Transmission for a motor vehicle

Abstract

Transmission 1 for a motor vehicle, wherein the transmission comprises a housing 2 with a gear set 3 with a transmission input shaft (4 fig. 3) and a transmission output shaft (5), and with a lubricat

Description

The invention relates to a transmission for a motor vehicle. Transmissions for motor vehicles, also for motor vehicles with an electric drive, are generally known. The transmission serves to transform an input speed of an input shaft of the transmission into a demand-based output speed of an output shaft of the transmission. The transmission usually has gear pairs that are engaged with one another. Publications EP 1 016 809 A2, US 3,489,034 A and DE 10 2015 004 991 B3 disclose a high-speed transmission for driving generators by turbines, wherein a partial vacuum is generated in a transmission housing with the aid of a pump. Publication DE 10 2011 015 733 A1 discloses a transmission for a motor vehicle, wherein a negative pressure or a partial vacuum can likewise be generated in the transmission with the aid of a pump. Publication EP 0 137 596 A1 discloses a transmission for a motor vehicle, wherein the transmission comprises a dry-sump lubrication, a transmission housing of the transmission being connected to a vacuum source of an internal combustion engine with the aid of a control valve in order to generate a defined negative pressure in the transmission housing. The present invention seeks to provide an improved transmission for a motor vehicle. This may be achieved according to an aspect of the invention with a transmission for a motor vehicle with the features of claim 1. Advantageous embodiments with expedient and non-trivial developments of the invention are specified in the respective subclaims. In a transmission according to an aspect of the invention for a motor vehicle, wherein the transmission comprises a housing with a gear set with a transmission input shaft and a transmission output shaft, and with a lubrication system, which comprises a conveying means for conveying a lubricant mixture out of the housing, wherein a dry-sump lubrication is brought about with the aid of the conveying means, a negative pressure in the housing is controllable in order to reliably bring about the dry-sump lubrication. The advantage of aspects of the invention is that so-called offload losses, i.e., losses, such as friction losses during idling, can be reduced. Losses in a powertrain of the motor vehicle can thus be reduced so that an efficient powertrain can be realized. Since available energy is limited, in particular in a battery-powered motor vehicle, the transmission according to aspects of the invention can lead to an improved range of the motor vehicle. The reduction of the off-load losses, which are present both statically and dynamically, relates in particular to sealing, splashing and ventilation losses. Advantageously, with the aid of the transmission according to aspects of the invention, an increase in the efficiency under load and in coasting phases can be achieved. In one embodiment of the transmission according to the invention, the negative pressure in the housing is controllable with the aid of a throttle formed in the lubrication system, so that simple structural components in the transmission can be used advantageously cost-effectively. Advantageously, the conveying means is designed in the form of an electric pump, the pumping power of which is controllable, so that an amount of lubricant to be sucked from the housing can be controlled in a simple manner. In a further embodiment, the lubrication system comprises a lubricant reservoir with a means for the material separation of the lubricant mixture into lubricant and air, wherein the means is advantageously designed in particular in the form of a centrifuge. The negative pressure can be controlled in a simple manner with the aid of the first throttle designed for the lubricant to flow through and / or the second throttle designed for the air to flow through and / or the third throttle of the lubrication system designed for the air to flow through. A further, improved control of the negative pressure can be achieved by the throttle being controllable. Additional advantages, features and details of the invention arise from the following description of preferred exemplary embodiments and with reference to the drawing. The features and feature combinations specified in the above description, as well as the features and feature combinations specified below in the description of the drawings and / or shown alone in the figures, can be used not only in the respectively specified combination but also in other combinations or on their own, without departing from the scope of the invention. Identical or functionally identical elements are associated with identical reference signs. The figures show: Fig. 1 a schematic representation of a transmission according to an embodiment of the invention for a motor vehicle, Fig. 2 a detailed schematic representation of a transmission according to the embodiment of the invention according to Fig. 1, Fig. 3 a perspective side view of the transmission according to an embodiment of the invention with drainage elements, Fig. 4 a perspective side view of the drainage elements of the transmission according to Fig. 3, and Fig. 5 a speed-power diagram of a power curve of a transmission according to the prior art and a power curve of the transmission according to an embodiment of the invention. Fig. 1 illustrates a schematic representation of a transmission 1 according to an embodiment of the invention, wherein this representation is a rough schematic. The transmission 1 according to the embodiment of the invention is furthermore shown in a detailed schematic representation in Fig. 2. The transmission 1, which is provided for a motor vehicle, in particular for a motor vehicle with an electric drive, comprises a housing 2, in which a gear set 3 with a transmission input shaft 4 and a transmission output shaft 5 is arranged. The transmission 1 is associated with a lubrication system 6 for supplying the gear set 3 with a lubricant mixture SG. The lubricant mixture SG consists of air L and lubricant S. At this point, it should be noted that the lubricant S flowing through the lubrication system 6, which is in particular designed in the form of a circuit, undergoes an introduction of air L, in particular due to circulation in the circuit, and is thus generally formed as a lubricant mixture SG in the lubrication system 6. The air L and the resulting material change of the lubricant S can lead to faster, unfavourable vapor bubble formation and / or to increased friction in the gear set 3 due to different material properties of the air L and of the lubricant S. The lubrication system 6 comprises a conveying means 7 for conveying the lubricant mixture SG in a circuit-like manner, wherein the lubricant mixture SG is sucked from the housing 2 and fed back to the housing 2 in an altered form. The conveying means 7 is advantageously designed in the form of an electrically operable pump, the pumping power of which is controllable. The lubricant mixture SG is altered to the extent that it is fed to a lubricant reservoir 8, and is separated into the two components of air L and lubricant S with the aid of a means 9 for material separation, the means 9 in the present exemplary embodiment being designed in the form of a centrifuge. Or, in other words, the lubricant mixture SG is degassed. It should furthermore be noted that even with the aid of the means 9, the component lubricant S in the lubrication system 6 is of course present not entirely separated from the air L. In other words, a certain, but minimal, amount of air L is also present in the lubricant S. This is a much smaller portion downstream of the means 9 and upstream of the housing 2 than upstream of the means 9 and downstream of the housing 2. The lubricant S is fed back to the housing 2 with the aid of a first throttle 10. The air L is fed to the housing 2 with the aid of a second throttle 11, wherein a compensating