Continuously variable transmission, control method and program for continuously variable transmission

Abstract

The present invention can suppress slippage of an annular component and achieve improved fuel efficiency. A continuously variable transmission comprises: a first pulley and a second pulley, each having a fixed pulley and a movable pulley; an annular component wound around the first pulley and the second pulley, wherein the thrust of the movable pulley is controlled by oil pressure to continuously change the speed ratio, wherein the thrust of the movable pulley is reduced as the rotation speed of the first pulley decreases, and when the rotation speed of the first pulley is lower than a predetermined speed, the thrust of the movable pulley is not reduced when the speed ratio is lower than the predetermined speed ratio, compared to when the speed ratio is higher than the predetermined speed ratio.

Description

Technical Field

[0001] The present invention relates to a continuously variable transmission, a control method for the continuously variable transmission, and a program. Background Art

[0002] Patent document 1 discloses a pulley thrust control method for a V-belt continuously variable transmission in which the speed ratio is continuously variable by controlling the movable pulley thrust of the two pulleys by means of oil pressure or the like with respect to the V-shaped groove spacing of the input pulley and the output pulley, wherein the movable pulley thrust determined based on the engine torque and the speed ratio is corrected in such a manner that it increases as the rotational speed of the input pulley increases.

[0003] Thus, even under operating conditions where the input pulley rotation speed is relatively high, belt slip can be effectively suppressed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 10-103437

[0007] Problems to be solved by the invention

[0008] However, the above-mentioned technology focuses on suppressing the slip of the belt (endless member) during high-speed rotation, and does not consider the influence of the slip of the belt caused by the difference in the speed ratio. Summary of the Invention

[0009] The present invention has been made in view of such technical problems, and an object of the present invention is to suppress the slippage of the annular member and to improve fuel efficiency.

[0010] According to one embodiment of the present invention, a continuously variable transmission is provided, which comprises: a first pulley and a second pulley respectively having a fixed pulley and a movable pulley; an annular component wound on the first pulley and the second pulley, which continuously changes the speed ratio by controlling the thrust of the movable pulley by oil pressure, wherein the thrust of the movable pulley decreases as the rotation speed of the first pulley decreases, and when the rotation speed of the first pulley is lower than a specified rotation speed, the thrust of the movable pulley does not decrease when the speed ratio is closer to the low gear side than the specified speed ratio, compared with when the speed ratio is closer to the high gear side than the specified speed ratio.

[0011] Effects of the Invention

[0012] In the above-described method, the thrust of the movable pulley is reduced as the rotational speed of the first pulley decreases. Therefore, the frictional resistance between the annular member and the first and second pulleys can be reduced, thereby suppressing the slip of the belt during high rotation and improving fuel efficiency. In addition, when the rotational speed of the first pulley is lower than the specified rotational speed, the thrust of the movable pulley does not decrease when the speed ratio is closer to the lower gear side than the specified speed ratio, compared to when the speed ratio is closer to the higher gear side than the specified speed ratio. Therefore, in a state where the speed ratio is closer to the lower gear side than the specified speed ratio, where the input torque to the first pulley increases more often, even if the rotational speed of the first pulley decreases, the thrust of the movable pulley does not decrease more than necessary, thereby suppressing the slip of the annular member. Therefore, according to these methods, the slip of the annular member caused by the difference in the speed ratio can be suppressed, and an improvement in fuel efficiency can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It 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 schematic diagram of the transmission controller.

[0015] Figure 3 is a diagram showing a correction coefficient map.

[0016] Figure 4 This is a diagram for explaining correction of the basic thrust when the primary rotation speed is lower than a predetermined rotation speed.

[0017] Figure 5 This is a diagram for explaining correction of the basic thrust when the primary rotation speed exceeds a predetermined rotation speed.

