An element for a metallic belt in a continuously variable transmission capable of reducing misalignment while ensuring friction force in a small diameter state is provided. An element 40 for a metallic belt in a belt-type continuously variable transmission has a structure in which a side edge of the element 40 of a metallic belt 7 that contacts a drive pulley 5 and a driven pulley 8 includes: a belt radial outer portion 46b that is located on a radial outer side of the metallic belt 7 and linearly shaped to follow a radial inner portion 11a as a constant-angle inclined generatrix portion; and a belt radial inner portion 46a that is located on a radial inner side of the metallic belt 7 and curved to taper inward in the belt radial direction to gradually increase an inclination angle.

TECHNICAL FIELD

The present invention relates to an element for a metallic belt wound around a drive pulley and a driven pulley in a continuously variable transmission.

BACKGROUND ART

A belt-type continuously variable transmission including a drive pulley, a driven pulley, and a metallic belt wound around the two pulleys is conventionally known (for example, see Patent Literature 1).

FIG. 6shows a deviation Δe in longitudinal center line of a metallic belt97in a cross section including the center axes of a drive pulley98and a driven pulley95, in the case where the contact surfaces (hereafter referred to as “V surfaces”) between the respective drive pulley98and driven pulley95and the metallic belt97in the cross section are linearly shaped. As shown inFIG. 6, when the gear ratio is changed from maximum (LOW ratio) through intermediate (MID ratio) to minimum (overdrive (OD) ratio), the metallic belt97moves in the direction of the center axes of the drive pulley98and driven pulley95according to changes in width of the pulley grooves of the two pulleys98and95. Here, since the amount of movement of the metallic belt97differs between the drive pulley98side and the driven pulley95side, the deviation Δe in longitudinal center line of the metallic belt97changes in the right-left direction, and the orientation99of the metallic belt97fluctuates right and left (this deviation in longitudinal center line of the metallic belt97is hereafter referred to as “misalignment”).

If the metallic belt is misaligned in this way, uneven wear occurs in the contact surfaces (V surfaces) between the respective drive and driven pulleys and the metallic belt, or the metallic belt is twisted and as a result decreases in durability.

In Patent Literature 1, misalignment is prevented in the following manner. The inclination angle (the angle with respect to a plane perpendicular to the center axis of the pulley) of the generatrix on the outer diameter side of the pulley is set larger than the inclination angle of the generatrix on the inner diameter side of the pulley to widen the pulley groove, while the boundary portion between the outer diameter side and inner diameter side of the pulley is shaped as a smooth convex curved surface. The side edge of the body portion of each element of the metallic belt is formed in correspondence with the pulley in such a manner that the angle on the outer diameter side of the metallic belt is set to make line contact with the inner diameter side of the pulley and the angle on the inner diameter side of the metallic belt is set to make line contact with the outer diameter side of the pulley.

A continuously variable transmission in which the generatrix from the inner diameter side to outer diameter side of the pulley is a smooth curve to prevent misalignment is also known (for example, see Patent Literature 2).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In Patent Literature 1, the boundary portion is a smooth convex curved surface, but the amount of change of the angle of the generatrix in the boundary portion is large. This causes a problem in that gear change control when the element contacts the boundary portion is difficult.

In Patent Literature 2, the part of contact between the pulley and the element is point contact. This causes a problem in that the friction coefficient between the element and the pulley decreases in a small diameter state where the element contacts the inner diameter side of the pulley.

In view of the above, the present invention has an object of providing an element for a metallic belt in a continuously variable transmission capable of reducing misalignment while ensuring friction force between an element and a pulley in a small diameter state.

