JP2010264940A - Vehicular control device and method for changing wheelbase - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicular control device capable of suppressing the deterioration of steering stability even when there is a sudden behavior change in the vehicle. <P>SOLUTION: The vehicular control device includes a controller 1 which detects yaw information generated in a vehicle body, and controls a linear actuator 2 to change a wheelbase. The controller 1 increases the wheelbase on the basis of the yaw information in the case when the vehicle suddenly changes when it is determined that the vehicular behavior suddenly changes from the yaw information. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a vehicle control device and a wheel base changing method for changing a wheel base of a vehicle.

  Conventionally, a technique for changing a wheel base in accordance with a running state of a vehicle is known in Patent Document 1 below. This Patent Document 1 describes that an actuator for supporting a rear axle so as to be movable back and forth with respect to a vehicle body frame and moving the rear axle forward and backward is provided. When the vehicle is traveling at a high speed, the rear axle is moved backward by the operation of the actuator. On the other hand, during low-speed traveling, the rear axle is moved forward by the operation of the actuator.

JP-A-1-106717

  However, when there is a sudden change in behavior of the vehicle, there is a problem that the wheel base is insufficient and the steering stability is lowered. However, with the above-described technology, the wheel base cannot be made variable with respect to the decrease in steering stability.

  Therefore, the present invention has been proposed in view of the above-described situation, and there is provided a vehicle control device and a wheel base changing method capable of suppressing a decrease in steering stability even when the vehicle has a sudden change in behavior. The purpose is to provide.

  The present invention determines the vehicle behavior based on the yaw information generated in the vehicle body, and when it is determined that the vehicle behavior has changed abruptly, the wheel base is increased based on the determined yaw information.

  According to the present invention, when the vehicle behavior changes rapidly, the wheel base is increased based on the information in the yaw direction, so that it is possible to suppress a decrease in steering stability.

It is a figure showing an example of 1 composition of vehicles carrying a vehicle control device shown as a 1st embodiment of the present invention. It is a block diagram which shows one functional structural example of the vehicle control apparatus shown as 1st Embodiment of this invention. In the vehicle control apparatus shown as 1st Embodiment of this invention, it is a figure which shows the relationship between a wheel base and a front-back weight distribution ratio. In the vehicle control apparatus shown as the first embodiment of the present invention, (a) shows a state when the wheel base is the shortest, and (b) shows a state when the wheel base is the maximum. It is a figure which shows the relationship between a wheel base and a yaw inertia moment in the vehicle control apparatus shown as 1st Embodiment of this invention. In the vehicle control apparatus shown as the first embodiment of the present invention, (a) is a diagram showing the relationship between the vehicle destabilizing factor and the wheel base, and (b) is the relationship between the vehicle destabilizing factor and the yaw natural frequency. It is a figure which shows a relationship. It is a flowchart which shows the process sequence which controls a wheel base in the vehicle control apparatus shown as 2nd Embodiment of this invention. In the vehicle control apparatus shown as the second embodiment of the present invention, (a) is a diagram showing the relationship between the vehicle destabilization factor and the wheel base, and (b) is the relationship between the vehicle destabilization factor and the yaw natural frequency. It is a figure which shows a relationship. In the vehicle control apparatus shown as the second embodiment of the present invention, (a) is a temporal change in the yaw natural frequency, (b) is a temporal change in a time differential value of the yaw natural frequency, and (c) is It is a figure which shows the time change of foil base. It is a flowchart which shows the process sequence which controls a wheel base in the vehicle control apparatus shown as 3rd Embodiment of this invention. In the vehicle control apparatus shown as the third embodiment of the present invention, (a) shows the relationship between the deceleration G and the wheel base, and (b) shows the relationship between the deceleration G and the rear wheel load. It is a flowchart which shows the process sequence which controls a wheel base in the vehicle control apparatus shown as 4th Embodiment of this invention. It is a figure which shows the relationship between a steering angle and wheel base in the vehicle control apparatus shown as 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
The vehicle control device shown as the first embodiment of the present invention is applied to the vehicle shown in FIG. This vehicle control device includes a controller 1, a linear actuator 2, a vehicle body 3, a front wheel 4F, and a rear wheel 4R. Further, the linear actuator 2 is connected to a piston rod 11 and a rear wheel suspension member 12 that are configured to change the wheel base of the vehicle.

  The piston tube side of the linear actuator 2 is fixed to the vehicle body 3, and the piston rod 11 side is fixed to the rear wheel suspension member 12. Thus, the distance between the front wheel 4F and the rear wheel 4R is variable by the operation of the linear actuator 2. Further, a rear wheel driving motor 13 that applies a driving force to the rear wheel 4R is disposed close to the rear wheel suspension member 12.

