JPH11171035A - Power steering - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the phase delay of lateral displacement/steering torque to a power steering non-mounted vehicle in a power steering mounted vehicle. SOLUTION: Steering torque T detected by a steering torque sensor 17, and vehicle speed V detected by a vehicle speed sensor 18 are inputted to a controller unit 15. In the controller unit 15, the steering auxiliary torque command value is computed on the basis of the steering torque and vehicle speed and supplied to an auxiliary steering motor 13 connected to a rack 8, so as to generate steering auxiliary force. When a target transfer function of lateral acceleration to steering torque in the controller unit 15 is made Gd and a control function of steering auxiliary force FA to the torsion angle ϕ of a torsion bar is made YC, a phase delay caused by the torsion bar or the like is dissolved by adding an advance element to the phase of the control function YC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering apparatus which detects a steering torque generated in a steering state and a steering state of a steering wheel and generates a steering assist torque according to the detected steering torque.

[0002]

2. Description of the Related Art A conventional power steering apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-77750.

In this conventional example, a vehicle speed and a steering angular velocity are repeatedly stored at predetermined time intervals, upper and lower ranges are deleted from these stored data, and the remaining stored data are averaged to obtain an average speed and an average steering angular velocity. An electric power steering apparatus is described in which a power assisting force is set by performing a calculation and comparing the calculation result with a standard steering pattern to determine whether or not the vehicle is sporty.

[0004]

However, the above-mentioned conventional power steering apparatus has the following unsolved problems.

That is, it is generally said that a driver steers a vehicle by "steering at a steering wheel angle at a low speed and a steering force at a high speed". The purpose of the driver operating the vehicle is to match the vehicle trajectory intended by the driver with the vehicle trajectory through which the vehicle passes. Therefore,
What is important for the driver is the "lateral displacement of the vehicle."

[0006] Therefore, an experiment was conducted on a vehicle not equipped with a power steering device, and the lateral displacement of the vehicle was measured.
The frequency response of the steering angle (steering wheel angle) and the lateral displacement / steering torque of the vehicle was examined during low-speed running (for example, 40 km / h) and high-speed running (for example, 120 km / h). The result was obtained.

As is apparent from FIGS. 8 and 9, the phase delay of the lateral displacement / steering angle of the vehicle is smaller than the phase delay of the lateral displacement / steering torque of the vehicle when the vehicle is running at a low speed. You can see that

When the driver controls the lateral displacement of the vehicle, it is needless to say that the smaller the phase lag, the better.
Therefore, it is considered that the driver selectively uses the steering angle at low speed and the steering torque at high speed.

As an aside, in a four-wheel steering vehicle, the phase lag of lateral displacement / steering angle is reduced so that the driver can control the vehicle based on the steering angle information at high speed as well as at low speed. It is intended to reduce the burden on the user.
However, a four-wheel steering vehicle requires a rear-wheel steering actuator and various sensors, and mounting these on a vehicle increases costs and weight.

In a power steering apparatus using hydraulic pressure which is currently mounted on a vehicle, the steering torque is detected by torsion of a torsion bar, so that a steering assist hydraulic pressure is generated with a delay. In addition, there is an unsolved problem that the phase of lateral displacement / steering torque is delayed with respect to a vehicle without power steering.

Further, in recent years, an electric power steering apparatus of a type in which steering assist torque is added by an electric motor instead of a hydraulic pressure has been proposed, and the aim of this electric power steering apparatus is to reduce the weight and improve the fuel efficiency. However, since the steering assist characteristic is intended to be close to that of a hydraulic power steering device, there is an unsolved problem that it does not make full use of a certain degree of control freedom.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and has a steering assist torque such that the phase advances with respect to the steering torque detected by the torsion angle of the torsion bar or the like. It is an object of the present invention to provide a power steering device capable of solving the above-mentioned unresolved problem by adding.

