JP2000289639A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of minimizing a cost increase while a work load for returning a steering wheel to a neutral position is being reduced. SOLUTION: This electric power steering device involves a steering angular velocity estimating means 17 estimating steering angular velocity estev based on the voltage and current of a power assist motor 3, a steering wheel reset determining means 18 determining whether steering wheel operation is under a reset condition or not based on a steering torque signal Ts and a steering angular velocity (estev), and a reset correction amount computing means 19 generating the reasonable reset correction amount (icr') when the steering wheel operation is under the reset condition, in a control unit 10. It is thus possible to minimize a cost increase because of no need for adding an extra sensor even in the case of a vehicle not equipped with ABS, in addition to attaining a more satisfactory reset steering sense.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of an electric power steering device mounted on a vehicle such as an electric vehicle that performs steering.

[0002]

2. Description of the Related Art In a steering apparatus for an automobile, an operation is usually performed in which a driver releases his / her hand from a steering wheel (steering wheel) which is turned to one side and the steering force is released, and the steered wheels naturally return to a neutral position. I have been. However, in a normal electric power steering device, there is a disadvantage that the steering wheel is difficult to return particularly at a low speed, if it is expected that the steered wheels naturally return to the neutral position. This is due to the influence of the moment of inertia and frictional resistance of the power assist motor and its speed reducer when the steering wheel naturally returns due to the force applied to each steering wheel from the road surface. As a result, even if the driver releases his hand from the steering wheel,
Since the steering wheel returned slowly or the steering wheel did not return to the neutral position, the driver had to actively return the steering wheel to the neutral position, and the workload was heavy.

[0003] In order to solve such inconvenience, Japanese Patent Publication No. Hei 3-11944 discloses that when the torque for turning the steering wheel to one side is reduced, return steering is automatically performed immediately and the steered wheels return to the neutral position. An electric power steering device is disclosed. That is, the electric power steering apparatus disclosed in the publication is provided with a steering angle sensor that directly detects a steering angle of a steered wheel by detecting a left and right position of a steering rack shaft. When it is determined that the steering wheel is in the returning state due to a sharp decrease in the steering torque applied to the steering column, the power assist motor is actively driven, and the steered wheels are quickly returned to the neutral position. ing. As a result, according to the technique disclosed in the publication, it is not necessary to perform an aggressive driving operation for returning the steering wheel to the neutral position, and there is an effect that the workload of the driver is reduced.

[0004]

However, the technique disclosed in the above publication requires a steering angle sensor for detecting a steering angle of a steered wheel, in addition to a hardware configuration of an ordinary electric power steering apparatus. However, cost increases were inevitable. Therefore, an object of the present invention is to provide an electric power steering apparatus capable of minimizing cost increase while reducing a workload for returning a steering wheel to a neutral position.

[0005]

In order to solve the above problems, the inventor has invented the following means. (First Means) A first means of the present invention is an electric power steering apparatus according to the first aspect. In this means, the control unit has an operation of driving the power assist motor based on the vehicle speed signal from the vehicle speed sensor and the steering torque signal from the torque sensor. In order to exhibit this effect, the control unit includes a steering angular velocity estimating unit, a steering wheel return determining unit, and a return control unit.

The steering angular velocity estimating means estimates a motor rotational angular velocity based on a motor terminal voltage applied to the power assist motor and a motor current detection value to calculate an estimated steering angular velocity of the steering wheel. It is. The steering wheel return determining means is a logical operation means for determining whether the steering wheel is in the returning state based on the steering torque signal and the estimated steering angular velocity. Further, when the steering wheel return determining means determines that the steering wheel is in the returning state, the return control means performs numerical control means for controlling the power assist motor to perform appropriate return steering via a motor control circuit or the like. It is. By operating these calculation means in association with each other in accordance with a predetermined control logic, the control unit drives the power assist motor so as to perform proper return steering when the steering wheel is in the return state. Can be.

That is, these calculation means can be realized by minor changes such as modifying software of a microcomputer provided in a control unit such as an ECU. Therefore, in this means, it is not necessary to newly provide hardware such as a steering angle sensor, and the cost is not increased accordingly. Nevertheless, according to the electric power steering apparatus of the present means, the workload for returning the steering wheel to the neutral position can be reduced.

