JPH11278290A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a driver from feeling discomfort by preventing sudden changes in assisting force even if the load of a motor becomes excessive. SOLUTION: A motor 5 imparting a steering assisting force by being placed at a steering gear 1 which steers a steering wheel according to a driver's control, a torque limiter 6 interposed between the motor 5 and the steering gear 1, and a controller 10 whereby the steering assisting force imparted by the motor 5 is controlled according to a steering force are designed so that an overloaded condition is recognized at least when the torque limiter 6 has slipped, in which case the assisting force is then reduced as the motor is braked to prevent overload.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electric power steering device mounted on a vehicle or the like.

[0002]

2. Description of the Related Art In a vehicle or the like, a power steering device has conventionally been employed in order to reduce a steering force of a steering wheel operated by a driver, and there is an apparatus which assists a steering force by an electric motor. Kaisho 64-906
No. 4 is known.

[0003] This is arranged coaxially with the rack side,
The motor directly applies an assisting force (steering assist force) to the steering gear via the speed reducer. When the steering reaches a predetermined locked position of the steering during steering or the steered wheel comes into contact with a curb or the like, In order to prevent the assist force from the motor from becoming excessive, when the motor overload is detected based on the steering force or the steering speed, the drive current of the motor is reduced.

[0004]

However, in the above conventional example, when the steering force becomes excessive, the current supplied to the motor is reduced to prevent the motor from being overloaded.
Despite the steering wheel reaching the predetermined maximum steering angle (lock end), if the driver tries to exceed the maximum steering angle by further operating the steering wheel, or if the steering wheel touches a curb, etc. If the driver further operates the steering wheel even though the above steering is impossible, the current to the motor will be reduced if the steering force is excessive, and the assist force will suddenly decrease, causing the driver to feel uncomfortable. There was a problem of giving.

The present invention has been made in view of the above problems, and has as its object to prevent a sudden change in assist force and prevent a driver from feeling uncomfortable even when the motor load becomes excessive. And

[0006]

According to a first aspect of the present invention, there is provided a motor provided on a steering for steering a steered wheel in response to a driver's operation and providing a steering assist force, and a motor provided in response to the steering force of the steering. Control means for controlling the steering assist force applied by the motor, overload state determination means for determining an overload state of the motor based on predetermined conditions, and when the overload state of the motor is determined. In an electric power steering apparatus including an overload prevention unit that reduces a steering assist force of a motor, a friction fastening unit that is interposed between the motor and a steering and that can transmit a predetermined steering assist force; And a slip detecting means for detecting slip of the friction fastening means, wherein the overload state determining means determines an overload state when at least slip of the friction fastening means is detected, Serial overload preventing means reduces the steering assist force while applying braking to the motor.

In a second aspect based on the first aspect, the overload prevention means applies braking to the motor by cutting off or reducing the power supply to the motor.

In a third aspect based on the first aspect, the overload prevention means applies braking to the motor by predetermined duty control.

In a fourth aspect based on the first aspect, the overload prevention means includes means for detecting a speed of the motor, and when the speed of the motor is high, the steering assist per unit time is provided. While reducing the amount of force reduction,
When the speed of the motor is low, the amount of reduction of the steering assist force per unit time is set to be large.

[0010]

Therefore, in the first invention, the steering assist force of the motor is given to the driver's steering force during normal driving. For example, when the steering amount reaches the maximum steering angle, the motor load is reduced. Temporarily becomes excessive, the assist force of the motor is reduced while braking is applied to the motor, so that the assist force gradually decreases, preventing idling and overheating of the motor and suppressing unnecessary power consumption. At the same time, energy loss can be reduced, and at the same time, abrupt changes in assist force can be suppressed, so that the driver does not feel uncomfortable and the drivability of the vehicle including the electric power steering device can be improved.

According to the second aspect of the present invention, since the braking of the motor is performed by interrupting or reducing the energization, the slippage of the frictional engagement element can be quickly suppressed, and wasteful power consumption can be suppressed.

[0013] In the third invention, the motor is braked by a predetermined duty control, so that the motor can be smoothly braked. Can be quickly suppressed.