[0013]

In order to achieve the above object, a power steering apparatus according to a first aspect of the present invention comprises a steering torque detecting means for detecting a steering torque generated in a steering state and a steering state of a steering wheel; An auxiliary steering torque generating means for generating a steering assist torque based on the steering torque detected by the steering torque detecting means, wherein the auxiliary steering torque generating means comprises: It is characterized by having a configuration in which a lead element is added to the transfer function of the auxiliary steering torque with respect to the torque.

According to the first aspect of the present invention, since the auxiliary steering torque generating means has an advance element added to a transfer function between the input steering torque and the auxiliary steering torque generated based on the input steering torque, the steering torque is generated. A phase delay of lateral displacement / steering torque due to a delay in the generation of the auxiliary steering torque due to a torsion of a torsion bar used in the torque sensor can be eliminated.

According to a second aspect of the present invention, in the power steering apparatus according to the first aspect, the advance element is set to a large value as the vehicle speed increases.

According to the second aspect of the present invention, since the advance element has a large value as the vehicle speed increases, it is possible to offset an increase in the lateral displacement / steering torque phase delay due to the increase in the vehicle speed. .

Further, in the power steering apparatus according to a third aspect of the present invention, the frequency at which the phase advance maximum value of the frequency response of the steering assist torque with respect to the steering torque occurs is determined when the steering assist torque is not generated. Is set near the frequency at which the maximum value of the phase delay of the frequency response of the lateral acceleration with respect to the steering torque occurs.

According to the third aspect of the present invention, the phase delay in the frequency region where the phase delay of the frequency response of the lateral acceleration / steering torque when the steering assist torque is not generated is large,
It can be surely canceled by the maximum value of the phase lead of the frequency response of the auxiliary steering torque / steering torque.

Further, in the power steering apparatus according to a fourth aspect, in the invention according to any one of the first to third aspects, the auxiliary steering torque generating means advances to the transfer function when the vehicle speed is equal to or higher than a predetermined vehicle speed. Is added.

According to the present invention, when the vehicle is traveling at a low vehicle speed lower than the predetermined vehicle speed, the driver can steer the vehicle based on the steering angle information. Thus, by adding the advance element to the transfer function, it is possible to perform optimal steering based on the steering torque.

[0021]

According to the first aspect of the present invention, a configuration is adopted in which a forward function is added to a transfer function for calculating an auxiliary steering torque corresponding to a detected steering torque value. The effect that the vehicle characteristic which is easy to handle based on the force can be realized is obtained.

According to the second aspect of the present invention, the advance element added to the transfer function is set to a large value in accordance with an increase in the vehicle speed, thereby realizing vehicle characteristics that are easy to handle in all vehicle speed ranges. Is obtained.

Further, according to the third aspect of the present invention, the frequency at which the phase advance maximum value of the frequency response of the steering assist torque to the steering torque occurs is determined by the frequency response of the lateral acceleration to the steering torque when the steering assist torque is not generated. Is set in the vicinity of the frequency at which the maximum value of the phase delay occurs, the phase lead increases in the frequency band where the phase delay is large, and the effect that the dynamic characteristics can be compensated can be obtained.

According to the fourth aspect of the present invention, the auxiliary steering torque generating means is configured to add an element to the transfer function when the vehicle speed is equal to or higher than a predetermined vehicle speed. By controlling the steering assist torque based on the angle information and adding the elements to the transfer function only in the high-speed region where the driver controls based on the steering torque,
An effect is obtained in that the steering feeling of the driver can be appropriately maintained and optimal steering torque control can be performed.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. In the drawing, a steering wheel 1 is connected to an upper end of a steering shaft 2, and the steering shaft 2 is rotatably supported by a fixed portion. .

The lower end of the steering shaft 2 is connected via a universal joint 3, a column shaft 4 and a universal joint 5 to a pinion shaft 7 having a pinion 6 attached to the lower end.