  The linear actuator 2 drives the rear wheel 4R in the vehicle front-rear direction according to the control of the controller 1 (driving means). At the shortest time of the wheel base, the distance between the rear end suspension member 12 and the piston tube (fixed to the vehicle body 3) that accommodates the piston rod 11 in the linear actuator 2 is shortened. On the other hand, when the wheel base is extended, the piston tube of the linear actuator 2 fixed to the vehicle body 3 is separated from the rear wheel suspension member 12 via the piston rod 11. Thereby, the wheel base that is the distance between the front wheel 4F and the rear wheel 4R is variable.

  Thereby, the linear actuator 2 makes variable the wheel base L which shows the distance of the axis | shaft of the front wheel 4F of a vehicle, and the axis | shaft of the rear wheel 4R. In this embodiment, the linear actuator 2 that moves the rear wheel suspension member is used as a configuration in which the wheel base L is variable. However, as a configuration in which the wheel base L is variable, it goes without saying that the wheel base control described below can be applied even to a vehicle having other wheel base variable means.

  The controller 1 functions as control means for driving the linear actuator 2 to change the wheel base L. The controller 1 is connected to at least a vehicle speed sensor that detects a vehicle speed and a steering angle sensor that detects a steering angle. Then, the controller 1 determines the vehicle behavior based on either the vehicle speed or the steering angle. Further, the controller 1 calculates yaw information indicating an operation state in the yaw direction generated in the vehicle. This yaw information includes the natural frequency (yaw natural frequency) in the yaw direction. The lower the value of the yaw natural frequency, the more rapid the vehicle is.

  In the vehicle, the rotational motion felt in the front-rear direction during sudden acceleration or braking is the pitch direction, the rotational motion felt in the left-right direction during sudden steering is the roll direction, and the yaw direction is perpendicular to the pitch direction and the roll direction. Rotation (rotational movement in the ground when the car is viewed from above).

  When the controller 1 determines that the vehicle behavior has changed rapidly, the controller 1 increases the wheel base L based on the yaw natural frequency. Specifically, a steering angle sensor 21, an accelerator opening sensor 22, a brake opening sensor 23, a wheel speed sensor 24, and a vehicle longitudinal / lateral acceleration sensor 25 are connected to the controller 1. Based on the signals detected by these sensors, the controller 1 controls the wheel base L.

  Such a vehicle control device includes a functional configuration as shown in FIG. The vehicle control device mainly includes a vehicle running state detection unit 31, a yaw natural frequency calculation unit 32, and a target wheel base calculation unit 33. The yaw natural frequency calculation unit 32 and the target wheel base calculation unit 33 are realized by the controller 1. The controller 1 is actually composed of a ROM, a RAM, a CPU, etc., but the functions that can be realized by the CPU performing processing according to the wheel base L control program stored in the ROM will be described as blocks. .

  The vehicle travel state detection unit 31 mainly detects a vehicle travel state necessary for calculating the yaw natural frequency. For this purpose, the vehicle running state detection unit 31 includes a vehicle longitudinal / lateral acceleration sensor 41 corresponding to the vehicle longitudinal / lateral acceleration sensor 25, a wheel base value sensor 42, and a wheel speed sensor 43 corresponding to the wheel speed sensor 24.

  The yaw natural frequency calculation unit 32 includes a wheel base-front / rear weight distribution ratio correspondence map 51, a wheel base-yaw inertia moment correspondence map 52, each wheel load calculation unit 53, a normalized cornering power calculation unit 54, and a normalized yaw inertia moment calculation unit. 55, a vehicle body speed calculation unit 56, and a yaw natural frequency calculation unit 57.

  The yaw natural frequency calculation unit 32 uses the vehicle longitudinal / lateral acceleration, the wheel base L, and the wheel speed acquired by the vehicle running state detection unit 31, and uses the yaw natural frequency when the wheel base is changed at rest. The wheel load of each wheel based on the load of each wheel calculated using the distribution ratio and the cornering power of each wheel, the yaw inertia moment based on the change of the inertia moment in the yaw direction when the wheel base is changed at rest, Update based on vehicle speed. The yaw natural frequency is used for calculating the target value of the wheel base L by the target wheel base calculation unit 33, and is actually used by the target wheel base calculation unit 33 to vary the wheel base L.

  The front-rear weight distribution ratio and the yaw moment of inertia are factors that can change as the wheel base L changes. For this reason, the yaw natural frequency calculation unit 32 prepares a wheel base / front / rear weight distribution ratio correspondence map 51 and a wheel base / yaw inertia moment correspondence map 52 in advance.

The wheel base-front / rear weight distribution ratio correspondence map 51 is map data describing the relationship between the wheel base L calculated in advance for the vehicle and the front / rear weight distribution ratio. As shown in FIG. 3, the wheel base-front / rear weight distribution ratio correspondence map 51 describes that the front / rear weight distribution ratio increases as the wheel base L increases. As shown in FIG. 4A, when the wheel base L is in the shortest state, the vehicle 100 has the same weight distribution (weight distribution ratio: R _L ) between the front wheels 4F and the rear wheels 4R. When the wheel base L increases and the wheel base L becomes the maximum, as shown in FIG. 4B, a large weight is added to the front wheel 4F, and the weight applied to the rear wheel 4R is relatively decreased. Thus, the front / rear weight distribution ratio _RH when the wheel base L is maximized is larger than _RL when the wheel base L is shortest.

