JPH0548383B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a hydraulic control device for a vehicle belt-type continuously variable transmission, and more particularly to oil temperature correction in electronic control of line pressure.

[Conventional technology]

Regarding the control of this type of continuously variable transmission, for example, there is a basic method shown in Japanese Unexamined Patent Publication No. 55-65755, which describes mechanical speed change and line pressure control. However, with mechanical control, the structures of valves and hydraulic control systems are complicated, and input information and control are inherently limited. Therefore, in recent years, there has been a trend to electrically process various information and requirements to optimally electronically control speed change and line pressure. The continuously variable transmission is based on the premise that power is transmitted through friction between pulleys and belts. For this reason, electronic line pressure control uses appropriate input information to accurately estimate the transmission torque of the pulley and belt.
It is desirable to control the transmitted torque so as to always apply the necessary minimum pulley pressing force that does not cause belt slip. Conventionally, regarding line piezoelectric control of the above-mentioned continuously variable transmission, there is a prior art, for example, disclosed in Japanese Patent Application Laid-Open No. 60-44649. In this prior art, signals of engine rotation speed, vehicle speed, and engine torque are input to a line pressure calculation means to calculate line pressure, and a control voltage calculation means calculates a control voltage according to the line pressure.
It is shown that this control voltage is output to the pressure regulating valve.

[Problem to be solved by the invention]

However, in the prior art described above, since signals of engine speed and vehicle speed are used, the gear ratio and line pressure cannot be calculated when the clutch is disengaged or slips. Furthermore, since the line pressure is simply calculated as a function of the engine rotation speed, vehicle speed, and engine torque, the line pressure corresponding to the transmission torque of the pulley and belt cannot be accurately calculated. Furthermore, since no correction measures are taken for the oil temperature, the control accuracy of the line pressure deteriorates as the viscosity of the oil changes depending on the oil temperature. In addition, it is necessary to control the line pressure to a high level in consideration of safety against changes in oil temperature, which causes problems such as increased pump loss. In view of these points, it is an object of the present invention to provide a hydraulic control device for a continuously variable transmission that appropriately corrects oil temperature in electronic control of line pressure.

[Means to solve the problem]

To achieve this objective, the configuration of the present invention will be explained with reference to FIG.
0 is configured to control the line pressure by an electrical signal from a control unit 70. The control unit 70 includes a means 75 for calculating the gear ratio based on the primary pulley rotation speed and the secondary pulley rotation speed, a means 82 for setting the required line pressure per unit torque according to the gear ratio, and a means 82 for setting the required line pressure per unit torque according to the engine rotation speed and the throttle opening. It includes a means 81 for setting engine torque, a means 83 for calculating a target line pressure based on the required line pressure per unit torque at each gear ratio and the engine torque, and a means 84 for setting a manipulated variable according to the target line pressure. . Also, as an oil temperature correction, a means 8 for setting a correction amount based on the relationship between the oil temperature and the operation amount according to the target line pressure.
7, and means 88 for outputting an electrical signal of the manipulated variable corrected according to the correction amount.

[Effect]

In the present invention having the above configuration, the line pressure of the continuously variable transmission is basically electronically controlled by operating the line pressure control valve 40 in response to an electric signal from the control unit 70. When the vehicle is stopped or running, the control unit 7
0, the actual gear ratio is always accurately calculated, and the required line pressure per unit torque is set according to this gear ratio. Further, the engine torque is estimated, and the target line pressure is calculated based on the required line pressure per unit torque and the engine torque in correspondence with the transmitted torque. Then, an electrical signal with a manipulated variable corresponding to the target line pressure is output, and the line pressure is continuously electronically controlled to the necessary minimum level without causing belt slip. Furthermore, for example, when the line pressure is controlled to be low, the influence of oil temperature is large, so this correction area is determined based on the operation amount according to the target line pressure. In the correction region, the operating amount of the electric signal is corrected to increase or decrease depending on the oil temperature, thereby preventing the line pressure from fluctuating due to changes in oil viscosity, and accurately controlling the line pressure at all times.

