Vehicle stabilizer system

A stabilizer system for a vehicle including: a stabilizer bar connected to left and right wheels at respective opposite ends thereof; an actuator which has an electric motor and which changes elastic force to be exhibited by the stabilizer bar, as a result of control of an operation of the electric motor; and a control device which controls the operation of the electric motor, wherein the control device includes an operation-mode changing portion which changes an operation mode of the electric motor that depends on a motor-phase-connecting formation and a power-supply status of the electric motor, on the basis of at least one of a vehicle running state and road surface condition.

This application is based on Japanese Patent Application No. 2004-381554 filed on Dec. 28, 2004, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a stabilizer system installed on a vehicle for reducing or restraining rolling of a body of the vehicle, and more particularly to such a stabilizer system in which elastic force to be exerted by a stabilizer bar is changeable by an actuator having an electric motor.

2. Discussion of Related Art

In recent years, there has been developed a so-called “active stabilizer”, in detail, a stabilizer system in which elastic force to be exerted by a stabilizer bar is changed for effectively controlling or restraining rolling of a body of a vehicle. For instance, JP-A-2002-518245 and JP-A-2000-71738 disclose such a stabilizer system. The disclosed stabilizer systems include an electric motor whose operation is controlled for thereby effectively restraining the rolling of the vehicle body. In the disclosed stabilizer systems, the control of the operation of the motor is executed based on a rolling angle, a rolling moment, and so on, whereas the control of the operation of the motor is not executed in a range wherein the rolling is uncontrollable by the motor or the motor is overloaded.

SUMMARY OF THE INVENTION

In actual running of the vehicle, a determination as to whether or not the operation of the motor should be controlled varies depending upon a running state of the vehicle, condition of a road surface on which the vehicle travels, etc. Accordingly, the disclosed stabilizer systems which are arranged not to execute the control of the operation of the motor in the uncontrollable range or in the overloaded range are not sufficiently practical. This invention has been developed in the light of the situations described above. It is therefore an object of the invention to improve utility of a stabilizer system having an electric motor and executing a control for restraining rolling of a vehicle body.

To achieve the object indicated above, a stabilizer system of the present invention that includes an actuator having an electric motor and changing elastic force to be exerted by a stabilizer bar is arranged such that an operation mode relating to the electric motor, in detail, the operation mode which depends on a motor-phase-connecting formation and a power-supply status of the electric motor is changeable on the basis of at least one of a running state of a vehicle and surface condition of a road on which the vehicle travels.

In the stabilizer system according to the present invention, the operation mode of the motor is arranged to be changeable on the basis of the at least one of the vehicle running state and the road surface condition. Therefore, the present stabilizer system can work so as to be adapted to actual running of the vehicle, thereby assuring high utility.

FORMS OF INVENTION

There will be described in detail various forms of an invention, which are considered claimable. Each of the forms of the invention is numbered like the appended claims and depends from the other form or forms, where appropriate, for easier understanding of the invention. It is to be understood that the invention is not limited to the technical features or any combinations thereof which will be described, and shall be construed in the light of the following descriptions of the various forms and preferred embodiments of the invention. It is to be further understood that a plurality of elements or features included in any one of the following forms of the invention are not necessarily provided all together, and that any form in which one or more elements or one or more features is/are added to any one of the following forms and any form in which one or more elements or one or more features is/are deleted from any one of the following forms may be considered claimable.

(1) A stabilizer system for a vehicle comprising:a stabilizer bar connected to left and right wheels at respective opposite ends thereof;an actuator which has an electric motor and which changes elastic force to be exhibited by the stabilizer bar, as a result of control of an operation of the electric motor; anda control device which controls the operation of the electric motor,wherein the control device includes an operation-mode changing portion which changes an operation mode of the electric motor that depends on a motor-phase-connecting formation and a power-supply status of the electric motor, on the basis of at least one of a vehicle running state and road surface condition.

The stabilizer system constructed according to the above-indicated form (1) is a so-called “active stabilizer system” in which elastic force to be exerted by a stabilizer bar is actively adjusted, thereby enabling active controlling of rolling of the vehicle body. In the stabilizer system according to the above form (1), the operation mode of the electric motor of the actuator is arranged to be changeable on the basis of at least one the vehicle running state and the road surface condition. Accordingly, the actuator can be controlled so as to be adapted to actual running of the vehicle, realizing the stabilizer system with high utility.

“Control of an operation of the electric motor” in the above form (1) means, for instance, that electric power to be supplied to the electric motor is controlled, namely, an operation amount, an operation force, etc., of the electric motor are controlled. (Where the electric motor is a rotary motor, a rotary amount, a torque, etc, are controlled.) As described above, “operation mode” of the electric motor depends on the motor-phase-connecting formation and the power-supply status of the electric motor. Here, “motor-phase-connecting formation” means a formation in relation to changing of phases of the motor in supplying electric power from a power source to the motor, connection between input lines of the respective phases of the electric motor and the power source, interrelation among the input lines of the respective phases, etc. The motor-phase-connecting formation will be explained in greater detail. “Power-supply status” means, for instance, a status as to whether or not electric power is under supply to the electric motor, how much power is supplied, and when or what timing electric power is supplied. As illustrated below, various modes can be set as the operation mode depending upon the motor-phase-connecting formation and the power-supply status, and the individual modes can have respective peculiar or inherent characteristics. Accordingly, by changing the operation mode of the electric mood while taking advantage of the inherent characteristics of the respective modes, the characteristics of the stabilizer can be variously changed. In this respect, the stabilizer system according to the form (1) assures high utility.

In the above-indicated form (1), the operation mode is changed based on at least one of the vehicle running state and the road surface condition. Here, “vehicle running state” is a concept including not only an actual running state of the vehicle, but also a posture of the vehicle, a posture of a body of the vehicle, a state in which the vehicle is operated, and so on. More specifically described, the vehicle running state includes various parameters which indicate various states such as: a running speed of the vehicle (which is a concept that also includes a wheel rotation speed and which may be hereinafter referred to as “vehicle speed”); posture-related amount such as a pitch angle or a rolling angle; a turning-state amount (which is a concept that includes a steering amount, a lateral force or a cornering force acting on the vehicle and the wheels, lateral acceleration generated in the vehicle, a yaw rate, a slipping angle, and the like); a braking state of the vehicle; an accelerating state of the vehicle; a magnitude of damping force generated by a suspension device. The vehicle running state, in detail, the above-indicated various parameters can be detected using appropriate known sensors. In this form (1), the operation mode can be changed based on detected values and detected results obtained by the sensors. Further, “road surface condition” means, for instance, a degree of roughness, bumpiness, ups and downs, waviness, inclination, or a surface friction coefficient μ, of the road on which the vehicle travels. Values of various parameters that indicate those described above can be a road-surface-condition amount indicative of the road surface condition. The road surface condition can be obtained as follows, for instance: There are detected using known sensors vertical acceleration of the vehicle body, a distance between upper and lower members which are respectively located above and below a suspension spring for each wheel, acceleration in a vertical movement of the upper member for each wheel, and so on. Based on the values detected by the sensors, the road surface condition can be obtained. In this form (1), the operation mode of the electric motor can be changed on the basis of the thus obtained road surface condition.

In the above-indicated form (1), it is to be understood that “stabilizer apparatus” is constituted by including the stabilizer bar and the actuator. The structure of the stabilizer bar is not particularly limited in this form (1). For instance, the stabilizer bar may be configured as follows: The actuator is disposed between one end of the stabilizer bar and a wheel-hold member to which the one end of the stabilizer bar is connected. A distance between the above-indicated one end of the stabilizer bar and the wheel-hold member is suitably adjusted by the actuator, whereby the elastic force to be exerted by the stabilizer bar is arranged to be changeable. Alternatively, the stabilizer bar may be configured as follows: The stabilizer bar is divided into two, namely, a pair of stabilizer bar members between which the actuator is disposed. The pair of stabilizer bar members are rotated relative to each other by the actuator, whereby the elastic force to be exerted by the stabilizer bar is arranged to be changeable. In this form (1), the structure of “actuator” is not particularly limited. The actuator may include, in addition to the electric motor, a decelerator, a mechanical brake, etc. As “electric motor”, any type may be employed, as long as its operation mode is arranged to be changeable. For instance, there may be employed a DC brushless motor which will be explained, an induction motor, a synchronous motor, a stepping motor or a reluctance motor. From the viewpoint of a motion, either a rotary motor or a linear motor may be employed.

