JP2010030505A - Vehicle steering unit and vehicles steering method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle steering unit which enables a driver to easily learn a steering reaction force corresponding to surrounding risks. <P>SOLUTION: A steering reaction force corresponding to the degree of risks surrounding a vehicle and a steering angle is added to a steering transmission system, while disturbances other than the operator's operating force acting on the vehicle operation equipment are compensated for, based on the steering reaction force from a steering wheel received by the operator and on an operating state of the vehicle operation equipment. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle steering apparatus and a vehicle steering method having a function of supporting a driver's steering operation.

As a conventional vehicle steering apparatus, there is an apparatus described in Patent Document 1, for example. Such an apparatus detects the situation around the vehicle and obtains a potential risk level at that time. Then, the steering assist torque is controlled based on the degree of risk. That is, the steering reaction force corresponding to the degree of risk is added to the steering transmission system to assist the driver's steering operation.
In such a vehicle steering system, the driver can easily understand which obstacle is the target of the reaction force control, and the risk around the own vehicle is reliably determined as the steering reaction force of the steering wheel. It is desired to communicate to the driver.
Japanese Patent Application Laid-Open No. 10-211886

The steering reaction force is controlled so that the steering reaction force from the road surface is corrected to add a steering reaction force component corresponding to the degree of risk.
However, in reality, an ideal steering reaction force characteristic cannot often be obtained due to the insensitive part of the steering transmission system, the influence of disturbance such as a side slope, a change in the side slope, and a saddle.
For example, the characteristic of the steering wheel (vehicle operating device) is that the steering reaction force suddenly rises with a minute operation at the start of turning and then the increase gradient of the steering reaction force becomes gentle. It is. As described above, the increase gradient of the steering reaction force (the characteristic of the steering reaction force) is the largest during a minute operation when the steering wheel starts to be turned, and the increase gradient is a certain maximum reaction force depending on the operation amount. It becomes the characteristic that it becomes small gradually toward. Therefore, the driver may not be able to accurately perceive the increasing tendency of the risk simply by adding the reaction force corresponding to the risk within a range that does not affect the driving of the driver. In other words, since the reaction force difference between the steering side and the steering side is already large in the normal state, even if the reaction force corresponding to the risk is added, it is difficult to make a difference in the sensitivity of the steering reaction force with respect to the steering amount. For this reason, it is difficult for the driver to accurately feel the increasing tendency of the risk.

On the other hand, when driving on a road surface with a single slope, a change in the single slope, or a saddle, the steering reaction force is arbitrarily changed by an input from the road surface regardless of the risk around the host vehicle. For this reason, it is difficult to reliably transmit risk in a configuration in which a force equivalent to SAT (equivalent to self-aligning torque) on a flat and ideal road surface is estimated based on the vehicle speed and the steering angle to correct the steering torque. That is, the driver must always consider whether the steering reaction force changes due to a change in the road surface or the steering reaction force corresponding to the surrounding risk. This means that the driver's burden may not be easy.
The present invention pays attention to the above points, and it is an object to make it easier for the driver to understand the steering reaction force corresponding to the surrounding risk.

  In order to solve the above problems, the present invention compensates for disturbances other than the driver's operating force acting on the vehicle operating device based on the steering reaction force from the vehicle operating device received by the driver and the operating state of the vehicle operating device. However, a steering reaction force corresponding to the degree of risk around the host vehicle and the steering angle is added to the steering transmission system.

According to the present invention, a steering reaction force corresponding to SAT (equivalent to self-aligning torque) is compensated, and a steering reaction force corresponding to the degree of risk is added to the steering transmission system. As a result, the steering reaction force characteristic with respect to the steering angle of the vehicle operating device becomes equal to or close to the steering reaction force characteristic according to the degree of risk.
As a result, even when there are insensitive characteristics and road surface changes existing in the normal steering transmission system, the steering reaction force corresponding to the risk during traveling can be reliably transmitted to the driver.
Further, the steering reaction force according to the risk degree becomes a value according to the steering angle. For this reason, for example, the initial steering force is small, and the more the vehicle operating device is increased, the more the steering reaction force increases, and the steering reaction force that makes it easier for the driver to understand the state of approaching the risk. It becomes a characteristic.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a driving steering assist device according to the present embodiment.
Reference numeral 3 denotes a steering wheel that is steered by the driver. The upper end portion of the steering shaft 4 is connected to the steering wheel 3. A lower end portion of the steering shaft 4 is connected to the rack shaft 2 via the rack and pinion mechanism 12. The rack shaft 2 is arranged with the shaft facing in the vehicle width direction. The left and right ends of the rack shaft 2 are connected to knuckles 13R and 13L via tie rods, respectively. The left and right knuckles 13R and 13L rotatably support the front wheels 1R and 1L as steering wheels, respectively. The steering transmission system is configured as described above. That is, the rotation of the steering wheel 3 is transmitted to the left and right front wheels 1R and 1L via the steering shaft 4 and the rack shaft 2, and the left and right front wheels 1R and 1L are steered. The steering shaft 4, the rack and pinion mechanism, and the rack shaft 2 constitute a steering transmission system that transmits the steering torque Th.

A steering torque sensor 5 is interposed in the steering shaft 4. The steering torque sensor 5 is a device that detects the steering torque Th. For example, the steering torque sensor 5 detects the steering torque Th from the amount of twist of the steering shaft 4. The steering torque sensor 5 outputs the detected steering torque Th to the control unit 8.
A steering angle sensor 6 is also provided. The steering angle sensor 6 detects the steering angle θ and the steering angular velocity dθ / dt of the steering wheel 3 steered by the driver. The steering angle sensor 6 outputs the detected steering angle and steering angular velocity to the control unit 8.
A wheel speed sensor 9 is provided. The wheel speed sensor 9 detects the wheel rotation speed and outputs it to the control unit 8.

