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

Abstract

[Problem] To suppress the slippage of an endless member and improve mileage. [Solution] A continuously variable transmission, which has a first pulley and a second pulley, each having a fixed pulley and a movable pulley, and an endless member wound around the first pulley and the second pulley: controls the thrust of the movable pulley with oil pressure, and continuously changes a gear ratio; makes the thrust of the movable pulley smaller, as the rotation speed of the first pulley becomes lower; and, when the rotation speed of the first pulley is lower than a prescribed rotation speed, does not make the thrust of the movable pulley smaller in a case where the gear ratio is in a Low side lower than a prescribed gear ratio in comparison to a case where the gear ratio is in a High side higher than the prescribed gear 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 type continuously variable transmission in which the V-groove interval between an input pulley and an output pulley is continuously variable by controlling the movable pulley thrust of both pulleys with hydraulic pressure or the like, and the movable pulley thrust determined according to the engine torque and the transmission ratio is corrected so as to increase as the rotational speed of the input pulley increases.

[0003] According to this, even under operating conditions where the rotational speed of the input pulley is relatively high, slippage of the belt can be effectively suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the above technology focuses on suppressing slippage of the belt (endless member) at high rotation, and does not consider the influence of belt slippage due to differences in the transmission ratio.

[0006] The present invention has been made in view of such technical problems, and aims to suppress slippage of the endless member and improve fuel efficiency.

Means for Solving the Problems

[0007] According to an aspect of the present invention, there is provided a continuously variable transmission having a first pulley and a second pulley each having a fixed pulley and a movable pulley, and an endless member wound around the first pulley and the second pulley, wherein the thrust of the movable pulley is controlled hydraulically to continuously change the transmission ratio. The thrust of the movable pulley is made smaller as the rotational speed of the first pulley decreases. When the rotational speed of the first pulley is lower than a predetermined rotational speed, the thrust of the movable pulley when the transmission ratio is on the Low side of the predetermined transmission ratio is not made smaller than the thrust of the movable pulley when the transmission ratio is on the High side of the predetermined transmission ratio.

Advantages of the Invention

[0008] In the above aspect, the thrust of the movable pulley is made smaller as the rotational speed of the first pulley decreases. Therefore, the frictional resistance between the endless member and the first and second pulleys can be reduced, so that the belt slip at high speeds can be suppressed and the fuel efficiency can be improved. Further, when the rotational speed of the first pulley is lower than the predetermined rotational speed, the thrust of the movable pulley when the transmission ratio is on the Low side of the predetermined transmission ratio is not made smaller than the thrust of the movable pulley when the transmission ratio is on the High side of the predetermined transmission ratio. Therefore, in a state where the transmission ratio is on the Low side of the predetermined transmission ratio, where the input torque to the first pulley often becomes large, the thrust of the movable pulley does not become smaller than necessary even when the rotational speed of the first pulley decreases, so that the slip of the endless member can be suppressed. Thus, according to these aspects, it is possible to suppress the slip of the endless member due to the difference in the transmission ratio and improve the fuel efficiency.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Hereinafter, when the speed ratio Rv is large (= when the reduction ratio is large), it is referred to as Low, and when the speed ratio Rv is small (= when the reduction ratio is small) (when the speed ratio (reduction ratio) is less than 1, it is a speed increase), it is referred to as High. Further, a change in the speed ratio Rv to the Low side is referred to as downshift, and a change to the High side is referred to as upshift.

[0011] FIG. 1 is a schematic configuration diagram of a vehicle 100 including an automatic transmission 20 as a continuously variable transmission according to an embodiment of the present invention. As shown in FIG. 1, the vehicle 100 includes an engine 10 as a drive source, an automatic transmission 20, and an engine controller 30.

[0012] The automatic transmission 20 includes a torque converter 2, a forward and reverse switching mechanism 3, a variator 4, a hydraulic control circuit 5, an oil pump 6, and a transmission controller 40.

[0013] In the vehicle 100, the rotation generated by the engine 10 is transmitted to the drive wheels 50 through the torque converter 2, the forward and reverse switching mechanism 3, the variator 4, the gear set 7, and the differential gear device 8.

