Method for recovering energy from the internal combustion engine during upshifting and control unit for carrying out the method

Description

[0001] The invention relates to a method for recovering energy from an internal combustion engine during upshifting and to a control unit designed to carry out the method. State of the art

[0002] In the field of automotive technology, there has been a trend towards hybrid vehicles for several years now, in which the drive power can be provided by an internal combustion engine and an electric motor. A general distinction is made here between so-called mild hybrid applications, in which the electric motor can only be used as the sole drive source for short periods of time and is mainly used as a boost drive. In so-called range extender drive trains, however, an electric motor serves as the main drive motor and the internal combustion engine is carried along to charge a battery. With regard to the layout of such drive trains, it is possible to arrange the internal combustion engine and the electric drive motor upstream of a clutch arrangement in the direction of power flow.

[0003] This layout is relatively easy to implement structurally, but has functional limitations. In such hybrid powertrains, a planetary gear arrangement is often used as the transmission arrangement, possibly in conjunction with a continuously variable transmission. However, the integration of a dual-clutch transmission into a hybrid powertrain is particularly advantageous, especially when the electric motor is connected to the input of a sub-transmission.

[0004] DE 10 2010 044 618 A1 discloses a dual-clutch transmission with a wet dual clutch, electromechanical actuation of the shift system and an electro-hydraulic actuator for the dual clutch.

[0005] With the electric actuators, the dual-clutch transmission is capable of automatically engaging and shifting gears when the combustion engine is disconnected. It is thus ready for a start / stop system and an extended coasting function, in which the vehicle coasts freely when the combustion engine is disconnected. The electric actuators also enable easy hybridization of the transmission using an additional electric motor.

[0006] Due to the tightening of emissions regulations for combustion vehicles, it makes sense to implement every possible reduction in fossil fuels and thus in emissions, even small ones.

[0007] The various hybrid powertrains offer the possibility of recovering energy stored in the vehicle during operation in a variety of ways. The simplest example is the recovery of energy from the vehicle's braking processes, which returns energy to the drive process with an efficiency of over 80%.

[0008] However, there are other areas in the vehicle that can be considered with regard to energy recovery.

[0009] An internal combustion engine, which reduces its speed during upshifts, contains rotational energy that, until now, has simply been converted into heat without being utilized as drag loss. Typically, combustion is artificially impaired during upshifts by adjusting the ignition angle to achieve a dynamic, short-term reduction in the engine's torque. This leads to worse emissions because combustion is no longer optimal.

[0010] A hybrid drive in a P1 configuration is known from US 2017 0 210 374 A1. Instead of controlling the throttle position of the combustion engine, a controller controls the torque output of the electric motor.

[0011] The new torque output changes the speed of the combustion engine because the combustion engine is coupled to the electric machine.

[0012] During an upshift, the speed input to a transmission is reduced. Thus, the controller controls the electric motor to reduce the engine's speed. This can be achieved by generating torque in the opposite direction of engine rotation. Because the transmission disconnects the electric motor and the differential during a shift, torque transfer between them is stopped.

[0013] EP 1 431 623 A1 proposes a method for controlling an electric motor of a series hybrid vehicle. The transmission input shaft, driven by a drive shaft of the internal combustion engine, is disconnected from the drive shaft during gear shifts. An electric motor, coupled to the engine shaft, provides auxiliary torque. If validation conditions are met, energy recovery is enabled during gear shifts.

[0014] DE 10 2010 044 618 A1 describes different processes for upshifting and downshifting in a hybrid vehicle that runs purely on electricity. The combustion engine is used as a flywheel without being ignited.

[0015] The object of the invention is to present a method for recovering energy from an internal combustion engine during the upshift process. Description of the invention

[0016] The object is achieved by a method for recovering kinetic energy of an internal combustion engine by reducing the speed of the internal combustion engine during a predetermined time when shifting up a transmission in a vehicle and converting the kinetic energy of the rotation of the internal combustion engine or a drive unit into electrical energy by at least one electrical machine.

[0017] The electric motor can be coupled to a sub-transmission in a dual-clutch transmission with a first and second sub-transmission.

[0018] The energy of the decelerating combustion engine is recovered by applying excessive torque with the second clutch in the second sub-transmission and applying negative torque to the coupled electric motor. The goal is to compensate for the excess torque from the clutch as output torque.

[0019] Advantageously, the process start is triggered by the request to shift up.

[0020] Advantageously, the process is stopped when the combustion engine reaches its target speed.

