Method for starting the combustion engine during a load shift in parallel hybrid vehicles

Abstract

Method for starting the internal combustion engine (1) in parallel hybrid vehicles with an internal combustion engine (1), a transmission (3) and an electric machine (2) connected to the transmission (3), wherein the internal combustion engine (1) can be connected to the electric machine (2) via a clutch (K1), wherein the internal combustion engine (1) is started via the electric machine (2) during a load shift in purely electric driving mode, wherein the clutch (K1) is closed during the load shift, wherein during the load shift the speed adjustment of the electric machine (2) required for synchronization to the new gear is carried out by a speed adjustment of the electric machine (2) in a speed control mode, and that during the speed adjustment of the electric machine (2) the internal combustion engine (1) is started by closing the clutch (K1), characterized in that,when the speed (n_EM) of the electric machine (2) reaches the target speed or the synchronous speed (n_gear_new) of the gear being engaged, the electric machine (2) is switched to torque-controlled mode and the switching element (K_new) being engaged is fully closed.

Description

[0001] The present invention relates to a method for starting the internal combustion engine during a power shift in parallel hybrid vehicles according to the preamble of patent claim 1.

[0002] Hybrid vehicles comprising a hybrid transmission are known from the prior art. In addition to the internal combustion engine, they comprise at least one electric motor or electric machine. In serial hybrid vehicles, a generator is driven by the internal combustion engine, with the generator supplying electrical energy to the electric motor driving the wheels. Parallel hybrid vehicles are also known in which the torques of the internal combustion engine and at least one electric machine connectable to the internal combustion engine are added together. In this case, the electric machines can be connected to the belt drive or to the crankshaft of the internal combustion engine. The torques generated by the internal combustion engine and / or the at least one electric machine are transmitted to the driven axle via a downstream transmission.

[0003] For example, DE 10 2006 019 679 A1 discloses a powertrain comprising an electrically variable hybrid transmission and an electrohydraulic control system, a plurality of electric power units, and a plurality of torque-transmitting mechanisms. The torque-transmitting mechanisms can be selectively engaged by the electrohydraulic control system to provide four forward gears, a neutral state, an electric low- and high-speed operating mode, an electrically variable low- and high-speed operating mode, and a hill-hold operating mode.

[0004] DE 10 2005 057 607 B3 discloses a hybrid drive for vehicles, comprising at least one main engine, in particular an internal combustion engine, a generator, an electric motor, and a planetary gear train comprising a sun gear, a ring gear, a planet carrier, and planetary gears, which includes at least one output shaft. It is provided that, for a first driving range of the vehicle, the drive shafts of the main engine and the electric motor are coupled to the sun gear of the planetary gear train to add the torques, and for a further driving range, one of the two motors can be coupled to the ring gear of the planetary gear train in a force-locking manner for mechanically adding the rotational speeds according to the superposition principle.

[0005] In a vehicle with a hybrid drive, it is state of the art to switch off the engine when the vehicle is stationary or immediately before it comes to a standstill in order to reduce the fuel consumption of the combustion engine.

[0006] US 2005 / 0 221 947 A1 discloses a drive control system for a hybrid motor vehicle, comprising an internal combustion engine, a transmission with discrete gear ratios, an electric machine arranged between the internal combustion engine and the transmission, and a first and a second clutch that can be selectively actuated to control the connection of the rotor of the electric machine to the transmission and to the internal combustion engine, respectively. Furthermore, the known drive control system comprises a control device for controlling the internal combustion engine, the electric machine, and the clutches, which is configured to perform a start-stop function in which, during a stop step, the internal combustion engine is disconnected from the electric machine and the transmission and switched off.

[0007] EP 1 785 305 A2 describes a system for a hybrid vehicle with an internal combustion engine, a motor / generator, a first clutch between the internal combustion engine and the motor / generator, and a multi-speed transmission between the motor / generator and a drive wheel. Upon an engine start command from an electric drive mode, a second clutch, which is part of the transmission, is selected, and slip control of this second clutch is performed while the internal combustion engine is started by engaging the first clutch.

[0008] DE 10 2005 051 382 A1 describes a device and method for implementing a hybrid drive. The electric motor is arranged between the single clutch arranged between the combustion engine and the manual transmission and the manual transmission in such a way that the electric motor can directly transmit a positive or negative torque to a transmission input shaft of the manual transmission.

