JPH06305438A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To prevent a wrong judgment made on the lock of a motor caused by disturbance from the road surface and detect the actual lock of the motor positively. CONSTITUTION:A motor-driven power steering has a motor M1 for generating steering assist force, a steering torque detecting device M2 for detecting steering torque, and a control device M3 for controlling the motor M1 according to at least the steering torque. A steering angle variation detecting device M4 detects the variation of a steering angle, and a steering torque variation detecting device M5 detects the variation of the steering torque. A lock judging device M6 then judges whether the variation of the steering torque to the variation of the steering angle is out of a specified range and judges the motor to be locked when the relation of two variations is out of the specified range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for vehicles such as automobiles, and more particularly to an electric power steering device.

[0002]

2. Description of the Related Art An electric power steering apparatus for a vehicle such as an automobile has heretofore generally been a motor for driving a steering linkage member such as a rack bar via a clutch and a steering gear box, and a controller for controlling the rotation of the motor. The control device is configured to generate a required steering assist force by controlling the motor based on the detection results of various sensors.

As one of such electric power steering devices, for example, as described in Japanese Patent Laid-Open No. 4-163280, a differential value of steering torque detected by a torque sensor attached to a steering shaft is calculated, 2. Description of the Related Art There has been known an electric power steering apparatus configured so that when a differential value of a steering torque exceeds a reference value, it is determined that a motor is locked, power supply to the motor is stopped, and a clutch is released. According to the thus configured electric power steering device, when an abnormality such as a lock in which the motor cannot be rotated occurs, the power assist can be reliably stopped by coping with the abnormality.

[0004]

However, in the conventional electric power steering apparatus as described above, when a sudden disturbance is input to the power steering apparatus from the road surface due to kickback or the like, the power from the motor is not used. Assistance may not be in time and the steering torque may change abruptly to cause the differential value to exceed the reference value.Therefore, it is possible to determine that the motor has locked even though the motor is not actually locked. There is a problem of being done.

Further, if the reference value for judging the magnitude of the steering torque is set high in order to solve such a problem, the differential value of the steering torque immediately becomes the reference value even if the motor is locked depending on the degree of lock of the motor. Since it does not exceed the limit, the judgment that the motor is locked is not made even though the motor is actually locked, and the power steering device cannot be promptly functioned as the manual steering device. A new problem arises in that steering must be performed against the excessive frictional force caused by slippage in the clutch.

In view of the above problems in the conventional electric power steering apparatus as described above, the present invention does not cause erroneous determination of motor lock due to disturbance from the road surface, and actually It is an object of the present invention to provide an improved electric power steering device that can reliably detect a motor lock when the motor is locked and immediately cause the power steering device to function as a manual steering device.

[0007]

According to the present invention, as described above, the above object is to provide a motor M1 for generating a steering assist force, a steering torque detecting means M2, and a steering torque detecting means M2.
An electric power steering apparatus having a control means M3 for controlling the steering assist force by controlling the motor according to at least the steering torque, and a steering angle change amount detection means M4 for detecting the change amount of the steering angle and a steering angle change amount detection means M4. A steering torque change amount detecting means M5 for detecting a change amount of the steering torque,
The present invention is achieved by an electric power steering apparatus characterized by further comprising lock determining means M6 for determining that the motor is locked when the relationship between the amount of change in steering angle and the amount of change in steering torque is outside a predetermined range. .

[0008]

When the motor for auxiliary steering is normal, the steering torque changes in response to changes in the steering angle, and a sudden disturbance is input from the road surface to the power steering device due to kickback and the steering torque changes rapidly. When the value changes to, the steering angle also changes abruptly correspondingly, so the relationship between the amount of change in the steering angle and the amount of change in the steering torque is within a predetermined range. On the other hand, when the motor locks, the steering torque becomes extremely high because the motor cannot rotate at all even if the steering wheel (steering wheel) is steered by the driver of the vehicle. The relationship of the change amount of is outside the predetermined range. Therefore, it is possible to determine whether or not the motor is locked by determining whether or not the relationship between the amount of change in steering angle and the amount of change in steering torque is outside a predetermined range.

According to the above-mentioned configuration of the present invention, the steering angle change amount detecting means M4 detects the steering angle change amount, and the steering torque change amount detecting means M5 detects the steering torque change amount, and the steering angle change amount is detected. When the relationship between the change amount of the steering torque and the change amount is outside the predetermined range, the lock determination means M6
Since it is determined that the motor is locked, it is possible to reliably detect the motor lock while preventing the erroneous determination of the motor lock due to the disturbance from the road surface. In this case, the power steering device can be quickly switched to the manual steering device.

