A method and apparatus for controlling an infinitely variabletransmission

The invention relates to a continuously variable transmission according to the preamble of patent claim 1 and a method for operating the transmission.

A continuously variable transmission of this type is known from British patent specification 1.989.227.

For certain uses of the continuously variable transmission, z. As the use in a vehicle that is driven by an internal combustion engine, very specific requirements are placed on the regulation of the transmissions of the transmission. There are z. B. a large variation of the incoming (primary) speed, and an associated variation of the torque to be transmitted and the power to be transmitted. It may be desired that a rapid change of the transmission ratio within a wide range and under heavy load transfer is possible. Of great importance is that the clamping force in the V-belt (or drive belt) is optimal and is always adapted to changing circumstances. A proper clamping force is particularly important for a good efficiency of the transfer of importance.

The invention has for its object to provide a control system for the continuously variable transmission of the type mentioned, which makes it possible to adequately maintain an optimal setting depending on the significant operating conditions, thereby achieving high efficiency and avoids excessive clamping force of the V-belt ,

The inventive solutions to this problem are the subject of claims 1 and 16. Because the regulation of the clamping force in the V-belt is separated from the setting of the transmission ratio, it is possible to always maintain the optimum operating conditions in the continuously variable transmission of the transmission.

It may be desirable for the transmission to always start at a low gear when starting a device provided with it, ie that the running diameter of the V-belt on the secondary pulley is maximum. In addition, it is desired that the V-belt - before the regulation of the transmission ratio takes effect - the required clamping force. In this connection, preferably, fluid pressure in the secondary cylinder is controlled by the first regulator valve, and the fluid supply and discharge to and from the primary cylinder are regulated by the second regulator valve. As a result, the structure of the fluid pressure by the first control valve also means that the desired low gear is maintained as long as no fluid pressure is built up in the primary cylinder.

Preferably, the second control valve is supplied with a liquid whose pressure is controlled by the first control valve. As a result, the fluid used to adjust the transmission ratio has a pressure which depends on the particular tension in the V-belt, whereby the speed at which this adjustment is made does not depend on the alternating loads on the V-belt. Because, when changing the gear ratio, the pinching force of the pulley that adjusts this gear ratio must be greater than the pinching force of the pulley that controls the clamping force in the V-belt, the effective cross section of the hydraulic cylinder-piston unit that adjusts the gear ratio will be appropriately greater as the effective cross section of the cylinder-piston unit, which regulates the clamping force in the drive belt.

So that a liquid pump with a fixed displacement can be used to supply the hydraulic control system, the first control valve is preferably designed as an overflow valve, which regulates the fluid pressure in the outgoing line of the fluid pump.

Furthermore, the fluid pressure can be regulated by the first control valve as a function of the respective transmission ratio and / or of the torque to be transmitted. In order to create a certain clamping force in the V-belt, it is necessary to move the other of the two conical disks of one of the pulleys towards one, with a force which depends on the magnitude of the belt's angle of wrap around the pulley. The greater the wrap angle, the greater the pinching force required to achieve a given belt tension. The wrap angle is directly dependent on the respective gear ratio, so that the pinching force or the regulated by the first control valve pressure can be made dependent on the gear ratio in order to control the clamping force in the belt. The fact that the pressure control of the first control valve is made dependent on the torque to be transmitted, has the purpose to increase the efficiency of the transmission in that you can tune the clamping force in the V-belt on the moment to be transmitted.

Preferably, the fluid pressure is controlled by the first control valve in dependence on the axial position of one of the sliding conical discs, which position is a direct measure of the transmission ratio, and / or in dependence on the speed of the primary pulley, which is a measure of the maximum Moment is that supplies the drive motor, z. B. when the drive motor is an internal combustion engine.

The second control valve is expediently designed as a balancing valve, by means of which liquid is supplied to and / or removed from one of the cylinders, as a function of the difference between two forces exerted on the valve.

