JPH072129A - Method for diagnosing abnormality of yaw rate sensor - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the control accuracy by using the yaw rate by comparing the simulated yaw rate calculated by dividing the speed difference between the right and left wheels while the vehicle is traveling by the tread with the signal of the yaw rate sensor to diagnose the presence of abnormality of the yaw rate sensor and its wiring. CONSTITUTION:The yaw rate is the rotational angular velocity around the vertical axis of a vehicle 1, and proportional to the speed difference DELTA N between the right and left wheels and inversely proportional to the tread Td of the vehicle 1. Thus, the pseudo yaw rate Y' equal to the rotational angular velocity to be generated in the vehicle 1 can be calculated by the expression Y'=DELTA N/Td by using the speed difference between the right and left wheels and the tread Td. In the vehicle 1 provided with a yaw rate sensor 44 to output the signal corresponding to the rotational angular velocity of the vehicle 1, the speed difference DELTA N between the right and left wheels when the vehicle is traveling is calculated by the signal from wheel speed sensors 44-48, and divided by the tread Td to calculate the pseudo yaw rate Y'. The calculated value is compared with the signal of the yaw rate sensor 44 to diagnose the presence of abnormalities of the yaw rate sensor 44 and its wiring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing an abnormality in a yaw rate sensor used in a four-wheel steering system (4WS) for vehicles such as automobiles.

[0002]

2. Description of the Related Art In recent years, a yaw rate sensor for directly detecting a yaw rate (rotational angular velocity) of a yawing motion of a vehicle with high accuracy has been developed. With this yaw rate sensor, not only in the case of steering the front wheels, but also changes in the behavior of the vehicle due to disturbances such as road surface conditions and side winds can be promptly detected. Therefore, for example, a method of positively using the yaw rate of a yaw rate sensor in a four-wheel steering system to control the rear wheel steering has been proposed. As this rear wheel steering control,
For example, the proportional gain of the steering wheel angle is set in the opposite phase direction in consideration of the maneuverability, and the proportional gain of the yaw rate is set in the in-phase direction in consideration of the stability. It is known to steer rear wheels by phase steering angle proportional control and yaw rate feedback control.

According to this control method, when the yaw rate sensor fails, the common mode control for keeping the vehicle on the stable side is lost. Then, the rear wheels may be steered in reverse phase only by the steering wheel angle, the vehicle may spin, and the reverse phase control mode may be maintained, resulting in a problem that the drivability is deteriorated. For this reason, it is desired to quickly and accurately diagnose the presence or absence of abnormality in the yaw rate sensor and its wiring to make it fail-safe.

Conventionally, the following methods have been considered as the abnormality diagnosis of the yaw rate sensor. That is, since the minimum and maximum values of the output voltage under normal conditions are known from the characteristics of the sensor, an abnormality is determined when the values deviate from these values.
Also, under running conditions such as a vehicle stop that does not produce a yaw rate, the neutral reference voltages on the left and right are checked to diagnose whether there is an abnormality.

[0005]

By the way, in the above-mentioned prior art, the minimum, maximum, and maximum yaw rate sensors are used.
Since this is a method of diagnosing an abnormality using a neutral reference output voltage, it only detects a state in which the sensor and its wiring have completely failed. Therefore, it is not possible to determine an abnormality in which the value of the output signal gradually becomes inaccurate due to secular change of the yaw rate sensor, and in this case, the control using the yaw rate causes a problem such as deterioration in accuracy.

SUMMARY OF THE INVENTION In view of the above points, an object of the present invention is to appropriately and early diagnose abnormalities in the signal of the yaw rate sensor and prevent deterioration of control accuracy using the yaw rate.

[0007]

In order to achieve this object, the present invention is a vehicle equipped with a yaw rate sensor that outputs a signal according to the rotational angular velocity of the vehicle, and calculates the speed difference between the left and right wheels when the vehicle is running, This speed difference is divided by the tread to calculate the pseudo yaw rate, and the signal from the yaw rate sensor is compared with this pseudo yaw rate to diagnose whether or not there is an abnormality in the yaw rate sensor and its wiring.

