DE102021202437A1 - Method for selecting a sequence for starting an internal combustion engine in a powertrain with an electrified double-clutch transmission - Google Patents

Abstract

The invention is based on a method for selecting a sequence for starting an internal combustion engine (VM) in a drive train (1) with an electrified dual-clutch transmission with two clutches (K1, K2) and two partial transmissions (TG1, TG2), with an electric machine (EM ) is connected to the electrified sub-transmission, and the combustion engine (VM) can be connected to both sub-transmissions (TG1, TG2) via a clutch (K0) and two clutches (K1, K2). a control is started, whereupon a decision for a possible process in a state (Z2) depends first on the vehicle speed (Z4), with a clutch start (Z3) taking place at a speed above a threshold value, with a standstill of the vehicle on a slope Direct start (Z9) takes place and at a low speed below the threshold value, the vehicle acceleration is also evaluated at the given drag torque of the w ird, with either a P2 start (Z6) or a direct start (Z9).

Description

The invention is based on a method for selecting a sequence for starting an internal combustion engine in a drive train with an electrified dual-clutch transmission with two clutches and two partial transmissions, with an electric machine being connected to the electrified partial transmission, and the internal combustion engine (VM) via a clutch and via two clutches can be connected to both sub-transmissions, with the process being started by a controller when driving purely electrically on slopes

State of the art

Vehicles with a hybrid drive structure have an internal combustion engine and a second drive unit, which can be an electric motor, for example. In this way, the drive torque can be applied by both drive units while the hybrid vehicle is being driven.

From the not yet published DE 10 2019 220 191 A1 a method for starting an internal combustion engine in a drive train with a hybrid double-clutch transmission with two clutches and two partial transmissions, an electric machine being connected to one electrified partial transmission, and the internal combustion engine being connectable to both partial transmissions via at least two clutches, starting with a purely electric Driving operation via the sub-transmission and a first gear of the electrified sub-transmission, the internal combustion engine is started, with the drive power of the electric machine EM being transmitted via both clutches to the non-electrified sub-transmission, and the electrified sub-transmission being switched to neutral, while the non-electrified sub-transmission is in a second gear is operated.

The first and the second gear are to be understood as meaning that a gear is selected for each of the partial transmissions, in the sense of a different gear. It is not said to correspond to the first gear and second gear of a transmission, corresponding to a conventional arrangement of low gear reduction to high gear ratio.

In one version of the powertrain, an additional separating clutch is used in order to be able to operate the internal combustion engine independently of the hybrid drive system.

From the unpublished DE 10 2020 202 139 a hybrid drive train with a separating element between the transmission with transmission clutches and the internal combustion engine is known, which element is at least partially fitted within a clutch input hub of the dual clutch. The separating element has a synchronizing ring, so that the separating element is first opened with a friction fit and then with a positive fit in its end position.

The unreleased DE10 2020 209 452 shows a method for starting an internal combustion engine in a drive train with a hybrid double-clutch transmission with two clutches and two partial transmissions, an electric machine being connected to one electrified partial transmission, and the internal combustion engine being connectable to both partial transmissions via a separating element and at least two clutches, with outgoing the internal combustion engine is started from purely electric driving via the partial transmission and a first gear of the electrified partial transmission, with clutch K0 having a blocking synchronization.

Cone synchronizers as used in the state of the art mentioned usually act first by friction and only positively in an end position.

The torque transmission capacity in the frictional phase is usually significantly smaller than that of the positive end position. The form-fit end position is reached when the drive train reaches the same speed, for which purpose the friction phase is used to match the speed of the input shaft and output shaft on the clutch. This frictional state is required in order to be able to tow the combustion engine to a minimum speed, regardless of the wheel speed. After the combustion engine has been started, clutch K0 can be brought into positive engagement.

For reasons of space, cost and weight, the torque capacity of the synchronization to be transmitted in the friction phase is designed for the normal case for the drive train, for example at around 70 Nm, which is sufficient for starting the internal combustion engine at operating temperature. In the worst case at very low temperatures, however, a torque of around 200 Nm is required to start the combustion engine.

If the engine cannot be started using the separating element K0 alone, it can also be started using the other clutches of the double-clutch transmission. However, the associated interruption in tractive power is perceived as uncomfortable or causes unwanted rolling backwards on slopes.

Therefore, starting the engine at a standstill or when driving close to a standstill, especially on a slope in cold temperatures/diesel (see above) alone, cannot be conveniently represented by the hybrid transmission system described above with the previously known starting methods.

The object of the invention is to prepare the starting of an internal combustion engine when driving or standing still on an incline and thus to ensure that the internal combustion engine can also be started in these situations, although the torque capacity in the frictional engagement phase of the separating clutch K0 is not designed for this.

