DE102020132715B3 - Procedure for determining an internal leak - Google Patents

Abstract

A motor vehicle drive train according to the invention has a hydrodynamic retarder. The hydrodynamic retarder comprises a rotating bladed primary wheel (rotor) and a stationary secondary wheel (stator) or bladed secondary wheel rotating in the opposite direction to the primary wheel (counter-rotating retarder), which together form a working chamber that can be filled with working medium. To switch on the retarder, the working space is filled with working medium, with the amount of working medium in the working space, which forms a hydrodynamic circulatory flow in the working space, determining the torque transmitted from the primary wheel to the secondary wheel and thus the braking torque. In order to improve the operational readiness of the retarder, the invention proposes that a level monitoring device is provided, which detects the current level of the working medium in the working space, and an actuating device which is in communicative or mechanical operative connection with the level monitoring device and triggers a closing of the separating clutch depending on the detected level.

Description

The present invention relates to a method for determining an internal leakage of a hydrodynamic retarder, which can be mechanically decoupled from the drive train of a motor vehicle by means of a separating clutch, and a control method for this.

Hydrodynamic retarders have been used for many years as wear-free retarders in motor vehicles both on rails and on the road, the latter in particular in trucks and buses. Although such wear-free retarders undeniably bring considerable advantages in terms of safety when braking the vehicle and in terms of reduced wear of the frictionally operating service brakes, the idling losses in non-braking operation of the hydrodynamic retarder are a point of criticism. It was possible to reduce these no-load losses by providing so-called ventilation screens or by providing a rotor (primary wheel) that moves away from the stator (secondary wheel) in non-braking mode, but the latter measure in particular is usually not sufficient to reduce the no-load losses to almost zero.

One way of reducing the idling losses of such a hydrodynamic retarder to zero is to design the hydrodynamic retarder so that it can be uncoupled from the drive train by means of a separating clutch. However, such a separating clutch, which is designed in particular as a friction clutch, makes it necessary for the filling level of the retarder not to exceed a specific value, or ideally for it to be as good as empty. When operating a retarder that can be switched off, it is therefore very important that the clutch is only opened when it is certain that there is not too much working medium in the retarder working space. If there is too much working medium in the working space, high loads occur, especially when the hydrodynamic retarder is switched on. These lead to an early need for service.

The patent specification EP 2 024 209 B1 proposes, in order to shorten the response time of a hydrodynamic retarder connected to the drive train via a separating clutch, to preventively close the separating clutch whenever the motor vehicle is not in traction mode and to couple the retarder in the emptied state.

The disclosure document DE 199 27 397 A1 proposes a self-reinforcing friction clutch for coupling the hydrodynamic retarder, which enables the hydrodynamic retarder to be coupled even when it is filled.

The disclosure document DE 10 2005 052 121 A1 proposes switching off a hydrodynamic retarder by emptying its working space and simultaneously releasing the stator so that it can spin with the rotor.

The disclosure document DE 10 2009 001 146 A1 proposes a coaxial arrangement of the rotor of the retarder and the rotor of an electric machine, which can be disconnected from the drive train together via a separating clutch, in particular an unsynchronized separating clutch.

The disclosure document EP 2 651 726 A1 ( DE 10 2011 120 644 A1 ) proposes that a fill level monitoring device is provided, which detects the current fill level of the working medium in the working chamber, with a separating clutch blocking device being provided, which is in communicative or mechanical operative connection with the fill level monitoring device and blocks the separating clutch from closing depending on the detected fill level. If the filling level is too high, the separating clutch can only be closed again when the speed falls below a primary speed of the drive train. As a result, the retarder can fail relatively quickly.

The present invention is based on the object of specifying a motor vehicle drive train with a hydrodynamic retarder that can be mechanically decoupled from the drive train by means of a separating clutch, and a control method for this, with which the operational readiness of the retarder can be further improved.

The object according to the invention is achieved by a motor vehicle drive train having the features of claim 1 and a method for controlling a motor vehicle drive train having the features of claim 6. The dependent claims describe advantageous and particularly expedient refinements of the invention.

A motor vehicle drive train according to the invention has a hydrodynamic retarder. The hydrodynamic retarder comprises a rotating bladed primary wheel (rotor) and a stationary secondary wheel (stator) or bladed secondary wheel rotating in the opposite direction to the primary wheel (counter-rotating retarder), which together form a working chamber that can be filled with working medium. To turn on the retarder, the working space is filled with working fluid, the amount of working fluid in the working space that a hydrodynamic circuit flow forms in the working chamber, which determines the torque transmitted from the primary wheel to the secondary wheel and thus the braking torque. As a rule, the retarder can be switched on in different braking stages.

