JP2003014450A - Steering angle estimation device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a steering angle having a reduced error with a small quantity of operation. SOLUTION: A speed detection part 2 detects the respective rotating speeds of left and right wheels based on the outputs from rotational sensors 1a-1d. A speed ratio arithmetic part 3 calculates the rotating speed ratio of the detected rotating speed of left wheel and rotating speed of right wheel. A steering angle arithmetic part 5 calculates a steering angle corresponding to the calculated rotating speed ratio according to a preset relation between rotating speed ratio and steering angle, typically to a linear functional relation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering angle estimating device for estimating a steering angle of a vehicle by using a pair of rotation sensors for detecting rotational states of left and right wheels, respectively.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 2000-25476 or Japanese Unexamined Patent Publication No. 9-178464 discloses a four-wheel drive vehicle based on a steering angle sensor or a wheel speed difference between the left and right wheels. A technique for performing differential limited differential control is disclosed.

[0003]

However, in the former case, since it is necessary to separately provide an expensive steering angle sensor, there is a disadvantage that the cost of the device is increased. Further, the latter has a disadvantage that control such as calculation based on the time interval and the phase difference becomes complicated.

The present invention has been made in view of such circumstances, and an object thereof is to detect a steering angle with a small error with a small amount of calculation.

[0005]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention uses a pair of rotation sensors for respectively detecting the rotational states of the left and right wheels to estimate the steering angle of the vehicle. Provide a device. This device detects the respective rotation speeds of the left and right wheels and calculates the rotation speed ratio between the detected rotation speed of the left wheel and the rotation speed of the right wheel based on the outputs from the pair of rotation sensors. And
The steering angle corresponding to the calculated rotation speed ratio is calculated according to a preset relationship between the rotation speed ratio and the steering angle, typically a linear function relationship.

Further, when the steering angle estimating device having the above-mentioned structure is mounted on a four-wheel drive vehicle, a pair of rotation sensors are provided on the driving front wheel side, and a pair of rotation sensors are also provided on the driving rear wheel side. The rotation speed of each wheel is detected. Then, in order to avoid an adverse effect due to the drive slip, it is preferable to calculate the steering angle based on the rotation speed ratio of the front wheel and the rear wheel, which has the smaller drive torque distribution.

Further, it may be determined whether or not the vehicle is in a steady running state based on the relationship between the rotational speeds of the four wheels. When it is determined that the vehicle is not in the steady running state, it is preferable to forcibly set the steering angle to a predetermined angle without applying the steering angle calculated from the rotation speed ratio.

It is also possible to judge the state of stop or extremely low speed. In this case, the previously calculated steering angle is held, and when either the stopped state or the extremely low speed state is applied, the steering angle calculated from the rotation speed ratio is not applied and the current steering angle is not applied. It is preferable to apply the conventional steering angle as the angle. In addition to the above-described extremely low speed state determination, it may be determined whether or not the power steering operation detection switch is turned on. When the power steering operation detection switch is turned on at a very low speed or lower, the lower limit value of the steering angle is set. When the conventional steering angle is equal to or larger than the lower limit value, the steering angle is set.

Further, the average value of the rotational speed ratios during medium-high speed traveling may be calculated. In this case, it is preferable to correct the rotation speed ratio with this average value and calculate the steering angle using the corrected rotation speed ratio. As a result, it is possible to reduce the influence of the degree of tire loss.

[0010]

FIG. 1 is a functional block diagram of a steering angle estimating device for a four-wheel drive vehicle. The right front wheel rotation sensor 1a is provided on the right front wheel, and the left front wheel rotation sensor 1b is provided on the left front wheel. The right rear wheel rotation sensor 1c is provided on the right rear wheel, and the left rear wheel rotation sensor 1c
d is provided on the left rear wheel. These rotation sensors 1a
For 1d, for example, an electromagnetic pickup can be used, and each independently detects the rotation state of the four wheels. In the present embodiment, the wheel speed sensor for ABS (anti-lock brake system) is shared as the rotation sensors 1a to 1d to save the sensor. In the case of a two-wheel drive vehicle, a pair of rotation sensors may be provided only on the left and right wheels on the non-driving side that are less affected by slippage and the like. The signals output from the rotation sensors 1a to 1d are sine waves as shown in FIG. 2 (a), but the frequency thereof increases in proportion to the rotation speed of the wheels.

