Damping control device and damping control method

A damping control device for a vehicle calculates a combined control force by adding together a control force when a front wheel passes through a predicted passing position and a control force when a rear wheel passes through a predicted passing position, and calculates a final control force for the front wheel and a final control force for the rear wheel by distributing the combined control force at a predetermined distribution ratio.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2020-097679 filed on Jun. 4, 2020, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a damping control device and a damping control method for a vehicle.

2. Description of Related Art

Hitherto, there is a proposal for a device (hereinafter referred to as “related-art device”) configured to perform damping control for a sprung portion of a vehicle by controlling actuators provided on front wheels and rear wheels of the vehicle using information related to vertical displacements of a road surface where the wheels are predicted to pass (road surface displacements) (for example, Japanese Unexamined Patent Application Publication No. 08-020212 (JP 08-020212 A)). Such control is referred to also as “preview damping control”.

SUMMARY

The related-art device executes the preview damping control without consideration of a relationship between the road surface displacement on the front wheel and the road surface displacement on the rear wheel. Therefore, unnecessary energy is consumed in the following situation. It is assumed that a vehicle travels along a road having repetitive undulations and the wheelbase of the vehicle agrees with a half of a wavelength of a waveform of a road surface displacement. In this case, no vertical displacement occurs at the center-of-gravity position of the vehicle. However, the related-art device controls the actuators of the front wheel and the rear wheel in the vertical direction in response to the road surface displacements. Thus, the related-art device may unnecessarily drive the actuators in the preview damping control. Therefore, a problem arises in that unnecessary energy is consumed in control force generating devices such as the actuators.

The present disclosure provides a technology that can reduce the possibility of unnecessary energy consumption in the control force generating device when the preview damping control is executed.

A first aspect of the present disclosure provides a damping control device for a vehicle having wheels including a front wheel and a rear wheel. The damping control device includes:a control force generating device configured to generate a vertical control force for damping a sprung portion of the vehicle between each of the wheels and a portion of a vehicle body that corresponds to a position of each of the wheels;an information acquirer configured to acquire pieces of road surface displacement related information related to vertical displacements of a road surface at a predicted passing position where each of the wheels is predicted to pass at a timing when a predetermined period has elapsed from a current time, each piece of the road surface displacement related information including at least one of road surface displacements (z0) that are the vertical displacements of the road surface at the predicted passing position, a road surface displacement speed (dz0) that is a time derivative of the road surface displacements at the predicted passing position, an unsprung displacement (z1) that is a vertical displacement of an unsprung portion of the vehicle at the predicted passing position, and an unsprung speed (dz1) that is a time derivative of the unsprung displacement at the predicted passing position; anda control unit configured to control the control force generating device to change the control force.

The control unit is configured to:calculate, as a first control force, the control force (Fct_f) for the front wheel when the front wheel passes through the predicted passing position, based on the road surface displacement related information at the predicted passing position of the front wheel;calculate, as a second control force, the control force (Fct_r) for the rear wheel when the rear wheel passes through the predicted passing position, based on the road surface displacement related information at the predicted passing position of the rear wheel;calculate a combined control force (Fcta) by adding together the first control force and the second control force;calculate a first final target control force (Fct_f′) that is a final target value of the control force for the front wheel and a second final target control force (Fct_r′) that is a final target value of the control force for the rear wheel by distributing the combined control force at a predetermined distribution ratio;control the control force generating device such that the control force generating device generates the control force that agrees with the first final target control force in the front wheel at the timing when the front wheel passes through the predicted passing position of the front wheel; andcontrol the control force generating device such that the control force generating device generates the control force that agrees with the second final target control force in the rear wheel at the timing when the rear wheel passes through the predicted passing position of the rear wheel.

For example, it is assumed that the vehicle travels along a road having repetitive undulations and the wheelbase of the vehicle agrees with a half of a wavelength of a waveform of road surface displacements of the road. In this situation, no vertical displacement occurs at the center-of-gravity position of the vehicle. According to the configuration described above, the damping control device calculates the combined control force by adding together the first control force and the second control force. Through this calculation, an upward control force and a downward control force are canceled out, and as a result, the magnitude of the combined control force decreases. The damping control device distributes the combined control force to the front wheel and the rear wheel at the predetermined distribution ratio. Through this control, a possibility of unnecessary driving of the control force generating device can be reduced in the situation in which the center-of-gravity position of the vehicle is not displaced in the vertical direction. The possibility of unnecessary energy consumption in the control force generating device can be reduced.

In the first aspect, the control force generating device may include active actuators provided on the wheels, respectively. The control unit may be configured to calculate the first final target control force (Fct_f′) and the second final target control force (Fct_r′) by distributing the combined control force (Fcta) at a higher ratio to an actuator having higher performance out of the active actuator of the front wheel and the active actuator of the rear wheel.

According to the configuration described above, the combined control force is distributed at the higher ratio to the actuator having higher performance. Thus, vibration of the sprung portion of the vehicle can effectively be reduced when the control force generating device is driven.

A second aspect of the present disclosure provides a damping control device for a vehicle having wheels including right and left front wheels and right and left rear wheels. The damping control device includes:a control force generating device configured to generate a vertical control force for damping a sprung portion of the vehicle between each of the wheels and a portion of a vehicle body that corresponds to a position of each of the wheels;an information acquirer configured to acquire pieces of road surface displacement related information related to vertical displacements of a road surface at a predicted passing position where each of the wheels is predicted to pass at a timing when a predetermined period has elapsed from a current time, each piece of the road surface displacement related information including at least one of road surface displacements (z0) that are the vertical displacements of the road surface at the predicted passing position, a road surface displacement speed (dz0) that is a time derivative of the road surface displacements at the predicted passing position, an unsprung displacement (z1) that is a vertical displacement of an unsprung portion of the vehicle at the predicted passing position, and an unsprung speed (dz1) that is a time derivative of the unsprung displacement at the predicted passing position; anda control unit configured to control the control force generating device to change the control force.

The control unit is configured to:calculate a first-situation control force (Fcd) adapted to a first situation in which a waveform of the road surface displacements on a right side of the vehicle and a waveform of the road surface displacements on a left side of the vehicle have opposite phases, based on the road surface displacement related information at the predicted passing position of the right front wheel, the road surface displacement related information at the predicted passing position of the left front wheel, the road surface displacement related information at the predicted passing position of the right rear wheel, and the road surface displacement related information at the predicted passing position of the left rear wheel;calculate a first front wheel control force (Fan_f) for the right and left front wheels adapted to the first situation and a first rear wheel control force (Fan_r) for the right and left rear wheels adapted to the first situation by distributing the first-situation control force at a predetermined distribution ratio;calculate a second front wheel control force (Fin_f) for the right and left front wheels adapted to a second situation in which the waveform of the road surface displacements on the right side of the vehicle and the waveform of the road surface displacements on the left side of the vehicle have identical phases, based on the road surface displacement related information at the predicted passing position of the right front wheel and the road surface displacement related information at the predicted passing position of the left front wheel;calculate a second rear wheel control force (Fin_r) for the right and left rear wheels adapted to the second situation based on the road surface displacement related information at the predicted passing position of the right rear wheel and the road surface displacement related information at the predicted passing position of the left rear wheel;calculate a first final target control force (Fct_fl′) that is a final target value of the control force for the left front wheel and a second final target control force (Fct_fr′) that is a final target value of the control force for the right front wheel based on the first front wheel control force and the second front wheel control force;calculate a third final target control force (Fct_rl′) that is a final target value of the control force for the left rear wheel and a fourth final target control force (Fct_rr′) that is a final target value of the control force for the right rear wheel based on the first rear wheel control force and the second rear wheel control force;control the control force generating device such that the control force generating device generates the control force that agrees with the first final target control force in the left front wheel at the timing when the left front wheel passes through the predicted passing position of the left front wheel;control the control force generating device such that the control force generating device generates the control force that agrees with the second final target control force in the right front wheel at the timing when the right front wheel passes through the predicted passing position of the right front wheel;control the control force generating device such that the control force generating device generates the control force that agrees with the third final target control force in the left rear wheel at the timing when the left rear wheel passes through the predicted passing position of the left rear wheel; andcontrol the control force generating device such that the control force generating device generates the control force that agrees with the fourth final target control force in the right rear wheel at the timing when the right rear wheel passes through the predicted passing position of the right rear wheel.

According to the configuration described above, the damping control device calculates the final target values of the control forces of the wheels (first final target control force, second final target control force, third final target control force, and fourth final target control force) based on the control force adapted to the first situation (first front wheel control force or first rear wheel control force) and the control force adapted to the second situation (second front wheel control force or second rear wheel control force) for the wheels (right and left front wheels and right and left rear wheels). Thus, the possibility of unnecessary driving of the control force generating device can be reduced in, for example, a situation in which no roll displacement occurs in the vehicle (first situation). Accordingly, the possibility of unnecessary energy consumption in the control force generating device can be reduced.

In actuality, the waveform of the road surface displacements on the right side of the vehicle and the waveform of the road surface displacements on the left side of the vehicle do not completely have opposite phases or identical phases. In many cases, those waveforms include both components in opposite phases and components in identical phases. According to the configuration described above, the damping control device can control the control force generating device by appropriate control forces in consideration of both the components in opposite phases and the components in identical phases. Thus, the vibration of the sprung portion of the vehicle can be reduced by the appropriate control forces while reducing the possibility of unnecessary driving of the control force generating device.

