JP2010280332A - Electric power steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering apparatus capable of exactly detecting a steering torque even when a magnetic yoke is eccentrically rotated. <P>SOLUTION: The electric power steering apparatus includes: a magnetic yoke 9Y for generating a magnetic flux corresponding to a steering torque; a torque sensor 9S which is attached to face the magnetic yoke 9Y in the diametrical direction and detects a magnetic field; a target 13 rotating integrally with the magnetic yoke 9Y; and an index sensor 10S which is attached to face the target 13 in the diametrical direction at the same angular position as the torque sensor 9S and generates an output changing according to a distance from the facing portion. With this structure, ECU 11 corrects the output of the torque sensor 9S based on the output of the index sensor 10S. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering device that is mounted on a vehicle such as an automobile and generates a steering assist force by a motor based on a steering torque.

  In the electric power steering apparatus, a configuration for detecting the steering torque is necessary to generate an appropriate steering assist force according to the steering torque of the driver. For example, a device combining a permanent magnet and a magnetic yoke generates a magnetic field corresponding to the torsion angle (ie, steering torque) of a torsion bar connected to a steering wheel, and this magnetic field is generated by a magnetism collecting ring and a Hall IC. A configuration is known in which the steering torque is obtained by detection (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2005-265593 (FIG. 1)

However, in the conventional electric power steering apparatus as described above, the magnetic yoke may rotate slightly eccentrically. In this case, the radial distance between the magnetic yoke and the magnetism collecting ring varies depending on the rotation angle, which affects the output of torque detection. As a result, the steering torque is determined on the basis of the error output and the steering assist force is determined, so that there are cases where an appropriate steering assist force cannot be applied.
In view of such a conventional problem, an object of the present invention is to provide an electric power steering device capable of accurately detecting a steering torque even if a magnetic yoke rotates eccentrically.

(1) The present invention is an electric power steering device that generates a steering assist force by a motor based on a steering torque,
A rotating body having a possibility of eccentric rotation based on rotation around an axis based on steering, a magnetic yoke that generates a magnetic field corresponding to the steering torque, a magnetic yoke provided in a radial direction opposite to the magnetic yoke, A target that rotates integrally with the magnetic yoke, and an angular position that corresponds to the same or a predetermined relationship as the first sensor, and is provided to face the target in a radial direction, A second sensor that generates an output that varies depending on the distance to the facing portion, and the output of the first sensor is corrected based on the output of the second sensor, and the steering torque is calculated based on the corrected output. And a computing device that can be obtained.

  In the electric power steering apparatus configured as described above, when the magnetic yoke rotates eccentrically, the output of the first sensor is affected by the eccentric rotation and deviates from the original value (value when there is no eccentricity). The second sensor is similarly affected or correlated. Therefore, in the arithmetic device, the steering torque excluding the influence of the eccentric rotation can be obtained by correcting the output of the first sensor based on the output of the second sensor.

(2) In the electric power steering apparatus, the arithmetic unit stores in advance the output C of the second sensor when the magnetic yoke rotates without eccentricity, and outputs the output of the first sensor as A, When the output of the sensor 2 is B, the correction may be made by multiplying A by (C / B).
In this case, even if the influences of the eccentric rotation on the outputs of the two sensors are not at the same level, the ratio (C / B) for returning the deviation of the output of the second sensor to the original output is the output of the first sensor. By multiplying by, the output of the first sensor can be appropriately corrected.

(3) In the electric power steering device according to (1) or (2), the second sensor may be an index sensor that detects one rotation of the magnetic yoke.
In this case, an index sensor for detecting one rotation can also be used for correction.

(4) Moreover, in the electric power steering apparatus of the above (3), the target may have a ring shape as a whole in which one portion of the outer peripheral surface is recessed.
In this case, the one location can be used as an index sensor for one rotation detection, and the other locations can be used as target portions for detecting a change in distance due to eccentricity.

