JP2010163099A - Estimation method for stiffness of tire, and vehicular suspension system which can estimate stiffness of tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an estimation method for stiffness of a tire based on strength of object vibration as one of vibration of a vehicle body and relative vibration between the vehicle body and a wheel, and to provide a vehicular suspension system which can execute the method. <P>SOLUTION: The estimation method includes: a step (S12) for generating a specific approaching/separating force f<SB>0</SB>in a device disposed between the wheel and the vehicle body; a step (S19) for detecting the strength ΔVu of the object vibration generated by the approaching/separating force; and a step (S20) for estimating the stiffness K<SB>T</SB>of the tire by using a transfer function indicating a relation between the approaching/separating force and the strength of object vibration, based on the detected vibration strength. The transfer function has the stiffness of the tire as a coefficient, the relation between the approaching/separating force and the strength of object vibration is changed along with change in value of the coefficient, and the value of the coefficient in which the strength of object vibration when the approaching/separating force in the transfer function is set to be the specific approaching/separating force becomes the detected object vibration strength, is estimated as the stiffness of the tire. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for estimating the spring constant of a tire based on the intensity of vertical vibration generated in a vehicle, and a vehicle suspension system capable of estimating the spring constant of a tire by the method.

  The tire air pressure is likely to change due to deterioration over time, puncture, and the like, and if the tire air pressure decreases, there is a possibility of causing a reduction in fuel consumption, a deterioration in riding comfort, and the like. For this reason, it is desirable to monitor the decrease in tire air pressure, and in the following patent document, in order to monitor the decrease in tire air pressure, the vibration intensity generated in the vehicle, that is, the intensity of vibration, for example, A technique relating to a method for estimating a spring constant of a tire based on vibration amplitude, vibration vertical speed, and the like is described.

JP 7-98268 A

  According to the method for estimating the spring constant of a tire described in the above-mentioned patent document, the tire is based on the speed of vibration in the vertical direction of the vehicle body, so-called absolute speed on the spring, and the speed of vibration in the vertical direction of the wheel, so-called unsprung absolute speed. The spring constant is estimated. That is, the spring constant of the tire is estimated based on the two types of vibration intensities, and it is necessary to provide a plurality of types of sensors in order to obtain the two types of vibration intensities. Since the sensor for detecting the intensity of vibration is expensive, it is desirable that the number of sensors mounted on the vehicle is as small as possible. Moreover, since such a sensor is delicate, it is not desirable to mount it in the unsprung part. The present invention has been made in view of such circumstances, and a method of estimating the spring constant of a tire without mounting a sensor for detecting the intensity of vibration in the lower part of the spring, and the method can be executed. It is an object to provide a vehicle suspension system.

  In order to solve the above-described problem, the tire spring constant estimation method of the present invention includes a wheel having a tire, a vehicle body, a suspension spring, and a force in a direction in which the vehicle body and the wheel are moved toward and away from each other by the force of an electromagnetic motor (hereinafter, referred to as a tire spring constant estimation method). , In a vehicle provided with an approaching / separating force generating device that controllably generates an approaching / separating force), the approaching / separating force generating device generates an approaching / separating force having a specific magnitude. Generation step, vibration intensity detection step for detecting the intensity of the target vibration which is one of the relative vibration between the wheel and the vehicle body caused by the approaching / separating force and the vibration of the vehicle body, and the target vibration detected in the vibration intensity detection step A tire spring constant estimating step for estimating a spring constant of the tire using a transfer function representing a relationship between the approaching / separating force and the intensity of the target vibration based on the strength of the tire. An estimation method, the transfer function of which has a spring constant of the tire as a coefficient, and the relationship between the approaching / separating force and the intensity of the target vibration is changed by changing the value of the coefficient. In the tire spring constant estimating step, the strength of the target vibration detected in the vibration strength detecting step is the strength of the target vibration when the approaching / separating force in the transfer function is the approaching / separating force having the specific magnitude. The value of the above coefficient is estimated as a tire spring constant.

  In order to solve the above-described problems, a vehicle suspension system according to the present invention includes a suspension spring, an approaching / separating force generating device that generates an approaching / separating force in a controllable manner, and a vibration intensity detecting device that detects the intensity of target vibration. And the approaching / separating force and the target vibration based on the specific vibration intensity detected by the vibration intensity detecting device when the approaching / separating force generating device generates the approaching / separating force having a specific magnitude. A tire spring constant estimating device for estimating a tire spring constant using a transfer function representing a relationship with the strength of the tire, wherein the transfer function has the tire spring constant as a coefficient The relationship between the approaching / separating force and the intensity of the target vibration is changed by changing the coefficient value, and the tire spring constant estimation device The intensity of the target vibration when between force is a displacement force of the specific size is configured to estimate the value of the coefficient such that the specific time vibration intensity as the spring constant of the tire.

  In the tire spring constant estimation method of the present invention, it is possible to estimate the tire spring constant based on the intensity of vibration of the vehicle body and the relative vibration of the vehicle body and the wheel. Therefore, according to the tire spring constant estimation method of the present invention, it is possible to estimate the tire spring constant without mounting a sensor for detecting the vibration intensity in the lower part of the spring. In the vehicle suspension system of the present invention, for example, a spring constant of a tire can be estimated by providing a sprung vertical acceleration sensor or a stroke sensor. Therefore, according to the system of the present invention, it is possible to estimate the spring constant of the tire without mounting a sensor in the unsprung portion.

Aspects of the Invention

  In the following, some aspects of the invention that can be claimed in the present application (hereinafter sometimes referred to as “claimable invention”) will be exemplified and described. As with the claims, each aspect is divided into sections, each section is numbered, and is described in a form that cites the numbers of other sections as necessary. This is merely for the purpose of facilitating the understanding of the claimable inventions, and is not intended to limit the combinations of the constituent elements constituting those inventions to those described in the following sections. In other words, the claimable invention should be construed in consideration of the description accompanying each section, the description of the embodiments, etc., and as long as the interpretation is followed, another aspect is added to the form of each section. In addition, an aspect in which constituent elements are deleted from the aspect of each item can be an aspect of the claimable invention.

  In each of the following items, the item (1) corresponds to the item 1, and the technical feature described in the item (2) is added to the item 1, the item 1, the item (3) ) Added with the technical features described in (3), (4) added in (4), and (4) added in (7) and (8). These correspond to claim 5 respectively.

(1) (a) a wheel having a tire, (b) a vehicle body, (c) a suspension spring disposed between the wheel and the vehicle body, and (d) disposed in parallel with the suspension spring. And an approaching / separating force generating device that generates an approaching / separating force that is a force in a direction for approaching / separating the wheel and the vehicle body based on a force generated by the electromagnetic motor. In a vehicle, a tire spring constant estimation method for estimating a spring constant of the tire,
A specific approaching / separating force generating step of operating the electromagnetic motor so that the approaching / separating force generating device generates an approaching / separating force of a specific magnitude;
A vibration intensity detection step of detecting a target vibration intensity which is one of a relative vibration between the wheel and the vehicle body generated by the approaching / separating force and a vibration of the vehicle body;
Based on the intensity of the target vibration detected in the vibration intensity detecting step, the tire uses the transfer function representing the relationship between the approaching / separating force generated by the approaching / separating force generating device and the intensity of the target vibration. Including a tire spring constant estimating step for estimating a spring constant of
The transfer function has a tire spring constant as a coefficient, and is set so that the relationship between the approaching / separating force and the intensity of the target vibration is changed by changing the value of the coefficient,
The tire spring constant estimation step includes
When the approaching / separating force in the transfer function is the approaching / separating force having the specific magnitude, the strength of the target vibration is the strength of the target vibration detected in the vibration strength detecting step. A tire spring constant estimating method, which is a step of estimating a value as a spring constant of the tire.

