JP3123295B2 - Power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for a vehicle such as an automobile, and more particularly, to a power steering device for a vehicle capable of changing a drive torque distribution of a steered wheel and a non-steered wheel.

[0002]

2. Description of the Related Art Generally, a power steering device for a vehicle such as an automobile includes a steering assist force generating device such as an assist motor or a power cylinder device for generating a steering assist force, and a steering assist device according to a steering torque generated on a steering shaft. It has a steering assist force adjustment device such as an electronic control device or a control valve that increases or decreases the force,
Power assist is performed by generating a required steering assist force according to the steering torque.

Further, as a power steering device for a vehicle such as an automobile, for example, as disclosed in Japanese Patent Application Laid-Open No. 59-130780, the steering assist force is reduced as the vehicle speed detected by a vehicle speed sensor increases. A so-called progressive power steering device is well known. According to such a power steering device, since the steering assist force is generated in accordance with the steering torque and the steering assist force is reduced as the vehicle speed increases, light steering in a low vehicle speed range is ensured and the medium to high speed is secured. Good steering stability in the area is secured.

[0004]

As is well known, a vehicle such as an automobile is generally provided with a positive kingpin offset, and has a four-wheel drive device that switches between a two-wheel drive mode and a four-wheel drive mode. In a vehicle equipped with a four-wheel drive device capable of changing the drive torque distribution of the front and rear wheels, when the mode is switched from the two-wheel drive mode to the four-wheel drive mode or the drive torque distribution of the front wheels is increased, the steering wheel is generally increased. Is increased to a relatively high value from zero or a relatively low value.

When a relatively high driving torque is thus applied to the front wheels, the front wheels receive a moment M equal to the product of the driving torque Td and the kingpin offset (scrub radius) R, so that the wheels will steer in the toe-in direction. However, due to the difference in driving torque between the left and right front wheels, the difference in the grounding load of the left and right wheels due to the load movement during turning of the vehicle, and the difference in the coefficient of friction of the road surface where the left and right wheels touch the ground, A difference occurs in the magnitude of the moment M of the front wheels, so that when the vehicle starts or suddenly accelerates, so-called torque steering in which the left and right front wheels are deflected in the right or left turning direction is likely to occur.

However, in a conventional power steering device incorporated in a vehicle equipped with a four-wheel drive device, the steering assist force is not adjusted to increase or decrease depending on whether or not torque steering is likely to occur. There is a problem that the feeling of steering response is different between the case where the driving torque of the front wheels is low and the case where the driving torque is high, and the steering feeling is poor.

[0007] The present invention has been made in view of the problems such as the in above the conventional power-steering device mounted modifiable vehicle drive torque distribution ratio between the steering wheel and the non-steering wheel, the driving torque of the steering wheel It is an object of the present invention to provide an improved power steering device such that the steering response does not significantly change even if the distribution is increased.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a vehicle, as shown in FIG. 1, which is capable of changing a drive torque distribution between steered wheels and non-steered wheels. A steering assist force generating means M1 for generating a steering assist force, a steering assist force adjusting means M2 for increasing or decreasing the steering assist force according to at least the steering torque, and a drive torque for the steered wheels. A driving torque distribution determining unit M3 for determining whether the distribution is high, and a driving torque distribution for the steered wheels when the driving torque distribution for the steered wheels is high .
Increasing corrects the steering assist force compared to when the drive torque distribution is low or augmentation correction result co the steering assist force
And a steering assist force correcting means M4 for increasing and correcting the hysteresis width.

[0009]

In a power steering apparatus for a vehicle such as an automobile, generally, the higher the steering assist force, the smaller the steering force required for the driver of the vehicle to steer, and the more the disturbance input to the wheels from the road surface is reduced. It becomes difficult to transmit to the steering wheel via the power steering device, and the larger the hysteresis width of the steering assist force at the time of turning back, the more difficult it is to transmit disturbance from the road surface to the steering wheel.The same applies to torque steering. It is.

According to the above configuration, the drive torque distribution detecting means M3 determines whether or not the drive torque distribution of the steered wheels is high. When the drive torque distribution of the steered wheels is high, the steering assist force correcting means M4 performs the steering. Wheel drive torque
Since the hysteresis width of the distribution as compared with at low steering assist force is increased corrected or steering assist force is increased corrected co Niso is increased corrected likely to occur when the high drive torque distribution of the steering wheel The change in the feeling of steering response due to torque steer is reduced, and the steering feeling is improved.

