JPH0289852A - Speed change control device for continuously variable transmission - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a belt slip by a method wherein at a tire lock time during brake of a low friction passage, a shift lock valve is closed to hold the primary pressure of a primary cylinder at a high value. CONSTITUTION:The primary pressure of a primary cylinder 38a is controlled to a high pressure by a change gear ratio control valve 100 to perform up shift to a high speed stage. In this case, when a Pitot pressure by a detecting means 152 is abnormally reduced from an ordinary and relatively high state, the occurrence of tire lock is decided by a deciding part 153. During tire lock, a drain oil passage 82 of the change gear ratio control valve 100 is shut off by a shift lock valve 84. By holding a primary pressure at a high value, tire lock is rendered ineffective by release of brake. When pulleys 36 and 37 and a belt 34 are rotated rapidly, especially a primary pulley 36b is rotated by means of the belt 34 without the occurrence of a slip. After restoration of a Pitot pressure, the shift lock valve 84 is opened to restart drainage of a primary pressure, resulting in return to a normal state.

Description

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

The present invention relates to a shift control device in a hydraulic control system of a belt-type continuously variable transmission for vehicles, and more specifically, to a low-friction road (low-μ
This invention relates to measures to prevent belt slippage caused by tire locking during braking on roads (roads) and subsequent release of the brakes.

[Conventional technology]

Conventionally, the speed change control of this type of continuously variable transmission includes a speed ratio control valve in the hydraulic control system, as shown in, for example, Japanese Unexamined Patent Publication No. 54-157930. Then, a spring force corresponding to the accelerator opening is applied to one side of the gear ratio control valve, and a pitot pressure corresponding to the engine speed is applied to the other side, and the primary pressure of the primary pulley is changed so that both are balanced, thereby changing gears. This is a control configuration. In this case, a sensor for detecting pitot pressure is installed on the primary boolean on the engine side. Additionally, the applicant has already developed an electromagnetic clutch for the engine as a drive system including a continuously variable transmission. Transmission is configured to the primary pulley via a forward/reverse switching device, while the secondary pulley, which is connected to the primary boot by a belt, has a transmission groove on the wheel side, and the electromagnetic clutch is automatically activated depending on the engine speed and vehicle speed. A device has been proposed that prevents engine stalling by connecting and disconnecting the engine. With such a drive system, when the clutch is engaged, the primary boolean is directly connected to the engine to generate Bi1~- pressure, making it possible to perform gear change control normally.

[Problem to be solved by the invention]

As mentioned above, pitot pressure is an important element in shift control, and if the pitot pressure is output normally during normal driving, there is no problem, but depending on the driving conditions, the generation of pitot pressure may be disrupted, causing problems. . One of them is low μ such as snowy roads.
There are driving conditions in which the tires lock due to lack of grip during sudden braking on the road, and the behavior in this case will be described using FIG. 3. First, when the tires are locked, the vehicle speed V11 gradually decreases, while the wheel speed Vv rapidly decreases to zero, and accordingly, the pitot pressure Pt and primary pressure Pp also decrease rapidly. On the other hand, the actual pulley and belt portion is separated from the engine side by disengaging the clutch, and is stopped and held in a high speed state where the belt has moved to the primary pulley side, and the line pressure PL is also low based on the gear ratio i. In this way, the gear ratio control valve of the hydraulic fi control system is shifted to a lower gear due to a decrease in pitot pressure, whereas the actual pulley and belt are in a state where they cannot shift to a lower gear because the line pressure is low and they are stopped. , or in the middle of a slow gear shift. Therefore, when the brakes are released, the tires are also unlocked and the wheels rotate, and when the wheel speed Vv rapidly recovers, the pulleys and belts are also turned by the wheels. At this time, an inertial mass from the driven side of the clutch is added to the primary pulley side, and the large inertial mass including the primary pulley is rapidly rotated by the secondary pulley via the belt. Also, when the tires are locked, the primary pulley is in the t-3 positive state, and the primary pressure is very low. When the brake is released from this state, the primary pressure is low, and the gear quickly shifts to the lower gear side and downshifts. However, the supply of line pressure cannot keep up, and the line pressure drops momentarily, and the rise of the primary pressure is delayed, resulting in insufficient belt clamping force at the primary pulley. Due to this sudden behavior, the primary boot cannot follow immediately and the belt slips against the boot.
As a result, the durability of the belt is impaired. Furthermore, the rotation of the primary boot is delayed, and the rise of the pitot pressure is also delayed, resulting in inconveniences such as unstable gear shifting. The present invention has been made in view of the above, and its object is to change the speed of a continuously variable transmission capable of preventing tire locking during braking on low μ roads and belt slipping when the brakes are subsequently released. The purpose is to provide a control device.

