Method of starting an internal combustion engine in a powertrain having a dual clutch transmission with hybridization

Abstract

The invention is based on a method for starting an internal combustion engine (VM) in a powertrain (1) having a hybrid dual clutch transmission with two clutches (K1, K2) and two sub-transmissions (TG1, TG2), wherein an electric machine (EM) is connected to the electrified sub-transmission and the internal combustion engine (VM) is connectable to the two sub-transmissions (TG1, TG2) via a clutch (K0) and via the two clutches (K1, K2), wherein the internal combustion engine (VM) is started on the basis of an electric-only driving operation via the electrified sub-transmission and a gear engaged in the electrified sub-transmission, wherein the drive power of the electric machine (EM) is transmitted to the non-electrified sub-transmission via the two clutches (TG1, TG2), wherein the clutch (K0) has a lockup synchronization.

Description

Technical Field

[0001] The present invention is based on a method for starting an internal combustion engine in a powertrain having a hybrid dual-clutch transmission having two clutches and two sub-transmissions, wherein an electric motor is connected to the sub-transmissions and the internal combustion engine is capable of engaging the two sub-transmissions via at least two clutches, wherein the internal combustion engine is started based on pure electric driving operation via one sub-transmission and in a first gear, wherein the drive power of the electric motor is transmitted to the non-electrified sub-transmissions via the two clutches. Background Technology

[0002] Vehicles with a hybrid drive system have an internal combustion engine and a second drive unit, which can be, for example, an electric motor. Therefore, driving torque can be applied by both drive units during the operation of the hybrid vehicle.

[0003] A method for starting such a hybrid vehicle is known from DE 10 2008 040 692 A1, the hybrid vehicle having an electric motor and an internal combustion engine, wherein the electric motor is disposed on a second sub-transmission of a dual-clutch transmission having two sub-transmissions, wherein the internal combustion engine is started by means of the electric motor when the hybrid vehicle is started, without interrupting the voltage applied to the powertrain including the dual-clutch transmission.

[0004] A method for starting an internal combustion engine in a powertrain is known from DE 10 2019 220 191, which is not yet publicly disclosed. The powertrain has a hybrid dual-clutch transmission with two clutches and two sub-transmissions, wherein an electric motor is connected to an electrified sub-transmission, and the internal combustion engine is connectable to the two sub-transmissions via at least two clutches. The internal combustion engine is started based on pure electric driving operation via the sub-transmissions and in the first gear of the electrified sub-transmission. The drive power of the electric motor EM is transmitted to the non-electrified sub-transmissions via the two clutches, and the electrified sub-transmission is switched to neutral, while the non-electrified sub-transmission operates in the second gear.

[0005] Here, "first gear" and "second gear" should be understood as selecting a gear for each sub-transmission in the sense of different gears. It does not mean that this corresponds to the first and second gears of the transmission according to the traditional arrangement of decelerating from a low gear to accelerating from a high gear.

[0006] In one version of the powertrain, an additional disengagement clutch is used to allow the internal combustion engine to operate independently of the hybrid drive system.

[0007] A hybrid powertrain with a dual-clutch transmission is known from DE 10 2017 214 396 A1, which also uses a disengagement clutch K0 between the internal combustion engine and the transmission. A method for starting the internal combustion engine is described therein, wherein energy is transferred from an electric drive to the internal combustion engine via the disengagement clutch.

[0008] A hybrid powertrain is known from the previously unpublished DE 10 2020 202 139, which has a separation element between a transmission with a transmission clutch and an internal combustion engine, said separation element being at least partially applied within the clutch input hub of a dual-clutch transmission. The separation element has a synchronizing ring, such that the separation element first disengages frictionally and then disengages form-fittingly in its end position. Summary of the Invention

[0009] The purpose of this invention is to optimize the starting of an internal combustion engine under conditions of minimum vehicle speed and further driving process by means of a special process.

