TECHNICAL FIELD

The present invention relates to a central motor unit for a vehicle. The invention also relates to a vehicle comprising such a central motor unit. The invention is applicable on vehicles, in particularly working machines such as e.g. wheel loaders, articulated haulers, dump trucks, etc. Although the invention will mainly be described in relation to a wheel loader, it may also be applicable for other type of vehicles.

BACKGROUND

In connection with transportation of heavy loads at construction sites or the like, a working machine is often used. The working machines may be utilized for transportations in connection with road or tunnel building, sand pits, mines, forestry and similar environments. Thus, the working machine is frequently operated with large and heavy loads in rough terrain and on slippery ground where no regular roads are present.

There is a demand from the market to be able to propel working machines in a more environmentally friendly manner, e.g. by electrification of the driveline. Such a driveline may consist of a central motor and a gearbox for achieving several gears. The number of gears as well as gear ratios and steps have to be optimized for the specific central motor which is used. With an optimized gearbox, the central motor will operate in its most efficient range and the desired combination of rim pull and top speed can be reached with a limited size of the central motor.

The gearbox comprises a transmission arrangement and depending on the specific type of gearbox, the transmission arrangement may comprise e.g. ordinary gear sets with cylindrical gear wheels in meshed connection with each other or planetary gear sets comprising a respective sun gear, ring gear and a planet carrier, or a

transmission having a combination of ordinary gear sets and one or more planetary gear sets. Such a transmission arrangement may be combined with the central motor to get a central motor unit. There is hence a desire to be able to operate a working machine with such a driveline containing a central motor unit as an alternative to a conventional purely mechanical driveline.

SUMMARY

It is an object of the present invention to provide a central motor unit which can be operated in a more environmentally friendly manner in comparison to the prior art. The object is at least partly achieved by a central motor unit according to claim 1 .

According to a first aspect of the present invention, there is provided a central motor unit for a vehicle, the central motor unit comprising a central motor and a

transmission arrangement, the transmission arrangement comprising a transmission housing, an input shaft, and an output shaft, the transmission arrangement further comprising a first, a second and a third planetary gear set each comprising a first, a second and a third planetary member, the planetary members being a sun gear, a planet carrier and a ring gear, the transmission arrangement further comprising five shift elements engageable in combinations of two to obtain six forward gear stages, wherein the ring gear of the first planetary gear set and the planet carrier of the second planetary gear set are operatively connected to each other, the ring gear of the second planetary gear set and the planet carrier of the third planetary gear set are operatively connected to each other, two planetary members of the third planetary gear set are selectively connectable to each other by a single one of the shift elements, and wherein the central motor is connected to the input shaft.

The wording“operatively connected to” should in the following and throughout the entire description be interpreted such that the components thereof are fixedly connected to each other, i.e. the rotational speed of the components which are operatively connected to each other is the same. Hence, no connecting mechanism or the like is arranged between the components that are operatively connected to each other and they can therefore not be disengaged from one another during operation. Accordingly, the ring gear of the first planetary gear set is always connected to the planet carrier of the second planetary gear set.

Moreover, the wording“selectively connectable to” should in the following and throughout the entire description be interpreted as an element being connectable at desirable points in time to another element. Hereby, gear shifts of the transmission arrangement can be executed by either connecting or disconnecting elements to/from each other. Components may be selectively connectable to each other by means of connecting/locking mechanisms and controlled by e.g. a control unit or the like. When a connecting/locking mechanism is positioned in an engaged state the components are connected to each other.

Furthermore, when stating that a component is merely“connected to” another component, this should be construed such that the components are connected to each other, either directly, i.e. operatively connected, or indirectly. Hence, the central motor may be connected to the input shaft, either directly or via a transmission component such as a clutch, a further planetary gear set, etc.

Moreover, the central motor should be construed as a machine which provides propulsive power to the vehicle via the transmission arrangement. The central motor may in turn be provided with power from a suitable power source for being able to propel the vehicle. According to an example embodiment as is also described below, the central motor may be an electric machine. In such a case, the electric machine may receive electric power from e.g. a generator connected to an internal combustion engine, which supplies electrical power to the electric machine. The electric machine may on the other hand be supplied with electrical power from a battery, etc. The central motor may also be a hydraulic machine, which receives hydraulic fluid from e.g. a hydraulic pump and/or a hydraulic accumulator, etc.