In the second aspect, the control unit may be configured to calculate the first-situation control force (Fcd) by adding together a control force adapted to a situation in which the waveform of the road surface displacements at the right front wheel and the waveform of the road surface displacements at the left front wheel have opposite phases (may be regarded as a first term on a right-hand side in Expression (14)) and a control force adapted to a situation in which the waveform of the road surface displacements at the right rear wheel and the waveform of the road surface displacements at the left rear wheel have opposite phases (may be regarded as a second term on the right-hand side in Expression (14)).

According to the configuration described above, the upward control force and the downward control force are canceled out through the addition described above in the first situation. As a result, the magnitude of the first-situation control force decreases. Thus, the possibility of unnecessary driving of the control force generating device in the first situation can be reduced.

In the second aspect, the control force generating device may include active actuators provided on the wheels, respectively. The control unit may be configured to calculate the first front wheel control force (Fan_f) and the first rear wheel control force (Fan_r) by distributing the first-situation control force (Fcd) at a higher ratio to an actuator having higher performance out of the active actuators of the front wheels and the active actuators of the rear wheels.

According to the configuration described above, the first-situation control force is distributed at the higher ratio to the actuator having higher performance. Thus, the vibration of the sprung portion of the vehicle can effectively be reduced when the control force generating device is driven.

A third aspect of the present disclosure provides a damping control device for a vehicle having wheels including right and left front wheels and right and left rear wheels. The damping control device includes:a control force generating device configured to generate a vertical control force for damping a sprung portion of the vehicle between each of the wheels and a portion of a vehicle body that corresponds to a position of each of the wheels;an information acquirer configured to acquire pieces of road surface displacement related information related to vertical displacements of a road surface at a predicted passing position where each of the wheels is predicted to pass at a timing when a predetermined period has elapsed from a current time, each piece of the road surface displacement related information including at least one of road surface displacements (z0) that are the vertical displacements of the road surface at the predicted passing position, a road surface displacement speed (dz0) that is a time derivative of the road surface displacements at the predicted passing position, an unsprung displacement (z1) that is a vertical displacement of an unsprung portion of the vehicle at the predicted passing position, and an unsprung speed (dz1) that is a time derivative of the unsprung displacement at the predicted passing position; anda control unit configured to control the control force generating device to change the control force.

The control unit is configured to:calculate a first-situation control force (Fcd) adapted to a first situation in which a waveform of the road surface displacements on a right side of the vehicle and a waveform of the road surface displacements on a left side of the vehicle have opposite phases, based on the road surface displacement related information at the predicted passing position of the right front wheel, the road surface displacement related information at the predicted passing position of the left front wheel, the road surface displacement related information at the predicted passing position of the right rear wheel, and the road surface displacement related information at the predicted passing position of the left rear wheel;calculate a first front wheel control force (Fan_f) for the right and left front wheels adapted to the first situation and a first rear wheel control force (Fan_r) for the right and left rear wheels adapted to the first situation by distributing the first-situation control force at a predetermined distribution ratio;control, based on the first front wheel control force, the control force to be generated by the control force generating device in the right front wheel at the timing when the right front wheel passes through the predicted passing position of the right front wheel, and the control force to be generated by the control force generating device in the left front wheel at the timing when the left front wheel passes through the predicted passing position of the left front wheel; andcontrol, based on the first rear wheel control force, the control force to be generated by the control force generating device in the right rear wheel at the timing when the right rear wheel passes through the predicted passing position of the right rear wheel, and the control force to be generated by the control force generating device in the left rear wheel at the timing when the left rear wheel passes through the predicted passing position of the left rear wheel.

In the third aspect, the control force generating device may be an active stabilizer device.

A fourth aspect of the present disclosure provides a damping control method for a vehicle. The vehicle has wheels including a front wheel and a rear wheel, and a control force generating device configured to generate a vertical control force for damping a sprung portion of the vehicle between each of the wheels and a portion of a vehicle body that corresponds to a position of each of the wheels.

The damping control method includes:acquiring pieces of road surface displacement related information related to vertical displacements of a road surface at a predicted passing position where each of the wheels is predicted to pass at a timing when a predetermined period has elapsed from a current time, each piece of the road surface displacement related information including at least one of road surface displacements (z0) that are the vertical displacements of the road surface at the predicted passing position, a road surface displacement speed (dz0) that is a time derivative of the road surface displacements at the predicted passing position, an unsprung displacement (z1) that is a vertical displacement of an unsprung portion of the vehicle at the predicted passing position, and an unsprung speed (dz1) that is a time derivative of the unsprung displacement at the predicted passing position; andcontrolling the control force generating device to change the control force.

The controlling includes:calculating, as a first control force, the control force (Fct_f) for the front wheel when the front wheel passes through the predicted passing position, based on the road surface displacement related information at the predicted passing position of the front wheel;calculating, as a second control force, the control force (Fct_r) for the rear wheel when the rear wheel passes through the predicted passing position, based on the road surface displacement related information at the predicted passing position of the rear wheel;calculating a combined control force (Fcta) by adding together the first control force and the second control force;calculating a first final target control force (Fct_f′) that is a final target value of the control force for the front wheel and a second final target control force (Fct_r′) that is a final target value of the control force for the rear wheel by distributing the combined control force at a predetermined distribution ratio;controlling the control force generating device such that the control force generating device generates the control force that agrees with the first final target control force in the front wheel at the timing when the front wheel passes through the predicted passing position of the front wheel; andcontrolling the control force generating device such that the control force generating device generates the control force that agrees with the second final target control force in the rear wheel at the timing when the rear wheel passes through the predicted passing position of the rear wheel.

A fifth aspect of the present disclosure provides a damping control method for a vehicle. The vehicle has wheels including right and left front wheels and right and left rear wheels, and a control force generating device configured to generate a vertical control force for damping a sprung portion of the vehicle between each of the wheels and a portion of a vehicle body that corresponds to a position of each of the wheels.

The damping control method includes:acquiring pieces of road surface displacement related information related to vertical displacements of a road surface at a predicted passing position where each of the wheels is predicted to pass at a timing when a predetermined period has elapsed from a current time, each piece of the road surface displacement related information including at least one of road surface displacements (z0) that are the vertical displacements of the road surface at the predicted passing position, a road surface displacement speed (dz0) that is a time derivative of the road surface displacements at the predicted passing position, an unsprung displacement (z1) that is a vertical displacement of an unsprung portion of the vehicle at the predicted passing position, and an unsprung speed (dz1) that is a time derivative of the unsprung displacement at the predicted passing position; andcontrolling the control force generating device to change the control force.

The controlling includes:calculating a first-situation control force (Fcd) adapted to a first situation in which a waveform of the road surface displacements on a right side of the vehicle and a waveform of the road surface displacements on a left side of the vehicle have opposite phases, based on the road surface displacement related information at the predicted passing position of the right front wheel, the road surface displacement related information at the predicted passing position of the left front wheel, the road surface displacement related information at the predicted passing position of the right rear wheel, and the road surface displacement related information at the predicted passing position of the left rear wheel;calculating a first front wheel control force (Fan_f) for the right and left front wheels adapted to the first situation and a first rear wheel control force (Fan_r) for the right and left rear wheels adapted to the first situation by distributing the first-situation control force at a predetermined distribution ratio;calculating a second front wheel control force (Fin_f) for the right and left front wheels adapted to a second situation in which the waveform of the road surface displacement on the right side of the vehicle and the waveform of the road surface displacement on the left side of the vehicle have identical phases, based on the road surface displacement related information at the predicted passing position of the right front wheel and the road surface displacement related information at the predicted passing position of the left front wheel;calculating a second rear wheel control force (Fin_r) for the right and left rear wheels adapted to the second situation based on the road surface displacement related information at the predicted passing position of the right rear wheel and the road surface displacement related information at the predicted passing position of the left rear wheel;calculating a first final target control force (Fct_fl′) that is a final target value of the control force for the left front wheel and a second final target control force (Fct_fr′) that is a final target value of the control force for the right front wheel based on the first front wheel control force and the second front wheel control force;calculating a third final target control force (Fct_rl′) that is a final target value of the control force for the left rear wheel and a fourth final target control force (Fct_rr′) that is a final target value of the control force for the right rear wheel based on the first rear wheel control force and the second rear wheel control force;controlling the control force generating device such that the control force generating device generates the control force that agrees with the first final target control force in the left front wheel at the timing when the left front wheel passes through the predicted passing position of the left front wheel;controlling the control force generating device such that the control force generating device generates the control force that agrees with the second final target control force in the right front wheel at the timing when the right front wheel passes through the predicted passing position of the right front wheel;controlling the control force generating device such that the control force generating device generates the control force that agrees with the third final target control force in the left rear wheel at the timing when the left rear wheel passes through the predicted passing position of the left rear wheel; andcontrolling the control force generating device such that the control force generating device generates the control force that agrees with the fourth final target control force in the right rear wheel at the timing when the right rear wheel passes through the predicted passing position of the right rear wheel.

A sixth aspect of the present disclosure provides a damping control method for a vehicle. The vehicle has wheels including right and left front wheels and right and left rear wheels, and a control force generating device configured to generate a vertical control force for damping a sprung portion of the vehicle between each of the wheels and a portion of a vehicle body that corresponds to a position of each of the wheels.