  Tire pressure is likely to change due to deterioration over time, puncture, etc. If the tire air pressure decreases, there is a risk of reducing fuel consumption and riding comfort. Is desirable. It would be convenient to be able to estimate the tire's spring constant in order to monitor the decrease in tire air pressure. In other words, it indicates the strength of vibration generated in the vehicle, in other words, indicating the strength of vibration, for example, the amplitude of vibration, A method for estimating the spring constant of a tire based on the vertical speed or the like has been studied. There are two or more types of methods for estimating the tire spring constant currently under consideration, such as the speed of vibration in the vertical direction of the vehicle body, so-called absolute speed on the spring, the speed of vibration in the vertical direction of the wheel, so-called unsprung absolute speed, etc. The spring constant of the tire is estimated based on the vibration intensity of the tire. In order to acquire two or more types of vibration intensities, it is necessary to provide a plurality of types of sensors. However, since the sensor for detecting the intensity of vibration is expensive, it is desirable that the number mounted on the vehicle is as small as possible. In addition, since such a sensor is delicate, it is not desirable to be mounted on an unsprung portion with a lot of dust or stepping stones.

  In the tire spring constant estimation method described in this section, it is possible to estimate the tire spring constant based on the vibration intensity of either the vibration of the vehicle body or the relative vibration of the vehicle body and the wheel. According to the tire spring constant estimation method described in the paragraph, it is possible to estimate the tire spring constant based on one type of vibration intensity without mounting a sensor for detecting the vibration intensity in the lower part of the spring. It becomes.

  In the “tire spring constant estimation step” described in this section, the vibration strength detected in the vibration strength detection step is input to the transfer function to calculate the coefficient of the transfer function as the tire spring constant. The calculated coefficient may be estimated as the tire spring constant, and the strength of the target vibration and the tire spring when the approaching / separating force in the transfer function is the approaching / separating force of the specific magnitude A relationship with a coefficient as a constant may be set in advance, and the tire spring constant may be estimated according to the relationship. The “transfer function” described in this section is a function for outputting the approaching / separating force input to the vehicle body and the wheel as the intensity of the target vibration, for example, by the ratio of the output Laplace transform to the input Laplace transform. A function that is defined.

(2) The target vibration is vibration of the vehicle body,
The tire spring constant estimation method according to item (1), wherein the vibration intensity detection step is a step of detecting a maximum speed of vertical vibration of the vehicle body.

(3) The target vibration is a relative vibration between the wheel and the vehicle body,
The tire spring constant estimation method according to item (1), wherein the vibration intensity detection step is a step of detecting a maximum amplitude of relative vibration between the wheel and the vehicle body.

  In the tire spring constant estimation methods described in the above two terms, the target vibration and the intensity of the target vibration are specifically limited. In the estimation method described in the former section, for example, a sensor capable of detecting the vibration intensity in the vertical direction of the sprung portion, specifically, a sprung acceleration sensor is provided, and the sprung vertical acceleration detected by the sensor. It is possible to detect the intensity of the target vibration. In the estimation method described in the latter section, for example, if a sensor capable of detecting the intensity of relative vibration between the vehicle body and the wheel, for example, a stroke sensor, is provided, the intensity of the target vibration can be detected. Become. Therefore, according to the estimation methods described in the above two terms, it is possible to estimate the tire spring constant without mounting a sensor for detecting the vibration intensity in the lower part of the spring such as a wheel.

(4) a suspension spring disposed between the wheel having the tire and the vehicle body;
An approaching / separating mechanism that is arranged in parallel with the suspension spring, has an electromagnetic motor, and generates an approaching / separating force that is a force in a direction for approaching / separating the wheel and the vehicle body based on the force generated by the electromagnetic motor. A force generator,
A vehicle suspension system comprising a vibration intensity detection device that detects the intensity of a target vibration that is one of a relative vibration between a wheel and a vehicle body and a vibration of the vehicle body,
The vehicle suspension system is
Generation of the approaching / separating force based on a specific vibration intensity detected by the vibration intensity detecting device when the approaching / separating force generating apparatus generates a specific approaching / separating force. A tire spring constant estimating device for estimating a spring constant of the tire using a transfer function representing a relationship between the approaching / separating force generated by the device and the intensity of the target vibration;
The transfer function has a tire spring constant as a coefficient, and is set so that the relationship between the approaching / separating force and the intensity of the target vibration is changed by changing the value of the coefficient,
The tire spring constant estimating device is
The value of the coefficient is estimated as a tire spring constant so that the target vibration strength when the approaching / separating force in the transfer function is the approaching / separating force of the specific magnitude is the specific-time vibration strength. A suspension system for a vehicle configured to be.

  The vehicle suspension system described in this section relates to a system for realizing the tire spring constant estimation method of the present invention. The configuration of the “approaching / separating force generator” described in this section is not particularly limited, and includes, for example, a vehicle body side unit connected to the vehicle body and a wheel side unit connected to the wheel. The two units move relative to each other with the approach and separation of the wheels and can be expanded and contracted. Based on the force generated by the electromagnetic motor, a force is generated in the direction to move the two units relative to each other. The configuration may be such that the force acts as an approaching / separating force. That is, a so-called electromagnetic shock absorber may be employed as the approaching / separating force generator. Also, an elastic body connected to one of the vehicle body and the wheel and an actuator that deforms the elastic body, and a force generated by the actuator is applied to the elastic body and the force is generated as an approaching / separating force. It may be. That is, the approaching / separating force generating device can be a constituent element of a so-called left and right independent stabilizer device.

(5) The target vibration is vibration of a vehicle body,
The vehicle suspension system according to item (4), wherein the target vibration detection device detects a maximum speed in a vertical direction of vibration of the vehicle body.

(6) The target vibration is a relative vibration between the wheel and the vehicle body,
The vehicle suspension system according to (4), wherein the target vibration detection device detects a maximum amplitude of relative vibration between the wheel and the vehicle body.

  In the vehicle suspension system described in the above two items, the technical features described in the above item (2) or (3) can be applied.

(7) The vehicle suspension system is
Using the tire spring constant estimated by the tire spring constant estimating device from the intensity of the target vibration detected by the target vibration detecting device, the wheel vertical speed that is the vertical speed of the wheel vibration is obtained. The vehicle suspension system according to any one of (4) to (6), comprising a wheel vertical speed estimation device for estimation.

  In the suspension system described in this section, the unsprung absolute speed can be estimated using a so-called observer. Although the observer will be described in detail later, information that is not detected by a sensor or the like is estimated from other information. Therefore, by using the observer, for example, the unsprung absolute speed can be estimated from the sprung absolute speed. However, in order to accurately estimate the unsprung absolute speed using an observer, the specifications of the vehicle, specifically, the spring constant of the suspension spring, the sprung mass of the vehicle, the unsprung mass, and the tire spring constant. An accurate numerical value such as is necessary. Many of the numerical values of these vehicles are not so different from the values at the time of shipment from the factory, but the numerical values of the spring constants of the tires are likely to change due to deterioration over time. For this reason, there is a possibility that the unsprung absolute speed cannot be accurately estimated unless an accurate value of the tire spring constant is acquired. Therefore, in the system described in this section, the effect of estimating the tire spring constant can be fully utilized.

