JP4788675B2 - Vehicle suspension system - Google Patents

Description

  The present invention relates to a suspension system for a vehicle that includes an electromagnetic shock absorber that generates a force with respect to relative movement between an unsprung portion and an unsprung portion.

In recent years, as an automotive suspension system, an electromagnetic suspension system that includes an electromagnetic shock absorber that relies on the force of an electromagnetic motor to generate a force for the relative motion of the sprung and unsprung parts has been studied. For example, there is a system described in Patent Document 1 below. This electromagnetic suspension system is expected as a high-performance system because of its advantage that vibration damping characteristics based on the so-called skyhook damper theory can be easily realized.
JP 2006-168399 A JP-A-8-175145

  In the above electromagnetic shock absorber, if it can be expanded and contracted, the frictional force for expansion and contraction, and if it has a screw mechanism, the frictional force of the shock absorber such as the frictional force between the screw rod and nut Is a resistance force to the relative movement of the sprung portion and the unsprung portion. Therefore, the impact of the frictional force of the shock absorber on the force generated by the shock absorber is large, and even if the motor is controlled, if the frictional force of the shock absorber changes, an appropriate force is applied to the upper and lower springs. I have a problem that I can't. In order to cope with this problem, it is desirable to first provide a means for estimating the frictional force of the shock absorber in the suspension system. In the system described in Patent Document 1, a torque sensor that detects torque acting on a screw rod and a nut constituting a screw mechanism that is rotatably provided is provided, and a screw is detected based on the torque change. It is configured to estimate the frictional force of the mechanism. In the system described in Patent Document 2, the transmission characteristics of the suspension device such as the transmission gain and the phase delay are detected from the vertical accelerations of the sprung portion and the unsprung portion, and the frictional force of the suspension device is estimated based on the detected transmission characteristics. It is configured. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a suspension system including means for estimating the frictional force of a shock absorber more simply.

  In order to solve the above-described problems, the suspension system of the present invention operates when an electromagnetic shock absorber is set to change the distance between the sprung and unsprung portions, which is the distance between the sprung portion and the unsprung portion. The frictional force between the unsprung unit and the unsprung unit of the shock absorber is estimated based on a supply current that is a current supplied from the power source to the electromagnetic motor.

  When changing the unsprung distance between the sprung part and the unsprung part, the supply current to the electromagnetic motor is a physical quantity on which the absorber force generated by the shock absorber depends. For example, it is possible to easily estimate the friction force of the shock absorber in consideration of the fact that the friction force of the shock absorber becomes a force that opposes the absorber force or a force that assists the absorber force. That is, according to the present invention, a system including means for simply estimating the frictional force of the shock absorber is realized.

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 some constituent elements are deleted from the aspect of each item can be an aspect of the claimable invention. In each of the following items, each of items (1) to (7) corresponds to each of claims 1 to 7.

(1) a suspension spring that elastically connects the sprung portion and the unsprung portion;
(A) a sprung unit connected to the sprung portion; and (b) the sprung portion connected to the sprung portion according to the approach / separation between the sprung portion and the sprung portion. An unsprung side unit capable of relative movement with the side unit; and (c) an electromagnetic motor, and depending on the force of the electromagnetic motor, the unsprung side unit and the unsprung side unit An electromagnetic shock absorber that generates an absorber force that is a force against movement;
A vehicle suspension system comprising a control device for controlling the operation of the shock absorber,
Supply current which is a current supplied from the power source to the electromagnetic motor when the control device controls the operation of the shock absorber to change the distance between the sprung portion and the unsprung portion. A suspension system for a vehicle, comprising: a frictional force estimating unit that estimates a frictional force between the unsprung side unit and the unsprung side unit.

  “Change the sprung unsprung distance” described in this section is not limited to actually changing the sprung unsprung distance, but the elastic force of the suspension spring and the shared load (one wheel shares the load). It is also included that the distance is changed from the neutral distance, which is the distance between the unsprung springs when the weight of the vehicle body is balanced. That is, the frictional force between the unsprung unit and the unsprung unit opposes the absorber force generated by the shock absorber when the unsprung distance is changed by the absorber force. It is a force that assists the force or the absorber force. Also, the supply current from the power source to the electromagnetic motor is a physical quantity on which the absorber force depends when changing the distance between the sprung and unsprung springs. Based on the supply current, the above friction force counters the absorber force. The frictional force can be easily estimated in consideration of whether the force is a force or an assisting force. Therefore, according to the aspect described in this section, a system capable of simply estimating the frictional force between the unsprung unit and the unsprung unit is realized. Furthermore, a system equipped with an electromagnetic shock absorber generally has a sensor for detecting an energization current that is actually flowing through the electromagnetic motor for the control of the electromagnetic motor. Can detect the supply current. That is, according to the aspect of this section, since it is not necessary to add an extra sensor or the like to the conventional electromagnetic suspension system, a system with a simple configuration can be obtained and an increase in cost can be avoided.

  “When changing the distance between the sprung and unsprung” described in this section is not limited to the case where the shock absorber is operated only to estimate the frictional force, but is actually performed by the control device. The shock absorber may be operated in the existing control. In the latter case, for example, a case where the shock absorber is operated in the control for changing the vehicle height at the time of getting on / off to facilitate getting on / off of an occupant and loading / unloading of luggage can be adopted.

  “Friction force between the unsprung unit and unsprung unit” described in this section means both static friction force (maximum static friction force) and dynamic friction force acting between them. Is included. When estimating the static frictional force, for example, as will be described in detail later, the supply current at the time the sprung sprung distance starts to change or the sprung sprung distance is changed from the neutral distance. It is possible to estimate based on the supply current or the like at the time when the distance is maintained. Further, when estimating the dynamic friction force, for example, it can be estimated from a supply current or the like when the distance between the sprung springs is changed so that the sprung portion operates at a certain speed. The “supply current when changing the distance between the sprung springs” may be at a certain point in time, or may be an average value, an integral value, or the like of the supply current within a set time.

  By the way, the static friction force acting at the start of the change of the sprung sprung distance and the dynamic friction force when changing the sprung sprung distance are the forces that oppose the absorber force, and the sprung sprung The static frictional force when the distance is maintained from the neutral distance is a force that assists the absorber force.Therefore, considering this fact, the frictional force is calculated based on the supply current at that time. It can be estimated. For example, the frictional force may be estimated by calculation based on a balance of forces, etc., and a computer or the like that stores the relationship between the supply current and the frictional force is stored in a computer included in the control device, and the map is referred to. It may be estimated.

