JP2006264622A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To arrange an electric motor without impairing collision safety, concerning a power steering device preferably used for a vehicle such as a heavy-duty truck or a bus. <P>SOLUTION: The power steering device comprises a steering column 2 having a steering shaft 2a transmitting rotation torque of a steering wheel 1, a steering gear box 3 disposed outside of an occupant space 14 and transmitting the rotation torque to steering wheels, an assist motor 17 provided outside of the occupant space 14 and above the steering gear box, and a hydraulic power steering mechanism 15 adding assist torque by oil pressure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power steering apparatus suitable for use in vehicles such as large trucks and buses.

Conventionally, a rigid suspension has been widely used in a so-called cabover type vehicle in which a driver's seat is disposed in front of an axle of a front wheel, such as a truck or a bus. Further, in a vehicle having such a rigid suspension, a ball nut type hydraulic power steering mechanism is widely applied as a steering device (steering device).
FIG. 5 is a diagram showing such a power steering mechanism, which includes a steering wheel 101, a steering column 102, a steering gear box 103, a pitman arm 104, and the like.

  The steering wheel 101 is connected to a steering gear box 103 via a steering shaft 102 a provided in the steering column 102, and a pitman arm 104 is connected to the steering gear box 103. Although not shown in detail, the steering gear box 103 is configured as a so-called ball nut type gear box that transmits the rotation of the steering shaft 102a to the pitman arm 104 via a steel ball (recirculating ball). Yes.

The steering gear box 103 is supplied with high-pressure hydraulic oil from a hydraulic source (not shown), and steering is assisted by the action of the high-pressure hydraulic oil during steering.
The pitman arm 104 is connected to the right front wheel 109 via the drag link 105 and the knuckle arm 106, and the right front wheel 109 is connected to the left front wheel 110 via the tie rod 107 and the tie rod arm 108.

  With such a configuration, when the steering wheel 101 is rotated, steering torque is transmitted to the steering gear box 103 via the steering shaft 102a, and assist torque is applied by hydraulic pressure. The pitman arm 104 is driven to swing by the total torque together with the torque. The drag link 105 is driven in the front-rear direction by the swinging motion of the pitman arm 104 to drive the knuckle arm 106, the tie rod 107, and the tie rod arm 108, and the left and right front wheels 109, 110 are steered. .

  By the way, in recent years, an image in front of the vehicle is acquired by a camera attached to the vehicle, and the vehicle lateral position (lateral deviation amount with respect to the center of the lane) is calculated from the result of image processing such as road lane recognition. A lane keeping assist device (lane keep assist system) that assists steering to maintain the lane so as to reduce the lane has been researched and developed, and has already been put into practical use in some passenger cars.

  On the other hand, an independent suspension type suspension device is generally adopted as a suspension in a passenger car, and a rack and pinion type steering mechanism is widely applied as a steering device for a vehicle having such an independent suspension type suspension device. . In general, such a rack and pinion type steering mechanism is also provided with a power steering device for assisting steering.

In a vehicle to which a hydraulic power steering mechanism is applied as such a power steering device, an electric motor (or an assist motor) is newly provided in the steering column when the lane keeping assist device is mounted, and the assist motor is operated. By doing so, steering assist is executed so as not to deviate from the lane (see, for example, Patent Document 1).
In addition, when an electric motor type power steering mechanism is employed as a power steering device of a rack and pinion type steering mechanism, a function as an assist motor is also provided for the electric motor for power steering when the lane keeping assist device is installed. I also use it.

  The reason why the electric motor is used for the steering control by the lane keeping assist device is that the structure for adjusting the assist torque is relatively simple, and the hydraulic power steering mechanism is applied as a steering actuator. This is because the structure becomes inevitable. This is because, in the hydraulic power steering mechanism, the assist force is adjusted by the hydraulic valve opening, but the hydraulic valve opening is determined by the relative angle between the steering wheel angle and the actual steering angle, so the assist torque is simply set. Because it cannot be adjusted.

