Automatic transmission, control method for automatic transmission, and program

Abstract

The present application suppresses the discomfort of the driver caused by the vehicle deceleration due to the driver's unintentional downshift caused by the failure of the rotational speed sensor or the like. An automatic transmission is provided with: a transmission mechanism that performs a speed change on the rotation of a drive source and transmits to a drive wheel; and a clutch that controls the torque transmission from the drive source to the drive wheel, and when the rate of change in the rotational speed of the drive source becomes a prescribed rate of change or more, the torque transmission capacity of the clutch is decreased.

Description

Technical Field

[0001] This invention relates to an automatic transmission, a control method for the automatic transmission, and a program for the automatic transmission. Background Technology

[0002] Patent document 1 discloses a control device for a vehicle with an automatic transmission, comprising: a fault downshift detection unit that detects a shift in gear ratio from a high-speed gear ratio to a low-speed gear ratio that acts as engine braking due to a fault; and a braking force reduction unit that reduces the braking force of the driving force source when the fault downshift detection unit detects a shift.

[0003] Faulty downshifting is determined by factors such as the second solenoid valve being in the off state when it should be in the on state, or the gear ratio calculated based on the input speed and output shaft speed of the automatic transmission being different from the gear ratio of the second speed.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 10-169768

[0007] The problem that the invention aims to solve

[0008] For example, if the calculated actual gear ratio becomes an abnormal value due to a malfunction of the speed sensor related to the gear ratio calculation, it can be considered that an unintentional downshift by the driver might occur due to a shift towards the target gear ratio. However, in this case, the aforementioned technique cannot be used for fault diagnosis. Therefore, the braking force reduction unit fails to activate, and the vehicle deceleration caused by downshifting could potentially cause discomfort to the driver. Summary of the Invention

[0009] The present invention was made in view of such a technical problem, and its purpose is to suppress the discomfort caused to the driver by unintentional downshifting of the vehicle due to a malfunction of the speed sensor or other reasons.

[0010] According to one aspect of the present invention, an automatic transmission is provided, comprising: a transmission mechanism that changes the rotational speed of a drive source and transmits it to a drive wheel; and a clutch that controls the torque transmission from the drive source to the drive wheel, wherein when the rate of change of the rotational speed of the drive source becomes greater than or equal to a predetermined rate of change, the torque transmission capacity of the clutch decreases.

[0011] Invention Effects

[0012] According to the above method, when the rate of change of the drive source's rotational speed exceeds a specified rate of change, the torque transmission capacity of the clutch decreases. Therefore, it can mitigate the braking force of the drive source, reduce deceleration, and thus suppress discomfort to the driver. Attached Figure Description

[0013] Figure 1 This is a schematic structural diagram of a vehicle equipped with an automatic transmission according to an embodiment of the present invention.

[0014] Figure 2 This is a function block diagram of the transmission controller.

[0015] Figure 3 It is a flowchart representing the braking force control process performed by the transmission controller. Detailed Implementation

[0016] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, a gear ratio of large is referred to as low gear, and a gear ratio of small is referred to as high gear. Furthermore, shifting the gear ratio towards a lower gear is called downshifting, and shifting the gear ratio towards a higher gear is called upshifting.

[0017] Figure 1 This is a schematic structural diagram of a vehicle 100 equipped with an automatic transmission 20 according to an embodiment of the present invention. Figure 1 As shown, the vehicle 100 includes: an engine 10 as a drive source, an automatic transmission 20, an engine controller 30, and a transmission controller 40.

[0018] The automatic transmission 20 includes: a hydraulic torque converter 2, a forward / reverse switching mechanism as a power transmission mechanism 3, a transmission mechanism 4 as a gear shifting mechanism, an oil pressure control circuit 5, and an oil pump 6.

[0019] In vehicle 100, the rotation generated by engine 10 is transmitted to drive wheel 50 via hydraulic torque converter 2, forward / reverse switching mechanism 3, transmission mechanism 4, gear set 7, and differential gear device 8.

[0020] A lock-up clutch 2a is provided in the torque converter 2. When the lock-up clutch 2a is engaged, the input shaft 2b, which is the input element of the torque converter 2, and the output shaft 2c, which is the output element, are directly connected, and the input shaft 2b and the output shaft 2c rotate at the same speed. Therefore, when the lock-up clutch 2a is engaged, the rotation of the output shaft 10a of the engine 1 is directly transmitted from the output shaft 2c of the torque converter 2 to the forward / reverse switching mechanism 3.

