Continuously variable transmission and a working machine including a continuously variable transmission

A continuously variable transmission includes a variator unit having a variator input shaft and a variator output shaft; a first planetary gear set having a first, a second and a third planetary member, the first planetary member being one of a ring wheel and a planet carrier, the second planetary member being the other one of the ring wheel and the planet carrier, and the third planetary member being a sun wheel, wherein the first planetary member of the first planetary gear set is operatively connected to a transmission input shaft; and a second planetary gear set having a sun wheel, a ring wheel and a planet carrier, the planet carrier being operatively connected to a transmission output shaft; wherein the variator input shaft is operatively connected to the second planetary member of the first planetary gear set; the variator output shaft is operatively connected to the sun wheel of the first planetary gear set, the sun wheel of the first planetary gear set being further operatively connected to the sun wheel of the second planetary gear set while having a variable gear ratio between the transmission input shaft and the transmission output shaft; and the ring wheel of the second planetary gear set being selectively connectable to the second planetary member of the first planetary gear set and to a gearbox housing of the continuously variable transmission.

BACKGROUND AND SUMMARY

The invention relates to a continuously variable transmission and to a working machine comprising such a continuously variable transmission.

The invention is applicable on working machines within the fields of industrial construction machines, in particular wheel loaders, graders and articulated haulers. Although the invention will be described hereinafter with respect to a wheel loader, the invention is not restricted to this particular machine, but may also be used in other heavy working machines, such as dump trucks, excavators or other construction equipments.

A continuously variable transmission is a transmission which speed ratio can be continuously varied over a designed range. Continuously variable transmissions are useful due to enabling operation of a prime mover at optimum speed or at optimum fuel economy while still providing a desired rotational speed at the output shaft of the transmission. In a continuously variable transmission a speed ratio between the output shaft speed to the input shaft speed of zero may be obtainable. Such a continuously variable transmission is usually referred to as an infinitely variable transmission. The existence of an output to input speed ratio of zero enables a geared neutral function where the input shaft is rotating when the output shaft stands still. The presence of a geared neutral position is useful in many industrial contexts, such as within gearboxes of working machines for example, since it may obviate the need of a starting clutch or a torque converter. Furthermore, infinitely variable transmissions facilitate separation of operation of a hydraulic system included for performing lifting operations and/or steering the working machine from the propulsion of the working machine, since the hydraulic system can be powered from a power take off at an input shaft, which may be kept running, while an output shaft connected to propulsion drive train can be kept at stand still. A typical arrangement of a continuously variable transmission includes a continuously variable unit, variator unit, having a variator input shaft and a variator output shaft connected to a planetary gear system.

An example of a continuously variable transmission is disclosed in U.S. Pat. No. 7,220,203. The continuously variable transmission in U.S. Pat. No. 7,220,203 comprises a battery coupled to two motor/generators, respectively.

Accordingly, the continuously variable transmission in U.S. Pat. No. 7,220,203 is an electrically continuously variable transmission. Moreover, the electrically continuously variable transmission includes an input member to receive power from an engine and an output member for transmitting torque to e.g. the wheels of a working machine. Also, the electrically continuously variable transmission comprises planetary gear sets and a plurality of clutches. An advantage with the electrically continuously variable transmission disclosed in U.S. Pat. No. 7,220,201 is that the plurality of clutches allows additional fixed speed ratios and an additional compound-power-split speed ratio range in relation to the prior art known to U.S. Pat. No. 7,120,203.

However, the continuously variable transmission disclosed in U.S. Pat. No. 7,220,203 is in need of further improvements in terms of e.g. reduced costs in terms of reduced number of components, as well as optimizing the utilization of the variator unit.

It is desirable to provide a continuously variable transmission having improved functionalities in relation to prior art solutions.

According to a first aspect of the present invention there is provided a continuously variable transmission, comprising a variator unit having a variator input shaft and a variator output shaft; a first planetary gear set having a first, a second and a third planetary member, the first planetary member being one of a ring wheel and a planet carrier, the second planetary member being the other one of the ring wheel and the planet carrier, and the third planetary member being a sun wheel, wherein the first planetary member of the first planetary gear set is operatively connected to a transmission input shaft; and a second planetary gear set having a sun wheel, a ring wheel and a planet carrier, the planet carrier being operatively connected to a transmission output shaft; wherein the variator input shaft is operatively connected to the second planetary member of the first planetary gear set; the variator output shaft is operatively connected to the sun wheel of the first planetary gear set, the sun wheel of the first planetary gear set being further operatively connected to the sun wheel of the second planetary gear set while having a variable gear ratio between the transmission input shaft and the transmission output shaft; and the ring wheel of the second planetary gear set being selectively connectable to the second planetary member of the first planetary gear set and to a gearbox housing of the continuously variable transmission.