[0011] It should be noted At a herein, the term "between the steering wheel and the non-steering wheels
A vehicle whose drive torque distribution can be changed between "steering wheels" and "non-steering wheels" as in a torque split type four-wheel drive system increases or decreases the drive torque distribution ratio of those wheels. A vehicle equipped with a four-wheel drive device that switches between a mode in which only non-steered wheels are driven and a mode in which both steered and non-steered wheels are driven, as well as vehicles equipped with four-wheel drive devices Is also included.

[0012] Further, "the drive torque distribution of the steered wheels is high" means that in the case of a four-wheel drive system in which the drive torque distribution ratio of the steered wheels and the non-steered wheels is increased or decreased, the drive torque distribution of the steered wheels is higher than the standard state. In the case of the four-wheel drive device of the mode switching type, it means that both the steered wheels and the non-steered wheels are driven.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention;

FIG. 2 shows an embodiment of a power steering device according to the present invention which is applied to a vehicle equipped with a four-wheel drive device that switches between a two-wheel drive mode and a four-wheel drive mode and is configured as an electric power steering device. FIG. 3 is a block diagram showing the electronic control device shown in FIG.

In FIG. 2, reference numeral 10 denotes a steering wheel. The steering wheel 10 drives a rack bar 16 via a steering shaft 12 and a steering gear box 14. A power unit 20 is drivingly connected to the steering shaft 12 by a gear reduction mechanism 18. The power unit 20 has a motor 22 and an electromagnetic clutch 24 for selectively drivingly connecting the gear reduction mechanism 18 and the motor 22.

In the illustrated embodiment, the steering shaft 12 has a torque sensor 28 for detecting a steering torque T.
Is provided, and the output of the torque sensor is supplied to the electronic control unit 32. A signal indicating the vehicle speed V detected by the vehicle speed sensor 34 and a drive mode detected by a position sensor 36 attached to a drive mode switching lever of a four-wheel drive device (not shown) are sent to the electronic control unit 32. Is also input.

In the four-wheel drive system, the drive mode is switched to the two-wheel drive mode or the four-wheel drive mode by operating the drive mode switching lever by the driver of the vehicle. In the four-wheel drive mode, all the wheels, that is, the rear two wheels and the front two wheels that are the steered wheels are driven.

As shown in detail in FIG. 3, the electronic control unit 32 includes a microcomputer 38, which includes a CPU 40, a ROM 42,
M44, input port device 46, output port device 48
These are connected to each other by a bidirectional common bus 50. A signal indicating the steering torque T detected by the torque sensor 28, a signal indicating the vehicle speed V detected by the vehicle speed sensor 34, and a signal indicating the drive mode detected by the position sensor 36 are input to the input port device 46. It has become.

The input port device 46 appropriately processes the signal inputted thereto, and in accordance with the instruction of the CPU 40 based on the control program stored in the ROM 42, the CPU and the R.
The processed signal is output to the AM 44. The ROM 42 stores a control program shown in FIG. 4 and maps corresponding to the graphs shown in FIGS. The CPU 40 performs various calculations and signal processing based on the control program shown in FIG. The output port device 48 outputs a control signal to the motor 22 via the drive circuit 52 according to the instruction of the CPU 40,
Further, a control signal is output to the electromagnetic clutch 24 via the drive circuit 54.

Next, the operation of the first embodiment will be described with reference to the flowchart shown in FIG. The control by the electronic control unit 32 is started when an ignition switch (not shown in FIG. 2) is closed.

First, in step 10, a control signal is output to the electromagnetic clutch 24 via the drive circuit 54 to connect the clutch. In step 20, the steering torque T detected by the torque sensor 28 is indicated. A signal, a signal indicating the vehicle speed V detected by the vehicle speed sensor 34, and a signal indicating the drive mode detected by the position sensor 36 are read. In step 30, it is determined whether or not the drive mode of the four-wheel drive device is the four-wheel drive mode. When it is determined that the drive mode is the two-wheel drive mode, the process proceeds to step 40, When it is determined that the drive mode is the four-wheel drive mode, step 8 is executed.
Go to 0.

In step 40, a time differential value Δθ of the steering angle is calculated, and the steering angle θ and its time differential value Δθ are calculated.
Is greater than or equal to 0, that is, whether the steering wheel is in a further turning state is determined.
If it is determined that ≧ 0, step 50
The basic assist amount Tab is calculated from the map Au of the graph shown in FIG. 5 based on the steering torque T, and θ · Δθ ≧
If it is determined that the value is not 0, step 60
The basic assist amount Tab is calculated from the map Ad of the graph shown in FIG.

