Powertrain with a transmission for a hybrid vehicle, and methods for shifting the transmission

Abstract

Powertrain with a transmission (20) for a hybrid vehicle, wherein the transmission (20) comprises a first drive shaft (1), a second drive shaft (2), an output shaft (4), an electric machine (EM) with a first and a second planetary gear set (P1, P2) in which a sun gear (11) of the first planetary gear set (P1) is permanently connected to a sun gear (21) of the second planetary gear set (P2), and at least four clutches (A, B, D, E), - wherein four forward gears can be selected between the drive shafts (1, 2) and the output shaft (4) by engaging the clutches (A, B, D, E) in pairs, - wherein the first drive shaft (1) is connected via the coupling (A) to the rotationally fixed sun gears (11, 21) of the planet gear sets (P1, P2) and can be connected via the second drive shaft (2) via the coupling (B) to the web (12) of the first planet gear set (P1), - wherein the bridge (22) of the second planetary gear set (P2) is permanently and rotationally fixedly connected to the output shaft (4), - wherein the electric machine (EM) is connected via a spur gear set (3) to the connected sun gears (11, 21) of the planetary gear sets (P1, P2) and wherein the internal combustion engine (VM) drives into the gearbox (20) via a disconnect clutch (K0), - wherein elements of the transmission are arranged in the following axial order: couplings (K0, A, B), first planetary gear set (P1), second planetary gear set (P2), output gear set (5), spur gear set (3).

Description

[0001] The invention relates to a drive train with a transmission for a hybrid vehicle, wherein the transmission comprises a first drive shaft, a second drive shaft, an output shaft, an electric machine, with a first and a second planetary gear set, and at least four clutches for providing four forward gears.

[0002] The invention further relates to a method for switching a gearbox in the drive train. State of the art

[0003] For a hybrid drive in a vehicle, the simplest possible transmission is desirable, as this saves weight and makes it inexpensive to manufacture.

[0004] This is a multi-speed transmission in which a multitude of gears, i.e., fixed gear ratios between an input shaft and an output shaft, can be selected by means of shifting elements. These shifting elements are clutches or brakes.

[0005] From EP 3 095 631 A1, a transmission for a hybrid vehicle is known which enables starting without slippage of the shifting elements. This transmission comprises an input shaft, an output shaft, an electric machine with a rotationally fixed stator and a rotatable rotor, a gear set, and at least three shifting elements. The gear set includes a first and second planetary gear set, which together comprise a total of four shafts, designated as the first, second, third, and fourth shafts in order of rotational speed. The gear set is thus designed as a two-shaft, four-shaft transmission.

[0006] By selectively closing the three switching elements in pairs, a plurality of forward gears, i.e., fixed gear ratios between the input shaft and the output shaft, can be selected. The input shaft is connected to the first shaft of the wheelset via the first switching element and to the third shaft of the wheelset via the second switching element. The second shaft of the wheelset is permanently connected to the output shaft. The fourth shaft of the wheelset can be locked in a rotationally fixed position via the third switching element by connecting it to a housing or another rotationally fixed component of the transmission. The rotor of the electric machine is permanently operatively connected to the third shaft of the wheelset via a fixed gear ratio.

[0007] This arrangement of the transmission elements enables an electrodynamic starting mode. Closing the first switching element connects the drive shaft to the first axle of the wheelset. Keeping the other switching elements involved in gear formation open does not automatically establish a fixed speed relationship between the four axles of the wheelset. Only when the electric motor applies a supporting torque to the third axle does a fixed speed relationship between the four axles of the wheelset result. By varying the rotor speed and the speed applied to the drive shaft, the speed of the output shaft can be continuously adjusted, thus enabling a starting process. Simultaneously, the transmission also allows for fixed gear ratios between the drive shaft and output shaft, as well as between the third axle and output shaft.This means that the hybrid vehicle also has fixed gears available for combustion engine driving as well as for purely electric driving.

[0008] However, this state-of-the-art transmission has the disadvantage that it only has three gear ratios.

[0009] Furthermore, starting the combustion engine while driving in the first gear of the electric motor is not possible, as it is not possible to switch to a mode with connection to the combustion engine by closing a single clutch.

[0010] From DE 10 2017 213 385 A1, a transmission for a hybrid drive arrangement is known which can be coupled to two drive units, with an input shaft and an output shaft, at least one first and one second switching element and at least one first and one second planetary gear set, wherein the input shaft can be coupled by means of the first switching element to the sun gear of the first planetary gear set, which is coupled to the sun gear of the second planetary gear set, and the input shaft can be coupled by means of the second switching element to the planet carrier of the first planetary gear set, which is coupled to the ring gear of the second planetary gear set, and wherein the output shaft is coupled to the planet carrier of the second planetary gear set.

[0011] However, the transmission design can only represent two electric gear stages.

[0012] DE 10 2015 216 896 A1, JP 2017 - 202 723 A and DE 10 2017 209 932 A1 show different designs for a hybrid transmission with two planetary gear sets.