(8) The vehicle suspension system is
An approaching / separating force control device for controlling an approaching / separating force generated by the approaching / separating force generating device by controlling an operation of the electromagnetic motor included in the approaching / separating force generating device;
The approaching / separating force control device is
The approaching / separating force is set so that at least a part of the approaching / separating force generated by the approaching / separating force generating device is a damping force having a magnitude corresponding to the wheel vertical direction speed estimated by the wheel vertical direction speed estimating device. The vehicle suspension system according to (7), further including a wheel vibration damping control unit that controls the vehicle.

  In the suspension system described in this section, it is possible to execute control based on a so-called pseudo ground hook damper theory that generates a damping force having a magnitude corresponding to the unsprung absolute speed. The “approaching / separating force control device” described in this section not only controls the approaching / separating force so that the approaching / separating force becomes a damping force against the vibration of the unsprung part, but also at least a part of the approaching / separating force of the upper part of the spring. The approaching / separating force may be controlled so as to be a damping force against vibration, so that at least a part of the approaching / separating force becomes a posture change suppressing force that suppresses a posture change of the vehicle body, for example, a roll, a pitch, etc. of the vehicle body. The approaching / separating force may be controlled. When a plurality of controls are executed in parallel in this way, for example, the approach / separation force generation device should generate the sum of the components of the approach / separation force to be generated in each of the plurality of controls. Power.

1 is a schematic diagram showing the overall configuration of a vehicle suspension system that is an embodiment of the claimable invention. It is a schematic diagram which shows the suspension apparatus with which the suspension system for vehicles of FIG. 1 is provided. It is a schematic sectional drawing which shows the electromagnetic actuator with which a suspension apparatus is provided. It is a block diagram of the observer which estimates unsprung absolute speed from unsprung absolute speed. It is a chart which shows roughly change with time passage of approaching / separating force and sprung absolute speed at the time of generating approaching / separating force of a specific magnitude. It is a graph which shows the relationship between the spring constant of a tire, and the intensity | strength of the vibration of a vehicle body. It is a flowchart which shows an actuator control program. It is a flowchart which shows a tire spring constant estimation control execution program. It is a block diagram which shows the function of the control apparatus which manages control of the suspension system for vehicles. It is a chart which shows roughly change with respect to passage of time of relative displacement of a body and a wheel at the time of generating approaching / separating force of a specific size. It is a graph which shows the relationship between the spring constant of a tire, and the intensity | strength of the relative vibration of a vehicle body and a wheel.

  Hereinafter, embodiments and modifications of the claimable invention will be described in detail with reference to the drawings. In addition to the following examples, the claimable invention includes various aspects in which various modifications and improvements have been made based on the knowledge of those skilled in the art, including the aspects described in the above [Aspect of the Invention] section. Can be implemented.

<Configuration of vehicle suspension system>
FIG. 1 schematically shows a vehicle suspension system 10 according to an embodiment mounted on a vehicle. The system 10 includes four suspension devices 20 provided corresponding to the front, rear, left and right four wheels 12 and a control device that controls the suspension devices 20. Since the front wheel suspension device 20 that is a steered wheel and the rear wheel suspension device 20 that is a non-steered wheel can be regarded as substantially the same configuration except for a mechanism that enables the wheel to steer, the simplification of the description is taken into consideration. The rear wheel suspension device 20 will be described as a representative. The wheel 12 includes a disc wheel 22 and a tire 24.

  As shown in FIG. 2, the suspension device 20 is an independent suspension type, and is a multi-link type suspension device. The suspension device 20 includes a first upper arm 30, a second upper arm 32, a first lower arm 34, a second lower arm 36, and a toe control arm 38, each of which is a suspension arm. One end of each of the five arms 30, 32, 34, 36, and 38 is rotatably connected to the vehicle body, and the other end is rotatable to an axle carrier 40 that rotatably holds the wheel 12. It is connected. With these five arms 30, 32, 34, 36, and 38, the axle carrier 40 can be moved up and down along a fixed locus with respect to the vehicle body.

  The suspension device 20 includes a coil spring 44 as a suspension spring and an electromagnetic actuator 46, which respectively mount a mount portion 48 provided on a tire housing, which is a component of the vehicle body, and a wheel 12. They are arranged in parallel with each other between the second lower arm 36 that is rotatably held. That is, it is disposed between the vehicle body and the wheels 12.

  As shown in FIG. 3, the electromagnetic actuator 46 includes a screw rod 50 as a male screw portion in which a thread groove is formed, and a nut 52 as a female screw portion that holds a bearing ball and is screwed with the screw rod 50. A ball screw mechanism including the electromagnetic motor 54 as a power source and a casing 56 that houses the electromagnetic motor 54 are provided. The casing 56 rotatably holds the screw rod 50 and is connected to the mount portion 48 via a vibration isolating rubber 58 at the outer peripheral portion.

  The electromagnetic motor 54 is arranged so as to face the coil 60, a plurality of coils 60 fixedly arranged on one circumference along the inner peripheral wall of the casing 56, a motor shaft 62 rotatably held in the casing 56, and the coil 60. And a permanent magnet 64 which is fixedly disposed on the outer periphery of the motor shaft 62. The electromagnetic motor 54 is a motor in which the coil 60 functions as a stator and the permanent magnet 64 functions as a rotor, and is a three-phase DC brushless motor. The motor shaft 62 has a hollow shape, and the screw rod 50 is fixed to the motor shaft 62 at the upper end through the inside thereof. That is, the electromagnetic motor 54 gives a rotational force to the screw rod 50. The electromagnetic motor 54 is provided with a motor rotation angle sensor 66 for detecting the rotation angle of the motor shaft 62, that is, the rotation angle of the electromagnetic motor 54. The motor rotation angle sensor 66 mainly includes an encoder, and the motor rotation angle detected thereby is used for control of the electromagnetic motor 54.

  The actuator 46 includes a bottomed cylindrical outer tube 70 and an inner tube 72 that is fitted into the outer tube 70 and protrudes upward from the upper end portion thereof. The outer tube 70 is connected to the second lower arm 36 via a mounting bush 76 provided at the lower end portion thereof, and the inner tube 72 is fixed to the casing 56 at the upper end portion with the threaded rod 50 inserted therethrough. ing. A nut support cylinder 78 is erected on the inner bottom portion of the outer tube 70, and the nut 52 is fixed inside the upper end portion of the outer tube 70 so as to be screwed to the screw rod 50.

  Furthermore, the actuator 46 has a cover tube 80, and the cover tube 80 is disposed on the lower surface side of the mount portion 48 via a vibration-proof rubber 82 at the upper end portion, and the casing 56, the outer tube 70, and the inner tube 72. It is connected in a state where the is inserted. A flange portion 84 (functioning as an upper retainer) is formed at the upper end portion of the cover tube 80, and the flange portion 84 and an annular lower retainer 86 provided on the outer peripheral surface of the outer tube 70. Thus, the coil spring 44 is supported in a sandwiched state.

  Due to the above-described structure, the actuator 46 includes the vehicle body side unit connected to the mount portion 48 including the screw rod 50, the electromagnetic motor 54, the casing 56, the inner tube 72, the cover tube 80, the nut 52, and the outer tube. 70, including a nut support cylinder 78 and the like, and a wheel side unit connected to the second lower arm 36. These two units cannot be rotated relative to each other, and the vehicle body and the wheel are close to each other. Along with the movement, relative movement in the axial direction is possible. That is, the actuator 46 has a structure that can be expanded and contracted.

