JP2949604B2 - Electric power steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power assist mechanism using an electric motor as a steering assist force generating means, and to change a steering angle on a steered wheel with respect to a steering angle of a steering wheel according to a vehicle speed. By using a variable transmission ratio mechanism of the steering force to be used, the steering feel during stationary or low-speed running to high-speed running can be improved, and the dynamic characteristics of the vehicle can be improved. The present invention relates to a power steering device.

[0002]

2. Description of the Related Art In general, a steering device for a vehicle or the like converts a rotational movement at the time of steering to a steering wheel into a linear movement of a tie rod through a steering gear mechanism of a rack and pinion type or the like, so that steering wheels are formed. The steering control can be performed to a required state. In this case, in a normal steering device, the transmission ratio is set to be constant by the steering gear mechanism. However, for example, when the vehicle is traveling at high speed, the transmission ratio of the steering wheel turning angle (steering wheel steering angle) to the steering rotation amount (steering wheel steering angle) of the steering wheel described above is increased to increase the steering wheel steering angle with respect to a constant steering wheel steering angle. It is preferable to reduce the magnitude of the steering wheel steering angle in order to secure running stability.
From the standpoint of obtaining a good driving feeling by accelerating the behavior of the vehicle or facilitating garage entry, the above-mentioned transmission ratio is made smaller on the contrary, and the steering wheel steering angle for a fixed steering wheel steering angle is increased. It is desired that the steering force transmission ratio variable mechanism having various structures be disclosed in, for example, Japanese Patent Laid-Open No. 58-224.
No. 852, for example. In other words, in order to obtain an appropriate steering state, it is necessary to change the turning angle of the steered wheels with respect to the steering wheel operation according to the driving conditions.
This is desirable for further improving running stability and the like, and measures have been taken for this purpose.

Further, in such a steering device, a steering operation can be performed with a light steering force as light as possible and with a good feeling, especially when the vehicle is stationary or when the vehicle is traveling at a low speed. It is also desired that such a configuration is adopted. For example, as shown in Japanese Patent Application Laid-Open No. Sho 62-31559, in a conventionally known power steering device of a hydraulic type or the like, the power steering device is provided in the middle of a steering gear mechanism of the device. There has also been proposed a configuration in which a transmission ratio variable mechanism of a steering force capable of varying a transmission ratio by an actuator such as a stepping motor is interposed. According to such a configuration, the transmission ratio set in consideration of the magnitude of the steering assist force (power assist force) by the power steering device is changed in accordance with the vehicle speed. The steering wheel steering angle can be variably controlled according to the vehicle speed and the like so as to be in a required state, and it is possible to obtain a better steering control characteristic according to the running state of the vehicle. .

[0004]

However, in the above-mentioned conventional device, a power assist mechanism constituting a power steering device is added to the steering gear mechanism.
A transmission ratio variable mechanism that responds to vehicle speed etc. is separately attached at another place, complicating the configuration of the entire steering device, problems in processing of each part, assemblability, and cost-effective Not only that, the control is complicated because both operation characteristics must be taken into consideration, and in operation, the operation of both mechanisms must be constantly controlled, and the control becomes complicated. Therefore, it is desired to take some measure to eliminate these problems. In particular, as a power steering device (power steering) provided with the above-described steering assisting force generating means, there are conventionally various configurations, and among them, an electric type using an electric motor as the steering assisting force generating means is known. Is desired from the viewpoint of the structure of the steering device and that it can be driven promptly only when necessary. For example, a device having a structure as disclosed in JP-A-61-26362 has been proposed. It is desired that such an electric power steering device be provided with the above-described steering force transmission ratio variable mechanism in parallel, but there is no device employing such a configuration. In addition, when the above-described conventional devices are simply combined, two mechanisms, a power assist mechanism and a variable transmission ratio mechanism, are provided in parallel, and two motors serving as driving sources are required. Inevitably, the problem of complicating the control and the like is unavoidable. In view of such a point, there is a demand for a new electric power steering apparatus capable of eliminating the above-mentioned problems.

