WO2014019576A2

WO2014019576A2 - Method for breaking free a wet clutch of a motor vehicle at low temperatures

Info

Publication number: WO2014019576A2
Application number: PCT/DE2013/200047
Authority: WO
Inventors: Andreas GÖTZ; Jens Kramer
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2012-08-02
Filing date: 2013-07-15
Publication date: 2014-02-06
Also published as: DE112013003779A5; DE102013213751A1; CN104583580B; CN104583580A; WO2014019576A3

Abstract

The invention relates to a method for breaking free a wet clutch of a motor vehicle at low temperatures, wherein the wet clutch transmits a rotary motion of an internal combustion engine via a transmission, preferably a dual clutch transmission, to a power take-off of the motor vehicle, wherein at low temperatures a cold start of the internal combustion engine is carried out. In a method in which breaking free of the clutch takes place without design changes to a synchronisation unit and/or to the clutches, an engine generates a breaking-free torque for the opened clutch.

Description

Method for breaking loose a wet-running clutch of a motor vehicle at low temperatures

The invention relates to a method for breaking a wet-running clutch of a motor vehicle at low temperatures, in which the wet-running clutch transmits a rotational movement of an internal combustion engine via a transmission, preferably a dual-clutch transmission, to an output of the motor vehicle, wherein at low temperatures, a cold start of the internal combustion engine is performed ,

Couplings are known which are operated for cooling purposes in a fluid, preferably a hydraulic medium such as oil, and are therefore referred to below as wet-running clutches. In dual-clutch transmissions, which include such wet-running clutches, a synchronization unit is present, which is loaded during synchronization of the rotational speed of a crankshaft driven by the engine with a speed of a gear wheel when inserting the gear on the one hand by masses to be accelerated and the differential speed at the synchronization unit. In addition, the synchronization unit must also overcome the drag torque in the transmission.

The drag torques of the gearbox in turn are strongly determined by the drag torque of the clutch in the cold. An extreme case is the first-time synchronization of a gear after a cold start of the engine. In this situation, the clutch plates are literally glued by the fluid, so that the actually open clutch plates of the clutch are rigidly interconnected. Such a connection must be torn loose by the synchronization unit. However, this Losreißmomente are required, which amount to a multiple of the drag torque at differential speed in the clutch. In overcoming these resistances, a synchronization unit can quickly reach its performance limits and must therefore be dimensioned accordingly. Even if the friction cone of the synchronization unit is sufficiently dimensioned, it can come when switching the gear to extremely high switching forces, since even after reaching the synchronous speed for a few seconds, a high clutch drag torque acts on the synchronization unit.

From DE 10 2009 053 040 A1, a fluid system is known, in which the toughness of the cooling oil, in which the clutch moves, is overcome by a preheat of the cooling oil during a cold start of the motor vehicle, so that the cooling oil again achieved its suppleness and can be dispensed with large Losbrechmomente the synchronization unit to activate the clutch. Although such a heater allows a smooth start of the motor vehicle, but delays the start of the motor vehicle by the heating of the cooling oil.

The invention is therefore based on the object to provide a method for breaking a wet-running clutch of a motor vehicle at low temperatures, in which without additional preparation time the motor vehicle can be started waiving high loads on the synchronization unit.

According to the invention the object is achieved in that an engine generates a breakaway torque for the open clutch. The use of an engine allows a reliable cold start of the engine at any time, since the engine can produce a sufficiently large breakaway torque even at low ambient temperatures. By this breakaway torque, the wet-running clutch is reliably activated even at low temperatures, so that a torque of the engine can be easily transferred to the wheels of the motor vehicle. An additional time-consuming treatment of the cooling oil can be omitted. The motor vehicle is thus ready to start at any time.

Advantageously, as an engine connected to the internal combustion engine, an electric motor, in particular a starter, or a hybrid motor is used, which generate the breakaway torque for the clutch by activating the internal combustion engine. In particular, the use of the starter present at the start of the internal combustion engine in the motor vehicle represents a very cost-effective option for breaking the wet-running clutch, since the components present in the motor vehicle are used. As a result, not only can additional power machines be dispensed with, but costs for constructive changes to the synchronization unit or to the clutch can be reduced.