In addition, in such an electric power steering mechanism for a passenger car, not only the lane keeping support function as described above but also a steering wheel return that actively performs steering wheel return using the high controllability by the electric motor. Improvement control, constant neutral position control that always maintains the steering neutral position, and fuel saving control that improves power consumption by stopping power supply when steering assist is unnecessary are applied.
JP 2002-29437 A

By the way, such a lane keeping support device is expected to be applied to a large truck that has many opportunities to travel a long distance at a high speed.
However, some small trucks and large buses that use independent suspensions use rack and pinion type steering mechanisms similar to passenger cars, but independent suspensions have an allowable axial load, component weight, There are very few examples that are adopted for large trucks from the standpoint of securing a small turning property, and a rigid suspension is usually used. Therefore, as the steering device, a ball nut type steering mechanism using a link mechanism such as the pitman arm 104 or the drag link as described above is applied.

As a power steering mechanism, a large truck requires a large steering assist torque. Therefore, an electric motor type power steering mechanism is not employed at all, and a hydraulic power steering mechanism is usually employed.
Therefore, in view of such technical background, in order to implement lane keeping support control by providing a lane keeping assist device in a vehicle such as a heavy truck, a new assist motor is added to the ball nut type hydraulic power steering mechanism. Is realistic. In this case, as shown in FIG. 6, it is conceivable to mount the assist motor 111 on the steering column 102, but when the assist motor 111 is simply mounted on the steering column 102, it is greatly increased toward the interior of the motor 111 (inside the cab). There is a problem that it is not preferable in view of collision safety.

  Although it is conceivable to provide a motor below the cab, if the motor is simply moved downward, the mounting position of the pitman arm 104 will also move downward. . In this case, the link mechanism may interfere with the steered wheels, and in the case of a rigid suspension vehicle, a deviation occurs in the center of instantaneous rotation between the steering link and the suspension. There is also a problem that it is not preferable from the aspect of securing the steering stability.

  The present invention has been devised in view of such problems, and is a power steering system in which an electric motor is disposed without impairing collision safety for a cabover type vehicle having a hydraulic power steering mechanism, particularly a large truck. An object is to provide an apparatus.

  For this reason, the power steering device of the present invention is disposed outside the occupant space and a steering column having a steering shaft that transmits the rotational torque of a steering wheel disposed inside the occupant space of the vehicle to the outside of the occupant space. A steering gear box that transmits the rotational torque to the steering wheel of the vehicle via a link mechanism, and is provided outside the passenger space and above the steering gear box, and is transmitted from the steering shaft. An assist motor that applies assist torque to the rotational torque that is applied, and a hydraulic power steering mechanism that applies assist torque by hydraulic pressure to the rotational torque transmitted from the steering shaft are provided.

The total value of the maximum assist torque of the assist motor and the maximum assist torque of the hydraulic power steering mechanism is set so as to substantially match the maximum value of the assist torque required for the vehicle. (Claim 2).
Further, when the steering wheel is steered to a predetermined angle, the application of the assist torque by the assist motor is stopped (claim 3).

When the vehicle is traveling in a high speed range, the application of the assist torque by the hydraulic power steering mechanism is stopped (Claim 4).
Further, the assist motor is arranged in the vicinity of the steering gear box (Claim 5).
Further, the assist motor and the steering gear box are assembled (claim 6).

Further, the vehicle is a cab-over type vehicle in which a driver's seat is provided in front of the steering wheel, and the vehicle includes a rigid suspension (claim 7).
The link mechanism includes a pitman arm that has a base end connected to the steering gear box and can swing around the base end, one end connected to the pitman arm, and the other end to the left and right steering of the vehicle. A drag link connected to one of the knuckle arms of the wheel and a tie rod connecting the left and right steered wheels are provided (claim 8).

  According to the power steering apparatus of the present invention, since the assist motor is not installed in the passenger space, the space for the driver's seat can be secured and sufficient collision safety can be secured. The assist motor generates heat due to internal resistance, but the influence on the passenger due to the generated heat can be reduced. Further, since the steering is assisted by the two mechanisms of the hydraulic power steering mechanism and the assist motor, even if one of the mechanisms breaks down, the other mechanism operates, so that the safety can be improved (claims). Item 1).

  Further, the maximum assist torque of the hydraulic power steering mechanism can be reduced as compared with the case where no assist motor is provided, and thus the hydraulic power steering mechanism can be reduced in size. Thus, even if an additional assist motor is provided, it is possible to avoid a situation in which the entire system including the hydraulic power steering mechanism and the assist motor is increased in size (claim 2).