  A steering actuator 7 is also provided. The steering actuator 7 is a device that adds auxiliary torque to the steering transmission system. FIG. 1 illustrates a case where auxiliary torque is applied to the steering shaft 4. The auxiliary torque may be applied to the rack shaft 2. In the present embodiment, an electric motor is illustrated as the steering actuator 7. That is, a torque proportional to the drive current is generated by the drive current corresponding to the command value from the control unit 8. That is, a steering assist force is added to the steering transmission system.

  The vehicle also includes a front camera 10. For example, the front camera 10 is composed of a small CCD camera or a CMOS camera mounted on the front window. The front camera 10 constitutes a traveling position detection sensor that detects a relative position between the traveling lane shape in front of the vehicle and the host vehicle. This front camera 10 images the front of the host vehicle. Then, a lane marker such as a road lane marking is detected from the captured image to detect a traveling lane. Further, the yaw angle Φ of the host vehicle with respect to the travel lane, the lateral displacements XL and XR from the travel lane dividing line, the curvature ρ of the travel lane, and the like are calculated. Then, the calculation information is output to the control unit 8.

The vehicle also includes a laser radar 11. The laser radar 11 detects an inter-vehicle distance, a relative speed, and an existing direction (relative angle) between an obstacle, an adjacent lane, or an oncoming vehicle that exist on the left and right and in front of the host vehicle. The laser radar 11 outputs the detection result to the control unit 8.
The control unit 8 calculates an actuator drive current I and supplies the actuator drive current I to the steering actuator 7 as a command value. The actuator drive current corresponding to the steering is calculated according to the steering torque Th, the traveling speed calculated from the wheel rotation speed, and the steering angular speed.

The control unit 8 also estimates the traveling state of the host vehicle based on information from the camera 10 and the laser radar 11. Then, based on the estimated traveling state, a steering torque Th and a steering reaction force to the driver are added to the steering assist force. This assists the driver in driving appropriately.
A control block of the control unit 8 is shown in FIG.
That is, the control unit 8 includes a steering assist calculation unit 81, a steering reaction force control unit 82, a friction compensation calculation unit 83, and a current control unit 84.

As shown in FIG. 3, the steering assist calculation unit 81 includes a steering assist calculation unit main body 81A and an assist correction unit 81B.
The steering assist calculation unit main body 81A calculates a steering assist current I1 corresponding to the steering torque Th. That is, the steering assist calculation unit main body 81A calculates the steering assist current I1 from the steering torque Th and the vehicle speed V input from each sensor according to the steering assist map shown in FIG. The steering assist current I1 is a command value for assist torque.

  In FIG. 3, for the sake of simplicity of explanation, components other than the basic steering assist current I1 are omitted. As with a normal electric power steering device, the steering angular velocity of the steering actuator 7 is fed back to improve the damping of the steering transmission system to improve the running stability of the host vehicle, and the rotational angular acceleration is fed back to provide steering. A term for compensating the inertial force of the actuator 7 may be added to the basic steering assist current I1.

The assist correction unit 81B corrects the steering assist current I1 calculated by the steering assist calculation unit main body 81A by the steering assist correction gain α (0 ≦ α ≦ 1) as in the following equation.
I1 ← I1 × α
Then, the corrected steering assist current I1 is output to the current control unit 84. The steering assist correction gain α is a value calculated by a steering reaction force control unit 82 described later.

  The steering assist correction gain α is a gain for correcting the normal steering assist current I1 to be close to “0” when the steering reaction force control is strongly applied. With the configuration in which the steering assist correction gain α and the steering reaction force gain k are corrected in a coordinated manner, normal power steering control and steering reaction force control corresponding to the risk during running can be switched smoothly and smoothly. It becomes the structure which can be done.

  Here, when performing steering assist as a normal electric power steering apparatus, the steering assist correction gain α is “1”. That is, it functions as a normal electric power steering device. That is, when the steering assistance for the risk does not operate, the current control unit 84 applies the steering assist current I1 calculated by the steering assist calculation unit 81 to the steering actuator 7, and functions as a normal electric power steering device.

The friction compensation calculation unit 83 is configured as shown in FIG. 4 and calculates the friction compensation current Id based on the following equation. Then, the friction compensation current Id is output to the current control unit 84.
Id (s) = (1 / Kt) · T ^ d (s)
= (1 / Kt) · {L (s) / P (s)) · ω (s)
−L (s) · (Th (s) + Kt · I (s))}

Next, the friction compensation current Id will be described with reference to FIG.
When the equation of motion of the steering transmission system is Laplace transformed, the following equation (1) is obtained.
ω (s) = P (s) {Th (s) + Tm (s) + Td (s)} (1)
However,
P (s) = 1 / (Js · s + Ds) (2)
Also,
Th: Steering torque by driver Tm: Torque generated by motor of steering actuator 7 Td: All disturbance torque to steering transmission system including friction and tire input Js: Moment of inertia of steering system (including motor) Ds: Steering system (motor (Including viscosity) ω: the rotational angular velocity of the steering shaft 4.