In one embodiment, the breakaway torque is generated during the cold start of the internal combustion engine at an engaged gear in the transmission, wherein the gear of the transmission is engaged in particular before the cold start of the internal combustion engine. By inserting a gear, which corresponds to a switched synchronization unit, the clutch disc connected to the transmission is to be activated at low temperatures Clutch held in position while the internal combustion engine is started by the engine, preferably the starter. In this case, with the synchronization switched and the vehicle stationary, the engine speed is identical to the differential speed in the clutch because the first clutch disk held by the transmission over the engaged gear has a zero speed while the second clutch disk , which is connected to the internal combustion engine having the speed of the internal combustion engine. The breakaway torque does not have to be applied by the synchronization unit in this case. As a result, the synchronization unit does not have to overcome any additional or excessive drag torques. The breakaway torque is realized during cold start of the internal combustion engine solely by the starter.

In one variant, the last engaged before parking the motor vehicle gear is maintained in its position. This requires a change in the shift strategy, since instead of usual, when stopping the vehicle all synchronizations increase, the last engaged gear remains engaged. Nevertheless, the solution is a very cost-effective and easy-to-set method, since this can only be achieved by a single change in the shift strategy of the transmission.

In one embodiment, the engaged gear is locked in its position. These

Locking ensures that the engaged gear can not jump out when the internal combustion engine starts cold.

In particular, the parking position is engaged when using an automatic transmission for locking the gear. Due to a mechanical locking of the transmission in the park position, the motor vehicle is secured against rolling away.

In an alternative, a spring-ramp detent is used for a mechanical synchronization unit of the transmission for locking the gear. Such a spring-ramp detent fixes the teeth of the mechanical synchronization unit in a predetermined position, so that even in this embodiment, the inserted gear remains in its position.

Advantageously, a self-locking gear is used for locking the gear in an electromechanical actuation of the transmission. A transmission is always then self-locking, if it can be driven only via the drive shaft of the engine but not via an output shaft.

In a further alternative, the electromechanical or the electro-hydraulic actuation is energized during the starting process for locking the gear. This energization ensures that the gear engaged by the electromechanical actuation, for example a spindle drive, is always pressed into the position occupied by the latter, so that slipping out of the gear is prevented.

In one embodiment, after leaving the parking position, the gear is designed independently of the operating state of the internal combustion engine. This is particularly important when the motor vehicle is to be towed at idle when not running internal combustion engine or an electrical start should be in another gear, as may occur, for example, in hybrid vehicles.

The invention allows numerous embodiments. One of them will be explained in more detail with reference to the figures shown in the drawing.

It shows:

Figure 1: Schematic representation of a drive train of a motor vehicle with a

Double clutch

FIG. 2 shows a synchronization unit of a dual-clutch transmission according to FIG. 1

FIG. 3 shows a hydraulic power pack for a dual-clutch transmission according to FIG. 1

Identical features are identified by the same reference numerals.

Figure 1 shows a schematic diagram of a drive train 1 of a motor vehicle with a dual-clutch transmission. In this case, a drive unit in the form of an internal combustion engine 2 is connected via a crankshaft 3 with the dual-clutch transmission, which will be described in more detail below. The dual-clutch transmission consists of two sub-trains. In this case, the first sub-line has a first sub-transmission clutch 4, which leads to a first sub-transmission line 9. The internal combustion engine 2 is also connected via the crankshaft 3 to a second drive train, which comprises a second partial transmission clutch 5, which leads to a second partial transmission line 8. The two sub-gear trains 8, 9 are guided via an axle differential 10 to a drive axle 1 1 of the motor vehicle. A starter 12 is also mechanically connected to the engine 2.

In the Teilgetriebesträngen 8, 9 different gears can be inserted. Thus, the first sub-transmission train 9 comprises the odd gears, such as 1, 3, 5, while the second sub-transmission train

8 includes the even gears, such as 2, 4, 6 and reverse. When changing from one gear to another gear, both partial transmission clutches 4, 5 must be actuated, since by means of the first sub-transmission clutch 4, one gear is decoupled from the crankshaft 3, while with the aid of the second sub-clutch 5, the other gear with the crankshaft 3 and thus the internal combustion engine 2 is connected. Each partial transmission clutch 4, 5 is actuated by a Teilgetriebekupplungsaktorik 6, 7, which includes an electric motor. The Teilgetriebekupplungsaktoriken 6, 7 are connected to a control unit 13 which controls the Teilgetriebekupplungsaktorik 6 and 7, if necessary.