In step 70, the absolute value of the basic assist amount Tab calculated in step 60 is calculated in step 50 or 60 one cycle before or the basic value set in step 120 described later. It is determined whether or not the assist amount Tab _n-1 is larger than the absolute value, and | Tab |>
| Tab _n-1 | a flow proceeds to step 130 when the determination of the effect is not been _{performed, | Tab |> | Tab n} -1 | when a is that the decision is made, the process proceeds to step 120.

Similarly, in step 80, the time differential value Δθ of the steering angle is calculated, and it is determined whether or not the product of the steering angle θ and the time differential value Δθ is 0 or more, that is, the steering wheel is increased. State is determined, and θ
When it is determined that Δθ ≧ 0, in step 90, the basic assist amount Tab is calculated from the map Bu of the graph shown in FIG.
If it is determined that Δθ ≧ 0, the basic assist amount Tab is calculated in step 100 from the map Bd of the graph shown in FIG.

In step 110, the absolute value of the basic assist amount Tab calculated in step 100 is calculated in step 90 or 100 one cycle before or the basic value set in step 120 described later. Assist amount Tab
_It is determined whether or not the absolute value is greater than the absolute value of _{n-1.
b |> | Tab n-1} | a flow proceeds to step 130 when the determination of the effect is not been _{performed, | Tab |> | Tab n} -1 | when a is that the decision is made, the process proceeds to step 120. In step 120, the basic assist amount Tab is set to the basic assist amount Tab _n-1 one cycle before.

In step 130, the vehicle speed coefficient Kv is calculated from a map corresponding to the graph shown in FIG. 6, and in step 140, steps 50, 60, 90, 10
The assist amount Ta is calculated as the product of the basic assist amount Tab calculated at step 0 or set at step 120 and the vehicle speed coefficient Kv calculated at step 130,
In step 150, a control signal corresponding to the assist amount Ta is output to the motor 22 via the drive circuit 52, so that the steering assist force is controlled to a value corresponding to the assist amount Ta, and thereafter, the process returns to step 20. .

Thus, according to the first embodiment shown, when the drive mode of the four-wheel drive device is the two-wheel drive mode, the basic assist amount Tab is calculated from the map Au in FIG. 5 when the steering wheel is turned further. When turning back the steering wheel, the basic assist amount Tab is calculated from the map Ad in FIG. 5 when the driving mode is the four-wheel drive mode. This is calculated from the map Bd when the steering wheel is turned back.

In this case, since the inclination of the map Bu is larger than the inclination of the map Au and the inclination of the map Bd is larger than the map Ad, the basic assist amount Tab in the four-wheel drive mode is higher than that in the two-wheel drive mode. Set to the value
As a result, the steering assist force is also set to a high value, so that the change in steering response feeling caused by torque steer at the time of turning and turning back of the steering wheel in the four-wheel drive mode is reliably reduced, and the steering feeling is improved. Is done.

In addition, according to the first embodiment shown in the drawings, regardless of whether the drive mode of the four-wheel drive device is the two-wheel drive mode or the four-wheel drive mode, step 70 or 110 is performed when the steering wheel is turned back. Since the basic assist amount Tab is maintained at the basic assist amount at the time of starting the turning back until the determination of NO is made, the turning back is performed after the steering wheel is turned further as shown in FIG. Is performed, hysteresis is given to the change in the basic assist amount, and the basic assist amount is maintained constant for a while after the turning-back operation is started, thereby also ensuring a good steering feeling.

Next, the operation of the second embodiment will be described with reference to the flowchart shown in FIG. In FIG. 8, steps corresponding to the steps shown in FIG. 4 are assigned the same step numbers as those given in FIG.

In this embodiment, steps 50 and 6
At 0, the basic assist amount Tab is calculated from the maps Au and Ad in the graph of FIG.
At 00, the basic assist amount Tab is calculated from the maps Au and Cd in the graph of FIG. 9, and the other steps are executed in the same manner as in the first embodiment.

Therefore, according to this embodiment, the basic assist amount Tb is set to a higher value at the time of turning back the steering wheel when the drive mode of the four-wheel drive device is the four-wheel drive mode than in the two-wheel drive mode. As a result, the steering assist force is also set to a high value, so that the change in steering response due to torque steer at the time of turning back the steering wheel in the four-wheel drive mode is reliably reduced, and the steering feeling is reduced. Be improved.