[0013] The object of the invention is to present an improved embodiment of such a hybrid transmission. Description of the invention

[0014] The problem is solved with a drivetrain with a transmission for a hybrid vehicle, wherein the transmission has a first input shaft, a second input shaft, an output shaft, an electric machine with a first and a second planetary gear set, and at least four clutches, wherein four forward gears can be selected between the input shafts and the output shaft by engaging clutches A, B, D, E in pairs, wherein the first input shaft is connected to the sun gears of the planetary gear sets via clutch A, and the second input shaft is connectable to the hub of the first planetary gear set via clutch B, and the hub of the second planetary gear set is permanently and rotationally fixed to the output shaft.wherein the electric machine is connected to the connected sun gears of the planetary gear sets and wherein the internal combustion engine drives into the gearbox via a disconnect clutch.

[0015] The solution according to the invention allows a compact representation of a four-speed transmission for the internal combustion engine as well as a three-speed transmission for the electric machine for purely electric operation.

[0016] The transmission comprises a first and second planetary gear set, which are designed as negative gear sets, and wherein the bridge of the first planetary gear set is connected to the ring gear of the second planetary gear set.

[0017] According to the invention, the electric machine is connected to the connected sun gears of the planetary gear sets in a rotationally fixed manner via a spur gear set.

[0018] It is advantageous that the ring gears of the planetary gear sets can each be fixed to a rotationally fixed point on the housing using couplings.

[0019] According to the invention, the elements of the transmission are arranged in the following axial sequence: couplings, first planetary gear set, second planetary gear set, output gear set, spur gear set.

[0020] The problem is further solved by a method for switching a transmission in the drive train according to one of the preceding claims, wherein four forward gears for the internal combustion engine are switched between the drive shafts and the output shaft by closing the four clutches in pairs when the clutch K0 is closed.

[0021] It is advantageous that in a first electrodynamic operating mode the couplings K0 and B are closed. Advantageously, with clutch K0 open and in purely electric operation, the drive shaft is connected to the output shaft via three gear stages.

[0022] It is advantageous that the combustion engine is started during purely electric driving by engaging the first electric gear stage by closing clutches A and E, and additionally closing clutch K0. Description of the characters

[0023] The invention is described below by way of example with reference to the attached drawing. Fig. Figure 1 shows a schematic representation of the gearbox, Fig. Figure 2 shows a table with overviews of the gear levels.

[0024] Fig. Figure 1 schematically shows a drive with a gearbox 20 according to the invention. The gearbox comprises a first planetary gear set P1 and a second planetary gear set P2. A sun gear 11 of the first planetary gear set P1 is permanently connected to a sun gear 21 of the second planetary gear set P2. A carrier 12 of the first planetary gear set P1 is permanently connected to a ring gear 23 of the second planetary gear set P2. The sun gear 11 of the first planetary gear set P1 and the sun gear 21 of the second planetary gear set P2 are components of a first input shaft 1. A carrier 22 of the second planetary gear set P2 is connected to an output gear set 5, which drives an output shaft 4 to a differential 6. The ring gear 23 can be connected to the housing 10 via a coupling E. A ring gear 13 of the first planetary gear set P1 can also be connected to the housing 10 via a coupling D.

[0025] An internal combustion engine VM drives into the gearbox via an unspecified torsional damping and a disconnect clutch K0.

[0026] A first drive shaft 1, driven directly by the internal combustion engine VM, is connected to the transmission 20 via a coupling A. Drive shaft 1 can be connected to the second drive shaft 2 via a further coupling B. The second drive shaft 2 encompasses the first drive shaft 1 and is designed as a hollow shaft. It is rigidly connected to the web 12 of the first planetary gear set P1 and thus to the hollow shaft 23 of the second planetary gear set P2. It can therefore be secured to the housing 10 by means of the coupling E.

[0027] The first drive shaft 1 is, viewed from the side of the internal combustion engine VM, rigidly connected to the sun gears 11, 21 of the planetary gear sets P1, P2. On the side opposite the internal combustion engine VM, an electric machine EM is connected to the first drive shaft 1 and the sun gears 11, 21 of the planetary gear sets P1, P2 via a spur gear set 3.

[0028] By connecting the electric motor EM to the sun gears 11 and 21 of the planetary gear sets P1 and P2, and by introducing a clutch E, a fourth gear is created. Furthermore, the combustion engine VM can be started from purely electric driving mode at low speeds with clutches A and E engaged by engaging clutch K0. This also results in a third purely electric gear.

[0029] Fig.Figure 2 shows a shift diagram of the transmission 20 according to the exemplary embodiment. The rows of the shift diagram indicate an electrically variable operating mode (EVT), four forward gears, a standstill charging mode, and three electric gears (E1, E2, and E3). In the columns of the shift diagram, an X indicates which of the clutches K0, A, B, D, and E are engaged in which gear or operating mode.

[0030] The last column shows the translations of the internal combustion engine i_ICE and the electric machines i_EM.

[0031] In the internal combustion engine's forward gears, three of the clutches K0, A, B, D, and E are engaged. This results in a fixed gear ratio between input shaft 1 or 2 and output shaft 4 in the four forward gears.