[0009] DE 600 22 593 T2 describes an automatic internal combustion engine start-stop control device, with an engine speed detection device, a clutch detection device, an automatic stop detection device and an automatic start detection device.

[0010] DE 698 31 468 T2 describes a drive control system for starting an internal combustion engine during electric travel, wherein a start request determination device is provided to determine a request to start the internal combustion engine, with an assistance setting device for increasing the output torque of the electric motor when the request to start the internal combustion engine is determined.

[0011] DE 11 2006 001 985 T5 describes a control device for driving an electric vehicle having a first and a second electric motor and a prime mover, a differential device having three rotary elements, the first rotary element being connected to the first electric motor, the second rotary element being connected to the second electric motor, and the third rotary element being connected to the prime mover, a transmission connected to the second electric motor, and a device for processing an execution of a simultaneous control for starting the prime mover and for downshifting the transmission.

[0012] DE 103 27 306 A1 relates to a method for operating a drive unit of a motor vehicle with an internal combustion engine, an electric machine and a transmission, wherein a first clutch is provided between the internal combustion engine and the electric machine and a second clutch is provided on the output side of the electric machine, wherein when the internal combustion engine is started, the electric machine is operated at a speed when the first clutch is slipping and when the second clutch is slipping, which speed drops after the first clutch is closed and when the second clutch is slipping under load to a speed whose magnitude is higher than a speed of the electric machine which occurs when the second clutch is additionally closed.

[0013] In a subsequent start step, the electric machine, operating as an electric motor, is connected to the transmission while a first gear ratio is engaged in the transmission, so that the vehicle is initially driven by the electric machine. A change from the first gear ratio to a second, higher gear ratio is then performed. During this shift, the connection between the combustion engine and the electric machine is established, thereby starting the combustion engine. Furthermore, it is provided that while the higher gear ratio is engaged in the transmission, the connection between the electric machine and the transmission is interrupted by disengaging the corresponding clutch, resulting in an interruption in tractive force.In a next step, the connection between the combustion engine and the transmission is established so that when the start step is completed, the vehicle is driven by the combustion engine and optionally by the electric motor.

[0014] The present invention is based on the object of providing a method for starting the internal combustion engine in parallel hybrid vehicles, the implementation of which allows for a comfortable engine start. Furthermore, the method according to the invention is intended to reduce the number of malfunctions in the drive train and increase comfort within the scope of a start-stop functionality.

[0015] This object is achieved by the features of patent claim 1. Further embodiments and advantages of the invention emerge from the subclaims.

[0016] Accordingly, it is proposed to start the combustion engine via the electric motor during a power shift in purely electric driving mode. In a vehicle in which the combustion engine can be connected to the electric motor via a clutch, this can be achieved by closing this clutch.

[0017] By combining the functions “power shift” and “start of the combustion engine” according to the invention, comfort is increased, since each of these functions is a disturbance in the drive train and, according to the invention, they are carried out simultaneously.

[0018] In a powershift carried out according to the state of the art, the engine speed adjustment required for synchronization to the new gear is carried out with the help of the switching elements involved and an engine torque intervention.

[0019] For example, in a traction upshift, the transmission capacity of the engaging shift element is initially increased to take over the load, while the transmission capacity of the disengaging shift element is simultaneously reduced. After the load has been transferred by the engaging shift element, the engine speed is adjusted with the help of the shift elements and an engine torque intervention. During a powershift in hybrid operation of a hybrid vehicle, the engine is formed by the combustion engine and the electric motor, whereas during a powershift in purely electric operation, the speed of the electric motor is adjusted. The disengaging shift element is then fully opened and the engaging shift element is fully closed.

[0020] According to the state of the art, the combustion engine and / or electric motor remain torque-controlled during such load shifts, with a target driving torque specified, and a corresponding torque intervention is carried out by the shift sequence control.

[0021] According to an advantageous development of the invention, for a hybrid vehicle in which a clutch is arranged between the internal combustion engine and the electric machine connected to the transmission, it is proposed that during the power shift the speed adjustment of the electric machine required for synchronization to the new gear is carried out by a speed adjustment of the electric machine in a speed control mode, wherein the electric machine is speed-controlled to the target speed or the connection speed (synchronous speed) of the new gear, so that the switching element to be engaged is synchronized and wherein during the speed adjustment the internal combustion engine is started by closing the clutch arranged between the internal combustion engine and the electric machine.

