GB2252369A

GB2252369A - V-belt continuously variable transmission has setting pressure dependent on torque sensor pressure and ratio

Info

Publication number: GB2252369A
Application number: GB9201707A
Authority: GB
Inventors: Norbert Indlekofer; Oswald Friedmann
Original assignee: LuK Lamellen und Kupplungsbau GmbH
Current assignee: LuK Lamellen und Kupplungsbau GmbH
Priority date: 1991-02-02
Filing date: 1992-01-27
Publication date: 1992-08-05
Anticipated expiration: 2012-01-27
Also published as: GB2252369B; DE4201692B4; IT1258849B; ITMI920199A1; JP3461846B2; JPH0579551A; DE4201692A1; FR2672364B1; FR2672364A1; GB9201707D0; ITMI920199A0

Abstract

An infinitely adjustable V-Belt continuously variable transmission has two mutually displaceable pairs of pulleys (1, 2). At least one of the pairs of pulleys is acted upon by a setting member (6). The setting member is biased by a variable and torque dependent pressure from a torque sensor (24) to tension the bolt (3). The pressure applied to the setting member is modified by device (25) responsive to the set transmission of the gearbox and the torque sensor pressure. The device (25) preferably comprises a pressure regulating valve (26) receiving the ratio via a balance arrangement. <IMAGE>

Description

2252369 Infinitely adjustable cone pulley/contact means cLearbox The

invention relates to a cone pulley/contact means gearbox with two mutually displaceable pairs of cone pulleys - one on the drive side and one on the driven side - wherein at least one of the pairs of cone pulleys can be biased by a setting member, such as a piston cylinder unit, biased with pressure medium by a torque sensor, for tensioning the contact means.

Devices of this kind are known for example from DE-PS 28 28 347 and DE-OS 35 a8 884. To produce the torque-dependent pressure at least between the drive and the pair of cone pulleys on the drive side there is a torque sensor which is designed as a valve controlled in dependence on torque. This valve is f ed by a pump and in the event of torque shocks is at least partially closed resulting in a corresponding rise in pressure in the setting members designed as piston and cylinder - of the pairs of cone pulleys and thus in a rise in the tensioning of the contact means corresponding to the torque shock. In order to adjust the valve the torque sensor has opposing pulleys provided with contact pressure curves with interposed rolling bodies which are to be braced relative to each other by the pressure produced in the valve chamber and by the pump. In the event of torque shocks from the drive side the two pulleys spread out and the axially movable pulley reduces or closes an outlet opening according to the torque shock. The drive moment is moreover transferred mechanically by the pulleys provided with the contact pressure curves, and the valve is closed and the contact pressure on the contact means, such as a chain, is adjusted corresponding to this transferred torque. Thus apart from when there are' very severe torque shocks whereby the outlet. opening can be completely closed, this valve allows a c. onstant flow, and in - 2 addition to the pressure which produces sufficient tensioning of the pressure curves to transfer the torque, an additional output must be applied by the pump corresponding to the medium f lowing through the valve under pressure, which means a permanent waste of output.

The same pump also serves to adjust the transmission ratio whereby controlled by a control valve, such as a four-way slide valve - a pressure difference is formed in the pressure chambers of the setting members and pressurised medium is accordingly supplied to the pressure chamber of the setting member s in which the higher pressure is built up, and discharged from the other.

This pump must now be designed so that on the one hand a considerably higher pressure can be produced - the torque dependent pressure requirement can be a multiple of that required to adjust the transmission - and on the other hand the pump must be designed so that it still produces a considerably high delivery in order to ensure the necessary adjustment speed of the transmission at this high pressure. These known devices are connected with a high permanent waste of output, namely proportional to the volumes conveyed at the corresponding high pressures. Furthermore with the known devices and drive units comparatively complicated and expensive means are required for control and regulation purposes.

The object of the present invention was to reduce the output loss in gearboxes of this kind whilst simultaneously increasing the service life of the gearbox, more particularly by reducing the tensioning and contact pressure between the contact means and the cone pulleys to the absolute minimum required. Furthermore an economical manufacture and optimum functioning are to be achieved. A further aim of the invention is to make the regulating and control means which are required to regulate the variator and cone pulley/contact means gearbox particularly simple and cost-effective.