(5) In the electric power steering apparatus according to (4), the target may be provided at the end of the steering shaft and fixed to the shaft end of the magnetic yoke.
In this case, since the target can be provided at the end of the steering shaft, the structure is simple in that it is not necessary to prepare a target member separately.

(6) In the electric power steering device according to any one of (1) to (5), a magnetic current collector is provided along the outer periphery of the magnetic yoke for the first sensor. Instead of the ring shape, the shape may be a half or less.
In this case, in particular, the output of the first sensor is easily affected by the eccentric rotation, but the influence can be eliminated by the correction. As a result, even if a simple and inexpensive structure having a half or less circumference is adopted for the magnetic current collector, the influence of the eccentric rotation can be prevented from appearing in the output, which contributes to the cost reduction as a whole.

  According to the electric power steering apparatus of the present invention, the steering torque excluding the influence of the eccentric rotation can be obtained by correcting the output of the first sensor based on the output of the second sensor. Therefore, it is possible to provide an electric power steering apparatus that can accurately detect the steering torque even if the magnetic yoke rotates eccentrically.

It is a figure showing a schematic structure of an electric power steering device concerning one embodiment of the present invention. It is a figure which shows the connection between a torque sensor, an index sensor, and ECU. It is a graph which shows the relationship between a torque and a sensor output. It is a disassembled perspective view which shows the structural example of a torque detection apparatus. It is a perspective view which shows only a magnetic yoke. It is a disassembled perspective view of a magnetic yoke. (A) is a graph which shows an example of the output of an index sensor, (b) is a graph which shows an example of the output of a torque sensor. It is a flowchart of the process regarding correction | amendment of the torque performed by ECU. (A) is a graph which shows an example of each output of a torque sensor and an index sensor with respect to an angle of 0 to 360 degrees when the steering torque is constant and the magnetic yoke rotates eccentrically, and (b) is a graph after correction. It is a graph which shows the output of a torque sensor with the output of an index sensor. It is a disassembled perspective view which shows another structural example of a torque detection apparatus.

  FIG. 1 is a diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. In the figure, the steering wheel 1 is connected to a first steering shaft 2. The first steering shaft 2 is connected to the second steering shaft 4 via a torsion bar 3. A steering assist force by the rotation of the motor 5 can be applied to the second steering shaft 4. A pinion 6 is formed at the lower end of the second steering shaft 4, and the pinion 6 meshes with the rack 7. When the rack 7 moves in the axial direction (lateral direction in the figure), a steered angle can be given to the steered wheels (generally front wheels) 8.

  The torque detection device 9 detects a twist of the torsion bar 3, that is, a relative rotation angle difference between the first steering shaft 2 and the second steering shaft 4 as a steering torque, and outputs an ECU (electronic control) as an arithmetic unit. Unit) 11. Further, in the vicinity of the torque detection device 9, there is provided a rotation detection device (detection device using an index sensor) 10 that detects the rotation of the second steering shaft 4 in units of one rotation, two rotations,. . The output of the rotation detection device 10 is given to the ECU 11. In addition, information on the steering angle of the steering wheel 1 and a vehicle speed signal from the vehicle speed sensor 12 are also input to the ECU 11. The ECU 11 drives the motor 5 in order to generate a necessary steering assist force based on the steering torque and the vehicle speed.

  FIG. 2 is a diagram illustrating a connection between the ECU 11 and the torque sensor 9S and the index sensor 10S which are sensor units of the detection devices 9 and 10 described above. The torque sensor 9S includes linear type Hall ICs 91 and 92 as a pair of sensor elements. There are four lines connecting the torque sensor 9S and the ECU 11, and a voltage of DC5V, for example, is applied from the ECU 11 between the power supply terminal TSV and the ground terminal TSG. Sensor outputs (voltages) of the Hall ICs 91 and 92 are generated at the terminals TS1 and TS2, respectively, according to the steering torque to be detected. Here, it is assumed that one of the two Hall ICs 91 and 92 is “main” and the other is “sub”.