Solution to Problem

[1] To achieve the object stated above, the present invention is an element for a metallic belt used in a belt-type continuously variable transmission, the belt-type continuously variable transmission including: a drive pulley and a driven pulley each of which has a pulley groove defined by a fixed pulley half and a movable pulley half; and a belt including an element and wound around the pulley groove of each of the drive pulley and the driven pulley, a constant-angle inclined generatrix portion in which a generatrix is inclined at a constant angle to widen the pulley groove radially outward being formed on a radial inner side of a surface of contact, with the element, of at least the fixed pulley half out of the fixed pulley half and the movable pulley half, a curved generatrix portion in which the generatrix is curved to gradually increase an inclination angle while widening the pulley groove radially outward being formed on a radial outer side of the surface of contact, the belt-type continuously variable transmission changing a gear ratio by: moving the movable pulley half of one pulley out of the drive pulley and the driven pulley away from the fixed pulley half of the pulley to increase a width of the pulley groove of the pulley; and moving the movable pulley half of the other pulley out of the drive pulley and the driven pulley closer to the fixed pulley half of the other pulley to decrease a width of the pulley groove of the other pulley, and the element being characterized in that a belt radial outer portion of a side edge of the element of the belt that contacts the drive pulley and the driven pulley is linearly shaped to follow the constant-angle inclined generatrix portion, and a belt radial inner portion of the side edge of the element is a curved shape curved to taper inward to gradually increase an inclination angle (an inclination angle with respect to a plane perpendicular to a center axis of the pulley).

According to the present invention, in the case where the belt is wound around the pulley in a small diameter, the constant-angle inclined generatrix portion of the pulley and the linear shaped portion of the side edge of the element contact each other, where the element and the pulley are in line contact with each other. In the case where the belt is wound around the pulley in a large diameter, the curved generatrix portion of the pulley and the curved shaped portion of the side edge of the element contact each other, where the element and the pulley are in point contact with each other. The present invention can thus prevent a decrease in friction coefficient in the case where the belt is wound around the pulley in a small diameter, and a decrease in durability of the belt and the pulley due to high surface pressure.

[2] Moreover, in the present invention, it is preferable that the curved belt radial inner portion of the side edge of the element is smoothly curved from the inclination angle of the linearly shaped belt radial outer portion of the side edge of the element to an angle greater than or equal to a tangent angle of an outermost diameter in a contact range in which the pulley and the element contact each other, in an inward direction.

The side edge of a conventional element is linear. Such a conventional element has a problem of low durability because, when the generatrix of the pulley is curved, the lower end of the side edge of the element and the pulley come into point contact with each other and the lower end of the side edge of the element wears out easily.

According to the present invention, the part of contact between the element and the pulley moves with gear ratio change. This prevents the same part of the element from being in contact with the pulley for a relatively long time during gear change, thus improving the durability of the element.

[3, 5] In the case where the belt wound around the pulley is in a small diameter, the radial outer portion of the side edge of the element and the radial inner portion of the pulley come into line contact with each other. Here, a failure to properly discharge lubricating oil present between the element and the pulley causes a fluid lubrication state and puts the belt in danger of slip.

If an oil drain groove extending in a plate thickness direction of the element is formed in the linearly shaped belt radial outer portion of the side edge of the element, the lubricating oil between the element and the pulley is properly discharged (released) from the oil drain groove, so that the belt can be kept from slipping.

[4, 6] Moreover, in the present invention, it is preferable that the oil drain groove is formed in the linearly shaped portion of the element except a boundary portion between the linearly shaped portion and the curved portion of the element. With such a structure, when the part of contact between the element and the pulley changes between the linear shaped portion of the pulley and the curved portion of the pulley according to gear change, the gear change is performed smoothly.

DESCRIPTION OF EMBODIMENTS

FIG. 1shows an overall structure of a belt-type continuously variable transmission1that uses an element according to an embodiment of the present invention. The belt-type continuously variable transmission1includes: a transmission input shaft2connected to an output shaft of an engine ENG as a drive source via a flywheel damper10; a transmission counter shaft3arranged in parallel with the transmission input shaft2; a metallic belt mechanism4placed between the transmission input shaft2and the transmission counter shaft3; and a forward/backward switching mechanism20placed on the transmission input shaft2. The belt-type continuously variable transmission1is provided with a hydraulic pump30and a gear change control valve60. The hydraulic pump30transmits hydraulic oil to the gear change control valve60via an oil passage30c. The gear change control valve60is capable of adjusting/controlling the hydraulic pressure of the transmitted hydraulic oil. The gear change control valve60transmits the pressure-adjusted hydraulic oil to the metallic belt mechanism4via oil passages30dand30e. The gear change of the belt-type continuously variable transmission1is controlled in this way.