Therefore, according to the electric power steering apparatus of the present invention, there is an effect that the cost can be minimized while the workload for returning the steering wheel to the neutral position is reduced. In addition, the present means has an effect that it can be applied to a vehicle having no ABS without adding a new sensor.

(Second Means) A second means of the present invention is an electric power steering apparatus according to the second aspect. In this means, the steering wheel return determining means is a logical operation means for determining whether or not the steering wheel is in the returning state based on the sign of the steering torque signal and the sign of the estimated steering angular velocity. Therefore, a complicated operation such as a numerical operation is unnecessary, and the logic of the logical operation is simplified.

Therefore, according to this means, in addition to the effect of the above-described first means, the logic of the logical operation relating to the determination of the return state of the steering wheel is simplified, so that the cost increase of the control unit is also minimized. It has the effect of being done. (Third Means) A third means of the present invention is an electric power steering apparatus according to the third aspect.

In this means, when the steering torque signal is rightward and the estimated steering angular velocity is leftward, it is determined by the steering wheel return determining means that the steering wheel is returning from the right-turn position to the neutral position. You. Conversely, if the steering torque signal is leftward and the estimated steering angular velocity is rightward, it is determined that the steering wheel is returning from the left-turn position to the neutral position.

When the handle enters the return state, the handle naturally has an angular velocity in the direction to return to the neutral position. On the other hand, regarding that the steering torque signal is still generated in the direction to turn the steering wheel more,
Some people may be in doubt. However, when the inventor conducted an experiment, it was found that the steering wheel began to have an angular velocity in the direction of returning to the neutral position (that is, the steering wheel returned to the neutral position) as long as the steering operation was performed no matter how fast the steering was performed. At the moment), it was discovered that the steering torque signal was still occurring in the direction to turn the steering wheel more. While the return steering is proceeding, the sign of the steering torque signal is often inverted, and a steering torque signal is generated in a direction to return the steering wheel to the neutral position.

In that case, if only the estimated steering angular velocity corresponding to the angular velocity of the steering wheel is observed, there may be a direction in which it may be determined that the vehicle has returned to the return state, but this is not the case. That is, in order to know that the estimated steering angular velocity is generated in the direction of the neutral position, the steering angle itself must be observed. However, since the power steering apparatus of the present invention does not have the steering angle sensor, even if the estimated steering angular velocity is known, it is determined whether the vehicle is heading toward the neutral position or in the direction of increasing the steering angle. The judgment cannot be made only from the estimated steering angular velocity. However, it has been experimentally found that the direction of the steering angle can be indirectly observed by using the sign of the steering torque signal at the moment when the sign of the estimated steering angular velocity changes. Therefore, in this means, it is determined that the vehicle has entered the return state with the assistance of the steering torque signal to the estimated steering angular velocity.

Therefore, according to the present invention, similarly to the above-described second means, it is possible to judge that the return state has been entered by a simple logical operation, although the steering angle sensor is unnecessary and the configuration is inexpensive. . (Fourth Means) A fourth means of the present invention is the electric power steering apparatus according to the fourth aspect.

In this means, it is determined in the third means that the return state is entered only when a predetermined combination of the sign of the steering torque and the sign of the estimated steering angular velocity has continued for a predetermined time. In actual operation with a vehicle such as an automobile, disturbances such as vibrations and hand tremors enter, so even though the driver has no intention to return the steering wheel, the steering torque can be reduced for a very short time. The sign and the sign of the estimated steering angular velocity may be combined when entering the return state. In such a case, if the control returns to the steering wheel, the steering feeling becomes uncomfortable, which is inconvenient. Therefore, if it is determined that the return state has been entered only when a predetermined combination of the sign of the steering torque and the sign of the estimated steering angular velocity has continued for a predetermined time as in the present means, such an erroneous state is obtained. Inconvenience due to the determination is avoided.