When the transmission is driven by an internal combustion engine, the liquid supply and removal by the second control valve can be controlled in dependence on the speed of the primary pulley and on the magnitude of the pressure of the gas sucked by the engine or on the position of the gas supply valve of the engine. From the pressure of the sucked gas, or engine vacuum, which depends on the position of the gas supply valve of the internal combustion engine and the primary speed, it can be deduced whether the transmission ratio, which is provided in a vehicle driven by an internal combustion engine, needs change. If the pressure of the intake gas is relatively high, the transmission is in too high a gear and the primary speed is relatively high, so the transmission is in a too low gear,

The inventions will, with reference to the drawing, described in more detail using an exemplary embodiment.

The single figure schematically shows a continuously variable transmission usable in a vehicle driven by an internal combustion engine.

623 902

According to the figure, the transmission is provided with a primary pulley 1 and a secondary pulley 2; These V-belt pulleys each consist of two, relative to each other axially displaceable conical discs. The pulley 1 consists of a conical disc 3 which is fixedly connected to the primary shaft 7 and a conical disc 4, which is axially displaceable on the primarén. Shaft 7 is mounted, and z. B. by Keilbahnen against rotation in. secured to the primary shaft 7. Similarly, the conical disc 5 of the pulley 2 is fixedly connected to the secondary shaft 8 and is conical disc 6 axially slidable on the secondary shaft 8. A belt (V-belt) 9 runs over both pulleys.

The primary or incoming shaft 7 may, for example, be rotated by an internal combustion engine, as a result of which the secondary or outgoing shaft 8 will rotate at a rotational speed that is adjustable relative to the primary shaft 7. This speed can be adjusted by adjusting the relative distance of the discs 3, 4; 5, 6 each of the pulley 1, 2nd varies.

The reproduced in the figure setting the pulley 1, 2 corresponds to a large gear ratio of the transmission, ie, that the value of incoming speed / outgoing speed is large. The axial distance between the conical discs 3 and 4 of the pulley 1 is relatively large, while the axial distance between the conical discs 5 and 6 of the pulley 2 is relatively small.

The position of the displaceable on the respective shafts 7 and 8 conical discs 4 and 6 is hydraulically controlled by piston-cylinder units. The disk 4 of the primary pulley 1 is designed as a piston, which is in a cylinder 10 which is fixedly connected to the primary shaft 7, movable. The cylinder space 11 formed thereby is filled with hydraulic fluid which can be supplied and discharged through the channel 12 in the primary shaft 7 and the conduit 13 connected thereto.

The axially displaceable disc 6 of the secondary pulley 2 is integrally connected to a cylinder 14 which can be displaced relative to a piston 15 connected to the secondary shaft 8. By building up a fluid pressure via the line 16 in the cylinder chamber 17, the conical disc 5 is pushed, which has a pinching force of the conical discs 5, 6 on the drive belt 9 result. This pinching force causes a certain tension in the drive belt 9, which is necessary to transmit a moment.

To control the size of the fluid pressure in the cylinder chamber 17, so the size of the pinching force, a first control valve 18 is provided, the effective as overflow valve, the pressure of a 19 supplied by a pump 20 via a filter 20 from a container 21 and pressurized liquid limited , As a result, a set fluid pressure is always present in the line 16. The first control valve comprises a piston body 22 with recesses 23, which in the open position of the piston body 22 (in the figure to the right) form a passage for liquid from the line 16 to the discharge line 24.

The Äbfuhrleitung 24 is held by means of a spring-loaded check valve 25 at a low fluid pressure to be able to supply via the line 26 liquid for lubricating the drive belt 9 to the drive belt, via the line 27, if necessary, to lubricate other items via the line 28 to be able to supply a portion of the liquid via a cooler 29 and the line 30 to the container and via the line 31 to convey liquid to a radially outwardly closed annular groove 32 fixed to the cylinder 10 of the primary piston Zylihdereinheit , 10 is connected.