[0021] The forward / reverse switching mechanism 3 uses a double-pinion planetary gear set as its main component. Its sun gear is connected to the engine 10 via the hydraulic torque converter 2, and the planetary gear carrier is connected to the input shaft 4d (primary pulley 4a) of the transmission mechanism 4. The forward / reverse switching mechanism 3 also includes a forward clutch 3a that directly connects the sun gear and the planetary gear carrier of the double-pinion planetary gear set, and a reverse brake 3b with a fixed gear ring. When the forward clutch 3a is engaged, the input rotation from the engine 10 via the hydraulic torque converter 2 is transmitted to the primary pulley 4a at a constant speed. When the reverse brake 3b is engaged, the input rotation from the engine 10 via the hydraulic torque converter 2 is reversed and decelerated before being transmitted to the primary pulley 4a.

[0022] The transmission mechanism 4 is a continuously variable transmission (CVT) mechanism that changes the speed of the rotation of the engine 10 transmitted to the input shaft 4d and transmits it from the output shaft 4e to the drive wheel 50. The transmission mechanism 4 includes: a primary pulley 4a disposed on the engine 10 side in the power transmission path; a secondary pulley 4b disposed on the drive wheel 50 side; and a belt 4c, which is a ring-shaped component, wound around the primary pulley 4a and the secondary pulley 4b.

[0023] In the transmission mechanism 4, the contact radius between each pulley 4a, 4b and belt 4c is changed by controlling the oil pressure supplied to the primary pulley 4a and the oil pressure supplied to the secondary pulley 4b, thereby changing the transmission ratio.

[0024] Oil pump 6 is a mechanical oil pump that is driven by a portion of the rotation of engine 10 and the power of engine 10. Oil discharged from oil pump 6 is supplied to oil pressure control circuit 5.

[0025] The hydraulic control circuit 5 includes: a regulating valve 5a that adjusts the pressure of the working oil supplied from the oil pump 6 and generates the necessary oil pressure; a primary solenoid valve 5b that adjusts the oil pressure supplied to the primary pulley 4a; a secondary solenoid valve 5c that adjusts the oil pressure supplied to the secondary pulley 4b; a lock-up solenoid valve 5d that adjusts the oil pressure supplied to the lock-up clutch 2a; a selection solenoid valve 5e that adjusts the oil pressure supplied to the forward clutch 3a and the reverse brake 3b; and a manual valve 5f that switches the supply path of the oil pressure supplied to the forward clutch 3a and the reverse brake 3b.

[0026] The hydraulic control circuit 5 supplies adjusted hydraulic pressure to various parts of the hydraulic torque converter 2, forward / reverse switching mechanism 3, and transmission mechanism 4 based on the control signal from the transmission controller 40.

[0027] The engine controller 30 is composed of a microcomputer equipped with a CPU, RAM, ROM, input / output interfaces, etc. The engine controller 30 performs various processes by reading and executing programs stored in the ROM through the CPU. The engine controller 30 can also be composed of multiple microcomputers.

[0028] The engine controller 30 controls the engine speed and torque of the engine 10 based on signals from various sensors that detect the state of various parts of the vehicle 100.

[0029] The transmission controller 40 is a microcomputer equipped with a CPU, RAM, ROM, input / output interfaces, etc., and is communicatively connected to the engine controller 30. The transmission controller 40 reads and executes programs stored in the ROM through the CPU to perform various processes. The transmission controller 40 can also be composed of multiple microcomputers. Alternatively, the transmission controller 40 and the engine controller 30 can be combined into a single controller.

[0030] The transmission controller 40 controls the engagement status of the lock-up clutch 2a, the gear ratio of the transmission mechanism 4, the engagement status of the forward clutch 3a and the reverse brake 3b, etc., based on signals from various sensors that detect the status of various parts of the vehicle 100.

