JP4019938B2 - Power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power steering apparatus.
[0002]
[Prior art]
Some power steering devices detect steering torque applied to a steering member (handle) based on torsion of a torsion bar, and generate an assist torque corresponding to the steering torque by an electric motor to perform steering assist. (For example, refer to Patent Document 1).
[0003]
[Patent Document 1]
[Patent Document 1] Japanese Patent Laid-Open No. 2002-116095
[Problems to be solved by the invention]
Conventionally, there is no theoretical knowledge about the dynamics distribution of the steering system mechanical system to achieve an appropriate steering feeling, and it is said that reducing inertia and viscosity uniformly leads to improved steering feeling (clean feeling). It was.
[0005]
However, steering devices generally tend to focus on assist responsiveness. For this reason, motor current control gain is set as high as possible, and compensation control for delay elements such as torque phase compensation and motor inertia compensation is introduced. I do. In addition, in order to improve the deterioration of the handle return due to friction, handle return control (logic that forcibly returns the handle by the motor) may be introduced.
For this reason, the system is always sensitive to torque fluctuations (torsion bar torsion). In addition, the upstream side (handle side) of the torsion bar has a low viscosity, and the upstream side includes a member having a large inertia called a handle, so that the entire system easily becomes a vibration system.
[0006]
For example, if the steering wheel is released during the transition from the vehicle turning state to the straight traveling state, there is no appropriate viscosity for the steering wheel inertia, so overshoot occurs when the steering wheel returns to the neutral position. The input / output angle phase difference on both sides of the bar is difficult to converge. In response to this, the entire system is difficult to converge, and the convergence of the vehicle behavior deteriorates.
In order to improve this by control, it is conceivable to introduce appropriate angular velocity control (viscous component) so that the steering wheel does not hunt when returning the steering wheel. Therefore, it is difficult to achieve both in control.
[0007]
The present invention intends to solve the above problem by a new finding that the viscosity on the upstream side of the torsion bar in the steering mechanical system is appropriately set.
[0008]
[Means for Solving the Problems]
The present invention relates to a power steering apparatus including a torque detecting device including a torsion member (such as a torsion bar) that is twisted by a steering torque to be a spring element in the middle of a steering mechanical system from a steering member to a steered wheel. ,
In the steering mechanical system, the viscosity C on the steering member side with respect to the torsion member is set so as to satisfy the formula (1), and the viscosity C is a member on the steering member side with respect to the torsion member. It is set by the preload adjustment of the bearing which supports the power steering device.
2JK ≦ C ² (1)
In the steering mechanical system, J is the inertia on the steering member side of the torsion member, and K is the elasticity of the torsion member.
[0009]
The present inventor typified by the steering member the viscosity C on the steering member side of the torsion member (hereinafter referred to as “upstream side”, and the side opposite to the upstream side with respect to the torsion member as “downstream side”). We obtained knowledge that the entire system can be easily converged by setting appropriate values for the elasticity represented by the inertia J and the torsional member.
[0010]
Here, the transfer function on the upstream side (input shaft angle with respect to the output shaft torque of the steering shaft) viewed from the downstream side is expressed as K / (Js ² + Cs + K). Note that s is a Laplace operator, ω _n is a natural angular frequency, and ζ is an attenuation coefficient.
In this transfer function, if K / J = ω _n ² and C / J = 2ζω _n , then it becomes ω _n ² / (S ² + 2ζω _n s + ω _n ² ). This is a secondary vibration system.
In such a secondary vibration system, the condition for the step response not to overshoot with respect to the steady state (the neutral position of the steering member) is theoretically ζ ≧ 2 ^−1/2 . That is, ζ may be set (ζ ≧ 2 ^−1/2 ) so that the gain does not have a peak in the natural frequency when the Bode diagram (gain diagram) of the mechanical system is drawn.
[0011]
From ζ ≧ 2 ^−1/2 , the viscosity C for preventing the steering member from overshooting in the steering machine system of the present invention is expressed by the above equation (1).
