JPH1159466A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power steering device with an air pressure drop detecting function for a tire. SOLUTION: Reference steering torque predetermined corresponding to a steering angle an a speed is stored in a ROM 33. A CPU 31 reads the reference steering torque corresponding to a steering angle detection value and a speed detection value detected by a steering angle sensor 11 and a speed sensor 12, respectively, out of the ROM 33. The CPU 31 judges air pressure to be abnormal in a tire for one of front right and left wheels FL, LR when the steering torque detection value detected by a torque sensor 13 is kept greater than the reference steering torque for a preset time.

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 applying a steering assist force according to a steering torque and a vehicle speed to a steering mechanism provided in a vehicle.

[0002]

2. Description of the Related Art Conventionally, a power steering apparatus has been used which transmits a driving force generated by an electric motor to a steering mechanism as a steering assist force. The operation of the electric motor is controlled based on the steering torque and the vehicle speed applied to the steering wheel. As the steering torque increases, a larger steering assist force is given to the steering mechanism, and as the vehicle speed increases, the steering assist force decreases. Is to be given.

[0003] On the other hand, a vehicle may be provided with a pneumatic pressure drop detecting device for detecting a pneumatic pressure drop of a tire and generating an alarm. Conventional air pressure drop detection devices include those configured to directly detect tire pressure and those configured to indirectly detect tire pressure reduction based on an increase in the number of rotations of wheels. Thus, when a decrease in tire air pressure occurs, the driver is immediately notified of the decrease, so that the driver can take appropriate measures promptly. Thereby, safe traveling of the vehicle can be expected.

[0004] Since a decrease in air pressure of a tire of a steered wheel has a great influence on steering, detection of a decrease in air pressure of a tire of a steered wheel is more important than detection of a decrease in air pressure of a tire of a non-steered wheel. And the need is high.

[0005]

The power steering apparatus is provided with a structure for collecting data related to the steered wheels, such as a torque sensor and a steering angle sensor. Therefore, it is considered that the use of these can detect a decrease in the air pressure of the tire of the steered wheel. If this is realized, the configuration of the electric system of the vehicle can be simplified and the cost can be reduced as compared with the related art in which an air pressure drop detecting device is provided separately from the power steering device. .

An object of the present invention is to solve the above-mentioned technical problems and to provide a power steering apparatus having a function of detecting a decrease in tire air pressure.

[0007]

Means for Solving the Problems and Effects of the Invention According to a first aspect of the present invention, there is provided a power steering apparatus for applying a steering assist force to a steering mechanism connected to a steered wheel of a vehicle. A vehicle speed sensor for detecting a vehicle speed, a torque sensor for detecting a steering torque, storage means for storing a reference steering torque predetermined according to the vehicle speed, and a reference steering torque corresponding to a vehicle speed detection value detected by the vehicle speed sensor Reading means for reading out from the storage means, and when the detected steering torque detected by the torque sensor is larger than the reference steering torque read by the reading means, an abnormality occurs in the tire air pressure of the steered wheels. And a malfunction determining means for determining that the power steering is present.

The invention according to claim 2 further includes a steering angle sensor for detecting a steering angle, wherein the storage means stores a reference steering torque predetermined according to the steering angle and the vehicle speed. The reading means reads the steering angle detection value detected by the steering angle sensor and the reference steering torque corresponding to the vehicle speed detection value detected by the vehicle speed sensor from the storage means. 2. The power steering device according to claim 1.

FIG. 1 is an illustrative view for explaining a principle for detecting a decrease in air pressure of a tire of a steered wheel based on a steering torque or the like, and shows the tire W of the steered wheel viewed from a side of the vehicle. The situation is represented. The torque T required to steer the tire around the kingpin is a proportional constant k,
The coefficient of friction f between the road surface and the tire W, the shared load N applied to the tire W in the total load of the vehicle, and the contact length a between the tire W and the road surface are given by the following formula (1).

T = k × f × N × a (1) When the air pressure of the tire W decreases, the contact length a increases, and accordingly, the torque T required for turning increases accordingly. . Therefore, if it is possible to detect that the torque T is excessive, it is possible to detect that a decrease in air pressure has occurred in the tire W of the steered wheel. Therefore, in the present invention, the reference steering torque determined in advance according to only the vehicle speed or the vehicle speed and the steering angle is compared with the steering torque detection value detected by the torque sensor, and the steering torque detection value exceeds the reference steering torque. In such a case, it is determined that an abnormality has occurred in the air pressure of the tire of the steered wheel.