[Means to solve the problem]

In order to achieve the above object, the speed change control device of the present invention includes a speed ratio control valve in a hydraulic control system of a continuously variable transmission to supply and drain oil to a primary cylinder. A shift lock valve is provided on the road to determine whether the tires are locked during braking on a low μ road, and when the tires are locked, the shift lock valve is closed to maintain the primary pressure in the primary cylinder at a high pressure.

[For production]

Based on the above configuration, the primary pressure in the primary cylinder is controlled to a high pressure by the gear ratio control valve to upshift to a high speed gear, and at this time, if the pitot pressure abnormally decreases from a normal relatively high state, it is determined that the tire is locked. . When the tires are locked, the shift lock valve shuts off the drain oil passage of the gear ratio control valve and maintains the primary pressure at a high pressure. When the brakes are released, the tires are unlocked and the pulleys and belts are turned rapidly. To rotate a primary boot by a belt without causing belt slip when carrying the vehicle. Further, after the pitot pressure is restored, the shift lock valve opens and draining of the primary pressure resumes, returning to the normal state.

【Example】

Embodiments of the present invention will be specifically described below based on the drawings. Referring to FIG. 1, a belt-type continuously variable transmission based on a front engine/front drive (FF) with a transverse transaxle and an electromagnetic clutch will be described. The symbol 1 is an electromagnetic clutch, 2 is a forward/reverse switching device, 3 is a continuously variable transmission, and 4 is a front differential device. An electromagnetic powder type clutch l is housed in one side of the clutch housing 6, and a main case 7 is connected to the other side of the clutch housing 6, and a side of the main case 7 that is connected to the side opposite to the clutch housing 6 is connected to the other side of the clutch housing 6. Inside the case 8, a forward/reverse switching device 2. Continuously variable speed #13. A fan differential device 4 is housed. The electromagnetic powder clutch 1 includes a ring-shaped drive member 12. which is integrally connected to the crankshaft lO of the engine via a drive plate 11. A disk-shaped driven member 1 that is integrally spline-coupled to the transmission manual shaft 13 in the rotational direction.
Do 4. A coil 15 is built into the outer peripheral side of the driven member 14, and a gap 16 is formed along the circumference between both members 12, 14, and the electromagnetic powder is contained in this gap 16. In addition, a power supply brush 9 is in contact with the slip ring 18 of the hub portion of the driven member 14 equipped with the coil 15, and is connected from the slip ring 18 through the inside of the driven member I4 to the coil I5 to form a clutch current circuit ( In this way, when the clutch current flows through the coil 15, the drive and driven member 12.1 pass through the gap 1B.
Due to the lines of magnetic force generated between I4 and I4, electromagnetic particles are combined and accumulated in a chain in the gap G, and the resulting bonding force causes the driven member I4 to slide and integrally connect with the drive member I4, resulting in a clutch connected state. . On the other hand, when the clutch current is cut, the drive by electromagnetic powder and the coupling force between the driven member 12° and 4 are lost, resulting in a clutch disengaged state. In this case, the clutch current is controlled by switching between forward and backward movement.
If this is done in conjunction with the operation of device 2, it will change from P (parking) or N to neutral) to forward D (drive), Ds (sporty drive) or reverse R.
Automatically clutch l when switching to (reverse) range
is connected and disconnected, eliminating the need for clutch pedal operation. Next, the forward/reverse switching device 2 includes a human power shaft 13 from the clutch l and a primary shaft 20 disposed coaxially therewith.
established between. That is, a reverse drive gear 21 that also serves as a forward engaged side is formed in the human power e+b 13, and a reverse engaged side gear 22 is rotatably fitted to the primary shaft 20. ,22 power(,(Yu2
Counter gear 24 supported by 3. One gear is constructed via an idler gear 26 supported by an f-mount 25. A switching mechanism 27 is provided between the primary shaft 20 and the gears 21 and 22. The gears 21, 24, 28, 22 that are always in mesh here are the coil 1 of the clutch 1.
