JP5405984B2 - Control device for continuously variable transmission - Google Patents

Description

  The present invention relates to a control device for a continuously variable transmission including a lock-up clutch.

  A continuously variable transmission (CVT) assembled in a power transmission system of a vehicle has a primary pulley provided on an input shaft, a secondary pulley provided on an output shaft, and a drive chain spanned between these pulleys. . By changing the groove width of each pulley and changing the winding diameter of the drive chain, the gear ratio can be continuously changed (see, for example, Patent Document 1). Further, a torque converter is incorporated between the engine and the continuously variable transmission in order to smoothly transmit engine power to the continuously variable transmission. A torque converter, which is a sliding element, incorporates a lockup clutch that directly connects the crankshaft of the engine and the input shaft of the continuously variable transmission.

  Also, in a continuously variable transmission, any gear ratio can be set by adjusting the pulley groove width, so that a plurality of fixed gear ratios can be switched and shifted like a manual transmission or an automatic transmission. Is possible. Thereby, even in a vehicle equipped with a continuously variable transmission, it is possible to obtain a shift feeling of a multi-speed shift, so that it is possible to improve the merchantability of the continuously variable transmission. Such a multi-stage speed change mode is set based on the traveling state of the vehicle and the driver's shift operation.

JP-A-5-79554

  By the way, as described above, when the continuously variable transmission is controlled in the multi-speed mode, the gear ratio before the shift is different from the gear ratio after the shift, so the continuously variable transmission that continuously changes the gear ratio. Shift speed is higher than in mode. However, when the shift control in the multi-speed mode is executed in a transitional state in which the lockup clutch is being engaged or released, the rotational speed of the primary pulley is suddenly changed with a high speed. For this reason, the rotational speed difference before and after the lock-up clutch fluctuates greatly, and the operation state of the lock-up clutch becomes unstable, which causes a reduction in the transmission quality in the multi-stage transmission mode.

  An object of the present invention is to improve the shift quality of a continuously variable transmission including a lock-up clutch.

The control device for a continuously variable transmission according to the present invention includes a lockup clutch provided between the engine and the transmission mechanism, and continuously changes the transmission ratio as the transmission mode and the transmission ratio in stages. a control device for a continuously variable transmission and a multi-speed mode which switches the plurality of fixed gear ratio which is set stepwise, the multi-speed control means for controlling the speed change mechanism in the multi-speed mode, the lock When the lock-up clutch is in a transient state when the clutch determining means for determining whether the operating state of the up clutch is a steady state or a transient state and when the transmission mechanism is controlled by the multi-stage shift control means to have a transmission speed limiting means lowers the transmission rate than when the lock-up clutch is a steady state, the speed change rate limiting means, a multi-speed motor When the lock-up clutch under conditions where de is set is transient state, lower the transmission speed by switching the shift mode from the multi-speed mode to the stepless speed change mode, and wherein the.

In the continuously variable transmission control device according to the present invention, the shift speed limiting means executes a continuously variable transmission mode for controlling the transmission mechanism using a target speed ratio set based on an accelerator opening and a vehicle speed. Thus, the shift speed is reduced.

  According to the present invention, when the speed change mechanism is controlled by the multi-stage speed change control means, if the lockup clutch is in a transient state, the shift speed is reduced. Can be stabilized, and the shift quality can be improved.

It is a skeleton figure which shows the continuously variable transmission mounted in a vehicle. It is the schematic which shows the hydraulic control system of a continuously variable transmission. It is explanatory drawing which shows an example of the fastening characteristic map used for lockup control. It is explanatory drawing which shows an example of the speed change characteristic map used in continuously variable transmission mode. It is explanatory drawing which shows an example of the shift pattern used in multistage transmission mode. It is explanatory drawing which shows an example of the fixed gear ratio used in multistage transmission mode. It is a block diagram which shows the transmission control system of a CVT control unit. It is a flowchart which shows the execution procedure of the transmission mode switching control performed under the state in which the multi-stage transmission mode is set. (A) And (B) is a diagram which shows the relationship between an engine speed and a turbine speed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a skeleton diagram showing a continuously variable transmission 10 mounted on a vehicle. As shown in FIG. 1, the continuously variable transmission 10 includes a primary shaft 12 that is driven by an engine 11 and a secondary shaft 13 that is parallel to the primary shaft 12. A speed change mechanism 14 is provided between the primary shaft 12 and the secondary shaft 13, and a speed reduction mechanism 16 and a differential mechanism 17 are provided between the secondary shaft 13 and the drive wheels 15.