According to a fourth aspect of the present invention, when the rotational speed of the motor is low, when the maximum steering angle is reached, the motor stops without the frictional fastening member slipping. When the speed is high, the assist force is large, so after reaching the maximum steering angle,
While the motor runs idle and suppresses the slip of the friction fastening member,
The assist force can be smoothly reduced without giving the driver a feeling of strangeness.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1 and 2 show an electric steering gear 1 which applies an assist force from a motor 5 via a speed reducer 3 which meshes with the rack 2 in addition to a steering gear box 4 which meshes with the rack 2. An example to which the present invention is applied will be described.

The steering gear 1 is provided with a reduction gear 3 connected to a steering gear box 4 and a motor 5, and the steering gear box 4 is connected to a steering shaft (not shown) to reduce the steering force of the driver to a rack. 2, the motor 5 is connected to the gear 30 of the speed reducer 3 via a torque limiter 6 (friction fastening means), and applies an assist force to the rack 2 via a pinion (not shown) meshed with the gear 30. I do.

Here, as shown in FIG. 2, the torque limiter 6 includes a friction member 8 connected to the gear 30 in a rotational direction on an inner periphery of a cylindrical case 6a connected to the gear 30 side.
The friction members 7 connected to the output shaft 50 of the motor 5 are housed so as to be in sliding contact with each other.
When the frictional member 7 is pressed by the disc spring 9 and the assist force from the motor 5 exceeds a predetermined value, the frictional members 7 and 8 are prevented from slipping and the load on the motor 5 is prevented from becoming excessive.

In order to detect the number of rotations of the gear 30, a slit 6b is formed on the outer periphery of the case 6a facing the Hall IC 13 provided with the Hall element, and the Hall IC 13 is a gear corresponding to a change in the magnetic field. The rotation speed Ng of 30 is sent to the controller 10.

The controller 10 is mainly composed of a microcomputer, and includes a vehicle speed VSP from a vehicle speed sensor 11, a steering torque Tin detected by a steering torque sensor 14, and an ignition switch 1 as driving conditions of the vehicle.
2, the drive current iM is determined, the drive current iM is determined, and the motor 5 is driven. Based on the difference between the rotational speed Nm of the motor 5 and the rotational speed Ng of the gear 30, the motor state is determined based on the driving state of the vehicle. The overload of No. 5 is determined, and if an overload is detected, an overload prevention process is performed as described later.

The rotation speed Nm of the motor 5 is detected by, for example, assuming that the applied voltage of the motor 5 is E _B , the current is iM, the winding resistance is Ra, and the power generation constant is Ke. Nm = (E _B −Ra × iM) / Ke (1) Of course, the rotation speed of the output shaft 50 of the motor 5 may be directly detected and used as the motor rotation speed Nm.

The steering torque sensor 14 is disposed in the steering gear box 4 or the like and detects a steering torque Tin by a driver's operation of the steering wheel, similarly to the conventional example. Although the sign changes according to the steering direction, a change in the sign is omitted in the following description because only a single steering direction is described.

Here, an example of the overload prevention control performed by the controller 10 is shown in the flowcharts of FIGS. 3 and 4, FIG. 3 shows a main routine, and FIG. 4 shows a subroutine of motor braking. The details of the control will be described in detail with reference to a flowchart.

The control shown in FIGS. 3 and 4 is executed at predetermined time intervals.

First, a counter t1 for measuring time is reset to 0 in step S1 of FIG.
At 2, the counter t1 is incremented to start measuring time.

Next, in step S3, the vehicle speed VSP from the vehicle speed sensor 11, the hall IC
13, the rotation speed Ng of the gear 30 and the steering torque sensor 1
In addition to reading the steering torque Tin from No. 4, the motor rotation speed Nm obtained from the above equation (1) and the current iM supplied to the motor 5 are read.

In steps S4 to S7, it is determined whether or not the motor 5 is overloaded. First, in step S4, it is determined whether or not the vehicle speed VSP has become equal to or lower than a predetermined value Vs1. If VSP is equal to or less than the predetermined value Vs1, the process proceeds to step S5. If not, the process proceeds to step S11 to perform a normal assist process. The predetermined vehicle speed Vs1 is set to an extremely low speed,
For example, it is set to 2-3 km / h.

As shown in FIG. 6, the normal assist process in step S11 includes the vehicle speed VSP and the steering torque Tin.
After setting the motor current iM according to
Then, the motor 5 is driven by the set motor current iM.

