Equalizing unit of a drive train of a motor vehicle and its construction for loss-minimizing oiling on demand

Abstract

The invention relates to an oiling concept of an equalizing unit of a drive train of a motor vehicle with a clutch device to be oiled in driving mode. In order to stop drag torques which act on the clutch device from the outside and result in increased dissipation when said clutch device is not required due to the operating state, measures are provided which promote the dry running of the clutch device. The measures include the spatial-functional separation of the oil delivery device from the clutch device and the provision of a braking or decoupling device by means of which the oil delivery device can be deactivated if there is no oil requirement.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is based upon and claims the benefit of priority from prior German Patent Application No. 10 2010 036 826.1, filed Aug. 3, 2010, the entire contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The invention relates to an equalizing unit of a drive train of a motor vehicle with a housing and with drive members comprising an input shaft and at least one first output shaft, wherein the first output shaft can be coupled to a second output shaft or to the input shaft or to an intermediate shaft driven by the input shaft via a clutch device, which is to be supplied with oil via a delivery device directly or indirectly driven via the drive members.

The construction of an equalizing unit described above is known from the German disclosure publication DE 10 2008 002 844 A1. There, a drive train for a motor vehicle is shown, which discloses a transverse equalizing unit without differential wherein the output shafts for driving the drive wheels are driven via two individually activatable side shaft clutches. The side shaft clutches are formed by disc packages which for cooling and lubrication have to be oiled. The outer discs of the disc package are connected in a rotationally fixed manner to an intermediate shaft driven by the input shaft—in DE 10 2008 002 844 A1 this is the crown wheel carrier shaft—and through their special configuration deliver the oil to the outside into an oil collection pocket provided in the housing, from where the oil via housing bores flows back to the interior of the disc package where it is again collected by the discs so that—based on a disc package of a side shaft clutch—an internal oil circuit is formed.

Because of this internal oil circuit a large part of the oil volume expended for the cooling and lubrication remains in the described internal oil circuit for a long time without the oil volume being sufficiently mixed with “fresh” oil or replaced with such. Oil volume, which has only just absorbed heat between the clutch discs, is directly returned to the discs again. The clutch temperature therefore rises disproportionally to the cooling output that could be achieved with the oil quantity present in the equalizing unit. The disproportionate heating of the clutch brings disadvantages with regard to the wear characteristics and thus the lifespan and also with regard to the response and control behavior.

A further disadvantage of the embodiment shown in DE 10 2008 002 844 A1 is that the clutch packages of the side shaft clutches stand in the oil in order to collect it and deliver it to the oil collection pocket. The concomitant splashing losses increase the dissipation of the drive train.

Added with respect to the undesirable dissipation is that even in the case descried in DE 10 2008 002 844 A1 that the secondary part of the drive train is decoupled from the drive wheels and the side shaft clutches are fully opened, the secondary drive wheels roll on the street in driving mode and drag the inner disc carrier and the inner discs connected with the latter in a rotationally fixed manner. The inner discs however are in permanent contact with the oil since they are immersed in it. Not only the region of the extremely narrow air gap (gap width approximately 0.1 mm) between inner and outer discs which is directly located in the oil is filled with oil but the oil is additionally delivered through the rotating inner discs also into the intermediate space between inner and outer discs of the disc clutch which do not stand in the oil. The fluid friction or hydrodynamic friction created as a consequence in turn transmits the drag torque acting from the secondary drive wheels to the inner discs to the outer discs and because of this drives the latter. However, as soon as these start to rotate these in turn deliver oil into the previously described internal oil circuit and on their part thus again increase the delivered oil volume and thus the friction loss or dissipation. The undesirable effect amplifies itself.

Tests have shown that because of this effect the secondary drive train contrary to the assumptions made in DE 10 2008 002 844 A1 does not come to a halt even when it is decoupled from the primary part of the drive train. Through the low-friction configuration of the surfaces of the inner discs proposed in DE 10 2008 002 844 A1 the negative consequences of this effect can only be reduced to a very minor degree. In addition, the low-friction surfaces of the inner discs result in a significantly poorer response and control behavior of the clutch package. A disadvantage, which weighs heavier than the advantages that can be achieved with the dissipation through these measures.

