JPH10100915A - Power steering gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power steering gear capable of preventing the occurrence of a feeling of interception. SOLUTION: In order to judge whether steering is performed or not, an electronic control unit installed in the power steering device, discriminates whether the absolute value of a torque signal T is above a threshold value The or not (S3), and drives a motor if the result of judgement is affirmative ($2). Further, based on a current signal IM which corresponds to the value of current consumption of the motor, which corresponds to viscous resistance of hydraulic fluid, the threshold value TTH is changed so that the higher the current signal IM the lower the threshold value. As a result, when viscous resistance of the hydraulic fluid is high as it is at lower temperatures, the motor is driven immediately after the steering is started. Thus, since supplementary steering is quickly performed, the occurrence of a feeling of interception can be prevented.

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, and more particularly, to a so-called hydraulic power steering apparatus in which an oil pump is driven by a motor to generate hydraulic pressure, and steering is assisted by the generated hydraulic pressure. . Note that the term "steering" used in this specification means that the steering wheel is operated while a torque equal to or more than a predetermined value is applied.

[0002]

2. Description of the Related Art Conventionally, there has been known a hydraulic power steering apparatus in which an oil pump is rotated by a motor and hydraulic oil is supplied from the oil pump to a power cylinder to reduce the operating force of a steering wheel.
In this type of power steering device, usually, a motor is driven only when the vehicle is being steered, and steering assist is performed.

[0003]

By the way, when the temperature is low in winter or the like, the hydraulic oil tends to cool down and its viscous resistance often increases. For example, when steering is not performed for a long time immediately after starting the engine at a low temperature or at a low temperature, the temperature of the hydraulic oil is low and its viscous resistance is high.

[0004] In such a case, even if the motor is driven to assist the steering, it takes some time until the required amount of hydraulic oil is supplied to the power cylinder. Therefore, even if the steering is started in such a case, the steering assist is not sufficiently performed, and there is a so-called catching feeling. This feeling of being caught is eliminated by the fact that the temperature of the hydraulic oil rises as a result of the repeated steering assist and the viscous resistance decreases. However, it takes a certain amount of time since steering assist must be repeatedly performed until the viscous resistance of the hydraulic oil is sufficiently reduced. As a result, the driver is uncomfortable for a long time.

In order to cope with this, it is conceivable to circulate the hydraulic oil at all times. However, in this case, even when the steering assist is not required, the motor is driven, so that useless electric power is consumed and fuel consumption is deteriorated, which is not preferable. Therefore, an object of the present invention is to solve the above technical problem,
An object of the present invention is to provide a power steering device that can prevent the occurrence of a feeling of being stuck.

[0006]

According to a first aspect of the present invention, there is provided a power supply for driving an oil pump by a motor to generate a hydraulic pressure, and using the generated hydraulic pressure to assist steering. A steering device, comprising: detection means for detecting steering data according to the degree of steering; and determination for determining whether the steering data detected by the detection means is equal to or greater than a predetermined threshold. Means, a control means for driving the motor when the steering data is determined to be equal to or greater than the threshold value, and a current detection means for detecting a current consumption value of the motor. And a threshold value changing means for changing the threshold value according to the current consumption value of the motor detected by the current detecting means. That.

According to the present invention, steering data corresponding to the degree of steering is detected, and when the detected steering data is equal to or greater than a threshold value, it is determined that steering is being performed, and the motor is driven. . The threshold value is changed according to the current consumption value of the motor. Specifically, as in the second aspect of the present invention, the motor current consumption value is changed so as to decrease as the current consumption value increases. Here, the current consumption value of the motor increases as the viscosity resistance of the hydraulic oil increases.
That is, when the viscosity resistance of the hydraulic oil is high, it is necessary to drive the oil pump with a larger driving force than when the viscosity resistance of the hydraulic oil is low. Therefore, the threshold value is set low when the viscosity resistance of the hydraulic oil is high, and is set high when the viscosity resistance of the hydraulic oil is low.