[0031] The transmission controller 40 receives the following signals: an accelerator pedal opening sensor 61 that detects the accelerator pedal opening APO; a brake hydraulic pressure sensor 62 that detects the brake hydraulic pressure BRP corresponding to the brake pedal operation; a circuit breaker 64 that detects the position of the shift device 63; a turbine speed sensor 65 that detects the rotational speed Nt (hereinafter referred to as turbine speed Nt) of the output shaft 2c of the torque converter 2; a primary speed sensor 66 that detects the rotational speed Np (hereinafter referred to as primary speed Np) of the input shaft 4d (primary pulley 4a) of the transmission mechanism 4; a secondary speed sensor 67 that detects the rotational speed Ns of the output shaft 4e (secondary pulley 4b) of the transmission mechanism 4; a primary hydraulic pressure sensor 68 that detects the primary hydraulic pressure Pp supplied to the primary pulley 4a; and a secondary hydraulic pressure sensor 69 that detects the secondary hydraulic pressure Ps supplied to the secondary pulley 4b.

[0032] However, as described above, the transmission controller 40 controls the gear ratio of the transmission mechanism 4. Here, in cases where the calculated actual gear ratio of the transmission mechanism 4 becomes an abnormal value due to a malfunction of the primary speed sensor 66 related to the gear ratio calculation, or in the event of a malfunction of the transmission controller 40, it is considered that an unintentional downshift by the driver might occur due to shifting to the target gear ratio. In such cases, the vehicle 100 decelerates due to the braking force of the engine 10 accompanying the downshift, which may cause discomfort to the driver.

[0033] In view of this situation, the transmission controller 40 of this embodiment detects downshifts caused by malfunctions of the primary speed sensor 66, and performs braking force control to mitigate the braking force of the engine 10 that accompanies the downshift.

[0034] The transmission controller 40 will now be described in detail.

[0035] Figure 2 This is a function block diagram of the transmission controller 40. Figure 2 Representing the functions of the transmission controller 40 as hypothetical units does not imply their physical existence. However, a microcomputer or device corresponding to each function may physically exist.

[0036] like Figure 2 As shown, the transmission controller 40 includes an input unit 40a, an input signal generation unit 40b, a target gear ratio calculation unit 40c, a target Pp calculation unit 40d, a target Ps calculation unit 40e, a target Ip calculation unit 40f, a target Is calculation unit 40g, a solenoid drive unit 40h, an input signal generation unit 40i, a downshift determination unit 40j, and a solenoid drive unit 40k.

[0037] Signals from the accelerator pedal opening sensor 61, the circuit breaker 64, the turbine speed sensor 65, the primary speed sensor 66, and the secondary speed sensor 67 are input to the input unit 40a.

[0038] The input signal generation unit 40b generates a signal indicating the accelerator pedal opening (APO) based on the signal input to the input unit 40a from the accelerator pedal opening sensor 61. Additionally, the input signal generation unit 40b generates a signal indicating the vehicle speed (VSP) based on the signal input to the input unit 40a from the secondary speed sensor 67.

[0039] The target gear ratio calculation unit 40c calculates the target gear ratio of the transmission mechanism 4 based on the accelerator pedal opening APO and the vehicle speed VSP generated by the input signal generation unit 40b. Alternatively, the throttle valve opening TVO input from the engine controller 30 can be used instead of the accelerator pedal opening APO.

[0040] The target Pp calculation unit 40d calculates the target primary pressure Pp to achieve the target gear ratio based on the target gear ratio calculated by the target gear ratio calculation unit 40c.

[0041] The target Ps calculation unit 40e calculates the target secondary pressure Ps to achieve the target gear ratio based on the target gear ratio calculated by the target gear ratio calculation unit 40c.

[0042] The target Ip calculation unit 40f calculates the target primary solenoid indicating current Ip, which is calculated by the target primary voltage Pp by the target Pp calculation unit 40d.

[0043] The target Is calculation unit 40g calculates the target secondary solenoid indicating current Is, which is calculated by the target secondary voltage Ps by the target Ps calculation unit 40e.

[0044] The solenoid drive unit 40h supplies an indication current to the primary solenoid valve 5b based on the target primary solenoid indication current Ip calculated by the target Ip calculation unit 40f. Additionally, the solenoid drive unit 40h supplies an indication current to the secondary solenoid valve 5c based on the target secondary solenoid indication current Is calculated by the target Is calculation unit 40g.

[0045] The input signal generation unit 40i generates a signal indicating the operating mode (SELMODE) of the automatic transmission 20 selected by the shift device 63, based on the signal input from the circuit breaker 64 to the input unit 40a. Additionally, the input signal generation unit 40i generates a signal indicating the turbine speed (Nt) based on the signal input from the turbine speed sensor 65 to the input unit 40a. Furthermore, the input signal generation unit 40i generates a signal indicating the primary speed (Np) based on the signal input from the primary speed sensor 66 to the input unit 40a. Finally, the input signal generation unit 40i generates a signal indicating the vehicle speed (VSP) based on the signal input from the secondary speed sensor 67 to the input unit 40a. Furthermore, the automatic transmission 20 of this embodiment has four operating modes: forward (D) mode, reverse (R) mode, neutral (N) mode, and park (P) mode.