The pinion 6 meshes with a rack 8 extending horizontally in the vehicle width direction to constitute a steering gear, and the rotational motion from the steering wheel 1 to the steering shaft 2 is a linear motion (translational motion) of the rack 8. Is converted to

Both ends of the horizontally extending rack 8 are connected to knuckles and steered wheels 10 via tie rods 9, respectively.
The left and right steered wheels 10 are steered by the rack 8 moving horizontally (translational movement).

The rack 8 has an assist pinion 1
The assist pinion 11 is connected via a speed reducer 12 to a rotation shaft of a steering assist motor 13 serving as a drive source, and the steering assist motor 13 is subjected to duty control output from a control unit 15 described later. The control is performed so as to generate a steering assist force corresponding to the steering torque by the generated pulse current.

Further, a torque detection mechanism 16 is provided on the pinion shaft 7. This torque detecting mechanism 1
Reference numeral 6 denotes a torsion bar (not shown) that connects the lower end of the pinion shaft 7 and the upper end of the pinion 6, and a steering torque sensor 17 disposed on the outer periphery thereof.

The steering torque sensor 17 detects the steering torque from the amount of twist of the torsion bar, and turns the steering wheel 1 to the right according to the magnitude of the steering torque (to the left from the input from the pinion 6). A torque detection value T composed of a voltage signal having a positive value when the steering wheel 1 is turned and a negative value when the steering wheel 1 is turned left (clockwise with respect to the input from the pinion 6) is supplied to a control unit 15 described later.

The vehicle is equipped with a vehicle speed sensor 18 for detecting the vehicle speed. The vehicle speed sensor 18 detects the vehicle speed in the front-rear direction of the vehicle, and the vehicle speed detection value is a voltage signal corresponding to the magnitude of the vehicle speed. V is supplied to a control unit 15 described later.

Then, in the control unit 15,
A predetermined calculation is performed based on the input vehicle speed detection value V and steering torque detection value T, and a steering torque command value for the steering assist motor 13 is calculated.
Output to

Here, the steering assist torque command value output from the control unit 15 and the actual steering assist force generated by the steering assist motor 13 based on the steering assist torque command value have a one-to-one correspondence. , There is no phase delay between them.

The transfer function of the steering assist torque to the steering torque T in the assist steering system torque generating means including the steering assist motor 13 and the control unit 15 is set as follows.

[0036] That is, the lateral acceleration detected value to the steering torque T alpha a target transfer function of (alpha / T) with the G _d, when the rigidity of the torsion bar and the K (Nm / rad), the torsion bar torsion angle φ Steering assist force F _{A for}
The control transfer function Y _C of _{(= F A · K / T} ) Distant, finding the control transfer function Y _C.

Here, the target of the transfer function G _d is as follows.
This is because the lateral displacement is the second-order integral value of the lateral acceleration, and the purpose of the present invention is to improve the phase of the lateral displacement / steering torque, as described above in the related art section.

To derive these functions G _d and Y _C , FIG.
Is used. In FIG. 2, L is the vehicle wheel base (m), L _f longitudinal distance between the front wheels and the center of gravity (m), L _r is the front-rear direction between the rear wheels and the center of gravity (m), alpha is the vehicle lateral acceleration (M / s ² ), β is the vehicle body slip angle (rad), γ is the yaw rate (rad / s), δ
Represents front wheel steering angle (rad), F _f represents front wheel lateral force (N), _Fr represents rear wheel lateral force (N), and V represents vehicle speed (m / s).

Firstly, the control transfer function of Y _C, obtaining the steering torque T when the steering assist force F _A is generated. When a certain self-aligning torque T _S and a steering assist force F _A are generated, the rack axial force is T _S / d−F _{A where a} knuckle arm radius is d (m).

The rack axial force is added to the pinion rotation radius r.
By multiplying by (m), a steering torque T is obtained as in the following equation (1). T = (T _S / d−F _A ) r (1) However, the self-aligning torque T _S and the steering assist force F _A can be expressed by the following equations (2) and (3). .