【Example】

Embodiments of the present invention will be described below based on the drawings. Referring to FIG. 2, an outline of a continuously variable transmission to which the present invention is applied will be explained. First, the drive system will be described. An engine 1 is connected to a main shaft 5 of a continuously variable transmission 4 via a clutch 2 and a forward/reverse switching device 3. In the continuously variable transmission 4, a subshaft 6 is arranged parallel to a main shaft 5, a primary pulley 7 is provided on the main shaft 5, a secondary pulley 8 is provided on the subshaft 6, and a drive belt 11 is provided on both pulleys 7, 8. is wrapped.
Both pulleys 7 and 8 are connected to the fixed side and the hydraulic cylinders 9 and 1.
0 and a movable side that is movable in the axial direction, the pulley interval is variable, and the primary cylinder 9 has a larger pressure receiving area than the secondary cylinder 10. There is also a control unit 70 that outputs electrical signals to control line pressure and speed change.
and a hydraulic circuit 20 that changes the primary pressure and the line pressure on the secondary side based on an electric signal, and the line pressure and the primary pressure are electronically controlled.
The belt is then properly clamped using line pressure.
The primary pressure causes the pulley 7 of the drive belt 11 to
The winding diameter is configured to be continuously variable by changing the ratio of the winding diameter to 8. The subshaft 6 also has a set of reduction gears 12,
It is connected to the output shaft 14 via 13. A drive gear 15 of the output shaft 14 is configured to be transmitted to drive wheels 19 via a final gear 16, a differential gear 17, and an axle 18. Referring to FIG. 3, a hydraulic control system including the hydraulic circuit 20 will be explained. First, it has an oil pump 21 driven by the engine 1, and a line pressure oil passage 22 on the discharge side of the oil pump 21 is communicated with the secondary cylinder 10, the line pressure control valve 40, and the speed change speed control valve 50, so that the speed change speed is controlled. A valve 50 is communicated with the primary cylinder 9 via an oil passage 23. Oil passage 24 on the drain side of the speed change control valve 50
is connected to an oil pan 26 and has a check valve 25 that prevents air from entering when draining oil from the primary cylinder 9. Further, the oil passage 27 on the drain side of the line pressure control valve 40 is provided with a regeneration valve 28 that generates a constant lubricating pressure. The oil passages 23 to the primary cylinder 9 are communicated via the prefilling valves 30, respectively. The line pressure control valve 40 has a spool 4 attached to a valve body 41.
2 is movably inserted, and this spool 42 communicates the port 41a of the oil passage 22 with the drain port 41b to regulate the pressure. One port 4 of spool 42
Line pressure PL acts on 1c through an oil passage 46 branching from the oil passage 22. Further, the other side of the spool 42 has a control port 4 for electrically controlling the line pressure.
1d is provided, mechanically setting the minimum line pressure PLmin
The spring 43 is biased. A duty pressure Pd for line pressure control is supplied to the control port 41d as a signal hydraulic pressure through an oil passage 47. Also, the end of the spring 43 is attached to the adjusting screw 4.
By adjusting the set load of the spring 43, it is possible to adjust the relationship between the duty ratio D and the minimum line pressure PLmin due to variations in each component. Therefore, line pressure PL, effective area SL, duty pressure Pd, effective area Sd, spring load Fs
Then, the following formula holds true. Fs+Pd・Sd=PL・SL PL=(Pd・Sd+Fs)/SL Therefore, line pressure PL is controlled to change continuously as a function of spring load Fs and duty pressure Pd. In particular, line pressure PL is duty pressure Pd
is controlled by an increasing function as shown in FIG. 5a. The variable speed control valve 50 has a valve body 51 and a spool 5.
2 is movably inserted, and by moving the spool 52 left and right, the oil supply position where the port 51a of the oil passage 22 is communicated with the port 51b of the oil passage 23, and the port 51
b and the oil drain position communicating with the drain port 51c. One port 51 of the spool 52
A constant reducing pressure is applied to d by the oil passage 53.
PR acts on the other port 51e, and the oil passage 54
Accordingly, duty pressure Pd for shift speed control acts as a signal hydraulic pressure. Further, a spring 55 for initial setting is applied to the spool 52 at the port 51e, and the spool 52 is configured to move toward the oil drain side when the duty pressure Pd is turned on. The duty pressure Pd of the signal hydraulic pressure is the duty ratio D of the electric signal using the reducing pressure PR as the source pressure.