[0008]

According to the present invention based on the above method, when the vehicle is traveling on a road surface of a high μ road in a state where the influence of side wind is small, the pseudo yaw rate substantially equal to the rotational angular velocity generated in the vehicle is generated by the speed difference between the left and right wheels and the tread. It is calculated. Therefore, by comparing the signal of the yaw rate sensor with this pseudo yaw rate, the accuracy of the sensor signal is judged when the yaw rate is generated during running, and when the signal gradually becomes inaccurate due to aging of the sensor, Abnormality is accurately diagnosed at the stage.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2, an outline of the vehicle drive system and the four-wheel steering system will be described. First, in the vehicle 1, the engine 2 is connected to the clutch 3 and the transmission 4, and the output side of the transmission 4 is configured to be transmitted to the front wheels 7 via the front differential 5, the axle 6, and the like. The output side of the transmission 4 is also configured to be transmitted to the rear wheel 11 via the propeller shaft 8, the rear differential 9, the axle 10, and the like.
Four-wheel drive runs. Further, it has a front wheel steering device 20 and a rear wheel steering device 30 as a four-wheel steering system.

In the front wheel steering system 20, a steering shaft 22 having a handle 21 has a hydraulic control valve 2.
3 is connected to the front wheels 7 via the power cylinder 24, the rod 25, and the knuckle arm 26, and the front wheels 7 are manually steered by operating the steering wheel. Rear wheel steering device 3
Reference numeral 0 denotes an electric motor 31, which is connected to an eccentric shaft 33 via a worm gear 32 for reduction, and which is connected to the eccentric shaft 33 via a link 34, a lever 35, a knuckle arm 36, and the like. It is connected to the wheels 11 and is configured to automatically steer the rear wheels 11 by driving a motor. In addition, when the motor power is turned off during an abnormality, the worm gear 32
Due to the non-reciprocity, the rear wheel 11 is maintained in a predetermined steering angle state with respect to the road surface external force.

The control system includes a steering wheel angle sensor 40 for detecting the steering wheel angle θ, a steering wheel angular velocity sensor 41 for detecting the steering wheel angular velocity dθ, a rear wheel steering angle sensor 42 for detecting the rear wheel steering angle Er, and a rear wheel steering angular velocity ωr. It has a rear wheel steering angular velocity sensor 43 for detecting. Further, it has a yaw rate sensor 44 for detecting a yaw rate γ of a rotational angular velocity according to the turning state of the vehicle. Further, in order to calculate the control vehicle speed V, a front left wheel speed sensor 45 for detecting the front left wheel speed Nfl and a rear right wheel speed sensor 46 for detecting the rear right wheel speed Nrr are provided, and these sensor signals are supplied to the control unit 50. Is input to the motor 31 to be electrically processed, and a motor signal corresponding to the steering direction of the rear wheels, the steering angle, and the steering angular velocity is output to the motor 31.

The control unit 50 controls the front left wheel speed Nfrl.
It has a vehicle speed calculation unit 51 to which the rear right wheel speed Nrr is input, and calculates the vehicle speed V for control by V = (Nfl + Nrr) / 2. The vehicle speed V is input to the steering wheel angle coefficient setting unit 52, the steering wheel angle coefficient Kθ is set as a function of the vehicle speed V, and simultaneously input to the yaw rate coefficient setting unit 53, and the yaw rate coefficient Kγ is similarly set as a function of the vehicle speed V. To do. The steering wheel angle coefficient Kθ has a reverse phase over the entire vehicle speed as shown in the steering angle gain map of FIG. 3A, and has a characteristic that the absolute value of the value decreases and decreases as the vehicle speed V decreases in the low and medium speed range. The yaw rate coefficient Kγ is in-phase throughout the vehicle speed as shown in the yaw rate gain map in the same figure, and has a characteristic that it gradually increases as the vehicle speed V increases. Therefore, both coefficients Kθ and Kγ are set with reference to this map.

