JP2008049934A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of achieving good steering feeling regardless of mounting weight of a person or baggage loaded on a vehicle. <P>SOLUTION: In this electric power steering device 11, a position sensor 37 detects increase or decrease of the mounting weight to the vehicle 10 as a load to a front suspension 27, that is, a shrinkage amount F of a damper 28. Based on the detected result, an assist gain G1 is determined, and an assist electric current command value I1 is corrected in accordance with increase or decrease of the mounting weight. Even when the mounting weight is increased or decreased, influence to steering feeling can be restrained. That is, good steering feeling can be achieved regardless of the mounting weight of the person or the baggage loaded on the vehicle 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that outputs an assist force for assisting steering of a steering wheel.

As a conventional electric power steering device, a motor current command value is determined according to the load torque applied to the rotating shaft of the steering wheel and the vehicle speed, and a drive current corresponding to the motor current command value is applied to the steering motor. And what outputs the assist force for assisting steering of a steering wheel is known (for example, refer to patent documents 1).
JP-A-2005-239011 (paragraphs [0031] to [0032])

  Incidentally, the motor current command value described above is determined from, for example, a current command value calculation map in which load torque, vehicle speed, and motor current command value are stored in association with each other. The current command value calculation map is normally set so that an optimum steering feeling can be obtained when the vehicle has an average weight of a person, luggage, or the like. Similarly, when the motor current command value is determined by an arithmetic expression instead of the current command value calculation map, similarly, an optimum steering feeling can be obtained when the vehicle has an average weight of a person, luggage, etc. Is set. However, regardless of which determination method is used to determine the motor current command value, the conventional electric power steering device described above does not correct the motor current command value based on the vehicle mounting weight. When changed, there was a case that the steering feeling was uncomfortable.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electric power steering device capable of providing a good steering feeling regardless of the weight of a person, luggage, etc. mounted on a vehicle. .

  The electric power steering device (11) according to the invention of claim 1 made to achieve the above object is an electric power steering device (11) for outputting an assist force for assisting steering of the handle (33). Assist force determining means (43, S2) for determining a target value of the assist force according to the vehicle speed (V) and the load torque (T1) for steering the steering wheel (33), and the steered wheels (50 The suspension load detection means (37) for detecting the load on the suspension (27) supporting the), and the target value of the assist force increases as the load detected by the suspension load detection means (37) increases. Target value correcting means (45, 46, S4, S5) for correcting to the target value and correcting by target value correcting means (45, 46, S4, S5) Characterized in place of outputting an assist force according to the target value of the assist force.

  According to a second aspect of the present invention, in the electric power steering apparatus (10) according to the first aspect, the target value correcting means (45, 46, S4, S5) includes a load on the suspension (27) and an assist gain (G1). And an assist gain correspondence map (mp22), and based on the assist gain correspondence map (mp22), the assist gain (G1) is determined from the load detected by the suspension load detecting means (37), A characteristic is that correction is performed by multiplying the determined assist gain (G1) by the target value of the assist force.

  According to a third aspect of the present invention, in the electric power steering apparatus (11) according to the first or second aspect, the suspension load detecting means (37) determines the amount of contraction of the damper (28) provided in the suspension (27). 27) is characterized in that it is a position sensor (37) that is detected as a substitute value for the load received.

  According to a fourth aspect of the present invention, in the electric power steering apparatus (11) according to the first or second aspect, the suspension load detecting means is a load that the suspension (27) receives the gas pressure in the air damper provided in the suspension (27). It is characterized in that it is a pressure sensor that is detected as a substitute value.

  As the weight of a person or luggage mounted on the vehicle increases, the frictional resistance between the tire and the road surface increases, and the force required for turning the steered wheels (that is, the combined force of the steering force and the assist force) also increases. On the other hand, in the electric power steering apparatus according to the first aspect, the suspension load detecting means detects the increase or decrease in the mounting weight as the magnitude of the load on the suspension. Then, based on the detection result, the target value correcting means corrects the target value of the assist force according to the increase / decrease of the mounted weight. Thereby, even if the mounting weight increases or decreases, the influence on the steering feeling is suppressed. That is, it is possible to give a good steering feeling regardless of the weight of the person, luggage, etc. mounted on the vehicle.