  Further, when estimating the frictional force, (i) the actual supply current when the distance between the sprung spring and the unsprung spring is changed by the operation of the shock absorber, and (ii) the unsprung unit and unsprung unit When the frictional force between them is the same as the design frictional force that is the frictional force between the unsprung unit and the unsprung unit determined by the structure of the shock absorber, the spring is activated by the operation of the shock absorber. A change amount of the frictional force from the design frictional force may be estimated based on a difference from a necessary supply current that is a supply current required when changing the distance between the upper springs.

  As the “suspension spring” in the aspect of this section, for example, various springs such as a coil spring and a fluid spring that elastically supports the vehicle body and the wheel by fluid pressure can be adopted.

  The “electromagnetic shock absorber” in the aspect of this section is not limited in its specific structure, and is not particularly limited in function. For example, in addition to the function of damping the vibration generated in the vehicle, the function of controlling the posture of the vehicle body is exhibited for the purpose of suppressing the roll, pitch, etc. of the vehicle body caused by turning, acceleration and deceleration of the vehicle. May be. The type of the “electromagnetic motor” that is the power source of the shock absorber is not particularly limited, and various types of motors such as a DC brushless motor can be adopted. Or a linear motor.

(2) The control device
Vibration damping control for generating an absorber force generated by the shock absorber as a damping force for attenuating at least the vibration of the sprung portion can be executed.
A target absorber force determination unit that determines a target absorber force that is a target absorber force in the vibration damping control based on the friction force estimated by the friction force estimation unit to a value in which the friction force is considered ( The vehicle suspension system according to item 1).

  The aspect described in this section is an aspect in which a method of using the estimated frictional force is limited. For the “vibration damping control” in the aspect of this section, it is possible to employ a control based on the so-called skyhook damper theory that generates a damping force against the sprung vibration. In addition to the control based on the Skyhook damper theory, control based on a pseudo groundhook theory that generates damping force against unsprung vibration can be executed, and control that executes both of them comprehensively is adopted. May be. Furthermore, it is also possible to employ control that generates a damping force for relative vibration between the unsprung unit and the unsprung unit. As described above, the frictional force between the unsprung side unit and the unsprung side unit is a resistance force to the relative movement of the unsprung side unit, and thus has an influence on the damping force generated by the shock absorber. According to the aspect described in this section, the target absorber force in the vibration damping control is determined based on the estimated friction force so as to reduce the influence of the friction force. Even if it exists, it is possible to generate an appropriate damping force.

  Note that in the system of the aspect of this section, the posture control of the vehicle body for the purpose of suppressing the roll and pitch of the vehicle body may be executable. In such a case, for example, the absorber force generated in the shock absorber is controlled based on the sum of the force generated in the posture control of the vehicle body and the force generated in the vibration damping control. It is possible to adopt a configuration in which the target absorber force for executing two controls simultaneously is determined in consideration of the estimated friction force.

(3) The control device can execute control based on the skyhook damper theory as vibration damping control,
The target absorber force determination unit causes the target absorber force to act between the sprung portion and the unsprung portion when generating a propulsive force with respect to the relative movement between the sprung portion side unit and the unsprung portion side unit. It is determined to be a value corresponding to the frictional force estimated by the frictional force estimation unit, compared to a reference absorber force that is a power-based absorber force, and the unsprung unit and unsprung unit When generating a resistance force relative to the relative movement of (2), it is determined to be a value smaller than the reference absorber force according to the friction force estimated by the friction force estimation unit (2) Vehicle suspension system.

  The mode described in this section is a mode in which a method for determining the target absorber force in consideration of the frictional force is embodied. In the control based on the skyhook damper theory, the shock absorber may generate not only a resistance force but also a propulsive force against the relative movement between the unsprung unit and the unsprung unit. When generating a resistance force to the shock absorber, the friction force is a force that assists the absorber force, and when generating a propulsion force, the friction force is a force that opposes the absorber force. By determining the absorber force, the damping force is made appropriate.

(4) The controller is
A failure determination unit that determines that the shock absorber is abnormal when the frictional force estimated by the frictional force estimation unit exceeds a set limit. The vehicle suspension system described.

  The aspect described in this section is an aspect in which a method of using the estimated frictional force is limited. According to the aspect of this section, since it is possible to detect an abnormality of the shock absorber at a relatively early stage, the system is excellent in terms of fail-safe. For example, when the value of the frictional force is calculated, the “defect determination unit” described in this section may determine whether the shock absorber is abnormal depending on whether the value is equal to or greater than a threshold value. The abnormality of the shock absorber may be determined by comparing the current with a threshold value thereof. Incidentally, in the latter case, two threshold values are required for the case where the frictional force is a force against the absorber force and the case where the friction force is a force assisting the absorber force.

  (5) The frictional force estimating unit estimates the frictional force between the sprung unit and the unsprung unit based on the supplied current at the time when the set sprung unsprung distance is maintained. The vehicle suspension system according to any one of items (1) to (4), configured as described above.

  The mode described in this section is a mode in which the supply current when changing the distance between the sprung springs is specifically limited, and the distance between the sprung springs is the neutral distance (the elastic force of the suspension spring and the shared load). The frictional force is estimated on the basis of the supply current when it is maintained in a state of being changed from (the distance when the two are balanced). When the set sprung unsprung distance is maintained, the balance between the elastic force of the suspension spring and the shared load is lost by the absorber force and the frictional force. Is maintained. Therefore, the absorber force can be obtained from the supply current, and the friction force can be easily calculated by the balance of the force.

  (6) The frictional force estimating unit estimates the frictional force between the unsprung side unit and the unsprung side unit based on the supply current at the time when the unsprung unsprung distance starts to change. The vehicle suspension system according to any one of (1) to (4), which is configured as follows.

  The aspect described in this section is an aspect that specifically limits the supply current when changing the distance between the sprung and unsprung parts. For example, the aspect of this section is configured to estimate the frictional force based on the supply current at the time of starting the change from the neutral distance, which is the distance when the elastic force of the suspension spring and the shared load are balanced. Then, the magnitude of the absorber force obtained from the supplied current can be considered as the magnitude of the friction force, and the friction force can be easily estimated.