Since excessive input does not act on the links and arms of the steering mechanism at the time of stationary, the links and arms can be reliably protected. Moreover, such an effect can be obtained with a simple and inexpensive configuration.
Further, when the vehicle is traveling in a high speed range, the required steering assist torque is small, so that the application of assist torque by the hydraulic power steering mechanism can be stopped to improve fuel efficiency. .

By arranging the assist motor and the steering gear box close to each other and assembling (integrating) the assist motor and the steering gear box, it is possible to reduce the size and improve the assembling property. 5, 6).
In addition, the lane keeping assist device can be easily applied to a cab-over type vehicle having a rigid suspension.

  In addition, the lane keeping assist device can be easily applied to a vehicle having a steering mechanism including a steering gear box, a pitman arm, a drag link, a tie rod, and the like.

Hereinafter, a power steering apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIGS. FIG. 4 is a schematic cross-sectional view showing the configuration of the main part, and FIG. 4 is a diagram for explaining the operation.
First, a vehicle to which the present invention is applied will be described. In this embodiment, a cab-over type vehicle in which a driver's seat is provided in front of front wheels (steering wheels) 9 and 10 (see FIG. 2) is applied. ing. Specific examples of such cab-over vehicles include trucks and buses.

Further, this vehicle includes a rigid suspension 12 as shown in FIG. 2 and is attached to the vehicle body via a leaf spring (not shown). 2 indicates a vehicle cab (cabin, ie, passenger space) 14.
Next, a vehicle steering device (steering device) will be described. As shown in FIGS. 1 and 2, a steering device to which the present embodiment is applied includes a steering wheel 1, a steering column 2 having a steering shaft 2a, and a steering. A gear box 3, a pitman arm 4, a motor (assist motor) 17 and the like are provided.

  The steering wheel 1 is connected to a steering gear box 3 via a steering shaft 2a, and a pitman arm 4 is connected to the steering gear box 3. Further, the steering gear box 3 is configured as a so-called ball nut type gear box that decelerates and outputs the rotation angle of the steering shaft 2a via a recirculating ball.

  As shown in FIG. 2, the steering gear box 3 is connected to the steering wheels 9 and 10 via the link mechanism 13. The link mechanism 13 has a pitman arm 4 whose base end is connected to the steering gear box 3 and can swing around the base end, one end is connected to the pitman arm 4 and the other end is a right steering wheel ( The drag link 5 is connected to the knuckle arm 6 of the right front wheel 9, and the tie rod 7 is connected to the left and right steering wheels 9 and 10 via the tie rod arm 8.

  Therefore, when the steering wheel 1 is rotated, this rotational torque (steering torque) is transmitted to the steering shaft 2a and the steering gear box 3, and the pitman arm 4 is driven to swing. The drag link 5 is driven in the front-rear direction by the swinging motion of the pitman arm 4 so that the knuckle arm 6 is swing-driven, and the left and right front wheels 9, 10 are steered.

  The steering column 2 is provided with an assist motor 17. Here, in the present embodiment, the assist motor 17 is a lane keeping assist device (lane keep assist system) described in the background section above or a steering actuator provided for application to automatic steering. The operation is controlled based on a control signal from the control means that does not. Various known techniques can be applied to the lane keeping assist device, and detailed description thereof is omitted here.

The assist motor 17 has an output shaft (not shown) connected to the steering shaft 2a, and a steering torque (assist torque) is applied to the steering wheel 1 by the drive torque generated by the assist motor 17. ing.
In the present embodiment, the assist motor 17 does not operate as a steering actuator only when the above-described lane keeping assist device is operated. During normal steering, the assist motor 17 and a hydraulic power steering mechanism 15 described later according to the driving situation. The steering assist is performed in cooperation.

  The steering device is also provided with a hydraulic power steering mechanism 15 that applies assist torque to the steering torque transmitted from the steering shaft 2a. Here, the hydraulic power steering mechanism 15 is configured to assist the driver's steering by supplying hydraulic oil pressurized by the hydraulic pump 16 to the steering gear box 3.

  Next, the main part of this apparatus will be described. As shown in FIGS. 1 and 2, the motor 17 described above is provided above the steering gear box 3 and below the cab 14. In particular, in the present embodiment, the motor 17 and the steering gear box 3 are disposed close to each other. Therefore, as shown in FIG. 3, the motor 17 and the steering gear box 3 are assembled (integrated). Has been configured.