  According to the invention of claim 2, when the vehicle mounting weight increases, the target value correction means determines the assist gain from the suspension load detected by the suspension load detection means based on the assist gain correspondence map. Then, the determined assist gain is multiplied by the target value of the assist force to correct the target value of the assist force to be larger than before the mounting weight increases.

  Here, the suspension load detection means may be a position sensor that detects the amount of contraction of the damper provided in the suspension as a substitute value of the load received by the suspension, as in the third aspect of the invention. Further, a pressure sensor that detects a gas pressure in an air damper provided in the suspension as a substitute value of a load received by the suspension may be used.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. The vehicle 10 shown in FIG. 1 includes the electric power steering apparatus 11 of the present invention, and can steer the steered wheels 50 and 50 by assisting the steering operation by the driver with the steered motor 19. Specifically, the inter-steering wheel shaft 16 is passed between the pair of steered wheels 50, 50, and the inter-steering wheel shaft 16 is inserted into the cylindrical housing 18. Both ends of the inter-steering wheel shaft 16 are connected to the respective steered wheels 50 and 50 via tie rods 17 and 17, and the cylindrical housing 18 is fixed to the main body of the vehicle 10. Moreover, the large diameter part 18D is provided in the intermediate part of the axial direction of the cylindrical housing 18, and the steering motor 19 is incorporated in the large diameter part 18D. The steered motor 19 includes a stator 20 that is fitted and fixed to the inner surface of the cylindrical housing 18, and a cylindrical rotor 21 that is loosely fitted inside the stator 20. The inter-steering wheel shaft 16 passes through the inside of the rotor 21. In addition, a rotational position sensor 25 (for example, an encoder or a resolver) for detecting the rotational position of the rotor 21 is provided at one end of the large-diameter portion 18D of the cylindrical housing 18.

  A ball nut 22 is assembled on the inner surface of the rotor 21. Further, a ball screw portion 23 is formed at an intermediate portion in the axial direction of the inter-steering wheel shaft 16. A ball screw mechanism 24 is constituted by the ball nut 22 and the ball screw portion 23. When the ball nut 22 is rotated together with the rotor 21, the ball screw portion 23 is directly moved with respect to the cylindrical housing 18, whereby the steered wheels 50, 50 are moved. Steer.

  A rack 30 is formed on one end of the inter-steering wheel shaft 16, and a pinion 31 provided at the lower end of the steering shaft 32 is engaged with the rack 30. A handle 33 is attached to the upper end portion of the steering shaft 32.

  A steering angle sensor 34 is attached to a position near the upper end of the steering shaft 32. The steering angle sensor 34 detects the rotation angle of the steering shaft 32 (that is, the steering angle θ2 of the handle 33).

  A steering torque sensor 35 is attached to a portion of the steering shaft 32 below the steering angle sensor 34. The steering torque sensor 35 includes a torsion spring (not shown) that is torsionally deformed by a load torque T1 applied to the steering shaft 32, and a pair of resolvers (not shown) for detecting the rotation angles of both ends of the torsion spring. The load torque T1 applied to the steering shaft 32 can be detected according to the difference between the rotation angles detected by the two resolvers. A vehicle speed sensor 36 for detecting the vehicle speed V based on the rotation of the steered wheels 50 is provided in the vicinity of the steered wheels 50.

  In the vehicle 10, suspension expansion / contraction position sensors 37 and 37 (hereinafter simply referred to as “position sensors 37”) are respectively provided in the vicinity of the pair of front suspensions 27 and 27 that support the steered wheels 50 and 50. Each is provided. The position sensor 37 includes an oil damper 28 provided in the front suspension 27, more specifically, a contraction amount F (hereinafter referred to as “a contraction amount of the damper 28”) of a piston (not shown) that directly moves with respect to the cylinder of the oil damper 28. F ”). In FIG. 1, only one of the pair of front suspensions 27, 27 and position sensors 37, 37 is shown.

