Patent Description:
In a vehicle, a differential is used for distributing an input torque (or input rotational speed) to two output shafts, wherein each output shaft is connected with a driving wheel. During driving, and especially during turns and cornering, the different rotational speeds of the wheels are taken care of by the differential.

A differential, or differential assembly, typically comprises a ring gear configured to receive torque from the input shaft, a carrier attached to, and rotatable with, the ring gear, a differential housing, and a bearing assembly supporting the carrier within the differential housing. The differential further comprises internal gearing, such at least one differential gear and bevel gears configured to transmit the torque from the ring gear to the output shafts. For example, <CIT> discloses a differential assembly for distributing torque from an input shaft to an output shaft, the differential assembly comprising a ring gear, a carrier, a differential housing and a bearing assembly supporting the carrier within the differential housing. The bearing assembly comprises a ball bearing and a tapered rolling bearing.

Typically, the bearing assembly comprises tapered rolling bearings which are able to take up both axial and radial loads. Tapered rolling bearing provide a very stable setup and great durability. However, the tapered rolling bearings are associated with drag losses due to the need of pre-load. Another problem is the shimming process required in the bearing assembly to set the pre-load. Moreover, a reliable pre-load over a wide temperature range, and over time, is difficult to maintain. This could for example lead to poor gear mesh contact.

Accordingly, it is desirable to develop an improved differential assembly.

In general, the disclosed subject matter relates to a differential assembly distributing torque from an input shaft to first and second output shafts via a ring gear, typically in a vehicle, such as in an electric vehicle, wherein a bearing assembly of the differential assembly comprises a cylindrical roller bearing and a ball bearing wherein the cylindrical roller bearing is arranged closer to the ring gear compared the ball bearing relative the ring gear. Hereby, the bearing assembly can take up both axial and radial loads with a minimum of drag losses as there is no, or at least less, need for pre-load. Moreover, the shimming process can be omitted, or at least kept to a minimum.

Thus, according to a first aspect of the present invention, a differential assembly which is configured to distribute torque from an input shaft to first and second output shafts is provided. The differential assembly comprises a ring gear configured to receive torque from the input shaft, a carrier attached to, and rotatable with, the ring gear, a differential housing, and a bearing assembly supporting the carrier within the differential housing, the bearing assembly comprising a ball bearing and a cylindrical roller bearing arranged on opposite sides of the ring gear, a distance between the cylindrical roller bearing and the ring gear being smaller than a distance between the ball bearing and the ring gear. The distance is an axial distance, i.e. a distance along an axial axis of the differential assembly which coincides with the longitudinal axis of the output shafts.

Hereby, as the stiffness of a cylindrical roller bearing is higher compared to the stiffness of a ball bearing, and with the additional specific arrangement in which the cylindrical roller bearing is arranged relatively closer to the ring gear, the differential assembly can minimize gear mesh deflection (or gear lead mismatch). Thus, when the differential is subject to a radial load, the differential assembly withstands any tendency of skewness induced by the radial load and enables the output shafts to remain parallel to the input shaft (i.e. tilting or gear mesh deflection of the differential assembly can be avoided). In this respect, the differential assembly is particularly suitable for offset transmission in which a longitudinal axis of the input shaft is arranged parallel to a longitudinal axis of the two output shafts. Thus, according to at least one example embodiment, the differential assembly is configured for an offset transmission.

According to at least one example embodiment, the bearing assembly of the differential assembly comprises no tapered roller bearings. Thus, in such embodiments, the differential assembly is free from any tapered roller bearings.

According to at least one example embodiment the carrier comprises a first journal portion holding the first output shaft, and a second journal portion arranged on an opposite side to the first journal portion, the second journal portion holding the second output shaft, wherein the ring gear is asymmetrically arranged on the carrier to form a relative smaller first carrier side arranged between the ring gear and the first journal portion, and a relative larger second carrier side arranged between the ring gear and the second journal portion, and wherein the cylindrical roller bearing supports the carrier to the differential housing at the first carrier side. Hereby, skewness induced by the radial load via the asymmetrically arranged ring gear can be reduced, or even avoided, by the relative stiff arrangement of the first carrier side which otherwise would be prone to tilt.

