APPARATUS FOR VENTING A TRANSMISSION

Abstract: The invention relates to a device for the ventilation of a transmission case (11). This is normally intended to hold liquid lubricant for transmission components, a residual volume of air in the transmission case being connected to the atmospheric pressure by way of a passage. With the aim of reducing the quantity of dirt particles than can get into the transmission case by way of the said passage, the latter comprises a first section (27) with a certain flow area and a second section (26) with, by comparison, an at least approximately 50 % larger flow area. The first section (27) is situated between the atmosphere and the second section (26). A compressed air source (18) is connected to the passage between the internal volume of the transmission case (11) and the first section (27).

Description: TITLE Apparatus for venting a transmission TECHNICAL SPHERE The present invention relates to a device for the ventilation of a transmission case, which is intended to hold liquid lubricant for transmission components, a residual volume - of air in the transmission case being connected to the atmospheric pressure by way of a passage. PRIOR ART In addition to transmission parts a transmission case, such as a gearbox, also contains space for lubricating oil and air. The volume of air changes when the temperature of the transmission parts, the oil or the air rises or falls. Temperature variations from approximately -40 °C to approximately 120 °C can occur. A connection between the volume of air inside the transmission case and the outer atmosphere is required in order to equalize the pressure, so that neither excess pressure nor negative pressure is formed in the transmission case. The said pressures may be harmful to the seals of the case. A hole is generally bored in the upper part of the transmission case, the hole being provided with a nipple and a short length of hose, or a nipple with protective cover or filters, which are intended to prevent water or dirt getting into the transmission case. The exchange of air with the surroundings is referred to as breathing and may amount to approximately 10 litres in the case of a large truck. The said exchange of air is achieved primarily when air is drawn into the gearbox, as it cools after driving, or on starting and subsequent driving on a long, steep incline. It has emerged that contamination such as sand and salt can get into the gearbox through breathing and can cause damage to bearings, gears, friction surfaces and seals. Filters that can be used to trap particles may clog if maintenance routines are not followed, which can lead to dangerous pressure changes in the transmission case. A filter may furthermore be provided with an overflow valve, which runs the risk of sticking in the open position and letting in contamination. DESCRIPTION OF THE INVENTION The object of the invention is therefore to produce a ventilation device which is maintenance-free and which effectively reduces the amount of dirt that might reach the inside of the transmission case. With this object in view, the device according to the pre-characterizing clause of Claim is 1 characterized in that the passage comprises a first section with a certain flow area and a second section with, by comparison, an at last approximately 50% larger flow area, the first section being situated between the atmosphere and the second section, and that a compressed air source is connected to the passage between the transmission case and the first section. This design according to the invention provides a simple and effective particle trap, which can be automatically blown clean of dirt particles. Advantageous exemplary embodiments of the invention are set out in the following subordinate claims. BRIEF DESCRIPTION OF FIGURES The invention will be described in more detail below with reference to an exemplary embodiment, which is shown in the drawing attached, in which Fig. 1 is a schematic diagram, which in a side view shows a transmission case with a ventilation device according to the invention, and Fig. 2 shows, on a larger scale, a section through the ventilation device shown in Figure 1. DESCRIPTION OF EXEMPLARY EMBODIMENTS The gearbox 10 shown in Figure 1 comprises a transmission case 11 having, among other things, an output shaft 12, and is provided in a known manner with bearings, shafts, gears, synchromesh elements and operating elements for shifting between various working positions, which are not shown. The inside of the transmission case is filled to a certain level 13 with oil and in addition accommodates a residual volume of air, which is connected to the surrounding atmosphere by way of a hose nipple 14 and a ventilation device 16, connected thereto by way of a flexible hose 15. The said device is in turn connected by way of a branch line 17 to a ventilation port 18 of an air cylinder and also has a combined inlet/outlet opening 19. As will be seen from Figure 2, the ventilation device 16 comprises a cylindrical casing part 20 with a connection 21 aligned transversely to the longitudinal axis and an axial connection 22, which is supported by a transverse centre wall 23. The connection 21 opens out into the casing part on one side of the said centre wall 23, which is provided with hole openings 24. The end of the casing part situated nearest to the connections is closed by means of an expansion-fit plug 25, which is provided with a central opening, which forms a bushing and seal against the connection 22. The opposite end of the casing part 20 accommodates a bottle-shaped end-piece 26 with a tapered neck opening 27 remote from the casing part. Both connections 21, 22 are provided with, conical ridging for securing the hose sections 15, 17. The ventilation device functions as follows: Dirt particles that get into the ventilation device by way of the neck opening 27 have a certain air velocity. Having passed through the neck opening 27, the said particles reach the space 28 formed by the casing part 20 and the end-piece 26, which space has a significantly larger flow area (an approximately 3 times larger flow area in the example shown) , which results in a significant reduction in the air velocity. This means that most particles that get into the space 28 loose their capacity for movement and therefore remain in the space. Particles collected in the said space 28 in the manner described above are not significantly affected by this flow. The space 28 is, however, periodically cleaned by a pressure surge each time the ventilation port 18, which is connected to the connection 21, is activated. This pressure surge may be triggered, for example, each time a pneumatically controlled gear is operated. The frequency of this operation naturally varies depending on how the vehicle is used, and how many air cylinders there are for changing. Pressure surges can normally be expected with a frequency between approximately twice every 10 km to approximately 20 times every 10 km. The connection 21 opens into a space 29 on the opposite side of the centre wall 23 to the space 28, the air flowing through openings 24 into the said space towards the hole opening 27. Consequently the air is forced away from the internal passage of the connection 22. A normal pressure surge can result in an air flow with a speed of approximately 15 metres per second. The ventilation device described above can be applied easily and cost-effectively to existing transmission cases. It is also possible to incorporate the ventilation device directly into the transmission case in new design constructions, it being feasible to form the passages from moulded wall sections, which are outwardly sealed by means of a cover. The invention must not be regarded as being confined to the exemplary embodiments described above, a number of other variants and modifications being conceivable within the scope of the following claims.