[0046] The downshift determination unit 40j determines whether an unintentional downshift by the driver has occurred based on the operating mode SELMODE, turbine speed Nt, primary speed Np, vehicle speed VSP, etc. generated by the input signal generation unit 40i.

[0047] In addition, as a cause of unintentional downshifting by the driver, possible causes include malfunctions of the primary speed sensor 66, primary solenoid valve 5b, and transmission controller 40 (abnormal calculation of actual gear ratio, target gear ratio, target Pp, target Ps, target Ip, and target Is).

[0048] When the downshift determination unit 40j determines that an unintentional downshift by the driver has occurred, it outputs a downshift detection signal to the solenoid drive unit 40k.

[0049] When a downshift detection signal is input from the downshift determination unit 40j, the solenoid drive unit 40k adjusts the selection solenoid indicator current supplied to the selection solenoid valve 5e to reduce the oil pressure supplied to the forward clutch 3a.

[0050] The forward clutch 3a experiences a decrease in torque transmission capacity due to a drop in supplied oil pressure. As a result, the forward clutch 3a slips, reducing the braking force transmitted from the engine 10 to the drive wheels 50. Therefore, the reduced deceleration of the vehicle 100 helps to suppress discomfort to the driver.

[0051] Alternatively, the oil pressure supplied to the forward clutch 3a can be reduced until the forward clutch 3a is released. A situation that reduces the torque transmission capacity of the forward clutch 3a also includes having the forward clutch 3a in a released state, resulting in zero torque transmission capacity.

[0052] Next, refer to Figure 3 At the same time, the processing of braking force control performed by the transmission controller 40 will be explained. Figure 3 This is a flowchart illustrating the braking force control process performed by the transmission controller 40. The braking force control process is executed at regular intervals.

[0053] In step S11, the transmission controller 40 determines whether the downshift determination condition is met.

[0054] The downshift determination conditions are as follows, for example.

[0055] (a) The forward clutch 3a is engaged.

[0056] (b) Vehicle speed VSP is a specified speed (e.g., 40 km / h or above).

[0057] (c) The automatic transmission 20 operates in forward (D) mode.

[0058] (d) Lock-up clutch 2a is engaged.

[0059] If all conditions (a) to (d) are met, the transmission controller 40 determines that the downshift determination condition is met.

[0060] When the downshift determination condition is determined to be met, the transmission controller 40 proceeds to step S12. Conversely, when the downshift determination condition is determined to be unmet, the transmission controller 40 terminates the process.

[0061] In step S12, the transmission controller 40 determines whether to downshift based on the rate of change of the turbine speed Nt. The rate of change of the turbine speed Nt is the amount of change of the turbine speed Nt per unit time [rpm / s]. Specifically, the transmission controller 40 determines whether the rate of change of the turbine speed Nt is above a predetermined rate of change.

[0062] Based on numerous parameters and experimental results of vehicle 100, the specified rate of change is set to a value at which the braking force of engine 10 may cause discomfort to the driver when the rate of change of turbine speed Nt exceeds the specified rate of change. In typical vehicles, the specified rate of change is, for example, 5000 [rpm / s] to 6000 [rpm / s].

[0063] The downshift determination in step S12 is performed with the lock-up clutch 2a engaged. Therefore, in other words, in step S12, it is determined whether the rate of change of engine speed 10 is above a predetermined rate of change.

[0064] When the transmission controller 40 determines that the rate of change of the turbine speed Nt is above a predetermined rate of change, the process proceeds to step S13. Conversely, when the transmission controller 40 determines that the rate of change of the turbine speed Nt is not above a predetermined rate of change, the process proceeds to step S15.

[0065] In step S13, the transmission controller 40 determines whether the state in which the rate of change of the turbine speed Nt is above a specified rate of change has lasted for more than a specified first time.

[0066] When the transmission controller 40 determines that the rate of change of the turbine speed Nt is above a predetermined rate of change for a predetermined first time or longer, it proceeds to step S14. Conversely, when the transmission controller 40 determines that the rate of change of the turbine speed Nt is above the predetermined rate of change, it terminates the process.

