JPH0260906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in toroidal continuously variable transmissions.

The so-called toroidal type is a rolling lubrication transmission type that includes traction disks provided on each input and output shaft and a power roller that engages with the traction disks, and transmits power from the input shaft to the output shaft via the power roller. Continuously variable transmissions have been proposed in the past. In this conventional toroidal continuously variable transmission, the traction disk and power roller are made of steel in order to improve the reliability of the contact portion and extend the service life. In order to keep the contact surface pressure between the traction disk and the power roller below a certain value and to transmit a constant power, it is necessary to increase the contact area, but it is necessary to increase the contact area by using a steel material with a high Young's modulus. As a result, the surface pressure at the contact portion between the traction disk and the power roller is reduced, and therefore, if pressed with a strong force, they will peel off at an early stage. Furthermore, if the contact surface pressure is lowered by lowering the pressing force, a large amount of power cannot be transmitted. Increasing the contact area by increasing the size of each of the traction disk and the power roller is not preferable because the result is a continuously variable transmission that is large despite its low transmission power. To solve this problem, an attempt has been made to increase the contact area by making the cross-sectional shapes of the contact portions of the traction disk and the power roller closer to each other. In order to obtain a sufficient contact area and transmit sufficient power between the traction disk and the power roller created through such an attempt, the radius a in the rotational direction of the contact ellipse and the radius b in the rotational direction of the contact ellipse must be adjusted. It was necessary to set the ratio a/b to 10 or more. However, setting a/b to 10 or more in this way results in the formation of a contact surface that extends for a long time in the direction perpendicular to the rotation, and the closest part and the farthest part of the contact surface to the rotation axis of the power roller are separated. The moving speeds of the traction disk and power roller that occur as the traction disk and power roller rotate differ considerably between the sections. This difference in moving speed causes friction loss on the contact surface, which causes deterioration of the lubricant due to an increase in the temperature of the lubricant, and also causes peeling of the contact surface, resulting in a short time between the traction disk and the power roller. This results in wear, ie, shortening the life of the continuously variable transmission. Increasing the gear ratio range of the traction disk and power roller will further increase this friction loss, so conventional continuously variable transmissions meet the requirements of being small, transmitting large power, and having a wide gear ratio range. There was nothing I could do.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of conventional toroidal continuously variable transmissions, and to provide a toroidal continuously variable transmission that has excellent power transmission efficiency and a wide shifting range.

Another object of the present invention is to provide a toroidal continuously variable transmission which is compact and has excellent durability and is not only resistant to wear but also resistant to peeling due to rolling fatigue.

In order to achieve the above object, the toroidal continuously variable transmission of the present invention has a ratio a of the radius a in the direction perpendicular to the rotation of the contact ellipse to the radius b in the rotation direction of the rolling contact surface between the traction disk and the power roller. /b
is set to be 1 or less.

When the radius ratio a/b of the contact ellipse of the rolling contact surface between the traction disk and the power roller is set to 7 or more, the spin moment at the contact surface increases and the spin loss increases. Therefore, heat generation of the lubricating oil film on the contact surface increases, and the viscosity of the lubricating oil decreases significantly. A decrease in the viscosity of the lubricating oil reduces the driving force transmitted by the lubricating oil film. If the pressing force of the power roller is increased in order to prevent a decrease in the transmitted driving force, the lubricating oil film will break and damage the traction disk and the rolling surface of the power roller. The heat generated in the lubricating oil film also accelerates the deterioration of the lubricating oil and shortens its life.

However, if the radius ratio a/b of the contact ellipse at the rolling contact surface between the traction disk and the power roller is 7 or less as in the present invention, the spin loss will be small because the spin moment at the contact surface is small. and the heat generation of the lubricating oil film is reduced. As a result of the reduction in heat generation of the lubricating oil film,
(1) The drop in viscosity of the lubricating oil is small, so large amounts of power can be transmitted. (2) The drop in viscosity of the lubricant is small, making it difficult for the oil film to break, resulting in improved durability of the traction disc and power roller. (3) Since the temperature rise of the lubricating oil is small, the lubricating oil is less likely to deteriorate and its lifespan is extended.

Furthermore, if the gear ratio range is designed to be wide, the spin loss will increase, but according to the present invention, the heat generation of the lubricating oil film is small, making it possible to have a wide gear ratio range.

In a preferred embodiment of the present invention, the traction disk and/or the power roller have a Young's modulus of 18,000 at least at the rolling contact surface.
It is preferable to use a material having a Young's modulus of Kgf/mm ² to 6000 Kgf/mm ² or a structurally equivalent Young's modulus.

In a conventional toroidal continuously variable transmission, the traction disk and power roller are made of hardened steel, and the rolling contact surfaces of the two have high rigidity, resulting in high contact surface pressure. Therefore, in order to reduce the contact pressure, the contact area is increased by reducing the difference in radius of the circular arc of the cross section of the rolling contact surface between the traction disk and the power roller that includes the rotating shaft. However, reducing the radius difference between the arcs of the cross section including the rotating shaft increases the radius ratio a/b of the contact ellipse, increases spin loss, causes heat generation in the lubricating oil film, and makes the oil film more likely to break.