  As the actuator 46 expands and contracts, the screw rod 50 and the nut 52 move relative to each other, and the screw rod 50 rotates with respect to the nut 52. Since the electromagnetic motor 54 provided in the actuator 46 can apply a rotational force to the screw rod 50, the actuator 46 depends on the rotational force, and the vehicle body side unit and the wheel side unit, that is, the vehicle body It is possible to generate an approaching / separating force that is a force in a direction for approaching / separating the wheel and the wheel, and functions as an approaching / separating force generating device. The approaching / separating force can act as a resistance force that prevents the stroke operation, which is an approaching / separating operation between the vehicle body and the wheel, and by using this resistance force as a damping force, the relative vibration between the vehicle body and the wheel can be achieved. Can be attenuated. The actuator 46 is also capable of generating a propulsive force for the stroke operation between the vehicle body and the wheel. The actuator 46 executes control based on the so-called skyhook damper theory or the like, and the vehicle body caused by turning of the vehicle. It is possible to effectively suppress the roll, the pitch of the vehicle body caused by the acceleration / deceleration of the vehicle, and the vehicle height of the vehicle.

  In the present suspension system 10, as shown in FIG. 1, an electronic control unit (ECU) 100 corresponding to four actuators 46 is provided. The ECU 100 is a control device that controls the operation of each actuator 46, more specifically, each electromagnetic motor 54, and includes four inverters 102 as drive circuits corresponding to each electromagnetic motor 54, a CPU, a ROM, a RAM, and the like. And a controller 103 mainly composed of a computer (see FIG. 8). Each of the inverters 102 is connected to the battery 106 via the converter 104, and is connected to the electromagnetic motor 54 of the corresponding actuator 46. The electromagnetic motor 54 is driven at a constant voltage, and the power supplied to the electromagnetic motor 54 is changed by changing the amount of supplied current. The supply current amount is changed by the inverter 102 changing the ratio (duty ratio) between the pulse-on time and the pulse-off time by PWM (Pulse Width Modulation).

  In addition to the motor rotation angle sensor 66, the controller 103 includes a steering sensor 110 for detecting an operation angle of the steering wheel, which is an operation amount of the steering operation member as a steering amount, and a lateral acceleration actually generated in the vehicle body. A lateral acceleration sensor 112 for detecting a certain actual lateral acceleration, a longitudinal acceleration sensor 114 for detecting longitudinal acceleration generated in the vehicle body, and four sprung longitudinal accelerations provided corresponding to the wheels 12 to detect sprung longitudinal acceleration. A sensor 116 and a spring constant reset switch 118 for resetting the spring constant of the tire 24 described later are connected. The controller 103 is further connected to a brake electronic control unit (hereinafter also referred to as “brake ECU”) 120 which is a control device of the brake system. The brake ECU 120 is connected to a wheel speed sensor 122 that is provided for each of the four wheels 12 and detects the respective rotational speeds. The brake ECU 120 is based on the detection values of the wheel speed sensors 122. It has a function of estimating the traveling speed of the vehicle (hereinafter sometimes referred to as “vehicle speed”). The controller 103 acquires the vehicle speed from the brake ECU 120 as necessary. The controller 103 is also connected to each inverter 102 and controls each inverter 102 to control the electromagnetic motor 54 of each actuator 46. Note that a ROM included in the computer of the controller 103 stores a program related to control of each actuator 46 described later, a program related to control for resetting the spring constant of the tire 24, various data, and the like.

<Control of vehicle suspension system>
i) Control of Actuator In the suspension system 10, each of the four actuators 46 can be controlled independently. In each of these actuators 46, the approaching / separating force is independently controlled to attenuate the vibration of the vehicle body and the wheel 12, that is, the control for damping the sprung vibration and the unsprung vibration (hereinafter referred to as “vibration damping control”). Control for suppressing the roll of the vehicle body caused by turning of the vehicle (hereinafter sometimes referred to as “roll suppression control”), control for suppressing the pitch of the vehicle body caused by acceleration / deceleration of the vehicle (hereinafter referred to as “pitch suppression”). May be called "control"). Vibration damping control, roll suppression control, and pitch suppression control are executed by causing the approaching / separating force to act as a damping force, a roll suppression force, and a pitch suppression force, respectively.

More specifically, a damping approach / separation force component (damping component) f _G that is an approaching / separating force for each control of vibration damping control, roll suppression control, and pitch suppression control, roll suppression approaching / separating force component (roll suppression component) f _R. , The target approaching / separating force f ^* obtained by adding the pitch restraining approaching / separating force component (pitch restraining component) f _P is determined, and the actuator 54 is controlled to generate the target approaching / separating force f ^*. To be executed. In the following, each of vibration damping control, roll suppression control, and pitch suppression control will be described in detail with a focus on a method for determining the approaching / separating force component in each of them, and operation control of the electromagnetic motor 64 for controlling the approaching / separating force. Will be described in detail. In the following description, the approaching / separating force and its component are positive values corresponding to the force in the direction separating the vehicle body and the wheel (rebound direction), and the direction causing the vehicle body and the wheel to approach (bound direction). ) Is treated as a negative value.

a) Vibration Attenuation Control In the vibration attenuation control, in order to attenuate the vibrations of the vehicle body and the wheel 12, the attenuation component f _G is determined so as to generate an approaching / separating force having a magnitude corresponding to the speed of the vibrations. In other words, the control is based on both the control based on the so-called skyhook damper theory and the control based on the pseudo groundhook damper theory. More specifically, based on the vertical movement speed of the mount 52 of the vehicle body, the so-called absolute sprung speed Vu, and the vertical movement speed of the wheel 12, the so-called unsprung absolute speed Vs, according to the following equation: The attenuation component f _G is calculated.
f _G = Cu · Vu−Cs · Vs
Here, Cu is a gain for generating a damping force corresponding to the vertical operating speed of the mount 48 of the vehicle body, and Cs is a damping force corresponding to the vertical operating speed of the wheel 12. For gain. That is, Cu and Cs can be considered as damping coefficients for so-called sprung and unsprung absolute vibrations.

In the system 10, the absolute sprung speed Vu is calculated based on the sprung vertical acceleration Gu detected by the sprung vertical acceleration sensor 116 provided on the mount portion 48 of the vehicle body. On the other hand, the unsprung absolute speed Vs as the wheel vertical speed is estimated using a so-called observer based on the calculated sprung absolute speed Vu. Since the observer is a known technique, a detailed description thereof is omitted, but the unsprung absolute velocity Vs is estimated according to the block diagram shown in FIG. Y is a determinant including the calculated sprung absolute velocity Vu, and Xc is an estimated unsprung displacement amount xsc, an estimated unsprung absolute velocity Vsc, an estimated unsprung displacement amount xuc, and an estimated unsprung absolute velocity. It is a determinant including Vuc. A, B, and D are determinants shown in the figure, where M ₁ is the unsprung mass, M ₂ is the sprung mass, K is the spring constant of the coil spring 44, and K _T is the spring constant of the tire 24. Each means. Further, f is the approaching / separating force generated by the actuator 46 when the sprung vertical acceleration Gu is detected, and L means a gain derived from the solution of the Riccati equation. 1 / S means an integral transfer function.

b) Roll suppression control In roll suppression control, when the vehicle is turning, the approaching / separating force in the bounce direction is applied to the actuator 46 on the inner ring side and the actuator 46 on the outer ring side is rebounded according to the roll moment resulting from the turn. A direction approaching / separating force is generated as a roll restraining force. Specifically, first, as the lateral acceleration that indicates the roll moment received by the vehicle body, the estimated lateral acceleration Gyc estimated based on the steering angle δ of the steering wheel and the vehicle traveling speed v, and the actually measured actual lateral acceleration Gyr. Based on the above, a control lateral acceleration Gy ^* , which is a lateral acceleration used for control, is determined according to the following equation:
Gy ^* = K _A · Gyc + K _B · Gyr (K _A , K _B : gain)
Based on the determined control lateral acceleration Gy ^* , the roll suppression component f _R is determined. The controller 103 stores map data of the roll suppression component f _{R using} the control lateral acceleration Gy ^* as a parameter, and the roll suppression component f _R is determined with reference to the map data.

