INFINITELY VARIABLE TRANSMISSION

Abstract: An infinitely variable transmission for a device with an internal combustion engine, provided with an endless trans­ mission member (14) which has been looped over two pul­ leys, (2,3;8,9) each having a groove situated between conical sheaves, (2,3;8,9) at least one of which in each pulley is axially displaceable through an associated hydraulic cylinder, (4, 12) and also provided with a first control valve (40) for regulation of the fluid pressure in the cylinder of the driven pulley (8,9) and in the supply line to a second control valve (20), the latter valve being intended for adjustment of the transmission ratio by regulation of the amount of fluid supplied to and dis­ charged from the cylinder (4) of the driving pulley, (2,3) wherein means (71) have been provided for the operation of the first control valve (40) which depend on the pressure of the gas drawn in by the internal- combustion engine inas­ much as upon an increase of this pressure (a lower vacuum), the fluid pressure in the cylinder (12) of the driven pulley (8,9) rises.

Description: Infinitely variable transmission The invention relates to an infinitely variable transmission for a device, for instance a vehicle, with an internal-combustion engine, provided with an endless transmission member which has been looped over two pulleys, each having a groove situated between conical sheaves, at least one of which in each pulley is axially displaceable through an associated hydraulic cylinder, and also provided with a first control valve for regulation of the fluid pressure in the cylinder of the driven pulley and in the supply line to a second control valve, the latter valve being intended for adjustment of the transmission ratio by regulation of the amount of fluid supplied to and discharged from the cylinder of the driving pulley. In such a device, which has earlier been proposed and described in the Netherlands patent application 7414914, the tension of the endless transmission member (i.e. the driving belt) is regulated separately from the adjustment of the transmission ratio by means of the first control valve. To this end, the first control valve reduces the fluid pressure which has been raised by a pump and the resultant reduced fluid pressure prevails in one of the operating cylinders for the adjustment of the tension of the driving belt. The other operating cylinder is supplied with fluid by a second control valve which transmits the reduced fluid pressure to or from that operating cylinder in order that, depending on a control signal, the transmission ratio may be asjusted by means of a certain position of the said operating cylinder. The tension in the endless transmission member must be sufficient under all conditions to transmit the torque of the engine without any slip. As this tension is, in the equilibrium position, determined in the driven pulley it is essential that the fluid pressure governing the pinching force between the pulley sheaves should at all times have a sufficient value under various conditions, of which the adjusted transmission ratio and the power to be transmitted, among other things, are significant. Accordingly, the control system provides a certain fluid pressure by means of the valves. This fluid pressure must, however, be higher than under normal, more or less constant load conditions in order to ensure non-slip operation in the case of extreme changes, for instance upon fierce acceleration if the device is intended for the propulsion of a vehicle. To safeguard against the occurrence of slip upon extreme changes, it has up to now been accepted practice to adjust the fluid pressure and hence also the pinching force in the driven pulley to a higher value than is required with the normal, more or less constant load. The tension in the transmission member (driving belt) is correspondingly higher, which may have an adverse effect on, for instance, performance and durability. It is an object of the present invention to minimize this disadvantage. A device according to the invention comprises an internal-combustion engine and an infinitely variable transmission, provided with an endless transmission member which has been looped over two pulleys, each having a groove situated between two conical sheaves, at least one of which sheaves in each pulley is axially displaceable through an associated hydraulic cylinder, and also provided with a first control valve for regulation of the fluid pressure in the cylinder of the driven pulley and in the supply line to a second control valve, the latter valve being intended for adjustment of the transmission ratio by regulation of the amount of fluid supplied to and discharged from the cylinder of the driving pulley, and is characterized in that means are provided for the operation of the first control valve which depend on the pressure of the gas drawn in by the internal-combustion engine inasmuch as upon an increase or a decrease of this pressure (a lower or a higher vacuum, respectively) the fluid pressure in the cylinder of the driven pulley rises or drops, respectively, It is known that when the fuel supply to an internal-combustion engine is increased, the pressure of the gas drawn in by the engine (in the manifold) rises, which is generally denoted