JPH04310475A - Motor driven power steering mechanism - Google Patents

Abstract

PURPOSE:To simplify entire mechanism and improve steering feeling when a motor driven power assisting mechanism is used togehter with a variable steering force transmission ratio mecanism which transmits the steering force from the steering wheel to the steered wheel. CONSTITUTION:Part of a steering gear mechanism 5 for transmitting the steering force from the steering wheel to the stored wheel is provided with a variable transmission ratio mechanism 10 for changing the steered angle on the steered wheel side relative to the steering wheel operation angle. A power assist mechanism 30 is employed to transmit the torque of an electric motor 20 to part of the steering gear mechanism 5. The variable transmission ratio mechanism and the power assist mechanism are arranged to be selectively driven and controlled by means of the single electric motor 20 according to the vehicle speed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an electric power assist mechanism that uses an electric motor as a steering assist force generating means, and a steering angle that changes the steering angle at the steering wheel side relative to the steering angle at the steering wheel depending on the vehicle speed. When used in conjunction with a variable steering force transmission ratio mechanism, the electric power system improves the steering feel and improves the dynamic characteristics of the vehicle from stationary steering and low-speed to high-speed driving. The present invention relates to a type power steering device.

0002

[Prior Art] Generally, a steering device for a vehicle, etc. converts the rotational motion of the steering wheel during steering into the linear motion of a tie rod through a rack-and-pinion type steering gear mechanism, etc. It is possible to perform steering control to a desired state, but in this case, in a normal steering device, the transmission ratio is set to a constant value by a steering gear mechanism. However, for example, when the vehicle is traveling at high speed, the turning angle of the steered wheels (steering wheel steering angle) with respect to the amount of steering rotation of the steering wheel (steering wheel steering angle) described above is increased, and the steering wheel steering for a constant steering wheel steering angle is increased. Reducing the size of the corners is preferable to ensure driving stability, while at low speeds, it makes the vehicle's behavior more agile, gives a good driving feeling, and makes it easier to park the vehicle in the garage. From the viewpoint of the This was proposed in Japanese Patent No. 58-224852 and the like. In other words, in order to obtain an appropriate steering condition, it is desirable to change the turning angle of the steered wheels relative to the steering wheel operation depending on the driving conditions in order to further improve driving stability. Measures were being taken.

[0003]Furthermore, with such a steering device, steering operations can be performed easily and with a good feeling using the lightest possible steering force, especially when turning stationary while stopped or when steering while driving at low speed. For example, as shown in Japanese Unexamined Patent Application Publication No. 62-31559, it is also desired to have a structure in which, in a conventionally well-known hydraulic power steering device, there is a structure in the middle of the steering gear mechanism of the device. There has also been proposed a structure in which a variable transmission ratio mechanism for steering force is interposed in which the transmission ratio can be varied by an actuator such as a stepping motor. According to such a configuration, the transmission ratio, which is set in consideration of the magnitude of the steering assist force (power assist force) provided by the power steering device, is changed according to the vehicle speed, and thereby the steering angle and the steering angle are changed. The steering wheel steering angle can be variably controlled according to the vehicle speed, etc., so that the desired state is achieved, and it is possible to obtain even better steering control characteristics according to the vehicle running condition. .

