Wheel hub unit

A wheel hub unit is provided including at least one planetary gear set, including a sun gear, one set of planet gears, a carrier, and a ring gear, wherein each of the planet gears of the set of planet gears is provided with an engagement arrangement adapted for engagement with a corresponding engagement arrangement of the ring gear, wherein the engagement is provided at an engagement area in which the engagement arrangement of the planet gears overlap the engagement arrangement of the ring gear, a bearing, including an inner bearing ring, an outer bearing ring and rolling elements, wherein the inner bearing ring constitutes the ring gear of the planetary gear set, and wherein a center of each of the respective rolling elements is axially displaced in relation to the engagement area. A vehicle including such a wheel hub unit is also provided.

BACKGROUND AND SUMMARY

The present invention relates to a wheel hub unit for a vehicle. The present invention also relates to a vehicle being provided with a wheel hub unit.

The invention is applicable on working machines within the fields of industrial construction machines or construction equipment; in particular wheel loaders and articulated haulers. Although the invention will be described with respect to a wheel loader, the invention is not restricted to this particular vehicle, but may also be used in other working machines, such as excavators and backhoe loaders. It may also be used in e.g. trucks, buses or cars.

Vehicles, for example wheel loaders, today are often provided with a final drive comprising a hub-mounted reduction gear. The hub-mounted reduction gear can be provided in the form of a hub unit and is provided in the wheel which is intended to be driven. The wheel hub unit may typically comprise at least one planetary gear set with an integral brake, and a bearing. The sun gear of the planetary gear set is rotationally locked to and driven by a drive shaft connected to the vehicle's drive source. The sun gear is in engagement with, and drives, planet gears which are arranged between the sun gear and a ring gear. The bearing is provided between the stationary ring gear of the planetary gear set and the rim. The planet carrier is fixedly connected to the rim, and thereby drives the wheel. An example of such a wheel hub unit is provided in EP 1 899 619.

There is a general desire in the industry to develop the drive systems of the vehicles, including i.a. the wheel hub units. The wheel hub units may be improved e.g. by adding further reduction gears or by adding electric motors to them, thereby enabling electric or hybrid drive of the vehicle. However, the size of the rim is usually fixed for the specific type of vehicle, and the wheel hub unit should preferably be able to fit in the rim. If portions of the wheel hub unit extend outside the rim, there is a risk that the ground clearance of the vehicle is compromised.

It is desirable to provide a wheel hub unit which may contain more and/or larger components, as compared to the prior art, and still fit into a rim of a specific size.

The wheel hub unit according to the present invention comprises at least one planetary gear set, comprising a sun gear, one set of planet gears, a carrier, and a ring gear, wherein each of the planet gears of the set of planet gears is provided with engagement means adapted for engagement with corresponding engagement means of the ring gear, and wherein said engagement is provided at an engagement area where said engagement means of the planet gears overlap said engagement means of the ring gear. The wheel hub unit also comprises a bearing, comprising an inner bearing ring, an outer bearing ring and rolling elements. The inner bearing ring constitutes the ring gear of the planetary gear set, wherein a center of each of the respective rolling elements is axially displaced in relation to said engagement area.

With axially displaced is meant to understand that a straight radially extending imaginary line which intersects an axial center line of the wheel hub unit perpendiculary and intersects the center of one of said rolling elements is axially displaced in relation to a straight radially extending imaginary line which intersects the axial center line of the wheel hub unit perpendiculary and intersects the portion of the engagement area that is closest to said rolling element. As is also understood, the imaginary lines that extend perpendicularly from the axial center of the wheel hub unit, and intersect the center of a rolling element of a bearing and the engagement area of the planetary gear set, respectively, are parallel with each other.