Further, the relationship between the motor applied current I and the motor generated torque Tm is expressed by the following equation (3).
Tm = Kt · I (3)
Where Kt is a motor torque constant.
Therefore, the disturbance torque Td can be obtained by the following equation (4).
Td (s) = (1 / P (s)) · ω (s) − {Th (s) + Kt · I (s)}
... (4)

However, there are cases where appropriate disturbance estimation is not performed due to noise generated in the differential term. Therefore, the low-pass filter L (s) as shown in the following equation is set with ωc as the disturbance elimination frequency band.
L (s) = ωc / (s + ωc)
When this low-pass filter L (s) is applied to the above equation (4), the estimated values T ^ d of all the disturbance torques Td to the steering transmission system including friction and tire input are expressed by the following equation (5). Can be described.
T ^ d (s) = (L (s) / P (s)) · ω (s)
−L (s) · {Th (s) + Kt · I (s)}
... (5)

Then, by applying the estimated value T ^ d of the disturbance torque Td to the above equation (3), the friction compensation current Id can be expressed by the following equation (6) as described above.
Id (s) = (1 / Kt) · T ^ d (s)
= (1 / Kt) · {L (s) / P (s)) · ω (s)
−L (s) · (Th (s) + Kt · I (s))}
... (6)

Next, the current control unit 84 calculates a value obtained by adding a steering assist current I1 (described later) to the steering assist current I1 and subtracting the friction compensation current Id as the steering actuator drive current I as shown in the following equation. . Then, by applying the steering actuator drive current I to the steering actuator 7, a steering reaction force characteristic corresponding to the vehicle surrounding risk is realized. Here, the steering assist current I1 becomes a command value for the steering reaction force.
I = I1 + I2-Id (7)
However, the steering assist current I1 is a value corrected by the correction gain α. When the steering actuator drive current I is described as the steering assist current I1 before correction, the following equation is obtained.
I = α · I1 + I2−Id

Next, the steering reaction force control unit 82 will be described with reference to FIG.
As shown in FIG. 5, the steering reaction force control unit 82 includes a risk calculation unit 82a, a target steering angle calculation unit 82b, and a reaction force control calculation unit 82c.
Here, the above-described laser radar 11 detects an obstacle existing in front of the left and right of the host vehicle, for example, the inter-vehicle distance to the vehicle in the adjacent lane or the oncoming vehicle, the relative speed, and the direction (relative angle). The detection information is output to the risk calculation unit 82a.
Further, the front camera 10 captures the front road scenery as an image. The detection area by the front camera 10 is about ± 45 degrees in the horizontal direction, and an obstacle situation around the host vehicle is detected from the front road scenery in the detection area. The detection information is output to the risk calculation unit 82a.

  Then, the risk calculation unit 82a calculates the relative distance D in the front-rear direction to the obstacle existing around the host vehicle and the relative speed Vr based on the signals input from the laser radar 11, the vehicle speed sensor 9, and the front camera 10. calculate. Based on the longitudinal relative distance D to the obstacle and the relative speed Vr, the risk potential RP in the lateral direction in the host vehicle is calculated. The risk potential RP is an index of the degree of risk around the host vehicle.

Specifically, the risk potential RPr related to the right direction of the host vehicle and the risk potential RP1 related to the left direction of the host vehicle are individually calculated. At this time, the front-rear direction inter-vehicle distance D between the host vehicle and the obstacle (including other vehicles; the same applies hereinafter), the front-rear direction relative speed Vr, and the obstacle existing direction with respect to the host vehicle are used.
Here, the obstruction presence direction uses a relative angle β in the left-right direction of the obstacle with respect to the traveling direction of the own vehicle with reference to the front of the own vehicle.

The risk potential RP is calculated using, for example, a margin time TTC in the front-rear direction to the obstacle, as in the following equation (8).
RP = sin | β | / TTC (8)
Here, the margin time TTC is expressed by the following equation.
TTC = D / Vr
The margin time TTC can determine whether the host vehicle is prone to approach or leave the obstacle or another vehicle according to the sign. A positive value is obtained when the host vehicle tends to approach other vehicles or obstacles.

And the risk potential RP becomes a large value, so that the margin time TTC of the front-back direction with respect to a surrounding vehicle etc. is small. Further, the closer to the parallel running state, such as the relative angle β = 90 degrees, the greater the risk potential RP.
Then, the risk potential RP is calculated individually for all detected objects such as other vehicles and obstacles existing around the host vehicle.
Next, the maximum value or the sum of the risk potentials RP with respect to other vehicles and obstacles existing in the rightward region is set as the rightward risk potential RPr. Similarly, the maximum value or the sum of the risk potentials RP for other vehicles and obstacles existing in the leftward region is defined as the leftward risk potential RPl. Here, when the right direction is set to be positive with respect to the relative angle β, it is possible to distinguish between the right direction and the left direction with respect to each risk potential RP based on the positive value and the negative value of the relative angle β.

Subsequently, a steering reaction force gain k is calculated based on the calculated right risk potential RPr and left risk potential RPl.
An example of the characteristic of the steering reaction force gain k with respect to the risk potential RP is shown on the right side of FIG.
The steering reaction force gain k is set as a function of the risk potential RP, and is set to increase as the risk potential RP increases as shown in FIG. Further, as the vehicle speed increases, the gain of the vehicle motion (yaw angular velocity, lateral acceleration) with respect to the steering angle increases. Based on this, the value of the steering reaction force gain k with respect to the risk potential RP is set so as to increase as the vehicle speed increases. However, when the risk potential RP is equal to or less than a predetermined value, the steering reaction force gain k is set to a constant value.

Further, as shown on the left side in FIG. 6, the steering reaction force gain k is corrected so as to increase as the increase rate of the risk potential RP increases.
For example, the steering reaction force gain k can be expressed as follows.
k = K1 * f (V) * RP + K2 * f (V) * dRP / dt
K1 and K2 are constants. f (V) is a function proportional to the vehicle speed V.
Here, the steering reaction force gain k may be output based on the larger one of the right direction and left direction risk potentials RPr and RPl. That is, if the configuration is such that the steering reaction force gains kr and kl corresponding to the left and right risk potentials are output and the characteristics of the steering reaction force can be set independently according to the direction of the risk, the risk can be more accurately determined for the driver. It can be set as the structure which can be grasped | ascertained.
Then, the risk calculation unit 82a outputs the calculated steering reaction force gain k (or kr and kl) to the reaction force control calculation unit 82c.