[0018] Figure 6 This is a diagram showing a process executed by the transmission controller in the form of a flowchart. DETAILED DESCRIPTION

[0019] The following describes an embodiment of the present invention with reference to the accompanying drawings. Hereinafter, a large speed ratio Rv (a large reduction ratio) is referred to as a low gear (Low), and a small speed ratio Rv (a small reduction ratio) (a speed ratio (reduction ratio) less than 1 is referred to as an increase in speed) is referred to as a high gear (High). Furthermore, changing the speed ratio Rv toward a low gear (Low) is referred to as a downshift, and changing it toward a high gear (High) is referred to as an upshift.

[0020] Figure 1 1 is a schematic structural diagram of a vehicle 100 equipped with an automatic transmission 20 as a continuously variable transmission according to an embodiment of the present invention. Figure 1 As shown, vehicle 100 includes an engine 10 as a driving source, an automatic transmission 20 , and an engine controller 30 .

[0021] The automatic transmission 20 includes a torque converter 2 , a forward / reverse switching mechanism 3 , a speed change mechanism 4 , a hydraulic control circuit 5 , an oil pump 6 , and a transmission controller 40 .

[0022] In vehicle 100 , rotation generated by engine 10 is transmitted to drive wheels 50 via torque converter 2 , forward / reverse switching mechanism 3 , speed change mechanism 4 , gear set 7 , and differential gear device 8 .

[0023] The torque converter 2 is equipped with a lockup clutch 2a. When the lockup clutch 2a is engaged, the input shaft 2b and output shaft 2c of the torque converter 2 are directly connected, and the input shaft 2b and output shaft 2c rotate at the same speed. Therefore, when the lockup clutch 2a is engaged, the rotation of the output shaft 10a of the engine 10 is directly transmitted to the forward / reverse switching mechanism 3 via the output shaft 2c of the torque converter 2.

[0024] The forward-reverse switching mechanism 3 is primarily composed of a double-pinion planetary gear set, whose sun gear is coupled to the engine 10 via the torque converter 2, and whose planetary carrier is coupled to the primary pulley 41, serving as the first pulley of the speed change mechanism 4. The forward-reverse switching mechanism 3 further includes a forward clutch 3a that directly connects the sun gear and the planetary carrier of the double-pinion planetary gear set, and a reverse brake 3b that fixes the ring gear. When the forward clutch 3a is engaged, the input rotation from the engine 10 via the torque converter 2 is directly transmitted unchanged to the primary pulley 41. When the reverse brake 3b is engaged, the input rotation from the engine 10 via the torque converter 2 is reversed, decelerated, and then transmitted to the primary pulley 41.

[0025] The speed change mechanism 4 is a continuously variable speed change mechanism that changes the speed of the rotation of the engine 10 transmitted to the primary pulley 41 and transmits the rotation from the secondary pulley 42 serving as the second pulley to the drive wheel 50 .

[0026] The speed change mechanism 4 includes a primary pulley 41 and a secondary pulley 42 arranged in a V-groove arrangement, and a belt 43 as an endless member wound around the V-grooves of the pulleys 41 and 42 .

[0027] In order to change the speed ratio Rv between the primary pulley 41 and the secondary pulley 42 during power transmission, the speed change mechanism 4 uses one of the conical plates forming the V-grooves of the primary pulley 41 and the secondary pulley 42 as a fixed pulley 41a, 42a, and the other as a movable pulley 41b, 42b that can be displaced in the axial direction.

[0028] The movable pulleys 41b and 42b are urged toward the fixed pulleys 41a and 42a by supplying the primary pulley pressure Pp and the secondary pulley pressure Ps to the primary pulley chamber 41c and the secondary pulley chamber 42c, thereby causing the belt 43 to frictionally engage with the conical plate, thereby transmitting power between the primary pulley 41 and the secondary pulley 42.

[0029] During the speed change, the width of the V-groove of the two pulleys 41 and 42 is changed by the pressure difference between the primary pulley pressure Pp and the secondary pulley pressure Ps generated corresponding to the target speed ratio TRv, so that the winding arc radius of the belt 43 relative to the pulleys 41 and 42 is continuously changed, thereby achieving the target speed ratio TRv.