The wording “selectively connectable” should in the following and throughout the entire description be interpreted as two or more components being arranged to be actively connected/disconnected to each other. When discussing “selectively connectable” by means of components in a planetary gear set, the connection between e.g. a sun wheel and a ring wheel via the planet wheels of a planet carrier should not be construed such as the sun wheel being connected to the ring wheel unless otherwise described, which will be discussed further below. Accordingly, in order for a component of a planetary gear set to be connected to another component of the same planetary gear set, the two components must, in order to be connectable to each other in accordance with the intended interpretation of the wording in the present application, be locked to each other in some way or another.

An advantage of the present invention is that the variator output shaft is connected to the sun wheel of the first planetary gear set and the sun wheel of the second planetary gear set, thereby providing a desired maximum speed of the variator output shaft, while having a variable gear ratio between the transmission input shaft and the transmission output shaft. Also, the continuously variable transmission comprises fewer components in relation to prior art solutions, or more specifically, the present invention is not in need of all the clutches described in the prior art.

According to an example embodiment, a first clutch unit may be arranged between the second planetary member of the first planetary gear set and the ring wheel of the second planetary gear set, and a second clutch unit may be arranged between the ring wheel of the second planetary gear set and the gearbox housing.

Hereby, the first clutch unit may be arranged to controllably connect the second planetary member of the first planetary gear set to the ring wheel of the second planetary gear set. Further, the ring wheel of the second planetary gear set is then also connected to the variator input shaft.

Moreover, the second clutch unit hence allows for connection between the ring wheel of the second planetary gear set to the gearbox housing of the continuously variable transmission, i.e. the ring wheel of the second planetary gear set can, by means of the second clutch unit, be locked to the gearbox housing of the continuously variable transmission.

By means of the first clutch unit and the second clutch unit, a first and a second operating mode of the continuously variable transmission is enabled. In the event the ring wheel of the second planetary gear set is connected to the gearbox housing, the continuously variable transmission will be worked in the first operating mode where the second planetary gear set will work as a reduction gear set enabling a large transmission ratio over the second planetary gear set. In the event the ring wheel of the second planetary gear set is connected to the second member of the first planetary gear set, the continuously variable transmission will be worked in the second operating mode, where the first and second planetary gear sets will work as a bridge, where the variator input shaft and the variator output shaft are neither connected to the transmission input shaft nor the transmission output shaft. Hence, in the first operating mode the second planetary gear set works as a reduction gear set and in the second operating mode the second planetary gear set merges power supplied to its sun wheel and ring wheel. Accordingly, a mode selection arrangement may be provided which enables different operating modes with different bands of continuously variable speed ratios between the transmission input shaft and the transmission output shaft.

Moreover, the mode selection arrangement may, in addition to the clutch units, comprise a set of actuators. The actuators may control the engagement and disengagement of the clutch units. Still further, the mode selection arrangement may include a control unit or the like for operating the actuators.

According to an example embodiment, the first clutch unit and/or the second clutch unit may be a friction disc clutch unit.

A friction disc clutch unit is well known and easy to control. Also, the friction disc clutch unit has the advantage of being able to slip into engagement, providing a relatively even and smooth transition from a disengaged state to an engaged state, or vice versa. The friction disc clutch unit may be either a wet friction disc clutch unit or a dry friction disc clutch unit. However, other types of clutches are of course also conceivable, such as e.g. a dog clutch.

According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the variator input shaft, and a gear wheel connected to the second planetary member of the first planetary gear set, the gear wheels are in meshed connection with each other. The gear wheel connected to the second planetary member of the first planetary gear set may be further selectively connectable to the ring wheel of the second planetary gear set.

An advantage is that, by means of these gear wheels, the maximum speed of the variator input shaft may be adapted to various types of machines used in the variator unit.

According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the sun wheel of the first planetary gear set, and a gear wheel connected to the sun wheel of the second planetary gear set; the gear wheels are in meshed connection with each other. The gear wheel connected to the sun wheel of the first planetary gear set may be further connected to the variator output shaft.

According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the second planetary member of the first planetary gear set, and a gear wheel selectively connectable to the ring wheel of the second planetary gear set, wherein the gear wheels are in meshed connection with each other.

By arranging a gear wheel connected to the sun wheel of the first planetary gear set which is in meshed connection with a gear wheel connected to the sun wheel of the second planetary gear set, in combination with arranging a gear wheel connected to the second planetary member of the first planetary gear set which is in meshed connection with a gear wheel selectively connectable to the ring wheel of the second planetary gear set, a difference in geometric level between the first and the second planetary gear sets is provided. Hereby, the prime mover of a working machine can be positioned at a higher geometric level in comparison to the wheels of the working machine. Also, the freedom of choosing basic speed ratios of the first and the second planetary gear sets may be increased by adjusting the gear ratios of the two gear stages obtained by the mentioned gear wheels.