This is achieved according to the invention in that with a cone pulley/contact means gearbox of the type described at the beginning special means are provided which in dependence on the set transmission of the gearbox and the pressure supplied by the torque sensor determine the pressure with which the setting member can be biased for tensioning the cone pulleys. The transmission of the gearbox or distance between the cone pulleys of at least one cone pulley pair and the pressure supplied by the torque sensor are thus used as parameters for setting the pressure with which the setting member of the at least one cone pulley pair is biased. Through the design according to the invention it can be guaranteed that the tensioning of the contact means and the contact pressure between the contact means and the cone pulleys interacting therewith can be reduced to a minimum, particularly also in the partial load area so that the losses caused by the tensioning between the contact means and the cone pulleys can be reduced to a minimum. Thus the said contact pressure can be reduced by the invention to only the amount which is absolutely necessary. The means which set or adjust the pressure for the setting member can thereby be designed so that they change by a certain factor, more particularly multiply, the pressure supplied by the torque sensor in dependence on this pressure and the set transmission. This factor is thus dependent on the set transmission, this means therefore that this factor changes with the transmission. Thus according to the invention, the pressure supplied and set by the torque sensor is corrected in dependence on this pressure by a certain percentage and then the at least one setting member of the cone pulley/ contact means gearbox is biased with the corrected pressure. Thus for example when the chain stands radially inwards on the drive side, this means therefore that a transmission is taking place slowly, the pressure supplied by the torque sensor cannot be changed, this means that the factor between the pressure supplied by the torque sensor and the pressure with which the setting member is biased, amounts to 1 and when the chain stands outside on the drive side, this means that a transmission is taking place rapidly, the pressure supplied by the torque sensor to bias the setting member can be reduced by 50% which thus means can be multiplied by the factor 0.5.

It can be particularly advantageous if the means for reducing the pressure supplied by the torque sensor comprise a pressure regulating valve such as in particular a pressure reducing valve which on one side is connected to the torque sensor and on the other is connected to the setting member and is controlled in dependence on the pressure supplied by the torque sensor and the transmission of the gearbox in order to adjust the pressure with which the setting member of at least one cone pulley pair is biased. The use of a pressure valve or pressure regulating valve as control means for regulating the pressure with which the setting member is biased allows a particularly simple and cost-effective structure of the device since the pressure supplied by the torque sensor can be used directly with the interposition of a transmission mechanism for regulating one such valve. Pressure valves designed as piston or sliding valves can be used in particularly advantageous manner. Such piston valves have the advantage that the static compressive forces which occur, ie the forces which are present as a result of pressure dif f erences in front of and behind the valve can be compensated so that then only flow forces still occur. A particularly accurate regulation of the valve is thereby possible.

It can be particularly expedient if the means by which the pressure supplied by the torque sensor is modulated have a setting member, such as a piston/cylinder unit which is fed by the torque sensor pressure and which in dependence on this pressure determines the pressure by which the setting member of at least one cone pulley pair is biased. The setting member for modulation or conversion of the pressure supplied by the torque sensor can thereby be biased directly by this pressure. This means that the pressure supplied by the torque sensor prevails in this setting member.

It can furthermore be advantageous for the function and structure of the device if the pressure regulating valve and the piston/cylinder unit influencing same forms one structural unit, thus that the piston or slider are housed in one common housing.

It can be particularly expedient if the pressure regulating valve can be operated or adjusted by the piston/cylinder unit interacting therewith with the interposition of a transmission. A transmission of this kind can advantageously have a lever which can swivel about a rotary point which shifts in dependence on the transmission of the gearbox thus in dependence on the relative position of the pulleys of at least one pulley pair. Such a swivel point can be provided in a particularly simple way on an axially movable component such as a rod or slide block which is eg axially displaced in dependence on at least one of the axially movable pulleys of the gearbox. To this end a component of this kind can be connected eg in force locking engagement, directly with one of the axially displaceable pulleys of the gearbox.

The invention can also be used in a particularly advantageous manner in cone pulley/contact means gearboxes wherein each cone pulley pair can be acted on by a setting member, such as a piston/cylinder unit biased with pressurised medium by the torque sensor in order to tension the contact means. As already described, the two setting members are thereby not biased directly by the pressure supplied by the torque sensor but this pressure is corrected in the manner according to the invention by means of the pressure supplied by the torque sensor and in dependence on the set transmission of the gearbox corresponding to the desired or required contact pressure between the cone pulleys and the contact means.

It should be mentioned that in order that the pressure supplied by the torque sensor can be adjusted by the pressure regulating valve, a certain leakage is necessary on the side of the regulated pressure, thus behind the pressure regulating valve. This leakage can be adjusted eg by means of a valve or however can occur in the or each setting member which is provided to tension the cone pulley pairs. It may be expedient if a leakage flow of about 200 ccm per minute exists per cone pulley pair.

For the functioning of the device, particularly when used in a motor vehicle, it can be particularly advantageous if the transmission change of the gearbox is controlled by pressurised means. To this end a circuit dependent at least on torque and a circuit provided for controlling the transmission can each be fed by at least one pump and at least in the case of one of the pulley pairs the axially displaceable pulley part is connected to the setting members which add the forces dependent at least on moment and the forces dependent on transmission. Reference is made to DE-P 40 36 683.9 regarding the possible arrangement and design of 7 the setting members provided on the cone pulley pairs. When using setting members which add the forces which are dependent at least on torque and the forces which are dependent on moment, it can be particularly advantageous if a pressure regulating valve is provided in the circuit dependent at least on moment.