  Thereby, the wheel base-front-and-rear weight distribution ratio correspondence map 51 acquires the current value of the front-rear weight distribution ratio of the vehicle in response to the current wheel base L being supplied from the wheel base value sensor 42. The relationship between the wheel base L and the front / rear weight distribution ratio is not limited to map data, and may be expressed by some function. In the present embodiment, the front / rear weight distribution ratio is calculated only from the value of the wheel base L. However, the front-rear weight distribution ratio acquired based on the wheel base L may be corrected with reference to, for example, other sensor data (wheel load, suspension stroke). As a result, a more accurate front-rear weight distribution ratio of the vehicle can be acquired.

The wheel base-yaw inertia moment correspondence map 52 is map data describing the relationship between the wheel base L and the yaw inertia moment. As shown in FIG. 5, the wheel base-yaw inertia moment correspondence map 52 describes that the yaw inertia moment increases as the wheel base L increases. If a wheel base L of the vehicle 100 is the shortest state, the yaw moment of inertia becomes M _L lowest value. When the wheel base L increases and the wheel base L becomes the maximum, the yaw moment of inertia becomes the maximum value _MH .

  Thus, the wheel base-yaw inertia moment correspondence map 52 acquires the current vehicle yaw inertia moment in response to the current wheel base L being supplied from the wheel base value sensor 42. Such a relationship between the wheel base L and the yaw moment of inertia is not limited to map data, and may be expressed by some function.

  Each wheel load calculation unit 53 calculates the load of each front wheel 4F and rear wheel 4R from the value of the wheel load movement amount in the vehicle and the value of the stationary wheel load. The value of the wheel load movement amount is obtained according to a predetermined arithmetic expression using the vehicle longitudinal acceleration and lateral acceleration acceleration supplied from the vehicle longitudinal / lateral acceleration sensor 41. The value of the stationary wheel load is obtained from the stationary front / rear weight distribution ratio obtained from the wheel base / front / rear weight distribution ratio correspondence map 51.

Each wheel load calculation part 53 calculates the load of a front left wheel, a front right wheel, a rear left wheel, and a rear right wheel according to the following formulas 1 to 4, for example.

In the above formulas 1 to 4, k is the weight sharing ratio of the front wheels (0 <k <1), W _total is the vehicle weight, A _x is a proportional constant of wheel load movement due to longitudinal acceleration, and A _yf is the front wheel load due to lateral acceleration. A proportional constant of movement, A _yr is a proportional constant of rear wheel load movement by lateral acceleration, a _x is longitudinal acceleration, and a _y is longitudinal acceleration.

Normalized yaw inertia moment calculation unit 55, the value of the normalized yaw inertia moment I _n, calculates according to equation 5 below.

  In Equation 5, m is the vehicle mass, I is the yaw moment of inertia acquired from the wheel base-yaw inertia moment correspondence map 52, L is the wheel base acquired from the wheel base value sensor 42, k is from the wheel base-front-and-rear weight distribution ratio correspondence map 51. This is the weight sharing ratio of the acquired front wheels.

  The vehicle body speed calculation unit 56 calculates the vehicle body speed from the wheel speed acquired from the wheel speed sensor 43.

The normalized cornering power calculation unit 54 calculates the normalized cornering power of each wheel from the load value of each wheel calculated by each wheel load calculation unit 53. The normalized cornering power calculation unit 54 handles the equivalent cornering power K expressed by the following equation 6 by approximating it with a quadratic function of the wheel load W. As shown in Equation 7, the value of the normalized cornering power C obtained by dividing the equivalent cornering power K by the wheel load W is obtained for each wheel.

Here, σ in the above formula is a CP amplification factor, which is a value depending on suspension characteristics and the like. C ₀ is the normalized cornering power initial value, which is a value depending on the tire performance. ε is a load fluctuation rate, and is a value depending on the performance deterioration due to the increase in wheel load and the tire performance. In the present embodiment, the cornering power is calculated based on the above equations 6 and 7. However, the normalized cornering power calculation unit 54 may separately calculate cornering power using a tire model separately from a road surface friction coefficient, a driving force estimation value, a tire slip angle estimation value, and the like.

The yaw natural frequency calculation unit 57 calculates the normalized cornering power value calculated by the normalized cornering power calculation unit 54, the normalized yaw inertia moment value calculated by the normalized yaw inertia moment calculation unit 55, and the vehicle body speed calculation. Based on the value of the vehicle body speed calculated by the unit 56, the value of the yaw natural frequency ω _n is calculated according to the following equation 8.

In the above equation 8, C _f is the left-right average value of the front wheel normalized cornering power, C _r is the left-right average value of the rear wheel normalized cornering power, V is the vehicle body speed, L is the wheel base, I _n is the normalized yaw moment of inertia.