[0010]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic configuration diagram showing one embodiment of the electric power steering apparatus according to the present invention, and FIG. 3 is FIG.
3 is a block diagram showing an electronic control device shown in FIG.

In FIG. 2, reference numeral 10 denotes a steering wheel. The steering wheel 10 drives a rack bar 16 via a steering shaft 12 and a steering gear box 14. A power unit 20 is drivingly connected to the steering shaft 12 by a gear reduction mechanism 18. The power unit 20 has a motor 22 and an electromagnetic clutch 24 for selectively drivingly connecting the gear reduction mechanism 18 and the motor 22.

In the illustrated embodiment, the steering shaft 12 is provided with a steering angle sensor 26 for detecting the steering angle θ and a torque sensor 28 for detecting the steering torque T, and the outputs of these sensors are electronic. It is supplied to the control device 32. A signal indicating the vehicle speed V detected by the vehicle speed sensor 34 is also input to the electronic control unit 32.

As shown in detail in FIG. 3, the electronic controller 32 includes a microcomputer 38, which is a central processing unit (CPU) 40.
, Read only memory (ROM) 42, random access memory (RAM) 44, and input port device 46
And an output port device 48, which are connected to each other by a bidirectional common bus 50.

The input port device 46 includes a steering angle sensor 26.
A signal indicating the steering angle θ detected by the torque sensor 2
A signal indicating the steering torque T detected by 8 and a signal indicating the vehicle speed V detected by the vehicle speed sensor 34 are input. The input port device 46 appropriately processes the signal input thereto, and in accordance with the instruction of the CPU 40 based on the control program stored in the ROM 42, the CPU
And the processed signal is output to the RAM 44.

The ROM 42 stores the control program shown in FIG. 4 and maps corresponding to the graphs shown in FIGS. 5 and 6. The CPU 40 is adapted to perform various calculations and signal processing as will be described later based on the control program shown in FIG. The output port device 48 outputs a control signal to the motor 22 via the drive circuit 52 according to an instruction from the CPU 40, and outputs a control signal to the electromagnetic clutch 24 via the drive circuit 54 to further determine that the motor is locked. The alarm lamp 56 is turned on when it goes off.

The operation of the illustrated embodiment will now be described with reference to the flow chart shown in FIG. The control by the electronic control unit 32 is started by closing an ignition switch not shown in FIG. Further, in the flowchart shown in FIG. 4, N indicates the number of times that the motor is locked.

First, in step 10, the control signal is output to the electromagnetic clutch 24 via the drive circuit 54 so that the clutch is engaged, and in step 20, the steering angle θ detected by the steering angle sensor 26 is changed. A signal indicating the steering torque T detected by the torque sensor 28,
A signal indicating the vehicle speed V detected by the vehicle speed sensor 34 is read.

In step 30, the basic assist amount Tab is calculated from the map corresponding to the graph shown in FIG. 5 based on the steering torque T read in step 20,
In step 40, the vehicle speed coefficient Kv is calculated from the map corresponding to the graph shown in FIG. 6 based on the vehicle speed V read in step 20, and in step 50 it is calculated in step 30. The assist amount Ta is calculated as the product of the basic assist amount Tab and the vehicle speed coefficient Kv calculated in step 40.

In step 60, it is judged whether or not the absolute value of the steering angle θ is greater than or equal to a reference value θe (a positive constant for judging the steering wheel end), and | θ | ≧ θe. When it is determined that the steering is substantially in the steering wheel end state, the process proceeds to step 110, and it is determined that | θ | ≧ θe is not satisfied, that is, the steering is substantially in the steering wheel end state. If it is determined that there is not, the process proceeds to step 70.

In step 70, the vehicle speed V is the reference value Vo.
Whether or not (a positive constant for determining a stopped state or a running state at an extremely low vehicle speed) or less is determined, and V ≦ V
When it is determined that o, that is, the vehicle is in the stopped state or the traveling state at an extremely low vehicle speed, the process proceeds to step 110, and it is determined that V ≦ Vo is not satisfied, that is, the vehicle is at a low vehicle speed. When it is determined that the vehicle is traveling at the above speed, the process proceeds to step 80.

At step 80, θn and T respectively.
Let n be the steering angle and steering torque in the current cycle, and θ
A steering angle change amount Δθ and a steering torque change amount ΔT are calculated according to the following equations 1 and 2 using nk and Tn-k as steering angles and steering torques before k cycles.

[0023]

[Formula 1] Δθ = θn−θn-k

(2) ΔT = Tn-Tn-k

In step 90, the steering angle change amount Δθ
It is determined whether the absolute value of is less than or equal to θo (small positive constant), and it is determined that Δθ ≦ θo, that is, the steering is not substantially performed. When it is determined that Δθ ≦ θo is not satisfied, that is, when it is determined that steering is being performed, the process proceeds to step 110.

