WO2022083891A2

WO2022083891A2 - Variable transmission with a variator unit for an electric vehicle and method for controlling the variable transmission

Info

Publication number: WO2022083891A2
Application number: PCT/EP2021/025412
Authority: WO
Inventors: Matijs VAN DEN BOER; Erik ROELOFFZEN
Original assignee: Robert Bosch Gmbh
Priority date: 2020-10-19
Filing date: 2021-10-19
Publication date: 2022-04-28
Also published as: WO2022083891A3

Abstract

The invention relates to a variable transmission (3) for an electric vehicle with an electric motor (1) and with two or more driven wheels (2), comprising a variator unit (40) for providing a continuously variable speed ratio between an input shaft (44) and an output shaft (45) thereof. According to the invention, the variable transmission (3) further comprises two planetary gear sets (50) respectively provided on a respective axial side of the output shaft (45) and each comprising three coaxially rotatable members (51, 52, 53) including a sun gear (51), a ring gear (52) and a planet carrier (53) rotatably carrying planet gears (54), whereof first members (51, 52, 53) rotate as one with the output shaft (45), whereof second members (51, 52, 53) respectively rotate as one with a respective one of the two driven wheels (2) and whereof third members (51, 52, 53) of each of the planetary gear sets (50) are connectable to a stationary part (39) of the variable transmission (3) via a respective clutch (65) and/or are rotationally connected in reverse by a coupling mechanism (55).

Description

VARIABLE TRANSMISSION WITH A VARIATOR UNIT FOR AN ELECTRIC VEHICLE AND METHOD FOR CONTROLLING THE VARIABLE TRANSMISSION

The present invention relates to a variable transmission for an electric vehicle, in particular a passenger car, with an electric motor that is also known as motor/generator-unit (MGU) and with two or more driven wheels, in which vehicle the variable transmission drivingly connects, i.e. rotationally couples, the electric motor to the driven wheels at a continuously variable transmission speed ratio. Within the context of the present disclosure the term electric vehicle is to be understood as referring to a vehicle with an electric powertrain, such as battery electric vehicles (BEV) and fuel cell electric vehicles (FCEV), which electric vehicle powertrain includes the electric motor as a prime mover of the said two driven wheels, but does, in particular, not include an internal combustion engine that is, or at least can be, connected to the said two driven wheels in addition to or instead of the electric motor.

The variable transmission according to the present invention is provided with a variator unit for setting a speed ratio between an input shaft and an output shaft thereof that is infinitely variable within a range of speed ratios.

In a widely applied embodiment thereof, the variator unit comprises two, adjustable pulleys, each pulley provided on and rotating as one with a respective one of the said input and output shafts, and a drive belt wrapped around the pulleys at an adjustable, effective radius at each pulley. The ratio between these effective belt radii at the two pulleys determines the speed ratio of the variator unit that can be varied by adjusting the pulleys. Such a variable transmission and electric vehicle provided therewith is well-known and is for example described in the European patent No. EP0572279B1 and more recently in the international patent application publication No. W02020/057779A1 .

In the electric vehicle the electric motor may be directly connected to and rotate as one with the input shaft of the variator unit, as illustrated in EP0572279B1 , but it is also known to apply a geared speed reduction there between as part of the variable transmission. Such an input speed reduction is illustrated in W02020/057779A1 . In any case, a geared speed reduction is normally applied in the variable transmission between the output shaft of the variator unit and the driven wheels, to account the rotational speed difference between the said output shaft and the driven wheels. Such an output speed reduction is illustrated in both W02020/057779A1 and EP0572279B1.

Also in the electric vehicle, a differential is applied as part of the variable transmission between the output shaft of the variator unit and the driven wheels, in particular between the output speed reduction and the driven wheels, for allowing the driven wheels to rotate at mutually different speeds (when cornering), while being driven by or driving the electric motor. The differential is, as such, well-known and widely applied. In one known embodiment thereof, the differential is constructed from two, co-axially arranged and rotationally connected, epicyclic or planetary gear sets. However, in the archetypical embodiment thereof, that is schematically illustrated in EP0572279B1 , the differential is constructed with bevel gears.

The known variable transmission greatly contributes to the acceleration performance and top speed of the electric vehicle and, moreover, can also improve the overall operating efficiency thereof. It does, however, come with the limitation that it takes up considerable space in the vehicle. In particular in case of the above-described belt-and-pulleys-type variator unit, the pulleys are mutually spaced in radial direction as well as relative to the rotation axis of the driven wheels and/or of the electric motor to accommodate the said geared speed reduction(s) and the differential of the variable transmission. Of course, the drawing figures of W02020/057779A1 and EP0572279B1 exacerbate this latter aspect of the known variable transmission by providing only the “unfolded” 2D representation of a typically tightly packed 3D design thereof. Nevertheless, according to the present invention, the known variable transmission can be improved upon towards a more compact design thereof, in particular in terms of its dimension in radial direction.