By axially displacing the rolling elements of the bearing and the engagement area where said engagement means of the planet gears overlap said engagement means of the ring gear engagement, the available space along the axial length of the wheel hub unit is better utilized, and the radial limitation is thereby to at least some extent handled. A benefit of axially displacing these two parts of the wheel hub unit is that the ring gear/inner bearing ring require a certain material thickness in order to reliably fulfill it tasks. It is therefore usually not acceptable to reduce the material thickness in order to make it fit within the constraints of a rim of a specific size. Reducing the material thickness may also not always be enough in order to fit a planetary gear set of a desired size radially inwards of a bearing. By the inventive axial displacement, the required material thickness may be achieved within the specified size constraints and the planetary gear set may be made larger and still be able to be used within a rim of a specific size. According to this first aspect, it is not required that there is no axial overlap between the rolling elements and the engagement area. Instead, it is only required that the portion of the engagement area being closest to the rolling elements is displaced in the axial direction in relation to the center of the rolling elements.

According to one exemplary embodiment, the rolling elements are axially displaced in relation to the engagement area of the planet gear engagement means and the ring gear engagement means, such that the entire rolling elements are arranged axially outside of the engagement area.

Hence, in this embodiment, a straight imaginary line that intersects the axial center line of the wheel hub unit perpendicularly and intersects one of said rolling elements at the portion of the rolling element being closest to the engagement area is axially displaced in relation to a straight radially extending imaginary line which intersects the axial center line of the wheel hub unit perpendicularly and intersects the portion of the engagement area that is closest to said rolling element.

Hence, according to this aspect of the present invention, the engagement area is ax tally distanced in relation to the rolling elements of the bearing, such that no axial overlap is present between the engagement area and the rolling elements of the bearing. By that, it is possible to provide for a ring gear/inner bearing ring having an even larger material thickness as compared to the first embodiment of the present invention. It may even be conceivable with a planetary gear set in which the root diameter of die ring gear is larger than the diameter of the raceway of the inner bearing ring. Hence, a larger planetary gear set may be provided within a rim of a specific size.

According to one exemplary embodiment, the bearing is a double-row bearing. According to this exemplary embodiment, the rolling elements of the double-row bearing are axially displaced in relation to the engagement area of the planet gear engagement means and the ring gear engagement means, such that both rolling elements in each pair of rolling elements are arranged axially outside of the engagement area.

Hence, a straight imaginary line that intersects the axial center line of the wheel hub unit perpendicularly and intersects a rolling element in the row of rolling elements that is closest to the engagement area is axially displaced in relation to a straight radially extending imaginary line which intersects the axial center line of the wheel hub unit perpendicularly and intersects the portion of the engagement area that is closest to said rolling element. Hence, according to this embodiment, the engagement area is axially displaced in relation the rolling elements being closest to the engagement means. As for the embodiment described above, a configuration according to this embodiment allows for the possibility to provide a larger planetary gear set.

According to an exemplary embodiment, the engagement means of the planet gears are provided in the form of teeth. According to one exemplary embodiment, corresponding teeth are provided on an inward facing surface of the ring gear, as seen in the radial direction of the wheel hub unit.

According to one exemplary embodiment, the wheel hub unit has an axial extension with an inner end being the end that is adapted to be connected to a vehicle, and an outer end being the end that is adapted to be connected to a rim for holding a wheel.

According to one exemplary embodiment, said inner bearing ring comprises a flange which extends in the axial direction of said wheel hub unit, and wherein the engagement means of the ring gear are provided on said flange. Providing the engagement means of the ring gear on a flange extending in the axial direction of the wheel hub unit is a beneficial way of axially distancing the engagement area from the rolling elements of the bearing.

According to one exemplary embodiment, the engagement area is provided closer to the outer end than said rolling elements of the bearing, as seen in the axial direction of the wheel hub unit. Hence, the engagement area is provided further axially away from where the wheel hub unit is connected to the vehicle body, as compared to where the rolling elements are provided. They do however not extend outside the outermost portion of the rim or the wheel when the wheel hub unit is fitted to a rim. In order to provide for a vehicle with good ground clearance, it is beneficial to provide all parts of the wheel hub unit within the rim or wheel.