(7) The shock absorber is
(A) a screw rod that forms at least a part of one of the sprung unit and the unsprung unit, and is formed with a male screw; and (B) the sprung unit and the unsprung unit. Comprising at least a part of the other, a nut formed with an internal thread and screwed into the threaded rod;
One of the threaded rod and the nut is rotatable with relative movement between the spring upper part and the unsprung part, and the electromagnetic motor applies a force to one rotation of the threaded rod and the nut. With structure,
The vehicle suspension system according to any one of (1) to (6), wherein the frictional force estimating unit is configured to estimate a frictional force between the screw rod and the nut.

  The mode described in this section is a mode in which the electromagnetic shock absorber is limited to the one adopting the screw mechanism, and the rotational force of the electromagnetic motor is applied to the relative operation between the unsprung unit and the unsprung unit. Can be easily converted into force. In the aspect of this section, it is arbitrary whether the rod is provided in either the unsprung side unit or the unsprung side unit and the nut is provided in any of them. Furthermore, it is good also as a structure which makes a rod non-rotatable and makes a nut rotatable, conversely, it is good also as a structure which makes a nut non-rotatable and makes a rod rotatable.

  Several embodiments of the claimable invention will now be described in detail with reference to the drawings. In addition to the following examples, the claimable invention is implemented in various modes including various modifications and improvements based on the knowledge of those skilled in the art, including the mode described in the above [Mode of Invention]. can do.

<< First Example >>
<Configuration of suspension system>
FIG. 1 schematically shows a vehicle suspension system 10 according to a first embodiment of the claimable invention. The suspension system 10 includes four independent suspension type suspension devices corresponding to the front, rear, left and right wheels 12, each of which is a spring absorber in which a suspension spring and a shock absorber are integrated. Assy20. The wheel 12 and the spring absorber assembly 20 are generic names, and when it is necessary to clarify which of the four wheels corresponds, as shown in FIG. In some cases, FL, FR, RL, and RR are attached to the front wheel, the right front wheel, the left rear wheel, and the right rear wheel.

  As shown in FIG. 2, the spring absorber assembly 20 is provided between a suspension lower arm 22 that holds the wheel 12 and constitutes a part of the unsprung part, and a mount part 24 that is provided on the vehicle body and constitutes a part of the unsprung part. And an actuator 26 as an electromagnetic shock absorber arranged so as to connect them, and an air spring 28 as a suspension spring provided in parallel therewith.

  The actuator 26 includes an outer tube 30 and an inner tube 32 that fits into the outer tube 30 and protrudes upward from the upper end portion of the outer tube 30. The outer tube 30 is connected to the lower arm 22 via a mounting member 34 provided at the lower end portion thereof, while the inner tube 32 is connected to the mount portion 24 at a flange portion 36 formed at the upper end portion thereof. ing. The outer tube 30 is provided with a pair of guide grooves 38 on the inner wall surface thereof so as to extend in the direction in which the axis of the actuator 26 extends (hereinafter sometimes referred to as “axial direction”). Each of a pair of keys 40 attached to the lower end of the inner tube 32 is fitted into each of the outer tube 30 and the inner tube 32 by the guide groove 38 and the key 40. Relative rotation is impossible and relative movement is possible in the axial direction. Incidentally, a seal 42 is attached to the upper end portion of the outer tube 30 to prevent air leakage from the pressure chamber 44 described later.

  The actuator 26 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 the bearing ball and is screwed with the screw rod 50. A mechanism and an electromagnetic motor 54 (hereinafter, simply referred to as “motor 54”) as a power source are provided. The motor 54 is fixedly accommodated in the motor case 56, and the flange portion of the motor case 56 is fixed to the upper surface side of the mount portion 24, and the flange portion 36 of the inner tube 32 is attached to the flange portion of the motor case 56. By being fixed, the inner tube 32 is connected to the mount portion 24 via the motor case 56. A motor shaft 58 that is a rotation shaft of the motor 54 is integrally connected to the upper end portion of the screw rod 50. That is, the screw rod 50 is disposed in the inner tube 32 with the motor shaft 58 extended, and is rotated by the motor 54. On the other hand, the nut 52 is fixedly supported on the upper end portion of the nut support cylinder 60 attached to the inner bottom portion of the outer tube 30 in a state of being screwed with the screw rod 50.

  The air spring 28 includes a housing 70 fixed to the mount portion 24, an air piston 72 fixed to the outer tube 30 of the actuator 26, and a diaphragm 74 connecting them. The housing 70 has a generally cylindrical shape with a lid, and is fixed to the lower surface side of the mount portion 24 on the upper surface side of the lid portion 76 in a state where the inner tube 32 of the actuator 26 is passed through a hole formed in the lid portion 76. Yes. The air piston 72 has a generally cylindrical shape, and is fixed to the upper portion of the outer tube 30 with the outer tube 30 fitted therein. The housing 70 and the air piston 72 are connected by a diaphragm 74 while maintaining airtightness, and the pressure chamber 44 is formed by the housing 70, the air piston 72, and the diaphragm 74. The pressure chamber 44 is filled with compressed air as a fluid. With such a structure, the air spring 28 elastically supports the lower arm 22 and the mount portion 24, that is, the wheel 12 and the vehicle body, by the pressure of the compressed air.

  From the structure as described above, when the spring upper portion and the spring lower portion approach and separate from each other, the outer tube 30 and the inner tube 32 can be relatively moved in the axial direction. Along with the relative movement, the screw rod 50 and the nut 52 relatively move in the axial direction, and the screw rod 50 rotates with respect to the nut 52. The motor 54 can apply a rotational torque to the screw rod 50, and generates a resistance force that prevents the stroke operation against the relative operation (stroke operation) between the sprung portion and the unsprung portion. Is possible. The actuator 26 functions as a so-called absorber (also referred to as “damper”) by causing this resistance force to act as a damping force against the stroke motion of the sprung portion and the unsprung portion. In other words, the actuator 26 has a function of applying a damping force to the stroke operation by an actuator force that is an axial force generated by the actuator 26 itself. The actuator 26 also has a function of causing the actuator force to act as a driving force, that is, a driving force for the stroke operation. With this function, a control based on the so-called skyhook damper theory that applies a damping force proportional to the sprung absolute speed to the action of the sprung spring, and a damping force proportional to the unsprung absolute speed to the action of the sprung part. It is possible to execute control based on the pseudo ground hook theory that causes Further, the actuator 26 positively changes the distance between the sprung portion and the unsprung portion in the vertical direction (hereinafter sometimes referred to as “distance between sprung springs”) by the actuator force, It also has a function of maintaining the distance at a predetermined distance. With this function, it is possible to effectively suppress the roll of the vehicle body at the time of turning, the pitch of the vehicle body at the time of acceleration / deceleration, and the adjustment of the vehicle height of the vehicle.