[0014] The torque converter 2 is provided with a lock-up clutch 2a. When the lock-up clutch 2a is engaged, the input shaft 2b and the output shaft 2c of the torque converter 2 are directly connected, and the input shaft 2b and the output shaft 2c rotate at the same speed. Therefore, in the state where the lock-up clutch 2a is engaged, the rotation of the output shaft 10a of the engine 10 is directly transmitted from the output shaft 2c of the torque converter 2 to the forward / reverse switching mechanism 3.

[0015] The forward / reverse switching mechanism 3 has a double pinion planetary gear set as a main component, its sun gear is coupled to the engine 10 via the torque converter 2, and the carrier is coupled to the primary pulley 41 as the first pulley of the variator 4. The forward / reverse switching mechanism 3 further includes a forward clutch 3a that directly connects between the sun gear and the 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 to the primary pulley 41, and when the reverse brake 3b is engaged, the input rotation from the engine 10 via the torque converter 2 is reversely decelerated and transmitted to the primary pulley 41.

[0016] The variator 4 is a continuously variable transmission mechanism that changes the rotation of the engine 10 transmitted to the primary pulley 41 and transmits it from the secondary pulley 42 as the second pulley to the drive wheels 50.

[0017] The variator 4 includes a primary pulley 41 and a secondary pulley 42 arranged such that the V-grooves are aligned, and a belt 43 as an endless member wound around the V-grooves of the pulleys 41 and 42.

[0018] In order to be able to change the transmission ratio Rv between the primary pulley 41 and the secondary pulley 42 during power transmission, the variator 4 has one of the conical plates forming the V-grooves of the primary pulley 41 and the secondary pulley 42 as fixed pulleys 41a and 42a, and the other as movable pulleys 41b and 42b that are displaceable in the axial direction.

[0019] These movable pulleys 41b and 42b are biased 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 frictionally engaging the belt 43 with the conical plate to perform power transmission between the primary pulley 41 and the secondary pulley 42.

[0020] During gear shifting, the difference in pressure between the primary pulley pressure Pp and the secondary pulley pressure Ps generated corresponding to the target gear ratio TRv is used to change the width of the V-grooves of both pulleys 41 and 42, and the target gear ratio TRv is realized by continuously changing the winding arc diameter of the belt 43 with respect to the pulleys 41 and 42.

[0021] The oil pump 6 is a mechanical oil pump that is driven by inputting the rotation of the engine 10 and utilizing 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.

[0022] The hydraulic control circuit 5 includes a regulator valve 5a that regulates the pressure of the hydraulic oil supplied from the oil pump 6 to generate the required hydraulic pressure, a primary solenoid valve 5b that adjusts the hydraulic pressure supplied to the primary pulley chamber 41c of the primary pulley 41, a secondary solenoid valve 5c that adjusts the hydraulic pressure supplied to the secondary pulley chamber 42c of the secondary pulley 42, a lock-up solenoid valve 5d that adjusts the hydraulic pressure supplied to the lock-up clutch 2a, a select solenoid valve 5e that adjusts the hydraulic pressure supplied to the forward clutch 3a and the reverse brake 3b, a manual valve 5f that switches the supply path of the hydraulic pressure to the forward clutch 3a and the reverse brake 3b, etc.

[0023] Based on the control signal from the transmission controller 40, the hydraulic control circuit 5 supplies the adjusted hydraulic pressure to each part of the torque converter 2, the forward and reverse switching mechanism 3, and the variator 4.

[0024] 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 the CPU reading out and executing the programs stored in the ROM. The engine controller 30 can also be composed of a plurality of microcomputers.

[0025] Based on signals from various sensors that detect the states of each part of the vehicle 100, the engine controller 30 controls the rotational speed of the engine 10, the torque Te (hereinafter referred to as the engine torque Te), etc.

[0026] The transmission controller 40 is composed of a microcomputer equipped with a CPU, RAM, ROM, input / output interfaces, etc., and is communicably connected to the engine controller 30. The transmission controller 40 performs various processes by the CPU reading out and executing the programs stored in the ROM. The transmission controller 40 can also be composed of a plurality of microcomputers. The transmission controller 40 and the engine controller 30 may be integrated into one controller.

[0027] Based on signals from various sensors that detect the states of each part of the vehicle 100, the transmission controller 40 controls the engagement state of the lock-up clutch 2a, the gear ratio Rv of the variator 4, the engagement states of the forward clutch 3a and the reverse brake 3b, etc.