by the expression the vacuum becomes lower" because the pressure in the manifold is virtually always a partial vacuum. It is this lowering of the vacuum which is utilized in a device according to the invention. Thus there is no need to adjust the tension of the driving member to the highest requisite value (for instance, with fierce accelaeration). According to the invention, the tension of the driving member can be allowed to depend on the instantaneous load, with the vacuum being used as a signal The conversion of this pressure in the engine manifold into a pressure rise or drop, respectively, for the driven pulley can be realized in several ways. Preferably, however, use is made of a third control valve which incorporates a sleeve that is moveable under the influence of a change in the pressure of the gas drawn in by the engine (partial vacuum), the said sleeve closing or opening ports in the fluid circuit supplying the pressure for operation of the first valve. The invention will now be elucidated with reference to a drawing of an embodiment with a third control valve. The embodiment schematically represented in the drawing comprises a primary or input shaft 1 provided with a fixed sheave and an axially displaceable conical sheave (2 and 3, respectively) which together form the primary pulley. Sheave 3 acts as piston of cylinder 5 which includes the cylindrical space 4 and can be displaced axially by the supply and discharge of fluid through line 6. Also present is a secondary or output shaft 7, likewise provided with a fixed and an axially displaceable conical sheave (B and 9, respectively) which together form the secondary pulley. Sheave 9 is integrally connected to cylinder 10 which accommodates piston 11 which is rigidly attached to the second ry shaft 7 so as to include the cylindrical space 12 through passage 13. A V-belt 14 has been looped round the primary and the secondary pulley. This may be, for instance, a driving belt made in a sythetic material, whether or not reinforced, or a metallic one. By the axial displacement of the conical sheaves 3 and 9 the running diameters of the drive belt 14 about the two pulleys can be changed such that the difference in rotation speed of shafts 1 and 7 can be varied infinitely. The fluid pressure in cylinder space 12 also resuits in the requisite tension being present in the driving belt 14. The embodiment further comprises a fluid pump 15 for drawing in and pressurizin fluid from a reservoir 16 via a filter 19. For sensing the actual transmission ratio, a rod 17 is provided which rests against the axially displaceable sheave 3 by means of a sensor shoe 18 under the influence of a tension spring 29. Depending on the transmission ratio, the rod 17 is displaced in axial direction. Also, a first valve 40 is present which acts as overflow valve for controlling the fluid pressure built up by pump 15, which fluid pressure also prevails in cylinder space 12. The valve 40 is fitted with an axially displaceable sleeve 41. Since this sleeve 41 is provided with a widened part 42 which is in contact with the fluid in space 43 supplied by the pump 15, a pressure build-up will cause the sleeve 41 to move to the left (in the drawing). The pressure increase in the space 43a is dependent on the position of the sleeve 70 in the control valve (third valve) 71. As appears from the drawing, this valve has ports which provide access through lines 72 and 73 to space 43a and pressure line 44, respectively. The movement of the sleeve 70 is governed by the displacement of the diaphragm 74 in chamber 75 which communicates through line 76 with the inlet manifold of the internal-combustion engine and by the difference in effective pressure area 5 of sleeve 70 itself. As a result, equilibrium is attained between the vacuum and the fluid pressure. As the throttle is opened, the gas pressure to the left of the diaphragm (lower vacuum) rises and the diaphragm moves to the right, thereby also displacing the sleeve 70 to the right. In consequence, the connection between the lines 72 and 73 is closed and port 77, which interconnects with the return line 45, is opened. The pressure in space 43a thereby drops, sleeve 41 moves to the right and the connection of line 44 to the the return line 45 in valve 40 is closed. The pressure in line 44 will then rise and hence also the pressure in cylinder 12 of the driven pulley. On account of this pressure increase, the pinching force exerted on the transmission member 14 will rise. On the diaphragm side of the sleeve 70 a chamber 80 is provided which communicates on the one hand through a narrow passage 79 with a chamber 81 and hence with line 72 which links up with space 43a and on the other hand through a line 78 with an annular chamber 82 situated on the left-hand side of valve 40. This annular chamber 82 either may be opened or closed by the cylindrical tube 83 which accommodates the spring 47 and whose diameter on the left-hand side is smaller than the bore of valve 40. The interplay of the third valve 71, the cylindrical tube 83, the annular chamber 82 and the line 78 makes it possible to obtain a greater decrease of the pinching force in the secondary pulley at low transmission ratios than at high transmission ratios. Sleeve 41, which thus controls the pressure of