  The primary shaft 12 is provided with a primary pulley 20, and the primary pulley 20 is composed of a fixed sheave 20a and a movable sheave 20b. A hydraulic oil chamber 21 is defined on the back side of the movable sheave 20b, and the pulley groove width can be changed by adjusting the pressure in the hydraulic oil chamber 21. Moreover, the secondary pulley 22 is provided in the secondary shaft 13, and this secondary pulley 22 is comprised by the fixed sheave 22a and the movable sheave 22b. A hydraulic oil chamber 23 is defined on the back side of the movable sheave 22b, and the pulley groove width can be changed by adjusting the pressure in the hydraulic oil chamber 23. Further, a drive chain 24 is wound around the primary pulley 20 and the secondary pulley 22. By changing the groove width of the pulleys 20 and 22 and changing the winding diameter of the drive chain 24, a continuously variable transmission from the primary shaft 12 to the secondary shaft 13 is possible.

  In order to transmit engine power to such a transmission mechanism 14, a torque converter 30 and a forward / reverse switching mechanism 31 are provided between the crankshaft 25 and the primary shaft 12. The torque converter 30 includes a pump impeller 33 connected to the crankshaft 25 via a front cover 32, and a turbine runner 35 facing the pump impeller 33 and connected to the turbine shaft 34. The torque converter 30 is configured to transmit engine power from the pump impeller 33 to the turbine runner 35 via hydraulic oil. The torque converter 30 that is a sliding element is provided with a lock-up clutch 36 that directly connects the crankshaft 25 and the turbine shaft 34 in order to improve the transmission efficiency of engine power. The lockup clutch 36 has a clutch plate 37 connected to the turbine runner 35, and the clutch plate 37 is disposed between the front cover 32 and the turbine runner 35. An apply chamber 38 is defined on the turbine runner 35 side of the clutch plate 37, and a release chamber 39 is defined on the front cover 32 side of the clutch plate 37.

  By supplying the hydraulic oil to the apply chamber 38 and discharging the hydraulic oil from the release chamber 39, the clutch plate 37 is pressed against the front cover 32, and the lockup clutch 36 is a fastening that directly connects the crankshaft 25 and the turbine shaft 34. It becomes a state. On the other hand, by supplying hydraulic oil to the release chamber 39 and discharging the hydraulic oil from the apply chamber 38, the clutch plate 37 is pulled away from the front cover 32, and the lockup clutch 36 separates the crankshaft 25 and the turbine shaft 34. Released state. Further, by adjusting the pressure in the release chamber 39 and the apply chamber 38, the lockup clutch 36 can be controlled to the slip lockup state. In the slip lock-up state, the lock-up clutch 36 is held in the slip state, so that vibration transmission via the lock-up clutch 36 can be suppressed, and the running quality of the vehicle can be improved.

  The forward / reverse switching mechanism 31 includes a double pinion planetary gear train 40, a forward clutch 41, and a reverse brake 42. By controlling the forward clutch 41 and the reverse brake 42, it is possible to switch the engine power transmission path. By engaging the forward clutch 41 and releasing the reverse brake 42, the rotation of the turbine shaft 34 can be transmitted to the primary pulley 20 as it is. On the other hand, by releasing the forward clutch 41 and fastening the reverse brake 42, the rotation of the turbine shaft 34 can be reversed and transmitted to the primary pulley 20. Note that the turbine shaft 34 and the primary shaft 12 can be separated by releasing both the forward clutch 41 and the reverse brake 42.