Here, the map of FIG. 6 is a map V0 set for each predetermined vehicle speed range according to the increase of the vehicle speed VSP.
V1, V2... Vn are selected, and based on the selected map Vn, the motor drive current iM, that is, the assist force applied by the motor 5 is determined from the vehicle speed range Vn and the steering torque Tin. V0 is VSP ≦
The vehicle speed range is set to 3 km / h.
Is set in a vehicle speed range such as VSP> 3 km / h, and the map Vn is set in advance so that the motor drive current iM decreases as the vehicle speed VSP increases, as shown in FIG.

Next, at step S5, the motor speed N
It is determined whether m is equal to or greater than a predetermined value N1. If m is equal to or greater than N1, the process proceeds to step S6. If not, the process proceeds to step S11 and subsequent steps. It is determined whether or not there is, and if N2 or less, the process proceeds to step S7. If not, the process proceeds to step S11 and subsequent steps. However, the predetermined value N2 is set to, for example, a value larger than the predetermined value N1.

In step S7, it is determined whether the motor drive current iM is equal to or greater than a predetermined threshold value iMB.
If iM or more, the process proceeds to step S8, otherwise, the process proceeds to step S11 and subsequent steps. The predetermined threshold value iMB for determining the motor drive current iM is set to a value smaller than the maximum drive current iMmax, as shown in FIG.

Then, in step S8, the counter t1
Is determined whether or not a predetermined time tc has elapsed, and a predetermined time tc is determined.
If c has elapsed, the process proceeds to step S9, while if the counter t1 is less than the predetermined time tc, the process returns to step S2 and the overload determination in steps S3 to S7 is performed again. The predetermined time tc is set to, for example, several seconds.

If all the overload conditions from step S4 to step S7 continue to be satisfied during the predetermined time tc,
It can be determined that the motor 5 has been overloaded by a predetermined amount and the torque limiter 6 has slipped, and the process proceeds to step S9 to reduce the motor drive current iM.

In step S9, since the vehicle speed VSP is equal to or less than the predetermined value V1 from the above step S4, the vehicle speed range is V0. In the case of the overload condition, the map for setting the motor drive current iM is V0 '. The target value iM1 of the motor drive current iM is switched to the threshold value iM
It is set to be smaller than B.

That is, in FIG. 5, the map V0 'set in advance to obtain the overload driving current iM is as follows:
The map of the vehicle speed range V0 at the time of the normal control is set in advance so that the motor drive current iM is reduced at a predetermined ratio, and the relationship between the maps of V0 and V0 ′ is shown in FIG. A ′ / B ′, the maximum value in the map V0 ′ is set to the drive current iM1 smaller than the threshold value iMB, and if the motor 5 is overloaded, the motor drive current during normal control is set. Although iM = iMmax, the target value iM1 of the motor drive current iM is the upper limit of the target value iM1 of the motor drive current iM according to the switched map V0 ′ in the overload prevention process.

In the map for obtaining the drive current iM at the time of overload, the current value iM of the map V0 is determined by a predetermined ratio α / β = α ′ / β ′ = α ″, as shown by the one-dot line in FIG. /
An intermediate fixed value reduced by β ″ may be used.

In step S10, as shown in the flowchart of FIG. 4 described later, the motor 5 is driven so that the drive current iM is set to the target value set in step S9 while the brake is applied to the motor 5. , For variably controlling the assist force to the steering gear 1.

Next, the subroutine of the motor braking process shown in FIG. 4 will be described in detail.

First, in step S20, a decrease ΔK per unit time of the motor drive current iM is calculated according to the motor speed Nm. The decrease amount ΔK is set, for example, by a monotonous decrease function so that the decrease amount ΔK is small when the motor rotation speed Nm is large, and is large when the motor rotation speed Nm is small.

In step S21, in order to apply braking to the motor 5, for example, as shown in FIG. 8, when the motor drive circuit is constituted by a bridge circuit using MOSFETs, the switching elements Sa to SS constituted by MOSFETs are used.
Among the Sd, the motor that sets the switching element Sb to ON, sets Sc and Sd to OFF, sets Sa to OFF, and overloads the torque limiter 6 in step S22 due to an overload condition. 5 is started.