[0010] The objective is achieved by means of a method for starting an internal combustion engine in a powertrain having a hybrid dual-clutch transmission having two clutches and two sub-transmissions, wherein an electric motor is connected to an electrified sub-transmission, and the internal combustion engine is capable of being connected to the two sub-transmissions via a separation element and at least two clutches, wherein the internal combustion engine is started based on pure electric driving operation via the sub-transmissions and the first gear of the electrified sub-transmissions, wherein clutch K0 has locking synchronization and is integrated in a clutch hub.

[0011] Here, "first gear" and "second gear" should be understood as selecting a gear for each sub-transmission in the sense of different gears. It does not mean that this corresponds to the first and second gears of the transmission according to the traditional arrangement of decelerating from a low gear to accelerating from a high gear.

[0012] In the powertrain configuration, the release clutch is used to implement locked synchronization so that the internal combustion engine can operate independently of the hybrid drive system.

[0013] By using a disengaging clutch, the speeds of the electric motor and the internal combustion engine can be set independently of each other.

[0014] To start the internal combustion engine, the clutch of the electrified sub-transmission engages first, while the clutch of the non-electrified sub-transmission slips, allowing the speeds of the electric motor and the internal combustion engine to be set independently of vehicle speed. This is the prerequisite for using the electric motor to drag the internal combustion engine to its minimum speed while maintaining output power, even at the lowest vehicle speeds.

[0015] Once a predetermined speed threshold is reached on the motor, the disengagement element can drag the internal combustion engine to a speed higher than the ignition speed during frictional engagement. Once the speed threshold is reached, the transmission control unit can disengage the disengagement element and grant the internal combustion engine start permission. During the disengagement phase, the torque on the disengagement element decreases to zero, thereby reducing the speed of the internal combustion engine, which has not yet been ignited. The aforementioned speed threshold must be selected such that at the point of start permission, the speed of the internal combustion engine is still higher than the ignition speed.

[0016] The electric motor is connected to the driven device in parallel with the start of the internal combustion engine by engaging the gear of the electrified sub-transmission and by disengaging the disengaging clutches K1 and K2.

[0017] After the two clutches K1 and K2 are disengaged, the release clutch K0 can connect the internal combustion engine and the primary side of the clutch to each other in a frictional fit and in a form fit at the end position. Attached Figure Description

[0018] The invention is described in detail with the aid of the accompanying drawings and the following description.

[0019] Figure 1 A powertrain with different power paths is shown in one exemplary embodiment;

[0020] Figure 2 A graph showing the parameters of the powertrain of the TG1, which includes an electrified transmission component. Detailed Implementation

[0021] Figure 1 An exemplary powertrain 1 is shown, as is known from the prior art. An internal combustion engine VM drives a transmission 2 having two sub-transmissions TG1 and TG2 and two shift clutches S1, S2, wherein the sub-transmissions TG1 and TG2 are decoupled from the internal combustion engine VM, more precisely from the transmission input shaft, via clutches K1 and K2. Additionally, clutch K0, as a disengagement element, separates the internal combustion engine VM from the transmission 2.

[0022] On the transmission output side, the powertrain connects to the differential D via two sub-transmissions. An electric motor EM is coupled to sub-transmission TG1.

[0023] According to the method of the invention, the vehicle is started in a driving state in which only the electric motor EM drives the vehicle. The internal combustion engine VM is stopped and not yet ignited. The internal combustion engine VM is decoupled from the rest of the powertrain via two disengaged clutches K1 and K2, and via a disengaged clutch K0. In the sub-transmission TG1, third gear is engaged for the purely electric drive with the electric motor EM. The shift clutch S1 is closed here. Thus, driving energy flows from the electric motor EM through the sub-transmission TG1 to the differential D in gear 3.

[0024] In the sub-transmission TG2, which is not directly connected to the motor E, the fourth gear is engaged and the clutch K2 and shift clutch S2 are disengaged during pure electric driving.