According to an example, the gear wheel selectively connectable to the ring wheel of the second planetary gear et may be further connected to the variator input shaft. According to another example, the gear wheel connected to the second member of the first planetary gear set may be further connected to the variator input shaft.

According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the sun wheel of the first planetary gear set, and a gear wheel connected to the variator output shaft; the gear wheels are in meshed connection with each other. The gear wheel connected to the variator output shaft may be further connected to the sun wheel of the second planetary gear set.

According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the ring wheel of the second planetary gear set, and a gear wheel selectively connectable to the variator input shaft; the gear wheels are in meshed connection with each other. The gear wheel selectively connectable to the variator input shaft may be further selectively connectable to the gearbox housing of the continuously variable transmission.

Hereby, a further difference in geometric level between the first and the second planetary gear sets is provided.

According to an example embodiment, one of the sun wheel, the ring wheel and the planet carrier of the second planetary gear set may be selectively connectable to another one of the sun wheel, the ring wheel and the planet carrier of the second planetary gear set.

Hereby, the continuously variable transmission enables for a third operating mode by simply selectively connecting one of the components of the second planetary gear set to another one of the components of the second planetary gear set. In this third operating mode, the second planetary gear set is by-passed or locked together as a direct gear without any increase/decrease in gear ratio, i.e. a 1:1 relationship of input to output of the second planetary gear set. By use of the third operating mode, the continuously variable transmission is provided with a mode which is faster than the second operating mode. Accordingly, the three operating modes are executed in its consecutive order when accelerating the vehicle, i.e. first the continuously variable transmission is operated by the first operating mode, then by the second operating mode and finally by the third operating mode.

It should be readily appreciated that the wording “selectively connectable” should be interpreted such that one of the sun wheel, the ring wheel and the planet carrier is able to be locked to another one of the sun wheel, the ring wheel and the planet carrier. Accordingly, the two components being connected to each other do not have a relative speed difference between themselves.

Furthermore, the components, i.e. one of the sun wheel, the ring wheel and the planet carrier may be selectively connectable to another one of the sun wheel, the ring wheel and the planet carrier by means of e.g. a clutch unit or the like. The clutch unit may, for example, be a friction disc clutch unit or any other suitable clutch unit such as those described above in relation to the description of the first clutch unit and the second clutch unit.

According, to an example embodiment, the sun wheel of the second planetary gear set may be selectively connectable to the planet carrier of the second planetary gear set.

Hereby, a clutch unit may be positioned between the sun wheel and the planet carrier of the second planetary gear set. When connecting the sun wheel to the planet carrier, the second planetary gear set will be by-passed and hence un-loaded.

According to an example embodiment, the planet carrier of the second planetary gear set may be selectively connectable to the ring wheel of the second planetary gear set.

Hereby, a clutch unit may be positioned between the planet carrier and the ring wheel of the second planetary gear set.

According to an example embodiment, the sun wheel of the second planetary gear set may be selectively connectable to the ring wheel of the second planetary gear set.

Hereby, a clutch unit may be positioned between the sun wheel and the dug wheel of the second planetary gear set. The power to the sun wheel and the power to the ring wheel will be merged together and thereafter provided to the planet carrier.

Accordingly, an advantage is that by simply providing the additional clutch unit enables for the third operating mode for the continuously variable transmission.

According to an example embodiment, the continuously variable transmission may further comprise a gear wheel selectively connectable to the sun wheel of the first planetary gear set, and a gear wheel connected to the ring wheel of the second planetary gear set; the gear wheels are in meshed connection with each other. The gear wheel connected to the ring wheel of the second planetary gear set may be further selectively connectable to the second planetary member of the first planetary gear set and to the gearbox housing of the continuously variable transmission.

Hereby, a further set of gear wheels are arranged between the sun wheel and the ring wheel of the second planetary gear set. This further gear set, in combination with the gear set having a gear wheel connected to the sun wheel of the second planetary gear set and a gear wheel connected to the sun wheel of the first planetary gear set and to the variator output shaft, enables for a fixed ratio in rotational speed between the sun wheel of the second planetary gear set and the ring wheel of the second planetary gear set. Accordingly, a clutch unit or the like may be positioned between this further gear set and the variator output shaft. Hereby, the further set of gear wheels, in combination with the gear set having a gear wheel connected to the sun wheel of the second planetary gear set and a gear wheel connected to the sun wheel of the first planetary gear set and to the variator output shaft, makes it possible to choose gear ratio between the sun wheel of the second planetary gear set and the ring wheel of the second planetary gear set.

Accordingly the above described 1:1 relationship for the second planetary gear set may be adjusted such that another gear ratio is provided, or keeping the 1:1 relationship if desired. Hence, the flexibility of choosing gear ratio between input and output for the second planetary gear set is increased.

Hence, the above description that the connection between components of the second planetary gear set should be interpreted as a connection which does not allow for a relative motion between the connected components is not fully applicable to this example embodiment of the present invention, since, as described, a relative motion is possible by means of the intermediate gear wheels.

