the said conversion table can be calculated | required by a test result, for example.

The control steering assist command value I calculated in this way is input to the subtractor 30a and also input to the differential compensator 34 for improving the transient response of the feedback system. The deviation (I-i) output from the subtractor 30a is input to the proportional calculator 35 and also to the integral calculator 36 for improving the steady-state characteristics of the feedback system. Along with the output of the differential compensator 34, the outputs of the proportional calculator 35 and the integral calculator 36 are also added to the adder 30b, and the current control value E, which is the addition result of the adder 30b, is output. Further, the current i of the motor 20 is detected by the motor current detection circuit 38 and fed back to the subtractor 30a, thereby constituting feedback control by PID compensation.
The current control value E is input to the motor drive circuit 37 as a motor drive signal.

  In the present embodiment, a brushless motor is used as the motor 20. A plurality of N poles and S poles are alternately arranged and fixed over the circumference of the rotor of the brushless motor, and a stator coil is arranged over the circumferential direction so as to enclose the rotor. . The brushless motor uses a Hall element as a magnetic pole position detection element, detects the phase of the magnetic pole of the rotor by the Hall element, and supplies a current to each stator coil according to the detected phase. A rotational torque is obtained by selectively switching. The motor drive circuit 37 supplies and switches the current, and performs an operation to achieve the current control value E. Thereby, the assist control for adding the assist torque by the motor 20 to the steering system is realized.

  Next, the operation procedure of the steering assist control unit 32 according to the present invention will be described in detail according to the flowchart of FIG.

  Simultaneously with the start of the vehicle, the temperature sensor 7 detects the ambient temperature and outputs a temperature signal Th that is the detection result (ie, S100). It is determined whether the temperature signal Th is less than the temperature threshold Th1. However, in the present embodiment, since the starting operation resistance increases rapidly from about −30 ° C. or lower (see FIG. 6), the temperature threshold Th1 is set to −20 degrees (ie, S101). If the temperature signal Th is equal to or greater than the temperature threshold Th1, the process is terminated. If the temperature signal Th is less than the temperature threshold Th1, the steering assist control unit 32 turns on the low temperature flag (ie, S102).

  On the other hand, a post-startup elapsed time S (IG ON start time), which is an elapsed time since the ignition key is turned on, is measured by a timer (not shown). Based on this measurement result, the elapsed time S after activation is compared with the time threshold S1, and it is determined whether the elapsed time S after activation has exceeded the time threshold S1 (S104). However, in the present embodiment, the time threshold S1 is set to 30 seconds or less. If the elapsed time S after activation has exceeded the time threshold value S1, the process is terminated, and if not, it is determined that the vehicle is in the initial activation state, and the steering assist control unit 32 turns on the activation flag. (S105).

  After the time threshold S1 has elapsed, the start operating resistance decreases due to steering by the steering operator, and the temperature of the lubricant in the steering mechanism and the steering mechanism increases due to engine heat, resulting in a low temperature state of the vehicle. This is resolved, and the starting operating resistance is greatly reduced to return to the normal value. Therefore, in the present embodiment, as described above, the elapsed time S after start-up is measured and the time threshold S1 is set, and these comparisons are performed to determine whether or not the vehicle is in the initial start-up state.

  Subsequently, the vehicle speed signal V is detected by the vehicle speed sensor 12 (S106), and the vehicle speed signal V is compared with the vehicle speed threshold value V1 (S107). In the present embodiment, the vehicle speed threshold value V1 is set to 5 km / h. If the vehicle speed signal V is equal to or higher than the vehicle speed threshold value V1, the process is terminated. If the vehicle speed signal V is less than the vehicle speed threshold value, it is determined that the vehicle is in a low speed state, and the steering assist control unit 32 turns on the speed flag (S108).

  Finally, the steering assist control unit 32 confirms that all of the low temperature flag, the start flag, and the speed flag are ON, calls the assist map 33 (FIG. 3), and is displayed on the assist map 33. Further, the assist curve a corresponding to the vehicle speed signal V detected by the vehicle speed sensor 12 is read out, and the assist curve a is multiplied by a gain value G (where G> 1) corresponding to the temperature signal Th, and the processing result is obtained. And the steering assist command value I are determined based on the steering torque signal TA (S109). Thereby, it is possible to perform compensation for the starting operation resistance related to the steering mechanism.