  On the other hand, the index sensor 10S is, for example, a proximity sensor that generates a high-frequency magnetic field, and the output to the ECU 11 changes according to the distance from an opposing magnetic target (described later in detail). The proximity sensor that generates a high-frequency magnetic field is merely an example, and various other sensors can be used. For example, it may be a sensor of a type that captures with a magnetic sensor that the distribution of magnetic field lines (magnetic flux) generated from a magnet changes depending on the degree of approach of the magnetic material.

  FIG. 3 is a graph showing a relationship between output characteristics of the torque sensor 9S as an example, that is, torque (steering torque) and sensor output. As for the torque of the horizontal axis, the sign on the right side from the origin is the right steering and the sign is positive, the sign on the left side from the origin is the left steering and the sign is minus. In this example, as shown in the figure, the two output characteristics of main and sub have a certain mutual relationship, and are X-shaped characteristics that cross at the neutral point of torque 0. This is a characteristic having vertical symmetry viewed from the neutral point (2.5V).

For each characteristic, the sensor output changes linearly until the absolute value reaches a predetermined torque, and the sensor output saturates when the absolute value exceeds the predetermined torque. The torque at the saturation point is about ± 10 N · m. The sensor output in the saturation region is 3.6 to 4 V on the upper limit side and 1 to 1.4 V on the lower limit side. The total value of the two sensor outputs is in the range of (1 + 3.6) to (1.4 + 4) from the numerical value on the graph, but in reality, it is almost 5V and the error is about ± 0.3. is there. These numerical values are only examples, and differ depending on the type of torque sensor. For example, when the main is 3V, the sub is 2V, and the torque at this time is 4 [N · m] by right steering (+). That is, the value (or vice versa) taken by the sub sensor output with respect to the main sensor output is determined, and the torque conversion value is the same.
Note that FIG. 3 is merely an example of the characteristics of the torque sensor, and is not limited to a sensor having such characteristics. For example, a torque sensor of the same output type that does not cross the sensor output may be used.

  The ECU 11 stores in advance the output characteristics of the torque sensor 9S as described above. Therefore, until the absolute value of the torque reaches the saturation point, the torque corresponding to the sensor output can be accurately detected based on the linear change characteristic.

FIG. 4 is an exploded perspective view showing a configuration example of the torque detection device 9. In the figure, the first steering shaft 2 and the second steering shaft 4 described above are connected to each other via a torsion bar 3. In addition, since it is an exploded view, the torsion bar 3 is shown as being divided into upper and lower parts, but actually, the upper end is fixed to the first steering shaft 2 and the lower end is fixed to the second steering shaft 4. One bar.
A cylindrical permanent magnet 9M that is magnetized with, for example, 24 poles (N, S poles × 12) in the circumferential direction is attached to the end plate 2a of the first steering shaft 2. On the other hand, a substantially cylindrical magnetic yoke 9 </ b> Y is attached to the end plate 4 a of the second steering shaft 4.

  The first steering shaft 2, the torsion bar 3, the permanent magnet 9M, the magnetic yoke 9Y, and the second steering shaft 4 are arranged coaxially with each other. When the driver rotates the steering wheel 1 (FIG. 1), the first steering shaft 2 and the permanent magnet 9M rotate, and the torsion bar 3 is twisted. The torsion bar 3 is twisted, that is, a steering assist force is generated by the motor 5 (FIG. 1) according to the steering torque, and the second steering shaft 4 and the magnetic yoke 9Y rotate so as to follow the rotation of the first steering shaft 2. .

  FIG. 5 is a perspective view showing only the magnetic yoke 9Y. FIG. 6 is an exploded perspective view of the magnetic yoke 9Y. In FIG. 6, the magnetic yoke 9Y is formed by resin-molding a pair of ring yokes 93 made of a soft magnetic material. The ring yoke 93 is formed with a plurality of claws 93a at equal intervals in the circumferential direction, and is molded into a cylindrical shape in a state where the claws 93a of the pair of ring yokes 93 are close to each other (see FIG. 5). .