[0032] In electrically variable operating mode (EVT), only clutch K0 and clutch B are engaged. This means that drive shaft 2, output shaft 4, and the electric machine EM are each connected to one element of the second planetary gear set P2. If the electric machine EM does not apply any torque, no power can be transmitted from drive shaft 2 to output shaft 4. Only by applying a supporting torque via the electric machine EM is power transmission via the second planetary gear set P2 possible in electrically variable operating mode (EVT). By varying the speed of the electric machine and a given drive shaft speed, a starting process can therefore be simulated.

[0033] By closing clutch B and keeping the remaining switching elements A, D, E open in standstill charging mode, the drive shaft 2 is connected to the electric machine EM without any power being transferred from the drive shaft 2 to the output shaft 4. This allows an internal combustion engine connected to the drive shaft 2 to charge an energy storage device through generator operation of the electric machine EM.

[0034] The electric gears E1, E2, E3 operate with the clutch K0 open and have a fixed gear ratio between the first drive shaft 1 and the output shaft 4.

[0035] For the design of the transmission according to the invention, a transmission ratio of i_PGS_P2=-2.2 is chosen for the first planetary gear set and a transmission ratio of -1.8 for the second planetary gear set.

[0036] The fourth gear of the combustion engine is automatically coupled to the second gear of the electric motor. Therefore, either the second electric gear must be designed so that the electric motor's limiting speed is not exceeded at the vehicle's maximum speed, or the third gear of the combustion engine must be designed so that the vehicle's maximum speed is reached in that gear, and the fourth gear of the combustion engine is thus used purely as an overdrive to reduce fuel consumption under partial load. Reference symbol list 20 gearboxes 1 drive shaft 2 Output shaft 3 Spur gear set 4 Output shaft 5 Output gear set 6 Differential 10 housings EM Electrical Machine P1 First planetary gear set 11 Sun gear of the first planetary gear set 12 Bridge of the first planetary gear set 13 Ring gear of the first planetary gear set P2 Second planetary gear set 21 Sun gear of the second planetary gear set 22 Bridge of the second planetary gear set 23 Ring gear of the second planetary gear set K0, A, B, D, E Switching elements EVT electrically variable operating mode E1 First electric gear E2 Second electric gear E3 Third electric gear Standstill: Standby charging mode VM internal combustion engine

Claims

[1] Drive train with a transmission (20) for a hybrid vehicle, wherein the transmission (20) has a first input shaft (1), a second input shaft (2), an output shaft (4), an electric machine (EM), with a first and a second planetary gear set (P1, P2), in which a sun gear (11) of the first planetary gear set (P1) is permanently connected to a sun gear (21) of the second planetary gear set (P2), and at least four clutches (A, B, D, E), - whereby by closing the clutches (A, B, D, E) in pairs, four forward gears can be switched between the input shafts (1, 2) and the output shaft (4), - wherein the first drive shaft (1) is connected via the clutch (A) to the rotationally fixed sun gears (11, 21) of the planetary gear sets (P1, P2) and is connectable via the second drive shaft (2) via the clutch (B) to the carrier (12) of the first planetary gear set (P1), - wherein the web (22) of the second planetary gear set (P2) is permanently connected to the output shaft (4) in a rotationally fixed manner, - wherein the electric machine (EM) is connected via a spur gear set (3) to the connected sun gears (11, 21) of the planetary gear sets (P1, P2) and wherein the internal combustion engine (VM) drives into the transmission (20) via a separating clutch (K0), - whereby elements of the transmission are arranged in the following axial order: clutches (K0, A, B), first planetary gear set (P1), second planetary gear set (P2), output gear set (5), spur gear set (3). [2] Drive train with transmission (20) according to claim 1, characterized by that the first and second planetary gear sets (P1, P2) are designed as minus gear sets, - and wherein the web (12) of the first planetary gear set (P1) is connected to the ring gear (23) of the second planetary gear set (P2). [3] Drive train with transmission (20) according to one of the preceding claims, characterized by that the ring gears (13, 23) of the planetary gear sets (P1, P2) can each be fixed with couplings (E, D) at a rotationally fixed point on the housing (10). [4] Method for shifting a transmission (20) in the drive train according to one of the preceding claims, characterized by that by closing the four clutches (A, B, D, E) in pairs, four forward gears for the internal combustion engine (VM) are switched between the input shafts (1, 2) and the output shaft (4) when the clutch (K0) is closed. [5] Method for shifting a transmission (20) in the drive train according to one of the preceding claims, characterized by that in an electrically variable operating mode (EVT) the clutches (K0 and B) are closed. [6] Method for shifting a transmission (20) in the drive train according to one of the preceding claims, characterized bythat the drive shaft (1) is connected to the output shaft (4) via three gear stages when the clutch (K0) is open and in purely electric operation. [7] Method for shifting a transmission (20) in the drive train according to one of the preceding claims, characterized by that the combustion engine (VM) is started when driving purely electrically by engaging the first electric gear stage by closing the clutches (A, E) and additionally closing the clutch K0.

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