Electric driveline and method of shifting gears

Abstract

An electric driveline comprising an electric drive motor and a transmission, and a method of shifting gears therefor. The transmission comprises an output shaft, a synchronizer, preferably a hydraulically actuatable synchronizer, for selectively drivingly engaging the electric drive motor with the output shaft via either one of a first gear providing a first gear ratio γ.sub.1 between the electric drive motor and the output shaft, and a second gear providing a second gear ratio γ.sub.2 between the electric drive motor and the output shaft, and an electronic shift controller for controlling a gear shift from the first gear to the second gear. The electronic shift controller is configured to actuate the synchronizer to disengage the first gear and to engage the second gear, and to synchronize a motor speed of the electric drive motor with a target speed.

Claims

1. An electric driveline, comprising: an electric drive motor; and a transmission, the transmission comprising: an output shaft, and a synchronizer for selectively drivingly engaging the electric drive motor with the output shaft via one of a first gear providing a first gear ratio γ.sub.1 between the electric drive motor and the output shaft and a second gear providing a second gear ratio γ.sub.2 between the electric drive motor and the output shaft; and an electronic shift controller for controlling a gear shift from the first gear to the second gear; wherein the electronic shift controller is configured to: actuate the synchronizer to disengage the first gear and to engage the second gear, and synchronize a motor speed of the electric drive motor with a target speed; wherein the electronic shift controller is configured to control the electric drive motor to provide a non-zero torque |T.sub.mot|>0 during disengagement of the first gear; and wherein the electronic shift controller is configured to limit an absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor during disengagement of the first gear to a first maximum torque |T.sub.mot|>0 until the first gear is disengaged, so that |T.sub.mot|≤|T.sub.dis| during disengagement of the first gear, wherein the first maximum torque |T.sub.dis| is the maximum torque that allows disengagement of the first gear.

2. The electric driveline of claim 1, wherein the synchronizer is hydraulically actuatable and comprises a hydraulic actuator and a control valve for controlling the hydraulic actuator, wherein the electronic shift controller is configured to actuate the synchronizer to disengage the first gear and/or to engage the second gear by changing a control position of the control valve.

3. The electric driveline of claim 1, wherein in order to minimize a time required for synchronizing the motor speed with the target speed the electronic shift controller is configured to set the absolute value |T.sub.mot| of the torque provided by the electric drive motor during disengagement of the first gear to the maximum torque |T.sub.dis| until the first gear is disengaged, so that |T.sub.mot|=|T.sub.dis|>0 during disengagement of the first gear.

4. The electric driveline of claim 1, wherein the electronic shift controller is configured to control the electric drive motor to provide a non-zero torque |T.sub.mot|>0 during synchronization of the motor speed with the target speed.

5. The electric driveline of claim 4, wherein the electronic shift controller is configured to limit an absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor during synchronization of the motor speed with the target speed to a second maximum torque |T.sub.sync|>0 until the motor speed has been synchronized with the target speed, so that |T.sub.mot|≤|T.sub.sync| during synchronization of the motor speed with the target speed.

6. The electric driveline of claim 5, wherein the electronic shift controller is configured to determine a point in time at which the limitation of the absolute value |T.sub.mot| of the torque provided by the electric drive motor to the second maximum torque |T.sub.sync| is initiated based on the motor speed and based on an output shaft speed.

7. The electric driveline of claim 6, wherein the electronic shift controller is configured to limit the absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor to the second maximum torque |T.sub.sync| when or once |ω.sub.mot−ω.sub.out.Math.γ.sub.1|>d.sub.1, wherein ω.sub.mot is a rotational speed of the electric drive motor, ω.sub.out is a rotational speed of the output shaft, and d.sub.1>0 is a first predetermined threshold value.

8. The electric driveline of claim 1, wherein the electronic shift controller is configured to control the electric drive motor to provide a non-zero torque |T.sub.mot|>0 during engagement of the second gear.

9. The electric driveline of claim 8, wherein the electronic shift controller is configured to limit an absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor during engagement of the second gear to a third maximum torque |T.sub.eng|>0 until the second gear is engaged, so that |T.sub.mot|≤|T.sub.eng| during engagement of the second gear, wherein the third maximum torque |T.sub.eng| is the maximum torque that allows engagement of the second gear.

10. The electric driveline of claim 9, wherein the electronic shift controller is configured to determine a point in time at which the limitation of the absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor to the third maximum torque |T.sub.eng| is initiated based on the motor speed and based on an output shaft speed.

11. The electric driveline of claim 10, wherein the electronic shift controller is configured to limit the absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor to the third maximum torque |T.sub.eng| when or once |ω.sub.mot−ω.sub.out.Math.γ.sub.2|<d.sub.2, wherein ω.sub.mot is the rotational speed of the electric drive motor, ω.sub.out is the rotational speed of the output shaft, and d.sub.2>0 is a second predetermined threshold value.