If ζ is smaller than “2 ^−1/2 ”, overshoot occurs. On the other hand, if ζ is larger than “2 ^−1/2 ”, overshoot does not occur, but if it is too large, responsiveness decreases.
[0012]
Therefore, the viscosity C is preferably set so as to satisfy the formula (2).
2JK ≦ C ² ≦ 4JK (2)
The C ² is set to be lower than or equal 4JK, it is sufficient responsiveness, while preventing overshoot of the steering member, can be made to return the deterioration of the steering member does not occur. C ² = 4JK is when ζ = 1.
[0013]
Furthermore, the present invention provides a power steering apparatus including a torque detection device including a torsion member that is twisted by a steering torque to be a spring element in the middle of a steering mechanical system from a steering member to a steered wheel.
In the steering mechanical system, the viscosity C on the steering member side with respect to the torsion member is set so as to satisfy Expression (3), and the viscosity C is a member on the steering member side with respect to the torsion member. It is set by the preload adjustment of the bearing which supports the power steering device.
2JK ≒ C ² (3)
In the steering mechanical system, J is the inertia on the steering member side of the torsion member, and K is the elasticity of the torsion member.
In this manner, the C ² is set to be substantially equal to the JK, can steering member side to obtain a maximum response within a range not overshoot.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of an electric power steering apparatus 1 in a vehicle. The electric power steering apparatus 1 includes a steering mechanical system 4 from a steering member (handle) 2 to a steered wheel 3. The steering mechanical system 4 includes a steering shaft 5 coupled to the steering member 2, and the rotation of the steering shaft 5 is converted into a linear motion in the left-right direction by the rack and pinion transmission mechanism 6 and steered via the left and right tie rods 7. Wheel 3 is steered.
[0016]
The steering shaft 5 is provided with a torque sensor 10 for detecting a steering torque at an intermediate position in the axial direction, and the steering shaft 5 has an input shaft 5a on the upstream side (the steering member 2 side) from the sensor 10. The downstream side of the sensor 10 is an output shaft 5b. The input shaft 5a and the output shaft 5b are rotatably supported by a bearing (not shown).
[0017]
The sensor 10 detects a steering torque based on a relative angle difference between the input shaft 5a and the output shaft 5b due to torsion of the torsion bar 10a interposed between the input shaft 5a and the output shaft 5b. The detected steering torque is given to a control unit (ECU) 12 that controls a motor 11 that generates a steering assist force (assist torque).
The motor 11 is provided on the output shaft 5b on the downstream side of the sensor 10, and assist torque is applied to the input from the steering member 2 to steer the steered wheels.
[0018]
FIG. 2 shows viscosity, inertia, and elasticity in the steering machine system 4 of FIG. As the viscosity, there are a viscosity Ch as a rotation resistance by a bearing or the like that supports the input shaft 5a, a viscosity Cm as a rotation resistance by a bearing or the like that supports the motor rotation shaft 11a, and the like. As the inertia, there are an inertia Jh by the steering member 2, an inertia Jm by the motor 11, and the like. As elasticity, there is elasticity K due to the torsion bar (twisted member) 10a.
[0019]
The response of the input shaft 5a viewed from the output shaft 5b is problematic in terms of viscosity, inertia and elasticity upstream of the torsion bar 10a. Therefore, when considering the response of the input shaft angle to the output shaft torque, viscosity C≈Ch, inertia J≈Jh, and elasticity K = K.
The transfer function of the steering machine system 4 is K / (Js ² + Cs + K), and the conditional expression for the input shaft angle not to overshoot (or hardly) the step response of the output shaft angle is the following ( Any one of 1) to (3).
2JK ≦ C ² (1)
2JK ≦ C ² ≦ 4JK (2)
2JK ≒ C ² (3)
And in order for the electric power stearin apparatus 1 which concerns on 1st Embodiment to satisfy | fill Formula (1), C should just satisfy | fill Formula (1 ').
2 ・ Jh ・ K ≦ Ch ² (1 ')
Similarly, the formulas (2) and (3) may satisfy the formulas (2 ′) and (3 ′).
