JP3655951B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus that detects a steering state using a magnetostrictive torque sensor.
[0002]
[Prior art]
Conventionally, in an automobile, a general power steering device using an electric motor is provided with an electric motor on a shaft directly below a steering wheel and a power steering control unit in a dashboard as disclosed in JP-A-5-254449 to 254451. A steering torque applied to the steering shaft is detected, the electric motor is controlled in accordance with the torque state, and a driving force is transmitted to the steering shaft to assist steering.
[0003]
A magnetostrictive torque sensor is used as one of torque sensors for detecting torque generated in the steering shaft during steering. This magnetostrictive torque sensor is superior to other torque sensors that detect the torsion angle by a torsion bar. Since there is no torsion bar part, the steering response is not hindered. There was an advantage that a feeling was obtained.
[0004]
[Problems to be solved by the invention]
However, the magnetostrictive torque sensor electrically captures the change in magnetic permeability caused by the distortion of the steering shaft, and the signal output from the detection coil is extremely weak. Therefore, if a weak signal is transmitted as it is from the magnetostrictive torque sensor to the power steering control unit via a long signal line, it becomes easy to ride noise, so that the weak signal is transmitted at the position of the magnetostrictive torque sensor. There was a need to amplify. Along with this, in order to prevent the influence of temperature and the like from being amplified and shifting the neutral point of the steering, the neutral point correction process (mechanical reversing switch) and the neutral point correction process The signal processing unit is also provided in the magnetostrictive torque sensor.
[0005]
Therefore, in addition to the magnetostriction detection coil, the excitation coil, and the excitation control unit, the magnetostrictive torque sensor includes a mechanism for correcting the neutral point and a signal processing unit and a signal processing unit on the steering shaft directly below the steering wheel. In some cases, the layout becomes difficult due to the increase in size and design.
[0006]
An object of the present invention is to reduce the size of the magnetostrictive torque sensor and improve the degree of design freedom.
[0007]
[Means for Solving the Problems and Effects of the Invention]
The invention described in claim 1
A rack bar that steers left and right wheels by moving left and right by a steering force from a steering shaft, a power steering control unit attached to a casing of the rack bar, and a drive unit controlled by the power steering control unit, An electric power steering device for assisting steering of the left and right wheels by the steering shaft by moving the rack bar to the left and right by controlling the drive unit according to a steering state. There,
A part or all of an amplifying unit or an excitation control unit in a magnetostrictive torque sensor provided in the vicinity of a position where a steering force is transmitted to the rack bar in the steering shaft and detecting the steering state is replaced with the power steering control unit. Provided in
Further, the casing of the rack bar, the casing of the power steering control unit, or the casing of the magnetostrictive torque sensor is made of metal, and a signal line between the magnetostrictive torque sensor and the power steering control unit is formed in the metal casing. An electric power steering apparatus characterized by passing through
[0008]
The invention according to claim 2
2. The electric power steering apparatus according to claim 1, wherein the power steering control unit itself performs processing of a detection signal amplified by the amplification unit of the magnetostrictive torque sensor.
[0009]
The invention described in claim 3
3. The electric power steering apparatus according to claim 2, wherein the power steering control unit performs neutral point correction of the magnetostrictive torque sensor based on data obtained in power steering control .
[0010]
The invention according to claim 4
The electric power steering apparatus according to any one of claims 1 to 3, wherein the power steering control unit has a dead zone of power steering control near a neutral point of the magnetostrictive torque sensor .
[0012]
Here, the electric power steering apparatus according to claim 1 is provided in the vicinity of the position where the steering force is transmitted to the rack bar in the steering shaft, and the amplifying part or the excitation control part of the magnetostrictive torque sensor for detecting the steering state. Since a part or all of them are provided in the power steering control unit, the magnetostrictive torque sensor does not increase in size, and it is not difficult to arrange by design.
[0013]
Since the magnetostrictive torque sensor is provided in the vicinity of the position where the steering shaft transmits the steering force to the rack bar, the magnetostrictive torque sensor and the power steering control unit attached to the casing of the rack bar are different from each other. It will be in a very close state in terms of distance. Therefore, by providing a part or all of the amplification unit or excitation control unit of the magnetostrictive torque sensor in the power steering control unit, a signal line is passed between the magnetostrictive torque sensor and the power steering control unit. This signal line is extremely short, and it is difficult for noise to ride.
Further, since the magnetostrictive torque sensor is provided in the vicinity of the position where the steering force is transmitted to the rack bar, the power steering control unit is the casing of the rack bar, the casing of the power steering control unit itself, or the magnetostrictive torque. A signal line can be passed through the sensor casing to connect the magnetostrictive torque sensor and the power steering control unit in a signal manner. As a result, the casing of the rack bar, the casing of the power steering control unit, or the casing of the magnetostrictive torque sensor is usually made of metal, so that electromagnetic shielding is possible, and external noise is less likely to ride on the signal line.