Therefore, when steering is performed when the viscosity resistance of the hydraulic oil is high, such as at low temperatures, the motor is driven even with a small amount of steering. That is, since steering assist is performed immediately after the start of steering, a so-called snagging feeling does not occur. The steering data includes, for example, torque data corresponding to the torque applied to the steering wheel or steering angle data corresponding to the steering angle of the steering wheel.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a configuration of a power steering device to which an embodiment of the present invention is applied. The power steering device is used, for example, by being mounted on a vehicle, and assists the steering of the steering mechanism 1.

[0010] The steering mechanism 1 is provided with a steering wheel 2. A steering shaft 3 is connected to the steering wheel 2, and a pinion gear 4 is attached to a tip of the steering shaft 3. The pinion gear 4 is a rack gear 5 extending in the vehicle width direction.
Is engaged. A tire 7 is attached to the rack gear 5 via a tie rod 6.

When the steering wheel 2 is operated and its rotational force is transmitted to the steering shaft 3, the pinion gear 4 at its tip rotates, and the rack gear 5
Moves in the vehicle width direction. As a result, the movement of the rack gear 5 is transmitted to the tie rod 6, and the direction of the tire 7 changes.
In connection with the rack gear 5, a power cylinder 20 for generating a steering assist force is provided. The power cylinder 20 includes a piston 21 connected to the rack gear 5 and a pair of cylinder chambers 2 defined by the piston 21.
0a and 20b. Hydraulic oil from a hydraulic control valve 23 is supplied to the cylinder chambers 20a and 20b via oil supply paths 22a and 22b indicated by broken lines, respectively.

The hydraulic control valve 23 is interposed in the oil circulation path 24 shown by a broken line. The oil circulation path 24
Hydraulic oil stored in the reservoir tank 25 is pumped out by the oil pump 26, and the pumped hydraulic oil is discharged from the oil pump 26, and is then returned to the reservoir tank 25.
This is the route to return to. The oil pump 26 is driven by a motor M. When the oil pump 26 is driven by the motor M, the hydraulic oil circulates in the oil circulation path 24, and when not driven, the circulation of the hydraulic oil is stopped.

The opening of the hydraulic control valve 23 changes according to the direction and amount of twist of the torsion bar 8 attached to the steering shaft 3, that is, the direction and magnitude of the torque applied to the steering shaft 3. As a result, the supply state of the hydraulic oil to the power cylinder 20 changes. More specifically, when the torsion bar 8 is twisted in one direction, the hydraulic oil is supplied to one cylinder chamber of the power cylinder 20 via one oil supply path. When the torsion bar 8 is twisted in the other direction, the hydraulic oil is supplied to the other cylinder chamber via the other oil supply path. When the torsion bar 8 is not twisted, the hydraulic control valve 23 is in a neutral state, so that the hydraulic oil is not supplied to the power cylinder 20.

When hydraulic oil is supplied to any of the cylinder chambers of the power cylinder 20, the piston 21 moves in any direction along the vehicle width direction. As a result, a steering assist force is generated, and the movement of the rack gear 5 is assisted. The driving of the motor M is controlled by the electronic control unit ECU. The electronic control unit ECU includes a microcomputer having a CPU, a ROM 29 and a RAM. The electronic control unit ECU includes a torque sensor 27
And current, respectively torque signal T and the current signal I _M from the detection circuit 28 is adapted to be applied respectively. The electronic control unit ECU, based on the given torque signal T and the current signal I _M, and controls the motor M.

The torque sensor 27 is provided in association with the torsion bar 8 attached to the steering shaft 3, and is proportional to the torque applied to the steering shaft 3,
Further, a torque signal T having a sign corresponding to the direction of the torque is output. As the torque sensor 27, any type such as a type having a mechanical contact formed of a potentiometer and a non-contact type torque sensor can be applied.

