GB2466179A

GB2466179A - Casing having a breather duct with a tank for balancing pressure changes

Info

Publication number: GB2466179A
Application number: GB0822219A
Authority: GB
Inventors: Ulrik Edlundh
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-12-05
Filing date: 2008-12-05
Publication date: 2010-06-16
Also published as: GB0822219D0; CN101749408A

Abstract

A casing 12, for a gearbox or differential in an amphibious vehicle, comprises a breather opening 14 communicating with an interior of the casing 12, a breather duct 16 having an inlet 20 which is connected with the breather opening 14, wherein the breather duct 16 encapsulates between the breather opening 14 and the inlet 20 an air volume for balancing a pressure change in the interior of the casing due to temperature changes. Breather duct 16 comprises a tank, which may be filled with an inert gas, for encapsulating a major part of the air volume and for receiving intruding liquid. Casing 12 has a plurality of casting ribs 22 which form cavities 24 that communicate with the breather opening 14 and the inlet 20, thereby providing the breather duct 16. At lease one of the casting cavities 24 is closed b a cover (26, fig 2) for encapsulating the air. Due to the encapsulated air volume it is safeguarded that only the air volume communicates with the interior of the casing 12 but not other substances. This assures a high life time and low wear since only transmission oil comes into contact with components in the casing 12.

Description

Casing

Description

The invention relates to a casing, by means of which for instance a gear assembly of a power transmission unit for a motor vehicle may be encapsulated.

It is known to use a casing for a power transmission unit (PTU), which comprises a breather opening at its highest position. Due to the breather opening a pressure in the interior of the casing can be balanced with a pressure outside the power transmission unit. At a low temperature of the power transmission unit ambient air is sucked in the casing and vented out at a higher temperature.

It is a disadvantage of such kind of a casing that power transmission units using such kind of a casing show a low life time and a high wear of the gear assembly components.

It is the object of the invention to provide a casing, which provides a good life time for components inside the casing.

The solution of the object is achieved by the features of claim 1. Preferred embodiments are given by the dependent claims.

The casing according to the invention for a power transmission unit of a motor vehicle comprises a breather opening communicating with an interior of the casing.

According to the invention a breather duct, which comprises an inlet, is connected with the breather opening, wherein the breather duct encapsulates between the breather opening and the inlet an air volume for balancing a pressure change in the interior of the casing due to temperature changes.

Due to the encapsulatedair volume it is safeguarded that only the air volume communicates with the interior of the casing but not other substances. Particularly water, for example rain water, can not intrude into the interior of the casing via the breather opening. Since no liquid can bypass the encapsulated air volume, it is assured that no liquid mixes with the transmission oil of the power transmission unit. Since it is assured that only the transmission oil comes into contact with the components of the power transmission unit, a high life time and a low wear is provided. The air volume inside the breather duct acts as a movable gas barrier, which can be partially sucked in at a low temperature of the power transmission unit and moved outwards inside the breather duct at a high temperature. Since always enough air volume is present inside the breather duct, it is no problem, when at certain circumstances the breather duct is partially filled with a liquid, like water.

Preferably the encapsulated air volume is chosen such, that a pressure change in the interior based on a temperature difference AT of AT �= 90 K, particularly AT �= 110 K, preferably AT �= 130 K and most preferred AT �= 150 K is balanced. The encapsulated air volume is chosen high enough, that during operation at temperatures above 100°C as well as during cold environments like during rain or during winter time the air volume provides a gas barrier.

Particularly the encapsulated air volume comprises a volume V of 0.01 1 �= V �= 1.0 1, particularly 0.05 1 �= V �= 0.8 1, preferably 0.1 1 �= V �= 0.6 1 and most preferred 0.2 1 �= V �= 0.4 1. One liter (1 1 = I dm3) or significantly less for the encapsulated air volume is sufficient to prevent an intrusion of water into power transmission units used for passenger cars.

Most preferred the inlet of the breather duct is positioned geodetically lower than the breather opening.

Due to this arrangement liquid can not intrude the casing via the breather opening by means of gravity. Even when the casing is put under water a rising water pressure would compress the air volume inside the breather duct but the gas barrier is still operable. A bypassing liquid is still prevented. Further mainly the whole volume of the breather duct may provide the encapsulated air volume.

Particularly the breather duct comprises an air tank for encapsulating a major part of the air volume and for receiving intruding liquid. Due to the air tank a high encapsulated air volume can be provided. Further it is possible to adjust the air volume to a specific casing design and/or a specific power transmission unit design.

Particularly the air tank is replaceable by another air tank of a different volume.

Preferably the casing comprises a plurality of casting rips forming at least one casting cavity, wherein the at least one casting cavity communicates with the breathing opening and the inlet for providing the breathing duct, whereby the at least one casting cavity is closed by a cover for encapsulating the air volume.

