Vehicle state estimating device, vehicle state estimating method, and vehicle control device

A vehicle state estimating device includes a wheel speed detection unit; a brake operation amount detection unit; a drive operation amount detection unit; a steering operation amount detection unit; a first state amount estimating unit configured to estimate a sprung state amount caused by an operation input; a first fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by an operation input; a second fluctuation estimating unit configured to estimate an actual wheel speed fluctuation amount from which a wheel speed fluctuation amount by a brake/drive force is excluded; a third fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by a road surface input; and a second state amount estimating unit configured to estimate at least one of a sprung state amount and an unsprung state amount caused by a road surface input.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2013-270333 filed in Japan on Dec. 26, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle state estimating device, a vehicle state estimating method, and a vehicle control device.

2. Description of the Related Art

A detection device for detecting a roll of a vehicle based on a wheel speed is conventionally known. For example, Japanese Patent Application Laid-open No. 5-319051 discloses a roll detection device for detecting a rotation movement about a front-back axis of a vehicle, the roll detection device including first and second wheel speed detection units that detect wheel speeds on the left and right of the vehicle, respectively; first and second wheel speed fluctuation amount extracting units for obtaining a fluctuation amount of the wheel speed in a sprung resonance frequency region for each of the left and right wheels based on detected left and right wheel speeds; and a roll computing unit for computing a magnitude of the rotation movement about the front-back axis of the vehicle based on a reverse phase component of the obtained fluctuation amount for the left and right wheels.

The fluctuation amount of the wheel speed is subjected to the influence of not only the behavior of a sprung portion but also the behavior of an unsprung portion. Thus, for example, the difference in the wheel speeds of the left and right wheels may not necessarily indicate the roll as is. Furthermore, the fluctuation amount of the wheel speed contains a component generated by the sprung behavior caused by an operation input. If the vehicle state is estimated from the fluctuation amount of the wheel speed containing such component, an accurate estimation may not be carried out. Thus, improvements still can be made in enhancing the accuracy of when estimating the state amount of the vehicle from the wheel speed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vehicle state estimating device, a vehicle state estimating method, and a vehicle control device capable of enhancing the estimation accuracy in estimating the state amount of the vehicle from the wheel speed.

According to one aspect of the present embodiment, a vehicle state estimating device includes a wheel speed detection unit configured to detect a wheel speed of each wheel; a brake operation amount detection unit configured to detect a brake operation amount; a drive operation amount detection unit configured to detect a drive operation amount; a steering operation amount detection unit configured to detect a steering operation amount; a first state amount estimating unit configured to estimate a sprung state amount of a vehicle caused by an operation input based on the brake operation amount, the drive operation amount, and the steering operation amount; a first fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by an operation input based on the sprung state amount caused by the operation input; a second fluctuation estimating unit configured to estimate an actual wheel speed fluctuation amount from which a wheel speed fluctuation amount by a brake/drive force is excluded based on the wheel speed detected by the wheel speed detection unit; a third fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by a road surface input by removing a wheel speed fluctuation amount caused by the operation input from the actual wheel speed fluctuation amount; and a second state amount estimating unit configured to estimate at least one of a sprung state amount and an unsprung state amount caused by the road surface input based on the wheel speed fluctuation amount caused by the road surface input.

According to another aspect of the present embodiment, in the vehicle state estimating device, the wheel speed fluctuation amount caused by the operation input is estimated based on an up-down displacement, a front-back displacement, and a pitch angle of a sprung gravity center estimated based on the brake operation amount and the drive operation amount, and a left-right displacement, a roll angle, and a yaw angle of a sprung gravity center estimated based on the steering operation amount.

According to still another aspect of the present embodiment, the vehicle state estimating device further includes a third state amount estimating unit configured to estimate a total sprung state amount, which is a sprung state amount obtained by adding an estimated value of the sprung state amount caused by the operation input and an estimated value of the sprung state amount caused by the road surface input.

According to one aspect of the present embodiment, a vehicle control device includes a wheel speed detection unit configured to detect a wheel speed of each wheel; a brake operation amount detection unit configured to detect a brake operation amount; a drive operation amount detection unit configured to detect a drive operation amount; a steering operation amount detection unit configured to detect a steering operation amount; a first state amount estimating unit configured to estimate a sprung state amount of a vehicle caused by an operation input based on the brake operation amount, the drive operation amount, and the steering operation amount; a first fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by an operation input based on the sprung state amount caused by the operation input; a second fluctuation estimating unit configured to estimate an actual wheel speed fluctuation amount from which a wheel speed fluctuation amount by a brake/drive force is excluded based on the wheel speed detected by the wheel speed detection unit; a third fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by a road surface input by removing a wheel speed fluctuation amount caused by the operation input from the actual wheel speed fluctuation amount; a second state amount estimating unit configured to estimate at least one of a sprung state amount and an unsprung state amount caused by the road surface input based on the wheel speed fluctuation amount caused by the road surface input; and a control unit configured to control a suspension device of the vehicle based on at least one of an estimated value of the sprung state amount and an estimated value of the unsprung state amount caused by the road surface input.

According to one aspect of the present embodiment, a vehicle state estimating method includes the steps of: detecting a wheel speed of each wheel; detecting a brake operation amount; detecting a drive operation amount; detecting a steering operation amount; estimating a sprung state amount of a vehicle caused by an operation input based on the brake operation amount, the drive operation amount, and the steering operation amount; estimating a wheel speed fluctuation amount caused by an operation input based on the sprung state amount caused by the operation input; estimating an actual wheel speed fluctuation amount from which a wheel speed fluctuation amount by a brake/drive force is excluded based on the wheel speed detected in the wheel speed detecting step; estimating a wheel speed fluctuation amount caused by a road surface input by removing a wheel speed fluctuation amount caused by the operation input from the actual wheel speed fluctuation amount; and estimating at least one of a sprung state amount and an unsprung state amount caused by the road surface input based on the wheel speed fluctuation amount caused by the road surface input.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vehicle state estimating device, a vehicle state estimating method, and a vehicle control device according to an embodiment of the present invention will be hereinafter described in detail with reference to the drawings. It should be recognized that the present invention is not to be limited by the embodiments. The configuring elements in the following embodiment include configuring elements easily contrived by those skilled in the art or substantially the same configuring elements.

Embodiment

An embodiment will be described with reference toFIGS. 1 to 25. The present embodiment relates to a vehicle state estimating device, a vehicle state estimating method, and a vehicle control device.FIG. 1is a block diagram of a vehicle state estimating device according to an embodiment of the present invention;FIG. 2is a schematic configuration diagram of a vehicle according to the embodiment;FIG. 3is a view describing a fluctuation amount of a rotation angle of a wheel;FIG. 4is an explanatory view of a front-back displacement fluctuation amount;FIG. 5is an explanatory view of a front-back displacement fluctuation amount by pitching;FIG. 6is an explanatory view of a front-back displacement fluctuation amount by a rotation of the vehicle;FIG. 7is an explanatory view of a front-back displacement fluctuation amount by a stroke of a suspension device;FIG. 8is an explanatory view of an unsprung pitch angle by the pitching;FIG. 9is an explanatory view of the unsprung pitch angle by the stroke of the suspension device; andFIG. 10is a view illustrating one example of an estimation result by the vehicle state estimating device according to the embodiment.

A vehicle state estimating device101according to the present embodiment estimates a sprung speed, and a relative speed of a sprung portion and an unsprung portion as state amounts of the vehicle. A method of estimating the state amount of the vehicle includes an estimating method based on a fluctuation amount of a wheel speed. However, the fluctuation amount of the wheel speed is subjected to the influence of not only a behavior of the sprung portion but also a behavior of the unsprung portion. Furthermore, the fluctuation amount of the wheel speed contains a component generated by the sprung behavior caused by an operation input. If the vehicle state is estimated from the fluctuation amount of the wheel speed containing such component, an accurate estimation may not be carried out.

The vehicle state estimating device101according to the present embodiment removes a wheel speed fluctuation amount by the sprung behavior caused by the operation input (accelerator, brake, steering) of the wheel speed fluctuation amount, and estimates a road surface input from a relationship between the road surface input and the wheel speed fluctuation amount. The behaviors of the sprung portion and the unsprung portion are estimated from the estimated road surface input. According to the vehicle state estimating device101of the present embodiment, the vehicle state can be estimated with satisfactory accuracy from the wheel speed.