The current detection circuit 28 is provided in connection with the motor M, and outputs a current signal I _M which is proportional to the consumption current value of the motor M. As shown in FIG. 2, the current consumption of the motor M increases as the temperature of the hydraulic oil decreases. That is, the hydraulic oil is supplied from the oil pump 26 driven by the motor M to the power cylinder 20 via the hydraulic control valve 23. If the temperature of the hydraulic oil is low and its viscous resistance is high, the hydraulic oil is operated at a required flow rate. In order to supply oil to the power cylinder 20, it is necessary to drive the oil pump 26 with a large driving force. That is, since the load on the motor M increases, the current value consumed by the motor M also increases.

The ROM 29 stores a table that can be expressed as shown in FIG. This table contains the motor M
In the drive control is for changing the threshold value T _TH used in the determination processing of whether the steering is being performed in accordance with a current signal I _M. To change in accordance with the threshold value T _TH into a current signal I _M is for improving the response of the generation of steering assist force.

In the table, the current signal I _M has the value I _M1
When less than the threshold T _TH corresponds to the maximum value T _TH0. The maximum value T _TH0 is set to a value that can ensure sufficient responsiveness when the viscosity resistance of the hydraulic oil is sufficiently low. In other words, this is a value that has conventionally been used as a reference when determining whether or not steering is being performed. When the current signal I _M is equal to or greater than the value I _M1 and less than the value I _M2 , the threshold value T _TH decreases linearly as the current signal I _M increases. The current signal I _M has the value I _M2
If so, the threshold value T _TH corresponds to the minimum value T _TH1 . The minimum value T _TH1 is set to a value that ensures sufficient responsiveness even when the viscosity of the hydraulic oil is high, such as at low temperatures.

FIG. 4 is a flowchart for explaining the drive control of the motor M by the electronic control unit ECU. When the ignition switch (IG) is turned on and the engine is started, the electronic control unit EC responds accordingly.
U sets a threshold value T _TH for determining whether or not steering is being performed to a maximum value T _TH0 which is an initial value (step S1). Thereafter, the assist control is started (Step S2). That is, driving of the motor M is started. As a result, the oil pump 26 is driven, and the working oil circulates in the oil circulation path 24.

The reason why the assist control is started after the engine is started and before it is determined whether or not the steering is being performed is to reduce the viscous resistance of the hydraulic oil immediately after the engine is started particularly at a low temperature. Then, the electronic control unit ECU
Determines whether the absolute value of the torque signal T provided from the torque sensor 27 is equal to or greater than the threshold value T _TH (step S3). As a result, when it is determined that the absolute value of the torque signal is equal to or larger than the threshold value _TTH, it is determined that steering is being performed, and the motor M is driven. At this time,
The torsion bar 8 is twisted in any direction. Therefore, the hydraulic oil is supplied to the power cylinder 20 via the hydraulic control valve 23. On the other hand, the torque signal T
Is determined to be less than the threshold value T _TH, it is determined that steering is not being performed, and
The threshold value T _TH is changed according to the current signal I _M based on the table stored in step S4 (step S4). Thereafter, the motor M is stopped, and the assist control ends (step S5).

For example, at low temperatures such as winter,
Start the engine immediately after starting the engine.
Often idling to warm, in this case
Indicates that the steering wheel 2 is not being steered.
Become. On the other hand, the viscosity of hydraulic oil
Since the resistance is high, it is
The current consumption of the motor M is high. That is,
Current signal I_MIs the value I _M2That's all. Accordingly
Then, in step S4, the threshold T_THIs the lowest value T_TH1
Is changed to Therefore, when steering is performed
Very small torque immediately after the start of steering
Even in the state, the driving of the motor M is started.

As described above, even when the viscous resistance of the hydraulic oil is high, the steering assist is started immediately after the slight steering immediately after the start of the steering, so that the feeling of being stuck does not occur. On the other hand, since the driving of the motor M is started from a state in which a very small torque is being applied, the viscous resistance of the working oil rapidly decreases. That is, the responsiveness when steering is improved. On the other hand, in this case, the motor M
, The threshold value T _TH is changed to a higher value. As a result, the drive start of the motor M is delayed. Thus, the steering assist can be started at an appropriate timing according to the viscosity resistance of the hydraulic oil.