According to one exemplary embodiment, the inner ring of the bearing is a split inner ring comprising two parts. A split inner ring comprises at least two parts that are connected through a suitable connecting element. Such a connecting element may e.g. be a bolt or screw. Providing the inner ring of the bearing as a split inner ring is beneficial in terms of simplified production whiles it at the same time provides for a sufficiently strong and robust bearing ring.

According to one exemplary embodiment, both parts of the split inner bearing ring are in contact with the rolling elements of the bearing. In other words, the bearing race is provided in a space defined by both parts of the inner bearing ring.

According to one exemplary embodiment, a first pan of the two parts of the split inner bearing ring constitutes the ring gear of the planetary gear set. Hence, the engagement means of the ring gear is provided on only one of the parts of split inner bearing ring.

According to one exemplary embodiment, said first part of the split inner bearing ring is provided closer to the outer end of the wheel hub unit than said other pan of the split inner bearing ring, as seen in the axial direction of the wheel hub unit. It is beneficial to provide the engagement means at the outer pan of the split inner bearing ring as the engagement means are intended to be in meshed engagement with the engagement means of the planetary gear set.

According to one exemplary embodiment, said wheel hub unit comprises a drive shaft, which extends along at least a portion of the axial center line of said wheel hub unit. The drive shaft may beneficially be connected to a drive source, such as e.g. an electrical motor, a hydraulic drive or an ICE.

According to one exemplary embodiment, said drive shaft is, directly or indirectly, drivingly connected to the sun gear of said at least one planetary gear set.

According to one exemplary embodiment, said wheel hub unit further comprises an electric machine as a drive source for driving the sun gear.

According to one exemplary embodiment, said wheel hub unit comprises at least two planetary gear sets coupled in series between the electric machine and the wheel hub. According to one exemplary embodiment, the wheel hub unit is provided with a gear shifting device. According to one exemplary embodiment, the gear shifting device comprises at least one further planetary gear set, and said gear shifting device is adapted for connecting and disconnecting, respectively, the planet gears of said one further planetary gear set from being driving) y connected to an electric machine. The present invention may be especially beneficial when more components, such as further planetary gear sets and an electric machine shall be fitted in the wheel hub unit.

According to one exemplary embodiment, said wheel hub unit comprises at least two planetary gear sets coupled in series, wherein one of said at least two planetary gear sets constitutes said at least one planetary gear set. Hence, it is not necessary that the engagement areas of all planetary gear sets of a wheel hub unit are axially displaced in relation to the rolling elements of a bearing of a wheel hub unit. The purpose of the present invention may well be achieved if the engagement areas of one of two or more planetary gear sets are axially displaced in relation to die rolling elements of the bearing.

According to one exemplary embodiment, the planetary gear set having the largest diameter of the at least two planetary gear sets constitutes said at least one planetary gear set. According to this exemplary embodiment, when the wheel hub unit comprises more than one planetary gear set, it is the planetary gear set with the largest diameter whose engagement areas are axially displaced in relation to the rolling element of the bearing. With diameter is meant to understand the diameter of the ring gear of the planetary gear set. As the purpose of the present invention is to provide for a wheel hub unit which may contain more and/or larger components and still fit into a rim of a specific size, the invention may be more beneficial if it is the planetary gear set with the largest diameter that is axially displaced. Hence, one planetary gear set having a smaller diameter may be provided at the same axial position as the bearing and there may still be sufficient material thickness for the ring gear/inner bearing ring.

According to one exemplary embodiment, a root diameter of the ring gear is in the range of 95-110% of an inner raceway diameter of the inner bearing ring. By axially displacing the engagement area of the engagement means of the ring gear and engagement means of the planet gears and the rolling elements of the bearing, it is possible to provide for a larger planetary gear set than what was possible with the prior art. Therefore, it is possible to provide for a wheel hub unit in which the ring gear has a root diameter which is 95% or more of the diameter of the inner raceway of the bearing. In other words, the diameter of the ring gear as measured at the bottom of the gears may be 95% or more of the distance between the radially innermost parts of two rolling elements of the bearing being positioned opposite each other. By the axial displacement, it is even possible to provide planetary gear sets having a larger diameter, for example up to 110%, than the diameter of the bearing, even though the inner bearing ring constitutes the ring gear.