According to an example embodiment, the variator unit may have a first hydraulic machine provided with the variator input shaft and a second hydraulic machine provided with the variator output shaft, the first and second hydraulic machines being hydraulically connected to each other.

According to an example embodiment, the variator unit may have a first electric machine provided with the variator input shaft and a second electric machine provided with the variator output shaft, the first and second electric machines being electrically connected to each other.

According to a second aspect of the present invention there is provided a continuously variable transmission, comprising a variator unit having a variator input shaft and a variator output shaft; a first planetary gear set having a first, a second and a third planetary member, wherein the first planetary member of the first planetary gear set is operatively connected to a transmission input shaft; and a second planetary gear set having a first, a second and a third planetary member, the third planetary member of the second planetary gear set being operatively connected to a transmission output shaft; wherein the variator input shaft is operatively connected to the second planetary member of the first planetary gear set; the variator output shaft is operatively connected to the third planetary member of the first planetary gear set, the third planetary member of the first planetary gear set being further operatively connected to the first planetary member of the second planetary gear set; the second planetary member of the second planetary gear set being selectively connectable to the second planetary member of the first planetary gear set and to a gearbox housing of the continuously variable transmission, and wherein one of the first, the second and the third member of the second planetary gear set is selectively connectable to another one of the first, the second and the third member of the second planetary gear set.

Effects and features of this second aspect of the present invention are largely analogous to those described above in relation to the first aspect of the present invention.

According to an example embodiment, the first planetary member of the second planetary gear set may be selectively connectable to the second planetary member of the second planetary gear set.

According to an example embodiment, the first planetary member of the second planetary gear set may be selectively connectable to the third planetary member of the second planetary gear set.

According to an example embodiment, the second planetary member of the second planetary gear set may be selectively connectable to the third planetary member of the second planetary gear set.

According to an example embodiment, the first planetary member of the first planetary gear set may be one of a ring wheel and a planet carrier, the second planetary member of the first planetary gear set may be the other one of the ring wheel and the planet carrier, and the third planetary member may be a sun wheel.

According to an example embodiment, the first planetary member of the second planetary gear set may be a sun wheel, the second planetary member may be a ring wheel, and the third planetary member may be a planet carrier.

According to an example embodiment, the variator unit may have a first hydraulic machine provided with the variator input shaft and a second hydraulic machine provided with the variator output shaft, the first and second hydraulic machines being hydraulically connected to each other.

According to an example embodiment, the variator unit may have a first electric machine provided with the variator input shaft and a second electric machine provided with the variator output shaft, the first and second electric machines being electrically connected to each other.

According to a third aspect of the present invention, there is provided a working machine comprising one of the above described continuously variable transmissions in relation to the first and second aspect of the present invention.

Effects and features of this third aspect of the present invention are largely analogous to those described above in relation to the first and second aspects of the present invention.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. For example, the above description of the different advantages of the present invention is only described in relation to driving the vehicle in a forward direction, the various embodiments of the invention are of course also applicable when providing the continuously variable transmission in reversed gear, i.e. when the working machine is driving backwards.

DETAILED DESCRIPTION

Reference is now made toFIG. 1, illustrating a working machine101, here in the form of a wheel loader having an implement102. The term “implement” is intended to comprise any kind of tool using hydraulics, such as a bucket, a fork or a gripping tool arranged on a wheel loader, or a container arranged on an articulated hauler. The implement illustrated comprises a bucket103which is arranged on an arm unit104for lifting and lowering the bucket103, and further the bucket103can be tilted or pivoted relative to the arm unit104. The wheel loader101is provided with a hydraulic system comprising at least one hydraulic machine (not shown). The hydraulic machine can be a hydraulic pump, although it is preferred that the hydraulic machine can work as a hydraulic pump as well as a hydraulic motor with a reversed flow of hydraulic fluid. Such a hydraulic machine with said both functions can be used as a pump for providing the hydraulic system with hydraulic fluid, for example to lift and tilt the bucket, and as a hydraulic motor for recuperation of energy, for example during a lowering operation of the implement102. In the example embodiment illustrated inFIG. 1the hydraulic system comprises two hydraulic cylinders105a,105bfor the operation of the arm unit104and a hydraulic cylinder106for tilting the bucket103relative to the arm unit04. Furthermore the hydraulic system comprises two hydraulic cylinders107a,107barranged on opposite sides of the wheel loader for turning the wheel loader by means of relative movement of a front body part108and a rear body part109. In other words; the working machine is frame-steered by means of the steering cylinders107a,107b.

The working machine101is also provided with a prime mover, such as an internal combustion engine, and a driveline with a gearbox for supplying power to the driving wheels112of the working machine101.