A particularly advantageous design f or the functioning of the device can be produced if the axially displaceable pulley parts of the pulley pairs on the drive and driven sides are each provided with paral 1 el connecting setting members which add the pressure at least dependent on moment and the pressure dependent on transmission.

In the possible embodiment last described there are thus two circuits wherein the one circuit serves only to set the transmission whilst the other circuit serves to determine and adjust the contact pressure between the cone pulleys and the contact means both in dependence on torque and in dependence on transmission. Although with such a design of the invention the two pressurised medium circuits can be supplied by a single pump with two different pressure outlets, it is particularly advantageous if the two pressurised medium circuits each have their own pump. The pump provided for producing the at least moment-dependent pressure can thereby be designed so that it only supplies as much volume as can be compensated in each case by the leakage losses. However, except for the leakage, practically no hydraulic energy need be produced for the torque-proportional pressure part since, with the change of the volumes contained in the relevant at least torquedependent setting members which occurs with the transmission-dependent adjustment. the pressurised medium, such as oil need only be pumped to and fro, thus exchanged, between the setting members.

The invention will now be described with reference to Figure 1 and the modified embodiment of Figure 2.

Figure 1 shows diagrammatically a cone pulley gearbox with a pair of pulleys 1 on the drive side rotationally secured with the drive shaft I drivable by an engine, and a pair of pulleys 2 mounted rotationally secured on the driven shaft II. Each pulley pair has an axially movable pulley part la or 2a and an axial fixed pulley pair 1b and 2b. A contact means in the form of a chain 3 is provided between the two pulley pairs to transfer the torque.

A transmission-dependent f orce is applied to the axially displaceable pulley part 2a on the driven side by a plate spring unit 4 which is installed and designed so that a higher force is applied to the chain 3 when this is located in the radially inner area of the pulley pair 1 on the drive side, and a lower f orce is exerted when the chain 3 is located on the drive-side pulley pair 1 in the larger diameter range.

The plate spring unit 4 is supported by its radially outer areas against the axially movable pulley 2a and radially inwards against the axially fixed component - here called a piston 5 - of a piston/cylinder unit 6 whose axially movable and rotatable cylinder part 7 is fixedly connected to the axially displaceable pulley part 2a.

With the pulley pair 1 on the drive side the axially movable pulley la is likewise connected to a rotating and axially movable cylinder part 8 of a piston/cylinder unit 9 whose co-rotating but axially fixed piston part is designed here as a ring piston 10.

A radially inner piston/cylinder 11 is connected mechanically in parallel with the piston/cylinder unit 9. The axially fixed cylinder part 12 of this unit 11 which rotates with the shaft I is fixed to the piston part 10 of the outer piston/cylinder unit 9 and its axially displaceable piston part 13 which is rotationally secured with the shaft I is fixedly connected to the cylinder part 8 of the outer piston/cylinder unit 9.

The drive shaft I drives the pump 14 which with the 10 interposition of a pressure regulating valve, which can be designed as a singleland slide valve 15 and is controlled or regulated by thp desired or required transmission ratio can convey pressurised medium through a pipe 16 into the pressure chamber 11a of the inner piston/cylinder unit 11. Depending on the position of the pressure regulating valve 15 pressurised medium can either be pumped through the pipe 16 into the pressure chamber 11a and thus the chain 3 is shifted outwards on the pulley pair 1 - against the force of the plate spring unit 4 - or however pressurised medium is supplied back through the pipe 17 into the oil sump through a corresponding positioning or regulating of the valve 15. The pump 14 sucks the pressurised medium such as oil in through a filter. A check valve 19 defining the permissible maximum pressure is mounted between the pump 14 and pressure regulating valve 15.

The pump 14 provided to adjust the transmission ratio requires considerably less output and therefore higher deliveries can be achieved than in the case of gearboxes according to the prior art since as a result of the small pressure chamber 11a this pump 14 need only supply a quarter of the volume required there.

In order to produce the pressure which is dependent on the 35 transmitted or ensuing torque the pump 20 is provided and feeds by way of the pipe 21 the pressure chamber 6a of the piston/cylinder unit 6 of the driven-side cone pulley pair 2 and the pressure chamber 9a of the radially outward piston/cylinder unit 9 of the drive-side pulley pair 1. A pipe 22 leads from the pipe 21 into the pressure chamber 24a of the torque sensor 24 which is designed as a torque controlled valve and transfers the torque directly from the drive or engine to the drive-side pulley pair 1. This torque sensor 24 has in known way (cf DE-PS 28 28 347) an axially fixed 24b and an axially displaceable cam plate 24c each with contoured run-up ramps between which there are expanding bodies in the form of balls 24d. The outlet opening 24e is closed or opened accordingly by the plate 24c acting as the control piston in dependence on the torque which arises between the two plates 24b and 24c and thus a pressure is produced in the pressure chamber 24a and in the pipes 21,22 corresponding to the torque which is arising at the torque sensor 24.