First, a vehicle100according to the present embodiment will be described with reference toFIG. 2. As illustrated inFIG. 2, the vehicle100is configured to include the vehicle state estimating device101, a wheel2(2FR,2FL,2RR,2RL), and a suspension device10(10FR,10FL,10RR,10RL). The vehicle state estimating device101of the present embodiment is configured to include an ECU1, a wheel speed detection unit4(4FR,4FL,4RR,4RL), a brake operation amount detection unit5, a drive operation amount detection unit6, and a steering operation amount detection unit7. As will be described later, the ECU1of the present embodiment has a function serving as a control unit for controlling the suspension device10(10FR,10FL,10RR,10RL). Therefore, the vehicle100is mounted with a vehicle control device102including the ECU1, the wheel speed detection unit4, the brake operation amount detection unit5, the drive operation amount detection unit6, and the steering operation amount detection unit7.

The vehicle100includes, for the wheel2, a front right wheel2FR, a front left wheel2FL, a rear right wheel2RR, and a rear left wheel2RL. The vehicle100includes, for the suspension device10, a front right suspension device10FR, a front left suspension device10FL, a rear right suspension device10RR, and a rear left suspension device10RL. In the present specification, a suffix FR of a reference symbol of each configuring element indicates association to the front right wheel2FR. Similarly, a suffix FL of a reference symbol indicates association to the front left wheel2FL, RR indicates association to the rear right wheel2RR, and RL indicates association to the rear left wheel2RL.

The suspension device10connects the unsprung portion and the sprung portion. Here, the unsprung portion includes front and rear arm members, a knuckle, and the like, and is a portion connected to the wheel2side with respect to the suspension device10in the vehicle100. The sprung portion is a portion supported by the suspension device10in the vehicle100, and is, for example, a body3. The suspension device10allows the relative displacement of the sprung portion and the unsprung portion by extending and contracting. The suspension device10is arranged inclined at a predetermined angle with respect to a vertical axis, for example.

The suspension device10is configured to include a shock absorber11(11FR,11FL,11RR,11RL) and a suspension actuator12(12FR,12FL,12RR,12RL). The shock absorber11generates an attenuating force for attenuating the relative movement of the sprung portion and the unsprung portion. The suspension actuator12adjusts the attenuating force (attenuation coefficient) generated by the shock absorber11. The suspension actuator12can change the attenuating property of the shock absorber11to an arbitrary property from a relatively soft attenuating property (small attenuating force) to a relatively hard attenuating property (large attenuating force).

Each wheel2FR,2FL,2RR,2RL is provided with the wheel speed detection unit4(4FR,4FL,4RR,4RL) that detects the respective wheel speed. The front right wheel speed detection unit4FR detects the wheel speed of the front right wheel2FR. Similarly, the front left wheel speed detection unit4FL, the rear right wheel speed detection unit4RR, and the rear left wheel speed detection unit4RL respectively detect the wheel speed of the front left wheel2FL, the rear right wheel2RR, and the rear left wheel2RL. A signal indicating the detection result of each wheel speed detection unit4FR,4FL,4RR,4RL is output to the ECU1.

The ECU1of the present embodiment is an electronic control unit including a computer. The ECU1has a function serving as each estimating unit that estimates the vehicle state. The ECU1is electrically connected to the suspension device10of each wheel2FR,2FL,2RR,2RL and controls the suspension device10.

The brake operation amount detection unit5detects a brake operation amount. The brake operation amount is, for example, a pedal stroke of a brake pedal, a depressing force input to the brake pedal, a pedal speed of the brake pedal, and the like. The drive operation amount detection unit6detects a drive operation amount. The drive operation amount is, for example, an opening degree of an accelerator pedal, a pedal speed of the accelerator pedal, an opening degree of a throttle valve, and the like. The steering operation amount detection unit7detects a steering operation amount. The steering operation amount is, for example, a steering angle, a steering torque, a steering speed, and the like of a steering wheel. Signals indicating the detection results of the brake operation amount detection unit5, the drive operation amount detection unit6, and the steering operation amount detection unit7are output to the ECU1.

As illustrated in the block diagram ofFIG. 1, the ECU1according to the present embodiment is configured to include a first state amount estimating unit21, a first fluctuation estimating unit22, a second fluctuation estimating unit23, a third fluctuation estimating unit24, a second state amount estimating unit25, and a third state amount estimating unit26.

First State Amount Estimating Unit

The first state amount estimating unit21estimates a sprung state amount of the vehicle100caused by the operation input based on the brake operation amount, the drive operation amount, and the steering operation amount. The sprung state amount is a state amount of the sprung portion of the vehicle100, and is, for example, the behavior of the sprung portion. The sprung state amount of the present embodiment includes a speed of displacement fluctuation in a front and back direction, left and right direction, and up and down direction of a gravity center position of the sprung portion, and a pitch angular speed, a roll angular speed, and a yaw angular speed of the sprung portion. The displacement fluctuation of the gravity center position of the sprung portion (hereinafter simply referred to as “gravity center position”) is a shift amount of an actual gravity center position with respect to a gravity center position determined from the vehicle speed of the vehicle100of a certain time.

For example, if the vehicle100bounded in the up and down direction due to the bumps of the road surface during the traveling of the vehicle100, the displacement fluctuation in the up and down direction of the gravity center position occurs. When the brake operation or the drive operation is carried out, the displacement fluctuation of the gravity center position in the front and back direction of the vehicle and the fluctuation of the pitch angle occur. Furthermore, when the steering operation is carried out, the displacement fluctuation of the gravity center position in the left and right direction, and the fluctuation in the yaw angle, the roll angle, and the like occur.

The first state amount estimating unit21estimates the sprung state amount caused by the operation input based on the brake operation amount detected by the brake operation amount detection unit5, the drive operation amount detected by the drive operation amount detection unit6, and the steering operation amount detected by the steering operation amount detection unit7. The first state amount estimating unit21includes an estimating unit21abased on the drive operation, an estimating unit21bbased on the brake operation, and an estimating unit21cbased on the steering operation.

The estimating unit21abased on the drive operation estimates the sprung state amount generated by the drive operation based on a drive operation amount a acquired from the drive operation amount detection unit6. The estimating unit21bbased on the brake operation estimates the sprung state amount generated by the brake operation based on a brake operation amount b acquired from the brake operation amount detection unit5. The estimating unit21cbased on the steering operation estimates the sprung state amount generated by the steering operation based on a steering operation amount δ acquired from the steering operation amount detection unit7. The sprung state amounts estimated by each of the estimating units21a,21b,21care added by an adding unit21d. A value output from the adding unit21dis a “sprung state amount caused by the operation input” in which the sprung state amount by the drive operation, the sprung state amount by the brake operation, and the sprung state amount by the steering operation are added. The sprung state amount caused by the operation input is input from the adding unit21dto the first fluctuation estimating unit22.

First Fluctuation Estimating Unit

The first fluctuation estimating unit22estimates the wheel speed fluctuation amount caused by the operation input based on the sprung state amount caused by the operation input. The change in the state amount occurs at the sprung portion of the vehicle100by each operation input of drive, brake, and steering. The first fluctuation estimating unit22estimates the wheel speed fluctuation amount of each wheel2generated by the sprung behavior.

The ECU1includes a wheel speed fluctuation estimating unit27by a brake/drive force. The wheel speed fluctuation estimating unit27by the brake/drive force includes an estimating unit27abased on the drive force and an estimating unit27bbased on the brake force. The estimating unit27abased on the drive force estimates the wheel speed fluctuation amount of each wheel2by the drive force based on the drive operation amount a. The estimating unit27bbased on the brake force estimates the wheel speed fluctuation amount of each wheel2by the brake force based on the brake operation amount b. The wheel speed fluctuation amount estimated by the estimating unit27abased on the drive force and the wheel speed fluctuation amount estimated by the estimating unit27bbased on the brake force are added by an adding unit27c. A value output from the adding unit27cis a wheel speed fluctuation amount by the drive·brake force (hereinafter referred to as “wheel speed fluctuation amount by the brake/drive force”) in which the wheel speed fluctuation amount by the drive force and the wheel speed fluctuation amount by the brake force are combined. The wheel speed fluctuation amount by the brake/drive force is input from the adding unit27cto the second fluctuation estimating unit23.

Second Fluctuation Estimating Unit

The second fluctuation estimating unit23estimates the actual wheel speed fluctuation amount from which the wheel speed fluctuation amount by the brake/drive force is excluded based on the wheel speed detected by the wheel speed detection unit4. In the present specification, the “actual wheel speed fluctuation amount” is obtained by excluding the wheel speed fluctuation amount generated by the brake/drive force, in other words, the wheel speed fluctuation amount by the change in the vehicle speed from the wheel speed fluctuation amount of the detected wheel speed. The actual wheel speed fluctuation amount includes a wheel speed fluctuation amount caused by the road surface input which is input to the wheel2from the bumps, and the like of the road surface, and a wheel speed fluctuation amount (wheel speed fluctuation amount caused by the operation input) by the change in the sprung state that occurs by the operation input.

