GB2051952A - Ventilating I.C. Engine Crankcases - Google Patents

Abstract

The crankcase emissions are returned to the engine air intake, preferably downstream of the air filter, via a control valve responsive to the crankcase pressure and set to open within a few inches of water pressure of atmospheric so that the crankcase pressure is maintained within a predetermined small range irrespective of engine speed, load or engine condition. <IMAGE>

Description

SPECIFICATION Crankcase Breathing Arrangements for Internal Combustion Engines This invention relates to crankcase breathing arrangements for internal combustion engines and particularly, but not exclusively, to such arrangements for diesel engines. It is known that in such engines there is an emission of oil fumes and vapour from the crankcase which in some cases can be allowed to breathe into the engine compartment. This is not always permissible however, and where this is the case it is known to take the crankcase emission directly back to the air induction port to be burnt in the engine. In the case of a turbocharged or supercharged engine it is known to take the emission directly back between the air filtration system and the turbocharger or supercharger inlet.Taking the emission back to the outlet of the air filtration system in this way has the disadvantage of not controlling the pressure or depression in the crankcase within acceptable limits for all conditions of such engine operation.

It is also known to take the emission to the air inlet side of the air filtration system but this has the disadvantage of prematurely blocking up the air filtration system to the detriment of the engine.

It is an object of the invention to provide a crankcase breathing system whereby emissions can be safely fed to the air filtration system outlet without suffering the above disadvantage regarding pressure variation.

According to the present invention, in an internal combustion engine the crankcase is vented to the combustion air intake path by means of a pressure-relief control valve operable at a predetermined crankcase pressure threshold.

The control valve is preferably connected to the air intake path on the downstream side of air filtration means. The control valve may be operable by crankcase pressure against a diaphragm, the back pressure on the diaphragm being atmospheric. The diaphragm is preferably subject to a mechanical bias to determine said pressure threshold, in the form of a compression spring or a tension spring engaging the diaphragm to set the threshold pressure within a small range around atmospheric pressure.

According to another aspect of the invention, a crankcase breathing arrangement for an internal combustion engine comprises an oil/vapour separator adapted for connection to the engine crankcase, an air intake path including air filtration means and a pressure-relief control valve providing a pathsfrom the outlet of the separator to the air intake path downstream of the air filtration means, the control valve being opened by pressure in the separator above a threshold value, and operation of the control valve causing the separator to be exposed to the pressure of the air intake path.

According to a further aspect of the invention, in a method of removing emission products from the crankcase of an internal combustion engine, the crankcase is vented to the air intake path of the engine by way of a pressure relief control valve which operates at a predetermined crankcase pressure threshold.

One embodiment of a crankcase breathing arrangement for an internal combustion engine in accordance with the invention will now be described, by way of an example, and to help understanding, reference is made to the accompanying drawing which is a diagrammatic section view of part of a diesel engine block, air filtration system and intake manifold for natural aspiration.

Referring to the drawing, the basic engine is shown in chain dotted outline i.e. the engine block and crankcase 1, cylinder head 2, and oil sump 3.

The engine is assumed to be naturally aspirated andphe air intake path comprises an air inlet manifold 4, and an air filtration system 5 connected by a pipe 6.

An oil/vapour separator 7 returnd oil droplets to the crankcase and passes the crankcase vapour emissions to the control valve 8 (shown enclosed by broken line and to a larger scale than the engine for clarity).

An inlet 11 to the control valve 8 opens into a chamber 12 on one side of a valve seating 13 and has a branch passage 14 connecting with one side of a diaphragm 1 5.

The diaphragm is mounted in the lower part 1 7 of the valve body 1 6 so closing off a chamber 1 8 except to the passage 14. The upper side of the diaphragm 15 is exposed to atmosphere by way of a hole 23. Attached to the diaphragm is the base of a valve stem 24 which protrudes freely up through a central portion 25 of the valve body into the chamber 1 2. The valve stem is sealed to the portion 25 of the body 16 by a flexible bellows 26 which effectively isolates the upper side of the diaphragm from the working-medium regions of the valve (apart of course from the effect of the vent hole 23).

The chamber 12 is separated from a low pressure output chamber 27 of the valve by the valve seating 1 3 and valve head 28, the latter being mounted on the valve stem 24.

A mechanical bias is imposed on the diaphragm by a spring 31 which couples the base of the valve stem 24 to an adjustable mount 33.

This spring may be a tension spring so increasing the pressure threshold in the chamber 1 8 (and thus in the oil/vapour separator 7 and crankcase 1) at which the diaphragm will rise to open the valve and relieve the crankcase pressure.

Altenatively the spring 31 may be a compression spring so assisting the valve opening and lowering the pressure threshold to a value below atmospheric.

