Continuously variable transmission provided with a roller parking zone

Generally stated, various embodiments described herein concern a toroidal CVT provided with parking zones where the rollers are brought when the CVT is powered down. More specifically, a portion of the toroidal surfaces of the disks is reserved as a parking zone therefore preventing premature wear and/or damages to the working portion of the disks.

FIELD

The present invention relates to traction drive toroidal continuously variable transmissions. More specifically, the present invention is concerned with such a transmission provided with roller parking zones to prevent possible damage to the surfaces of the working zones.

BACKGROUND

Toroidal Continuously Variable Transmissions (hereinafter generically referred to as “CVT”) are believed well known in the art. The operation of such a CVT will therefore only be briefly discussed herein.

Generally stated, a toroidal CVT is provided with a drive disk having a toroidal surface, a driven disk also having a toroidal surface facing the toroidal surface of the drive disk. Both disks being linked by rollers in contact with their respective toroidal surfaces. The angle of the rollers with respect to the drive and driven disks dictates the speed ratio between the driven and drive disks.

Often, toroidal CVTs are designed according to the so-called “dual cavity” configuration including two drive disks and a single driven disk having opposed toroidal surfaces and located between the two drive disks.

A clamping mechanism is conventionally used to bias the disks towards one another to therefore ensure that the rollers are adequately contacted by both the driving and the driven disks to thereby transfer torque therebetween. However, this clamping mechanism may cause premature wear of portions of the disks and rollers caused by vibrations to which the CVT may be subjected when the CVT is not in operation, for example during transport or maintenance thereof.

Indeed, while the CVT is in operation, a thin film of traction oil is present between the contacting surfaces of the rollers and disks. This film of oil is not maintained when the CVT is stopped or operated under low rotational speeds. Accordingly, when no oil film is present the metal-to-metal contact between the rollers and disks in conjunction with acting forces may cause damages in the form of scratches and other marks on both the disks and the rollers that may cause a premature wear of these surfaces. These forces may take the form of vibrations that occur during transportation (unit in a trailer while being transported over the road, railroad associated vibration or vibration occurring on a mobile application where the CVT is at rest while being moved from one site to another), when a unit is not operating but is positioned next to a vibration source such as an operating prime mover, or caused by the engine startup/shutdown torque spikes.

Generally speaking, the wear occurring during transport is going to be caused by fretting, which generates marks and scratches over the disk and roller surfaces and produces metallic debris. The metallic debris may enter the traction oil reservoir to thereby contaminate it and eventually cause more damages to be created on the rollers and disks. Furthermore, microstructural damage to the material may be caused, which is very difficult to detect.

DETAILED DESCRIPTION

In the present specification in the appended claims, various terminology which is directional, geometrical and/or spatial in nature such as “longitudinal”, “horizontal”, “front”, “rear”, “upwardly”, “downwardly”, etc. is used. It is to be understood that such terminology is used for ease of description and in a relative sense only and is not to be taken in any way as a limitation upon the scope of the present disclosure.

It is to be noted that the expression “damages”, when related to the disks and rollers, is to be construed herein and in the appended claims as any scratches, marks, indentations, smearing, adhesive wear, microstructural damage, plastic deformations and the like of these surfaces.

In an illustrative embodiment, there is provided a continuously variable transmission comprising:

a first disk provided with a first toroidal surface defining a first working zone and a first parking zone;

a second disk provided with a second toroidal surface defining a second working zone and a second parking zone; the second toroidal surface facing the first toroidal surface;

at least one roller in contact with both the first and second toroidal surfaces; wherein, a) when the CVT is in operation, the at least one roller is in contact with both the first and second working zones and b) when the CVT is not in operation, the at least one roller is in contact with both the first and second parking zones.

According to another aspect, there is provided a method to prevent damages to the working zones of a toroidal CVT, the method comprising:

providing a first disk having a first toroidal surface defining a first working zone and a first parking zone;

providing a second disk having a second toroidal surface defining a second working zone and a second parking zone; the second toroidal surface facing the first toroidal surface;

providing at least one roller in contact with both the first and second toroidal surfaces;

wherein, a) when the CVT is in operation, the at least one roller is maintained in contact with both the first and second working zones and b) when the CVT is not in operation, the at least one roller is maintained contact with both the first and second parking zones.