[0067] In step S14, the transmission controller 40 reduces the oil pressure supplied to the forward clutch 3a, thereby reducing the torque transmission capacity of the forward clutch 3a.

[0068] The reason why the torque transmission capacity of the forward clutch 3a is reduced when the rate of change of the turbine speed Nt is above the specified rate of change for a specified first time is because even if the rate of change of the turbine speed Nt is above the specified rate of change, as long as it is short, the possibility of causing discomfort to the driver is low. From this point of view, the specified first time is, for example, tens [ms] to hundreds [ms].

[0069] In step S15, the transmission controller 40 determines whether to downshift based on the turbine speed Nt. Specifically, the transmission controller 40 determines whether the turbine speed Nt is above a specified speed.

[0070] Even if a downshift is not detected in the downshift determination in step S12, the braking force generated by the engine 10 when the engine speed is in the high-speed range may still cause discomfort to the driver. Therefore, the transmission controller 40 determines that a downshift has occurred even when the turbine speed Nt is above a specified speed.

[0071] Based on numerous parameters and experimental results of vehicle 100, a specified speed is set at a value that, when the turbine speed Nt exceeds the specified speed, the braking force of engine 10 may cause discomfort to the driver. In a typical vehicle, the specified speed is, for example, 6000 to 7000 rpm. The specified speed can be the same as the ultra-high speed setting of engine 10.

[0072] The downshift determination in step S15 is performed while the lock-up clutch 2a is engaged. Therefore, in other words, in step S15, it is determined whether the engine speed of 10 is above a specified speed.

[0073] When the transmission controller 40 determines that the turbine speed Nt is above a specified speed, the process proceeds to step S16. Conversely, when the transmission controller 40 determines that the turbine speed Nt is not above a specified speed, the process proceeds to step S17.

[0074] In step S16, the transmission controller 40 determines whether the state in which the turbine speed Nt is above a specified speed has lasted for more than a specified second time.

[0075] When the transmission controller 40 determines that the state of the turbine speed Nt being above a specified speed has lasted for a specified second time or more, it proceeds to step S14. Conversely, when the transmission controller 40 determines that the state of the turbine speed Nt being above a specified speed has not lasted for a specified second time or more, it terminates the process.

[0076] The reason for performing step S16 is the same as the reason for performing step S13. Therefore, the second time is specified as, for example, tens to hundreds of ms. The second time can be the same as the first time. However, when the specified speed is the same as the ultra-high speed operation setting value of engine 10, from the viewpoint of protecting engine 10, it is preferable to set a shorter time.

[0077] In step S17, the transmission controller 40 determines whether to downshift based on the rate of change of the primary speed Np. Specifically, the transmission controller 40 determines whether the rate of change of the primary speed Np is above the aforementioned predetermined rate of change.

[0078] Even if the primary speed sensor 66 is functioning normally, for example, in the case of a malfunction in the transmission controller 40 preventing normal operation of various calculations, or in the case of a malfunction in the primary solenoid valve 5b, the driver's unintentional downshifting due to the shift to the target gear ratio is taken into account. Here, if the turbine speed sensor 65 also malfunctions, downshifting cannot be correctly detected in the downshift determination in step S12 and step S15.

[0079] Therefore, in addition to performing downshift determination in step S12 and step S15, the transmission controller 40 in this embodiment also performs downshift determination based on the rate of change of the primary speed Np.

[0080] The downshift determination in step S17 is performed with the lock-up clutch 2a and the forward clutch 3a engaged. Therefore, in other words, in step S17, it is determined whether the rate of change of engine speed 10 is above a predetermined rate of change.

[0081] When the transmission controller 40 determines that the rate of change of the primary speed Np is above a predetermined rate of change, the process proceeds to step S18. Conversely, when the transmission controller 40 determines that the rate of change of the primary speed Np is not above the predetermined rate of change, the process ends.

[0082] In step S18, the transmission controller 40 determines whether the state in which the rate of change of the primary speed Np is above a specified rate of change has lasted for more than a specified third time.

[0083] If the transmission controller 40 determines that the rate of change of the primary speed Np is above a predetermined rate of change for a predetermined third time or more, it proceeds to step S14. Conversely, if the transmission controller 40 determines that the rate of change of the primary speed Np is above the predetermined rate of change, it terminates the process.