[0005]

In order to meet such a demand, an electric power steering apparatus according to the present invention is provided with a part of a steering gear mechanism for transmitting a steering force from a steering wheel to a steered wheel side. A variable transmission ratio mechanism for changing the steering angle on the steering wheel side with respect to the steering wheel steering angle, and a power assist mechanism for transmitting the rotational driving force from the electric motor to a part of the steering gear mechanism. The drive is selectively controlled by two electric motors according to the vehicle speed.

[0006]

According to the present invention, when the vehicle is stopped or running at a low speed, the steering assist function by the electric power assist mechanism is exhibited, so that the steering can be performed with a light and appropriate steering force, and at the time of running at a high speed. The power assist mechanism is stopped and the transmission ratio by the variable steering force transmission ratio mechanism is controlled to the required state, so that the steering angle of the steered wheels can be maintained properly and running stability can be exhibited. The steering feeling from the turning to the high-speed running state is optimized, and thereby the dynamic characteristics of the vehicle can be improved.

[0007]

1 to 3 show an embodiment of an electric power steering apparatus according to the present invention.
The schematic configuration of an electric power steering apparatus generally denoted by reference numeral 1 will be briefly described with reference to FIG. 1. Reference numeral 2 denotes an input shaft connected to a steering handle (not shown); An output shaft 4 connected via a planetary gear mechanism 10 as a variable ratio mechanism is integrally connected to the output shaft 3 by press fitting or the like, and a pinion shaft as a steering shaft constituting a steering gear mechanism 5. A rack that has rack teeth 6a meshing with the pinion 4a of the pinion shaft 4 and constitutes a part of the steering link mechanism. The well-known rack and pinion type steering gear mechanism 5 is formed by the pinion shaft 4 and the rack 6. Be composed. Here, details of such a steering gear mechanism 5 are well known, and a specific description thereof will be omitted. Also, 7,
7, 7 are bearings for rotatably supporting the output shaft 3 and the pinion shaft 4 in the steering body 8. It is needless to say 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 a steering force from the steering wheel to the steered wheels (not shown). The sun gear 11 has a drive gear provided on the input shaft 2. It is provided on a drive shaft 15 having a transmission gear 14 meshing with the side gear 13. Reference numeral 16 denotes one or a plurality of planetary gears arranged around the sun gear 11 in a state meshed with the sun gear 11, and 17 denotes an outer ring gear arranged around the sun gear 11 and having an internal tooth portion 17 a meshed with the planetary gear 16. On the outer peripheral portion of the outer ring gear 17, a worm gear 1 serving as a rotation transmitting unit for an electric motor 20 described later is provided.
The external gear portion 17b meshing with the gear 8 is formed to be a worm wheel, whereby the rotation can be transmitted from the motor side, and the rotation cannot be transmitted from the planetary gear mechanism 10 side. Transmission gear mechanism 21
Is configured. In the drawing, reference numeral 19 denotes a rotation transmitting disk provided on the output shaft 3 side, and a support shaft 16a of the planetary gear 16 is connected to an eccentric position thereof. Note that members such as the outer ring gear 17 and the like that constitute these planetary gear mechanisms 10 include:
Needless to say, it is disposed so as to be rotatable by a bearing or the like at an appropriate position. According to such a configuration, the steering force accompanying the steering operation with the steering wheel is transmitted from the input shaft 2 to the drive shaft 15 side, and the sun gear 11, the planetary gear 16 of the planetary gear mechanism 10, and the support shaft thereof. 1
The power is transmitted to the rotation transmitting disk 19 via 6a, and is transmitted to the output shaft 3 and the pinion shaft 4 integrally connected to the output shaft 3 with a required transmission ratio by the planetary gear mechanism 10. Then, by transmitting the rotation of the pinion shaft 4 to the rack 6 side, required turning control is performed on unillustrated steered wheels.