The switching mechanism 27 is connected to the hub 28 of the primary shaft 20 in response to the fact that the inertia mass of this part is relatively large when the clutch is disengaged.
The sleeve 29 that is spline-fitted to the synchro machine IM
11 and 5 are connected to each gear 21 and 22 through gears 30 and 31, respectively. As a result, in the neutral position of the P or N range, the sleeve 29 of the switching mechanism 27 is fitted only with the hub 28, and the primary shaft 20 is separated from the human power shaft 13. Next, when the sleeve 29 is meshed with the gear 21 side via the synchronizing mechanism 30, the primary shaft 20 is directly connected to the human power shaft 13, resulting in a forward movement state in the D or Ds range. On the other hand, when the sleeve 29 is meshed with the gear 22 side via the synchronizing mechanism 31, the human power shaft 13 is moved to the gear 21°2.
4, connected to the primary shaft 20 via 26.22,
The engine power is reversed and the R range is in reverse mode. In the continuously variable transmission 3, a secondary shaft 35 is arranged parallel to the primary shaft 20, and primary pulleys 36. A secondary pulley 37 is provided, and an endless drive belt 34 runs between both pulleys 36,37. Primary pulley 3
6. The secondary pulleys 37 are each divided into two parts, and one of the fixed pulleys 3Ga, 37a is movable to make the other movable pulleys 30b, 37b variable in the distance between the pulleys, and the movable pulleys 36b, 37b are movable. is equipped with a hydraulic servo device o, 39 which itself has a piston, and is further equipped with a movable pulley 37b of the secondary pulley 37.
A spring 40 is biased in a direction to narrow the boob interval. Further, as a hydraulic control system, it is installed next to the oil pump 4, which is the operating source, or the primary pulley 36. This oil pump 41 is a high-pressure gear pump, and the pump drive shaft 42 is connected to the primary pulley 36. It penetrates the inside of the primary partition 20 and the manpower 13 and is directly connected to the crankshaft IO, so that hydraulic pressure is constantly generated during engine operation. Then, the oil pressure of the oil pump 41 is controlled to supply and drain oil to each hydraulic servo device 38, 39, and the pulley spacing between the primary pulley 36 and the secondary pulley 37 is changed to an inverse relationship, so that the pulley 3G of the drive belt 34 , 37 are converted steplessly, and steplessly variable power is output to the secondary shaft 35. The front differential device 4 has a minimum boolean ratio of 1 for the secondary shaft 35 in view of the fact that the minimum boolean ratio on the high speed side of the continuously variable transmission 3 is very small, for example 0.5, and therefore the rotation speed of the secondary 1135 is high. Set of intermediate reduction gears 43a, 43
An output shaft 44 is connected via b. And this output?
+I+44 drive gear 45, final gear 46
meshes, differential 1m from final gear 46 4147
Through the left and right front c11 cars 111148a, 48b
Transmission is configured. In FIG. 2, □ describes the hydraulic control system of the continuously variable transmission 3. In the primary hydraulic servo device 38,
A movable pulley 36b is fitted into a cylinder 38a that is integral with the primary flap 20, and primary pressure is generated by supplying and discharging oil into the cylinder 38a. Also, secondary hydraulic servo equipment b! 139, the movable boob J37b is fitted into the cylinder 39a which is integral with the secondary fId 135, and line pressure is applied within the cylinder 39a. Here, the movable pulley 36b has a larger pressure receiving area than the movable pulley 37b, making it possible to perform speed change control using only the primary pressure. The oil pumped up from the oil reservoir 70 by the oil pump 41 is passed through the oil passage 71a to the line pressure regulating valve 90.
A line pressure oil passage 71 that is guided by the oil passage 71a and branches from the oil passage 71a.
b communicates to always introduce line pressure to the secondary cylinder 39a. An oil passage 71c branching from the oil passage 71a communicates with a gear ratio control valve 100.
An oil passage 72 communicates between the primer cylinder 38a and the primer cylinder 38a. In addition, a pitot pressure sensor 73 is installed at the primary cylinder 38a to take out a pitot pressure as a control pressure according to the engine speed during shift control after clutch engagement, and the pitot pressure from this pitot pressure sensor 73 is , line pressure regulating valve 90 . Gear ratio control well 10
Dedicated to 0. Furthermore, the engine speed is low! In contrast to the D range, which performs shift control over a wide range including 9, the hydraulic system performs shift control only in a high engine speed range and obtains the Ds range, which applies engine braking when the accelerator is released.