  And among each sensor 25, 34-37 mentioned above, the detected value by each sensors 34-37 other than the rotation position sensor 25 is acquired by the steering control apparatus 41 mentioned below, and assist force is received from the steering motor 19. FIG. The steered wheels 50 and 50 are steered by the resultant force of the assist force and the steering force of the handle 33 by the driver. The rotational position of the rotor 21 detected by the rotational position sensor 25 is acquired by the motor drive circuit 42. The drive current applied to the steered motor 19 is feedback controlled based on the rotational position of the rotor 21.

  The steering control device 41 executes, for example, the motor current command value calculation program PG1 shown in FIG. 2 at a predetermined cycle (for example, 4.0 [msec] cycle). Specifically, when the motor current command value calculation program PG1 is executed, the steering control device 41 detects each detection result (steering angle θ2,...) From the steering angle sensor 34, the steering torque sensor 35, the vehicle speed sensor 36, and the position sensor 37. The load torque T1, the vehicle speed V, and the amount of contraction F of the damper 28 are acquired (S1).

  Next, the steering control device 41, based on the torque / vehicle speed-current command value map mp1 (see FIG. 3), determines the basic current command value I11 corresponding to the load torque T1 and the vehicle speed V ("target value of assist force in the present invention"). (S2). Next, a compensation current command value I12 is determined based on the steering angle θ2, the load torque T1, and the vehicle speed V (S3).

  Next, the contraction amount F of the damper 28 is converted into a load received by the front suspension 27 based on the contraction amount / load conversion map mp21 (see FIG. 3), and based on the suspension load-gain map mp22 (see FIG. 3). The assist gain G1 corresponding to the load received by the front suspension 27 is determined (S4). The suspension load-gain map mp22 corresponds to the “assist gain corresponding map” of the present invention.

  Then, the assist current command value I1 (= G1 · (I11 + I12)) is calculated by multiplying the value obtained by adding the compensation current command value I12 to the basic current command value I11 and the assist gain G1 (S5). The assist current command value I1 corresponds to the “target value of assist force corrected by the target value correcting means” according to the present invention.

  Next, the maximum current command value I2 corresponding to the vehicle speed V is determined based on the vehicle speed-maximum current command value map mp3 (see FIG. 3) (S6). Then, the maximum current command value I2 is compared with the assist current command value I1 (S7). When the assist current command value I1 does not exceed the maximum current command value I2 (S7: YES), The assist current command value I1 is output to the motor drive circuit 42 (S8). On the other hand, if the assist current command value I1 exceeds the maximum current command value I2 (S7: NO), the maximum current command value I2 is output to the motor. It outputs to the drive circuit 42 (S9). When the assist current command value I1 or the maximum current command value I2 is output, the motor current command value calculation program PG1 ends and is re-executed after a predetermined period.

  The control system shown in the block diagram of FIG. 3 is configured by executing the motor current command value calculation program PG1. In the figure, the basic current command value calculation unit 43 is configured by step S2, the compensation current command value calculation unit 44 is configured by step S3, and the gain calculation unit 45 is configured by step S4. The assist current command value calculation unit 46 is configured by step S5, the maximum current command value calculation unit 47 is configured by step S6, and the current command value determination unit 48 is configured by steps S7 to S9. Here, the basic current command value calculation unit 43 (step S2) corresponds to “assist force determination means” of the present invention. The gain calculation unit 45 (step S4) and the assist current command value calculation unit 46 (step S5) correspond to the “target value correction means” of the present invention. This completes the description of the motor current command value calculation program PG1.

  As shown in FIG. 3, according to the contraction amount / load conversion map mp21 and the suspension load-gain map mp22, the contraction amount F of the damper 28, that is, the load received by the front suspensions 27 and 27 is a normal load. Is set such that the assist gain G1 is “1”, the assist gain G1 is larger than “1” when it is larger than normal, and the assist gain G1 is smaller than “1” when smaller than normal. . Here, the “normal load” means that the load weight of people, luggage, etc. (including gasoline) on the vehicle 10 is an average load weight (for example, in the case of a passenger car with a capacity of 5 persons, 1 to 2 persons) Is set to a load that the front suspensions 27 and 27 receive.

  As a result, when the load weight of people, luggage, etc. on the vehicle 10 is larger than the average load weight, the assist force output by the steering motor 19 can be increased accordingly, and the driver can The steering wheel can be operated with a steering force that is almost the same as that of a typical mounted weight.