During the rotation of the primary pulley 1, and thus the groove 32 concentric relative to the primary shaft 7, the liquid present in the groove 32 will rotate therewith. The velocity of the liquid in the groove 32 is measured by means of a pitot tube 33, wherein a fluid pressure is built up therein, depending on the speed of the pulley 1. Via the lines 34 and 35, this pressure to the space 36 of the first control valve 18 forwarded. As the primary speed increases, the fluid pressure in the space 36 is increased, which, as shown in the figure, pushes the piston bodies 22 to the right, resulting in a reduction in fluid pressure in the conduit 16.

The piston body 22, however, undergoes a leftward force by the coil spring 37, the pressure force is influenced by a thrust member 38 which is axially displaceable over a rod 39 according to the axial displacement of the conical disc 6 of the secondary pulley 2. This is with the rod 39 a receiving member 40 is connected, which rests on a rotating flange 41 on the secondary cylinder 14. The pickup 40 is kept pushed against the flange under the action of the spring 37. As is apparent from the figure, the left-hand force on the piston body 22 is reduced when the conical disk 6 moves to the right, that is, when the relative distance of the conical disks 5, 6 of the pulley 2 is increased. This relative distance, and consequently the position of the thrust member 38, is a direct measure of the respective transmission ratio. At a large gear ratio, the thrust member 38 is shifted to the left (the position as shown in the figure), while a small gear ratio results in a shifted to the right position of the thrust member 38 and thus in a lower bias of the spring 37, so a smaller force to the left on the piston body 22, which has a liquid pressure reduction in the line 16 result. The latter has a reduction in the pinching force through the discs 5, 6 of the secondary pulley 2 on the drive belt 9 result.

As indicated above, the pinching force exerted on the drive belt 9 by the conical discs 5, 6 of the secondary pulley 2 is dependent on the primary speed and the gear ratio. The pinching force is increased by reducing the primary speed and increasing the transmission ratio.

In the continuously variable transmission, the gear ratio is regulated by fluid supply and discharge to and from the cylinder space 11 of the primary piston-cylinder unit 4,10. When liquid is supplied to the cylinder space 11, liquid pressure will be built therein and, under sufficient pressure, the piston 4 forming the conical disk 4 is moved from the primary pulley 1 to the conical disk 3, whereby the running diameter of the belt 9 on the pulley 1 is increased. Due to the substantially fixed circumferential length of the drive belt 9 and the fixed distance between the primary shaft 7 and the secondary shaft 8 while the conical discs 5 and 6 of the secondary pulley 2 are pushed apart by the drive belt 9, of course, while maintaining by the first control valve 18 regulated pinching force of these discs 5, 6. This has a reduction of the transmission ratio.

The cylinder chamber 11 is filled with liquid from the line

623 902 fed, which liquid has the regulated by the first control valve 18 pressure. Because this fluid pressure on the conical disc 4 must be able to exert a greater force than on the conical disc 6, in order. 'To be able to reduce the transmission ratio, the primary piston-cylinder unit 4.10 has a greater effective transverse surface than the secondary piston-cylinder unit.

The liquid supply and discharge to and from the cylinder chamber 11 is controlled by the second control valve 42, ver with a piston body 43, controlled. The piston body 43 is under the influence of a rightward force, which is caused by fluid pressure in the space 44, and a leftward force, which is exerted by the coil spring 45 in an equilibrium position. In this equilibrium position either liquid via the line 46, the space 47 and the lines 13 and 12 is supplied to the cylinder chamber 11, or liquid discharged via the lines 12,13, the space 47 and the line 48 to the container 21, or the amount the liquid in the cylinder chamber 11 kept constant.

The fluid pressure in the space 44 corresponds to the measured by the pitot tube 33 pressure, which is passed through the conduit 34 to the space 44. A pressure increase in the space 44, which is the result of an increase in the primary speed, has a shift of the equilibrium position of the piston body 43 to the right and thus a liquid supply or a reduced liquid discharge to or from the cylinder chamber 11 to the sequence. Fluid supply to the cylinder chamber 11 leads to a reduction of the transmission ratio. Increasing the primary speed therefore tends to reduce the gear ratio.