Further, by arranging the motor 17 below the cab 14 in this way, it is possible to avoid a situation in which the motor 17 enters the driver's seat at the time of a vehicle collision, and to protect passengers at the time of the collision. Will be able to.
If the assist motor 17 is simply arranged to be integrated with the steering gear box 3 below the cab 14, the mounting position of the steering gear box 3 is moved downward by the amount of the assist motor 17, and pitman. Since the rotation center of the arm is lowered, the steering structure is likely to interfere with the link mechanism 13.

  Therefore, in the present embodiment, the assist motor 17 is arranged below the cab 14 while minimizing the amount of change in the position of the gear box 3 as follows. In other words, when only the hydraulic power steering mechanism 15 is provided without providing the assist motor 17, the maximum assist torque required for the hydraulic power steering mechanism 15 (that is, the maximum assist torque required for the vehicle) is T. The total value (T1 + T2) of the maximum drive torque (maximum assist torque) T1 of the motor 17 and the maximum assist torque T2 of the power steering mechanism 15 applied in the present embodiment is the maximum assist torque T required for the vehicle. It is set so as to substantially match.

As a result, the hydraulic pump 16 and the steering gear box 3 of the power steering mechanism 15 can be made smaller than the conventional one, and the motor 17 is disposed in the space obtained by this miniaturization, whereby the gear box 3 Thus, the motor 17 can be disposed below the cab 14 while minimizing the amount of change in the position.
By the way, large trucks mainly driven by long distances have a high ratio of traveling on highways, and the frequency of using the maximum assist torque region of power steering is low. Therefore, in the present embodiment, the hydraulic power steering mechanism 15 is stopped in the region where the required assist torque is low, and the steering is assisted only by the operation of the motor 17. Output can be reduced. Further, when a large assist torque is required, sufficient assist torque can be obtained by operating the hydraulic power steering mechanism 15 in addition to the assist motor 17.

Further, in the present embodiment, when the steering wheel 1 is steered to a predetermined angle, the assist motor 17 is turned off and the application of the assist torque is interrupted. This is because an excessive load is not applied to the link mechanism 13 when the steered wheels 9 and 10 are steered to the maximum steering angle (at the time of stationary or full steering). This is for protection.
That is, when the steering wheel is fully turned, a regulating member such as a stopper is normally brought into contact with the link mechanism 13 and the steering angle is restricted. However, when the driver further inputs steering torque during such full turning, In the hydraulic power steering mechanism 15 using a torsion bar as will be described later, steering assist torque is generated, and an excessive input acts on the link mechanism 13.

  On the other hand, in this embodiment, for example, when it is determined that the steering angle is a predetermined steering angle before the full turning based on information from the steering angle sensor, the motor 17 is turned off. This makes the driver feel heavier in steering. Therefore, since the driver can recognize that the steering angle is a predetermined steering angle before full steering, it can be expected to suppress unnecessary steering input during full steering, and even if full steering, Since the application of the assist torque by the assist motor 17 is interrupted, the torque acting on the link mechanism 13 is reduced, and the link mechanism 13 can be protected.

FIG. 3 is a sectional view of the steering gear box 3 in which the power steering mechanism 15 and the assist motor 17 are integrated. The steering shaft 2a is connected to the input shaft 31 on the left side in the drawing. .
A stub shaft (worm shaft) 32 is provided in the housing 36, and a nut 33 is connected to the outer periphery of the stub shaft 32 via a steel ball (recirculating ball) 34.

A gear 33 a is formed on the outer periphery of the nut 33, and a sector gear 37 formed on the upper end portion of the pitman arm 4 is engaged with the gear 33 a of the nut 33.
Further, a torsion bar 35 is provided coaxially with the stub shaft 32 in the stub shaft 32, and the torsion bar 35 and the stub shaft 32 are at the lower end (the right end in the figure) by serrations not shown. It is connected. The upper end of the torsion bar 35 is connected to the input shaft 31.

On the other hand, the housing 36 is formed with an inlet port 38 that is connected to the hydraulic pump 16 and is supplied with high-pressure hydraulic oil, and an outlet port 39 that is connected to an oil tank (not shown) and discharges the hydraulic oil. The space in the housing 36 is divided into a first hydraulic chamber 40 and a second hydraulic chamber 41 by the nut 33.
Further, a rotary valve 42 is provided in the vicinity of the upper end of the torsion bar 35 so that the inlet port 38 and the outlet port 39 are communicated with or blocked from the first hydraulic chamber 40 or the second hydraulic chamber 41.