(2) The stabilizer system according to the above form (1), wherein the operation-mode changing portion changes the operation mode of the electric motor between (a) a control mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor is controllable and wherein electric power is supplied to the electric motor and (b) a non-control mode wherein the control of the operation of the electric motor is not executed by the control device.

“Control mode” in the above-indicated form (2) is an operation mode in which the amount of electric power supplied to the electric motor is controlled while changing phases of the electric motor in supplying electric power to the motor, thereby controlling the operation of the motor. That is, the control mode is an operation mode for executing a so-called “ordinary control” of the motor. The control mode is to be understood as an operation mode that intends to actively change the elastic force to be exerted by the stabilizer bar by controlling the actuator. On the contrary, unlike the control mode described above, “non-control mode” is an operation mode in which the electric motor is not controlled in a manner similar to that in the control mode. The non-control mode is to be understood as an operation mode that does not intend to actively control the actuator. For instance, the non-control mode may be an operation mode in which electric-power supply from a power source to the electric motor is not conducted. By changing the operation mode to such an operation mode, power consumption of the stabilizer system can be reduced.

(3) The stabilizer system according to the above form (2), wherein the operation-mode changing portion changes the operation mode of the electric motor between the control mode and one of operation modes each as the non-control mode selected from (b-1) a stand-by mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor is controllable and wherein electric power is not supplied to the electric motor, (b-2) a braking mode wherein the motor-phase-connecting formation is a formation in which phases of the electric motor are connected to each other, and (b-3) a free mode wherein the motor-phase-connecting formation is a formation in which electric power is inhibited from being supplied to phases of the electric motor.

In the above-indicated form (3), the non-control mode described above is limited to one of operation modes selected from three concrete operation modes. The three modes (b-1)-(b-3) do not intend to actively control the actuator. Further, in the three modes, electric-power supply from a control power source to the electric motor is not conducted. The three modes have respective peculiar or inherent characteristics described below. By appropriately selecting one of the three operation modes, the actuator can be optimally controlled taking advantage of the characteristic of the selected operation mode. In this form (3), it is not necessary that the control device be arranged to execute all of the three operation modes. The control device may be arranged to execute at least one of the three modes. Namely, this form (3) includes an arrangement in which only one of the three modes is executed and the operation mode of the motor is changed between that one mode and the control mode described above.

“Stand-by mode” in the above-indicated form (3) is considered as an operation mode wherein changing of the phases of the electric motor is executed whereas electric-power supply to the motor is not conducted. For instance, in the stand-by mode, as explained in detail below, where a power source device for supplying electric power to the motor is constituted by including an inverter, changing of switching elements of the inverter on one of a plus(+) side and a minus(−) side is carried out whereas duty control by switching elements on the other of the plus(+) side and the minus(−) side is not carried out. The stand-by mode assures excellent readiness and responsiveness in shifting to the control mode. Further, because the stand-by mode can permit regeneration of an electromotive force generated by the electric motor as explained below, it is possible to apply, to the actuator, braking effect owing to the regeneration and to achieve power saving of the stabilizer system.

“Braking mode” in the above-indicated form (3) is considered as an operation mode wherein the motor-phase-connecting formation is a formation in which the input lines of the electric motor are connected to each other. Where the phases of the motor are connected to each other without any resistance intervened, namely, where the phases are short-circuited, there can be obtained effect of so-called “short-circuit braking”. The short-circuit braking is one kind of braking utilizing the electromotive force generated in the electric motor, and assures relatively large braking effect among braking utilizing the electromotive force. Accordingly, owing to the short-circuit braking, the stabilizer bar is nearly locked, thereby enabling the stabilizer bar to exhibit a function close to that of a non-active, conventional stabilizer bar. Where the phases are connected to each other with resistances intervened, medium-degree braking effect can be obtained. Though the medium-degree braking provides braking force smaller than that provided by the short-circuit braking, a part of the electromotive force is consumed by the resistances, thereby inhibiting generation of heat in the electric motor. As explained below in detail, where a power source device for supplying electric power to the motor is constituted by including an inverter, this braking mode is realized, for instance, by placing the switching elements of the respective phases on one of the plus(+) side and the minus(−) side, into ON state (into a closed state).

“Free mode” in the above-indicated form (3) is generally an operation mode wherein the input lines of the respective phases of the electric motor and a power source are disconnected from each other, in other words, an operation mode wherein each phase of the electric motor is placed in an open state. In this free mode, the electromotive force is not generated and substantially no braking effect is obtained. Accordingly, by employing this operation mode, the stabilizer bar exerts little elastic force and therefore it may be considered that the vehicle is not equipped with the stabilizer. In this respect, under this operation mode, independency is maintained on the right side and the left side of the vehicle in a situation wherein there acts an external force that moves the right-side and left-side wheels vertically in opposite directions, e.g., in a situation wherein the right-side wheel or left-side wheel runs onto a projection. Therefore, it is possible to improve ride comfort as felt by passengers of the vehicle during traveling on a bumpy road, a mogul road, or the like. As explained below in detail, where a power source device for supplying electric power to the motor is constituted by including an inverter, this free mode is realized, for instance, by placing all of the switching elements of the respective phases into OFF state (into an open state).

Where a plurality of operation modes among the above-indicated three operation modes (b-1)-(b-3) are executable and one operation mode is selected from the plurality of operation modes based on certain conditions, the operation mode of the motor can be also changed among the plurality of operation modes. Thus, above-indicated form (3) includes an arrangement in which the changing of the operation mode can be conducted among the non-control modes. In other words, the system according to a claimable invention can be practiced in a form in which the operation-mode changing portion changes the operation mode of the electric motor between: (a) the control mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor is controllable and wherein electric power is supplied to the electric motor; and at least two of operation modes selected from (b-1) the stand-by mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor is controllable and wherein electric power is not supplied to the electric motor, (b-2) the braking mode wherein the motor-phase-connecting formation is a formation in which phases of the electric motor are connected to each other, and (b-3) the free mode wherein the motor-phase-connecting formation is a formation in which electric power is inhibited from being supplied to the phases of the electric motor.

(4) The stabilizer system according to any one of the above forms (1)-(3), wherein the operation-mode changing portion includes a vehicle-speed-dependent determining portion which determines the operation mode of the electric motor to be changed, on the basis of a running speed of the vehicle as the vehicle running state.

In actual running of the vehicle, the degree of rolling of the vehicle body depends on the running speed of the vehicle. In detail, in turning of the vehicle, where the vehicle speed is large, namely, where the vehicle is running at a high speed, the rolling of the vehicle body is relatively large. On the contrary, where the vehicle speed is small, namely, where the vehicle is running at a low speed, the rolling of the vehicle body is relatively small. In other words, demand for the control of the stabilizer apparatus depends on the vehicle running state such as the vehicle speed. The above-indicated form (4) is arranged to determine the operation mode in the light of the above and permits the stabilizer apparatus to be controlled so as to be adapted to the actual running of the vehicle.

(5) The stabilizer system according to the above form (4), wherein the vehicle-speed-dependent determining portion determines the operation mode of the electric motor to be (b-3) a free mode wherein the motor-phase-connecting formation is a formation in which electric power is inhibited from being supplied to phases of the electric motor, where the running speed of the vehicle is smaller than a predetermined threshold speed.