c) Pitch suppression control In the pitch suppression control, the nose dive of the vehicle body generated during braking of the vehicle body is rebounded to the actuator 46 provided corresponding to the front wheel side according to the pitch moment that causes the nose dive. The approaching / separating force in the direction is generated as the pitch restraining force in the bounding direction by the actuator 46 provided corresponding to the rear wheel side. Further, for the squat of the vehicle body generated during the acceleration of the vehicle body, the approaching / separating force in the rebound direction is applied to the actuator 46 provided corresponding to the rear wheel side in accordance with the pitch moment that generates the squat. An approaching / separating force in the bounce direction is generated as a pitch suppression force in the actuator 46 provided corresponding to the above. Specifically, the measured longitudinal acceleration Gzg is adopted as the longitudinal acceleration indicating the pitch moment received by the vehicle body, and the pitch suppression component f _P is determined according to the following equation based on the actual longitudinal acceleration Gzg.
f _P = K _C · Gzg (K _C : gain)

d) Operation control of electromagnetic motor When the damping component f _G , the roll suppression component f _R and the pitch suppression component f _P are determined as described above, in order to unify the vibration damping control, roll suppression control, and pitch suppression control, The target approach / separation force f ^* is determined according to the equation.
f ^* = f _G + f _R + f _P
Then, the electromagnetic motor 54 is controlled so as to generate the determined target approach / separation force f ^* .

Operation control of the electromagnetic motor 54 for generating the target approaching / separating force f ^* is performed by the inverter 102. More specifically, based on the determined target approaching / separating force f ^* , a command for the duty ratio corresponding to the direction in which the motor force is generated and the magnitude of the motor force is issued to the inverter 102 by the controller 103. Switches the switching element provided on its own based on the command to drive the electromagnetic motor 54. The electromagnetic motor 54 has an approaching / separating force having a magnitude corresponding to the issued motor force direction and the duty ratio. It is generated.

<Resetting tire spring constant>
The suspension system 10 is not provided with an unsprung acceleration sensor. As described above, the unsprung absolute velocity Vs is estimated using the observer based on the unsprung absolute velocity Vu, and vibration damping control is performed. Is running. The determinant used for the observer includes the unsprung mass M ₁ , the sprung mass M ₂ , the spring constant K of the coil spring 44, and the spring constant K _T of the tire 24. It is set in advance. However, the spring constant K _T of the tire 24, since it is easy to change over time, continued use of the spring constant K _T of the tire 24 that is set in advance, difficult to estimate accurately unsprung absolute speed There is a risk of becoming. Therefore, in the present system 10, based on the driver's intention, and is it possible to re-set the spring constant K _T of the tire 24. Actuator 46 to generate a displacement force of a specific size, the displacement force of a particular magnitude by utilizing the transmission characteristics of the actuator 46 as it is transmitted to the vehicle body, the spring constant K _T of the tire 24 estimated, it is to re-set the spring constant K _T. The following describes in detail how to estimate the spring constant K _T of the tire 24.

First, the transfer characteristic of the actuator 46 will be described in detail. The approaching / separating force with time t as a parameter is f (t), the displacement amount of the wheel 12 in the vertical direction is the unsprung displacement amount x ₁ (t), and the displacement amount in the vertical direction of the vehicle body is the sprung displacement amount x _2. In the case of (t), the equation of motion for the vehicle body is represented by the following equation.
M ₂ · d ² x ₂ (t) / dt ² = −C · {dx ₂ (t) / dt−dx ₁ (t) / dt}
−K · {x ₂ (t) −x ₁ (t)} + f (t) (1)
Here, C is a damping coefficient when the actuator 46 functions as a shock absorber. That is, this is a damping coefficient when the approaching / separating force is applied as a damping force with respect to the relative vibration between the vehicle body and the wheel. By performing Laplace transform on the expression (1) using s as a Laplace operator as a parameter, the following expression is obtained.
M ₂ · s ² · X ₂ (s) = − C · s · {X ₂ (s) −X ₁ (s)}
−K · {X ₂ (s) −X ₁ (s)} + F (s) (2)
X ₁ (s), X ₂ (s), and F (s) are functions obtained by Laplace transform of x ₁ (t), x ₂ (t), and f (t), respectively.

On the other hand, the equation of motion for the wheel 12 is expressed by the following equation.
M ₁ · d ² x ₁ (t) / dt ² = −C · {dx ₁ (t) / dt−dx ₂ (t) / dt}
−K · {x ₁ (t) −x ₂ (t)} − K _T · x ₁ (t) −f (t) (3)
By performing Laplace transform on the expression (3) using s as a Laplace operator as a parameter, the following expression is obtained.
M ₁ · s ² · X ₁ (s) = − C · s · {X ₁ (s) −X ₂ (s)}
_{-K · {X 1 (s)} -X 2 (s)} - K T · X 1 (s) -F (s) ··· (4)

When X ₁ (s) is eliminated based on the above equations (2) and (4), the following equation is obtained.
s · X ₂ (s) / F (s) =
(M ₁ · s ³ + K _T · s) / [M ₁ · M ₂ · s ⁴ + (M ₁ + M ₂ ) · C · s ³ +
{M ₁ · K + M ₂ · (K + K _T )} · s ² + C · K _T · s + K · K _T ] (5)
By this equation (5), F (s) is converted to s · X ₂ (s). That is, equation (5) can be said to be a transfer function that outputs the sprung absolute speed when the approaching / separating force is input to the vehicle body.

In the above equation (5), which is a transfer function that represents the relationship between the approaching / separating force and the sprung absolute speed, the approach when the actuator 46 generates a specific approaching / separating force f ₀ that is an approaching / separating force of a specific magnitude. FIG. 5 shows a difference between the separation force f (t) and the sprung displacement amount x ₂ (t), that is, how the sprung absolute velocity Vu changes with time. The actuator 46 generates a specific approaching / separating force f ₀ , and the unsprung mass M ₁ , the sprung mass M ₂ , the damping coefficient C, the spring constant K of the coil spring 44, and the spring constant K of the tire 24, which are coefficients of the above transfer function. _{When T} is set to a specific value, the sprung absolute speed Vu changes with time as shown by the solid line in the figure.

Further, the spring constant K _T of the tire 24 which is one of the coefficients of the transfer function is smaller than the specific value, the coefficient M ₁ other than the spring constant K _T, M _2, C, the specific value of K In this case, the sprung absolute speed Vu changes with time as shown by the dotted line in the figure. In this system 10, the actuator 46 also has a function as a shock absorber, but the actuator 46 generates only the approaching / separating force f ₀ having a specific magnitude. That is, since the actuator 46 does not generate a damping force, the damping coefficient C that is a coefficient of the transfer function is set to zero.