The dual-clutch transmission is an automatic transmission in which these two sub-transmission lines 8, 9 are likewise controlled by the control unit 13. Before shifting, the gear to be shifted is first engaged in the load-free partial transmission train 8, 9. Then, the partial transmission clutch 4, 5 of the load-free sub-transmission line 8, 9 is closed and the second sub-transmission clutch 4, 5, which the second sub-transmission line 8,

9 is assigned, open at the same time. This can be switched without interruption of traction.

In the present case, the partial transmission clutches 4, 5 surrounded by a cooling oil, which is contained in a non-illustrated, so-called oil sump of the motor vehicle. This cooling oil serves to reduce the temperature of each switching partial transmission clutch 4, 5, which increases due to friction forces occurring, reduce. Especially at lower ambient temperatures, the cooling oil assumes a certain viscosity, which can lead to the gluing of the disks of the clutch disks of the respective partial transmission clutches 4, 5. In order to solve the bonding of the partial transmission clutches 4 and 5, the starter 12, which is designed as an electric motor used. First, the parking position P is set when using an automatic transmission when the motor vehicle is stopped in order to lock the dual-clutch transmission. The last set gear in one of the sub-transmission line 8, 9 remains inserted. This is usually the first gear. The gear is shifted via a synchronization unit 14, as shown in FIG. 2, which is a component of each of the sub-transmission lines 8, 9. The circuit of the synchronization unit 14 is effected by the control of a gear actuator not shown by a signal of the control unit thirteenth

When the internal combustion engine 2 starts cold, the breakaway torque for one of the partial transmission clutch 4 or the partial transmission clutch 5 is applied by the starter 12 at the start of the starting process of the internal combustion engine 2. During a cold start of the internal combustion engine 2 at low ambient temperatures, the crankshaft 3 of the internal combustion engine 2 is set in motion by the starter 12 by meshing a starter ring gear, not shown in detail, with the crankshaft 3. With switched synchronization and stationary motor vehicle while the speed of the engine 2 is identical to the differential speed of the partial transmission clutch 4 or the partial transmission clutch 5, depending on which of the two partial transmission clutches 4, 5 is to be broken. Due to the engaged gear, the first clutch disc, not shown, of the partial transmission clutch 4 or 5, which is firmly connected to the associated partial transmission train 8 or 9, remains approximately motionless. By the starter 12 of the internal combustion engine 2 and thus the crankshaft 3 is set in motion, whereby the second clutch disc of the respective partial transmission clutch 4, 5 is set in rotary motion. As a result, 2 forces are released automatically during the starting process of the internal combustion engine, causing a breakaway of the partial transmission clutches 4 or 5.

During the cold start of the internal combustion engine 2, it must be ensured that the gear engaged in the respective sub-transmission train 8 or 9 remains in its position and can not jump out.

For this purpose, 14 tooth flanks 15 at one of the synchronization unit

Sliding sleeve 16 is formed. The sliding sleeve 16 is arranged on a synchronous carrier body 17 which is positively connected to a transmission shaft 18 (Figure 2). The synchronization unit 14 has the function of controlling the rotational speed of the internal combustion engine 2 of the rotary engine. number of the respective sub-transmission line 8 or 9. By a synchronizer ring 19, which is the sliding sleeve 16 upstream, a friction between a ratchet wheel 20 and the transmission shaft 18 is generated. Through this friction, the speed equalizes until the sliding sleeve 16 engages. The body 21 of the partial transmission clutch 4 or 5 in this case has an undercut to receive the sliding sleeve 17. However, it is also conceivable that the sliding sleeve 16 has, as an alternative to the toothing 15, a spring-ramp detent which also ensures that the gear already engaged during the starting process of the internal combustion engine 2 can not pop out.