Therefore, according to this means, in addition to the effect of the third means described above, the number of erroneous determinations in the determination that the steering operation has returned to the return state is reduced, and the determination can be made more reliably. This has the effect of improving the steering feeling. (Fifth Means) A fifth means of the present invention is the electric power steering apparatus according to the fifth aspect.

In this means, when the steering wheel return determining means determines that the steering wheel is in the return state from the right-turn position, the steering angular velocity becomes zero or rightward when the estimated steering angular velocity becomes zero or rightward. It is determined that the player has escaped from the return state. Conversely, if it is determined that the steering wheel is in the return state from the left-turn position, it is determined that the vehicle has escaped from the return state from the left-turn position when the estimated steering angular velocity becomes zero or leftward.

That is, if the return direction is clear during the steering wheel return control, it is determined that the steering wheel return control has ended when the estimated steering angular velocity becomes zero or the sign is inverted. Most simply, when the estimated steering angular velocity becomes zero or the sign is inverted during the steering wheel return control, it is determined that the steering wheel return control has been completed.

Therefore, according to this means, in addition to the effect of the first means described above, the logic for judging the escape from the return state becomes extremely simple, and the operation means such as a microcomputer can be made more inexpensive. This has the effect. (Supplementary Note) As shown in Example 1 below, the combination of the fourth means and the fifth means is the best mode of the embodiment of the present invention.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the electric power steering apparatus according to the present invention will be clearly and sufficiently described in the following embodiments so that those skilled in the art can understand the present invention. Embodiment 1 (Configuration of Embodiment 1) An electric power steering apparatus according to Embodiment 1 of the present invention is a steering apparatus for an electric vehicle, and as shown in FIG. , A control unit 10 and a power assist motor 3.

The vehicle speed sensor 1 is a sensor for generating a vehicle speed signal v for a speedometer, and is already provided as standard equipment in a vehicle. On the other hand, the torque sensor 2 is a sensor that detects a steering torque applied to a steering column and generates a steering torque signal Ts, and is already standard equipment in a power steering device that performs power assist. In the electric power steering apparatus of this embodiment, only these two types of sensors are employed as sensors for detecting the state of the vehicle, and a steering angle sensor such as a potentiometer for detecting a steering angle of a steered wheel is not required. Also,
Since there is no need to detect the difference in rotational speed between the left and right wheels,
This embodiment can be applied to a vehicle not equipped with an ABS without adding a new sensor.

The power assist motor 3 is a DC motor that is driven while being appropriately controlled by the control unit 10 and reinforces the steering torque applied to the steering wheel by the driver to increase the steering force for giving a steering angle to the steered wheels. On the other hand, the control unit 10 is an ECU that appropriately drives the power assist motor 3 based on the vehicle speed signal v and the steering torque signal Ts.

That is, the control unit 10 comprises a vehicle speed calculator 11, a current command value calculator 12 and a motor control circuit 1.
3, motor drive circuit 14, motor current detection circuit 15, motor terminal voltage detection circuit 16, steering angular velocity estimation means 1
7, handle return determination means 18, return correction amount calculation means 1
9 and an adder 20. Among these components, a vehicle speed calculator 11, a current command value calculator 12,
The motor control circuit 13, the motor drive circuit 14, the motor current detection circuit 15, and the motor terminal voltage detection circuit 16
Since it is basically the same as that of an ordinary electric power steering device, a detailed description is omitted.

The current command value calculating means 12, the steering angular velocity estimating means 17, the steering wheel return determining means 18, the return correction amount calculating means 19, and the adding means 20 include a control unit 1
The digital arithmetic means are respectively realized by microcomputers (not shown) built in the CPU. Here, the current command value calculating means 12, the return correction amount calculating means 19
The addition means 20 constitutes a return control means.

That is, the steering angular velocity estimating means 17 calculates the motor terminal voltage V applied to the power assist motor 3.
Numerical operation means for calculating an estimated steering angular velocity estev from the motor rotational angular velocity estimated based on m and the motor current detection value Im. On the other hand, the steering wheel return determining means 18 is a logical operation means for determining whether or not the steering wheel is in the returning state based on the steering torque signal Ts and the estimated steering angular velocity estev. further,
When the steering wheel return determining means 18 determines that the steering wheel is in the return state, the return correction amount calculating means 19 generates a return correction amount icr 'for causing the power assist motor 3 to perform appropriate return steering. Numerical calculation means.