[0022] According to the invention, the torque at the clutch between the internal combustion engine and the electric motor is transmitted to the electric motor's speed controller as a pilot torque. After the clutch has engaged, the torque of the internal combustion engine is used as the pilot torque for the speed controller. The torques of the clutches involved in the shifting, acting on the electric motor, also serve as additional pilot torques for speed control.

[0023] In an advantageous manner - regardless of the type of upshift - the mass moment of inertia of the electric machine can be used as the starting torque for the combustion engine during an upshift.

[0024] According to the invention, the speed curve of the electric machine is also designed such that the speed of the electric machine approaches the target speed with a small gradient.

[0025] When the speed of the electric motor reaches the target speed or the synchronous speed of the gear to be engaged, the electric motor is transferred back to torque-controlled mode and the engaging shift element is fully closed. After the powershift is completed, the combustion engine and the electric motor are coupled to the transmission output via the new gear.

[0026] The inventive starting of the combustion engine during a power shift in purely electric operation of a hybrid vehicle can advantageously be carried out within the framework of a start / stop function. This means that the vehicle initially starts in purely electric operation, whereby, if the driving speed exceeds a threshold or if the driver requests more torque, a power shift is performed while the combustion engine is simultaneously started.

[0027] Since the combustion engine is started while shifting elements in the transmission are slipping, it is advantageously decoupled from the output and can be conveniently represented, since the output torque is determined by the state of the shifting elements in the transmission.

[0028] The inventive concept of speed control of the electric machine during a powershift shortens shifting times because the speed of an electric machine can be precisely and dynamically controlled. Furthermore, the smooth run-in of the speed of the electric machine to the target speed or the synchronous speed of the new gear ensures particularly high shifting comfort because the change in the dynamic torque of the combustion engine and the electric machine, caused by the mass moment of inertia of the motors, experiences only a slight change at the moment the engaging shifting element begins to stick. A further advantage of the method according to the invention is that the loadshift sequence is easier to implement and coordinate than with a loadshift with torque intervention according to the prior art.

[0029] The invention is explained in more detail below with reference to the accompanying figures. They show: Fig. 1: An exemplary, schematic and simplified representation of the powertrain of a parallel hybrid vehicle; and Fig. 2: A diagram illustrating the speed variation of the electric motor during a pull upshift.

[0030] Referring to Fig. 1, the drive train of a parallel hybrid vehicle comprises an internal combustion engine 1 and at least one electric machine 2, which are connected in series in this order, wherein the internal combustion engine 1 can be decoupled from the electric machine 2 and thus from the drive train by opening a clutch K1.

[0031] In the direction of power flow downstream of the electric machine 2, a powershift transmission 3 is arranged, which in the exemplary simplified representation shown, which serves to illustrate the method according to the invention, comprises an engaging clutch K_new for the new gear to be engaged and a disengaging clutch K_old for the old gear, wherein each clutch or each gear is assigned a gear ratio with the ratio i_new or i_old. Fig. 1, the output of the powershift transmission 3 is provided with the reference number 4.

[0032] As already explained, according to the invention the combustion engine is started via the electric machine during a load shift in purely electric driving mode, whereby this is the case in the Fig. 1 shown drive train by closing the clutch K1.

[0033] The power shift can be carried out in such a way that the speed adjustment of the electric machine 2 required for synchronization to the new gear is carried out by a speed adjustment of the electric machine 2 in a speed control mode, which is explained below using a pull upshift from i_old to i_new.

[0034] According to the invention, the shift begins like a conventional shift; first, the transmission capacity of the engaging clutch K_new is increased to take over the load, and simultaneously, the transmission capacity of the disengaging clutch K_old is reduced. After the load has been taken over by the clutch K_new, the electric machine 2 is transferred from the torque-controlled mode to a speed control mode, and a speed adjustment of the electric machine 2 is carried out in this speed control mode, wherein the electric machine 2 is speed-controlled to the target speed or the synchronous speed of the new gear; simultaneously, the disengaging shift element K_old is fully opened. During this speed control phase of the electric machine, the clutch K1 is closed, whereby the combustion engine is started.