Another variant consists in the use of a self-locking gear, in particular when the sub-transmission line 8, 9 are actuated electromechanically. In addition, energization of the electromechanical actuation or of an electro-hydraulic power pack during the starting phase of the internal combustion engine 2 is also possible. The energization ensures that the inserted gear is always pressed into the position once taken and is therefore firmly locked.

An electro-hydraulic power pack 22 is shown in FIG. An electrohydraulic powerpack is an alternative solution to an electromechanical gear actuator of the dual clutch transmission. The Powerpack 22 is integrated as a unit without expensive connecting elements such as hoses and cables in the dual-clutch transmission. At the same time, a plate-spring-based pressure accumulator 23 for providing the hydraulic fluid for moving the dual-clutch transmission is installed. On the control plate 24 valve seats 25, 26 and 27 are arranged directly. A rotary valve 28 takes over the selection function of the gear actuator not shown.

It is to be ensured that when leaving the shift position "parking position P", the synchronization of the synchronization unit 14 can be re-designed, regardless of whether the engine 2 is running or not, which is particularly important for towing the motor vehicle when the internal combustion engine is not running or an electric start in another gear, which often occurs especially in hybrid vehicles.

The solution described has the advantage that at low ambient temperatures for a short time, very high drag torques in the partial transmission clutch 4, 5 are not applied by the synchronization unit 14 but by the starter 12. Since the starter 12th Part of each motor vehicle, eliminating design changes to the synchronization unit 14 and to the partial transmission clutches 4, 5, whereby costs are reduced.

LIST OF REFERENCES

1 powertrain

internal combustion engine

crankshaft

Part transmission clutch

Teilgetriebekupplungsaktorik

Teiltriebekupplungsaktorik

8 partial transmission line

Part gear train

10 axle differential

11 drive axle

12 starters

13 control unit

14 synchronization unit

15 tooth flanks

16 sliding sleeve

17. Synchronous carrier body

18 gear shaft

19 synchronizer ring

20 ratchet wheel

21 Body of a partial transmission clutch

22 Electrohydraulic Powerpack

23 accumulator

24 control plate

25 valve seat

26 valve seat

27 valve seat

28 rotary valve

P Parking position

R reverse gear

ADJUSTED SHEET (R. 91) ISA / EP

Claims

claims

1 . Method for breaking loose a wet-running clutch of a motor vehicle at low temperatures, in which the wet-running clutch (4, 5) rotational movement of an internal combustion engine (2) via a transmission (4, 5, 8, 9), preferably a dual-clutch gearbox, to an output ( 10, 1 1) of the motor vehicle transmits, wherein at low temperatures a cold start of the internal combustion engine (2) is executed, characterized in that an engine (12) generates a breakaway torque for the opened clutch (4, 5).

2. The method according to claim 1, characterized in that as an internal combustion engine connected to the engine (12) an electric motor, in particular a starter, or a hybrid motor is used, the breakaway torque for the clutch (4, 5) by activation of the internal combustion engine (2 ) produce.

3. The method according to claim 1 or 2, characterized in that the breakaway torque during the cold start of the internal combustion engine (2) at an engaged gear in the transmission (4, 5, 8, 9) is generated, wherein the gear of the transmission (4, 5 , 8, 9), in particular before the cold start of the internal combustion engine (2), is inserted.

4. The method according to claim 3, characterized in that the last engaged before parking the motor vehicle gear is maintained in its position.

5. The method according to at least one of the preceding claims 1 to 4, characterized in that the inserted gear is locked in its position.

6. The method according to claim 5, characterized in that for latching the gear when using an automatic transmission (4, 5, 8, 9), the parking position (P) is inserted.

7. The method according to claim 5 or 6, characterized in that for locking the gear, a spring-ramp detent for a mechanical synchronization unit (14) of the transmission (4, 5, 8, 9) is used.

8. The method according to claim 5 or 6, characterized in that for latching the gear in electromechanical actuation, a self-locking gear (4, 5, 8, 9) is used.

9. The method according to claim 5 or 6, characterized in that for latching the gear, the electromechanical or electro-hydraulic actuation (22) of the transmission (4, 5, 8, 9) is energized during the starting process.

10.A method according to at least one of the preceding claims, characterized in that after leaving the parking position (P) the gear is designed independently of the operating state of the internal combustion engine (2).