JP4760015B2 - Vehicle steering system - Google Patents

Description

  The present invention belongs to the technical field of a vehicle steering apparatus including a variable steering angle mechanism and a power steering mechanism.

A conventional vehicle steering device includes a steering force sensor for measuring the steering force of a driver input to a steering wheel, and outputs the power steering mechanism in accordance with a traveling state such as the steering force, vehicle speed, and lateral acceleration. The assist torque is controlled (see, for example, Patent Document 1).
JP 2002-308132 A

  However, in the above prior art, since the steering force is estimated from the amount of twist of the steering shaft, if the design is made so that the steering force does not increase without losing the steering rigidity, it is necessary to detect a slight twist. There is. Therefore, there is a problem that high processing accuracy is required for the steering force sensor. Further, if the processing accuracy of the steering force sensor is poor, there is a problem that the relationship between the amount of twist and the force is not unique, and an appropriate assist torque cannot be output.

  The present invention has been made paying attention to the above-described problems, and the object of the present invention is to provide a vehicle steering apparatus that can increase steering rigidity and realize significant cost reduction by eliminating the need for a steering force sensor. It is to provide.

In order to achieve the above object, the present invention provides:
An angle addition type that is provided between the input shaft connected to the steering wheel and the output shaft connected to the steering mechanism, and adds the output of the angle assist motor to the rotation angle of the input shaft to vary the rotation angle of the output shaft. Variable steering angle mechanism of
A power steering mechanism that outputs an assist torque for reducing a steering burden on the driver with respect to the steering mechanism;
Motor current value detecting means for detecting a current value of the angle assist motor;
Motor rotation angle detection means for detecting the rotation angle of the angle assist motor;
Input shaft rotation angle detection means for detecting the rotation angle of the input shaft;
Output shaft rotation angle detection means for detecting the rotation angle of the output shaft;
Rotation angle of the front Symbol angle assist motor, on the basis of the input shaft rotational angle and the output shaft rotation angle, and a variable steering angle control means for driving and controlling the angle assist motor,
Current value of the angular assist motor, the rotation angle of the variable steering angle control unit before Symbol angle assist motor input to, on the basis of the input shaft rotational angle and the output shaft rotation angle, drivers input to the handle Steering force estimation means for estimating the steering force;
Power steering control means for driving and controlling the power steering mechanism based on the estimated steering force;
It is characterized by providing.

In the vehicle steering apparatus of the present invention, based on the current value of the angle assist motor, the rotation angle of the angle assist motor, the input shaft rotation angle, and the output shaft rotation angle that are directly proportional to the output torque of the angle assist motor. to estimate the steering force of the driver input to the steering wheel, and the current value of the angle assist motor, the contact and the rotation angle output shaft angles being measured for the actual variable steering angle control, precise steering force Can be estimated. Since the power steering mechanism is driven based on the estimated steering force, the assist torque can be determined based on the load applied to the angle assist motor and the friction torque generated in the steering system. Accordingly, a steering force sensor that is difficult to design and manufacture can be omitted, and it is not necessary to provide a twisted portion of the steering force sensor on the steering shaft, so that the steering rigidity can be increased and the cost can be significantly reduced.

  Hereinafter, the best mode for carrying out the vehicle steering system of the present invention will be described based on Examples 1 and 2.

First, the configuration will be described.
FIG. 1 is a block diagram illustrating the configuration of the vehicle steering apparatus according to the first embodiment.
A steering mechanism (not shown) for steering the steering wheel 1 and a front wheel (not shown) is connected via an input shaft 2 and an output shaft 3, and the input shaft 2 and the output shaft 3 are connected via a variable steering angle mechanism 4. It is connected. The input shaft 2 is provided with an input angle sensor 5 that detects the rotation angle of the input shaft 2. The output shaft 3 is provided with an output angle sensor 6 that detects the rotation angle of the output shaft 3 and an electric power steering device (power steering mechanism) 7.

  The variable rudder angle mechanism 4 adds the output of the angle assist motor 8 to the rotation angle of the input shaft 2 and adds or subtracts the rotation angle of the output shaft 3, thereby rotating the output shaft 3 relative to the rotation angle of the input shaft 2, That is, it is an angle addition type variable steering angle mechanism that varies a steering angle ratio that is a ratio of a steering angle of the front wheels to a steering angle of the steering wheel 1. The output of the angle assist motor 8 is controlled by the variable steering angle control device 9.