The above-indicated form (5) is one form relating to determination of the operation mode of the motor based on the vehicle speed. As explained above, when the vehicle is running at a low speed, there is a little chance that the rolling amount is large. Therefore, the necessity to actively control the rolling is low. In view of this, the free mode is employed, in this form (5), as the operation mode of the motor when the vehicle is running at a low speed. The free mode assures good ride comfort as felt by the passengers of the vehicle as explained above, so that this form (5) realizes the stabilizer system which gives priority to the ride comfort of the vehicle during low-speed running. This form (5) may be regarded as one form that employs the non-control mode when the vehicle is running at a low speed. There may be realized a stabilizer system which employs, during the low-speed running, other two non-control modes except for the free mode, though this stabilizer system does not belong to this form (5).

(6) The stabilizer system according to any one of the above forms (1)-(5), wherein the operation-mode changing portion includes a steering-amount-dependent determining portion which determines the operation mode of the electric motor to be changed, on the basis of a steering amount of the vehicle as the vehicle running state.

In actual running of the vehicle, the degree of rolling of the vehicle body depends on the steering amount of the vehicle. In detail, in turning of the vehicle, where the steering amount is large, the rolling of the vehicle body is relatively large. On the contrary, where the steering amount is small, the rolling of the vehicle body is relatively small. In other words, demand for the control of the stabilizer apparatus depends on the vehicle running state such as the steering amount. The above-indicated form (6) is arranged to determine the operation mode in the light of the above and permits the stabilizer apparatus to be controlled so as to be adaptable to the actual running of the vehicle. “Steering amount” in this form (6) may be an operation amount of a steering-operating member such as a steering wheel (e.g., a steering angle), a steered amounts of wheels indicated by an amount of movement of a steering rod of a wheel-steering device, or the like

The above-indicated form (6) can be practiced as a form in which the steering-amount-dependent determining portion determines the operation mode of the electric motor to be the non-control mode described above where the steering amount is not greater than a predetermined threshold steering amount. As explained above, where the steering amount is small, there is a little chance that the rolling amount is large. Therefore, the necessity to actively control the rolling is low. This form (6) takes into account this.

(7) The stabilizer system according to any one of the above forms (1)-(3), wherein the operation-mode changing portion includes: a vehicle-speed-dependent determining portion which determines the operation mode of the electric motor to be changed, on the basis of a running speed of the vehicle as the vehicle running state; and a steering-amount-dependent determining portion which determines the operation mode of the electric motor to be changed, on the basis of a steering amount of the vehicle as the vehicle running state.

In the above-indicated form (7), the operation-mode changing portion includes both of the vehicle-speed-dependent determining portion and the steering-amount-dependent determining portion described above. This form (7) permits the stabilizer apparatus to be controlled so as to be adapted to the running state of the vehicle owing to the two determining portions. This form (7) may be regarded as a form in which the vehicle-speed-dependent determining portion and the steering-amount-dependent determining portion cooperate with each other to determine the operation mode of the electric motor. More specifically described, this form (7) includes, for instance, an arrangement in which the vehicle-speed-dependent determining portion initially determines a plurality of operation modes and the steering-amount-dependent determining portion then determines one operation mode among the determined plurality of operation modes, and an arrangement in which the steering-amount-dependent determining portion initially determines a plurality of operation modes and the vehicle-speed-dependent determining portion then determines one operation mode among the determined plurality of operation modes.

(8) The stabilizer system according to the above form (7), wherein the vehicle-speed-dependent determining portion determines the operation mode of the electric motor to be changed, by comparison between the running speed of the vehicle and a predetermined threshold speed, and the steering-amount-dependent determining portion determines the operation mode of the electric motor to be changed, by comparison between the steering amount of the vehicle and a predetermined threshold steering amount.

In the above-indicated form (8), the two determining portions are arranged to determine the operation mode on the basis of the thresholds respectively set for the two determining portions. According to this form (8), the operation mode of the electric motor can be determined in a simple manner. One of, or both of, the threshold speed and the threshold steering amount may be a fixed value or respective fixed values, or may be varied continuously or in steps (ultimately between two values), based on certain conditions, parameters, or the like.

(9) The stabilizer system according to the above form (7) or (8), wherein the operation-mode changing portion is arranged such that the vehicle-speed-dependent determining portion and the steering-amount-dependent determining portion determine the operation mode of the electric motor to be changed to be (b-3) a free mode wherein the motor-phase-connecting formation is a formation in which electric power is inhibited from being supplied to phases of the electric motor, where the steering amount of the vehicle is smaller than a predetermined threshold steering amount and the running speed of the vehicle is smaller than a predetermined threshold speed and such that the vehicle-speed-dependent determining portion and the steering-amount-dependent determining portion determine the operation mode of the electric motor to be changed to be (b-1) a stand-by mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor is controllable and wherein electric power is not supplied to the electric motor, where the steering amount of the vehicle is smaller than the predetermined threshold steering amount and the running speed of the vehicle is not smaller than the predetermined threshold speed.

The above-indicated form (9) is one concrete form of determining the operation mode of the electric motor by the two determining portions. For instance, this form (9) may be arranged such that the steering-amount-dependent determining portion selects the free mode and the stand-by mode explained above where the steering amount is small and such that the vehicle-speed-dependent determining portion selects one of those two operation modes selected by the steering-amount-dependent determining portion, thereby determining the operation mode of the electric motor. According to this form (9), because the rolling of the vehicle body is small and therefore the necessity to actively control the actuator is low where the vehicle speed and the steering amount are small, the ride comfort of the vehicle has priority taking advantage of the characteristics of the free mode. In a case where the vehicle speed is increased to a higher level, the operation mode is changed from the free mode to the stand-by mode in which the active rolling control is executable with good readiness taking advantage of the characteristics of the stand-by mode when the rolling becomes large due to a variation in the steering amount.

(10) The stabilizer system according to any one of the above forms (7)-(9), wherein the operation-mode changing portion is arranged such that the vehicle-speed-dependent determining portion and the steering-amount-dependent determining portion determine the operation mode of the electric motor to be changed to be (b-2) a braking mode wherein the motor-phase-connecting formation is a formation in which phases of the electric motor are connected to each other, where the steering amount of the vehicle is not smaller than a predetermined threshold steering amount and the running speed of the vehicle is smaller than a predetermined threshold speed and such that the vehicle-speed-dependent determining portion and the steering-amount-dependent determining portion determine the operation mode of the electric motor to be changed to be (a) a control mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor is controllable and wherein electric power is supplied to the electric motor, where the steering amount of the vehicle is not smaller than the predetermined threshold steering amount and the running speed of the vehicle is not smaller than the predetermined threshold speed.

The above-indicated form (10) is one concrete form of determining the operation mode of the electric motor by the two determining portions. For instance, this form (10) may be arranged such that the steering-amount-dependent determining portion selects the control mode and the braking mode explained above where the steering amount is large and such that the vehicle-speed-dependent determining portion selects one of those two operation modes selected by the steering-amount-dependent determining portion, thereby determining the operation mode of the electric motor. According to this form (10), because the rolling of the vehicle body is large where the vehicle speed and the steering amount are large, the operation mode of the electric motor is determined to be the control mode wherein the actuator is actively controllable. Though the necessity to actively control the actuator is comparatively small where the vehicle speed is relatively small, the braking mode is determined as the operation mode making good use of the characteristic of the braking mode that the elastic force is exerted by the stabilizer bar to some extent.

(11) The stabilizer system according to any one of the above forms (8)-(10), wherein the operation-mode changing portion includes a threshold changing portion which changes at least one of the threshold steering amount and the threshold speed which is set for one of the steering amount of the vehicle and the running speed of the vehicle, on the basis of the other of the steering amount of the vehicle and the running speed of the vehicle.