  As shown in FIG. 1, the suspension system 10 includes a fluid inflow / outflow device for inflowing / outflowing air (air) as a fluid with respect to an air spring 28 included in each spring / absorber assembly 20. An air supply / discharge device 80 is connected to the pressure chamber 44 of the spring 28, supplies air to the pressure chamber 44, and discharges air from the pressure chamber 44. Although detailed description is omitted, the suspension system 10 can adjust the amount of air in the pressure chamber 44 of each air spring 28 by the air supply / discharge device 80. The spring length of the air spring 28 can be changed to change the distance between the sprung springs for each wheel 12. Specifically, it is possible to increase the amount of air in the pressure chamber 44 to increase the distance between the sprung springs and decrease the amount of air to decrease the distance between the sprung springs.

  As shown in FIG. 1, the suspension system 10 includes a suspension electronic control unit 140 (hereinafter also referred to as “ECU 140”) serving as a control device, and the operation of the spring / absorber assembly 20, that is, the actuator 26 and the air spring. 28 is controlled. Specifically, the operation of the motor 54 of the actuator 26 and the operation of the air supply / discharge device 80 are controlled. The ECU 140 is a controller 142 composed mainly of a computer having a CPU, ROM, RAM, etc., a driver 144 as a drive circuit of the air supply / discharge device 80, and a drive circuit corresponding to the motor 54 of each actuator 26. Inverter 146. The driver 144 and the inverter 146 are connected to the battery 150 via the converter 148, and each control valve, pump motor, and the like of the air supply / discharge device 80 and the motor 54 of each actuator 26 are connected to the converter 148. Power is supplied from a power source including the battery 150 and the battery 150.

  The vehicle includes an ignition switch [I / G] 160, a vehicle speed sensor [v] 162 for detecting a vehicle traveling speed (hereinafter sometimes abbreviated as “vehicle speed”), and a sprung unsprung state for each wheel 12. Four height sensors [h] 164 for detecting the distance, vehicle height change switch [HSw] 166 operated by the driver for the vehicle height change instruction, and an operation angle sensor [δ for detecting the operation angle of the steering wheel 170, longitudinal acceleration sensor [Gx] 172 that detects actual longitudinal acceleration that is the longitudinal acceleration actually generated in the vehicle body, and lateral acceleration sensor [Gy] 174 that detects actual lateral acceleration that is the lateral acceleration actually generated in the vehicle body , Four sprung vertical acceleration sensors [Gzs] 176 for detecting the vertical acceleration (vertical acceleration) of each mount 24 of the vehicle body corresponding to each wheel 12, each wheel 1 There are four unsprung vertical acceleration sensors [Gzg] 178 for detecting the longitudinal acceleration of the engine, a throttle sensor [Sr] 180 for detecting the opening of the accelerator throttle, a brake pressure sensor [Br] 182 for detecting the master cylinder pressure of the brake, etc. They are provided and connected to the controller 142. The ECU 140 controls the operation of the spring absorber assembly 20 based on signals from these switches and sensors. Incidentally, the character [] is a symbol used when the above-mentioned switch, sensor, etc. are shown in the drawing. The ROM of the computer of the controller 142 stores a program related to the control of the actuator 26 described later, various data, and the like.

  As shown in FIG. 3, the motor 54 of each actuator 26 is a three-phase brushless DC motor in which coils are star-connected (Y-connected), and is controlled and driven by the inverter 146 as described above. The inverter 146 is a general one as shown in the figure, corresponds to each of the high side (high potential side) and the low side (low potential side), and the U phase which is the three phases of the motor 54. Six switching elements HUS, HVS, HWS, LUS, LVS, and LWS corresponding to each of the V, W, and W phases. The switching element control circuit 190 included in the inverter 146 includes a resolver [θ] 192 that is provided in the motor 54 and detects the rotation angle of the motor 54, and a current that is provided in the inverter 146 and actually flows through the motor 54. An energizing current sensor [I] 194 for measuring a certain energizing current is connected. The switching element control circuit 190 determines the motor rotation angle (electrical angle) by the resolver 192 and opens and closes the switching element based on the motor rotation angle. The inverter 146 drives the motor 54 by so-called sine wave drive, and the current flowing in each of the three phases of the motor 54 changes in a sine wave shape, and the phase difference differs by 120 ° in electrical angle. In addition, the switching element is controlled. Further, the inverter 146 has a structure capable of regenerating electric power (current) generated by electromotive force as a power source, and the motor 54 not only has a motor force depending on a supply current but also a motor force depending on a generated current. May occur. That is, the inverter 146 controls the motor force by adjusting the current flowing through the motor 46, that is, the energization current of the motor 54, regardless of whether the current is supplied from the power source or the generated current caused by the electromotive force. It is supposed to be a structure. The energization current is performed by each inverter 146 changing a ratio (duty ratio) between a pulse-on time and a pulse-off time by PWM (Pulse Width Modulation) control.

<Control of suspension system>
In the present suspension system 10, each of the four spring absorber assemblies 20 can be controlled independently. In each of these spring absorber assemblies 20, normally, the actuator force of the actuator 26 is independently controlled to control vibrations of the vehicle body and the wheels 12, that is, control for damping the sprung vibration and the unsprung vibration (hereinafter referred to as the spring vibration). , Sometimes referred to as “vibration damping control”). In addition, 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 “roll control”). (Sometimes referred to as “pitch suppression control”). In the vibration damping control, roll suppression control, and pitch suppression control, the target actuator force is determined by adding the vibration damping component, roll suppression component, and pitch suppression component, which are components of the actuator force for each control. It is executed comprehensively by being controlled to generate the target actuator force. In the following description, the actuator force and its component are positive values corresponding to the force in the direction (rebound direction) separating the sprung portion and the unsprung portion, and the direction causing the sprung portion and the unsprung portion to approach each other. It is assumed that the one corresponding to the force in the (bound direction) is a negative value.