The hydrodynamic retarder can be mechanically decoupled from the drive train by means of a separating clutch. The separating clutch is designed in particular as a wet or dry-running friction clutch, for example as a multi-plate clutch. The separating clutch can have a bridging circuit, which locks the primary side and the secondary side of the clutch together after synchronization, in particular in a form-fitting manner or by engaging behind one another, in order to increase the torque that can be transmitted. According to one embodiment, the separating clutch is dimensioned in such a way that in the frictional state it has a maximum torque transmission capacity that is below that of the hydrodynamic retarder that is filled or fully filled to a certain extent.

In the present case, a separating clutch is to be understood as meaning any component which produces power transmission, in particular mechanical power transmission, in a first operating state and interrupts power transmission in a second operating state, thus for example synchronizing elements, friction clutches and others.

In order to improve the operational readiness of the retarder, it is proposed according to the invention that a filling level monitoring device is provided, which detects the current filling level of the working medium in the working chamber, and an actuating device which is in communicative or mechanical operative connection with the filling level monitoring device and closes the separating clutch as a function of the detected level triggers.

If the fill level in the working area is too high and makes it impossible to engage or close the separating clutch, this must be detected in good time. If the separating clutch is closed, the working space is emptied or the filling level is reduced again. Recognizing this in good time means that the synchronizing device is still able to synchronize the retarder without suffering any damage at this level.

Levels above a limit value lead to a high hydrodynamic retarder torque when closing or when synchronizing and closing, which the synchronizing device can no longer synchronize, at least not without being damaged.

The filling level monitoring device provided detects the current filling level of the working medium in the working space. The detection can take place directly in the working space or indirectly outside of the same. For example, the filling level can be detected in an adjoining room of the hydrodynamic retarder, which is more or less filled with working medium depending on the filling level in the working room and which is referred to here as the communicating adjoining room of the retarder, based on the principle of communicating vessels.

The filling level can be detected quantitatively or qualitatively. In the case of a quantitative filling level detection, it is only determined whether there is any working medium in the working space of the retarder or whether it is empty. In the case of qualitative recording, the specific fill level is recorded steplessly or in different stages. Furthermore, the detection can take place continuously or at intervals.

The filling level monitoring device can comprise an electrical, optical or acoustic sensor and an associated evaluation unit, by means of which the filling level of the working chamber or of a side chamber of the retarder communicating with the working medium with regard to the filling level is detected by electrical resistance measurement, optical signal measurement or acoustic signal measurement.

The fill level monitoring device and/or the separating clutch can also be assigned to or integrated into a control device which detects, receives or calculates the current speed of the transmission output shaft as an input variable and additionally controls closing of the separating clutch as a function of the speed.

Furthermore, the control device can be used to calculate a level-dependent limit speed or a level-dependent limit speed characteristic curve can be stored in the control device. Provision can be made for the control device to close the separating clutch when the associated current speed exceeds an associated limit speed or limit speed characteristic.

A method for controlling a motor vehicle drive train is also proposed, in which a fill level of the working medium is detected by means of a fill level monitoring device in a working chamber of the retarder formed by a bladed primary wheel and a bladed secondary wheel, and the separating clutch is closed when a detected fill level that can be defined in a control device is exceeded. The filling level is therefore lowered again each time a filling height in the working space is exceeded, so that even in the event of an internal leak, in which the working space is unintentionally filled, it is emptied again. The retarder can therefore be switched on at any time for braking operation, so that improved operational readiness is achieved.

Furthermore, the separating clutch can be closed as a function of the fill level in the working chamber and the current speed of the drive train, with the closing taking place earlier when the fill level is high and/or high speeds than when the fill level is low and/or low speeds. This adjustment to fill level and/or speed makes sense in order to increase the range in which the clutch can still be closed in order to couple the retarder to the drive train.

A cycle is started each time the working chamber needs to be emptied in order to keep the retarder ready for braking. The cycle is started as described above when there is too much working medium in the working space, e.g. B. 600ml working medium. When the separating clutch is switched on, the pumping effect in the retarder begins and the excess working medium is pumped out of the working chamber, except for around 200ml, for example. An entry can also be made in the control device if a closing process is triggered without an activation request for the retarder, with an error message being output by the control device if a definable number of switching operations is exceeded within a time interval. If many cycles are detected within a time cycle, maintenance of the retarder can make sense in order to prevent major damage.

• 1 eine schematische Ansicht eines Sekundärretarders, der über eine Trennkupplung am Antriebsstrang eines Kraftfahrzeugs angeschlossen ist;
• 2 eine schematische Detailansicht des Retarders aus der 1.

The invention will be described below using an exemplary embodiment. Show it:

• 1 a schematic view of a secondary retarder which is connected via a separating clutch to the drive train of a motor vehicle;
• 2 a schematic detailed view of the retarder from FIG 1 .

The figures show the hydrodynamic retarder 1, which is connected via a separating clutch 2 to the motor vehicle drive train 3, here to a power take-off 3 in the form of a step-up drive of the transmission 4. The transmission 4 is a multiple-ratio transmission, in particular an automatic transmission or automated manual transmission of a motor vehicle, which is driven on the input side by the engine, in particular internal combustion engine 5, and on the output side via a transmission output shaft 6 drives drive wheels 7 of the motor vehicle. The retarder 1 is assigned a control device 8 which at least controls the opening and closing of the separating clutch 2 or, if this is controlled by another device, blocks the closing of the separating clutch 2 . The control device 8 can either represent the separating clutch locking device itself or access one in which 1 denoted by the reference numeral 9.