  A target 13 made of a magnetic material is attached to the mold portion 94 made by the mold by screwing or the like. The target 13 includes a target portion 13a that forms an outer peripheral portion, and a fitting portion 13b that is fitted in the mold portion 94 and serves for positioning. Although the target 13 has a ring shape as a whole, the target 13 is recessed at one location on the outer peripheral surface to form a recess 13c. In general, the target of the index sensor has a concave / convex relationship opposite to that shown in the figure, and a detection convex portion is formed only at one location on the outer peripheral surface, and the other (other than the convex portion) is used for detection. It is a part not provided. The magnetic yoke 9Y (FIG. 5) in which the fitting portion 13b of the target 13 is fitted to the mold portion 94 forms a cylindrical rotating body.

  Returning to FIG. 4, the permanent magnets 9 </ b> M are inserted inside the magnetic yoke 9 </ b> Y, and face each other with a slight radial gap between the inner surface of the magnetic yoke 9 </ b> Y. The cylindrical magnetic yoke 9Y generates a magnetic field corresponding to the twist angle between the first steering shaft 2 and the second steering shaft 4 connected to each other via the torsion bar 3 based on the magnetic flux generated by the permanent magnet 9M. Let The target 13 is not functionally part of the magnetic yoke 9Y, but is physically integrated with the magnetic yoke 9Y and rotates integrally. The magnetic yoke 9Y is based on rotation around the axis A (coaxial rotation) based on steering, but is actually a rotating body that may rotate slightly eccentrically.

  On the outer peripheral side of the magnetic yoke 9Y, a magnetic current collector 9C that collects magnetic flux that comes out on the outer peripheral side of the magnetic yoke 9Y is attached and fixed to a housing (not shown). The magnetic collector 9C is made of, for example, permalloy, and surrounds the magnetic yoke 9Y in an arc shape. For convenience of explanation, the drawings are illustrated with a slight separation in the radial direction, but actually, the magnetic current collector 9C is closer to the magnetic yoke 9Y. The length of the magnetic current collector 9C in the circumferential direction is ½ or less, such as ½ or ¼. In the first place, it is more convenient for the magnetic current collector to be a ring (magnetic current collection ring) that goes around the magnetic yoke 9Y. However, the material cost of the permalloy and the manufacturing cost of wrapping the whole with a mold or the like are relatively low. It will be expensive. However, the magnetic collector 9C thus shortened and simplified can be manufactured at low cost.

  The torque sensor 9S described above is attached to the center of the magnetic collector 9C in the circumferential direction. The mounting position of the torque sensor 9S can be other than the center in the circumferential direction of the magnetic collector 9C. However, since the magnetic collector 9C also has a magnetic resistance, it is preferable to take in the magnetic flux as close to the torque sensor 9S as possible. For this, the center is preferred.

  On the other hand, the above-described index sensor 10S is attached and fixed to a housing (not shown) so as to face the target portion 13a in the radial direction. The angular position of the index sensor 10S in the circumferential direction is the same as the angular position of the torque sensor 9S in the circumferential direction. In addition, the index sensor 10S is shown slightly away from the target portion 13a in the radial direction, but actually, the index sensor 10S is closer to the target portion 13a.

  (A) of FIG. 7 is a graph which shows an example of the output of the index sensor 10S. When the magnetic yoke 9Y rotates around the axis A (FIG. 4) without any eccentricity, the output of the index sensor 10S is basically at a constant level, but the output is drastically reduced only when facing the recess 13c. Accordingly, since the output decreases once every rotation (360 degrees), the number of rotations can be detected by counting the number of times from the neutral position of the steering. The detected number of rotations can be used for calculation for determining the steering assist force.

FIG. 7B is a graph showing an example of the output of the torque sensor 9S. Assuming that the steering wheel 1 is steered once with a constant steering torque, the output of the torque sensor 9S is at a constant level as shown in the figure.
However, when the magnetic yoke 9Y rotates eccentrically, the output varies depending on the rotation angle even if the steering torque is constant, and the output level deviates from the original value (value when there is no eccentricity). If such a deviation occurs, accurate steering torque cannot be detected. That is, considering such a case, it is necessary to correct the steering torque.