  The electric power steering device 7 is composed of, for example, an electric motor and a speed reducer, and outputs assist torque that reduces the steering burden on the driver to the output shaft 3. This assist torque is controlled by a power steering control device (power steering control means) 10.

The variable steering angle control device 9 includes an input angle detected by the input angle sensor 5 , an output angle detected by the output angle sensor 6, and an angle assist motor 8 detected by the motor encoder (motor rotation angle detection means) 11. And the vehicle speed detected by the vehicle speed sensor 12 are input.

  The variable rudder angle control device 9 calculates a current command value for obtaining a desired rudder angle ratio based on the detection value of each sensor, and drives and controls the angle assist motor 8. The steering angle ratio is, for example, large in the low vehicle speed range and small in the high vehicle speed range, thereby achieving both turning performance in the low vehicle speed range and running stability in the high vehicle speed range.

  Further, the variable steering angle control device 9 is based on the rotation angle of the angle assist motor 8 detected by the motor encoder 11 and the current value of the angle assist motor 8 detected by the current sensor (motor current value detection means) 13. The steering force of the driver input to the input shaft 2 is estimated and output to the electric power steering apparatus 10.

  The electric power steering control device 10 calculates a current command value based on the steering force estimated by the variable steering angle control device 9 and the vehicle speed detected by the vehicle speed sensor 12, and drives and controls the electric power steering device 7.

FIG. 2 is a configuration diagram of the variable steering angle mechanism 4 according to the first embodiment.
In the variable steering angle mechanism 4 of the first embodiment, two planetary mechanisms (planetary gear mechanisms) 15 and 16 as shown in FIG. 3 are arranged facing each other.

  As shown in FIG. 3, the input shaft 2 is connected to the planet carrier 15d of the planetary mechanism 15 on the input shaft 2 side, and the ring gear 15c is fixed to a housing not shown. The sun gears 15 a and 16 a of the two planetary mechanisms 15 and 16 are connected to each other, and the planet carrier 16 d of the planetary mechanism 16 on the output shaft 3 side is connected to the output shaft 3.

  A worm wheel 14 a is connected to the ring gear 16 c of the planetary mechanism 16, and the worm wheel 14 a meshes with a worm 14 b connected to a motor output shaft (not shown) of the angle assist motor 8. The output of the angle assist motor 8 is decelerated and output to the planetary mechanism 16 by the worm gear mechanism including the worm wheel 14a and the worm 14b.

Next, the operation will be described.
[Steering force estimation method]
In the planetary mechanism 15 (16) of the first embodiment, the following formula (1) is obtained for the sun gear 15a (16a), the pinion 15b (16b), and the ring gear 15c (16c) from the balance of forces as shown in FIG. ~ (4) holds.
T _s = F _ps × r _s (1)
_{T c = F sp × r s} + F rp × (r s +2 rp) ... (2)
T _p = F _sp × r _p = F _rp × r _p (3)
Tr = F _pr × (r _s + 2r _p ) (4)
However, the subscripts of each variable are as follows: s represents the sun gear 15a (16a), c represents the planet carrier 15d (16d), p represents the pinion 15b (16b), and r represents the ring gear 15c (16c). T represents torque, F represents force acting on the circumference, and r represents radius.

The following formula (5) is established by the formulas (1) to (3).
_{T c = T s × (2r} s + 2r p) / r s ... (5)
Further, the following formula (6) is established by the formulas (1), (2), and (4).
T _r = T _s × (r _s + 2r _p ) / r _s (6)

If the speed ratio from the sun gear 15a (16a) to the planet carrier 15d (16d) is K _sc and the speed ratio from the sun gear 15a (16a) to the ring gear 15c (16c) is K _sr ,
_{K sc = r s / (2r} s + 2r p)
K _sr = r _s / (r _s + 2r _p )
Equations (5) and (6) are
T _c = T _s / K _sc (5) ′
T _r = T _s / K _sr (6) ′
Thus, the rotational torque at each part is in a directly proportional relationship.

Speed ratio of the two planetary mechanisms 15 and 16 and _{K sc1, K sr1, K sc2} , K sr2 respectively, the steering force _{T h,} the angle assist motor load torque _{T m,} the steering reaction force torque from a front wheel _{T strg} Then, from Equations (5) 'and (6)',
T _h = T _strg × K _sc2 / K _sc1 (7)
T _m = T _h × K _sc1 / K _sr2 (8)
Thus, it is possible to obtain the steering force from the angle assist motor load torque T _m , and it is understood that the steering force is not affected by the output torque of the angle assist motor 8. However, the influence of friction or the like is ignored here as an ideal state.