  As described above, the yaw natural frequency calculation unit 32 prepares the wheel base-front / rear weight distribution ratio correspondence map 51 and the wheel base-yaw inertia moment correspondence map 52 in advance. Thus, the yaw natural frequency calculation unit 32 can obtain the yaw natural frequency in consideration of the change in the weight distribution ratio in the front and rear when the wheel base is changed when the vehicle is stationary and the moment of inertia in the yaw direction. it can. The yaw natural frequency calculation unit 32 is based on at least the vehicle speed V, the wheel load of each wheel, the cornering power of each wheel, the wheel base, the front / rear weight distribution ratio (at rest), and the variable values of the yaw moment of inertia. Can be updated.

The target wheel base calculation unit 33 determines that a sudden behavior has occurred in the vehicle based on the vehicle speed and / or the steering angle. When a sudden change occurs in the vehicle behavior, the yaw natural frequency becomes a small value as shown in FIG. On the other hand, the target wheel base calculation unit 33 performs control so as to increase the wheel base L as shown in FIG. Specifically, the wheel base L changes as in the following formulas 9, 10, and 11 according to the value of the natural yaw frequency ω.

In the above formulas 9 to 11, L ₀ is the initial value (shortest value) of the wheel base L, V ₀ is a threshold value that specifies that the wheel base L is not increased in the low speed range, A is a proportional constant set for each vehicle, ω _n0 is the wheel base is yaw natural frequency when the L ₀ and the vehicle speed V _0.

When the vehicle body speed V is equal to or less than the predetermined value V ₀ as in Expression 9, the target wheel base calculation unit 33 sets the wheel base L as the wheel base L ₀ with the shortest distance. When the yaw natural frequency ω _n is an intermediate value as in Expression 10, the target wheel base calculation unit 33 increases the wheel base L with respect to the wheel base L ₀ having the shortest distance. As a result, as shown in FIG. 6A, the wheel base L is increased as the vehicle destabilization factor increases. Then, the longest when the yaw natural frequency omega _n as a predetermined value TH from greater becomes equation 11 vehicle instability factor shown by a dotted line in FIG. 6 is equal to or greater than a predetermined value, the target wheel base calculation unit 33, the wheel base L Increase to L _{max of} distance. Accordingly, as shown in FIG. 6B, the wheel base L can be lengthened as the vehicle anxiety factor increases and the yaw natural frequency decreases. That is, according to the vehicle control device, the wheel base L is increased even if the yaw natural frequency decreases during a sudden vehicle behavior. Thereby, with respect to the comparative example in which the wheel base L is constant as shown by the dotted line in FIG. 6B, the vehicle control device of the present embodiment can suppress a decrease in the yaw natural frequency. As a result, the vehicle control device can always improve the steering stability.

  As described above, according to the vehicle control device according to the first embodiment, when the target wheel base calculation unit 33 determines that the vehicle behavior has suddenly changed, the wheel base L is increased based on the information in the yaw direction. Thereby, according to the vehicle control device, it is possible to suppress a decrease in steering stability even when the vehicle has a sudden change in behavior. That is, according to this vehicle control device, when the vehicle behavior changes suddenly, such as when decelerating, turning sharply, or traveling on a low μ road, the wheel base L is insufficient, and the steering stability is reduced. Can be prevented.

  Further, according to the vehicle control apparatus of the first embodiment, the yaw natural frequency that is the natural frequency in the yaw direction is calculated as the operation state in the yaw direction. And, the vehicle control device, the change of the load of each wheel and the moment of inertia in the yaw direction calculated using the front-rear weight distribution ratio when the wheel base is changed when the yaw natural frequency is stationary for each vehicle, The vehicle speed, wheel load of each wheel, cornering power of each wheel, wheel base, front / rear weight distribution ratio when the vehicle is stationary, and yaw moment of inertia are updated. According to such a vehicle control device, it is possible to accurately determine the stability of the vehicle sequentially in consideration of the front / rear weight distribution ratio, the yaw moment of inertia, and the like that can be changed by changing the wheel base L. . Therefore, according to this vehicle control device, it is possible to further improve the stability of the vehicle.

  Furthermore, according to the vehicle control apparatus of the first embodiment, the wheel base L is increased as the yaw natural frequency is smaller, so that the amount of decrease in the yaw natural frequency can be suppressed. Moreover, the vehicle control apparatus can always suppress the decrease amount of the natural frequency by updating the yaw natural frequency. Thereby, the vehicle control device improves steering stability when it is necessary to lengthen the wheel base L so that the yaw natural frequency is reduced as compared with the vehicle state when the wheel base L is the shortest. Can do.

[Second Embodiment]
Next, a vehicle control device shown as a second embodiment of the present invention will be described. In addition, about the part similar to the above-mentioned 1st Embodiment, the detailed description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In the vehicle control apparatus shown as the second embodiment, when the yaw natural frequency updated by the yaw natural frequency calculating unit 32 is equal to or less than a predetermined first threshold, the target wheel base calculating unit 33 performs the yaw natural frequency. The wheel base L is increased until the yaw natural frequency updated by the calculation unit 32 reaches the predetermined threshold. On the other hand, when the yaw natural frequency updated by the yaw natural frequency calculating unit 32 is larger than the predetermined first threshold, the vehicle control device causes the target wheel base calculating unit 33 to maintain the wheel base L in the shortest state.

