JP7525366B2 - Steering system - Google Patents

Description

The present invention relates to a steering system that is mounted on a vehicle and steers the wheels by moving the steering shaft.

Patent document 1 describes a steering system that steers wheels by moving a steering shaft. This steering system includes a steering shaft, an electric motor, a conversion device that converts the rotation of the electric motor into the movement of the steering shaft, a rotation angle sensor that detects the rotation angle of the electric motor, a movement amount detection device that detects the amount of movement of the steering shaft, and an abnormality detection unit that detects an abnormality in the conversion device. The abnormality detection unit detects the rotation angle of the electric motor and the movement amount of the steering shaft when the electric motor is operated, and detects that the conversion device is abnormal if the relationship between the rotation angle of the electric motor and the movement amount of the steering shaft deviates from a predetermined relationship.

JP 2019-104488 A

The objective of the present invention is to improve the steering system, for example by making it possible to detect an abnormality in the conversion device using the current flowing through the electric motor.

In the steering system according to the present invention, for example, if the current value, which is the magnitude of the current flowing through the electric motor, is greater than a set value, or is greater than the amount of movement related to the amount of movement of the steering shaft, the conversion device is detected as being abnormal. For example, if the conversion device becomes rusty or foreign matter is mixed in, the frictional force during operation of the conversion device increases, the load applied to the electric motor increases, and the current flowing through the electric motor increases. In this way, if the current value of the current flowing through the electric motor is greater than the set value, or is greater than the amount of movement related to the amount of movement, it is possible to detect that the conversion device is abnormal. In other words, an abnormality in the conversion device can be detected by using the current flowing through the electric motor.

1 is a diagram conceptually illustrating a steering system according to a first embodiment of the present invention; 5 is a diagram showing the relationship between a current value flowing through an electric motor, which is a component of the steering system, and a movement amount related amount. FIG. 5 is a flowchart showing an abnormality detection program stored in a storage unit of the steering ECU. 5 is a flowchart showing a steering control program stored in the storage unit. 10 is a flowchart showing another movement detection program stored in the storage unit.

EMBODIMENTS OF THE PRESENT DISCLOSURE

Below, a steering system for steering the wheels of a vehicle, which is one embodiment of the present invention, will be described with reference to the drawings.

As shown in FIG. 1, the steering system of the first embodiment is of the so-called steer-by-wire type, and includes a steering device 20 equipped with a housing 8, a steering shaft (which can be called a rack bar) 10 extending in the width direction of the vehicle, an electric motor 14 as a drive source, and a conversion device 16 that converts the rotation of the electric motor 14 into movement of the steering shaft 10 in the width direction of the vehicle (hereinafter, sometimes referred to as the axial direction of the steering shaft 10, or simply the axial direction. In FIG. 1, the axis is marked with the symbol L).

The steering shaft 10 is a shaft (bar) that steers the wheels by moving in the axial direction, and is held in the housing 8 so that it cannot rotate relative to the housing 8 but can move relative to the housing 8 in the axial direction. Tie rods 23, 24 are connected to the steering shaft 10, and wheels 25, 26 are connected to the steering shaft 10 via knuckle arms (not shown), so that the wheels 25, 26 are steered by moving the steering shaft 10 in the axial direction.

The electric motor 14 is held in the housing 8 by the main body 14h. The output shaft (which can also be called the rotating shaft) 12 of the electric motor 14 is in a position extending parallel to the steering shaft 10.

In this embodiment, the conversion device 16 includes a rotation transmission unit 30, a screw mechanism 32 as a motion conversion mechanism, and the like. The rotation transmission unit 30 has the function of a reducer, and reduces the rotation speed of the output shaft 12 of the electric motor 14, and doubles the torque of the output shaft 12 before transmitting it to the nut member 40. The rotation transmission unit 30 includes a small diameter pulley 38 that is integrally and rotatably fitted to the output shaft 12 of the electric motor 14, a large diameter pulley 44 that is integrally and rotatably fitted to the nut member 40, and a belt 46 that is stretched around the small diameter pulley 38 and the large diameter pulley 44.