An advantage is that a vehicle provided with the central motor unit can be operated in a more environmentally friendly manner in comparison to operation through a conventional driveline. The internal combustion engine is decoupled from vehicle speed and may be operated in its most efficient range, especially in combination with an energy storage device according to an example embodiment described below. The vehicle may in such a case occasionally be operated with the internal combustion engine shut off. Other types of power sources are also possible, e.g. hydrogen fuel cells or direct connection to the grid. The inventors of the present disclosure have realized that the specific transmission arrangement can be advantageously used in combination with a central motor to form an environmentally friendly central motor unit. According to a further advantage, the transmission arrangement is not in need of dedicated reverse gear functionality when connected to the above described central motor. The reverse functionality can instead be achieved by operating the central motor in opposite direction. As such, an equal number of forward gears and reverse gears are obtainable.

According to an example embodiment, the input shaft may be operatively connected to the sun gear of the third planetary gear set.

According to an example embodiment, the central motor unit may further comprise a fourth planetary gear set comprising a sun gear, a planet carrier and a ring gear, the fourth planetary gear set being operatively connected between the central motor and the input shaft.

According to an example embodiment, the central motor may be operatively connected to the sun gear of the fourth planetary gear set.

According to an example embodiment, the planet carrier of the fourth planetary gear set may be operatively connected to the input shaft.

According to an example embodiment, the ring gear of the fourth planetary gear set may be operatively connected to the transmission housing. Hereby, a suitable gear ratio between the central motor and the transmission arrangement is provided.

According to an example embodiment, the sun gear and the ring gear of the third planetary gear set may be selectively connectable to each other. Hereby, power can be transferred from the input shaft to the ring gear of the second planetary gear set via the planet carrier of the third planetary gear set without power recirculation in the third planetary gear set.

According to an example embodiment, the sun gear and the planet carrier of the third planetary gear set may be selectively connectable to each other. Hereby, power can be transferred from the input shaft to the ring gear of the second planetary gear set via the planet carrier of the third planetary gear set by by-passing the third planetary gear set.

According to an example embodiment, the planet carrier and the ring gear of the third planetary gear set may be selectively connectable to each other.

According to an example embodiment, the five shift elements may comprise two locking mechanisms and three connecting mechanisms.

A locking mechanism should be construed as a shift element which e.g. locks a planetary member of one of the planetary gear sets to the transmission housing. Hence, when a locking mechanism is positioned in the engaged state, the planetary member connected thereto is held stationary. A connecting mechanism on the other hand should be construed as a shift element which e.g. connects two planetary members to each other, or connects a planetary member to the input shaft or the output shaft of the transmission arrangement. Hereby, the members on a respective side of the connecting mechanism rotate with the same rotational speed when the connecting mechanism is positioned in the engaged state. The locking mechanisms and the connecting mechanisms may also be positioned in a slipping state, whereby a relative rotational speed is obtained between the members connected thereto.

According to an example embodiment, the central motor may be operatively connected to an energy storage device. Hereby, the central motor is supplied with power for propelling the vehicle. The central motor may also be arranged to regenerate power to the energy storage device when the vehicle is operated in a power regenerating mode, such as when driving downhill, etc.

According to an example embodiment, the planet carrier of the first planetary gear set and the output shaft may be operatively connected to each other.

According to an example embodiment, the sun gear of the first planetary gear set and the sun gear of the second planetary gear set may be operatively connected to each other. According to an example embodiment, the sun gear of the first planetary gear set and the transmission housing may be selectively connectable to each other.

According to an example embodiment, the sun gear of the second planetary gear set and the transmission housing may be selectively connectable to each other.

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

According to an example embodiment, the ring gear of the third planetary gear set and the transmission housing may be selectively connectable to each other.

According to an example embodiment, the sun gear of the third planetary gear set and the planet carrier of the second planetary gear set may be selectively

connectable to each other.

