Patent Application
20140208892
This invention relates to breather systems for internal combustion (IC) engines.
Inside an engine internal pressure is produced within the crankcase. This pressure is generally caused by a small leakage of combustion gasses past the piston rings, which is known as blow-by. If this pressure is not released, the subsequent build up can cause gaskets and seals to fail, creating engine oil leaks.
Breather systems to alleviate this are commonplace in internal combustion engines and commonly include a labyrinth type passage way to separate oil from vented gas. As there is typically oil present within the internal structures of IC engines and their associated gearboxes etc, it is common for oil droplets to become entrained into the breather gas. The labyrinth passageways, which comprise a plurality of bends, separates oil droplets that are entrained within the air flow and prevents them from being drawn back into the combustion chambers of the engine as part of the positive crankcase ventilation system. If lubricant oil from the crankcase housing were to be drawn back into the combustion chambers(s) this would have a negative effect and is therefore undesirable.
Currently the labyrinth passageways are located in a number of different places dependant upon the design, but may be in the cam cover, crankcase, clutch chamber, airbox, or other location, The inlet into the labyrinth may be at a remote location so as to draw in the blow-by gasses.
Although the existing labyrinth passageways enable separation of oil entrained in the gasses there remains space for improvement of existing solutions.
The object of the present invention is a breather system for an IC engine, and a gearbox incorporating that breather system, that is simple in structure, requires only a minimal change, if any, of the number of parts, and which reduces the speed of gasses at the inlet to the breather system.
According to one aspect of the invention a breather system for an internal combustion engine is provided. The breather system includes a gearbox having a gearbox housing forming a gearbox cavity. The gearbox cavity having a selector drum therein, movement of which mechanically moves gears within the gearbox so as to shift from one gear to another gear. The selector drum has an elongate hollow structure having an outlet opening at or adjacent a first end, and at least one inlet hole provided in a sidewall thereof within the gearbox cavity. In this manner a breather flow path is provided which extends from the at least one inlet to said outlet opening.
According to another aspect of the invention there is provided a gearbox for an internal combustion engine powered motor vehicle. The gearbox includes a gearbox housing forming a gearbox cavity. Arranged within the gearbox cavity are a plurality of gears and a selector drum. The selector drum has an elongate hollow structure with an outlet opening at or adjacent a first end thereof, and at least one inlet hole provided therein, within the gearbox cavity. In this manner a breather flow path is defined internally of said selector drum extending between said at least one inlet and said outlet opening.
According to a further aspect of the invention there is provided a motor vehicle. The vehicle includes an internal combustion engine, a gearbox having a gearbox housing forming a gearbox cavity, a selector drum within the gearbox cavity, and a breather flow path. The selector drum has an elongate hollow structure which has an outlet opening at or adjacent a first end thereof and at least one inlet hole provided in a sidewall thereof within the gearbox cavity such that the breather flow path extends inside the selector drum from the at least one inlet to the outlet opening.
In all the aspects of the invention a plurality of inlet holes may be provided along the length of the selector drum. Providing plurality of inlet holes decreases the inlet velocity at any one of said holes for any particular airflow, thus reducing the amount of oil that is entrained within the blow-by gases entering the breather flow path.
A preferred embodiment is described below, by way of example only, with reference to the accompanying drawings in which:
With initial reference to
With reference to
As described above the gearbox and crankcase are an integral component and the gearbox cavity is in fluid communication with the crank side of the pistons of the IC engine. In this manner, when the engine is running, blow-by gasses, which escape the piston from the engine piston chamber of the engine 4 to the crankcase housing 12, can pass into the gearbox cavity 20. Although the gearbox 8 is described herein as integral with the crankcase in the described embodiment, it will be appreciated that the crankcase and the gearbox may be separate components, for example separate castings, that are assembled together in a manner such that there is fluid communication between them, and such arrangements are within the scope of the invention.
Within the gearbox cavity 20 are provided a plurality of gears 22 which can be moved into and out of engagement to control the gear ratio. In order to move the gears 20 within the gearbox cavity there are provided shifter plates 26 which are slideably movable of a guide rod 28. Movement of the shifter plates 26 in a sideways direction (
The selector drum 30 has a plurality of surface features in the form of cam tracks 32 disposed on and extending radially from its outer surface. The cam tracks 32 engage with the shifter plates 26 such that as the shifter drum 30 rotates about its longitudinal axis the cam tracks move the shifter plates 26 on the guide rod 28 to change gear.
The selector drum 30 has a selector drum drive 34 attached to one end thereof by which drive 34 the selector drum may be rotated. The drive may be driven by a mechanical or electro-mechanical mechanism as known in the art.
The selector drum 30 has an elongate hollow structure which is open at a first end and closed at a second end 38. As can be seen the second end is closed by a bolt 40 which forms part of the selector drum drive 34, attaching it to the selector drum 30. A plurality of openings 42 are provided in the side walls of the selector drum 30 and are positioned between the cam tacks 32. The selector drum 30 thereby defines a breather flow path for blow-by gasses within the gearbox cavity 20 such that the gasses can enter the selector drum 30 via inlet openings 42, and exit the selector drum 30 via an outlet opening 44 in the first end.
As can be seen in
Referring now to
An oil drain 70 is provided in the second labyrinth chamber 58 from which separated oil can drain back to an oil sump of the engine.
As will be understood the structure described above provides an alternative to current designs for a breather system for an IC engine which vents blow-by gasses from the crankcase housing via a selector drum within the gearbox. The design vents gas directly from the gearbox and the design enables for a large surface area for the inlet to the breather passageway. This reduces inlet gas velocity which assists in reducing the amount of entrained oil within the blow-by gasses being vented.
Furthermore there is a benefit to having the entrance to the labyrinth passageway in the gearbox when the labyrinth is in the clutch cavity, as opposed to placing both in the clutch cavity. In the clutch cavity there is a greater tendency for the oil therein to produce an oil foam. If this gets drawn into the inlet to the labyrinth passageway the foam simply gets pumped through the breather system. The foam is created, for example, by such things as the oil being flung from the crank at high speed and from the oil pump drive chain and sprocket which is often positioned behind, and driven from, the clutch.
Although there is oil mist in the gearbox cavity there tends to be less aerated foam. These reasons do depend on engine architecture but are particularly common in motorcycle engines.
As will be appreciated from the above description the inlet openings in the selector drum are radial and the flow path through the selector drum is axial. This provides the advantage of causing a gas direction change immediately after the entry points. The gas enters the drum radially and then immediately has to change direction to travel axially along the drum. This assists in separating large oil droplets.
The increased benefits of enabling the selector drum itself, through virtue of its low gas entry speed and initial 90 degree turns can assist in enabling a reduced labyrinth volume which therefore provides a space and packaging advantage.
The above description is presented for exemplary purposes only. This description is not meant to limit the scope of protection insofar as it is understood that certain departures may be taken form the above-described embodiment without departing from the overall spirit and scope of the invention.