The coil spring 45 experiences a bias under the action of the thrust member 49 which is connected to the diaphragm 50, behind which the coil spring 51 is arranged. Thereby, the bias of the coil spring 45 can be controlled depending on the pressure difference of the gas on both sides of the diaphragm 50. The diaphragm case 53 is divided into two spaces 54 and 55 by means of the diaphragm 50. The space 55 is connected via the opening 56 with the environment and the space 54 in which the coil spring 51 is located, for. B. connected by the line 57 via a valve 58 and the line 59 to the inlet port of the internal combustion engine, which drives the transmission. When the valve 58 is open (the position as shown in the figure), the same pressure prevails in the space 54 as in the inlet port of the drive motor, resulting in a specific position of the diaphragm 50. If the pressure in the inlet port is increased during the acceleration, ie when the output power of the drive motor is increased, the diaphragm 50 will shift to the left, which will result in an increase of the leftward force on the piston body 43. This results in an increased liquid discharge from or a reduced supply of liquid to the primary cylinder chamber 11, ie a tendency to increase the transmission ratio of the transmission.

The membrane 50 is provided with a stop 52 which limits the displacement of the membrane to the right.

This ensures that a further reduction in pressure in the inlet nozzle below a predetermined value has no influence.

When the transmission is mounted in a vehicle and driven by an internal combustion engine, the valve 58 serves as a so-called mountain brake. When braking the vehicle at the engine is in the inlet port a very low¹⁰ Pressure exists while a relatively small gear ratio is desired. The valve 58 is provided with a valve body 63 which is held by the coil spring 64 in the open position (upwards in the figure), whereby the lines 57 and 59 with each other¹⁵ keep in touch. By the switch 60, the electrical winding 65 can be energized, which presses a core 66 and thus the valve body 63 against the force of the spring 64 and the mouth 67 of the conduit 59 shuts off. The line 59 is daduch on the space 62 with the line 57 in Ver²⁰ binding. The space 62 is separated by a membrane 68 from a space 69 in which atmospheric pressure prevails. By the coil spring 61, the diaphragm 68 of the second mouthpiece 70 of the conduit 59 is pushed.

When the mountain brake is switched on, ie when the brake is switched off ²⁵ Mouth 67 will fall at a low pressure in line 59, the pressure in space 62 until the diaphragm 68 is pressed against the force of the coil spring 61 so far that the mouth 70 is shut off by diaphragm 68. By switching on the mountain brake is there³⁰ limited the pressure drop of the gas in the space 54, whereby the transmission ratio of the transmission does not increase too much.

If between the transmission and the drive motor ₃₅ a clutch, for. As a centrifugal clutch or a fluid coupling, is arranged, it may be desirable to bring the transmission in a decoupled state to a halt, z. B. when the direction of rotation of the output shaft is reversed by a arranged on the outgoing or secondary shaft 8 sweeping. To the Ge^υ gear to bring to a halt, a line 71 via the valve 72 and the line 73 to a brake cylinder 74 is connected. By displacement of the actuating rod 75 with the cam surface 76, the valve rod 77 is axially displaced with the cam follower 78, whereby Flüssigkeitslg⁴⁵ keit in the line 16 can come into communication with the brake cylinder 74, in which a pressure can be built, which pushes the piston formed in the brake cylinder 74 brake shoe 79 against a brake disc forming part 80 of the conical disc 3 of the pulley 1. At a certain displacement of the actuating rod 75, which can also operate the sweeping, the transmission is brought to a standstill.

When the transmission is applied in a vehicle, the bias of the spring 45 may also depend on the ³ Position of the throttle lever of the vehicle, by a mechanical connection between the throttle lever and the piston 49th