Internal-combustion engines – Valve – Rotary
Reexamination Certificate
2000-03-20
2001-05-29
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Valve
Rotary
Reexamination Certificate
active
06237556
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to rotary valves for internal combustion engines. In particular, the present invention concerns sealing systems employed to minimise gas leakage problems present with rotary valve types having a cylindrical valve rotor which rotates with a predetermined radial clearance within a receiving bore of the engine.
BACKGROUND OF THE INVENTION
Different types of rotary valves for internal combustion engines have been known since the early days of conception of such engines as an alternative to poppet type valves to selectively and periodically enable and prevent flow of intake fluids and exhaust gases through a transfer port leading to a combustion chamber of the engine.
The potential advantages which use of rotary valves can provide as compared to conventional poppet type valves are well documented and include improved smoothness of operation, rapid and precise opening and closing of transfer ports, reduction or inhibition of intake-exhaust overlap and the larger port opening sizes that can be provided to achieve higher volumetric ratios of fluid transfer into/from the combustion chamber. The major drawback in their practical implementation is the hitherto unsatisfactorily resolved sealing problems.
In the following, rotary valves will be described in the context of their use with reciprocating type internal combustion engines. However, neither some of the known nor the rotary valve embodiments in accordance with the present invention are limited to such applications. They may find equal use with other type of engines, such as rotary piston engines (Wankel motor), in which combustion energy is transformed into mechanical power in an intermittent operating cycle of the engine. The operating cycle, as used herein, encompasses the induction of a working fluid (air, fuel) into, compression and subsequent ignition of the working fluid within, expansion of resultant combustion gases within and exhaustion of combustion gases from a combustion chamber of the engine. These are also referred to below as the operating phases or strokes (in the case of reciprocating type engines) of the engine.
One such rotary valve type broadly consists of a cylindrical shaped rotor body which is coaxially supported for rotation within a valve bore formed in the cylinder head of the engine. Gas exchange ports formed on the peripheral surface of the rotor body periodically align with an associated transfer port opening in the bore and which leads to a combustion chamber of the engine. Examples of such valves include valve rotors with radial gas flow only, in which one or more gas exchange ducts have diametrically opposing ports in an otherwise continuos peripheral surface (see eg U.S. Pat. No. 4,019,499), and valve rotors with “axial—radial gas flow” having two gas exchange ducts commencing on opposite axial side faces of the valve rotor and extending therethrough so as to respectively terminate in an intake and an exhaust port in the peripheral surface of the rotor body (see eg U.S. Pat. No. 5,052,349). Rotary valves can be equally employed for two and four stroke engines, specific layout of the gas transfer ducts and ports on the rotor being also dependant on the operating speeds of the rotor with respect to the crankshaft.
It is necessary to emphasise at the outset that the present invention is concerned with those types of rotary valve constructions in which the cylindrical rotor body is coaxially supported for rotation within the valve bore so as to maintain a relatively “small” radial clearance gap between the bore surface and the peripheral rotor body surface; “small” in this context is a 0.2 to 0.4 mm radial clearance gap which will ensure rotation of the rotor without risk of seizure within the bore and allows for manufacturing tolerances that are achievable without excessive costs.
Such rotary valves require a “seal system” arranged to define a frame around the transfer port which bridges and closes the radial gap so as to minimise gas leakage from the transfer port while the latter is to be maintained closed by the rotary valve, in particular during the ignition phase. This class of rotary valves is exemplified by the one disclosed in U.S. Pat. No. 4,852,532 (“the first Bishop patent”). The contents of this first Bishop patent is included herein by way of short hand cross reference, in particular in so far as it contains a succinct evaluation of some relevant prior rotary valve types and their relative drawbacks, see in particular column 3, line 56 to column 4, line 62.
In the rotary valve construction proposed in the first Bishop patent, a sleeve-like rotor has separate intake and exhaust ducts beginning in opposite axial side faces of the rotor body. The ducts respectively terminate in an inlet and exhaust port angularly spaced apart on the peripheral surface of the rotor body at the same axial location. The ports are dimensioned such that upon rotation of the valve rotor within the valve bore formed in the cylinder head of the engine, the inlet and exhaust ports periodically align with and pass over a single transfer port communicating the bore with the combustion chamber defined within the cylinder. The location and circumferential extension of the peripheral ports and herein between extending rotor surface zone, termed in Bishop “sealing zone”, are chosen and dimensioned such that given a properly timed rotor revolution speed with respect to the operating cycle of the engine, gas passage to/from the transfer port is enabled through the intake and exhaust ports of the rotor body and prevented while the “sealing surface” covers the transfer port. In other words, specific or “discrete” zones on the periphery of the rotor body (including those surface zones which contain the ports) are “associable” with a respective one of the phases of the operating cycle, eg the same “discrete surface zone” of the rotor body always passes over and covers the transfer port during the exhaust, intake and combined compression and expansion phases.
In the first Bishop patent is disclosed a system of so-called “floating seals” which consists of two longitudinal sealing elements, rectangular in cross-section, which are received in grooves extending parallel with respect to the axis of rotation of the rotor and formed on either circumferential side of the transfer port within the bore surface. This axially extending sealing elements are loaded against the peripheral surface of the rotor body portion which includes the gas exchange ports, thereby to bridge the radial gap and prevent gas flow from the transfer port past the seals in circumferential direction of the rotor body. Such seals will hereinafter also be referred to as “seal elements against circumferential flow”.
The seal elements against circumferential flow are abutted at either longitudinal end at a sealing ring respectively received within an annular groove formed on either axial side of the transfer port within the bore surface. The radially inward facing inner peripheral surface of the sealing rings sealingly rubs against the peripheral surface of the rotor body thereby to prevent gas flow from the transfer port past the sealing rings in axial direction of the rotor body. Such sealing rings will herein after also be referred to as “seal elements against axial flow”.
The main function of the “floating seal frame” disclosed in the first Bishop patent is to prevent leakage of high pressure combustion gases primarily created during and subsequent the ignition phase of the operating cycle of the engine into the radial gap volume outside the framed transfer port, and thereby into the gas exchange ports of the rotor body and the axially adjoining rotor zones at which the rotor is supported in roller bearings. The effectiveness of the sealing system depends on the ability of the sealing elements against circumferential and axial flow to maintain a “closed” frame in particular during the critical compression, ignition and expansion phases. With the “seal frame” of the first Bishop patent this is not possible.
Due t
Smith Brian
Smith Wayne
Ali Hyder
Bliss McGlynn P.C.
Kamen Noah P.
Rovasco Pty Ltd.
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