It is generated in a pulse shape according to the Therefore, by changing the on/off ratio (duty ratio) of the duty pressure Pd, the oil supply and drain times, that is, the inflow and outflow flow rates, are changed, making it possible to control the speed change. That is, the shift speed di/dt is the primary cylinder 9.
Since the flow rate Q is a function of the duty ratio D, line pressure PL, and primary pressure Pp, the following equation holds. di/dt=f(Q)=f(D, PL, Pp) Here, line pressure PL is controlled by gear ratio i and engine torque T, and primary pressure Pp is determined by line pressure PL and gear ratio i, so T Assuming that is constant, di/dt=f(D,i). On the other hand, since the gear change speed di/dt is determined based on the deviation between the target gear ratio is and the actual gear ratio i in steady state, the following equation holds true. di/dt=k(is-i) From this, at each gear ratio i, the target gear ratio
If is is determined and the speed change speed di/dt is determined, the duty ratio D can be found from the relationship between the speed change speed di/dt and the speed change ratio i. Therefore, it can be seen that if the shift speed control valve 50 is operated at this duty ratio D, the shift speed can be controlled over the entire shift range. Next, a circuit that generates the duty pressure Pd as the signal oil pressure will be explained. First, as a circuit for generating a constant reducing pressure PR, a line pressure oil passage 22 branches into an oil passage 31 via an orifice 32 that restricts the flow rate, and this oil passage 31 is communicated with a reducing valve 60. In the reducing valve 60, a spool 62 is movably inserted into a valve body 61, and one side of the spool 62 is biased by a spring 63. In addition, an inlet port 61a, an outlet port 61b, which communicates with the oil passage 31,
A drain port 61c is provided, and reducing pressure from the outlet port 61b acts through the oil passage 33 on the port 61d of the spool 62 on the opposite side from the spring 63. One block 64 of the spring 63
can be moved using an adjustment screw or the like to adjust the reducing pressure PR along with the spring load. As a result, the line pressure PL is restricted by the orifice 32 and supplied to the port 61a, and when the reducing pressure PR in the oil passage 33 decreases, the spring 63 causes the spool 62 to be supplied to the ports 61a and 61b.
Line pressure PL is introduced by communicating with Further, due to the increase in the oil pressure in the port 61d, the spool 62 is returned to communicate with the ports 61b and 61c to reduce the reducing pressure PR. In this way, the line pressure PL is replenished by the amount of decrease in the reducing pressure PR, and a constant reducing pressure PR equal to the load of the spring 63 is always generated. The oil passage 33 for this reducing pressure PR is connected to a line pressure control solenoid valve 65, an accumulator 66 and a duty pressure Pd via an orifice 34.
The oil passage 37 is connected to the oil passage 37. and solenoid valve 6
5 intermittently drains a constant reducing pressure PR according to the duty signal to generate pulsed hydraulic pressure, smooths this hydraulic pressure to a predetermined level of duty pressure Pd with an accumulator 66, and controls line pressure through an oil passage 37. Supplied to valve 40. Further, an oil passage 53 branches off from the upstream side of the orifice 34 of the oil passage 33 and communicates with the transmission speed control solenoid valve 67 and the oil passage 54 through an orifice 35 in the middle of the oil passage 53 . and solenoid valve 67
Similarly, due to the duty signal, the duty pressure Pd
This duty pressure Pd is directly supplied to the speed change control valve 50 through the oil passage 54. The solenoid valve 65 is configured to drain oil when the duty signal is turned on. Then, the duty pressure Pd is set with respect to the duty ratio D by a decreasing function as shown in FIG. 5b. Therefore, the line pressure PL with respect to the duty ratio D has a characteristic that changes with a decreasing function as shown in FIG. 5c. Therefore, the duty ratio D is 0
% maximum line pressure at least drained oil
PLmax and when the duty ratio D is 100% and the oil is drained the most, the lowest line pressure PLmin is reached, and this lowest line pressure PLmin is determined only by the load of the spring 43 of the line pressure control valve 40. Since the solenoid valve 67 has a similar configuration, when the duty ratio D is large, the shift speed control valve 50
If it takes a long time to switch to the oil supply position, it will shift up, and vice versa, it will take a long time to switch to the oil drain position, and it will shift down. The larger the deviation of is-i, the larger the change in duty ratio D, so that the shift speed is controlled faster. Further, referring to FIG. 4, an electric control system including a control unit 70 will be explained. First, the primary pulley rotation speed sensor 71 detects the primary pulley rotation speed Np, and the secondary pulley rotation speed Ns