According to at least one example embodiment, the cylindrical roller bearing comprises an inner race, an outer race, and a plurality of cylindrical rollers disposed between the inner and outer races, and wherein the inner race is circumferentially attached to the carrier at the first carrier side, and the outer race is non-rotatably arranged with respect to the differential housing. Such arrangement provides a stable and yet compact configuration of the cylindrical roller bearing. The cylindrical roller bearing may comprise, or be referred to as, a needle roller bearing. In a needle roller bearing, the plurality of cylindrical rollers are formed as needles.

According to at least one example embodiment, the ball bearing comprises an inner race, an outer race, and a plurality of balls disposed between the inner and outer races, and wherein the inner race is circumferentially attached to the carrier at the second carrier side, and the outer race is non-rotatably arranged with respect to the differential housing. Such arrangement provides a stable and yet compact configuration of the ball bearing.

According to at least one example embodiment, the differential assembly further comprises retaining rings holding the ball bearing in axial position relative the differential housing and the carrier respectively. Hereby, the ball bearing can better take up axial loads, and axial loads in both directions.

According to at least one example embodiment, the cylindrical roller bearing is configured and arranged to, when torques is transferred from the input shaft to the two output shafts, withstand a higher radial load compared to the ball bearing. Thus, by having the cylindrical roller bearing arranged closer to the ring gear, at the relatively smaller carrier side, skewness or tilting of the differential assembly can be reduced, or even avoided, as the cylindrical roller bearing can withstand a relatively higher radial load.

According to at least one example embodiment, the cylindrical roller bearing is arranged co-axially with the ring gear, and the ring gear at least partly encircles the cylindrical roller bearing. Hereby, the cylindrical roller bearing can be brought very close to the ring gear, and thus close to the point of application of the (asymmetrical) radial load, and thereby counteract the tendency for skewedness and gear mesh deflection.

According to at least one example embodiment, the cylindrical roller bearing is arranged co-axially with the ring gear, and at least a portion of the cylindrical roller bearing is arranged in the same geometrical plane as a cross section of the ring gear. Thus, a cross section, such as a circular or annular cross section, of the cylindrical roller bearing and the ring gear overlap at least along an axial portion of differential assembly.

According to at least one example embodiment, the carrier is windowless. Hereby, the carrier has a rotational symmetry along the axial axis of the differential assembly.

According to at least one example embodiment, the carrier comprises at least two separate carrier parts, a relative larger first carrier part, and a relative smaller second carrier part, the second carrier part being a detachable cap in relation to the first carrier part. Hereby, the interior of the carrier can be accessible without providing a window in the carrier.

According to at least one example embodiment, the cylindrical roller bearing is larger than the ball bearing. For example, the inner race of the cylindrical roller bearing has a larger diameter compared to the inner race of the ball bearing. Hereby, the cylindrical roller bearing can be arranged closer to the ring gear with advantageous as previously described.

According to at least one example embodiment, the input shaft has a first longitudinal axis, and the common longitudinal axis of the two output shafts is a second longitudinal axis, wherein the first and second longitudinal axis are parallel. Thus, such differential assembly is an offset differential assembly.

According to at least a second aspect of the present invention, a vehicle, such as an electrical vehicle or hybrid is provided. The vehicle comprises a differential assembly according to the first aspect of the invention.