[0030] The oil pump 6 is a mechanical oil pump that is input with the rotation of the engine 10 and is driven by a part of the power of the engine 10. The oil discharged from the oil pump 6 is supplied to the hydraulic control circuit 5.

[0031] The oil pressure control circuit 5 includes: a regulating valve 5a for regulating the pressure of the working oil supplied from the oil pump 6 to generate the necessary oil pressure, a primary solenoid valve 5b for adjusting the oil pressure supplied to the primary pulley chamber 41c of the primary pulley 41, a secondary solenoid valve 5c for adjusting the oil pressure supplied to the secondary pulley chamber 42c of the secondary pulley 42, a locking solenoid valve 5d for adjusting the oil pressure supplied to the locking clutch 2a, a selection solenoid valve 5e for adjusting the oil pressure supplied to the forward clutch 3a and the oil pressure supplied to the reverse brake 3b, a manual valve 5f for switching the supply path of the oil pressure to the forward clutch 3a and the reverse brake 3b, etc.

[0032] The hydraulic control circuit 5 supplies regulated hydraulic pressure to the torque converter 2 , the forward / reverse switching mechanism 3 , and the speed change mechanism 4 based on a control signal from the transmission controller 40 .

[0033] The engine controller 30 is composed of a microcomputer including a CPU, RAM, ROM, an input / output interface, etc. The engine controller 30 performs various processes by the CPU reading and executing programs stored in the ROM. The engine controller 30 may also be composed of a plurality of microcomputers.

[0034] The engine controller 30 controls the rotation speed and torque Te (hereinafter referred to as engine torque Te) of the engine 10 based on signals from various sensors that detect the states of various parts of the vehicle 100 .

[0035] The transmission controller 40 is comprised of a microcomputer equipped with a CPU, RAM, ROM, and input / output interfaces, and is communicatively connected to the engine controller 30. The CPU reads and executes programs stored in the ROM to perform various processes. The transmission controller 40 may also be comprised of multiple microcomputers. Alternatively, the transmission controller 40 and the engine controller 30 may be combined into a single controller.

[0036] The transmission controller 40 controls the engagement state of the lockup clutch 2a, the speed ratio Rv of the speed change mechanism 4, the engagement states of the forward clutch 3a and the reverse brake 3b, etc. based on signals from various sensors that detect the states of various parts of the vehicle 100.

[0037] Inputs to the transmission controller 40 include: a signal from an accelerator opening sensor 61 that detects the accelerator opening APO, a signal from a brake hydraulic pressure sensor 62 that detects the brake hydraulic pressure BRP corresponding to the operation amount of the brake pedal, a signal from a circuit breaker 64 that detects the position of the shift device 63, a signal from a turbine speed sensor 65 that detects the rotational speed Nt of the output shaft 2c of the torque converter 2, a signal from a primary speed sensor 66 that detects the rotational speed Np of the primary pulley 41 (hereinafter referred to as the primary speed Np), a signal from a secondary speed sensor 67 that detects the rotational speed Ns of the secondary pulley 42 (hereinafter referred to as the secondary speed Ns), a signal from a primary oil pressure sensor 68 that detects the primary pulley pressure Pp, a signal from a secondary oil pressure sensor 69 that detects the secondary pulley pressure Ps, and the like.

[0038] However, as described above, the speed change mechanism 4 applies force to the movable pulleys 41b, 42b toward the fixed pulleys 41a, 42a through the primary pulley pressure Pp and the secondary pulley pressure Ps (the force that applies the movable pulleys 41b, 42b toward the fixed pulleys 41a, 42a based on the primary pulley pressure Pp and the secondary pulley pressure Ps is called "thrust"), so that the belt 43 frictionally engages with the conical plate, and power is transmitted between the primary pulley 41 and the secondary pulley 42.

[0039] Therefore, in the transmission mechanism 4, it is important to control the thrust F of the movable pulleys 41b and 42b (hereinafter referred to as the pulley thrust F) to prevent the belt 43 from slipping. On the other hand, if the pulley thrust F is increased beyond necessity, the frictional resistance between the belt 43 and the pulleys 41 and 42 increases, which may affect the fuel efficiency of the vehicle 100.