The steering wheel angle θ and the steering wheel angle coefficient Kθ are input to the multiplication unit 54 to calculate a multiplication value Kθ · θ of both, and the yaw rate γ and the yaw rate coefficient Kγ are also input to the multiplication unit 55 to be both multiplication values Kγ · θ. Calculate γ. These two multiplication values Kθ · θ and Kγ · γ are input to the target rear wheel steering angle calculation unit 56, and the target rear wheel steering angle ET is calculated by ET = Kγ · γ + Kθ · θ. Therefore, the term of Kγ · γ is a stabilizing element that keeps the vehicle on the stable side, and the term of Kθ · θ is a turning element that promotes turning.

Here, the yaw rate γ is generated in accordance with the turning state of the vehicle due to turning or disturbance in the entire vehicle speed, and the coefficient Kγ is a characteristic of the increasing function of the vehicle speed V. Therefore, the value of Kγ · γ becomes larger as the vehicle speed V increases. growing. The steering wheel angle θ is generally very small in the medium-high speed range, and therefore the value of Kθ · θ becomes close to zero even if the coefficient Kθ is small in the opposite phase direction. Therefore, when the yaw rate γ is detected in the medium-high speed range, the target rear wheel steering angle ET is in the in-phase direction due to the value of Kγ · γ, and stability-oriented control is performed. In the low speed range where the steering wheel angle θ is large, the turning property is controlled with emphasis on the value of Kθ · θ in the opposite phase direction, and at this time, the yaw rate γ is corrected to the stable side by the value of Kγ · γ in the in-phase direction.

The target rear wheel steering angle ET and the rear wheel steering angle Er are input to the deviation calculating section 57 to calculate the deviation ED by ED = ET-Er. This deviation ED is the target rear wheel turning speed setting unit 5
8, and the target rear wheel turning speed ωo corresponding to the deviation ED is set by the map of FIG. 3 (b). Further, the target rear wheel turning speed ωo and the rear wheel steering angular speed ωr are input to the speed difference calculation unit 59, and the speed difference ωd is calculated by ωd = ωo−ωr. Then, the speed difference ωd is input to the control amount setting unit 60,
The control amount Kp of the proportional component is set according to the speed difference ωd, and the driving unit 61 supplies the forward or reverse motor current I according to the control amount Kp to the motor 31.

In the above control system, the yaw rate sensor 4
The abnormality diagnosis of No. 4 will be described. First, the yaw rate γ is the rotational angular velocity of the vehicle 1 about the vertical axis, and is proportional to the speed difference ΔN between the left and right wheels and inversely proportional to the tread Td of the vehicle 1.
Therefore, using the speed difference ΔN between the left and right wheels and the tread Td,
Pseudo yaw rate γ'equal to the rotational angular velocity generated in the vehicle 1
Can be calculated by γ ′ = ΔN / Td. Vehicle 1
By comparing the signal of the yaw rate sensor 44, which is attached to, and detects the rotational angular velocity, with the pseudo yaw rate γ ′, it is possible to constantly diagnose whether the signal of the yaw rate sensor 44 is abnormal. Further, in the case of the four-wheel drive vehicle of the embodiment, the four wheels are the drive wheels, and therefore the accuracy of the diagnosis can be improved by eliminating the influence of wheel slip or the like when calculating the speed difference ΔN.