a secondary pulley rotation speed sensor 72 that detects
It has an engine rotation speed sensor 74 that detects the engine rotation speed Ne, and a throttle opening sensor 73 that detects the throttle opening degree θ. These sensor signals are input to a control unit 70. The transmission speed control system in the control unit 70 will be explained. It has an actual gear ratio calculation unit 75 into which the primary pulley rotation speed Np and the secondary pulley rotation speed Ns are input, and the actual gear ratio i is calculated as i=Np/Ns.
Calculated by Also, the secondary pulley rotation speed
Ns and throttle opening θ are determined by the target gear ratio search unit 76.
Enter. Here, the table shown in FIG. 6b is set based on the shift pattern shown in FIG. 6a,
The target gear ratio is is searched from the values of Ns and θ of this enable. The actual gear ratio i, the target gear ratio is in steady state, and the coefficient k of the coefficient setting unit 77 are calculated by the gear shifting speed calculating unit 78.
is input, and the shifting speed di/dt is calculated as di/dt=k(is-i). Further, if the sign of the shift speed di/dt is positive, it is determined to be a downshift, and if it is negative, it is determined to be a shift up. The shift speed di/dt and the actual gear ratio i are further input to a duty ratio search section 79, and a duty ratio D is set as a manipulated variable according to the shift speed di/dt and the actual gear ratio i. Here, the duty ratio D is D=f(di/dt, i)
According to the relationship, a table is set as shown in FIG. 6c based on ±di/dt and i. In other words, in the table of -di/dt and i for shift up, D = 50%, where oil supply and oil drain are balanced.
In the table of +di/dt and i for downshifting, D=50 to 0% are assigned to values of ~100%. In the shift-up table, the duty ratio D is set as a decreasing function for i and as an increasing function for -di/dt. In the downshift table, the duty ratio D is set as an increasing function for i and as a decreasing function for di/dt. So, referring to this table, di/dt
The duty ratio D corresponding to i is searched. Then, an electric signal with a duty ratio D is outputted to the solenoid valve 67 via the drive section 80. Next, the line pressure control system will be explained. First, the control principle will be explained. This type of belt-type continuously variable transmission transmits torque through friction between the pulley and the belt while the belt is clamped by line pressure at the secondary pulley. Therefore, allowable input torque (torque that can be transmitted without slipping) Tmax, belt clamping force Fs at the secondary pulley, friction coefficient μ between the pulley and belt, belt pitch radius R1 at the primary pulley, belt pitch radius R2 at the secondary pulley, Assuming that the pulley belt pinching angle α, line pressure PL, secondary piston effective pressure receiving area As, pulley ratio (speed ratio) i, pulley angle β at primary pulley, and distance between pulley centers C, the torque transmission capacity at secondary pulley is From the viewpoint of mechanical balance, it can be simply expressed by the following formula. Tmax=Fs・2・μ・R1/cosα...(1) Also, Fs=PL・As R2=R1−C・sinβ i=R2/R1 Therefore, R1=1/f(1−i), R1 becomes a function of i. Furthermore, in equation (1), if 1/f'(i)=As・2・μ・/cosα・f(1−i), then Tmax=PL/f′(i). Therefore, if we calculate the required line pressure PLu per unit torque by assuming the minimum line pressure that can transmit a constant torque without belt slip, then PLu=f'(i) becomes a function of i. That is, the required line pressure PLu per unit torque is set to be high at low gears where the gear ratio i is large, as shown in FIG. 6e, and to decrease as the gear ratio i becomes smaller. Therefore, the required line pressure PLu per unit torque
By calculating the target line pressure PLt from and engine torque T, it becomes possible to accurately calculate the minimum necessary target line pressure PLt corresponding to the transmission torque of the pulley and belt. Therefore, in the line pressure control system, the throttle opening θ
and the engine rotation speed Ne are determined by the engine torque setting section 8.
1 and set the engine torque T by referring to the θ-Ne table in FIG. 6d. In addition, the required line pressure setting section 82 determines the required line pressure PLu per unit torque using the table shown in FIG.