A check valve 20a is connected across the pump 20 in order to limit the maximum pressure.

The pressure supplied by the torque sensor 9 does not impinge directly on the pressure chambers 6a,9a of the piston/cylinder units 6 and 9 but is modulated in dependence on the adjusted transmission of the gearbox by means of a device 25. This device 25 comprises a pressure regulating valve 26 which is connected by the pipes 21,22 to the pressure chamber 24a of the torque sensor 24. The pressure regulating valve 26 is designed as a piston valve whose piston 27 is moved or adjusted in dependence on the pressure supplied by the torque sensor 24 in order to regulate the pressure which impinges on the piston/cylinder units 6 and 9. on the outlet or downstream side the pressure regulating valve 26 is connected to the pressure chambers 6a,9a by pipes 28,29. The outflow and inflow sides of the pressure regulating valve 26 are connected together by a non-return valve 30. This non-return valve 30 is thereby mounted so that it closes in the direction from the inflow side to the outflow side. In the illustrated embodiment the non-return valve 30 is provided between the pipe 22 pressurised directly from the torque sensor 24, and the pipes 28,29.

In order to modulate or alter, more particularly reduce, the pressure supplied from the torque sensor 24 by means of the pressure regulating valve 27 to the required or desired pressure which impinges on the cylinder/piston units 6 and 9, the device 25 has a setting member in the form of a piston/cylinder unit 31 whose pressure chamber is is pressurised directly with the pressure supplied by the torque sensor 24. The cylinder/piston unit 31 acts on the pressure regulating valve 26 by a transmission mechanism in the form of a lever system 32.

The lever mechanism 32 has a lever 33 which on one side is biased by the piston 31a of the piston/cylinder unit 31 and on the other is supported on the displaceable component which sets the pressure, namely on the piston 27 of the pressure regulating valve 26. The lever 33 serves as the transmission lever. To this end the lever is mounted to swivel about a rotary point 34. The fulcrum 34 is displaceable between the point of attachment 33a with the piston 31a and the support point 36 on the valve piston 27. The fulcrum 34 for the lever 33 shifts in dependence on the change in the gearbox transmission so that the transmission caused by the lever 33 is in dependence on the set transmission ratio between the pulley pair 1 provided on the drive shaft I and the pulley pair 2 provided on the driven shaft II. In the illustrated embodiment the fulcrum 34 is provided on a further lever 35 which can be connected in f orce-locking engagement to the axially displaceable pulley 2a on the driven shaft II and can thus be displaced synonymously with the axial displacement of the cone pulley 2a.

The pressure supplied by the torque sensor 24 can be modulated, more particularly reduced, by the device 25 in dependence on the set gearbox transmission.

The f actor by which the pressure set and supplied by the torque sensor for impinging on the setting members 6,9 is corrected is dependent on the transmission ratio set by the lever mechanism 33+35. The one extreme position which the swivel point 34 can occupy is marked by 34a. This position 34a of the fulcrum 34 (or lever 35) corresponds to that transmission of the gearbox where the chain 3 on the pulley pair 1 is located in its radially innermost position (thus on the smallest possible radius) and on the pulley pair 2 is located radially outwards (thus on the largest possible radius). This transmission of the gearbox corresponds to the largest possible speed reduction from the drive shaft I to the driven shaft II, thus this means that the driven shaft II has a lower speed than the drive shaft I. With this transmission setting the contact pressure between the cone pulley pairs 1,2 and the chain 3 must be at its greatest in order to be able to transfer the torque arising. As can be seen from the drawing, with this transmission setting the fulcrum 34a can be located above the biasing point 33a so that the force exerted by the piston 31a has practically no effect on the pressure regulating valve 27 since in this position of the fulcrum 34a the lever 33 does not have or cannot undertake any transmission. Thus the pressure chambers 6a, 9a can be fed practically directly with the pressure supplied by the torque sensor 24.