0004

[Problems to be Solved by the Invention] However, in the above-mentioned conventional device, a power assist mechanism constituting a power steering device is attached to the steering gear mechanism, and
A transmission ratio variable mechanism that responds to vehicle speed, etc. is separately attached to a separate location, which complicates the overall configuration of this steering device, which poses problems in terms of processing and assembly of each part, and is not desirable from a cost perspective. Not only is this difficult, but the control is also complicated because it has to take into account the operating characteristics of both mechanisms.Furthermore, both mechanisms must be constantly controlled during operation, making the control complicated. It is desired that some kind of countermeasure be taken to eliminate these problems. In particular, power steering devices (power steering) equipped with the above-mentioned steering assist force generation means have conventionally had various configurations, and among them, an electric type that uses an electric motor as the steering assist force generation means A steering wheel is desired for reasons such as the structure of the steering device and the ability to drive quickly only when necessary, and a structure such as that shown in, for example, Japanese Unexamined Patent Publication No. 61-26362 has already been proposed. Although it is desired that such an electric power steering device be provided with the above-mentioned variable steering force transmission ratio mechanism in parallel, there is no device that adopts such a configuration. Furthermore, when the conventional devices described above are simply combined, two mechanisms, a power assist mechanism and a variable transmission ratio mechanism, are installed in parallel, and two motors are required as drive sources. The problem of complicated control is unavoidable.
Taking these points into consideration, there is a demand for a new electric power steering device that can eliminate the above-mentioned problems.

[0005]

[Means for Solving the Problems] In order to meet such demands, an electric power steering device according to the present invention includes a steering gear mechanism that is interposed in a part of a steering gear mechanism that transmits steering force from a steering wheel to a steered wheel side. A variable transmission ratio mechanism, which is provided at The vehicle is configured to be selectively driven and controlled by two electric motors depending on the vehicle speed.

[0006]

[Operation] According to the present invention, when the vehicle is stopped or traveling at low speeds, the electric power assist mechanism exerts a steering assist function, and not only is it possible to perform steering with light and appropriate steering force, but also when traveling at high speeds. By stopping the power assist mechanism and controlling the transmission ratio by the variable steering force transmission ratio mechanism to the required state, the turning angle of the steered wheels can be maintained at an appropriate level and driving stability can be achieved. This optimizes the steering feel from turning to high-speed driving, thereby improving the vehicle's dynamic characteristics.

[0007]

Embodiment FIGS. 1 to 3 show an embodiment of an electric power steering device according to the present invention.
The schematic structure of the electric power steering device, which is generally designated by the reference numeral 1, will be briefly explained using FIG. An output shaft connected via a planetary gear mechanism 10 as a variable ratio mechanism, 4 a pinion shaft as a steering shaft that is integrally connected to this output shaft 3 by press fitting etc. and forming a steering gear mechanism 5, 6 this This rack has rack teeth 6a that mesh with the pinion 4a of the pinion shaft 4 and constitutes a part of the steering link mechanism.The pinion shaft 4 and the rack 6 form a well-known rack and pinion type steering gear mechanism 5. configured. Here, the details of such a steering gear mechanism 5 are well known, and a specific explanation will be omitted. Also, 7, 7 in the figure
, 7 are bearings that rotatably support the above-mentioned output shaft 3 and pinion shaft 4 within the steering body 8. It goes without saying that such a steering gear mechanism 5 is not limited to such a rack and pinion type.

Reference numeral 10 denotes a planetary gear mechanism serving as a variable transmission ratio mechanism for transmitting steering force from the above-mentioned steering wheel to the steering wheels (not shown), and its sun gear 11 is a drive gear mechanism provided on the input shaft 2. It is provided on a drive shaft 15 having a transmission gear 14 that meshes with a side gear 13 . Reference numeral 16 designates one or more planetary gears disposed around the sun gear 11 in mesh with it, and reference numeral 17 designates an outer ring gear disposed around the sun gear 11 and having an internal tooth portion 17a meshing with the planet gear 16. The outer ring gear 17 has a worm gear 1 on its outer periphery, which is a rotation transmitting means with an electric motor 20, which will be described later.
An external tooth portion 17b that meshes with the gear mechanism 8 is formed and is configured to function as a worm wheel, which allows rotation to be transmitted from the motor side, but does not allow rotation to be transmitted from the planetary gear mechanism 10 side. Transmission gear mechanism 21 with
is configured. Further, reference numeral 19 in the figure is a rotation transmission disk provided on the output shaft 3 side, and the support shaft 16a of the planetary gear 16 is connected to an eccentric position thereof. Note that the members such as the outer ring gear 17 that constitute these planetary gear mechanisms 10 are as follows:
It goes without saying that it is rotatably held and disposed at an appropriate position by bearings or the like. According to such a configuration, the steering force accompanying the steering operation with the steering handle is transmitted from the input shaft 2 to the drive shaft 15 side, and is transmitted to the sun gear 11 of the planetary gear mechanism 10, the planet gears 16, and their supporting shafts. 1
6a to the rotation transmission disk 19, the planetary gear mechanism 10 transmits the rotation to the output shaft 3 with a required transmission ratio, and furthermore, the pinion shaft 4 integrally connected to the shaft.
is transmitted to. By transmitting the rotation of the pinion shaft 4 to the rack 6 side, necessary steering control is performed at the steering wheel (not shown).