reservoir 12 of the lubrication system 6, to which the air L is fed with the aid of a third throttle 13, is arranged between the lubricant reservoir 8, which has a positive pressure pu, and the housing 2. It should be noted at this point that the positive pressure po is greater than the negative pressure pu. In principle, a diameter of the first throttle 10 is greater than a diameter of the third throttle 13, which diameter in turn is greater than a diameter of the second throttle 11. This leads to a stable supply of the gear set 3 and to the correspondingly provided negative pressure pu being brought about in the housing 2. From this compensating reservoir 12, a first air portion L1 is fed to an environment with an ambient pressure pamb and a second air portion L2 is fed with the aid of the second throttle 11 to the housing 2 in order to bring about the required negative pressure pu. This means that the transmission 1 according to this embodiment of the invention comprises a dry-sump lubrication, which can be brought about with the aid of the controllable negative pressure pu. In the present exemplary embodiment, the negative pressure pu is controlled with the aid of the second throttle 11. Likewise, the first throttle 10 and / or the third throttle 13 could also be designed to control the negative pressure pu or, in other words, be used functionally to control the negative pressure pu. The third throttle 13 can also be designed to control the negative pressure pu and the positive pressure po in the lubricant reservoir 8. Fig. 2 shows the transmission 2 according to the embodiment of the invention in the detailed schematic representation. For the preferred control of the negative pressure pu, the conveying means 7 is designed in the form of the electric, controllable pump. This electric pump 7 furthermore advantageously comprises a first suction side 14 and a second suction side 15, wherein the first suction side 14 and the second suction side 15 are connected, so as to allow flow-through, to the housing 2 with the aid of a first conveying line 18 to a first location 16 of the housing 2 and with the aid of a second conveying line 19 to a second location 17 of the housing 2, respectively. The first location 16 is spaced apart from the second location 17 in such a way that the lubricant mixture SG can be reliably sucked as a function of different orientations of the housing 2. Each of the two conveying lines 18, 19 has a lubricant filter 20. Likewise, the conveying means 7 could also have only one suction side 14; 15. Downstream of the conveying means 7, a further lubricant filter 21 of the lubrication system 6 is received, so as to allow flow-through, in a system line 22, allowing flow-through, of the lubrication system 6. The conveying means 7 conveys the lubricant mixture SG sucked from the housing 2 into the system line 22 in a controlled manner. The lubricant reservoir 8, comprising the means 9 in the form of the centrifuge, is arranged downstream of the further lubricant filter 21 in the lubrication system 6. After separation of the lubricant mixture SG into air L and lubricant S and before the lubricant S is fed to the housing 2, said lubricant is cooled with the aid of a heat exchange 23 via the system line 22, which is connected to the lubricant reservoir 8 so as to allow flow-through. The air L is conveyed with the aid of the third throttle 13 from the lubricant reservoir 8 into the compensating reservoir 12 and, as already described above, is divided into the first air portion L1 and the second air portion L2. The first air portion L1 is filtered with the aid of an additional lubricant filter 40 before it enters the environment. The throttles 10, 11, 13 are each designed as controllable throttles. The throttle 10; 11; 13 could, for example, be designed in a simplest design in the form of a screw with a hole. The second throttle 11 is connected to the housing 2 so as to allow flow-through and is designed in the present exemplary embodiment to be screwed into the housing. The second throttle 11 could likewise be received in the compensating reservoir 12. As illustrated in particular in Fig. 3, the gear set 3 in the present exemplary embodiment comprises the transmission input shaft 4 with a first transmission gear 25, which is operatively connected to a second transmission gear 26. The second transmission gear 26 is connected to a third transmission gear 27 with the aid of a common shaft 28, wherein the third transmission gear 27 is via gear engagements with a fourth transmission gear 29, having the transmission output shaft 5. With the aid of the lubrication system 6, a first bearing 30 and a second bearing 31 of the transmission input shaft 4, a third bearing 32 and a fourth bearing 33 of the transmission output shaft 5 as well as a fifth bearing 34 of the shaft 28 are in particular supplied with lubricant S. In order to supply lubricant to the bearings 30, 31, 32, 33, 34, a plurality of additional lines 41 of the lubrication system 6 are designed to branch off from the system line 22. The bearings 30, 32, 33, 34 are furthermore each associated with single throttles 42. Due to the separation in the means 9, the lubricant S has a reduced proportion of the air L of the lubricant mixture SG, whereby a friction-reduced gear set 3 is realized. Additionally, a spraying device 35 of the lubrication system 6 is formed in the housing 3 and is designed to spray a first gear stage 36 of the gear set 3, comprising the first gear wheel 25 and the second gear wheel 26, and to spray a second gear stage 37 of the gear set 3, comprising the third gear wheel 27 and the fourth gear wheel 29. The spraying device 35 comprises a first spraying element 38 for spraying the first gear stage 36 and a second spraying element 39 for spraying the second gear stage 37. The spraying elements 38, 39 are supplied with lubricant with the aid of the plurality of additional lines 41. Fig. 3 illustrates the transmission 2 according to the invention in a further exemplary embodiment. In order to improve the reduction of friction in the gear set 3, the drainage elements 24 are formed and at least partially comprise or cover the individual gearwheels 25, 26, 27, 29. For improved clarity, Fig. 4 illustrates the drainage elements 24 separately from the gear set 3. Any lubricant spatters flung into the housing 2 in a non-directed manner during operation of the transmission 2 due to, for example, centrifugal forces are purposefully collected with the aid of the drainage elements 24. One or more sealing rings (not shown in more detail) of the transmission 1 are designed to be adapted to the negative pressure pu prevailing in the housing 2. Fig. 5 shows a speed-power diagram of a first power curve P1 of a transmission 1 according to the prior art and a second power curve P2 of the transmission 1 according to the invention according to the further exemplary embodiment. With the aid of the transmission 1 according to this embodiment of the invention, a significant reduction in an energy demand for operating the transmission 1 is realized. List of reference signs 1 Transmission 2 Housing 3 Gear set 4 Transmission input shaft 5 Transmission output shaft 6 Lubrication system 7 Conveying means 8 Lubricant reservoir 9 Means for material separation 10 First throttle 11 Second throttle 12 Compensating reservoir 13 Third throttle 14 First suction side 15 Second suction side 16 First location 17 Second location 18 First conveying line 19 Second conveying line 20 Lubricant filter 21 Further lubricant filter 22 System line 23 Heat exchanger 24 Drainage element 25 First gear wheel 26 Second gear wheel 27 Third gear wheel 28 Shaft 29 Fourth gear wheel 30 First bearing 31 Second bearing 32 Third bearing Fourth bearing Fifth bearing Spraying device First gear stage Second gear stage First spraying element Second spraying element Additional lubricant filter Plurality of additional lines Single throttle Air First air portion Second air portion First power curve Second power curve Lubricant Lubricant mixture Ambient pressure Positive pressure Negative pressure