[0028] The transmission controller 40 receives signals from an accelerator opening sensor 61 that detects the accelerator opening APO, 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 an inhibitor switch 64 that detects the position of the shifter 63, a signal from a turbine rotational speed sensor 65 that detects the rotational speed Nt of the output shaft 2c of the torque converter 2, a signal from a primary rotational speed sensor 66 that detects the rotational speed Np of the primary pulley 41 (hereinafter referred to as the primary rotational speed Np), a signal from a secondary rotational speed sensor 67 that detects the rotational speed Ns of the secondary pulley 42 (hereinafter referred to as the secondary rotational speed Ns), a signal from a primary hydraulic pressure sensor 68 that detects the primary pulley pressure Pp, a signal from a secondary hydraulic pressure sensor 69 that detects the secondary pulley pressure Ps, and so on.

[0029] Incidentally, as described above, in the variator 4, the movable pulleys 41b and 42b are urged toward the fixed pulleys 41a and 42a by the primary pulley pressure Pp and the secondary pulley pressure Ps (the force that urges the movable pulleys 41b and 42b toward the fixed pulleys 41a and 42a by the primary pulley pressure Pp and the secondary pulley pressure Ps is referred to as "thrust"), whereby the belt 43 is frictionally engaged with the conical plate and power is transmitted between the primary pulley 41 and the secondary pulley 42.

[0030] Therefore, in the variator 4, it is important to control the thrust F of the movable pulleys 41b and 42b (hereinafter referred to as the pulley thrust F) so that the belt 43 does not slip. On the other hand, if the pulley thrust F is increased more than necessary, the frictional resistance between the belt 43 and each pulley 41, 42 may increase, which may affect the fuel efficiency of the vehicle 100.

[0031] 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 the slip of the belt 43 and improve the fuel efficiency.

[0032] Hereinafter, the transmission controller 40 will be described in detail.

[0033] FIG. 2 is a schematic configuration diagram of the transmission controller 40. Note that FIG. 2 shows a part of the functions of the transmission controller 40 as a block diagram, and each block does not mean a physical configuration.

[0034] As shown in FIG. 2, the transmission controller 40 includes an input unit 40a, an input signal generation unit 40b, a target gear ratio calculation unit 40c, a basic thrust calculation unit 40d, a correction coefficient calculation unit 40e, a target hydraulic pressure calculation unit 40f, a target current calculation unit 40g, and a solenoid drive unit 40h.

[0035] Signals from the engine controller 30, signals from the accelerator opening sensor 61, signals from the primary rotation speed sensor 66, signals from the secondary rotation speed sensor 67, etc. are input to the input unit 40a.

[0036] The input signal generation unit 40b generates a signal indicating the engine torque Te based on the signal input from the engine controller 30 to the input unit 40a, generates a signal indicating the accelerator opening APO based on the signal input from the accelerator opening sensor 61 to the input unit 40a, generates a signal indicating the primary rotation speed Np based on the signal input from the primary rotation speed sensor 66 to the input unit 40a, and generates a signal indicating the secondary rotation speed Ns and a signal indicating the vehicle speed VSP based on the signal input from the secondary rotation speed sensor 67 to the input unit 40a.

[0037] The target gear ratio calculation unit 40c refers to a preset gear shift map based on the specifications of the vehicle 100, experiments, etc., and calculates the target gear ratio TRv of the variator 4 based on the accelerator opening APO and the vehicle speed VSP. Note that instead of the accelerator opening APO, the throttle valve opening TVO input from the engine controller 30 may be used.

[0038] The basic thrust calculation unit 40d refers to a basic thrust map preset based on the specifications of the vehicle 100, experiments, etc., and calculates a basic thrust Fb that is the basis of the target pulley thrust TF based on the engine torque Te and the gear ratio Rv. The gear ratio Rv is obtained from the primary rotational speed Np and the secondary rotational speed Ns.

[0039] The basic thrust map is a map in which, using the engine torque Te and the gear ratio Rv as parameters, when the primary rotational speed Np (= engine rotational speed) is a predetermined rotational speed Nps, the pulley thrust F at which no slip occurs in the belt 43 is set as the basic thrust Fb. The predetermined rotational speed Nps can be, for example, about 2500 rpm to 3500 rpm, which is the rotational speed of the engine 10 with the highest usage frequency, or the intermediate rotational speed in the frequently used rotational speed range, etc.