According to the present invention, the differential and output speed reduction of the variable transmission is embodied by two planetary gear sets that are respectively provided on a respective axial side of the output shaft of the variator unit, preferably coaxial therewith, which planetary gear sets each comprise three coaxially rotatable members including a central sun gear, an outer ring gear and a planet carrier that rotatably carries one or more planet gears located between and meshing with both the sun gear and the ring gear, whereof first members of each of the planetary gear sets are rotationally connected to and rotate as one with the output shaft of the variator unit, whereof second members of each of the planetary gear sets can be rotationally connected to and rotate as one with a respective one of the two driven wheels of the electric vehicle and whereof third members of each of the planetary gear sets are connectable to a stationary part of the variable transmission via a respective clutch. In particular, the clutches are controllable such that these can be maintained in a fully closed state, wherein the respective third member is prevented from rotating, or in a slipping or fully opened state, wherein the respective third member can rotate relative to the said stationary transmission part. The clutch slip -and thus the friction that is exerted by the clutch on a respective third member- is preferably hydraulically controllable, if the pulleys are hydraulically adjusted as well, or is preferably mechanically controllable, if the adjustable pulleys are mechanically adjusted as well. When the clutches of the two planetary gear sets are closed, i.e. when the said third members thereof are both locked, i.e. cannot rotate, the two driven wheels rotate at the same speed (i.e. so-called differential lock), whereas when at least one of the clutches is controlled to slip or is fully opened, the driven wheels can have different rotational speeds, as is required when the electric vehicle is cornering. By thus combining the differential and output speed reduction functions in the planetary gear sets, the novel variable transmission allows for a favourably compact design thereof.

In particular, when the electric vehicle is driven by the electric motor, preferably the clutch of the planetary gear set that is associated with the inner driven wheel in cornering is controlled to slip, whereas during regenerative braking of the electric vehicle (i.e. when the electric motor is being driven by the inertia of the electric vehicle), preferably the clutch of the planetary gear set that is associated with the outer driven wheel in cornering is controlled to slip. In fact, to minimise power loss through friction in the respectively slipping clutch, it is fully opened, in which case no drive force, i.e. no torque is transmitted to or from the respective driven wheel. However, in a more sophisticated control method the amount of slip, i.e. the slip speed of the slipping clutch is actively controlled, such that oversteer or understeer of the electric vehicle can be favourably introduced in a controlled manner (i.e. so-called torque steering). In particular, the clutch slip speed is preferably controlled in relation to at least the torque that is to be received or generated by each driven wheel. Preferably also one or more further control parameters are taken into account, such as the (individual) rational speeds of the driven wheels, a steering angle of the front wheels of the electric vehicle (that can be the same as the said two driven wheels), an angular speed of the electric vehicle, or the (individual) rational speeds of the driven wheels.

Furthermore, the clutches are preferably actively controlled not only when these are slipping, but also when these are closed. In particular, the clutches are controlled with a safety margin between a torque that is actually transmitted thereby and a maximum torque that can be instantaneously transmitted by the clutches, which clutch safety margin that is smaller than a further safety margin that is applied between a torque that is actually transmitted by the variator unit and a maximum torque that can be instantaneously transmitted by the variator unit. In this way, if a torque spike (i.e. a sudden and/or unanticipated increase in the torque level) occurs in the powertrain, a resulting slip favourably occurs in the clutches rather than in the variator unit that is more susceptible to be damaged by such slip. Alternatively, but to the same effect, the clutches are not controlled to fully close, but rather are controlled to slip also when the two driven wheels rotate at the same speed, i.e. also when the electric vehicle is not cornering. Preferably such latter controlled clutch slip is as small as possible (e.g. only a few rpm or less) to minimise the power loss in the clutches. Effectively, this latter control method is a convenient way to control the clutches of the two planetary gear sets, since it is easier to measure, i.e. to detect, and control the clutch slip than it is to control the said clutch safety margin in relation to the torque that is transmitted by the clutch. In this latter control method, the clutch slip of a respective one of the two clutches is controlled to increase relative to the clutch slip of the respective other one clutch when the electric vehicle is cornering.

Further according to the present invention, the said third members of each of the planetary gear sets can be mutually rotationally connected in reverse, i.e. in opposite rotational direction, through a coupling mechanism, which coupling mechanism can be applied either alternative or in addition to the clutches mentioned hereinabove. By such coupling mechanism, the differential function of the transmission is realised more simply, i.e. without requiring clutch (slip) control. Either way, the novel variable transmission according to the present invention favourably combines the differential and output speed reductions thereof, allowing for a compact transmission design.