According to one exemplary embodiment, a root diameter of the ring gear is in the range of 95-100% of an inner raceway diameter of the inner bearing ring. According to this exemplary embodiment, the root diameter of the ring gear is at most the same as the inner raceway diameter of the inner bearing ring. It is however larger than what would have been possible if the planet gears and the rolling elements had not been axially displaced in relation to each other, as a certain material thickness is required for the inner bearing ring/ring gear.

The vehicle according to the second aspect of the present invention comprises a wheel hub unit according to the first aspect of the present invention. The wheel hub unit according to the first aspect of the present invention may be beneficial to use in a work machine, or in a truck, a bus or a car.

According to one exemplary embodiment, said vehicle is a work machine, such as a wheel loader.

According to one exemplary embodiment, said wheel hub unit is provided in a rim of said vehicle, and wherein the rolling elements of the bearing are closer to a center of the rim, as seen in the width direction of said rim, than the engagement area. It is beneficial, in terms of bearing load and torque subjected to the bearing and thereby the expected life length of the bearing, to provide the bearing center close to the axial center of the rim that the wheel hub unit is connected to. It is therefore more beneficial to displace the engagement area along the axial direction of the rim.

DETAILED DESCRIPTION

FIG. 1shows a wheel loader101. The body of the wheel loader101comprises a front section102and a rear section103, which each has a pair of wheels116,117,118,119, of which only one wheel in each pair is shown inFIG. 1. Each of the wheels116,117,118,119is connected to, and driven by, a wheel hub unit1. The wheel hub unit1will be described in greater detail below and in connection withFIGS. 2-4. The rear section103comprises a cab114. The vehicle sections102,103are arranged to rotate in relation to one another about a vertical axis with the aid of two first actuators in the form of hydraulic cylinders104,105arranged between the two sections. The hydraulic cylinders104,105are arranged on either side of a horizontal center line through the vehicle for the purpose of steering the vehicle.

The wheel loader101comprises a device111for moving objects or material. The device111comprises a load arm unit106and an implement107in the form of a bucket, which is arranged on the load arm unit106. A first end of the load arm unit106is rotatably connected to the front vehicle section102. The implement107is rotatably connected to a second end of the load arm unit106.

The load arm unit106can be raised and lowered in relation to the front section102of the vehicle by means of two other actuators in the form of two hydraulic cylinders108,109, which are each connected to by one end to the from vehicle section102and by the other end to the load arm unit106. The bucket107can be tilted in relation to the load arm unit106by means of a third actuator in the form of a hydraulic cylinder110, which is connected by a first end to the front vehicle section102and by its second end to the bucket107via a linkage arm system115.

FIGS. 2aand 2billustrate a first embodiment of the wheel hub unit1of the present invention in greater detail. The wheel hub unit has an axial extension with an outer end33and an inner end34. The outer end33is on the side on which a wheel is intended to be fitted to a rim2connected to the wheel hub unit1. The inner end34is on the side on which the wheel hub unit1is connected to a drive source, which may be either a drive axle of a vehicle, or an electric machine forming a part of the wheel hub unit, and the vehicle.

The wheel hub unit1comprises a planetary gear set10, which comprises a sun gear3, a set of planet gears, for example four planet gears4(of which only two are visible inFIG. 2a), a carrier5, and a ring gear6. The carrier5holds the planet gears4. Each of the planet gears4of the set of planet gears is provided with engagement means20in the form of teeth12aadapted for engagement with corresponding engagement means21, of the ring gear6, which also are in the form of teeth12b. The engagement area. i.e. the area where the engagement means20and the engagement means21overlap and engage each other, is denoted32.