The speed detecting section 2 is based on the output signals of the rotation sensors 1a to 1d, and the rotation speeds VFR, VFR of the respective wheels,
VFL, VRR and VRL are detected. Where the subscript "FR" of "V"
Is the front right wheel, "FL" is the front left wheel, "RR" is the rear right wheel, and "RL" is the rear left wheel. In the following description, when the rotational speeds of the respective wheels are collectively referred to, they are simply expressed as "V" without any suffix (the same applies to the period T and frequency f described later).

In order to detect the rotation speed V of each wheel, the speed detecting section 2 performs waveform processing on the sine wave from each of the rotation sensors 1a to 1d, and a step signal (sine wave) as shown in FIG. And the same period), and each period T is obtained. Since the cycle T and the rotation speed V have the following relationship,
The rotation speed V can be uniquely specified from the cycle T. The detected rotation speed V of each wheel is output in a predetermined cycle (for example, every 10 ms).

## EQU1 ## T = 1 / f = aV (a is a constant)

Each block after the speed detecting unit 2 performs arithmetic processing based on the rotation speed V. However, from the relationship of the above-mentioned formula 1, the calculation may be performed using the frequency f or the period T instead of the rotation speed V. These variables f,
This is because T is a variable uniquely calculated from the rotation speed V.

The speed ratio calculation unit 3 calculates the rotation speed ratio RV between the left wheel and the right wheel based on the rotation speed V output from the speed detection unit 2. At that time, in order to reduce the influence of the drive slip, the rotation speed ratio RV is calculated from the left and right wheels of the front and rear drive wheels having the smaller drive torque. That is, when the driving torque on the front wheel side is smaller than that on the rear wheel side, the rotational speed ratio RV is calculated based on the rotational speed VFR of the right front wheel and the rotational speed VFL of the left front wheel according to the following equation.

[Formula 2] RV = VFR / VFL

On the other hand, when the driving torque on the rear wheel side is smaller than that on the front wheel side, according to the following formula, based on the rotational speed VRR of the right rear wheel and the rotational speed VRL of the left rear wheel, The rotation speed ratio RV is calculated.

[Formula 3] RV = VRR / VRL

The rotation speed ratio may be calculated from the ratio of the cycle T (RV is an inverse number).

The rotational speed ratio RV is theoretically the same when the rotational speeds of the left and right wheels are the same, that is, when traveling straight ahead.
It becomes 1.0. When the vehicle turns right, the rotation speed ratio RV is
It becomes larger than 1.0, and becomes larger as the turning radius becomes smaller. When the vehicle turns left, the rotation speed ratio RV
Becomes smaller than 1.0, and becomes smaller as the turning radius becomes smaller. That is, in either case of turning left or right, the smaller the turning radius is, the larger the offset amount from the reference value 1.0 is. In the case of a two-wheel drive vehicle, the rotation speed ratio RV is calculated from the left and right wheels on the non-drive side.

The speed ratio correcting means 4 corrects the rotational speed ratio RV calculated by the speed ratio calculating section 3 and corrects the rotational speed ratio RV '(hereinafter referred to as "corrected rotational speed ratio RV'" or simply "rotational speed ratio RV '"). (The speed ratio RV '")
Output to. Although the details will be described later, this correction removes an error in the rotation speed ratio RV due to the tire reduction degree and the like.

The steering angle calculator 5 calculates the steering angle θ of the vehicle based on the rotation speed ratio RV '. FIG. 3 is a diagram showing a trace model of the wheels C to F when the vehicle turns. The Ackermann-Shunt theory, which is a general theory for steering mechanisms, is applied. Here, when the vehicle axle distance is L, the kingpin distance between both axles is K, the inner wheel steering angle is α, and the outer wheel steering angle is β, the relationship between the steering angle and the turning center is as follows.