Reference numerals 22 and 23 denote first and second shafts attached to the input shaft 2 on the steering wheel side and the output shaft 3 on the steering wheel side in the steering force transmission ratio variable mechanism configured as described above. These two steering angle sensors 22
, 23 during steering, it is detected whether the steering request on the steering wheel side and the turning state on the steering wheel side match. In this case, if there is a difference in the outputs from these two sensors 22 and 23, the motor 20 is driven and its rotational force is transmitted to the outer ring gear 17, thereby making use of the planetary gear mechanism 10. , a control operation is performed to eliminate misalignment between the output shafts 2 and 3. 24 is a torque sensor for detecting a steering request transmitted from the steering wheel side by detecting the rotational displacement of the output shaft 3 forming a part of the steering shaft within the steering body 8; , a case is illustrated in which a magnetostrictive rotation detector such as that disclosed in, for example, Japanese Unexamined Patent Publication No. 2-281115 is used. That is,
A strain detection layer made of a high magnetic permeability soft magnetic material is provided on the output shaft 3, and a detection coil is provided on the body 8 side surrounding the strain detection layer to detect changes in magnetic permeability due to strain in the strain detection layer. The structure is as follows. Then, the output obtained by this detection coil is sent to a detection circuit 25, and a signal controller 2 for controlling an electrical control system described later.
A detection signal is sent to 6. Note that signals from the first and second steering angle sensors 22 and 23 described above are also sent to the signal controller 26, and information from the vehicle speed sensor 27 is also input. Here, in the figure, 28 is a power controller connected to the signal controller 27, and 29 is a battery, which is provided as an intervening electric motor 20 and its rotation transmission system by an electric system control means constituted by these components, which will be described later. The electromagnetic clutches 31 and 32 are controlled to be turned on and off.

Reference numeral 30 denotes a power assist mechanism that transmits the rotational driving force of the electric motor 20 described above to the pinion shaft 4, which is the steering shaft, as a steering assist force;
a first motor output shaft 3 connected to one end of a motor shaft 33 of the electric motor 20 via a first electromagnetic clutch 31;
A small gear 35 is fixed to the pinion shaft 4 by press-fitting or the like, and a large gear 36 meshing with the small gear 35 is fixed to the outer end of the pinion shaft 4 by press-fitting or the like. According to such a configuration, by driving the electric motor 20 and transmitting the rotational driving force to the pinion shaft 4 through the transmission system including the small gear 35 and the large gear 36, the planetary gear mechanism is connected from the steering handle side. This power assists the steering force transmitted through the steering wheel 10, thereby reducing the steering force of the helmsman. Further, 37 is a second motor output shaft connected to the other end of the motor shaft 33 of the electric motor 20 by press fitting or the like, and as is clear from FIG. A bevel gear 38 is provided which meshes with a bevel gear 39 provided at the end of the worm gear 18 which is disposed perpendicularly. These bevel gears 38 and 39 are configured so that rotation from the motor shaft 33 side can be transmitted to the planetary gear mechanism 10 side. Note that this FIG. 2 is a schematic diagram viewed from the direction of arrow A in FIG.