Generally stated, various embodiments described herein concern a toroidal CVT provided with parking zones where the rollers are brought when the CVT is powered down. More specifically, a portion of the toroidal surfaces of the disks is reserved as a parking zone therefore preventing premature wear and/or damage of the working portion of the disks.

Turning now toFIGS. 1 to 5of the appended drawings, which illustrate a portion of a dual-cavity toroidal CVT10according to a first illustrative embodiment. The CVT10includes a first disk12having a toroidal surface14; a second disk16having a toroidal surface18(seeFIG. 2) facing the toroidal surface14; a plurality of rollers20(only one shown for clarity purpose) in contact with both toroidal surfaces14and18.

As can be seen fromFIG. 1, the toroidal surface14is virtually divided into an outer working zone14A and an inner parking zone14B. Similarly,FIG. 2shows that the toroidal surface18is virtually divided into an inner working zone18A and an outer parking zone18B.

FIG. 2shows the rollers20of the CVT10in an overdrive position, since the disk12is the transmission input and the disk16is the transmission output. This overdrive position is a first limit of the working zone of the CVT10. It is to be noted that the rollers20contact the disks12and16at the limit of the toroidal surfaces14and18.

Similarly,FIG. 3shows the rollers20of the CVT10in an underdrive position, which is a second limit of the working zone of the CVT10. It is to be noted that the rollers20contact the disks12and16at the limit of the working zones14A and18A of the toroidal surfaces14and18.

During the CVT operation, the rollers20may be pivoted between the positions illustrated inFIGS. 2 and 3to provide a desired transmission ratio between the first disk12and the second disk16.

As can be seen fromFIG. 4, when the CVT10is not operational, the rollers20are pivoted so that they are in contact with the parking zones14B and18B of the toroidal surfaces14and18. Accordingly, should the CVT be vibrated, for example during transport, maintenance, start-up/shutdown or any other situation when the transmission isn't rotating, the working zones14A and18A of the respective toroidal surfaces14and18remain free of scratches and wear since there is no contact between the rollers20and the working zones14A and18A.

One skilled in the art will understand that the movements of the rollers are controlled by a controller (not shown) that can act on the rollers via actuators (not shown). The controller generally has inputs that are associated with the prime mover (not shown) to be in a position to know that a shut down or start-up is imminent, for example.

FIG. 5is a close-up view of the roller20in contact with the parking zone14B of the toroidal surface14.

Turning now toFIGS. 6-6Aof the appended drawings, which are close-up views similar toFIG. 5, illustrating a portion of a CVT100according to a second illustrative embodiment. It is to be noted that since the CVT100is very similar to the CVT10illustrated inFIGS. 1 to 5and described hereinabove, only the differences therebetween will be discussed hereinbelow.

Generally stated, the shape of the parking zone102B is modified with respect to the shape of the parking zone14B. More specifically, the radius of the parking zone102B is greater than the radius of the adjacent working zone102A. The transition between the radiuses of the parking and working zones being seamless.

Accordingly, as can be seen inFIG. 6A, only a portion of the roller20contacts the parking zone102B and the contacting surface of the roller20is therefore less likely to be damaged by vibration when it is parked. As a result the scratches and wear is not only controlled to be avoided on the operating surfaces of the disks but also on the surfaces of the rollers20since the potential wear and scratches will now occur on the side surface of the roller, a section that isn't used in operation.

Of course, the other disk (not shown) also has this parking zone shape.

Turning now toFIG. 7of the appended drawings, which is a close-up view similar toFIG. 5, illustrating a portion of a CVT200according to a third illustrative embodiment. It is to be noted that since the CVT200is very similar to the CVT10illustrated inFIGS. 1 to 5and described hereinabove, only the differences therebetween will be discussed hereinbelow.

Generally stated, the shape of the parking zone202B is modified with respect to the shape of the parking zone14B. More specifically, the radius of the parking zone202B is smaller than the radius of the working zone202A. The transition between the radiuses of the parking and working zones being seamless.

Accordingly, only the portions of the rollers20that are not used during operation contact the parking zone202B therefore no damage can occur on the operational portions of the roller surfaces.

Of course, the other disk (not shown) also has this parking zone shape.

Turning now toFIG. 8of the appended drawings, which is a close-up view similar toFIG. 5, illustrating a portion of a CVT300according to a fourth illustrative embodiment. It is to be noted that since the CVT300is very similar to the CVT10illustrated inFIGS. 1 to 5and described hereinabove, only the differences therebetween will be discussed hereinbelow.