Description of the invention

The object is achieved with a method for selecting a sequence for starting an internal combustion engine in a drive train with an electrified double-clutch transmission with two clutches and two partial transmissions, with an electric machine being connected to the electrified partial transmission, and the internal combustion engine being connected via a clutch and via two clutches both sub-transmissions can be connected, with the method being started by a controller when driving purely electrically on a slope, whereupon a decision for a possible sequence in one state depends first on the vehicle speed, with a clutch start taking place at a speed above a threshold value, with When the vehicle is stationary on a slope, a direct start takes place and, at a low speed below the threshold value, the vehicle acceleration at a given drag torque is also evaluated, with either a P2 start or a direct start taking place.

It is advantageous that, in the event that the combustion engine has sufficient drag torque to keep the vehicle on a slope, after a dual-mass flywheel of the combustion engine has been preloaded and the torque of the electric machine has been reduced to 0 Nm and the gear in the electrified sub-transmission has been disengaged , a direct start takes place.

It is advantageous that at low vehicle speeds the clutch between the combustion engine and the transmission is closed and initially transmits a frictional torque, whereby the combustion engine is accelerated to synchronous speed and in the following phase the combustion engine is positively coupled to the transmission by the clutch K0 until it is closed in the end position.

Advantageously, before the synchronization is closed, it can be ensured that there is no differential speed, and the form-fitting end position can be used directly.

character list

• 1 zeigt einen Antriebsstrang in einer beispielhaften Ausführungsform,
• 2a, 2b, 2c zeigen einen Motorstart aus einer P2 Konfiguration.
• 3a, 3b, 3c zeigen einen Startablauf B mit Verbrennungsmotorstart aus einem Interlock.
• 4 zeigt ein Schema zur Entscheidung über einen geeigneten Starverlauf.

The invention is explained in more detail with the figures and the following description.

• 1 shows a drive train in an exemplary embodiment,
• 2a , 2 B , 2c show an engine start from a P2 configuration.
• 3a , 3b , 3c show a start sequence B with an internal combustion engine start from an interlock.
• 4 shows a scheme for deciding on a suitable cataract.

the 1 shows an exemplary drive train 1 as is known from the prior art. An internal combustion engine VM drives a transmission 2 with two partial transmissions TG1 and TG 2 and two clutches S1, S2, whereby the partial 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. In addition, a clutch K0 separates the internal combustion engine VM from the transmission 2 as a separating element.

On the transmission output side, the drive train from the two sub-transmissions TG1, TG2 ends at a differential D. The electric machine EM is coupled to the sub-transmission TG1.

2a starts with a driving condition in which only the electric machine EM drives the vehicle. The internal combustion engine VM is at a standstill and has not yet been ignited. The internal combustion engine VM is decoupled from the rest of the drive train via the open clutch K0. The two clutches K1 and K2 are closed and the electric machine drives the vehicle via the second sub-transmission TG2. A neutral stage is engaged in the sub-transmission TG1 for the purely electric drive with the electric machine EM. The shift clutch S2 is closed. The drive energy thus flows from the electric machine EM via the sub-transmission TG2 with gear stage 4 to the differential D.

Starting the internal combustion engine VM can under certain circumstances, for. B are requested by the system at low vehicle speeds and take place with the help of the separating element, the clutch K0. For this purpose, as in 2 B shown, the clutch K0 is closed and initially transmits a torque by friction, whereby the internal combustion engine VM is accelerated to synchronous speed. In the following phase the internal combustion engine is positively coupled to the transmission 2 by closing the clutch K0 up to the end position. Only when the internal combustion engine VM is positively connected to the transmission, i.e. the clutch K0 is fully closed, is it allowed to fire and thus provide torque.

If the vehicle is stationary, the separating element K0 is closed in the form-fitting end position without a differential speed.

2c shows that during the next start-up process, the internal combustion engine VM is started by the electrical machine EM via closed clutches K1 and K0 and the required output torque is transmitted to the differential D in parallel via the slipping clutch K2 of the non-electrified sub-transmission. This start from a standing start is called a direct start.

If it is ensured before closing the synchronization that there is no differential speed, the frictional phase can be "skipped" and the form-fitting end position can be changed directly. This is achieved by bringing the transmission into a defined preparatory state, namely the P2 configuration, and waiting for the vehicle to come to a standstill. The preparatory change to the P2 configuration is necessary in order to be able to start the engine on an incline without interrupting traction (if necessary, rolling backwards). A direct start known in the prior art can then be carried out. The P2 configuration means that the drive behaves as if the electric machine EM were mounted on the transmission input.

3a shows scenario B, in which the system requests a start of the internal combustion engine because the vehicle is stationary on a slope and is only held by the electric machine EM. The separating clutch K0 is closed.