In step 100, the amount of change in steering angle Δ
Whether or not the ratio ΔT / Δθ of the steering torque change amount ΔT to θ is calculated, and whether the absolute value of the ratio ΔT / Δθ is greater than or equal to a reference value K (a positive constant for determining motor lock). If it is determined that | ΔT / Δθ | ≧ K, that is, if the motor is not locked, the motor lock determination count N is reset to 0 in step 110. , | ΔT / Δθ | ≧ K, that is, when it is determined that the motor is locked, the number N is incremented by 1 in step 120.

The reference values .theta.e, Vo, .theta.o for the judgments made at the above-mentioned steps 60, 70 and 90, 100,
The K may be obtained, for example, experimentally so that the corresponding determination can be properly performed.

In step 130, it is judged whether or not the number of times N is 3, and when it is judged that N = 3 is not satisfied, in step 140, a control signal corresponding to the assist amount Ta is obtained. Is output to the motor 22 via the drive circuit 52, the steering assist force is controlled to a value corresponding to the assist amount Ta, and then the process returns to step 20 and N = 3.
If it is discriminated that it is, the routine proceeds to step 150.

At step 150, the energization of the motor 22 is stopped and the output of the control signal to the electromagnetic clutch 24 is stopped, so that the clutch is released.
In step 160, the alarm lamp is turned on by outputting a control signal to the alarm lamp 56, and thus the alarm indicating that the motor is locked is issued to the driver of the vehicle.

Thus, according to the illustrated embodiment, in step 30, the basic assist amount Tab is calculated from the map corresponding to the graph shown in FIG. 5, and in step 40 the vehicle speed coefficient Kv is shown in FIG. The assist amount Ta is calculated as a product of the basic assist amount Tab and the vehicle speed coefficient Kv in step 50.

If the motor is steered in a state where it is not locked and is operating normally, it is determined at step 60 and 70 that the steering wheel is not at the end of steering or stationary steering, that is, no is determined. In this case, the ratio of the steering torque change amount ΔT to the steering angle change amount Δθ is a value within the shaded area in FIG. 7, and the absolute value of the change amount ratio ΔT / Δθ is the reference value K.
Therefore, a negative determination is made in step 90, and a negative determination is always made in step 100, so that a control signal corresponding to the assist amount Ta is output to the motor 22 in step 140. As a result, the steering assist force is controlled so as to correspond to the steering torque and become lower as the vehicle speed increases, ensuring light steering in the low vehicle speed range and good steering stability in the high vehicle speed range. Reserved.

On the other hand, when the motor is locked, the motor cannot rotate at all even when the steering wheel 10 is steered, and the ratio of the steering torque change amount Δθ to the steering angle change amount Δθ is the diagonal line in FIG. A value other than the region, for example, a value indicated by *, and the absolute value of the change ratio ΔT / Δθ is equal to or greater than the reference value K, so that the determination in step 100 is YES. When this determination, that is, the determination that the motor is locked is performed three times in succession, a yes determination is made in step 130, and the energization of the motor 22 is stopped in step 150 and the clutch 2
When the output of the control signal to 4 is stopped, the clutch is disengaged, whereby the power steering device is switched to the manual steering device, and further, in step 160, the alarm lamp 56 is turned on to notify the driver of the vehicle. A warning is given that the motor has locked.

Further, according to the illustrated embodiment, when a sudden disturbance is input from the road surface to the power steering device due to kickback or the like in a situation where the motor is not locked and is operating normally, the steering torque is changed. The amount of change Δθ changes abruptly due to a sudden change in T, but in that case, the steering angle θ also changes abruptly due to the steering wheel 10 being steered by disturbance, and the amount of change Δ in the steering angle changes.
Since θ also changes rapidly, the absolute value of the change amount ratio ΔT / Δθ does not exceed the reference value K. Therefore, it is determined that the motor is locked even though the motor is not locked. Nothing.

Further, according to the illustrated embodiment, steps 150 and 160 are not executed unless the determination that the motor is locked is performed three times in succession, so it is erroneously determined that the motor is locked. Based on the determination result, step 150 is executed although the motor is not actually locked.
And 160 are executed, that is, the alarm lamp 5
It is reliably prevented that 6 is turned on and the power steering device is switched to the manual steering device.

Further, according to the illustrated embodiment, the ratio of the steering torque change amount ΔT to the steering angle change amount Δθ is shown in FIG. 7 even when the motor is operating normally without being locked. When the steering wheel end or the stationary steering becomes a value other than the shaded area, the determination in step 60 and 70 is NO, so step 100 is not executed, so the motor is locked even though the motor is normal. It is reliably prevented from being erroneously determined to be doing.