The large diameter pulley 44 is held in the housing 8 via a bearing device 52 so that it can rotate around the axis L. A nut member 40 is attached to the inner periphery of the large diameter pulley 44. The small diameter pulley 38, the large diameter pulley 44, and the belt 46 are all toothed, and the rotation of the small diameter pulley 38 is transmitted to the large diameter pulley 44 via the belt 46 through the meshing of the teeth, and then to the nut member 40.

In this embodiment, the bearing device 52 includes two bearings 53, 54 arranged side by side in the axial direction, and a pair of disc springs 55, 56 located on either side of the bearings 53, 54. The disc springs 55, 56 are elastically deformable by a force acting in the axial direction, and have the function of absorbing assembly errors of the bearings 53, 54 and reducing noise generated by the movement of the steering shaft 10.

The ball screw mechanism 32, which is a screw mechanism, converts the rotation of the nut member 40 into linear movement and outputs it to the steered shaft 10. The ball screw mechanism 32 includes a male threaded portion 28 formed on the outer periphery of the steered shaft 10, a female threaded portion 48 formed on the inner periphery of the nut member 40, and a number of balls 50 interposed between them, and the female threaded portion 48 and the male threaded portion 28 are screwed together via the balls 50.

A threaded portion 60 is provided on a portion of the steered shaft 10 away from the conversion device 16 in the axial direction, while a pinion 62 that can be screwed into the threaded portion 60 is held in the housing 8. The pinion 62 is rotated in association with the relative movement of the steered shaft 10 with respect to the housing 8 in the axial direction.
In this embodiment, the belt 46 is moved as the electric motor 14 rotates, which causes the nut member 40 to rotate and the steered shaft 10 to move in the axial direction. The pinion 62 is rotated by the axial movement of the steered shaft 10 relative to the housing 8. Therefore, the amount of movement of the steered shaft 10 can be estimated based on the rotation angle of the pinion 62, and the rotation angle of the electric motor 14 can be estimated. In this case, when the conversion device 16 is normal, the specifications of the steering system are set so that the rotation angle of the electric motor 14 from the zero point position and the rotation angle of the pinion 62 at the zero point position are the same.

This steering system is provided with a steering ECU 70, which is mainly a computer. The steering ECU 70 is equipped with an execution unit 70a, a storage unit 70b, an input/output unit 70c, etc. The input/output unit 70c is connected to an operation state detection device 74 that detects the operation state of an operating member 72 operated by the driver, a vehicle speed sensor 76 that detects the traveling speed of the vehicle, a surrounding environment acquisition device 78, a current sensor 79 that detects the current flowing through the electric motor 14, a motor rotation angle sensor 80 that detects the rotation angle of the electric motor 14 from the zero point position, a pinion rotation angle sensor 82 that detects the rotation angle of the pinion 62 from the zero point position, an outside air temperature sensor 84 that detects the outside air temperature, a motor temperature sensor 86 that is provided in the electric motor 14 and detects the temperature of the electric motor 14, a main switch 88 of the vehicle, etc., as well as an alarm device 90, the electric motor 14, etc.

The operating member 72 may be a steering wheel, but may also be a joystick, a mouse-shaped grip, or the like. The operating state detection device 74 detects the operating force and amount of operation applied to the operating member 72, and may include an operating force sensor, an operating amount sensor, or the like. The vehicle speed sensor 76 detects the traveling speed of the vehicle. The surrounding environment acquisition device 78 includes a radar device, a camera, and the like, and detects objects and the like around the host vehicle, which is the vehicle on which the steering system is mounted, and acquires the relative positional relationship between the objects and the host vehicle, and recognizes the lane markings and acquires the distance between the host vehicle and the lane markings.