[0014]
In addition, since the power steering control unit normally performs control processing by software logic based on a program, the actual torque is calculated from the detection signal amplified by the amplification unit of the magnetostrictive torque sensor. By including the processing for performing the processing and other processing, the signal processing unit of the magnetostrictive torque sensor can be omitted, so that the overall size can be reduced, the number of parts can be reduced, and the manufacturing cost can be reduced.
[0016]
Further, if the power steering control unit is configured to perform processing of the detection signal amplified by the amplification unit of the magnetostrictive torque sensor, the power steering control unit can also obtain data obtained or used in the power steering control. Since it can be used, the neutral point correction of the magnetostrictive torque sensor may be performed based on the data. Also, if the power steering control unit detects its own temperature, the power steering control unit and the magnetostrictive torque sensor are close in distance, so the power steering control unit itself is regarded as the temperature of the magnetostrictive torque sensor. The neutral point can be corrected.
[0017]
In this way, when a mechanical reversal switch or temperature sensor is provided in the magnetostrictive torque sensor as in the past, the neutral point of the detected value is obtained according to the switch reversal or the detected temperature. In contrast, the magnetostrictive torque sensor does not require a mechanical reversing switch or a temperature sensor. When such a mechanical reversing switch or temperature sensor is not provided in the magnetostrictive torque sensor, the volume of the magnetostrictive torque sensor around the steering shaft is reduced, and the design is facilitated.
[0018]
The power steering control unit may perform power steering control having a dead zone near the neutral point of the magnetostrictive torque sensor. In the vicinity of the neutral point, due to mechanical play, temperature, etc., there may be a signal as if steered even if it is actually the neutral point, so power steering control is executed in a complicated manner. Can be prevented.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a partially broken explanatory view showing the electric power steering apparatus 2.
The electric power steering device 2 includes a rack bar 4, a motor unit 6, a power steering control unit 8, a steering shaft 10, and a magnetostrictive torque sensor 12.
[0020]
The rack bar 4 is formed with ball joints 4a and 4b at both ends thereof and is connected to partially shown tie rods 14 and 16. The tie rods 14 and 16 are connected to the knuckle arms of the left and right wheels of the automobile (not shown), and the movement of the rack bar 4 to the left and right is reflected in the direction change of the left and right wheels.
[0021]
The rack bar 4 is supported in the casing 18 so as to be slidable left and right. In the casing 18, the rotor 20 of the motor unit 6 is disposed, and the rotor shaft 22 has a cylindrical shape, and the rack bar 4 passes through the inside so as to be slidable. Further, the stator 24 of the motor unit 6 is disposed outside the rotor 20. In the motor unit 6, the rotation of the rotor 20 is controlled by the power steering control unit 8 via a current control power driver 54 (FIG. 4) in the power steering control unit 8.
[0022]
A rotor shaft 22 that rotates integrally with the rotor 20 is connected to a ball nut 26 at the right end of FIG. The ball nut 26 is fitted through a ball 28 into a spiral groove 30 having a semicircular cross section formed in a part of the rack bar 4. Therefore, when the power steering control unit 8 controls forward / reverse rotation of the rotor 20, the ball nut 26 rotates forward / reversely via the rotor shaft 22, and gives an auxiliary moving force to the rack bar 4 in any left and right directions. be able to. As a result, power steering control can be executed.
[0023]
As shown in the partially enlarged explanatory view of the electric power steering apparatus 2 in FIG. 2, the steering shaft 10 receives the steering force of a steering wheel (not shown) from the input side serration portion 32, and the output side pinion portion 34 This is transmitted to the rack 36 formed in a part of the bar 4 to move the rack bar 4 to the left and right.
[0024]
A steering shaft 10 intermediate between the serration unit 32 and the pinion unit 34 is provided with a magnetostrictive torque sensor 12 that detects distortion associated with steering of the steering wheel. In the magnetostrictive torque sensor 12, only the detection coil 40 and the excitation coil 41 are arranged in the casing 12 a of the magnetostrictive torque sensor 12.
[0025]
The casing 12a of the magnetostrictive torque sensor 12 is made of an aluminum alloy, and is formed integrally with the casing 18 of the rack bar 4 that is also made of an aluminum alloy.
The casing 12 a and the casing 18 extending from the magnetostrictive torque sensor 12 to the power steering control unit 8 on the casing 18 are provided with line insertion holes 42, and the inside thereof is a signal line from the detection coil 40 of the magnetostrictive torque sensor 12. 44 and an exciting current line 46 from the power steering control unit 8 pass therethrough.