The above-indicated form (11) includes, for instance, an arrangement in which the threshold steering amount is changed depending upon the vehicle speed in determination of the operation mode by the steering-amount-dependent determining portion, an arrangement in which the threshold speed is changed depending upon the steering amount in determination of the operating mode by the vehicle-speed-dependent determining portion, and an arrangement in which those two arrangements are combined. Where the operation mode is changed as a result of a change in the vehicle speed or the steering amount across the threshold, the vehicle operator may feel a control gap. Briefly speaking, there is a possibility that the vehicle operator feels discomfort in the behavior of the vehicle at transition of the operation modes from one to another, due to difference in characteristics between the operation modes. According to this mode (11) wherein the threshold is changeable, it is possible to change the operation mode while allowing the vehicle operator to feel the control gap as minimum as possible.

(12) The stabilizer system according to any one of the above forms (1)-(11), wherein the operation-mode changing portion includes a road-surface-condition-dependent determining portion which determines the operation mode of the electric motor to be changed, on the basis of the road surface condition.

The surface condition of the road on which the vehicle travels is a factor that influences the ride comfort of the vehicle. In the light of this, the stabilizer apparatus is preferably controlled depending upon the road surface condition. For instance, it is preferable that the characteristic of the stabilizer apparatus during running on a flat road and the characteristic of the stabilizer apparatus during running on a bad-condition road such as a bumpy road, a mogul road, or the like be made different from each other. According to this form (12), the operation mode of the electric motor can be changed depending upon the road surface condition, whereby the stabilizer apparatus can be controlled so as to be suited to the actual running state of the vehicle. This form (12) may be modified such that the operation-mode changing portion has at least one of the vehicle-speed-dependent determining portion and steering-amount-dependent determining portion explained above, in addition to the road-surface-condition-dependent determining portion. This modified form may be arranged to give precedence to the determination by the road-surface-condition-dependent determining portion, irrespective of the determination by at least one of the vehicle-speed-dependent determining portion and steering-amount-dependent determining portion. Further, the modified form may be arranged such that the road-surface-condition-dependent determining portion determines the operation mode while taking into account or being influenced by the determination made by at least one of the vehicle-speed-dependent determining portion and steering-amount-dependent determining portion, briefly speaking, in cooperation with at least one of the vehicle-speed-dependent determining portion and steering-amount-dependent determining portion.

(13) The stabilizer system according to the above form (12), wherein the road-surface-condition-dependent determining portion determines the operation mode of the electric motor to be (b-3) a free mode wherein the motor-phase-connecting formation is a formation in which electric power is inhibited from being supplied to phases of the electric motor, where the road surface condition is bad.

Where the vehicle is running on the bad-condition road, either a right-side wheel or a left-side wheel tends to run onto a projection. In this state, the elastic force to be exerted by the stabilizer bar may adversely influence the ride comfort of the vehicle. According to this form (13), the free mode is selected when the vehicle is running on the bad-condition road. Therefore, this form assures good ride comfort of the vehicle during running on the bad-condition road by taking advantage of the characteristic of the free mode that the substantially no elastic force is exerted by the stabilizer bar for thereby assuring independency in the vertical movement of the right-side and left-side wheels.

(14) The stabilizer system according to any one of the above forms (1)-(13), wherein the electric motor is a DC brushless motor.

Because the DC brushless motor has good controllability, it can be suitably used as a drive source for the actuator of the stabilizer apparatus. Further, owing to use of the DC brushless motor, the characteristics of the above-indicated three non-control modes can be appropriately realized depending upon the motor-phase-connecting formation and the power-supply state.

(15) The stabilizer system according to any one of the above forms (1)-(14),further comprising a power source device constituted by including an inverter, for supplying electric power to the electric motor,wherein the operation mode of the electric motor is changed by changing switching elements of the inverter.

Because the power source device constituted by including the inverter permits easy and accurate control of the operation of the electric motor, it is suitably used as the control power source for the stabilizer apparatus. Further, owing to the inverter, the above-indicated three non-control modes can be easily established by changing combinations of the ON (closed) and OFF (open) states of the switching elements such as FET provided for each phase.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

There will be described in detail one embodiment of the claimable invention, referring to the drawings. It is to be understood, however, that the invention is not limited to the following embodiment, but the invention may be embodied with various changes and modifications, such as those described in the SUMMARY OF THE INVENTION, which may occur to those skilled in the art.

1. Overall Structure of Stabilizer System

FIG. 1conceptually shows a stabilizer system10for a vehicle according to one embodiment of the invention. The stabilizer system10includes two stabilizer apparatuses14which are disposed respectively on a front-wheel side and a rear-wheel side of the vehicle. Each stabilizer apparatus14includes a stabilizer bar20connected at opposite ends thereof to respective wheel holding members (FIG. 2) which respectively hold front and rear wheels16. The stabilizer bar20is divided at a middle portion thereof into two parts, i.e., a right stabilizer bar member22and a left stabilizer bar member24. The pair of stabilizer bar members22,24are connected rotatably relative to each other with an actuator30interposed therebetween. Roughly speaking, the stabilizer apparatus14is arranged such that the actuator30rotates the right and left stabilizer bar members22,24relative to each other (as shown in arrows indicated by solid line and arrows indicated by broken line inFIG. 1), thereby changing elastic force to be exerted by the stabilizer bar20as a whole, for controlling the rolling of the vehicle body.

FIG. 2schematically shows a portion of the stabilizer apparatus14ranging from its middle part in a widthwise direction of the vehicle to a wheel16on one of the right-side and the left-side of the vehicle. The vehicle on which the present stabilizer system10is installed includes four independent suspension apparatuses38provided respectively for the four wheels16. Each suspension apparatus38is a double wishbone type well known in the art and includes an upper arm42and a lower arm44which cooperate with each other to function as the wheel holding member. Each of the upper and lower arms42,44is rotatably connected at one end thereof to a vehicle body and connected at the other end thereof to the corresponding wheel16. Each of the upper and lower arms42,44is pivotably moved or swung about the above-indicated one end (vehicle-body-side end) while the other end (wheel-side end) is moved generally in the vertical direction relative to the vehicle body, as the corresponding wheel16and the vehicle body approach toward and remove away from each other (namely, as the wheel16and the vehicle body move relative to each other in the vertical direction). The suspension apparatus38further includes a shock absorber46and a suspension spring48(which is an air spring in the present embodiment). Each of the shock absorber46and spring48is connected to a member on the vehicle-body side and a member on the wheel side. The thus constructed suspension apparatus38elastically support the corresponding wheel16and the vehicle body and has a function of generating damping force with respect to a vibration which is accompanied by the relative displacement between the wheel16and the vehicle body toward and away from each other.

The stabilizer apparatus14includes the pair of stabilizer bar members, i.e., the right stabilizer bar member22and the left stabilizer bar member24. (InFIG. 2, one of the right and left bar members22,24is shown.) Each of the right and left bar members22,24has a torsion bar portion60extending substantially in the widthwise direction of the vehicle, and arm portion62formed integrally with the torsion bar portion60and intersecting the same60so as to extend generally in a frontward or a rearward direction of the vehicle. The torsion bar portion60of each bar member22,24is rotatably supported, at a position thereof near to the arm portion62, by a support member66which is fixedly disposed at a stabilizer-apparatus mounting portion64that is a part of the vehicle body. Thus, the torsion bar portions60of the respective right and left bar members22,24are disposed coaxially relative to each other. Between respective ends of the torsion bar portions60of the right and left bar members22,24, which ends are located near to a widthwise middle portion of the vehicle, the actuator30is disposed. As explained below in detail, the respective ends of the torsion bar portions60are connected to the actuator30. In the meantime, one end of each arm portion62remote from the corresponding torsion bar portion60is connected to a stabilizer-bar connecting portion68of the corresponding lower arm44so as to be rotatable relative to the same68.