Reference numerals 22 and 23 are first and second attached to the input shaft 2 on the steering wheel side and the output shaft 3 on the steered wheel side in the variable steering force transmission ratio mechanism having the above-described configuration. The two steering angle sensors 2
By constantly comparing the outputs from the steering wheels 2 and 23 during steering, it is detected whether the steering request on the steering wheel side and the turning state on the steered wheels are in agreement. Then, in this case, these two sensors 22, 23
When there is a difference in the output from the motor, the motor 20 is driven and its rotational force is transmitted to the outer ring gear 17,
The planetary gear mechanism 10 is used to perform a control operation for eliminating a shift between the input and output shafts 2 and 3. Reference numeral 24 denotes a torque sensor for detecting a steering request transmitted from the steering wheel side by detecting a rotational displacement of the output shaft 3 forming a part of the steering shaft in the steering body 8, and in this embodiment, For example, a case where a magnetostrictive rotation detector as disclosed in Japanese Patent Application Laid-Open No. 2-281115 is used. That is, a strain detecting layer made of a soft magnetic material having a high magnetic permeability is provided on the output shaft 3, and a detecting coil for detecting a change in magnetic permeability due to the strain of the strain detecting layer is provided on the body 8 side so as to surround the periphery. The configuration is Then, an output obtained by the detection coil is sent to a detection circuit 25, and a detection signal is sent to a signal controller 26 for controlling an electric control system described later. The signal from the first and second steering angle sensors 22 and 23 is also sent to the signal controller 26, and information from the vehicle speed sensor 27 is also input.
Here, in the drawing, reference numeral 28 denotes a power controller connected to the signal controller 27, and 29 denotes a battery, which is provided by the electric system control means constituted by these components and interposed in the electric motor 20 and the rotation transmission system described later. The on / off control of the electromagnetic clutches 31 and 32 is performed.

Reference numeral 30 denotes a power assist mechanism for transmitting the rotational driving force of the electric motor 20 to the pinion shaft 4 serving as 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, the planetary gear mechanism is driven from the steering handle side by driving the electric motor 20 to transmit the rotational driving force to the pinion shaft 4 via the transmission system including the small gear 35 and the large gear 36. The steering force transmitted through the steering wheel 10 is to be power-assisted, whereby the steering operation force of the driver can be reduced. Reference numeral 37 denotes a second motor output shaft which is connected to the other end of the motor shaft 33 of the electric motor 20 by press-fitting or the like. A bevel gear 38 is provided which meshes with a bevel gear 39 provided at an end of the worm gear 18 arranged orthogonally.
The bevel gears 38 and 39 are configured to transmit rotation from the motor shaft 33 to the planetary gear mechanism 10. Note that FIG. 2 is a schematic diagram viewed from the direction of arrow A in FIG.

According to the present invention, in the above-described electric power steering apparatus, a part of the steering gear mechanism 5 (on, output shafts 2, 3) for transmitting the steering force from the steering wheel to the steered wheels. The planetary gear mechanism 10 as a transmission ratio variable mechanism that changes the steering angle on the steered wheel side with respect to the steering wheel steering angle, and the rotational driving force from the electric motor 20 is applied to the steering gear mechanism 5. One electric motor 20 selectively drives and controls the power assist mechanism 30 transmitting to a part (the end of the pinion shaft 4 on the opposite side to the output shaft 3 side in this embodiment) according to the vehicle speed. It has a feature in the configuration. That is, in the present invention, the electric motor 20 described above is disposed in parallel with the steering body 8 constituting the steering gear mechanism 5, and one end of the motor shaft 33 of the electric motor 20 is
A transmission gear mechanism including a first electromagnetic clutch 31, a small gear 35 and a large gear 36 of a first motor output shaft 34 is connected to a pinion shaft 4 as a steering shaft, and the other end of the motor shaft 33 is connected to a second shaft. Electromagnetic clutch 32, second
The variable transmission ratio of the steering force is provided by the worm gear 18 having the bevel gear 38 and the bevel gear 39 of the motor output shaft 37, and the outer ring gear 17 which meshes with the worm gear 18 and constitutes the worm wheel 21 having the reverse rotation preventing function. The transmission ratio in the planetary gear mechanism 10 is configured to be variable. The first and second electromagnetic clutches 31 and 32 have a conventionally well-known structure, and a description of a specific configuration and operation thereof will be omitted.