Next, the target steering angle calculation unit 82b will be described.
The above-described front camera 10 has a function of a traveling position detection sensor that detects a relative position between the traveling lane shape in front of the vehicle and the host vehicle from the front road scenery in the detection area. That is, this front camera 10 detects a lane marker by detecting a lane marker such as a road marking line from a captured image in front of the host vehicle. Further, the vehicle travel state such as the yaw angle Φ of the host vehicle relative to the travel lane, the lateral displacement Y from the center of the travel lane, and the curvature ρ of the travel lane is calculated. The front camera 10 outputs the calculated detection signal to the target steering angle calculation unit 82b.

Then, the target steering angle calculation unit 82b calculates a target steering angle θr necessary for the vehicle to travel so as to approach the center position of the travel lane, and the target steering angle θr is converted to the reaction force control calculation unit 82c. Output. The required target steering angle θr is calculated based on the vehicle traveling state input from the front camera 10, the traveling lane shape sensors, and the own vehicle speed V input from the vehicle speed sensor 9.
Alternatively, the target steering angle θr may be calculated based on a map in which the target steering angle θr increases as the lateral displacement amount increases based on the lateral displacement amount of the host vehicle from the center of the lane. In this case, the target steering angle θr may be corrected so as to increase as the vehicle speed V increases.

Then, the reaction force control calculation unit 82c calculates a steering reaction force control current I2 for the risk and outputs it to the steering assist calculation unit 81.
That is, first, as shown in the following equation, a deviation Δθ between the target steering angle θr calculated by the target steering angle calculation unit 82b and the steering angle θ input from the steering angle sensor 66 is calculated.
Δθ = θr−θ (9)
Next, as shown in the following equation, a value obtained by multiplying the deviation Δθ by the steering reaction force gain k calculated by the risk calculation unit 82a is set as a steering reaction force control current I2. Then, the steering reaction force control current I 2 is output to the steering assist calculation unit 81.
I2 = k · Δθ (10)

Further, the reaction force control calculation unit 82 c calculates the correction gain α and outputs it to the steering assist calculation unit 81. The correction gain α is a gain for adjusting the steering assist current I1 to realize an arbitrary steering reaction force.
The correction gain α is a value represented by the following equation. As can be seen from this equation, the correction gain α decreases as the steering reaction force gain k increases.
α = (1 / f (Th)) {(p / k) −1}
here,
k: Steering reaction force gain k
p: Maximum value of steering reaction force gain k Th: Steering torque

Next, the correction gain α will be described.
The upper limit of the steering reaction force gain k is determined from the stability of the steering transmission system and the host vehicle, regardless of the driver's operation status. The upper limit value is the maximum value p of the steering reaction force gain k.
Considering the balance of forces around the steering transmission system, it can be described as follows:
Kt · p · Δθ + (α · f (Th) +1) · Th = 0 (11)
Here, f (Th) is a gain for calculating the steering assist current I1 from the detected steering torque Th.

The steering reaction force gain k for calculating the steering reaction force transmitted to the driver that is actually desired is expressed by the following equation.
k = (1 / Kt) · (Th / Δθ) (12)
Accordingly, the correction gain α is calculated by the following equation from the equations (30) and (31).
α = (1 / f (Th)) {(p / k) −1} (13)
Here, since the maximum value of the steering reaction force gain k is p and the correction gain α is 1 when performing steering assist as a normal electric power steering device,
1 ≧ α ≧ 0.

Next, processing of the control unit 8 that performs the steering reaction force control described above will be described with reference to FIG. FIG. 7 is a flowchart showing a processing procedure for calculating the risk potential RP and steering reaction force control. The processing of the control unit 8 is continuously performed at a predetermined sampling period, for example, every 30 msec.
First, the driving state detected by the laser radar 11, the vehicle speed sensor 9, and the front camera 10, such as the host vehicle speed V and the obstacle state, is read (see step S110).

Here, the information about the obstacle state includes a relative distance D in the front-rear direction to the obstacle existing around the host vehicle, a relative speed Vr, a relative angle β, and the like.
Next, the steering torque Th and the steering angle θ detected by the steering torque sensor 55 and the steering angle sensor 10 are read (see step S120).
Next, a steering assist current I1 as a normal power steering system is calculated using a steering assist map as shown in FIG. 3 (see step S130).

Next, the disturbance torque Td input as a disturbance is estimated. Then, a friction compensation current Id necessary to cancel the disturbance torque estimated value T ^ d is calculated (step S140).
When calculating the disturbance torque Td, the model P (s) driven by the control input and the driver operating force is used. The sum of the control input and the operation input that can be obtained when the steering angular velocity ω is passed through the inverse characteristic of the model P (s) by using the equations (5), (6), and (7). The disturbance torque Td is estimated from the difference between this estimated value and the total value of the actual control input and operation input.

Next, risk potentials RPr and RPl in the vehicle left-right direction are calculated using equation (8) (step S150).
Next, in order to perform the steering reaction force control, the steering reaction force gain k is calculated using FIG. 6 (step S160).
Next, based on the state of the front lane and the driving state of the host vehicle, a target steering angle θr is calculated such that the host vehicle is guided toward the center of the traveling lane (step S170).