Particularly when the casing is manufactured by casting the casting rips and the casting cavities have to be provided anyway due to the casting process. By using the present casting cavitiesfor encapsulating the air volume it is not necessary to provide additional components, which would increase the building space.

io Particularly a plurality of casting cavities are provided, wherein two neighboring casting cavities are communicating with each other by means of a communicating opening provided in a casting rip between the two neighboring casting cavities. Due to the communicating openings several casting cavities could by added to form the breathing duct and to provide the encapsulated air volume. The communicating openings could be provided curing casting by using appropriate casting forms and/or by drilling, milling or the like after the casting process.

Most preferred the communicating opening is positioned at a mainly geodetically lowest position of the casting rip between the two neighboring casting cavities. When one casting cavity is at least partially filled with a liquid, the liquid can escape the casting cavity via the low positioned communicating opening. This means, when the pressure inside the casing increases, an intruded liquid may be mainly completely depleted.

Particularly the intruded liquid may escape by its own weight by means of gravity.

Preferably several casting cavities are closed by the same cover. Particularly every casting cavity, which is part of the breathing duct, can be closed by only one cover. Additional covers are not necessary.

In a preferred embodiment the interior of the casing is connected to at least one, particularly only one, casting cavity via a channel provided by the casing, particularly by boring or milling. For example it is possible to drill a bore starting in a casting cavity, which is part of the breathing duct, and ending in the interior of the casing, wherein the breathing opening is provided at the end of the bore on the side of the interior of the casing. A difficult design for providing the channel is not necessary.

Particularly the breather opening is provided geodetically above an oil level in the interior of the casing. Due to the comparatively high position of the breather opening it is prevented that oil, particularly transmission oil, escapes from the interior of the casing. An oil loss via the breather opening is prevented.

In a further embodiment the air volume is filled with an inert and/or sterile gas, particularly N2 and/or C02. The gas filled in the air volume is particularly mainly free of 02. Due to the inert and/or sterile gas an aging of the oil inside the casing may be prevented, since oxidation processes may be prevented and/or significantly slow down.

The invention further relates to a power transmission unit, particularly a gear box or a differential gear, for a motor vehicle, comprising a casing, which may be designed as previously described.

The power transmission unit comprises a gear assembly arranged inside the casing and transmission oil for lubricating the gear assembly. Due to the encapsulated air volume it is safeguarded that only the air volume communicates with the interior of the casing but not other substances. Since it is assured that only the transmission oil comes into contact with the components of the power transmission unit a high life time and a low wear is provided.

The invention further relates to a motor vehicle, particularly amphibian vehicle, comprising a power transmission unit, which may be designed as previously described. Due to the encapsulated air volume it is safeguarded that only the air volume communicates with the interior of the casingbut not other substances.

Since it is assured that only the transmission oil comes into contact with the components of the power transmission unit a high life time and a low wear is provided. Since an intrusion of water into the power transmission unit is prevented, the motor vehicle may be used as amphibian vehicle.

These and other aspects of the invention will be apparent from and elucidated with reference to preferred embodiments described hereinafter.

In the drawings: Fig. 1 is a schematic perspective view of a power transmission unit in a first embodiment, Fig. 2 is a schematic perspective partially exploded view of a power transmission unit in a second embodiment and Fig. 3 is a schematic perspective partially exploded sectional view of the power transmission unit illustrated in Fig. 2.

The power transmission unit 10 illustrated in Fig. 1 comprises a casing 12 with a breathing opening 14. The breathing opening 14 is provided at a mainly high position of the casing 12. The breathing opening 14 communicates with the interior of the casing 12. A breathing duct 16 is connected to the breathing opening 14. The breathing duct 16 comprises an air tank 18, which provides a specific volume. Below the air tank 18 the breathing duct 16 comprises an inlet 20. The level of the inlet 20 is significantly lower than the level of the breathing opening 14, so that air can be encapsulated in the duct 16 between the breathing opening 14 and the inlet 20 without the need of vents or closed doors.

As can be derived from Fig. 2, the casing 12 comprises a plurality of casting rips 22, which forms casting cavities 24. The casting cavities 24 may be closed by one cover 26. Neighboring casting cavities 24 may communicate with each other via communicating openings 28 provided in the casting rip 22 between the neighboring casting cavities 24. By means of the communicating casting cavities 24 the breathing duct 16 may be formed.

For connecting the communicating casting cavities 24 with the breathing opening 14 a channel 30 is provided, which communicates with one of the communicating casting cavities 24 and via the breathing opening 14 with the interior of the casing 12 (Fig. 3). In the illustrated embodiment the channel 30 is provided by a bore 32 starting at the casting cavity 24, wherein the bore 32 ends in a pocket 34 provided by the casing 12 during the casting process. The pocket 34 communicates with the interior of the casing 12 via the breathing opening 14.

R e f e r e n c e S g n s power transmission unit 12 casing 14 breathing opening 16 breathing duct 18 air tank inlet 22 casting rib 24 casting cavity 26 cover 28 communicating opening channel 32 bore 34 pocket