  FIG. 2 is a schematic diagram showing a hydraulic control system of the continuously variable transmission 10. As shown in FIG. 2, an oil pump 50 driven by the engine 11 is provided in the hydraulic control system in order to supply hydraulic oil to the primary pulley 20, the secondary pulley 22, the torque converter 30, and the like. The secondary pressure path 51 connected to the oil pump 50 is connected to the hydraulic oil chamber 23 of the secondary pulley 22 and is connected to the pressure adjustment port 52 a of the secondary pressure control valve 52. The secondary pressure as the line pressure regulated via the secondary pressure control valve 52 is regulated based on the engine torque, the target gear ratio, etc. so as not to cause the drive chain 24 to slip. The secondary pressure path 51 is connected to the input port 53 a of the primary pressure control valve 53, and the primary pressure path 54 extending from the output port 53 b of the primary pressure control valve 53 is connected to the hydraulic oil chamber 21 of the primary pulley 20. Yes. The primary pressure regulated through the primary pressure control valve 53 is regulated based on the target gear ratio, the secondary pressure, and the like so as to control the groove width of the primary pulley 20 toward the target gear ratio.

  Further, in order to supply hydraulic oil to the lockup clutch 36, a clutch pressure control valve 55 for adjusting the clutch pressure and a switch valve 56 for switching the oil path are provided between the torque converter 30 and the secondary pressure path 51. ing. A branch oil passage 57 branched from the secondary pressure passage 51 is connected to an input port 55a of the clutch pressure control valve 55, and a clutch pressure passage 58 extending from an output port 55b of the clutch pressure control valve 55 is connected to a switch valve 56. Yes. A branch oil passage 60 branched from the lubrication pressure passage 59 is connected to the switch valve 56. Further, an apply pressure path 61 that communicates with the apply chamber 38 and a release pressure path 62 that communicates with the release chamber 39 are connected to the switch valve 56. When the lockup clutch 36 is switched to the engaged state, the spool valve shaft in the switch valve 56 is switched to the engaged position. As a result, the clutch pressure is supplied from the apply pressure path 61 to the apply chamber 38, and the hydraulic oil in the release chamber 39 is discharged from the release pressure path 62. On the other hand, when the lockup clutch 36 is switched to the released state, the spool valve shaft in the switch valve 56 is switched to the released position. As a result, the hydraulic oil in the apply chamber 38 is discharged from the apply pressure passage 61, and the lubricating pressure is supplied from the release pressure passage 62 to the release chamber 39.

  Here, FIG. 3 is an explanatory diagram showing an example of a fastening characteristic map used for lock-up control. As shown in FIG. 3, the engagement characteristic map includes a lockup region where the lockup clutch 36 is engaged and a converter region where the lockup clutch 36 is released based on the vehicle speed V and the accelerator opening Acc. It is partitioned. The CVT control unit 70 controls the clutch pressure control valve 55 and the switch valve 56 to control the lockup clutch 36 by referring to the engagement characteristic map of FIG. 3 based on the vehicle speed V and the accelerator opening Acc. It will be. Note that, during acceleration, deceleration, etc., slip lockup control for holding the lockup clutch 36 in a slip state is executed.

  The CVT control unit 70 that outputs a control signal to such a hydraulic control system includes a microprocessor (CPU) (not shown). The CPU has ROM, RAM, and I / O ports via a bus line. Connected. The ROM stores control programs and various map data, and the RAM temporarily stores data calculated by the CPU. In addition, detection signals indicating vehicle states are input from various sensors to the CPU via the I / O port. Various sensors connected to the CVT control unit 70 include a primary rotational speed sensor 71 that detects the rotational speed of the primary pulley 20, a secondary rotational speed sensor 72 that detects the rotational speed of the secondary pulley 22, and a vehicle speed sensor 73 that detects the vehicle speed. An engine speed sensor 74 that detects the engine speed, an accelerator position sensor 75 that detects an accelerator position that is the amount of depression of the accelerator pedal, a throttle position sensor 76 that detects the throttle position of the throttle valve, and a select lever 77 Inhibitor switch 78 and the like for detecting the operation status are provided.

  Subsequently, the shift control of the continuously variable transmission 10 will be described. The CVT control unit 70 includes a continuously variable transmission mode in which the gear ratio is continuously changed and a multi-speed transmission mode in which the gear ratio is changed stepwise. These shift modes are switched according to the operation of the driver's select lever. As shown in FIG. 2, the gate 80 for guiding the select lever 77 is composed of a continuously variable transmission gate 81 and a multi-stage transmission gate 82. Moving the select lever 77 to the continuously variable transmission gate 81 sets the continuously variable transmission mode, while moving the select lever 77 to the multi-speed transmission gate 82 sets the multi-speed transmission mode. Note that the shift mode may be automatically switched for each preset shift region without switching the shift mode by operating the select lever. Here, FIG. 4 is an explanatory diagram showing an example of a shift characteristic map used in the continuously variable transmission mode. FIG. 5 is an explanatory diagram showing an example of a shift pattern used in the multi-speed mode. FIG. 6 is an explanatory diagram showing an example of a fixed gear ratio used in the multi-speed mode.