[0040] The correction coefficient calculation unit 40e refers to a correction coefficient map preset based on the specifications of the vehicle 100, experiments, etc., and calculates a correction coefficient for correcting the basic thrust Fb based on the primary rotational speed Np and the gear ratio Rv. The correction coefficient map will be described in detail later.

[0041] The target hydraulic pressure calculation unit 40f multiplies the basic thrust Fb obtained by the basic thrust calculation unit 40d by the correction coefficient obtained by the correction coefficient calculation unit 40e to calculate the target pulley thrust TF. Then, it calculates the target primary pulley pressure TPp and the target secondary pulley pressure TPs for realizing the target pulley thrust TF and the target gear ratio TRv.

[0042] The target current calculation unit 40g calculates the primary solenoid command current Ip and the secondary solenoid command current Is for realizing the target primary pulley pressure TPp and the target secondary pulley pressure TPs obtained by the target hydraulic pressure calculation unit 40f.

[0043] The solenoid drive unit 40h supplies drive currents to the primary solenoid valve 5b and the secondary solenoid valve 5c based on the primary solenoid command current Ip and the secondary solenoid command current Is obtained by the target current calculation unit 40g.

[0044] Next, the correction of the basic thrust Fb will be described with reference to FIGS. 3 to 5. FIG. 3 is a diagram showing a correction coefficient map. FIG. 4 is a diagram for explaining the correction of the basic thrust Fb when the primary rotational speed Np is lower than the predetermined rotational speed Nps. FIG. 5 is a diagram for explaining the correction of the basic thrust Fb when the primary rotational speed Np is higher than the predetermined rotational speed Nps.

[0045] As shown in FIG. 3, the correction coefficient map has a region A where the primary rotational speed Np is lower than the predetermined rotational speed Nps and the gear ratio Rv is on the High side of the predetermined gear ratio Rvs, a region B where the primary rotational speed Np is lower than the predetermined rotational speed Nps and the gear ratio Rv is on the Low side of the predetermined gear ratio Rvs, and a region C where the primary rotational speed Np is higher than the predetermined rotational speed Nps.

[0046] As described above, the basic thrust map is a map that sets the pulley thrust F when the primary rotational speed Np is the predetermined rotational speed Nps. Therefore, when the primary rotational speed Np is the predetermined rotational speed Nps, there is no need to correct the basic thrust Fb, and thus the correction coefficient is set to "1".

[0047] Therefore, when the primary rotational speed Np is the predetermined rotational speed Nps, "1" is multiplied by the basic thrust Fb, and the basic thrust Fb directly becomes the target pulley thrust TF.

[0048] In region A, with the correction coefficient "1" as a reference, as indicated by the arrow, the lower the primary rotational speed Np and the higher the gear ratio Rv on the High side, the smaller the correction coefficient becomes. That is, in region A, the correction coefficient is a value smaller than "1".

[0049] Therefore, when the primary rotational speed Np is lower than the predetermined rotational speed Nps and the transmission ratio Rv is on the High side compared to the predetermined transmission ratio Rvs, as the primary rotational speed Np becomes lower and as the transmission ratio Rv becomes higher on the High side, a small correction coefficient is multiplied by the basic thrust Fb, and the target pulley thrust TF becomes smaller.

[0050] For example, in FIG. 4, when the primary rotational speed Np is lower than the predetermined rotational speed Nps and the transmission ratio Rv is the transmission ratio RvH on the High side compared to the predetermined transmission ratio Rvs, the basic thrust Fb is the basic thrust Fb1.

[0051] Here, since the primary rotational speed Np is lower than the predetermined rotational speed Nps and the transmission ratio Rv is on the High side compared to the predetermined transmission ratio Rvs, the basic thrust Fb1 is corrected using the correction coefficient in region A of the correction coefficient map. As a result, as shown by the arrow, the target pulley thrust TF1 having a value smaller than the basic thrust Fb1 is obtained.

[0052] As the primary rotational speed Np becomes lower, the centrifugal force acting on the belt 43 becomes smaller, so that slippage of the belt 43 is less likely to occur. Also, as the transmission ratio Rv becomes higher on the High side, the input torque to the primary pulley 41 is less likely to increase.