Here, the steering wheel return determining means 18 determines the sign of the steering torque signal Ts and the estimated steering angular velocity estev.
Is a logical operation means for determining whether or not the steering wheel is in the return state based on the sign. That is, when the state where the steering torque signal Ts is rightward and the steering angular velocity estimated value estev is leftward for more than a predetermined time,
Judge that the steering wheel is in the return state from the right turn position,
The steering torque signal Ts is directed to the left and the steering angular velocity estimated value e
If the state in which stev is directed rightward continues beyond the predetermined time, the logic operation means determines that the steering wheel is in a state of returning from the left-turn position. When it is determined that the steering wheel is in the return state from the right-turn position, when the steering angular velocity estimated value estev becomes zero or rightward, it is determined that the vehicle has escaped from the return state from the right-turn position. Is determined to be in the return state from the left-turn position, the steering angular velocity estimated value estev
Is a logical operation means for judging that it has escaped from the return state from the left-turning position when becomes zero or leftward.

The input and output of various signals in the electric power steering apparatus of this embodiment are as shown in FIG.
Characteristic part of the present embodiment (particularly, handle return determination means 1
The operation of 8) will be described in detail later in a later section. (Outline of operation of the first embodiment) Since the electric power steering apparatus of the present embodiment is configured as described above, the following operation and effect are exhibited. For readers, Figure 1
Please read while referring to.

The steering angular velocity estimating means 17 calculates an estimated steering angular velocity e based on the motor terminal voltage Vm applied to the power assist motor 3 and the detected motor current Im.
A numerical operation for estimating stev is performed. Here, the motor terminal voltage Vm is detected by a motor terminal voltage detecting circuit 16 attached to the motor driving circuit 14, and is input to the steering angular velocity estimating means 17 via an A / D converter (not shown). . On the other hand, the motor current detection value Im is measured by the motor current detection circuit 15 forming a minor feedback loop together with the motor control circuit 13 and the like.
It is also input to the steering angular velocity estimating means 17 via an A / D converter (not shown). Also, the estimated steering angular velocity est
ev is an estimated value of the rotation angle of the steering wheel, not an estimated value of the steering angular velocity of the steered wheels.

That is, the estimated steering angular velocity estev
Is calculated by the steering angular velocity estimating means 17 according to the following equation 1.

[0030]

Estev = ｛(Vm−Im · Rm) / K
t｝ · (360 / Nmr) Here, as described above, Vm is a motor terminal voltage, and Im is a motor current detection value. Rm is a motor winding resistance, Kt is an induced voltage constant, and Nmr is a reduction ratio from the power assist motor 3 to the steering column. The estimated steering angular velocity estev calculated by the steering angular velocity estimating means 17 is transmitted to the steering wheel return determining means 18. A steering torque signal Ts from the aforementioned torque sensor 2 is also input to the steering wheel return determination means 18.

The steering wheel return determining means 18 performs a logical operation to determine whether the steering wheel is in the returning state based on the steering torque signal Ts and the estimated steering angular velocity estev. The result of this determination by the steering wheel return determination means 18 is supplied to the return correction amount calculation means 19 in parallel with the vehicle speed signal v measured by the vehicle speed calculator 11. In addition,
The determination logic, which is an operation of the steering wheel return determination means 18, will be described later in detail in a different section.

Finally, when the steering wheel return determining means 18 determines that the steering wheel is in the returning state as described above, the return correction amount calculating means 19 performs a numerical calculation to make the power assist motor 3 appropriate. A return correction amount icr ′ for performing return steering is generated. This numerical calculation is performed in accordance with a predetermined calculation logic based on the vehicle speed signal v measured by the vehicle speed calculator 11 when the steering wheel return determining means 18 determines that the steering wheel has returned to the neutral position. A return correction amount is generated.
The determination logic of the logical operation performed by the return correction amount calculating means 19 will be described in detail in the next section.