The wheel hub unit1also comprises a bearing22. The bearing comprises an inner bearing ring6, an outer bearing ring7and rolling elements8. The inner bearing ring6constitutes the ring gear6of the planetary gear set10. Hence, the rolling element8is in contact with the surface11of the inner bearing ring6, which is directed outwards as seen in the radial direction of the wheel hub unit. The engagement means21are provided on the surface13of the ring gear6, which is directed inwards as seen in the radial direction of the wheel hub unit. The engagement means20,21and the bearing22are shown in greater detail inFIG. 2b. The carrier5is connected to the outer bearing ring7through bolts23. The wheel hub unit1is also fixedly connected to a rim2for holding any one of the wheels116,117,118and119. This connection is established by the rim2being connected to the carrier5and the outer bearing ring7through the bolts23. The sun gear3is connected to a drive shaft17, which is driven by a non-illustrated drive source. Hence, when the drive shaft17and thereby the sun gear3rotate, the planet gears4and the carrier5also rotate. The ring gear6is held stationary. As the ring gear6also constitutes the inner bearing ring of the bearing22, the outer bearing ring7is free to rotate together with the carrier5. Thus, the wheel116,117,118,119connected to the rim2may be driven by the wheel hub unit1.

As is clear fromFIGS. 2aand 2b, the rolling elements8of the bearing22are axially displaced in relation to the engagement area32. Hence, a straight radially extending imaginary line L1which intersects an axial center line9, which in this embodiment coincides with the axial center of drive shaft17, of the wheel hub unit1perpendiculary and intersects the center of one of said rolling elements8is axially displaced in relation to a straight radially extending imaginary line12which intersects the axial center line9of the wheel hub unit1perpendiculary and intersects the portion of the engagement means20of said planet gears4, or the engagement area32, that is closest to said rolling element8. In the embodiment illustrated inFIGS. 2aand 2b, the axial displacement is in fact so large that a straight imaginary line L3that intersects the axial center line9of the wheel huh unit1perpendiculary and intersects one of said rolling elements8at the portion of the rolling element being closest to the engagement means20of the planet gears4, or the engagement area32, is axially displaced in relation to the straight radially extending imaginary line L2which intersects the axial center line9of the wheel hub unit1perpendiculary and intersects the portion of the engagement means20of said planet gears4, or engagement area32, that is closest to said rolling element8. Hence, in this embodiment, there is no overlap at all between the engagement area32and the rolling elements8. The ring gear/inner bearing ring6may therefore have a sufficiently thickness, and all components still fit within the rim2. The root diameter D1of the ring gear6is in this embodiment somewhat larger than 95% of the inner raceway diameter D2. However, due to the axial displacement of the engagement area32and the rolling elements8, it is possible to provide for planetary gear sets in which the root diameter of the ring gear is even as large as 110% of the inner raceway diameter D2.

The axial displacement of the engagement area32and the rolling elements8of the bearing22are achieved by means of a flange14of the ring gear6. The engagement means21of the ring gear6are provided on this flange14, which extends in the axial direction of said wheel hub unit, and it is thereby possible to provide a meshed engagement with the engagement means20of the planet gears4that is axially distanced from the rolling elements8of the bearing22.

The axial displacement is such that die rolling elements8of the bearing are closer to the center L5of the rim2, as seen in the axial direction of the rim, than the engagement area32. Furthermore, the engagement area32is provided closer to an outer end33, which is the end of the wheel hub unit that is adapted to be connected to a rim for holding a wheel, than said rolling elements8of the bearing, as seen in the axial direction of the wheel hub unit. Hence, die rolling elements8of the bearing are provided closer to an inner end34, which is the end of the wheel hub unit that is adapted to be connected to a vehicle, than the engagement area32.