  In the suspension system 10, a control for changing the vehicle height based on the driver's intention (hereinafter referred to as “vehicle height change”) for the purpose of coping with traveling on a road with large road undulations by the air spring 28. Is also executed). The vehicle height change control will be briefly described. The vehicle height change control is executed when a target set vehicle height that is a set vehicle height to be realized by an operation of the vehicle height change switch 166 based on the driver's intention is changed. A sprung unsprung distance as a target for each wheel 12 is set according to each of the target set vehicle heights, and a sprung spring for each wheel 12 is set based on a detection value of the height sensor 164. The operation of the air supply / discharge device 80 is controlled so that the lower distance becomes the target distance, and the unsprung distance between the springs of each wheel 12 is changed to a distance corresponding to the target set vehicle height. Further, in this vehicle height change control, so-called auto leveling control is also performed for the purpose of dealing with changes in vehicle height due to, for example, changes in the number of passengers and changes in the load capacity of luggage.

i) Vibration damping control In the vibration damping control, a vibration damping component F _V of the actuator force is determined so as to generate an actuator force having a magnitude corresponding to the vibration speed in order to attenuate the vibration of the vehicle body and the wheel 12. . That is, the control is based on both the control based on the so-called skyhook damper theory and the control based on the pseudo groundhook theory. More specifically, the vertical movement speed of the vehicle body mount 24 calculated from the spring vertical acceleration detected by the spring vertical acceleration sensor 176 provided on the vehicle mount 24, the so-called spring velocity Vs. Based on the vertical movement speed of the wheel 12 calculated from the unsprung longitudinal acceleration detected by the unsprung longitudinal acceleration sensor 178 provided in the lower arm 22, so-called unsprung speed Vg, vibration damping is performed according to the following equation. The component F _V is calculated.
F _V = Cs · Vs−Cg · Vg
Here, Cs is a gain for generating a damping force in accordance with the vertical operation speed of the mount 24 of the vehicle body, and Cg generates a damping force in accordance with the vertical operation speed of the wheel 12. For gain. That is, Cs and Cg can be considered as damping coefficients for so-called sprung and unsprung absolute vibrations.

ii) Roll suppression control When the vehicle turns, the roll moment resulting from the turn separates the sprung and unsprung parts on the turning inner ring side and causes the sprung and unsprung parts on the turning outer ring side to approach each other. It is done. In the roll suppression control, in order to suppress the separation on the turning inner ring side and the approach on the turning outer ring side, the actuator force in the bounce direction is applied to the actuator 26 on the turning inner ring side, and the actuator force in the rebound direction is applied to the actuator 26 on the turning outer ring side. Each is generated as a roll restraining force. Specifically, first, as a lateral acceleration indicating the roll moment received by the vehicle body, an estimated lateral acceleration Gyc estimated based on the steering angle δ of the steering wheel and the vehicle speed v, and a lateral acceleration sensor 174 were measured. Based on the actual lateral acceleration Gyr, a control lateral acceleration Gy ^* , which is a lateral acceleration used for control, is determined according to the following equation.
Gy ^* = K ₁ · Gyc + K ₂ · Gyr (K ₁ , K ₂ : gain)
Such based on the determined control-use lateral acceleration Gy ^*, the roll restrain component F _R is determined according to the following equation.
F _R = K ₃ · Gy ^* (K ₃ : Gain)

iii) Pitch suppression control For the nose dive of the vehicle body that occurs during deceleration, such as when braking the vehicle body, the sprung moment causing the nose dive brings the front spring side and the unsprung part closer together, The sprung part on the ring side and the unsprung part are separated from each other. In addition, for the squat of the vehicle body generated during the acceleration of the vehicle body, the sprung moment that generates the squat separates the front wheel side spring top and the spring bottom, and the rear wheel side spring top and spring bottom. Is approached. In the pitch suppression control, the actuator force is generated as the pitch suppression force in order to suppress the approach / separation distance in those cases. Specifically, as longitudinal acceleration indicative of the pitch moment acting on the vehicle body, is employed the actual longitudinal acceleration Gx that is actually measured by the longitudinal acceleration sensor 172, and based on the actual longitudinal acceleration Gx, the pitch restrain component F _P has the following formula Determined according to.
F _P = K ₄ · Gx (K ₄ : Gain)
It should be noted that the pitch suppression control is executed when the throttle opening detected by the throttle sensor 180 or the master cylinder pressure detected by the brake pressure sensor 182 exceeds a set threshold.

iv) Target Actuator Force and Motor Operation Control The actuator 26 is controlled based on a target actuator force that is an actuator force that should be generated. In detail, as described above, the vibration damping component F _V of the actuator force, a roll restrain component F _R, the pitch restrain component F _P is determined on the basis of their, to be applied to the sprung portion and the unsprung portion A reference absorber force F _B which is a reference absorber force is obtained according to the following equation.
F _B = F _V + F _R + F _P
Then, its reference absorber force F _B, based on the frictional force fr between the sprung-side unit and the unsprung-side unit to be described later in detail, so that the influence of the frictional force fr is reduced, the target according to the following equation The actuator force F ^* is determined.
F ^* = F _B ± fr
Incidentally, the frictional force fr is determined in consideration to the target actuator force F ^* is the direction of the reference absorber force F _B, sprung-side unit and the direction of relative movement of the unsprung-side unit (hereinafter, "relative movement direction" It may be referred to as Specifically, when the direction and the relative movement direction of the reference absorber force F _B is the same direction, since it becomes a force the frictional force opposing the reference absorber force, by the amount of dynamic friction than the reference absorber force to generate a large force, when the direction and the relative movement direction of the reference absorber force F _B are opposite, since it becomes a force that the friction force assists the reference absorber force, by an amount small force of dynamic friction force It is generated. In addition, when the unsprung unit and unsprung unit are not moving relative to each other, that is, by suppressing the roll of the vehicle body during turning, the pitch of the vehicle body during acceleration / deceleration, etc. When generating a force to maintain a predetermined distance, the frictional force is a force that maintains the unsprung distance between the unsprung springs at a predetermined distance. Therefore, a force that is smaller than the reference absorber force by the static friction force is applied. It is generated.