12. A method of shifting gears of an electric driveline from a first gear to a second gear, the electric driveline comprising: an electric drive motor; and a transmission, the transmission comprising: an output shaft, and a synchronizer for selectively drivingly engaging the electric drive motor with the output shaft via one of the first gear providing a first gear ratio γ.sub.1 between the electric drive motor and the output shaft and the second gear providing a second gear ratio γ.sub.2 between the electric drive motor and the output shaft; the method comprising the steps of: actuating the synchronizer to disengage the first gear and to engage the second gear, and synchronizing a motor speed of the electric drive motor with a target speed, wherein the method includes at least one of: (i) during the step of disengaging the first gear, controlling the electric drive motor to provide a non-zero torque while limiting an absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor to a first maximum torque |T.sub.dis|>0 until the first gear is disengaged, so that |T.sub.mot|≤|T.sub.dis| during disengagement of the first gear, wherein the first maximum torque |T.sub.dis| is the maximum torque that allows disengagement of the first gear; (ii) during the step of synchronizing the motor speed with the target speed, controlling the electric drive motor to provide a non-zero torque while limiting an absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor to a second maximum torque |T.sub.sync|>0 until the motor speed has been synchronized with the target speed, so that |T.sub.mot|≤|T.sub.sync| during synchronization of the motor speed with the target speed; and (iii) during the step of engaging the second gear, controlling the electric drive motor to provide a non-zero torque while limiting an absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor to a third maximum torque |T.sub.eng|>0 until the second gear is engaged, so that |T.sub.mot|≤|T.sub.eng| during engagement of the second gear, wherein the third maximum torque |T.sub.eng| is the maximum torque that allows engagement of the second gear.

13. An electric driveline, comprising: an electric drive motor; and a transmission, the transmission comprising: an output shaft, and a synchronizer for selectively drivingly engaging the electric drive motor with the output shaft via one of a first gear providing a first gear ratio γ.sub.1 between the electric drive motor and the output shaft and a second gear providing a second gear ratio γ.sub.2 between the electric drive motor and the output shaft; and an electronic shift controller for controlling a gear shift from the first gear to the second gear; wherein the electronic shift controller is configured to: actuate the synchronizer to disengage the first gear and to engage the second gear, and synchronize a motor speed of the electric drive motor with a target speed; wherein the electronic shift controller is configured to control the electric drive motor to provide a non-zero torque |T.sub.mot|>0 during synchronization of the motor speed with the target speed; and wherein the electronic shift controller is configured to limit an absolute value |T.sub.mot| of the non-zero torque provided by the electric drive motor during synchronization of the motor speed with the target speed to a second maximum torque |T.sub.sync|>0 until the motor speed has been synchronized with the target speed, so that |T.sub.mot|≤|T.sub.sync| during synchronization of the motor speed with the target speed.

14. The driveline of claim 13, wherein the synchronizer is adapted to selectively drivingly engage the electric drive motor with the output shaft via one of the first gear providing a first gear ratio γ.sub.1 between the electric drive motor and the output shaft and the second gear providing a second gear ratio γ.sub.2 between the electric drive motor and the output shaft.

15. The driveline of claim 13, wherein the electronic shift controller is configured to control the electric drive motor to provide a non-zero torque |T.sub.mot|>0 during disengagement of the first gear.

16. The driveline of claim 13, wherein the electronic shift controller is configured to control the electric drive motor to provide a non-zero torque |T.sub.mot|>0 during engagement of the second gear.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The accompanying drawings are incorporated herein as part of the specification. The drawings described herein illustrate embodiments of the presently disclosed subject matter, and are illustrative of selected principles and teachings of the present disclosure. However, the drawings do not illustrate all possible implementations of the presently disclosed subject matter, and are not intended to limit the scope of the present disclosure in any way.

(2) Embodiments of the invention are described in the following detailed description and are depicted in the accompanying drawing in which:

(3) FIG. 1 shows a schematic of an embodiment of an electric driveline comprising a two-speed transmission with a hydraulically actuatable synchronizer;

(4) FIG. 2 shows a schematic of a detailed view of the hydraulically actuatable synchronizer of FIG. 1;

(5) FIG. 3 shows time traces of shift control parameters during an upshift; and

(6) FIG. 4 shows time traces of shift control parameters during a downshift.

DETAILED DESCRIPTION

(7) It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific assemblies and systems illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application.

(8) FIG. 1 shows a schematic of an electric driveline 1 according to the invention. The driveline 1 comprises an electric drive motor 2, a transmission 3 and an electronic transmission controller 4 configured to control the motor 2 and the transmission 3.

(9) The transmission 3 comprises an input shaft 5 drivingly engaged or selectively drivingly engaged with the motor 2 and an output shaft 6. It is understood that in variations of the embodiment depicted in FIG. 1 the input shaft 5 may be drivingly engaged or selectively drivingly engaged with the motor 2 via one or more intermediate shafts and a plurality of intermediate gears. The output shaft 6 may be drivingly engaged or selectively drivingly engaged with a ground engaging structure which may comprise one or more vehicle wheels, for example. The transmission 3 comprises gears 5a and 5b fixedly disposed on the input shaft 5 so that the gears 5a and 5b rotate with the input shaft 5 at all times. A radius and diameter of the gear 5a are larger than a radius and diameter of the gear 5b. And the transmission 3 comprises a high range gear 6a and a low range gear 6b that are rotatably disposed on the output shaft 6. The high range gear 6a is drivingly engaged or in mesh with the gear 5a, and the low range gear 6b is drivingly engaged or in mesh with the gear 5b. A radius and diameter of the high range gear 6a are smaller than a radius and diameter of the low range gear 6b.