In many cases, the power steering apparatus is originally provided with a steering angle sensor, a torque sensor, and the like. Therefore, according to the present invention, the existing structure of the power steering apparatus is used to reduce the tire air pressure. Can be detected. As a result, the configuration of the electrical components mounted on the vehicle is simplified as compared with the case where the air pressure drop detecting device is specially provided, and it is possible to contribute to cost reduction.

According to a third aspect of the present invention, the reference steering torque is set to be equal to or higher than a maximum steering torque assumed when a tire pressure of a steered wheel is normal. 3. The power steering device according to 2. According to this configuration, since a value equal to or greater than the maximum steering torque assumed when the tire air pressure is normal is set as the reference steering torque, when a steering torque exceeding this value is detected by the torque sensor, It can be determined that the air pressure is abnormal.

According to a fourth aspect of the present invention, the abnormality determination means has maintained the state where the steering torque detection value detected by the torque sensor is larger than the reference steering torque read by the reading means for a predetermined time or more. The power steering apparatus according to any one of claims 1 to 3, wherein it is determined that an abnormality occurs in the air pressure of the tire of the steered wheel under the condition.

According to this structure, the condition that the detected torque value exceeds the reference steering torque must be maintained for a predetermined time or more, so that the influence of noise is eliminated and abnormal air pressure of the tire is reliably detected. can do.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 2 is a conceptual diagram showing a basic configuration of the power steering device according to the first embodiment of the present invention. This power steering device is provided in association with a steering mechanism 1 of a vehicle, and is for applying a steering assist force to the steering mechanism 1.

The steering mechanism 1 includes a steering wheel 2 operated by a driver, a steering shaft 3 connected to the steering wheel 2, a pinion gear 4 provided at the tip of the steering shaft 3, and a pinion gear 4 Has a rack gear portion 5a that meshes with
And a rack shaft 5 extending in the left-right direction of the vehicle. Tie rods 6 are respectively connected to both ends of the rack shaft 5, and the tie rods 6 are respectively connected to knuckle arms 7 that support front left and right wheels FL and FR as steering wheels. The knuckle arm 7 is provided rotatably around the king pin 8.

With this configuration, the steering wheel 2
Is operated to rotate the steering shaft 3, the rotation is converted by the pinion gear 4 and the rack shaft 5 into a linear motion along the left-right direction of the vehicle. This linear motion
The rotation is converted into the rotation of the knuckle arm 7 around the king pin 8, whereby the steering of the front left and right wheels FL and FR is achieved.

The steering shaft 3 is divided into an input shaft 3a on the side of the steering wheel 2 and an output shaft 3b on the side of the pinion 4, which are adapted to the direction and magnitude of the steering torque applied to the steering wheel 2. They are connected by a torsion bar 9 which produces a corresponding twist.
The steering assist force from the electric motor 40 is applied to the output shaft 3b via the electromagnetic clutch 41 and the speed reducer 42. The electromagnetic clutch 41 is provided for disconnecting the motor 40 from the steering mechanism 1 when an abnormality occurs in the system.

The magnitude of the steering assist force is adjusted by controlling the voltage applied to the motor 40. The motor 40 is controlled by the electronic control unit 30. The electronic control unit 30 outputs an output signal of a steering angle sensor 11 for detecting a steering angle of the steering wheel 2, an output signal of a vehicle speed sensor 12 for detecting a speed of the vehicle, and a direction of a torque applied to the torsion bar 9. A voltage applied to the motor 40 is determined on the basis of the output signal of the torque sensor 13 for detecting the magnitude, and thereby, a steering assisting force corresponding to the steering angle, the vehicle speed and the steering torque is given to the steering mechanism 1. become. The vehicle speed sensor 12 may directly detect the speed of the vehicle, or may calculate the speed of the vehicle based on output pulses of a wheel speed sensor provided in connection with the wheels. .

The electronic control unit 30 includes a CPU 31, C
A RAM 32 for providing a work area of the PU 31; a ROM 33 for storing an operation program of the CPU 31 and a reference steering torque for detecting a decrease in tire air pressure; and a bus 34 for interconnecting these. I have. The CPU 31 operates according to the operation program stored in the ROM 33, and controls the voltage applied to the motor 40 so that an appropriate steering assist force corresponding to the steering angle, the vehicle speed, and the steering torque is applied to the steering mechanism 1.

Further, the CPU 31 executes the air pressure drop detection processing according to a predetermined air pressure drop detection program stored in the ROM 33, so that the front left and right wheels FL, FR.
Of any of the tires has a decrease in air pressure. If it is determined that a decrease in tire air pressure has occurred, an alarm lamp 15 disposed on an instrument panel or the like of the vehicle is turned on.

