WO1990011462A1

WO1990011462A1 - Continuously variable transmissions

Info

Publication number: WO1990011462A1
Application number: PCT/GB1990/000244
Authority: WO
Inventors: Forbes George De Brie Perry
Original assignee: Perry Forbes G D
Priority date: 1989-03-28
Filing date: 1990-02-15
Publication date: 1990-10-04
Also published as: EP0465477A1; AU5152390A; JPH04504895A; GB2229780A; GB8906911D0

Abstract

A toroidal race rolling traction transmission unit comprises confronting input (1) and output (2) members defining a toroidal race, a set of rollers (3) each mounted in a carriage and each engaging the input and output members, a plurality of rocker arms (13) each connected to opposite ends of a pair of carriages and each having a rotary coupling to a rotary member (5) which is rotatable to change in unison the attitudes of the rollers and thereby the transmission ratio of the unit, a support (10) for the rotary member and at least one resilient damping ring (6) which is interposed between the support and the said rotary member.

Description

CONTINUOUSLY VARIABLE TRANSMISSIONS

This invention relates to continuously variable transmissions which typically comprise two coaxial confronting discs defining a toroidal race rolling traction unit in which there is a set of rollers which engage input and output raceways and are moveable in unison to alter the alignments of the rollers and thereby the transmission ratio of the unit.

It is normal to urge the discs towards each other by a suitable end load in order to provide sufficient traction between the toroidal race of each disc and the rollers. By varying, usually in unison, the common attitude of the rollers with respect to the main, common axis of the input and output discs the transmission ratio may be changed. It is in practice necessary to change the attitude of the rollers by steering them in helical paths with respect to the discs. In a common form of construction, each roller is mounted in a carriage which has a rotary axis lying in a plane substantially normal to the main common axis of the discs. Each carriage may have its rotary axis defined by, at one end of the carriage, a sliding pivot such as a ball guide, and at the other end a spherical ball joint comprising a race and a ball which may be connected to a rocker arm which is or can be pivoted in unison with corresponding rocker arms for the other carriages. Each rocker arm has a rotary coupling to a member which is rotatable substantially coaxial with the discs to achieve a change in the attitude of the rollers and accordingly a change in the transmission ratio between the input and output discs. Toroidal race rolling traction units of the general type are described in GB 979062 and GB 1069874; an arrangement including rocker arms is described in GB 2107009.

Radial equalisation of torque between the rollers of a set in a continuously variable transmission is achieved by allowing the rocker arms to swing relative to each other under an out-of-balance roller torque reaction on the rocker ball-end, until an equal reaction feedback from each roller carriage is once more obtained. However, the roller ratio angle correction, which harmonises the distribution of torque between rollers, has a lag in operation which promotes overshoot of the correction signal and hence an oscillation about the proper position. Relative to the stationary parts, this oscillation can be seen not as a simple radial movement to a new radial position, but as a continuous circular hunting motion.

One method of damping this circular motion is disclosed in British Patent No. 1209322, where a viscous damper is used. The damper creates a resistance to movement when the rotatable member moves quickly, but provides little resistance to slow movements. The damper comprises a toroidal sheath filled with an extremely viscous material such as silicone fluid of the type in which the resistance to deformation increases with the speed of deformation. Damping is thereby achieved by obliging the circular motion to pump the viscous fluid filling around the toroidal chamber.

According to the present invention there is provided a toroidal race rolling traction transmission unit comprising confronting input and output members defining a toroidal race, a set of rollers each mounted in a respective carriage and each engaging the input and output members, a plurality of rocker arms each connected to opposite ends of a respective pair of carriages and each having a rotary coupling to a member which is rotatable to change in unison the attitudes of the rollers and thereby the transmission ratio of the unit, a support for the rotary member and a resilient damping ring which is interposed between the support and the said rotary member.

A number of preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:-

Figure 1 shows a cross-sectional view of part of a continuously variable transmission;

Figure 2 shows further details of the transmission in a section taken on the line A-A in Figure 1;

Figures 3, 4, 5, 6 and 7 show details of the ring damper in four different embodiments; and

Figure 8 shows three examples of differing shapes of groove in the locating member.

A continuously variable transmission as shown in Figure 1 and Figure 2 has an input member 1 comprising a toroidal race confronting a second output member 2, likewise comprising a toroidal race. A set of rollers 3 engage the two toroidal races, and by means of control arm 4, rotatable member 5 and rocker arms 13, the rollers can be moved between attitude 3 and attitude 3' to provide a continuously variable transmission ratio between the input and output members of the unit. A more specific description of such a transmission may be found in GB 2107009.