[0084] The reason for performing step S18 is the same as the reason for performing step S12. Therefore, the third time is specified as, for example, tens [ms] to hundreds [ms]. The third time can be the same as the first time.

[0085] The main functions and effects of the automatic transmission 20 configured as described above are summarized and explained.

[0086] (1)(5)(7)(8) The automatic transmission 20 includes: a transmission mechanism 4 that changes the rotation of the engine 10 and transmits it to the drive wheel 50; and a forward clutch 3a that controls the torque transmission from the engine 10 to the drive wheel 50, and reduces the torque transmission capacity of the forward clutch 3a when the speed of change of the engine 10 is above a predetermined speed of change.

[0087] Therefore, when the rate of change of engine speed 10 exceeds a predetermined rate of change, the torque transmission capacity of the forward clutch 3a decreases. Thus, even if unintentional downshifting by the driver occurs due to a malfunction of the primary speed sensor 66, the braking force transmitted from the engine 10 to the drive wheels 50 can be reduced, decreasing the deceleration of the vehicle 100 and suppressing discomfort to the driver. More specifically, downshifting is detected based on the rate of change of engine speed 10. Therefore, unintentional downshifting by the driver caused by a malfunction of the primary speed sensor 66 can be detected. Furthermore, when unintentional downshifting by the driver due to a malfunction of the primary speed sensor 66 is detected, the torque transmission capacity of the forward clutch 3a located between the engine 10 and the drive wheels 50 decreases, thus reducing the braking force transmitted from the engine 10 to the drive wheels 50. Therefore, the deceleration of the vehicle 100 decreases, suppressing discomfort to the driver.

[0088] (2) The automatic transmission 20 also includes: a hydraulic torque converter 2, which is disposed between the engine 10 and the transmission mechanism 4, with the input shaft 2b connected to the output shaft 10a of the engine 10; a lock-up clutch 2a, which is built into the hydraulic torque converter 2. When engaged, the input shaft 2b of the hydraulic torque converter 2 is directly connected to the output shaft 2c. When the lock-up clutch 2a is engaged, when the speed of change of the output shaft 2c Nt (turbine speed Nt) is above a specified speed of change, the torque transmission capacity of the forward clutch 3a is reduced.

[0089] As a result, the rotational speed Nt of the output shaft 2c of the torque converter 2 increases, causing a decrease in the torque transmission capacity of the forward clutch 3a. Therefore, even if the driver intentionally downshifts, the braking force transmitted from the engine 10 to the drive wheels 50 can be reduced, thereby reducing the deceleration of the vehicle 100 and suppressing discomfort to the driver. Furthermore, since downshifting can be detected by the increase in the rotational speed Nt of the output shaft 2c of the torque converter 2, unintentional downshifting by the driver can be detected even if the primary speed sensor 66 or the transmission controller 40 malfunctions, or even if there is no information on the engine speed of the 10.

[0090] (3) When the speed of change of the input shaft 4d of the transmission mechanism 4, Np (primary speed Np), becomes above the specified speed of change, the automatic transmission 20 reduces the torque transmission capacity of the forward clutch 3a.

[0091] As a result, the rotational speed Np of the input shaft 4d of the transmission mechanism 4 increases, causing a decrease in the torque transmission capacity of the forward clutch 3a. Therefore, even if the driver intentionally downshifts, the braking force transmitted from the engine 10 to the drive wheels 50 can be reduced, decreasing the deceleration of the vehicle 100 and thus suppressing discomfort to the driver. Furthermore, since downshifting can be detected by the increase in the rotational speed Np of the input shaft 4d of the transmission mechanism 4, even if the turbo speed sensor 65 malfunctions, unintentional downshifting by the driver can be detected.

[0092] (4) The transmission mechanism 4 of the automatic transmission 20 is a continuously variable transmission mechanism having a primary pulley 4a on the engine 10 side, a secondary pulley 4b on the drive wheel 50 side, and a belt 4c wound between the primary pulley 4a and the secondary pulley 4b.

[0093] In a continuously variable transmission (CVT), even if a driver unintentionally downshifts due to a malfunction, the braking force transmitted from the engine 10 to the drive wheels 50 is reduced, thus reducing the deceleration of the vehicle 100 and suppressing discomfort to the driver.

[0094] (6) When the torque transmission capacity of the forward clutch 3a is reduced, the automatic transmission 20 can also reduce the torque transmission capacity until the forward clutch 3a is released.