<FIG> is a schematic illustration of a differential assembly <NUM> arranged in a vehicle <NUM>. <FIG> further illustrates a plurality of battery packs <NUM> and an electric motor <NUM> driven by the battery packs <NUM>. The vehicle <NUM> further comprises a transmission arrangement <NUM> comprising an input shaft <NUM> coupled to the electric motor <NUM>, and two output shafts <NUM>, <NUM> configured to transfer rotational motion to the front wheels <NUM>, <NUM> of the vehicle <NUM>. The differential assembly <NUM> enables the output shafts <NUM>, <NUM> to rotate with different rotational speeds while delivering torque to both of them. The differential assembly <NUM> forms a part of the transmission arrangement <NUM>. Thus, the battery packs <NUM> powers the electric motor <NUM> which drives the front wheels <NUM>, <NUM> of the vehicle <NUM> via the transmission arrangement <NUM> and differential assembly <NUM>. The differential assembly <NUM> is thus configured to distribute torque (rotational motion) from the input shaft <NUM> to the first and second output shafts <NUM>, <NUM>.

<FIG> illustrate perspective views of a differential assembly <NUM>, and <FIG> illustrates a top view of the same differential assembly <NUM>. <FIG> will be described jointly in the following.

The differential assembly <NUM> may be used as the differential assembly <NUM> in vehicle <NUM> of <FIG>, and is thus configured to distribute torque from an input shaft to first and second output shafts (as shown in <FIG>). The differential assembly <NUM> comprises a ring gear <NUM> configured to receive torque from the input shaft, a carrier <NUM> attached to, and rotatable with, the ring gear <NUM>, a differential housing <NUM> (only shown in part), and a bearing assembly <NUM> supporting the carrier <NUM> within the differential housing <NUM>. The carrier <NUM> is windowless, and thus, rotational symmetric along the axial axis A. Moreover, a windowless carrier <NUM> is advantageous due to improved rigidity and stiffness.

As will be described in greater detail with reference to <FIG>, but briefly mentioned here, the bearing assembly <NUM> comprises cylindrical roller bearing <NUM> and a ball bearing <NUM> arranged on opposite sides of the ring gear <NUM>. As is clear from the differential assembly <NUM> of <FIG>, a distance, such as an axial distance along the axial axis A, between the cylindrical roller bearing <NUM> and the ring gear <NUM> is smaller than a distance, such as an axial distance, between the ball bearing <NUM> and the ring gear <NUM>. In other words, the cylindrical roller bearing <NUM> is arranged closed to the ring gear <NUM> as compared to the ball bearing <NUM>. In other words, the cylindrical roller bearing <NUM> and the ball bearing <NUM> are space apart aligned along the axial axis A of the differential assembly <NUM>, the axial axis A coinciding with output shaft axes of the first and second output shafts (as shown in <FIG>).

As shown in <FIG>, the cylindrical roller bearing <NUM> is arranged co-axially with the ring gear <NUM>, and at least a portion of the cylindrical roller bearing 240A is housed within the ring gear <NUM>. The cylindrical roller bearing <NUM> is thus at least partly contained or held within the ring gear <NUM>. In other words, said portion 240A is arranged in the same geometrical plane as a cross section of the ring gear <NUM>, the cross section being perpendicular to the axial axis A (i.e. the axial axis A is a normal to said cross section). Stated differently, the ring gear <NUM> has a circular (or annular) cross section in the geometrical plane, wherein at least a portion 240A of the cylindrical roller bearing <NUM> along the axial axis A has a circular cross section in the same geometrical plane. Thus, at least a portion 240A of the cylindrical roller bearing <NUM> is housed inside a geometrical cylinder for which outer surfaces are defined by the ring gear <NUM>. As a result, the cylindrical roller bearing <NUM> is arranged close to the ring gear <NUM> and can provide the needed stiffness to withstand any tendency of skewness induced by a radial load (e.g. via the ring gear <NUM>). As is clear from <FIG>, the ball bearing <NUM> is not housed inside the ring gear <NUM>, i.e. a circular (or annular) cross section of the ball bearing <NUM> is distant from the above-mentioned geometrical plane, or any circular cross section of the ring gear <NUM>.