In the more detailed view of the 2 the bladed primary wheel 10 of the retarder 1 is shown. This is opposite the bladed secondary wheel 11 , designed here as a stator, and together with it forms the working space 12 . Furthermore, the hydrodynamic retarder 1 has an ancillary space 13 whose filling level with working medium is proportional to that of the working space 12 . A filling level monitoring device 14 is provided in the side room 13, here with a float 15.

The control device 8 has an input 16 for the speed of the primary side 17 of the separating clutch 2 . Furthermore, the control device 8 has a retarder activation signal input 17 at which a signal is present that signals an activation request for the retarder. Such an activation request can be issued, for example, by the driver of the vehicle by actuating an actuator or shift lever or by a control device of the vehicle, for example distance controller or speed controller.

A characteristic curve or several characteristic curves of a level-dependent limiting speed are stored in a memory 19 in the control device 8 . As an alternative or in addition, the control device 8 can always calculate a corresponding limiting speed from current input variables. Input variables can be made available, for example, by a CAN bus.

Reference List

1

retarders

2

disconnect clutch

3

automotive powertrain

4

transmission

5

engine

6

transmission output shaft

7

drive wheels

8th

control device

9

Storage

10

primary wheel

11

secondary wheel

12

working space

13

adjoining room

14

level monitoring device

15

swimmer

16

entry

17

switching signal

18

actuating device

Claims (9)

Motor vehicle drive train with a hydrodynamic retarder (1), comprising a rotating bladed primary wheel (10) and a stationary bladed secondary wheel (11) or rotating in the opposite direction, which together form a working chamber (12) that can be filled with working medium to switch on the retarder (1), wherein the hydrodynamic retarder (1) can be mechanically uncoupled from the drive train by means of a separating clutch (2), characterized in that a filling level monitoring device (14) is provided, which detects the current filling level of the working medium in the working chamber (12), and an actuating device (18) is provided which is in communicative or mechanical operative connection with the filling level monitoring device (14) and which triggers a closing of the separating clutch (2) as a function of the filling level detected. Motor vehicle powertrain claim 1 , characterized in that the filling level monitoring device (14) has a float (15) arranged in the working chamber (12) of the retarder (1) or in a secondary chamber (13) of the retarder communicating with the working chamber (12) with regard to the filling level with working medium. Motor vehicle powertrain claim 1 , characterized in that the fill level monitoring device (14) comprises an electrical, optical or acoustic sensor and an associated evaluation unit, by means of which the fill level of the working chamber (12) or an adjacent chamber (13) of the retarder (1) that communicates with the working medium with regard to the fill level electrical resistance measurement, optical signal measurement or acoustic signal measurement is recorded. Motor vehicle powertrain claim 1 , characterized in that the level monitoring device (14) and/or the separating clutch (2) is assigned to or integrated in a control device (8) which detects, receives or calculates the current speed of the transmission output shaft (6) as an input variable and closes the Separating clutch (2) also controls depending on the speed. Motor vehicle powertrain claim 1 , characterized in that the control device (8) calculates a level-dependent limit speed or a level-dependent limit speed characteristic is stored in the control device (8) and the control device (8) closes the separating clutch (2) when the associated current speed exceeds an associated limit speed or limit speed characteristic . Method for controlling a motor vehicle drive train with a hydrodynamic retarder (1) that can be filled and emptied with working medium and that can be mechanically decoupled from the drive train (6) by means of a separating clutch (2), with the following steps according to one of the preceding claims, characterized in that a filling level of the working medium is detected by means of a filling level monitoring device (14) in a working chamber (12) of the retarder (1) formed by a bladed primary wheel (10) and a bladed secondary wheel (11) and the closing of the separating clutch (2) when one in one Control device (8) detectable level detected. procedure according to claim 6 , characterized in that the separating clutch (2) is closed as a function of the fill level in the working chamber (12) and the current speed of the drive train (6), with the closing taking place earlier when the fill level is high and/or high speeds than when the fill level is low and /or low speeds. procedure according to claim 6 , characterized in that the fill level monitoring device (14) comprises an electrical, optical or acoustic sensor and an associated evaluation unit, by means of which the fill level of the working chamber (12) or an adjacent chamber (13) of the retarder (1) that communicates with the working medium with regard to the fill level electrical resistance measurement, optical signal measurement or acoustic signal measurement is recorded. Method according to one of Claims 6 until 8th , characterized in that an entry in the control device (8) takes place when a closing operation without an activation request for the retarder (1), according to one of Claims 6 until 8th is triggered, wherein when exceeded a definable switching number within a time interval an error message is issued by the control device (8).

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