As schematically shown inFIG. 3, the actuator30includes an electric motor70and a decelerator72connected to the electric motor70for decelerating rotation of the electric motor70. The electric motor70and the decelerator72are disposed inside a housing74as an outer frame member of the actuator30. The housing74is held, at the stabilizer-apparatus mounting portion64, by a housing holding member76so as to be rotatable and immovable in the axial direction (i.e., substantially in the widthwise direction of the vehicle) relative to the hosing holding member76. As shown inFIG. 2, two output shafts80,82extend respectively from opposite ends of the housing74. The output shafts80,82are unrotatably connected by serration engagement, at their leading ends remote from the housing74respectively to ends of the respective right and left bar members22,24. Further, as shown inFIG. 3, one80of the two output shafts80,82is fixedly connected to one of the opposite ends of the housing74while the other82of the two output shafts80,82is disposed so as to extend into the housing74and is held by the housing74so as to be rotatable and axially immovable relative to the same74. One end of the output shaft82located within the housing74is connected to the decelerator72as explained below in detail.

The electric motor70includes: a plurality of stator coils84fixedly disposed on one circumference along an inner circumferential surface of the cylindrical wall of the housing74; a hollow motor shaft86rotatably held by the housing74; and permanent magnets88fixedly disposed on one circumference along an outer circumferential surface of the motor shaft86so as to face the stator coils84. The electric motor70is a motor in which each stator coil84functions as a stator and each permanent magnet88functions as a rotor, and is a three-phase DC brushless motor.

In the present embodiment, the decelerator72is constituted as a harmonic gear mechanism (called as “HARMONIC DRIVE” (trademark), a strain wave gear ring mechanism, etc.) including a wave generator90, a flexible gear92, and a ring gear94. The wave generator90includes an oval cam and ball bearings fitted on a periphery of the cam, and is fixed to one end of the motor shaft80. The flexible gear92is a cup-like member whose cylindrical wall portion is elastically deformable. A plurality of teeth are formed on an outer circumference of the open end portion of the cup-like flexible gear92. The flexible gear92is connected to the output shaft82described above and is held by the same82. In detail, the output shaft82penetrates the motor shaft86and has an end portion extending from or beyond the one end of the motor shaft86. To this end portion of the output shaft82, a bottom portion of the flexible gear92is fixed, whereby the flexible gear92and the output shaft82are connected to each other. The ring gear94is a generally ring-like member and is fixed to the housing74. A plurality of teeth are formed on an inner circumference of the ring gear94. The number of teeth formed on the inner circumference of the ring gear94is slightly larger (e.g., larger by two) than the number of teeth formed on the outer circumference of the flexible gear92. The flexible gear92is fitted at its cylindrical wall portion on the wave generator90, and is elastically deformed into an oval shape. The flexible gear92meshes the ring gear94at two portions thereof corresponding to opposite ends of the long axis of the oval and does not mesh the same94at the other portion thereof. With one rotation of the wave generator90(i.e., after rotation of the wave generator90by 360°), in other words, after one rotation of the motor shaft86of the electric motor70, the flexible gear92and the ring gear94are rotated relative to each other by an amount corresponding to the difference in the number of teeth therebetween. Because the structure of the harmonic gear mechanism is known in the art, a detailed illustration of the decelerator72is dispensed with and its explanation is limited to brief one given above.

In the thus constructed stabilizer apparatus14, where the electric motor70is rotated, namely, where the actuator30operates, the torsion bar portions60of the respective right and left stabilizer bar members22,24are rotated relative to each other, so that the stabilizer bar20which is considered as one stabilizer bar constituted by the right and left stabilizer bar members22,24is twisted. Force generated by the twisting of the right and left stabilizer bar members22,24acts as force that causes the right and left wheels16and the vehicle body to approach toward and remove away from each other. In other words, the present stabilizer apparatus14is arranged such that the actuator30operates to change the elastic force, namely, the rigidity, of the stabilizer bar20.

The actuator30is provided, in the housing74, with a motor rotational angle sensor100for detecting a rotational angle of the motor shaft86, i.e., a rotational angle of the electric motor70. The motor rotational angle sensor100of the present actuator30is constituted principally by an encoder. A value detected by the sensor100is utilized in changing phases of the electric motor70and in control of the actuator30, i.e., in roll-restraining control by the stabilizer apparatus14, as an index indicating a relative rotational angle (a relative rotational position) of the right and left stabilizer bar members22,24.

To the electric motor70of the actuator30, electric power is supplied from a power source device. In the present stabilizer system10, there are provided a battery102and two inverters104connected to the battery102, as shown inFIG. 1. Each inverter104functions as a drive circuit. Electric power is supplied to the electric motors70of the respective two stabilizer apparatuses14from the respective inverters104. Namely, the battery102and each inverter104cooperate to constitute the power source device for the corresponding electric motor70.

As shown inFIG. 1, the present stabilizer system10includes a stabilizer electronic control unit (stabilizer ECU)110(hereinafter may be simply referred to as “the ECU110”) as a control device for controlling operation of the stabilizer apparatus14, in detail, operation of the actuator30. The ECU110is constituted principally by a computer including a CPU, a ROM, a RAM, etc. To the ECU110, there are connected, in addition to the aforementioned motor rotational angle sensor100, an operation-angle sensor120for detecting an operation angle of a steering wheel which is an operation amount of a steering operating member as a steering amount, a vehicle-speed sensor122for detecting a running speed of the vehicle (hereinafter may be simply referred to as “vehicle speed”), a lateral-acceleration sensor124for detecting actual lateral acceleration which is lateral acceleration actually generated in the vehicle, and a vertical-acceleration sensor126which is disposed on a mount portion of each wheel for detecting acceleration for a vertical movement of that portion of the vehicle body. InFIG. 1, these sensors100,120,122,124,126are shown as θ, δ, v, Gy and Gt, respectively. The ECU110is connected also to each of the inverters104, whereby the ECU110controls the operation of each actuator30by controlling each inverter104. In the ROM of the computer of the ECU110, there are stored various programs (that will be explained) such as a roll-restraining control program, operation-mode-changing programs, various data relating to the control of the stabilizer apparatus14, and so on.

2. Functional Structure of Control Device

FIG. 4conceptually expresses functions of the ECU110as the control device for controlling the stabilizer apparatus14. The ECU110is constituted by including an operation-mode changing portion140which changes an operation mode of the electric motor70of the actuator30(that will be explained in greater detail) and an operation controlling portion142which controls the electric motor70to be operated for active roll controlling. The operation-mode changing portion140is constituted by including three determining portions for determining the operation mode to be changed, i.e., a vehicle-speed-dependent determining portion,144, a steering-amount-dependent determining portion146and a road-surface-condition-dependent determining portion148. The vehicle-speed-dependent determining portion144is a functional portion that determines the operation mode to be changed based on the vehicle speed. The steering-amount-dependent determining portion146is a functional portion that determines the operation mode to be changed based on the steering amount. The road-surface-condition-dependent determining portion148is a functional portion that determines the operation mode to be changed based on surface condition of a road on which the vehicle runs. At least two of these three determining portions144,146,148cooperate with each other to determine the operation mode to be changed, or only one of these three determining portions144,146,148determines the operation mode to be changed. The operation-mode changing portion140further includes a threshold changing portion150as a functional portion for changing a threshold speed and a threshold steering amount which are thresholds respectively used by the vehicle-speed-dependent determining portion144and the steering-amount-dependent determining portion146in determination of the operation mode. The operation controlling portion142works in an operation mode for actively controlling the actuator30and is a functional portion that permits the electric motor70to be operated for roll-restraining control. Detailed functions of the above-indicated functional portions will be explained in description about processing according to the roll-restraining control program and operation-mode changing programs executed by the ECU110.