Third Fluctuation Estimating Unit

The third fluctuation estimating unit24estimates the wheel speed fluctuation amount caused by the road surface input by removing the wheel speed fluctuation amount caused by the operation input from the actual wheel speed fluctuation amount. The third fluctuation estimating unit24subtracts the value output by the first fluctuation estimating unit22from the value output by the second fluctuation estimating unit23. That is, the third fluctuation estimating unit24removes the wheel speed fluctuation amount caused by the operation input from the actual wheel speed fluctuation amount for each wheel2. The output of the third fluctuation estimating unit24is input to the second state amount estimating unit25.

Second State Amount Estimating Unit

The second state amount estimating unit25estimates at least one of the sprung state amount and the unsprung state amount caused by the road surface input based on the wheel speed fluctuation amount caused by the road surface input. The second state amount estimating unit25includes a road surface input estimating unit25a, a sprung state amount estimating unit25b,and a relative speed estimating unit25c. The road surface input estimating unit25aestimates the road surface input from the wheel speed fluctuation amount caused by the road surface input.

The sprung state amount estimating unit25bestimates the sprung state amount caused by the road surface input based on the road surface input estimated by the road surface input estimating unit25a. The relative speed estimating unit25cestimates the relative speed of the sprung portion and the unsprung portion based on the road surface input estimated by the road surface input estimating unit25a.

Third State Amount Estimating Unit

The third state amount estimating unit26estimates a total sprung state amount, which is the sprung state amount in which the estimated value of the sprung state caused by the operation input and the estimated value of the sprung state amount caused by the road surface input are added. The third state amount estimating unit26adds the estimated value of the sprung state amount caused by the road surface input which is output from the sprung state amount estimating unit25b, and the estimated value of the sprung state amount caused by the operation input which is output from the adding unit21d. The total sprung state amount output from the third state amount estimating unit26is the estimated value of the actual sprung state amount of the vehicle100. The ECU1of the present embodiment controls the suspension device10based on the estimated total sprung state amount and the relative speed.

A theoretical formula related to the estimation of the vehicle state amount by the vehicle state estimating device101of the present embodiment will now be described in detail. First, a tire rotation speed fluctuation amount ω can be calculated with the following [Formula 1]. The tire rotation speed fluctuation amount ω is a fluctuation amount of the rotation speed of the wheel2. The tire rotation speed fluctuation amount ω is the fluctuation amount of a rotation speed with respect to the rotation speed of the wheel2corresponding to the current vehicle speed, and is, for example, the fluctuation amount generated by the road surface input and the behavior of the sprung portion. In other words, the tire rotation speed fluctuation amount ω is the fluctuating portion (dynamic fluctuating portion) with respect to the steadily moving portion. As will be described below with reference toFIG. 3, the tire rotation speed fluctuation amount ω can be expressed with the [Formula 1] by a radius r of the wheel2and a front-back displacement fluctuation amount XAof the unsprung portion. The dot (•) symbol above the character indicates a differential value.
ω={dot over (X)}A/r=[{dot over (X)}B+({dot over (X)}A−{dot over (X)}B)]/rFormula 1

The position of the wheel2indicated with a broken line inFIG. 3is the wheel position of when the wheel2steadily moves, and is, for example, the wheel position at a certain predetermined time determined according to the vehicle speed. The position of the wheel2indicated with a solid line indicates the actual wheel position at the predetermined time. The fluctuation of the position in the front and back direction of the vehicle occurs between the wheel position indicated with the broken line and the wheel position indicated with the solid line by the road surface input and the operation input. The fluctuation of the wheel position in the front and back direction of the vehicle corresponds to the front-back displacement fluctuation amount XAof the unsprung portion. The fluctuation amount β of the rotation angle of the wheel2corresponding to the front-back displacement fluctuation amount XAof the unsprung portion can be approximated with XA/r, as illustrated inFIG. 3. The tire rotation speed fluctuation amount ω is a value obtained by differentiating the fluctuation amount β of the rotation angle, and thus can be approximately obtained as in the [Formula 1].

A first term in the parentheses on the right side of the [Formula 1] will now be described. The first term is a differential value of a front-back displacement fluctuation amount XBof the sprung portion at an axle position TC (seeFIG. 4). The axle position TC is a middle point in the width direction of the wheel2on the center axis line of each wheel2. The front-back displacement fluctuation amount XBof the sprung portion at the axle position TC can be expressed as a sum of a front-back displacement fluctuation amount XBGof the sprung portion (gravity center position PG) illustrated in FIG.4, a fluctuation amount based on a sprung pitch angle θBGillustrated inFIG. 5, and a fluctuation amount based on a sprung yaw angle ΨBGillustrated inFIG. 6.

As illustrated inFIG. 4, when the sprung portion position fluctuates in the front and back direction of the vehicle, the front-back displacement fluctuation amount XBof the sprung portion viewed at the axle position TC includes a component XBaby the position fluctuation in the front and back direction of the sprung portion. The component XBaby the position fluctuation in the front and back direction is expressed as the front-back displacement fluctuation amount XBGof the sprung portion at the gravity center position PG, as expressed with equation (1) below.
XBa=XBG(1)

When pitching occurs in the vehicle100as illustrated inFIG. 5, the front-back displacement fluctuation amount XBof the sprung portion viewed at the axle position TC contains a component XBbby the pitching. The component XBbby the pitching is expressed with the following equation (2) based on the sprung pitch angle θBG. Here, H is a distance in a height direction between the axle position TC and the gravity center position PG.
XBb=−θBG×H(2)

When a behavior in a yaw direction (rotation about a vertical axis) occurs in the vehicle100as illustrated inFIG. 6, the front-back displacement fluctuation amount XBof the sprung portion viewed at the axle position TC contains a component XBcby the behavior in the yaw direction. The component XBcby the behavior in the yaw direction is expressed with the following equation (3) based on the sprung yaw angle ΨBG. Here, W is a distance between the gravity center position PG and the axle position TC in the vehicle width direction.
XBc=ΨBG×W(3)

The sum of the above three components XBa, XBb, XBcis the front-back displacement fluctuation amount XBof the sprung portion viewed at the axle position TC. That is, equation (4) is derived.
XB=−θBG×H+XBG+ΨBG×W(4)

Next, a second term in the parentheses on the right side of the [Formula 1] will be described. The second term is a term related to the relative displacement of the sprung portion and the unsprung portion, that is, the up-down stroke of the suspension device10. The wheel2and the body3, which is the sprung portion, relatively displace in the up and down direction, as illustrated inFIG. 7, by the stroke of the suspension device10. If the suspension device10is inclined in the front and back direction of the vehicle with respect to the up and down direction, the wheel2and the body3relatively displace also in the front and back direction of the vehicle. A difference (XA−XB) which is a difference of the front-back displacement fluctuation amount between the sprung portion and the unsprung portion can be expressed with the following equation (5).
XA−XB=αX(ZA−ZB)   (5)

Here, ZAis the up-down displacement fluctuation amount of the unsprung portion, ZBis the up-down displacement fluctuation amount of the sprung portion at the axle position TC in the front and back direction of the vehicle, and αXis the relative displacement amount in the front and back direction of the vehicle between the sprung portion and the unsprung portion per unit stroke amount of the suspension device10.

The following [Formula 2] is derived from the [Formula 1] and the equations (1) to (5).
ω=[(−{dot over (θ)}BGH+{dot over (X)}BG+{dot over (ψ)}BGW)+αX(ŻZ−ŻB)]/rFormula 2

An unsprung pitch angle θAwill now be described with reference toFIG. 8andFIG. 9. The unsprung pitch angle θAis the pitch angle of the unsprung portion, and indicates an inclination angle in the front and back direction of the vehicle of the unsprung portion with respect to the road surface. In the vehicle100, the sprung pitch angle θBGand the unsprung pitch angle θAmay differ by the extension and contraction of the suspension device10. In other words, the unsprung pitch angle θAcontains a component ΘAacorresponding to the sprung pitch angle θBGand a component θAbby the extension and contraction of the suspension device10.

As illustrated inFIG. 8, the component θAacorresponding to the sprung pitch angle θBGis equal to the sprung pitch angle θBG. That is, the component θAacorresponding to the sprung pitch angle θBGis expressed with the following equation (6).
θAa=θBG(6)

FIG. 9illustrates a state in which the suspension devices10FR,10FL of the front wheels2FR,2FL of the vehicle100are contracted by the road surface input, and the like, and the suspension devices10RR,10RL of the rear wheels2RR,2RL are not extended or contracted. The component θAbby the extension and contraction of the suspension device10is expressed with the following equation (7), as illustrated inFIG. 9.
θAb=−αθ(ZA−ZB)   (7)

Here, αθis the unsprung pitch angle per unit stroke amount of the suspension device10.