Next, the steering reaction force control current I2 is calculated by multiplying the deviation Δθ between the target steering angle θr and the actual steering angle θ by the steering reaction force gain k (step S180). At the same time, the steering assist correction gain α is calculated using equation (13).
Next, an actuator drive current is calculated from the calculated steering assist current I1, steering reaction force control current I2, and steering assist correction gain α using equation (7) (step S190).
The calculated actuator driving current I is output to the steering actuator 7.

(Function)
Here, the higher the potential risk around the host vehicle due to the steering reaction force control current I2, the stronger the steering reaction force is generated even with a small deviation Δθ, and the risk state of the host vehicle through the operation of the steering wheel 3 to the driver. To communicate. Further, as the deviation Δθ increases, steering control is performed such that the vehicle is returned to the center of the lane with a greater force. This helps the driver with lane keeping.
The steering actuator 7 is driven and controlled by the friction compensation current Id calculated by the above-described friction compensation calculation unit 83 so that the SAT as the road surface reaction force is not transmitted to the steering wheel 3 together with the friction of the steering transmission system.

For this reason, the steering reaction force felt by the driver is only a difference between the target steering angle θr calculated by the target steering angle calculator 82b and the actual steering angle θ, that is, a force corresponding to the steering angle θ.
As described above, the risk calculation unit 82a does not calculate the steering reaction force only from the surrounding risk, but generates a reaction force according to the difference between the actual operation amount and the recommended operation amount as a result of the operation by the driver. Like to do. For this reason, the steering reaction force rises according to the amount of operation of the user. As a result, it is possible for the driver to accurately determine whether the operation being performed is appropriate or not appropriate when the operation is not appropriate.

FIG. 8A is a diagram showing a steering angle-steering torque characteristic. Even if a steering reaction force corresponding to the risk is added to the steering transmission system as shown in FIG. 8B, the influence of the large hysteresis is dominant, so the steering reaction force with respect to the steering amount of the driver is dominant. The sensitivity does not change much.
On the other hand, in this embodiment, when there is a risk as shown in FIG. 9, the steering angle-steering torque characteristic is obtained. That is, the steering torque increases by an amount corresponding to the steering reaction force gain k according to the steering, and it becomes easy to transmit the risk to the driver as described above.

  Here, the reaction force control calculation unit 82c calculates the steering reaction force control current I2 obtained by multiplying the deviation Δθ between the target steering angle θr and the steering angle θ by the steering reaction force gain k, and sends it to the current control unit 84. Output. However, since the current control unit 84 calculates the steering actuator drive current by combining the steering assist current I1 and the steering reaction force control current I2, the steering assist current I1 cancels a part of the steering reaction force control current I2. . This leads to the fact that the steering reaction force characteristic calculated by the risk calculator 82a is not correctly reflected in the driver's steering reaction force.

  In addition, when the risk calculation unit 82a calculates a large steering reaction force gain k that outputs a steering reaction force control current I2 that only overcomes the steering assist current I1, the steering torque Th suddenly decreases according to the driver's intention. . This leads to a sudden control of the steering wheel 3 toward the target steering angle θr when the steering torque Th cannot be detected. The steering wheel 3 may vibrate depending on the magnitude of the steering reaction force gain k.

In view of the above, an arbitrary steering reaction force can be realized by adjusting the steering assist current I1 with the correction gain α.
Here, the steering wheel 3 constitutes a vehicle operating device. The camera 10 and the laser radar 11 constitute surrounding recognition means. The front wheels 1R and 1L constitute a steering wheel.
The steering reaction force control current I2 corresponds to the steering reaction force calculated by the risk calculation means. The steering assist current I1 corresponds to the assist torque.

The risk calculator 82a constitutes a risk calculation means. The reaction force control calculation unit 82c constitutes a reaction force characteristic adjusting unit.
The current control unit 84 and the friction compensation calculation unit 83 constitute reaction force characteristic control means.
The friction compensation calculation unit 83 constitutes friction compensation means. The target steering angle calculation unit 82b constitutes a target steering angle calculation unit.
The risk potentials RP, RPr, and RPl constitute the degree of risk. The steering reaction force gain k constitutes a gain that determines the characteristics of the steering reaction force.

(Effect of this embodiment)
(1) The risk calculating means calculates the degree of risk around the host vehicle. The reaction force characteristic adjusting means calculates a steering reaction force characteristic according to the degree of risk and the steering angle of the vehicle operating device. Then, the reaction force characteristic control means controls the steering reaction force characteristic with respect to the steering angle so as to coincide with or approach the steering reaction force characteristic calculated by the reaction force characteristic adjustment means.
The steering reaction force according to the risk degree becomes a value according to the steering angle. For this reason, for example, the initial steering force is small, and the more the vehicle operating device is added, the more the steering reaction force increases, and the steering reaction force characteristic that makes it easier for the driver to understand the approaching risk. Become.

(2) The friction compensation means compensates disturbances other than the driver's operating force acting on the vehicle operating device based on the steering reaction force from the vehicle operating device received by the driver and the operating state of the operating device. The reaction force characteristic control means adds a steering reaction force according to the degree of risk calculated by the reaction force characteristic adjustment means to the steering transmission system while compensating for disturbance by the friction compensation means.
That is, a steering reaction force equivalent to SAT (equivalent to self-aligning torque) is compensated, and a steering reaction force corresponding to the degree of risk is added to the steering transmission system. As a result, the steering reaction force characteristic with respect to the steering angle of the vehicle operating device becomes equal to or close to the steering reaction force characteristic according to the degree of risk.