3. Operation Mode of Electric Motor

In the present stabilizer system10, the electric motor of the actuator30of each stabilizer apparatus14is arranged to be operable in four operation modes and is operated in one of the four operation modes selected on the basis of predetermined conditions. The operation mode of the electric motor70depends on a motor-phase-connecting formation and a power-supply status of the electric motor70. The four operation modes differ from one another in at least one of the motor-phase-connecting formation and the power-supply status. The operation mode is changed by changing ON/OFF states of switching elements of each inverter104. As shown inFIG. 5, the electric motor70is a delta-connected, three-phase, DC brushless motor. The inverter104has two switching elements (FET), i.e., a high(plus) side-switching element and a low(minus) side-switching element, for each of the three phases (U, V, W) of the electric motor70. Hereinafter, the six switching elements of the inverter104will be referred to as “UHC”, “ULC”, “VHC”, “VLC”, “WHC”and “WLC”, respectively. The operation mode of the electric motor70is changed by changing the ON/OFF states of the respective six switching elements.

More specifically described, the four operation modes of the electric motor70consist of: a control mode in which the operation of the electric motor70is controllable; and three non-control modes in which the control of the operation of the electric motor is not executed. The three non-control modes consist of a stand-by mode, a braking mode and a free mode. Each operation mode will be explained referring toFIG. 6showing changing patterns of the switching elements of each inverter104.

(i) Control Mode

The control mode is an operation mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor is controllable and wherein electric power is supplied to the electric motor70. In the control mode, according to a system called as 120° rectangular-wave drive system, the ON/OFF states of the respective switching elements UHC, ULC, VHC, VLC, WHC, WLC are changed depending upon the motor rotational angle θ of the electric motor70according to changing patterns shown inFIG. 6which are classified in two cases, i.e., a case in which the electric motor70is rotated clockwise (CW) and a case in which the electric motor70is rotated counterclockwise (CCW). Described more specifically, each pattern shown inFIG. 6is set for every 60° of an electric angle. Since the electric motor70in the present embodiment is a three-phase and six-pole motor, the pattern is sequentially changed for every 20° of the motor rotational angle corresponding to 60° of the electric angle. Under this motor-phase-connecting formation, the switching elements ULC, VLC, WLC on the low side are subjected to duty control. Here, “duty control” is a control in which a ratio (duty ratio) of a pulse-on time to a pulse-off time by PWM (Pulse Width Modulation) is changed, thereby changing an amount of electric power to be supplied to the electric motor70. Each symbol “1*” inFIG. 6indicates a state in which those switching elements are under the duty control. It is noted that phase-changing timing and pulse-on/pulse-off timing are controlled by a phase switching circuit on the basis of signals generated by the motor rotation angle sensor100of the actuator70.

As explained above, in the control mode, the rotating direction of the electric motor70and the amount of electric power supplied to the electric motor70can be controllable. Accordingly, the ordinary roll-restraining control, in detail, the active roll-restraining control can be executed in this control mode. Owing to the roll-restraining control (which will be explained in greater detail), the elastic force to be exerted by the stabilizer bar20can be actively changed by controlling the actuator30.

The stand-by mode is one kind of the non-control modes. The stand-by mode is an operation mode wherein the motor-phase-connecting formation is a formation in which the operation of the electric motor70is controllable and wherein electric power is not actually supplied to the electric motor70. As shown inFIG. 6, as in the control mode described above, the ON/OFF states of the respective switching elements UHC, ULC, VHC, VLC, WHC, WLC are changed in accordance with the rotational angle θ of the electric motor70. The stand-by mode differs from the control mode in that the switching elements ULC, VLC, WLC on the low side are not subjected to the Duty control. It may be said that the Duty control is performed such that the Duty ratio is zero. In other words, there exist no pulse-on times and no electric power is actually supplied to the electric motor70. Each symbol “0*” inFIG. 6shows this state.

In the stand-by mode, since no electric power is supplied to the electric motor70, the operation of the electric motor70is not controllable, so that the actuator30does not actively operate. On the other hand, the changing of the phases is executed as described above, so that this stand-by mode deals with transition to the control mode with readiness. Therefore, the stand-by mode does not suffer from control delay and is excellent in responsiveness or readiness. Further, in this mode, the phases are changed in accordance with the motor rotational angle θ, so that regeneration utilizing diodes which are disposed together with the respective switching elements UHC, ULC, VHC, VLC, EHC, WLC can be expected. In other words, it is expected that the battery102is charged with electric power arising electromotive force that is generated in the electric motor70upon reverse input action of the stabilizer bar20(which means, for instance, that the stabilizer bar20is twisted as upper and lower members which are disposed respectively above and below the suspension spring for each wheel approach toward and remove away from each other and that the electric motor70is rotated as a result of twisting of the stabilizer bar20). In this connection, braking force arising from the regeneration is generated in the electric motor70, whereby the actuator30exerts resistance force with respect to the reverse input action to some extent.

The braking mode is one kind of the non-control modes. In this braking mode, the motor-phase-connecting formation is a formation in which the phases of the electric motor70are connected to each other. Described more specifically, all of the switching elements UHC, VHC, WHC on the high side are placed in ON states (in closed states), as shown inFIG. 6. Owing to these switching elements UHC, VHC, WHC placed in the ON states and diodes disposed together with those switching elements, the phases of the electric motor70are kept as if they were short-circuited to each other. Accordingly, upon the reverse input action of the stabilizer bar20, relatively large electromotive force is generated in the electric motor70, so that relatively large braking force is given to the electric motor70. Therefore, the actuator30is brought into a state in which it is nearly locked with respect to the reverse input action with a relatively high speed, whereby the pair of stabilizer bar members22,24work as an integral unit. Namely, in this braking mode, the stabilizer apparatus14is kept in a state close to a stabilizer apparatus equipped with a conventional stabilizer bar without an actuator, so that the stabilizer bar20exerts the elastic force generally corresponding to that exerted by the conventional stabilizer bar.

(iv) Free Mode

The free mode is one kind of the non-control modes. In the free mode, the motor-phase-connecting formation is a formation in which electric power is inhibited from being supplied to the phases of the electric motor70. More specifically explained, all of the switching elements UHC, ULC, VHC, VLC, WHC, WLC are placed in OFF states (open states), whereby the phases of the electric motor70are kept in a state close to that in which the phases of the electric motor70and the corresponding inverter104are disconnected from each other. Accordingly, even upon the reverse input action to the stabilizer bar20, no electromotive force is generated in the electric motor70. Hence, there is obtained in the motor70only braking force that results in a cogging torque, a sliding resistance, or the like, namely, the motor70exerts almost no resistance. In other words, the pair of stabilizer bar members22,24are allowed to rotate relative to each other in a comparatively free state, so that the stabilizer bar20does not exert the elastic force and therefore the stabilizer apparatus14is placed in a state in which it does not work as a stabilizer apparatus. In this mode, too, there is formed a regenerative circuit utilizing diodes and the electric motor70per se works as a generator. However, since a regenerative current does not flow until the electric motor70generates a voltage in excess of the voltage of the power source, substantially no regenerative current flows and there is obtained substantially no braking effect by regeneration.

In the present stabilizer system10, the roll-restraining control, namely, the control for actively restraining rolling of the vehicle body is carried out under the control mode explained above. The roll-restraining control is carried out such that a roll-restraining control program shown in a flow chart ofFIG. 7is executed in the ECU110at short time intervals (e.g., time intervals ranging from ten to several tens of milliseconds). It is noted that the roll-restraining control program is executed only for a time period during which the operation mode of the electric motor70is placed in the control mode. It is further noted that a portion of the ECU110that executes the roll-restraining control program corresponds to the operation controlling portion142described above.

In the roll-restraining control, a vehicle speed v is initially obtained in step S1(hereinafter “step” is omitted where appropriate) on the basis of a detected value of the vehicle-speed sensor122. Next, in S2, there is obtained, as a steering amount, an operation angle δ of a steering wheel on the basis of a detected value of the operation-angle sensor120. S2is followed by S3in which estimated lateral acceleration Gyc is obtained on the basis of the obtained vehicle speed v and operation angle δ. For the estimated lateral acceleration Gyc, there is formed in advance a map using vehicle speed and operation angle as variables based on vehicle characteristics. The ECU110stores data indicative of the map. The estimated lateral acceleration Gyc is obtained in S3referring to the map data.