[0040] Therefore, the transmission controller 40 of the present embodiment controls the primary pulley pressure Pp and the secondary pulley pressure Ps that generate the pulley thrust F so as to suppress slippage of the belt 43 and improve fuel efficiency.

[0041] Hereinafter, the transmission controller 40 will be described in detail.

[0042] Figure 2 : is a schematic structural diagram of the transmission controller 40. Figure 2 A portion of the functions of the transmission controller 40 is shown in a block diagram, and each block does not represent a physical structure.

[0043] like Figure 2 As shown, the transmission controller 40 includes an input unit 40a, an input signal generating unit 40b, a target speed ratio calculating unit 40c, a basic thrust calculating unit 40d, a correction coefficient calculating unit 40e, a target oil pressure calculating unit 40f, a target current calculating unit 40g, and a solenoid driving unit 40h.

[0044] The input unit 40 a receives inputs such as a signal from the engine controller 30 , a signal from the accelerator opening sensor 61 , a signal from the primary rotation speed sensor 66 , and a signal from the secondary rotation speed sensor 67 .

[0045] The input signal generating unit 40b generates a signal representing the engine torque Te based on the signal input from the engine controller 30 to the input unit 40a, generates a signal representing the accelerator opening APO based on the signal input from the accelerator opening sensor 61 to the input unit 40a, generates a signal representing the primary speed Np based on the signal input from the primary speed sensor 66 to the input unit 40a, and generates a signal representing the secondary speed Ns and a signal representing the vehicle speed VSP based on the signal input from the secondary speed sensor 67 to the input unit 40a.

[0046] The target speed ratio calculation unit 40c calculates the target speed ratio TRv of the speed change mechanism 4 based on the accelerator opening APO and the vehicle speed VSP, referring to a speed change map that is preset based on various factors of the vehicle 100, experiments, etc. Alternatively, the throttle valve opening TVO input from the engine controller 30 may be used instead of the accelerator opening APO.

[0047] The base thrust calculation unit 40d calculates the base thrust Fb, which serves as the basis for the target pulley thrust TF, based on the engine torque Te and the speed ratio Rv, referring to a base thrust map preset based on various factors of the vehicle 100, experiments, etc. The speed ratio Rv is obtained based on the primary speed Np and the secondary speed Ns.

[0048] The basic thrust map (basic thrust diagram) uses engine torque Te and gear ratio Rv as parameters and sets the pulley thrust F required to prevent belt 43 slippage when the primary speed Np (=engine speed) is at a predetermined speed Nps as the basic thrust Fb. The predetermined speed Nps can be, for example, set to approximately 2500 rpm to 3500 rpm, the most frequently used speed of the engine 10, or to a speed in the middle of the commonly used speed range.

[0049] The correction coefficient calculation unit 40e calculates a correction coefficient for correcting the base thrust Fb based on the primary rotation speed Np and the speed ratio Rv, referring to a correction coefficient map preset based on various factors of the vehicle 100, experiments, etc. The correction coefficient map will be described in detail later.

[0050] The target hydraulic pressure calculation unit 40f calculates the target pulley thrust TF by multiplying the base thrust Fb calculated by the base thrust calculation unit 40d by the correction coefficient calculated by the correction coefficient calculation unit 40e. The target hydraulic pressure calculation unit 40f then calculates the target primary pulley pressure TPp and target secondary pulley pressure TPs for achieving the target pulley thrust TF and the target speed ratio TRv.

[0051] The target current calculation unit 40g calculates the primary solenoid indicated current Ip and the secondary solenoid indicated current Is for realizing the target primary pulley pressure TPp and the target secondary pulley pressure TPs determined by the target oil pressure calculation unit 40f.

[0052] The solenoid driving unit 40h supplies the indicated current to the primary electromagnetic valve 5b and the secondary electromagnetic valve 5c based on the primary solenoid indicated current Ip and the secondary solenoid indicated current Is obtained by the target current calculation unit 40g.