  When the continuously variable transmission mode is set by operating the select lever, the CVT control unit 70 refers to the transmission characteristic map of FIG. 4 based on the vehicle speed V and the accelerator opening Acc, and from this transmission characteristic map, the target primary rotation speed Np Is calculated. The CVT control unit 70 calculates a target speed ratio based on the target primary speed Np, and controls the primary pressure Pp and the secondary pressure Ps based on the target speed ratio. As shown in FIG. 4, a characteristic line Low indicating the maximum speed ratio and a characteristic line High indicating the minimum speed ratio are set in the speed change characteristic map referred to in the continuously variable transmission mode, and the characteristic lines Low, High Between these, a plurality of characteristic lines A1 to A8 corresponding to the accelerator opening Acc are set. For example, when the accelerator pedal is depressed from the traveling state indicated by the symbol α in FIG. 4 to the accelerator opening corresponding to the characteristic line A6, Np1 is set as the target primary speed and Tr1 is set as the target speed ratio. Will be. Further, when the accelerator pedal is depressed from the traveling state indicated by the symbol α in FIG. 4 to the accelerator opening corresponding to the characteristic line A2, Np2 is set as the target primary rotational speed, and Tr2 as the target gear ratio. Will be set. Thus, in the continuously variable transmission mode, the target gear ratio is set continuously based on the vehicle speed V and the accelerator opening Acc that change every moment.

  On the other hand, when the multi-speed mode is set by operating the select lever, the CVT control unit 70 refers to the shift pattern of FIG. 5 based on the vehicle speed V and the accelerator opening degree Acc, and the fixed pattern used for shift control from this shift pattern. Gear ratios R1-R5 are selected. As shown in FIG. 6, fixed speed ratios R <b> 1 to R <b> 5 used in the multi-speed mode are set in advance in a speed change region defined between the characteristic line Low and the characteristic line High. Further, as shown in FIG. 5, a plurality of upshift lines (solid lines) defining upshifts between the fixed gear ratios R1 to R5 are set in the shift pattern, and between the fixed gear ratios R1 to R5. A plurality of downshift lines (broken lines) defining the downshift are set. When the vehicle speed V or the accelerator opening degree Acc changes so as to straddle each shift line, an upshift or a downshift is performed between the fixed speed ratios R1 to R5. As described above, by executing the shift control using the fixed gear ratios R1 to R5, it is possible to obtain the same shift feeling as that of the five-stage forward transmission although it is the continuously variable transmission 10. .

  As shown in FIG. 2, the select lever 77 can be moved in the front-rear direction within the multi-stage shift gate 82. An upshift is possible by moving the select lever 77 forward (+ direction), and a downshift is possible by moving the select lever 77 backward (− direction). Thus, not only the fixed transmission gear ratios R1 to R5 are switched according to the shift pattern, but also the fixed transmission gear ratios R1 to R5 can be switched according to the driver's select lever operation. Further, in the illustrated case, the fixed speed ratios R1 to R5 are set in five stages, but the present invention is not limited to this, and the number of fixed speed ratios set may be increased or decreased.