However, by reducing the rigidity at the rolling contact surface between the traction disk and the power roller to correspond to the above-mentioned Young's modulus, the contact area can be increased without reducing the difference in radius of the arc of the cross section including the rotating shaft. However, the surface pressure on the rolling contact surface decreases. On the other hand, the radius ratio a/b of the contact ellipse becomes smaller, and spin loss at the contact surface decreases. Breaking of the oil film is therefore prevented.

Furthermore, when the traction disk and power roller are formed from hardened steel as in the past, even if the radius ratio a/b of the contact ellipse in the contact area between them is 7 or less, the contact surface pressure increases. This is undesirable because it tends to cause wear on the rolling surface due to breakage of the lubricating oil film and peeling due to rolling fatigue, resulting in poor durability.

The present invention will be explained in more detail below with reference to the drawings.

FIGS. 1 and 2 show a specific example of a toroidal continuously variable transmission, in which a housing 1 supports an input shaft 2 and an output shaft 3, which are opposed to each other and are freely rotatable. Inside the housing 1, traction disks 5 and 6 are fixed to the input shaft 2 and the output shaft 3, respectively. The traction disks 5 and 6 are opposed to each other and additionally form circular arc surfaces 5a and 6a of rotation, passing through the center line of rotation. In order to transmit power from the input shaft 2 to the output shaft, the rotating arcuate surfaces 5a and 6a of both disks
Power rollers 8 and 9 are arranged facing each other in the space formed between them. Power rollers 8, 9
is a disk-shaped member having a toroidal convex surface that faces and engages the rotating arc surfaces 5a and 6a, and is fixed to the shaft 10, respectively. The shaft 10 is rotatably supported by an intermediate support cylinder 12 (only the power roller 9 side is shown). The intermediate support cylinder 12 is movably supported by the outer support member 13 in the axial direction of the shaft 10, and therefore slides the shaft 10 to apply the contact pressure of the power rollers 8, 9 to the traction disks 5, 6. can be adjusted accordingly. Lubricating oil is appropriately supplied to the contact surfaces between the traction disk and the power rollers 8 and 9 by means not shown.

The outer support member 13 has an axis 1 perpendicular to the plane of the paper of FIG.
8, 19 (19 is shown only in FIG. 2) are rotatably supported by the housing 1, and the inclination of the power rollers 8, 9 with respect to the center axes of the traction disks 5, 6 can be adjusted. This allows for continuously variable speed.

Gears 21 and 22 are fixed to the shafts 18 and 19. Gears 21 and 22 engage teeth 24a and 24b formed on opposite sides of a single rack member 24, respectively. Rack member 24 can be slid by rotating handle 25 to change the inclination of the power roller to the traction disk. A rotation limiting member 2 is provided on the shaft 19 and the housing 1 to prevent the power roller from tilting excessively with respect to the traction disk.
6 and 27 are provided. A scale 28 is provided on the gear 21, and together with an index 29 on the housing side, the inclination is displayed.

Now, FIG. 3 schematically shows the main parts of the apparatus shown in FIGS. 1 and 2. In FIG. 3, the traction discs 5, 6 have a common axis of rotation I. In FIG. The center of rotation for changing the inclination of the power roller 8 (or 9) with respect to the traction disks 5, 6 is at the center Q of the circle formed by the rotating arcuate surfaces 5a, 6a. The center Q lies on a perpendicular line extending through the center point C between the traction disks 5 and 6 to the axis of rotation I. Let J be the intersection of the straight line passing through points Q and C and the circle formed by the rotating arc surfaces 5a and 6a. E is the intersection of the rotation center of the power roller 8 (or 9) and the rotation center line I of the traction disks 5 and 6. The contact point between the traction disk 5 and the power roller 8 (center point of the contact portion) is designated as O.

The toroidal continuously variable transmission diagrammed in this way can be thought of as two rotating bodies that rotate while being pressed together under a high load. Hertz's basic theory of elastic contact (Timoshenko “Theory of
According to Mcgraw Hill), it is well known that the contact area between two rotating bodies is an ellipse with major axis radius a and minor axis radius b as described above, and the average Hertzian pressure at the contact area is If pm is pm, and Fc is the pressing force between the two rotating bodies (ie, traction disk and power roller), then the relational expression pm=Fc/πab (1) holds true.

Therefore, we focused on the relationship between the radius ratio a/b of the contact ellipse and the average Hertzian pressure pm at the contact part,
When the transmission efficiency was plotted against the radius ratio a/b of the contact ellipse when the average Hertzian pressure was kept constant, the graphs shown in FIGS. 4 and 5 were obtained. Note that in both graphs, point E in Figure 3 is
The radius R 1 of the arc of the cross section that lies on the extension of the QC line and therefore includes the rotational axis of the traction disk 7 when the spin loss is maximum at gear shift _1.
(=)=50mm; Angle θ between straight line QE and QO and straight line
The angle ₀ between QJ and QO is equal, and θ = ₀ =
50°; power roller pressing force Fc = 750Kg・f; and input shaft angular acceleration w ₁ = 104.7rad/sec,
The numerical value k=JC/QJ related to the gear ratio range is 0.462 in the case of FIG. 4 and 0.3 in the case of FIG.