According to an example embodiment, the central motor may be an electric machine. In particular, the electric machine should preferably be a high-speed electric machine. According to a non-limiting example, the electric machine may have a maximum speed of around 8000 - 10000 rpm.

According to a second aspect of the present invention, there is provided a vehicle comprising a power source and a driveline connected to the power source, wherein the driveline comprises a central motor unit according to any one of the example embodiments described above in relation to the first aspect.

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

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. DEFINITIONS

The relationship between the rotational speeds of the different members in a planetary gear set is defined according to the following: w ₅ -w _R _ ^

(Eq. 1 ) wherein w ₅ is the speed of rotation of the sun gear;

w _R is the speed of rotation of the planet carrier;

w _k is the speed of rotation of the ring gear; and

R is the stationary gear ratio of the planetary gear set. As used herein, the expression“stationary gear ratio” R for a planetary gear set is defined as the ratio of the speed of rotation of the sun gear to the speed of rotation of the ring gear in a situation in which the planet carrier is stationary, i.e.:

R = for single planet gear wheels (Eq. 2)

¾ and

R = +— for double planet gear wheels (Eq. 3) wherein z _R is the number of teeth of the ring gear; and

z ₅ is the number of teeth of the sun gear. In a similar manner, the expression“ratio” for a transmission should be understood to relate to the number of revolutions of the input shaft of the transmission divided by the number of revolutions of the output shaft of the transmission. Furthermore, the expression“step” should be understood to mean the quotient achieved when the ratio of a gear is divided by the ratio of an adjacent gear of a transmission. BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, wherein:

Fig. 1 is a lateral side view illustrating a working machine in the form of a wheel loader;

Fig. 2 schematically illustrates a central motor unit according to an example embodiment of the present invention; and

Fig. 3 schematically illustrates a central motor unit according to another example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.

Fig. 1 is a lateral side view illustrating an example embodiment of a working machine in the form of a loader vehicle 1 having an implement 2 for loading operations. The loader vehicle 1 depicted in Fig. 1 is in the form of an articulated wheel loader. The term“implement” is intended to comprise any kind of hydraulically operated tool, such as a bucket, a fork or a gripping tool arranged on the loader vehicle 1 . The implement 2 illustrated in Fig. 1 comprises a bucket 3 which is arranged on a loading unit assembly 4 for lifting and lowering the bucket 3. The bucket 3 can also be tilted or pivoted relative to the loading unit assembly 4. The loader vehicle 1 is provided with a hydraulic system comprising at least one hydraulic machine (not shown), such as e.g. a hydraulic pump. The loader vehicle 1 further comprises a hydraulic lift cylinder 5, for lifting operation of the loading unit assembly 4 and a hydraulic tilt cylinder 6 for tilting the bucket 3 relative to the loading unit assembly 4. Furthermore, the hydraulic system comprises steering cylinders 7a, 7b for turning the loader vehicle 1 by means of relative movement of a front unit 8 and a rear unit 9 around a substantially vertical geometric axis 10 of an articulated joint arrangement 12. The front unit 8 and the rear unit 9 comprise a respective pair of ground engaging members 20, 22. The ground engaging members 20, 22 are in the example embodiment a respective pair of wheels. In other words, the loader vehicle 1 is frame-steered by means of the steering cylinders 7a, 7b.

Turning now to Fig. 2, which schematically illustrates a central motor unit 100 according to an example embodiment which is suitable for the above described loader vehicle 1. The central motor unit 100 comprises a transmission arrangement 900 which is arranged to obtain a plurality of gear stages as will be described further below. The transmission arrangement 900 comprises a first planetary gear set 102 comprising a sun gear 102S, a planet carrier 102P and a ring gear 102R, a second planetary gear set 104 comprising a sun gear 104S, a planet carrier 104P and a ring gear 104R, and a third planetary gear set 106 comprising a sun gear 106S, a planet carrier 106P and a ring gear 106R. The central motor unit 100 further comprises a central motor 200 for providing a rotary motion/torque to the transmission arrangement 900. The transmission arrangement 900 thus further comprises an input shaft 136 for receiving the rotary motion/torque from the central motor, and an output shaft 1 12 for providing a rotary motion/torque to the driven wheels of the loader vehicle 1. The output shaft 1 12 may also be connected to a so-called drop box.