The return correction amount icr 'is generated by the return correction amount calculating means 19 in this manner, and is added to the current command value ic output from the current command value calculating means 12 by the adding means 20.
The current command value ic + ic that has been added and corrected back.
r ′ is generated. Then, the current command value ic + icr ′ after the return correction is provided to the motor control circuit 13 and regulates the output of the power assist motor 3.

(Judgment Logic of Embodiment 1) In this section, of the above-mentioned actions, the action of the steering wheel return judgment means 18 will be described more specifically with reference to the flowchart of FIG. As shown in FIG.
When the judgment logic 8 is started, first, in processing step S1, the process waits until 20 milliseconds have passed since the previous judgment logic started. That is, this determination logic is executed every 20 milliseconds.

When the determination logic starts at a predetermined time interval, in a processing step S2, the double return determination timer starts counting up. That is, a timer for counting the time during which the steering wheel is returning from the right-turn position to the neutral position (return-from-right determination timer),
Increment is performed with a timer for counting the time during which the steering wheel is returning from the left-turn position to the neutral position (return-from-left determination timer).

Next, in a judgment step S3, it is judged whether or not the result of the previous judgment by the steering wheel return judgment means 18 is under normal control, that is, whether or not the return control is under control. As a result, the previous steering wheel return determination means 18
If it is determined in step S4 that normal control is being performed and return control is not being performed, it is determined in steps S4 to S7 and steps S14 to S17 whether or not the current steering operation is being returned. Enter a routine to

That is, in the judgment step S4, if the steering torque signal Ts is positive (to the right) and the estimated steering angular velocity estev is negative (to the left), the steering wheel is returning from the right. The process proceeds to the next determination step S5 as there is a possibility of the presence. Here, some readers may be concerned that the steering torque signal Ts may become negative (leftward) when the return operation from the right is performed by the rapid steering. However, when the inventor confirmed through experiments, it was confirmed that the steering torque signal Ts was always positive (to the right) even in a short time in the initial stage of the return operation from the right. The criterion of S4 is reliable. Note that this is the same as the determination of the return operation from the left, except that the left and right are reversed, so that the determination criterion in the determination step S14 described below is also reliable.

In the determination step S5, it is determined whether or not the returning determination timer counting from the right counted up in the above-described processing step S2 has exceeded a predetermined threshold value tmmh. When it is determined in this determination that the return determination timer from the right has exceeded the threshold value tmmh, return control is started in the next processing step S6, and a return control flag is set. Conversely, if it is not determined that the returning determination timer from the right has exceeded the threshold value tmmh,
It is considered that the return state has not yet been definitely entered, and the determination is kept under the normal control. By determining whether or not the returning determination timer has exceeded the threshold value tmmh as in the processing step S6, an erroneous determination that the return control is started due to noise such as minute vibration is prevented. Such an erroneous determination prevention action is similarly effective in a determination step S15 described later in which the left and right are reversed from the determination step S5.

Conversely, if it is determined in the determination step S4 that there is no possibility that the vehicle is returning from the right, the determination logic performs the determination step S1 in parallel with the determination step S.
Proceeding to 4, it is determined whether the steering wheel is returning from the left. That is, in the determination step S14, the steering torque signal Ts is negative (leftward), and
If the estimated steering angular velocity estev is positive (to the right), it is determined that the steering wheel may be returning from the left, and the process proceeds to the next determination step S15. In the determination step S15, the returning determination timer counting from the left counted up in the processing step S2 is determined by the predetermined threshold value tmm.
h is determined. If it is determined in this determination that the returning determination timer from the left has exceeded the threshold value tmmh, return control is started in the next processing step S16, and a return control flag is set. Conversely, if it is not determined that the return determination timer from the left has exceeded the threshold value tmmh, it is considered that the return state has not yet been reliably entered, and the determination is maintained under normal control. .

If it is determined that the steering wheel is not in the returning state in both the determination step S4 and the determination step S14, the normal control is continued and the determination logic proceeds to the processing step S27. Then, in processing step S27, both the return determination timer from the right and the return determination timer from the left are reset to zero, and the determination logic maintains the determination that the steering wheel is not returned and the normal control is continued.