SUMMARY OF PREFERRED EMBODIMENTS

Before this background it is the object of the invention to make available an equalizing unit of the type mentioned at the outset, with which the disadvantages described above are avoided. In particular, the oiling concept described in DE 10 2008 002 844 A1 is to be optimized with regard to the dissipation caused by this upon a secondary part decoupled from the primary part of the drive train without having to accept compromises with the response and control behavior of the clutch packages.

According to the invention, the object is solved in that the delivery device is formed by a oil delivery wheel arranged distant from the clutch device.

The arrangement of the oil delivery wheel distant from the clutch device results in that the oil following a passage through the clutch device to be oiled always flows back into the oil sump of the equalizing unit before it is again fed into the oil circuit. Thus, adequate mixing-through of the entire oil volume and consequently the utilization of the maximum cooling output of the total oil quantity is guaranteed at all times, which in turn reduces thermal loading of the clutch devices.

The equalizing gear can be both a transverse as well as a longitudinal equalizing unit. Particularly preferably the invention however is employed with a transverse equalizing unit, particularly with a transverse equalizing unit acting in a purely frictionally connected manner without a differential, wherein the side shafts of the drive wheels are coupled into the drive power flow via side shaft clutches, as is already shown in DE 10 2008 002 844. In principle, the invention can also be employed with conventional longitudinal and transverse differentials acting in a positively connected manner in order to oil clutch packages of the differential locks, be it in shaft-shaft arrangement or in shaft-cage arrangement. The intermediate shaft with a conventional differential is formed by the differential cage.

The mentioned configuration additionally makes possible designing the oil delivery wheel in such a manner that it is able to deliver the cooling and lubricating oil from an oil sump with an oil level located below the clutch device. The clutch device, that is particularly also the dragged clutch components, can thus be permanently located above the oil level. Even the outer disc carrier located radially outside and the outer discs do not cause any splashing losses either under load, that is for example with connected secondary part of the drive train, nor in the opened mode, that is with disconnected secondary part.

Preferably, the oil delivery wheel is formed by a crown wheel arranged on the intermediate shaft, via which as part of the angular gear the drive power introduced by the input shaft is transmitted to the intermediate shaft. If because of the dimensioning of the crown wheel the crown wheel itself does not have an adequate diameter for immersing itself in an oil sump even located below the clutch device it can be provided that the oil delivery wheel comprises the crown wheel arranged on the intermediate shaft, wherein the crown wheel is radially expanded to the outside by an oil delivery ring. The oil delivery ring can be designed as integral material-unitary part of the crown wheel. For weight and cost reasons and in order to keep masses to be accelerated and decelerated low it is appropriate however to produce the oil delivery ring as a separate component from a lighter material and to join it, particularly screw it to the crown wheel.

The realization of the oil delivery wheel with the help of a gear wheel of the equalizing gear standing in the power flow is not absolutely essential. An oil delivery wheel that is separate from the crown wheel can also be provided on the input shaft or the intermediate shaft.

In order to increase the oil flow, at least part-circumferential bulkheads can be provided which minimize the lateral outflow of the oil taken along by the oil delivery wheel.

Despite the improvement measures described above it has been shown that the oiling concept can be optimized further still. The self-amplifying effect of an undesirable clutch oiling caused through the drag torques of the wheels which are not driven but rolling on the road despite decoupled secondary part of the drive train was observed during tests despite the remedial measures described above.

