METHOD FOR STARTING A HYBRID VEHICLE AT LOW TEMPERATURES AND SOFTWARE MODULE

Description

[0001] The invention relates to a method for starting a hybrid vehicle at low temperatures, wherein the vehicle has an electric machine which can be separated from an internal combustion engine by a friction clutch. State of the art

[0002] Hybrid electric vehicles (HEVs) represent a technology transitioning from conventionally powered vehicles to electric vehicles. In HEVs, a combustion engine is combined with an electric motor to provide the necessary drive torque. This combined drive system enables several new driving modes, such as boosting, recuperation, or purely electric driving. The powertrain structure differs from that of a conventional powertrain.

[0003] Hybrid electric vehicles require a battery management system, while, depending on the design, the starter-generator is superfluous due to the integration of the electric motor. To ensure smooth engine starts, especially while driving, the power flows through the clutches and the electric motor must be properly coordinated.

[0004] From DE 10 2018 104 472 A1, a method for starting an internal combustion engine in a hybrid electric vehicle is known. The method comprises cranking the vehicle's engine by controlling the capacity of a clutch in a dual-clutch transmission located downstream of the engine. This clutch compensates for power transmission disturbances caused by the cranking process via an electric machine also located downstream of the dual-clutch transmission. In this way, the engine can be started under a wide variety of vehicle operating conditions. The engine is cranked under conditions where the vehicle speed is below a minimum vehicle speed threshold, which includes a synchronous engine idle speed for a first gear of the dual-clutch transmission.

[0005] Starting the combustion engine from a standstill is relatively unproblematic, whereas starting it while driving (e.g., from purely electric mode) presents a significant challenge due to high demands on comfort and driver acceptance. To ensure the best possible combustion engine start, precise coordination of all powertrain components is essential.

[0006] From DE 10 2019 211 916 A1, a method for starting an internal combustion engine in a drive train of a vehicle is known, wherein at least one internal combustion engine, one electric machine and at least one transmission are present, wherein both the internal combustion engine and the electric machine are effectively connected to the wheels of the vehicle via the transmission, and wherein both the internal combustion engine and the electric machine are effectively connected to the wheels of the vehicle via the transmission, and wherein both a torque of the drive and a wheel speed of the wheels are controlled.

[0007] At very low temperatures, starting the combustion engine from a standstill is more difficult. Due to the opposing drag torque in the open clutch at extremely low temperatures, the electric motor takes a very long time to reach operating speed. The temperature also limits the battery's power output, resulting in a start-up phase of approximately 3 seconds, which negatively impacts starting times.

[0008] DE 10 2018 129 769 A1 relates to a hybrid drive arrangement for a powertrain of an electrically powered motor vehicle, in particular a hybrid motor vehicle, comprising an internal combustion engine, a first electric machine and a power output device. The hybrid drive arrangement also includes at least one flow system by means of which heat from a fluid heated by the first electric machine can be transferred, at least partially, to the internal combustion engine in order to give it a higher temperature level, particularly during the starting process.

[0009] DE 10 2020 129 524 A1 describes a method for starting a hybrid vehicle with an electric machine and an internal combustion engine for generating traction and a hydraulically actuated disconnect clutch for connecting the electric machine and the internal combustion engine, wherein in a first step the electric machine is turned up to a target speed, in a second step the disconnect clutch is hydraulically pre-filled, in a third step the disconnect clutch is filled and the electric machine and the internal combustion engine are thus connected for towing the internal combustion engine, in a fourth step the internal combustion engine is ignited, wherein the third step is triggered by a start signal from a driver, wherein the first step is triggered by a wake-up signal preceding the start signal.

[0010] Furthermore, the documents DE102015118568A1, FR3132258A1, EP2848446A2 and DE102018212943A1 describe methods for starting an internal combustion engine in a hybrid electric vehicle.

[0011] The object of the invention is to propose a simple and efficient method for starting an internal combustion engine at very low temperatures. Description of the invention

[0012] The problem is solved by a method for starting a hybrid vehicle at low temperatures, wherein the vehicle has an electric machine which can be disconnected from an internal combustion engine by a friction clutch, wherein the method starts when the driver opens the vehicle, and wherein a software module is provided in a controller.

[0013] It is advantageous that the software module starts the procedure when all predetermined parameters meet the starting conditions, where the predetermined parameters and the starting conditions are: driver request, indicating a starting of the combustion engine, temperature in the oil sump below a critical temperature, battery charge level above a minimum threshold, selector lever in the Park / Neutral position.

[0014] The process includes closing the separating friction clutch and establishing the rotary connection with the internal combustion engine VM, whereby the internal combustion engine, VM, is pulled up to an ignition speed and ignited.

[0015] The electric machine is regulated to a predetermined speed for the duration of an active phase, provided the parameters are known.

[0016] According to the invention, a pause is taken after each active phase, during which the predetermined parameters of the starting condition are checked again.

[0017] The process is terminated when the termination criteria are met, i.e., when one of the predetermined parameters no longer meets the starting conditions, or the maximum number of iterations has been reached, or the combustion engine is ready to be ignited.

[0018] The task can also be solved with a software module for carrying out the procedure, wherein the software module is arranged in a control unit of the vehicle, the transmission or the electric machine.

[0019] According to the invention, the software module can be started when the vehicle is started. Description of the characters

[0020] Figure 1 shows a hybrid powertrain with dual-clutch transmission in a P2.5 configuration, Figure 2 shows a hybrid powertrain in a P2 configuration, Figure 3 shows a graph of the process over time, Figure 4 shows a flowchart.