As can be seen from the figure, the amplitude of the sprung absolute speed Vu, that is, the upper maximum speed Vu _UMAX that is the maximum speed of the sprung absolute speed Vu when the vehicle body moves upward, and the absolute spring speed when the vehicle body moves downward. sprung maximum speed difference which is a difference between a lower maximum speed Vu _DMAX is the maximum speed of Vu ΔVu (Vu _UMAX -Vu _DMAX), the more the spring constant K _T of the tire 24 is reduced, tends to increase. That, sprung maximum speed difference DerutaVu _S when the spring constant K _T of the tire 24 is small, larger than the spring on the maximum speed difference DerutaVu _B when the spring constant K _T of the tire 24 is large, the spring constant K _T of the tire 24 Is sequentially changed, the sprung maximum speed difference ΔVu changes as shown in FIG. That is, by detecting the sprung maximum speed difference DerutaVu, by referring to the map data set as shown in FIG. 6, it become possible to estimate the spring constant K _T of the tire 24.

Therefore, in the present system 10, according to the relationship between the spring constant K _T and sprung maximum speed difference ΔVu tires 24 derived from the transfer function, execution tire spring constant estimation control for estimating the spring constant K _T of the tire 24 Is done. That is, the tire spring constant estimation control using the transfer function is executed. The tire spring constant estimation control is allowed to be executed when a preset allowable condition (hereinafter, sometimes referred to as “set allowable condition”) is satisfied. Specifically, if it is satisfied that the vehicle is stopped and that the distance between the four vehicle body wheels is within a certain allowable range, execution of the tire spring constant estimation control is permitted. Therefore, during this control, except for the approaching / separating force generated by the actuator 46, it is considered that the force that vibrates the vehicle body is not acting, and the maximum sprung speed difference ΔVu changes according to the above transfer function.

In the tire spring constant estimation control, first, a specific approaching / separating force f ₀ is generated in the actuator 46. Then, the sprung maximum speed difference ΔVu, which is the difference between the upper maximum speed Vu _UMAX and the lower maximum speed Vu _DMAX of the vehicle body vibration that is the target vibration generated by the specific approaching / separating force f ₀ , is acquired. Specifically, the sprung vertical acceleration Gu is detected by a sprung vertical acceleration sensor 116 provided in the mount portion 48 of the vehicle body. Based on the detected sprung vertical acceleration Gu, the sprung absolute speed Vu is determined by the controller of the ECU 100. 103. The upper maximum speed Vu _UMAX and the lower maximum speed Vu _DMAX are extracted from the calculated sprung absolute speed Vu, and the sprung maximum speed difference ΔVu, which is the difference between them, is calculated. In the present system 10, the sprung maximum speed difference ΔVu as the vibration intensity of the vehicle body is acquired by the sprung vertical acceleration sensor 116 and the controller 103, and the vibration intensity by the sprung vertical acceleration sensor 116 and the controller 103 is acquired. A detection device is configured. Then, based on the calculated sprung maximum speed difference DerutaVu, by referring to the map data set as shown in FIG. 6, it is the spring constant K _T of the tire 24 is estimated. The tire spring constant estimation control is executed by the driver's operation of the spring constant reset switch 118, and the spring constant K _T estimated by this control is reset as the latest tire spring constant K _T.

<Control program>
In this system 10, the approaching / separating force generated by the actuator 46 is controlled by a short time interval (for example, several milliseconds) while the ignition switch is turned on by the actuator control program shown in the flowchart of FIG. This is performed by being repeatedly executed by the controller 103. Also, the tire spring constant estimation control for estimating the spring constant K _T of the tire 24, the tire spring constant estimation control execution program indicated by a flow chart of FIG. 8, the tire spring constant resetting switch 118 has been operated by the driver Only in some cases, it is performed by being repeatedly executed by the controller 103 with a short time interval (for example, several milliseconds). Below, the flow of each control is demonstrated easily, referring the flowchart shown in a figure. The actuator control program and the tire spring constant estimation control execution program are executed for each of the four actuators 46 provided for each wheel 12. In the following description, processing by each program for one actuator 46 will be described in consideration of simplification of description.

i) Actuator control program In the process by the actuator control program, first, in step 1 (hereinafter simply referred to as “S1”. The same applies to other steps), the sprung vertical acceleration sensor 116 provided in the mount portion 48 is used. Based on the detected sprung vertical acceleration Gu, the sprung absolute speed Vu is calculated. In S2, the sprung absolute speed Vs is estimated using the observer based on the calculated sprung absolute speed Vu. . In S3, the damping component f _G for vibration damping control is determined based on the sprung absolute speed Vu and the unsprung absolute speed Vs as described above. Next, in S4, a control lateral acceleration Gy ^* is calculated based on the actual lateral acceleration Gyr detected by the lateral acceleration sensor 112 and the estimated lateral acceleration Gyc, and in S5, based on the control lateral acceleration Gy ^*. The roll suppression component f _R for roll suppression control is determined. Subsequently, in S6, the longitudinal acceleration sensor 114 detects the longitudinal acceleration Gzg, and in S7, the pitch suppression component f _P for pitch suppression control is determined based on the detected longitudinal acceleration Gzg. Then, in S8, by a damping component f _G and roll-reduction component f _R and the pitch restrain component f _P is total, the target displacement force f ^* is determined, at S9, it determined target displacement force f ^A control signal based on ^* is transmitted to the inverter 102. After the series of processes described above, one execution of this program ends.

ii) Tire spring constant estimation control execution program The processing according to the tire spring constant estimation control execution program is executed only when a command from the spring constant reset switch 118 is issued. In the process according to the program, first, in S11, whether they meet the allowable conditions described above is determined, if it is determined to be satisfied, in S12, to generate a specific displacement force f ₀ Therefore, a control signal based on the specific approaching / separating force f ₀ is transmitted to the inverter 102. That, S12 functions as a specific force generator step of generating the displacement force f ₀ of a particular size.

In S13, the sprung absolute speed Vu is calculated based on the sprung vertical acceleration Gu detected by the sprung vertical acceleration sensor 116. In S14, the calculated sprung absolute speed Vu and the vehicle body move upward. The upper maximum speed Vu _UMAX that is the maximum speed of each is compared and determined. If it is determined that the calculated sprung absolute speed Vu is greater than the upper maximum speed Vu _UMAX , the calculated sprung absolute speed Vu is set to the upper maximum speed Vu _UMAX in S15. If it is determined in S14 that the sprung absolute speed Vu is equal to or lower than the upper maximum speed Vu _UMAX, it is determined in S16 whether or not the calculated sprung absolute speed Vu is less than zero. When it is determined that the calculated sprung absolute speed Vu is smaller than 0, in S17, the calculated sprung absolute speed Vu is compared with the lower maximum speed Vu _DMAX that is the maximum speed when the vehicle body moves downward. Determined. When it is determined that the calculated sprung absolute speed Vu is smaller than the lower maximum speed Vu _DMAX , the calculated sprung absolute speed Vu is set to the lower maximum speed Vu _DMAX in S18. Further, when the calculated sprung absolute speed Vu is determined to lower the maximum speed Vu _DMAX more in S17, in S19, based on the above maximum speed Vu _UMAX and lower maximum speed Vu _DMAX, sprung maximum speed difference ΔVu is calculated. That is, in S13 to S19, the sprung maximum speed difference ΔVu as the vibration intensity at the specific time, which is the vibration intensity of the vehicle body when the specific approaching / separating force is generated, is detected, and S13 to S19 function as a vibration intensity detecting step. ing.

In S20, by referring to the map data set as shown in FIG. 6, the spring constant K _T of the tire 24 is estimated based on the calculated sprung maximum speed difference DerutaVu. That is, S20 functions as a tire spring constant estimation step for estimating the tire spring constant based on the vibration strength of the vehicle body. In S21, the upper maximum speed Vu _UMAX and the lower maximum speed Vu _DMAX are reset, and in S22, a control signal for setting the approaching / separating force generated by the actuator 46 to 0 is transmitted to the inverter 102. As described above, by executing the tire spring constant estimation control execution program, the tire spring constant is estimated by the tire spring constant estimation method including the specific approach / separation force generation step, the vibration strength detection step, and the tire spring constant estimation step. It can be done.

