Internal-combustion engines – Charge forming device – Supercharger
Patent
1995-10-13
1998-08-11
Koczo, Michael
Internal-combustion engines
Charge forming device
Supercharger
4182012, F02B 3336
Patent
active
057913153
DESCRIPTION:
BRIEF SUMMARY
This invention is in the field of superchargers, as commonly used in the automotive industry. It has a particular relevance to supercharging spark ignition engines using a screw type positive displacement compressor. The invention also finds application in screw expander and compressor machines in general.
Screw rotor positive-displacement machines for an elastic working fluid are well known both as compressors and expanders. In such machines there is a casing comprising two intersecting bores, each bore containing one of a pair of inter meshing rotors. The rotors differ in that one rotor is of a male form having convex lands, while the other rotor is of a female type having concave lands, both rotors incorporating intervening grooves.
It has been found that partial rotation of the rotors causes the voids formed by the surfaces of the grooves of the rotors and the casing to expand. This action sucks gas into the voids through an inlet port. However, further rotation of the rotors causes the voids formed by the surfaces of the rotor grooves and the inner surfaces of the casing bores to interconnect and to decrease in volume causing a compression of the gas contained therein. Thus, it can be seen that within a screw rotor positive displacement machine of this type it is possible to both expand and compress a working fluid. This is particularly achieved where the inlet port of the machine is closed prior to the voids formed by the grooves of the rotors and the inner surfaces of the casing having reached their maximum volume, such that, as the rotors continue to rotate and the voids consequently increase in volume, an expansion is effected of the working fluid trapped therein. Further rotation of the said rotors causes the voids to decrease in volume and the working fluid is compressed. The outlet part is positioned to open and allow the gas to discharge when the desired compression has been achieved.
Accordingly, with judicious choice of the inlet port closing position and outlet port opening position a screw rotor positive displacement machine of this type has the ability to act simultaneously as an expander and a compressor.
One application where this is of potential benefit is in the supercharging of engines. In spark ignition engines the amount of fuel and air drawn into the engine per induction stroke is required to be varied and regulated according to the power output required of the engine. This part load regulation has in the past been achieved by throttling the flow of air into the engine. Nevertheless, this is undesirable as throttling is a non-reversible process and as such is associated with power loss at the engine pistons during the induction stroke.
Effectively, at part load engine power requirements the supercharger is still working even though the supercharging effect is not required. The pressure at the supercharger discharge (the engine inlet-manifold pressure) is greater than the pressure at the supercharger inlet. This results in lower overall engine efficiency than could be achieved with a naturally aspirated engine because the engine has to provide the power to drive the supercharger. This problem is common to all types of mechanically driven positive displacement superchargers.
Accordingly, it is a primary object of the present invention to provide a supercharging system wherein this problem is obviated or mitigated.
More specifically, an object of the present invention is to increase the efficiency for part load engine operation by using the expansion ability of a screw supercharger to reduce the charge air density. This gives rise to some of the engine piston work associated with the induction stroke being recovered.
In order to achieve the above objective it is required to provide a suitable means for controlling the size of or flow through the inlet and outlet ports.
Inlet arrangements are disclosed in GB2233041 and GB2233042 permitting control area variation of the gas inlet port, such arrangements facilitating the machine operating selectively in a compressing mode or in an expan
REFERENCES:
patent: 2519913 (1950-08-01), Lysholm
McGruer John
Riach Alan Bryson
Koczo Michael
Sprintex Australasia Pty Ltd.
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