[Formula 4] FO / CF = cot α EO / DE = cot β CF = DE ∴FO / EO = cot α / cot β (1)

FO and EO are the radii of rotation of the inner and outer rings, respectively, and when considering the amount of movement per unit time, equation (1)
The left side of can be called the speed ratio. On the other hand, the right side of the equation (1) is the steering angle, which is a value uniquely determined by the steering angle θ. In other words, Expression (1) indicates that if the speed ratio of the inner and outer wheels is obtained, the steering angle can be uniquely calculated from a preset relational expression. FIG. 4 shows the relationship between the rotation speed ratio and the steering angle, and has a relatively simple linear function relationship.

The steering angle calculator 5 outputs a steering angle θ corresponding to the input rotation speed ratio RV ′ according to a linear function relationship between the rotation speed ratio RV ′ and the steering angle θ. The relationship between the two variables RV ′ and θ is set in advance by a steering angle calculation map or a linear function formula created through simulation or experiment. When the steering angle calculation map is used, the correspondence relationship between both variables RV ′, θ is stored in a series of addresses in the ROM in the computer. The steering angle θ calculated by the steering angle calculator 5 can be used for various controls including torque distribution control of four wheels, steering force control of power steering, and vehicle motion control.

The steering angle calculation unit 5 outputs the steering angle θ in a predetermined cycle (for example, every 10 ms). However, for the reason to be described later, the steering angle calculation unit 5 retains an appropriately calculated previous sample.

By the way, when the vehicle goes straight, the rotational speed ratio RV is theoretically 1.0. However, since the degree of tire loss is slightly different for each wheel, the turning radii of the left and right wheels do not necessarily match. Therefore, in actuality, the rotational speed ratio RV often slightly deviates from the theoretical value of 1.0 even when going straight. Therefore, the average speed calculation unit 6 statistically averages the rotation speed ratio RV to obtain the average rotation speed ratio RVave, and the speed ratio correction unit 4 uses the speed ratio RVave to determine the rotation speed ratio RVave.
V is corrected.

Specifically, the average speed ratio calculation unit 6 calculates the rotation speed ratio RV calculated by the speed ratio calculation unit 4 under a condition of medium-high speed (for example, 60 km / h or more) by a predetermined number of samples (for example, Hold 1000 pieces. Then, as shown in FIG. 5, the distribution of the appearance frequencies of the held sample group is obtained, and the rotation speed ratio RV (≈1.0) having the highest frequency is set as the average rotation speed ratio RVave. As a rule of thumb, when traveling at medium and high speeds, most of the vehicle is in a straight traveling state. Therefore, from a statistical point of view, the value of the rotation speed ratio RV that is the most frequent appearance frequency can be regarded as the straight traveling value RVave.

The speed ratio correction unit 4 corrects the rotation speed ratio RV based on the average rotation speed ratio RVave according to the following equation. Then, the steering angle calculation unit 5 calculates the steering angle θ using the corrected rotation speed ratio RV ′. By removing the influence of the turning radii of the left and right wheels, it is possible to calculate the steering angle θ with high accuracy.

[Formula 5] RV: RV '= 1.0: RVave (≈1.0) ∴RV '= RV / RVave

Further, when the vehicle is not in a steady traveling state such as traveling on a rough road, passing a step, slipping, or sudden braking, the wheel rotation speed V fluctuates even when traveling on a straight road. It becomes difficult to properly calculate the steering angle θ. Therefore, a steady state determination unit 7 and a steering angle compulsory setting unit 8 are added to monitor whether or not the vehicle is in a steady traveling state in which the steering angle θ can be calculated appropriately. Forced to set the steering angle.