(10) The transmission 3 further comprises a synchronizer 7. In the embodiment depicted in FIG. 1 the synchronizer 7 is configured as a hydraulically actuatable synchronizer including a hydraulic unit 8 for actuating a movable member 9 by means of hydraulic forces. A more detailed view of the hydraulic unit 8 is depicted in FIG. 2 and described further below. It is understood that in variations of the embodiment depicted in FIG. 1 the transmission 3 may comprise further gears and/or shafts configured to selectively provide further gear ratios between the motor 2 and the output shaft 6.

(11) The hydraulic unit 8 is configured to move the movable member 9 relative to the output shaft 6 to selectively drivingly engage the motor 2 with the output shaft 6 via either one of the high range gear 6a and the low range gear 6b. For example, the synchronizer 7 may comprise a synchromesh unit and the movable member 9 may be configured as a movable shift collar configured to selectively frictionally engage with either one of the high range gear 6a and the low range gear 6b, and configured to selectively lock either one of the high range gear 6a and the low range gear 6b to the output shaft 6 so that either one of the high range gear 6a and the low range gear 6b may selectively rotate with the output shaft 6, respectively. Synchromesh units of this type are generally known in the art of automotive transmissions. It is understood that in variations of the embodiment depicted in FIG. 1 the synchronizer 7 may be configured as an electrically actuatable synchronizer including an electric actuator for moving the movable member 9, rather than the hydraulic unit 8 depicted in FIG. 1.

(12) When the motor 2 is drivingly engaged with the output shaft 6, the gear ratio γ between the motor 2 and the output shaft 6 is generally defined as γ=ω.sub.mot/ω.sub.out, wherein ω.sub.mot is the rotational speed of the electric drive motor and wherein ω.sub.out is the rotational speed of the output shaft. When the movable member 9 locks the high range gear 6a to the output shaft 6, the output shaft 6 and the motor 2 are drivingly engaged via the high range gear 6a and the gear 5a, thereby providing a gear ratio γ.sub.a between the motor 2 and the output shaft 6. And when the movable member 9 locks the low range gear 6b to the output shaft 6, the output shaft 6 and the motor 2 are drivingly engaged via the low range gear 6b and the gear 5b, thereby providing a gear ratio γ.sub.b between the motor 2 and the output shaft 6.

(13) In the embodiment shown in FIG. 1 the gears 5a, 5b, 6a, 6b are dimensioned such that γ.sub.a<γ.sub.b. That is, given a motor speed ω.sub.mot and a motor output torque T.sub.mot, engaging the high range gear 6a with the output shaft 6 provides a high output shaft speed ω.sub.out,a=ω.sub.mot/γ.sub.a and a low output shaft torque T.sub.out,a=T.sub.mot.Math.γ.sub.a. And given the same motor speed ω.sub.mot and the same motor output torque T.sub.mot, engaging the low range gear 6b with the output shaft 6 provides a low output shaft speed ω.sub.out,b=ω.sub.mot/γ.sub.b and a high output shaft torque T.sub.out,b=T.sub.mot.Math.γ.sub.b, wherein ω.sub.out,a>ω.sub.out,b and wherein T.sub.out,a<T.sub.out,b.

(14) The transmission 3 further includes a speed sensor 10 configured to measure a rotational speed of the output shaft 6. The electric drive motor 2, the hydraulic unit 8 and the speed sensor 10 are connected with the controller 4 via wired or wireless connections 4a-c. The controller 4 is configured to actuate the synchronizer 7, for example based on at least one of the motor speed ω.sub.mot, the motor torque T.sub.mot, the output shaft speed ω.sub.out and an engagement position of the movable member 9. And the controller 4 is configured to control the motor speed ω.sub.mot and/or the motor torque T.sub.mot, for example based on at least one of the motor speed ω.sub.mot, the motor torque T.sub.mot, the output shaft speed ω.sub.out and an engagement position of the movable member 9.

(15) FIG. 2 shows a schematic of the hydraulically actuatable synchronizer 7 including a detailed view of the hydraulic unit 8. Here and in the following recurring features are designated with the same reference signs. The hydraulic unit 8 includes a high pressure source 8a such as a hydraulic pump, a low pressure tank 8b, an electrically controllable 4/3-way control valve 8c and a hydraulic actuator 8d such as a hydraulic cylinder coupled to the movable member 9 of the synchronizer 7. The valve 8c has control positions A, B and N. The controller 4 is configured to selectively switch the valve 8c to either one of the control positions A, B by controlling an electrical current in one or more solenoids.

(16) Depending on the control position of the valve 8c, the hydraulic actuator 8d may selectively move the movable member 9 in either one of two directions, for example in either one of two directions along the output shaft 6, to selectively engage either one of the high range gear 6a and the low range gear 6b with the output shaft 6. When the valve 8c is switched to control position A, the hydraulic actuator 8d moves the movable member 9 toward engagement with the high range gear 6a (i. e. toward the left in FIG. 2). When the valve 8c is switched to control position B as shown in FIG. 2, the hydraulic actuator 8d moves the movable member 9 toward engagement with the low range gear 6b (i. e. toward the right in FIG. 2).