According to the equation (6) and the equation (7), the angular speed fluctuation of the unsprung pitch angle θA(differential value of the unsprung pitch angle θA) is expressed with the following [Formula 3].
{dot over (θ)}A={dot over (θ)}BG+αθ(ŻA−ŻB)   Formula 3

A wheel speed fluctuation amount Δω will now be described. The wheel speed fluctuation amount Δω is the fluctuation amount of the wheel speed detected by the wheel speed detection unit4. The wheel speed fluctuation amount Δω is expressed with the following [Formula 4]. The wheel speed detected by the wheel speed detection unit4not only includes the rotation speed component by the relative movement in the front and back direction with respect to the road surface, but also includes the rotation speed component by the change of the unsprung pitch angle θA. In other words, the wheel speed fluctuation amount Δω is the difference of the tire rotation speed fluctuation amount ω and the angular speed fluctuation of the unsprung pitch angle θAas expressed in the [Formula 4]. The ECU1includes a wheel speed fluctuation amount estimating unit for calculating the wheel speed fluctuation amount Δω by excluding the wheel speed corresponding to the current vehicle speed from the wheel speed detected by the wheel speed detection unit4.
Δω=ω−{dot over (θ)}AFormula 4

[Formula 5] is derived by substituting the [Formula 2] and the [Formula 3] to the [Formula 4].
Δω=[(−{dot over (θ)}BGH+{dot over (X)}BG+{dot over (ψ)}BGW)+αX(ŻA−ŻB)]/r−[{dot over (θ)}BG+αθ(ŻA−Ż5)]  Formula 5

The up-down displacement fluctuation amount will now be described. The up-down displacement fluctuation amount ZBof the sprung portion at the axle position TC can be expressed with equation (8). The first term on the right side of the equation (8) is the up-down displacement fluctuation amount of the gravity center position PG of the sprung portion. The second term on the right side of the equation (8) is the up-down displacement fluctuation amount (approximate value) by the pitching of the sprung portion. The third term on the right side of the equation (8) is the up-down displacement fluctuation amount (approximate value) by the roll of the sprung portion.
ZB=ZBG±L×θBG±W×φBG(8)

Here, L is the distance between the axle position TC and the gravity center position PG in the front and back direction of the vehicle (seeFIG. 4), and φBGis the sprung roll angle. For the distance L between the axle position TC and the gravity center position PG, the distance LFin the case of the front wheel2FR,2FL and the distance LRin the case of the rear wheel2RR,2RL may take different values.

Describing the equation (8) with regard to the front right wheel2FR for, the up-down displacement fluctuation amount ZB1of the sprung portion at the axle position TC of the front right wheel2FR can be obtained by adding or subtracting the up-down displacement fluctuation amount by the pitching of the sprung portion and the up-down displacement fluctuation amount by the roll of the sprung portion with respect to the up-down displacement fluctuation amount ZBGof the gravity center position PG. For example, when the sprung portion is pitched such that the front wheel side sinks in, the up-down displacement fluctuation amount (L×θBG) by the pitching of the sprung portion is subtracted from the up-down displacement fluctuation amount ZBGof the gravity center position PG. When the sprung portion is rolled such that the right side of the vehicle sinks in, the up-down displacement fluctuation amount (W×φBG) by the roll of the sprung portion is subtracted.

On the contrary, when the sprung portion is pitched such that the front wheel side lifts up, the up-down displacement fluctuation amount (L×θBG) by the pitching of the sprung portion is added to the up-down displacement fluctuation amount ZBGof the gravity center position PG. When the sprung portion is rolled such that the right side of the vehicle lifts up, the up-down displacement fluctuation amount (W×φBG) by the roll of the sprung portion is added. With respect to the other wheels2FL,2RR,2RL as well, the up-down displacement fluctuation amount ZBof the sprung portion at the axle position is similarly calculated.

According to the equation (8), the up-down displacement fluctuating speed of the sprung portion at the axle position TC is expressed with [Formula 6].
ŻB=ŻBG∓L{dot over (θ)}BG∓WφBGFormula 6

Expanding the [Formula 1] to [Formula 6], and notating the wheel speed fluctuation amounts for the four wheels in a matrix form, the following [Formula 7] is obtained. The matrix [D] is indicated in the following [Formula 8], the matrix [G] is indicated in the following [Formula 9], the matrix [E] is indicated in the following [Formula 10], the matrix [F] is indicated in the following [Formula 11], and the matrix [C] is indicated in the following [Formula 12].

Here, Δω1is the wheel speed fluctuation amount of the front right wheel2FR, Δω2is the wheel speed fluctuation amount of the front left wheel2FL, Δω3is the wheel speed fluctuation amount of the rear right wheel2RR, and Δ4is the wheel speed fluctuation amount of the rear left wheel2RL. In other words, the suffix1of each variable indicates a value related to the front right wheel2FR, the suffix 2 indicates a value related to the front left wheel2FL, the suffix 3 indicates a value related to the rear right wheel2RR, and the suffix 4 indicates a value related to the rear left wheel2RL.

The other variables are as follows.

XB1, XB2, XB3, XB4: front-back displacement fluctuation amount of the sprung portion at the axle position TC of each wheel2of front right, front left, rear right, rear left.

ZB1, ZB2, ZB3, ZB4: up-down displacement fluctuation amount of the sprung portion at the axle position TC of each wheel2of front right, front left, rear right, rear left.

YBG: left-right displacement fluctuation amount of the gravity center position PG of the sprung portion.

rF: radius of the front wheel2FR,2FL.

rR: radius of the rear wheel2RR,2RL.

LF: distance in the front and back direction of the vehicle between the axle position TC of the front wheel2FR,2FL and the gravity center position PG.

LR: distance in the front and back direction of the vehicle between the axle position TC of the rear wheel2RR,2RL and the gravity center position PG.

WF: distance in the left and right direction (vehicle width direction) between the axle position TC of the front wheel2FR,2FL and the gravity center position PG.

WR: distance in the left and right direction (vehicle width direction) between the axle position TC of the rear wheel2RR,2RL and the gravity center position PG.

HF: distance in the up and down direction between the axle position TC of the front wheel2FR,2FL and the gravity center position PG.

HR: distance in the up and down direction between the axle position TC of the rear wheel2RR,2RL and the gravity center position PG.

αXF: relative displacement amount in the front and back direction of the vehicle of the sprung portion and the unsprung portion at each front wheel2FR,2FL per unit stroke amount of the suspension device10FR,10FL.

αXR: relative displacement amount in the front and back direction of the vehicle of the sprung portion and the unsprung portion at each rear wheel2RR,2RL per unit stroke amount of the suspension device10RR,10RL.

αθF: unsprung pitch angle at each front wheel2FR,2FL per unit stroke amount of the suspension device10FR,10FL.

α74 R: unsprung pitch angle at each rear wheel2RR,2RL per unit stroke amount of the suspension device10RR,10RL.

The sprung behavior of the vehicle100can be expressed with the following [Formula 13]. In the [Formula 13], the vehicle100is assumed to be left and right symmetric.

Here, Z1to Z4represent the road surface input. The suffix of the road surface input Z is different from the suffixes of other variables, and is defined as below.

Z1: left-right in-phase input with respect to the front wheel2FR,2FL

Z2: left-right reverse-phase input with respect to the front wheel2FR,2FL

Z3: left-right in-phase input with respect to the rear wheel2RR,2RL

Z4: left-right reverse-phase input with respect to the rear wheel2RR,2RL

That is, the front wheel in-phase input Z1is the road surface input that causes the in-phase up-down displacement fluctuation with respect to the front right wheel2FR and the front left wheel2FL. For example, the road surface input with which the front right wheel2FR and the front left wheel2FL each ride on the projecting portion of the road surface at the same time is the front wheel in-phase input Z1. Furthermore, the input with which the front right wheel2FR and the front left wheel2FL each sink into the recessed portion of the road surface at the same time is the front wheel in-phase input Z1. The rear wheel in-phase input Z3is the road surface input that causes the in-phase up-down displacement fluctuation with respect to the rear right wheel2RR and the rear left wheel2RL.

The front wheel reverse-phase input Z2is the road surface input that causes the up-down displacement fluctuation of reverse phase with respect to the front right wheel2FR and the front left wheel2FL. For example, the road surface input with which the front right wheel2FR rides on the projecting portion of the road surface, and at the same time, the front left wheel2FL sinks into the recessed portion of the road surface is the front wheel reverse-phase input Z2. The rear wheel reverse-phase input Z4is the road surface input that causes the up-down displacement fluctuation of reverse-phase with respect to the rear right wheel2RR and the rear left wheel2RL.