  Further, for example, when the vehicle 10 that is a rear wheel drive vehicle is suddenly accelerated or when a heavy load or the like is loaded on the rear trunk of the vehicle 10, the front side of the body of the vehicle 10 is slightly lifted, and the front suspensions 27, 27 May be less than normal. In such a case, the steering operation can be made heavy by reducing the assisting force of the steering motor 19 to prevent sudden steering.

  The vehicle speed / torque-current command value map mp1 is set so that the basic current command value I11 increases as the load torque T1 increases as shown in FIG. 3, and the load torque T1 is the same. Is set such that the basic current command value I11 decreases as the vehicle speed V increases. That is, the assist force of the steering motor 19 increases as the load torque T1 during steering of the steering wheel increases, while the assist force of the steering motor 19 decreases as the vehicle speed V increases.

  Further, the vehicle speed-maximum current command value map mp3 is set so that the maximum current command value I2 decreases as the vehicle speed V increases, corresponding to the vehicle speed / torque-current command value map mp1.

  Next, the operation of the present embodiment configured as described above will be described. For example, when the load weight of people, luggage, etc. on the vehicle 10 is an average load weight (for example, only one driver is mounted on a passenger car with a capacity of 5 people), that is, the front suspension 27 is If it is under load: When the steering wheel 33 is steered in this state, the basic current command value I11 is calculated based on the load torque T1 applied to the steering shaft 32 and the vehicle speed V, and the compensation current command is calculated based on the load torque T1, the vehicle speed V, and the steering angle θ2. The value I12 is calculated. Further, the assist gain G1 is calculated based on the amount of contraction F of the damper 28 provided in the front suspension 27. Based on these calculation results, an assist current command value I1 is calculated. Here, since the load received by the front suspension 27 is a normal load, the assist gain G1 is set to “1”.

  The assist current command value I1 is compared with the maximum current command value I2 calculated according to the vehicle speed V. Here, since the assist gain G 1 is “1”, the assist current command value I 1 is always smaller than the maximum current command value I 2, and the assist current command value I 1 is output to the motor drive circuit 42. Then, the motor drive circuit 42 applies a drive current corresponding to the assist current command value I1 to the steered motor 19, and the steered motor 19 outputs an assist force corresponding to the drive current (assist current command value I1). Then, the steered wheels 50 and 50 are steered. As a result, the driver can operate the steering wheel while feeling a stable steering reaction force regardless of the load torque T1.

  For example, when the number of passengers of the vehicle 10 increases and the mounting weight of the vehicle 10 exceeds the average mounting weight (for example, when the number of passengers is changed from one to five), the following is performed. It is. That is, the contraction amount F of the damper 28, that is, the load received by the front suspension 27 increases and exceeds the normal load. Then, the assist gain G1 is set to a value larger than “1”, and the assist current command value I1 is corrected to a value larger than usual when steering the steering wheel. When the assist current command value I1 is smaller than the maximum current command value I2, the assist current command value I1 is output to the motor drive circuit 42. Then, the steered motor 19 outputs the assist force that has become larger than normal by the correction by the assist gain G1 to steer the steered wheels 50 and 50. Thereby, even when the mounting weight of the vehicle 10 exceeds the average mounting weight, the steering wheel 33 can be steered with a steering force that is almost the same as the average mounting weight.

  More specifically, when the weight of a person or luggage placed on the vehicle 10 increases, the frictional resistance between the tire and the road surface increases, and the force required for turning the steered wheels 50 and 50 (ie, steering force and assist force). The combined power) also increases. In the conventional apparatus, the shortage of assist force due to an increase in frictional resistance can be dealt with only by feedback control using a steering torque sensor. On the other hand, in the electric power steering apparatus 11 of the present embodiment, the position sensor 37 is used to detect an increase in the frictional resistance as a load (shrink amount F of the damper 28) received by the front suspension 27, and the detection result In response to the so-called feed-forward control that corrects the assist current command value I1 accordingly, the optimum assist force corresponding to the mounted weight is output from the start of steering of the steering wheel, and good steering feeling is achieved. Can be given.