The damping control method includes:acquiring pieces of road surface displacement related information related to vertical displacements of a road surface at a predicted passing position where each of the wheels is predicted to pass at a timing when a predetermined period has elapsed from a current time, each piece of the road surface displacement related information including at least one of road surface displacements (z0) that are the vertical displacements of the road surface at the predicted passing position, a road surface displacement speed (dz0) that is a time derivative of the road surface displacements at the predicted passing position, an unsprung displacement (z1) that is a vertical displacement of an unsprung portion of the vehicle at the predicted passing position, and an unsprung speed (dz1) that is a time derivative of the unsprung displacement at the predicted passing position; andcontrolling the control force generating device to change the control force.

The controlling includes:calculating a first-situation control force (Fcd) adapted to a first situation in which a waveform of the road surface displacements on a right side of the vehicle and a waveform of the road surface displacements on a left side of the vehicle have opposite phases, based on the road surface displacement related information at the predicted passing position of the right front wheel, the road surface displacement related information at the predicted passing position of the left front wheel, the road surface displacement related information at the predicted passing position of the right rear wheel, and the road surface displacement related information at the predicted passing position of the left rear wheel;calculating a first front wheel control force (Fan_f) for the right and left front wheels adapted to the first situation and a first rear wheel control force (Fan_r) for the right and left rear wheels adapted to the first situation by distributing the first-situation control force at a predetermined distribution ratio;controlling, based on the first front wheel control force, the control force to be generated by the control force generating device in the right front wheel at the timing when the right front wheel passes through the predicted passing position of the right front wheel, and the control force to be generated by the control force generating device in the left front wheel at the timing when the left front wheel passes through the predicted passing position of the left front wheel; andcontrolling, based on the first rear wheel control force, the control force to be generated by the control force generating device in the right rear wheel at the timing when the right rear wheel passes through the predicted passing position of the right rear wheel, and the control force to be generated by the control force generating device in the left rear wheel at the timing when the left rear wheel passes through the predicted passing position of the left rear wheel.

In the aspects described above, the control unit may be implemented by a microprocessor programmed to perform one or more functions described herein. In the aspects described above, the control unit may entirely or partially be implemented by hardware including one or more application-specific integrated circuits, that is, ASICs.

In the description above, constituent elements corresponding to those in one or more embodiments described later are accompanied with parenthesized names and/or reference symbols used in the embodiments. The constituent elements are not limited to those in the embodiments defined by the names and/or the reference symbols. Other objects, other features, and accompanying advantages of the present disclosure will easily be understood from the description of one or more embodiments with reference to the drawings below.

DETAILED DESCRIPTION OF EMBODIMENTS

Structure

A damping control device according to one or more embodiments is applied to a vehicle10illustrated inFIG.1. As illustrated inFIG.2, the damping control device is hereinafter referred to also as “damping control device20”.

As illustrated inFIG.1, the vehicle10includes a right front wheel11FR, a left front wheel11FL, a right rear wheel11RR, and a left rear wheel11RL. The right front wheel11FR is rotatably supported on a vehicle body10aby a wheel support member12FR. The left front wheel11FL is rotatably supported on the vehicle body10aby a wheel support member12FL. The right rear wheel11RR is rotatably supported on the vehicle body10aby a wheel support member12RR. The left rear wheel11RL is rotatably supported on the vehicle body10aby a wheel support member12RL.

The right front wheel11FR, the left front wheel11FL, the right rear wheel11RR, and the left rear wheel11RL are referred to as “wheels11” unless otherwise distinguished. Similarly, the right front wheel11FR and the left front wheel11FL are referred to as “front wheels11F”. Similarly, the right rear wheel11RR and the left rear wheel11RL are referred to as “rear wheels11R”. The wheel support members12FR to12RL are referred to as “wheel support members12”.

The vehicle10further includes a right front wheel suspension13FR, a left front wheel suspension13FL, a right rear wheel suspension13RR, and a left rear wheel suspension13RL. Details of the suspensions13FR to13RL are described below. The suspensions13FR to13RL are independent suspensions, but other types of suspension may be employed.

The right front wheel suspension13FR suspends the right front wheel11FR from the vehicle body10a, and includes a suspension arm14FR, a shock absorber15FR, and a suspension spring16FR. The left front wheel suspension13FL suspends the left front wheel11FL from the vehicle body10a, and includes a suspension arm14FL, a shock absorber15FL, and a suspension spring16FL.

The right rear wheel suspension13RR suspends the right rear wheel11RR from the vehicle body10a, and includes a suspension arm14RR, a shock absorber15RR, and a suspension spring16RR. The left rear wheel suspension13RL suspends the left rear wheel11RL from the vehicle body10a, and includes a suspension arm14RL, a shock absorber15RL, and a suspension spring16RL.

The right front wheel suspension13FR, the left front wheel suspension13FL, the right rear wheel suspension13RR, and the left rear wheel suspension13RL are referred to as “suspensions13” unless otherwise distinguished. Similarly, the suspension arms14FR to14RL are referred to as “suspension arms14”. Similarly, the shock absorbers15FR to15RL are referred to as “shock absorbers15”. Similarly, the suspension springs16FR to16RL are referred to as “suspension springs16”.

The suspension arm14couples the wheel support member12to the vehicle body10a. InFIG.1, one suspension arm14is provided for one suspension13. In another example, a plurality of suspension arms14may be provided for one suspension13.

The shock absorber15is provided between the vehicle body10aand the suspension arm14. The upper end of the shock absorber15is coupled to the vehicle body10a. The lower end of the shock absorber15is coupled to the suspension arm14. The suspension spring16is provided between the vehicle body10aand the suspension arm14via the shock absorber15. That is, the upper end of the suspension spring16is coupled to the vehicle body10a, and the lower end of the suspension spring16is coupled to a cylinder of the shock absorber15. In this structure of the suspension spring16, the shock absorber15may be provided between the vehicle body10aand the wheel support member12.

In this example, the shock absorber15is a non-adjustable shock absorber. In another example, the shock absorber15may be an adjustable shock absorber. The suspension spring16may be provided between the vehicle body10aand the suspension arm14without intervention of the shock absorber15. That is, the upper end of the suspension spring16may be coupled to the vehicle body10a, and the lower end of the suspension spring16may be coupled to the suspension arm14. In this structure of the suspension spring16, the shock absorber15and the suspension spring16may be provided between the vehicle body10aand the wheel support member12.

Regarding the members such as the wheel11and the shock absorber15of the vehicle10, a portion close to the wheel11with respect to the suspension spring16is referred to as “unsprung portion50or unsprung member50(seeFIG.3)”. Regarding the members such as the vehicle body10aand the shock absorber15of the vehicle10, a portion close to the vehicle body10awith respect to the suspension spring16is referred to as “sprung portion51or sprung member51(seeFIG.3)”.

A right front wheel active actuator17FR, a left front wheel active actuator17FL, a right rear wheel active actuator17RR, and a left rear wheel active actuator17RL are provided between the vehicle body10aand the suspension arms14FR to14RL, respectively. The active actuators17FR to17RL are provided in parallel to the shock absorbers15FR to15RL and the suspension springs16FR to16RL, respectively.

The right front wheel active actuator17FR, the left front wheel active actuator17FL, the right rear wheel active actuator17RR, and the left rear wheel active actuator17RL are referred to as “active actuators17” unless otherwise distinguished. Similarly, the right front wheel active actuator17FR and the left front wheel active actuator17FL are referred to as “front wheel active actuators17F”. Similarly, the right rear wheel active actuator17RR and the left rear wheel active actuator17RL are referred to as “rear wheel active actuators17R”.

The active actuator17generates a control force Fc based on a control command from an electronic control unit30illustrated inFIG.2. The control force Fc is a vertical force acting between the vehicle body10aand the wheel11(that is, between the sprung portion51and the unsprung portion50) to damp the sprung portion51. The electronic control unit30is referred to as “ECU30”, and may be referred to as “control unit or controller”. The active actuator17may be referred to as “control force generating device”. The active actuator17is an electromagnetic active actuator. The active actuator17serves as an active suspension in cooperation with, for example, the shock absorber15and the suspension spring16.

As illustrated inFIG.2, the damping control device20includes the ECU30, a storage device30a, a positional information acquiring device31, a wireless communication device32, and a preview sensor33. The damping control device20further includes the active actuators17FR to17RL.

The ECU30includes a microcomputer. The microcomputer includes a CPU, a read-only memory (ROM), a random-access memory (RAM), and an interface (I/F). The CPU executes instructions (programs or routines) stored in the ROM to implement various functions.

The ECU30is connected to the non-volatile storage device30ain which information is readable and writable. In this example, the storage device30ais a hard disk drive. The ECU30can store information in the storage device30a, and can read information stored in the storage device30a. The storage device30ais not limited to the hard disk drive, and may be a known storage device or storage medium in which information is readable and writable.

The ECU30is connected to the positional information acquiring device31, the wireless communication device32, and the preview sensor33.

The positional information acquiring device31includes a global navigation satellite system (GNSS) receiver and a map database. The GNSS receiver receives, from an artificial satellite, a signal (for example, GNSS signal) for detecting a position of the vehicle10at a current time (current position). The map database stores road map information and the like. The positional information acquiring device31acquires the current position (for example, latitude and longitude) of the vehicle10based on the GNSS signal. Examples of the positional information acquiring device31include a navigation device.

The ECU30acquires “vehicle speed V1of vehicle10and traveling direction Td of vehicle10” at a current time from the positional information acquiring device31.

The wireless communication device32is a wireless communication terminal for communicating information with a cloud40via a network. The cloud40includes “management server42and at least one storage device44” connected to the network.