[0041] _{T S = C f (θ /} N-β-L F · γ / V) t r ............ (2) F A = Y C · φ = Y C · T / K ............ ( 3) where C _f is the front wheel cornering power (N / ra
d) and θ are steering angles (rad), N is a steering gear ratio, and _tr is a front wheel trail (m).

By substituting the equations (2) and (3) into the equation (1), the following equation (4) is obtained. _{T = K · r · C f} · t r (θ / N-β-L F · γ / V) / d (K + r · Y C) ............ (4) Accordingly, the steering torque T to the steering angle theta The transfer function T (s) / θ (s) can be expressed by the following equation (5).

[0043]

(Equation 1)

Here, s is a Laplace operator. now,
Since the transfer function of the lateral acceleration alpha / steering torque T to G _d ie α (s) / T (s ) = G d is a target,

[0045]

(Equation 2)

It suffices if Here, assuming that the wheel slip angular velocity is β ′, the lateral acceleration α is represented by α = V (β ′ + γ) (7).

[0047]

(Equation 3)

Is as follows. Then, since the above equations (5) and (8) match,

[0049]

(Equation 4)

Is as follows. From this equation (9), the steering assist force F_A
/ Control transfer function Y of torsion bar torsion angle φ _C(s)
Can be

Here, first, β (s) / θ in the equation (9)
(s) and γ (s) / θ (s) are determined. The equation of motion of the vehicle is

[0052]

(Equation 5)

Is as follows. Here, m is the vehicle mass (kg),
C_rIs rear wheel cornering power (N / rad), I is car
Both yaw moments of inertia (kgm^Two), Γ 'is yaw acceleration
(Rad / s ^Two).

Then, when the above equations (10) and (11) are arranged,

[0055]

(Equation 6)

Where a ₁₁ = − (L _f ² C _f + L _r ² C _r ) / IV a ₁₂ = (L _r C _r −L _f C _f ) / I a ₂₁ = (L _r C _r −L _{f ^{= C f) / mV 2 -1}} a 22 (- since the _{C f -C r) / mV b} 11 = L f C f / IN b 21 = C f / mVN, γ (s) / θ (s) And β _(s) / θ _(s) are

[0057]

(Equation 7)

Is as follows. The formulas (13) to (15) are substituted into the formula (9) for rearranging. In this case, a delay in controlling the vehicle, as the better is no phase lag of target transfer function G _d is zero at all frequencies. That is, the target transfer function _Gd is treated as a constant.

Then, the control transfer function Y _{C to be obtained} is

[0060]

(Equation 8)

However, A = −P ₁ (a ₁₁ + a ₂₂ ) + P ₂ b ₂₁ + P ₃ (−b ₂₁ a ₁₁ +
b ₁₁ a ₂₁ ) + P ₄ b ₁₁ B = P ₁ (a ₁₁ a ₂₂ −a ₁₂ a ₂₁ ) C = P ₂ (−b ₂₁ a ₁₁ + b ₁₁ a ₂₁ ) D = P ₄ (−b ₁₁ a ₂₂ + b) _{21 a 12) E = P 5} (-b 21 a 11 + b 11 a 21 + b 11) F = P 5 (-b 11 a 22 + b 21 a 12) P 1 = (K / N) C f t r G d _{r P 2 = -C f t r} G d rK P 3 = -KdV P 4 = -K (L f C f t r G d r / V + dV) P 5 = drV next, as a secondary / secondary transfer function Can be represented.

Next, a description how to calculate the value of the target transfer function G _d. Assuming that the steady gain of the transfer function of the lateral acceleration α with respect to the steering torque T at the time of not assisting the steering, that is, at the time of manual steering is G _d0 , the steady gain G _d0 is

[0063]

(Equation 9)

Where X = (a ₁₁ a ₂₂ −a ₁₂ a ₂₁ ) / N Y = −b ₁₁ a ₂₁ + a ₁₁ b ₂₁ Z = L _f (b ₂₁ a ₁₂ −b ₁₁ a ₂₂ ) / V Is done.