Then, the inverter 146 performs operation control of the motor 46 for generating the target actuator force F ^* determined as described above. More specifically, a target duty ratio is determined based on the target actuator force F ^* determined as described above, and a command based on the duty ratio is transmitted to the inverter 146. The inverter 146 controls the actuator force by controlling the opening and closing of the switching element and adjusting the current flowing through the motor 54 under the appropriate duty ratio.

v) Estimation of friction force (vehicle height change control when getting on and off)
Hereinafter, a method for estimating the frictional force fr between the unsprung unit and the unsprung unit will be described in detail. In the present suspension system 10, control for changing the vehicle height of the vehicle at the time of getting on and off as the control for facilitating getting on and off of the occupant and loading and unloading of the luggage by the actuator 26 (hereinafter referred to as “vehicle height change control at the time of getting on and off”). Is also executed, and the frictional force is estimated when the control is executed. In the vehicle height change control at the time of getting on and off, when the ignition switch 160 is turned OFF, the distance between the sprung springs is equal to the distance L ₀ between the sprung springs corresponding to the vehicle height at the time of getting on and off (hereinafter referred to as “the distance at getting on and off”). L ₀ ”), and when the occupant carrying the electronic key moves out of the range that can be detected by the sensor, the original unsprung distance before the start of control, that is, each wheel 12 is returned to a reference distance L _B which is the distance between the unsprung springs maintained by the air spring 28. On the contrary, when the passenger carrying the electronic key enters the range that can be detected by the sensor, the distance between the sprung and unsprung springs is the distance L ₀ when getting on and off, and the ignition switch 160 is turned on. , it is returned to the reference distance L _B.

Passenger when the vehicle height changing control is a passenger when the distance L ₀ or a reference distance L _B, sprung unsprung distance as a target for each wheel 12 (hereinafter, simply referred to as "target distance") as L ^* The target actuator force F ^* is determined in order to set and control the actuator 26 so that the distance between the sprung and unsprung portions becomes the target distance. Specifically, a sprung unsprung distance deviation ΔL (= L ^* −L _r ), which is a deviation of the actual sprung unsprung distance L _r detected by the height sensor 164 from the target distance L ^*, is recognized. The target actuator force F ^* is determined so that the sprung unsprung distance deviation ΔL becomes zero. The target actuator force F ^* is determined in the ECU 140 based on the PID control law of the following equation based on the sprung unsprung distance deviation ΔL.
F ^* = K _P · ΔL + K _I · int (ΔL) + K _D · ΔL ′
Here, the first term, the second term, and the third term are a proportional term component (P term component), an integral term component (I term component), and a differential term component (D term component), respectively, in the target actuator force F ^* . , K _P , K _I , and K _D mean proportional gain, integral gain, and differential gain, respectively. Int (ΔL) corresponds to an integral value of the sprung unsprung distance deviation ΔL. Incidentally, the integral term component generates a force for maintaining the sprung unsprung distance at a distance changed from the neutral position. As in the normal control of the actuator 26, a command based on the target duty ratio determined from the target actuator force F ^* is transmitted to the inverter 146, and the inverter 146 controls the actuator force.

In the above-described vehicle height change control at the time of getting on and off, when the distance between the unsprung springs is changed to the target getting on and off distance L ₀ by the actuator 26, the distance is reached against the elastic force of the air spring 28. Therefore, the actuator force F _A generated by the actuator 26, the unsprung side unit, and the unsprung side unit are obtained by losing the balance between the elastic force of the air spring 28 and the shared load when the target is reached. The distance L ₀ when getting on and off is maintained by the static frictional force fr _S between the two. That is, the static friction force fr _S can be estimated by the following equation.
fr _S = k · (L _B −L ₀ ) − | F _A |
Here, k is a spring constant of the air spring 28. The generated actuator force F _A can be obtained based on the detection value of the energization current sensor 194 in the inverter 146. That is, the energization current at the boarding time of the vehicle height changing control is a current supplied from the battery 150 to the motor 54, based on the supply current i _r, it can be determined according to the following equation. K _T is a torque constant of the motor 54.
F _A = K _T · _ir
From the static friction force fr _S , the dynamic friction force fr _D is also estimated according to the equation fr _D = C · fr _S (C: constant).

As described above, the static friction force fr _S and the dynamic friction force fr _{D that} are the estimated friction forces fr between the unsprung-side unit and the unsprung-side unit are the target in the control of the actuator 26 at the normal time. It is used to determine the actuator force. The estimated frictional force fr _S is also used for determining the failure of the actuator 26. Specifically, the actuator 26 is abnormal when the frictional force fr _S becomes equal to or greater than a set value fr ₀ that is a value set with reference to the frictional force that the actuator 26 has due to the structure of the actuator 26. It is determined. In addition, when the actuator 26 is abnormal, the driver is made to recognize it by a warning lamp or the like.

<Actuator control program>
The above-described control of the actuator 26 is performed by repeatedly executing the actuator control program shown in the flowchart of FIG. 4 by the controller 142 at a short time interval (for example, several milliseconds to several tens of milliseconds). A vehicle equipped with the suspension system 10 employs an electronic key, and a sensor (not shown) provided in the vehicle uses the electronic key when the electronic key is within a predetermined range from the vehicle. It can be detected. The above program is executed until a certain time (for example, 60 seconds) elapses after the electronic key is not detected after the electronic key is detected by the sensor. The control flow will be briefly described below with reference to the flowchart shown in the drawing. These control programs are executed for each of the actuators 26 of the spring absorber assembly 20 provided on each of the four wheels 12. In the following description, processing by this program for one actuator 26 will be described in consideration of simplification of description.

In the actuator control program, first, in step 1 (hereinafter abbreviated as “S1”, the same applies to other steps) to S3, vehicle height change control at S4 or less is executed, or normal time of S16 or less. It is determined whether to execute control for damping the vibration and suppressing the roll and pitch of the vehicle body. The vehicle height change control at the time of getting on and off is executed when an occupant carrying an electronic key enters a range that can be detected by the sensor, or when the ignition switch 160 is turned from ON to OFF, First, in S4, a boarding / alighting flag, which is a flag indicating that the vehicle height change control during boarding / exiting is being executed, is turned ON. Then, in S5 the following, the target distance L ^* is a distance between the sprung unsprung as a target, is a passenger when boarding at a distance L ₀ is sprung unsprung distance corresponding to the vehicle height, which is the determined The unsprung distance deviation ΔL (= L ^* −L _r ), which is the deviation of the actual unsprung distance L _r with respect to the target distance L ^*, is recognized, and the unsprung distance deviation ΔL is 0. Thus, the target actuator force F ^* in the vehicle height change control at the time of getting on and off is determined, and based on the determined target actuator force F ^* , the energization current, that is, the duty ratio of the motor 54 included in the actuator 26 is determined. A control signal for is sent to the inverter 146.
F ^* = K _P · ΔL + K _I · int (ΔL) + K _D · ΔL ′
The process is repeatedly executed until the electronic key is not detected or until the ignition switch 160 is turned ON, and the distance between the sprung spring and the unsprung spring is changed until the boarding / leaving distance L ₀ is maintained. Will be.