The other extreme position of the fulcrum 34 is marked 34b. This position 34b of the fulcrum 34 corresponds to that transmission setting of the gearbox where the chain 3 is located on the largest radius on the pulley pair 1 and on the smallest radius on the pulley pair 2. With this transmission setting a speed transmission takes place from the drive shaft I to the driven shaft II which means that the driven shaft II rotates more slowly than the drive shaft I. It is evident that in the position 34b of the fulcrum 34 the lever 33 acts as a double-armed lever and the angular force exerted by the piston 31a on the lever 33 has the greatest effect on,the piston 27 of the pressure regulating valve 26. With this transmission ratio of the levers 33,35 the lowest pressure is produced according to the pressure regulating valve 26. Through the device 25 the pressure which acts on the pressure chambers 6a,9a of the piston/cylinder units 6,9 can be set in addition in dependence on transmission wherein the pressure supplied by the torque sensor 24 is used to set this also transmission dependent pressure, namely by this pressure acting by the cylinder/piston unit 31 via the lever mechanism 33+35 on the piston 27 of the pressure regulating valve 26. The ratio between the pressure supplied by the torque sensor 24 and the pressure actually arising at the piston/cylinder units 6,9 as well as the change in this ratio can be affected by a corresponding design of the piston/cylinder unit 31 of the lever 33 and lever 35.

As a result of the parallel connection of the 30 piston/cylinder unit 11 and 9 the force produced on the pulley la through the pressure set by the pressure regulating device 25 is added to the force which is produced by the transmission-dependent pressure on the piston part 13.

14 - The pump 20 for producing the torque-dependent pressure which is modified in dependence on transmission by the device 25 need only convey enough volume to compensate in each case f or the leakage losses in the pipes and the setting members 6,9 as well as the amounts flowing through the opening 24e and the volume increases which occur as the pipes or setting members expand. However except f or the leakage no hydraulic energy need be produced for this torque-proportional or torque and transmission dependent pressure part according to the device 25 since in order to compensate for the volume changes in the pressure chambers 9a and 6a connected simultaneously with the change in the transmission the pressurised medium need only be pumped to and fro, thus need only be exchanged. The capacity required for this pump 20 lies in the area of a sixth of the overall capacity required in the devices known up until now. The sum of the capacities required by the pumps 14 and 20 is therefore considerably lower.

The drive unit or gearbox is provided on the driven side, which means seen in the direction of the force flow from the engine, behind the cone pulley pair 2 with a first clutch 37 for driving the output shaft III in one direction of rotation, eg for forward travel, and with a second clutch 38 for driving the output shaft III in the other direction of rotation eg for reverse travel.

The clutch 37 comprises a driven part 37a fixed on the drive shaft II and provided with a friction surface, and a pressure plate 37b with counter friction surface wherein this pressure plate 37b is designed as a piston and is axially movable but rotationally secure on the part 37a. Furthermore the friction clutch 37 has a clutch plate 37c rotationally secured to the shaft III wherein its friction area can be clamped axially between the friction face and - is - counter friction face. A pressure chamber 37d is formed between the driven part 37a and pressure plate 37b.

The clutch 38 consists of a counter pressure plate 38a with 5 counter friction face and a pressure plate 38b with a friction surface. The counter pressure plate 38a is axially fixed and non-rotatable eg with a gearbox casing whilst the pressure plate 38b which is designed as a piston is axially displaceable but rotationally secured relative to the counter pressure plate 38a. The friction clutch 38 furthermore comprises a clutch plate 38c whose friction area can be clamped axially between the counter pressure plate 38a and the pressure plate 38b. The clutch plate 38c supports the outer gear wheel 39a of a planetary transmission 39 whose sun wheel 39b is rotationally secured with the output shaft III. The planetary gearwheels 39c which are spaced around the circumference are supported or driven by the driven part 37a of the clutch 37. The piston 38b defines a pressure chamber 38d.

The pressure plates or pistons 37b and 38b are, as known, f orced by an energy accumulator such as by a plate spring in the disengagement direction so that with a lack of pressure in the pressure chambers 37d, 38d the corresponding clutch 37,38 is completely opened whereby it is ensured that no torque and in practice also no slip moment is transferred to the corresponding clutch disc 37c,38c.

A first change-over valve 40 and a second change-over valve 30 41 are mounted in active connection between the pressure regulating valve 15 and the two clutches 37,38 in order to supply the two pressure chambers 37d and 38d. The first change-over valve 40 is connected both by a pipe 40a to the pressurised medium circuit fed by the pump 20 and by a pipe 40b to the pressurised medium circuit fed by the pump 14.

on the outlet side the change-over valve 40 is connected on the one side by a pipe 42 to the change-over valve 41 and on the other side by the pipe 16a to the pressure chamber 11a of the piston/cylinder unit 11 which influences the transmission ratio of the cone pulley gearbox. In the illustrated embodiment, the change-over valve 40 is formed by a so-called 5/2 way valve. The change-over valve 41 provided between the two clutches 36,37 and the change-over valve 40 is formed by a so-called 4/2 way valve. The clutches 37,38 can be connected by the change-over valve 40, in dependence on specific operating parameters eg of a motor vehicle fitted with such gearbox, to the pressurised medium circuit with torquedependent pressure or to the pump 14 which builds up a pressure dependent on the pressure regulating valve 15. The change-over valve 40 serves to ensure that only one of the friction clutches 37,38 can be selectively closed, thus biased with pressurised medium. It is thereby possible to choose, via the valve 41 between forward travel wherein the clutch 37 is or becomes closed, and reverse travel wherein the clutch 37 is opened andthe clutch 38 is or becomes closed. Changing over the valve 41 can be carried out directly manually or indirectly by a regulator which detects the corresponding positions of a selector lever for adjusting the operating mode of the motor vehicle.