The management server42includes a CPU, a ROM, a RAM, and an interface (I/F). The management server42retrieves and reads data stored in the storage device44, and writes data into the storage device44.

The storage device44stores preview reference data45. “Road surface displacement related information and positional information” are registered in the preview reference data45while being linked to (associated with) each other.

The road surface displacement related information is related to a vertical displacement of a road surface of a road, which indicates undulations of the road surface. Specifically, the road surface displacement related information includes at least one of a road surface displacement z0that is the vertical displacement of the road surface, a road surface displacement speed dz0that is a time derivative of the road surface displacement z0, an unsprung displacement z1that is a vertical displacement of the unsprung portion50, and an unsprung speed dz1that is a time derivative of the unsprung displacement z1. In this example, the road surface displacement related information is the unsprung displacement z1. When the vehicle10travels along the road surface, the unsprung portion50is displaced in the vertical direction in response to the displacement of the road surface. The unsprung displacement z1is a vertical displacement of the unsprung portion50associated with a position of each wheel11of the vehicle10.

The positional information indicates a position (for example, latitude and longitude) of the road surface associated with the road surface displacement related information.FIG.2illustrates an unsprung displacement “Z1a” and positional information “Xa, Ya” as examples of “unsprung displacement z1and positional information” registered as the preview reference data45.

The preview sensor33acquires a value indicating a vertical displacement of a road surface ahead of the vehicle10(that is, road surface displacement z0). The preview sensor33may be any publicly known preview sensor in this technical field as long as the road surface displacement z0ahead of the vehicle10can be acquired. Examples of the preview sensor33include a camera sensor, a Light Detection and Ranging (LIDAR) sensor, a radar, and combinations of those sensors.

As illustrated inFIG.2, the preview sensor33is attached to, for example, an upper-end inner surface of a windshield of the vehicle10at the center in a vehicle width direction, and detects a road surface displacement z0at a position that is a predetermined preview distance Lpreahead of the front wheel11F. The preview distance Lpreis larger than a front wheel preview distance Lpf(described later) when the vehicle speed of the vehicle10is a maximum rated vehicle speed.FIG.2illustrates one preview sensor33, but a pair of preview sensors may be provided in association with the right and left front wheels. The preview sensor33is used in a modified example described later.

The ECU30is connected to the right front wheel active actuator17FR, the left front wheel active actuator17FL, the right rear wheel active actuator17RR, and the left rear wheel active actuator17RL via drive circuits (not illustrated).

The ECU30calculates a target control force Fct for damping the sprung portion51of each wheel11, and controls the active actuator17to generate a control force that corresponds to (agrees with) the target control force Fct when each wheel11passes through a predicted passing position.

Overview of Basic Preview Damping Control

An overview of basic preview damping control to be executed by the damping control device20is described below.FIG.3illustrates a single-wheel model of the vehicle10on a road surface55.

A spring52corresponds to the suspension spring16. A damper53corresponds to the shock absorber15. An actuator54corresponds to the active actuator17.

InFIG.3, a mass of the sprung portion51is referred to as “sprung mass m2”. A vertical displacement of the sprung portion51is referred to as “sprung displacement z2”. The sprung displacement z2is a vertical displacement of the sprung portion51associated with a position of each wheel11. A spring rate (equivalent spring rate) of the spring52is referred to as “spring rate K”. A damping coefficient (equivalent damping coefficient) of the damper53is referred to as “damping coefficient C”. A force generated by the actuator54is referred to as “control force Fc”. Similarly to the above, a symbol “z1” represents a vertical displacement of the unsprung portion50(unsprung displacement).

Time derivatives of z1and z2are represented by “dz1” and “dz2”, respectively. Second-order time derivatives of z1and z2are represented by “ddz1” and “ddz2”, respectively. In the following description, an upward displacement of each of z1and z2is defined to be positive, and an upward force generated by each of the spring52, the damper53, and the actuator54is defined to be positive.

In the single-wheel model of the vehicle10illustrated inFIG.3, an equation of motion regarding a vertical motion of the sprung portion51can be represented by Expression (1).
m2ddz2=C(dz1−dz2)+K(z1−z2)−Fc(1)

In Expression (1), the damping coefficient C is assumed to be constant. However, an actual damping coefficient changes depending on a stroke speed of the suspension13. Therefore, the damping coefficient C may be set to, for example, a value that changes depending on a time derivative of the stroke H.

When vibration of the sprung portion51is completely canceled out by the control force Fc (that is, when the sprung acceleration ddz2, the sprung speed dz2, and the sprung displacement z2are “0”), the control force Fc is represented by Expression (2).
Fc=Cdz1+Kz1(2)

Vibration of the sprung displacement z2when the control force Fc is represented by Expression (3) is discussed. In Expression (3), α is an arbitrary constant larger than 0 and equal to or smaller than 1.
Fc=α(Cdz1+Kz1)  (3)

When Expression (3) is applied to Expression (1), Expression (1) can be represented by Expression (4).
m2ddz2=C(dz1−dz2)+K(z1−z2)−α(Cdz1+Kz1)  (4)

Expression (5) is obtained when Expression (4) is subjected to Laplace transform and the resultant expression is rearranged. That is, a transfer function from the unsprung displacement z1to the sprung displacement z2is represented by Expression (5). In Expression (5), “s” represents a Laplace operator.

According to Expression (5), the transfer function changes depending on a. When α is an arbitrary value larger than 0 and equal to or smaller than 1, it is observed that the magnitude of the transfer function is securely smaller than “1” (that is, the vibration of the sprung portion51can be reduced). When α is 1, the magnitude of the transfer function is “0”. Therefore, it is observed that the vibration of the sprung portion51is completely canceled out. The target control force Fct can be represented by Expression (6) based on Expression (3).
Fct=α·C·dz1+α·K·z1(6)

Thus, the ECU30calculates the target control force Fct by acquiring in advance (previewing) an unsprung displacement z1at a position where the wheel11passes in the future (predicted passing position), and applying the acquired unsprung displacement z1to Expression (6).

The ECU30causes the actuator54to generate a control force Fc corresponding to the target control force Fct at a timing when the wheel11passes through the predicted passing position (that is, at a timing when the unsprung displacement z1applied to Expression (6) occurs). With this configuration, the vibration of the sprung portion51can be reduced when the wheel11passes through the predicted passing position (that is, when the unsprung displacement z1applied to Expression (6) occurs).

The ECU30may calculate the target control force Fct based on Expression (7) obtained by omitting the derivative term (α·C·dz1) from Expression (6). Also in this case, the ECU30can cause the actuator54to generate the control force Fc for reducing the vibration of the sprung portion51. Thus, the vibration of the sprung portion51can be reduced as compared to a case where the control force Fc is not generated.
Fct=α·K·z1(7)

The control described above is damping control for the sprung portion51, which is referred to as “preview damping control”.

In the single-wheel model, the mass of the unsprung portion50and elastic deformation of tires are ignored, and the road surface displacement z0that is the vertical displacement of the road surface55is assumed to be identical to the unsprung displacement z1. In another example, similar preview damping control may be executed by using the road surface displacement z0and/or the road surface displacement speed dz0in place of or in addition to the unsprung displacement z1and the unsprung speed dz1.

Overview of Preview Damping Control for Front Wheel and Rear Wheel

Next, an overview of the preview damping control for the front wheel and the rear wheel is described with reference toFIG.4toFIG.6. In the following description, a suffix “_f” assigned to various control forces (Fct and Fc) represents correspondence to the front wheel11F, and a suffix “_r” assigned to various control forces (Fct and Fc) represents correspondence to the rear wheel11R.

FIG.4illustrates the vehicle10traveling at a vehicle speed V1in a direction indicated by an arrow AR at a current time tp. In the following description, the front wheel11F and the rear wheel11R are right or left wheels, and the moving speeds of the front wheel11F and the rear wheel11R are equal to the vehicle speed V1.

InFIG.4, a line Lt is a virtual time axis t. Unsprung displacements z1of the front wheel11F on a movement path at current, past, and future times t are represented by a function z1(t) of the times t. Thus, an unsprung displacement z1of the front wheel11F at a position (contact point) pf0at the current time tp is represented by z1(tp). An unsprung displacement z1of the rear wheel11R at a position pr0at the current time tp corresponds to an unsprung displacement z1of the front wheel11F at a time “tp−L/V1” earlier than the current time tp by “period (L/V1) required for front wheel11F to move by wheelbase L”. Thus, the unsprung displacement z1of the rear wheel11R at the current time tp is represented by z1(tp−L/V1).

Preview Damping Control for Front Wheel11F

The ECU30determines a predicted passing position pf1of the front wheel11F at a time later (in the future) than the current time tp by a front wheel preview period tpf. The front wheel preview period tpf is preset to a period required from the timing when the ECU30determines the predicted passing position pf1to the timing when the front wheel active actuator17F outputs a control force Fc_f corresponding to a target control force Fct_f.

The predicted passing position pf1of the front wheel11F is a position spaced away from the position pf0at the current time tp by a front wheel preview distance Lpf(=V1×tpf) along a predicted path of the front wheel11F. The predicted path of the front wheel11F means a path where the front wheel11F is predicted to move. As described later in detail, the position pf0is calculated based on a current position of the vehicle10that is acquired by the positional information acquiring device31.

The ECU30acquires in advance a part of the preview reference data45in an area near the current position of the vehicle10(preparatory z0ne described later) from the cloud40. The ECU30acquires an unsprung displacement z1(tp+tpf) based on the determined predicted passing position pf1and the part of the preview reference data45acquired in advance.