In this embodiment, the motor rotation angle sensor 80 and the pinion rotation angle sensor 82 are both absolute angle sensors, and the zero point position is set as the position of the electric motor 14 and the position of the pinion 62 when the steering angle of the wheels 25, 26 is zero when the temperature of the steering system is at a predetermined set temperature (e.g., 20°C) before the vehicle is shipped. In other words, when the electric motor 14 and the pinion 62 are at the zero point position, the position of the steering shaft 10 is in the neutral position, the steering angle of the wheels 25, 26 is zero, and the vehicle moves straight. In this embodiment, the motor rotation angle sensor 80 corresponds to the motor rotation angle acquisition device, and the pinion rotation angle sensor 82 corresponds to the pinion rotation angle acquisition device.

In addition, since the pinion 62 is rotated in accordance with the axial movement of the steering shaft 10, the rotation angle θp of the pinion 62 from the zero point position corresponds one-to-one to the amount of movement of the steering shaft 10 from the neutral position. Therefore, the rotation angle θp of the pinion 62 from the zero point position is an example of a movement amount related amount, and the pinion rotation angle sensor 82 can be considered as an example of a movement amount related amount acquisition device. In addition, the rotation angle θp of the pinion 62 from the zero point position corresponds to the steering angle of the wheels 25, 26, and the change speed of the rotation angle θp of the pinion 62 from the zero point position corresponds to the steering speed. Therefore, in this embodiment, the rotation angle θp of the pinion 62 from the zero point position is adopted as a physical quantity that corresponds one-to-one to the steering angle of the wheels 25, 26, and the change speed dθp of the rotation angle of the pinion 62 from the zero point position is adopted as the movement speed of the steering shaft 10, i.e., a value that corresponds one-to-one to the steering speed.

Furthermore, since a predetermined relationship (e.g., the same relationship) is established between the rotation angle θp from the zero point position of the pinion 62 and the rotation angle θm from the zero point position of the electric motor 14, it is possible to estimate the rotation angle θm from the zero point position of the electric motor 14 based on the rotation angle θp from the zero point position of the pinion 62. Therefore, the movement amount related quantity acquisition device can also be considered as a rotation angle estimation device that estimates the rotation angle of the electric motor 14.
Hereinafter, the rotation angle θp of the pinion 62 from the zero point position and the rotation angle θm of the electric motor 14 from the zero point position may be simply referred to as the rotation angle θp of the pinion 62 or the pinion rotation angle θp, the rotation angle θm of the electric motor 14 or the motor rotation angle θm. In addition, the movement amount of the steered shaft 10 from the neutral position may be simply referred to as the movement amount of the steered shaft 10.

The outside air temperature sensor 84 detects the outside air temperature, and the motor temperature sensor 86 detects the temperature inside the electric motor 14. The motor temperature sensor 86 can tell the heat generation state of the electric motor 14. The main switch 88 is a switch that is turned ON when the driver or the like starts the vehicle. The alarm device 90 alerts the driver of abnormalities in the steering system, and may alert the driver visually or audibly, and may include one or more of a display, a light source, a sound generating device, a buzzer, etc.

The memory unit 70b of the steering ECU 70 stores an abnormality detection program shown in the flowchart of FIG. 3, a steering control program shown in the flowchart of FIG. 4, a normal state map shown by the solid line in FIG. 2, etc.

In the steering system configured as described above, the target steering angle of the wheels 25, 26 is acquired based on the operating state of the operating member 72, the relative positional relationship between the vehicle and objects in the vicinity of the vehicle acquired by the surrounding environment acquisition device 78, etc., and the electric motor 14 is operated to steer the wheels 25, 26 so that the actual steering angle approaches the target steering angle. The steering control program is executed at predetermined set time intervals.

In step 101 (hereinafter, simply referred to as S101, and the same applies to the other steps), a value indicating the operation state of the operating member 72 detected by the operation state detection device 74, a relative positional relationship between the vehicle and surrounding objects, etc., acquired by the surrounding environment acquisition device 78, etc. are acquired. In S102, based on these, a target steering angle of the wheels 25, 26 is acquired, and in this embodiment, a target movement amount of the steering shaft 10 corresponding to the target steering angle of the wheels 25, 26 is acquired. In S103, the electric motor 14 is operated so that the actual movement amount of the steering shaft 10 acquired based on the pinion rotation angle θp approaches the target movement amount. As a result, the steering shaft 10 is moved in the axial direction, and the wheels 25, 26 are steered.

