Vehicle vibration control system

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 control device that suppresses vibrations caused by torsional vibration in the power transmission system of a vehicle.

Background Art

[0002] A vehicle has a power transmission system that forms a path for transmitting the output of a power plant to drive wheels. The power transmission system includes at least a part of a clutch, a transmission, a propeller shaft, a final reduction gear, a drive shaft, etc. The final reduction gear includes a differential device for absorbing the speed difference between the left and right drive wheels when the vehicle turns. Patent Document 1 below shows a differential device having a function of restricting differential operation by frictional force generated between elements that move relative to each other during vehicle turning. When restricting the differential operation, this device reduces the shock caused by a sudden rise in the amount of friction at the start of differential restriction by gradually increasing the frictional force.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power transmission system of a vehicle, torsion may occur due to a change in the output torque of the power plant, and vibrations may occur in the vehicle due to this torsion.

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

Means for Solving the Problems

[0006] The vehicle to which the vibration control device according to the present invention applies includes a power unit that drives the vehicle and a power transmission system that transmits the output of the power unit to the drive wheels and includes a differential with a differential limiting function. The vibration control device for the vehicle includes an accelerator operation amount acquisition unit that acquires the amount of operation of the accelerator pedal, a steering angle acquisition unit that acquires the steering angle of the steering wheels, a torsion angle acquisition unit that acquires the torsion angle of the power transmission system, and a differential limiting control unit that controls the differential limiting amount of the differential. When the amount of operation of the accelerator pedal exceeds a predetermined value, the steering angle of the steering wheels exceeds a predetermined value, and the amplitude of the fluctuation in 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. [Effects of the Invention]

[0007] The torque transmitted by the power transmission system is increased or decreased by increasing or decreasing the differential limit in accordance with the increase or decrease in the torsional angle of the power transmission system. When the torsional angle is increasing, the differential limit is decreased to decrease the torque transmitted by the power transmission system. This suppresses the increase in the torsional angle. Conversely, when the torsional angle is decreasing, the differential limit is increased to increase the torque transmitted. This suppresses the decrease in the torsional angle. Therefore, fluctuations in the torsional angle converge quickly. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram schematically shows the configuration of the power unit, power transmission system, and vibration control device of the vehicle according to this embodiment. [Figure 2] This figure shows the fluctuations in the torsional angle of the power transmission system and the differential limiting amount by the differential gear. [Figure 3] This chart shows the flow of vibration control. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram showing the power unit 10 and power transmission system 12 of the vehicle according to this embodiment, and the vibration control device 14 for suppressing vehicle vibrations.

[0010] The power unit 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 by either one. The power unit may also consist of only one of the engine or the electric motor. The electric motor 18 is housed in a transaxle 22 which 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 the drive shaft 24, and transmits the output of the power unit 10 to the left and right drive wheels 26. The drive wheels 26 are also the steering wheels. The final reduction gear 20 includes a differential 28 that absorbs the speed difference between the left and right drive wheels 26 when the vehicle turns. The differential 28 includes a differential limiting mechanism 30 that limits the amount of differential.

[0011] The differential gear 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 left and right drive shafts 24 are coupled to the two side gears 40, respectively. 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 shafts 24. By pressing the outer discs 41 and inner discs 42 into contact using a hydraulic actuator (not shown), a frictional force is generated between the two discs 41 and 42. This frictional force can suppress the relative motion between the differential case 34 and the drive shafts 24. In other words, the differential amount of the differential gear 28 can be suppressed. When there is a speed difference between the left and right drive wheels 26, the differential limiting mechanism 30 generates frictional force. If there were no frictional force, some of the torque that would otherwise be transmitted to the drive wheel 26 rotating at high speed would be transmitted to the drive wheel 26 rotating at low speed. If the outer disc 41 and the inner disc 42 are brought into close contact so that there is no relative speed, the differential 28 will not perform differential operation. Also, when frictional force is acting while allowing relative rotation between the outer disc 41 and the inner disc 42, differential operation is restricted. The amount of restriction on differential operation, i.e., the differential limit amount, can be adjusted by adjusting the frictional force. Increasing the frictional force increases the differential limit amount, and the differential limit amount is maximized when the outer disc 41 and the inner disc 42 rotate as a single unit. Decreasing the frictional force decreases the differential limit amount, and when the differential limit amount becomes 0, normal differential operation occurs.