[0026]
As shown in the schematic diagram of FIG. 3 and the block diagram of FIG. 4, the power steering control unit 8 has a microprocessor unit (MPU) 52 as a center, a current control power driver 54, a motor current control field effect transistor (FET) 56. , An FET temperature sensor 58, a power supply system switch 60, a power supply voltage sensor 62, a normal operation monitoring device 64, and an RS232C interface (I / F) 66.
[0027]
In the power steering control in the microprocessor unit 52, the detection signal from the magnetostrictive torque sensor 12 is processed as a torque detection circuit to obtain the steering torque and the steering direction, and according to the steering torque and direction. The direction of rotation of the motor unit 6 and the amount of torque are instructed to the current control power driver 54. The current control power driver 54 controls the rotation direction and output torque of the motor unit 6 via the motor current control field effect transistor 56 based on the direction and torque amount instructed from the microprocessor unit 52. During this power steering control, the microprocessor unit 52 monitors the rotational position of the motor unit 6 from the rotational position sensor 68 and the actual amount of current flowing from the current amount sensor 70 to the motor unit 6.
[0028]
In the power steering control, the output pattern of the rotation direction and torque amount of the motor unit 6 based on the steering torque and direction obtained from the signal of the magnetostrictive torque sensor 12 according to the vehicle speed obtained from the vehicle speed sensor 72. For example, the steering wheel 74 is controlled so that it can be steered lighter at low speeds and at the time of stationary, so that the steering feeling is responsive at medium and high speeds.
[0029]
If the FET temperature sensor 58 determines that the motor current control field effect transistor 56 is overheated, or if the power supply voltage sensor 62 determines that the battery B is not sufficiently supplied, the microprocessor The unit 52 stops the power steering control, turns off the power supply system switch 60, and stops the power supply to the current control power driver 54. When the normal operation monitoring device 64 determines that the microprocessor unit 52 itself is abnormal, the normal operation monitoring device 64 turns off the power supply system switch 60 and stops supplying power to the current control power driver 54. To do. The RS232C interface 66 is provided for communication processing with other control devices and the like. The excitation coil 41 of the magnetostrictive torque sensor 12 is supplied with an excitation current via an excitation current line 46 by an excitation control unit (not shown) arranged in the power steering control unit 8.
[0030]
As described above, the microprocessor unit 52 also includes a detection signal amplification unit from the detection coil 40 of the magnetostrictive torque sensor 12, and amplifies the detection signal from the detection coil 40 to obtain a digital value. Conversion is performed, and a calculation process as a torque detection circuit is performed to obtain a steering torque and a steering direction. As shown in FIGS. 3 and 4, the microprocessor unit 52 obtains data from other control devices via the vehicle speed, the rotational position of the motor unit 6, or the RS232C interface 66 for power steering control. Further, temperature data of the field effect transistor 56 for controlling the motor current, which is a part of the power steering control unit 8, is obtained from the temperature sensor 58 for FET. Therefore, the neutral point of the detection signal from the magnetostrictive torque sensor 12 can be determined based on these data.
[0031]
In addition to the detection coil 40 and the excitation coil 41, a torque detection circuit, a temperature sensor, or a mechanical reversing switch is provided in the casing 12a as in the prior art, and the detection signal is amplified by the torque detection circuit. Unlike the case where the neutral point of the detected value is obtained according to the polarity of the pole switch or the temperature detected by the temperature sensor, only the detection coil 40 and the excitation coil 41 are required in the casing 12a. Therefore, it is not necessary to arrange other than the detection coil 40 and the excitation coil 41 in the casing 12a of the magnetostrictive torque sensor 12, the volume of the magnetostrictive torque sensor 12 around the steering shaft 10 is reduced, and the design is easy. It becomes. Further, since the magnetostrictive torque sensor 12 has no electronic circuit therein, the casing 12a itself can be cheaper than the conventional one.
[0032]
In the electric power steering apparatus 2, the magnetostrictive torque sensor 12 is provided in the vicinity of a pinion portion 34 that contacts a rack 36 formed in a part of the rack bar 4 and transmits a steering operation. For this reason, the magnetostrictive torque sensor 12 exists at a position very close to the power steering control unit 8 provided in the casing 18 of the rack bar 4.
[0033]
Accordingly, even a weak signal from the detection coil 40 can be transmitted to the power steering control unit 8 through the signal line 44 with almost no noise.