Line pressure 1! A relief valve 76 is provided in the drain oil passage 75a from the J adjustment valve 90, and an oil passage 75b of the Junhoho pressure circuit that branches from the upstream side of the relief valve 76 meets the select position detection valve 130, and the oil passage An oil passage 75c further branches from 75b and communicates with the engine brake actuator 140 of the gear ratio control valve 100. Oil passage 7 branching from oil passage 75a of the AjJ hydraulic pressure circuit
5d communicates with a belt lubricating nozzle 77 disposed on the inner circumference of the belt 34, an oil passage 75c communicates with an oil supply lower 8 of a bi-pressure sensor 73, and an oil passage 75c communicates with a check valve 79° oil cooler 80. It communicates with the oil sump 70 side through it. A balancer chamber 39c is provided on the side opposite to the hydraulic chamber 39b of the secondary cylinder 39a, and an outlet oil passage 81 of an oil cooler 80 communicates with the balancer chamber 39c to fill it with oil, and the centrifugal hydraulic pressure of the pressure chamber 39b is transferred to the balancer chamber. It is designed to cancel out with 39C. Further, a shift lock valve 84 equipped with a check valve 83 is provided in the middle of the drain oil passage 82 of the gear ratio control valve 100.
A pre-feeling oil passage 8 is provided between the oil passage 75b and the oil passage 75b.
5 is connected. Note that an orifice 86 is provided in the middle of each oil passage and at an opening to the atmosphere. The line pressure regulating valve 90 has a valve body 91. A sensor shoe 95 engages the primary movable pulley 3Gb to detect the actual gear ratio by pushing a spring 94 biased between the spool 92 and one bush 93 of the spool 92.
It is movably supported by a shaft tube 96 that also serves as a lubrication passage and connected to a bushing 93. In the valve body 91, the spool 9
An oil passage 7 is connected to the port 91a on the opposite side of the spring 94 of No. 2.
The pitot pressure of No. 4 acts on this port 91a, and the line pressure of the oil passage 7La acts on the adjacent port 91c via the drain port 91b. In addition, there is a port 91d for exclusive line pressure and a drain boat 91o adjacent to the port 91c. A two-stage line pressure switching boat 91r is provided on the spring 94 side adjacent to 91c. On the other hand, a line pressure two-stage switching solenoid valve 97 is provided in the line pressure oil path 7tc. This two-stage line pressure switching solenoid valve 97 is a three-way valve that selectively communicates the oil passage 98 connected to the two-stage line pressure switching port 911' with the oil passage 71c side and the drain side, and is energized. connects the oil passages 71c and 98 and connects the line pressure two-stage switching port 1-
The configuration is such that the line pressure is exclusively applied to 911', and the oil passage 98 is drained by de-energizing. In this way, the spring force of the spring 94 of the spool 92 increases as the gear ratio increases, and this spring force acts on the line pressure increasing side. Further, the line pressure of port 91c and line pressure two-stage switching port 911' acts on the line pressure decreasing side, and the line pressure is controlled by the balance between these two. The pitot pressure at the end of spool 92 acts to adjust the balance point of spool 92 as the pump outlet changes with engine speed. Therefore, the spring force F at the balance point of the spring 94 is
, line pressure PL, and the pressure receiving area difference between the boat 91c and the line pressure two-stage switching boat 91r as AL and Ac, and when the line pressure two-stage switching solenoid valve 97 is de-energized, A-L PL■F is established, and the line pressure is controlled at high pressure by PL-F/AL. Also, when the solenoid valve 97 is energized, (AL+Ac)
・PL-F is established, and the line pressure is PL-F/(AL +Ac)
Controlled by low pressure. In this way, the line pressure is controlled steplessly by a spring force that changes according to the gear ratio, and the line pressure level is controlled in two stages, low and high, by the two-stage line pressure switching solenoid valve 97, resulting in a pulley pressing force. begins to occur. Gear ratio control valve! 00, the spool 102 is attached to one side of the valve body 101 (f L,, port 1 at one end of the spool 102
Pit pressure acts on 0Ia via check valve 1 (13) or orifice 104, and low speed spring 105 and high speed spring 106 are biased on the other end. Port 1O1b in the center of spool 102 is connected to the oil passage. 72, the left and right poles l-101e, 101d