The metallic belt mechanism4includes: a drive pulley5provided rotatably on the transmission input shaft2; a driven pulley8provided on the transmission counter shaft3so as to rotate together with the transmission counter shaft3; and a metallic belt7wound around the two pulleys5and8.

The metallic belt7includes: many circularly connected elements40; and two bundles of ring50attached to the elements40in a stacked state, as shown inFIG. 2. Each element40is formed like a flat plate, and includes: a head portion41with an ear portion42extending right and left; a body portion44extending right and left over the ear portion42; and a neck portion43connecting the body portion44and the head portion41, as shown inFIG. 3.

A nose hole41ais formed on one surface of the head portion41, and a nose portion41bthat can be inserted into the nose hole41aof the adjacent element40is formed on the other surface of the head portion41. The adjacent elements40are connected to each other by the nose portion41bof one element40being fit into the nose hole41aof the other element40.

The ring50is formed by radially stacking ring-shaped endless metallic bands. The ring50is located in the space defined by the ear portion42, the neck portion43, and the body portion44on the right and left of the element40, and sandwiched between the lower edge of the ear portion42and the upper edge (a saddle surface45) of the body portion44. A V surface46shaped like a letter V so as to gradually taper inward in the belt radial direction is formed on both right and left side edges of the body portion44. The V surfaces46contact and are sandwiched between V surfaces11of the drive pulley5or the driven pulley8described later.

The drive pulley5includes: a fixed pulley half5A provided rotatably but axially non-movably on the transmission input shaft2; and a movable pulley half5B axially movable relative to the fixed pulley half5A. A drive-side cylinder chamber6is formed on the side of the movable pulley half5B, and an axial thrust (drive pulley axial thrust) for axially moving the movable pulley half5B is generated by the hydraulic pressure supplied from the gear change control valve60via the oil passage30d. A V surface11is formed in the part of contact (contact surface) of the fixed pulley half5A with the metallic belt7. The V surface11is also formed in the movable pulley half5B so as to face the fixed pulley half5A. The metallic belt7is sandwiched between the V surfaces11formed in the fixed pulley half5A and the movable pulley half5B.

The driven pulley8includes: a fixed pulley half8A arranged joined onto the transmission counter shaft3; and a movable pulley half8B axially movable relative to the fixed pulley half8A. A driven-side cylinder chamber9is formed on the side of the movable pulley half8B, and an axial thrust (driven pulley axial thrust) for axially moving the movable pulley half8B is generated by the hydraulic pressure supplied from the gear change control valve60via the oil passage30e. The V surfaces11are formed in the driven pulley8as in the drive pulley5, and the metallic belt7is sandwiched between the V surfaces11in the fixed pulley half8A and the movable pulley half8B.

As shown inFIG. 4, a radial inner portion11aof the V surface11is a constant-angle inclined generatrix portion in which the generatrix is inclined at a constant angle θ (where θ is an angle with respect to a plane perpendicular to the center axis of the pulley) so that a pulley groove5C or8C defined between the fixed pulley half5A or8A and the movable pulley half5B or8B widens radially outward. A radial outer portion11bof the V surface11is a curved generatrix portion in which the generatrix is curved so that the pulley groove5C or8C gradually widens radially outward to gradually increase the inclination angle. The inclination angle of the outermost diameter of the V surface11as the contact range that contacts the element40is θ′+Δθ where θ′=θ.