When a steering assist force is generated by the steering assist motor 13, the steering force is reduced.
_d may be set as follows: G _d = η × G _d0 (η> 1) (19) Incidentally, when η = 1, the steering force at a low frequency is the same as that of a manually steered vehicle.

Therefore, for example, when the vehicle speed is 100 km / h
When traveling with η = 8/5, the target transfer function G _d
Is calculated, and a control transfer function Y _C of the steering assist force F _a / torsion angle φ of the torsion bar is calculated, and tuning of the control unit 15 is performed so that the control transfer function Y _C is obtained. At this time, the frequency characteristic of the control transfer function Y _C is, as shown in FIG.
It becomes a relatively low constant value up to the vicinity of Hz, but rises from 1 Hz to 2 Hz, and thereafter gradually decreases as the frequency increases, and the phase gradually increases from 0.1 Hz. From 0.6 Hz to 1.3 Hz.
Peaks at around 30 Hz, then sharply decreases to 3H
The characteristic gradually decreases after z.

For this reason, the frequency characteristic of the lateral acceleration α / steering torque T has a constant value near “0” regardless of the frequency as shown by the solid line in FIG. ) "0" regardless of the frequency as shown by the solid line
Is maintained, and it is understood that the initial characteristics are realized. Further, the control transfer function Y _C constitutes a high-pass filter.

When the control of the present invention is not performed, as shown by broken lines in FIGS. 4A and 4B, the gain decreases relatively sharply when the gain exceeds 1 Hz, and gradually decreases when the gain exceeds 2 Hz. As the frequency increases, the phase gradually decreases from 0.1 Hz and sharply decreases from around 0.8 Hz to 1.4H.
It peaks at about z, then rapidly increases, and gradually increases at 3 Hz or more, causing a large phase delay between 1 Hz and 2 Hz. In the above embodiment, the gain and phase at the time of non-control, that is, at the time of manual steering, FIG. 3 shows that the gain and phase of the control transfer function Y _{C in} the frequency region where
By setting the characteristics to be opposite as shown in (a) and (b), fluctuations in gain and phase are reliably suppressed, and optimal steering assist control according to the driver's steering feeling can be performed.

In particular, as apparent from FIG. 3A, the phase characteristic of the control transfer function Y _C is such that the amount of phase lead increases in the frequency range where the phase of the lateral acceleration α / steering torque T is delayed in the case of manual steering. To compensate for the dynamic characteristics.

That is, when tuning the control unit 15, first, the frequency characteristic of the lateral acceleration α / steering torque T is measured in the state of manual steering, and the phase is shifted in the frequency range where the phase lead angle is large in the frequency range where the phase delay is large. What is necessary is just to adjust the control unit 15 so that advance may become large.

Further, with respect to the amount by which the phase is advanced, a case has been described in the above embodiment where the ideal state is derived by a mathematical expression. However, if at least the phase of the control transfer function Y _C is advanced even a little, the lateral acceleration α / Since the phase of the steering torque T is improved, the amount may be tuned in accordance with the driver's feeling.

In the power steering system described in the above embodiment, it is assumed that the steering assist force with respect to the target value of the steering assist amount is generated on a one-to-one basis. This is essentially different from ordinary PD control or PID control in which a phase advance is added to realize hardware performance in order to realize the assisting force.

Next, a second embodiment of the present invention will be described with reference to FIGS. The second embodiment is that the characteristics of the control transfer function Y _C of the steering assist force F _A against the torsion bar twist angle φ so as to vary in accordance with the vehicle speed change.

In the second embodiment, when the vehicle speed increases, the phase lag of the lateral acceleration α / the steering torque T increases, so that the amount of advance of the control transfer function Y _{C by} the controller 15 also depends on the increase of the vehicle speed. Need to be larger. Here, it should be originally called lateral displacement / steering torque,
Since the lateral acceleration α is a second-order differential value of the lateral displacement, the lateral acceleration α is used instead.