On the other hand, in the above-mentioned determination step S3, when it is determined that the previous determination by the steering wheel return determination means 18 is not under normal control but under return control, the determination logic is to the right in the figure. The process proceeds to step S31. Then, steps S31 to S34 and steps S42 to S
At 44, a routine is entered to determine whether the current steering operation is maintained during return.

That is, when it is determined in the determination step S31 that the vehicle is returning from the right, the processing step S3
In step 2, both the return determination timer from the right and the return determination timer from the left are reset to zero. The processing in the processing step S32 is intended to prevent the erroneous determination from occurring in the aforementioned determination steps S5 and S15 after the two timers continue to count up. Then, in the judgment step S33, it is judged whether or not the estimated steering angular velocity estev is equal to or larger than zero, that is, whether or not the steering wheel has stopped or has started reverse rotation. If an affirmative determination is made in this determination step S33, it is determined that the return control has been completed in processing step S34, and the return control flag is lowered. Conversely, if a negative determination is made in determination step S33, it is considered that the return control has not been completed and is continued.
The return control flag is left standing.

Conversely, if it is not determined in step S31 that the vehicle is returning from the right, it means that it has already been determined in the aforementioned step S3 that the vehicle is in the return control state. It is under control.
In this case as well, as in the case of the above-described return control from the right, in the processing step S42, both the return determination timer from the right and the return determination timer from the left are reset to zero. (Since the processing of the processing step S42 is the same as the processing of the above-described processing step S32, both the processing steps S may be combined and brought immediately before the determination step S31.) Then, in the determination step S43. It is determined whether the estimated steering angular velocity estev is equal to or less than zero, that is, whether the steering wheel has stopped or has started to reverse.

If a positive determination is made in this determination step S43, it is determined that the return control has been completed in processing step S44, and the return control flag is lowered. vice versa,
If a negative determination is made in determination step S43,
It is considered that the return control has not been completed and is continued, and the return control flag is left standing.
(Since the same processing is performed in the processing steps S34 and S44, the two determination steps S32 and
It may be placed immediately after S42. Since the determination as to whether or not the steering wheel is under return control has been completed, the determination logic proceeds to one of the processing steps S9 and S10 after the determination step S8. That is, if it is determined in the determination step S8 that the return control is currently being performed, the determination logic proceeds to the processing step S9, and the return correction amount icr 'is calculated by the return correction amount calculating means 19 described later. Conversely, if it is determined in the determination step S8 that the return control is not being performed at the present time but the normal control is being performed, the return correction without the time delay corresponding to the calculation result of the expression 2 by the return correction amount calculating means 19 described later. The quantity icr is forced to zero.
The completion of one of the processing steps S9 and S10 causes the determination logic of the handle return determination means 18 to complete one cycle.

To summarize the above-described steering wheel return determination logic, the steering wheel return determination means 18 generates the torque signal Ts
And the sign of the estimated steering angular velocity estev, it is determined as follows whether or not the steering wheel is in the return state. That is, when the state where the steering torque signal Ts is rightward and the steering angular velocity estimated value estev is leftward continues for more than the predetermined time tmmh, it is determined that the steering wheel is in the return state from the right-turn position. If it is determined that the steering wheel is in the return state from the right-turn position, it is determined that the steering wheel has escaped from the return state from the right-turn position when the estimated steering angular velocity estev becomes zero or rightward. You. Therefore, even if the sign of the steering torque signal Ts reverses and turns left during the return control from the right, the return control from the right is maintained unless the estimated steering angular velocity estev becomes zero or right. .

Conversely, if the state where the steering torque signal Ts is leftward and the estimated steering angular velocity estev is rightward continues for more than a predetermined time tmmh, it is determined that the steering wheel has returned from the left-turn position. Is done. When it is determined that the steering wheel is in the return state from the left-turn position, it is determined that the steering wheel has escaped from the return state from the left-turn position when the estimated steering angular velocity estev becomes zero or leftward. You. Therefore, even if the sign of the steering torque signal Ts is reversed and turned rightward during the return control from the left, the return control from the left is maintained unless the estimated steering angular velocity estev becomes zero or left. .