[0053] Next, refer to Figures 3 to 5 Correction of the basic thrust Fb will be described. Figure 3 is a diagram showing a correction coefficient map. Figure 4 This is a diagram for explaining correction of the basic thrust Fb when the primary rotation speed Np is lower than the predetermined rotation speed Nps. Figure 5 This is a diagram for explaining correction of the basic thrust Fb when the primary rotation speed Np is higher than the predetermined rotation speed Nps.

[0054] like Figure 3 As shown, the correction coefficient mapping has: area A where the primary speed Np is lower than the specified speed Nps and the speed ratio Rv is closer to the high gear side than the specified speed ratio Rvs; area B where the primary speed Np is lower than the specified speed Nps and the speed ratio Rv is closer to the low gear side than the specified speed ratio Rvs; and area C where the primary speed Np is higher than the specified speed Nps.

[0055] As described above, the basic thrust map is a map of the pulley thrust F when the primary rotation speed Np is set to the predetermined rotation speed Nps. Therefore, when the primary rotation speed Np is the predetermined rotation speed Nps, the basic thrust Fb does not need to be corrected, and thus the correction coefficient is "1".

[0056] Therefore, when the primary rotation speed Np is the predetermined rotation speed Nps, the basic thrust Fb is multiplied by "1", and the basic thrust Fb becomes the target pulley thrust TF as it is.

[0057] In region A, with the correction coefficient "1" as a reference, as indicated by the arrow, the lower the primary rotation speed Np and the higher the speed ratio Rv, the smaller the correction coefficient. That is, in region A, the correction coefficient is smaller than "1."

[0058] Therefore, when the primary speed Np is lower than the specified speed Nps and the speed ratio Rv is closer to the high gear side than the specified speed ratio Rvs, the lower the primary speed Np and the closer the speed ratio Rv is to the high gear side, the smaller the correction coefficient is multiplied by the basic thrust Fb, and the smaller the target pulley thrust TF is.

[0059] For example, in Figure 4 The basic thrust Fb when the primary rotation speed Np is lower than the predetermined rotation speed Nps and the speed ratio Rv is the speed ratio RvH higher than the predetermined speed ratio Rvs is the basic thrust Fb1.

[0060] Here, because the primary rotational speed Np is lower than the predetermined rotational speed Nps and the speed ratio Rv is higher than the predetermined speed ratio Rvs, the base thrust Fb1 is corrected using the correction coefficient in area A of the correction coefficient map. As a result, as indicated by the arrow, a target pulley thrust TF1 is obtained that is smaller than the base thrust Fb1.

[0061] The lower the primary rotation speed Np, the smaller the centrifugal force applied to the belt 43, and thus the less likely the belt 43 will slip. In addition, the higher the speed ratio Rv is, the less likely the input torque to the primary pulley 41 will increase.

[0062] Therefore, in region A, even when the pulley thrust F is reduced compared to when the primary rotational speed Np is the predetermined rotational speed Nps, slippage of the belt 43 can be suppressed. Furthermore, since the pulley thrust F is reduced, the frictional resistance between the belt 43 and the pulleys 41 and 42 is also reduced. Consequently, the fuel efficiency of the vehicle 100 can be improved.

[0063] In region B, the correction coefficient is set to “1.” That is, even if the primary rotation speed Np is lower than the predetermined rotation speed Nps, the target pulley thrust TF does not decrease compared to when the speed ratio Rv is higher than the predetermined speed ratio Rvs.

[0064] Therefore, when the primary rotation speed Np is lower than the predetermined rotation speed Nps and the speed ratio Rv is lower than the predetermined speed ratio Rvs, the basic thrust Fb is multiplied by 1 and becomes the target pulley thrust TF as it is.

[0065] For example, in Figure 4 The basic thrust Fb when the primary rotation speed Np is lower than the predetermined rotation speed Nps and the speed ratio Rv is the speed ratio RvL which is lower than the predetermined speed ratio Rvs is the basic thrust Fb2.