Therefore, the lateral acceleration α in the case of the ideal characteristic
/ Shows the frequency response of the control transfer function Y _C of the frequency response and the steering assist force F _A / torsion bar twist angle φ of the steering torque T, respectively FIGS.

FIGS. 5 and 6 show that the vehicle speed is 40 km / km.
FIG. 5A shows the frequency response when the frequency is changed every 20 km / h from h to 120 km / h. When the control of the present invention is not performed, the gain characteristic of the lateral acceleration α / steering torque T is shown in FIG. ), The gain increases as the vehicle speed increases in the range of 0.3 to about 1.4, and conversely, the gain increases in the range of about 1.4 to 1.4.
4, the phase characteristic decreases as the vehicle speed increases, and the phase characteristic decreases as the vehicle speed increases when the frequency is between 0.1 Hz and 1 Hz as shown in FIG.
On the contrary, the phase lag increases as the vehicle speed increases in the range from about Hz to about 2.3 Hz.

Therefore, the control transfer function Y _C of the steering assist force F _A / torsion bar torsion angle φ is calculated as shown in FIG.
As shown in FIG.
It decreases with the increase of the vehicle speed between about 1.4 Hz, increases with the increase of the vehicle speed between about 1.4 to 3 Hz, and changes the phase characteristic to zero as shown in FIG. .1 to
The phase lag amount is increased with the increase of the vehicle speed between 0.8 Hz and the phase advance amount is set with the increase of the vehicle speed between 0.8 and about 2.2 Hz.

[0078] Thus, the characteristics of the lateral acceleration G / steering torque T is delayed in case of no steering assist can be compensated by a control transfer function Y _C, characteristic in FIG. 5 (a) and (b) as shown by lines L ₁ and L _2, it is possible to perform an optimum steering assist control without phase delay while maintaining a constant gain regardless of a change in vehicle speed.

In the first and second embodiments, the case where the phase delay of lateral displacement (= general lateral acceleration) / steering torque is reduced in all vehicle speed ranges has been described. As described in the section of the related art described above, the driver steers the vehicle based on the steering angle information at low speed, so that the driver steers based on the steering torque. Control transfer function Y only in high vehicle speed range
_{The process} may proceed to _C to add an element.

The phase characteristic in the frequency response of the transfer function of lateral displacement / steering angle and lateral displacement / steering torque is expressed as 4
0km / h, 50km / h, 60km / h and 70km
/ H, the results of these measurements were as shown in FIGS. 7 (a), (b), (c) and (d).

As is apparent from FIG. 8, when the vehicle speed is 40
When the vehicle speed is km / h, the transfer function of the lateral displacement / steering torque has a phase lag with respect to the transfer function of the lateral displacement / steering angle, but the vehicle speed is 50 to 60 km / h.
The phase lag between the transfer function of lateral displacement / steering angle and the transfer function of lateral displacement / steering torque is reversed between (b) and FIG. 8 (c).

Therefore, a predetermined vehicle speed, for example, 50 km / h
Without adding the amount of phase lead to the control transfer function Y _C of the steering assist force F _A / torsion bar twist angle φ is less than, 50 km / h
As described above, it is preferable to gradually increase the amount of phase advance.

In each of the above embodiments, the case where the assist pinion 11 connected to the auxiliary steering motor 13 is meshed with the rack 8 has been described. However, the present invention is not limited to this. The auxiliary steering motor 13 may be connected via a power transmission means such as the above. In short, the auxiliary steering motor 13 may be configured to be capable of transmitting the auxiliary steering torque generated by the auxiliary steering motor 13 to the steering system.