<FIG> is a cross sectional view along the axial axis A of the differential assembly <NUM> of <FIG>, In <FIG>, the differential assembly <NUM> is disclosed as being part of a transmission arrangement <NUM>. The transmission arrangement <NUM> comprises an input shaft <NUM>, a first output shaft <NUM>, and a second output shaft <NUM>. The differential assembly <NUM> is thus configured to transmit and distribute a torque from the input shaft <NUM> to the two output shafts <NUM>, <NUM>. The transmission arrangement <NUM> of <FIG> is an offset transmission as the input shaft <NUM> has a first longitudinal axis L1, and the two output shafts <NUM>, <NUM> have a common section longitudinal axis L2 which is parallel to the first longitudinal axis L1. The second longitudinal axis L2 is here coinciding with the axial axis A of the differential assembly <NUM>. The input shaft <NUM> is coupled to the ring gear <NUM> via a gear arrangement <NUM>, here referred to as an input gear arrangement <NUM>. The input shaft <NUM> and input gear arrangement <NUM> are supported by various bearings <NUM>, not described further here.

The differential assembly <NUM> further comprises a gear arrangement <NUM>, here being referred to as a differential gear arrangement <NUM>. The differential gear arrangement <NUM> comprises the ring gear <NUM>, a differential pinion gear <NUM>, a first side gear or bevel gear <NUM> arranged to mesh with the differential pinion gear <NUM> and configured to transmit torque to the first output shaft <NUM>. The differential gear arrangement <NUM> further comprises a second side gear or bevel gear <NUM> arranged to mesh with the differential pinion gear <NUM> and configured to transmit torque to the second output shaft <NUM>. The first and second bevel gears <NUM>, <NUM> are freely rotatably held inside of the carrier <NUM> such that the gear arrangement <NUM> is configured to permit different rotational speeds of the first and second output shafts <NUM>, <NUM>. The first and second bevel gears <NUM>, <NUM> are thus configured to rotate around the axial axis A, and the torques is transmitted from the input shaft <NUM> via the input gear arrangement <NUM>, and the differential gear arrangement <NUM> to the first and second output shafts <NUM>, <NUM>.

As seen in <FIG>, the carrier <NUM> comprises a first journal portion <NUM> configured to hold the first output shaft <NUM>, and a second journal portion <NUM> configured to hold the second output shaft <NUM>. The first and second journal portions <NUM>, <NUM> arranged on an opposite sides of the carrier <NUM>, and on opposite sides of the ring gear <NUM>. Moreover, the ring gear <NUM> is asymmetrical arranged on the carrier <NUM> to form a relative smaller first carrier side <NUM> arranged between the ring gear <NUM> and the first journal portion <NUM>, and a relative larger second carrier side <NUM> arranged between the ring gear <NUM> and the second journal portion <NUM>. The journal portions <NUM>, <NUM> may be referred to as stub shafts.

The bearing assembly <NUM>, here the cylindrical roller bearing <NUM> and the ball bearing <NUM>, are disclosed to support the carrier <NUM> within the differential housing <NUM> (of which only a part is shown). The cylindrical roller bearing <NUM> supports the carrier <NUM> to the differential housing <NUM> at the first carrier side <NUM>, and the ball bearing <NUM> supports the carrier <NUM> to the differential housing <NUM> at the second carrier side <NUM>. The cylindrical roller bearing <NUM> comprises an inner race <NUM>, an outer race <NUM>, and a plurality of cylindrical rollers <NUM> (of which only one is shown in <FIG>) disposed between the inner and outer races <NUM>, <NUM>. The inner race <NUM> is circumferentially attached to the carrier <NUM> at the first carrier side <NUM>, and the outer race is non-rotatably arranged with respect to the differential housing <NUM>. Correspondingly, the ball bearing <NUM> comprises an inner race <NUM>, an outer race <NUM>, and a plurality of balls <NUM> disposed between the inner and outer races <NUM>, <NUM>. The inner race <NUM> of the ball bearing <NUM> is circumferentially attached to the carrier <NUM> at the second carrier side <NUM>, and the outer race <NUM> of the ball bearing <NUM> is non-rotatably arranged with respect to the differential housing <NUM>. Furthermore, in the embodiment shown in <FIG>, the second journal portion <NUM> project into the bearing seat of the ball bearing <NUM>, and thus holds the inner race <NUM> of the ball bearing <NUM>. The first journal portion <NUM> does not project into the bearing seat of the cylindrical roller bearing <NUM>, but is instead separated from the inner race <NUM> of the cylindrical roller bearing <NUM>.