2 · Jh · K ≤ Ch ² ≤ 4 · Jh · K (2 ')
2 ・ Jh ・ K ≒ Ch ² ...... (3 ')
[0020]
And Ch adjustment for satisfying the equation as described above can be performed by preload management of the bearing supporting the input shaft 5a.
When the viscosity C is appropriately set as described above, the dynamic characteristics of the mechanical system upstream (on the spring) from the torsion bar 10a are improved, and the steering member is moved when the vehicle is shifted from the turning state to the straight traveling state. Even in the released state, the steering member immediately converges to the neutral position.
[0021]
FIG. 3 shows viscosity, inertia, and elasticity in the steering machine system 4 according to the second embodiment. Here, the motor 11 is configured to apply a steering assist force to the upstream side of the torsion bar 10a, that is, the input shaft 5a.
Also in the case of FIG. 3, the viscosity includes a viscosity Ch as a rotational resistance by a bearing or the like that supports the input shaft 5a, a viscosity Cm as a rotational resistance by a bearing or the like that supports the motor rotation shaft 11a, and the like. As the inertia, there are an inertia Jh by the steering member 2, an inertia Jm by the motor 11, and the like. As elasticity, there is elasticity K due to the torsion bar (twisted member) 10a.
[0022]
However, the response of the input shaft 5a viewed from the output shaft 5b has problems of viscosity, inertia, and elasticity upstream of the torsion bar 10a. Therefore, when considering the response of the input shaft angle to the output shaft torque, the viscosity C≈Ch + Cm, inertia J≈Jh + Jm, elasticity K = K.
Therefore, in order for the electric power stearin device according to the second embodiment to satisfy any of the expressions (1) to (3), C must satisfy the corresponding expressions (1 ″) to (3 ″). Good.
2 (Jh + Jm) K ≦ (Ch + Cm) ² ...... (1 ″)
2 (Jh + Jm) K ≦ (Ch + Cm) ² ≦ 4 (Jh + Jm) K (2 ″)
2 (Jh + Jm) K≈ (Ch + Cm) ² ...... (3 ″)
The power steering device may be a hydraulic type equipped with a torque twisting device in addition to the electric type.
[0023]
【The invention's effect】
According to the present invention, the upstream viscosity C is appropriately set by the torsion member, so that the entire system is easily converged, and the convergence of the vehicle behavior can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus according to a first embodiment.
FIG. 2 is a diagram showing viscosity, inertia, and elasticity in the mechanical system of FIG.
FIG. 3 is a diagram showing viscosity, inertia, and elasticity of a mechanical system in an electric power steering apparatus according to a second embodiment.
[Explanation of symbols]
1 Electric power steering device 2 Steering member (handle)
3 Steering wheel 4 Steering machine system 10a Torsion bar (twist member; spring element)
10 Torque detector C Viscosity K Elasticity J Inertia

Claims (2)

In a power steering apparatus provided with a torque detection device including a torsion member that is twisted by a steering torque and becomes a spring element in the middle of a steering machine system from a steering member to a steered wheel,
In the steering mechanical system, the viscosity C on the steering member side with respect to the torsion member is set so as to satisfy the formula (1), and the viscosity C is a member on the steering member side with respect to the torsion member. The power steering device is set by adjusting the preload of the bearing that supports the motor .
2JK ≦ C ² (1)
In the steering mechanical system, J is the inertia on the steering member side of the torsion member, and K is the elasticity of the torsion member. In a power steering apparatus provided with a torque detection device including a torsion member that is twisted by a steering torque and becomes a spring element in the middle of a steering machine system from a steering member to a steered wheel,
In the steering mechanical system, the viscosity C on the steering member side with respect to the torsion member is set so as to satisfy Expression (3), and the viscosity C is a member on the steering member side with respect to the torsion member. The power steering device is set by adjusting the preload of the bearing that supports the motor .
2JK ≒ C ² (3)
However, J is the inertia of the steering member side than members twist in the steering mechanical system, K is an elastic torsion member.

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