  When the assist current command value I1 becomes larger than the maximum current command value I2 due to the correction by the assist gain G1, the maximum current command value I2 is output to the motor drive circuit 42 instead of the assist current command value I1. The As a result, the drive current flowing through the steered motor 19 is limited, preventing overheating of the steered motor 19 and preventing the assist force from becoming larger than necessary.

  Further, for example, when the vehicle 10 which is a rear wheel drive vehicle is accelerated rapidly or a heavy load or the like is loaded on the rear trunk of the vehicle 10, the front side of the body of the vehicle 10 is slightly lifted. F, that is, the load received by the front suspensions 27 and 27 is reduced compared to the normal time. Then, the assist gain G1 is set to a value smaller than “1”, and the assist current command value I1 is corrected to a value smaller than normal. At this time, since the assist current command value I1 is smaller than the maximum current command value I2, the assist current command value I1 is output to the motor drive circuit 42. Then, the steered motor 19 outputs the assist force that is smaller than normal by the correction by the assist gain G1 to steer the steered wheels 50 and 50. As a result, the steering operation becomes heavier than usual, and sudden steering can be prevented.

  As described above, according to the electric power steering apparatus 11 of the present embodiment, the position sensor 37 detects the increase or decrease in the weight mounted on the vehicle 10 as the load on the front suspension 27, that is, the contraction amount F of the damper 28. Then, based on the detection result, the assist gain G1 is determined, and the assist current command value I1 is corrected according to the increase or decrease of the mounted weight. Thereby, even if the mounting weight increases or decreases, the influence on the steering feeling is suppressed. That is, it is possible to give a good steering feeling regardless of the weight of the person / luggage mounted on the vehicle 10.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

  (1) Although the oil damper 28 is used for the front suspension 27 in the above embodiment, an air damper may be used. When an air damper is used, the gas pressure in the air damper may be detected by a pressure sensor, and the detected gas pressure may be used as a substitute value for the load received by the front suspension 27.

  (2) In the above embodiment, the basic current command value I11, the assist gain G1, and the maximum current command value I12 are determined from the maps mp1, mp21, mp22, and mp3 according to the detection values of the sensors 34 to 37. It may be determined by an arithmetic expression.

  (3) Only the contraction amount F of the damper 28 provided in one front suspension 27 may be detected.

The conceptual diagram of the vehicle which concerns on one Embodiment of this invention. Motor current command value calculation program flowchart Steering control device block diagram

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vehicle 11 Electric power steering apparatus 27 Front suspension (suspension)
28 Oil damper (damper)
33 Handle 37 Suspension expansion / contraction position sensor (position sensor)
43 Basic current command value calculation unit (assist force determination means)
45 Gain calculation section (target value correction means)
46 Current command value calculation unit for assist (target value correction means)
50 Steered wheel G1 Assist gain I1 Assist current command value I11 Basic current command value I12 Compensation current command value T1 Load torque V Vehicle speed θ2 Steering angle mp1 Current command value map mp21 Shrinkage / load conversion map mp22 Gain map (map for assist gain) )
mp3 Vehicle speed-maximum current command value map

Claims (4)

In an electric power steering device that outputs an assist force for assisting steering of a steering wheel,
Assist force determining means for determining a target value of the assist force according to a vehicle speed and a load torque for steering the steering wheel;
Suspension load detecting means for detecting a load on a suspension supporting the steered wheels of the vehicle;
Target value correction means for correcting the target value of the assist force to increase as the load detected by the suspension load detection means increases,
An electric power steering apparatus that outputs the assist force according to a target value of the assist force corrected by the target value correcting means. The target value correcting means has an assist gain correspondence map in which a load on the suspension and an assist gain are associated with each other.
Based on the assist gain correspondence map, the assist gain is determined from the load detected by the suspension load detecting means, and correction is performed by multiplying the determined assist gain by a target value of the assist force. The electric power steering apparatus according to claim 1.   The electric power steering apparatus according to claim 1 or 2, wherein the suspension load detection means is a position sensor that detects a contraction amount of a damper provided in the suspension as a substitute value of a load received by the suspension.   The electric power steering apparatus according to claim 1 or 2, wherein the suspension load detecting means is a pressure sensor that detects a gas pressure in an air damper provided in the suspension as a substitute value of a load received by the suspension. .

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