[0021] The problem is solved with a controller designed to carry out the method. The controller is an engine controller and / or a transmission controller with respective data exchange. Description of the drawings

[0022] The invention is described below by way of example with reference to the accompanying drawings. Fig. 1 and 2 show the time course of engine speed and torque in the state of the art, Figure 3 shows the temporal course of torques with an embodiment of the inventive solution, Fig. 4 shows a schematic representation of the hybrid architecture in two different variants, Figure 5 shows a schematic diagram of the process.

[0023] In Figure 4 A hybrid solution with the integration of an electric motor EM into a dual-clutch transmission is schematically shown. The arrangement includes a starter generator 13 as an additional electric machine.

[0024] The solution according to the invention can be implemented both with the hybridization dual-clutch transmission alone and with the starter generator alone.

[0025] The drivetrain 10 includes an internal combustion engine (ICE) VM connected to a starter generator 13. Furthermore, the drivetrain 10 includes a dual-clutch transmission 14, the output side of which is connected to a differential 16. The differential 16 distributes drive power to a left and a right driven wheel 18L, 18R.

[0026] The dual-clutch transmission 14 includes a first friction clutch 30 and a first sub-transmission TG 1 . The first sub-transmission TG 1 includes, for example, gear stages N, 1, 3, 5, etc., which can be engaged and disengaged by means of schematically indicated shift clutches 34. The first friction clutch 30 and the first sub-transmission TG 1 form a first power transmission path 36 for transmitting power from the drive motor VM to the differential 16.

[0027] The dual-clutch transmission 14 further includes a second friction clutch 20 and a second sub-transmission TG 2 . The second sub-transmission TG 2 includes, for example, the odd gear stages N, 2, 4, 6, and R, which can be engaged and disengaged by means of associated shift clutches 24. The second friction clutch 20 and the second sub-transmission TG 2 form a second power transmission path 26 for transmitting drive power from the drive motor VM to the differential 16.

[0028] Furthermore, the drive train 10 includes an electric machine EM, which is connected to a controller 42 for control and power supply. The controller 42 can also include power electronics and a battery.

[0029] The electric machine EM is permanently connected to the second sub-transmission TG 2, for example, by means of a spur gear set or the like. Alternatively, the electric machine EM can be connected to the second sub-transmission TG 2 by means of a coupling arrangement.

[0030] The connection of the electric machine EM to the second partial transmission TG 2 , which has a high gear and a reverse gear, enables electric driving in almost all operating situations.

[0031] The drive train 10 is designed to operate in three different operating modes. In a conventional drive mode, drive power is generated solely by the drive motor, the internal combustion engine VM. Gear shifts occur without interrupting traction by routing drive power via one of the power transmission paths 26, 36, with a gear stage being preselected in the sub-transmission of the other power transmission path.

[0032] A gear change then occurs by transferring the power transmission flow from one path to the other by actuating the friction clutches 20, 30 in an overlapping manner. This drive mode is well known in the field of dual-clutch transmissions.

[0033] Furthermore, a second hybrid drive mode can be set up, in which drive power is provided by both the combustion engine VM and the electric motor EM. In this case, the drive powers can essentially be added together via the summing point at the input of the second sub-transmission TG 2.

[0034] Finally, a third drive mode is possible in which only the electric machine EM is controlled to generate drive power, whereas the combustion engine (VM) VM is shut down.

[0035] In this third drive mode, the electric machine EM recuperates energy via the drive wheels 18 R and 18 L and the second sub-transmission TG 2.

[0036] In a first variant of the invention, the solution is described as it can be represented using a hybridized dual-clutch transmission.

[0037] To do this, we first assume the situation without recuperation, as used in the state of the art and in the Figures 1 and 2 is shown.

[0038] Fig. 1shows the upshift situation as it occurs without a special solution for energy recovery in a dual clutch transmission. The two sub-transmissions of the dual clutch transmission rotate at different speeds. In this example, the combustion engine VM is initially coupled to the first sub-transmission TG 1 starting at time 0, which therefore has a torque of 500 Nm, for example, while the second sub-transmission TG 2 contributes no torque. The upshift is triggered at time 0.5 s. The speed of the combustion engine is to be reduced by the upshift. The first clutch 30 is opened, the second clutch 20 is closed. As a result, by time 0.7 s the torque of the first sub-transmission TG 1 drops to zero, while the torque of the second sub-transmission TG 2 increases to the target torque.

[0039] After the clutch fade-out period, the torque of the combustion engine VM_trq is reduced for a specific period by changing the ignition angle, which is indicated by the curve VM_trq. This influences the air supply and the ignition angle, while the injection rate normally remains constant.

[0040] This intervention in the ignition of the combustion engine is generally achieved by a later ignition angle, whereby the combustion engine operates in a less favorable range and consumes more fuel.