Therefore, in addition to the wheel speed sensors 45 and 46 described above, the front right wheel speed sensor 4 for detecting the front right wheel speed Nfr.
7. Rear left wheel speed sensor 48 for detecting rear left wheel speed Nrl
Therefore, the wheel speeds of the four wheels can be detected. Further, it has an accelerator switch 49, and this switch signal is input to the acceleration / deceleration determination unit 62, and when it is ON, acceleration is turned OFF.
If it is, judge the deceleration. The acceleration / deceleration signal and the wheel speeds Nfl, Nfr, Nrl, and Nrr of the four wheels are calculated by the diagnostic coefficient calculation unit 6
3 and input the pseudo yaw rate γ'for acceleration and deceleration.
And a larger constant a considering the fluctuation range in the case of driving wheels
(For example, ± 0.25), two diagnostic coefficients K1 and K2
To calculate. The two diagnostic coefficients K1 and K2 and the yaw rate γ of the yaw rate sensor 44 are calculated by the sensor abnormality diagnosis unit 64.
Is input to the sensor 44 and the two are compared to diagnose whether or not there is an abnormality in the sensor 44 and its wiring.

In the rear wheel steering control of the embodiment, the fail safe when the yaw rate sensor 44 is abnormal will be described. Here, when the yaw rate sensor 44 is abnormal,
It is controlled only by the steering wheel angle θ. Therefore, an abnormal signal is input to the steering wheel angle coefficient setting unit 52 and switched to the first-generation temporary proportional gain Kθ ′ as indicated by the alternate long and short dash line in FIG. Further, the failure signal is input to the target rear wheel steering angle calculation unit 56, and the target rear wheel steering angle ET is calculated only by the steering wheel angle θ and the temporary proportional gain Kθ ′, and the rear wheel steering control is performed.

Next, the operation of this embodiment will be described. First, the engine 2 is operated, and the transmission power of the transmission 4 is transmitted to the front wheels 7 and the rear wheels 11 by the drive system, so that the vehicle 1 moves
Drive with wheel drive. At this time, when the driver operates the steering wheel 21, the front wheel steering device 20 steers the front wheels 7 to manually steer the vehicle, and the rear wheel steering device 30 drives the vehicle in a traveling state.
The rear wheel 11 is automatically steered according to the steering wheel operation and the behavior of the vehicle.

At this time, the flow chart of FIG. 4 is executed every predetermined time to diagnose whether the yaw rate sensor 44 is abnormal. That is, in step S1, the four wheel speeds Nfl, N
The fr, Nrl and Nrr and the yaw rate γ are read, and the accelerator switch 49 is checked in step S2. Then, when accelerating the switch ON, the process proceeds to step S3, and in order to prevent deterioration of the diagnostic accuracy when any of the four wheels slips, the slower wheel speed of the left front wheel and the right front wheel, for example, Nfl and Nfr are selected respectively. To do. Then step S
The speed difference ΔN between the left and right wheels is calculated by subtracting Nfl and Nfr, which are slower in the left and right wheels, in Step 4, and the speed difference ΔN is calculated in Step S5.
Is divided by the average value Td of the front and rear treads to calculate the pseudo yaw rate γ '. Therefore, the influence of disturbance such as side wind is small on the road surface of the high μ road, and the pseudo yaw rate γ ′ is substantially equal to the rotational angular velocity generated in the vehicle 1 when the vehicle travels following the driver's steering wheel operation.

Then, in step S6, the smaller diagnostic coefficient K1 and the larger diagnostic coefficient K1 are calculated using the pseudo yaw rate γ'and the constant a depending on the fluctuation range in the normal case, and the process proceeds to step S7. Two diagnostic coefficients K1 and K2 corresponding to the rotational angular velocity are compared with the yaw rate γ of the yaw rate sensor 44. When the value of the yaw rate γ is accurate and falls within the range of the two diagnostic coefficients K1 and K2,
The process proceeds to step S8 and is determined to be normal. When the value of the yaw rate γ deviates to one side in the increasing / decreasing direction and is out of the range, the process proceeds to step S9, and it is determined whether the wiring of the sensor 44 or the harness thereof is abnormal. Therefore, when the yaw rate is actually generated under a certain running condition, the yaw rate sensor 44
The accuracy of the signal is judged, and when the signal gradually becomes inaccurate due to the secular change of the sensor 44 or the like, the abnormality is appropriately diagnosed at an early stage.