The clutch of the non-electrified sub-transmission, in the example K2, is closed, with the preselected gear in this sub-transmission TG2 having to be geared shorter than the active gear in the electrified sub-transmission.

The torque of the electric machine is reduced. As a result, the vehicle rolls backwards a small, permissible distance as a result of the downhill slope force and the dual-mass flywheel of the internal combustion engine VM is tensioned in a targeted manner, since the drag torque of the internal combustion engine counteracts rotation on the primary side of the dual-mass flywheel. As soon as the dual-mass flywheel is tensioned, the vehicle can be held on a slope if the combustion engine's drag torque is sufficiently high. This drag torque is not exactly known, which is why the vehicle can roll backwards if the drag torque is too low. In any case, uncontrolled backward rolling must be avoided, which is why the maximum backward rolling distance, which corresponds to the twisting angle of the two-mass flywheel, must be limited via the electric machine EM.

After the dual-mass flywheel has been preloaded and the torque of the electric machine EM has been reduced to 0 Nm, third gear is selected in the electrified sub-transmission. However, a prerequisite for this is a sufficiently high drag torque of the internal combustion engine VM in order to hold the vehicle.

In 3c shows that during the next start-up process, the internal combustion engine VM is started and the required output torque is transmitted in parallel via the clutch K2 of the non-electrified sub-transmission in order to carry out a direct start.

To the procedures previously shown 2a-2c As Scenario A and 3a-3c as Scenario B, these are integrated in a general schedule that includes different start strategies in 4 shown.

The individual start types are already part of the state of the art, except for the processes below 2a-2c Scenario A and 3a-3c Scenario B to comfortably prepare a direct start on a slope, even if the required starting torques exceed the capacity of the K0 clutch.

The following flowchart is to be understood in such a way that states that are shown in the individual rectangles are only exited when the respective exit conditions are met.

The method for selecting the starting modalities for an internal combustion engine begins with the operating state Z1 of the vehicle in purely electric driving on a slope. The driver requests a positive wheel torque for the vehicle by operating the accelerator pedal or by operating a gearshift. Since the electric machine alone is not up to the requirement, a hybrid manager requests that the internal combustion engine VM be started as a control element. The request to start the internal combustion engine causes a change to state Z2. The reason for such a start request can e.g. B. also be a low battery charge level.

In this state Z2, a decision is made as a function of the vehicle speed which one further procedure is selected. For vehicle speeds greater than a threshold value of approximately 15 km/h, a change is made to state Z3 and a clutch start is carried out via the torque of the driven wheels, the non-electrified sub-transmission TG2 and the closed clutches K2 and K0.

For vehicle speeds less than 15 km/h and greater than 0 km/h, the process jumps to the branch with the state Z4. In state Z4, a decision is additionally made as a function of measured vehicle acceleration a_veh as to which further method sequence must be selected.

For vehicle accelerations a_veh greater than a value that can be calibrated (eg 1.5 m/s ² ), the system changes back to state Z2 and vehicle speed v_veh is evaluated again. Alternatively, the same applies to the situation when the vehicle acceleration a_veh is positive and the drag torque of the combustion engine is non-ignited when stationary and is greater than a threshold value, e.g. B. is 80Nm. The intention of this condition is that with positive acceleration the vehicle speed of 15 km/h is exceeded within a foreseeable time and then a clutch start can be carried out as in Z3. This is the preferred starting method.

For vehicle accelerations a_veh less than a calibratable value, eg 1.5 m/s ² and a drag torque of the non-ignited internal combustion engine at standstill less than a threshold value, eg 80Nm, there is a changeover to state Z5.

In state Z5, the power of the electric machine is routed to the non-electrified other sub-transmission by closing the two clutches K1 and K2, and a P2 configuration is produced.

The method sequence in state Z6 then uses the separating clutch K0 to start the internal combustion engine VM in a so-called P2 start. P2 start means that the electric machine acts by switching the clutches as with a P2 connection of the electric machine at the transmission input and the internal combustion engine VM is turned on by closing the clutch K0.

For vehicle accelerations a_veh less than or equal to 0 m/s ² and a drag torque of the unignited internal combustion engine when stationary is greater than a threshold value, for example 80 Nm, there is a change to state Z7.

In state Z7, the power of the electric machine is fed to the non-electrified, other sub-transmission by closing the two clutches K1 and K2. The separating clutch K0 initially remains open, which is why the system can be operated independently of the combustion engine in this state. In this state Z7, both the vehicle speed v_veh and the driver's desired torque T_driver_req are considered. For vehicle speeds v_veh equal to 0 km/h, there is a change to state Z8.

In state Z8, the separating element K0 is closed up to the form-fitting end position and a direct start is carried out in state Z9, which 2c is equivalent to. A subsequent starting process is used to start the internal combustion engine VM according to scenario A and at the same time to provide the requested output torque via the slipping clutch K2.