[0021] The Figure 1Figure 1 shows an exemplary powertrain 1 in a P2.5 configuration, as known from the prior art in a hybrid vehicle 20. An internal combustion engine VM drives a transmission 2 with two sub-transmissions TG1 and TG2 and two shift clutches S1, S2, wherein the sub-transmissions TG1 and TG2 can be decoupled from the internal combustion engine VM, more precisely from the transmission input shaft, via clutches K1 and K2.

[0022] On the transmission output side, the drive train from both sub-transmissions terminates at a differential D and the two wheels 18R and 18L. The electric machine EM is coupled to sub-transmission TG2. At least the electric machine EM is controlled by a controller 10.

[0023] Figure 2Figure 1 shows a powertrain in a P2 configuration, where the electric machine EM is connected to the transmission input shaft outside the dual-clutch transmission. Additionally, a clutch K0 separates the combustion engine VM from the transmission.

[0024] In the exemplary embodiment, the method according to the invention is controlled via the control unit 10 of the electric machine. However, it is also possible to equip a different vehicle control unit with the appropriate software module and run the method there.

[0025] When starting a vehicle from a standstill that no longer has a starter motor, a pulse start is used. This requires bringing the electric motor, which is located downstream of the combustion engine (VM) via a friction clutch, up to speed. Speeds of 10,000 rpm are recommended.

[0026] The disengaging friction clutch closes quickly, establishing the rotary connection with the VM internal combustion engine. This is then revved up to ignition speed and ignited.

[0027] The process begins in an environmental situation where the outside temperature is significantly below freezing, generally below -10°C.

[0028] The process is step-by-step in the Figure 4 As shown. In the first step S1, the vehicle is unlocked by the driver or opened by an opening mechanism. Simultaneously, a software module in the control unit 10 is started, which controls the steps of the procedure and receives the incoming parameter values.

[0029] The software module is always started, regardless of the outside temperature.

[0030] The software module running in controller 10 queries the following parameters in step S2: Does the driver want to start the combustion engine (VM), resulting in a pulse start, or does the driver want to start electrically? What is the temperature? The oil temperature measured in the oil sump is checked for a critical temperature drop. If the measured value T is less than T_crit, another parameter is available for the procedure. What is the position of the gear selector? It is checked whether the gear selector is in the Park / Neutral position. What is the battery status? Another parameter is the state of charge (SOC) of the vehicle's batteries. To prevent deep discharge, batteries should not have a state of charge below 30%.

[0031] Are all parameters for the low-temperature start met, which is what happens in Figure 4 If marked with a +, the electric machine EM is brought to a preset speed.

[0032] According to the invention, a rotational speed ω is selected in S3 that results in a differential speed of approximately 600 revolutions per minute at the clutch, at which the viscous drag torque in the open clutch K1 is already relatively high. Due to the differential speed, the clutch plates and the oil located between them are heated and flung out by the frictional energy. This significantly reduces the drag torque during the speed ramp-up phase of the electric machine for the subsequent impulse start.

[0033] After a certain operating time x of the electric machine, a pause of duration y is inserted in step S5. The software module then returns to step S2 and checks the parameters for the next step.

[0034] If the conditions for the procedure are still met since the beginning, steps S3 and S5 are repeated.

[0035] Only when one of the parameters in step S2 no longer falls under the selection criteria, or the combustion engine VM is about to ignite, or the preset number of repetitions has been reached, is the procedure terminated if the termination criteria AK in S4 are met.

[0036] This significantly reduces the start-up time of the VM combustion engine.

[0037] In Figure 3 The upper graph shows the rotational speed ω of the electric machine EM over time. The lower graph shows the development of the frictional torque M over time.

[0038] The process begins with an open coupling between the electric machine EM and the combustion engine VM. Once the start parameters are available, the speed of the electric machine EM is increased for a period of time in an active phase x1. The pause y1 is shorter than the active phase x1 of the electric machine EM. During this pause y1, it is particularly important to check whether the battery's state of charge is still adequate. Then, another iteration begins until the active phase xi and the pause yi.

[0039] The clutch's drag torque decreased significantly over the iterations.

[0040] At the end of the pause yi, the impulse start of the combustion engine is initiated and the clutch K1 is closed.

[0041] An additional advantage arises when the combustion start is triggered during the active phase xi. The ramp-up then begins from an electric motor speed instead of zero, thus further reducing the ramp-up time.

Claims

1. Method for starting a hybrid vehicle (20) at low temperatures, wherein the hybrid vehicle (20) has an electric machine, EM, which can be separated from an internal combustion engine, VM, by a friction clutch, K1, K0, wherein the method starts when the driver opens the hybrid vehicle (20), wherein a software module in a controller (10) is started and the software module starts the method when all predetermined parameters satisfy the starting conditions, wherein the predetermined parameters and the starting conditions are: driver request, comprising starting the internal combustion engine, VM, temperature in the oil sump below a critical temperature, battery state of charge above a minimum threshold, selector lever in the park / neutral position, and wherein the method comprises closing the separating friction clutch and establishing the rotational connection to the internal combustion engine VM, wherein the internal combustion engine, VM, is cranked up to an ignition rotational speed and fired, characterized in that, when the parameters are present, the electric machine, EM, is regulated to a specified rotational speed, ω, for a duration of an active phase, x1...xi, and wherein a pause, y1...yi, is inserted after each active phase, x1...xi, the predetermined parameters of the starting condition being checked again in the pause.

2. Method according to Claim 1, wherein the method is ended when termination criteria AK are present, that is to say when one of the predetermined parameters no longer satisfies the starting conditions, or the maximum number of iterations (i) is reached or the internal combustion engine, VM, is scheduled for firing.

3. Software module for carrying out the method according to either of Claims 1 and 2, wherein the software module is arranged in a controller (10) of the hybrid vehicle (20), of the gearbox or of the electric machine, EM.

4. Software module according to Claim 3, wherein the software module can be started before the hybrid vehicle (20) is started.