Set accordingly. These engine torque T and required line pressure PLu per unit torque are input to the target line pressure calculating section 83, and the target line pressure PLt is calculated by PLt=PLu·T. The target line pressure PLt is input to the duty ratio setting section 84, and the duty ratio D as an operation amount corresponding to the target line pressure PLt is set in a decreasing function manner. Here, the line pressure control valve 40 is a pressure regulating valve, and the oil pump 21 is driven by the engine 1. Therefore, if the pump discharge amount changes depending on the engine rotation speed Ne, the actual line pressure will change even if the operation amount of the electric signal is the same, so it is necessary to correct the operation amount with respect to the engine rotation speed Ne. Therefore, the duty ratio D of the manipulated variable is the engine speed
Ne and target line pressure PLt are set as shown in FIG. 5f. Therefore, in this table, search for the maximum line pressure Pmax and minimum line pressure Pmin at the engine speed Ne, and D = (Pmax -
Duty ratio D is determined by PL)/(Pmax-Pmin)
Calculate. Furthermore, correction measures for oil temperature will be explained. Here, when the oil temperature To changes, the viscosity of the oil changes, so the error in the line pressure PL increases. Further, when the line pressure is controlled by converting the duty ratio D of the electric signal into the duty pressure Pd as in the embodiment, the duty pressure Pd itself changes depending on the oil temperature To, so the influence is particularly large. For example, if the duty pressure control width is 4 kg/cm ² and the line pressure control width is set to 20 kg/cm ² , which is 4 to 5 times that, the line pressure PL will change significantly with the same magnification due to changes in oil temperature To. Therefore, correction is particularly required for the duty pressure Pd. When considering the fluctuation state of the duty pressure Pd with respect to the oil temperature To and the duty ratio D, it becomes as shown in Fig. 7. That is, when the duty ratio D is large, for example, 50% or more, and the duty pressure Pd is low, it fluctuates greatly. Then, the oil temperature To for the set value to is
When To > to, the oil viscosity is low, so the duty pressure Pd decreases, and conversely, when To < to, the oil viscosity is high, so the duty pressure Pd increases. Therefore, the duty ratio D may be corrected so that the duty pressure Pd remains constant despite changes in the oil temperature To. Therefore, an oil temperature sensor 86 is provided to detect the oil temperature To. And oil temperature To and duty ratio setting section 84
The duty ratio D is input to the correction amount setting section 87,
Determine the area where D>50% requires correction. In this correction area, if To<to, a predetermined correction amount +ΔD is determined, and if To>to, a predetermined correction amount −ΔD is determined. This correction amount ±ΔD is determined by the duty ratio correction section 8 added to the output side of the duty ratio setting section 84.
8 and correct it by calculating D±ΔD. Then, an electric signal of the corrected duty ratio D±ΔD is outputted to the solenoid valve 65 via the drive section 85. Next, the operation of this embodiment will be explained. First, the oil pump 2 is activated by the operation of the engine 1.
1 is driven, the line pressure PL of the oil passage 22 is supplied only to the secondary cylinder 10, and the gear ratio is set to the lowest gear, which is the maximum. At this time, a constant reducing pressure PR is taken out by the reducing valve 60 using the line pressure PL, and this reducing pressure PR is guided to each solenoid valve 65, 67, making it possible to electronically control the line pressure and speed change. Become. Further, signals of the primary pulley rotation speed Np, the secondary pulley rotation speed Ns, the throttle opening θ, and the engine rotation speed Ne are input to the control unit 70. In the line pressure control system, the actual gear ratio i is calculated from the primary pulley rotation speed Np and the secondary pulley rotation speed Ns, and the required line pressure PLu per unit torque is set according to this gear ratio i. In addition, the engine torque T is estimated from the engine speed Ne and the throttle opening θ, and the required line pressure PLu per unit torque is calculated as the engine torque T.
The target line pressure PLt is calculated by multiplying by Therefore, when the vehicle is stopped and idling, the secondary pulley rotation speed Ns becomes zero, resulting in the maximum gear ratio, and the required line pressure PLu per unit torque is set to a large value. Therefore, even if the engine torque T is small, the target line pressure PLt is calculated to be relatively large, and a signal with a small duty ratio D is output to the solenoid valve 65. Therefore, the amount of oil discharged from the solenoid valve 65 decreases and is converted into a large duty pressure Pd, and this duty pressure Pd is transferred to the line pressure control valve 4.