[0012] The operation of the differential limiting mechanism 30 is controlled by the differential limiting control unit 44. The differential limiting control unit 44 controls the differential limiting amount, i.e., the frictional force between the outer disc 41 and the inner disc 42, according to the vehicle's driving conditions. The vehicle's driving conditions are acquired based on various on-board sensors. On-board sensors include, for example, a vehicle speed sensor 46 for detecting the vehicle's speed, an accelerator pedal operation sensor 50 for detecting the amount of operation of the accelerator pedal 48, and a steering angle sensor 54 for detecting the rotation angle of the steering wheel 52, i.e., the steering angle. Furthermore, the torsion angle of the power transmission system 12 may be included as a physical quantity representing the vehicle's driving conditions. The torsion angle of the power transmission system 12 is acquired by the torsion angle acquisition unit 56. The torsion angle acquisition unit 56 may acquire the relative rotation angle, i.e., the torsion angle, based on the rotational speed or rotation angle of the output shaft of the power unit 10 and the drive wheels 26. Alternatively, the torsion angle may be acquired using an observer, which is a calculation model of the power transmission system 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 wheel 26. The twist angle of the power transmission system 12 is then obtained from the rotational speed of the electric motor 18 and the obtained rotational speed of the drive wheel 26.

[0013] Figure 2 shows the changes in the torsional angle Θ and differential limit R of the power transmission system 12. In particular, it shows the torsional angle Θ and differential limit R when the driver presses the accelerator pedal 48 and the vehicle begins to accelerate. The torsional 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 pressed, the torsional angle Θ increases along with the increase in drive shaft torque, fluctuates, and then converges. The converged value of the torsional angle Θ is determined by the accelerator operation amount. The relative value of the torsional angle Θ to this converged value is denoted as the torsional angle fluctuation Φ. The converged value of the torsional angle Θ is represented by a torsional angle fluctuation Φ of 0. When the accelerator pedal 48 is pressed, the torsional angle Θ rises, increases beyond the converged value (Φ=0), and then begins to decrease. Furthermore, the torsional angle Θ exceeds the converged value (Φ=0) and then begins to increase again. The twist angle Θ repeatedly increases and decreases, but its amplitude decreases and it eventually converges.

[0014] When the power transmission system 12 experiences the fluctuating torsion described above, the driving force that propels the vehicle forward fluctuates, and this fluctuating driving force becomes an excitatory force, causing the vehicle to vibrate. To suppress this vehicle vibration, the differential limit R of the differential gear 28 is used. Reducing the differential limit R, that is, reducing the frictional force, reduces the transmitted torque of the power transmission system 12, and suppresses the increase in the torsional angle Θ. Conversely, increasing the differential limit R increases the transmitted torque, which promotes the increase in the torsional angle Θ. However, since the differential gear 28 only operates when the vehicle is turning, vibration damping by the differential gear 28 is only performed during turning.

[0015] When vibrations occur in the power transmission system 12 where the amplitude of the torsional angle fluctuation Φ exceeds γ, vibration damping control is performed by the differential gear 28. The torsional angle fluctuation Φ can be obtained by the torsional angle estimation method using the observer described above. If the observer estimates that the amplitude of the torsional angle fluctuation Φ will be greater than a predetermined value γ, then when the torsional angle Θ is increasing, i.e., when the torsional angular velocity is positive, the differential limit amount R is reduced by ΔR compared to the differential limit amount R0 in the normal state, i.e., when no vibration is occurring (R=R0-ΔR). This reduces the transmitted torque and suppresses the increase in the torsional angle Θ. By suppressing the increase in the torsional angle Θ, the height of the upward convex peak of the torsional angle Θ becomes smaller. When the torsional angle Θ is decreasing, the differential limit amount R is increased by ΔR compared to the differential limit amount R0 in the normal state (R=R0+ΔR). This increases the transmitted torque and suppresses the decrease in the torsional angle Θ. By suppressing the decrease in the torsional angle Θ, the depth of the trough in the downward-convex peak of the torsional angle Θ becomes smaller. As a result, the torsional vibration of the power transmission system 12 converges earlier.