The gearbox is a continuously variable transmission which gives a plurality of advantages in relation to a stepped gearbox. For example, the velocity of the working machine01can be controlled independently of the speed of rotation of the prime mover. If the continuously variable transmission has a speed of rotation range comprising a mode where the rotation speed of the output shaft of the gearbox is zero or close to zero independently of the rotation speed of the input shaft of the gearbox at the same time as torque can be transmitted from the input shaft to the output shaft (usually referred to as an infinitely variable transmission (IVT) with geared neutral), the torque converter traditionally used in working machines can be omitted. By the expression “zero or close to zero” is meant a speed of rotation of the output shaft which is zero or in the size of a few rotations per minute.

By the continuously variable transmission and the geared neutral function, the operation of the hydraulic system can be separated from the propulsion of the working machine for all vehicle speeds. Furthermore, the hydraulic system can be driven by the prime mover when the working machine stands still without using any clutch for disengagement of the prime mover relative to the driveline.

Turning now toFIGS. 2a-2billustrating a continuously variable transmission200according to an example embodiment of the present invention. To the continuously variable transmission200is a forward-reverse gear unit202added to a transmission input shaft204of the continuously variable transmission200. The forward-reverse gear unit202includes an input shaft205having a first gear wheel208being in meshed connection to a second gear wheel210connected to a mid shaft212. Moreover, a forward clutch unit214is connected to the mid shaft212. The forward clutch unit214is further connected to a third gear wheel26being in meshed connection to a fourth gear wheel218. Furthermore, a reverse clutch unit224is connected to the input shaft205of the forward-reverse gear unit202. A fifth gear wheel220is selectively connectable to the input shaft206of the forward-reverse gear unit202by means of the reverse clutch unit224. The fifth gear wheel220also being in meshed connection to the fourth gear wheel218. When the forward clutch unit214is engaged, the vehicle is driving in a forward direction and when the reverse clutch unit224is engaged, the vehicle is driving in a reverse direction. Accordingly, the forward clutch unit214and the reverse clutch unit224cannot be engaged at the same time.

The present invention mainly relates to the continuously variable transmission200. The forward-reverse gear unit202is more or less identical for all embodiments described herein and will therefore be omitted in the following text.

Now, the transmission input shaft204is coupled to a first planetary gear set226. More specifically, the transmission input shaft204is coupled to a first planetary member228of the first planetary gear set226. In the depicted example embodiment ofFIGS. 2aand 2b, the first planetary member228is a ring wheel of the first planetary gear set226. Furthermore, the first planetary gear set226also comprises a second planetary member230and a third planetary member232. In the illustrated example embodiment, the second planetary member230being a planet carrier of the first planetary gear set226, while the third planetary member232being a sun wheel. It should however be noted that although the first228, second230and third232planetary members are illustrated as a ring wheel, a planet carrier and a sun wheel, respectively, other configurations are of course conceivable.

Accordingly, the planet carrier may constitute the first planetary member228, while the ring wheel may constitute the second planetary member230, etc.

Furthermore, as depicted inFIG. 2b, the second planetary member230of the first planetary gear set226, which is the planet carrier in the example embodiment, comprises double planet wheels. Accordingly, one of the planet wheels is in meshed connection with the sun wheel and the other one of the planet wheels is in meshed connection with the ring wheel. The planet wheels are also in meshed connection with each other.

Furthermore, the continuously variable transmission200comprises a variator unit234having a variator input shaft236and a variator output shaft238. The variator unit234may be of a hydraulic type including a first hydraulic machine233provided with the variator input shaft236and a second hydraulic machine235provided with the variator output shaft238, the first233and second235hydraulic machines being hydraulically connected to each other, or of an electric type including a first electric machine provided with the input shaft236of the variator unit234and a second electric machine provided with the output shaft238of the variator unit234, the first and second electric machines being electrically connected to each other.

Still further, the continuously variable transmission200also comprises a second planetary gear set240. The second planetary gear set240comprises a first planetary member242, a second planetary member244, and a third planetary member246. In the illustrated example embodiment depicted inFIGS. 2aand 2b, the first planetary member242is a sun wheel, the second planetary member244is a ring wheel, and the third planetary member246is a planet carrier. However, other dispositions of the second planetary gear set are of course conceivable, such as e.g. the second planetary member244being constituted by the planet carrier, the third planetary member246being constituted by the ring wheel, etc. In order to simplify the intelligibility of the text, the first planetary member242will in the following and throughout the remaining description be referred to as the sun wheel242, the second planetary member will be referred to as the ring wheel244, and the third planetary member will be referred to as the planet carrier246.

Finally, the continuously variable transmission200comprises a first clutch unit252and a second clutch unit248. The first clutch unit252being configured to selectively connect the planet carrier230of the first planetary gear set226to the ring wheel244of the second planetary gear set240. The first clutch unit252also selectively connects the ring wheel244of the second planetary gear set240to the variator input shaft236. The second clutch unit248is positioned between the ring wheel244of the second planetary gear set240and a gearbox housing250of the continuously variable transmission200.