Other variables are as follows.

Transfer function related to road surface input

∂ZBG/∂Z1: transfer function of the up-down displacement of the gravity center position PG with respect to the road surface input Zi(i=1, 2, 3, 4).

∂θBG/∂Zi: transfer function of the sprung pitch angle with respect to the road surface input Zi.

∂YBG/∂Zi: transfer function of the left-right displacement of the sprung gravity center position with respect to the road surface input Zi.

∂φBG/∂ZBi: transfer function of the sprung roll angle with respect to the road surface input Zi.

∂ΨBG/∂Zi: transfer function of the sprung yaw angle with respect to the road surface input Zi.

∂ZAF/∂Zi: transfer function of the up-down displacement of the unsprung portion of the front wheel2FR,2FL with respect to the road surface input Zi.

∂ZAR/∂Zi: transfer function of the up-down displacement of the unsprung portion of the rear wheel2RR,2RL with respect to the road surface input Z.

Transfer Function Related to Brake/Drive Input

∂ZBG/∂a: transfer function of the up-down displacement of the sprung gravity center position PG with respect to the accelerator input.

∂ZBG/∂b: transfer function of the up-down displacement of the sprung gravity center position PG with respect to the brake input.

∂ZBG/∂a: transfer function of the sprung pitch angle with respect to the accelerator input.

∂ZBG/∂b: transfer function of the sprung pitch angle with respect to the brake input.

∂XBG/∂a: transfer function of the front-back displacement of the sprung gravity center position PG with respect to the accelerator input.

∂XBG/∂b: transfer function of the front-back displacement of the sprung gravity center position PG with respect to the brake input.

Transfer Function Related to Steering Input

∂YBG/∂δ: transfer function of the left-right displacement of the sprung gravity center position PG with respect to the steering input.

∂φBG/∂δ: transfer function of the sprung roll angle with respect to the steering input.

∂ΨBG/∂δ: transfer function of the sprung yaw angle with respect to the steering input.

The first term on the right side of the [Formula 13] indicates the sprung behavior by the road surface input, and the second term on the right side indicates the sprung behavior by the operation input. The matrix [A] of the first term on the right side is illustrated in [Formula 14] below, and the matrix [P] of the second term on the right side is illustrated in [Formula 15].

For the in-phase road surface inputs Z1, Z3, it is assumed that the up-down displacement and the pitching of the gravity center position PG occur, but the behavior in the lateral direction, the roll direction, and the yaw direction does not occur. Thus, in the matrix [A], an element that indicates the relationship between the in-phase road surface inputs Z1, Z3and the speed in the lateral direction, the roll direction, and the yaw direction is set to zero. Furthermore, for the reverse-phase road surface inputs Z2, Z4, it is assumed that the behavior in the lateral direction, the roll direction, and the yaw direction occurs, but the up-down displacement and the pitching of the gravity center position PG do not occur. Thus, in the matrix [A], an element that indicates the relationship between the reverse-phase road surface inputs Z2, Z4and the up-down fluctuating speed and the pitch angular speed of the gravity center position PG is set to zero.

In the accelerator operation and the brake operation, it is assumed that the behavior in the lateral direction, the roll direction, and the yaw direction does not occur. Thus, in the matrix [P], an element that indicates the relationship between the drive operation amount a and the brake operation amount b, and the speed in the lateral direction, the roll direction, and the yaw direction is set to zero. It is assumed that the displacement of the gravity center position in the up and down direction and the front and back direction and the pitching do not occur by the steering operation. Thus, in the matrix [P], an element that indicates the relationship between the steering operation amount δ and the up-down fluctuating speed, the front-back fluctuating speed, and the pitch angular speed of the gravity center position PG is set to zero.

The unsprung behavior of the vehicle100can be expressed with the following [Formula 16]. In the [Formula 16], the vehicle100is assumed to be left and right symmetrical. The right side of the [Formula 16] indicates the unsprung behavior by the road surface input. In the present embodiment, the unsprung behavior by the operation input is assumed to not occur. The matrix [B] on the right side of the [Formula 16] is illustrated in [Formula 17] below.

The [Formula 13] and the [Formula 16] are substituted to the [Formula 7] to obtain [Formula 18]. The [Formula 18] is separated to the element caused by the road surface input and the element caused by the operation input, whereby [Formula 19] is obtained.

The first term on the right side of the [Formula 19] is a term indicating the wheel speed fluctuation amount Δω by the behavior of the sprung portion and the unsprung portion caused by the road surface input Z. The second term on the right side of the [Formula 19] is a term indicating the wheel speed fluctuation amount Δω by the sprung behavior caused by the operation input. When the wheel speed fluctuation amount Δω by the sprung behavior caused by the operation input is removed from the [Formula 19], the wheel speed fluctuation amount Δω′ caused by the road surface input remains, as indicated in [Formula 20].

Here, Δω1′ indicates the wheel speed fluctuation amount of the front right wheel2FR caused by the road surface input. Similarly, Δω2′ indicates the wheel speed fluctuation amount caused by the road surface input of the front left wheel2FL, Δω3′ indicates that of the rear right wheel2RR, and Δω4′ indicates that of the rear left wheel2RL.

[Formula 21] is obtained from the [Formula 20]. Therefore, if the wheel speed fluctuation amount Δω′ caused by the road surface input of each wheel2can be calculated, the road surface input Zican be estimated by the [Formula 21].

The sprung speed can be estimated by [Formula 22] based on the estimated road surface input Zi. The relative speed of the unsprung portion with respect to the sprung portion can be estimated by [Formula 23] based on the estimated road surface input Zi.

The correspondence relationship, and the like between the estimating method of the vehicle state by the vehicle state estimating device101according to the present embodiment and the theoretical formula will now be described. The estimating unit21abased on the drive operation of the first state amount estimating unit21corresponds to the first column of the matrix [P]. The estimating unit21bbased on the brake operation corresponds to the second column of the matrix [P], and the estimating unit21cbased on the steering operation corresponds to the third column. In the present embodiment, the value of each element of the matrix [P] is stored in the vehicle state estimating device101in advance as a specification value of the vehicle100.

The first state amount estimating unit21has a function of carrying out the estimation of the second term on the right side of the [Formula 13]. The first state amount estimating unit21estimates the up-down displacement ZBG, the front-back displacement XBG, and the pitch angle θBGof the sprung gravity center position PG based on the drive operation amount a and the brake operation amount b. The first state amount estimating unit21estimates the left-right displacement YBG, the roll angle φBGand the yaw angle ΨBGof the sprung gravity center position PG based on the steering operation amount δ.

The estimating unit21abased on the drive operation calculates the speed component caused by the drive operation amount a for each of the six directions of the sprung speed, that is, the up-down direction (ZBG), the sprung pitch angle direction (θBG), the vehicle front-back direction (XBG), the vehicle left-right direction (YBG) the sprung roll angle direction (φBG) and the sprung yaw angle direction (ΨBG). As apparent from the elements of the matrix [P], the estimating unit21abased on the drive operation of the present embodiment estimates the speed component in substantially three directions of the up-down direction (ZBG), the sprung pitch angle direction (θBG) and the vehicle front-back direction (XBG).

The estimating unit21bbased on the brake operation calculates the speed component caused by the brake operation amount b for the six directions of the sprung speed. The estimating unit21bbased on the brake operation of the present embodiment estimates the speed component in substantially three directions of the up-down direction (ZBG), the sprung pitch angle direction (θBG) and the vehicle front-back direction (XBG). The estimating unit21cbased on the steering operation calculates the speed component caused by the steering operation amount δ for the six directions of the sprung speed. The estimating unit21cbased on the steering operation of the present embodiment estimates the speed component in substantially three directions of the vehicle left-right direction (YBG), the sprung roll angle direction (φBG) and the sprung yaw angle direction (ΨBG). The adding unit21dadds the values of the speed components calculated by each estimating unit21a,21b, and21cfor the six directions of the sprung speed.

The first fluctuation estimating unit22corresponds to [(D−G)−(E−F)C] of the second term on the right side of the [Formula 19]. That is, the first fluctuation estimating unit22of the present embodiment estimates a component caused by the operation input of the wheel speed fluctuation amount Δω based on a correspondence relationship (transfer function) between the sprung behavior by the operation input and the wheel speed fluctuation amount Δω of each wheel2. In other words, the first fluctuation estimating unit22estimates the wheel speed fluctuation amount caused by the operation input based on the up-down displacement, the front-back displacement, and the pitch angle of the sprung gravity center estimated based on the brake operation amount b and the drive operation amount a, and the left-right displacement, the roll angle, and the yaw angle of the sprung gravity center estimated based on the steering operation amount δ. The transfer function used by the first fluctuation estimating unit22is, for example, stored in advance in the vehicle state estimating device101.