FIG. 3 is a flowchart for explaining the air pressure drop detecting process. First, the timer T for judging a decrease in air pressure is cleared, and its time counting operation is started (step S1). Next, the CPU 31 takes in the respective detection values of the steering angle sensor 11, the vehicle speed sensor 12, and the torque sensor 13 (Step S2). Next, the CPU 31
A reference steering torque as a reference value for detecting a decrease in tire air pressure is read from the ROM 33 based on the steering angle detection value and the vehicle speed detection value taken in step S2 (step S3 (reading means)). As shown in the graph of FIG. 4, the ROM 33 stores a reference steering torque value determined in advance according to the steering angle and the vehicle speed V as a table, and the table corresponds to the steering angle detection value and the vehicle speed detection value. The reference steering torque thus set is read.

The CPU 31 compares the read reference steering torque with the detected steering torque detected by the torque sensor 13 (step S4). If the detected steering torque value is equal to or smaller than the reference steering torque, the time counted by the timer T is cleared to 0 (step S5), and the processing from step S2 is repeated. On the other hand, if the detected steering torque value exceeds the reference steering torque, the timer T counts a predetermined reference time Tref (for example, 1800 seconds).
Is compared with (step S6). If the time measured by the timer T has not reached the reference time Tref, the processing from step S2 is repeated.

As described above, the processing of steps S4 to S6 corresponds to the function of the CPU 31 as the abnormality determining means. When the state where the detected steering torque value exceeds the reference steering torque continues, the time measured by the timer T reaches the reference time Tref, and the determination in step S6 is affirmed. In response to this, the CPU 1 performs an abnormal process including a process of lighting the alarm lamp 15 (step S7). The driver turns on the front left and right wheels FL, FR, which are the steered wheels, by turning on the alarm lamp 15.
It can be recognized that a decrease in air pressure has occurred in any of the tires.

The reference steering torque shown in FIG. 4 is set to be equal to or slightly larger than the steering torque required when the vehicle is fully loaded (that is, when the overall load of the vehicle is maximized). That is, test running is performed under the condition that the overall load of the vehicle is maximized, and the steering torque for each steering angle during the stationary steering (steering while the vehicle is stationary) and during running at various vehicle speeds V is determined in advance. Detected, and a value equal to or larger than the detected value is set as the reference steering torque. The table of the reference steering torque determined in this way is stored in the ROM 33. Since the larger the steering angle, the larger the steering force is required, the reference steering torque is also increased. Further, as the vehicle speed V increases, the steering can be performed with a small steering force, so that the reference steering torque is reduced.

During the test run, it is preferable that at least the tire pressure of the steered wheels has a value near the lower limit of the specified range. The above-described conditions during the test run are conditions that require the maximum steering torque at each vehicle speed and steering angle. Therefore, if the detected torque value detected by the torque sensor 13 exceeds the reference steering torque, any of the steered wheels FL, F
It is considered that the decrease in the air pressure of the tire R increased the contact area of the tire. In the air pressure drop detection process shown in FIG.
On the condition that the air pressure has continued for only one of the steered wheels FL and FR, it is determined that a decrease in air pressure has occurred in one of the tires. Since the continuation of the predetermined time Tref is a condition, an accurate determination can be made without the influence of noise.

As described above, according to this embodiment, it is possible to detect a decrease in the air pressure of the tires of the steered wheels FL and FR by using the torque sensor 13 attached to the power steering device. For this reason, it is not necessary to provide a special air pressure drop detecting device, so that the cost of electrical components provided in the vehicle can be reduced. Moreover, it is possible to avoid running under adverse conditions in which the tire pressure of the steered wheels is reduced, and as a result,
The vehicle can run safely.

FIG. 5 is a conceptual diagram showing a basic configuration of a power steering apparatus according to a second embodiment of the present invention. In FIG. 5, portions corresponding to those in FIG. 2 described above are denoted by the same reference numerals, and description thereof is omitted. The power steering device of this embodiment is configured to apply a steering assist force to the steering mechanism 1 by using a hydraulic pressure generated by an oil pump 26 driven by an electric motor 27.

That is, between the input shaft 3a and the output shaft 3b, a hydraulic control valve 23 whose opening changes in accordance with the direction and size of the torsion bar 9 is interposed. The hydraulic control valve 23 is provided in the middle of the rack shaft 5 and is connected to a power cylinder 20 that applies a steering assist force to the steering mechanism 1. Power cylinder 20
Is a piston 21 provided integrally with the rack shaft 5,
It has a pair of cylinder chambers 20a, 20b partitioned by the piston 21.
0b are oil supply / return paths 22a and 22b, respectively.
Through a hydraulic control valve 23.