As a result, even when there are insensitive characteristics and road surface changes existing in the normal steering transmission system, the steering reaction force corresponding to the risk during traveling can be reliably transmitted to the driver.
Further, the steering reaction force according to the risk degree becomes a value according to the steering angle. For this reason, for example, the initial steering force is small, and the more the vehicle operating device is added, the more the steering reaction force increases, and the steering reaction force characteristic that makes it easier for the driver to understand the approaching risk. Become.

(3) The steering actuator adds auxiliary torque to the steering transmission system according to the steering torque generated by the steering of the vehicle operating device. The reaction force characteristic control means fixes or suppresses the steering reaction force calculated by the reaction force characteristic adjustment means to a predetermined value or less when there is no risk or the risk degree is less than a predetermined value.
Thereby, when the risk around the host vehicle is not detected or is small, the characteristic of the steering reaction force with respect to the steering angle of the vehicle operating device is fixed to a constant value.
Thus, when the risk around the vehicle is small and the driver performs an aggressive operation such as changing lanes, the reaction force characteristic of a normal power steering device can be obtained. As a result, it is possible to prevent as much as possible from giving unnecessary information to the driver and giving an uncomfortable feeling of steering.

(4) The virtual travel locus is a travel locus toward the center of the lane in which the host vehicle is traveling. Then, the steering reaction force is calculated according to the deviation between the target steering angle and the actual steering angle so as to draw an ideal traveling locus toward the center of the lane in which the vehicle is traveling.
When there is a risk around the vehicle and the driver's free steering is restricted, the driver only slightly loosens the steering of the vehicle operating device and moves toward the center of the lane in which the vehicle is traveling. Is immediately induced. As a result, support for lane keeping is provided.
In this case, it is possible to recognize a travel lane marking as a risk and obtain a travel locus of the host vehicle that reliably moves away from surrounding risks. As a result, not only the magnitude of the steering force of the vehicle operating device but also the direction of low risk can be intuitively understood from both the movement of the vehicle operating device and the vehicle behavior.

(5) The reaction force characteristic adjusting means changes the gain for determining the characteristic of the steering reaction force to a larger value as the vehicle speed is higher.
That is, the gain for setting the steering reaction force characteristic with respect to the steering angle of the vehicle operating device is set to a larger value as the vehicle speed is higher according to the vehicle speed. As a result, when the vehicle speed is high and the gain of the vehicle behavior is high due to the operation amount of the vehicle operating device, a firm steering reaction force is applied to suppress the vehicle behavior. On the other hand, a small steering reaction force characteristic is set at a low speed at which low speed and quick operation of the vehicle operating device is required. As a result, it is possible to transmit the surrounding risks to the driver while maintaining the vehicle characteristics that facilitate driving.
In addition, even when steering reaction force is generated, the gain that determines the characteristics of the steering reaction force according to the change in the vehicle speed is corrected and changed so that the vehicle reaction behavior does not become unstable according to the vehicle speed. The characteristics can always be maintained.

(6) The risk calculation means individually calculates the risk level of the left area and the right area for the host vehicle. Then, the reaction force characteristic adjusting means individually calculates the steering reaction force characteristics of the left region and the right region.
This makes it possible to more appropriately sense the risk according to the left and right risks.
(7) The auxiliary torque is corrected to decrease in accordance with the steering reaction force calculated by the reaction force characteristic adjusting means.
Accordingly, when transmitting the reaction force according to the risk, the driver can transmit the reaction force according to the risk by reducing the auxiliary torque according to the degree of risk.
In addition, the configuration in which the steering assist correction gain α and the steering reaction force gain k are corrected in a coordinated manner allows continuous normal power steering control and steering reaction force control corresponding to the risk during running. It becomes the structure which can be switched smoothly.

(8) The reaction force characteristic adjusting means corrects the gain that determines the characteristic of the steering reaction force in accordance with the change in the risk degree, and increases the gain when the risk degree changes in the increasing direction.
When the surrounding risk tends to increase significantly, the steering reaction force characteristics have been corrected. If the surrounding risk tends to increase significantly and the driver is not aware of the risk, steering Risk can be transmitted through reaction force.

(Modification)
(1) In the above-described embodiment, an example using the front camera 10 and the direction laser radar 11 directed toward the front of the vehicle is shown. A surrounding recognition device using a camera 10 or a laser radar 11 directed to the side or rear of the vehicle may be used. In this case, risk transmission can be performed more reliably.
(2) The steering reaction force characteristic corresponding to the risk can be obtained without necessarily obtaining the correction gain α strictly as described above. For example, the correction gain α may be corrected between 0.5 and 0 so that the magnitude of the risk potential RP calculated by the risk calculation unit 82a can be transmitted to the driver.

(3) In the above-described embodiment, taking the lane departure into account, the travel locus toward the center of the lane in which the host vehicle is traveling is used as the virtual travel locus.
Taking into account obstacles in front of the host vehicle, based on the detection result of the surrounding recognition means, the area in the lane where the obstacle position is removed is obtained and the area in which the vehicle can travel is determined. A virtual traveling locus of the host vehicle is set for traveling, that is, traveling at a position away from the risk. For example, it sets to the locus | trajectory which drive | works the vehicle width direction center side of the area | region which can drive | work. Then, a target steering angle for drawing the virtual traveling locus may be calculated.

That is, the target steering angle calculation means calculates the target steering angle θr for drawing a virtual traveling locus of the host vehicle that travels in a direction away from the risk. Then, the reaction force characteristic adjusting means calculates a steering reaction force according to the deviation between the target steering angle θr and the actual steering angle θ and the risk degree k.
In this case, steering assistance is performed so as to avoid an obstacle.