(17) FIGS. 3 and 4 illustrate steps of a method of shifting gears in the electric driveline 1 of FIG. 1. Specifically, FIG. 3 shows time traces of a set of control parameters during an upshift from the low range gear 6b to the high range gear 6a. And FIG. 4 shows time traces of the same set of control parameters during a downshift from the high range gear 6a to the low range gear 6b. In particular, FIGS. 3 and 4 each show time traces of a valve control signal 11, of a motor speed 12, of a motor speed setpoint 13, and of a motor torque limit 14. The values “A” and “B” of the valve control signal 11 in FIGS. 3 and 4 correspond with the control positions A and B of the control valve 8c as depicted in FIG. 2, respectively. That is, when the valve control signal 11 takes on the value “A” the valve 8c is switched to the control position A, and when the valve control signal 11 takes on the value “B” the valve 8c is switched to the control position B.

(18) The following is a description of the method steps carried out during the upshift from the low range gear 6b to the high range gear 6a depicted in FIG. 3.

(19) At time t.sub.0 the valve 8c is switched to the control position B and the synchronizer 7 locks the low range gear 6b to the output shaft 6 so that the low range gear 6b rotates with the output shaft 6. The gear ratio between the motor 2 and the output shaft 6 is given by γ.sub.b. The high range gear 6a is free to rotate relative to the output shaft 6. The motor 2 turns at motor speed ω.sub.mot,b.

(20) At time t.sub.1 (t.sub.1>t.sub.0) the controller 4 initiates the upshift from the low range gear 6b to the high range gear 6a by switching the control valve 8c to the control position A, thereby causing the synchronizer 7 including the actuator 8d to gradually disengage the low range gear 6b. Time t.sub.1 marks the beginning of a disengagement phase 15. The controller 4 may initiate the upshift at time t.sub.1 based on at least one of an input command provided by an operator, a current motor speed and a current motor torque, for example. At the beginning of the disengagement phase 15 at time t.sub.1 the controller 4 further sets the motor torque limit 14 to a lower limit of −T.sub.dis, thereby limiting the torque exerted by the motor 2 to values T.sub.mot≥−T.sub.dis or |T.sub.mot|≤|T.sub.dis|. |T.sub.dis| may be the maximum torque the motor 2 may exert during disengagement of the low range gear 6b without causing a torque or stress exerted on the low range gear 6b and/or on the synchronizer 7 to exceed a predetermined threshold torque, thereby guaranteeing a smooth disengagement of the low range gear 6b. Preferably, |T.sub.dis| is non-zero, i. e. |T.sub.dis|>0, and the controller 4 may control the electric drive motor 2 to provide a non-zero torque |T.sub.mot|>0 during the disengagement phase or throughout the disengagement phase.

(21) During the disengagement phase 15 the controller 4 determines an updated value of the motor speed setpoint 13, also termed target speed ω.sub.tar, based on a current speed ω.sub.out of the output shaft 6 measured by the speed sensor 10 and based on the gear ratio γ.sub.a provided by the high range gear 6a after completion of the upshift to the high range gear 6a. Specifically, the target speed determined by the controller 4 is given by ω.sub.tar=γ.sub.a.Math.ω.sub.out. When the motor speed setpoint is set to ω.sub.tar, the controller 4 starts synchronizing the motor speed ω.sub.mot with the previously calculated target speed ω.sub.tar=γ.sub.a.Math.ω.sub.out by actively controlling the motor torque T.sub.mot and/or the motor speed ω.sub.mot. However, the motor speed starts to change only once the disengagement phase has been completed at time t.sub.2. Updating the motor speed setpoint 13 before the disengagement phase 15 has been completed allows making the motor speed variation happen right upon completion of the disengagement phase.

(22) At time t.sub.2 (t.sub.2>t.sub.1) the synchronizer 7 has fully disengaged the low range gear 6b from the output shaft 6. Time t.sub.2 marks the beginning of a synchronization phase 16. During the synchronization phase 16 both the low range gear 6b and the high range gear 6a are disengaged from the output shaft 6 and free to rotate relative to the output shaft 6. At the beginning of the synchronization phase 16 at time t.sub.2 the motor speed starts to change under the effect of the synchronizer friction torque and of the motor torque T.sub.mot, thereby speeding up the synchronization process and reducing wear of the synchronizer 7 and/or the of high range gear 6a. The controller 4 may be configured to continuously update the value of the target speed ω.sub.tar=γ.sub.a.Math.ω.sub.out during the synchronization phase 16 based on continuous measurements of the speed ω.sub.out of the output shaft 6 using the speed sensor 10.

(23) During the synchronization phase 16 or throughout the synchronization phase 16 the controller 4 controls the motor 2 to exert or apply a non-zero torque on the input shaft 5, in particular a negative torque, resulting in a deceleration of the motor 2. Or in other words, during the synchronization phase 16 the controller 4 controls the motor 2 to reduce the absolute value of the difference between the motor speed ω.sub.mot and the target speed ω.sub.tar=γ.sub.a.Math.ω.sub.out. The controller 4 may synchronize the motor speed ω.sub.mot with the target speed ω.sub.tar=γ.sub.a.Math.ω.sub.out using closed loop (feedback) control, for example.