A belt radial outer portion46bof the V surface46which is the side edge of the element40is linearly shaped to follow the radial inner portion11aof the V surface11as a constant-angle inclined surface of the pulley5or8, and is set to have an inclination angle of θ. A plurality of oil drain grooves47extending in the plate thickness direction of the element40are provided in the belt radial outer portion46b. A belt radial inner portion46aof the V surface46is a shape which curves so as to come into point contact with the radial outer portion11bof the V surface11as a curved inclined surface of the pulley5or8. No oil drain groove47is provided in the boundary portion between the belt radial outer portion46band the belt radial inner portion46a.

The curved shape of the radial inner portion46aof the side edge of the element40is smoothly curved so that the inclination angle gradually changes from the inclination angle θ (θ=θ′) of the linearly shaped radial outer portion46bof the side edge of the element40to the tangent angle (θ′+Δθ) of the outermost diameter of the V surface11as the contact range in which the pulley5or8contacts the element40, inward in the belt radial direction.

The gear change control valve60controls the hydraulic pressure (pulley pressure control hydraulic pressure) supplied to the drive-side cylinder chamber6and the driven-side cylinder chamber9, as a result of which a pulley axial thrust (referred to as “slip prevention axial thrust”) for preventing the metallic belt7from slipping can be set, and the pulley widths of the drive pulley5and driven pulley8can be set variably. This enables the belt-type continuously variable transmission1to continuously change the winding radius of the metallic belt7on each of the pulleys5and8to steplessly (continuously) control the gear ratio.

The forward/backward switching mechanism20includes: a planetary gear set PGS; a forward clutch24; and a backward brake25. The planetary gear set PGS has a single pinion structure made up of: a sun gear21connected to the transmission input shaft2; a ring gear23connected to the fixed pulley half5A; and a carrier22that pivotally supports a pinion22awhich meshes with the sun gear21and the ring gear23rotatably and revolvably.

The backward brake25is capable of fixing the carrier22to and holding it in a casing Ca. The forward clutch24is capable of connecting the sun gear21and the ring gear23. When the forward clutch24is engaged, the sun gear21, the carrier22, and the ring gear23rotate together with the transmission input shaft2, and the drive pulley5is driven in the same direction (forward direction) as the transmission input shaft2. When the backward brake25is engaged, on the other hand, the carrier22is fixed to and held in the casing Ca, and the ring gear23is driven in the opposite direction (backward direction) to the sun gear21.

The planetary gear set PGS may have a double pinion structure. In such a case, the fixed pulley half5A is connected to the carrier, and the ring gear is provided with the backward brake.

Power from the engine ENG is transmitted to the transmission counter shaft3through gear change via the metallic belt mechanism4and the forward/backward switching mechanism20. The power transmitted to the transmission counter shaft3is transmitted to a differential mechanism29via a start clutch26and gears27a,27b,28a, and28b, and then transmitted from the differential mechanism29separately to right and left wheels (not shown).

The gear change control valve60controls the hydraulic pressure supply to the drive-side cylinder chamber6and the driven-side cylinder chamber9to perform gear change control, as mentioned earlier. Here, the operation of the gear change control valve60is controlled by gear change control signals CDRand CDNfrom a gear change control unit70.

The gear change control valve60has two solenoid valves for controlling the respective hydraulic pressures supplied to the drive-side cylinder chamber6and the driven-side cylinder chamber9. These solenoid valves are operated according to the gear change control signals CDRand CDNoutput from the gear change control unit70, for gear change control. The hydraulic pressures in the cylinder chambers6and9are set respectively based on the gear change control signals CDRand CDN, thus setting the drive pulley axial thrust applied to the drive pulley5and the driven pulley axial thrust applied to the driven pulley8.

For such gear change control, an engine rotation signal Ne, an engine throttle opening degree signal TH, a vehicle velocity signal V, a drive pulley rotation signal NSRobtained by a drive rotation speed detector71, and a driven pulley rotation signal NDNobtained by a driven rotation speed detector72are detected and input to the gear change control unit70.