  The vehicle control apparatus updates the yaw natural frequency calculation unit 32 when the time differential value of the yaw natural frequency updated by the yaw natural frequency calculation unit 32 is equal to or less than a predetermined second threshold value. Even if the yaw natural frequency is larger than the predetermined first threshold, the target wheel base calculation unit 33 increases the wheel base L from the shortest state.

  Such a vehicle control device controls the wheel base L, for example, by performing the processing shown in FIG.

  The vehicle control device performs the processing shown in FIG. 7 every predetermined time when the vehicle is traveling.

  First, in step S1, the controller 1 detects the vehicle speed and the steering angle of the vehicle.

  In the next step S2, the controller 1 refers to the vehicle speed and steering angle acquired in step S1, and determines whether or not a sudden behavior change has occurred in the vehicle. If it is determined that a sudden change in behavior has occurred in the vehicle, the process proceeds to step S3. If no sudden change in behavior has occurred in the vehicle, the process ends.

  In step S <b> 3, the controller 1 uses the yaw natural frequency calculation unit 32 to calculate the yaw natural frequency.

  In the next step S4, the controller 1 determines whether or not the yaw natural frequency calculated in step S3 is equal to or less than a predetermined threshold value. If the yaw natural frequency is equal to or lower than the predetermined threshold, the process proceeds to step S9. If the yaw natural frequency is not equal to or lower than the predetermined threshold, the process proceeds to step S5. If the yaw natural frequency is less than or equal to a predetermined threshold, the vehicle behavior is unstable.

  In step S <b> 9, the controller 1 controls the linear actuator 2 by the target wheel base calculation unit 33 and refers to the yaw natural frequency updated by the yaw natural frequency calculation unit 32 to increase the wheel base L. The target wheel base calculation unit 33 increases the wheel base L until the yaw natural frequency updated by the yaw natural frequency calculation unit 32 reaches a predetermined threshold, and ends the process.

  In step S5, the controller 1 calculates the time differential value of the yaw natural frequency calculated in step S3 by the target wheel base calculation unit 33.

  In the next step S6, the controller 1 uses the target wheel base calculation unit 33 to determine whether or not the time differential value of the yaw natural frequency calculated in step S5 is a negative value equal to or less than a predetermined threshold value. If the time differential value of the yaw natural frequency is a negative value equal to or less than a predetermined threshold, the process proceeds to step S7, and if not, the process proceeds to step S8. If the time differential value of the yaw natural frequency becomes a negative value equal to or less than a predetermined threshold value, it indicates that the vehicle is expected to become unstable in the future. Conversely, if the time derivative of the yaw natural frequency is not a negative value equal to or less than a predetermined threshold, it indicates that the yaw natural frequency is stable without becoming unstable in the future.

  In step S8, the controller 1 controls the linear actuator 2 by the target wheel base calculation unit 33, maintains the wheel base L at the initial shortest state, and ends the process.

  In step S <b> 7, the controller 1 controls the linear actuator 2 by the target wheel base calculation unit 33 and refers to the time differential value of the yaw natural frequency to increase the wheel base L. The target wheel base calculation unit 33 increases the wheel base L until the time differential value of the yaw natural frequency updated by the yaw natural frequency calculation unit 32 reaches a predetermined threshold, and ends the process.

As described above, the vehicle control device has a yaw natural frequency higher than the predetermined threshold TH1, as shown in FIG. 8B, and includes an increase in vehicle speed, an increase in deceleration G, a sudden change in steering angle, and the like. When the vehicle destabilizing factor is lower than the predetermined threshold value TH2, as shown in FIG. 8A, the wheel base L is not controlled. In this case, wheel base L is a wheel base L ₀ of the shortest value. Such an operation is realized by the processing of step S1, step S2, step S4, step S5, step S6, and step S8 in FIG.

  On the other hand, when the yaw natural frequency is lower than the predetermined threshold TH1 and the vehicle instability factor is higher than the predetermined threshold TH2, as shown in FIG. The foil base L is increased as follows. At this time, the wheel base L is increased so as to keep the yaw natural frequency constant. Such an operation is realized by the processing of step S1, step S2, step S4, and step S9 in FIG.

  On the other hand, a comparative example in which the foil base L is constant is shown by dotted lines in FIGS. 8 (a) and 8 (b). In this case, since the wheel base L is constant, the yaw natural frequency is lowered and the vehicle becomes unstable.