(24) At time t.sub.3 (t.sub.3>t.sub.2) the controller 4 determines that |ω.sub.mot−ω.sub.out.Math.γ.sub.b|>d.sub.1, indicating that the low range gear 6b has been disengaged from the output shaft 6. d.sub.1 may be a predetermined threshold value, for example. At time t.sub.3 the controller 4 then sets the motor torque limit 14 to a lower limit of −T.sub.sync, thereby limiting the torque exerted by the motor 2 to values T.sub.mot≥−T.sub.sync or |T.sub.mot|≤|T.sub.sync|. Preferably, |T.sub.sync|>0. Limiting the motor torque during the synchronization phase 16 may reduce a torque or stress exerted on the high range gear 6a and/or on the synchronizer when the synchronizer 7 starts engaging the high range gear 6a.

(25) At time t.sub.4 (t.sub.4>t.sub.3) the controller 4 determines that |ω.sub.mot−ω.sub.out.Math.γ.sub.a|<d.sub.2, indicating that the motor speed ω.sub.mot has been synchronized with the target speed ω.sub.tar=γ.sub.a.Math.ω.sub.out and that the synchronizer 7 including the hydraulic actuator 8d is about to engage the high range gear 6a with the output shaft 6. d.sub.2 may be a predetermined threshold value, for example. At time t.sub.4 the controller 4 then sets the motor torque limit 14 to a lower limit of −T.sub.eng, thereby limiting the torque exerted by the motor 2 to values T.sub.mot≥−T.sub.eng or |T.sub.mot|≤|T.sub.eng|. Preferably, |T.sub.eng| is non-zero, i. e. |T.sub.eng|>0, and the controller 4 may control the electric drive motor 2 to provide a non-zero torque |T.sub.mot|>0 during the engagement phase or throughout the engagement phase. Limiting the motor torque before the synchronizer 7 starts engaging the high range gear 6a with the output shaft 6 may reduce a torque or stress exerted on the high range gear 6a and/or on the synchronizer 7 during engagement of the high range gear 6a. In the embodiment shown in FIG. 3 |T.sub.sync|≥|T.sub.dis| and |T.sub.sync|≥|T.sub.eng| in order to speed up synchronization of the motor speed ω.sub.mot with the target speed ω.sub.tar=γ.sub.a.Math.ω.sub.out. It is understood that in alternative embodiments ⊕T.sub.sync| may be chosen such that |T.sub.sync|≤|T.sub.eng|, for example in order to guarantee a maximally smooth engagement of the high range gear 6a once the motor speed ω.sub.mot and the target speed ω.sub.tar=γ.sub.a.Math.ω.sub.out have been synchronized.

(26) At time t.sub.5 (t.sub.5>t.sub.4) the synchronizer 7 including the hydraulic actuator 8d starts engaging the high range gear 6a with the output shaft 6. Time t.sub.5 marks the end of the synchronization phase 16 and the beginning of an engagement phase 17. Throughout the engagement phase 17 the motor torque is limited to |T.sub.mot|≤|T.sub.eng|.

(27) At time t.sub.6 (t.sub.6>t.sub.5) the synchronizer 7 has completed engagement of the high range gear 6a with the output shaft 6 so that the high range gear 6a is locked to the output shaft 6 and rotates with the output shaft 6. The gear ratio between the motor 2 and the output shaft 6 is now given by γ.sub.a.

(28) The following is a description of the method steps carried out during the downshift from the high range gear 6a to the low range gear 6b depicted in FIG. 4.

(29) At time t.sub.0 the valve 8c is switched to the control position A and the synchronizer 7 locks the high range gear 6a to the output shaft 6 so that the high range gear 6a rotates with the output shaft 6. The gear ratio between the motor 2 and the output shaft 6 is given by γ.sub.a. The low range gear 6b is free to rotate relative to the output shaft 6. The motor 2 turns at motor speed ω.sub.mot,a.

(30) At time t.sub.1 (t.sub.1>t.sub.0) the controller 4 initiates the downshift from the high range gear 6a to the low range gear 6b by switching the control valve 8c to the control position B, thereby causing the synchronizer 7 including the actuator 8d to gradually disengage the high range gear 6a. Time t.sub.1 marks the beginning of the disengagement phase 15. The controller 4 may initiate the downshift at time t.sub.1 based on at least one of an input command provided by an operator, a current motor speed and a current motor torque, for example. At the beginning of the disengagement phase 15 at time t.sub.1 the controller 4 further sets the motor torque limit 14 to an upper limit of T.sub.dis, thereby limiting the torque exerted by the motor 2 to values T.sub.mot≤T.sub.dis or |T.sub.mot|≤|T.sub.dis|. Again, |T.sub.dis| may be the maximum torque the motor 2 may exert during disengagement of the high range gear 6a without causing a torque or stress exerted on the high range gear 6a and/or on the synchronizer 7 to exceed a predetermined threshold torque, thereby minimizing wear and guaranteeing a smooth disengagement of the high range gear 6a. Preferably, |T.sub.dis| is non-zero, and the controller 4 may control the electric drive motor 2 to provide a non-zero torque |T.sub.mot|>0 during the disengagement phase or throughout the disengagement phase.