When the accelerator switch is decelerated, the process proceeds from step S2 to step S10. Then, in order to prevent deterioration of the diagnostic accuracy when any of the four wheels is locked during deceleration, the faster wheel speed of the left front wheel and the right front wheel, for example, Nrl, Nrr, is selected, respectively, and then the process proceeds to step S4 and thereafter. Do the same with. Therefore, when the four wheels are drive wheels, the signal of the yaw rate sensor 44 is diagnosed with high accuracy in a state where there is no influence of slip and lock of the wheels.

Next, the rear wheel steering control when the yaw rate sensor 44 is normal will be described. The steering wheel angle coefficient Kθ and the yaw rate coefficient Kγ are set in accordance with the vehicle speed V, and the steering wheel angle θ and the coefficient Kθ, the yaw rate γ and the same. Coefficient Kγ
The target rear wheel steering angle ET is calculated by. Then, the deviation ED between the target rear wheel steering angle ET and the rear wheel steering angle Er is calculated, and the deviation ED
The target rear wheel turning speed ωo is set according to the above, the speed difference ΔNωd between the target rear wheel turning speed ωo and the rear wheel steering angular speed ωr is calculated, and the motor current I of the control amount Kp corresponding to the speed difference ΔNωd is calculated.
Is output to drive the motor 31. Therefore, in the rear wheel steering device 30, the worm gear 32 and the eccentric shaft 33 are rotated by the motor 31, the link 34 and the lever 35 are swung left and right, and the rear wheel 11 is automatically steered. Rear wheel 1 in this case
Reference numeral 1 denotes an in-phase or anti-phase, which is subjected to anti-phase steering angle proportional control and yaw rate feedback control so as to obtain a desired steering angle or steering angular velocity.

Therefore, when the steering wheel 21 is greatly turned at a low speed such as starting, the target rear wheel steering angle ET becomes negative due to the value of Kθ · θ, and the rear wheel 11 is reverse-phase steered to make a small turn.
At this time, if the vehicle makes a sharp turn or the yaw rate γ increases due to the vehicle turning due to the road surface μ, the value of Kγ · γ causes the rear wheel 1
The reverse-phase steering of 1 is reduced and corrected, and the behavior of the vehicle is stabilized. When turning at medium and high speeds, the target rear wheel steering angle ET is mainly K
The value of γ · γ becomes positive and the rear wheels 11 are steered in phase,
Therefore, the stability of the vehicle when turning is improved. If the vehicle suddenly turns left or right due to a disturbance such as a crosswind, the yaw rate γ
Is greatly increased or decreased, and the behavior change of the vehicle 1 is quickly detected. The rear wheel 11 is driven by the vehicle 1 depending on the value of Kγ · γ.
Is steered to maintain the in-phase state despite the turning. For this reason, the vehicle 1 stably assumes an opposite posture so as not to be swept away by a side wind, and smoothly returns to the original course.

On the other hand, when the yaw rate sensor 44 is abnormal, diagnosis is performed at an early stage when the accuracy of the signal is lost, and an abnormal signal is output early. Then, the proportional gain for the steering wheel angle θ is switched to the temporary proportional gain Kθ ′, the target rear wheel steering angle ET is calculated from the steering wheel angle θ and the temporary proportional gain Kθ ′, and the rear wheel 11 is a function of the steering wheel angle θ and the vehicle speed V. Steering is controlled by. Therefore, the control of the inappropriate rear wheel steering by the inaccurate yaw rate γ is stopped early, and the turning property at low speed and the stability at high speed are secured in the control mode of the temporary proportional gain Kθ ′.