The same spring may, of course, be used for both functions by suitable adjustment of the mount 33.

The upper part 35 of the valve body has an outlet passage 36 connecting the chamber 27 to a pipe 37 which vents into the air intake path in a pipe 6 between the air filtration system 5 and the inlet manifold 4.

In operation of the arrangement where it is required to maintain a slight pressure above atmospheric in the crankcase, the spring 31 is adjustable in tension and is overcome at a predetermined crankcase pressure, caused by emissions of vapour, acting on the underside area of diaphragm 1 5. In turn through valve stem 24, valve head 28 is lifted to connect the chamber 1 2 with the chamber 27. As a slight depression below atmospheric always exists in the pipe 6 due to the pressure drop across the air filtration system, the chambers 27 and 12 are subjected to reduced pressure such as to tend to evacuate the separator 7.

As the diaphragm 1 5 is also subjected to reduced pressure now via the passage 14, the valve head moves towards the valve seat 13 under its own weight, that of the valve stem 24 and diaphragm 1 5, and also under the influence of the tension spring 31. In so doing, the valve 28 is closed so isolating chambers 1 2 and 27 from each other. It will not now re-open until pressure builds up in the crankcase and separator to the predetermined threshold value.

To prevent the crankcase pressure and air filtration system depression generated at 6 and in passage 27 acting on the upper (value) side of the diaphragm an efficient seal 26 is fitted, as mentioned above, between the valve stem 24 and the body 25 of the valve. This is shown as a bellows seal but could be a sliding '0' ring type of seal.

It is seen that the seal 26 is subjected to only crankcase pressure/depression, this arrangement being more satisfactory than it being subjected to the higher depressions from the pipe 6.

By replacing tension spring 31 with a compression spring, a slight depression may be maintained instead of a slight pressure above atmospheric. The valve 28 will close when a set depression exists in the crankcase. When the emission pressure builds up within the crankcase the valve 28 will open as before and again the depression existing in the pipe 6 will tend to evacuate the crankcase until the vacuum acting on the underside of diaphragm 1 5 closes the valve 28.

The arrangement is such that a small pressure or depression either side of atmospheric pressure and within a range of several inches of water gauge is maintained in the engine crankcase independent of air filtration blockage to the engine manufacturer's limits or of excessive emissions through wear. The arrangement also has the significant merit of maintaining the crankcase pressure within the threshold value irrespective of changes in load and/or speed, or engine condition.

The same arrangement of pressure relief valve could be course be used when venting the crankcase to the input side of the air filtration system but, while the desired crankcase pressure would be achieved the auxiliary disadvantage of a prematurely blocked filter would still obtain.

For a turbocharged or supercharged engine, the principle is exactly the same except that the emission inlet pipe is incorporated between the air filtration system and the compressor air inlet instead of the air manifold.

Claims (10)

Claims

1. An internal combustion engine wherein the crankcase is vented to the combustion air intake path by means of a pressure-relief control valve operable at a predetermined crankcase pressure threshold.

2. An internal combustion engine according to Claim 1, wherein said control valve is connected to the air intake path on the downstream side of air filtration means.

3. An internal combustion engine according to Claim 2, wherein said control valve is operable by crankcase pressure against a diaphragm, the back pressure on the diaphragm being atmospheric.

4. An internal combustion engine according to Claim 3 wherein said diaphragm is subject to a mechanical bias to determine said pressure threshold.

5. An internal combustion engine according to Claim 4 wherein said mechanical bias is provided by a compression spring or a tension spring engaging the diaphragm to set the threshold pressure within a small range around atmospheric pressure.

6. A naturally aspirated multi-cylinder engine in accordance with any of Claims 2 to 5, wherein said control valve is vented to a pipe connecting said air filtration means to the inlet manifold.

7. A turbocharged or supercharged engine in accordance with any of Claims 2 to 5, wherein said control valve is connected to the air intake path between the air filtration means and the aspirated air inlet of the turbocharger or supercharger.

8. A crankcase breathing arrangement for an internal combustion engine and comprising an oil/vapour separator adapted for connection to the engine crankcase, an air intake path including air filtration means and a pressure-relief control valve providing a path from theoutlet of the separator to said air intake path downstream of said air filtration means, the control valve being opened by pressure in said separator above a threshold value, operation of the control valve causing said separator to be exposed to the pressure of said air intake path.

9. A method of removing emission products from the crankcase of an internal combustion engine wherein the crankcase is vented to the air intake path of the engine by way of a pressure relief control valve which operates at a predetermined crankcase pressure threshold.

10. A crankcase breathing arrangement substantially as hereinbefore described, with reference to the accompanying drawing.