  Equation (8) indicates that the load applied to the angle assist motor 8 and the steering force are in a proportional relationship. Moreover, in a general DC motor, it is known that there is a linear relationship between the output torque and the current value, and it is possible to estimate the motor output torque from the current during motor rotation. .

[Problems of conventional technology]
At present, many force-controlled power steering devices are put into practical use, but in any method, it is necessary to install a steering force sensor for measuring the steering force of the steering wheel. In the technique described in Japanese Patent Laid-Open No. 2002-308132, an assist power is changed according to a vehicle speed, a lateral acceleration, and the like by an electric power steering device that changes an assist force according to a vehicle state. In the technique described in Japanese Patent Application Laid-Open No. 2002-12159, an automatic steering function is realized by a combination of a variable rudder angle mechanism and an electric power steering mechanism.

  As described above, a steering force sensor for measuring the steering force is necessary to determine the assist torque of the power steering in both a general force control type power steering device and a combination with a variable steering angle mechanism. there were. As a sensor for measuring a steering force, a method of measuring a force from a twist amount using a twist portion of a torsion bar or the like provided on a steering shaft is generally used.

  However, if the design is made so that the steering rigidity is not lost and the steering force is not increased, it is necessary to set the torsional portion rigidity high and detect a small torsion, which makes designing the steering force sensor very difficult. It was. In addition, if the processing accuracy of the twisted portion is poor, the relationship between the amount of twist and the force cannot be obtained uniquely, and there is a problem that processing must be performed with high accuracy.

[Steering force estimation action based on current value of angle assist motor]
On the other hand, in the first embodiment, the steering force applied to the handle 1 is estimated from the operation state of the angle assist motor 8, thereby omitting the conventionally required steering force sensor, simplifying the design, and improving the overall mechanism. Axial size can be reduced and costs can be reduced. For example, in the combination with the electric power steering device 7, as shown in FIGS. 4 (a) and 4 (b), the steering force sensor is also provided when the variable steering angle mechanism 4 and the electric power steering device 8 are integrated. This eliminates the need for the mechanism and makes the mechanism size and design very easy.

[Steering force estimation action based on rotation speed of angle assist motor]
Here, when the variable rudder angle mechanism 4 and the angle assist motor 8 have ideal configurations, the steering force can be obtained by the equation (8), but in reality, the influence of the motor inertia and the friction of each part is ignored. Can not do it.

  Thus, in the first embodiment, the steering force is estimated from the operation state of the entire mechanism. Since the variable rudder angle mechanism 4 performs an operation of enlarging / reducing the steering input angle from the handle 1 and outputting it to the output shaft 3, the input / output rotational speed is always repeatedly accelerated and decelerated. Similarly, the rotation of the angle assist motor 8 is repeatedly accelerated and decelerated, and an acceleration torque or the like is generated due to the inertia or rotational viscosity of the motor. Therefore, the output torque of the motor is not equal to the load torque as it is. Therefore, by sequentially measuring the rotational speed of the motor, it is possible to predict torque fluctuation due to acceleration / deceleration of the motor and estimate the steering force together with the current value.

  When the friction of each input / output unit and the torque transmission mechanism is sufficiently small and the transmission efficiency is good, the steering force can be easily obtained from the angle assist motor current by the equation (8). Thus, when the worm gear (14a, 14b) is used for the angle assist motor input, the steering force cannot be directly obtained due to the influence of the worm gear friction.

  Therefore, the friction torque generated in the worm gear using the internal model of the variable rudder angle mechanism 4 is calculated from the input / output shaft angle measured for the variable rudder angle control, the current value of the angle assist motor 8 and the rotation speed. By estimating, the steering force can be estimated more accurately.

  Considering the state mounted on the vehicle, the road surface reaction force varies greatly depending on the situation, but the characteristics of the variable steering angle mechanism 4 do not change greatly. Therefore, by preparing sufficient data in advance, it is possible to create a table of the relationship between the steering force and the angle assist motor current value, and to estimate the steering force from only the current value. By calculating the assist torque from the steering force thus obtained, assist control can be performed without complicated processing.