In this embodiment, an abnormality in the conversion device 16 is detected in parallel with the execution of the steering control program. For example, if the ball screw mechanism 32 in the conversion device 16 becomes rusty or foreign matter gets mixed in, the frictional force between the nut member 40 and the steering shaft 10 increases. Therefore, when the steering shaft 10 is moved, a large force is applied to the steering shaft 10, the load applied to the electric motor 14 increases, and the current that flows increases. As a result, the current that flows through the electric motor 14 increases relative to the amount of movement.

An example of this case is shown in FIG. 2. In FIG. 2, dashed line A shows the relationship between the amount of movement s of the steering shaft 10 from the neutral position and the current value I flowing through the electric motor 14 when the conversion device 16 is abnormal, for example, when the conversion device 16 is rusted to a certain extent, and solid line B shows these relationships when the conversion device 16 is normal, for example, when there is no rust or only a small amount of rust. Even if the amount of movement-related quantity is the same, the current value flowing through the electric motor 14 varies depending on the lateral G, the friction coefficient of the road surface, the traveling speed of the vehicle, etc., but solid line B shows these relationships when the resistance applied to the wheels 25, 26 is large and a large current value flows when the conversion device 16 is normal. The normal state map, which is the relationship represented by solid line B, is stored in the memory unit 70b.

From dashed line A and solid line B, it is clear that when the conversion device 16 is abnormal, the current flowing through the electric motor 14 is greater than when the conversion device 16 is normal, when the amount of movement s of the steering shaft 10 is the same.

As is clear from the dashed line A in FIG. 2, when the amount of movement s of the steering shaft 10 from the neutral position increases, the current value I increases rapidly. Therefore, in this embodiment, the amount of movement s of the steering shaft 10 at which the current value I begins to increase at a large gradient is set as the set amount of movement sc, and the gradient of change dI/ds of the current value I relative to the amount of movement s of the steering shaft 10 when the amount of movement s of the steering shaft 10 reaches the set amount of movement sc is obtained, and the estimated maximum amount of movement s*, which is the amount of movement s of the steering shaft 10 when the current value I reaches the allowable upper limit value Imax, is estimated based on the gradient of change dI/ds. Then, if the estimated maximum amount of movement s* is smaller than the abnormality determination threshold value s*th, the conversion device 16 is detected as abnormal.

The allowable upper limit value Imax is the upper limit of the current that is allowable to be supplied to the electric motor 14, as determined by the specifications of the electric motor 14. Furthermore, the abnormality determination threshold value s*th can be set based on the amount of movement of the steered shaft 10 in the case of a full stroke. Theoretically, when a current equal to the allowable upper limit value Imax is supplied to the electric motor 14, the amount of movement of the steered shaft 10 will normally be greater than the amount of movement in the case of a full stroke.
In this embodiment, the amount of movement s of the steered shaft 10 from the neutral position is represented by the rotation angle θp from the zero point position of the pinion 62. This is because there is a one-to-one correspondence between the rotation angle θp of the pinion 62 and the amount of movement s of the steered shaft 10 and they are proportional to each other. Also, the set pinion rotation angle that is the pinion rotation angle corresponding to the set amount of movement sc is represented by θps, and the pinion rotation angle that corresponds to the abnormality determination threshold value s*th is represented by θp*t.

In this embodiment, the abnormality detection program is executed at predetermined intervals in parallel with the steering control program.
In S1, the value of the current flowing through the electric motor 14 is detected by the current sensor 79, in S2, the pinion rotation angle θp is detected by the pinion rotation angle sensor 82, and in S3, it is determined whether the rotation angle θp of the pinion 62 has reached a set rotation angle θps. If the determination is YES, in S4, it is determined whether the current value I in that case is larger than a current value Ir corresponding to a set movement amount s of the current value in a normal state represented by a solid line B.