[0066] Here, because the primary rotational speed Np is lower than the predetermined rotational speed Nps and the speed ratio Rv is lower than the predetermined speed ratio Rvs, the base thrust Fb2 is corrected using the correction coefficient "1" in area B of the correction coefficient map. As a result, a target pulley thrust TF2 having the same value as the base thrust Fb2 is obtained.

[0067] In other words, when the primary rotation speed Np is lower than the predetermined rotation speed Nps and the speed ratio Rv is lower than the predetermined speed ratio Rvs, the pulley thrust F does not vary depending on the primary rotation speed Np.

[0068] The lower the speed ratio Rv is, the greater the input torque to the primary pulley 41 is. Therefore, in region B, even if the primary rotational speed Np is lower than the predetermined rotational speed Nps, the pulley thrust F is not reduced, thereby suppressing slippage of the belt 43, compared to a case where the speed ratio Rv is higher than the predetermined speed ratio Rvs.

[0069] Specifically, the predetermined speed ratio Rvs is a threshold value such that, when the speed ratio Rv is lower than the predetermined speed ratio Rvs, the input torque to the primary pulley 41 is likely to increase, and it is preferable to prioritize suppressing slip of the belt 43. The predetermined speed ratio Rvs is set in advance based on various factors of the vehicle 100, experiments, and the like.

[0070] As described above, the lower the primary rotation speed Np, the smaller the centrifugal force applied to the belt 43. Therefore, the correction coefficient in region B can be set within a range that allows the pulley thrust F to be reduced in response to the reduction in centrifugal force. In this case, the correction coefficient in region B is a value between the "maximum value of the correction coefficient in region A" and "1."

[0071] In region C, with the correction coefficient "1" as a reference, as indicated by the arrow, the higher the primary rotation speed Np and the lower the speed ratio Rv, the larger the correction coefficient. That is, in region C, the correction coefficient is greater than "1."

[0072] Therefore, when the primary rotation speed Np is higher than the predetermined rotation speed Nps, the higher the primary rotation speed Np is and the lower the speed ratio Rv is, the larger the correction coefficient is multiplied by the basic thrust Fb, and the larger the target pulley thrust TF is.

[0073] For example, in Figure 5 The basic thrust Fb when the primary rotation speed Np is higher than the predetermined rotation speed Nps and the speed ratio Rv is the speed ratio RvH higher than the predetermined speed ratio Rvs is the basic thrust Fb3.

[0074] Here, since the primary rotation speed Np is higher than the predetermined rotation speed Nps, the basic thrust Fb3 is corrected using the correction coefficient in the correction coefficient map in region C. As a result, as shown by the arrow, a target pulley thrust TF3 having a value greater than the basic thrust Fb3 is obtained.

[0075] In addition, for example, Figure 5 The basic thrust Fb when the primary rotation speed Np is higher than the predetermined rotation speed Nps and the speed ratio Rv is the speed ratio RvL which is lower than the predetermined speed ratio Rvs is the basic thrust Fb4.

[0076] Here, because the primary rotational speed Np is higher than the predetermined rotational speed Nps, the correction coefficient in area C of the correction coefficient map is used to correct the basic thrust Fb4. As a result, as indicated by the arrow, a target pulley thrust TF4 is calculated, which is greater than the basic thrust Fb4. Furthermore, in the case of the speed ratio RvL, the correction coefficient is larger than that in the case of the speed ratio RvH, so the correction ratio for the basic thrust Fb4 is greater than the correction ratio for the basic thrust Fb3.

[0077] The higher the primary rotation speed Np, the greater the centrifugal force applied to the belt 43, and thus the belt 43 is more likely to slip. In addition, the lower the speed ratio Rv is, the greater the input torque to the primary pulley 41 is in many cases.

[0078] In contrast, in region C, as the primary rotation speed Np increases and the speed ratio Rv moves toward the lower gear, the base thrust Fb is corrected to a larger value, and the target pulley thrust TF increases. As a result, the pulley thrust F increases, and slippage of the belt 43 can be suppressed.