  FIG. 7 is a block diagram showing a shift control system of the CVT control unit 70. As shown in FIG. 7, the CVT control unit 70 includes a target primary rotational speed calculation unit 90 and a gear ratio calculation unit 91 in order to calculate a target gear ratio in the continuously variable transmission mode. The target primary rotational speed calculation unit 90 calculates the target primary rotational speed Np with reference to the speed change characteristic map of FIG. 4 based on the vehicle speed V and the accelerator opening Acc. Further, the gear ratio calculation unit 91 calculates the target gear ratio ia based on the target primary rotation speed Np and the actual secondary rotation speed Ns ′. Then, the calculated target gear ratio ia is input to the target gear ratio setting unit 92, and the target gear ratio setting unit 92 sets the target gear ratio ia as the target gear ratio i for calculation. The CVT control unit 70 that functions as a multi-stage transmission control means includes a transmission ratio selection unit 93 for setting a target transmission ratio ib in the multi-stage transmission mode. The gear ratio selection unit 93 selects the target gear ratio ib from the fixed gear ratios R1 to R5 with reference to the shift pattern of FIG. 5 based on the vehicle speed V and the accelerator opening Acc. The selected target gear ratio ib is input to the target gear ratio setting unit 92, and the target gear ratio setting unit 92 sets the target gear ratio ib as the target gear ratio i for calculation.

  The CVT control unit 70 also includes a shift mode setting unit 94 for switching the shift mode. The shift mode setting unit 94 detects the operation position of the select lever 77 based on a signal from the inhibitor switch 78 and sets the continuously variable transmission mode or the multi-stage transmission mode based on the operation position of the select lever 77. When the continuously variable transmission mode is set, the target speed ratio ia is calculated by the speed ratio calculation unit 91 and the target speed ratio ia is output to the target speed ratio setting unit 92. On the other hand, when the multi-stage transmission mode is set, the target transmission ratio ib is selected by the transmission ratio selection unit 93 and the target transmission ratio ib is output toward the target transmission ratio setting unit 92. That is, the target speed ratio ia is set as the target speed ratio i in the continuously variable transmission mode, while the target speed ratio ib is set as the target speed ratio i in the multi-speed mode.

  In order to calculate the target primary pressure Pp based on such a target speed ratio i, the CVT control unit 70 includes a hydraulic pressure ratio calculation unit 95 and a target primary pressure calculation unit 96. The hydraulic ratio calculation unit 95 calculates a hydraulic ratio (Pp / Ps) between the target primary pressure Pp and the target secondary pressure Ps corresponding to the target speed ratio i, and the target primary pressure calculation unit 96 sets the target secondary pressure to the hydraulic ratio. The target primary pressure Pp is calculated by multiplying Ps. In addition, the CVT control unit 70 includes an actual gear ratio calculation unit 97, a feedback value calculation unit 98, and an addition unit 99 for feedback control of the target primary pressure Pp. The actual gear ratio calculation unit 97 calculates the actual gear ratio i ′ based on the actual primary rotation speed Np ′ and the actual secondary rotation speed Ns ′, and the feedback value calculation unit 98 calculates the actual gear ratio i ′ and the target gear ratio. A feedback value F is calculated based on i. Subsequently, the feedback value F is input to the adding unit 99, and the adding unit 99 adds the feedback value F to the target primary pressure Pp. Thus, the target primary pressure Pp is feedback-controlled so that the actual speed ratio i ′ approaches the target speed ratio i.

  Furthermore, the CVT control unit 70 includes an input torque calculation unit 100, a required secondary pressure calculation unit 101, and a target secondary pressure calculation unit 102 in order to calculate the target secondary pressure Ps. The input torque calculation unit 100 calculates the input torque Ti input from the engine 11 to the primary shaft 12 based on the engine speed Ne and the throttle opening degree To, and the required secondary pressure calculation unit 101 calculates the target gear ratio i. Based on the above, the required secondary pressure Psn is calculated. The input torque Ti and the required secondary pressure Psn are input to the target secondary pressure calculation unit 102, and the target secondary pressure calculation unit 102 calculates the target secondary pressure Ps. Then, the secondary pressure control valve 52 is controlled toward the target secondary pressure Ps, and the secondary pulley 22 is controlled with a tightening force commensurate with the transmission torque of the drive chain 24.