<Functional configuration of controller>
The controller 103 that executes the above two programs can be considered to have a functional configuration as shown in FIG. 9 in view of its execution processing. As can be seen from the drawing, the controller 103 uses the approach / separation force control unit 130 as the tire spring constant estimation function as a function unit that executes the actuator control program, that is, a function unit that controls the approach / separation force generated by the actuator 46. A tire spring constant estimation control execution unit 132 is provided as a functional unit that executes processing of the control execution program, that is, a functional unit that executes tire spring constant estimation control. Incidentally, the approach / separation force control unit 130 functions as an approach / separation force control device, and the tire spring constant estimation control execution unit 132 functions as a tire spring constant estimation device.

  The approaching / separating force control unit 130 functions as a function unit that executes the processes of S1 and S3, that is, a function unit that attenuates vibrations of the vehicle body, and the function of executing the processes of S2 and S3. As a functional unit for attenuating the vibration of the wheel, the wheel vibration damping control unit 136 is a functional unit for executing the processing of S4 to S7, that is, suppressing the roll and pitch of the vehicle body to suppress the posture variation of the vehicle body. Each of the function units has a posture variation suppression control unit 138. Further, the wheel vibration damping control unit 136 includes a wheel vertical speed estimation unit 140 as a function unit that executes the process of S2, that is, a function unit that estimates the unsprung absolute speed Vs based on the sprung absolute speed Vu. is doing. Incidentally, the wheel vertical speed estimation unit 140 functions as a wheel vertical speed estimation device and functions as the above-described observer.

  Further, the tire spring constant estimation control execution unit 132 sets the specific approach / separation force generation unit 142 as S14 to S19 as a function unit that executes the process of S12, that is, a function unit that generates an approach / separation force of a specific magnitude. As a function unit that executes the process of (i.e., a function part that detects the maximum sprung speed difference ΔVu that is the vibration intensity of the vehicle body), the vibration intensity detection unit 144 is a function unit that executes the process of S20, i.e., The tire spring constant estimation unit 146 is provided as a functional unit that estimates the tire spring constant based on the vibration intensity.

Modified example

In the suspension system 10, a sprung vertical acceleration sensor 116 is provided, and the spring constant of the tire 24 is determined based on the vibration intensity of the vehicle body calculated from the sprung vertical acceleration sensor 116 detected by the sprung vertical acceleration sensor 116. It is estimated. As a vibration intensity detection device, a stroke sensor is provided instead of the sprung vertical acceleration sensor, and the intensity of the target vibration detected by the stroke sensor, specifically, the relative displacement of the vehicle body and the wheel during relative vibration Based on the above, the spring constant of the tire 24 may be estimated. That is, the transmission characteristic of the actuator 46 when the approaching / separating force f ₀ having a specific magnitude is transmitted between the vehicle body and the wheel, in other words, the approaching / separating force input to the vehicle body and the wheel is relative to the vehicle body and the wheel. using the transfer function for converting the amount of displacement may be estimated spring constant K _T of the tire 24.

Since the relative displacement between the vehicle body and the wheel is the difference between the sprung displacement x ₂ (t) and the unsprung displacement x ₁ (t) (x ₂ (t) −x ₁ (t)), A transfer function G (s) for converting the approaching / separating force f (t) input to the vehicle body and the wheel into a relative displacement amount between the vehicle body and the wheel is expressed by the following equation.
G (s) = {X ₂ (s) −X ₁ (s)} / F (s) (6)
Moreover, the following relational expression can be derived by transforming the above expressions (2) and (4).
{X ₂ (s) −X ₁ (s)} / F (s) =
{(M ₁ + M ₂ ) · C · s ³ + (M ₁ + M ₂ ) · K · s ² + C · K _T · s + K · K _T } /
[M ₁ · M ₂ · C · s ⁵ + {M ₁ · M ₂ · K + (M ₁ + M ₂ ) · C ² } · s ⁴
+ {2M ₁ · K + M ₂ · (2K + K _T )} · C · s ³
+ {C ² · K _T + M ₁ · K + M ₂ · (K + K _T )} · K · s ²
+ 2C · K · K _T · s + K ² · K _T ] (7)
That is, equation (7) can be said to be a transfer function for converting the approaching / separating force input to the vehicle body and the wheel into the relative displacement amount between the vehicle body and the wheel.

In the above equation (7), the actuator 46 generates the specific approaching / separating force f ₀ , and after the relative vibration between the vehicle body and the wheel due to the specific approaching / separating force has converged, the generation of the specific approaching / separating force f ₀ is stopped. FIG. 10 shows how the relative displacement amount (x ₂ (t) −x ₁ (t)) changes with time. As can be seen from the figure, by generating the specific approaching / separating force f ₀ , the vehicle body and the wheel relatively vibrate and the relative displacement varies around the specific relative displacement amount f ₀ / K, and the relative vibration is attenuated. Thus, the relative displacement amount is maintained at the specific relative displacement amount f ₀ / K. If the maximum relative displacement amount when the specific approaching / separating force f ₀ is generated is the first maximum displacement amount L _1MAX and the minimum relative displacement amount is the first minimum displacement amount L _1min , the relative relationship between the vehicle body and the wheel The first maximum amplitude ΔL ₁ that is the intensity of vibration is a difference (L _1MAX −L _1min ) between the first maximum displacement L _1MAX and the first minimum displacement L _1min . Its maximum amplitude [Delta] L _1, like the sprung maximum speed difference ΔVu previously described, changes to alter the spring constant K _T of the tire 24. Specifically, the maximum amplitude [Delta] L ₁ is, the more the spring constant K _T of the tire 24 is reduced, is in the larger trend, when sequentially varying the spring constant K _T of the tire 24, the first maximum amplitude [Delta] L ₁ is As shown by the solid line in FIG. That is, if the first maximum amplitude ΔL ₁ when the specific approaching / separating force f ₀ is generated is detected, the spring constant of the tire 24 is referred to by referring to the map data set as shown by the solid line in FIG. It is possible to estimate _KT .

Incidentally, in order to converge the relative vibration between the vehicle body and the wheel, the actuator 46 actually generates an approaching / separating force having a magnitude obtained by adding a damping force for the relative vibration between the vehicle body and the wheel to the specific approaching / separating force f _0. ing. Specifically, the relative speed Vr between the vehicle body and the wheel is calculated based on the relative displacement amount detected by the stroke sensor. Then, the actuator 46 causes generate a damping force corresponding to the relative speed Vr, so to generate a certain displacement force f _0, displacement force fr to actually actuator 46 generates is determined according to the following equation.
fr = f ₀ + C ₁ · Vr
Here, C ₁ is a gain for generating a damping force corresponding to the relative speed, and is a damping coefficient for relative vibration. That is, the attenuation coefficient C of the coefficient of the transfer function used when obtaining the first maximum amplitude ΔL ₁ is C ₁ .