At the torque, at which the clutch device is opened for decoupling the secondary part from the primary part of the drive train oil is still delivered by the rotating oil delivery wheel, among other things because of a running-down due to mass inertia. In addition, oil is still present between the two clutch sides despite opened clutches so that the clutch, although it is in the open state, transmits a drag power from the one clutch side to the other clutch side. The latter clutch side as drive member of the secondary part of the drive train in turn drives the oil delivery wheel which as a consequence does not completely cease the oil delivery as actually desired, but continues to deliver oil to the clutch device. As a consequence of the non-interrupted oil flow and supported by the drag power introduced via the drag torque a state of equilibrium is established which prevents the complete stoppage of the drive members of the secondary part of the drive train. The secondary part continuously co-rotates and causes dissipation although it is not integrated in the drive power flow.

In order to interrupt this equilibrium a braking or decoupling device is provided, by means of which the oil delivery wheel can be stopped when there is no oiling need for the clutch device. With such a braking or decoupling device the state of equilibrium which would otherwise materialize can be effectively prevented for the braking or decoupling device brings about that—depending on where and how the braking or decoupling device intervenes—the drag power can no longer be transmitted from the one clutch side to the other clutch side since the former is already braked and/or since through the decoupling of the oil delivery wheel from its drive member the drag power is not transmitted to the oil delivery wheel. However, as soon as the oil delivery wheel is stationary the oil flow is interrupted and the undesired oiling in the drag state is terminated. The clutch device briskly runs dry and the two clutch sides rotate with significantly lower loss.

Since the braking torque, which the braking device has to provide for stopping the oil delivery wheel, is only small the braking device can also be realized with the help of smaller drive train components of the secondary part. For example it can be provided that the braking device comprises the sliding sleeve of a synchronizing device which interacts with a fixed part of the motor vehicle via a friction surface and is capable of generating a braking torque for braking the drive members of the secondary part to be stopped. Here, the sliding sleeve for generating the frictional torque can support itself for example against a bearing block or another component that is capable of supporting the braking torque. Alternatively or additionally the sliding sleeve for creating the frictional torque can comprise a friction surface facing a shifting fork of the synchronizing device.

The inventive idea of stopping the oil delivery device through a braking or decoupling device cannot only be realized with oil delivery devices which are formed by an oil delivery wheel. This inventive idea can rather be transferred also to other oil delivery devices delivering oil to the clutch device by other means.

For this reason, a construction of a drive train for a motor vehicle is considered as belonging both to the invention mentioned at the outset as well as being an independent invention, wherein the drive train comprises an equalizing gear with drive members comprising an input shaft and at least one first output shaft, wherein the first output shaft can be coupled to a second output shaft or to the input shaft or to an intermediate member driven by the input shaft via a clutch device to be oiled, which is to be supplied with oil via a delivery device directly or indirectly driven via the drive members, wherein in the drive train a braking or decoupling device is provided, by means of which the delivery device can be stopped if there is no oiling need for the clutch device.

The previously described braking device cannot only act on drive members of the equalizing unit. Particularly with a drive train having a permanently driven primary part for the permanent driving of primary drive wheels as well as a secondary part for the driving of secondary drive wheels, wherein the secondary part if required can be decoupled from the primary part and the secondary drive wheels or connected to these, the braking device can act on any parts of the secondary part of the drive train.

The braking device thus need not necessarily be part of the equalizing unit, it merely needs to generate an adequate frictional torque somewhere in the secondary part of the drive train to be deactivated.

For this reason, a construction of a drive train for a vehicle is seen as both belonging to the invention mentioned at the outset as well as an independent invention, wherein the drive train comprises a permanently driven primary part for the permanent driving of primary drive wheels and a secondary part for the driving of secondary drive wheels, wherein the secondary part if required can be decoupled from the primary part and the secondary drive wheels or connected to these, and wherein in the secondary part at least one clutch device is provided whose at least one clutch side is dragged via the secondary axle drive wheels which are rolling when operating the vehicle even with decoupled secondary part is to be supplied with oil via a delivery device directly or indirectly driven via drive members of the secondary part, wherein a braking device is provided by means of which the secondary part can be braked in the state decoupled from the primary part.