  Further, as shown in FIG. 9A, at time t2 before time t2 when the yaw natural frequency becomes the predetermined threshold TH1, the time differential value of the yaw natural frequency is obtained as shown in FIG. 9B. Assume that the threshold value is less than or equal to a predetermined threshold value TH3. In this case, the vehicle control device can determine in step S6 in FIG. 7 that the time differential value of the yaw natural frequency is equal to or less than the predetermined threshold value TH3. Corresponding to this determination, the vehicle control apparatus can increase the wheel base L as shown in FIG. 9C by performing the process of step S7 of FIG.

  Thereby, as shown by the solid line in FIG. 9, the vehicle control apparatus can start increasing the wheel base L even at time t1 when the yaw natural frequency is not less than or equal to the predetermined threshold value TH1. Thereby, the decrease in the yaw natural frequency is suppressed, and the time differential value of the yaw natural frequency increases. When the yaw natural frequency becomes equal to or lower than a predetermined threshold TH1 at time t2, the wheel base L is maintained so as to maintain the yaw natural frequency.

  On the other hand, the dotted line in FIGS. 9A, 9B, and 9C indicates the yaw natural frequency when the time differential value of the yaw natural frequency is not used, the time differential value of the yaw natural frequency, The change of the foil base L is shown. In this case, the wheel base L is increased when it is determined that the yaw natural frequency is equal to or lower than the predetermined threshold value TH1 at time t2. In this case, the yaw natural frequency overshoots and falls below the predetermined threshold value TH1.

  Therefore, the stability of the vehicle can be further improved by controlling the wheel base L using the time differential value of the yaw natural frequency.

  As described above, the vehicle control apparatus shown as the second embodiment increases the wheel base L until the yaw natural frequency reaches the predetermined threshold TH1 when the yaw natural frequency is equal to or less than the predetermined first threshold TH1. Let On the other hand, the vehicle control device maintains the wheel base L in the shortest state when the yaw natural frequency is larger than the predetermined first threshold value TH1.

  Thus, according to the vehicle control device, the wheel base L is lengthened only when the vehicle is unstable. Therefore, the wheel base L has advantages such as daily turning ability of a small vehicle having a short wheel base L and good handling such as parking. It is possible to achieve both the merit of high handling stability under an unstable situation in an emergency of a long vehicle.

  Further, according to this vehicle control device, it is possible to maintain a substantially constant yaw natural frequency within a range in which the control for increasing the wheel base L is performed. Traveling is possible.

  Further, when the time differential value of the yaw natural frequency is equal to or less than the predetermined second threshold value TH3, the vehicle control device can control the wheel base even if the yaw natural frequency is greater than the predetermined first threshold value TH1. L is increased from the shortest state. Thereby, according to this vehicle control device, it is possible to prevent the yaw natural frequency from becoming equal to or less than the threshold value TH1 in a scene where the stability of the vehicle is suddenly lost. In addition, according to the vehicle control device, it is possible to ensure the stability of the vehicle in response to a transitional vehicle state transition without extremely increasing the wheel base variable speed depending on the performance of the linear actuator 2. .

[Third Embodiment]
Next, a vehicle control device shown as a third embodiment of the present invention will be described. Note that parts similar to those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The vehicle control device shown as the third embodiment is mounted on a vehicle in which the front and rear weight distribution ratio changes closer to the front wheels when the wheel base L is increased. When it is determined that the vehicle behavior has suddenly changed when the vehicle decelerates, the vehicle control device limits the width by which the wheel base is increased so that the rear wheel load of the vehicle becomes equal to or greater than a predetermined threshold.

  Such a vehicle control apparatus performs an operation as shown in FIG.

  When the controller 1 does not have a sudden vehicle behavior, the yaw natural frequency is not less than the predetermined threshold TH1, and the time derivative of the yaw natural frequency is not a negative value less than the predetermined threshold TH3 ( In steps S1 to S6) and step S14, the wheel base L is maintained at the shortest value.

  If the time differential value of the yaw natural frequency is a negative value equal to or less than the predetermined threshold TH3 in step S6, the process proceeds to step S11. In step S11, the controller 1 refers to the rear wheel load value. The rear wheel load value is a value acquired when the yaw natural frequency calculation unit 32 calculates the yaw natural frequency. In the next step S12, the controller 1 determines whether or not the rear wheel load value referred to in step S11 is equal to or greater than a predetermined threshold value. If the rear wheel load value is equal to or greater than the predetermined threshold value, the process proceeds to step S13; otherwise, the process proceeds to step S18.

  In step S13, the controller 1 increases the wheel base L until the time differential value of the yaw natural frequency reaches a predetermined threshold value TH3. On the other hand, in step S18, the controller 1 limits the width of the wheel base L to be increased until the rear wheel load value becomes equal to or greater than a predetermined threshold value.

  If it is determined in step S4 that the yaw natural frequency is equal to or less than the predetermined threshold value TH1, the processes in steps S15 and S16 are performed. This step S15 refers to the rear wheel load value as in step S11. In step S16, it is determined whether or not the rear wheel load value is equal to or greater than a predetermined threshold as in step S12. If the rear wheel load value is equal to or greater than the predetermined threshold value, the process proceeds to step S17. If not, the process proceeds to step S18.