In the drawing the valves 40,41 are located relative to the pipes connected thereto in a position which corresponds to that used for starting the drive unit or cone pulley/contact means gearbox, thus that position which is required for building up a torque f low f rom the drive shaf t I to the output shaft III, thus for introducing the torque transfer. During this torque build-up phase when introducing a forward travel the pressure chamber 37d is connected by the valve 41 and 40 to the pump 14 which builds up a pressure dependent on the regulation or control of the pressure regulating valve 15. In this starting phase the pressure regulating valve is regulated by a regulator 43 wherein this regulation can be carried out in dependence on a fuel supply regulator member, furthermore in dependence on the slip arising at the corresponding clutch and where applicable also further parameters such as engine temperature, position of the selector lever for determining the operating mode, such as eg normal travelling, sporty motoring, forward travel, reverse travel. The regulator can also comprise a processor with a memory in which the individual values for the starting phase cai be read out wherein these values, as known can be constantly updated during travel. The values can thereby correspond to a quite definite position or a quite definite operation of a member controlling the fuel supply such as the accelerator.

The pressure regulating valve 15 can be formed by a proportional valve which is supplied by the electronic regulator 43 with a voltage which as already described can be associated with various parameters which are stored or also detected in the regulator, eg when starting up. Thus for example a quite definite engine speed corresponding to the accelerator position can be regulated for starting. If the actual speed of the engine and drive shaft I is less than the ideal speed then the pressure in the pipes 16, 42 is increased by the proportional valve 15. This happens by the voltage at the electric adjustment means 15a altering accordingly so that the clutch 37 is further closed.

During the starting or torque build-up phase it is furthermore ensured by the torque sensor 24 that in the event of torque shocks or torque alterations the contact pressure force or tension force which the cone pulleys la,lb; 2a,2b exert on the chain 3 is correspondingly adjusted in order to prevent this chain 3 from slipping through. The pressure medium circuit which is dependent on the arising torque is thus regulated mechanically by itself during the starting phase, thus without any electronics and without influence from outside. This automatic regulation of the circuit which is fed by the pump 20 and which builds up a pressure which is dependent on the arising torque, makes it possible to use the pressure- proportional valve 15 which is expensive in relation to the valves 40,41 during the torque build-up phase or starting phase both f or the forward and also for the reverse travel clutch.

The design of the illustrated embodiment was based on the knowledge that when starting up the cone pulley gearbox this need not be regulated transmission-wise since during starting up and in the starting-up phase, the plate spring unit provided on the secondary or driven-side pulley pair 2, which tensions the two pulleys 2a,2b axially towards each other, ensures that the correct transmission ratio is present. With this transmission ratio the chain 3 is located on the primary-side pulley pair 1 on the smallest diameter and on the secondary- side pulley pair 2 on the largest diameter. This means that the largest speed reduction is present between the drive shaft 1 and the driven shaft 2.

After the starting phase, thus after the clutch 37 is closed, which means that there is no or only a predetermined slip in the friction clutch, eg for vibration insulation, the pressure chamber 37d of the clutch 37 is connected by switching over the valve 40 to the pressurised medium circuit which is fed by the pump 20 and builds up a pressure which is dependent on the ensuing torque. Furthermore the transmission-dependent pressure part or circuit is connected to the cylinder/piston unit 11. The valve 40 is thereby located in the position shown in the right square.

The actions or regulations described in connection with the clutch 37 also occur in connection with the clutch 38 when the valve 41 is switched over. However instead of the reverse clutch 38 other known devices can also be used to change the direction of rotation so that then the clutch 38 and the valve 41 can be dispensed with.

The change-over from the left to the right position of the valve 40 must then be carried out at the latest when the transmission of the gearbox is to be changed in the direction of the smaller reduction or greater transmission, that is in the direction of a higher number of revolutions at the shaft II and faster speed for the vehicle.

After starting up, the pressure which sets the corresponding transmission is regulated by the proportional valve 15, that is as already mentioned in dependence on the motor vehicle parameters, more particularly the engine parameters and fuel supply setting member parameters.