The generatrix in the radial inner portion11aof the V surface11of the pulley5or8is linearly shaped to form a constant-angle inclined surface, and the radial outer portion46bof the V surface46of the element40is linearly shaped to follow the constant-angle inclined surface of the radial inner portion11aof the pulley5or8. This ensures a sufficient friction coefficient μ between the pulley5or8and the metallic belt7, and prevents the metallic belt7from slipping from the pulley5or8. The reason is described below.

The friction coefficient μ between the V surface11of the pulley5or8and the V surface46of the element40is not constant. The friction coefficient μ increases when the V surface11and the V surface46are in line contact with each other, and decreases when the V surface11and the V surface46are in point contact with each other.

This is because the pulley5or8and the metallic belt7are not in direct contact with each other but a reaction film (boundary film) made of an additive in lubricating oil is present in the part of contact between the pulley5or8and the metallic belt7. When the V surface11and the V surface46are in point contact with each other, the area of the part of contact is smaller than when the V surface11and the V surface46are in line contact with each other, so that the shear strength of the oil film between the V surface11and the V surface46decreases and the friction coefficient μ decreases. When the V surface11and the V surface46are in line contact with each other, the area of the part of contact is larger than when the V surface11and the V surface46are in point contact with each other, so that the shear strength of the oil film between the V surface11and the V surface46increases and the friction coefficient μ increases.

Thus, of the radial inner portion11aand radial outer portion11bof the V surface11, the radial inner portion11ain which the generatrix is linearly shaped is in line contact with the radial outer portion46bof the V surface46to increase the friction coefficient μ, and the radial outer portion11bin which the generatrix is curved, is in point contact with the radial inner portion46aof the V surface46to decrease the friction coefficient μ.

FIG. 5Ashows the state of the metallic belt7when a gear ratio i is LOW. The winding radius of the metallic belt7is small on the drive pulley5side and large on the driven pulley8side. Accordingly, the number of elements40engaging with the drive pulley5is smaller than the number of elements40engaging with the driven pulley8.

Transmission torque is given by the product of the friction force of each individual element40, the number of elements40engaging with the pulley5or8, and the distance between the axis to the winding position. On the drive pulley5side, the number of elements40engaging with the drive pulley5and the distance from the axis to the winding position are both small, which increases the friction force of each individual element40. On the driven pulley8side, on the other hand, the number of elements40engaging with the driven pulley8and the distance from the axis to the winding position are both large, which decreases the friction force of each individual element40.

Hence, whether or not a slip occurs between the pulley5or8and the metallic belt7depends on whether or not a sufficient friction coefficient μ between the radial inner portion11aof the drive pulley5and the element40is ensured, while the friction coefficient μ between the radial outer portion11bof the driven pulley8and the element40has little effect.

In this embodiment, the generatrix of the radial inner portion11aof the drive pulley5is linearly shaped, and the radial outer portion46bof the V surface46comes into line contact with the radial inner portion11aof the drive pulley5to increase the friction coefficient μ. This reliably prevents the metallic belt7from slipping. Moreover, even when the generatrix of the radial outer portion11bof the drive pulley5and the radial inner portion46aof the element40are curved to compensate for misalignment, the metallic belt7is kept from slipping because the friction force of each individual element40is small on the large diameter side.

FIG. 5Bshows the state of the metallic belt7when the gear ratio i is OD. The winding radius of the metallic belt7is small on the driven pulley8side and large on the drive pulley5side. Accordingly, the number of elements40engaging with the driven pulley8on the small diameter side is smaller than the number of elements40engaging with the drive pulley5on the large diameter side.

Transmission torque is given by the product of the friction force of each individual element40, the number of elements40engaging with the pulley5or8, and the distance between the axis to the winding position. On the driven pulley8side, the number of elements40engaging with the driven pulley8and the distance from the axis to the winding position are both small, which increases the friction force of each individual element40. On the drive pulley5side, on the other hand, the number of elements40engaging with the drive pulley5and the distance from the axis to the winding position are both large, which decreases the friction force of each individual element40.