Eccentric oscillations of the rotatable member are damped by extracting frictional energy and material strain energy from a ring 6 of a flexible material such as synthetic rubber having a circular cross-section. The ring 6 is disposed between a grooved damper sleeve 12, which forms an extension of the rotatable member 5 and a reaction member 10 which in this embodiment is a sleeve integral with the control arm 4 and is coupled to the rotatable member 5. Off-centre circumferential motion of the rotatable member 5 not only compresses one side of the ring and releases the other, but imposes relative sliding on it since both co-operating metal damper sleeves 10 and 12 are secured against rotation, for example by keying as shown in Figure 4, or by an interference fit as shown at 14 in figure 6, of any loose sleeves.

The ring may be continuous or discontinuous, and may be of solid or annular cross-section.

The unit is held in the assembled position shown in Figure 1 by the ring 6 which is seated in corresponding grooves in the inner sleeve 10 and the outer sleeve 5. If necessary a sealing shoulder 11, see Figure 3, could be held in frictional engagement with the damper sleeve 12. Fluid maintained between the shoulder and the ring 6 would then be pumped circumferentially by the oscillation and would exert its own viscous damping effect.

Only at the central position of the damper will there be zero radial force from the flexible ring acting on the rotatable member 5. However, these off-centre forces are small relative to the torque reaction feed-back and such minor departures from exact roller torque sharing are of negligible importance.

Variations in damping effect can be obtained by varying the hardness of the flexible ring material, varying the size of the ring and its percentage deflection, or varying the initial pre-compression of the ring in its central position.

The damping effect can also be altered by changing the shape of the ring. The rate of force build-up with radial compression can be changed by using rings with different cross-sections. Figure 4 shows the use of a ring with a rectangular cross-section 7, and Figure 5 shows a ring having a triangular cross-section 8.

The shape of the supporting groove can also alter the damping effect of the ring. The three examples shown in Figure 8 of different groove angles 9, 9' and 9" will give different radial rates and frictional resistance to sliding as the ring is pressed into the groove.

One further significant alteration of the damping effect can be achieved by varying the number of rings. By way of example Figure 6, illustrates a double ring unit 15, but more than two rings could be used.

The moving sleeve may be the internal damper component with the stationary component external, or vice versa. In addition both components could have angle groove sides, or neither - in which case the ring will merely slide on its circular seating; this latter configuration is shown in Figure 7 where the flexible ring is merely supported in a location groove 16 in one of the two annular sleeves which in this case are integral with the control members and do not exist as separate components. The mode of operation is the same for all these differing shapes.

Claims

1. A toroidal race rolling traction transmission unit comprising confronting input (1) and output (2) members defining a toroidal race, a set of rollers (3) each mounted in a respective carriage and each engaging the input and output members, a plurality of rocker arms (13) each connected to opposite ends of a respective pair of carriages and each having a rotary coupling to a rotary member (5) which is rotatable to change in unison the attitudes of the rollers and thereby the transmission ratio of the unit, a support (10) for the rotary member ^• and at least one resilient damping ring (6) which is interposed between the support and the said rotary member.

2. A toroidal race rolling traction transmission unit according to claim 1 wherein the said damping ring is continuous.

3. A toroidal race rolling traction transmission unit according to claim 1 wherein the said damping ring is discontinuous.

4. A toroidal race rolling traction transmission unit according to any of the preceding claims wherein the said rotary member is rotatable to change in unison the attitudes of the rollers by means of a control arm (4) having an extension (10) substantially coaxial with the rotary member.

5. A toroidal race rolling traction transmission unit according to claim 4 wherein a sleeve (12) extends from the said rotary member, the said sleeve having at least one groove which co-operates with the said at least one damping ring, the damping ring being interposed between the said sleeve and the extension of the said control arm.

6. A toroidal race rolling traction transmission unit according to claim 4 wherein a sleeve (12) is supported on the extension of the control arm, the said sleeve having at least one groove which co-operates with the said at least one damping ring, the damping ring being interposed between the said sleeve and the said rotary member.

7. A toroidal race rolling traction transmission unit according to claim 5 or claim 6 wherein a sealing shoulder (11) is held in frictional engagement with the said sleeve and fluid is maintained between the shoulder and the said damping ring.