It is noted that when the said clutches are applied, the speed reduction provided by the two planetary gear sets is preferably equal, in order to avoid the slipping of, i.e. drag losses in the clutches when the driven wheels rotate at the same speed (when driving straight). The said coupling mechanism, on the other hand, can be arranged to provide a speed ratio between the two planetary gear sets that is the inverse value of a difference of the speed reductions provided thereby, to compensate for such difference. Nevertheless, in this case too, the speed reduction provided by the two planetary gear sets is preferably equal, in which case the coupling mechanism only reverses the direction of rotation, rather than additionally providing a speed ratio/speed difference between the two planetary gear sets. To this end, the two planetary gear sets are preferably identical in terms of the outer diameter of the sun gears thereof, the outer diameter of the planet gears thereof and of the inner diameter of the ring gears thereof. Nevertheless, some design aspects will typically be different there between Of course, to minimise manufacturing cost, the two planetary gear sets are preferably identical also in several other design aspects thereof.

In a preferred, more detailed embodiment of the variable transmission according to the present invention, the said first members of the planetary gear sets are the sun gears thereof, the said second members of the planetary gear sets are the planet carriers thereof and the said third members of the planetary gear sets are the ring gears thereof. In this latter transmission embodiment, the ring gears are preferably provided both with internal teeth, for meshing with the planet gears of the respective planetary gear set, and with external teeth, for realizing the said reverse rotational connection there between by meshing with a respective gear provided on a respective one of two sub shafts that are mutually rotationally coupled to counter-rotate. Also in this latter transmission embodiment, the sun gears are each preferably, i.e. to add to the compactness of the variable transmission, provided on or integral with a stub shaft that is fitted inside a respective, axially oriented, central bore of the output shaft. Alternatively, the sun gears are fitted on a respective end of the output shaft. In both such constructions, a well-known spline connection can be applied to rotationally connect the sun gear and the output shaft together.

In another preferred embodiment of the variable transmission according to the present invention, an annular gear with internal teeth is attached to the side of the pulley on the input shaft of the variator unit. This annular gear is intended to mesh with a pinion gear on a motor shaft of the electric motor and thus provide a speed reduction there between. In this latter transmission embodiment, the necessary offset in radial direction between the input shaft and the electric motor is favourably provided for without excessive margin, thus contributing to the compact design thereof. In this respect, i.e. to maximise the compactness of the design, the diameter of the annular gear preferably corresponds to the diameter of the said pulley, while the diameter of the pinion gear is chosen to provide an input speed reduction in the range between 2.5:1 and 4.0:1 (defined as diameter/number of teeth of annular gear divided by diameter/number of teeth of pinion gear), preferably about (i.e. within 5%) 2.8:1 . Such an input speed reduction is ideally combined with a variator unit that is designed provide a (largest) speed reduction from its input shaft to its output shaft in the range between 1.7:1 and 2.7:1 , preferably about (i.e. within 5%) 2.1 :1 and with planetary gear sets that are designed to provide the output speed reduction between the output shaft of the variator unit and the driven wheels in the range between 3.0:1 and 6.5:1 depending on the specific vehicle application of the transmission and with the boundary condition that the total speed reduction ratio of the variable transmission, i.e. the product of the former three individual speed reductions, amounts to between 20:1 and 35:1 .

Another benefit of the variable transmission according to the present invention, especially in its latter embodiment with the input speed reduction (but irrespective of the design thereof), is that it can be conveniently adapted to wide range of vehicle applications that differ in terms of either their respective curb weight, their intended use (e.g. economic vs. “sporty”; towing capability vs. top speed; passenger vs. freight; city vs. highway; private vs. commercial; etc.) and/or the nominal specification (i.e. maximum torque, speed and power output) of the electric motor applied therein. In particular, the variable transmission can be thus adapted by varying the output speed reduction thereof, in particular by modifying the diameter of the sun gear of each planetary gear set on the output shaft in relation to the diameter of the respective ring gear. Of course, the diameter of the planet gears of the planetary gear sets has to be modified as well, to fit between the (modified) sun and ring gears, but the diameter of the ring gear preferably remains unchanged. In this case, the outer dimensions, i.e. the so-called envelope or cocoon of the variable transmission can favourably remain the same throughout the said wide range of vehicle applications, as can almost all of the components thereof with the exception of the said sun and planetary gears and, possibly, the ring gears of the planetary gear sets and/or the said input speed reduction.

The present invention thus also relates to a method for designing a variable transmission in relation to two or more electric motors of mutually different specification and/or to two or more vehicle specifications, wherein, with the possible exception of the input speed reduction and/or the diameter of the ring gears of the planetary gear sets, only the diameters of the sun and planetary gears of the planetary gear sets on the output shaft of the variable transmission are adapted to such electric motor specification.