[0053] Therefore, in region A, even if the pulley thrust F is made smaller compared to the case where the primary rotational speed Np is the predetermined rotational speed Nps, slippage of the belt 43 can be suppressed. Also, since the pulley thrust F is decreased, the frictional resistance between the belt 43 and each of the pulleys 41, 42 also decreases. Therefore, the fuel efficiency of the vehicle 100 can be improved.

[0054] In region B, the correction coefficient is set to "1". That is, even when the primary rotational speed Np is lower than the predetermined rotational speed Nps, the target pulley thrust TF is not made smaller compared to the case where the transmission ratio Rv is on the High side compared to the predetermined transmission ratio Rvs.

[0055] Therefore, when the primary rotational speed Np is lower than the predetermined rotational speed Nps and the transmission ratio Rv is on the Low side of the predetermined transmission ratio Rvs, "1" is multiplied by the basic thrust Fb, and the basic thrust Fb directly becomes the target pulley thrust TF.

[0056] For example, in FIG. 4, when the primary rotational speed Np is lower than the predetermined rotational speed Nps and the transmission ratio Rv is the transmission ratio RvL on the Low side of the predetermined transmission ratio Rvs, the basic thrust Fb is the basic thrust Fb2.

[0057] Here, since the primary rotational speed Np is lower than the predetermined rotational speed Nps and the transmission ratio Rv is on the Low side of the predetermined transmission ratio Rvs, the basic thrust Fb2 is corrected using the correction coefficient "1" in region B of the correction coefficient map. As a result, the target pulley thrust TF2 having the same value as the basic thrust Fb2 is obtained.

[0058] In other words, the pulley thrust F does not change depending on the primary rotational speed Np when the primary rotational speed Np is lower than the predetermined rotational speed Nps and the transmission ratio Rv is on the Low side of the predetermined transmission ratio Rvs.

[0059] As the transmission ratio Rv becomes lower, the input torque to the primary pulley 41 often increases. Therefore, in region B, even when the primary rotational speed Np is lower than the predetermined rotational speed Nps, by preventing the pulley thrust F from being reduced compared to the case where the transmission ratio Rv is on the High side of the predetermined transmission ratio Rvs, slippage of the belt 43 is suppressed.

[0060] That is, the predetermined transmission ratio Rvs is a threshold value that is considered preferable to prioritize suppression of slippage of the belt 43 because the input torque to the primary pulley 41 often increases when the transmission ratio Rv is on the Low side of the predetermined transmission ratio Rvs. The predetermined transmission ratio Rvs is set in advance based on the specifications of the vehicle 100, experiments, etc.

[0061] Note that, as described above, the lower the primary rotational speed Np, the smaller the centrifugal force acting on the belt 43. Therefore, within a range where it is possible to reduce the pulley thrust F in response to the decrease in the centrifugal force, the correction coefficient in region B can also be set. 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".

[0062] In region C, with the correction coefficient "1" as a reference, as shown by the arrow, the higher the primary rotational speed Np and the lower the speed ratio Rv on the Low side, the larger the correction coefficient becomes. That is, in region C, the correction coefficient is a value larger than "1".

[0063] Therefore, when the primary rotational speed Np is higher than the predetermined rotational speed Nps, the higher the primary rotational speed Np and the lower the speed ratio Rv on the Low side, the larger the correction coefficient is multiplied by the basic thrust Fb, and the target pulley thrust TF becomes larger.

[0064] For example, in FIG. 5, when the primary rotational speed Np is higher than the predetermined rotational speed Nps and the speed ratio Rv is the speed ratio RvH on the High side of the predetermined speed ratio Rvs, the basic thrust Fb is the basic thrust Fb3.

[0065] Here, since the primary rotational speed Np is higher than the predetermined rotational speed Nps, the basic thrust Fb3 is corrected using the correction coefficient in region C of the correction coefficient map. As a result, as shown by the arrow, the target pulley thrust TF3 with a value larger than the basic thrust Fb3 is obtained.

[0066] Also, for example, in FIG. 5, when the primary rotational speed Np is higher than the predetermined rotational speed Nps and the speed ratio Rv is the speed ratio RvL on the Low side of the predetermined speed ratio Rvs, the basic thrust Fb is the basic thrust Fb4.