The ECU30calculates a target control force Fct_f of the front wheel11F by applying the unsprung displacement z1(tp+tpf) to the unsprung displacement z1in Expression (8). The symbol “af” represents a gain for the front wheel11F. The symbol “Kf” represents a spring rate of the right front wheel suspension13FR and the left front wheel suspension13FL.
Fct_f=αf·Kf·z1(8)

The ECU30transmits a control command containing the target control force Fct_f to the front wheel active actuator17F to cause the front wheel active actuator17F to generate a control force Fc_f that corresponds to (agrees with) the target control force Fct_f.

As illustrated inFIG.5, the front wheel active actuator17F generates the control force Fc_f corresponding to the target control force Fct_f at “time tp+tpf” (that is, at a timing when the front wheel11F actually passes through the predicted passing position pf1) later than the current time tp by the front wheel preview period tpf. Thus, the front wheel active actuator17F can generate, at an appropriate timing, the control force Fc_f for reducing the vibration of the sprung portion51that occurs due to the unsprung displacement z1of the front wheel11F at the predicted passing position pf1.

Preview Damping Control for Rear Wheel11R

As illustrated inFIG.4, the ECU30determines a predicted passing position pr1of the rear wheel11R at a time later (in the future) than the current time tp by a rear wheel preview period tpr. The rear wheel preview period tpr is preset to a period required from the timing when the ECU30determines the predicted passing position pr1to the timing when the rear wheel active actuator17R outputs a control force Fc_r corresponding to a target control force Fct_r. If the front wheel active actuator17F and the rear wheel active actuator17R have different responses, the front wheel preview period tpf and the rear wheel preview period tpr are preset to different values. If the front wheel active actuator17F and the rear wheel active actuator17R have the same response, the front wheel preview period tpf and the rear wheel preview period tpr are preset to the same value.

The ECU30determines, as the predicted passing position pr1, a position spaced away from the position pr0at the current time tp by a rear wheel preview distance Lpr(=V1×tpr) along a predicted path of the rear wheel11R under the assumption that the rear wheel11R moves along the same path as that of the front wheel11F. As described later in detail, the position pr0is calculated based on the current position of the vehicle10that is acquired by the positional information acquiring device31. An unsprung displacement z1at the predicted passing position pr1can be represented by z1(tp−L/V1+tpr) because this unsprung displacement z1occurs at a time later than “time (tp−L/V1) when front wheel11F was located at position pr0of rear wheel11R at current time” by the rear wheel preview period tpr. The ECU30acquires the unsprung displacement z1(tp−L/V1+tpr) based on the determined predicted passing position pr1and the part of the preview reference data45acquired in advance.

The ECU30calculates a target control force Fct_r of the rear wheel11R by applying the unsprung displacement z1(tp−L/V1+tpr) to the unsprung displacement z1in Expression (9). The symbol “αr” represents a gain for the rear wheel11R. The symbol “Kr” represents a spring rate of the right rear wheel suspension13RR and the left rear wheel suspension13RL. In this example, the gain of in Expression (8) and the gain αr in Expression (9) are set to different values. The spring rate Kf of the right front wheel suspension13FR and the left front wheel suspension13FL and the spring rate Kr of the right rear wheel suspension13RR and the left rear wheel suspension13RL differ from each other as well.
Fct_r=αr·Kr·z1(9)

The ECU30transmits a control command containing the target control force Fct_r to the rear wheel active actuator17R to cause the rear wheel active actuator17R to generate a control force Fc_r that corresponds to (agrees with) the target control force Fct_r.

As illustrated inFIG.6, the rear wheel active actuator17R generates the control force Fc_r corresponding to the target control force Fct_r at “time tp+tpr” (that is, at a timing when the rear wheel11R actually passes through the predicted passing position pr1) later than the current time tp by the rear wheel preview period tpr. Thus, the rear wheel active actuator17R can generate, at an appropriate timing, the control force Fc_r for reducing the vibration of the sprung portion51that occurs due to the unsprung displacement z1of the rear wheel11R at the predicted passing position pr1.

First Embodiment

As illustrated inFIG.7, it is assumed that the vehicle10travels along a road70having repetitive undulations. In this example, an amplitude A of a waveform of a road surface displacement of the road70is constant. A wheelbase L of the vehicle10agrees with a half of a wavelength λ of the waveform of the road surface displacement.

InFIG.7, the vehicle10at a certain time ta is indicated by continuous lines. At the time ta, the front wheel11F is in contact with a convex road surface, and the contact point of the front wheel11F is located at a peak (the highest point) of the waveform of the road surface displacement. The rear wheel11R is in contact with a concave road surface, and the contact point of the rear wheel11R is located at a valley (the lowest point) of the waveform of the road surface displacement. In this case, the ECU30controls the front wheel active actuator17F in a downward direction and the rear wheel active actuator17R in an upward direction.

InFIG.7, the vehicle10at a time tb later than the time ta by a half period is indicated by dashed lines. At the time tb, the front wheel11F is in contact with a concave road surface, and the contact point of the front wheel11F is located at a valley of the waveform of the road surface displacement. The rear wheel11R is in contact with a convex road surface, and the contact point of the rear wheel11R is located at a peak of the waveform of the road surface displacement (point where the front wheel11F was located at the time ta). In this case, the ECU30controls the front wheel active actuator17F in an upward direction and the rear wheel active actuator17R in a downward direction.

In this situation, no vertical displacement occurs at a center-of-gravity position10G of the vehicle10as indicated by a long dashed short dashed line71. When the front wheel active actuator17F and the rear wheel active actuator17R are controlled based on pieces of road surface displacement related information in the situation ofFIG.7, the active actuators17are driven unnecessarily. Therefore, a problem arises in that unnecessary energy is consumed in the active actuators17.

In view of the above, the ECU30calculates a combined control force Fcta by adding together the target control force Fct_f for the front wheel11F and the target control force Fct_r for the rear wheel11R, and calculates a final target control force Fct_f′ for the front wheel11F and a final target control force Fct_r′ for the rear wheel11R by distributing the combined control force Fcta at a predetermined distribution ratio.

Specifically, the ECU30calculates the target control force Fct_f for the front wheel11F by applying road surface displacement related information (z1) at the predicted passing position pf1of the front wheel11F to Expression (8). The target control force Fct_f is hereinafter referred to as “first control force Fct_f”. The ECU30calculates the target control force Fct_r for the rear wheel11R by applying road surface displacement related information (z1) at the predicted passing position pr1of the rear wheel11R to Expression (9). The target control force Fct_r is hereinafter referred to as “second control force Fct_r”.

The ECU30calculates the combined control force Fcta based on Expression (10). The combined control force Fcta is a value obtained by adding together the first control force Fct_f and the second control force Fct_r.
Fcta=Fct_f+Fct_r(10)

The ECU30sets, as the final target control force Fct_f′ of the front wheel11F, a value obtained by multiplying the combined control force Fcta by a first ratio Ra (<1). The target control force Fct_f′ is hereinafter referred to as “first final target control force Fct_f′”. The ECU30sets, as the final target control force Fct_r′ of the rear wheel11R, a value obtained by multiplying the combined control force Fcta by a second ratio Rb (<1). The target control force Fct_r′ is hereinafter referred to as “second final target control force Fct_r′”.

The first ratio Ra and the second ratio Rb have a relationship represented by Expression (11).
Rb=1−Ra(11)

In this example, the performance of the front wheel active actuator17F is higher than the performance of the rear wheel active actuator17R. The performance of the active actuator herein includes output performance (magnitude of an output of the control force) and/or response performance (speed of an output of the control force relative to an input of the control command). In this example, the first ratio Ra is higher than the second ratio Rb (Ra>Rb).

If the performance of the front wheel active actuator17F is equal to the performance of the rear wheel active actuator17R, the first ratio Ra and the second ratio Rb may be set to the same value (that is, 0.5).

The configuration described above attains the following effects. At the time to inFIG.7, the road surface at the front wheel11F is convex, and therefore the first control force Fct_f is a downward control force. The road surface at the rear wheel11R is concave, and therefore the second control force Fct_r is an upward control force. In this situation, the ECU30calculates the combined control force Fcta by adding together the first control force Fct_f and the second control force Fct_r. The upward control force and the downward control force are canceled out, and as a result, the magnitude of the combined control force Fcta decreases. The ECU30distributes the combined control force Fcta to the front wheel11F and the rear wheel11R at the predetermined distribution ratio. Also at the time tb, the ECU30executes the same process. The upward control force and the downward control force are canceled out, and as a result, the magnitude of the combined control force Fcta decreases. Through this control, the possibility of unnecessary driving of the active actuators17can be reduced in the situation in which the center-of-gravity position10G of the vehicle10is not displaced in the vertical direction. The possibility of unnecessary energy consumption in the active actuators17can be reduced.

The first ratio Ra is higher than the second ratio Rb. A greater control force is distributed to the high-performance front wheel active actuator17F. The vibration of the sprung portion51can be reduced more effectively when the front wheel active actuator17F is driven.

Damping Control Routine

The CPU of the ECU30(“CPU” hereinafter refers to the CPU of the ECU30unless otherwise noted) executes a damping control routine illustrated in a flowchart ofFIG.8every time a predetermined period has elapsed. The CPU executes the damping control routine for each of the right wheels (11FR and11RR) and the left wheels (11FL and11RL).