According to the second embodiment, as shown in FIG. 10, after the steering wheel is turned further, the basic assist amount in the case where the turning back is performed is hysteresis. since Rishi-width increases at a case of the four-wheel drive mode than in the two-wheel drive mode, not only the response change of the switching-back time of steering of the steering wheel, also effectively the response changes during steering hold Can be reduced.

Although the present invention has been described in detail with reference to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments may be made within the scope of the present invention. The possibilities will be clear to the skilled person.

For example, in the illustrated embodiment, the four-wheel drive is a mode-switching four-wheel drive, and the basic assist amount depends on whether the drive mode is the two-wheel drive mode or the four-wheel drive mode. Although the calculation map is switched, when the four-wheel drive device is a four-wheel drive device that increases or decreases the drive torque distribution ratio of the steered wheels and the non-steered wheels,
A plurality of maps for calculating the basic assist amount are set according to the drive torque distribution of the steered wheels so that the basic assist amount is calculated to be a higher value as the drive torque distribution of the steered wheels increases with respect to the same steering torque, The basic assist amount may be calculated by selecting those maps according to the drive torque distribution of the steered wheels.

Although the illustrated embodiment is an electric power steering apparatus, it has a bypass passage communicating and connecting the left and right cylinder chambers, and a flow control valve provided in the middle of the bypass passage, and has The power steering device of the present invention may be configured as a hydraulic power steering device as long as the steering assist force can be increased and corrected in accordance with the drive torque distribution or the hysteresis width of the steering assist force can be increased and corrected.

[0037]

As is apparent from the above description, according to the present invention, when the drive torque distribution of the steered wheels is high, the steering assist force correcting means M4 controls the drive torque distribution of the steered wheels.
Since minute steering assist force increases corrected also <br/> than when low Rutotomoni its hysteresis width steering assist force is increased correction is increased corrected, when the high drive torque distribution of the steering wheel It is possible to reduce a change in steering response feeling caused by torque steering that is likely to occur, thereby improving steering feeling.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a power steering device according to the present invention in correspondence with the description in the claims.

FIG. 2 shows an embodiment of a power steering device according to the present invention applied to a vehicle equipped with a four-wheel drive device that switches between a two-wheel drive mode and a four-wheel drive mode and configured as an electric power steering device. It is a schematic block diagram.

FIG. 3 is a block diagram showing the electronic control device shown in FIG. 2;

FIG. 4 is a flowchart showing a first embodiment of a control flow achieved by the electronic control device shown in FIGS. 2 and 3.

FIG. 5 is a graph showing a relationship between a steering torque T detected by a torque sensor and a basic assist amount Tab.

FIG. 6 is a graph showing a relationship between a vehicle speed V detected by a vehicle speed sensor and a vehicle speed coefficient Kv.

FIG. 7 is a graph showing an example of a change in the basic assist amount Tab when the steering wheel is turned back after the steering wheel is turned further in the first embodiment.

FIG. 8 is a flowchart showing a second embodiment of a control flow achieved by the electronic control device shown in FIGS. 2 and 3;

FIG. 9 is a graph showing a relationship between a steering torque T detected by a torque sensor and a basic assist amount Tab.

FIG. 10 is a graph showing an example of a change in the basic assist amount Tab when the steering wheel is turned back after the steering wheel is turned further in the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Steering wheel 12 ... Steering shaft 14 ... Steering gear box 16 ... Rack bar 22 ... Motor 24 ... Electromagnetic clutch 28 ... Torque sensor 32 ... Electronic control unit 34 ... Vehicle speed sensor 36 ... Position sensor

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-262250 (JP, A) JP-A-62-120276 (JP, A) JP-A-1-95970 (JP, A) JP-A-4- 87882 (JP, A) JP-A-59-130780 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (1)

(57) [Claims] [Claim 1] In a power steering apparatus mounted modifiable vehicle drive torque distribution between the steering wheel and the non-steering wheels, a steering assist force generating means for generating a steering assist force, at least the steering torque wherein a steering assist force adjusting means for increasing or decreasing adjusts the steering assist force, the and determines the drive torque distribution determining means for determining whether or not the drive torque distribution is higher in the steering wheel, when the drive torque distribution of the steering wheel is high in accordance with the ; and a steering assist force correction means driving torque distribution of the steering wheel is the that the steering assist force increases correction or increases corrects the steering assist force increases the hysteresis width of the co-Niso correction than when low Power steering device.