[0079] In this manner, the transmission controller 40 obtains the basic thrust Fb based on the engine torque Te and the speed ratio Rv, and corrects the basic thrust Fb using the correction coefficient obtained based on the primary rotation speed Np and the speed ratio Rv to obtain the target pulley thrust TF.

[0080] Thus, when the engine torque Te and the speed ratio Rv are considered constant, the pulley thrust F decreases as the primary rotation speed Np decreases. Therefore, the fuel efficiency of the vehicle 100 can be improved.

[0081] However, when the speed ratio Rv is lower than the predetermined speed ratio Rvs, the transmission controller 40 does not reduce the pulley thrust F compared to when the speed ratio Rv is higher than the predetermined speed ratio Rvs, even if the primary rotational speed Np is lower than the predetermined rotational speed Nps. This suppresses slippage of the belt 43 when the speed ratio Rv is lower than the predetermined speed ratio Rvs.

[0082] Next, refer to Figure 6 The processing executed by the transmission controller 40 will be described. Figure 6 4 is a flowchart showing the processing executed by the transmission controller 40 .

[0083] In step S11 , the transmission controller 40 refers to a shift map preset based on various factors of the vehicle 100 , experiments, etc., and calculates a target speed ratio TRv of the speed change mechanism 4 based on the accelerator opening APO and the vehicle speed VSP.

[0084] In step S12 , the transmission controller 40 refers to a base thrust map preset based on various factors of the vehicle 100 , experiments, etc., and calculates a base thrust Fb serving as a basis for the target pulley thrust TF based on the engine torque Te and the speed ratio Rv.

[0085] In step S13 , the transmission controller 40 refers to a correction coefficient map preset based on various factors of the vehicle 100 , experiments, etc., and calculates a correction coefficient for correcting the basic thrust Fb based on the primary rotation speed Np and the speed ratio Rv.

[0086] In step S14, the transmission controller 40 multiplies the base thrust Fb by the correction coefficient to calculate the target pulley thrust TF, and then calculates the target primary pulley pressure TPp and target secondary pulley pressure TPs for achieving the target pulley thrust TF and the target speed ratio TRv.

[0087] In step S15 , the transmission controller 40 calculates the primary solenoid indicated current Ip and the secondary solenoid indicated current Is for achieving the target primary pulley pressure TPp and the target secondary pulley pressure TPs.

[0088] In step S16 , the transmission controller 40 supplies a command current to the primary solenoid valve 5 b and the secondary solenoid valve 5 c .

[0089] The main functions and effects of the automatic transmission 20 configured as described above will be summarized.

[0090] (1)(3)(4) The automatic transmission 20 comprises: a primary pulley 41 and a secondary pulley 42 each having a fixed pulley 41a, 42a and a movable pulley 41b, 42b; a belt 43 wound around the primary pulley 41 and the secondary pulley 42, and the speed ratio Rv is continuously changed by controlling the thrust F of the movable pulleys 41b, 42b by oil pressure, wherein the thrust F of the movable pulleys 41b, 42b is reduced as the rotation speed Np of the primary pulley 41 decreases, and when the rotation speed Np of the primary pulley 41 is lower than the prescribed rotation speed Nps, the thrust F of the movable pulleys 41b, 42b does not decrease when the speed ratio Rv is closer to the low gear side than the prescribed speed ratio Rvs, compared with when the speed ratio Rv is closer to the high gear side than the prescribed speed ratio Rvs.

[0091] As a result, the thrust F of the movable pulleys 41b and 42b decreases as the rotational speed Np of the primary pulley 41 decreases. This reduces the frictional resistance between the belt 43 and the primary and secondary pulleys 41 and 42, thereby improving fuel efficiency. Furthermore, when the rotational speed Np of the primary pulley 41 is lower than the specified rotational speed Nps, the thrust F of the movable pulleys 41b and 42b does not decrease when the speed ratio Rv is lowered compared to when the speed ratio Rv is higher than the specified speed ratio Rvs. Therefore, even when the rotational speed Np of the primary pulley 41 decreases, the thrust F of the movable pulleys 41b and 42b does not decrease more than necessary, thereby suppressing slippage of the belt 43. This suppresses slippage of the belt 43 while improving fuel efficiency.