The CPU executes a routine (not illustrated) every time a predetermined period has elapsed to acquire in advance preview reference data45in a preparatory z0ne from the cloud40and temporarily store the preview reference data45in the RAM. The preparatory z0ne has a start point at a front wheel predicted passing position pf1when the vehicle10reaches the end point of a previous preparatory z0ne, and has an end point at a position spaced away from the front wheel predicted passing position pf1by a predetermined preparatory distance along a traveling direction Td of the vehicle10. The preparatory distance is preset to a value sufficiently larger than the front wheel preview distance Lpf.

At a predetermined timing, the CPU starts a process from Step800ofFIG.8, and executes Step801to Step808in this order. Then, the CPU proceeds to Step895to temporarily terminate this routine.

Step801: The CPU determines current positions of the wheels11.

More specifically, the CPU determines (acquires) a current position of the vehicle10, a vehicle speed V1, and a traveling direction Td of the vehicle10from the positional information acquiring device31. The ROM of the ECU30prestores positional relationship data indicating relationships between a mounting position of the GNSS receiver in the vehicle10and the positions of the wheels11. The current position of the vehicle10that is acquired from the positional information acquiring device31corresponds to the mounting position of the GNSS receiver. Therefore, the CPU determines the current positions of the wheels11by referring to the current position of the vehicle10, the traveling direction Td of the vehicle10, and the positional relationship data.

Step802: The CPU determines predicted passing positions of the wheels11as follows.

The CPU determines a predicted path of the front wheel11F and a predicted path of the rear wheel11R. As described above, the predicted path of the front wheel11F is a path where the front wheel11F is predicted to move in the future, and the predicted path of the rear wheel11R is a path where the rear wheel11R is predicted to move in the future. For example, the CPU determines the predicted path of the front wheel11F based on the current positions of the wheels11, the traveling direction Td of the vehicle10, and the positional relationship data. For example, the CPU determines the predicted path of the rear wheel11R under the assumption that the rear wheel11R moves along the same path as that of the front wheel11F.

As described above, the CPU calculates a front wheel preview distance Lpfby multiplying the vehicle speed V1by the front wheel preview period tpf. The CPU determines, as a front wheel predicted passing position pf1, a position of the front wheel11F that advances from its current position by the front wheel preview distance Lpfalong the predicted path of the front wheel11F.

The CPU calculates a rear wheel preview distance Lprby multiplying the vehicle speed V1by the rear wheel preview period tpr. The CPU determines, as a rear wheel predicted passing position pr1, a position of the rear wheel11R that advances from its current position by the rear wheel preview distance Lpralong the predicted path of the rear wheel11R.

Step803: The CPU acquires road surface displacement related information (z1) at the front wheel predicted passing position pf1and road surface displacement related information (z1) at the rear wheel predicted passing position pr1from the RAM.

Step804: The CPU calculates a first control force Fct_f based on Expression (8) by using the road surface displacement related information (z1) at the front wheel predicted passing position pf1.

Step805: The CPU calculates a second control force Fct_r based on Expression (9) by using the road surface displacement related information (z1) at the rear wheel predicted passing position pr1.

Step806: The CPU calculates a combined control force Fcta based on Expression (10).

Step807: The CPU calculates a first final target control force Fct_f′ for the front wheel11F based on Expression (12). The CPU calculates a second final target control force Fct_r′ for the rear wheel11R based on Expression (13). Relationships of “Ra<1” and “Rb=1−Ra” hold.
Fct_f′=Ra×Fcta(12)
Fct_r′=Rb×Fcta(13)

Step808: The CPU transmits a control command containing the first final target control force Fct_f′ to the front wheel active actuator17F. Thus, the CPU controls the front wheel active actuator17F such that the front wheel active actuator17F generates a control force Fc_f that agrees with the first final target control force Fct_f′ in the front wheel11F at a timing when the front wheel11F passes through the predicted passing position pf1. The CPU transmits a control command containing the second final target control force Fct_r′ to the rear wheel active actuator17R. Thus, the CPU controls the rear wheel active actuator17R such that the rear wheel active actuator17R generates a control force Fc_r that agrees with the second final target control force Fct_r′ in the rear wheel11R at a timing when the rear wheel11R passes through the predicted passing position pr1.

As understood from the above, the damping control device20can reduce the possibility of unnecessary driving of the active actuators17in the situation in which the center-of-gravity position10G of the vehicle10is not displaced in the vertical direction. Thus, the possibility of unnecessary energy consumption in the active actuators17can be reduced.

To clearly describe the effects of this embodiment,FIG.7illustrates the example in which the wheelbase L of the vehicle10completely agrees with the half of the wavelength λ of the waveform of the road surface displacement. The configuration of this embodiment attains the effects also in situations other than that in the example ofFIG.7. For example, the upward control force and the downward control force are canceled out also in a situation in which the wheelbase L of the vehicle10does not completely agree with the half of the wavelength of the waveform of the road surface displacement. Therefore, the possibility of unnecessary driving of the active actuators17can be reduced. Thus, the possibility of unnecessary energy consumption in the active actuators17can be reduced as compared to the related-art device.

Second Embodiment

Next, damping control for the front wheels and the rear wheels according to a second embodiment is described with reference toFIG.9andFIG.10. In the following description, a suffix “_f” corresponds to the front wheels11F, and a suffix “_r” corresponds to the rear wheels11R. A suffix “_fr” corresponds to the right front wheel11FR, a suffix “_fl” corresponds to the left front wheel11FL, a suffix “_rr” corresponds to the right rear wheel11RR, and a suffix “_rl” corresponds to the left rear wheel11RL.

As illustrated inFIG.9, it is assumed that the vehicle10travels along a road90having irregularities. In this example, amplitudes A of waveforms of road surface displacements of the road90are equal on the right and left sides of the vehicle10.

As illustrated inFIG.10, the right front wheel11FR is in contact with a concave road surface, and the contact point of the right front wheel11FR is located at a valley (the lowest point) of the waveform of the road surface displacement. The right rear wheel11RR is in contact with a convex road surface, and the contact point of the right rear wheel11RR is located at a peak (the highest point) of the waveform of the road surface displacement. The left front wheel11FL is in contact with a convex road surface, and the contact point of the left front wheel11FL is located at a peak of the waveform of the road surface displacement. The left rear wheel11RL is in contact with a concave road surface, and the contact point of the left rear wheel11RL is located at a valley of the waveform of the road surface displacement. Thus, the waveform of the road surface displacement on the right side of the vehicle10and the waveform of the road surface displacement on the left side of the vehicle10have opposite phases.

In the situation illustrated inFIG.9andFIG.10, no roll displacement occurs in the vehicle10. When the active actuators17are controlled based on pieces of road surface displacement related information in this situation, the active actuators17are driven unnecessarily. Therefore, a problem arises in that unnecessary energy is consumed in the active actuators17.

The “situation in which waveform of road surface displacement on right side of vehicle10and waveform of road surface displacement on left side of vehicle10have opposite phases” as illustrated inFIG.9andFIG.10is hereinafter referred to as “first situation”. The “situation in which waveform of road surface displacement on right side of vehicle10and waveform of road surface displacement on left side of vehicle10have identical phases” is hereinafter referred to as “second situation”.

In view of the above, the ECU30of this embodiment calculates control forces adapted to the first situation and control forces adapted to the second situation by using road surface displacement related information of the right front wheel11FR, road surface displacement related information of the right rear wheel11RR, road surface displacement related information of the left front wheel11FL, and road surface displacement related information of the left rear wheel11RL. The ECU30calculates final target control forces for the right and left front wheels11and the right and left rear wheels11(“Fct_fr′”, “Fct_rr′”, “Fct_fl′”, and “Fct_rl′” described later) by using the control forces.

Specifically, the ECU30determines predicted passing positions of the wheels11as follows. The ECU30determines a predicted path of the right front wheel11FR and a predicted path of the left front wheel11FL. As described above, the predicted path of the right front wheel11FR is a path where the right front wheel11FR is predicted to move in the future, and the predicted path of the left front wheel11FL is a path where the left front wheel11FL is predicted to move in the future. For example, the ECU30determines the predicted path of the right front wheel11FR and the predicted path of the left front wheel11FL based on current positions of the wheels11, a traveling direction Td of the vehicle10, and the positional relationship data. The ECU30determines a predicted path of the right rear wheel11RR under the assumption that the right rear wheel11RR moves along the same path as that of the right front wheel11FR. The ECU30determines a predicted path of the left rear wheel11RL under the assumption that the left rear wheel11RL moves along the same path as that of the left front wheel11FL.

The ECU30determines, as a predicted passing position pfr1of the right front wheel11FR, a position of the right front wheel11FR that advances from its current position by a front wheel preview distance Lpfalong the predicted path of the right front wheel11FR. The ECU30determines, as a predicted passing position pfl1of the left front wheel11FL, a position of the left front wheel11FL that advances from its current position by the front wheel preview distance Lpfalong the predicted path of the left front wheel11FL.

The ECU30determines, as a predicted passing position prr1of the right rear wheel11RR, a position of the right rear wheel11RR that advances from its current position by a rear wheel preview distance Lpralong the predicted path of the right rear wheel11RR. The ECU30determines, as a predicted passing position prl1of the left rear wheel11RL, a position of the left rear wheel11RL that advances from its current position by the rear wheel preview distance Lpralong the predicted path of the left rear wheel11RL.