[0095] This allows the engine 10 to be separated from the drive wheels 50, thereby further suppressing the deceleration of the vehicle 100 caused by unintentional downshifting by the driver.

[0096] The embodiments of the present invention have been described above, but the above embodiments are only a part of the application examples of the present invention, and the technical scope of the present invention is not limited to the specific structure of the above embodiments.

[0097] For example, in the above embodiment, the case where the clutch controlling the torque transmission from the drive source to the drive wheel is described as a forward clutch 3a. However, the clutch controlling the torque transmission from the drive source to the drive wheel may also be other clutches provided in the power transmission path from the drive source to the drive wheel.

[0098] Furthermore, in the above embodiment, the case where the transmission mechanism is transmission mechanism 4 has been described. However, the transmission mechanism can be other continuously variable transmission mechanisms or stepped transmission mechanisms.

[0099] The various programs executed by the transmission controller 40 may be, for example, programs stored on a non-transitory recording medium such as a CD-ROM.

[0100] Symbol Explanation

[0101] 10. Engine (Drive Source)

[0102] 10a output shaft

[0103] 20 automatic transmission

[0104] 40. Transmission Controller (Computer)

[0105] 50 drive wheels

[0106] 2. Hydraulic torque converter

[0107] 2a Lock-up Clutch

[0108] 2b Input Shaft (Input Element)

[0109] 2c output shaft (output element)

[0110] 3a Forward Clutch (Clutch)

[0111] 4. Transmission Mechanism (Transmission Mechanism, Continuously Variable Transmission Mechanism)

[0112] 4a Primary Pulley

[0113] 4b secondary pulley

[0114] 4c belt (ring-shaped component)

[0115] 4D input axis

Claims

1. An automatic transmission, wherein, have: A speed-changing mechanism that changes the speed of the rotation of the drive source and transmits it to the drive wheels; A clutch that controls the transmission of torque from the drive source to the drive wheel. When the selected operating mode is forward mode, when the speed of change of the rotational speed of the drive source increases to a certain level, the torque transmission capacity of the clutch decreases, thereby reducing the braking force transmitted from the drive source to the drive wheel.

2. The automatic transmission as claimed in claim 1, wherein, It also has: A hydraulic torque converter is disposed between the drive source and the transmission mechanism, and its input element is connected to the output shaft of the drive source. A lock-up clutch, which is built into the torque converter, when engaged, directly connects the input and output elements of the torque converter. When the lock-up clutch is engaged, if the speed of change of the output element's rotational speed exceeds the specified speed of change, the torque transmission capacity of the clutch decreases.

3. The automatic transmission as described in claim 1 or 2, wherein, When the speed of change of the input shaft of the transmission mechanism exceeds the specified speed of change, the torque transmission capacity of the clutch decreases.

4. The automatic transmission as claimed in claim 1 or 2, wherein, The transmission mechanism is a continuously variable transmission mechanism comprising: a primary pulley disposed on the drive source side, a secondary pulley disposed on the drive wheel side, and an annular component wound between the primary pulley and the secondary pulley.

5. The automatic transmission as claimed in claim 1 or 2, wherein, The clutch mentioned is a forward clutch.

6. The automatic transmission as claimed in claim 1 or 2, wherein, When the torque transmission capacity of the clutch is reduced, the torque transmission capacity is reduced until the clutch is released.

7. A control method for an automatic transmission, the automatic transmission comprising: a transmission mechanism for changing the speed of rotation of a drive source and transmitting it to drive wheels; and a clutch for controlling the torque transmission from the drive source to the drive wheels, wherein... When the selected operating mode is forward mode, when the speed of change of the rotational speed of the drive source increases to a certain level, the torque transmission capacity of the clutch decreases, thereby reducing the braking force transmitted from the drive source to the drive wheel.

8. A storage medium storing a program, the program being a computer-executable program of an automatic transmission, the automatic transmission comprising: a transmission mechanism for changing the speed of rotation of a drive source and transmitting it to drive wheels; and a clutch for controlling the transmission of torque from the drive source to the drive wheels, wherein... The program causes the computer to perform the following steps: when the selected operating mode is forward mode, when the rate of change of the rotational speed of the drive source becomes higher than a predetermined rate of change, the torque transmission capacity of the clutch is reduced, thereby reducing the braking force transmitted from the drive source to the drive wheel.

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