The variable transmission according to the present invention is explained in more detail hereinafter by means of non-limiting, illustrative embodiments thereof and with reference to the drawing, in which:

- figure 1 is a schematic representation of the basic functional arrangement of the main components of a known electric vehicle powertrain with an electric motor and a variable transmission including a variator unit;

- figure 2 schematically depicts the variable transmission according to the present invention in the electric vehicle powertrain, illustrating the relevant components thereof and the preferred functional relationship there between;

- figure 3 provides two 3D solid models of the novel variable transmission of figure 2;

- figure 4 provides a schematic cross-sectional view of the novel variable transmission, illustrating several preferred constructional features thereof; and

- figure 5 schematically depicts the variable transmission according to the present invention in an alternative embodiment thereof.

Figure 1 shows a basic example of a known powertrain for an electric vehicle such as a battery electric passenger car. In addition to a battery and power electronics (not shown) for powering an electric motor 1 and/or for storing electric power generated by the electric motor 1 , the known electric vehicle powertrain comprises such electric motor 1 , two driven wheels 2 of the electric vehicle and a variable transmission 3 that drivingly connects the electric motor 1 to the driven wheels 2 via respective half shafts 38. In the specific embodiment of figure 1 thereof, the known variable transmission 3 includes a variator unit 40 that provides a continuously variable speed ratio between an input shaft 44 and an output shaft 45 thereof. The known variable transmission 3 further includes a differential 37 for allowing the driven wheels 2 to rotate at different speeds, an input speed reduction 31 between the electric motor 1 and the variator unit 40 and an output speed reduction 32 between the variator unit 40 and the differential 37, each composed of a pair of meshing gears 33, 34 and 35, 36 respectively, for increasing the operating speed of the electric motor 1 relative to the driven wheels 2. In this respect it is noted that at least the input speed reduction 31 is not an essential feature of the known variable transmission 3.

The variator unit 40 is, as such, well-known, in particular in the form comprising a drive belt 41 that is wrapped around and in frictional contact with both an input pulley 42 on the input shaft 44 and an output pulley 43 on the output shaft 45. An effective radius of the friction contact between the drive belt 41 and a pulley 42, 43 can be varied in mutually opposite directions between the two pulleys 42, 43 by means of a control and actuation system (not shown) of the variator unit 40 to vary the said speed ratio thereof between a most decelerating ratio, i.e. Low, and a most accelerating ratio, i.e. Overdrive. By including the variator unit 40 in the electric vehicle powertrain several advantages and/or optimisation strategies are unlocked. For example, the take-off acceleration and/or top speed of the electric vehicle can be increased thereby. Alternatively, these vehicle performance parameters can be maintained at the same level, while applying an electric motor 1 that is downsized in terms of, for example, its maximum torque generating capability.

The present invention sets out to improve the known variable transmission 3 in terms of the installation space that it requires in the electric powertrain. In figure 2, a novel variable transmission 3 according to the present invention is illustrated in a preferred embodiment thereof. In the novel variable transmission 3 the output pulley 43 and the output shaft 45 are arranged coaxially with the half shafts 38 and driven wheels 2 of the vehicle. The output speed reduction 32 and the differential 37 of the known variable transmission 3 are replaced by two planetary gear sets 50, one on either axial side of output pulley 43. Each such planetary gear set 50 comprises three coaxially rotatable members 51 , 52, 53, including a central sun gear 51 , an outer ring gear 52 and a planet carrier 53 that rotatably carriers one or more planet gears 54 located between and meshing with both the sun gear 51 and the ring gear 52. The sun gears 51 of the planetary gear sets 50 are rotationally connected to and rotate as one with the output shaft 45 of the variator unit 40. The planet carriers 53 of the planetary gear sets 50 are each rotationally connected to and rotate as one with a respective one of the two driven wheels 2 via a respective one of the said half shafts 38. The ring gears 52 of these two planetary gear sets 50 are mutually rotationally connected in reverse by means of a coupling mechanism 55.

In the illustrated, preferred embodiment thereof, the said coupling mechanism 55 is composed of two sub shafts 56, 57 provided with two gears 58, 59 each, whereof first gears 58 are mutually meshing to rotationally connect the sub shafts 56, 57 in reverse and whereof second gears 59 are respectively meshing with the ring gear 52 of a respective one of the said two planetary gear sets 50 that is thereto provided with external teeth. It is noted that, in principle, the two gears 58, 59 of either sub shaft 56, 57 can be embodied as a single gear wheel.

Moreover, any coupling mechanism 55, i.e. irrespective of its embodiment, can be braked or completely stopped from rotating, for example by (partly) closing a clutch (not illustrated) that connects a rotating part thereof, such as one of the said sub shafts 56; 57, to a non-rotating part of the variable transmission 3, such as its housing, or by appropriately actuating a secondary electric motor (not illustrated) that is connected to the such rotating part of the coupling mechanism 55, in order to implement a so-called limited slip differential function or differential lock function. Alternatively or additionally, such rotating part of the coupling mechanism 55 can be driven in either direction of rotation by such secondary electric motor, in order to implement a so-called a torque steering function between the two driven wheels 2, i.e. to actively distribute the driving torque between the two driven wheels 2.