The ECU30acquires road surface displacement related information (z1_fr) at the predicted passing position pfr1of the right front wheel11FR, road surface displacement related information (z1_fl) at the predicted passing position pfl1of the left front wheel11FL, road surface displacement related information (z1_rr) at the predicted passing position prr1of the right rear wheel11RR, and road surface displacement related information (z1_rl) at the predicted passing position prl1of the left rear wheel11RL. In this example, each piece of road surface displacement related information is an unsprung displacement z1.

The road surface displacement related information may include at least one of a road surface displacement z0, a road surface displacement speed dz0, the unsprung displacement z1, and an unsprung speed dz1.

In the following description, various control forces are calculated by using the unsprung displacements z1(that is, based on Expression (7)). However, the calculation of the control forces is not limited to that in this example. For example, each control force may be calculated by using the unsprung displacement z1and the unsprung speed dz1(for example, based on Expression (6)). As described above, each control force may be calculated by using the road surface displacement z0and/or the road surface displacement speed dz0in place of or in addition to the unsprung displacement z1and the unsprung speed dz1.

The ECU30calculates a control force Fcd adapted to the first situation based on Expression (14). The control force Fcd is hereinafter referred to as “first-situation control force Fcd”. In Expression (14), K1_frepresents a spring rate of the right front wheel suspension13FR and the left front wheel suspension13FL, and K1_rrepresents a spring rate of the right rear wheel suspension13RR and the left rear wheel suspension13RL. The spring rates K1_fand K1_rdiffer from each other.
Fcd=(z1_fl−z1_fr)K1_f+(z1_rl−z1_rr)K1_r(14)

The ECU30calculates a control force Fan_f for the right and left front wheels11FR and11FL adapted to the first situation and a control force Fan_r for the right and left rear wheels11RR and11RL adapted to the first situation by distributing the first-situation control force Fcd at a predetermined distribution ratio. The control force Fan_f is hereinafter referred to as “first front wheel control force Fan_f”. The control force Fan_r is hereinafter referred to as “first rear wheel control force Fan_r”.

Specifically, the ECU30calculates the first front wheel control force Fan_f based on Expression (15). The ECU30calculates the first rear wheel control force Fan_r based on Expression (16). The symbols “αan_f” and “αan_r” represent gains. The sum of αan_f and αan_r is a predetermined value αan (that is, αan_f+αan_r=αan).
Fan_f=αan_f×Fcd(15)
Fan_r=αan_r×Fcd(16)

In this example, the performance of each front wheel active actuator17F is higher than the performance of each rear wheel active actuator17R. In this case, αan_f is larger than αan_r (αan_f>αan_r). If the performance of each front wheel active actuator17F is equal to the performance of each rear wheel active actuator17R, αan_f and αan_r may be set to the same value.

In Expression (14), the first term on the right-hand side represents a control force adapted to a situation in which the waveform of the road surface displacement at the right front wheel11FR and the waveform of the road surface displacement at the left front wheel11FL have opposite phases. In other words, the first term on the right-hand side is a value obtained by multiplying components of the road surface displacements in opposite phases at the front wheels11F by the spring rate K1_f. The second term on the right-hand side represents a control force adapted to a situation in which the waveform of the road surface displacement at the right rear wheel11RR and the waveform of the road surface displacement at the left rear wheel11RL have opposite phases. In other words, the second term on the right-hand side is a value obtained by multiplying components of the road surface displacements in opposite phases at the rear wheels11R by the spring rate K1_r. Since the first-situation control force Fcd is a value obtained by adding together the first term and the second term, the value of the first term and the value of the second term are canceled out in, for example, the situation illustrated inFIG.9andFIG.10. As a result, the first-situation control force Fcd decreases. That is, the possibility of unnecessary driving of the active actuators17can be reduced in the situation in which no roll displacement occurs. Thus, the possibility of unnecessary energy consumption in the active actuators17can be reduced.

The gain αan_f is larger than the gain αan_r. Greater control forces are distributed to the high-performance front wheel active actuators17F. Thus, the vibration of the sprung portion51can be reduced more effectively when the active actuators17are driven.

The ECU30calculates a control force Fin_f for the right and left front wheels11FR and11FL adapted to the second situation based on Expression (17). The ECU30calculates a control force Fin_r for the right and left rear wheels11RR and11RL adapted to the second situation based on Expression (18). The control force Fin_f is hereinafter referred to as “second front wheel control force Fin_f”. The control force Fin_r is hereinafter referred to as “second rear wheel control force Fin_r”.
Fin_f=αin_f(z1_fl+z1_fr)K2_f(17)
Fin_r=αin_r(z1_rl+z1_rr)K2_r(18)

The symbols “αin_f” and “αin_r” represent gains. Since the performance of each front wheel active actuator17F is higher than the performance of each rear wheel active actuator17R, αin_f is larger than αin_r (αin_f>αin_r). If the performance of each front wheel active actuator17F is equal to the performance of each rear wheel active actuator17R, αin_f and αin_r may be set to the same value.

The symbol “K2_f” represents a spring rate of the right front wheel suspension13FR and the left front wheel suspension13FL. The symbol “K2_r” represents a spring rate of the right rear wheel suspension13RR and the left rear wheel suspension13RL. The spring rates K2_fand K2_rdiffer from each other. The spring rates applied to the first situation differ from the spring rates applied to the second situation. Thus, K1_fin Expression (14) differs from K2_fin Expression (17), and K1_rin Expression (14) differs from K2_rin Expression (18).

The second front wheel control force Fin_f is a control force adapted to a situation in which the waveform of the road surface displacement at the right front wheel11FR and the waveform of the road surface displacement at the left front wheel11FL have identical phases. In other words, the second front wheel control force Fin_f is a value obtained by multiplying components of the road surface displacements in identical phases at the front wheels11F by the spring rate K2_fand the gain αin_f. The second rear wheel control force Fin_r is a control force adapted to a situation in which the waveform of the road surface displacement at the right rear wheel11RR and the waveform of the road surface displacement at the left rear wheel11RL have identical phases. In other words, the second rear wheel control force Fin_r is a value obtained by multiplying components of the road surface displacements in identical phases at the rear wheels11R by the spring rate K2_rand the gain αin_r.

The ECU30calculates a final target control force Fct_fl′ of the left front wheel11FL based on Expression (19). The ECU30calculates a final target control force Fct_fr′ of the right front wheel11FR based on Expression (20). The ECU30calculates a final target control force Fct_rl′ of the left rear wheel11RL based on Expression (21). The ECU30calculates a final target control force Fct_rr′ of the right rear wheel11RR based on Expression (22). The target control force Fct_fl′ is hereinafter referred to as “first final target control force Fct_fl′”. The target control force Fct_fr′ is hereinafter referred to as “second final target control force Fct_fr′”. The target control force Fct_rl′ is hereinafter referred to as “third final target control force Fct_rl′”. The target control force Fct_rr′ is hereinafter referred to as “fourth final target control force Fct_rr′”.
Fct_fl′=(Fin_f+Fan_f)/2  (19)
Fct_fr′=(Fin_f−Fan_f)/2  (20)
Fct_rl′=(Fin_r+Fan_r)/2  (21)
Fct_rr′=(Fin_r−Fan_r)/2  (22)

The first final target control force Fct_fl′ is a half of the sum of the second front wheel control force Fin_f and the first front wheel control force Fan_f. The second final target control force Fct_fr′ is a half of a difference between the second front wheel control force Fin_f and the first front wheel control force Fan_f. The third final target control force Fct_rl′ is a half of the sum of the second rear wheel control force Fin_r and the first rear wheel control force Fan_r. The fourth final target control force Fct_rr′ is a half of a difference between the second rear wheel control force Fin_r and the first rear wheel control force Fan_r. Therefore, a predetermined proportion (½ in this example) of the sum of the control force adapted to the first situation and the control force adapted to the second situation (Fan_f+Fin_f or Fan_r+Fin_r) and a predetermined proportion (½ in this example) of the difference between the control force adapted to the first situation and the control force adapted to the second situation (Fan_f−Fin_f or Fan_r−Fin_r) are distributed to the right and left front wheels11F and to the right and left rear wheels11R. According to this configuration, the active actuators17of the right and left front and rear wheels11FR to11RL can be controlled by appropriate control forces in consideration of both the components of the road surface displacements in opposite phases and the components of the road surface displacements in identical phases.

Damping Control Routine

The CPU of the ECU30executes a damping control routine illustrated inFIG.11in place of the flowchart ofFIG.8every time a predetermined period has elapsed.

At a predetermined timing, the CPU starts a process from Step1100ofFIG.11, and executes Step1101to Step1107in this order. Then, the CPU proceeds to Step1195to temporarily terminate this routine.

Step1101: The CPU determines current positions of the wheels11.

Step1102: The CPU determines predicted passing positions of the wheels11as described above.

Step1103: The CPU acquires, from the RAM, road surface displacement related information (z1_fr) at the predicted passing position pfr1of the right front wheel11FR, road surface displacement related information (z1_fl) at the predicted passing position pfl1of the left front wheel11FL, road surface displacement related information (z1_rr) at the predicted passing position prr1of the right rear wheel11RR, and road surface displacement related information (z1_rl) at the predicted passing position prl1of the left rear wheel11RL.

Step1104: The CPU calculates a first-situation control force Fcd based on Expression (14). The CPU calculates a first front wheel control force Fan_f based on Expression (15) and a first rear wheel control force Fan_r based on Expression (16).