The central motor 200 is arranged to receive power from an external power source (not shown). The central motor may be an electric machine which receives electric power from an internal combustion engine connected to a generator. Thus, the generator supplies electrical power to the electric machine. Other alternatives are also conceivable, such as a charge depleting battery or a fuel cell connected to the electric machine. According to the example embodiment depicted in Fig. 2, the central motor unit 100 comprises an energy storage device 202 connected to the central motor 200. Depending on the driving situation, the energy storage device 202 is arranged to either receive power from the central motor 200, or to supply power to the central motor 200. If the central motor is an electric machine, the energy storage device 202 is a battery or a capacitor. The central motor 200 must however not be an electric machine; a hydraulic machine may also suitably be used. In such case, the energy storage device 202 is preferably a hydraulic accumulator.

Furthermore, the different members of the planetary gear sets 102, 104, 106 of the transmission arrangement 900, i.e. the sun gear, the planet carrier and the ring gear, are in the example embodiment depicted in Fig. 2 configured according to the following. It should be readily understood that the different members described below are connected to each other, either directly, i.e. operatively connected, or via a connecting mechanism, i.e. selectively connectable. The members can be operatively connected to each other by means of e.g. a connector element. Such connector element can be e.g. a solid shaft, a hollow shaft or a drum, or other suitable element for connecting two members to each other, which elements are known to the person skilled in the art. Hence, no explicit explanation is given below in regards to the means connecting the members to each other.

The planet carrier 102P of the first planetary gear set 102 is operatively connected to the output shaft 1 12 of the transmission arrangement 900, i.e. the planet carrier 102P is at all times directly connected to the output shaft 1 12 of the transmission arrangement 900. Further, the ring gear 102R of the first planetary gear set 102 is operatively connected to the planet carrier 104P of the second planetary gear set 104. The ring gear 102R of the first planetary gear set 102 is also selectively connectable to the sun gear 106S of the third planetary gear set 106 as well as the input shaft 136 of the arrangement 900 by means of a second connecting

mechanism 144. The sun gear 102S of the first planetary gear set 102 is operatively connected to the sun gear 104S of the second planetary gear set 104. Furthermore, the sun gear 102S of the first planetary gear set 102 and the sun gear 104S of the second planetary gear set 104 are selectively connectable to a transmission housing 160 of the arrangement 900 by means of a first locking mechanism 142. Hence, the first locking mechanism 142, when being engaged, initially reduces the rotational speed of the respective sun gears 102S, 104S, and thereafter locks the respective sun gears 102S, 104S to the transmission housing 160. The ring gear 104R of the second planetary gear set 104 is operatively connected to the planet carrier 106P of the third planetary gear set 106. Furthermore, the planet carrier 104P of the second planetary gear set 104 is also selectively connectable to the ring gear 106R of the third planetary gear set 106 by means of a first connecting mechanism 146.

The sun gear 106S of the third planetary gear set 106 is operatively connected to the input shaft 136. The ring gear 106R of the third planetary gear set 106 is selectively connectable to the transmission housing 160 by means of a second locking mechanism 138. Hence, the second locking mechanism 138, when being engaged, initially reduces the rotational speed of the ring gear 106R, and thereafter locks the ring gear 106R to the transmission housing 160. Furthermore, the input shaft 136 is selectively connectable to the ring gear 106R of the third planetary gear set 106 by means of a third connecting mechanism 150. Accordingly, the sun gear 106S and the ring gear 106R of the third planetary gear set 106 are selectively connectable to each other by means of the third connecting mechanism 150.

It should be readily understood that the third connecting mechanism 150 may equally as well be positioned between the sun gear 106S and the planet carrier 106P of the third planetary gear set 106, as well as between the planet carrier 106P and the ring gear 106R of the third planetary gear set 106. However, the following will be described in relation to the embodiment depicted in Fig. 2, i.e. that the sun gear 106S and the ring gear 106R of the third planetary gear set 106 are selectively connectable to each other by means of the third connecting mechanism 150.