Now, the following will describe the interconnection between the above described components of the continuously variable transmission200depicted inFIGS. 2aand 2b. As described above, the transmission input shaft204is coupled to the ring wheel228of the first planetary gear set226, i.e. torque from the prime mover of the working machine101is received to the ring wheel228of the first planetary gear set226, via the above described forward-reverse gear unit202. The sun wheel232of the first planetary gear set226is further connected to the variator output shaft238and to the sun wheel242of the second planetary gear set240. Accordingly, the variator output shaft238is also coupled to the sun wheel242of the second planetary gear set240.

Moreover, the planet carrier230of the first planetary gear set226is coupled to the variator input shaft236via a gear stage comprising gear wheels254,256which are in meshed connection with each other.

Accordingly, the first planetary gear set226and the variator input shaft236are positioned at different levels from each other in the gearbox. It should however be noted that the embodiment depicted inFIGS. 2aand 2bis not limited to the use of the gear wheels254,256. Also, and as described above, the planet carrier230of the first planetary gear set226is selectively connectable to the ring wheel244of the second planetary gear set240by means of the first clutch unit252. The ring wheel244of the second planetary gear set240is further selectively connectable to the gearbox housing250of the continuously variable transmission200by means of the second clutch unit248. Finally, the planet carrier246of the second planetary gear set240is coupled to a transmission output shaft258, in the depicted example embodiment, via two gear stages.

With the above described first clutch unit252and second clutch unit248, the continuously variable transmission200is able to operate in a first and second operating mode. When connecting the ring wheel244of the second planetary gear set240to the gearbox housing250, i.e. engaging the second clutch unit248, the continuously variable transmission200is operated in the first operating mode and the second planetary gear set240will work as a reduction gear set enabling a large transmission ratio over the second planetary gear set240. When, on the other hand, engaging the first clutch unit252, i.e. selectively connecting the ring wheel244of the second planetary gear set240to the planet carrier230of the first planetary gear set226as well as to the variator input shaft236, the continuously variable transmission200operates in the second operating mode. In the second operating mode the second planetary gear set240merges power supplied to the sun wheel242and the ring wheel244. A further description of the operating modes will be described further below in relation to the description ofFIG. 8.

Turning now toFIGS. 3aand 3b, illustrating another example embodiment of the continuously variable transmission200according to the present invention. A difference between the embodiment depicted inFIGS. 3a-3band the embodiment depicted inFIGS. 2a-2bis that a gear stage302is arranged between the sun wheel232of the first planetary gear set226and the sun wheel242of the second planetary gear set240. The gear stage302comprises a pair of gear wheels301,303which are in meshed connection with each other. One of the gear wheels301is connected to the sun wheel232of the first planetary gear set226and to the variator output shaft238. The other gear wheel303is connected to the sun wheel242of the second planetary gear set240.

Moreover, another difference between the embodiment depicted inFIGS. 3a-3band the embodiment depicted inFIGS. 2a-2bis that a further gear stage306is arranged between the second planetary member230of the first planetary gear set226and the variator input shaft236as well as the first clutch unit252. The second planetary member230is in the example embodiment depicted inFIGS. 3a-3ba ring wheel. The first planetary member228of the first planetary gear set226is the planet carrier. The gear stage comprises a pair of gear wheels305,307which are in meshed connection with each other. One of the gear wheels307is connected to the variator input shaft236, via the above described gear wheel256in relation to the description ofFIGS. 2a-2b, as well as selectively connectable to the ring wheel244of the second planetary gear set240by means of the first clutch unit252. The year wheels307and254are one and the same for the embodiment depicted inFIGS. 3a-3b. The other gear wheel305is connected to the ring wheel230of the first planetary gear set226. Still further, the transmission output shaft258is in the depicted embodiment ofFIGS. 3a-3bprovided with only one gear stage instead of two as was the case in the depicted embodiment ofFIGS. 2a-2b.

Reference is now made toFIGS. 4aand 4b, illustrating yet another example embodiment of the continuously variable transmission200according to the present invention. In the embodiment depicted inFIGS. 4a-4b, the gear wheel305that was previously connected to the ring wheel230of the first planetary gear set226is now further connected to the variator input shaft236via the above described gear wheel256in relation to the description ofFIGS. 2a-2b. The gear wheel305and the gear wheel254are one and the same in the embodiment depicted inFIGS. 4a-4b. Moreover, the gear wheel307that previously was connected to the variator input shaft is now instead only selectively connectable to the ring wheel244of the second planetary gear set240via the first clutch unit252.

By providing the gear sets302and306illustrated inFIGS. 3a-4b, a difference in geometric level may be arranged between the first226and second240planetary gear sets. Also, by means of the two gear sets302,306an adjustment of the basic speed ratios of the first226and second240planetary gear sets may be provided.