Hence, whether or not a slip occurs between the pulley5or8and the metallic belt7depends on whether or not a sufficient friction coefficient μ between the radial inner portion11aof the driven pulley8on the small diameter side and the element40is ensured, and the friction coefficient μ between the radial outer portion11bof the drive pulley5and the element40has little effect.

In this embodiment, the generatrix of the radial inner portion11aof the driven pulley8is linearly shaped, and the radial outer portion46bof the V surface46comes into line contact with the radial inner portion11aof the driven pulley8to increase the friction coefficient μ. This reliably prevents the metallic belt7from slipping. Moreover, even when the generatrix of the radial outer portion11bof the drive pulley5and the radial inner portion46aof the element40are curved to compensate for misalignment, the metallic belt7is kept from slipping because the friction force of each individual element40is small on the large diameter side.

In the continuously variable transmission1that uses the element40according to this embodiment, in the case where the metallic belt7is wound around the pulley5or8in a small diameter, the radial inner portion11aas the constant-angle inclined generatrix portion of the pulley5or8and the belt radial outer portion46bas the linear portion of the side edge of the element40contact each other, where the element40and the pulley5or8are in line contact with each other.

In the case where the metallic belt7is wound around the pulley5or8in a large diameter, the radial outer portion11bas the curved generatrix portion of the pulley5or8and the belt radial inner portion46aas the curved shaped portion of the side edge of the element40contact each other, where the element40and the pulley5or8are in point contact with each other.

Therefore, the decrease in friction coefficient in the case where the metallic belt7is wound around the pulley5or8in a small diameter can be prevented by line contact, and the decrease in durability of the pulleys5and8and the element40due to high surface pressure occurring in point contact can be prevented by line contact.

In the case where the metallic belt7is wound around the pulley5or8in a large diameter, the part of contact between the element and the pulley moves as the gear ratio changes. This prevents the same part of the element from being in contact with the pulley for a long time during gear change, thus improving the durability of the element.

In the case where the metallic belt7wound around the pulley5or8is in a small diameter, the side edge of the element40and the radial inner portion11aof the pulley5or8come into line contact with each other. Here, a failure to properly discharge lubricating oil present between the element40and the pulley5or8causes a fluid lubrication state and puts the metallic belt7in danger of slip.

If the oil drain groove47extending in the plate thickness direction of the element40is formed in the linearly shaped radial outer portion, i.e. the belt radial outer portion46b, of the side edge of the element40, the lubricating oil between the element40and the pulley5or8is properly discharged (released) from the oil drain groove47, so that the metallic belt7can be prevented from slipping.

Moreover, in this embodiment, the plurality of oil drain grooves47are formed on the side edge of the element40, in the linearly shaped belt radial outer portion46bof the element40except the boundary portion between the linearly shaped belt radial outer portion46band the curved shaped belt radial inner portion46aof the element40. With such a structure, the part of contact between the element40and the pulley5or8smoothly changes between the radial inner portion11aand radial outer portion11bof the pulley5or8according to gear change.

DESCRIPTION OF REFERENCE NUMERALS

2: transmission input shaft

3: transmission counter shaft

4: metallic belt mechanism

5A: fixed pulley half

5B: movable pulley half

8A: fixed pulley half

8B: movable pulley half

11: V surface

21: sun gear

23: ring gear

26: start clutch

30c,30d,30e: oil passage

41: head portion

42: ear portion

43: neck portion

44: body portion

46: V surface

47: oil drain groove

60: gear change control valve

70: control unit

71: drive rotation speed detector

72: driven rotation speed detector

CDR, CDN: gear change control signal

PGS: planetary gear set

Ne: engine rotation speed signal

TH: engine throttle opening degree signal

V: vehicle velocity signal

NDR: drive pulley rotation signal

NDN: driven pulley rotation signal