  In step S17, the controller 1 increases the wheel base L until the yaw natural frequency reaches a predetermined threshold value TH1. On the other hand, in step S18, the controller 1 limits the width of the wheel base L to be increased until the rear wheel load value becomes equal to or greater than a predetermined threshold value.

  In the vehicle control device that performs such processing, when the gravity G during deceleration increases as shown in FIG. 11A, the rear wheel load value decreases as shown in FIG. 11B. And the higher the gravity G during deceleration, the higher the front wheel load value, so the rear wheel load value decreases. When the gravity G at the time of deceleration is lower than G1, the vehicle control device maintains the wheel base L at the shortest value L0. This operation is realized in step S14 of FIG.

  When the gravity G at the time of deceleration becomes higher than G1, the vehicle control device determines that an abrupt vehicle behavior has occurred in step S2, and increases the wheel base L. This operation is realized by steps S13 and S17 in FIG.

  When the gravity G during deceleration becomes higher than G2, the vehicle control device determines that the rear wheel load value has become equal to or less than a predetermined threshold value TH4 in steps S12 and S16. In this case, the vehicle control device restricts the operation of increasing the wheel base L, and even if the gravity G during deceleration is further increased as shown in FIG. 11B, the wheel base L as shown in FIG. Is kept constant. This operation is realized by step S18 in FIG.

  On the other hand, the vehicle control apparatus shown as the second embodiment increases the yaw natural frequency as the gravity G at the time of deceleration becomes higher and the vehicle behavior becomes unstable as shown by the dotted line in FIG. On the other hand, the foil base L is increased. When the wheel base L is increased in this manner, the load movement in the front-rear direction due to deceleration and the weight distribution due to the extension of the wheel base L overlap, and the rear wheel load may become excessive. If the rear wheel load is too small in the vehicle, the rear wheel may actually lock and the vehicle may become unstable.

  On the other hand, according to the vehicle control apparatus shown as the third embodiment, when the rear wheel load value is not equal to or greater than the predetermined threshold value TH4, it is determined that the rear wheel load is insufficient, and the rear wheel load is insufficient. To ensure the stability of the vehicle even during sudden deceleration.

  As described above, according to the vehicle control apparatus shown as the third embodiment, even when the wheel base L is increased, the rear and rear weight distribution ratio when the wheel base L is increased changes to the front wheels. The width by which the wheel base is increased can be limited so that the wheel load is equal to or greater than a predetermined threshold. Therefore, according to this vehicle control device, it is possible to prevent the rear wheel load from becoming excessive due to the load movement in the front-rear direction due to deceleration, and it is possible to ensure the stability of the vehicle even during sudden deceleration.

[Fourth Embodiment]
Next, a vehicle control device shown as a fourth embodiment of the present invention will be described. Note that parts similar to those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The vehicle control apparatus shown as the fourth embodiment decreases the wheel base L in accordance with an increase in the steering amount when the absolute value of the steering angle is equal to or greater than a predetermined threshold and the yaw natural frequency is equal to or greater than the predetermined threshold. Further, the vehicle control device maintains the wheel base L in the longest state when the absolute value of the steering angle is not equal to or greater than a predetermined threshold or when the yaw natural frequency is not equal to or greater than the predetermined threshold.

  Such a vehicle control apparatus performs a process as shown in FIG. The vehicle control device detects the steering angle in step S21 after step S2. Of course, the value detected in step S1 may be used as the steering angle.

  In the next step S22, the vehicle control device determines whether or not the absolute value of the steering angle detected in step S21 is greater than or equal to a predetermined threshold value. If the absolute value of the steering angle is greater than or equal to a predetermined threshold, the process proceeds to step S23, and if not, the process proceeds to step S26.

  In step S26, the vehicle control device maintains the wheel base L in the longest settable state.

  In step S23, the vehicle control device calculates a yaw natural frequency.

  In the next step S24, the vehicle control device determines whether or not the yaw natural frequency calculated in step S23 is greater than or equal to a predetermined threshold value. If the yaw natural frequency is greater than or equal to the predetermined threshold, the process proceeds to step S25, and if not, the process proceeds to step S26.

  In step S25, the vehicle control device decreases the wheel base L in accordance with the increase in the steering angle. On the other hand, in step S26, the vehicle control device maintains the wheel base L in the longest settable state.

Such vehicle control apparatus, as shown in FIG. 13, when the absolute value of the steering angle becomes a predetermined threshold value theta ₀ or more, reduces the wheel base L according to the absolute value of the steering angle. Then, when the absolute value of the steering angle becomes the maximum value theta _max is the L ₀ of the shortest value wheel base L.

As a result, the vehicle control device shortens the wheel base L only when it is determined that the vehicle is stable based on the yaw natural frequency at the time of a large turning that requires a small turning geometrically. , otherwise maintaining the wheel base L of the longest state to L _max.