[0067] Here, since the primary rotational speed Np is higher than the predetermined rotational speed Nps, the basic thrust Fb4 is corrected using the correction coefficient in region C of the correction coefficient map. As a result, as indicated by the arrow, a target pulley thrust TF4 having a value larger than the basic thrust Fb4 is obtained. In the case of the gear ratio RvL, since the correction coefficient is larger than in the case of the gear ratio RvH, the correction ratio for the basic thrust Fb4 is larger than the correction ratio for the basic thrust Fb3.

[0068] The higher the primary rotational speed Np, the greater the centrifugal force acting on the belt 43, so the belt 43 is more likely to slip. Also, the lower the gear ratio Rv is on the Low side, the greater the input torque to the primary pulley 41 often becomes.

[0069] On the other hand, in region C, the higher the primary rotational speed Np and the lower the gear ratio Rv is on the Low side, the greater the basic thrust Fb is corrected and the greater the target pulley thrust TF becomes. As a result, since the pulley thrust F becomes larger, slippage of the belt 43 can be suppressed.

[0070] In this way, the transmission controller 40 obtains the basic thrust Fb based on the engine torque Te and the gear ratio Rv, and corrects the basic thrust Fb using the correction coefficient obtained based on the primary rotational speed Np and the gear ratio Rv to obtain the target pulley thrust TF.

[0071] Thereby, when considering the engine torque Te and the gear ratio Rv to be constant, the pulley thrust F becomes smaller as the primary rotational speed Np becomes lower. Thus, the fuel efficiency of the vehicle 100 can be improved.

[0072] However, when the gear ratio Rv is on the Low side of the predetermined gear ratio Rvs, the transmission controller 40 does not make the pulley thrust F smaller even if the primary rotational speed Np is lower than the predetermined rotational speed Nps compared to the case where the gear ratio Rv is on the High side of the predetermined gear ratio Rvs. Thereby, slippage of the belt 43 when the gear ratio Rv is on the Low side of the predetermined gear ratio Rvs is suppressed.

[0073] Next, with reference to FIG. 6, the processing executed by the transmission controller 40 will be described. FIG. 6 is a diagram showing the processing executed by the transmission controller 40 in a flowchart.

[0074] In step S11, the transmission controller 40 refers to a preset shift map based on the specifications of the vehicle 100, experiments, etc., and calculates the target shift ratio TRv of the variator 4 based on the accelerator opening APO and the vehicle speed VSP.

[0075] In step S12, the transmission controller 40 refers to a preset basic thrust map based on the specifications of the vehicle 100, experiments, etc., and calculates the basic thrust Fb that is the basis of the target pulley thrust TF based on the engine torque Te and the gear ratio Rv.

[0076] In step S13, the transmission controller 40 refers to a preset correction coefficient map based on the specifications of the vehicle 100, experiments, etc., and calculates a correction coefficient for correcting the basic thrust Fb based on the primary rotational speed Np and the gear ratio Rv.

[0077] In step S14, the transmission controller 40 multiplies the basic thrust Fb by the correction coefficient to calculate the target pulley thrust TF. Then, the target primary pulley pressure TPp and the target secondary pulley pressure TPs for realizing the target pulley thrust TF and the target shift ratio TRv are calculated.

[0078] In step S15, the transmission controller 40 calculates the primary solenoid command current Ip and the secondary solenoid command current Is for realizing the target primary pulley pressure TPp and the target secondary pulley pressure TPs.

[0079] In step S16, the transmission controller 40 supplies command currents to the primary solenoid valve 5b and the secondary solenoid valve 5c.

[0080] The main operational effects of the automatic transmission 20 configured as described above will be summarized and described.

[0081] (1) An automatic transmission 20 having a primary pulley 41 and a secondary pulley 42 each having fixed pulleys 41a and 42a and movable pulleys 41b and 42b, and a belt 43 wound around the primary pulley 41 and the secondary pulley 42, controls the thrust F of the movable pulleys 41b and 42b hydraulically to continuously change the gear ratio Rv. The thrust F of the movable pulleys 41b and 42b is made smaller as the rotational speed Np of the primary pulley 41 decreases. When the rotational speed Np of the primary pulley 41 is lower than a predetermined rotational speed Nps, the thrust F of the movable pulleys 41b and 42b when the gear ratio Rv is on the Low side of a predetermined gear ratio Rvs is not made smaller than when the gear ratio Rv is on the High side of the predetermined gear ratio Rvs.