is the drain oil path 82. The primary cylinder 3 is connected to the line pressure oil passage 71c through the groove 102a of the spool 102.
Primary pressure is generated by supplying and discharging oil to 8a. The other side of the valve body 101 has a plunger 107, and one end of a rod 108 is connected to the plunger 107 with a spring 1.
09 and the roller 1 at the other end of the rod IO8.
Shift cam 11 rotates according to the accelerator opening at 08a.
0 comes into sliding contact. A guide 111 is attached to the plunger 107 and receives the spring 105, thus changing the force of the spring 105 in accordance with the rotation of the shift cam 110. Here, the plunger 107 has an oil passage 74.
The pitot pressure is guided, and the spring reaction force acting on the plunger 107 is received by the pitot pressure, and the shift cam +1
It is designed to reduce the operating force of 1. Additionally, a mechanical modulator mechanism 120 is provided between plunger 107 and spring 10B. This modulator mechanism 120 has a variable mechanism 121 between the plunger 107 and a spring receiver 112 inside the guide 111, and this variable mechanism 121 is connected to the sensor shoe 95 via a link 122. And shifting/
Is it a variable machine as you move to a high speed stage where the ratio is small? +Yi
l 21 acts as a modulator to gradually increase the force of spring 1013. In this way, the spool 102 has the pitot pressure and the shift cam 1
The force of the spring 105 is applied according to the accelerator opening degree. A predetermined primary pressure is generated by the balance between the two to determine the gear ratio, and the gear ratio is controlled to upshift to a high speed gear as the pitot pressure increases with the increase in vehicle speed. At this time, the spool 102 has a modulator Ij
lll'! 2[1 further applies the force of the spring IOG according to the la ratio, so that the engine speed gradually increases in response to an upshift to a high speed gear. The select position detection valve 130 has a valve body 131 inserted with a valve body 133 that opens a drain hole 132, and a cam 13 that rotates in accordance with the operation of the select lever IH.
5 is the contact. Here, cam 185 smell-C, D,
The N and R range positions are on the convex portion 135a, and the P and R ranges at both ends are
The range position of Ds is the fourth part 135b, and as described above, the drain hole 132 is closed in each of the N and R ranges to generate operating oil pressure. Furthermore, when the P and Ds cylinder drain holes 132 are opened, the orifice 86 prevents the oil pressure in the upstream oil passage 75a from decreasing. The engine brake actuator 140 has a piston 142 inserted into a cylinder 141.
The return spring 143 is biased to one side of the piston chamber 144, and the operating hydraulic pressure of the oil passage 75b is applied to the other piston chamber 144 via the oil passage 75c. Also, the hook 142a at the tip of the piston 142, the rod 10 of the gear ratio control valve 100,
Ds range characteristics with the push lever set to 4 between the roller bin 108b of 8 and the sensor shoe 95? iD tl
L river modification 4m +7. Eye 45 lever 14G
It is provided so that it can be centered. In this way, when there is no hydraulic pressure for operating the P and Ds cylinders, the lever 14G is swung by the hook 142a of the piston 142 to force the rod 108 (push the rod 108 by a predetermined stroke to change the speed range to the higher side of the engine speed). limited to;
This causes the Ds cylinder to act as an engine brake. In this state, when the predetermined gear ratio is reached, the lever 14
The sensor shoe 95 engages with G, and from this point forward, the sensor shoe 95 swings the lever 146 in the opposite direction as the gear ratio increases, and the piston 142 and rod 108 are sequentially pulled back to the light position. On the other hand, as a measure to prevent belt slip when the tires are locked, as already mentioned, a shift lock valve 84 with a check valve 83 integrally connected to the drain oil path 82 from the drain port l01c of the gear ratio control valve 100 is provided. ing. The check valve 83 is connected to the cylinder 84a of the shift lock valve 84.
A ball 83c biased by a spring 83b is provided inside the spool 84b which is fitted into the spool 84b to regulate the drain m of oil from the drain boat 84c. Keep it filled with oil. Further, the shift lock valve 84 is connected to the cylinder 8.