If the distance between the unsprung spring has reached boarding at a distance L ₀ is based on the supply current i _r to the motor 54 obtained from the detection value of the energizing current sensor 194, sprung-side unit and the unsprung-side The static frictional force fr _S with the unit is estimated by the expression fr _S = k · (L _B −L ₀ ) − | K _T · _ir |. From the static friction force fr _S , the dynamic friction force fr _D is also estimated according to the equation fr _D = C · fr _S. Note that, in S9, the estimated static friction force fr _S is, whether the threshold value fr ₀ or more is determined, when a threshold fr ₀ or more, as the actuator 26 is abnormal, in S10, The driver is made aware of the abnormality by turning on a warning lamp or sounding a warning buzzer.

If the electronic key is no longer detected, or if the ignition switch 160 is turned on, the reference distance L ^* is the distance between the unsprung spring maintained by the air spring 28 in S11. The distance is L _B. As in the case described above, the target actuator force F ^* is determined so that the sprung unsprung distance becomes the target distance L ^*, and a control signal is transmitted to the inverter 146. If the sprung unsprung distance is returned to the reference distance L _B , the boarding / alighting flag is turned off in S13, and the boarding / alighting vehicle height change control is terminated.

When the above-described vehicle height change control at the time of getting on and off is not executed, the control of the actuator 26 at the normal time is executed in S17 and after. Briefly, in S17 to S19, in the manner previously described, the vibration damping component F _V, the roll restrain component F _R, pitch restrain component F _P is determined, in S20, plus those three components In addition, a reference absorber force F _B that is a force to be applied to the sprung portion and the unsprung portion is determined. In S21 and 22, the target actuator force F ^* is determined so that the influence of the frictional force fr estimated in the vehicle height change control at the time of getting on and off becomes small. Specifically, the stroke speed V _st is calculated from the detection value of the height sensor 164 at the time of executing the current program and the previous program, and based on the stroke speed V _st , the frictional force is set so as to be a resistance force to the stroke. The sign is determined and the target actuator force F ^* (= F _B ± fr) is determined. Based on the determined target actuator force F ^* , the duty ratio is determined, and a control signal for the duty ratio is transmitted to the inverter 146. After the series of processes described above, one execution of this program ends.

<Functional configuration of control device>
The ECU 140 that executes the above-described actuator control program can be considered to have various functional units that execute various processes according to these programs. More specifically, as shown in FIG. 5, the ECU 140 executes the processing of S17 as a functional unit that determines the vibration damping component F _V , and performs the processing of S18 and roll suppression component F as a functional unit that determines the vibration damping component F _V. as a functional unit for determining the _R, the roll control section 202, as a functional portion to determine the pitch restrain component F _P and executes the processing of S19, a pitch reduction control unit 204 respectively have. Moreover, ECU140 has the vehicle height change control part 206 at the time of getting on / off as a function part which performs the process of S4-S15 and determines the actuator force for changing the vehicle height at the time of getting on / off. The boarding / alighting vehicle height change control unit 206 executes the processes of S6 to S8 to estimate the frictional force fr between the sprung-side unit and the unsprung-side unit. Each of the failure determination units 210 is provided as a function unit that determines that the actuator 26 is abnormal when the frictional force fr estimated by the frictional force estimation unit 208 is greater than or equal to a set limit. Further, the ECU 140 includes a target actuator force determination unit 212 as a functional unit that executes the processes of S21 and S22 and determines the target actuator force F ^* in consideration of the friction force fr estimated by the friction force estimation unit 208. is doing.

  Due to the above configuration, the suspension system 10 maintains the supplied current when changing the distance between the unsprung springs by controlling the operation of the actuator 26, more specifically, the set distance between the unsprung springs. The frictional force between the sprung-side unit and the unsprung-side unit is estimated based on the supply current at the time. Therefore, the present system 10 is a system that can easily estimate the frictional force between the unsprung unit and the unsprung unit. In addition, since the energizing current sensor 194 provided for controlling the motor 54 is used for detecting the supply current, it is not necessary to add an extra sensor or the like, so that the system has a simple configuration. .

  Further, since the system 10 determines the target actuator force in consideration of the estimated friction force, even if the friction force changes, an appropriate force is applied to the sprung portion and the unsprung portion. Therefore, it is possible to prevent deterioration of the ride comfort, maneuverability and stability of the vehicle.

<Modification>
In the first embodiment, the frictional force between the unsprung unit and the unsprung unit has been directly calculated and estimated. For example, (i) by controlling the operation of the actuator 26, The actual supply current when changing the distance between the sprung and unsprung springs, and (ii) the design frictional force in which the frictional force between the unsprung and unsprung units is determined by the structure of the actuator 26. The frictional force is designed based on the difference from the required supply current, which is the supply current required when the distance between the sprung and unsprung parts is changed by controlling the operation of the actuator 26. A change from the frictional force may be estimated.

<< Second Embodiment >>
Since the vehicle suspension system of the second embodiment has the same hardware configuration as that of the system of the first embodiment, in the description of this embodiment, components having the same functions as the system of the first embodiment are described. Indicates that they correspond by using the same reference numerals, and a description thereof will be omitted. The system of this embodiment is different from the system of the first embodiment in that the control of the actuator 26 by the ECU 140 is different from the system of the first embodiment. Specifically, in the system of the first embodiment, the frictional force is estimated based on the supply current at the time when the set sprung unsprung distance is maintained. Is estimated based on the supply current at the time when the change starts from the distance when the elastic force of the air spring 28 and the shared load are balanced. Hereinafter, a method for estimating the frictional force will be described in detail.