The estimating unit27abased on the drive force calculates the wheel speed fluctuation amounts Δω1to Δω4of the four wheels based on the correspondence relationship (transfer function) between the wheel speed fluctuation amount Δω of each wheel2and the drive operation amount a, for example. The estimating unit27bbased on the brake force calculates the wheel speed fluctuation amounts Δω1to Δω4of the four wheels based on the correspondence relationship (transfer function) between the wheel speed fluctuation amount Δω of each wheel2and the brake operation amount b, for example. The transfer function used by the wheel speed fluctuation estimating unit27by the brake/drive force is, for example, stored in advance in the vehicle state estimating device101. The adding unit27cadds the wheel speed fluctuation amount Δω calculated by the estimating unit27abased on the drive force and the wheel speed fluctuation amount Δω calculated by the estimating unit27bbased on the brake force for each of the wheels2FR,2FL,2RR,2RL.

The wheel speed fluctuation amount Δω calculated based on the detected wheel speed of each wheel2is input to the second fluctuation estimating unit23. The wheel speed fluctuation amounts Δω1, Δω2, Δω3, Δω4are fluctuating components of the wheel speed detected by the wheel speed detection units4FR,4FL,4RR,4RL, respectively. For example, the fluctuation amount from the rotation speed corresponding to the current vehicle speed in the rotation speed detected by the wheel speed detection unit4is input to the second fluctuation estimating unit23as the wheel speed fluctuation amount Δω.

The second fluctuation estimating unit23calculates the actual wheel speed fluctuation amount by excluding the wheel speed fluctuation amount by the brake/drive force estimated by the wheel speed fluctuation estimating unit27by the brake/drive force from the wheel speed fluctuation amount Δω of each wheel2. The second fluctuation estimating unit23outputs the estimated value of the actual wheel speed fluctuation amount to the third fluctuation estimating unit24.

The third fluctuation estimating unit24estimates the wheel speed fluctuation amount Δω′ caused by the road surface input by removing the wheel speed fluctuation amount caused by the operation input acquired by the first fluctuation estimating unit22from the actual wheel speed fluctuation amount acquired by the second fluctuation estimating unit23.

The road surface input estimating unit25acalculates the road surface input Zibased on the wheel speed fluctuation amount Δω′ caused by the road surface input acquired from the third fluctuation estimating unit24. The road surface input estimating unit25aestimates, for example, the road surface input Zibased on the correspondence relationship (transfer function) between the wheel speed fluctuation amount Δω′ caused by the road surface input and the road surface input Zi. The road surface input estimating unit25aof the present embodiment, for example, estimates the road surface input Zibased on the [Formula 21]. The transfer function used by the road surface input estimating unit25ais, for example, stored in advance in the vehicle state estimating device101.

The sprung state amount estimating unit25bestimates the sprung speed based on the road surface input Ziacquired from the road surface input estimating unit25a. The sprung state amount estimating unit25bestimates, for example, the sprung speed based on the correspondence relationship (transfer function) between the sprung speed in six directions and the road surface input Zi. The sprung state amount estimating unit25bof the present embodiment, for example, estimates the sprung speed based on the [Formula 22]. The transfer function used by the sprung state amount estimating unit25bis, for example, stored in advance in the vehicle state estimating device101.

The relative speed estimating unit25cestimates the relative speed of the sprung portion and the unsprung portion based on the road surface input Ziacquired from the road surface input estimating unit25a. The relative speed estimating unit25cestimates, for example, the relative speed based on the correspondence relationship (transfer function) between the relative speed in the up and down direction of the sprung portion and the unsprung portion, and the road surface input Zi. The relative speed estimating unit25cof the present embodiment calculates, for example, the relative speed in the up and down direction of the sprung portion and the unsprung portion for each of the four wheels based on the [Formula 23]. The transfer function used by the relative speed estimating unit25cis, for example, stored in advance in the vehicle state estimating device101.

The third state amount estimating unit26adds the sprung speed estimated by the sprung state amount estimating unit25band the sprung speed calculated by the adding unit21dto estimate the total sprung speed. The sprung speed estimated by the sprung state amount estimating unit25bis an estimated value of the sprung state amount caused by the road surface input, and the sprung speed calculated by the adding unit21dis an estimated value of the sprung state amount caused by the operation input. Therefore, the total sprung speed indicates the total sprung state amount in which the sprung state amount caused by the operation input and the sprung state amount caused by the road surface input are added.

The estimation result of the vehicle state estimating device101according to the present embodiment will be described with reference toFIG. 10. InFIG. 10, the horizontal axis indicates time [sec], and the vertical axis indicates the relative speed [mm/s] in the up and down direction of the unsprung portion and the sprung portion. InFIG. 10, the broken line indicates the actual measurement value of the relative speed of the unsprung portion and the sprung portion, and the solid line indicates the estimated value of the relative speed of the unsprung portion and the sprung portion estimated by the vehicle state estimating device101according to the embodiment.

As apparent fromFIG. 10, the estimated value (solid line) of the relative speed is a value close to the actual measurement value (broken line). The estimated value of the relative speed accurately estimates the timing at which the plus/minus of the value of the relative speed switches. When controlling the suspension device10, it is desirable the plus/minus of the relative speed is estimated with satisfactory accuracy. If the plus/minus of the relative speed is not accurately estimated, the attenuating property corresponding to the contracting operation may be set although the suspension device10is extending, or on the other hand, the attenuating property corresponding to the extending operation may be set although the suspension device10is contracting. Thus, unless the actual operation of the suspension device10and the attenuating property match, the comfortableness in riding and the vehicle behavior may be affected and the drivability may become lower.

According to the vehicle state estimating device101of the present embodiment, the plus/minus, or the absolute value of the relative speed of the unsprung portion and the sprung portion can be accurately estimated. This is because the sprung speed, and the relative speed of the unsprung portion and the sprung portion are estimated based on the wheel speed fluctuation amount Δω′ caused by the road surface input Ziwhich is obtained by once removing the wheel speed fluctuation amount Δω caused by the operation input, for example. The behavior of the unsprung portion is mainly caused by the road surface input. The behavior of the sprung portion, on the other hand, contains a component caused by the operation input and a component caused by the road surface input. The vehicle state estimating device101according to the present embodiment can accurately estimate the sprung speed and the relative speed of the sprung portion and the unsprung portion by estimating the state amount based on the wheel speed fluctuation amount Δω′ caused by the road surface input Ziobtained by removing the wheel speed fluctuation amount caused by the operation input.

The vehicle state estimating device101according to the present embodiment has an advantage in that the estimation accuracy is satisfactory since the estimated value and the detection value used for the estimation are both speed. For example, instead of the estimating method of the present embodiment, consideration can be made in estimating the sprung speed and the relative speed of the unsprung portion and the sprung portion based on the stroke amount (displacement) of the suspension device10. In this case, the detected stroke amount needs to be differentiated to be converted to speed. The differentiation leads to lowering in accuracy since the phase is advanced.

On the other hand, the vehicle state estimating device101of the present embodiment estimates the sprung speed, and the like based on the detected speed, whereby the problem of the lowering in accuracy by differentiation can be avoided. Furthermore, the detection result of the existing wheel speed detection unit4that detects the vehicle speed, and the like can be used to estimate the sprung speed, and the like, and thus increase in the device to be installed in the vehicle100can be suppressed. Moreover, the vehicle state can be estimated using the existing wheel speed detection unit4.

Calculation Method of the Sprung Speed One example of the result estimated by the vehicle state estimating device101of the present embodiment and the calculation method of the sprung speed based on the estimation result will be specifically described with reference toFIG. 11toFIG. 16.FIG. 11is a view illustrating frequency characteristics of a gain of a bounce speed with respect to the wheel speed fluctuation amount, andFIG. 12is a view illustrating frequency characteristics of a phase of the bounce speed having the phase of the road surface input as a reference. The bounce speed is, for example, a speed in the up and down direction of the gravity center position PG of the sprung portion.

In bothFIG. 11andFIG. 12, the horizontal axis indicates the frequency [Hz] of the road surface input. The vertical axis ofFIG. 11indicates the gain [(m/s)/(rad/s)] of the bounce speed with respect to the wheel speed fluctuation amount Δω of each wheel2. The vertical axis ofFIG. 12indicates the phase [deg] of the bounce speed having the phase of the road surface input to each wheel2as a reference. For example, describing a case in which the road surface input of 1 Hz is made, the value obtained by multiplying the gain of about 0.2 to the wheel speed fluctuation amount Δω becomes the magnitude of the bounce speed according toFIG. 11. Furthermore, when obtaining the phase of the bounce speed according toFIG. 12, it is apparent that the phase is a value in which the phase is advanced by about 20 [deg] with respect to the road surface input to the rear wheel.