In such a configuration, the steering assist function of the electric power assist mechanism 30 is exerted when the vehicle is stationary and the vehicle is stationary or when the vehicle is traveling at a low speed.
The first electromagnetic clutch 31 is turned on and the motor 20 is driven to rotate in a required direction so that the steering can be performed with a light and appropriate steering force. At this time, the second electromagnetic clutch 32 constituting the motor transmission system to the planetary gear mechanism 10 is off and its rotation transmission is interrupted. On the other hand, during steering during high-speed running, the power assist mechanism 30
The first electromagnetic clutch 31 is turned off to stop its operation, and the second electromagnetic clutch 32 is turned on to connect the motor 20 so that the transmission ratio of the steering force transmission ratio variable mechanism is set to a required value. It is configured to be controllable to a state. 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
1. Based on the gear ratio of the planetary gear 16 and the outer ring gear 17,
By rotating the outer ring gear 17 in a required direction with a required number of rotations by the motor 20, the transmission ratio can be variably controlled with the characteristics shown in FIG. 3 from the relationship with the sun gear 11 and the planetary gear 16. Things. That is, the characteristic is such that the transmission ratio of the steering wheel steering angle to the steering wheel steering angle increases as the transmission ratio decreases during high-speed running and the vehicle speed increases, that is, the magnitude of the steering wheel steering angle for a constant steering wheel steering angle. The electric motor 20 is connected to the power controller 2 so that the electric motor 20 has such a characteristic that it becomes smaller as the vehicle speed increases.
8. It is better to control with the signal controller 26. According to such a configuration, when the electric power assist mechanism 30 is used in combination with the steering device having the planetary gear mechanism 10 as the variable steering force transmission ratio mechanism from the steering wheel to the steered wheels, The structure can be simplified and the steering feeling can be improved. Especially,
According to the present invention, the steering angle of the steering wheel and the steering wheel steering angle as described above are controlled to required states by changing the vehicle speed.
By operating the steering assist force to maintain the steering angle of the steered wheels appropriately, exhibiting running stability and optimizing the steering sensation from stationary to high-speed driving, and as a result, the dynamic characteristics of the vehicle Can be improved.

As described above, when the power assist mechanism 30 is operated by the electric motor 20 during low-speed running and the planetary gear mechanism 10 as a variable steering force transmission ratio mechanism during high-speed running, the two mechanisms 30, 10 are used. Is controlled in the following state in order to ensure the running stability and the like of the vehicle. That is, in the structure of the above-described embodiment, the vehicle speed signal is taken into the signal controller 26, and the transmission ratio of the steering force is variably controlled by the planetary gear mechanism 10 when the vehicle speed is equal to or higher than the predetermined vehicle speed.
The steering assist force is applied by the power assist mechanism 30. However, the switching operation between the two mechanisms 10 and 30 is limited when the steering angle of the steering wheel is in the neutral state, that is, when the vehicle is in the vicinity of the substantially straight traveling state. It is necessary to perform the operation only within the range 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 as described above. It is. In addition, when steering is performed during low-speed traveling and the vehicle is in a high-speed state with power assist still operating, even if the steering angle of the steering wheel is in the neutral position (straight-forward state), a certain vehicle speed is maintained. It is necessary to perform control so as not to switch to the transmission ratio variable mechanism 10 unless the following occurs. That is, if the power assist is canceled in such a case, the steering force may suddenly increase,
It is not preferable from the viewpoint of running stability. By setting the switching control between the two mechanisms 10 and 30 in this way in consideration of the running conditions of the vehicle and the running stability, etc.,
This prevents sudden changes in the characteristics of the vehicle and allows the vehicle to exhibit its performance as a steering device. Here, the electromagnetic clutches 31 and 32 for transmitting the rotation from the electric motor 20 by the DC motor to any one of the mechanisms 10 and 30 are always in an off state to interrupt the rotation transmission, and as necessary, The steering system is naturally turned into a manual steering state via the planetary gear mechanism 10 even if both are turned off due to a failure in the electric system or the like. 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, and the like of each part of the electric power steering device 1 can be freely modified and changed as necessary, and various modifications are possible. An example could be considered. For example, in the embodiment described above,
As a mechanism for connecting the steering handle to the steering gear mechanism 5 side so that the transmission ratio of the steering force can be changed, a sun gear 11 is provided on the handle side, and a rotation transmitting disc is provided on the output shaft 3 side integral with the pinion shaft 4 serving as a steering shaft. The case where the planetary gear 16 is connected via the transmission 19 and the outer ring gear 17 is connected to the transmission gear mechanism 21 having a reverse rotation preventing function by the worm gear on the motor 20 side has been described, but the present invention is not limited to this. As shown in FIG.
7 is connected to the output shaft 3 side, and the planetary gear 1
External teeth 19a meshing with the worm gear 18 are formed on the outer peripheral portion of the rotation transmitting disc 19 connected to the sixth side,
It will be easily understood that the same effects as those of the above-described embodiment can be obtained even if the disk 19 is used as a worm wheel. In short, any configuration may be used as long as the transmission ratio can be variably controlled by rotation control from the motor side when transmitting the steering force from the input shaft 2 to the output shaft 3 side.