As is likewise illustrated in figure 2 and as optional feature of the novel variable transmission 3 according to the present invention, the said input speed reduction 31 thereof comprises an annular gear 34 rotationally connected to the input shaft 44 of the variator unit 40 and a pinion gear 33 on a motor shaft of the electric motor 1 . The annular gear 34 is internally provided with teeth for meshing with the (external) teeth of the pinion 33. This particular design feature of the novel variable transmission 3 favorably results in a minimal radial offset between the (motor shaft of the) electric motor 1 and the (input shaft 44 of the) input pulley 42 of the variator unit 40. Also, the said radial offset that is still available, provides space to place a bearing of the input shaft 44 and thus allows for also a minimal offset in axial direction between the electric motor 1 and the input pulley 42. Alternatively, i.e. to completely remove the said radial offset at the expense of a larger axial offset, the input speed reduction 31 can comprise a (third) planetary gear set (not illustrated), whereof the sun gear is embodied by the said pinion gear 33, whereof the planet carrier is co-axial with and rotationally connected to the input shaft 44 and whereof the ring gear is blocked from rotating, e.g. is connected to a non-rotating part of the variable transmission 3.

The novel variable transmission 3 according to the present invention is illustrated in figure 3 by way of two 3D (solid) models thereof (excluding the drive belt 41 ) that are mutually identical other than being mirrored for showing the coupling mechanism 55 from both axial sides.

In figure 3, the planet carriers 53 of the planetary gear sets 50 are shown to include two parts 53a, 53b, namely a radially aligned carrier plate or cage 53a that supports the planet gears 54 of the respective planetary gear set 50 and an axially aligned carrier hub 53b for receiving a respective one of the said half shafts 38. Also in figure 3, a special embodiment of the planetary gear sets 50 is illustrated as regards to the ring gears 52 thereof. Rather than being composed of a single ring with internal and external teeth, the ring gears 52 according to the present invention each include two ring sections 52a, 52b that are mutually axially disposed side-by-side and that are respectively provided with either internal teeth or external teeth. In particular, a first ring section 52a of each planetary gear set 50 has internal teeth for meshing with the (teeth of the) planet gears 54 of the respective planetary gear set 50 and a second ring section 52b of each planetary gear set 50 has external teeth for meshing with a respective one of the said two second gears 59 of the coupling mechanism 55. In this embodiment thereof, the diameter of the said second ring section 52b can correspond to, or even be smaller than the diameter of the said first ring section 52a. In this way, the coupling mechanism 55 can be positioned favorably close to the (outer diameter of the) pulleys 42, 43 of the variator unit 40, contributing to the compact design of the variable transmission 3 and without putting a limit on the said output speed reduction provided by the planetary gear sets 50.

Figure 4 provides a cross-sectional view B-B as indicated in the box at the top right of the novel variable transmission 3 in relation to the design thereof illustrated in figure 3. In figure 4 several preferred constructional features of the novel variable transmission 3 are visible.

As is well-known in the art, the pulleys 42, 43 are each provided with a fixed pulley disc 46 that is formed integral with (or that is at least fixed to) the respective pulley shaft 44, 45 and an axially moveable pulley disc 47 that is slidably fitted on the respective pulley shaft 44, 45. Furthermore, each pulley 42, 43 is provided with a respective pressure chamber 48 for urging the respective moveable pulley disc 47 in the direction of the respective fixed pulley disc 46 by exerting a hydraulic pressure in the said pressure chamber 48. During operation of the variable transmission 3, the drive belt 41 is clamped between the two pulley discs 46 ,47 of each pulley 42, 43 as a result of the hydraulic pressures exerted in the respective pressure chambers 48. A rotational speed and an accompanying torque can then be transmitted between the pulleys 42, 43 by the drive belt 41 by means of friction between. Moreover, a ratio between the clamping forces that are exerted on the drive belt 41 by the input pulley 42 and the output pulley 43 respectively, determines the radii of curvature of the drive belt 41 at the pulleys 42, 43. In turn, a ratio of these radii of curvature determines the speed ratio of the variator unit 40, i.e. between the input shaft 44 and the output shaft 45 thereof. For generating and controlling the said hydraulic pressures in the pressure chambers 48, the variable transmission 3 is known to include an electro-hydraulic control system (not illustrated) including a hydraulic pump. As an alternative to such hydraulic application of the belt clamping forces at the pulleys 42, 43, it is also known to apply these forces electro-mechanically as, for instance, taught by EP1579126.

Conventionally, the (rotating) pulley shafts 44, 45 are respectively provided with a central, axially oriented bore 49 functioning as a channel for communicating hydraulic fluid between the respective pressure chamber 48 and a non-rotating supply (and discharge) tube 60 that is coaxial with the shaft bore 49 and that is partly inserted therein in a sealing manner, i.e. in a manner preventing or at least minimising the leakage of hydraulic fluid. Also in the novel variable transmission 3, the input shaft 44 defines such known shaft bore 49 and hydraulic channel. However, due the coaxial arrangement of the planetary gear sets 50 (and of the said half shafts 38) on either side of the output pulley 43 according to the present invention, such known solution is not available for the output shaft 45.