Turning now toFIGS. 5a-5b, illustrating a still further example embodiment of the continuously variable transmission200according to the present invention. The embodiment depicted inFIGS. 5a-5bcomprises, in comparison to the embodiment depicted inFIGS. 3a-3b, a year stage502which is positioned between the ring wheel244of the second planetary gear set240and the first252and second248clutch units. The gear stage502comprises two gear wheels501,503which are in meshed connection with each other, wherein one of the gear wheels501is connected to the ring wheel244of the second planetary gear set240and the other gear wheel503being selectively connectable to the variator input shaft236as well as to the gearbox housing250. It should however be noted that the gear wheel503may be positioned such that it is not selectively connectable to the gearbox housing250. In such a case, the ring wheel244of the second planetary gear set240is selectively connectable directly to the gearbox housing250.

Moreover, the embodiment depicted inFIGS. 5a-5bfurther comprises a gear stage506positioned between the sun wheel232of the first planetary gear set226and the variator output shaft238as well as the sun wheel242of the second planetary gear set240. The gear stage506comprises two gear wheels505,507which are in meshed connection with each other. One of the gear wheels505is connected to the sun wheel232of the first planetary gear set226, while the other one of the gear wheels507is connected to the variator output shaft238as well as to the sun wheel242of the second planetary gear set240, via the gear stage302described above in relation to the description ofFIGS. 3a-3b.

Finally, the gear stage306described in relation toFIGS. 3a-4bis in the exemplified embodiment depicted inFIGS. 5a-5bpositioned as illustrated inFIGS. 3a-3b. Accordingly, one of the gear wheels305is connected to the ring wheel230of the first planetary gear set226, while the other one of the gear wheels307is connected to the variator input shaft236as well as selectively connectable to the ring wheel244of the second planetary gear set240via the first clutch unit252. However, it should be noted that, the gear stage306may be equally positioned as illustrated inFIGS. 4a-4b. Also, there is no gear stage arranged on the transmission output shaft258.

Accordingly, the planet carrier246of the second planetary gear set240constitutes the transmission output shaft258for the embodiment depicted inFIGS. 5a-5b. Hereby, the bearing arrangement fir the second planetary gear set240may be simplified in comparison to the other described example embodiments.

The above description in relation toFIGS. 2a-5bhence relates to different embodiments of a continuously variable transmission according to the present invention. Although gear stages have been described and positioned differently in the different embodiments, other configurations and alternations are of course conceivable. Also, the embodiments depicted and described in relation toFIGS. 2a-5benables the continuously variable transmission to operate in a first and a second operating mode. However, by slightly modifying the continuously variable transmission, also a third operating mode can be provided.

Therefore, reference is now made toFIGS. 6a-6c, which illustrate three different example embodiments for providing a third operating mode to the continuously variable transmission200described above in relation to the description ofFIGS. 2a-5b. Accordingly, the example embodiments ofFIGS. 6a-6care applicable for all the previously described example embodiments of the present invention.

Turning first toFIG. 6a, the sun wheel242of the second planetary gear set240is selectively connectable to the planet carrier246of the second planetary gear set240by means of a clutch unit602. Hereby, the second planetary gear set240can be locked together providing a 1:1 gear ratio between sun wheel242and the planet carrier246. Hence, in this case, the second planetary gear set240is by-passed.

InFIG. 6b, on the other hand, the sun wheel242of the second planetary gear set240is selectively connectable to the ring wheel244of the second planetary gear set240by means of a clutch unit604. Hereby, the second planetary gear set240can be locked together providing a 1:1 gear ratio between sun wheel242and the ring wheel244.

Finally, inFIG. 6c, the ring wheel244of the second planetary gear set240is selectively connectable to the planet carrier246of the second planetary gear set240by means of a clutch unit606. Hereby, the second planetary gear set240can be locked together providing a 1:1 gear ratio between ring wheel244and the planet carrier246.

With the embodiments depicted inFIGS. 6a-6c, the second planetary gear set240is locked together or by-passed, thereby not using the second planetary gear set240as a reduction gear which enables for a third operating mode providing increased output speed of the continuously variable transmission. A further description of the third operating mode will be provided below in relation to the description ofFIG. 8.

A further example embodiment of the continuously variable transmission for providing the third operating mode is illustrated inFIGS. 7a-7b. The depicted embodiment inFIGS. 7a-7bis more or less a modification of the embodiment depicted inFIGS. 5a-5b. By providing a clutch unit702between the ring wheel244of the second planetary gear set240and the sun wheel242of the planetary gear set240, the above described third operating mode may be provided by selectively engaging the clutch unit702. Also, a gear stage704is arranged between the ring wheel244of the second planetary gear set240and the clutch unit702. The gear stage704comprises a pair of gear wheels703,705which are in meshed connection with each other. One of the gear wheels703is selectively connectable to the variator output shaft238, the sun wheel232of the first planetary gear set226and the sun wheel242of the second planetary gear set240. The connection between the sun wheels232,242of the respective planetary gear sets226,240is made via the above described gear stages506,302. The other one of the gear wheels705is connected to the ring wheel244of the second planetary gear set240and to the first252and second248clutch units.