It can also be seen inFIGS. 2aand 2bthat the inner ring6of the bearing22is a split inner ring. The split inner ring comprises two parts15,16that are held together by bolts29. The two parts15,16are also connected to a stationary part31of the wheel hub unit through the bolts29. Both parts15,16of the split inner bearing ring6are in contact with the rolling elements8of the bearing. However, only a first part15of the split inner bearing ring constitutes the outer ring6of the planetary gear set10. The first part15of the split inner bearing ring, i.e. the part of it that is provided with the flange14and the engagement means21, is provided closer to the outer end33than the other part16of the split inner bearing ring, as seen in the axial direction of the wheel hub unit.

Another embodiment of the wheel hub unit1according to the present invention is illustrated inFIG. 3. This embodiment has most features in common with the first embodiment, and features being similar will not be elaborated upon. The difference between this embodiment and the first embodiment is that the bearing is a double-row bearing22and a straight imaginary line14that intersects the axial center line9of the wheel hub unit1perpendiculary and intersects a rolling element8in the row of rolling elements that is closest to the engagement area32is axially displaced in relation to the straight radially extending imaginary line L2which intersects the axial center line9of the wheel hub unit1perpendicularly and intersects the portion of the engagement area32that is closest to said rolling element8. Hence, in this embodiment, there is an axial displacement between the rolling elements8being closest to the engagement area32, and the engagement area32. Similarly to the first embodiment, this second embodiment also fulfills the purpose of fitting more and/or larger components into a rim of a specific size.

A yet further embodiment of the present invention is illustrated inFIG. 4, which shows a part of a wheel hub unit1. This embodiment has most features in common with the first and second embodiments, and features being similar will not be elaborated upon. A difference between this embodiment and the first and second embodiment is that in this embodiment, a second planetary gear set30comprising a set of planet gears24, for example four planet gears, (of which only two are shown inFIG. 4), is provided. The planet gears24of this second planetary gear set30are engaged with, and driven by, a sun gear25. The sun gear25is directly or indirectly connected to a transmission18that is driven by a drive source in the form of an electric motor19. In this embodiment, there is no drive shaft illustrated. Instead, the transmission18may comprise e.g. one or more further planetary gear sets. The transmission18and electric motor19may however be embodied in many different ways and are therefore only schematically illustrated in the drawings. They will also not be further elaborated upon herein.

The ring gear of the second planetary gear set30is also formed by the inner bearing ring6, and similarly to the first planet gears4, the planet gears24are provided with engagement means26in the form of teeth12cthat are in meshed engagement with corresponding engagement menus27of the ring gear, which are also in the form of teeth12d.

The first planetary gear set10is coupled in series with the second planetary gear set30. I.a., the planet gears21are held by a carrier28, which is connected to the sun gear3of the first planetary gear set10. Hence, the first planetary gear set10is driven by the carrier28of the second planetary gear set30.

As can be seen inFIG. 4, it is sufficient that only one of said at least two planetary gear sets is axially displaced in relation to the rolling elements8of the bearing22in order to achieve the aim of the present invention. In the illustrated embodiment, it is the first planetary gear set10that constitutes the at least one planetary gear set that is axially displaced. It can also be seen that the first planetary gear set10has a larger diameter than the second planetary gear set30. Hence, the second planetary gear set may be provided radially inside the bearing22without the wheel hub unit exceeding the radial size limitations of the rim2.

A person skilled in the art also realizes that the different alternative embodiments and aspects mentioned above may be combined with each other in various suitable embodiments within the scope of the claims.

The means for driving the sun gear of the first planetary gear set has been described as a drive shaft in one embodiment and a non-specified transmission and a second set of planet gears in another embodiment. It is however possible to utilize other means, or combine the illustrated embodiments in different manners. It is also conceivable to drive the drive shaft or the other transmission with any suitable drive source, such as e.g. an electrical drive source, an ICE or a hydraulic drive.

The illustrated planetary gear sets have been described as comprising four planet gears. It is however also conceivable with another number of planet gears in the planetary gear sets.

Furthermore, any reference signs in the claims should not be construed as limiting the scope.