[0025] The internal combustion engine VM is connected to two transmission inputs via K0, specifically to input shaft 1 and input shaft 2. Clutch K0 is designed as a locking-synchronization disengagement element. Preferably, a design from the prior art as cited above is shown here. This disengagement clutch integrated into the clutch hub is extremely space-saving. This space-constrained disengagement clutch K0 is implemented not only via a friction clutch. A lock-synchronization solution is chosen for reliable engagement of the internal combustion engine VM.

[0026] Locking synchronization can be configured in different ways. Locking synchronization must be based on synchronized operation between the front gear of the component and the shift sleeve. Unless such synchronized operation is achieved, the locking synchronization should prevent the shift sleeve from engaging with the front gear. At different speeds, the synchronizing body blocks the shift sleeve and prevents form-fitting engagement.

[0027] The internal combustion engine VM can be started under specific conditions, such as at low vehicle speeds, by means of the disengagement element, clutch K0. For this purpose, clutch K0 is engaged and initially transmits torque frictionally, thereby accelerating the internal combustion engine VM to synchronous operating speed. In a subsequent phase, the internal combustion engine is coupled to the transmission 2 in a form-fitting manner by disengaging clutch K0 until it reaches its final position. The phase between the friction-fitting and form-fitting phases is called the free-flight phase because there is no mechanical connection between the two sides to be synchronized for a short period.

[0028] Therefore, the clutch K0 is only fully engaged when the internal combustion engine VM is properly connected to the transmission, allowing the internal combustion engine to ignite and provide torque.

[0029] During the free-flight phase, a speed difference can form between the internal combustion engine VM and connecting components, such as the clutch input hub.

[0030] This results in high mechanical loads when the exemplary claw teeth are close together, which also causes noise during connection.

[0031] The torsional capacity of the claw teeth must be designed so that the internal combustion engine VM can twist in the opposite direction to its drag torque. This must be considered in this design and has an impact on the design.

[0032] If the drag torque of the internal combustion engine is greater than the torsional capacity of the teeth, reliable coupling of the internal combustion engine cannot be guaranteed.

[0033] To improve the situation, the method described below should be applied.

[0034] The process of controlling the components is in Figure 2 As shown in the image.

[0035] exist Figure 2 The process of starting an internal combustion engine and driving it is described in different diagrams. Figure 1 The method for a vehicle with a transmission variant shown in the figure.

[0036] The method begins with a request to start the internal combustion engine VM, for example, when the battery is in a low state of charge.

[0037] Starting from the top, Figure 2 The diagram shows the time-dependent curve distribution of the gear setting as the shift drum position. Here, it is shown that the motor EM operates in third gear in sub-transmission TG1, then shifts to neutral so that it eventually operates in third gear again. Sub-transmission TG2 initially remains in fourth gear so that it subsequently operates in second gear. The bottom graph in the uppermost section depicts the time-dependent curve distribution of clutch K0. Clutch K0 disengages until neutral shift of the first sub-transmission TG1 and engages during neutral shift until friction engagement, and disengages again during neutral shift. Form engagement occurs after synchronization.

[0038] exist Figure 2 The intermediate diagram shows the curve distribution of the rotational speeds of different components of the powertrain with respect to time.

[0039] The two input shafts of the dual-clutch transmission 2 rotate at different speeds n1 and n2. The speed-time curve is linear for the input shaft 2 of the second sub-transmission TG2 until shifting, while the curve for the input shaft 1 of the first sub-transmission TG1 is affected by the clutch K0 and the ignition of the internal combustion engine, which will be described in detail later.

[0040] The rotational speed of the internal combustion engine VM is also shown.

[0041] The bottommost speed curve represents the wheel speed, which is continuous and linear. A constant curve distribution of the ignition speed is also shown.

[0042] exist Figure 2 The lower region shows the torque with respect to time.