According to the example depicted in Fig. 2, the transmission arrangement 900 is adapted to assume the gears as presented in Table 1 below. In Table 1 below, the locking mechanisms are denoted simply as“Brakes” while the connecting mechanisms are denoted simply as“Clutches”. A cell marked with a dot indicates an engaged state and a blank cell indicates a disengaged state. The table also indicates non-limiting examples of the gear ratios and steps obtainable by the transmission arrangement 900 for the various gears. According to a non-limiting example, the stationary gear ratio for the first planetary gear set 102 may be -2.871 , the stationary gear ratio for the second planetary gear set 104 may be -1 .754, and the stationary gear ratio for the third planetary gear set 106 may be -1.737. Table 1 - Shift diagram for the different forward gears of the embodiment in Fig. 2.

As can be seen in Table 1 , the transmission arrangement 900 in Fig. 2 comprises six forward gear stages F1 - F6, wherein each of the six gear stages is obtained by positioning two of the shift elements in the engaged state. The switching of gears can preferably be executed by one-step gear shifts or with two-step gear shifts. One- step gear shift should be understood to mean that a gear shift is executed from one gear to the next coming consecutive gear, for example, gear shift from the first gear stage to the second gear stage, from the second gear stage to the third gear stage, from the third gear stage to the second gear stage, etc. Two-step gear shift should be understood to mean that a gear shift is executed to exclude a next coming consecutive gear stage, for example, gear shift from the first gear stage to the third gear stage, from the second gear stage to the fourth gear stage, from the third gear stage to the first gear stage, etc.

As can be seen from Table 1 , one-step gear shifting includes only single shifts of the connecting mechanisms and the locking mechanisms, i.e. when executing one-step gear shifts, only one of the connecting mechanisms/locking mechanisms is shifted from an engaged state to a disengaged state, and only one of the connecting mechanisms/locking mechanisms is shifted from a disengaged state to an engaged state. As an example, when shifting from the first gear stage to the second gear stage, it is only the second locking mechanism 138 that is changed from an engaged state to a disengaged state, and only the first connecting mechanism 146 that is changed from a disengaged state to an engaged state. Likewise, also two-step gear shifting only includes single shifts of the connecting mechanisms and the locking mechanisms.

An advantage of the transmission arrangement 900 is hence that the shiftability is improved since a low number of connecting mechanisms/locking mechanisms need activation/deactivation during gear shifting. In detail, during both one-step gear shifting as well as during two-step gear shifting, only single shifts occur.

Furthermore, the central motor unit 100 enables for the same number of reverse gears as the forward gears presented in Table 1 . In particular, reverse gears are obtained by operating the central motor 200 in opposite direction in comparison to operation in forward driving. Thus, the reverse gears will be provided with the same gear ratios as presented in Table 1.

Reference is now made to Fig. 3 which schematically illustrates a central motor unit 100 according to another example embodiment. As can be seen the central motor unit 100 comprises a fourth planetary gear set 108 which is operatively connected to the transmission arrangement 900 and the central motor 200. The fourth planetary gear set 108 comprises a sun gear 108S, a planet carrier 108P and a ring gear 108R. The planet carrier 108P supports a number of planet gears as for the other planet carriers 102P, 104P and 106P (not shown).

In detail and as can be seen in Fig. 3, the fourth planetary gear set 108 is operatively connected to the input shaft 136. In further detail, the sun gear 108S of the fourth planetary gear set 108 is operatively connected to the central motor 200. The planet carrier 108P of the fourth planetary gear set 108 is operatively connected to the input shaft 136, which in turn is operatively connected to the sun gear 106S of the third planetary gear set 106. The ring gear 108R of the fourth planetary gear set 108 is operatively connected to the transmission housing 160. Hence, the ring gear 108R of the fourth planetary gear set 108 is stationary.

By means of the fourth planetary gear set, a gear ratio between the central motor 200 and the transmission arrangement 900 can be provided which is suitable for operating the vehicle by means of the central motor 200.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. For example, although the present invention has mainly been described in relation to a wheel loader, the invention should be understood to be equally applicable for any type of vehicle. Further, it should also be understood that the embodiments depicted in Figs. 2 - 3 may be arranged in connection to a drop box downstream the output shaft, which may be particularly suitable for the wheel loader application.