  Therefore, the steering force is estimated by each of the above methods, and the steering force sensor is omitted by controlling the power steering mechanism according to the flow shown in FIG. 5 (b) with respect to the flow of the conventional device shown in FIG. 5 (a). can do.

Next, the effect will be described.
In the electric power steering apparatus according to the first embodiment, the following effects can be obtained.

  (1) A current sensor 13 that detects a current value of the angle assist motor 8 and a power steering control device 10 that drives and controls a power steering mechanism (electric power steering device 7) based on the detected current value. Therefore, a steering force sensor that is difficult to design and manufacture can be omitted, and it is not necessary to provide a twisted portion of the steering force sensor on the input shaft 2, so that the steering rigidity can be increased and the cost can be greatly reduced.

(2) a motor encoder 11 for detecting the rotation angle of the angle assist motor 8, the variable steering angle control unit 9 estimates the steering force on the basis of the detected current value and the rotation angle rotation angle and. That is, the steering force can be estimated more accurately than the case of only the current value by obtaining the acceleration torque, viscosity resistance, and the like of the angle assist motor 8 from the rotation speed and the rotation angular velocity of the angle assist motor 8.

(3) The variable steering angle control device 9 calculates the steering force from the detected current value based on a predetermined calculation formula (Formula (8)). That is, since the output torque of the angle assist motor 8 and the current value flowing through the motor at that time are in a directly proportional relationship, the load torque applied to the variable steering angle mechanism 4 from the current value is calculated by an extremely simple linear equation (9). The steering force can be estimated.

(4) The variable steering angle control device 9 estimates the steering force using a table of steering force with respect to the current value of the angle assist motor 8 measured in advance. That is, a calculation amount in the control unit can be reduced by creating a table for obtaining the relationship between the current value of the angle assist motor 8 and the steering force from data measured in advance and determining the assist torque using this table.

  (5) Since the power steering mechanism is an electric power steering mechanism using a motor, the number of parts can be reduced and the cost and the size of the mechanism can be reduced as compared with the hydraulic power steering mechanism.

FIG. 6 is a diagram illustrating a configuration of a variable steering angle device according to the second embodiment.
The vehicle steering apparatus according to the second embodiment is an example in which a hydraulic power steering apparatus (hydraulic power steering mechanism) 17 is used as a power steering mechanism.

  The steering mechanism 18 is provided with a hydraulic piston 20 that urges the rack shaft 18 a in the left-right direction in accordance with the hydraulic pressure supplied from the hydraulic pump 19. The hydraulic pressure generated by the hydraulic pump 19 can be arbitrarily changed by the motor 21, and the operating direction of the hydraulic piston 20 can be arbitrarily switched by the left-off valve 22a and the right-off valve 22b.

  In the power steering control device 10, the steering force can be freely controlled by driving the motor 21, the left turn valve 22 a and the right turn valve 22 b by the control logic as shown in the first embodiment.

FIG. 7 is a configuration diagram of the variable steering angle mechanism 20 of the second embodiment.
The variable rudder angle mechanism 20 according to the second embodiment is coaxial with the input shaft 2 and the output shaft 3 in which the stator 21a is connected to the input shaft 2 and the rotor 21b is connected to the output shaft 3 via the speed reducer 22. An angle assist motor 21 is provided.

  The variable steering angle mechanism 20 includes a connecting device 23 that mechanically connects the input shaft 2 and the output shaft 3. The connecting device 23 is in a disconnected state when the variable rudder angle control is operating normally, and is in a connected state when the variable rudder angle control is not operating normally, such as when the angle assist motor 21 is malfunctioning. Thereby, even when the angle assist motor 21 fails, it is possible to prevent the driver from being disabled.

Next, the operation will be described.
[Steering force estimation action]
The variable steering angle device according to the second embodiment has a simpler configuration as compared with the configuration according to the first embodiment. The stator 21a of the angle assist motor 21 is connected to the input shaft 2 and the rotor 21b is connected to the output shaft 3. Since they are connected, the output torque of the angle assist motor 21 and the steering force are equalized according to the law of action and reaction. Therefore, the steering force can be estimated easily and accurately.

  In the second embodiment, since the hydraulic power steering device 17 using a hydraulic servo is used as the power steering mechanism, high response can be obtained and the steering force and the steering angle can be freely controlled.