The case of a two-wheel drive vehicle will be described as another embodiment of the present invention. In this two-wheel drive vehicle, the speed difference ΔN between the left and right undriven wheels is always calculated and divided by the tread Td between the left and right wheels to obtain the pseudo yaw rate γ '. In addition, a small constant a considering the small fluctuation range in the case of non-driving wheels
(For example, ± 0.15), two diagnostic coefficients K1 and K2
To calculate. Then, by comparing the two diagnostic coefficients K1 and K2 with the yaw rate γ of the yaw rate sensor 44, it is possible to similarly diagnose the abnormality of the sensor and its wiring.

Although the embodiment of the present invention has been described above, the temporary proportional gain Kθ 'is provided when the yaw rate sensor is abnormal.
Instead of steering the rear wheels, the control may be fixed to a so-called two-wheel steering system (2WS) in which the target rear wheel steering angle ET is zero, and general vehicle characteristics may be secured. In the case of abnormality diagnosis of the yaw rate sensor, various conditions can be added as necessary.

[0028]

As described above, according to the present invention,
In the abnormality diagnosis of the yaw rate sensor, the pseudo yaw rate is calculated from the speed difference between the left and right wheels and the tread, and the pseudo yaw rate is compared with the signal of the yaw rate sensor to diagnose whether there is any abnormality. The abnormality can be accurately diagnosed in the early stage, and the diagnostic accuracy is improved. For this reason, the accuracy of control such as rear wheel steering using the yaw rate is also greatly improved, and erroneous steering can be prevented. In the case of a four-wheel drive vehicle, the accuracy of the abnormality diagnosis is improved because it is a method of calculating the speed difference between the left and right wheels by removing the effects of wheel slip and lock. In the case of a two-wheel drive vehicle,
Diagnosis can be performed with high accuracy based on the speed difference between the non-driven left and right wheels.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system suitable for an abnormality diagnosis method for a yaw rate sensor according to the present invention.

FIG. 2 is a configuration diagram showing an outline of a vehicle drive system and a four-wheel steering system.

FIG. 3 is a diagram showing a map of a steering wheel angle coefficient, a yaw rate coefficient, and a target rear wheel turning speed.

FIG. 4 is a flowchart showing abnormality diagnosis control of a yaw rate sensor.

[Explanation of symbols]

 1 Vehicle 30 Rear Wheel Steering Device 44 Yaw Rate Sensor 45-48 Wheel Speed Sensor 50 Control Unit 62 Acceleration / Deceleration Judgment Section 63 Diagnostic Coefficient Calculation Section 64 Sensor Abnormality Diagnosis Section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B62D 117: 00 137: 00

Claims (3)

[Claims] 1. In a vehicle having a yaw rate sensor that outputs a signal according to a rotational angular velocity of the vehicle, a speed difference between left and right wheels is calculated when the vehicle is running, and the speed difference is divided by a tread to calculate a pseudo yaw rate. A method for diagnosing an abnormality in the yaw rate sensor, characterized by comparing the signal from the yaw rate sensor with the pseudo yaw rate to diagnose the presence or absence of abnormality in the yaw rate sensor and its wiring. 2. When the vehicle is a four-wheel drive vehicle, the driving state is judged, and the speed difference between the slower left and right wheels of each other is determined during acceleration.
At the time of deceleration, the pseudo yaw rate is calculated by using the speed difference between the fast left and right wheels, the two diagnostic coefficients based on this pseudo yaw rate and a large constant are calculated, and these two diagnostic coefficients and the yaw rate sensor signal are compared. The yaw rate sensor abnormality diagnosis method according to claim 1. 3. When the vehicle is a two-wheel drive vehicle, the pseudo yaw rate is calculated using the speed difference between the left and right wheels that are not driven, and two diagnostic coefficients are calculated by the pseudo yaw rate and a small constant, and these two are calculated. 2. The abnormality diagnosis method for the yaw rate sensor according to claim 1, wherein the diagnosis coefficient is compared with the signal from the yaw rate sensor.