(Return Correction Amount of First Embodiment) After the steering wheel return determining means 18 determines whether or not the steering wheel is in the returning state, if the steering wheel is in the returning state,
An appropriate return correction amount ic by the return correction amount calculating means 19
r ′ is calculated. Here, the return correction amount calculating means 19
Adds the return correction amount icr 'to the current command value ic as calculated by the current command value calculating means 12 based on the following Expression 3 and Expression 4 described later. That is, first, the return correction amount icr without time delay is calculated by the following equation (2).

[0048]

Icr = ir (estev) · K3 (v) Here, icr is a correction amount with no time delay to the motor current command value by the steering wheel return control. Also, ir
Is an intermediate variable of the return correction amount determined by the function shown in FIG. 3 from the estimated steering angular velocity estev, and K3 is a vehicle speed coefficient of the return correction amount determined by the function shown in FIG.

As shown in FIG. 3, the intermediate value ir [A] of the return correction amount is the largest when the absolute value of the estimated steering angular velocity estev is in the range of 30 to 120 [deg / s].
The absolute value of the estimated steering angular velocity estev is 10
A dead zone is formed in the range of [deg / s] or less. This is because it is better not to actively assist and return the steering wheel to the neutral position in such a small range of the estimated steering angular velocity estev. In other words, when the return steering is performed slowly, it is better that the driver adjusts the return angular velocity as needed to obtain a superior steering feeling. The intermediate variable ir [A] of the return correction amount is set to decrease when the absolute value of the estimated steering angular velocity estev exceeds 120 [deg / s]. This is because, when the absolute value of the estimated steering angular velocity estev is already large during the return steering, the steering angular velocity is assisted to prevent the return angular velocity from becoming excessive.

On the other hand, as shown in FIG. 4, the vehicle speed coefficient K3 (dimensionless number) of the return correction amount is 0 to 20 [k
m / h], a high value is maintained, but 20 to 60
It decreases within the range of [km / h], and is zero at 60 [km / h] or more. This is because the self-aligning action of the steered wheels increases as the running speed of the vehicle increases, so that there is no need to assist in returning steering. That is, at low speeds of 20 km / h or less, the self-aligning effect is small, so the necessity of power assist for return steering is high, and the need for power assist for return steering diminishes as the running speed of the vehicle increases. It is.

When the correction amount icr without time delay is calculated by the above equation (2) in the return correction amount calculating means 19, it is passed through a digital low-pass filter shown in the following equation (3) to return the correction amount icr. Make sure there is no sudden change in icr '.

[0052]

(3) icr ′ (n) = ｎicr (n) + (β−
1) · icr ′ (n−1)｝ / β Here, the return correction amount icr ′ is calculated by
2 is a correction amount for the return control added by the adding means 20 to the current command value ic calculated by 2. on the other hand,
β is a constant larger than 1 which defines the time constant of the digital low-pass filter in relation to the operation cycle of Expression 3.

The digital low-pass filter defined by the above equation (3) prevents the return correction amount icr 'from suddenly changing. Such discontinuity of the steering torque is prevented. Then, as shown in FIG. 1 again, the return correction amount icr ′ calculated by the return correction amount calculating means 19 is transmitted to the adding means 20, and the adding means 20 outputs the current command value icr ′ which is the output of the current command value calculating means 12. The value is added to the value ic and transmitted to the motor control circuit 13.

As a result, an appropriate current command value is given to the motor control circuit 13 even at the time of the return operation, and the return steering of the steering wheel is smoothly performed. That is, the digital low-pass filter defined by Equation 3 prevents the sudden change in the return correction amount icr '. Discontinuity of the steering torque is prevented. Therefore, even at the moment of entering the return control or at the moment of exiting the return control, discontinuous sudden change of the steering feeling is avoided and a continuous steering feeling can be obtained,
The steering feeling in the returning operation of the steering wheel is improved.

(Effect of Embodiment 1) As described above in detail,
Each arithmetic unit operates in a microcomputer built in the control unit 10, and the control unit 10 can drive the power assist motor 3 so as to perform appropriate return steering when the steering wheel is in the return state. .