0 port 41d. Therefore, in the line pressure control valve 40, the load of the spring 43 that sets the minimum line pressure PLmin and the duty pressure Pd act in a direction to increase the line pressure PL.
PL is highly controlled. Furthermore, when the engine torque T increases during starting or acceleration, the target line pressure PLt is calculated to be even larger. Therefore, the duty ratio D is set smaller, and the line pressure PL is controlled to be higher by the amount of the engine torque T by the line pressure control valve 40. Further, as the vehicle speed increases, shift control is started, the gear ratio i becomes smaller, and the engine torque T also becomes smaller, so the duty ratio D becomes larger. Therefore, the duty pressure Pd in the solenoid valve 65 decreases due to an increase in the amount of discharged oil, and the line pressure PL in the line pressure control valve 40 is sequentially controlled to decrease. In this case, at the minimum gear ratio and the minimum engine torque, the duty pressure Pd becomes approximately zero and is controlled to the minimum line pressure PLmin by the spring load. In this way, the line pressure PL is continuously electronically controlled so that it is lower as the gear ratio i is smaller and higher as the engine torque T is larger. Then, the required line pressure PLu corresponding to the gear ratio i makes the target line pressure PLt correspond to the torque transmitted between the pulley and the belt, and the line pressure PL always maintains the necessary minimum pulley pressing force that does not cause belt slip. will be added. In the above-mentioned electronic control of line pressure, the correction area is always determined based on the duty ratio D. If the line pressure is controlled to be high due to a small duty ratio D and a large duty pressure Pd during low speed gear or acceleration, no correction is made because the oil temperature To has almost no influence. On the other hand, when D>50% in a driving state where the engine torque is small in proportion to the gear ratio in the high speed gear, it is determined that the vehicle is in the correction region. In this case, the correction amount setting section 87 compares the oil temperature To with the set value to, and when the engine is cold, To<to, and the duty ratio correction section 88 corrects the duty ratio by increasing it by D+ΔD. Therefore, in the solenoid valve 65, the duty pressure Pd is converted to a lower value by increasing the duty ratio D, thereby preventing the duty pressure Pd from becoming higher due to high oil viscosity. Furthermore, when the oil temperature To rises and becomes To > to, the duty ratio D is corrected to decrease, and the solenoid valve 65 converts the duty pressure Pd to a higher one, so that the oil viscosity is low and the duty pressure Pd is lower. It is prevented from becoming. In this way, the duty pressure Pd converted by the solenoid valve 65 corresponds to each duty ratio D without being influenced by the oil temperature To, as shown by the dashed line in FIG.
And this duty pressure Pd is the line pressure control valve 4.
By introducing the line pressure PL to 0, the line pressure PL is always accurately controlled. Note that when the line pressure control valve 40 is operated directly by an electric signal, the operation of the line pressure control valve 40 changes slightly in the control region where the line pressure is low due to the increase/decrease correction of the electric signal, and the line pressure fluctuations are similarly prevented. Prevented. On the other hand, after the vehicle has started, the control unit 70 further calculates the shift speed di/dt using is-i.
A signal of the duty ratio D set according to the relationship between di/dt and i is output to the solenoid valve 67, and the duty ratio is
Converted to Pd. This duty pressure Pd is then introduced into the speed change control valve 50, which operates to supply and drain line pressure PL to and from the primary cylinder 9 at a predetermined flow rate to change the primary pressure Pp. Therefore, the actual gear ratio i follows the target gear ratio is, and the gear change is controlled appropriately according to the driving and driving conditions. In this case, as in the transient state, the larger is-i is, the faster the gear change speed is. . Although one embodiment of the present invention has been described above,
The on/off relationship of the solenoid valve can also be reversed. An oil temperature switch, water temperature sensor or switch can also be used instead of the oil temperature sensor. Furthermore, the oil temperature correction is not limited to the one using the characteristics shown in FIG. That is, a change in viscosity or the like may be used, and the correction method may also be such that a correction coefficient is determined and the manipulated variable is multiplied.