Subsequently, in S4, there is obtained actual lateral acceleration Gy that is lateral acceleration actually generated in the vehicle, on the basis of a detected value of the lateral-acceleration sensor124. S4is followed by S5in which there is determined index lateral acceleration Gy* that is utilized as an index in the roll-restraining control, on the basis of the estimated lateral acceleration Gyc and the obtained actual lateral acceleration Gy. More specifically, the index lateral acceleration Gy* is determined according to the following formula:
Gy*=K1·Gyc+K2·Gy
wherein K1and K2indicate gains and are variables using vehicle speed, steering speed, etc., as parameters.

S5is followed by S6in which a target motor rotational angle θ* of the electric motor70is determined based on the index lateral acceleration Gy* determined in S5. Described in detail, it is possible to get, on the basis of the index lateral acceleration Gy*, elastic force to be exerted by the stabilizer bar20to cancel rolling moment generated by the index lateral acceleration Gy*, whereby it is possible to get a relative rotational angle of the pair of stabilizer bar members22,24. In the actuator30constructed as described above, the relative rotational angle has correspondence with the rotational angle of the electric motor70, so that it is possible to determined the target motor rotational angle θ* which is a target rotational angle of the electric motor70. The ECU110stores map data of the target motor rotational angle θ* using index lateral acceleration Gy* as a variable. Actually, the target motor rotational angle θ* is determined referring to the map data.

Subsequently, in S7, the rotation of the electric motor70is controlled on the basis of the determined target motor rotational angle θ*. In detail, the rotating direction of the electric motor70and the amount of the current to be supplied to the motor70are determined on the basis of a motor rotational angle deviation Δθ between an actual motor rotational angle θ detected by the motor rotational angle sensor100and the target motor rotational angle θ*. Information indicative of the rotating direction and the current-supply amount are fed as a command to the corresponding inverter104. The inverter104controls the corresponding motor70to be rotated so as to establish the commanded rotating direction and the current-supply amount.

The above explanation of the roll-restraining control merely states an outline of the contents of the control. In the present stabilizer system10, two stabilizer apparatuses14are provided, and the roll-restraining control described above is practiced for each of the two stabilizer apparatuses14. Actually, various complicated processing is carried out such as a determination of the target motor rotational angles θ* that are target values for the control in the respective two apparatuses14, which determination takes into consideration roll stiffness distribution between the front and rear wheels, etc., However, because the roll-restraining control per se is not directly related to the claimable invention, its explanation is limited to brief one described above.

5. Changing of Operation Mode of Electric Motor

The changing of the operation mode of the electric motor70is carried out such that the operation-mode-changing programs are executed by the ECU110. In the present stabilizer system10, nine programs shown in respective flow charts ofFIGS. 8-16are prepared as the operation-mode-changing programs. Any of the nine programs is executed as a result of arbitrary selection by the vehicle driver. All of the nine programs are executed at considerably short time intervals (e.g., time intervals ranging from ten to several tens of milliseconds) with an ignition switch placed in an ON state. In some cases, the selected program is executed in parallel with the previously explained roll-restraining control program by time sharing. The nine programs have respective inherent or peculiar characteristics. Accordingly, the characteristic of the vehicle, in detail, the characteristic of the stabilizer apparatus varies depending upon the kind of the programs to be executed. Hereinafter, various operation-mode-changing arrangements by the respective nine programs will be explained referring to the respective flow charts.

A first operation-mode-changing arrangement is an arrangement in which a first operation-mode-changing program shown inFIG. 8is executed. According to processing of this program, a vehicle speed v is initially detected in S11on the basis of a detected value of the vehicle-speed sensor122. Next, in S12, an operation angle δ of the steering wheel is obtained on the basis of a detected value of the operation-angle sensor120. S13is then implemented to judge whether the vehicle speed v is not smaller than a threshold speed v1. Where the vehicle speed v is judged to be not smaller than the threshold v1in S13, S14is implemented to judge whether the operation angle δ is not smaller than a threshold angle δ1(which is one kind of a threshold steering amount). Where the operation angle δ is judged to be not smaller than a threshold angle δ1in S14, S15is implemented to determine a current mode M (i.e., an operation mode determined by the current execution of the program) to be “the control mode”. On the contrary, where the vehicle speed v is judged to be smaller than the threshold speed v1in S13and where the operation angle δ is judged to be smaller than the threshold angle δ1in S14, the control flow goes to S16in which the current mode M is determined to be “the free mode”. After determination of the current mode M, S17is implemented to judge whether the current mode M is identical with a previous mode M′ (i.e., an operation mode determined by the previous execution of the program). Where the current mode M is identical with the previous mode M′, the control flow goes to S18in which the operation mode of the electric motor70is maintained. Where the current mode M differs from the previous mode M′, the control flow goes to S19in which the operation mode of the motor70is changed to the current mode M determined in the currently executed program. Namely, a signal for maintaining or changing the operation mode is outputted to the inverter104. After implementation of S18or S19, S20is implemented to perform processing for updating the previous mode M′ to the current mode M. Thus, one execution of the first operation-mode-changing program is completed.

As a result of a series of processing executed by the first operation-mode-changing program, under the first operation-mode-changing arrangement, the operation mode of the electric motor70is determined to be the control mode where the vehicle speed is high and the steering amount is large, for thereby carrying out the roll-restraining control, whereas the operation mode of the electric motor70is determined to be the free mode as the non-control mode where the vehicle speed is low and where the steering amount is small. In this connection, the threshold speed vi is set at a level (e.g., 20-30 km/h) at which large rolling does not occur even upon turning of the vehicle while the threshold operation angle δ1is set at a level corresponding to a steering amount at which large rolling does not occur even upon running of the vehicle at a comparatively high speed. According to this first operation-mode-changing arrangement, in a situation wherein the rolling is comparatively large, the rolling can be effectively restrained. At the same time, in a situation wherein the rolling is comparatively small, the stabilizer apparatus14is not allowed to exhibit a function of a stabilizer in response to the reverse input action from the road surface, whereby the ride comfort of the vehicle is given priority.

The previously explained operation-mode changing portion140is constituted by including a portion of the ECU110that executes the processing according to the first operation-mode-changing program. The vehicle-speed-depending determining portion144is constituted by including a portion of the ECU110that executes the judging processing at S13and the processing of determining the operation mode based on the result of judgment. The steering-amount-dependent determining portion146is constituted by including a portion of the ECU110that executes the judging processing at S14and the processing of determining the operation mode based on the result of judgment. In this first operation-mode-changing arrangement, the vehicle-speed-dependent determining portion144and the steering-amount-dependent determining portion146cooperate with each other to determine the operation mode of the electric motor70.

In the following second through ninth operation-mode-changing arrangements, respective programs similar to the first operation-mode-changing program are executed. Accordingly, in the following explanation of those programs and respective processing by those programs, portions of those programs which are identical to the aforementioned first operation-mode-changing program are not explained. In each of the following operation-mode-changing arrangements, too, the operation-mode changing portion140is constituted by including a portion of the ECU110that executes processing according to the implemented operation-mode-changing program. Similarly, the vehicle-speed-dependent determining portion144is constituted by including a portion of the ECU110that executes the judging processing based on the vehicle speed and the processing of determining the operation mode based on the result of judgment while the steering-amount-dependent determining portion146is constituted by including a portion of the ECU110that executes the judging processing based on the steering amount and the processing of determining the operation mode based on the result of judgment. Therefore, explanation as to which portion of the ECU110constitutes the vehicle-speed-dependent determining portion144or the steering-amount-dependent determining portion146is dispensed with in the interest of brevity.