In the illustrated embodiment a pressure restricting valve 44 is provided on the torque sensor 24 or in the outflow circuit of the torque sensor 24 and this ensures that even in the absence of any torque a minimum pressure eg 2 bar is maintained in the circuit with torque -dependent pressure. This minimum pressure is dependent on the resetting f orce of the energy accumulator such as the plate spring which impinges in the disengagement direction on the piston or the pressure plate 37b of the clutch 37 or the piston 38b of the clutch 38. The minimum pressure which is set by the valve 44 must be sufficiently high in order to hold the starting or reverse starting clutch 47,48 in a sliding or slip position when torque = 0 so that practically no or only a predetermined torque can be transferred. It is thus ensured by the valve 44 that when practically torque = 0 the friction faces of the corresponding pressure plate and counter pressure plate of the clutch remain in engagement with the friction linings of the clutch plate. The advantage of the valve 44 lies in the f act that in the event of changes in load, thus when changing f rom a positive torque area to negative torque area, the corresponding clutch 37,38 does not open since the pump 20 must bridge the pressure valve 44 which sets a minimum pressure and thus a sufficiently high pressure is present to keep the correspondingly engaged clutch partially closed. The closing force which arises at the clutch 37 or 38 when torque = 0 can be selected so that no or only a very slight or average torque is transferred which is sufficiently small to filter torque peaks or vibration peaks by slipping the clutch between the engine and output shaft III.

According to an embodiment not illustrated, instead of using 20 a pressure regulating valve 44 which is set constant, it is also possible to use a controllable or adjustable pressure regulating valve which is regulated accordingly eg by the regulator 43 so that the minimum pressure set by the valve 44 can be correspondingly varied in dependence on specific operating parameters, such as vehicle parameters, more particularly engine parameters such as fuel supply parameters and/or oil temperature or the like. The torque which can be transferred by the clutch 37 or 38 with an ensuing torque = 0 can thereby be changed in dependence on the said operating parameters.

The starting clutch 37 and where applicable also the reverse clutch 38 can be regulated eg in a similar way or similar parameters or the same parameters can be used to regulate these clutches, as described in the German patent Application P 40 11 850.9 wherein it should be taken into account however that in the case of the said application a hydraulic pressure must be built up in order to disengage the clutches whereas with the embodiment of the present invention described the clutch or clutches are closed by the hydraulic pressure.

The pumps 14,20 can be driven by the engine, such as an internal combustion engine, which drives the drive shaft 1.

In many cases it can however also be expedient if at least one of the pumps 14,20 has its own drive motor such as an electric motor. " The electric motor can thereby be controlled or regulated in dependence on specific operating parameters eg of a vehicle or internal combustion engine so that the operating point of the pump can also be altered which means that the delivery volume or pressure of the pump can be influenced.

In the embodiment described according to Figure 1 an energy 20 accumulator in the form of a plate spring unit 4 is provided on the driven side pulley pair 2 to produce a transmissiondependent force. This energy accumulator 4 can however be replaced by a piston/cylinder unit which is designed and arranged on the pulley pair 2 in a similar way to the piston/cylinder unit 11 of the pulley pair 1 provided on the drive shaft I. A design of this kind is described in connection with Figure 2 of DE Application P 40 36 683.9. The valve 36 described in this DE application would have to be provided in the present embodiment behind the valve 40, thus in the area of the pipe 16a and then a second connecting pipe would be necessary leading from this additional valve to the cylinder/piston unit of the drivenside cone pulley pair 2 which sets the transmission.

With the embodiment illustrated in Figure 1, the clutches 37,38 are impinged practically directly by the pressure supplied by the torque sensor 24. The pipe 40a which is connected to the valve 40 can however also be connected after the pressure regulating device 25 eg to the pipe 28 or 29 so that then the clutches 37,38 can be impinged with the same hydraulic pressure as the cylinder/piston units 6.9.

Figure 1 shows various oil return lines. These return lines can open into a common oil collecting receptacle or oil sump.

Instead of the setting member shown in Figure 1 in the form of a pressure regulating valve 26 which is regulated by means of the piston/cylinder unit 31 and lever mechanism 32, it is possible to use the setting member or pressure regulating valve 126 shown in Figure 2. The valve 126 can be adjusted and operated by a setting device in the form of a solenoid 131 in order to set the desired pressure by modulating the pressure supplied by the torque sensor 24.

The pressure regulating valve 126 is connected, in the same way as the valve 26 according to Figure 1, on the inf low side to the pipe 21 and on the outf low side to the pipes 28,29. With the illustrated pressure regulating valve 126 resetting takes place by mens of a spring 132. However it is also possible to use a pressure regulating valve with a combined or different resetting such as eg hydraulic resetting. It is particularly advantageous to use pressure regulating valves 126 which are designed as piston or sliding valves.