In summary a revised oiling concept of an equalizing unit of a drive train of a motor vehicle with a clutch device to be oiled in driving mode and measures connected with this is proposed. In order to stop drag torques which act on the clutch device from the outside and lead to increased dissipation when said clutch device is not required due to the operating state, measures are provided which promote the dry-running of the clutch device. The measures include the spatial-functional separation of the oil delivery device from the clutch device and the provision of a braking or decoupling device, by means of which the oil delivery device can be deactivated when no oil is required.

DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention are obtained from the subclaims and from the following description of preferred exemplary embodiments by means of the drawings.

In the drawing it shows:

FIG. 1 a drive train construction known from the prior art with permanently driven primary part and a secondary part that can be connected when required with a equalizing unit without differential for driving the secondary drive wheels,

FIG. 2 a equalizing unit without differential during the operation with an oil delivery wheel formed by the crown wheel for clutch oiling,

FIG. 3 an alternative embodiment of the equalizing unit without differential in the stationary state with a schematically represented oil delivery ring fastened to the crown wheel, and

FIG. 4 a power takeoff unit (PTU) provided for a drive train according to FIG. 1 with an additional braking device for braking the secondary part of the drive train.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a drive train construction know from the prior art with permanently driven primary part and a secondary part only driven when required with a equalizing unit 1 without differential for driving the secondary drive wheels 2. The secondary part of the drive train, whose drive members can be decoupled from or connected to the primary part depending on requirement, is shown obliquely hatched, while those drive members, which interact with the secondary part in driving mode for power transmission and rotate permanently are marked black throughout.

The equalizing unit 1 is an equalizing unit without differential, wherein the power flow is transmitted to the secondary drive wheels 2 via two individually activatable clutch devices formed through side shaft clutches 3, and via the half shafts 4. Here, the side shaft clutches 3, which are formed by disc clutches acting in a frictionally connected manner not only compensate for the different rolling paths of the secondary axle drive wheels 2 when driving through curves but are also utilized for actively influencing the dynamic driving behavior. In operation, the clutches have to be oiled with cooling and lubricating oil.

Tests with the system shown in FIG. 1 have shown that even then, when the secondary part of the drive train is decoupled from the primary part, particularly when said secondary part is decoupled while driving and at a speed from approximately 50 km/h, the drive members of the secondary part do not stand still as desired, but continue to rotate through the drag power introduced into the side shaft clutches 3 by the secondary drive wheels 4 and thus cause dissipation. The reason for this is particularly the oiling concept selected in the prior art as described at the outset.

FIG. 2 shows an equalizing unit 1 without differential during the operation with an oil delivery wheel for clutch oiling formed by the crown wheel 5. The crown wheel 5 because of its rotation scoops the oil along the housing inner wall to an oil collection pocket 6 provided in the housing. From there it reaches the side shaft clutches 3 via oil feed channels 7. The crown wheel 5 is arranged on the intermediate shaft 19 and is driven via an input shaft (not shown).

By utilizing the crown wheel as oil delivery wheel or bucket wheel it is ensured, compared with a solution where the discs of the side shaft clutches predominantly deliver the oil, that the oil flowing back from the clutches—before it is again fed to the oil circuit—collects in the oil sump and is mixed with the entire oil volume. It is prevented that an inner oil circuit forms, because of which the oil after it has flowed through the clutches is directly fed back to these again so that the oil in consequence would be heated up disproportionately.

FIG. 3 shows the equalizing unit from FIG. 2, wherein with the embodiment shown in FIG. 3 the equalizing unit is stationary. It is evident that the diameter of the crown wheel 5 is not adequate to immerse itself in the oil. For this reason, an only schematically represented oil delivery ring is provided on the crown wheel 5, which radially expands the active diameter of the crown wheel 5 with respect to the oil delivery capability. The oil delivery ring 8 need not necessarily be a ring-shaped component but individual non-continuous blades can also be arranged on the crown wheel 5 which are distributed over its circumference.