  Incidentally, as shown in FIG. 6, in the multi-speed mode, the gear ratio is changed as compared with the continuously variable speed mode in which the speed ratio is continuously changed because the speed is changed between the fixed speed ratios R1 to R5 that are separated from each other. The speed, i.e. the shifting speed, is increased. In particular, in the multi-shift mode, it is important to increase the shift speed and achieve an agile shift operation in order to improve the shift quality with respect to an accelerator operation such as kickdown or a shift operation in the manual mode. However, in the multi-speed mode with a high shift speed, when the lock-up clutch 36 is controlled to be in a transitional state during engagement or release, there is a risk that engine speed fluctuation or torque fluctuation will be caused and the transmission quality will be reduced. It was. That is, in the transient state of the lockup clutch 36, the lockup clutch 36 is controlled based on the differential rotation between the engine speed Ne on the clutch input side and the turbine speed (rotation speed of the turbine shaft 34) Nt on the clutch output side. The hydraulic oil supplied to the apply chamber 38 and the release chamber 39 is adjusted. In such a transient control of the lock-up clutch 36, when a shift is performed in the multi-speed mode with a high shift speed, the primary rotation speed (turbine rotation speed) changes suddenly, so that the engine rotation speed Ne and the turbine rotation speed are changed. The differential rotation with the number Nt varies greatly. Since the fluctuation of the differential rotation affects the transient control of the lockup clutch 36, the operation state of the lockup clutch 36 becomes unstable, resulting in engine rotation fluctuation, torque fluctuation, and the like.

  Therefore, as shown in FIG. 7, the clutch determination unit 103 is provided in the CVT control unit 70 functioning as a clutch determination unit, and the operation state of the lockup clutch 36 is determined by the clutch determination unit 103. The CVT control unit 70 is provided with a lockup control unit 104, and a control signal for the lockup clutch 36 is calculated by the lockup control unit 104. The lockup control unit 104 determines whether or not the lockup clutch 36 is to be engaged by referring to the engagement characteristic map of FIG. 3 based on the vehicle speed V and the accelerator opening degree Acc. Further, detection signals relating to clutch judder and the like are also input to the lockup control unit 104, and it is determined whether or not the lockup clutch 36 is to be engaged in consideration of these detection signals.

  Subsequently, based on the control signal from the lockup control unit 104, the clutch determination unit 103 determines whether the lockup clutch 36 is in a steady state (engaged state, released state, slip lockup state) or the lockup clutch 36. Is in a transitional state that shifts to a steady state. The clutch determination unit 103 determines that the lockup clutch 36 is in a transient state until a predetermined time has elapsed after the control signals (engagement signal, release signal, slip lockup signal) for the lockup clutch 36 are output. After a predetermined time has elapsed, it is determined that the lockup clutch 36 is in a steady state. The determination method is not limited to this. The operating state of the lockup clutch 36 may be determined based on the pressure in the apply chamber 38 or the release chamber 39, and the lockup may be performed based on the engine speed Ne or the turbine speed Nt. The operating state of the clutch 36 may be determined.

  When the clutch determination unit 103 determines that the lockup clutch 36 is in a transient state, the clutch determination unit 103 outputs a determination signal indicating the transient state to the transmission mode setting unit 94. When a determination signal indicating a transient state is input to the transmission mode setting unit 94, the transmission mode setting unit 94 sets the transmission mode to the continuously variable transmission mode. That is, when the lockup clutch 36 is controlled to be in a transition state under the state where the multi-stage transmission mode is set, the transmission mode is switched from the multi-stage transmission mode to the continuously variable transmission mode.

  Next, the shift mode switching procedure described above will be described with reference to a flowchart. FIG. 8 is a flowchart showing the execution procedure of the shift mode switching control executed under the state where the multi-stage shift mode is set. As shown in FIG. 8, in step S10, it is determined whether or not the lockup clutch 36 is in a transient state. If it is determined in step S10 that the lockup clutch 36 is in a steady state (released state, engaged state, slip lockup state), the process proceeds to step S11, and the multi-stage transmission mode is maintained as the transmission mode. Then, the process proceeds to step S12, and shift control is executed in accordance with the multi-stage shift mode. On the other hand, if it is determined in step S10 that the lock-up clutch 36 is in a transitional state in which it is shifted to the disengaged state or the engaged state, the process proceeds to step S13, and the shift mode is switched from the multi-speed mode to the continuously variable mode. . Then, the process proceeds to step S12, and the shift control is executed according to the continuously variable transmission mode.