  Therefore, when a steering torque is input to the input shaft 31, this torque is transmitted to the stub shaft 32 via the torsion bar 35, but the stub shaft 35 receives the road surface resistance of the steered wheels 9 and 10, thereby preventing rotation. Thus, the torsion bar 35 is twisted by this amount. When the torsion bar 35 is twisted in this way, the inlet port 38 is connected to one of the first and second hydraulic chambers 40 and 41 according to the amount of twist, and the outlet port 39 is connected to the first and second hydraulic chambers 40 and 41. Connected to the other one of the second hydraulic chambers 41 and 40, the high-pressure hydraulic oil is supplied to the one hydraulic chamber and the hydraulic oil in the other hydraulic chamber is drained. In this case, the side surface of the nut 33 facing the hydraulic chamber communicating with the inlet port 38 is pressed by the hydraulic pressure to assist the steering input.

  The assist motor 17 is provided close to the steering gear box 3 so that its output shaft (not shown) is parallel to the input shaft 31 described above. As shown in the figure, the assist motor 17 is provided with an electromagnetic clutch mechanism 51 for connecting / disconnecting an assist torque, a torque transmission mechanism 52 including a pulley and a belt (not shown), and the like. The drive torque of the motor 17 is transmitted to the input shaft 31 via the torque transmission mechanism 52.

Since the power steering apparatus according to one embodiment of the present invention is configured as described above, its operation will be described as follows.
When the lane keeping assist device (not shown) is operated, an image ahead of the vehicle is acquired by a camera attached to the vehicle, and a lateral deviation amount with respect to the center of the traveling lane is calculated from a result of image processing such as road lane recognition. Then, a control signal is output from the controller to the assist motor 17 so that the lateral deviation amount is reduced, whereby steering torque is applied to the steered wheels 9 and 10 to prevent lane departure of the vehicle (lane keeping). Is supported.

  Further, when such a lane keeping assist device is not operated, steering assist is executed in cooperation with the hydraulic power steering mechanism 15 according to the driving situation. More specifically, FIG. 4 is a diagram showing the characteristics of the output torque with respect to the steering input torque, and the line a represents the characteristics of the steering torque when neither the hydraulic power steering mechanism nor the assist motor is provided. Line b is a characteristic of assist torque of the hydraulic power steering mechanism (that is, a torque characteristic when a conventional hydraulic power steering mechanism is used) when only the hydraulic power steering mechanism is provided without providing the assist motor 17. (Assist torque characteristic originally required for the vehicle), line c is the torque characteristic of the assist motor 17, line d is the torque characteristic of the power steering mechanism 15 applied in this embodiment, and line e is the torque of the assist motor 17. And the total torque of the power steering mechanism 15 applied in this embodiment. Each shows.

  As shown in FIG. 4, the assist motor 17 has a smaller output than the hydraulic power steering mechanism 15, but in a high-speed traveling region (for example, 65 km / h or more), the steering wheel steering region is small (for example, ± 15 °). ) Since a large steering torque is not required, only the assist motor 17 is operated and the operation of the hydraulic power steering mechanism 15 is stopped during such high speed traveling. In this case, for example, the hydraulic pump 16 is turned off and control is performed so that no hydraulic pressure is generated.

  Further, the assist motor 17 and the hydraulic power steering mechanism 15 cooperate in a medium speed range (for example, 25 to 65 km / h) or a low speed range (for example, 25 km / h or less) where a larger steering torque is required than in the high speed range. As a result, even if the power steering mechanism 15 having a lower output than the conventional one is mounted, an assist torque equivalent to or higher than that of the conventional hydraulic power steering mechanism indicated by the line b can be obtained (see the line e).

  As described above in detail, the power steering apparatus according to this embodiment has the following advantages. That is, according to the power steering apparatus, since the assist motor 17 is not installed in the cab (occupant space) 14, the space for the driver's seat can be secured, and sufficient collision safety can be secured. Moreover, although the assist motor 17 may generate heat due to internal resistance, the influence on the passenger due to the generated heat can be reduced. Further, since the steering is assisted by the two mechanisms of the hydraulic power steering mechanism 15 and the assist motor 17, even if one of them breaks down, the other mechanism operates so that a highly safe system can be constructed.