[0082] According to this, the thrust F of the movable pulleys 41b and 42b becomes smaller as the rotational speed Np of the primary pulley 41 decreases. Therefore, the frictional resistance between the belt 43, the primary pulley 41, and the secondary pulley 42 can be reduced, improving fuel efficiency. Also, when the rotational speed Np of the primary pulley 41 is lower than the predetermined rotational speed Nps, the thrust F of the movable pulleys 41b and 42b when the gear ratio Rv is on the Low side of the predetermined gear ratio Rvs does not become smaller than when the gear ratio Rv is on the High side of the predetermined gear ratio Rvs. Therefore, in a state where the gear ratio Rv, in which the input torque to the primary pulley 41 often becomes large, is on the Low side of the predetermined gear ratio Rvs, even if the rotational speed Np of the primary pulley 41 decreases, the thrust F of the movable pulleys 41b and 42b does not become smaller than necessary, so slippage of the belt 43 can be suppressed. Thus, slippage of the belt 43 can be suppressed while improving fuel efficiency.

[0083] (2) The thrust F of the movable pulleys 41b and 42b does not change depending on the rotational speed Np of the primary pulley 41 when the rotational speed Np of the primary pulley 41 is lower than the predetermined rotational speed Nps and the gear ratio Rv is on the Low side of the predetermined gear ratio Rvs.

[0084] According to this, when the rotational speed Np of the primary pulley 41 is lower than a predetermined rotational speed Nps and the speed ratio Rv is on the Low side of a predetermined speed ratio Rvs, even if the primary rotational speed Np changes, the thrust F of the movable pulleys 41b and 42b does not change. 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, so slippage of the belt 43 can be suppressed.

[0085] As described above, the embodiments of the present invention have been explained. However, the above embodiments merely show a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0086] For example, in the above embodiment, the primary rotational speed Np is used for setting and calculating various maps. However, the setting and calculation of various maps may be performed using the secondary rotational speed Ns.

[0087] Various programs executed by the transmission controller 40 may use those stored in a non-transitory recording medium such as a CD-ROM.

Explanation of Reference Numerals

[0088] 20 Automatic transmission (continuously variable transmission) 40 Transmission controller (computer) 41 Primary pulley (first pulley) 41a Fixed pulley 41b Movable pulley 42 Secondary pulley (second pulley) 42a Fixed pulley 42b Movable pulley 43 Belt (endless member)

Claims

1. A continuously variable transmission having a first pulley and a second pulley each having a fixed pulley and a movable pulley, and an endless member wound around the first pulley and the second pulley, wherein the thrust of the movable pulley is controlled hydraulically to continuously change the transmission ratio, the thrust of the movable pulley is made smaller as the rotational speed of the first pulley decreases, when the rotational speed of the first pulley is lower than a predetermined rotational speed, the thrust of the movable pulley when the transmission ratio is on the Low side of the predetermined transmission ratio is not made smaller than when the transmission ratio is on the High side of the predetermined transmission ratio, Continuously variable transmission.

2. A method for controlling a continuously variable transmission having a first pulley and a second pulley each having a fixed pulley and a movable pulley, and an endless member wound around the first pulley and the second pulley, wherein the thrust of the movable pulley is controlled hydraulically to continuously change the transmission ratio, the thrust of the movable pulley is made smaller as the rotational speed of the first pulley decreases, when the rotational speed of the first pulley is lower than a predetermined rotational speed, the thrust of the movable pulley when the transmission ratio is on the Low side of the predetermined transmission ratio is not made smaller than when the transmission ratio is on the High side of the predetermined transmission ratio, Method for controlling a continuously variable transmission.

3. A computer-executable program for a continuously variable transmission having a first pulley and a second pulley each having a fixed pulley and a movable pulley, and an endless member wound around the first pulley and the second pulley, wherein the thrust of the movable pulley is controlled hydraulically to continuously change the transmission ratio, a procedure for making the thrust of the movable pulley smaller as the rotational speed of the first pulley decreases, when the rotational speed of the first pulley is lower than a predetermined rotational speed, a procedure for not making the thrust of the movable pulley when the transmission ratio is on the Low side of the predetermined transmission ratio smaller than when the transmission ratio is on the High side of the predetermined transmission ratio, A program for causing the computer to execute.

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