With respect to all the wheels2, a product of the wheel speed fluctuation amount Δω and the gain is obtained, and such products are added for the four wheels for each phase to obtain the bounce speed of the body3. The vehicle state estimating device101can obtain the frequency characteristics of the gain with respect to the wheel speed fluctuation amount Δω and the frequency characteristics of the phase having the phase of the road surface input as the reference not only for the bounce speed but also for the front-back direction speed and the left-right direction speed of the gravity center position PG of the sprung portion. A product of the wheel speed fluctuation amount Δω and the gain is also obtained for the front-back direction speed and the left-right direction speed of the gravity center position PG of the sprung portion and such products are added for the four wheels to obtain the front-back direction speed and the left-right direction speed of the body3.

FIG. 13is a view illustrating frequency characteristics of a gain of the sprung pitch angular speed with respect to the wheel speed fluctuation amount, andFIG. 14is a view illustrating frequency characteristics of a phase of the sprung pitch angular speed having the phase of the road surface input as a reference. The horizontal axes ofFIG. 13andFIG. 14indicate the frequency of the road surface input. The vertical axis ofFIG. 13indicates the gain [(rad/s)/(rad/s)] of the sprung pitch angular speed with respect to the wheel speed fluctuation amount Δω of each wheel2. The vertical axis ofFIG. 14indicates the phase of the sprung pitch angular speed having the phase of the road surface input to each wheel2as a reference.

FIG. 15is a view illustrating frequency characteristics of the gain of the sprung roll angular speed with respect to the wheel speed fluctuation amount, andFIG. 16is a view illustrating frequency characteristics of the phase of the sprung roll angular speed having the phase of the road surface input as a reference. The horizontal axes ofFIG. 15andFIG. 16indicate the frequency of the road surface input. The vertical axis ofFIG. 15indicates the gain [(rad/s)/(rad/s)] of the sprung roll angular speed with respect to the wheel speed fluctuation amount Δω of each wheel2. The vertical axis ofFIG. 16indicates the phase of the sprung roll angular speed having the phase of the road surface input to each wheel2as a reference.

The vehicle state estimating device101can obtain the frequency characteristics of the gain with respect to the wheel speed fluctuation amount Δω and the frequency characteristics of the phase having the phase of the road surface input as the reference not only for the pitch angular speed and the roll angular speed but also for the yaw angular speed. With respect to such angular speeds as well, a product of the wheel speed fluctuation amount Δω and the gain is obtained for all the wheels2and such products are added for the four wheels to obtain the pitch angular speed, the roll angular speed, the yaw angular speed, and the like.

The sprung state amount estimating unit25baccording to the present embodiment estimates the sprung speed through the methods described with reference toFIG. 11toFIG. 16, for example.

Calculation Method of the Relative Speed

One example of the result estimated by the vehicle state estimating device101of the present embodiment and the calculation method of the relative speed of the sprung portion and the unsprung portion based on the estimation result will be specifically described with reference toFIG. 17toFIG. 24. The horizontal axes inFIG. 17toFIG. 24indicate the frequency of the road surface input.FIG. 17andFIG. 18relate to the relative speed of the sprung portion and the unsprung portion of the front right wheel2FR (hereinafter simply referred to as “front right relative speed”).FIG. 17is a view illustrating frequency characteristics of a gain of the front right relative speed with respect to the wheel speed fluctuation amount, andFIG. 18is a view illustrating frequency characteristics of a phase of the front right relative speed having the phase of the road surface input as a reference.

The vertical axis ofFIG. 17indicates the gain [(m/s)/(rad/s)] of the front right relative speed with respect to the wheel speed fluctuation amount Δω of each wheel2. The vertical axis ofFIG. 18indicates the phase of the front right relative speed having the phase of the road surface input to each wheel2as a reference. As apparent fromFIG. 17, the wheel speed fluctuation amounts Δω2′, Δω3′, Δω4′ caused by the road surface input of the other wheels2FL,2RR,2RL each influence the front right relative speed. In the low frequency region in which the frequency of the road surface input is lower than 1 [Hz], the influence of the wheel speed fluctuation amount Δω2′, Δω3′, Δω4′ of the other wheels2FL,2RR,2RL on the front right relative speed is larger than in the region of higher frequency.

With respect to all the wheels2, a product of the wheel speed fluctuation amount Δω and the gain is obtained, and such products are added for the four wheels to obtain the front right relative speed.

FIG. 19andFIG. 20relate to the relative speed of the sprung portion and the unsprung portion of the front left wheel2FL (hereinafter simply referred to as “front left relative speed”).FIG. 19is a view illustrating frequency characteristics of a gain of the front left relative speed with respect to the wheel speed fluctuation amount, andFIG. 20is a view illustrating frequency characteristics of a phase of the front left relative speed having the phase of the road surface input as a reference. The vertical axis ofFIG. 19indicates a gain of the front left relative speed with respect to the wheel speed fluctuation amount Δω of each wheel2. The vertical axis ofFIG. 20indicates the phase of the front left relative speed having the phase of the road surface input to each wheel2as a reference.

FIG. 21andFIG. 22relate to the relative speed of the sprung portion and the unsprung portion of the rear right wheel2RR (hereinafter simply referred to as “rear right relative speed”).FIG. 21is a view illustrating frequency characteristics of a gain of the rear right relative speed with respect to the wheel speed fluctuation amount, andFIG. 22is a view illustrating frequency characteristics of a phase of the rear right relative speed having the phase of the road surface input as a reference. The vertical axis ofFIG. 21indicates a gain of the rear right relative speed with respect to the wheel speed fluctuation amount Δω of each wheel2. The vertical axis ofFIG. 22indicates the phase of the rear right relative speed having the phase of the road surface input to each wheel2as a reference.

FIG. 23andFIG. 24relate to the relative speed of the sprung portion and the unsprung portion of the rear left wheel2RL (hereinafter simply referred to as “rear left relative speed”).FIG. 23is a view illustrating frequency characteristics of a gain of the rear left relative speed with respect to the wheel speed fluctuation amount, andFIG. 24is a view illustrating frequency characteristics of a phase of the rear left relative speed having the phase of the road surface input as a reference. The vertical axis ofFIG. 23indicates a gain of the rear left relative speed with respect to the wheel speed fluctuation amount Δω of each wheel2. The vertical axis ofFIG. 24indicates the phase of the rear left relative speed having the phase of the road surface input to each wheel2as a reference.

The front left relative speed, the rear right relative speed, and the rear left relative speed can be calculated, similarly to the front right relative speed. The relative speed estimating unit25cof the present embodiment estimates the relative speed of the sprung portion and the unsprung portion of each wheel2through the method described with reference toFIG. 17toFIG. 24, for example.

Suspension Control

The vehicle control device102according to the present embodiment controls the suspension device10of the vehicle100based on the estimated value of the sprung state amount and the estimated value of the unsprung state amount caused by the road surface input. Specifically, the ECU1serving as the control unit of the present embodiment controls the suspension device10based on the total sprung speed calculated from the estimated value of the sprung state amount caused by the road surface input, and the relative speed of the sprung portion and the unsprung portion. The estimated value of the relative speed of the sprung portion and the unsprung portion includes the estimated value of the sprung state amount and the estimated value of the unsprung state amount caused by the road surface input. Therefore, the ECU1controls the suspension device10based on both the estimated value of the sprung state amount and the estimated value of the unsprung state amount caused by the road surface input.FIG. 25is an explanatory view of the suspension control of the present embodiment.

InFIG. 25, the horizontal axis indicates the total sprung speed in the up and down direction of the sprung portion, and the vertical axis indicates the relative speed in the up and down direction of the sprung portion and the unsprung portion. In the horizontal axis, the right side of the origin indicates the speed at which the sprung portion moves upward, and the left side of the origin indicates the speed at which the sprung portion moves downward. The absolute value of the total sprung speed becomes larger as being away from the origin. In the vertical axis, the upper side of the origin indicates the relative speed in the direction in which the suspension device10contracts, and the lower side of the origin indicates the relative speed in the direction in which the suspension device10extends. The absolute value of the relative speed of the sprung portion and the unsprung portion becomes larger as being away from the origin.