[0043] The method begins with pure electric creep in stage 1 of the sub-transmission TG1, where both clutches of the sub-transmission are disengaged. However, the input shaft speed of input shaft 1 is insufficient to start the internal combustion engine.

[0044] In stage 2, torque transfer is prepared so that the power of the motor EM can be transferred to another sub-transmission, such as to the second sub-transmission TG2.

[0045] To do this, clutch K1 is first engaged. Shortly before the point at which third gear is disengaged in sub-transmission TG1, the torque of motor EM is increased. Clutch K2 is additionally partially engaged and operates in slippery mode.

[0046] In stage 3, clutch K2 reaches its desired torque level and further increases the torque of motor EM. Simultaneously with the increase in motor EM torque, the disengagement element, clutch K0, is engaged until friction engagement occurs. The speed of motor EM continues to increase, making starting via lock-up synchronization feasible and ensuring that the lock-up conditions of lock-up synchronization are not compromised at any point in time. The torque of the internal combustion engine VM is distributed in opposition to its drag torque during the aforementioned stage of friction engagement of clutch K0.

[0047] The clutch K0 engages briefly to start the internal combustion engine VM. The speed of the electric motor EM is selected such that the lock-up conditions for lock-up synchronization are not compromised at any point in time.

[0048] Directly after the internal combustion engine VM is ignited in stage 4, clutch K0 is fully disengaged. The internal combustion engine VM is injected and is self-propelled. The speed is initially slightly reduced by disengaging clutch K0 before ignition, so that it subsequently increases and adjusts to the desired value with ignition. The torque of the electric motor EM continues to be reduced and the slipping clutch K2 adjusts to low torque transmission.

[0049] In stage 5, the speed of motor EM is synchronized to the third gear and engaged, with both clutches K1 and K2 disengaged. Clutch K0 is engaged until the final position of the form engagement is reached.

[0050] In stage 6, the internal combustion engine VM adjusts the idle speed, while the torque on the internal combustion engine VM increases. At the same time, the torque of the electric motor EM is reduced and the clutch K2 is engaged.

[0051] During phase 8, it is feasible to charge the battery during the creeping process using the internal combustion engine VM. To this end, torque is transmitted to the sub-transmission TG1 and the electric motor EM via the output of the sub-transmission TG2 and the closed shift clutch S1, and the electric motor EM operates as a generator.

Claims

1. Method for starting an internal combustion engine (VM) in a powertrain (1) having a hybridized double clutch transmission with two clutches (K1, K2) and two sub-transmissions (TG1, TG2), wherein an electric machine (EM) is connected to an electrified sub-transmission and the internal combustion engine (VM) is connectable to both sub-transmissions (TG1, TG2) via a clutch (K0) and via both clutches (K1, K2), wherein the internal combustion engine (VM) is started on the basis of an electric-only driving operation via the electrified sub-transmission and a gear engaged in the electrified sub-transmission, wherein the drive power of the electric machine (EM) is transmitted to a non-electrified sub-transmission via both clutches, characterized in that the clutch (K0) has a lockup synchronization and is integrated in a clutch hub, wherein the clutches (K1, K2) of the electrified sub-transmission are closed and the clutches (K1, K2) of the non-electrified sub-transmission are slidingly operated and the clutch (K0) is frictionally engaged, whereby after at least partial closure of both clutches (K1, K2) for the sub-transmissions (TG1, TG2) the internal combustion engine (VM) is accelerated to a synchronization rotational speed and the clutch (K0) is frictionally closed, wherein the closure takes place simultaneously with an increase in the torque of the electric machine (EM), and the torque of the electric machine (EM) is increased with the closure or partial closure of the clutches (K1, K2, K0), and after the rotational speed of the internal combustion engine (VM) has reached a desired value the clutch (K0) is opened, and after the two clutches (K1, K2) of the sub-transmissions (TG1, TG2) are opened the clutch (K0) is positively closed.

Images