[0041] The combustion engine is braked because it has less torque than the partial transmission TG 2 in the torque reduction range VM_r.

[0042] In this example, the electric motor EM in the transmission makes no contribution to the resulting torque trq_out at the wheels, which is indicated by the zero line EM_trq. Furthermore, in most cases, no electric motor is present in the current state of the art.

[0043] The speed curve is shown schematically in Figure 2 shown. This graph plots the speed of the internal combustion engine eng_spd over time. At time 0.7 seconds, the torque of the internal combustion engine is reduced, as described above, and the speed of the internal combustion engine is reduced by a partial transmission.

[0044] The course according to the invention is described in the Figure 3 The combustion engine is no longer affected at all. No further ignition timing intervention is performed.

[0045] In order to implement the solution according to the invention, an electrical machine EM must be present.

[0046] In this example too, the combustion engine VM is initially coupled to the first sub-transmission TG 1 starting at time 0, which thus has a torque of, for example, 500 Nm, while the second sub-transmission TG 2 contributes no torque. At time 0.5 s, the upshift is triggered again. The first clutch 30 is opened, the second clutch 20 is closed. As a result, the torque of the first sub-transmission TG 1 drops back to zero by time 0.7 s, while the torque of the second sub-transmission TG 2 increases. However, an excessive torque TG 2 _max is set with the second clutch 20, which is maintained for a certain period of time, 0.2 s in the example.

[0047] Simultaneously with the excessive torque of the second sub-gearbox, the electric machine EM is operated with a negative torque EM_trq.

[0048] This reduces the kinetic energy of the combustion engine and converts it into electrical energy. The electrical energy is stored in batteries for later use.

[0049] The combustion engine is used as in Figure 2 shown, braked.

[0050] The location of the electric motor and its connection to the transmission are irrelevant. The point is simply to operate the electric motor with negative torque, thus using the engine's reduced speed for recuperation.

[0051] The method according to the invention is implemented in a software solution that can be included in the vehicle control system, more precisely either in an engine control system, a transmission control system or a combination of the controls.

[0052] The method according to the invention is shown schematically in the Figure 5The procedure begins with the "Start" block, which is triggered by the upshift request.

[0053] In process step S1, an excessive torque TG 2 _max is set with the second clutch 20 of the second sub-transmission TG 2, while in S2 the first clutch 30 is opened. At the same time, the torque of the electric machine EM_trq is set to negative.

[0054] This state is maintained for a short time, as shown in step S3. During this time t, which in the example shown is 0.2 seconds, energy is recovered via the electric machine and stored in batteries.

[0055] The process is stopped at this point, the excessive torque of the second clutch 20 is set back to the target value and the torque of the electric machine is reset to zero or another target value.

[0056] The process is applicable to various hybrid configurations. It is also possible to arrange the electric motor EM on the input side in front of the transmission or to arrange the electric motor EM at the transmission output with a direct connection to the transmission output shaft. List of reference symbols

[0057] 10 Drivetrain 13 Starter generator VM Combustion engine 14 Dual clutch transmission 16 Differential 18 L, 18 R right and left wheel 30 First friction clutch 34 Shift clutch 36 First power transmission path 20 Second friction clutch 24 Second shift clutch 26 Second power transmission path 42 Control EM Electric machine TG 1 First sub-transmission TG 2 Second sub-transmission S1-S4 Process steps

Claims

1. Method for recovering kinetic energy from a combustion engine (VM) by reducing the speed of the combustion engine (VM) for a predetermined time (t) during changing up of a transmission (14) in a vehicle and converting the kinetic energy of the rotation of the combustion engine (eng_spd) or of a drive unit into electrical energy by way of at least one electric machine (EM, 13), characterized in that, in a double-clutch transmission (14), the electric machine (EM) can be coupled to a first and second sub-transmission (TG1, TG2) and a first and second clutch (20, 30) on one of the sub-transmissions (TG1, TG2), and that energy is recovered from the braking combustion engine (VM) by adjusting an excessive torque (TG2_max) with the second clutch (20) in the second sub-transmission (TG2) and by adjusting a negative torque of the coupled electric machine (EM tq).

2. Method for recovering kinetic energy from a combustion engine (VM) according to Claim 1, characterized in that the start of the method (Start) is triggered by the request for changing up.

3. Method for recovering kinetic energy from a combustion engine (VM) according to either one of the preceding claims, characterized in that the method (Stop) is stopped when the combustion engine (VM) reaches its target speed.

4. Controller designed for carrying out the method according to the preceding claims, wherein the controller (42) is a motor controller and / or a transmission controller with respective data exchange.