Accordingly, a first preferred constructional feature of the variable transmission 3 according to the present invention concerns a novel supply (and discharge) arrangement for communicating hydraulic fluid to and from the pressure chamber 48 of the output pulley 43. In this novel supply arrangement the carrier hub 53b is provided with a cylindrical core 61 , either as an integral part thereof (not illustrated), or as a separate part fitted inside in the carrier hub 53b in a sealing manner, which hub core 61 includes both a radial bore 62 and an axial bore 63 that are mutually connected.

The radial bore 62 of the hub core 61 is indirectly -i.e. via an opening in the wall of the carrier hub 53b- connected to a non-rotating supply (and discharge) ring 64 that is fitted on the (rotatable) carrier hub 53b in a sealing manner. Preferably, the hub core 61 is fixed relative to the planet carrier 53, for example by means of a force fit. Otherwise, the radial bore 62 of the hub core 61 ends in a ring shaped recess included in the outer circumference of the hub core 61 , via which recess the radial bore 62 of the relatively rotating hub core 61 remains in fluid communication with the opening in the wall of the carrier hub 53b.

The axial bore 63 of the hub core 61 is -directly or indirectly- connected to the known, shaft bore 49 of the output shaft 45 in a sealing manner. In particular, if the sun gear 51 is an integral part of a stub shaft 51 that is fitted inside such shaft bore 49 (as is illustrated in figure 4), the stub shaft 51 includes an axial bore 65 over its full axial length. In this case:

- either the hub core 61 extends completely through the bore 65 of the stub shaft 51 and, beyond the stub shaft 51 , is partly inserted in the shaft bore 49 of the output shaft 45 in a sealing manner,

- or the hub core 61 is partly inserted in the bore 65 of the stub shaft 51 in a sealing manner, while the stub shaft 51 is partly inserted in the shaft bore 49 of the output shaft 45 also in a sealing manner (as is illustrated in figure 4). A second preferred constructional feature of the variable transmission 3 according to the present invention concerns a support 70 that carries one end of at least the input shaft 44 of the variator unit 40. Hereto, the support 70 defines a cylindrical hub 71 , around which hub 71 a bearing ring 72 is fitted that is also fitted inside a recess or hollow provided in the said one end of the input shaft 44. In this way, the compact build of the variable transmission 3 that is pursued by the present invention is enhanced further, in particular when the support hub is combined with and placed on the same side of the input pulley 42 as the annular gear 34 of the input speed reduction 31 with the annular gear 34 and the pinion gear 33. Moreover, since the bearing ring 72 is fitted inside the input shaft 44 rather than around it, a favorably large diameter input shaft 44 can be applied without exceeding the maximum (tangential) speed of the bearing ring 72.

Preferably, the support 70 also carries one end of the output shaft 45 of the variable transmission 3. However, in this case, a shaft-internal support is not available, due the coaxial arrangement of the planetary gear sets 50 (and of the said half shafts 38) on either side of the output shaft 45. Instead, in this case, the support 70 defines a circular opening, wherein a further bearing ring 73 is fitted and in which further bearing ring 73 the output shaft 45 is mounted.

In figure 5, a novel variable transmission 3 according to the present invention is illustrated in an alternative or complementary embodiment thereof, relative to the embodiment illustrated in figure 2. In the alternative embodiment of the novel variable transmission 3 the ring gears 52 of the planetary gear sets 50 are each connected to a stationary part 39 of the variable transmission 3 via a respective clutch 65.

In figure 5 the clutches 65 are schematically represented in the form of well-known plate clutches 65 by way of example. The clutches 65 each include two sets of ring-shaped clutch plates 65a, 65b. A first set of clutch plates 65a is attached to the respective ring gear 52 and a second set of clutch plates 65b is attached to the said stationary transmission part 39. The clutches 65 can be closed to rotationally lock the respective ring gear 52, or opened to allow rotation thereof by allowing the sets of clutch plates 65a, 65b to slip relative to one another. The amount of slip between the sets of clutch plates 65a, 65b, i.e. the friction exerted on a respective ring gear 52 by a respective clutch 65 can be controlled, typically by means of a controlled hydraulic pressure.

When the clutches 65 of the two planetary gear sets 50 are closed, the ring gears 52 thereof cannot rotate and the two driven wheels 2 rotate at the same speed, whereas when at least one of the clutches 65 is controlled to slip, i.e. when it is partly or fully opened, the driven wheels 2 can have different rotational speeds, as is required when the electric vehicle is cornering. By thus combining the differential and output speed reduction functions of the variable transmission 3 in the said planetary gear sets 50 thereof, a favourably compact design thereof is provided.