Generally stated, the shape of the parking zone302B is modified with respect to the shape of the parking zone14B. More specifically, the parking zone302B has a radial offset with respect to the working zone302A. Accordingly, only a corner portion of the roller20contacts the parking zone302B. As mentioned above, this protects the roller20operating surface from being damaged by vibration when it is parked.

Of course, the other disk (not shown) also has this parking zone shape.

Turning toFIG. 9of the appended drawings, which is a close-up view similar toFIG. 5, illustrating a portion of a CVT400according to a fifth illustrative embodiment. It is to be noted that since the CVT400is very similar to the CVT10illustrated inFIGS. 1 to 5and described hereinabove, only the differences therebetween will be discussed hereinbelow.

Generally stated, the contact surface of the parking zone402B is provided with a softer metal insert404onto which the roller20is parked. Accordingly, since the metal insert404is softer that the metal forming the roller20, it is less likely that the contact surface of the roller20will be damaged by vibration when the roller20is parked. The softer material insert, for example brass, could also be replaced by a special coating or any other material (not shown) that can reduce or prevent wear between contacting surfaces. Of course, other types of materials could be made into an insert such as404.

One skilled in the art will understand that instead of having a softer metal insert404, the rollers could be made of harder metal so that any vibration occurring when the rollers are in the parking zone causes wear on the disks and not on the rollers. It is believed that a two to four Rockwell C unit (2 to 4 HRC) difference is sufficient between the materials forming the rollers and the disks.

Finally turning toFIG. 10of the appended drawings, which is a close-up view similar toFIG. 5, illustrating a portion of a CVT500according to a sixth illustrative embodiment. It is to be noted that since the CVT500is very similar to the CVT10illustrated inFIGS. 1 to 5and described hereinabove, only the differences therebetween will be discussed hereinbelow.

Generally stated, the contact surface of the parking zone502B is provided with a groove504over which the roller20is parked. Accordingly, since the working portion of the roller20is registered with the groove504when parked, it is less likely that the contact surface of the roller20will be damaged by vibration.

One skilled in the art will understand that many more elements are required for a toroidal CVT to properly operate. These elements were omitted from the present disclosure and from the appended drawings since they are not concerned with the present invention.

One skilled in the art will understand that while a dual-cavity toroidal CVT was described herein, the basic principles described herein apply to single cavity toroidal CVTs and to half toroidal CVTs.

Of course, one skilled in the art will understand that the rollers are brought in the parking zone while the disks are rotating. Similarly, the rollers are moved out of the parking zones while the disks are rotating. All under the control of the transmission electronic controller (not shown). This is interesting since, at start-up and/or shutdown of a prime mover (not shown), connected to one of the disks12and16, some harmful vibrations may be induced in the transmission by the prime mover. Since the electronic controller may be configured so as to bring and keep the rollers in the parking zones when the prime mover is starting up or shutting down, these induced vibrations are less likely to cause surface deterioration on the rollers and/or disks.

Furthermore, at start-up and/or shutdown, i.e. when the CVT is powered up or powered down, the oil film (not shown) provided on the disks to prevent premature wear thereof, may be insufficient. The electronic controller may thus be configured so as to wait for a predetermined speed to be reached after the prime mover is starting up so that an adequate oil film is present on the disks surfaces before the rollers are brought in contact with the working zones. One skilled in the art should be in a position to determine the predetermined speed according to the CVT parameters.

It is also to be noted that the disk12is viewed as an input disk and that the disk16is viewed as an output disk. Accordingly, the parking zones are provided near the center of rotation of the disk12and near the periphery of the disk16so as to park the rollers in an underdrive configuration. Should the disk12be an output disk and the disk16be an input disk, the position of the parking zones could be reversed. This underdrive parking is interesting since it minimizes the inertia viewed from the prime mover at start-up. Of course, one could decide to design a transmission where the parking zones are in an overdrive position of the rollers or elsewhere if the application requires it.

One skilled in the art will understand that the shape of the rollers20and of the toroidal surfaces14,18,102,202,302and402have been exaggerated herein for illustration purposes. It is believed that one skilled in the art will be in a position to design rollers and toroidal surfaces according to the above teachings while providing more efficient contact surfaces, for example. It is to be understood that the CVT is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The CVT is capable of other embodiments and of being practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. Hence, although the CVT has been described hereinabove by way of illustrative embodiments thereof, it can be modified, without departing from the spirit, scope and nature of the subject invention.