That is, the electric power steering apparatus of the present embodiment can be realized by minor changes such as modifying software of a microcomputer provided in a control unit (ECU) 10 already provided in the electric vehicle. . Therefore, in this embodiment,
By using the vehicle speed sensor 1 that is provided as a standard feature in an automobile, it is not necessary to newly provide hardware such as a steering angle sensor, and the cost is not increased accordingly. Further, since it is not necessary to measure the speed difference between the left and right wheels, the present embodiment can be applied to a vehicle not equipped with an ABS without adding a new sensor. However, according to the present embodiment, not only the driver's workload for returning the steering wheel to the neutral position can be reduced, but also, particularly in a speed range from a very low vehicle speed to a middle vehicle speed, the feeling of returning steering of the steering wheel can be reduced. Can be improved.

Therefore, according to the electric power steering apparatus of the present embodiment, the steering feeling for returning the steering wheel to the neutral position is improved, and the work load on the driver is reduced, while minimizing the cost increase. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an electric power steering device according to a first embodiment.

FIG. 2 is a flowchart illustrating a steering wheel return determination logic according to the first embodiment.

FIG. 3 is a graph for determining an intermediate variable of a return correction amount in the first embodiment.

FIG. 4 is a graph for determining a vehicle speed coefficient from a vehicle speed signal in the first embodiment.

[Explanation of symbols]

1: Wheel speed sensor (pair of left and right) 2: Torque sensor (equipped on steering column) 3: Power assist motor (DC motor) 10: Control unit (ECU) 11: Vehicle speed calculator 12: Current command value calculation means 13: Motor Motor control circuit 14: Motor drive circuit 15: Motor current detection circuit 16: Motor terminal voltage detection circuit 17: Steering angular velocity estimating means 18: Steering wheel return determining means 19: Return correction amount calculating means 20: Addition means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B62D 119: 00

Claims (5)

[Claims] 1. A vehicle speed sensor for detecting a speed of a vehicle to generate a vehicle speed signal, a torque sensor for detecting a steering torque applied to a steering column to generate a steering torque signal, and a steering force based on the steering torque signal. And a control unit that drives the power assist motor based on the vehicle speed signal and the steering torque signal. The control unit is added to the power assist motor. Steering angular velocity estimating means for calculating a steering angular velocity estimation value based on the motor terminal voltage and the motor current detection value, and determining whether or not the steering wheel is in a return state based on the steering torque signal and the steering angular velocity estimation value. Handle return determination means for determining, and the steering wheel return determination means An electric power steering device, comprising: return control means for causing the power assist motor to perform appropriate return steering when it is determined that the vehicle is in the return state. 2. The steering wheel return determining means is a logical operation means for determining whether or not the steering wheel is in a return state based on a sign of the steering torque signal and a sign of the estimated steering angular velocity. Item 2. The electric power steering device according to Item 1. 3. The steering wheel return determining means determines that the steering wheel is in a return state from a right-turn position to a neutral position when the steering torque signal is rightward and the steering angular velocity estimated value is leftward. If the steering torque signal is leftward and the estimated steering angular velocity is rightward, the logic operation means determines that the steering wheel is returning from the left-turn position to the neutral position. An electric power steering device as described in the above. 4. The steering wheel returning determination means, when the steering torque signal is rightward and the steering angular velocity estimated value is leftward for more than a predetermined time, the steering wheel is returned from a right-turn position. When it is determined that the steering wheel is in the return state, and the state in which the steering torque signal is leftward and the steering angular velocity estimated value is rightward continues beyond the predetermined time, the steering wheel returns to the left turn position. 4. The electric power steering device according to claim 3, wherein the electric power steering device is a logic operation unit that determines that there is a power steering device. 5. The steering wheel return determination means, when the steering wheel is determined to be in the return state from the right-turn position, when the estimated steering angular velocity becomes zero or rightward, the right-turn position is determined. It is determined that the steering wheel has escaped from the return state, and if it is determined that the steering wheel is in the return state from the left-turn position, the left-turn position is obtained when the estimated steering angular velocity becomes zero or leftward. The electric power steering device according to claim 1, wherein the electric power steering device is a logic operation unit that determines that the vehicle has escaped from the return state from the vehicle.