[0092] (2) When the rotation speed Np of the primary pulley 41 is lower than the predetermined rotation speed Nps and the speed ratio Rv is lower than the predetermined speed ratio Rvs, the thrust F of the movable pulleys 41 b and 42 b does not vary depending on the rotation speed Np of the primary pulley 41 .

[0093] Thus, when the rotational speed Np of the primary pulley 41 is lower than the predetermined rotational speed Nps and the speed ratio Rv is lower than the predetermined speed ratio Rvs, the thrust F of the movable pulleys 41b and 42b does not change even if the primary rotational speed Np changes. Therefore, even if the rotational speed Np of the primary pulley 41 decreases, the thrust F of the movable pulleys 41b and 42b does not decrease, thereby suppressing slippage of the belt 43.

[0094] While the embodiments of the present invention have been described above, the above embodiments merely illustrate a part of application examples of the present invention, and the technical scope of the present invention is not limited to the specific configurations of the above embodiments.

[0095] For example, in the above-described embodiment, the primary rotational speed Np is used in setting and calculating various maps. However, the secondary rotational speed Ns may be used in setting and calculating various maps.

[0096] As various programs executed by the transmission controller 40 , programs stored in a non-transitory recording medium such as a CD-ROM can be used.

[0097] Explanation of symbols

[0098] 20: Automatic transmission (Continuously Variable Transmission)

[0099] 40: Transmission controller (computer)

[0100] 41: Primary pulley (first pulley)

[0101] 41a: Fixed pulley

[0102] 41b: Movable pulley

[0103] 42: Secondary pulley (second pulley)

[0104] 42a: Fixed pulley

[0105] 42b: Movable pulley

[0106] 43: Belt (ring part)

Claims

1. A continuously variable transmission comprising: a first pulley and a second pulley each having a fixed pulley and a movable pulley; an annular member wound around the first pulley and the second pulley, wherein the speed ratio is continuously changed by controlling the thrust of the movable pulley by hydraulic pressure, wherein: The thrust of the movable pulley is reduced as the rotation speed of the first pulley decreases, When the rotation speed of the first pulley is lower than a predetermined rotation speed, the thrust of the movable sheave is not reduced when the speed ratio is lowered than when the speed ratio is higher than the predetermined speed ratio.

2. The continuously variable transmission according to claim 1, wherein: When the rotation speed of the first pulley is lower than the predetermined rotation speed and the speed ratio is lower than the predetermined speed ratio, the thrust of the movable pulley is changed independent of the rotation speed of the first pulley.

3. A method for controlling a continuously variable transmission comprising: a first pulley and a second pulley each having a fixed pulley and a movable pulley; an annular member wound around the first pulley and the second pulley, wherein the speed ratio is continuously changed by controlling the thrust of the movable pulley by hydraulic pressure; The thrust of the movable pulley is reduced as the rotation speed of the first pulley decreases, When the rotation speed of the first pulley is lower than a predetermined rotation speed, the thrust of the movable sheave is not reduced when the speed ratio is lowered than when the speed ratio is higher than the predetermined speed ratio.

4. A storage medium storing a program executable by a computer for a continuously variable transmission, the continuously variable transmission comprising: a first pulley and a second pulley each having a fixed pulley and a movable pulley; an annular member wound around the first pulley and the second pulley, wherein the speed ratio is continuously changed by controlling the thrust of the movable pulley by oil pressure; in, The program causes the computer to execute the following steps: The thrust of the movable pulley is reduced as the rotation speed of the first pulley decreases, When the rotation speed of the first pulley is lower than a predetermined rotation speed, the thrust of the movable sheave is not reduced when the speed ratio is lowered than when the speed ratio is higher than the predetermined speed ratio.

Images