If the determination in S4 is YES, the gradient of change dI/dθp of the current value I relative to the pinion rotation angle θp is obtained in S5, and the estimated maximum pinion rotation angle θp*, which is the rotation angle of the pinion 62 when the current value I reaches the allowable upper limit value Imax, is obtained in S6. Then, in S7, it is determined whether the estimated maximum pinion rotation angle θp* is greater than the abnormality determination threshold value θp*th, and if the determination is NO, it is determined that the conversion device 16 is abnormal, and in S8, this fact is notified by the alarm device 90.

Thus, in this embodiment, an abnormality in the conversion device 16 is detected based on the relationship between the value of the current flowing through the electric motor 14 and the amount of movement s of the steering shaft 10, and an abnormality in the conversion device 16 can be detected using the current value.
Also, a change gradient dI/ds of the current value I flowing through the electric motor 14 with respect to the movement amount s of the steered shaft 10 when the movement amount s of the steered shaft 10 reaches the set movement amount sc is obtained, an estimated maximum movement amount s*, which is the movement amount when the current value I reaches the allowable upper limit value Imax, is obtained based on the change gradient, and it is determined whether the estimated maximum movement amount s* is smaller than the abnormality determination threshold value s*th, making it possible to detect an abnormality in the conversion device 16 at an early stage. In other words, an abnormality in the conversion device 16 can be detected before the current actually flowing through the electric motor 14 reaches the allowable upper limit value Imax or before the actual movement amount of the steered shaft 10 reaches the full stroke.

In the above embodiment, the steering ECU 70 and the like constitute the control device, and the abnormality detection unit is constituted by a part that stores and executes the abnormality detection program shown in the flowchart of FIG. 3, and the steering control device and steering control unit are constituted by a part that stores and executes the steering control program shown in the flowchart of FIG. 4.

It is not essential to provide both step S4 and steps S5 and S6, and either one of them may be provided.
In other words, when the movement amount-related quantity is the same, the conversion device 16 can be detected as abnormal if the current value flowing through the electric motor 14 is greater than the current value Ir when the conversion device 16 is normal, or the conversion device 16 can be detected as abnormal if the maximum estimated movement amount-related quantity, which is the movement amount-related quantity when a current of the allowable upper limit value obtained based on the change gradient when the movement amount-related quantity reaches the set movement amount-related quantity is supplied, is smaller than the abnormality determination threshold value.

In the above embodiment, the abnormality detection program is executed in parallel with the steering control, but the abnormality detection program can also be executed when steering control is not being performed, such as during an initial check. In that case, the electric motor 14 is operated to detect an abnormality in the conversion device 16.

Furthermore, an abnormality in the conversion device 16 can be detected by executing an abnormality detection program represented by the flowchart of Fig. 5. In this embodiment, when the value of the current flowing through the electric motor 14 reaches an allowable upper limit, the conversion device 16 is detected as being abnormal.
This abnormality detection program is executed in parallel with the steering control.
In S21, the current value I is detected, and in S22, it is determined whether the current has reached an allowable upper limit value Imax. If the determination in S22 is YES, it is determined that the converter 16 is abnormal, and this fact is notified in S23.

As shown in FIG. 2, when the conversion device 16 is normal, even if the movement of the steering shaft 10 reaches the full stroke, a current of the allowable upper limit Imax will not flow to the electric motor 14. On the other hand, when the frictional force of the conversion device 16 increases due to rust or the like, a large current may be supplied to the electric motor 14 to achieve the target steering angle. Therefore, in steering control, if the current value flowing through the electric motor 14 reaches the allowable upper limit Imax, it is possible to detect that the conversion device 16 is abnormal.