The vehicle control device102adjusts the attenuating property of the suspension device10according to the combination of the total sprung speed and the relative speed of the sprung portion and the unsprung portion. In the present embodiment, when the sprung speed is the upward speed and the relative speed is in the direction in which the suspension device10contracts (first quadrant) and when the sprung speed is the downward speed and the relative speed is in the direction in which the suspension device10extends (third quadrant), the attenuating properties of the suspension device10are relatively soft properties. For example, when the sprung portion is moving upward and the sprung portion and the unsprung portion are relatively moving in the direction in which the front right suspension device10FR contracts in the front right wheel2FR, the vehicle control device102sets the attenuating properties of the front right suspension device10FR as the relatively soft properties.

When the sprung speed is the downward speed and the relative speed is in the direction in which the suspension device10contracts (second quadrant) and when the sprung speed is the upward speed and the relative speed is in the direction in which the suspension device10extends (fourth quadrant), the attenuating properties of the suspension device10are set to relatively hard properties.

When the attenuating properties of the suspension device10are controlled in such manner, the attenuating properties of the suspension device10are switched between the hard properties and the soft properties when the relative speed of the sprung portion and the unsprung portion is switched from the extending direction to the contracting direction or switched from the contracting direction to the extending direction. Furthermore, when the sprung speed is switched from upward to downward or when switched from downward to upward, the attenuating properties of the suspension device10are switched.

Therefore, if the estimation accuracy of the relative speed of the sprung portion and the unsprung portion is low, the attenuating properties of the suspension device10may be switched although the direction of the relative speed is not switched, or the attenuating properties of the suspension device10may not be switched although the direction of the relative speed is switched. Similarly for the sprung speed, if the estimation accuracy of the sprung speed is low, the attenuating properties of the suspension device10may be switched although the direction of the sprung speed is not switched, or the attenuating properties of the suspension device10may not be switched although the direction of the sprung speed is switched.

On the other hand, the vehicle state estimating device101of the present embodiment can accurately estimate the sprung speed and the relative speed of the sprung portion and the unsprung portion. Therefore, according to the vehicle state estimating device101and the vehicle control device102of the present embodiment, conflict between the actual value of the sprung speed and the relative speed of the sprung portion and the unsprung portion, and the attenuating properties of the suspension device10is suppressed.

Vehicle State Estimating Method

As described above, the vehicle state estimating device101and the vehicle control device102of the present embodiment can execute the vehicle state estimating method illustrated below.

The vehicle state estimating method executed by the vehicle state estimating device101and the vehicle control device102includes a wheel speed detecting procedure of detecting a wheel speed of each wheel; a brake operation amount detecting procedure of detecting a brake operation amount; a drive operation amount detecting procedure of detecting a drive operation amount; a steering operation amount detecting procedure of detecting a steering operation amount; an operation input caused state amount estimating procedure of estimating a sprung state amount of the vehicle caused by the operation input based on the brake operation amount, the drive operation amount, and the steering operation amount; an operation input caused fluctuation estimating procedure of estimating a wheel speed fluctuation amount caused by the operation input based on the sprung state amount caused by the operation input; an actual fluctuation estimating procedure of estimating the actual wheel speed fluctuation amount from which the wheel speed fluctuation amount by the brake/drive force is excluded based on the wheel speed detected in the wheel speed detecting procedure; a road surface input caused fluctuation estimating procedure of estimating the wheel speed fluctuation amount caused by the road surface input by removing the wheel speed fluctuation amount caused by the operation input from the actual wheel speed fluctuation amount; and a road surface input caused state amount estimating procedure of estimating at least one of the sprung state amount and the unsprung state amount caused by the road surface input based on the wheel speed fluctuation amount caused by the road surface input.

In the present embodiment, the wheel speed detection unit4executes the wheel speed detecting procedure. The brake operation amount detection unit5executes the brake operation amount detecting procedure. The drive operation amount detection unit6executes the drive operation amount detecting procedure. The steering operation amount detection unit7executes the steering operation amount detecting procedure.

The first state amount estimating unit21executes the operation input caused state amount estimating procedure. The first fluctuation estimating unit22executes the operation input caused fluctuation estimating procedure. The second fluctuation estimating unit23executes the actual fluctuation estimating procedure. The third fluctuation estimating unit24executes the road surface input caused fluctuation estimating procedure. The second state amount estimating unit25executes the road surface input caused state amount estimating procedure.

The vehicle state estimating method may further include a total sprung state amount estimating procedure of estimating a total sprung state amount, which is the sprung state amount in which the estimated value of the sprung state amount caused by the operation input and the estimated value of the sprung state amount caused by the road surface input are added. In the present embodiment, the third state amount estimating unit26executes the total sprung state amount estimating procedure.

The executing order of each procedure of the vehicle state estimating method of the present embodiment can be appropriately defined, and thus is not limited to the described order.

Variant of Embodiment

A variant of the embodiment described above will now be described. In the embodiment described above, the vehicle state estimating device101estimates both the sprung speed and the relative speed of the sprung portion and the unsprung portion based on the wheel speed fluctuation amount Δω′ caused by the road surface input, but is not limited thereto. The vehicle state estimating device101may estimate only the sprung speed, estimate only the unsprung speed, or estimate only the relative speed of the sprung portion and the unsprung portion based on the wheel speed fluctuation amount Δω′ caused by the road surface input. In place of the method based on the wheel speed fluctuation amount Δω′ caused by the road surface input, the vehicle state estimating device101may estimate one of the sprung speed or the relative speed of the sprung portion and the unsprung portion through other methods.

For example, the sprung speed may be estimated from the detection value of an acceleration detection unit that detects the acceleration of the sprung portion. The acceleration detection unit includes, for example, an acceleration sensor that detects the acceleration in the front and back direction, the left and right direction, and the up and down direction of the vehicle, an acceleration sensor that detects the yaw angle, and the like. The relative speed of the sprung portion and the unsprung portion, and the unsprung speed may be estimated from the detection result of a stroke detection unit that detects the stroke of the suspension device10.

The second state amount estimating unit25can directly estimate the sprung speed and the relative speed of the sprung portion and the unsprung portion from the wheel speed fluctuation amount Δω′ caused by the road surface input without estimating the road surface input Zi. For example, the second state amount estimating unit25can calculate the sprung speed from the wheel speed fluctuation amount Δω′ caused by the road surface input based on the [Formula 22]. The second state amount estimating unit25can also calculate the relative speed of the sprung portion and the unsprung portion from the wheel speed fluctuation amount Δω′ caused by the road surface input based on the [Formula 23].

In the embodiment described above, the approximate expression is sometimes used in the theoretical formula, but a more detailed (high order) expression may be used instead of the approximate expression. For example, the high-order expression that takes into consideration the deformation of the tire of the wheel2, and the like may be used.

In the embodiment described above, the attenuating properties of the suspension device10are switched in two stages, soft and hard, but the control mode of the attenuating properties is not limited thereto. For example, the attenuating properties of the suspension device10may be switched to a plurality of hardnesses of three or more stages.

In the embodiment described above, the ECU1serving as the control unit controls the suspension device10based on the total sprung speed and the relative speed of the sprung portion and the unsprung portion, but the state amount used in the control is not limited thereto. The control unit controls the suspension device10based on at least one of the estimated value of the sprung state amount and the estimated value of the unsprung state amount caused by the road surface input.

The target of control based on the sprung speed and the relative speed of the sprung portion and the unsprung portion may be other than the suspension device10. Other devices controlled based on the behavior of the vehicle100such as the acceleration/deceleration device and the steering device may be controlled by the control unit.

The contents disclosed in the embodiments and the variants described above can be appropriately combined and executed.

A vehicle state estimating device according to the present invention includes a wheel speed detection unit configured to detect a wheel speed of each wheel; a brake operation amount detection unit configured to detect a brake operation amount; a drive operation amount detection unit configured to detect a drive operation amount; a steering operation amount detection unit configured to detect a steering operation amount; a first state amount estimating unit configured to estimate a sprung state amount of a vehicle caused by an operation input based on the brake operation amount, the drive operation amount, and the steering operation amount; a first fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by an operation input based on the sprung state amount caused by the operation input; a second fluctuation estimating unit configured to estimate an actual wheel speed fluctuation amount from which a wheel speed fluctuation amount by a brake/drive force is excluded based on the wheel speed detected by the wheel speed detection unit; a third fluctuation estimating unit configured to estimate a wheel speed fluctuation amount caused by a road surface input by removing a wheel speed fluctuation amount caused by the operation input from the actual wheel speed fluctuation amount; and a second state amount estimating unit configured to estimate at least one of a sprung state amount and an unsprung state amount caused by a road surface input based on the wheel speed fluctuation amount caused by the road surface input. According to the vehicle state estimating device of the present invention, the estimation accuracy in estimating the state amount of the vehicle from the wheel speed can be enhanced.