Now, according to the present invention, in the electric power steering device as described above, a part of the steering gear mechanism 5 (
A planetary gear mechanism 10 as a transmission ratio variable mechanism that is provided between the input and output shafts 2 and 3 and changes the steering angle on the steering wheel side with respect to the steering angle, and rotational drive from an electric motor 20. A power assist mechanism 30 that transmits power to a part of the steering gear mechanism 5 (in this embodiment, the end of the pinion shaft 4 opposite to the output shaft 3 side) is connected to a single electric motor 2.
The feature is that the drive is selectively controlled according to the vehicle speed by setting 0. That is, in the present invention, the above-mentioned electric motor 20 is arranged in parallel to the steering body 8 constituting the steering gear mechanism 5, and one end of the motor shaft 33 of the electric motor 20 is connected to the first electromagnetic clutch 31, The first motor output shaft 34 is connected to the pinion shaft 4 as a steering shaft by a transmission gear mechanism including a small gear 35 and a large gear 36, and the other end of the motor shaft 33 is connected to the second electromagnetic clutch 32 and the second A steering force transmission ratio variable mechanism is achieved by a worm gear 18 having a bevel gear 38 and a bevel gear 39 on a motor output shaft 37, and an outer gear 17 which becomes a worm wheel that meshes with the worm gear 18 and constitutes a transmission gear mechanism 21 with a reverse rotation prevention function. The transmission ratio in the planetary gear mechanism 10 is configured to be variable. Note that the first and second electromagnetic clutches 31 and 32 described above have a conventionally known structure, and a detailed explanation of their structure and operation will be omitted here.

[0012] In this configuration, when the vehicle is stationary at a standstill or when steering while driving at low speed, the electric power assist mechanism 30 exerts a steering assist function.
The first electromagnetic clutch 31 is turned on and the motor 20 is rotationally driven in a desired direction so as to enable light and appropriate steering with an appropriate steering force. At this time, the second electromagnetic clutch 32, which constitutes the motor transmission system to the planetary gear mechanism 10 described above, is off, and its rotation transmission is interrupted. On the other hand, during steering while traveling at high speed, the power assist mechanism 30
By turning off the first electromagnetic clutch 31, its operation is stopped, and by turning on the second electromagnetic clutch 32 and connecting the motor 20, the transmission ratio by the variable steering force transmission ratio mechanism is set to the desired state. It is configured to be controllable. That is, the transmission ratio of the steering force from the input shaft 2 to the output shaft 3 by the planetary gear mechanism 10 is as follows:
By rotating the outer gear 17 in a desired direction at a desired rotation speed by the motor 20 using the ratio of the number of teeth between the planetary gear 16 and the outer ring gear 17 as a reference, from the relationship with the sun gear 11 and the planetary gear 16, The transmission ratio can be variably controlled with the characteristics shown in FIG. In other words, the transmission ratio is small when driving at low speeds, and as the speed increases, the transmission ratio of the steered wheel angle to the steering wheel angle becomes larger.
In other words, it is preferable that the electric motor 20 is controlled by the power controller 28 and the signal controller 26 so that the magnitude of the steering wheel steering angle with respect to a constant steering wheel steering angle decreases as the vehicle speed increases. It is something. According to such a configuration, when the electric power assist mechanism 30 is used in conjunction with the steering device having the planetary gear mechanism 10 as a variable steering force transmission ratio mechanism from the steering wheel to the steering wheel, the overall system This makes it possible to simplify the configuration and improve the steering feel. In particular, according to the present invention, the above-mentioned steering wheel steering angle and steering wheel steering angle are controlled to desired states by changes in vehicle speed, and
When stopped or when driving at low speeds, the power assist mechanism 30 is activated to apply steering assist force to maintain the appropriate steering angle of the steering wheels and achieve driving stability. The steering feeling can be optimized and the dynamic characteristics of the vehicle can be improved as a result.