In addition to the above examples, the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

8: Housing 10: Steering shaft 14: Electric motor 16: Conversion device 20: Steering device 60: Threaded part 62: Pinion 70: Steering ECU 79: Current sensor 82: Pinion rotation angle sensor 90: Notification device

Patentable inventions

(1) A steering system that steers wheels by moving a steering shaft,
The steering shaft,
An electric motor;
a conversion device that converts rotation of the electric motor into movement of the steering shaft;
a current sensor for detecting a current flowing through the electric motor;
a movement amount related quantity acquisition device that acquires a movement amount from a neutral position of the steering shaft or a movement amount related quantity including a physical quantity that has a one-to-one correspondence with the movement amount from the neutral position;
a control device for controlling the electric motor,
The control device of the steering system includes an abnormality detection unit that detects that the conversion device is abnormal when a current value, which is the magnitude of the current flowing through the electric motor detected by the current sensor, is larger than the movement amount-related amount detected by the movement amount-related amount detection device.

The movement amount-related quantity acquisition device may, for example, directly detect the amount of movement of the steering shaft from the neutral position or a physical quantity that corresponds one-to-one to the amount of movement from the neutral position, or may include a sensor that detects a physical quantity that corresponds one-to-one to the amount of movement or the change in the amount of movement of the steering shaft from the previous position to the current position, and acquire the amount of movement from the neutral position or a physical quantity related to the amount of movement based on the detection value of the sensor.

(2) The steering system described in (1) in which the abnormality detection unit obtains a gradient of change in the current value with respect to the movement amount related amount when the movement amount related amount reaches a preset movement amount related amount that is a predetermined set value, obtains an estimated maximum movement amount related amount, which is the movement amount related amount when the current value reaches a set current value, based on the gradient of change, and detects that the conversion device is abnormal if the estimated maximum movement amount related amount is smaller than an abnormality determination threshold value.

The set current value can be the upper allowable limit determined by the electric motor's specifications, etc.

(3) the control device includes a storage unit that stores a relationship between a current value of a current flowing through the electric motor and the movement amount related amount when the conversion device is normal,
The steering system according to claim 1 or 2, wherein the abnormality detection unit detects that the conversion device is abnormal if the current value of the current flowing through the electric motor when the movement amount-related amount reaches a set movement amount-related amount, which is a predetermined set value, is greater than the current value determined by the relationship stored in the memory unit.

(4) The control device includes a steering control unit that controls the electric motor to control a movement amount of the steering shaft and steers the wheels,
The steering system according to any one of claims (1) to (3), wherein the abnormality detection unit detects an abnormality in the conversion device during control by the steering control unit.

(5) A steering system that steers wheels by moving a steering shaft,
The steering shaft,
An electric motor;
a conversion device that converts rotation of the electric motor into movement of the steering shaft;
a current sensor for detecting a current flowing through the electric motor;
a steering control device that controls the electric motor to control a movement amount of the steering shaft and steers the wheels;
and an abnormality detection unit that detects that the conversion device is abnormal when a current value of a current flowing through the electric motor reaches an allowable upper limit value during control by the turning control device.
The steering system described in this section can employ any of the technical features described in sections (1) to (4).

Claims (1)

A steering system for steering wheels by moving a steering shaft,
The steering shaft,
An electric motor;
a conversion device that converts rotation of the electric motor into movement of the steering shaft;
a current sensor for detecting a current flowing through the electric motor;
a movement amount related quantity acquisition device that acquires a movement amount of the steering shaft from a neutral position or a movement amount related quantity including a physical quantity that has a one-to-one correspondence with the movement amount of the steering shaft from the neutral position;
a control device for controlling the electric motor,
the control device includes an abnormality detection unit that detects that the conversion device is abnormal when a current value, which is a magnitude of a current flowing through the electric motor detected by the current sensor, is larger than the movement amount related amount acquired by the movement amount related amount acquisition device ,
The abnormality detection unit obtains a change gradient of the current value with respect to the movement amount-related amount when the movement amount-related amount reaches a set movement amount-related amount that is a predetermined set value, obtains an estimated maximum movement amount-related amount, which is the movement amount-related amount when the current value reaches a set current value, based on the change gradient, and detects that the conversion device is abnormal if the estimated maximum movement amount-related amount is smaller than an abnormality determination threshold .

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