The spool 84b is movably inserted into the inside of the drain tube 4a, and the spool 84b is moved by the actuator +50 to close the drain bow 1-84c. Here, tire lock can be determined by an abnormal drop in pitot pressure at a high speed gear where the gear ratio is small, so the gear ratio detecting means 151, the pitot pressure detecting means 152 are provided, and the gear ratio detecting means 151. The pitot pressure detecting means 152 (U) is input to the tire mouth/ink determination section 153 of the control unit and determined.Then, the tire lock no. Next, the operation of the continuously variable transmission control system configured with J, j, and i will be explained. First, before the vehicle stops or the start of a shift at the beginning of running, the line pressure regulating valve 90 Pressured line pressure or oil line 711
), only the secondary cylinder 39a has 9 people, and the primary cylinder 38a has the gear ratio control valve 100.
It communicates with the drain oil passage 82 by. Therefore, in the continuously variable transmission 3, the winding (=1 diameter) of the secondary pulley 37 is the largest with respect to the primary pulley 36 of the drive belt 34, and becomes the low speed gear with the maximum gear ratio IL. When the pitot pressure rises and moves the spool 102 of the gear ratio control valve 100, and the line pressure of the oil passage 71c is supplied to the primary cylinder 38a via the oil passage 72, the primary pressure is immediately generated by the prefill action. An upshift is started.Then, as the primary pressure increases, the diameter of the winding of the drive belt 34 around the primary pulley 36 increases, and finally the speed is continuously variable to the high speed gear with the minimum gear ratio iI+. In the high speed gear, the primary cylinder 38a is supplied with oil by the gear ratio control valve 100 and the primary pressure is high, and the pitot pressure corresponding to the engine speed as well as the vehicle speed is also high, and the gear ratio and pitot pressure are used for gear ratio detection. It is detected by means 151 and pitot pressure detection means 152.Here, when the vehicle speed and wheel speed decrease substantially in agreement with each other during braking on a dry road, and the degree of pitot pressure drop is relatively small, , Control unit tire lock judgment QIN53
is considered normal. Therefore, in the shift lock valve 84, the drain boat 84C is held in an open state by the retreat of the spool 84b, and as a result, as the vehicle speed and engine speed decrease during braking, the gear ratio control valve 100 controls the primary cylinder 3.
8a communicates with the oil passage 82, the high primary pressure is immediately released from the drain boat 84c of the shift lock valve 84 via the check valve 83, resulting in a downshift. On the other hand, if the wheel speed and pitot pressure abnormally decrease during braking on a low μ road and the tires lock, the tire lock determination unit 153
It is determined that the tires are locked, and the actuator 15[1 moves the spool 84b of the shift lock valve 84 to cover the ball 83c of the check valve 83 from the outside, and operates to close the drain port 1-83d. Therefore, even if the primary cylinder 38a communicates with the drain oil passage 82, the transmission ratio control valve 100 restricts the primary pressure from leaking out, and thus the primary pressure is reduced by the broken line P' in FIG.
A high value of p is maintained. This corresponds to the fact that the primary pulley 3B, secondary pulley 37 and belt 34 are stopped and held on the high speed side due to the tire lock, and the primary pressure P°p is high even in the hydraulic control system.
The shift will be locked. When the brake is released, the wheel speed Vw recovers as shown in Fig. 3, and the secondary pulley 37 and belt 34 are rapidly rotated, but a high primary pressure P'p exists in the primary cylinder 38a. , primary pulley 3G
In order to apply a sufficient boolean pressing force to the inertia mass on the side, the primary pulley 36 is rotated by the belt 34 without slipping, and a gear ratio corresponding to this primary pressure P'p is maintained. When the pitot pressure recovers and rises due to the rotation of the primary pulley 3G, the tire lock determination section 153 of the control unit determines that the tire lock is released, and the spool 84a of the shift lock valve 84 reopens the drain boat 84c.
The primary pressure P″p is released and the downshift starts as shown at t9 in FIG. 3(d). After the tires are locked, the actual primary pulley 36 and secondary pulley
7 and the belt 34, the vehicle can be gently downshifted and returned from the high speed state immediately before the tire lock without slipping. Note that the shift lock valve and check valve may not be integrated, but may be provided separately. The shift lock valve may be opened and closed directly by electrical signals or may be operated by mechanical means. The determination of tire lock is not limited to the example.

