Damping control device for vehicle

Abstract

To suppress vehicle vibration caused by torsion of a power transmission system of a vehicle.SOLUTION: A power transmission system of a vehicle includes a differential device having a differential limitation function. A differential limit capacity R is made to be reduced (R=R0-ΔR) during increase in a torsion angle Θ of the power transmission system. A transmission torque of the power transmission system is reduced by reduction in the differential limit capacity R, and increase in the torsion angle Θ of the power transmission system is suppressed. The differential limit capacity R is increased (R=R0+ΔR) during reduction in the torsion angle Θ. The differential limit capacity R is increased and thereby the transmission torque is increased, so that the reduction in the torsion angle Θ is suppressed. As a result of this, a variation in the torsion angle is converged earlier.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a vibration damping control device that suppresses vibrations caused by torsion in a power transmission system of a vehicle. [Background technology]

[0002] A vehicle has a power transmission system that forms a path for transmitting the output of a power unit to drive wheels. The power transmission system includes at least a part of a clutch, a transmission, a drive shaft, a final reduction gear, a drive shaft, etc. The final reduction gear includes a differential gear for absorbing the speed difference between the left and right drive wheels when the vehicle turns. The following Patent Document 1 shows a differential gear that has a function of limiting differential operation by frictional force generated between elements that move relative to each other when the vehicle turns. This device reduces the shock caused by a sudden increase in friction amount at the start of differential limiting by gradually increasing the frictional force when limiting the differential operation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-19227 Summary of the Invention [Problem to be solved by the invention]

[0004] In the power transmission system of a vehicle, torsion occurs due to a change in the output torque of the power unit, and this torsion may cause vibration in the vehicle.

[0005] An object of the present invention is to suppress vibrations in a vehicle caused by torsion in the power transmission system. [Means for solving the problem]

[0006] A vehicle that is an object of the vibration damping control device according to the present invention includes a power plant that drives the vehicle, and a power transmission system that transmits the output of the power plant to drive wheels and includes a differential gear having a differential limiting function. The vibration damping control device for the vehicle includes an accelerator operation amount acquisition unit that acquires an operation amount of an accelerator pedal, a steering angle acquisition unit that acquires a steering angle of steered wheels, a torsion angle acquisition unit that acquires a torsion angle of the power transmission system, and a differential limiting control unit that controls a differential limiting amount of the differential gear. When the operation amount of the accelerator pedal exceeds a predetermined value, the steering angle of the steered wheels exceeds a predetermined value, and the amplitude of the fluctuation of the torsion angle of the power transmission system exceeds a predetermined value, the differential limiting control unit decreases the differential limiting amount while the torsion angle is increasing, and increases the differential limiting amount while the torsion angle is decreasing. Effect of the Invention

[0007] The amount of differential limiting is increased or decreased in accordance with an increase or decrease in the torsional angle of the power transmission system, thereby increasing or decreasing the transmission torque of the power transmission system. When the torsional angle is increasing, the amount of differential limiting is decreased to decrease the transmission torque of the power transmission system, thereby suppressing an increase in the torsional angle. Conversely, when the torsional angle is decreasing, the amount of differential limiting is increased to increase the transmission torque, thereby suppressing a decrease in the torsional angle. Therefore, fluctuations in the torsional angle converge early. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a schematic configuration of a power unit, a power transmission system, and a vibration damping control device of a vehicle according to an embodiment of the present invention; [Diagram 2] 5 is a diagram showing the torsion angle of the power transmission system and the fluctuation of the amount of differential limitation by a differential gear. FIG. [Diagram 3] 4 is a chart showing a flow of vibration damping control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing a power unit 10 and a power transmission system 12 of a vehicle according to this embodiment, and a vibration damping control device 14 that suppresses vibrations of the vehicle.

[0010] The power plant 10 includes an engine 16 and an electric motor 18 that drive the vehicle. The vehicle can be driven by both the engine 16 and the electric motor 18, or can be driven by only one of them. The power plant may also include only one of the engine and the electric motor. The electric motor 18 is disposed in a transaxle 22 that integrates a transmission (not shown) and a final reduction gear 20. The power transmission system 12 includes the transmission, the final reduction gear 20, and a drive shaft 24, and transmits the output of the power plant 10 to left and right drive wheels 26. The drive wheels 26 are also steered wheels. The final reduction gear 20 includes a differential gear 28 that absorbs the speed difference between the left and right drive wheels 26 when the vehicle turns. The differential gear 28 includes a differential limiting mechanism 30 that limits the amount of differential.

[0011] The differential device 28 includes a differential case 34 that rotates integrally with the driven gear 32 of the final reduction gear 20, a pinion shaft 36 that rotates integrally with the differential case 34, two differential pinions 38 rotatably supported on the pinion shaft 36, and two side gears 40 that mesh with the two differential pinions 38, respectively. The two side gears 40 are respectively coupled to the left and right drive shafts 24. The differential limiting mechanism 30 includes a plurality of outer discs 41 that rotate integrally with the differential case 34, and a plurality of inner discs 42 that rotate integrally with the drive shaft 24. A hydraulic actuator (not shown) presses the outer discs 41 and the inner discs 42 together, thereby generating a frictional force between the two discs 41, 42. This frictional force can suppress the relative motion between the differential case 34 and the drive shaft 24. In other words, the amount of differential movement of the differential device 28 can be suppressed. When there is a speed difference between the left and right drive wheels 26, if frictional force is generated by the differential limiting mechanism 30, a part of the torque that would otherwise be transmitted to the drive wheel 26 that rotates at a high speed is transmitted to the drive wheel 26 that rotates at a low speed. If the outer disk 41 and the inner disk 42 are brought into close contact with each other so that there is no relative speed, the differential device 28 does not perform differential operation. Also, in a state in which the outer disk 41 and the inner disk 42 are allowed to rotate relative to each other while frictional force is applied, differential operation is limited. The amount of restriction of differential operation, that is, the amount of differential limiting, can be adjusted by adjusting the frictional force. If the frictional force is increased, the amount of differential limiting increases, and when the outer disk 41 and the inner disk 42 rotate together, the amount of differential limiting is maximum. If the frictional force is decreased, the amount of differential limiting decreases, and when the amount of differential limiting becomes zero, normal differential operation occurs.

[0012] The operation of the differential limiting mechanism 30 is controlled by a differential limiting control unit 44. The differential limiting control unit 44 controls the amount of differential limiting, i.e., the frictional force between the outer disk 41 and the inner disk 42, depending on the driving conditions of the vehicle. The driving conditions of the vehicle are acquired based on various sensors mounted on the vehicle. The sensors mounted on the vehicle include, for example, a vehicle speed sensor 46 that detects the driving speed of the vehicle, an accelerator operation amount sensor 50 that detects the operation amount of an accelerator pedal 48, and a steering angle sensor 54 that detects the rotation angle of a steering wheel 52, i.e., the steering angle. Furthermore, the torsion angle of the power train 12 may be included as a physical quantity representing the driving conditions of the vehicle. The torsion angle of the power train 12 is acquired by a torsion angle acquisition unit 56. The torsion angle acquisition unit 56 may acquire the relative rotation angle between the output shaft of the power unit 10 and the drive wheels 26, i.e., the torsion angle, based on the rotation speed or rotation angle of these. Alternatively, the torsion angle may be acquired using an observer that is a calculation model of the power train 12. For example, if the output shaft of the power unit 10 is the output shaft of the electric motor 18, an observer is configured whose inputs are the torque command to the electric motor 18 and the rotational speed of the output shaft of the electric motor 18, and whose output is the rotational speed of the drive wheels 26, and the torsion angle of the power transmission system 12 is obtained from the rotational speed of the electric motor 18 and the obtained rotational speed of the drive wheels 26.

[0013] FIG. 2 is a diagram showing the change in the torsion angle Θ and the differential limiting amount R of the power transmission system 12. In particular, the torsion angle Θ and the differential limiting amount R are shown when the driver depresses the accelerator pedal 48 and the vehicle starts accelerating. The torsion angle Θ of the power transmission system 12 is proportional to the torque acting on the drive shaft 24. When the accelerator pedal 48 is depressed, the torsion angle Θ also increases with an increase in the drive shaft torque, and converges while fluctuating. The convergence value of the torsion angle Θ is determined by the accelerator operation amount. The relative value of the torsion angle Θ with respect to the convergence value of the torsion angle Θ is represented as the torsion angle fluctuation amount Φ. The convergence value of the torsion angle Θ is represented by the torsion angle fluctuation amount Φ being 0. When the accelerator pedal 48 is depressed, the torsion angle Θ rises, increases beyond the convergence value (Φ=0), and then starts to decrease. Furthermore, the torsion angle Θ exceeds the convergence value (Φ=0), and then starts to increase again. The twist angle Θ increases and decreases repeatedly, decreasing in amplitude and then converging.

[0014] When the above-mentioned fluctuating torsion occurs in the power transmission system 12, the driving force that moves the vehicle forward fluctuates, and the fluctuating driving force becomes a vibratory force, causing the vehicle to vibrate. In order to suppress this vehicle vibration, the differential limiting amount R of the differential device 28 is utilized. If the differential limiting amount R is reduced, that is, if the frictional force is reduced, the transmission torque of the power transmission system 12 is reduced and an increase in the torsion angle Θ is suppressed. Conversely, if the differential limiting amount R is increased, the transmission torque increases and an increase in the torsion angle Θ is promoted. However, since the differential device 28 only operates when the vehicle is turning, vibration suppression by the differential device 28 is only performed when the vehicle is turning.

[0015] When vibration occurs in the power transmission system 12, the amplitude of the torsion angle fluctuation Φ exceeds γ, and vibration suppression control is performed by the differential device 28. The torsion angle fluctuation Φ can be obtained by the above-mentioned torsion angle estimation method using the observer. When the observer is used to estimate that the amplitude of the torsion angle fluctuation Φ will be greater than a predetermined value γ, the differential limiting amount R is reduced by ΔR with respect to the differential limiting amount R0 in normal times, i.e., when no vibration is occurring, while the torsion angle Θ is increasing, that is, when the torsion angular velocity is positive (R=R0-ΔR). This reduces the transmission torque and suppresses the increase in the torsion angle Θ. By suppressing the increase in the torsion angle Θ, the height of the upwardly convex peak of the torsion angle Θ becomes smaller. When the torsion angle Θ is decreasing, the differential limiting amount R is increased by ΔR with respect to the differential limiting amount R0 in normal times (R=R0+ΔR). This increases the transmission torque and suppresses the decrease in the torsion angle Θ. By suppressing the decrease in the torsion angle Θ, the depth of the valley of the downwardly protruding peak of the torsion angle Θ becomes smaller. As a result, the torsional vibration of the power transmission system 12 converges early.

[0016] FIG. 3 is a flow chart relating to the differential limiting control when torsional fluctuation of the power transmission system 12 occurs. When the ignition switch is in the ON state (S100), the differential limiting control unit 44 judges whether the accelerator operation amount exceeds a predetermined value β (S102). When the accelerator operation amount is large, the transmission torque of the power transmission system 12 also increases, the torsional angle Θ increases rapidly, and the vibration of the vehicle also increases. If the accelerator operation amount is equal to or greater than the predetermined value β, it is next judged whether the steering angle exceeds a predetermined value α (S104). The vibration suppression method of this embodiment utilizes the differential limiting of the left and right drive wheels 26, so it can be executed only when a differential occurs. The predetermined value α of the steering angle is the lower limit value of the steering angle at which a normal differential limiting is executed. If the steering angle exceeds the predetermined value α, it is next judged whether the amplitude of the torsional angle fluctuation Φ exceeds a predetermined value γ (S106). The predetermined value γ is a value for judging the occurrence of a torsional angle fluctuation that should suppress vibration. If steps S102, S104, and S106 are all positive (Yes), the process determines whether the time rate of change of the torsion angle Θ, that is, the torsion angular velocity, is positive or negative (S108). If the torsion angular velocity is positive, the amount of differential limiting is decreased (S110). If the amount of differential limiting is decreased, the transmission torque of the power train 12 is decreased, and the increase in the torsion angle Θ is suppressed. On the other hand, if the torsion angular velocity is not positive, the amount of differential limiting is increased (S112). If the amount of differential limiting is increased, the transmission torque of the power train 12 is increased, and the decrease in the torsion angle Θ is suppressed. After the processing of steps S110 and S112, the process returns to step S104.

[0017] If the determination is negative in each of steps S102, S104, and S106, the vibration suppression control using the differential limit is terminated (S114). After the vibration suppression control is terminated, if the ignition switch is not turned off (S116), the process returns to step S102 and the above-mentioned process is repeated. If the ignition switch is turned off in step S116, the control is terminated.

[0018] In a vehicle that does not have an observer for acquiring the torsion angle Θ of the powertrain 12, the amount of limited slip differential may be changed at a period based on the natural frequency of the torsional fluctuation of the powertrain. A sensor for detecting the torque applied to the driveshaft 24 is provided on the driveshaft 24. When the torque of the driveshaft 24 reaches a torque corresponding to the accelerator operation amount (i.e., a convergence value), the amount of limited slip differential is reduced for a period that is half the natural period of the powertrain. Thereafter, the amount of limited slip differential is increased for the period of the natural period, and then the amount of limited slip differential is reduced for the period of the natural period. When the increase and decrease of the amount of limited slip differential is repeated a predetermined number of times, the vibration suppression control is terminated. It is possible to simply suppress the vibration of the vehicle caused by the torsion of the powertrain. [Explanation of symbols]

[0019] 10 power unit, 12 power transmission system, 14 vibration damping control device, 16 engine, 18 electric motor, 20 final reduction gear, 22 transaxle, 24 drive shaft, 26 drive wheels, 28 differential device, 30 limited slip differential mechanism, 34 differential case, 41 outer disc, 42 inner disc, 44 limited slip differential control unit, 46 vehicle speed sensor, 48 accelerator pedal, 50 accelerator operation amount sensor, 52 steering wheel, 54 steering angle sensor, 56 torsion angle acquisition unit.

Claims

[Claim 1] A vibration damping control device that performs vibration damping control on a vehicle having a power unit that drives the vehicle and a power transmission system that transmits an output of the power unit to drive wheels and includes a differential gear having a differential limiting function, an accelerator operation amount acquisition unit that acquires an operation amount of an accelerator pedal; A steering angle acquisition unit that acquires a steering angle of a steering wheel; a torsion angle acquisition unit that acquires a torsion angle of the power transmission system; a differential limiting control unit that, when an operation amount of the accelerator pedal exceeds a predetermined value, a steering angle of the steered wheels exceeds a predetermined value, and an amplitude of a fluctuation in a torsion angle of the power transmission system exceeds a predetermined value, reduces a differential limiting amount of the differential device while the torsion angle is increasing and increases the differential limiting amount while the torsion angle is decreasing; A vibration damping control device for a vehicle having the same.

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