Accordingly, the main difference between the embodiment depicted inFIGS. 7a-7band the embodiment depicted inFIG. 6bis that the sun wheel242and the ring wheel244of the second planetary gear set240are selectively connectable via gear stages302,704. Hereby, a relative motion between the sun wheel242and the ring wheel244of the second planetary gear set240can be provided if the gear ratio of the gear stages302,704are chosen differently. Also, when adding a gear stage302between the clutch unit702and the sun wheel242as depicted inFIGS. 7a-7b, the rotational direction of the shafts are different on each side of the gear stage302. It is therefore suitable to provide a further gear stage704between the sun wheel242and the ring wheel244of the second planetary gear set240, such that the rotational direction is altered twice. Furthermore, the gear wheel705and the gear wheel501are, in the example embodiment, one and the same.

Now, turning toFIG. 8, a graph illustrating the three operating modes is depicted. The x-axis802of the graph indicates the variator speed ratio. The variator speed ratio is the ratio between the rotational speed of the variator output shaft238and the rotational speed of the variator input shaft236, i.e. ω238/ω236. The y-axis804of the graph on the other hand indicates the overall speed ratio of the gearbox. The overall speed ratio of the gearbox is the ratio between the rotational speed of the transmission output shaft258and the rotational speed of the transmission input shaft204, i.e. ω258/ω204.FIG. 8shows an example when the variator speed ratio is positive, which is the case for the embodiments depicted inFIGS. 3a-3b, 5a-5band 7a-7b. For the embodiments depicted inFIGS. 2a-2band 4a-4b, on the other hand, the variator speed ratio varies in the same way but is negative.

In the first operating mode806, the ring wheel244of the second planetary gear set240is connected to the gearbox housing250by means of the second clutch unit248. The first clutch unit252is in a disengaged state. The variator speed ratio802as well as the overall speed ratio804continuously increases. The first operating mode806is utilized until the variator speed ratio802is infinite, which means that the variator input shaft236is standing still, i.e. the relative speed over the first clutch unit252is zero, or close to zero.

When the variator speed ratio802has reached infinity the continuously variable transmission200is arranged to shift from the first operating mode806to the second operating mode808. Hereby, and as described above, the first clutch unit252is positioned in an engaged state while the second clutch unit248is positioned in a disengaged state. Accordingly, in the second operating mode808the ring wheel244of the second planetary gear set240is connected to the second planetary member230of the first planetary gear set226as well as to the variator input shaft236. The shift between the first operating mode806and the second operating mode808is made synchronously and the variator speed ratio802as well as the overall speed ratio804have the same value before and after the shift. Now, in the second operating mode808the variator speed ratio802is continuously decreasing while the overall speed ratio804is continuously increasing. Moreover, the second operating mode808can either be utilized until the variator speed ratio802has reached a level of zero, or close to zero, or the second operating mode808can be utilized until the variator speed ratio802has decreased to an intersection point810with the third operating mode812. The intersection point810is defined as the point where the curve of the third operating mode812crosses the curve of the second operating mode808if the third operating mode811was utilized from the beginning of the working process, i.e. instead of starting with the first operating mode806. If the shift from the second operating mode808to the third operating mode812is made at the intersection point810, the shift is made synchronously while if shifting from the second operating mode808to the third operating mode812when the variator speed ratio has reached zero, or is close to zero, there will be a non-synchronous mode shift, illustrated by numeral814. In the latter case, the variator speed ratio802will have different values before and after the shift. An advantage of the non-synchronous mode shift814is that there will be less losses in the variator unit since the amount of power going through the variator unit is less at the end of the second operating mode808in comparison to the beginning of the third operating mode812.

Now, the third operating mode812is provided by engaging the clutch unit602,604,606,702described in relation toFIGS. 6a-7babove and disengaging the first clutch unit252. These operations may, as described above, be effected either when the variator speed ratio802is zero, or close to zero, or when the variator speed ratio has decreased to the intersection point810. In the third operating mode812, the variator speed ratio802as well as the overall speed ratio804is continuously increasing.

Although the invention has been described in relation to specific combinations of gear wheels, use of the different gear wheels may be combined in other configurations as well which is clear for the skilled person when studying the present application. Also, the present disclosure has mainly been made for running a working machine in the forward direction and it should hence be readily understood that the invention is equally applicable for reverse driving as well. Thus, the above description of the example embodiment of the present invention and the accompanying drawings are to be regarded as a non-limiting example of the invention and the scope of protection is defined by the appended claims. Any reference sign in the claims should not be construed as limiting the scope.