Claims

1. Transmission for a motor vehicle, wherein the transmission comprises a housing with a gear set with a transmission input shaft and a transmission output shaft, and with a lubrication system, which comprises a conveying means for conveying a lubricant mixture from the housing, wherein a drysump lubrication can be brought about with the aid of the conveying means, whereina negative pressure in the housing is controllable in order to reliably bring about the dry-sump lubrication.

2. Transmission according to claim 1, whereinthe negative pressure in the housing is controllable with the aid of a throttle formed in the lubrication system.

3. Transmission according to claim 1 or 2, whereinthe conveying means is designed in the form of an electric pump.

4. Transmission according to any one of the preceding claims, whereinthe lubrication system comprises a lubricant reservoir with a means for the material separation of the lubricant mixture into lubricant and air.

5. Transmission according to claim 4, whereinthe means is designed in the form of a centrifuge.

6. Transmission according to claim 4 or 5, whereinthe negative pressure is controllable with the aid of the first throttle designed for the lubricant to flow through and / or with the aid of the second throttledesigned for the air to flow through and / or with the aid of the third throttle of the lubrication system designed for the air to flow through.

7. Transmission according to claim 6,whereinthe throttle is controllable.

8. Transmission according to claim 6 or 7,whereinthe second throttle is connected to the housing so as to allow flow-through.

9. Transmission according to claim 8,whereinthe second throttle is designed to be screwed into the housing.

10. Transmission according to any one of Claims 4 to 9, whereinthe lubrication system comprises a compensating reservoir, which is formed between the lubricant reservoir and the housing.11 .Transmission according to claim 10,whereinthe third throttle is designed to control the negative pressure and a positive pressure in the lubricant reservoir.

12. Transmission according to any one of the preceding claims, whereina sealing ring of the transmission is designed to be adapted to the negative pressure.

13. Transmission according to any one of the preceding claims, whereinthe lubrication system comprises at least one lubricant filter.