RECIPROCATING INTERNAL COMBUSTION ENGINES

Abstract: In a reciprocating internal combustion engine, which may be turbocharged or normally aspirated, the inlet manifold is connected by a duct 10 to a bypass 9 which in turn connects the crankcase 8 to a point upstream of the throttle. Non-return valves 11 and 12 are disposed in the duct 10 and bypass 9 respectively. An adjustable diaphragm valve 14, whose operation is controlled by the pressure in a pressure sensor line 15 leading to crankcase 8, is disposed in a bypass 13 to the valve 12. The arrangement operates to prevent crankcase overpressure under normal operating conditions of the engine.

Description: The present invention relates to a reciprocating internal combustion engine. In such engines under certain conditions pressure may build up in the crank case leading to leaks through the seals. This problem is more likely to occur in turbo charged engines although it may also happen in normally aspirated engines. According to the present invention, there is provided a receiprocating internal combustion engine comprising means for venting the engine crankcase to the air input to the engine, means for connecting the air input to the means for venting, valve means for controlling air flow through the means for venting and the means for connecting to maintain the pressure in the crankcase below a certain level. In a preferred embodiment of the invention as applied to a turbocharged engine, the air input leads to the engine via an air filter, a turbo compressor an air-meter, throttle and inlet manifold. The means for venting connects the crankcase of the engine to the air input to the engine just downstream of the air filter. The means for connecting comprises a duct connecting the air input at the inlet manifold to the means for venting. The valve means comprises a non-return valve in the connecting duct and a non-return valve in the means for venting. A further valve, advantageously a diaphragm valve, is disposed in a bypass around the non-return valve in the means for venting. This further valve is controlled by a sensor responsive to the pressure in the crankcase. When the pressure falls below a certain value the valve opens to permit air flow from the air input limiting crankcase depression. The non-return valves permit flow through the duct to the means for venting and through the means for venting when the pressure differentials are appropriate to that. In order that the invention may be more clearly understood, one emlodiment thereof will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 shows an air flow diagram of an existing turbo-charged internal combustion engine, Figure 2 shows an air-flow diagram of a turbo­ charged internal combustion engine in accordance with the invention, and Figures 3, 4 and 5 respectively illustrate air­ flow for the engine of Figure 2 under idle intermediate load and high load conditions. Referring to Figure 1, in the breather system and induction system of the existing turbo-charged internal combustion engine, air flows through an air filter 1, the turbo compressor 2, past an air meter 3 and throttle 4, through the inlet manifold 5 into the combustion chambers 6 (one cylinder only shown) of the engine. About 0.4% of this flow blows by the pistons 7, the remainder exiting the engine through the exhaust. The blow by gas flows into the crankcase 8 and this can lead to an unacceptable pressure build up in the crankcase under certain conditions despite the provision of the bypass 9 which connects crankcase 8 to the point between the air filter 1 and compressor 2. This build up may be prevented by the arrangement of Figure 2. For this purpose, the inlet manifold is connected to the bypass 9 by a duct 10 in which a non-return valve 11 is disposed. A further non-return valve 12 is disposed in the bypass 9 and this valve is bypassed by a bypass 13, the flow through which is controlled by an adjustable spring loaded diaphragm valve 14 whose operation is controlled by the pressure in a pressure sensor line 15 leading to the crankcase 8. A flame trap 20 is also incorporated in the bypass 9. The operation of the system will now be described with reference to Figures 3, 4 and 5. Figure 3 shows the system under engine idle conditions when exemplary pressure values are -0.5"H₂O just downstream of the air filter 1, and -19.5"Hg at the inlet manifold. This large depression at the inlet manifold, which is caused at engine start up, sucks gas out of the crankcase. When the crankcase pressure reaches -4"H₂O, valve 14 opens premitting filtered air flow through bypasses 9 and 13, and duct 10 into the inlet manifold. Valve 12 is closed and valve 11 opens at that time. This air flow, which is indicated by dashed arrows, maintains the crankcase vacuum to that set by the springloaded diaphragm valve 14. The double headed arrows indicate the blow by gas flow which flows past the piston 7 into the crankcase and thence out of the crankcase 8 via flametrap 20 bypass 9 and duct 10 into the inlet manifold 5. Figure 4 shows the system under intermediate load conditions. Exemplary pressures are -4"H₂0 just downstream of the air filter 1, -17"Hg at the inlet manifold 5 and -4"H₂0 in the crankcase. Valve 14 remains open, but valve 12 is unstable because the pressures on both sides are substantially equa. Some blowby gas flows to the inlet manifold via duct 11 and some flows to the point downstream of the air filter via valves 12 and 14. Figure 5 shows the system under high load conditions. Examplary pressures are -15"H₂0 just downstream of the air filter, +14"Hg just downstream of the throttle 4, and -10"H₂0 in the crankcase 8. The inlet manifold 5 is now under boost conditions, valve 11 is closed and blowby gas, again indicated by double headed arrows flows via valves 12 and 13. The above described arrangement therefore prevents overpressure arising in the crankcase 8 over the normal operating range of the engine. It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention. For example, the invention although described for a turbocharged engine wouid be equally applic­ able to a normally aspirated engine.

Claims: 1. A reciprocating internal combustion engine comprising means for venting the engine crankcase to the air input to the engine via an air filter, means for connecting the air input to the means for venting, valve means for controlling air flow through the means for venting and the means for connecting to maintain the pressure in the crankcase below a certain level. 2. A reciprocating internal combustion engine as claimed in claim 1, in which the air input leads to the engine via an air filter, a turbo compressor, an air-meter, throttle and inlet manifold. 3. A reciprocating internal combustion engine as claimed in claim 1 or 2, in which the means for venting connects the crankcase of the engine to the air input to the engine just downstream of the air filter. 4. A reciprocating internal combustion engine as claimed in claim 1,2 or 3, in which the means for connecting comprises a duct connecting the air input at the inlet manifold to the means for venting. 5. A reciprocating internal combustion engine as claimed any preceding claim, in which the valve means comprises a non-return valve in the means for connecting and a non return valve in the means for venting. 6. A reciprocating internal combustion engine as claimed in claim 4, in which a further valve is disposed in a bypass around the non-return valve in the means for venting. 7. A reciprocating internal combustion engine as claimed in claim 5 or 6, in which the further valve is a diaphragm valve. 8. A reciprocating internal combustion engine as claimed in claim 5 or 6, in which control means are provided for the further valve for controlling the valve in response to the pressure in the crankcase such that when the pressure falls below a certain value the valve opens to permit air flow from the air input thus limiting crankcase depression. 9. A reciprocating internal combustion engine as claimed in claim 5, 6 or 7, in which the control means comprises a sensor.

Inventors: HUMPHRIES, DAVID TREVOR
Applicants: ROLLS-ROYCE MOTOR CARS LIMITED
Application year: 1986
Main classification: F01M13
IPC codes: F01M13