The present invention, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all of the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as a non-limiting example of a respective feature. Separately claimed features can be applied separately in a given product, or in a given process as the case may be, but these can also be applied simultaneously therein in any combination of two or more of such features. The invention is not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompasses straightforward amendments, modifications and practical applications thereof that lie within reach of the person skilled in the relevant art.

Claims

1 . A variable transmission (3) for an electric vehicle, in particular a passenger car, with an electric motor (1 ) and with two or more driven wheels (2), in which electric vehicle the variable transmission (3) drivingly connects, i.e. rotationally couples, the electric motor (1 ) to the driven wheels (2), which variable transmission (3) comprises a variator unit (40) for providing a speed ratio between an input shaft (44) and an output shaft (45) of the variator unit (40) that is continuously variable within a range of speed ratios, characterised in that the variable transmission (3) further comprises two planetary gear sets (50) that are respectively provided on a respective axial side of the output shaft (45) of the variator unit (40), preferably coaxial therewith, and that each comprise three coaxially rotatable members (51 , 52, 53) including a central sun gear (51 ), an outer ring gear (52) and a planet carrier (53) that rotatably carries one or more planet gears (54) located between and meshing with both the sun gear (51 ) and the ring gear (52), whereof first members (51 , 52, 53) of each of the planetary gear sets (50) are rotationally connected to and rotate as one with the output shaft (45) of the variator unit (40), whereof second members (51 , 52, 53) of each of the planetary gear sets (50) can be rotationally connected to and rotate as one with a respective one of the two driven wheels (2) and whereof third members (51 , 52, 53) of each of the planetary gear sets (50) are mutually rotationally connected in reverse through a coupling mechanism (55).

2. The variable transmission (3) according to claim 1 , characterised in that the said first members (51 , 52, 53) of each of the planetary gear sets (50) are the sun gears (51 ) thereof, the said second members (51 , 52, 53) of each of the planetary gear sets (50) are the planet carriers (53) thereof and the said third members (51 , 52, 53) of each of the planetary gear sets (50) are the ring gears (52) thereof.

3. The variable transmission (3) according to claim 2, characterised in that the ring gear (52) of one or both of the planetary gear sets (50) is provided both with internal teeth for meshing with the planet gears (54) of the respective planetary gear set (50), and with external teeth for engaging the coupling mechanism (55).

4. The variable transmission (3) according to claim 2, characterised in that the ring gear (52) of one or both of the planetary gear sets (50) includes two, side-by-side disposed ring sections (52a, 52b), whereof a first ring section (52a) is provided with internal teeth for meshing with the planet gears (54) of the respective planetary gear set (50), and whereof a second ring section (52b) is provided with external teeth for engaging the coupling mechanism (55), which second ring section (52b) is preferably provided with an outer diameter that is equal to or smaller than an outer diameter of the first ring section (52a).

5. The variable transmission (3) according to a preceding claim, characterized in that the coupling mechanism (55) thereof comprises two sub shafts (56, 57), each provided with two gears (58, 59), whereof first gears (58) are mutually meshing to rotationally connect the sub shafts (56, 57) in reverse, and whereof second gears (59) are respectively meshing with a respective one of the said third members (51 , 52, 53) of each of the planetary gear sets (50) that are mutually coupled in reverse by the coupling mechanism (55).

6. The variable transmission (3) according to a preceding claim, characterized in that the coupling mechanism (55) thereof further comprises means, such as including a secondary electric motor or a clutch, for braking, stopping or driving the coupling mechanism (55), in particular a shaft (56; 57) thereof.

7. A variable transmission (3) for an electric vehicle, in particular according to claim 1 or 2, with an electric motor (1 ) and with two or more driven wheels (2), in which electric vehicle the variable transmission (3) drivingly connects, i.e. rotationally couples, the electric motor (1 ) to the driven wheels (2), which variable transmission (3) comprises a variator unit (40) for providing a speed ratio between an input shaft (44) and an output shaft (45) of the variator unit (40) that is continuously variable within a range of speed ratios, characterised in that the variable transmission (3) further comprises two planetary gear sets (50) that are respectively provided on a respective axial side of the output shaft (45) of the variator unit (40), preferably coaxial therewith, and that each comprise three coaxially rotatable members (51 , 52, 53) including a central sun gear (51 ), an outer ring gear (52) and a planet carrier (53) that rotatably carries one or more planet gears (54) located between and meshing with both the sun gear (51 ) and the ring gear (52), whereof first members (51 , 52, 53) of each of the planetary gear sets (50) are rotationally connected to and rotate as one with the output shaft (45) of the variator unit (40), whereof second members (51 , 52, 53) of each of the planetary gear sets (50) can be rotationally connected to and rotate as one with a respective one of the two driven wheels (2) and whereof third members (51 , 52, 53) of each of the planetary gear sets (50) are connectable to a stationary part (39) of the variable transmission (3) via a respective clutch (65).