If the driver's desired torque T_driver_req exceeds an adjustable value, e.g. 1000 Nm at the wheel, the outgoing Z7 changes to the state Z10.

In this state Z10, the power of the electrical machine EM is transmitted to the electrified sub-transmission by opening both clutches K1, K2, with the sequence jumping back to state Z2.

State Z2 permits a further branch of the curve, namely at a vehicle speed v_veh equal to 0 km/h. The next method step changes to state Z11.

In this state, the vehicle is held on a slope in accordance with the driver's request by closing both clutches K1 and K2 while the gears are engaged at the same time, with backward rolling beyond a permissible distance being prevented. The aim here is to hold the vehicle on a slope either with the help of the ICE drag torque or by specifically tightening the wheelset.

State Z11 results in two separate processes.

Gears are engaged in both partial transmissions TG1, TG2 of transmission 2, with the gear ratio in the non-electrified partial transmission TG2 having to be shorter. In this phase, the vehicle is held on a slope by the electric machine EM.

First, the clutch of the non-electrified sub-transmission TG2 is closed. The separating element K0 between the clutch and the combustion engine must also be closed so that a The frictional connection between the wheel and the combustion engine VM is created.

The torque of the electrical machine EM is reduced. As a result, the vehicle rolls backwards a small, permissible distance as a result of the downhill force and the dual-mass flywheel is tensioned in a targeted manner. As soon as the dual-mass flywheel is tensioned, the vehicle can be held on a slope if the combustion engine's drag torque is sufficiently high. This drag torque is not exactly known, which is why the vehicle can roll backwards if the drag torque is too low. Uncontrolled rolling backwards must be avoided in any case, which is why the maximum travel must be limited via the electric machine according to the twisting angle of the dual mass flywheel.

After the dual-mass flywheel has been preloaded, clutch K1 of the electrified sub-transmission TG1 can also be fully engaged. Both clutches are overpressed in this phase. Overpressing the clutch means that the clutch is in its closed position and is closed to such an extent that no differential speeds occur in the clutch or between the axles, or no slippage occurs.

The torque on the electrical machine can now be reduced.

If the torque of the electric machine has been reduced to 0Nm without the vehicle rolling backwards too far, this means that the drag torque of the combustion engine VM is sufficient to keep the vehicle on the slope. In this case, there is a change to state Z12. In state Z12, the gear in the electrified partial transmission TG1 is disengaged in order to prepare for a subsequent start of the internal combustion engine VM.

A direct start follows in state Z9.

If the vehicle rolls backwards further than desired during the holding phase, this means that the drag torque of the internal combustion engine VM is not sufficient to hold the vehicle on the slope. In this case, there is a change to state Z13.

The hybrid controller recognizes the negative vehicle speed v_veh and sends a signal to the vehicle to trigger braking intervention. If no automatic braking intervention is possible, the vehicle asks the driver to brake manually. As soon as the vehicle brake is active, the gear in the electrified sub-transmission TG1 can be disengaged. This is followed by a start with the electrical machine in state Z14.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102019220191 A1 [0003]
• DE 102020202139 [0006]
• DE 102020209452 [0007]

Claims (4)

Method for selecting a sequence for starting an internal combustion engine (VM) in a drive train (1) with an electrified double-clutch transmission with two clutches (K1, K2) and two partial transmissions (TG1, TG2), with an electric machine (EM) connected to the electrified partial transmission and the internal combustion engine (VM) can be connected to both sub-transmissions (TG1, TG2) via a clutch (K0) and via two clutches (K1, K2), the process being started by a controller when driving purely electrically on slopes, whereupon a decision for a possible sequence in a state (Z2) first depends on the vehicle speed (Z4), with a clutch start (Z3) taking place at a speed above a threshold value, with a direct start (Z9) taking place when the vehicle is stationary on a slope and at a low speed below the threshold value, the vehicle acceleration is also evaluated at a given drag torque, with either a P2 start (Z6) or a direct start (Z9) takes place. procedure after claim 1 characterized in that in the event that the internal combustion engine (VM) has sufficient drag torque to hold the vehicle after a dual-mass flywheel of the internal combustion engine (VM) has been prestressed and the torque of the electric machine (EM) has been reduced to 0Nm, and the gear was designed in the electrified sub-transmission, a direct start takes place. procedure after claim 1 characterized in that at low vehicle speeds the clutch (K0) between the internal combustion engine (VM) and the transmission (2) is closed and initially transmits a torque by friction, whereby the internal combustion engine (VM) is accelerated to synchronous speed and in the following phase the internal combustion engine is positively locked coupled with the gearbox by closing clutch K0 up to the end position. procedure after claim 3 characterized in that before the synchronization is closed, it is ensured that there is no differential speed, and the form-fitting end position is used directly.

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