(31) During the disengagement phase 15 the controller 4 determines an updated value of the motor speed setpoint 13, also termed target speed ω.sub.tar, based on a current speed ω.sub.out of the output shaft 6 measured by the speed sensor 10 and based on the gear ratio γ.sub.b provided by the low range gear 6b after completion of the downshift to the low range gear 6b. Specifically, the target speed determined by the controller 4 is given by ω.sub.tar=γ.sub.b.Math.ω.sub.out. At this time the controller 4 starts synchronizing the motor speed ω.sub.mot with the previously calculated target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out by actively controlling the motor torque T.sub.mot.

(32) At time t.sub.2 (t.sub.2>t.sub.1) the synchronizer 7 has fully disengaged the high range gear 6a from the output shaft 6. Time t.sub.2 marks the beginning of the synchronization phase 16. At time t.sub.2 the motor speed starts changing. During the synchronization phase 16 both the high range gear 6a and the low range gear 6b are disengaged from the output shaft 6 and free to rotate relative to the output shaft 6. At the beginning of the synchronization phase 16 at time t.sub.2 the motor speed ω.sub.mot starts to vary towards the previously calculated target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out under the action of the synchronizer friction torque and of the motor torque, thereby speeding up the synchronization process and reducing wear of the synchronizer 7 and/or the of low range gear 6b. The controller 4 may be configured to continuously update the value of the target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out during the synchronization phase based on continuous measurements of the speed ω.sub.out of the output shaft 6 using the speed sensor 10.

(33) During the synchronization phase 16 the controller 4 controls the motor 2 to exert or apply a non-zero torque on the input shaft 5, in particular a positive torque, resulting in an acceleration of the motor 2. Or in other words, during the synchronization phase 16 the controller 4 controls the motor 2 to decrease the absolute value of the difference between the motor speed ω.sub.mot and the target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out. The controller 4 may synchronize the motor speed ω.sub.mot with the target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out using open loop control or closed loop (feedback) control, for example.

(34) At time t.sub.3 (t.sub.3>t.sub.2) the controller 4 determines that |ω.sub.mot−ω.sub.out.Math.γ.sub.a|>d.sub.3, indicating that the high range gear 6a has been disengaged from the output shaft 6. d.sub.3 may be a predetermined threshold value, for example. At time t.sub.3 the controller 4 then sets the motor torque limit 14 to an upper limit of T.sub.sync, thereby limiting the torque exerted by the motor 2 to values T.sub.mot≤T.sub.sync or |T.sub.mot|≤|T.sub.sync|. Preferably, |T.sub.sync|>0. Limiting the motor torque during the synchronization phase 16 may reduce a torque or stress exerted on the low range gear 6b and/or on the synchronizer 7 when the synchronizer 7 starts engaging the low range gear 6b.

(35) At time t.sub.4 (t.sub.4>t.sub.3) the controller 4 determines that |ω.sub.mot−ω.sub.out.Math.γ.sub.b|<d.sub.4, indicating that the motor speed ω.sub.mot has been synchronized with the target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out and that the synchronizer 7 including the hydraulic actuator 8d is about to engage the low range gear 6b with the output shaft 6. d.sub.4 may be a predetermined threshold value, for example. At time t.sub.4 the controller 4 then sets the motor torque limit 14 to an upper limit of T.sub.eng, thereby limiting the torque exerted by the motor 2 to values T.sub.mot≤T.sub.eng or |T.sub.mot|≤T.sub.eng|. Preferably, |T.sub.eng| is non-zero, i. e. |T.sub.eng|>0, and the controller 4 may control the electric drive motor 2 to provide a non-zero torque during the engagement phase or throughout the engagement phase. Limiting the motor torque before the synchronizer 7 starts engaging the low range gear 6b with the output shaft 6 may reduce a torque or stress exerted on the low range gear 6b and/or on the synchronizer 7 during engagement of the low range gear 6b. In the embodiment shown in FIG. 4 |T.sub.sync|≥|T.sub.dis| and |T.sub.sync|≥|T.sub.eng| in order to speed up synchronization of the motor speed ω.sub.mot with the target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out. It is understood that in alternative embodiments |T.sub.sync| may be chosen such that |T.sub.sync|≤|T.sub.eng|, for example in order to guarantee a maximally smooth engagement of the low range gear 6b once the motor speed ω.sub.mot and the target speed ω.sub.tar=γ.sub.b.Math.ω.sub.out have been synchronized.

(36) At time t.sub.5 (t.sub.5>t.sub.4) the synchronizer 7 including the hydraulic actuator 8d starts engaging the low range gear 6b with the output shaft 6. Time t.sub.5 marks the end of the synchronization phase 16 and the beginning of an engagement phase 17. Throughout the engagement phase 17 the motor torque is limited to |T.sub.mot|≤|T.sub.eng|.

(37) At time t.sub.6 (t.sub.6>t.sub.5) the synchronizer 7 has completed engagement of the low range gear 6b with the output shaft 6 so that the low range gear 6b is locked to the output shaft 6 and rotates with the output shaft 6. The gear ratio between the motor 2 and the output shaft 6 is now given by γ.sub.b.