The hydraulic control valve 23 further includes an oil circulation passage 24 that passes through a reservoir tank 25 and an oil pump 26.
It is interposed in the middle of. The oil pump 26 is driven by the motor 27, draws out the working oil stored in the reservoir tank 25, and supplies it to the hydraulic control valve 23. Excess hydraulic oil is returned from the hydraulic control valve 23 to the reservoir tank 25 via the oil circulation path 24.

When the torsion bar 9 is twisted in one direction, the hydraulic control valve 23 is connected to one of the cylinder chambers 20a, 20b of the power cylinder 20 via one of the oil supply / return paths 22a, 22b. Supply hydraulic oil to one of the two. When the torsion bar 9 is twisted in the other direction, the oil supply / return path 22a,
22b via the other one of the cylinder chambers 20a, 20b.
Supply hydraulic oil to the other of the two. When the torsion bar 9 is hardly twisted, the hydraulic control valve 23 is in a so-called equilibrium state, and the hydraulic oil circulates in the oil circulation path 24 without being supplied to the power cylinder 20.

When hydraulic oil is supplied to any one of the cylinder chambers of the power cylinder 20, the piston 21 moves in the vehicle width direction. As a result, the steering assist force acts on the rack shaft 5. The magnitude of the steering assist force is adjusted by controlling the voltage applied to the motor 27 that operates the oil pump 26. The motor 27 is controlled by the electronic control unit 30.

Also in the configuration of this embodiment, the steering angle sensor 11, the vehicle speed sensor 12, and the torque sensor 13
The electronic control unit 30 operates in the same manner as in the above-described first embodiment based on the output signal of the first embodiment to detect a decrease in the air pressure of any of the front left and right wheels FL and FR as the steered wheels. it can. Although the embodiments of the present invention have been described above, the present invention can be embodied in other forms. For example, the present invention can be applied to a power steering device other than the configurations shown in FIGS. 2 and 5 described above. However, the present invention is preferably applied to a power steering device having a torque sensor. In this case, by using the torque sensor,
By simply changing the program of the electronic control unit, it is possible to add a function of detecting a decrease in the tire pressure of the steered wheel to the power steering device.

In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of the drawings]

FIG. 1 is an illustrative view for describing a principle of detection of a decrease in tire air pressure according to the present invention;

FIG. 2 is a conceptual diagram showing a basic configuration of a power steering device according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating a process for detecting a decrease in air pressure.

FIG. 4 is a graph for explaining the contents of a table of reference steering torque.

FIG. 5 is a conceptual diagram showing a basic configuration of a power steering device according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 steering mechanism 2 steering wheel 3 steering shaft 11 steering angle sensor 12 vehicle speed sensor 13 torque sensor 20 power cylinder 26 oil pump 27 motor 30 electronic control unit 31 CPU 32 RAM 33 ROM 40 motor FL front left wheel FR front right wheel

Claims (4)

[Claims] 1. A power steering device for applying a steering assist force to a steering mechanism connected to a steered wheel of a vehicle, wherein a vehicle speed sensor for detecting a vehicle speed, a torque sensor for detecting a steering torque, and a predetermined value according to the vehicle speed. Storage means for storing a reference steering torque; reading means for reading a reference steering torque corresponding to a vehicle speed detection value detected by the vehicle speed sensor from the storage means; and reading of a steering torque detection value detected by the torque sensor. A power steering apparatus comprising: an abnormality determination unit configured to determine that an abnormality has occurred in the tire pressure of a steered wheel when the reference steering torque is larger than the reference steering torque read by the unit. 2. The vehicle according to claim 1, further comprising a steering angle sensor for detecting a steering angle, wherein said storage means stores a reference steering torque determined in advance in accordance with a steering angle and a vehicle speed, and said reading means includes: 2. The power steering apparatus according to claim 1, wherein a steering angle detection value detected by a sensor and a reference steering torque corresponding to a vehicle speed detection value detected by the vehicle speed sensor are read from the storage unit. 3. The reference steering torque according to claim 1, wherein the reference steering torque is set to be equal to or higher than a maximum steering torque assumed when a tire pressure of a steered wheel is normal.
A power steering device as described. 4. The steering control apparatus according to claim 1, wherein the abnormality determining means determines whether the steering torque detected by the torque sensor is greater than a reference steering torque read by the reading means for a predetermined time or more. 4. The power steering apparatus according to claim 1, wherein it is determined that an abnormality has occurred in the tire pressure of the wheels.