Specifically, the steady state determination unit 7 determines that the vehicle is in a steady running state (a state in which the steering angle θ can be calculated appropriately) if all three conditions below are satisfied, and if none of them satisfies the following conditions: For example, it is determined to be an unsteady traveling state (a state in which it is difficult to properly calculate the steering angle θ). (Conditions for Steady Running State) (1) The rotational speeds V of the four wheels satisfy the relationship during steering traveling (front outer wheel speed> rear outer wheel speed> front inner wheel speed> rear inner wheel speed) (2) front If the rotation speed ratio of the left and right wheels (Vfr / Vfl) is greater than 1.0, the rotation speed ratio of the rear left and right wheels (Vrr / Vrl)
Is also greater than 1.0. Rotational speed ratio of front left and right wheels (Vfr
/ Vfl) is 1.0 or less, the rotational speed ratio of the rear left and right wheels (Vr
r / Vrl) is also 1.0 or less. (3) Absolute value of the difference between the rotational speed ratio of the front left and right wheels (Vfr / Vfl) and the rotational speed ratio of the rear left and right wheels (Vrr / Vrl) | (Vfr /
Vfl)-(Vrr / Vrl) | is less than or equal to a predetermined judgment threshold value (for example, 0.1)

When the steady state determination unit 7 detects a state where the vehicle is not in steady state, the steady state determination unit 7 notifies the steering angle forced setting unit 8 to that effect. In response to this, the steering angle forced setting unit 8
The steering angle calculation unit 5 is instructed to forcibly set the steering angle θ to the predetermined angle θ1. The steering angle calculation unit 5 uses the predetermined angle θ1 instead of the steering angle θ specified by the rotation speed ratio RV ′.
Is forcibly set and output. The value of the predetermined angle θ1 is
It is set according to the control contents of the latter stage using the steering angle θ.
It is preferable to set it to 0 ° in the case of control in which it is safer to process the vehicle straight.

Furthermore, it becomes difficult to properly calculate the steering angle θ even when the vehicle is stopped or at an extremely low speed when the above-described rotational speed ratio RV cannot be calculated appropriately. So stop /
An extremely low speed determination unit 9, an operation state detection unit 11 for detecting ON / OFF of the power steering operation detection switch 10 and a stationary cutoff determination unit 12 are added to force a predetermined steering angle at the time of stop or extremely low speed. Set to.

Specifically, first, the stop / extremely low speed determination unit 9
Monitors the rotation speed V from the speed detection unit 2 and determines whether the rotation speed ratio RV cannot be calculated, that is, whether the rotation speed ratio RV is stopped or extremely low (for example, 2 km / h or less). Then, when the state becomes such an extremely low speed or lower, the determination unit 9 notifies the steering angle compulsory setting unit 8 via the stationary steering determination unit 12 to that effect. In response to this, the steering angle compulsory setting unit 8 outputs the previous steering angle θn-1 held in the steering angle calculation unit 5 as the current steering angle θn, except when the steering wheel is set up. Then, the steering angle calculation unit 5 is instructed. The steering angle calculation unit 5 determines the rotation speed ratio R
Instead of the steering angle θn specified by V ′, the previous steering angle θn−1 is output.

On the other hand, the stationary steering determining section 12 determines whether or not the power steering has been switched off, that is, in a state of extremely low speed or less. The operation state of the power steering is enabled by monitoring the on / off state of the power steering operation detection switch 10 in the operation state detection unit 11. That is, when the turning of the power steering exceeds a predetermined angle, the power steering operation detection switch 10 for detecting the power steering operation oil pressure is turned on. When the operating state detection unit 11 detects this ON state, the stationary cutoff determination unit 1
Notify 2 to that effect. The stationary steering determination unit 12 operates the power steering operation detection switch 1 in an extremely low speed or lower state.
When 0 is turned on, it is determined to be stationary and the steering angle θ
The steering angle compulsory setting unit 8 is instructed to set the lower limit value θ2. Then, in response to the instruction from the steering angle compulsory setting unit 8, the steering angle calculation unit 5 outputs the lower limit value θ2 if the value of the steering angle θ specified by the rotation speed ratio RV ′ is smaller than the lower limit value θ2. However, when the lower limit value θ2 or more, the steering angle θ is output as it is. Although the lower limit value θ2 is set according to the control content of the subsequent stage using the steering angle θ, it is set to 180 in the case of performing control in the direction of weakening the transfer torque differential limitation.
It is preferable to set to ° (large steering angle).