  FIG. 8 is a flowchart of processing related to correction of torque (steering torque) executed by the ECU 11 as an arithmetic unit. This process is executed every time a main calculation for determining a necessary steering assist force is performed. In FIG. 8, first, the ECU 11 measures the output of the torque sensor 9S (step S1), and measures the output of the index sensor 10S (step S2).

  Next, the ECU 11 determines whether the index sensor 10S is at the index position, that is, whether the index sensor 10S is at the rotational angle position where the recess 13c faces the index sensor 10S, based on whether the output is greatly reduced (step S3). If it is not the index position, the ECU 11 detects a magnetic field from the output of the index sensor 10S (step S4). Next, the ECU 11 determines whether or not the detected magnetic field is within an appropriate range (step S5). Here, an appropriate range is set in advance.

If within the appropriate range, the ECU 11 corrects the torque (step S6). Here, assuming that the output measurement value of the torque sensor 9S is A, the output measurement value of the index sensor 10S is B, and the output measurement value of the index sensor 10S stored in advance without eccentricity is C, the corrected torque value A '
A ′ = A × (C / B) (1)
It is.

FIG. 9A is a graph showing an example of each output of the torque sensor 9S and the index sensor 10S with respect to an angle of 0 to 360 degrees when the steering torque is constant and the magnetic yoke 9Y rotates eccentrically. Due to the eccentric rotation, the distance (gap) between the torque sensor 9S and the magnetic yoke 9Y becomes smaller or larger than the normal value without eccentricity. Similarly, the distance (gap) between the index sensor 10S and the target portion 13a also becomes smaller or larger than the normal value (C) without eccentricity. In general, the torque sensor 9S has higher sensitivity and a higher output level. Therefore, a change in output as shown in FIG.
Here, if processing for obtaining a corrected torque value A ′ based on the values of A, B, and C at an arbitrary angle θ is performed, as shown in FIG. The output of the torque sensor 9S is obtained.

As described above, in the electric power steering apparatus according to the present embodiment, when the magnetic yoke 9Y rotates eccentrically, the output of the torque sensor 9S is affected by the eccentric rotation, and the original value (value when there is no eccentricity). Although deviating, the index sensor 10S is similarly affected or correlated. Therefore, the ECU 11 can obtain the steering torque excluding the influence of the eccentric rotation by correcting the output of the torque sensor 9S based on the output of the index sensor 10S.
Further, even if the influence of the eccentric rotation on the outputs of the two sensors 9S and 10S is not the same level, the ratio (C / B) for returning the deviation of the output of the index sensor 10S to the original value is output from the torque sensor 9S. By multiplying by, the output of the torque sensor 9S can be appropriately corrected.

  Returning to FIG. 8, the ECU 11 determines whether or not the corrected torque is an abnormal value, that is, a value that is not normally possible (step S7), and if it is not an abnormal value, the electric power is based on the corrected torque. The motor 5 is driven to control the steering device (EPS) (step S8).

  On the other hand, if it is the index position in step S3, the B value that is originally required cannot be obtained, so the ECU 11 performs torque correction using the alternative value (step S9). As an alternative value, for example, the value of (C / B) used in the process of immediately preceding step S6 can be used, and the calculation of the above equation (1) is thereby performed. The subsequent processing (steps S7 and S8) is the same.

  Further, if the detected magnetic field is not an appropriate value in step S5, a failure of the index sensor 10S is expected, so the ECU 11 sets an abnormality flag (step S10) and shifts to a predetermined fail-safe logic. (Step S11). In addition to such processing, when the detected magnetic field is not an appropriate value in step S5, correction using an alternative value may be performed as in the processing of step S9. It is also possible to perform normal control based on the output of the torque sensor 9S without performing it (that is, giving up correction).

  In the above embodiment, the angular position in the circumferential direction of the index sensor 10S and the angular position in the circumferential direction of the torque sensor 9S are the same. However, this is not necessarily the same, and has a predetermined relationship. The corresponding angular position may be used. For example, if the positions are 180 degrees different from each other, the direction of the deviation of the output of the index sensor can be reversed and used for correction.