The pressure regulating valve 126 can be formed by a proportional valve wherein to adjust the required or desired pressure on the outflow side of the valve 126 the solenoid 131 is impinged with a setting value eg in the f orm of a voltage, by the regulating device which comprises an electronic unit or processor 43 (Figure 1). This setting value can be associated with various parameters or regulating and/or breakdown values which are detected and processed in the electronic unit or processor 43. The values or parameters which affect the valve 126 and are processed by the electronic unit or processor 43 comprise in particular the transmission set on the cone pulley gearbox. The oil temperature of the engine and/or of the gearbox and/or of the two hydraulic circuits which are fed by the pumps 14 and 20 according to Figure 1 can be used as further parameters. Further parameters can also be the amount of fuel supplied or the position of a fuel supply member, the engine speed, the output speed at the gearbox, the position of the selector lever for the operating mode of the vehicle fitted with a cone pulley/contact means gearbox according to the invention, and if required further parameters which have a bearing on the torque supplied by the engine and on the torque to be transferred by the cone pulley gearbox.

In a particularly advantageous way the pressure regulating valve 126 can be designed so that with a non-responding solenoid 131 the valve 126 is open so that even with a loss of control of the solenoid 131 tensioning of the cone pulley/contact means gearbox is possible and indeed the full pressure released by the torque sensor 24 is passed to the corresponding pressure chambers 6a,9a of the two cone pulley pairs 1, 2. The degree of efficiency of the gearbox is indeed thereby reduced but the torque transmission function still remains.

The solenoid 131 is connected by the conductor 133 to the regulator 43.

A sensor or scanner which interacts with at least one of the 35 axially displaceable pulleys la.1b can be used to scan the transmission ratios set by the gearbox. A sensor of this kind can be f ormed f or example by an inductive path recorder such as for example a linear potentiometer which is connected by a corresponding conductor to the electronic unit 43 and reports the relative position of at least one axially displaceable pulley relative to the fixed pulley.

Claims

PATENT CLAIMS

1. Infinitely adjustable cone pulley/contact means gearbox with two mutually displaceable pairs of cone pulleys - one on the drive side and on the driven side - wherein at least one of the pairs of cone pulleys can be biased by a setting member, such as a piston/cylinder unit, itself biased with pressurised medium by a torque sensor, to tension the contact means, characterised in that means are provided which in dependence on the set transmission of the gearbox and the pressure supplied by the torque sensor determine the pressure with which the setting member can be biased.

2. cone pulley/contact means gearbox according to claim 1 characterised in that the means which determine the pressure comprise a pressure regulator valve, which on one side is connected to the torque sensor and on the other side is connected to the setting member and is regulated in dependence on the pressure supplied by the torque sensor and the transmission of the gearbox.

3. Cone pulley/contact means gearbox according to one of claims 1 or 2 characterised in that the means by which the pressure supplied by the torque sensor is modulated has a setting member such as a piston/cylinder unit, which is biased by the torque sensor pressure and which in dependence on this pressure determines the pressure with which the setting member of at least one pair of cone pulleys is biased.

4. Cone pulley/contact means gearbox according to one of claims 1 to 3 characterised in that the pressure regulator valve and the piston/cylinder unit controlling same form one structural unit.

26 -

5. Cone pulley/contact means gearbox according to one of claims 3 and 4 characterised in that the pressure regulator valve is operable by the setting member with the interposition of a transmission.

is

6. Cone pulley/contact means gearbox according to claim 5 characterised in that the transmission has a lever which can pivot about a fulcrum which shif ts in dependence on the transmission of the gearbox.

7. Cone pulley/contact means gearbox according to claim 6 characterised in that the fulcrum is provided on an axially movable structural part which is connected to one of the axially movable pulleys of the gearbox.

8. cone pulley/contact means gearbox according to one of claims 1 to 7 characterised in that each pair of cone pulleys can be acted upon by a setting member such as a piston/cylinder unit, biased with pressurised medium by the 20 torque sensor.

9. Cone pulley/contact means gearbox according to one of claims 1 to 8 characterised in that the change in transmission is controlled by the pressurised medium.

10. Cone pulley/contact means gearbox according to one of claims 1 to 9 characterised in that a circuit dependent at least on torque and a circuit provided to control the transmission can each be fed by at least one pump, and at least at one of the pairs of cone pulleys the axially movable pulley part is connected to the setting members which are at least dependent on torque and add up the forces which are dependent on transmission.

11. Cone pulley/contact means gearbox according to claim 10 characterised in that the pressure regulator valve is provided in the circuit which is at least dependent on torque.

12. Cone pulley/contact means gearbox according to one of claims 1 to 11 characterised in that the axially movable pulley parts of the pair of pulleys on the drive and driven side are each provided with the parallelconnected setting members which add the at least torque- and transmissiondependent pressure.

13. Cone pulley/contact means gearbox, according to one of claims 1 to 12 characterised in that the means which determine the pressure with which the at least one setting member of one of the pairs of cone pulleys can be acted upon, comprise a pressure regulating valve which is regulated by an adjustment device such as eg by a solenoid, wherein the adjustment device is set in dependence on the operating parameters processed by a processor.