【Effect of the invention】

As explained above, according to the present invention, in a hydraulic control device that electronically controls line pressure in a continuously variable transmission, the control unit calculates the actual gear ratio from the primary pulley rotation speed and the secondary pulley rotation speed, and The required line pressure per unit torque is determined according to the ratio, and the target line pressure is calculated from the required line pressure per unit torque and the engine torque, so the line pressure is controlled to the minimum necessary to prevent belt slip in response to the transmitted torque. can. In addition, since the electric signal is corrected by the operation amount according to the oil temperature and target line pressure, it is possible to control the line pressure with high precision in response to changes in oil temperature. Furthermore, since the area to be corrected is determined based on the operating amount corresponding to the target line pressure, unnecessary corrections are not required, and areas that are largely influenced by oil temperature can be appropriately corrected. When correcting based on the relationship between oil temperature, operation amount according to target line pressure, and signal oil pressure as in the example,
Fluctuations in signal oil pressure can be effectively suppressed. Therefore, fluctuations due to oil temperature when controlling the line pressure using signal oil pressure can be effectively prevented.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing a hydraulic control system for a continuously variable transmission according to the present invention, FIG. 2 is a block diagram schematically showing a continuously variable transmission to which the present invention is applied, and FIG. 3 is a hydraulic pressure control system according to the present invention. A hydraulic circuit diagram showing an embodiment of the control device, Fig. 4 is a block diagram of the electric control system, Figs. f is a diagram showing characteristics and tables of shift control and line pressure control, and FIG. 7 is a diagram showing fluctuation states of signal oil pressure with respect to operating amounts of oil temperature and target line pressure. 4...Continuously variable transmission, 5...Main shaft, 11...Drive belt, 6...Subshaft, 7...Primary pulley,
8...Secondary pulley, 9...Primary cylinder, 10...Secondary cylinder, 21...Oil pump, 22, 23...Oil passage, 40...Line pressure control valve, 50...Shift speed control valve, 70... …
Control unit, 75...Actual gear ratio calculation section, 81...
...Engine torque setting section, 82...Required line pressure setting section, 83...Target line pressure calculation section, 84...
Duty ratio setting section, 86...Oil temperature sensor, 87
...Correction amount setting section, 88...Duty ratio correction section.

Claims (1)

[Scope of Claims] 1 A primary pulley with variable pulley spacing is provided on the main shaft on the engine side, a secondary pulley with variable pulley spacing is provided on the subshaft on the wheel side, which is arranged parallel to the main shaft, and a driving pulley is provided between the two pulleys. A belt is wound around the oil path from the hydraulic source, and a line pressure control valve is provided to control line pressure and supply the line pressure to the cylinder of the secondary pulley to apply pulley pressing force. A variable speed control valve is installed to change the primary pressure by supplying and discharging line pressure to the oil passage, and the continuously variable speed changes the speed by changing the ratio of the winding diameter of the drive belt to both pulleys based on the primary pressure. In the machine, the line pressure control valve 40 is configured to control the line pressure by an electric signal from a control unit 70, and the control unit 70 has means 75 for calculating a gear ratio based on the primary pulley rotation speed and the secondary pulley rotation speed. means 82 for setting the required line pressure per unit torque according to the gear ratio; means 81 for setting the engine torque according to the engine speed and throttle opening; and means 81 for setting the required line pressure per unit torque at each gear ratio. means 83 for calculating the target line pressure based on engine torque; means 84 for setting the manipulated variable according to the target line pressure; and means 87 for setting the correction amount according to the relationship between the manipulated variable according to the oil temperature and the target line pressure. , means 88 for outputting an electrical signal of the operation amount corrected according to the correction amount. 2 The line pressure control valve 40 has a spring 43 for setting a predetermined line pressure and a control port 41d, and a solenoid valve 65 provided in the oil passage 31 that branches from the line pressure oil passage 22 via the flow rate restriction means 32. is configured to generate a signal hydraulic pressure according to the electric signal of the control unit 70 and introduce it to the control port 41d of the line pressure control valve 40, and to variably control the line pressure as a function of the spring load and the signal hydraulic pressure. A hydraulic control device for a continuously variable transmission according to claim 1, characterized in that: