Drive axle for electric vehicles

A drive axle of an electrically drivable vehicle including first and second drive wheels (R1, R2), first and second manual transmissions (G1, G2) and first and second electrical machines (EM1, EM2) which each have a respective drive shaft (1a, 1b). The first electrical machine (EM1) drives the first drive wheel (R1), via the first manual transmission (G1), and the second electrical machine (EM2) drives the second drive wheel (R2), via the second manual transmission (G2). The manual transmissions are each designed as three-speed transmissions (G1, G2) which have identical transmission ratios (i1, i2, i3).

FIELD OF THE INVENTION

The invention relates to a drive axe of an electrically drivable vehicle having two electric machines and manual transmissions downstream thereof and use of the manual transmissions of the electrically drivable vehicle.

BACKGROUND OF THE INVENTION

From DE 10 2009 002 437 A1 several variants of a purely electrically driven vehicle are known, wherein one variant according to FIG. 2 thereof has a purely electrically driven rear axle having single-wheel drives, i.e. a so-called individual-wheel drive. One electric machine having a manual transmission downstream thereof is assigned to every drive wheel, wherein both single-wheel drives are separated from each other. The manual transmissions are designed as two-speed transmissions and are shifted by means of a dog clutch, i.e. during shifting there is an interruption of traction torque. If, for instance, only the transmission on the right, which drives the right wheel, is shifted, a yawing moment occurs around the vertical axis of the vehicle as a result of the interruption of traction torque for the right wheel, which attempts to steer the vehicle to the right. To prevent such a yawing moment, gearshifts are performed simultaneously on both sides. On the other hand, a yawing moment may be desirable, e.g. when cornering, to improve the agility of the vehicle. In such a case, the yawing moment can be generated specifically by differing torque distributions to the right and to the left drive wheels (so-called torque-vectoring).

SUMMARY OF THE INVENTION

One problem addressed by the invention consists in arranging the drive components, i.e. the electrical machines and the transmission, in the area of the drive axle of an electrically drivable vehicle of the type mentioned above in a manner reducing the required space and weight.

The invention comprises the features of the independent claims. Advantageous embodiments will become apparent from the dependent claims.

According to a first aspect of the invention, the two manual transmissions (gearboxes), i.e. the manual transmission on the right and the manual transmission on the left, are each designed as a three-speed transmission, which can be used to achieve three gears, i.e. three different transmission ratios. The transmission ratios are used to reduce the speed of the electric machine to the speed of the drive wheel. This results in a higher torque at the drive wheel and a wider speed range for the vehicle. Both manual transmissions are identical, i.e. they each have the same transmission ratios and are arranged symmetrically to a central or symmetrical plane. The description below therefore mainly refers to one side only, as the other side is identical or a mirror image. The individual-wheel drive permits the function of torque vectoring.

According to a preferred embodiment, the first and second manual transmissions each comprise a first and a second shiftable planetary gearset, wherein both planetary gearsets are intercoupled, i.e. the first and second planetary gearsets form a linkage for shifting three gears or transmission ratios, respectively.

According to a further preferred embodiment, each planetary gearset is designed as an epicyclic gear having three shafts, namely a carrier shaft, a ring gear shaft and a sun shaft. Alternatively, the terms carrier or planet carrier, ring gear or sun gear are also used, which each have the same kinematic function.

According to a further preferred embodiment, the carrier shaft of the first planetary gearset is coupled to the ring gear shaft of the second planetary gearset. This coupling kinematically interconnects both planetary gearsets.

According to a further preferred embodiment, the sun shafts of the first planetary gearsets are each driven by an electric machine, i.e. the sun shafts are each firmly connected to the drive shafts of the electric machines, below also referred to as E-machines.

According to a further preferred embodiment, the sun shaft of the second planetary gearset is permanently immobilized, i.e. connected to the housing. This results in a defined transmission ratio of the second planetary gearset.

According to a further preferred embodiment, both manual transmissions, i.e. the right and the left one each have a shift device, also called shift element, having three shift positions, wherein the first shift position is provided for the first gear, the second shift position is provided for the second gear and the third shift position is provided for the third gear.

According to a further preferred embodiment, in the first shift position, i.e. in first gear, the ring gear shaft of the first planetary gearset is immobilized, preferably connected to the housing of the transmission by the shift device. In this way, a fixed speed ratio is established between the input and output of the linkage.

According to a further preferred embodiment, in the second shift position, i.e. for the second gear, the ring gear shaft of the first planetary gearset is coupled to the carrier shaft of the second planetary gearset. In this way, the second transmission ratio is determined for the second gear.

According to a further preferred embodiment, in the third shift position, i.e. for the third gear, the ring gear shaft of the first planetary gearset is coupled to the ring gear shaft of the second planetary gearset. In this way, the ring gear shaft of the first planetary gearset is also connected to the carrier shaft of the first planetary gearset, i.e. the ring gear shaft and carrier shaft are interlocked—the first planetary gearset is in direct drive.

According to a further preferred embodiment, the shift device is designed as an unsynchronized, positive-locking shift device, in particular as a dog clutch. The advantage of the dog clutch is the low manufacturing cost, but an interruption of traction torque occurs during shifting. However, the electrical machines can achieve synchronization during shifting:

When shifting on the left using the left electric machine, when shifting on the right using the right electric machine.

According to a further preferred embodiment, the carrier shaft of the second planetary gearset is designed as the output shaft of the manual transmission. This results in favorable efficiency of the linkage.

In another preferred embodiment, a constant transmission stage, which is located close to the wheel and can also be integrated into the drive wheel, is installed downstream of the manual transmission. The constant ratio stage permits a further reduction of the input speed, i.e. the speed of the electric machine, and an increase in torque or tractive force at the drive wheel, which is particularly advantageous for commercial vehicles because of their increased traction torque requirements.

According to a further preferred embodiment, the constant transmission stage is designed as a third planetary gearset, which has a sun shaft, a carrier shaft and a ring gear shaft attached to the housing. The carrier shaft of the second planetary gearset is used to drive the third planetary gearset via its sun shaft. The carrier shaft of the third planetary gearset, which forms the output shaft of the drive train between the electric machine and the drive wheel, provides the output.

According to a further preferred embodiment, an axle differential gear having a differential cage is arranged between the drive wheels, wherein the carrier shafts of the second planetary gearsets, i.e. of the right and left drive train, are firmly connected to the differential cage. Both drive trains are conjoined in the differential gear to establish a connection between the right and left drive train—then the drive is no longer an individual-wheel drive. One advantage of the differential gear is that when traction torque is interrupted during shifting on one side, the electric machine on the other side can support it, i.e. drive the differential gear, which then transmits the power equally to both drive wheels. In this way there is no interruption of traction torque.

According to a further preferred embodiment, the axle differential gear has a first and a second output shaft, which are designed as axle shafts for the right and left drive side.

According to a further preferred embodiment, a third planetary gearset is arranged between the differential gear and the drive wheels forming a constant transmission stage, i.e., a further gear down. In that case, the axle shafts are connected to the sun shafts of the third planetary gearsets and the carrier shafts are connected to the drive wheels. The ring gear is attached to the housing. The third planetary gearset can preferably be integrated into the drive wheel.

According to a further preferred embodiment, the electrical machines are arranged in the outer or near-wheel area with respect to the axial extension of the drive axle, while the second planetary gearsets are arranged in the central area, i.e., the second planetary gearsets, which are used to provide the output of the manual transmissions, are arranged in the immediate vicinity of the axle differential gear. In addition, the shift elements can also be arranged in the central area.

According to a further preferred embodiment, the shift devices, also called shift elements, are operated by actuators, wherein both actuators are arranged in a plane extending in parallel to the center plane between the two drive wheels. This has the advantage of reducing installation space in the axial direction.

According to a further preferred embodiment, the axle differential gear has a locking function, which can preferably be activated by means of another shift element. The differential gear can thus be locked as needed by actuating the shift element, wherein the differential cage is coupled to or locked with one of the differential gear output shafts or axle shafts. When the differential gear is locked, the drive wheel can no longer spin in case of different grip on either side.

According to a further preferred embodiment, the constant transmission stage is designed as a stationary gear, which preferably has an axle offset between input shaft and output shaft. The axle offset results in increased ground clearance of the vehicle. This axle configuration is also known as a portal axle.

According to a further preferred embodiment, a first variant of the stationary transmission is designed as a planetary gearset having a carrier and planetary gears, a sun gear and a ring gear, wherein the carrier is immobilized, i.e. the planetary gearset operates at a stationary transmission ratio. The drive is provided by one of the planetary gears, resulting in a power split. The ring gear provides the output via the drive gear.

According to a further preferred embodiment, a second variant of the stationary gear is designed as a spur gear unit having one input gear, two intermediate gears and one output gear, wherein the intermediate gears mesh with both the input gear and the output gear. As well, the two intermediate gears achieve a power split.

According to a further preferred embodiment, the electric machines have rotors, which are arranged coaxially with the axle shafts. The coaxial arrangement of the motor and gear components results in an extremely compact design.

According to a further preferred embodiment, the planetary gearsets, the axle differential gear and/or the shift elements are at least partially arranged inside the rotors, i.e. in the cavity formed by the rotors. This design considerably reduces installation space in the axial direction, because the planetary gearsets are not axially offset or only slightly offset from the rotors.

According to another aspect of the invention, the manual transmissions, which are designed as three-speed transmissions, can also be used as two-speed transmissions by deactivating or removing the third gear stage. This results in the advantage of the shiftable linkage, consisting of a first and second planetary gearset, being convertible from a three-speed transmission into a two-speed transmission with little effort. A further advantage is that relatively large stage increments between the two transmission ratios in the range of 1.5 to 2.0 can be implemented. Such stage increments can only be achieved by superimposing two planetary gearsets, wherein this stage increment range is particularly advantageous for the operation of the electric drive due to a very good utilization of the speed range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a drive axle1(first drive axle) of an electrically drivable vehicle, hereinafter also referred to as electric vehicle for short, having two drive wheels R1, R2, which are driven by a first electric machine EM1and a second electric machine EM2as a first exemplary embodiment of the invention. The drive wheels R1, R2and the electric machines EM1, EM2are arranged coaxially with an axis of rotation a—the drawing only shows the half above the axis of rotation a, the lower half is a mirror image of the upper half. A first power flow between the first electric machine EM1and the first drive wheel R1, hereinafter also referred to as wheel R1for short, extends from an input shaft1a, which is connected to the rotor RO1of the electric machine EM1, to a first output shaft2a, which is connected to the first wheel R1. Independently of the first power flow, a second power flow extends from the second input shaft1bof a second rotor RO2of the second electric machine EM2to the second output shaft2h, which is connected to the wheel R2. A first manual transmission comprising a first shiftable planetary gearset PS1and a second shiftable planetary gearset PS2, and a constant transmission stage PS3, which is designed as a third planetary gearset PS3, are arranged between the input shaft1aand the output shaft2a. The same applies to the right side in the drawing, wherein the same designations PS1, PS2, PS3are used for the three planetary gearsets. The planetary gearsets PS1, PS2, PS3on the right side are mirror images of the planetary gearsets PS1, PS2, PS3on the left side, i.e. they have the same gear ratios and kinematic structure. The first planetary gearset PS1and the second planetary gearset PS2are each designed as epicyclic gears having three shafts, namely carrier shafts ST1, ST2, sun shafts SO1, SO2and ring gear shafts HR1, HR2. The first planetary gearset PS1is coupled to the ring gear shaft HR2of the second planetary gearset via the carrier shaft ST1of the first planetary gearset PS1, thus both planetary gearsets PS1, PS2form a linkage. The linkage has a shift device SE1having three shift positions A, B, C, corresponding to three different coupling options. The shift device SE1is controlled by an actuator AK1. Similarly, a second shift device SE2having three mirror-image shift positions D, E, F and a second actuator AK2for actuating the second shift element SE2are provided for the right side.

The description below refers only to the left side, i.e. to the power flow from the first electric machine EM1to the wheel R1. The description applies in a similar manner to the right side, i.e. to the power flow from the second electric machine EM2to the second drive wheel R2. The first planetary gearset PS1is driven by the drive shaft1avia the sun shaft SO1. To achieve first gear, corresponding to the first shift position A, the ring gear shaft HR1of the first planetary gearset is connected to the housing GH, i.e. immobilized. In this way, the first speed ratio between sun shaft SO1and the carrier shaft ST1is defined. The housing GH is represented by hatching (three parallel lines). The sun shaft SO2of the second planetary gear PS2is immobilized, i.e. permanently connected to the housing GH thus the speed ratio of the second planetary gear PS2is also defined. The carrier shaft ST2of the second planetary gearset PS2provides the output into the third planetary gearset PS3, which is designed as a constant transmission stage and has a ring gear shaft HR3attached to the housing and a sun shaft SO3driven by the carrier shaft ST2. The carrier shaft ST3provides the output to the output shaft2a, which drives the left wheel R1.

To achieve second gear, the shift position B is controlled by the actuator AK1: in this way a coupling of the ring gear shaft HR1of the first planetary gearset PS1to the carrier shaft ST2of the second planetary gearset PS2is attained.

To achieve third gear, the shift position C is controlled by the actuator AK1, thus coupling the ring gear shaft HR1of the first planetary gearset PS1to the ring gear shaft HR2of the second planetary gearset and to the carrier shaft ST1of the first planetary gearset PS1. The ring gear shaft HR1is thus interlocked with the carrier shaft ST1, such that the first planetary gearset PS1revolves in the block.

In the neutral positions, i.e. between the shift positions A, B, C, the electric machine EM1can be uncoupled, e.g. in so-called coasting mode, in which the electric vehicle rolls freely without losses caused by the co-rotating rotor of the electric machine EM1.

The shift devices SE1, SE2are preferably designed as unsynchronized dog clutches, in which—as mentioned—an interruption of traction torque occurs. Synchronization during the shift process can, however, be performed by the electric machine. In principle, shift elements other than positive-locking ones can also be used, e.g. frictional clutches or brakes.

The rotors RO1, RO2of the electric machines EM1, EM2are designed to be hollow cylindrical and have an axis of rotation identical to that of the wheel axles a and of the output shafts2a,2b, i.e. the planetary gearsets PS1, PS2, PS3are arranged coaxially with the rotors RO1, RO2. In the case of drive axle1shown inFIG. 1, the electric machines EM1, EM2are arranged in the central area between the two drive wheels R1, R2, i.e. in the immediate area of the center plane and symmetry plane M. The three planetary gearsets PS1, PS2, PS3are arranged one behind the other in the direction of the power flow, i.e. from inside to outside, on both the right and the left side.

FIG. 2shows a further exemplary embodiment of the invention for a drive axle2(second drive axle), wherein inFIG. 2the same reference numerals are used for identical or similar parts. The drive axle2differs from the drive axle1on the one hand by a modified arrangement of the first and second planetary gearsets PS1, PS2and the electric machines EM1, EM2and on the other hand by the arrangement of a differential gear DI, which is designed as an axle differential gear or a transverse differential gear and is arranged between the two drive wheels R1, R2. The power flow from the two electric machines EM1, EM2, which are arranged on the outside if viewed in the axial direction, is effected via the first shiftable planetary gearset PS1and then via the second shiftable planetary gearset PS2into the differential gear DI, where the first power flow from the left side is combined with the second power flow from the right side. From the differential gear DI, the power is routed to the drive wheels R1, R2via the axle shafts3a,3band the third planetary gearset PS3, which is designed as a constant transmission stage, via the output shafts2a,2b. The actuators AK1, AK2and the shift elements SE1, SE2are arranged on the drive axle2in the area of the center plane M, i.e. between the two electric machines EM1, EM2. The design of the first and second planetary gearsets PS1, PS2kinematically corresponds to the design according toFIG. 1, i.e. there is the same linkage.

The shift elements SE1, SE2, which each have three shift positions A, B, C and D, E, F for three gears, are preferably designed as unsynchronized dog clutches, wherein an interruption of traction torque occurs during shifting. Due to the arrangement of the differential gear DI, however, such an interruption of traction torque can be avoided by the second (right) electric machine EM2supporting on the left side during the shift operation, e.g. during a changeover from shift position B to shift position A, i.e. during an interruption of traction torque on the left side, the second electric machine on the right side supplies power to the differential gear DI, which the differential gear DI delivers symmetrically to the two drive wheels R1, R2via the two axle shafts3a,3b.

To achieve first gear, corresponding to shift position A, the ring gear shaft HR1of the first planetary gearset PS1is connected to the housing GH, i.e. immobilized. The sun shaft SO2of the second planetary gearset PS2is attached to the housing, resulting in fixed transmission ratios in the first and second planetary gearsets PS1, PS2, which, when connected in series, result in the transmission ratio ii of the first gear.

To achieve second gear, corresponding to shift position B, the carrier shaft ST1of the first planetary gearset PS1is coupled to the ring gear shaft HR1of the first planetary gearset PS1. The power from the first electric machine EM1is thus transmitted to the first planetary gearset PS1via the drive shaft1aand the sun shaft SO1and from the first planetary gearset PS1via its ring gear shaft HR1and its carrier shaft ST1into the second planetary gearset PS2, therefrom the output is transmitted to the differential gear DI, i.e. its differential cage (without reference numeral), via its carrier shaft ST2. The linkage then turns at the ratio i2.

To achieve third gear, corresponding to shift position C, the ring gear shaft HR1and the carrier shaft ST1of the first planetary gearset PS1are coupled, i.e. interlocked, i.e. the first planetary gearset PS1is in direct drive. Simultaneously, the ring gear shaft HR2of the second planetary gearset PS2is connected to the ring gear shaft HR1and the carrier shaft ST1. Again, the carrier shaft ST2provides the output to the differential gear DI via the second planetary gearset PS2. The linkage then turns at the ratio i3.

Obviously, the couplings of the individual transmission links for first, second and third gears are identical for the linkages of drive axle1and drive axle2.

As mentioned above, the gears on the right side are shifted in the same way for the shift positions D, E, F. The shift elements SE1SE2are actuated by means of the actuators AK1, AK2. The planetary gearsets PS1, PS2, PS3are arranged coaxially with the electric machines EM1, EM2, i.e. coaxially with the axis of rotation and the wheel axle a. In the drawing again only the upper half (above axis a) is shown; the lower half matches the upper half and is obtained by mirroring along the axis of rotation a.

FIG. 3shows a third exemplary embodiment of the invention for a drive axle3(third drive axle), which essentially matches the drive axle2according toFIG. 2. The same reference numerals are used for identical parts. The arrangement of the two actuators AK1AK2, which trigger shifting in the two shift elements SE1, SE2, is different for drive axle3. Both actuators AK1, AK2are arranged in a common plane, which extends approximately in parallel to the center plane and symmetry plane M. This has the advantage of reduced installation space. A housing structure GH, for instance a housing wall GH, is arranged in the area of the center plane M, i.e. in the center between the two shift devices SE1, SE2. In the shift positions A and D, which are on the inside if viewed in the axial direction, the joint, centrally arranged housing structure GH can be used—likewise for the two immobilized sun shafts SO2of the second planetary gearsets PS2. The connection (shown as a dotted line) between the second actuator AK2, which is located to the left of the center plane M, and the shift element SE2on the right side runs through an opening in the housing structure GH.

FIG. 4shows a fourth exemplary embodiment of the invention for a drive axle4(fourth drive axle), which essentially matches the drive axle2according toFIG. 2. The drive axle4is different in that the differential gear DI has a locking function for locking the differential and for unlocking (unlocking the lock), which locking function is performed by a shift element SE3. The shift element SE3can be used to achieve a shift position G, in which the cage of the differential gear DI can be coupled, i.e. locked, to an axle shaft, in the drawing to the axle shaft3b. When the differential gear DI is locked in the shift position G, there is no longer any speed compensation between the two drive wheels R1, R2, but rather there is a rigid connection between the two drive wheels R1, R2.

FIG. 5shows a fifth exemplary embodiment of the invention (fifth drive axle), which matches the drive axle1according toFIG. 1with respect to the arrangement of the electric machines EM1, EM2and the shiftable planetary gearsets PS1, PS2. The difference is that the third planetary gearset PS3, which is designed as an epicyclic gear and is shown inFIG. 4and forms a constant transmission stage, is replaced by a stationary transmission StG1inFIG. 5, namely on both sides in the area of the drive wheels R1, R2. The stationary transmission StG1is designed as a planetary gearset and has a carrier51, planetary gears52,53, which are mounted opposite the carrier51, a sun gear54and a ring gear55. The carrier51is attached to the housing, i.e. the planetary gearset provides a stationary transmission ratio. The carrier shaft ST2of the second planetary gearset PS2provides the drive to the planetary gear52. The ring gear55provides the output to the output shaft2aand thus to the drive wheel R1. The stationary gear StG1has an axle offset h1between its input shaft ST2and its output shaft2a. This transmission arrangement having an axle offset is known as a so-called portal axle and has the advantage of greater ground clearance for the vehicle compared to the variants described above. Because of the drive via the planetary gear52and due to additional planetary gears on the circumference, the power flow from the input to the output is divided. The stationary transmission StG1on the right side, which drives the right drive wheel R2, is a mirror image of the stationary transmission StG1on the left side and shows the same gear down.

FIG. 6shows a sixth exemplary embodiment of the invention for a drive axle6(sixth drive axle), which matches the drive axle5according toFIG. 5with regard to the design and the arrangement of the electric machines EM1, EM2and the first and second planetary gearsets PS1, PS2. The difference here is that a modified stationary transmission StG2is used for the constant transmission stage in the area close to the wheel.

The stationary transmission StG2is designed as a spur gear and has an input gear61, driven by the carrier shaft ST2of the second planetary gearset PS2, two intermediate gears62,63and an output gear64, which drives the wheel R1via the output shaft2a. There is an axle offset h2between the input shaft of the stationary gear StG2, i.e. the carrier shaft ST2, and the output shaft2b. The two intermediate gears62,63are rotated into the drawing plane for reasons of illustration—they mesh with both the input gear61and the output gear64. The centers of the gears61,62,63,64form the tips of an imaginary rhombus, which is symbolically represented by a dotted line z (the centers of the gears and the rhombus formed thereof lie in a radial plane perpendicular to the drawing plane). The second stationary gear StG2on the right side is a mirror image and has the same gear ratio.

With regard to the drive axles1to6described above in accordance withFIGS. 1 to 6, there is considerable potential for reducing installation space, in particular because the first and second planetary gearsets and possibly also the shift elements can be arranged at least partially within the rotors RO1, RO2of the electrical machines EM1, EM2. The rotors RO1, RO2have a hollow cylindrical design and, starting from the axis of rotation a, have a cylindrical cavity that can be used to accommodate the planetary gearsets. This reduces installation space in particular in the axial direction.

REFERENCE NUMERALS