In the illustrated embodiment, the torque sensor 2
Since it is not determined whether or not 8 is normal, if an abnormality such as a disconnection or a short circuit occurs in the torque sensor, a YES determination is made in step 100, which determines whether or not the motor has locked. However, the power steering device is switched to the manual steering device. However, if an abnormality such as a wire break or short circuit occurs in the torque sensor, the assist amount Ta becomes an inappropriate value. Therefore, it is preferable not to continue the power assist control even in this case. Therefore, according to the illustrated embodiment, the torque sensor is not used. Even if an abnormality occurs, it is possible to reliably prevent inappropriate power assist.

Although the present invention has been described above in detail with reference to specific embodiments, the present invention is not limited to such embodiments, and other various embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art that it is possible.

For example, in the above-mentioned embodiment, it is determined in step 100 whether the motor is locked or not by the steering angle θ.
Ratio of change amount of steering torque T to change amount of ΔT / Δθ
The determination is made by whether or not the absolute value of is greater than or equal to the reference value K, but the determination as to whether or not the motor is locked may be made by the determination of Equation 3 below.
The determination may be performed by the following Expression 4 using a and A as positive constants.

[0038]

[Formula 3] ΔT ≧ K · Δθ ΔT ≦ K · Δθ

[Formula 4] ΔT ≧ Ka · Δθ + A ΔT ≦ Ka · Δθ−A

Further, in the above-described embodiment and the modified example by the equation 3 or the equation 4, the reference value K of the determination in step 100 and the coefficient Ka of the above equation 3 are constants, but the steering angle θ
Ratio of change amount of steering torque T to change amount of ΔT / Δθ
The absolute value of is generally smaller as the vehicle speed V is higher, and the steering angle θ
The reference value K and the coefficient Ka may be set as a function of the vehicle speed and the steering angle such that the reference value K and the coefficient Ka decrease as the vehicle speed increases and increase as the absolute value of the steering angle increases.

Further, the control routine shown in FIG. 4 determines whether or not the torque sensor 28 is normal before step 60, and when it is determined that the torque sensor is abnormal, proceeds to step 110. If the torque sensor is normal, the routine may be modified to proceed to step 60. In this case, the determination as to whether or not the torque sensor is normal is made by using the method described in the specification and drawings of Japanese Patent Application No. 4-276616, which is the application of the same applicant as the present applicant, and the torque sensor. It may be performed by determining whether or not the difference between the detected values is greater than or equal to a predetermined value.

[0041]

As is apparent from the above description, according to the present invention, the steering angle change amount detecting means M4 detects the steering angle change amount, and the steering torque change amount detecting means M5 detects the steering torque change amount. Is detected and the relationship between the amount of change in the steering torque and the amount of change in the steering angle is outside the predetermined range, the lock determination means M6 determines that the motor is locked. Therefore, the motor locks due to the disturbance from the road surface. It is possible to reliably detect the lock of the motor while preventing the erroneous determination of 1., and thus, when the motor is locked, the power steering device can be quickly switched to the manual steering device.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an electric power steering device according to the present invention in correspondence with the description of the claims.

FIG. 2 is a schematic configuration diagram showing one embodiment of an electric power steering device according to the present invention.

FIG. 3 is a block diagram showing the electronic control device shown in FIG. 2.

4 is a flowchart showing a control routine achieved by the electronic control device shown in FIGS. 2 and 3. FIG.

FIG. 5 is a graph showing a relationship between a steering torque T detected by a torque sensor and a basic assist amount Tab.

FIG. 6 is a graph showing a relationship between a vehicle speed V detected by a vehicle speed sensor and a vehicle speed coefficient Kv.

FIG. 7 is a graph showing the relationship between the steering torque change amount ΔT and the steering torque change amount ΔT when the motor is operating normally.

[Explanation of symbols]

 10 ... Steering wheel 12 ... Steering shaft 14 ... Steering gear box 22 ... Motor 24 ... Electromagnetic clutch 26 ... Steering angle sensor 28 ... Torque sensor 32 ... Electronic control unit 34 ... Vehicle speed sensor 56 ... Warning lamp

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Tsuboi, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor, Tomoyuki Watanabe 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation

Claims (1)

[Claims] 1. An electric power steering apparatus having a motor for generating a steering assist force, a steering torque detecting means, and a control means for controlling the steering assist force by controlling the motor according to at least the steering torque. Then, the relationship between the steering angle change amount detecting means for detecting the change amount of the steering angle, the steering torque change amount detecting means for detecting the change amount of the steering torque, and the relationship between the change amount of the steering torque and the change amount of the steering angle is predetermined. An electric power steering device, comprising: lock determining means for determining that the motor is locked when the power is out of the range.