Then, in step S23, the motor rotation speed Nm and the gear rotation speed Ng are read, and then in step S23.
In 24, in order to determine the drive current iM after the braking of the motor 5, the value obtained by subtracting the decrease amount ΔK per unit time obtained in step S20 from the current drive current iM is set as a new target drive current iM. After setting, step S2
At 5, it is determined whether or not the motor rotation speed Nm has been reduced to the gear rotation speed Ng.

If the motor rotation speed Nm has been reduced to the gear rotation speed Ng, the process proceeds to step S26, while if the motor rotation speed Nm is higher than the gear rotation speed Ng, the process returns to step 23 to brake again. To continue. During this braking period, as shown in FIG. 8, the switching elements Sb, Sb
A braking current is generated between the motor d and the motor 5 by the back electromotive force, and the braking of the motor 5 is promoted.

After the motor rotation speed Nm has been reduced to the gear rotation speed Ng, in step S26, the switching element S
After turning on both a and Sb, the process proceeds to step S27, where the motor drive current iM calculated in step S24 is calculated.
, The driving of the motor 5 is restarted.

Next, in step S28, the current motor drive current iM is set to the target value iM obtained in step S9.
It is determined whether or not the motor drive current iM is equal to or smaller than 1. If the motor drive current iM is larger than the target value iM1, the motor drive current iM is again reduced by the decrease amount ΔK in step S29, and the process returns to step S27 to return to the motor drive current iM Is the target value iM1
This loop is repeated until the motor drive current iM has decreased to the target value iM1, and it is determined that the braking process of the motor 5 has been completed, and the control is terminated.

By repeating the processing of steps S1 to S29, as shown in FIG. 7, the motor rotation speed Nm becomes larger than the gear rotation speed Ng, and a predetermined time tc after the overload state is reached. , The overload prevention control is started, and the motor 5 is braked until the motor speed Nm matches the gear speed Ng as shown in FIG.

During the braking period (Δtd in the figure),
The subtraction of the motor drive current iM toward the target value iM1 obtained in step S9 is performed as shown by the dashed line in the figure, and after the motor rotation speed Nm matches the gear rotation speed Ng, a predetermined slope (per unit time) is obtained. The motor drive current iM gradually decreases in accordance with the decrease amount ΔK), and becomes the target drive current iM1 after a time Δta from the start of the overload prevention control.

Therefore, in the low speed region where the vehicle speed VSP is equal to or lower than the predetermined value Vs1, the torque limiter 6 slips (Nm ≠).
Ng) If the state in which the motor drive current iM is equal to or greater than the threshold value iMB has continued for a predetermined time tc or more, if it is determined that the motor 5 is in an overload state, then step S
After the target value iM1 for reducing the drive current iM is calculated in step 9, braking is applied to the motor 5 until the motor speed Nm matches the gear speed Ng, and thereafter, the motor drive current iM gradually decreases. As a result, the assist force also gradually decreases, preventing overheating of the motor 5 and suppressing wasteful power consumption to reduce energy loss. Despite reaching the steering angle, the driver may further operate the steering wheel to try to exceed the maximum steering angle, or even if the steering wheel touches a curb etc. and further steering is impossible, Even when the driver further operates the steering wheel, a sudden change in the assist force is suppressed, so that the driver does not feel discomfort, and the drivability of the vehicle equipped with the electric power steering device is improved. Rukoto but they can.

The decrease ΔK of the motor drive current iM
7 is set smaller as the motor rotation speed Nm is larger, and is set larger as the motor rotation speed Nm is smaller, as shown by the broken line in FIG. 7. Therefore, when the motor rotation speed Nm is smaller as shown in FIG. When the steering angle is reached, the motor rotation speed Nm also becomes 0 along with the gear rotation speed Ng, and the assist force can be reduced smoothly by rapidly reducing the motor drive current iM.

On the other hand, as shown in FIG. 9 (b), when the motor rotation speed Nm is high, the assisting force is large, and after reaching the maximum steering angle, the motor rotation speed Nm is reduced to the gear rotation speed Nm.
Since the motor driving current iM is gradually reduced, the assist force can be reduced smoothly without giving the driver a sense of incongruity while suppressing the wear of the torque limiter 6 by gradually reducing the motor drive current iM.

FIG. 10 shows the maps of FIGS. 5 and 6 of the first embodiment. When the maps V0 to V2 are used, the motor drive current iM exceeds the threshold value iMB.
Is set large, and the other configuration is the same as that of the first embodiment.