  As described above, according to the vehicle control device shown as the fourth embodiment, when the absolute value of the steering angle is equal to or greater than the predetermined threshold and the yaw natural frequency is equal to or greater than the predetermined threshold, The foil base L can be reduced. Further, the vehicle control device can maintain the wheel base L in the longest state when the absolute value of the steering angle is not equal to or greater than the predetermined threshold or when the yaw natural frequency is not equal to or greater than the predetermined threshold.

  As a result, according to the vehicle control device, the wheel base L is shortened only when a small turning is required geometrically and the vehicle is stable. While enjoying, it becomes possible to shorten the wheel base L only when necessary, and to ensure a small turnability and good handling.

  The above-described embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and various modifications can be made depending on the design and the like as long as the technical idea according to the present invention is not deviated from this embodiment. Of course, it is possible to change.

DESCRIPTION OF SYMBOLS 1 Controller 2 Linear actuator 3 Car body part 4F Front wheel 4R Rear wheel 11 Piston rod 12 Rear wheel suspension member 13 Rear wheel drive motor 21 Steering angle sensor 22 Acceleration opening sensor 23 Brake opening sensor 24 Wheel speed sensor 25 Vehicle front / rear / lateral Acceleration sensor 31 Vehicle running state detection unit 32 Yaw natural frequency calculation unit 33 Target wheel base calculation unit 41 Vehicle longitudinal / lateral acceleration sensor 42 Wheel base value sensor 43 Wheel speed sensor 51 Front / rear weight distribution ratio correspondence map 52 Yaw inertia moment correspondence map 53 Wheel Load calculation unit 54 Normalized cornering power calculation unit 55 Normalized yaw moment of inertia calculation unit 56 Vehicle body speed calculation unit 57 Yaw natural frequency calculation unit

Claims (8)

Yaw information detecting means for detecting yaw information generated in the vehicle body;
Vehicle behavior determination means for determining vehicle behavior based on yaw information detected by the yaw information detection means;
Drive means for changing a wheel base indicating a distance between a front wheel shaft and a rear wheel shaft of the vehicle;
Control means for controlling the drive means to change the wheel base,
The control means increases the wheel base based on yaw information when it is determined that the vehicle behavior has changed abruptly when the vehicle behavior determination means determines that the vehicle behavior has changed abruptly. Vehicle control device. The yaw information calculation means calculates a yaw natural frequency that is a natural frequency in the yaw direction as an operation state in the yaw direction generated in the vehicle,
The yaw information calculation means includes the wheel load of each wheel and the cornering power of each wheel based on the load of each wheel calculated using the front and rear weight distribution ratio when the wheel base is changed when the wheel base is stationary. 2. The vehicle control device according to claim 1, wherein the vehicle control device is updated based on a yaw inertia moment based on a change in the inertia moment in the yaw direction when the wheel base is changed when stationary and a vehicle speed.   The vehicle control device according to claim 2, wherein the control unit increases the wheel base as the yaw natural frequency updated by the yaw information calculation unit decreases. The control means includes
When the yaw natural frequency updated by the yaw information calculating means is equal to or less than a predetermined first threshold, the wheel base is used until the yaw natural frequency updated by the yaw information calculating means reaches the predetermined first threshold. Increase
The vehicle control device according to claim 2, wherein the wheel base is maintained in the shortest state when the yaw natural frequency updated by the yaw information calculation means is larger than a predetermined first threshold value.   When the time differential value of the yaw natural frequency updated by the yaw information calculation unit is equal to or less than a predetermined second threshold, the control unit determines that the yaw natural frequency updated by the yaw information calculation unit is predetermined. 5. The vehicle control device according to claim 4, wherein the wheel base is increased more than the shortest state even if it is greater than the first threshold value. When the wheel base is increased, it is mounted on a vehicle in which the front and rear weight distribution ratio changes toward the front wheels when stationary,
It has a vehicle speed sensor that detects the vehicle speed,
When the vehicle behavior determination means determines that the vehicle behavior has suddenly changed when the vehicle speed sensor detects deceleration of the vehicle, the control means causes the rear wheel load of the vehicle to be equal to or greater than a predetermined third threshold value. The vehicle control device according to claim 2, wherein a width for increasing the wheel base is limited. A steering angle sensor for detecting the steering angle;
The control means includes
When the absolute value of the steering angle detected by the steering angle sensor is equal to or greater than a predetermined value and the yaw natural frequency updated by the yaw information calculation means is equal to or greater than a predetermined value, the wheel base is decreased as the steering amount increases. Let
When the absolute value of the steering angle detected by the steering angle sensor is not greater than or equal to a predetermined value, or when the yaw natural frequency updated by the yaw information calculation means is not greater than or equal to the predetermined value, the wheel base is maintained in the longest state. The vehicle control device according to claim 2, wherein:   The vehicle behavior is determined based on yaw information indicating the operation state in the yaw direction generated in the vehicle, and when it is determined that the vehicle behavior has changed suddenly, the wheel base is increased based on the determined yaw information. A method of changing the foil base, characterized by

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