[0016] Figure 3 is a flowchart relating to differential limiting control when torsional fluctuations occur in the power transmission system 12. With the ignition switch ON (S100), the differential limiting control unit 44 determines whether the accelerator pedal operation exceeds a predetermined value β (S102). If the accelerator pedal operation 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 pedal operation is greater than or equal to the predetermined value β, the next step is to determine whether the steering angle exceeds a predetermined value α (S104). The vibration damping method of this embodiment utilizes the differential limiting of the left and right drive wheels 26, and therefore can only be executed when differential occurs. The predetermined value α of the steering angle is the lower limit of the steering angle at which normal differential limiting is performed. If the steering angle exceeds the predetermined value α, the next step is to determine whether the amplitude of the torsional angle fluctuation Φ exceeds a predetermined value γ (S106). The predetermined value γ is a value used to determine the occurrence of a torsional angle fluctuation that should suppress vibration. If steps S102, S104, and S106 are all affirmative (Yes), then the sign of the torsional angle Θ, i.e., the torsional angular velocity, is determined (S108). If the torsional angular velocity is positive, the differential limit is reduced (S110). If the differential limit is reduced, the transmission torque of the power transmission system 12 decreases, and the increase in the torsional angle Θ is suppressed. On the other hand, if the torsional angular velocity is not positive, the differential limit is increased (S112). If the differential limit is increased, the transmission torque of the power transmission system 12 increases, and the decrease in the torsional angle Θ is suppressed. After processing steps S110 and S112, the process returns to step S104.

[0017] If a negative result is obtained in each of steps S102, S104, and S106, the vibration damping control using differential limiting is terminated (S114). After the vibration damping control is terminated, if the ignition switch is not turned off (S116), the process returns to step S102 and the above process is repeated. In step S116, if the ignition switch is turned off, the control is terminated.

[0018] In vehicles that do not have an observer for acquiring the torsional angle Θ of the power transmission system 12, the differential limit amount may be changed in a period based on the natural frequency of the torsional fluctuation of the power transmission system. A sensor for detecting the torque applied to the drive shaft 24 is provided on the drive shaft 24. When the torque of the drive shaft 24 reaches the torque corresponding to the accelerator operation amount (i.e., the converged value), the differential limit amount is decreased for a period of half the natural period of the power transmission system. Thereafter, the differential limit amount is increased for the period of the natural period, and then decreased for the period of the natural period. The vibration control is terminated when the increase and decrease of the differential limit amount is repeated a predetermined number of times. This makes it possible to easily suppress vehicle vibrations caused by torsion of the power transmission system. [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 wheel, 28 Differential, 30 Differential limiting mechanism, 34 Differential case, 41 Outer disc, 42 Inner disc, 44 Differential limiting 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 control device for controlling vibrations of a vehicle comprising a power unit for driving the vehicle and a power transmission system that transmits the output of the power unit to the drive wheels and includes a differential with a differential limiting function, An accelerator pedal operation amount acquisition unit acquires the amount of operation of the accelerator pedal, A steering angle acquisition unit that acquires the steering angle of the steering wheels, A torsion angle acquisition unit that acquires the torsion angle of the power transmission system, When the amount of operation of the accelerator pedal exceeds a predetermined value, the steering angle of the steering wheels exceeds a predetermined value, and the amplitude of the fluctuation in the twist angle of the power transmission system exceeds a predetermined value, a differential limiting control unit decreases the differential limiting amount of the differential while the twist angle is increasing, and increases the differential limiting amount while the twist angle is decreasing. A vibration control device for a vehicle having a vibration control system.

Images