(38) Although identical symbols have been used to designate the times t.sub.1-t.sub.6 and the torque limit values T.sub.dis, T.sub.sync and T.sub.eng for both the upshift illustrated in FIG. 3 and the downshift illustrated in FIG. 4, it should be noted that the values these quantities assume during an upshift may be different from the values these quantities assume during a downshift.

(39) Inter alia, the present disclosure may relate to the following aspects: 1. Electric driveline (1), comprising: an electric drive motor (2); and a transmission (3), the transmission (3) comprising: an output shaft (6), and a hydraulically actuatable synchronizer (7) for selectively drivingly engaging the electric drive motor (2) with the output shaft (6) via one of a first gear providing a first gear ratio γ.sub.1 between the electric drive motor (2) and the output shaft (6) and a second gear providing a second gear ratio γ.sub.2 between the electric drive motor (2) and the output shaft (6); and an electronic shift controller (4) for controlling a gear shift from the first gear to the second gear; wherein the electronic shift controller (4) is configured to: actuate the synchronizer (7) to disengage the first gear and to engage the second gear, and synchronize a motor speed of the electric drive motor (2) with a target speed. 2. The electric driveline (1) of aspect 1, wherein the hydraulically actuatable synchronizer (7) comprises a hydraulic actuator (8d) and a control valve (8c) for controlling the hydraulic actuator (8d), wherein the electronic shift controller (4) is configured to actuate the synchronizer (7) to disengage the first gear and/or to engage the second gear by changing a control position of the control valve (8c). 3. The electric driveline (1) of any one of the preceding aspects, wherein the electronic shift controller (4) is configured to determine the target speed based on an output shaft speed and based on the second gear ratio γ.sub.2. 4. The electric driveline (1) of any one of the preceding aspects, wherein the electronic shift controller (4) is configured to limit an absolute value |T.sub.mot| of a torque provided by the electric drive motor (2) during disengagement of the first gear to a first maximum torque |T.sub.dis| until the first gear is disengaged, so that |T.sub.mot|≤|T.sub.dis| during disengagement of the first gear, wherein the first maximum torque |T.sub.dis| is the maximum torque that allows disengagement of the first gear. 5. The electric driveline (1) of aspect 4, wherein in order to minimize a time required for synchronizing the motor speed with the target speed the electronic shift controller (4) is configured to set the absolute value |T.sub.mot| of the torque provided by the electric drive motor (2) during disengagement of the first gear to the maximum torque |T.sub.dis| until the first gear is disengaged, so that |T.sub.mot|=|T.sub.dis| during disengagement of the first gear. 6. The electric driveline (1) of any one of the preceding aspects, wherein the electronic shift controller (4) is configured to limit an absolute value |T.sub.mot| of a torque provided by the electric drive motor (2) during synchronization of the motor speed with the target speed to a second maximum torque |T.sub.sync| until the motor speed has been synchronized with the target speed, so that |T.sub.mot|≤|T.sub.sync| during synchronization of the motor speed with the target speed. 7. The electric driveline (1) of any one of the preceding aspects, wherein the electronic shift controller (4) is configured to limit an absolute value |T.sub.mot| of a torque provided by the electric drive motor (2) during engagement of the second gear to a third maximum torque |T.sub.eng| until the second gear is engaged, so that |T.sub.mot|≤|T.sub.eng| during engagement of the second gear, wherein the third maximum torque |T.sub.eng| is the maximum torque that allows engagement of the second gear. 8. The electric driveline (1) of any one of aspects 6 and 7, wherein the electronic shift controller (4) is configured to determine a point in time at which the limitation of the absolute value |T.sub.mot| of the torque provided by the electric drive motor (2) to the second maximum torque |T.sub.sync| is initiated based on the motor speed and based on an output shaft speed; and/or wherein the electronic shift controller (4) is configured to determine a point in time at which the limitation of the absolute value |T.sub.mot| of the torque provided by the electric drive motor (2) to the third maximum torque |T.sub.eng| is initiated based on the motor speed and based on an output shaft speed. 9. The electric driveline (1) of any one of the preceding aspects, wherein the transmission (3) further comprises an input shaft (5), wherein the input shaft (5) is drivingly engaged with the electric drive motor (2) and selectively drivingly engaged with the output shaft (6) via one of the first gear and the second gear, and wherein when the electric drive motor (2) is drivingly engaged with the output shaft (6) the gear ratio γ between the electric drive motor (2) and the output shaft (6) is given by γ=ω.sub.mot/ω.sub.out, wherein ω.sub.mot is the rotational speed of the electric drive motor (2) and wherein ω.sub.out is the rotational speed of the output shaft (6);  wherein γ.sub.1>γ.sub.2 (upshift) and wherein the electronic shift controller (4) is configured to synchronize the motor speed with the target speed by controlling the electric drive motor (2) to exert a negative torque on the input shaft (5) to decelerate the motor speed. 