  Further, since the maximum assist torque of the hydraulic power steering mechanism 15 can be reduced as compared with the case where the assist motor 17 is not provided, the hydraulic power steering mechanism 15 can be reduced in size. As a result, even if the assist motor 17 is additionally provided, it is possible to avoid an increase in the size of the entire system including the hydraulic power steering mechanism 15 and the assist motor 17 and to minimize the downward movement amount of the pitman arm rotation center position. The motor 17 can be arranged outside the cab (occupant space) 14 while limiting to the limit.

  Moreover, since an excessive input does not act on the link mechanism 13 during full turning, the link mechanism 13 can be reliably protected. Moreover, there exists an advantage which can obtain such an effect with a simple and cheap structure. Further, when the vehicle is traveling in a high speed range, the required steering assist torque is small, so that the application of assist torque by the hydraulic power steering mechanism 15 can be stopped to improve fuel efficiency.

Furthermore, the assist motor 17 and the steering gear box 3 can be arranged close to each other, and the assist motor 17 and the steering gear box 5 can be assembled (integrated) to reduce the size and to be assembled. It is possible to improve the performance.
Further, there is an advantage that the lane keeping assist device can be easily applied to a cab-over type vehicle having the rigid suspension 12. Further, there is an advantage that the lane keeping assist device can be easily applied to a vehicle having the link mechanism 13 including the steering gear box 3, the pitman arm 4, the drag link 5, the tie rod 7, and the like.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, a rack and pinion type gear box may be applied to the steering gear box, or it may be applied to vehicles other than the cab-over type. Further, the present invention may be applied to a vehicle having an independent suspension type suspension.

1 is a schematic diagram showing a structure of a vehicle steering system to which a power steering device according to an embodiment of the present invention is applied. 1 is a schematic diagram showing a structure of a vehicle steering system to which a power steering device according to an embodiment of the present invention is applied. It is typical sectional drawing which shows the principal part of the power steering apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the effect | action of the power steering apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the prior art. It is a schematic diagram which shows the structure of the power steering apparatus devised in the creation process of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering column 2a Steering shaft 3 Steering gear box 4 Pitman arm 5 Drag link 6 Knuckle arm 7 Tie rod 8 Tie rod arm 9 Steering wheel (right front wheel)
10 Steering wheel (front left wheel)
12 Rigid suspension 13 Link mechanism 14 Cab or cabin (occupant space)
15 Hydraulic power steering mechanism 17 Assist motor

Claims (8)

A steering column having a steering shaft for transmitting a rotational torque of a steering wheel disposed inside the passenger space of the vehicle to the outside of the passenger space;
A steering gear box that is disposed outside the passenger space and transmits the rotational torque to a steering wheel of the vehicle via a link mechanism;
An assist motor that is provided outside the occupant space and above the steering gear box and applies an assist torque to a rotational torque transmitted from the steering shaft;
A power steering apparatus comprising: a hydraulic power steering mechanism that applies assist torque to the rotational torque transmitted from the steering shaft by hydraulic pressure. The total value of the maximum assist torque of the assist motor and the maximum assist torque of the hydraulic power steering mechanism is set so as to substantially match the maximum value of the assist torque required for the vehicle. The power steering apparatus according to claim 1. 3. The power steering apparatus according to claim 1, wherein when the steering wheel is steered to a predetermined angle, application of the assist torque by the assist motor is stopped. The power steering apparatus according to any one of claims 1 to 3, wherein the application of the assist torque by the hydraulic power steering mechanism is stopped when the vehicle is traveling in a high speed range. The power steering device according to any one of claims 1 to 4, wherein the assist motor is disposed in the vicinity of the steering gear box. The power steering apparatus according to any one of claims 1 to 5, wherein the assist motor and the steering gear box are assembled. The vehicle according to any one of claims 1 to 6, wherein the vehicle is a cab-over type vehicle in which a driver's seat is provided in front of a steered wheel, and the vehicle includes a rigid suspension. Power steering device. The link mechanism includes a pitman arm that has a base end connected to the steering gear box and can swing around the base end, one end connected to the pitman arm, and the other end connected to left and right steering wheels of the vehicle. The power steering apparatus according to any one of claims 1 to 7, further comprising a drag link connected to any one of the knuckle arms and a tie rod connecting the left and right steering wheels.

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