The configuration and arrangement of the bearing assembly <NUM> enables the differential assembly <NUM> to withstand a higher radial load without skewing as compared to prior art solutions. More specifically, the configuration and arrangement of the cylindrical roller bearing <NUM> enables it to withstand a higher radial load compared to a ball bearing, when torques is transferred from the input shaft <NUM> to the two output shafts <NUM>, <NUM>. In more detail, the stiffness of a cylindrical roller bearing is higher compared to the stiffness of a ball bearing, and with the additional specific arrangement in which the cylindrical roller bearing <NUM> is arranged relatively close to the ring gear <NUM>, when the differential is subject to a radial load, the differential assembly <NUM> withstands any tendency of skewness induced by the radial load and enables the output shafts <NUM>, <NUM> to remain parallel to the input shaft <NUM>.

The differential assembly <NUM> of <FIG> further comprises retaining rings <NUM> arranged to hold the ball bearing <NUM> in axial position relative the differential housing <NUM> and the carrier <NUM> respectively. The retaining rings <NUM> enable the ball bearing <NUM> to accommodate axial loads in both directions (i.e. loads along the axial axis A).

As mentioned with reference to <FIG>, the carrier <NUM> is windowless. However, parts of the differential gearing arrangement <NUM> may be accessed by a detachable carrier cap <NUM>. In more detail, the carrier <NUM> comprises two separate carrier parts, <NUM>, <NUM>. That is, a relative larger first carrier part <NUM>, and a relative smaller second carrier part <NUM>, the second carrier part <NUM> being arranged as a detachable carrier cap <NUM> in relation to the first carrier part <NUM>. In the embodiment of <FIG>, the detachable carrier cap <NUM> comprises the first journal portion <NUM>, while the first carrier part <NUM> supports the bearing assembly <NUM>. Hereby, the differential pinion, and bevel gears <NUM>, <NUM>, <NUM> held in the carrier <NUM> can be accessed by removing the detachable carrier cap <NUM>.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the system may be omitted, interchanged or arranged in various ways, the differential assembly and transmission arrangement yet being able to perform the functionality of the present invention. The differential assembly <NUM> described with reference to <FIG> may used as the differential assembly <NUM> of the vehicle <NUM> in <FIG>. Correspondingly, the transmission arrangement <NUM> of <FIG> may be used as the transmission arrangement <NUM> of <FIG>.

Claim 1:
A differential assembly (<NUM>, <NUM>) distributing torque from an input shaft (<NUM>, <NUM>) to first and second output shafts (<NUM>, <NUM>, <NUM>, <NUM>), the differential assembly (<NUM>, <NUM>) comprising a ring gear (<NUM>) receiving torque from the input shaft (<NUM>, <NUM>), a carrier (<NUM>) attached to and rotatable with the ring gear (<NUM>), a differential housing (<NUM>), and a bearing assembly (<NUM>) supporting the carrier (<NUM>) within the differential housing (<NUM>), the bearing assembly (<NUM>) comprises a ball bearing (<NUM>) and another bearing (<NUM>) arranged on opposite sides of the ring gear (<NUM>), wherein along a common longitudinal axis (L2) of the two output shafts (<NUM>, <NUM>, <NUM>, <NUM>) an axial distance between the other bearing (<NUM>) and the ring gear (<NUM>) is smaller than an axial distance between the ball bearing (<NUM>) and the ring gear (<NUM>),
characterised by that the other bearing (<NUM>) is a cylindrical roller bearing.