Claims: C13079, KS, 01-03-20 CLAIMS 1. A device for the ventilation of a transmission case (11), which is intended to hold liquid lubricant for transmission components, a residual volume of air in the transmission case being connected to the atmospheric pressure by way of a passage, characterized in that the passage comprises a first section (27) with a certain flow area and a second section (26) with, by comparison, an at least approximately 50% larger flow area, the first section (27) being situated between the atmosphere and the second section (26) , and that a compressed air source (18) is connected to the passage between the internal volume of the transmission case (11) and the first section (27) . 2. The device according to Claim 1, characterized in that the passage comprises a third section (15;20), which extends between the internal volume of the transmission case (11) and the second section (26) . 3. The device according to Claim 2, characterized in that the third passage section (15,-20) comprises a connection (21) leading to the compressed air source (18) . 4. The device according to Claim 3, characterized in that the connection (21) opens into the second passage section (26) and is directed towards the first passage section (27 ) . 5. The device according to any of Claims 1 to 4, characterized in that the second section (26) of the passage is designed as a cylindrical chamber with a largely vertical longitudinal axis. 6. The device according to any of Claims 1 to 5, characterized in that the compressed air source consists of a ventilation port (18) from an air cylinder. 7. The device according to Claim 6, characterized in that the air cylinder is intended to be used for the operation of transmission components in the transmission case (10) . 8. The device according to any of Claims 2 to 7, characterized in that the third passage section (15; 20) is designed so that it presents a greater flow resistance than the first passage section (27) .

Inventors: JOHANNESSON STIG-ERIK, JOHANNESSON, STIG-ERIK
Applicants: JOHANNESSON STIG ERIK, VOLVO LASTVAGNAR AB, JOHANNESSON, STIG-ERIK
Application year: 2001
Main classification: F16H57
IPC codes: F16H57