In Figures 4 and 5, the average Hertzian pressure
The straight lines marked with pm indicate the relationship between the contact radius a/b and the power transmission efficiency η ₀ for the same Hertzian pressure (therefore, the same contact ellipse area from equation (1)), and E = 0.6. ×10 ⁴ Kgf/mm ² ;0.8;1.0;
The curves labeled 1.2; 1.4; 1.6; 1.8; 2.1 indicate the same Young's modulus portion. Furthermore, the dashed line indicates the practical limit line.

The practical limit for this type of transmission is the power transmission efficiency η ₀ excluding power losses from wheel seals, bearings, etc.
is at least 90%, and from the viewpoint of durability, it is desirable that the average Hertzian pressure pm is 80 Kgf/mm ² or less. When the average Hertzian pressure pm exceeds 80 Kgf/ ^mm2 , the thickness of the lubricating oil film on the contact surface becomes about the roughness of the contact member, and as a result, the lubricating oil film ruptures, the contact surface wears out, and there is a risk of peeling due to rolling fatigue. be.

In a conventional transmission in which both the traction disk and power roller are made of hardened steel, the average Hertzian pressure pm must be 80 kg to achieve transmission efficiency of 90% or more.
f/mm ² , and therefore the lubricating oil film at the contact portion is likely to break and rolling fatigue occurs, making it impractical.

However, as in the present invention, if the radius ratio a/b of the contact ellipse is set to 7 or less, the transmission efficiency is 90% or more, and the contact area average Hertzian pressure pm is 80 Kgf/mm2 ^or less without worrying about breakage of the lubricating oil film. can do.

The material of the traction disk and power roller used in the present invention may be cast iron, aluminum alloy, or other materials that can be used as is.
A suitable alloy or a composite sintered material having a high surface layer density and a low internal density may be used. However, even if an apparent Young's modulus equivalent to that of, for example, an aluminum alloy could be obtained by forming the traction disk or power roller from a hollow rope with a high Young's modulus, the present invention would not be possible with such a configuration. It is not possible to transmit such high torque. In other words, in a hollow rope structure, the surface of the contact part has a high Young's modulus, so the contact part itself is difficult to deform, and in order to obtain a contact shape and area equivalent to those made of a material with a low Young's modulus, The wall thickness must be made considerably thinner to make it easier to deform overall. Therefore, the empty structure for obtaining an apparently low Young's modulus also reduces the rigidity of the traction disk or power roller, making the structure unsuitable for transmitting high torque. As described above, according to the toroidal continuously variable transmission of the present invention, even though the traction disk or the power roller is formed using a soft material with a relatively low Young's modulus, high torque is achieved. can be transmitted, and furthermore, problems such as wear and peeling of the rolling surface due to use can be prevented.

[Brief explanation of drawings]

Figure 1 is a partially cutaway diagram showing the main parts of a toroidal continuously variable transmission, Figure 2 is a partially cutaway plan view of the same machine, and Figure 3 is a schematic diagram of the toroidal continuously variable transmission. 4 and 5 are diagrams showing the relationship between the radius ratio a/b of the contact ellipse at the contact portion of the traction disk and the power roller and the transmission efficiency η ₀ ,
FIG. 6 is a diagram showing a cross-sectional structure of a power roller suitable for adjusting the apparent Young's modulus at the contact portion to a desired range. [Explanation of symbols of main parts], 2...Input shaft, 3
...Output shaft, 5, 6...Traction disk,
8, 9...Power roller.

Claims (1)

[Claims] 1. The input shaft and the output shaft each include a traction disk and a power roller that engages with the traction disk, and power is transmitted from the input shaft to the output shaft via the power roller. In the toroidal continuously variable transmission for transmitting power, the ratio a/b of the radius a in the rotational direction of the contact ellipse to the radius b in the rotational direction of the rolling contact surface of both the traction disk and the power roller is 7 or less. Further, the traction disk and/or the power roller have a Young's modulus at the rolling contact surface.
A continuously variable transmission characterized in that it is formed of a material having a power of 18,000 Kgf/mm ² to 6,000 Kgf/mm ² . 2. In claim 1, the traction disk and/or the power roller has a portion forming a rolling contact surface made of a first material having a relatively high Young's modulus, and the first material portion is a base portion. The continuously variable transmission has a composite structure with a second material portion having a relatively low Young's modulus forming the rolling contact surface, and has a structure in which a spring effect is imparted to the portion forming the rolling contact surface. 3. The continuously variable transmission according to claim 2, wherein the first material portion and the second material portion have a bonded structure. 4. The continuously variable transmission according to claim 1, wherein the traction disk and/or the power roller are made of a composite sintered material having a high density on the surface layer and a low density on the inside. 5. The continuously variable transmission according to claim 1, wherein the traction disk and/or the power roller are made of cast iron or aluminum alloy.