As described above, in order to operate the power assist mechanism 30 during low speed driving by the electric motor 20 and the planetary gear mechanism 10 as a steering force transmission ratio variable mechanism during high speed driving, both mechanisms 30, 10 are operated by the electric motor 20. It is necessary to control the following conditions in order to ensure the running stability of the vehicle. That is, in the structure of the embodiment described above, a vehicle speed signal is input to the signal controller 26, the transmission ratio of the steering force is variably controlled by the planetary gear mechanism 10 at a predetermined vehicle speed or higher, and the electric motor 20 is variably controlled at a predetermined vehicle speed or lower.
However, the switching operation between these two mechanisms 10 and 30 is limited to when the steering wheel angle is in the neutral state, that is, when the vehicle is approximately in a straight-ahead state. A configuration in which switching is performed only within this range is necessary in order to maintain the running stability of the vehicle, and it is desirable that the controllers 26 and 28 control the switching operation timing in this manner. It will be done. In addition, if steering is performed while driving at low speed and the vehicle reaches a high speed with power assist still operating, even if the steering wheel angle is at the neutral position (straight ahead), the vehicle speed will be reduced to a certain level. It is also necessary to perform control so that switching to the variable transmission ratio mechanism 10 side is not performed unless the following conditions occur. In other words, if power assist is canceled in such a case, the steering force may suddenly become heavier.
This is not preferable from the viewpoint of running stability. By setting the switching control between the two mechanisms 10 and 30 in this way, taking into consideration the vehicle running conditions and running stability,
This prevents sudden changes in characteristics of the vehicle and allows the steering device to exhibit its performance. Here, the electromagnetic clutches 31 and 32 that transmit the rotation from the electric motor 20 by the DC motor described above to either of the mechanisms 10 and 30 are normally in an OFF state to cut off rotation transmission, and are turned off as necessary. The steering system is controlled so that it is turned on and transmits rotation, and even if both are turned off due to a failure in the electrical system, etc., the steering system will naturally go into the manual steering state via the planetary gear mechanism 10. The necessary steering can be secured.

It should be noted that the present invention is not limited to the structure of the embodiment described above, and the shape, structure, etc. of each part of the electric power steering device 1 may be modified or changed as necessary, and various modifications may be made. An example can be considered. For example, in the embodiment described above,
As a mechanism for connecting the steering wheel to the steering gear mechanism 5 side so that the transmission ratio of the steering force can be changed, a sun gear 11 is installed on the steering wheel side, and a rotation transmission disk is installed on the output shaft 3 side that is integrated with the pinion shaft 4 as a steering shaft. Although the case has been described in which the planetary gear 16 is connected via the gear 19 and the outer ring gear 17 is connected to the transmission gear mechanism 21 having a reverse rotation prevention function using a worm gear on the motor 20 side, the present invention is not limited to this. As shown in FIG. 4, the outer ring gear 1
7 to the output shaft 3 side, and the planetary gear 1
An external tooth portion 19a that meshes with the worm gear 18 is formed on the outer peripheral portion of the rotation transmission disk 19 connected to the 6 side,
It will be easily understood that even if the disc 19 is used as a worm wheel, the same effects as those of the above embodiment can be achieved. In short, when transmitting the steering force from the input shaft 2 to the output shaft 3 side, any configuration is sufficient as long as the transmission ratio can be variably controlled by rotational control from the motor side.

Furthermore, in the above-described embodiment, the planetary gear mechanism 10 and the motor 20 exemplified as the above-described variable steering force transmission ratio mechanism are replaced by a transmission gear mechanism 21 having a reversal prevention function that allows rotation only from the motor side. Although a worm gear mechanism is illustrated as an example, it is obvious that the present invention is not limited to this, and may be a gear mechanism using, for example, a hypoid gear. Furthermore, the gear mechanism for transmitting steering assist force that constitutes the power assist mechanism 30 from the motor 20 is not limited to a transmission gear mechanism consisting of a small gear 35 and a large gear 36 using helical gears, but also includes hypoid gears, spur gears, etc. A gear mechanism consisting of off-axis gears such as helical gears, planetary gears, bevel gears, etc. may be used, and various modifications may be considered. Further, in the above-described structure of the embodiment, a directly-extractable magnetostrictive rotation detector is used as the torque sensor 24 for detecting the steering direction, steering speed, steering force, etc. at the steering wheel on the steering shaft side. The present invention is not limited thereto, and a detection mechanism may be used that connects two shafts using a torsion bar and detects the above-mentioned steering request based on their relative rotational displacement.