[0035] Here, the torque at clutch K1 is transmitted to the speed controller of electric machine 2 as a pilot torque. After clutch K1 is engaged, the torque of combustion engine 1 is used as the pilot torque for the speed controller. The torques of the clutches K_old and K_new acting on the electric machine 2, which are involved in the shift, also serve as additional pilot torques for speed control. Furthermore, it can be provided that the mass moment of inertia of electric machine 2 is used as the starting torque for the combustion engine.

[0036] The speed curve during the speed adjustment of the electric machine 2 in speed control mode is preferably designed such that the speed approaches the target speed or the connecting speed of the new gear with a small gradient. An exemplary curve of the target speed of the electric machine 2 n_EM as a function of time t is the subject of Fig.2. Here, n_gear_old denotes the speed of the electric motor 2 with the old gear engaged (ie with the clutch K_old closed); n_gear_new is the synchronous speed of the new gear during the pull upshift to be performed.

[0037] When the speed subsequently reaches the synchronous speed n_gear_new, the electric machine 2 is transferred to the torque-controlled mode and the clutch K_new is fully closed, so that the now started combustion engine 1 and the electric machine 2 are coupled to the output of the transmission via the new transmission gear.

[0038] During a traction downshift, the transmission capacity of the disengaging clutch K_old is preferably first reduced. As soon as slippage is detected at K_old, the electric machine 2 is transferred from torque-controlled mode to speed-controlled mode. Subsequently, the speed of the electric machine 2 is increased to a speed above the synchronous speed at the engaging clutch K_new, since a positive speed difference is required at K_new for this clutch to transmit traction torque.

[0039] In the next step, the transmission capacity of the engaging clutch K_new is increased and the transmission capacity of the disengaging clutch K_old is further reduced, thus ensuring continuous load transfer by K_new. After the load has been transferred by the engaging clutch K_new, the disengaging clutch K_old is fully opened, and the speed of the electric motor is adjusted to the synchronous speed of the engaging clutch K_new. As already explained, clutch K1 is closed during the speed control phase of the electric motor, which starts the combustion engine.

[0040] When the synchronous speed is reached, the electric machine is transferred back to the torque-controlled mode and the engaging clutch K_new is fully closed.

[0041] In the case of a coasting downshift, the transmission capacity of the engaging clutch K_new is initially increased to transfer the load, while simultaneously reducing the transmission capacity of the disengaging clutch K_old. After the load is transferred by K_new, the electric machine is transferred from torque-controlled mode to speed-controlled mode, and the disengaging clutch K_old is fully opened. The electric machine is then speed-controlled to the synchronous speed, with the speed preferably approaching the target speed with a slight gradient. When the synchronous speed is reached, the electric machine is transferred back to torque-controlled mode, and the engaging clutch K_new is fully closed.

[0042] A coasting upshift and a coasting downshift are essentially similar, with the difference that the signs of the torques are different and the speed curve goes in the other direction. Accordingly, in a coasting upshift, the transmission capacity of the disengaging clutch K_old is first continuously reduced. As soon as slippage is detected at K_old, the electric machine is transferred from torque-controlled mode to a speed control mode in which the speed is reduced to a speed below the synchronous speed at the engaging shift element K_new, since a negative speed difference is required for the engaging shift element to transmit torque. The transmission capacity of the engaging shift element K_new is then increased and the transmission capacity of the disengaging shift element K_old is reduced, so that continuous load transfer by K_new is realized.

[0043] After the load has been transferred by the engaging clutch K_new, the disengaging clutch K_old is fully opened, and the speed of the electric machine is controlled in speed control mode to the synchronous speed at the engaging clutch K_new. When the synchronous speed is reached, the electric machine is transferred back to torque-controlled mode, and the engaging clutch K_new is fully closed. Reference symbol 1 combustion engine 2 electric machine 3 powershift transmissions 4 Output of the powershift transmission K1 clutch K_new clutch Cold clutch n_EM speed of the electric machine n_Gang_alt Speed ​​of the electric motor with the old gear engaged n_Gang_neu Synchronous speed of the new gear i_alt translation i_new translation