Further, after the relative vibration of the vehicle body and the wheel by a specific displacement force f ₀ converged, when stopping the generation of the specific displacement force f _0, as shown in FIG. 10, and the vehicle body and the wheel Relative vibration occurs again, and the relative displacement varies around 0. The relative vibration is attenuated and the relative displacement is maintained at 0. The maximum relative displacement amount when stopping the occurrence of a specific displacement force f ₀ and a second maximum displacement L _2MAX, if the minimum relative displacement between the second minimum displacement L _2min, first in that case 2 maximum amplitude [Delta] L ₂ is a difference between the second maximum displacement L _2MAX and second minimum displacement _{L 2min (L 2MAX -L 2min)} . Also the maximum amplitude [Delta] L _2, similarly to the maximum amplitude [Delta] L _1, as the spring constant K _T of the tire 24 is reduced, is in the larger trend, when sequentially varying the spring constant K _T of the tire 24, the second The maximum amplitude ΔL ₂ changes as shown by the dotted line in FIG. That is, by detecting the second maximum amplitude [Delta] L ₂ when stopping the occurrence of a specific displacement force f _0, it is possible to estimate the spring constant K _T of the tire 24.

Incidentally, the generation of the approaching / separating force f _{0 having} a specific magnitude is stopped, but in order to converge the relative vibration between the vehicle body and the wheel, the actuator 46 generates a damping force for the relative vibration between the vehicle body and the wheel. ing. Specifically, the approaching / separating force fr is determined according to the following equation so that the actuator 46 generates a damping force corresponding to the relative speed Vr.
fr = C ₂ · Vr
Here, C ₂ is an attenuation coefficient set to a value smaller than the attenuation coefficient C ₁ , and the attenuation coefficient C of the transfer function coefficient used when obtaining the second maximum amplitude ΔL ₂ is C ₂

As described above, with estimating the spring constant K _T of the tire 24 when that caused the displacement force f ₀ of a particular size, of the tire 24 when stopping the generation of the displacement force f ₀ spring be estimated constant K _T, it is possible to improve the accuracy of estimation of the spring constant K _T. Also, by changing the damping coefficient C of the coefficients of the transfer function in each case, it is possible to improve the accuracy of estimation of the spring constant K _T. By the way, in this system in which a stroke sensor is provided instead of the sprung acceleration sensor, the sprung absolute speed Vu and the unsprung absolute speed Vs are obtained from the relative displacement between the vehicle body and the wheel detected by the stroke sensor using an observer. Is estimated, and vibration damping control is executed based on the estimated absolute velocities Vu and Vs. Since this observer is substantially the same as the observer used in the system 10, the detailed description is omitted. However, if the determinant D in FIG. 4 is changed to the one shown in the following expression, the relative displacement between the vehicle body and the wheel will be described. The sprung absolute speed Vu and the unsprung absolute speed Vs can be estimated from the quantity.
D = [-1 0 1 0]

Incidentally, the spring constant K _T, which is estimated as described above, for example, is smaller than a preset threshold, assumes that the tire pressure has dropped, some means, e.g., by a warning indicator, such as You may comprise so that a driver | operator may be notified of the fall of the air pressure of a tire. With such a configuration, it is possible to monitor a decrease in tire air pressure.

  DESCRIPTION OF SYMBOLS 10: Vehicle suspension system 12: Wheel 24: Tire 44: Coil spring (suspension spring) 46: Actuator (approaching / separating force generator) 48: Mount part (vehicle body) 103: Controller (vibration intensity detector) 116: On spring Longitudinal acceleration sensor (vibration intensity detection device) 130: Approaching / separating force control unit (approaching / separating force control device) 132: Tire spring constant estimation control execution unit (tire spring constant estimation device) 136: Wheel vibration damping control unit 140: Wheel vertical motion Direction speed estimation unit (wheel vertical speed estimation device) 142: Specific approaching / separating force generating unit (specific approaching / separating force generating step) 144: Vibration intensity detecting unit (vibration intensity detecting step) 146: Tire spring constant estimating unit (tire spring) Constant estimation process)

Claims (5)

(a) a wheel having a tire; (b) a vehicle body; (c) a suspension spring disposed between the wheel and the vehicle body; and (d) an electromagnetic wave disposed in parallel with the suspension spring. In a vehicle having a motor and an approaching / separating force generating device that generates an approaching / separating force that is a force in a direction of approaching / separating the wheel and the vehicle body based on a force generated by the electromagnetic motor, A tire spring constant estimating method for estimating a spring constant of the tire,
A specific approaching / separating force generating step of operating the electromagnetic motor so that the approaching / separating force generating device generates an approaching / separating force of a specific magnitude;
A vibration intensity detecting step of detecting a target vibration intensity which is one of a relative vibration between the wheel and the vehicle body generated by the approaching / separating force and a vibration of the vehicle body;
Based on the intensity of the target vibration detected in the vibration intensity detecting step, the tire uses the transfer function representing the relationship between the approaching / separating force generated by the approaching / separating force generating device and the intensity of the target vibration. Including a tire spring constant estimating step for estimating a spring constant of
The transfer function has a tire spring constant as a coefficient, and is set so that the relationship between the approaching / separating force and the intensity of the target vibration is changed by changing the value of the coefficient,
The tire spring constant estimation step includes
When the approaching / separating force in the transfer function is the approaching / separating force having the specific magnitude, the strength of the target vibration is the strength of the target vibration detected in the vibration strength detecting step. A tire spring constant estimating method, which is a step of estimating a value as a spring constant of the tire. The target vibration is vibration of the vehicle body,
The tire spring constant estimation method according to claim 1, wherein the vibration intensity detection step is a step of detecting a maximum speed of vibration in a vertical direction of vibration of the vehicle body. The target vibration is a relative vibration between the wheel and the vehicle body,
The tire spring constant estimating method according to claim 1, wherein the vibration intensity detecting step is a step of detecting a maximum amplitude of relative vibration between the wheel and the vehicle body. A suspension spring disposed between the wheel having the tire and the vehicle body;
An approaching / separating mechanism that is arranged in parallel with the suspension spring, has an electromagnetic motor, and generates an approaching / separating force that is a force in a direction for approaching / separating the wheel and the vehicle body based on the force generated by the electromagnetic motor. A force generator,
A vehicle suspension system comprising a vibration intensity detection device that detects the intensity of a target vibration that is one of a relative vibration between a wheel and a vehicle body and a vibration of the vehicle body,
The vehicle suspension system is
Generation of the approaching / separating force based on a specific vibration intensity detected by the vibration intensity detecting device when the approaching / separating force generating apparatus generates a specific approaching / separating force. A tire spring constant estimating device for estimating a spring constant of the tire using a transfer function representing a relationship between the approaching / separating force generated by the device and the intensity of the target vibration;
The transfer function has a tire spring constant as a coefficient, and is set so that the relationship between the approaching / separating force and the intensity of the target vibration is changed by changing the value of the coefficient,
The tire spring constant estimating device is
The value of the coefficient is estimated as a tire spring constant so that the target vibration strength when the approaching / separating force in the transfer function is the approaching / separating force of the specific magnitude is the specific-time vibration strength. A suspension system for a vehicle configured to be. The vehicle suspension system is
Using the tire spring constant estimated by the tire spring constant estimating device from the intensity of the target vibration detected by the target vibration detecting device, the wheel vertical speed that is the vertical speed of the wheel vibration is obtained. A wheel vertical speed estimation device to estimate,
An approaching / separating force control device for controlling the approaching / separating force generated by the approaching / separating force generating device by controlling the operation of the electromagnetic motor of the approaching / separating force generating device;
The approaching / separating force control device is
The approaching / separating force is set so that at least a part of the approaching / separating force generated by the approaching / separating force generating device is a damping force having a magnitude corresponding to the wheel vertical direction speed estimated by the wheel vertical direction speed estimating device. The vehicle suspension system according to claim 4, further comprising a wheel vibration damping control unit that controls the vehicle suspension system.

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