In the above-described embodiment, the planetary gear mechanism 10 exemplified as the steering force transmission ratio variable mechanism described above and the motor 20 are replaced by a transmission gear mechanism 21 having a reverse rotation preventing function capable of rotating only from the motor side. Although the worm gear mechanism has been described as an example, the present invention is not limited to this, and it is apparent that a gear mechanism using a hypoid gear or the like may be used. Further, the gear mechanism for transmitting the steering assist force constituting the power assist mechanism 30 from the motor 20 is not limited to the transmission gear mechanism using the small gear 35 and the large gear 36 by the helical gear, but includes a hypoid gear and a spur gear. A gear mechanism including an off-axis gear such as a helical gear, a planetary gear, a bevel gear, or the like may be used, and various modifications may be considered. Further, in the structure of the above-described embodiment, the direct take-out type magnetostrictive rotation detector is illustrated as the torque sensor 24 for detecting the steering direction, the steering speed, the steering force, and the like with the steering handle on the steering shaft side. The present invention is not limited to this. For example, a detection mechanism that connects the two shafts with a torsion bar and detects the above-described steering request based on the relative rotational displacement may be used.

[0016]

As described above, according to the electric power steering apparatus of the present invention, the transmission which is interposed in a part of the steering gear mechanism and changes the steering angle on the steered wheels with respect to the steering wheel angle. Since the ratio variable 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 selectively controlled by one electric motor according to the vehicle speed, it is simple. Despite the simple configuration, with the minimum number of components required, the steering assist function by the electric power assist mechanism is exhibited during stationary stop and steering during low-speed driving, and light and appropriate steering Not only can steering by force be possible, but also during high-speed driving, the power assist mechanism is stopped,
By controlling the transmission ratio by the variable steering force transmission ratio mechanism to the required state, the steering angle of the steered wheels can be maintained properly, and running stability can be exhibited. There are various excellent effects such that the dynamic characteristics can be improved by optimizing the dynamic characteristics of the vehicle. In particular, according to the present invention, it is necessary to use one DC motor, leave the electromagnetic clutch in the off state at all times, and turn on one of the clutches as needed to perform variable control of the power assist or the steering force transmission ratio. In this state, the desired function can be exhibited while simplifying the arrangement state and the assembly structure of each part, and the advantage is large.

[Brief description of the drawings]

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

FIG. 2 is a schematic enlarged view showing 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, as viewed in the direction of arrow A in FIG. It is.

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

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

[Explanation of symbols]

 Reference Signs List 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 (steering force transmission ratio variable mechanism) 11 sun gear 13 drive side gear 14 transmission Gear 15 Drive shaft 16 Planetary gear 16a Support shaft 17 Outer ring gear (weam wheel) 17a Internal gear 17b External gear 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

Continuation of front page (56) References JP-A-62-31559 (JP, A) JP-A-58-224852 (JP, A) JP-A-62-247973 (JP, A) JP-A-1-204864 (JP) JP-A-64-32969 (JP, A) JP-A-62-46774 (JP, A) JP-A-62-178474 (JP, A) JP-A-1-309873 (JP, A) (58) Surveyed field (Int.Cl. ⁶ , DB name) B62D ^6/ 00-6/02 B62D 5/04

Claims (1)

(57) [Claims] 1. A variable transmission ratio mechanism interposed in a part of a steering gear mechanism for transmitting a steering force from a steering wheel to a steered wheel side and changing a steering angle on the steered wheel side with respect to a steering wheel angle. A power assist mechanism for transmitting a rotational driving force from an electric motor to a part of the steering gear mechanism. 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 apparatus characterized in that it is configured to perform drive control in a dynamic manner.