In particular, in the electric power steering apparatus 2, the signal line 44 for transmitting a weak signal of the detection coil 40 is completely exposed to the outside through the line insertion hole 42 penetrating the aluminum alloy casings 12 a and 18. Without being inserted, the power steering control unit 8 is inserted. Therefore, external noise can be almost completely blocked by the electromagnetic shielding effect of the casings 12a and 18.
[0034]
Also in the power steering control unit 8, the signal processing unit for the calculation processing of the detection signal of the magnetostrictive torque sensor 12 becomes unnecessary due to the change of the software logic, and it is not necessary to increase the size accordingly. As a result, the overall size can be reduced, the degree of freedom in designing the automobile is increased, and the cost is reduced.
[0035]
[Others]
The power steering control unit 8 has obtained a neutral point of steering, but in the vicinity of the neutral point, a subtle torque change unrelated to steering is caused by mechanical play between the pinion unit 34 and the rack 36, temperature, or the like. May occur. When such a torque change occurs, the power steering control may be executed in a complicated manner. Therefore, in the vicinity of the neutral point, this complicated control process is performed by having a dead zone in the power steering control corresponding to the calculated steering torque. May be prevented.
[0036]
The signal line 44 and the excitation current line 46 are inserted through the line insertion hole 42 of the casing 18 of the rack bar 4, but a part of the casing of the power steering control unit 8 is extended to form the casing of the magnetostrictive torque sensor 12. 12a, a line insertion hole may be formed in a part of the casing of the power steering control unit 8, and the signal line 44 and the excitation current line 46 may be inserted therethrough. Further, a part of the casing 12a of the magnetostrictive torque sensor 12 is extended to the power steering control unit 8, a line insertion hole is formed in a part of the casing 12a of the magnetostrictive torque sensor 12, and the signal line 44 and The exciting current line 46 may be inserted.
[0037]
Furthermore, the signal line 44 and the excitation current line 46 may be independent insertion holes, that is, insertion holes dedicated to each line.
In addition, when a temperature sensor is provided near the magnetostrictive torque sensor 12 in order to perform torque detection with a particularly high accuracy requirement, any of the above-described insertion holes may be inserted through the signal line of the temperature sensor. .
[Brief description of the drawings]
FIG. 1 is a partially broken explanatory view showing an electric power steering apparatus.
FIG. 2 is a partially enlarged explanatory view thereof.
FIG. 3 is a schematic diagram of an electric power steering apparatus.
FIG. 4 is a block diagram of an electric power steering apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 2 ... Electric power steering apparatus 4 ... Rack bar 4a, 4b ... Ball joint 6 ... Motor part 8 ... Power steering control part 10 ... Steering shaft 12 ... Magnetostrictive torque sensor 12a, 18 ... Casing 14, 16 ... Tie rod 20 ... Rotor 22 ... rotor shaft 24 ... stator 26 ... ball nut 32 ... serration part 34 ... pinion part 36 ... rack 40 ... detection coil 41 ... excitation coil 42 ... line insertion hole 44 ... signal line 46 ... excitation current line 52 ... microprocessor unit 54 ... Current control power driver 56 ... Motor current control field effect transistor 58 ... FET temperature sensor 60 ... Power supply system switch 62 ... Power supply voltage sensor 64 ... Normal operation monitoring device 66 ... RS232C interface 68 ... Rotational positive Sensor 70 ... current sensor 72 ... vehicle speed sensor 74 ... steering wheel

Claims (4)

A rack bar that steers left and right wheels by moving left and right by a steering force from a steering shaft, a power steering control unit attached to a casing of the rack bar, and a drive unit controlled by the power steering control unit, An electric power steering device that assists steering of the left and right wheels by the steering shaft by moving the rack bar to the left and right by controlling the drive unit according to a steering state. There,
A part or all of an amplifying unit or an excitation control unit in a magnetostrictive torque sensor which is provided in the vicinity of a position where a steering force is transmitted to the rack bar in the steering shaft and detects the steering state is replaced with the power steering control unit. Provided in
Furthermore, the casing of the rack bar, the casing of the power steering control unit, or the casing of the magnetostrictive torque sensor is made of metal, and a signal line between the magnetostrictive torque sensor and the power steering control unit is provided in the metal casing. The electric power steering device characterized by passing through .   2. The electric power steering apparatus according to claim 1, wherein the power steering control unit itself also performs processing of a detection signal amplified by the amplification unit of the magnetostrictive torque sensor. 3. The electric power steering apparatus according to claim 2, wherein the power steering control unit performs neutral point correction of the magnetostrictive torque sensor based on data obtained in power steering control . The electric power steering apparatus according to any one of claims 1 to 3, wherein the power steering control unit has a dead zone of power steering control near a neutral point of the magnetostrictive torque sensor .

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