  As described above, when it is determined that the lockup clutch 36 is in a transitional state under the state where the multi-speed mode is set, the CVT control unit 70 functioning as a shift speed limiting unit sets the shift mode. The multi-speed mode is switched to the continuously variable mode. In the continuously variable transmission mode, the target speed ratio i is set according to the vehicle speed V and the accelerator opening degree Acc, so that the speed change speed can be reduced. As a result, even when the lockup clutch 36 is controlled to be in a transitional state, a sudden change in the primary rotational speed is suppressed due to a decrease in the shift speed, so that the operation state of the lockup clutch 36 can be stabilized. It becomes. Therefore, engine rotation fluctuation and torque fluctuation can be suppressed, and the shift quality can be improved. Note that when the lock-up clutch 36 transitions to a steady state through a transient state, the multi-speed mode is set again according to the driver's select lever operation.

  Here, FIGS. 9A and 9B are graphs showing the relationship between the engine speed Ne and the turbine speed Nt. FIG. 9 (A) shows a situation when the shift speed is not limited in the multi-stage shift mode, and FIG. 9 (B) shows a situation when the shift speed is limited in the multi-stage shift mode. FIGS. 9A and 9B show the engine speed Ne and the turbine speed Nt obtained under the same traveling conditions. First, as shown in FIG. 9A, when the multi-speed mode is maintained in the transient state of the lock-up clutch 36, the turbine rotational speed Nt changes suddenly at a high speed as shown by symbol α. It will be. For this reason, the operation state of the lockup clutch 36 becomes unstable, and overshoot and undershoot of the engine speed Ne occur. On the other hand, as shown in FIG. 9B, when the lockup clutch 36 is transitioned from the multi-stage transmission mode to the continuously variable transmission mode in the transient state, the turbine is moved at a low transmission speed as indicated by the symbol β. The rotational speed Nt changes gently. For this reason, the operating state of the lock-up clutch 36 is stabilized, and it becomes possible to suppress overshoot and undershoot of the engine speed Ne.

  As described above, when the lock-up clutch 36 is in a transitional state, the shift mode is switched from the multi-speed mode to the continuously variable mode. However, the present invention is not limited to this, and other methods are used. To reduce the speed. For example, as shown in FIG. 7, the CVT control unit 70 includes a feedback value calculation unit 98 that performs feedback control of the target primary pressure Pp based on the difference between the target speed ratio i and the actual speed ratio i ′. However, it is also possible to limit the feedback speed F to suppress the shift speed. Further, by setting a speed limit mode in which the shift speed is limited, the shift mode may be switched from the multi-stage shift mode to the speed limit mode when the lockup clutch 36 is in a transitional state.

  It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, in the above description, the shift control and the lockup control are executed using the accelerator opening Acc, but the throttle opening To may be used instead of the accelerator opening Acc. Although the belt drive type continuously variable transmission 10 has been described as the continuously variable transmission, the present invention is not limited to this, and the present invention may be applied to a toroidal continuously variable transmission. Furthermore, although the drive chain 24 is wound around the primary pulley 20 and the secondary pulley 22, the present invention is not limited to this, and a drive belt holding a number of elements in bands may be wound.

10 continuously variable transmission 11 engine 14 transmission mechanism 36 lock-up clutch 70 CVT control unit (multi-stage transmission control means, clutch determination means, transmission speed limiting means)

Claims (2)

A continuously variable transmission having a continuously variable transmission mode in which a gear ratio is continuously changed as a transmission mode and a multi-speed transmission mode in which a transmission ratio is changed step by step is provided as a shift mode . A control device,
Switching a plurality of fixed gear ratio set stepwise, and the multi-speed control means for controlling the speed change mechanism in a multi-speed mode,
Clutch determining means for determining whether the operation state of the lock-up clutch is a steady state or a transient state;
When controlling the speed change mechanism by the multi-stage speed change control means, if the lockup clutch is in a transient state, a speed change speed limiting means for lowering the speed change than when the lockup clutch is in a steady state ;
Have
The shift speed limiting means switches the shift speed from the multi-speed mode to the continuously variable speed mode when the lockup clutch is in a transitional state with the multi-speed mode set. A continuously variable transmission control device characterized by being pulled down . The control device for a continuously variable transmission according to claim 1,
The shift speed limiting means reduces the shift speed by executing a continuously variable transmission mode for controlling the transmission mechanism using a target speed ratio set based on an accelerator opening and a vehicle speed. Control device for step transmission.

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