Claims

[1] Method for starting the internal combustion engine (1) in parallel hybrid vehicles with an internal combustion engine (1), a transmission (3) and an electric machine (2) connected to the transmission (3), wherein the internal combustion engine (1) is connectable to the electric machine (2) via a clutch (K1), wherein the internal combustion engine (1) is started via the electric machine (2) during a power shift in purely electric driving mode, wherein the clutch (K1) is closed during the power shift, wherein during the power shift, the speed adjustment of the electric machine (2) required for synchronization to the new gear is carried out by a speed adjustment of the electric machine (2) in a speed control mode, and that during the speed adjustment of the electric machine (2), the internal combustion engine (1) is started by closing the clutch (K1), characterized bythat when the speed (n_EM) of the electric machine (2) reaches the target speed or the synchronous speed (n_Gang_neu) of the gear to be engaged, the electric machine (2) is transferred to the torque-controlled mode and the engaging switching element (K_neu) is completely closed. [2] Method according to claim 1, characterized by in that, in order to carry out a load shift, the speed curve is designed in such a way that the speed (n_EM) of the electric machine (2) approaches the target speed (n_Gang_neu) with a small gradient. [3] Method according to claim 1 or 2, characterized byin that, in order to carry out a load shift, the torque at the clutch (K1) is passed to the speed controller of the electric machine (2) as a pilot control torque, wherein after the clutch (K1) has stuck, the torque of the internal combustion engine (1) is used as a pilot control torque for the speed controller and wherein the torques of the clutches (K_old) and (K_new) involved in the shift, which act towards the electric machine (2), also serve as further pilot control torques for the speed control. [4] Method according to one of the preceding claims, characterized by that in order to carry out a load shift during an upshift, the mass moment of inertia of the electric machine (2) is used as the starting torque for the internal combustion engine (1). [5] Method according to one of the preceding claims, characterized byin that, in order to carry out a load shift in the event of a traction upshift, the transmission capacity of the engaging clutch (K_new) for load transfer is increased and, at the same time, the transmission capacity of the disengaging clutch (K_old) is reduced, wherein after the load has been transferred by the engaging shifting element (K_new), the electric machine (2) is transferred to a speed control mode and a speed adjustment of the electric machine (2) is carried out in order to achieve the synchronous speed of the gear to be shifted, so that the electric machine (2) is guided in a speed-controlled manner to the target speed or the synchronous speed of the new gear, wherein, at the same time, the disengaging shifting element (K_old) is fully opened. [6] Method according to one of the preceding claims 1 to 4, characterized bythat in order to carry out a load shift in the event of a traction downshift, the transmission capacity of the disengaging switching element (K_old) is reduced, wherein as soon as slippage is detected at the disengaging switching element (K_old), the electric machine (2) is transferred from the torque-controlled mode to a speed control mode, wherein the speed of the electric machine (2) is then increased to a speed above the synchronous speed at the engaging switching element (K_new), wherein in a next step the transmission capacity of the engaging switching element (K_new) is increased and the transmission capacity of the disengaging switching element (K_old) is further reduced, so that a continuous load transfer by the engaging switching element (K_new) is realized,wherein, after the load has been taken over by the switching element (K_new) to be switched on, the switching element (K_old) to be switched off is fully opened and the speed of the electrical machine (2) is brought to the synchronous speed at the switching element (K_new) to be switched on. [7] Method according to one of the preceding claims 1 to 4, characterized byin that, in order to carry out a load shift in the event of a coasting downshift, the transmission capacity of the engaging shift element (K_new) is increased, wherein at the same time the transmission capacity of the disengaging clutch (K_old) is reduced, wherein after the load has been taken over by the engaging shift element (K_new), the electric machine (2) is transferred from the torque-controlled mode to a speed control mode and the disengaging shift element (K_old) is fully opened and wherein the electric machine (2) is then speed-controlled to the synchronous speed, wherein at the same time the disengaging shift element (K_old) is fully opened. [8] Method according to one of the preceding claims 1 to 4, characterized bythat in order to carry out a load shift in the event of a coasting upshift, the transmission capacity of the disengaging switching element (K_old) is first continuously reduced, wherein as soon as slip is detected at the disengaging switching element (K_old), the electric machine (2) is transferred from the torque-controlled mode to a speed control mode in which the speed is reduced to a speed below the synchronous speed at the engaging switching element (K_new), wherein the transmission capacity of the engaging switching element (K_new) is subsequently increased and the transmission capacity of the disengaging switching element (K_old) is reduced,so that a continuous load transfer is realized by (K_new) and wherein after the load has been transferred by the switching element (K_new) to be switched on, the switching element (K_old) to be switched off is fully opened and the speed of the electrical machine (2) is controlled in speed control mode to the synchronous speed at the switching element (K_new).

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