Further, in each of the above embodiments, the case where the steering assist force is generated by the steering assist motor 13 has been described. However, the present invention is not limited to this.
Even hydraulic power steering, by adding a control transfer function Y _C in lead element of the steering assist force F _A / torsion bar twist angle φ in the hydraulic control system, the first
The same operation and effect as those of the second embodiment can be obtained.

Further, in each of the above embodiments, the case where there is no delay in the actual steering assist torque actually generated by the steering assist motor 13 with respect to the command torque from the control unit 15 has been described. If there is a delay between the command torque and the actual steering assist torque generated by the steering assist motor 13, it goes without saying that the delay is compensated for. For example, when the transfer function of the actual steering assist torque / command torque is H (s) and the control transfer function to be realized is Y _c (s),

[0086]

(Equation 10)

May be set.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a two-wheel model for deriving a function.

[Figure 3] is a characteristic diagram showing the frequency response of the control transfer function Y _C of the helix angle of the steering assist force / torsion bars, (a)
Indicates a gain characteristic, and (b) indicates a phase characteristic.

FIG. 4 is a characteristic diagram showing a frequency response of lateral acceleration / steering torque, wherein (a) shows a gain characteristic and (b) shows a phase characteristic.

FIGS. 5A and 5B are characteristic diagrams illustrating a frequency response of lateral acceleration / steering torque according to the second embodiment of the present invention, wherein FIG. 5A illustrates a gain characteristic and FIG. 5B illustrates a phase characteristic.

FIG. 6 is a characteristic diagram showing a frequency response of a control transfer function Y _C in the second embodiment, where (a) shows a gain characteristic;
(B) shows the phase characteristics respectively.

FIG. 7 is a characteristic diagram showing phase characteristics of lateral displacement / steering angle and lateral displacement / steering torque in another embodiment of the present invention.

FIG. 8 is a characteristic diagram showing the frequency response of lateral displacement / steering angle and lateral displacement / steering torque during low-speed running in a vehicle not equipped with a conventional power steering, where (a) shows a gain characteristic; (B) shows the phase characteristics respectively.

FIG. 9 is a characteristic diagram showing a frequency response of lateral displacement / steering angle and lateral displacement / steering torque during high-speed running in a vehicle not equipped with a conventional power steering, where (a) shows a gain characteristic; (B) shows the phase characteristics respectively.

FIGS. 10A and 10B are characteristic diagrams showing frequency responses of lateral acceleration / steering torque of a vehicle equipped with a hydraulic power steering and a vehicle not equipped with the hydraulic power steering, wherein FIG. 10A shows a gain characteristic and FIG. 10B shows a phase characteristic.

[Explanation of symbols]

 Reference Signs List 1 steering wheel 2 steering shaft 6 pinion 8 rack 10 steered wheel 11 steering assist pinion 13 steering assist motor 15 control unit 16 torque detection mechanism 17 steering torque sensor 18 vehicle speed sensor

Claims (4)

[Claims] 1. A steering torque detecting means for detecting a steering torque generated in a steering state and a steering holding state of a steering wheel, and an auxiliary steering torque for generating a steering assist torque based on the steering torque detected by the steering torque detecting means. A power steering apparatus including a generating means, wherein the auxiliary steering torque generating means has a configuration in which an advance element is added to a transfer function of an auxiliary steering torque with respect to the steering torque detected by the steering torque detecting means. Power steering device. 2. The system according to claim 1, wherein the advance element is set to a large value according to an increase in vehicle speed.
A power steering device as described. 3. The frequency at which the maximum value of the phase advance of the frequency response of the steering assist torque with respect to the steering torque is generated is set near the frequency at which the maximum value of the phase delay of the frequency response of the lateral acceleration with respect to the steering torque when the steering assist torque is not generated is generated. The power steering apparatus according to claim 1, wherein the power steering apparatus is set to: 4. The system according to claim 1, wherein the auxiliary steering torque generating means is configured to add an element to the transfer function when the vehicle speed is equal to or higher than a predetermined vehicle speed.
A power steering device according to any one of the above.