The actuator 26 in the system of this embodiment is controlled by a short time interval (for example, several milliseconds to several tens of milliseconds) while the ignition switch 160 is turned on by the actuator control program shown in the flowchart of FIG. It is performed by being repeatedly executed by the controller 142. In this system, instead of the vehicle height change control at the time of getting on and off in the first embodiment, control for changing the vehicle height in order to estimate the friction force of S32 or less (hereinafter referred to as “vehicle height change control for friction force estimation”). Is sometimes executed). The frictional force estimation vehicle height change control is executed first after the ignition switch 160 is turned on, and the frictional force between the sprung-side unit and the unsprung-side unit is estimated. Specifically, in the frictional force estimation vehicle height change control, in S32, the target energization current i ^* (supply current) to the motor 54 is determined, and the energization current i ^* is determined based on the execution of the program. Every time δi is increased. Then, when there is a change in the actual sprung unsprung distance L _r detected from the height sensor 164, the actuator force exceeds the frictional force between the sprung unit and the unsprung unit. Become. That is, it can be considered that the frictional force between the unsprung unit and the unsprung unit is substantially equal to the magnitude of the actuator force during the previous program execution. Therefore, based on the supply current i _r detected by electric current sensors 194 during execution of the previous program, together with the static friction force fr _S is estimated (S34), the dynamic friction force fr _D from the static friction force fr _S It is estimated (S35).
fr _S = K _T · _ir
fr _D = C · fr _S
By the way, after the frictional force fr is estimated, the target supply current i ^* is set to 0 in S37. Therefore, in the system of this embodiment, the frictional force is estimated almost without changing the vehicle height. Is possible.

Then, the estimated frictional force fr is used for determining the target actuator force in the control of the actuator 26 at the normal time, and is determined according to the following equation. (S45, S46)
F ^* = F _B ± fr
The estimated static friction force fr _S is also used for determining the failure of the actuator 26. When the static friction force fr _S becomes equal to or greater than the set value fr ₀ , it is determined that the actuator 26 is abnormal. (S38, S39).

  With the configuration as described above, the suspension system of this embodiment starts to change the supply current when changing the distance between the unsprung springs by controlling the operation of the actuator 26, specifically, the distance between the unsprung springs. The frictional force between the sprung-side unit and the unsprung-side unit is estimated based on the supply current at the time of doing. Therefore, the system of the present embodiment is also a system that can easily estimate the frictional force between the sprung-side unit and the unsprung-side unit, similarly to the system of the first embodiment.

1 is a schematic diagram showing an overall configuration of a vehicle suspension system according to a first embodiment of the claimable invention. It is front sectional drawing which shows the spring absorber Assy shown in FIG. FIG. 3 is a circuit diagram of a drive circuit or the like that controls an electromagnetic motor included in the actuator of FIG. 2. It is a flowchart showing the actuator control program performed by the suspension electronic control unit shown in FIG. It is a block diagram regarding the function of the suspension electronic control unit which the suspension system for vehicles shown in FIG. 1 has. It is a flowchart showing the actuator control program executed by the suspension electronic control unit in the vehicle suspension system of the second embodiment.

Explanation of symbols

  10: Vehicle suspension system 12: Wheel 20: Spring absorber assembly 22: Lower arm (lower part of spring) 24: Mount part (upper part of spring) 26: Actuator (shock absorber) 28: Air spring (suspension spring) 50: Screw rod ( Male thread part) 52: Nut (female thread part) 54: Electromagnetic motor 80: Air supply / discharge device 140: Suspension electronic control unit (ECU) 142: Controller 146: Inverter 150: Battery (power source) 164: Height sensor 194: Current flow Sensor 200: Vibration damping control unit 202: Roll suppression control unit 204: Pitch suppression control unit 206: Vehicle height change control unit during boarding / exiting 208: Friction force estimation unit 210: Failure determination unit 212 : Target actuator force determination unit (Target absorber force determination unit)

Claims (7)

A suspension spring that elastically connects the sprung portion and the unsprung portion;
(A) a sprung unit connected to the sprung portion; and (b) the sprung portion connected to the sprung portion according to the approach / separation between the sprung portion and the sprung portion. An unsprung side unit capable of relative movement with the side unit; and (c) an electromagnetic motor, and depending on the force of the electromagnetic motor, the unsprung side unit and the unsprung side unit An electromagnetic shock absorber that generates an absorber force that is a force against movement;
A vehicle suspension system comprising a control device for controlling the operation of the shock absorber,
Supply current which is a current supplied from the power source to the electromagnetic motor when the control device controls the operation of the shock absorber to change the distance between the sprung portion and the unsprung portion. A suspension system for a vehicle, comprising: a frictional force estimating unit that estimates a frictional force between the unsprung side unit and the unsprung side unit. The control device is
Vibration damping control for generating an absorber force generated by the shock absorber as a damping force for attenuating at least the vibration of the sprung portion can be executed.
A target absorber force determination unit that determines a target absorber force, which is a target absorber force in the vibration damping control, based on the friction force estimated by the friction force estimation unit to a value in which the friction force is considered. Item 2. The vehicle suspension system according to Item 1. The control device is capable of executing control based on the Skyhook damper theory as vibration damping control,
The target absorber force determination unit causes the target absorber force to act between the sprung portion and the unsprung portion when generating a propulsive force with respect to the relative movement between the sprung portion side unit and the unsprung portion side unit. It is determined to be a value corresponding to the frictional force estimated by the frictional force estimation unit, compared to a reference absorber force that is a power-based absorber force, and the unsprung unit and unsprung unit 3. When the resistance force is generated with respect to the relative movement, the determination is made to be smaller than the reference absorber force according to the friction force estimated by the friction force estimation unit. Vehicle suspension system. The control device is
4. The failure determination unit according to claim 1, further comprising a failure determination unit that determines that the shock absorber is abnormal when the friction force estimated by the friction force estimation unit exceeds a set limit. 5. Vehicle suspension system.   The frictional force estimating unit estimates the frictional force between the unsprung unit and the unsprung unit based on a supply current at the time when the set sprung unsprung distance is maintained. The vehicle suspension system according to any one of claims 1 to 4, wherein the vehicle suspension system is configured.   The frictional force estimating unit is configured to estimate a frictional force between the unsprung unit and the unsprung unit based on a supply current at the time when the distance between the sprung and unsprung parts starts to change. The vehicle suspension system according to any one of claims 1 to 4. The shock absorber is
(A) a screw rod that forms at least a part of one of the sprung unit and the unsprung unit, and is formed with a male screw; and (B) the sprung unit and the unsprung unit. Comprising at least a part of the other, a nut formed with an internal thread and screwed into the threaded rod;
One of the threaded rod and the nut is rotatable with relative movement between the spring upper part and the unsprung part, and the electromagnetic motor applies a force to one rotation of the threaded rod and the nut. With structure,
The vehicle suspension system according to any one of claims 1 to 6, wherein the frictional force estimating unit is configured to estimate a frictional force between the screw rod and the nut.

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