A second operation-mode-changing arrangement is an arrangement in which a second operation-mode-changing program shown inFIG. 9is executed. This second operation-mode-changing arrangement differs from the first operation-mode-changing arrangement in that the stand-by mode is selected where the vehicle speed is high and the steering amount is small. Hence, in this arrangement, the ride comfort of the vehicle is somewhat inferior where the vehicle speed is high and the steering amount is small. This arrangement, however, assures good readiness or responsiveness of the stabilizer apparatus14when the roll-restraining control is executed as a result of an increase in the steering amount at the high-speed running of the vehicle.

A third operation-mode-changing arrangement is an arrangement in which a third operation-mode-changing program shown inFIG. 10is executed. In this third operation-mode changing arrangement, the operation mode is changeable among the aforementioned four operation modes. As in the second operation-mode-changing arrangement explained above, during high-speed running of the vehicle, the control mode is selected for executing the roll-restraining control where the steering amount is large whereas the stand-by mode is selected where the steering amount is small. Unlike the second operation-mode-changing arrangement, this third operation-mode-changing arrangement is arranged such that, during low-speed running of the vehicle, the braking mode is selected where the steering amount is large whereas the free mode is selected where the steering amount is small. Accordingly, where the vehicle speed is low and the steering amount is large, the braking mode is selected, thereby assuring the roll-restraining effect as large as that in the conventional stabilizer. In this connection, the control mode may be employed in place of the braking mode where the vehicle speed is low and the steering amount is large, though this modified arrangement does not belong to the third operation-mode-changing arrangement.

A fourth operation-mode-changing arrangement is an arrangement in which a fourth operation-mode-changing program shown inFIG. 11is executed. As in the above-mentioned operation-mode-changing arrangements, in this fourth operation-mode-changing arrangement, the control mode is selected where the vehicle speed is high and the steering amount is large and the free mode is selected where the vehicle speed is low and the steering amount is small. This fourth operation-mode-changing arrangement differs from the above-mentioned operation-mode-changing arrangements in that the braking mode is selected where the vehicle speed is high and the steering amount is small and where the vehicle speed is low and the steering amount is large.

Further, in this fourth operation-mode-changing arrangement, the threshold steering amount, i.e., the threshold operation angle δ1used for judgment of the steering amount at high-speed running (at S74) and the threshold steering amount, i.e., the threshold operation angle δ2used for judgment of the steering amount at low-speed running (at S75) are made different from each other. In detail, the threshold operation angle δ1is made larger than the threshold operation angle δ2(δ1>δ2). The amount of rolling of the vehicle body depends on the vehicle speed and the steering amount. The amount of rolling of the vehicle body increases with an increase in the vehicle speed. The amount of rolling of the vehicle body increases with an increase in the steering amount. Therefore, because the threshold operation angle δ1is made larger than the threshold operation angle δ2(δ1>δ2), the operation mode is prevented from being changed between the control mode and the free mode where the vehicle speed v changes across the threshold speed v1upon turning of the vehicle under a constant steering amount in which the operation angle δ is in a range from δ1to δ2, for instance. Accordingly, this arrangement prevents changing of the operation mode between those having a great gap or difference therebetween. In other words, this arrangement effectively avoids so-called “hunting”. In this connection, to employ the mutually different threshold steering amounts respectively in the judgment of the steering amount at S74and in the judgment of the steering amount at S75may be conceived that the threshold steering amount is changed depending upon the vehicle speed. Hence, the threshold changing portion150is constituted by including a portion of the ECU110that executes the processing of making the threshold used in the processing at S74and the threshold used in the processing at S75different from each other.

In the fourth operation-mode-changing arrangement, the threshold steering amount is varied depending upon the vehicle speed. This arrangement may be modified, for instance, as follows: The judgment of the steering amount precedes the judgment of the vehicle speed, and the threshold speed used in the judgment of the vehicle speed where the steering amount is large and the threshold speed used in the judgment of the vehicle speed where the steering amount is small are made different from each other, thus reducing a control gap upon turning of the vehicle during running at a constant speed, for instance.

A fifth operation-mode-changing arrangement is an arrangement in which a fifth operation-mode-changing program shown inFIG. 12is executed. In this fifth operation-mode-changing arrangement, the operation mode is changed depending upon whether the vehicle is running on a bad-condition road such as a bumpy road, a mogul road, or the like. Described more specifically, where the vehicle speed is high and the steering amount is small, it is judged at S95whether vehicle is running on the bad-condition road. Where it is judged that the vehicle is running on the bad-condition road, the free mode is selected as the operation mode. On the other hand, it is judged that the vehicle is not running on the bad-condition road, the stand-by mode is selected. In the judgment of running of the vehicle on the bad-condition road, there is initially obtained vertical acceleration Gt on the basis of a detected value of the vertical acceleration sensor124. Based on the obtained vertical acceleration Gt and a set of vertical acceleration Gt which had been obtained in the previous execution of this program prior to the current execution of the program, it is judged that the vehicle is running on the bad-condition road if a degree of change in the vertical acceleration Gt satisfies a predetermined condition. As an algorithm for the judgment of the running of the vehicle on the bad-condition road, any known one may be employed and therefore a detailed explanation of the algorithm is not given here. In the present arrangement, a so-called “wavy” road is judged as the bad-condition road.

In this fifth operation-mode-changing arrangement, the free mode is selected during running on the bad-condition road, thereby assuring good riding comfort of the vehicle while running on the bad-condition road. In this arrangement, where the vehicle speed is low, the free mode is selected irrespective of whether the vehicle is running on the bad-condition road or not. Further, since it is conceivable that, during running on the bad-condition road, a large steering operation is hardly made at a high speed, this fifth operation-mode-changing arrangement widely deals with the running on the bad-condition road. In this arrangement, the road-surface-condition-dependent determining portion148is constituted by including a portion of the ECU110that executes the judging processing at S95and the processing of determining the operation mode based on the result of judgment.

A sixth operation-mode-changing arrangement is an arrangement in which a sixth operation-mode-changing program shown inFIG. 13is executed. This sixth operation-mode-changing arrangement is an arrangement in which changing of the operation mode based on the judgment of running on the bad-condition road is added to the previously explained third operation-mode-changing arrangement. More specifically described, in this sixth operation-mode-changing arrangement, S116is implemented to judge whether the vehicle is running on the bad-condition road where the vehicle speed is high and the steering amount is small while S117is implemented to judge whether the vehicle is running on the bad-condition road where the vehicle speed is low and the steering amount is large. Where it is judged that the vehicle is running on the bad-condition road in each of the judgment at S116and S117, the operation mode of the electric motor70is determined to be the free mode. Like the fifth operation-mode-changing arrangement, this sixth operation-mode-changing arrangement gives priority to the ride comfort of the vehicle during running on the bad-condition road. In this arrangement, the road-surface-condition-dependent determining portion148is constituted by including a portion of the ECU110that executes the judging processing at S116, S117and the processing of determining the operation mode based on the result of judgment.

This seventh operation-mode-changing arrangement is an arrangement in which the free mode is replaced with the stand-by mode in the aforementioned first operation-mode-changing arrangement. Because the stand-by mode permits the regeneration of the electromotive force as explained above, this seventh operation-mode-changing arrangement realizes the stabilizer system10that assures good power efficiency, in other words, excellent power-saving characteristics.

An eighth operation-mode-changing arrangement is an arrangement in which an eighth operation-mode-changing program shown inFIG. 15is executed. In this eighth operation-mode-changing arrangement, the free mode is replaced with the stand-by mode in the aforementioned third operation-mode-changing arrangement. As explained above with respect to the seventh operation-mode-changing arrangement, this eighth operation-mode-changing arrangement realizes the stabilizer system10that assures excellent power-saving characteristics.

A ninth operation-mode-changing arrangement is an arrangement in which a ninth operation-mode-changing program shown inFIG. 16is executed. In this ninth operation-mode-changing arrangement, the free mode is replaced with the stand-by mode in the aforementioned fourth operation-mode-changing arrangement. As explained above with respect to the seventh and eighth operation-mode-changing arrangements, this ninth operation-mode-changing arrangement realizes the stabilizer system10that assures excellent power-saving characteristics.