(4) The reaction force characteristic adjusting means may correct the gain k that determines the characteristic of the steering reaction force so as to increase in accordance with the deviation between the target steering angle and the actual steering angle.
That is, the gain k for determining the steering reaction force characteristic is set so that the gain for determining the steering reaction force characteristic also increases in accordance with the deviation between the target steering angle and the actual steering angle. As a result, the steering reaction force gain k increases as the vehicle operating device is operated in a higher risk direction, and the steering reaction force suddenly rises above a certain steering angle. For example, when it is determined that the relative speed is extremely large and the risk is extremely high like an oncoming vehicle, it is possible to immediately transmit the surrounding risk to the driver.

(5) The friction compensation means may perform compensation only when the vehicle is steered in a direction with a high risk level according to the right and left risk levels with respect to the host vehicle.
That is, the friction compensation calculation unit compares the risk potential RPr in the right direction with the risk potential RPl in the left direction, determines the direction with the higher risk, and only when the risk is steered toward the higher risk. The compensation current Id may be output to the current control unit 84.

Alternatively, the friction compensation current Id may not be output to the current control unit 84 when the degree of risk in the steering direction is zero or less than a predetermined value.
Even if steering is performed in such a direction that the surrounding risk does not occur or in a direction where the risk is low, friction compensation is not performed, and normal steering characteristics can be obtained, so that the driver's feeling of discomfort can be suppressed.
(6) In the above embodiment, the deviation Δθ (= θr−θ) is used as a value corresponding to the steering angle θ. In the above equation (10), the steering angle θ may be used instead of the deviation Δθ.

(Second Embodiment)
Next, a second embodiment will be described with reference to the drawings. The same devices as those in the first embodiment will be described with the same reference numerals.
The basic configuration of this embodiment is the same as that of the first embodiment.
FIG. 11 shows processing in the control unit 8 of the second embodiment.
As can be seen from FIG. 11, steps S110 to S140 and S150 to S190 are the same as in the first embodiment.

  That is, in steps S110 to S140, the running state such as the host vehicle speed V and the obstacle state (the relative distance D in the front-rear direction to the obstacle existing around the host vehicle, the relative speed Vr, the relative angle β, etc.) and the steering torque Th And the steering angle θ is read. Then, a steering assist current I1 as a normal power steering system is calculated using a steering assist map as shown in FIG. Further, the torque Td input as a disturbance is estimated using the equations (5), (6), and (7). Further, a friction control current Id necessary for canceling the estimated disturbance torque T ^ d is calculated.

Next, in step S145, the magnitude of the steering torque read in step S120 is determined. When the steering speed is constant or the steering is maintained, the steering torque and the steering reaction force are substantially equal.
When it is determined that a steering torque greater than a predetermined value is generated and the driver has already operated the steering wheel, updating from the previously calculated value is not performed. That is, the calculation process of risk potential RPr and RPl in the vehicle left-right direction in step S150 is not performed.

On the other hand, if it is determined in step S145 that the steering torque is equal to or less than the predetermined value and the driver is not actively operating the steering wheel in a direction in which the risk increases, the process proceeds to step S150, and the vehicle left-right direction is determined. The risk potentials RPr and RPl are updated, and then a steering reaction force is added when the driver steers in the risk increasing direction.
Next, in steps S160 to S190, a steering reaction force gain corresponding to the risk potentials RPr and RPl in the vehicle left-right direction, a target steering angle θr that guides the host vehicle toward the center of the traveling lane, and a target steering angle θr The steering reaction force control current I2 is calculated by multiplying the deviation Δθ from the actual steering angle θ by the steering reaction force gain calculated in step S160. Further, the actuator drive current is calculated from the steering assist current I1, the steering reaction force control current I2, and the friction compensation current Id using the equation (7).

(Function)
When the driver is operating the steering wheel, the fluctuation of the steering reaction force characteristic is suppressed even when the risk potential due to the environment around the vehicle fluctuates. For this reason, a natural steering reaction force characteristic for the driver can be obtained.
In addition, when the steering reaction force characteristics change from a state where a large risk has occurred, and the steering reaction force changes to a side where the reaction force becomes smaller, the driver is in spite of the fact that the absolute value of the risk has not yet decreased. May misunderstand that the risk has decreased and may steer further. However, in this embodiment, since the steering reaction force characteristic with respect to the steering wheel angle can be kept constant, such misunderstanding of the driver is reduced.
FIG. 11 shows a time chart example of the present embodiment.
A solid line is a transition diagram in the case of the second embodiment. Even if the risk potential RP fluctuates, the steering reaction force gain k is a constant value in a state where the steering reaction force is generated.

(Effect of this embodiment)
(1) The reaction force characteristic adjusting means modifies and changes the gain that determines the characteristic of the steering reaction force while the steering reaction force is not generated. To do.
In the case of steering in a state where a risk has occurred, by setting a constant steering reaction force gain k, the steering reaction force can be prevented from changing arbitrarily due to a cause other than the driving operation. As a result, it is possible to prevent an uncomfortable feeling that the steering reaction force changes in a state where the driver understands the risk.

It is a schematic block diagram of the apparatus which concerns on embodiment based on this invention. It is a block diagram which shows the control unit which concerns on embodiment based on this invention. It is a block diagram which shows the steering assist calculating part which concerns on embodiment based on this invention. It is a block diagram which shows the friction compensation calculating part which concerns on embodiment based on this invention. It is a block diagram which shows the steering reaction force control part which concerns on embodiment based on this invention. It is a figure which shows the example of a characteristic of risk potential RP-steering reaction force gain k which concerns on embodiment based on this invention. It is a figure explaining the process of the control unit which concerns on 1st Embodiment based on this invention. It is a figure which shows the steering angle-steering torque characteristic of a normal EPS apparatus. It is a figure which shows the characteristic of the steering reaction force which concerns on embodiment based on this invention. It is a figure explaining the process of the control unit which concerns on 2nd Embodiment based on this invention. It is a figure which shows the example of a time chart which concerns on 2nd Embodiment based on this invention.