the fluid supplied by pump 15, is also influenced by the input speed of shaft 1. For sensing this speed, cylinder 5 is fitted with an annular channel 23 which is radially closed from the outside and which is filled with fluid from cylindrical space 4 via a passage 24. Filling may obviously also be effected from the outside via a seperate fluid supply line. By means of a pitot tube 25, the fluid in channel 23 rotating with the primary shaft 1 is converted into a fluid pressure, which is passed on through line 26 to space 46 in which the fluid pressure therefore depends on the speed of the primary shaft 1. At its other end, sleeve 41 is loaded by the compression of spring 47 which is tensioned through a rod 17 and the lever 51 rotating about axis 50, depending on the actual transmission ratio. It will be clear that in this manner the tensioning force in the drive belt 14 is controlled through the fluid pressure in the cylindrical space 12 as a function of input speed, transmission ratio and engine vacuum. The transmission ratio of the infinitely variable transmission is controlled by means of valve 20, which is provided with an axially displaceable pilot sleeve 21. On one side, pilot sleeve 21 is loaded by the fluid pressure in space 22, which fluid pressure depends on the primary or input speed of shaft 1. On the other side, pilot sleeve 21 is loaded by the compression of a spring 27 which is tensioned by means of an actuation member 28. To this end, the actuation member 28 can be displaced in axial direction by rotation about an axis 32 of a cam 31 against which cam follower 33 of the actuation member 28 rests. The control of the transmission ratio is effected as follows. As long as the transmission is in a given ratio (i.e. not the lowest or the highest transmission ratio at which one of the axially displaceable sheaves 3 and 9 rests against a stop), the pilot sleeve 21 is in an equilibrium position in which no fluid is discharged from or supplied to cylinder space 4. In this equilibrium position of the pilot sleeve 21, which is represented in the drawing, the force of spring 27 equals the force exerted by the fluid in space 22 on the pilot sleeve 21. The force of spring 27, (i.e. the rotation position of cam 31) therefore corresponds to the input speed (i.e. the fluid pressure in space 22). When the output speed (the rotation speed of shaft 7) increases at constant position of cam 31 (i.e. a constant external control signal), the transmission will shift to a lower transmission ratio (i.e. a higher gear), because a proportional rise of the input speed (of shaft 1) results in an increased fluid pressure in space 22 moving pilot sleeve 21 to tke left, so that fluid is conducted to the cylindrical space 4 through lines 44 and 6. This shifting continues until the equilibrium of the pilot sleeve 21 is restored. During this shifting, however, the fluid pressure in cylindrical space 12 is changed because the rod 17 is axially displaced, thereby influencing valve 40. The fluid pressure in space 12 is also influenced by the position of diaphragm 74, i.e. the partial vacuum in line 76. In the Netherlands patent application 165821 (published December 15, 1980) a description is given of the variation of the vacuum in the inlet manifold of an internal-combustion engine which is connected to a continuously variable transmission of the same type as described herinbefore, intended to be used for the joint control of the second control valve.

Claims: CLAIMS 1. An infinitely variable transmission for a device with an internal combustion engine, provided with an endless transmission member which has been looped over two pulleys, each having a groove situated between conical sheaves, at least one of which in each pulley is-axially displaceable through an associated hydraulic cylinder, and also provided with a first control valve for regulation of the fluid pressure in the cylinder of the driven pulley and in the supply line to a second control valve, the latter valve being intended for adjustment of the transmission ratio by regulation of the amount of fluid supplied to and discharged from the cylinder of the driving pulley, characterized in that means have been provided for the operation of the first control valve which depend on the pressure of the gas drawn in by the internal-combustion engine inasmuch as upon an increase of this pressure (a lower vacuum) the fluid pressure in the cylinder of the driven pulley rises. 2. A device according to claim 1, characterized in that the means consist of a third control valve which incorporates a sleeve that is movable under the influence of a change in the pressure of the gas drawn in by the engine, the said sleeve closing or opening ports in the fluid circuit supplying the pressure for operation of the first valve. 3. A device according to claim 2, characterized in that the valve has an additional port which can be closed or opened by the moving slieve and which communicates via a line with a port in the first valve which can be closed or opened by a movable tube which connects with the sleeve in the said valve.

Inventors: CADEE, THEODORUS PETRUS MARIA, Cadée, Theodorus Petrus Maria
Applicants: VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1985
Main classification: F16H11
IPC codes: F16H61