In this embodiment, the rotation speed ratio R of the left and right wheels is
From the linear function relationship between V ′ and the steering angle θ,
The steering angle θ is uniquely calculated by inputting the rotation speed ratio RV. Therefore, the steering angle θ with a small error can be calculated with a relatively small amount of calculation, and the response is excellent.

Further, in this embodiment, it is not necessary to newly add an expensive steering angle sensor, and the system can be constructed by utilizing the existing ABS wheel speed sensor. Therefore,
The system according to this embodiment can be realized at low cost.

[0034]

According to the present invention, the steering angle can be detected with a small amount of calculation, the estimated steering angle error is small, and the steering angle estimation responsiveness is excellent.

[Brief description of drawings]

FIG. 1 is a functional block configuration diagram of a steering angle estimation device according to the present embodiment.

FIG. 2 is a diagram showing processing of an output signal of a rotation sensor.

FIG. 3 is a diagram showing a trace model of wheels when the vehicle is turning.

FIG. 4 is an explanatory diagram showing a relationship between a rotation speed ratio and a steering angle.

FIG. 5 is a diagram showing a method of calculating an average speed.

[Explanation of symbols]

1a-1d rotation sensor, 2 speed detector, 3 Speed ratio calculator, 4 Speed ratio correction unit, 5 Steering angle calculator, 6 Average speed ratio calculator 7 Steady state determination unit, 8 Forced steering angle setting section, 9 Stop / ultra-low speed judgment section, 10 Power steering operation detection switch, 11 Operating state detector, 12 Dead-end decision part

Claims (7)

[Claims] 1. A vehicle steering angle estimating device for estimating a steering angle of a vehicle by using a pair of rotation sensors for detecting respective rotational states of the left and right wheels, the left and right wheels being based on outputs from the pair of rotation sensors. Speed detecting means for detecting respective rotation speeds, speed ratio calculating means for calculating a rotation speed ratio between the left wheel rotating speed and the right wheel rotating speed detected by the speed detecting means, and the speed ratio calculating means A steering angle estimating device for a vehicle, comprising: a steering angle calculating means for calculating a steering angle of the vehicle based on the rotation speed ratio calculated by. 2. The steering angle calculation means calculates the steering angle from the rotation speed ratio calculated by the speed ratio calculation means according to a linear function relationship between the rotation speed ratio and the steering angle. The vehicle steering angle estimating device according to claim 1. 3. A steering angle estimating device for a four-wheel drive vehicle, wherein a pair of rotation sensors are provided on the front drive wheel side, and a pair of rotation sensors are provided on the rear drive wheel side. The detection means detects the respective rotation speeds of the front and rear wheels, and the speed ratio calculation means calculates the steering angle of the vehicle based on the rotation speed ratio of the front and rear wheels with the smaller drive torque distribution. The steering angle estimating device for a vehicle according to claim 1 or 2, wherein. 4. A first determining means for determining whether or not the vehicle is in a steady traveling state on the basis of the relationship between the rotational speeds of the four wheels, wherein the first determining means determines that the vehicle is not in the steady traveling state. In this case, the steering angle estimation device for a vehicle according to claim 3, wherein the steering angle calculation means is instructed to forcibly set the steering angle to a predetermined angle. 5. A second determination means for determining a stopped state or an extremely low speed state is further provided, wherein the steering angle calculation means holds the steering angle previously calculated, and the second determination means. Is either the stopped state or the extremely low speed state, the steering angle calculation means,
The steering angle estimation device for a vehicle according to claim 3, wherein the steering angle estimation device instructs the vehicle to forcibly set the steering angle to the previous steering angle. 6. The second determining means, when the power steering operation detecting switch is turned on, instructs the steering angle calculating means to set a lower limit value of the steering angle. The vehicle steering angle estimating device according to claim 5. 7. An average speed ratio calculation means for calculating an average value of rotation speed ratios during medium-high speed traveling, wherein the steering angle calculation means is an average of the rotation speeds calculated by the average speed ratio calculation means. The steering angle estimating device for a vehicle according to claim 1, wherein the steering angle is calculated using the rotation speed ratio corrected by the value.