8. The variable transmission (3) according to claim 7, characterised in that each clutch (65) is capable of being maintained in a fully closed state, wherein the respective third 15 member (52) of the respective planetary gear set (50) is prevented from rotating, or in a slipping or fully opened state, wherein the respective third member (52) can rotate relative to the said stationary transmission part (39).

9. The variable transmission (3) according to claim 8, characterised in that each clutch (65) is hydraulically or mechanically controllable.

10. The variable transmission (3) according to a preceding claim, characterised in that the sun gear (51 ) of one or both of the planetary gear sets (50) is provided on, or is integral with a stub shaft (51 ) that is fitted inside an axially oriented, central shaft bore (49) of the output shaft (45), which stub shaft (51 ) and shaft bore (49) are preferably rotationally connected by means of a spline.

11 . The variable transmission (3) according to a preceding claim, characterised in that the variator unit (40) thereof comprises two adjustable pulleys (42, 43), each pulley (42; 43) provided on and rotating as one with a respective one of the said input shaft (44) and output shaft (45), and a drive belt (41 ) that wrapped around the pulleys (42, 43) at an adjustable radius at each pulley (42; 43).

12. The variable transmission (3) according to claim 11 , characterized in that it further comprises an annular gear (34) with internal teeth that is attached to the side of the pulley (42) on the input shaft (44) of the variator unit (40), having a diameter that essentially corresponds to the diameter of such pulley (42), and that meshes with a pinion gear (33) of the electric motor (1 ), having a diameter that provides a speed reduction in the range between 2.5:1 and 4.0:1 , preferably of about 2.8:1 , between such pinion gear (33) and the annular gear (34).

13. The variable transmission (3) according to claim 11 , characterized in that it further comprises a third planetary gear set, whereof the sun gear is embodied by a pinion gear (33) of the electric motor (1 ), whereof the planet carrier is coaxial with, rotationally connected to and rotates as one with the input shaft (44) of the variator unit (40) and whereof the ring gear is, or at least can be, blocked from rotating.

14. The variable transmission (3) according to claim 11 , 12 or 13, characterized in that:

- the planet carrier (53) of at least one of the planetary gear sets (50) includes an axially aligned carrier hub (53b) for receiving a half shaft (38), 16

- a hub core (61 ) with a radial bore (62) and with an axial bore (63) that are mutually connected, either is fitted inside the carrier hub (53b) in a sealing manner or is formed as an integral part of the carrier hub (53b), and in that:

- the axial bore (63) of the hub core (61 ) is connected to an axial bore (49) of the output shaft (45) in a sealing manner.

15. The variable transmission (3) according to claim 14, characterised in that:

- the sun gear (51 ) of the at least one planetary gear set (50) is provided on, or is integral with a stub shaft (51 ) that is fitted inside the axial bore (49) of the output shaft (45) and that itself is provided with an axial bore (65) over its full axial length, and in that:

- either the hub core (61 ) extends completely through such axial bore (65) of the stub shaft (51 ) and is partly inserted in the axial bore (49) of the output shaft (45) in a sealing manner,

- or the hub core (61 ) is partly inserted in the axial bore (65) of the stub shaft (51 ) in a sealing manner, while the stub shaft (51 ) is partly inserted in the axial bore (49) of the output shaft (45) in a sealing manner.

16. The variable transmission (3) according to claim 14 or 15, characterised in that:

- a non-rotating supply ring (64) is fitted on the carrier hub (53b) in a sealing manner that is in fluid communication with the radial bore (62) of the hub core (61 ) via a wall opening of the carrier hub (53b), and in that:

- either the hub core (61 ) is fixed relative to the planet carrier (53),

- or the radial bore (62) of the hub core (61 ) ends in a ring shaped recess included in the outer circumference of the hub core 61 .

17. The variable transmission (3) according to claim 11 , 12 or 13, characterized in that it further comprises a support (70) defining a cylindrical hub (71 ), around which hub (71 ) a bearing ring (72) is fitted that carries one end of the input shaft (44) of the variator unit (40).

18. The variable transmission (3) according to claim 17, characterized in that the support (70) further defines a circular opening wherein a further bearing ring (73) is fitted that carries one end of the output shaft (45) of the variator unit (40).

19. Method for controlling the variable transmission (3) according to claim 7, 8 or 9 during operation of the electric vehicle, characterised in that, when the electric vehicle is cornering while being driven by the electric machine (1 ), at least the clutch (55) of the planetary gear set (50) that is associated with the inner driven wheel (2) is controlled to slip, whereas when 17 the electric vehicle is cornering while the electric machine (1 ) is being driven, at least the clutch (55) of the planetary gear set (50) that is associated with the outer driven wheel (2) is controlled to slip.

20. Method for controlling the variable transmission (3) according to a claim 19, characterised in that, a maximum torque that can be transmitted by either clutch (55) is actively controlled, also when it is maintained in a fully closed state.