【Effect of the invention】

As described above, according to the present invention, in the shift control of a continuously variable transmission, tire lock is determined during braking on a low-friction road, and the hydraulic control system is shift-locked to maintain the primary pressure high. , to reliably prevent belt slip when releasing the brake? 11. Furthermore, since the drain oil passage of the gear ratio control valve is temporarily blocked by the shift lock valve, the primary pressure can be maintained at a high level reliably, and it is easy to move from A1 to A1. Also, the gear ratio and pi!・Tire lock can be accurately determined based on the pressure, and even after the brake is released, there is a delayed return due to recovery of the pitot pressure, so the belt slip prevention effect is large and the speed change control can be returned smoothly.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an example of a continuously variable transmission to which the present invention is applied; Fig. 2 is a hydraulic circuit diagram showing an embodiment of the speed change control device of the present invention; Fig. 3 (a) to 0). are each RIS when the tires are locked.
FIG.

Claims (2)

[Claims] (1) In a continuously variable transmission that has a gear ratio control valve in the hydraulic control system to supply and drain oil to the primary cylinder, a shift lock valve is provided in the drain oil path of the gear ratio control valve, and a low friction path A shift control device for a continuously variable transmission, characterized in that it determines whether a tire is locked during braking, and when the tire is locked, the shift lock valve is closed to maintain the primary pressure of the primary cylinder at a high pressure. (2) The shift control device for a continuously variable transmission according to claim 1, wherein the tire lock is determined based on a decrease in pitot pressure at a gear ratio of a high speed gear, and the shift lock is released upon recovery of the pitot pressure.