Next, the effect will be described.
In the vehicle steering apparatus of the second embodiment, the following effects are obtained in addition to the effects (1) to (4) of the first embodiment.

  (6) Since the power steering mechanism is a hydraulic power steering mechanism using a hydraulic servo, a vehicle steering device that can freely control the steering force and the steering angle by using a hydraulic power steering mechanism with good response. Can be realized.

  (7) Since the variable rudder angle mechanism 20 includes the stator 21a connected to the input shaft 2, the rotor 21b connected to the output shaft 3, and the angle assist motor 21 coaxial with the input / output shafts 2 and 3, the steering angle steering mechanism 20 Force estimation can be performed easily and accurately.

(Other examples)
The best mode for carrying out the present invention has been described based on the first embodiment. However, the specific configuration of the present invention is not limited to each embodiment and does not depart from the gist of the present invention. Such design changes are included in the present invention.

1 is a block diagram illustrating a configuration of a vehicle steering apparatus according to a first embodiment. 1 is a configuration diagram of a variable rudder angle mechanism 4 of Example 1. FIG. It is a figure which shows the balance of the force of a planetary mechanism. It is an example of the steering apparatus for vehicles which integrated the variable steering angle mechanism and the electric power steering apparatus. It is a block diagram which shows the difference of the control structure of Example 1 and the conventional vehicle steering device. It is a block diagram which shows the structure of the steering apparatus for vehicles of Example 2. FIG. FIG. 6 is a configuration diagram of a variable steering angle mechanism according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Handle 2 Input shaft 3 Output shaft 4 Variable steering angle mechanism 5 Input angle sensor 6 Output angle sensor 7 Electric power steering apparatus (power steering mechanism)
8 Angle assist motor 9 Variable steering angle control device 10 Power steering control device (power steering control means)
11 Motor encoder (motor rotation state detection means)
12 Vehicle speed sensor 13 Current sensor (Motor current value detection means)
14a worm wheel 14b worm 15 planetary gear mechanism 15a sun gear 15b pinion 15c ring gear 15d planet carrier 16 planetary gear mechanism 16a sun gear 16b pinion 16c ring gear 16d planet carrier

Claims (6)

An angle addition type that is provided between the input shaft connected to the steering wheel and the output shaft connected to the steering mechanism, and adds the output of the angle assist motor to the rotation angle of the input shaft to vary the rotation angle of the output shaft. Variable steering angle mechanism of
A power steering mechanism that outputs an assist torque for reducing a steering burden on the driver with respect to the steering mechanism;
Motor current value detecting means for detecting a current value of the angle assist motor;
Motor rotation angle detection means for detecting the rotation angle of the angle assist motor;
Input shaft rotation angle detection means for detecting the rotation angle of the input shaft;
Output shaft rotation angle detection means for detecting the rotation angle of the output shaft;
Rotation angle of the front Symbol angle assist motor, on the basis of the input shaft rotational angle and the output shaft rotation angle, and a variable steering angle control means for driving and controlling the angle assist motor,
Current value of the angular assist motor, the rotation angle of the variable steering angle control unit before Symbol angle assist motor input to, on the basis of the input shaft rotational angle and the output shaft rotation angle, drivers input to the handle Steering force estimation means for estimating the steering force;
Power steering control means for driving and controlling the power steering mechanism based on the estimated steering force;
A vehicle steering apparatus comprising: The vehicle steering apparatus according to claim 1,
The vehicle steering apparatus according to claim 1, wherein the steering force estimating means estimates the steering force from a current value of the angle assist motor based on a predetermined calculation formula. The vehicle steering apparatus according to claim 1 ,
The vehicle steering apparatus, wherein the steering force estimating means estimates the steering force using a table of steering force with respect to the current value of the angle assist motor measured in advance. The vehicle steering apparatus according to any one of claims 1 to 3 ,
The vehicle steering apparatus, wherein the power steering mechanism is an electric power steering mechanism using a motor. The vehicle steering apparatus according to any one of claims 1 to 4, wherein:
The vehicle steering apparatus, wherein the power steering mechanism is a hydraulic power steering mechanism using a hydraulic servo. The vehicle steering apparatus according to any one of claims 1 to 5 ,
The variable steering angle mechanism includes a motor coaxial with the input shaft and the output shaft, wherein one of a rotor and a stator is connected to the input shaft, and the other is connected to the output shaft. Steering device.

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