At a low temperature, if the steering is not performed for a long time after the viscosity resistance of the hydraulic oil once decreases, the viscosity resistance of the hydraulic oil increases again. But,
In this case, the current consumption value of the motor M becomes high and the threshold value T _TH is set low, so that the feeling of catch does not occur. As described above, according to the power steering apparatus according to this embodiment, when the viscosity resistance of the hydraulic oil is high, the threshold value T _TH for determining the steering is set low, so that the steering assist is provided immediately after the start of the steering. Begun early. Therefore, a feeling of catching does not occur.
Therefore, a power steering device with good operability can be provided.

Further, since the steering assist is performed promptly from the start of the steering, the time for circulating the hydraulic oil becomes longer.
Therefore, the viscous resistance of the hydraulic oil can be reduced more quickly than when the threshold value T _TH is fixed. The description of one embodiment of the present invention is as described above, but the present invention is not limited to the above-described embodiment. For example, in the above embodiment, the steering is detected by the torque sensor 27. However, for example, the steering may be detected by a steering angle sensor, and other various sensors may be applied. In the case where the steering angle sensor is used, when the steering angle of the steering wheel 2 is equal to or more than a certain value, it is highly possible that a torque equal to or more than a certain value is applied to the steering wheel 2. Therefore, when a steering angle sensor is used, the term "steering" may be meant to mean a state where the steering angle is equal to or larger than a predetermined value.

In the above embodiment, the current signal I_MWhen
Threshold T_THAnd the current signal I_MIs the value
I_M1And the value I_M2Threshold when less than
Value T _THChange is linear, but the change is
For example, the shape may be step-like or curved. Sa
In addition, the current signal I_MIs the value I_M1And the current signal
No. I_M2Above, the threshold T_THThe best of each
Value T_TH0And the minimum value T_TH1Corresponding to a constant value of
However, also in this case, the current signal I_MLinearly as the
Lowered, stepped, or curved
Or may be lowered. In short, the current signal I_MIs large
Threshold value T so that_THChange
What should I do?

Further, in the above-described embodiment, a case is described in which a table is provided for the process of changing the threshold value T _TH . However, for example, a change equation corresponding to the relationship shown in FIG. It is needless to say that the threshold value T _TH may be changed by storing it and performing arithmetic processing according to the changing formula. In addition, various design changes can be made within the scope described in the claims.

[0027]

As described above, according to the present invention, the threshold value for steering discrimination is changed according to the current consumption value of the motor corresponding to the degree of the viscous resistance of the hydraulic oil. Even if the viscosity resistance of the hydraulic oil is high, the response of the steering assist can be improved. Therefore, the feeling of snagging does not occur. Therefore, a power steering device with good operability can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a power steering device according to an embodiment of the present invention.

FIG. 2 is a graph showing a correspondence between a current consumption value of a motor and a temperature of hydraulic oil.

FIG. 3 is a diagram for explaining a table representing a correspondence relationship between a current signal and a threshold.

FIG. 4 is a flowchart for explaining drive control of a motor in the electronic control unit.

[Explanation of symbols]

Reference Signs List 1 steering mechanism 2 steering wheel 20 power cylinder 26 oil pump 27 torque sensor 28 current detection circuit 29 ROM ECU electronic control unit _IM current signal M motor T torque signal

Claims (2)

[Claims] 1. A power steering device for driving an oil pump by a motor to generate a hydraulic pressure, and assisting the steering with the generated hydraulic pressure, wherein the power steering device detects steering data according to a degree of the steering. Detecting means; determining means for determining whether the steering data detected by the detecting means is equal to or greater than a predetermined threshold; and determining that the steering data is equal to or greater than the threshold value. A control means for driving the motor when determined, a current detection means for detecting a current consumption value of the motor; and a control means for detecting a current consumption value of the motor detected by the current detection means. A power steering apparatus, comprising: threshold changing means for changing a threshold. 2. The power steering apparatus according to claim 1, wherein the threshold value changing means changes the threshold value so that the threshold value decreases as the current consumption of the motor increases.