  If at least one of the low temperature flag, the start flag, and the speed flag is not ON, the steering assist control unit 32 determines that the vehicle is in a normal traveling state, and uses the gain value G to assist map. The steering assist command value I is determined with reference to the assist map 33 on the basis of the steering torque signal TA and the vehicle speed signal V as in the prior art without adjusting 33, and a transition to a normal running state is made. ing.

  The temperature threshold value Th1, the time threshold value S1, and the vehicle speed threshold value V1 are values set in advance according to the type of vehicle, the age of use of the vehicle, the type of lubricant, and the like, and can be appropriately changed from the outside. Value.

  Therefore, according to this embodiment, the temperature sensor 7 is provided, and the control unit 30 changes the assist map 33 based on the temperature signal Th detected by the temperature sensor 7 during low-speed driving immediately after starting the vehicle. Since the start-up operation resistance related to the steering mechanism is corrected, the effect of the start-up operation resistance during low-speed driving immediately after starting the vehicle in a low temperature state is reduced, and the deterioration of the steering feeling is suppressed. be able to. Therefore, good steering can be performed as in normal driving.

  The description of the specific embodiments is finished above, but the aspect of the present invention is not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate. For example, in the present embodiment, most of the processing is performed by software, but a part or all of the processing may be realized by hardware such as FPGA (Field Programmable Gate Array).

  In this embodiment, the gain for adjusting the assist curve is calculated using the conversion table obtained from the test results. However, the present invention is not limited to this, and parameter optimization such as fuzzy control and genetic algorithm is possible. A technique or the like may be used.

  In the present embodiment, the gain is illustrated as an example of changing the assist curve of the assist map. However, the present invention is not limited to this, and the present invention is not limited to this, according to the temperature signal Th during low-speed driving immediately after starting the vehicle in a low temperature state. It is sufficient if the steering control command value I can be corrected. For example, an assist map represented by a multidimensional assist curve that directly corresponds to the steering torque signal T, the vehicle speed signal V, and the temperature signal Th may be applied, or the temperature signal Th may be applied to the temperature signal Th. A plurality of corresponding assist maps may be set in advance, and the assist maps may be switched according to the detected temperature signal Th.

  The present invention is applicable to all electric power steering devices regardless of the type of electric power steering device (column type, pinion type, rack type) and the type of motor (with brush, brushless, etc.).

  Further, in the present embodiment, the control in the control unit has been described by exemplifying feedback control by PID compensation. However, the present invention is not limited to this, and depending on the motor to be selected, H∞ control, robust compensation control, d · q axis vector Various controls such as control can be applied as appropriate.

1 is a schematic diagram showing an electric power steering apparatus according to the present invention. It is a block block diagram of the steering drive control apparatus of the electric power steering apparatus which concerns on this invention. It is a figure which shows the assist map of the electric power steering apparatus which concerns on this invention. The flowchart which shows operation | movement of the electric power steering which concerns on this invention. It is a figure which shows the conventional assist map. It is a characteristic view of starting operation resistance and atmospheric temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 2 Axis 3 Reduction gear 4 Universal joint 5 Pinion rack mechanism 6 Tie rod 7 Temperature sensor 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 14 Battery 20 Motor 30 Control unit 31 Phase compensator 32 Steering auxiliary control part 33 Assist map 34 Differentiation Compensator 35 Proportional calculator 36 Integral calculator 37 Motor drive circuit 38 Motor current detector

Claims (3)

A motor for applying assist force to the steering mechanism,
In an electric power steering apparatus comprising: a steering control drive device that controls the motor based on an assist map that stores a control command value of the motor that changes according to a steering torque and a vehicle speed;
Temperature detecting means for detecting a temperature related to the steering mechanism, and
The electric power steering apparatus according to claim 1, wherein the steering control driving apparatus performs compensation for the starting operation resistance based on a detection result of the temperature detecting means during low-speed driving immediately after starting the vehicle. In the electric power steering apparatus according to claim 1,
The electric power steering device according to claim 1, wherein the steering control drive device performs the compensation by changing the assist map based on a detection result of the temperature detection means. In the electric power steering apparatus according to claim 1 or 2,
The steering control drive device determines that the detection result of the temperature detection means is not more than a predetermined temperature, that the elapsed time since the start of the vehicle is within a predetermined time, and that the vehicle speed is not more than a predetermined speed. The electric power steering apparatus is characterized in that the compensation is carried out at the time.

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