  In the above embodiment, the output of the index sensor 10S is used to perform correction. However, such a sensor is not limited to the index sensor. For example, a pure distance sensor that detects a radial distance (gap) may be used. However, in the above embodiment, a sensor is not provided exclusively for correction, but the concave and convex portions of the target are devised (reversed) by using an index sensor for detecting one rotation so that a concave portion can be detected by one rotation. Since the other portions are used as target portions for detecting a change in distance, the structure is simple and the manufacturing cost is low.

In the above-described embodiment, the magnetic current collector 9C is not in a ring shape with one round, but in a shape with a half or less. However, the present invention is not limited to this. That is, a magnetism collecting ring that makes one round may be used as the magnetism collector. In the case of the magnetic flux collecting ring, since the magnetic flux is taken in all around, the influence of the eccentric rotation is mitigated, but the accuracy of torque detection can be further improved by performing the above correction.
However, according to the above-described embodiment, it is possible to suppress the influence of eccentric rotation from appearing in the output by performing the above correction while adopting a simple and inexpensive magnetic current collector having a half or less circumference. It is possible to provide a practical structure that contributes.

In the above embodiment, the target 13 is a member on the magnetic yoke 9Y side. However, the target may be configured to rotate integrally with the magnetic yoke 9Y, and is not necessarily a member on the magnetic yoke 9Y side. May be.
For example, FIG. 10 is an exploded perspective view showing another configuration example of the torque detection device 9. In this configuration example, the target 13 is provided at the end of the second steering shaft 4 and is fixed to the shaft end of the magnetic yoke 9Y. In this case, since the target 13 can be provided at the end of the second steering shaft 4, it can be said that the structure is simple in that it is not necessary to prepare a target member separately.

  Further, in the above embodiment, the high frequency magnetic field is generated from the index sensor 10S and the target 13 is made of a magnetic material, but conversely, the index sensor is magnetized on the target side, and the index sensor detects the magnetic field by a Hall IC or the like. The structure of performing may be sufficient.

4: 2nd steering shaft, 5: motor, 9C: magnetism collector, 9S: torque sensor (first sensor), 9Y: magnetic yoke, 10S: index sensor (second sensor), 11: ECU (arithmetic unit) , 13: target, 13c: recess

Claims (6)

An electric power steering device that generates a steering assist force by a motor based on a steering torque,
A rotating body that has a possibility of eccentric rotation while being based on rotation around an axis based on steering, and generates a magnetic field corresponding to steering torque, and
A first sensor that is provided to face the magnetic yoke in a radial direction and detects a magnetic field;
A target that rotates integrally with the magnetic yoke;
A second sensor that is provided to face the target in a radial direction at an angular position corresponding to the same or a predetermined relationship as the first sensor, and that generates an output that varies depending on a distance from the facing portion;
An electric power steering comprising: an arithmetic unit capable of correcting the output of the first sensor based on the output of the second sensor and obtaining a steering torque based on the corrected output. apparatus.   The arithmetic unit stores in advance the output C of the second sensor when the magnetic yoke rotates without eccentricity, the output of the first sensor is A, and the output of the second sensor is B. The electric power steering apparatus according to claim 1, wherein the correction is made by multiplying A by (C / B).   The electric power steering apparatus according to claim 1, wherein the second sensor is an index sensor that detects one rotation of the magnetic yoke.   The electric power steering apparatus according to claim 3, wherein the target has a ring shape as a whole in which one portion of the outer peripheral surface is recessed.   The electric power steering apparatus according to claim 4, wherein the target is provided at an end portion of a steering shaft and is fixed to a shaft end portion of the magnetic yoke.   6. A magnetic current collector is provided along the outer periphery of the magnetic yoke for the first sensor, and the magnetic current collector is not a ring shape that makes one round, but a shape that is less than a half circumference. The electric power steering device according to the item.

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