Likewise only schematically shown is a part-circumferential oil bulkhead 9, which prevents that the oil during the delivery process can laterally flow out of the oil sump to the oil collection pocket located above due to centrifugal force. The application of a bulkhead 9 can not only be used with an oil delivery ring. It is likewise suitable for a configuration according to FIG. 2 or for other arrangements of oil deliver wheels on the intermediate shaft. The bulkhead 9 is preferably provided on both sides of the oil delivery wheel and can either be formed by a part to be separately inserted or directly by a projection protruding to the inside or a rib of the housing, wherein installation space and installation aspects obviously have to be taken into account.

In addition it is evident in FIG. 2 and FIG. 3 that the oil level in the oil sump both in the operating state as well as when stationary is located below the side shaft clutches. This also contributes to minimizing the dissipation since the clutch members dragged by the half shafts 4 do not stand in the oil and can thus not deliver any oil between the clutch discs. In the case that the secondary part of the drive train is decoupled from the primary part the clutches can thus run in a completely dry and thus low-friction manner.

Despite the spatial-functional separation of clutch device and oil delivery device it can happen, as described at the outset, that the secondary part of the drive train after separation from the primary part particularly as a consequence of the continuing running down of oil in the clutch device continues to rotate and causes dissipation. In order to stop this and in order to make it possible that the oil flow can be completely stopped a braking device is provided which in the following is explained exemplarily by means of a special configuration of the power takeoff unit 10 (PTU) shown in FIG. 1.

So as to make it possible that the secondary part of the drive train shown in FIG. 1 can also be connected to or decoupled from the drive train even while driving, the PTU 10 has a synchronizing device 11. FIG. 4 shows a PTU 10 that can be employed in a drive train according to FIG. 1 with an additional braking device 12 for braking the secondary part of the drive train, wherein the braking device 12 is provided on the synchronizing device 11.

The synchronizing device 11 comprises a sliding sleeve 13 which is slid onto a guide sleeve 14 in a rotationally fixed but axially displaceable manner. A shifting fork 15, by means of which the sliding sleeve 13 can be actuated, rests in the sliding sleeve 13. In FIG. 4 the sliding sleeve 13 is shown in a position in which the secondary part of the drive train is decoupled from the primary part. In order to connect the secondary part of the drive train to the primary part the sliding sleeve in FIG. 4 therefore would have to be shifted to the left in order to come into engagement with the driver ring 16.

Laterally, next to the sliding sleeve 13, a schematically shown additional friction surface 17′ is provided, which interacts with a fixed component capable of supporting a braking torque (for example bearing block 18). The friction surface is preferably arranged on the sliding sleeve 13 but can just as well be additionally or alternatively provided on the fixed component.

A further friction surface 17″ can act between sliding sleeve 13 and shifting fork 15 additionally or alternatively to the friction surface 17′. Here, too, the friction surface 17″ can be provided on one of the two or on both components.

If the secondary part of the drive train is now decoupled from the primary part by sliding the synchronizing device into the position shown in FIG. 4 a frictional torque can be created in that the sliding sleeve 13 and the shifting fork 15 respectively are specifically set against the friction surfaces 17′ and 17″ respectively, through which the drive members of the secondary part of the drive train are braked. This interrupts the oil flow in the equalizing unit shown in FIGS. 2 and 3 so that the clutches can run dry and the transmission of the drag torque from the secondary drive wheels via the half shafts into the secondary part-sided clutch device is significantly minimized The clutch discs subsequently run in an extremely low-friction manner, the secondary part of the drive train stands still.

The synchronizing device 11 shown in FIG. 4 is additionally particularly low in friction because of its special arrangement. While usually the guide sleeve 14 is positioned on the permanently rotating drive members of the primary part of the drive train and the driver ring 16 is located on the drive members of the secondary part of the drive train to be accelerated during the synchronizing process this is exactly the opposite with the version shown in FIG. 4. This results in that when the secondary part of the drive train is decoupled and stationary, the guide sleeve 14 and the sliding sleeve 13 also stand still so that between shifting fork 15 and sliding sleeve no friction and thus no dissipation can occur. In addition, only this configuration makes possible braking the secondary part of the drive train via the synchronizing device, since no braking torque acting on the drive members of the secondary part of the drive train could otherwise be generated via the sliding sleeve or the shifting fork. This arrangement of the components of the synchronizing device is considered as separate invention independent of the oiling concept and the remaining construction of the drive train.