[0016]

As explained above, according to the electric power steering device according to the present invention, there is a transmission that is interposed in a part of the steering gear mechanism and changes the steering angle on the steering wheel side with respect to the steering wheel steering angle. The variable ratio mechanism and the power assist mechanism that transmits the rotational driving force from the electric motor to a part of the steering gear mechanism are configured to be selectively driven and controlled by a single electric motor according to the vehicle speed, making it easy to use. Despite this configuration, the minimum number of components allows the electric power assist mechanism to provide a steering assistance function when turning stationary while stopped or when steering while driving at low speeds, allowing for light and appropriate steering. Not only is it possible to steer by force, but the power assist mechanism is stopped while driving at high speeds.
By controlling the transmission ratio to the required state using the variable steering force transmission ratio mechanism, it is possible to maintain the appropriate turning angle of the steering wheels and achieve driving stability, which improves the steering feel from stationary steering to high-speed driving. This has various excellent effects in that the dynamic characteristics of the vehicle can be improved. In particular, according to the present invention, a single DC motor is used, both electromagnetic clutches are kept off at all times, and either one is turned on as needed to perform power assist or variable control of the steering force transmission ratio. This is a method that can be performed under the following conditions, and the desired function can be achieved while simplifying the arrangement and assembly structure of each part, which has great advantages.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of the entire device showing an embodiment of an electric power steering device according to the present invention.

FIG. 2 is a schematic enlarged view of a transmission gear mechanism portion interposed between a planetary gear mechanism as a steering force transmission ratio variable mechanism and a rotation transmission system from the electric motor side, viewed from the direction of arrow A in FIG. 1; It is.

FIG. 3 is a characteristic diagram showing the change characteristics of the transmission ratio according to the vehicle speed by the steering force transmission ratio variable mechanism according to the present invention.

FIG. 4 is a schematic configuration diagram showing another embodiment of the steering force transmission ratio variable mechanism portion in the device of the present invention.

[Explanation of symbols]

1 Electric power steering device 2 Input shaft 3 Output shaft 4 Pinion shaft (steering shaft) 5
Steering gear mechanism 6 Rack 8 Steering body 10 Planetary gear mechanism (variable steering force transmission ratio mechanism) 1
1 Sun gear 13 Drive side gear 14 Transmission gear 15 Drive shaft 16 Planetary gear 16a Support shaft 17 Outer gear (weam wheel) 17a
Internal tooth section 17b External tooth section 18 Worm gear 19 Rotation transmission disk 20 Electric motor 21 Transmission gear mechanism 22 First steering angle sensor 23 Second steering angle sensor 24 Torque sensor 25 Detection circuit 26 Signal controller 27 Vehicle speed sensor 28 Power controller 30 Power assist mechanism 31 Electromagnetic clutch 32 Electromagnetic clutch 33 Motor shaft 34 First motor output shaft 35 Small gear 36 Large gear 37 Second motor output shaft 38 Bevel gear 39 Bevel gear

Claims (1)

[Claims] 1. A variable transmission ratio mechanism that is provided as part of a steering gear mechanism that transmits steering force from a steering wheel to a steering wheel, and that changes a steering angle on the steering wheel side with respect to a steering angle. and a power assist mechanism that transmits the rotational driving force from the electric motor to a part of the steering gear mechanism, and the variable transmission ratio mechanism and the power assist mechanism are selected by one electric motor according to the vehicle speed. An electric power steering device characterized in that it is configured to control drive automatically.