In this case, the steering force (steering torque Ti
n) and the assist force (motor drive current iM) are arbitrarily set, and when the load of the motor 5 becomes excessive, the assist force can be prevented from suddenly changing without giving a sense of incongruity to the driver, and smoothly. The idling of the motor 5 can be suppressed.

FIGS. 11 and 12 show a third embodiment.
Motor 5 performed in step S22 of the first embodiment
Is performed by duty control, and the other configuration is the same as that of the first embodiment.

During the braking period of the motor 5 (Δtd in the drawing), the switching element Sa shown in FIG. 8 is driven at a predetermined duty ratio every predetermined period X.
The switching element Sa is, for example, a normal P every 2 msec.
The WM control and the OFF period are repeated, and braking is performed in the OFF period. Thereby, the braking of the motor 5 is performed smoothly,
It is intended to suppress a sudden decrease in assist power and improve drivability. Note that the switching element Sb maintains the ON state, as described above.

In FIG. 12, 1 during PWM control is set.
By setting the cycle to a frequency equal to or higher than the human audible frequency such as 50 μsec (20 KHz), noise during the PWM control period can be reduced.

In the above embodiment, the case where the steering gear 1 is provided with the steering gear box 4 and the speed reducer 3 having the motor 5 is described. To provide an assist force (1 pinion type), to provide an assist force by directly engaging the motor 5 with the rack 2 (rack type), or to apply an assist force of the motor 5 to a steering shaft. (Column type).

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a motor and a torque limiter.

FIG. 3 is a main routine of a flowchart illustrating an example of control performed by a controller and illustrating an example of an overload prevention process;

FIG. 4 is a flowchart illustrating a subroutine of a motor braking process, similarly illustrating an example of control performed by a controller.

FIG. 5 is a map showing the relationship between the drive current iM of the motor used in the overload prevention process and the absolute value | Tin | of the steering torque.

FIG. 6 is a map showing a relationship between a drive current iM of a motor used for normal control and an absolute value | Tin | of a steering torque.

FIG. 7 is a graph showing the operation, showing the relationship between the motor drive current iM and time.

FIG. 8 is a schematic diagram illustrating an example of a motor drive circuit.

FIGS. 9A and 9B are graphs showing a relationship between a motor rotation speed and a gear rotation speed and time, wherein FIG. 9A is a schematic diagram showing a low rotation speed, and FIG. 9B is a schematic diagram showing a high rotation speed.

FIG. 10 shows a second embodiment, in which a motor drive current i
6 is a map showing the relationship between M and the absolute value | Tin | of the steering torque.

FIG. 11 shows a second embodiment, and shows a motor drive current iM.
Shows the relationship between time and time.

FIG. 12 is a graph showing an example of duty control of a switching element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering gear 2 Rack 3 Reduction gear 4 Steering gear box 5 Motor 6 Torque limiter 7, 8 Friction member 9 Disc spring 10 Controller 11 Vehicle speed sensor 12 Ignition switch 13 Hall IC 14 Steering torque sensor 30 Gear

Claims (4)

[Claims] 1. A motor provided on a steering wheel for steering a steering wheel in response to a driver's operation and providing a steering assist force, and a steering assist force provided by the motor in accordance with the steering force of the steering wheel. Control means for controlling; overload state determining means for determining an overload state of the motor based on a predetermined condition; and reducing the steering assist force of the motor when the overload state of the motor is determined. An electric power steering apparatus comprising an overload preventing means, a friction fastening means interposed between the motor and the steering and capable of transmitting a predetermined steering assist force, and a slip detecting the slip of the friction fastening means. Detection means, wherein the overload state determination means determines an overload state when at least slippage of the friction fastening means is detected, and the overload prevention means An electric power steering device characterized in that the steering assist force is reduced while applying braking to the motor. 2. The electric power steering apparatus according to claim 1, wherein the overload prevention unit applies braking to the motor by cutting off or reducing the power supply to the motor. 3. The electric power steering apparatus according to claim 1, wherein the overload prevention means applies a brake to the motor by a predetermined duty control. 4. The overload prevention means includes means for detecting the speed of a motor. When the speed of the motor is high, the amount of reduction of the steering assist force per unit time is set to be small. 2. The electric power steering apparatus according to claim 1, wherein the amount of reduction of the steering assist force per unit time is set to be large when is small.