10. The electric driveline (1) of any one of aspects 1 to 8, wherein the transmission (3) further comprises an input shaft (5), wherein the input shaft (5) is drivingly engaged with the electric drive motor (2) and selectively drivingly engaged with the output shaft (6) via one of the first gear and the second gear, and wherein when the electric drive motor (2) is drivingly engaged with the output shaft (6) the gear ratio γ between the electric drive motor (2) and the output shaft (6) is given by γ=ω.sub.mot/ω.sub.out, wherein ω.sub.mot is the rotational speed of the electric drive motor (2) and wherein ω.sub.out is the rotational speed of the output shaft (6); wherein γ.sub.1<γ.sub.2 (downshift) and wherein the electronic shift controller (4) is configured to synchronize the motor speed with the target speed by controlling the electric drive motor (2) to exert a positive torque on the input shaft (5) to accelerate the motor speed. 11. Method of shifting gears of an electric driveline (1) from a first gear to a second gear, the electric driveline (1) comprising: an electric drive motor (2); and a transmission (3), the transmission (3) comprising: an output shaft (6), and a hydraulically actuatable synchronizer (7) for selectively drivingly engaging the electric drive motor (2) with the output shaft (6) via one of a first gear providing a first gear ratio γ.sub.1 between the electric drive motor (2) and the output shaft (6) and a second gear providing a second gear ratio γ.sub.2 between the electric drive motor (2) and the output shaft (6); the method comprising the steps of: actuating the synchronizer (7) to disengage the first gear and to engage the second gear, and synchronizing a motor speed of the electric drive motor (2) with a target speed. 12. The method of aspect, further including at least one of: (i) during the step of disengaging the first gear, limiting an absolute value |T.sub.mot| of a torque provided by the electric drive motor (2) to a first maximum torque |T.sub.dis| until the first gear is disengaged, so that |T.sub.mot|≤|T.sub.dis| during disengagement of the first gear, wherein the first maximum torque |T.sub.dis| is the maximum torque that allows disengagement of the first gear; (ii) during the step of synchronizing the motor speed with the target speed, limiting an absolute value |T.sub.mot| of a torque provided by the electric drive motor (2) to a second maximum torque |T.sub.sync| until the motor speed has been synchronized with the target speed, so that |T.sub.mot|≤|T.sub.sync| during synchronization of the motor speed with the target speed; and (iii) during the step of engaging the second gear, limiting an absolute value |T.sub.mot| of a torque provided by the electric drive motor (2) to a third maximum torque |T.sub.eng| until the second gear is engaged, so that |T.sub.mot|≤|T.sub.eng| during engagement of the second gear, wherein the third maximum torque |T.sub.eng| is the maximum torque that allows engagement of the second gear. 13. The method of aspect 12, wherein the step of limiting the absolute value |T.sub.mot| of the torque provided by the electric drive motor (2) to the first maximum torque |T.sub.dis| includes setting the absolute value |T.sub.mot| of the torque provided by the electric drive motor (2) to the maximum torque |T.sub.dis| until the first gear is disengaged, so that |T.sub.mot|=|T.sub.dis| during disengagement of the first gear. 14. The method of any one of aspects 11-13, wherein the transmission (3) further comprises an input shaft (5), wherein the input shaft (5) is drivingly engaged with the electric drive motor (2) and selectively drivingly engaged with the output shaft (6) via one of the first gear and the second gear, and wherein when the electric drive motor (2) is drivingly engaged with the output shaft (6) the gear ratio γ between the electric drive motor (2) and the output shaft (6) is given by γ=ω.sub.mot/ω.sub.out, wherein ω.sub.mot is the rotational speed of the electric drive motor (2) and wherein ω.sub.out is the rotational speed of the output shaft (6); wherein γ.sub.1>γ.sub.2 (upshift) and wherein the step of synchronizing the motor speed with the target speed includes controlling the electric drive motor (2) to exert a negative torque on the input shaft (5) to decelerate the motor speed. 15. The method of any one of aspects 11-13, wherein the transmission (3) further comprises an input shaft (5), wherein the input shaft (5) is drivingly engaged with the electric drive motor (2) and selectively drivingly engaged with the output shaft (6) via one of the first gear and the second gear, and wherein when the electric drive motor (2) is drivingly engaged with the output shaft (6) the gear ratio γ between the electric drive motor (2) and the output shaft (6) is given by γ=ω.sub.mot/ω.sub.out, wherein ω.sub.mot is the rotational speed of the electric drive motor (2) and wherein ω.sub.out is the rotational speed of the output shaft (6); wherein γ.sub.1<γ.sub.2 (downshift) and wherein the step of synchronizing the motor speed with the target speed includes controlling the electric drive motor (2) to exert a positive torque on the input shaft (5) to accelerate the motor speed.

(40) The embodiments described herein may include one or more range of values (for example, size, displacement and field strength etc.). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range that lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range. For example, a person skilled in the field will understand that a 10% variation in upper or lower limits of a range can be totally appropriate and is encompassed by the disclosure. More particularly, the variation in upper or lower limits of a range will be 5% or as is commonly recognized in the art, whichever is greater.

(41) Throughout this specification relative language such as the words ‘about’ and ‘approximately’ may be used. Unless otherwise specified or described, this language seeks to incorporate at least 10% variability to the specified number or range. That variability may be plus 10% or negative 10% of the particular number specified.

(42) The foregoing description is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and processes shown and described herein. Accordingly, all suitable modifications and equivalents may be considered as falling within the scope of the invention as defined by the claims which follow.