Step1105: The CPU calculates a second front wheel control force Fin_f based on Expression (17) and a second rear wheel control force Fin_r based on Expression (18).

Step1106: The CPU calculates a first final target control force Fct_fl′ based on Expression (19), a second final target control force Fct_fr′ based on Expression (20), a third final target control force Fct_rl′ based on Expression (21), and a fourth final target control force Fct_rr′ based on Expression (22).

Step1107: The CPU transmits a control command containing the first final target control force Fct_fl′ to the left front wheel active actuator17FL. Thus, the CPU controls the left front wheel active actuator17FL such that the left front wheel active actuator17FL generates a control force Fc_fl that agrees with the first final target control force Fct_fl′ in the left front wheel11FL at a timing when the left front wheel11FL passes through the predicted passing position pf11.

The CPU transmits a control command containing the second final target control force Fct_fr′ to the right front wheel active actuator17FR. Thus, the CPU controls the right front wheel active actuator17FR such that the right front wheel active actuator17FR generates a control force Fc_fr that agrees with the second final target control force Fct_fr′ in the right front wheel11FR at a timing when the right front wheel11FR passes through the predicted passing position pfr1.

The CPU transmits a control command containing the third final target control force Fct_rl′ to the left rear wheel active actuator17RL. Thus, the CPU controls the left rear wheel active actuator17RL such that the left rear wheel active actuator17RL generates a control force Fc_rl that agrees with the third final target control force Fct_rl′ in the left rear wheel11RL at a timing when the left rear wheel11RL passes through the predicted passing position prl1.

The CPU transmits a control command containing the fourth final target control force Fct_rr′ to the right rear wheel active actuator17RR. Thus, the CPU controls the right rear wheel active actuator17RR such that the right rear wheel active actuator17RR generates a control force Fc_rr that agrees with the fourth final target control force Fct_rr′ in the right rear wheel11RR at a timing when the right rear wheel11RR passes through the predicted passing position prr1.

As understood from the above, the damping control device20calculates the final target control forces (Fct_fr′, Fct_fl′, Fct_rr′, and Fct_rl′) based on the control force adapted to the first situation (Fan_f or Fan_r) and the control force adapted to the second situation (Fin_f or Fin_r) for the right and left front wheels and the right and left rear wheels. Thus, the possibility of unnecessary driving of the active actuators17can be reduced in, for example, the situation in which no roll displacement occurs in the vehicle10illustrated inFIG.9andFIG.10. The possibility of unnecessary energy consumption in the active actuators17can be reduced.

In actuality, the waveform of the road surface displacement on the right side of the vehicle10and the waveform of the road surface displacement on the left side of the vehicle10do not completely have opposite phases or identical phases. In many cases, those waveforms include both the components in opposite phases and the components in identical phases. According to the configuration described above, the damping control device20can control the active actuators17by appropriate control forces in consideration of both the components in opposite phases and the components in identical phases. Thus, the vibration of the sprung portion51of the vehicle10can be reduced by the appropriate control forces while reducing the possibility of unnecessary driving of the active actuators17.

The present disclosure is not limited to the embodiments described above, and various modified examples may be adopted within the scope of the present disclosure.

Modified Example 1

The ECU30may acquire the unsprung displacement z1(tp+tpf) as follows. First, the ECU30transmits the predicted passing position pf1to the cloud40. The cloud40acquires the unsprung displacement z1(tp+tpf) linked to positional information indicating the predicted passing position pf1based on the predicted passing position pf1and the preview reference data45. The cloud40transmits the unsprung displacement z1(tp+tpf) to the ECU30.

Modified Example 2

The preview reference data45need not be stored in the storage device44in the cloud40, but may be stored in the storage device30a.

Modified Example 3

The road surface displacement related information may be acquired by the preview sensor33provided in the vehicle10. The ECU30acquires the road surface displacement related information from the preview sensor33. For example, the ECU30acquires the road surface displacement z0at the predicted passing position based on the road surface displacement z0acquired by the preview sensor33.

Modified Example 4

Pieces of road surface displacement related information detected by various sensors provided on the front wheels11F may be used as pieces of road surface displacement related information for the preview damping control on the rear wheels11R. For example, vertical acceleration sensors may be provided on the vehicle body10a(sprung portion51) at positions corresponding to the positions of the right front wheel11FR and the left front wheel11FL, respectively. Stroke sensors may be provided on the right front wheel suspension13FR and the left front wheel suspension13FL, respectively. A sprung acceleration detected by the vertical acceleration sensor provided on the front wheel11F is hereinafter represented by “ddz2_f”. A stroke detected by the stroke sensor provided on the front wheel11F is hereinafter represented by “H_f”.

The ECU30determines a sprung displacement z2_f based on the sprung acceleration ddz2_f, and calculates an unsprung displacement z1_f by subtracting the stroke H_f from the sprung displacement z2_f. The ECU30saves the unsprung displacement z1_f in the RAM as an unsprung displacement ahead of the rear wheel11R by linking the unsprung displacement to information on a position of the front wheel11F when the sprung acceleration ddz2_f is detected. The ECU30may calculate various control forces described above by acquiring an unsprung displacement z1_f at a rear wheel predicted passing position pr1from among the unsprung displacements z1_f ahead of the rear wheel11R that are saved in the RAM. In this manner, the vertical acceleration sensors and the stroke sensors provided on the front wheels11F may function as devices configured to acquire pieces of road surface displacement related information ahead of the right and left rear wheels11RR and11RL.

Modified Example 5

The suspensions13FR to13RL may be any type of suspension as long as the wheels11FR to11RL are allowed to be displaced in the vertical direction relative to the vehicle body10a. The suspension springs16FR to16RL may be arbitrary springs such as compression coil springs or air springs.

Modified Example 6

In the embodiments described above, the active actuator17is used as the control force generating device, but the control force generating device is not limited to the active actuator17. That is, the control force generating device may be an actuator configured to adjustably generate a vertical control force for damping the sprung portion51based on a control command containing the target control force.

The control force generating device may be an active stabilizer device (not illustrated). The active stabilizer device includes a front wheel active stabilizer and a rear wheel active stabilizer. When the front wheel active stabilizer generates a vertical control force between the sprung portion51and the unsprung portion50corresponding to the left front wheel11FL (left front wheel control force), the front wheel active stabilizer generates a control force in a direction opposite to the direction of the left front wheel control force between the sprung portion51and the unsprung portion50corresponding to the right front wheel11FR (right front wheel control force). Similarly, when the rear wheel active stabilizer generates a vertical control force between the sprung portion51and the unsprung portion50corresponding to the left rear wheel11RL (left rear wheel control force), the rear wheel active stabilizer generates a control force in a direction opposite to the direction of the left rear wheel control force between the sprung portion51and the unsprung portion50corresponding to the right rear wheel11RR (right rear wheel control force). The structure of the active stabilizer device is well known, and is incorporated herein by reference to Japanese Unexamined Patent Application Publication No. 2009-96366 (JP 2009-96366 A). The active stabilizer device may include at least one of the front wheel active stabilizer and the rear wheel active stabilizer.

The control force generating device may be a device configured to generate vertical control forces Fc based on geometry of the suspensions13FR to13RL by increasing or reducing braking or driving forces on the wheels11of the vehicle10. The structure of this device is well known, and is incorporated herein by reference to, for example, Japanese Unexamined Patent Application Publication No. 2016-107778 (JP 2016-107778 A). Using a well-known method, the ECU30calculates braking or driving forces for generating control forces Fc corresponding to target control forces Fct. The device includes driving devices (for example, in-wheel motors) configured to apply driving forces to the wheels11, and braking devices (brakes) configured to apply braking forces to the wheels11. The driving device may be a motor or an engine configured to apply driving forces to the front wheels, the rear wheels, or the four wheels. The control force generating device may include at least one of the driving device and the braking device.

The control force generating device may be each of the adjustable shock absorbers15FR to15RL. In this case, the ECU30controls the damping coefficients C of the shock absorbers15FR to15RL to change damping forces of the shock absorbers15FR to15RL by values corresponding to target control forces Fct.

Modified Example 7

Regarding the second embodiment, the ECU30may control the control force generating device by using only the first front wheel control force Fan_f and the first rear wheel control force Fan_r. Also in this configuration, the possibility of unnecessary driving of the control force generating device can be reduced in the situation in which no roll displacement occurs in the vehicle10illustrated inFIG.9andFIG.10. For example, this configuration may be adopted when the control force generating device is the active stabilizer device.

In this configuration, the ECU30calculates the control force Fcd adapted to the first situation based on Expression (14). The ECU30calculates the first front wheel control force Fan_f based on Expression (15) and the first rear wheel control force Fan_r based on Expression (16). The ECU30converts the first front wheel control force Fan_f into a control amount of the front wheel active stabilizer, and controls the front wheel active stabilizer based on the control amount. The ECU30converts the first rear wheel control force Fan_r into a control amount of the rear wheel active stabilizer, and controls the rear wheel active stabilizer based on the control amount.

Modified Example 8

The configurations of the first and second embodiments may be applied to damping control for generating control forces for the right and left front and rear wheels based on pieces of road surface displacement related information acquired by using, for example, “vertical acceleration sensors (sprung acceleration sensors) and stroke sensors” provided on the right and left front and rear wheels. Further, the configurations of the first and second embodiments may be applied to feedback damping control (skyhook control) for generating control forces for the right and left front and rear wheels based on pieces of information acquired by using vertical acceleration sensors (sprung acceleration sensors) provided on the right and left front and rear wheels.