Explanation of symbols

1R, 1L Front wheel (steering wheel)
3 Steering wheel (vehicle operation equipment)
7 Steering actuator 8 Control unit 10 Camera 10 Front camera (ambient recognition means)
11 Laser radar (Ambient recognition means)
81 Steering assist calculation unit 81A Steering assist calculation unit main body 81B Assist correction unit 82 Steering reaction force control unit 82a Risk calculation unit (risk calculation means)
82b Target steering angle calculation unit (target steering angle calculation means)
82c Reaction force control calculation unit (reaction force characteristic adjusting means)
83 Friction compensation calculation unit (friction compensation means)
84 Current control unit I Actuator drive current I1 Steering assist current I2 Steering reaction force control current Id Friction compensation current k Steering reaction force gain RP Risk potential Td Disturbance torque T ^ d Disturbance torque estimated value Th Steering torque V Vehicle speed α Steering assist correction gain β Relative angle θ Steering angle θr Target steering angle

Claims (12)

In a vehicle steering apparatus that includes a vehicle operating device that is steered by a driver, and steered wheels are steered according to the steering of the driver,
Surrounding recognition means for detecting the traveling state of the host vehicle and the driving environment around the vehicle, and risk calculating means for calculating the degree of risk around the host vehicle based on the detection result of the surrounding recognition means;
Reaction force characteristic adjusting means for calculating a characteristic of the steering reaction force according to the degree of risk calculated by the risk calculating means and the steering angle of the vehicle operating device;
Reaction force characteristic control means for controlling the steering reaction force characteristic with respect to the steering angle of the vehicle operating device so as to match or approach the characteristic of the steering reaction force calculated by the reaction force characteristic adjustment means;
A vehicle steering apparatus comprising: friction compensation means for compensating for disturbances other than the driver's operating force acting on the vehicle operating device.   2. The vehicle steering apparatus according to claim 1, wherein the friction compensation unit performs compensation only when the vehicle is steered in a direction in which the degree of risk is high in accordance with the degree of risk in the right direction and the left direction with respect to the host vehicle. . A steering actuator for adding an auxiliary torque to the steering transmission system according to the steering torque by steering of the vehicle operating device;
The reaction force characteristic control means fixes the steering reaction force calculated by the reaction force characteristic adjustment means to a fixed value or less than a predetermined value when there is no risk based on the risk degree calculated by the risk calculation means or when the risk degree is less than a predetermined value. The vehicle steering apparatus according to claim 1, wherein the vehicle steering apparatus is suppressed. Based on the detection result of the surrounding recognition means, comprising target steering angle calculation means for calculating a target steering angle for drawing a virtual traveling locus of the host vehicle that travels in a direction away from the risk,
The said reaction force characteristic adjustment means calculates the said steering reaction force according to the deviation of the said target steering angle and an actual steering angle, and the said risk degree, The said steering reaction force is characterized by the above-mentioned. The vehicle steering apparatus described in item 1. Target steering angle calculation means for calculating a target steering angle for drawing a virtual travel locus of the host vehicle such that the host vehicle travels toward the center of the traveling lane based on the detection result of the surrounding recognition unit With
The said reaction force characteristic adjustment means calculates the said steering reaction force according to the deviation of the said target steering angle and an actual steering angle, and the said risk degree, The said steering reaction force is characterized by the above-mentioned. The vehicle steering apparatus described in item 1.   The said reaction force characteristic adjustment means increases the gain which determines the characteristic of a steering reaction force according to the deviation of the said target steering angle and an actual steering angle, The Claim 4 or Claim 5 characterized by the above-mentioned. Vehicle steering system.   The vehicle reaction device according to any one of claims 1 to 6, wherein the reaction force characteristic adjusting means changes a gain for determining a characteristic of the steering reaction force to a larger value as the vehicle speed is higher. Steering device.   The reaction force characteristic adjusting means corrects the gain for determining the characteristic of the steering reaction force according to the change in the risk degree, and increases the gain when the risk degree changes in a direction of increasing. The vehicle steering apparatus according to any one of claims 1 to 7.   The reaction force characteristic adjusting means changes a gain for determining the characteristic of the steering reaction force while the steering reaction force is not generated, and does not change when the steering reaction force is generated. The vehicle steering apparatus according to any one of claims 1 to 8. The risk calculation means individually calculates the risk level of the left area and the right area for the host vehicle,
The vehicle steering apparatus according to any one of claims 1 to 9, wherein the reaction force characteristic adjusting means individually calculates the characteristics of the steering reaction force in the left region and the right region. A steering actuator for adding auxiliary torque to the steering transmission system according to the steering torque by steering of the vehicle operating device;
11. The vehicle steering apparatus according to claim 1, wherein the auxiliary torque is corrected to decrease in accordance with the steering reaction force calculated by the reaction force characteristic adjusting means. In a vehicle steering method including a vehicle operating device that is steered by a driver, and steered wheels are steered according to the steering of the driver,
While compensating for disturbances other than the driver's operating force acting on the vehicle operating device based on the steering reaction force from the vehicle operating device received by the driver and the operating state of the operating device, the degree of risk around the host vehicle and the vehicle operating device By adding a steering reaction force corresponding to the steering angle to the steering transmission system, the steering reaction force characteristic with respect to the steering angle of the vehicle operating device matches or approaches the steering reaction force characteristic calculated by the reaction force characteristic adjusting means. A vehicle steering method characterized by comprising:

Images