LIST OF REFERENCE NUMBERS

• 1 Equalizing unit
• 2 Secondary drive wheels
• 3 Side shaft clutch
• 4 Half shafts
• 5 Crown wheel
• 6 Oil collection pocket
• 7 Oil feed channels
• 8 Oil delivery ring
• 9 Bulkhead
• 10 Power takeoff unit (PTU)
• 11 Synchronizing device
• 12 Braking device
• 13 Sliding sleeve
• 14 Guide sleeve
• 15 Shifting fork
• 16 Driver ring
• 17′, 17″ Friction surface
• 18 Bearing block
• 19 Intermediate shaft

Claims

1. The invention relates to an equalizing unit of a drive train of a motor vehicle with drive members comprising an input shaft and at least one first output shaft, wherein the first output shaft can be coupled to a second output shaft or to the input shaft or to an intermediate shaft driven by the input shaft via a clutch device, which is to be supplied with oil via a delivery device directly or indirectly driven via the drive members, wherein the delivery device is formed by an oil delivery wheel arranged distant from the clutch device.

2. The equalizing unit according to claim 1, wherein the oil delivery wheel is designed in such a manner that it is capable of delivering the oil from an oil sump with an oil level located below the clutch device.

3. The equalizing unit according to claim 1, wherein the oil delivery wheel is formed by a crown wheel arranged on the intermediate shaft.

4. The equalizing unit according to claim 1, wherein the oil delivery wheel comprises a crown wheel arranged on the intermediate shaft, wherein the crown wheel is radially expanded to the outside by an oil delivery ring.

5. The equalizing unit according to claim 1, wherein on the inside of the housing at least part-circumferential bulkheads are provided which during the oil delivery process minimize the lateral outflow of the oil taken along by the oil delivery wheel.

6. The equalizing unit according to claim 1, wherein a braking or decoupling device is provided, by means of which the oil delivery wheel can be deactivated if there is no oiling requirement for the clutch device.

7. The equalizing unit according to claim 6, wherein the braking device comprises a sliding sleeve of a synchronizing device which interacts with a fixed part of the motor vehicle via a friction surface and is capable of generating a braking torque for braking the drive members to be deactivated.

8. The equalizing unit according to claim 7, wherein the sliding sleeve for generating the friction torque supports itself against a bearing block.

9. The equalizing unit according to claim 7, wherein the sliding sleeve for generating the friction torque supports itself against a shifting fork of the synchronizing device.

10. A construction of a drive train for a motor vehicle, wherein the drive train comprises an equalizing unit with drive members, particularly an equalizing unit according to claim 1, wherein the drive members comprise an input shaft and at least one first output shaft, wherein the first output shaft can be coupled to a second output shaft or to the input shaft or to an intermediate shaft driven by the input shaft via a clutch device to be oiled, which via a delivery device directly or indirectly driven via the drive members is to be supplied with oil, wherein in the drive train a braking or clutch device is provided, by means of which the delivery device can be braked if there is no oiling requirement for the clutch device.

11. The construction of a drive train for a motor vehicle, particularly with an equalizing unit according to claim 1, wherein the drive train comprises a permanently driven primary part for the permanent driving of primary drive wheels and a secondary part for the driving of secondary drive wheels, wherein the secondary part if required can be decoupled from or connected to the primary part and the secondary drive wheels, wherein a braking device is provided by means of which the secondary part in the state decoupled from the primary part can be braked.

12. A drive train construction according to claim 11, wherein in the secondary part at least one clutch device is provided, whose at least one clutch side is dragged via the secondary axle drive wheels which in vehicle operation roll even with decoupled secondary part and which with connected secondary part is to be supplied with oil via a delivery device directly or indirectly driven via drive members of the secondary part.