Patent Application
20140140878
This application is a non-provisional application claiming priority from UK Application No. 1220888.0 filed on Nov. 21, 2012, incorporated herein by reference in its entirety.
The present description relates generally to rotary engines and more particularly to cooling systems for rotary engines.
In a number of applications rotary internal combustion engines (for example, the Wankel layout) provide an attractive alternative to the more commonly utilized reciprocating piston engine.
In a rotary engine a rotor is mounted eccentrically on an output shaft. The rotor is geared to the shaft such that rotation of the output shaft causes eccentric rotation of the rotor, and vice versa. For example, a Wankel engine uses a three-side (approximately triangular) rotor within an epitrochoidal chamber.
Cooling of a rotary engine can present challenges. Reciprocating piston engines are typically either air cooled through the crankcase, cylinder block and heads, or water cooled by water flow paths in the cylinder block. Oil supplied to the crank shaft also assists with cooling. Although a similar water cooling system can be implemented for a rotary engine, cooling of the output shaft and gearing linking that shaft to the rotor is inefficient as those components are far removed from the cooling medium.
Furthermore, the gears and bearings in the interior of the rotor must be lubricated, which makes circulating cooling media in that area difficult.
There is therefore a requirement for improved cooling systems for rotary engines.
The embodiments described below are not limited to implementations that solve any or all of the disadvantages of known publish/subscribe systems.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
There is provided a rotary internal combustion engine, comprising a closed-loop cooling system having a closed-loop fluid flow path through the interior of a rotor of the engine and a heat exchanger, and a fan configured to circulate a fluid around the flow path, wherein the fan is mounted on and driven directly by the engine's output shaft.
The fluid may be a gas.
The gas may be a gas which has blown-past the rotor's side-seals.
The fan may be a centrifugal fan.
The fan may have a diameter of 160 mm or greater.
The closed-loop cooling system may comprise a pressure-relief valve configure to limit the maximum pressure in the closed-loop fluid flow path.
The closed-loop cooling system may comprise an oil injector for injecting oil into gas flowing in the closed-loop fluid flow path for lubricating the interior of the rotor.
The closed-loop cooling system may comprise an oil injector for injecting oil into gas flowing in the closed-loop fluid flow path for lubricating the interior of the rotor.
There is also provided a rotary internal combustion engine, comprising an output shaft having an internal cooling chamber with a closed distal end within the output shaft, and an open proximal end at an end of the output shaft; a tube within the cooling chamber spaced from the internal wall of the cooling chamber and from the distal end of the cooling chamber, the tube and cooling chamber forming a cooling flow-path through the center of the tube, between the end of the tube and the distal end of the cooling chamber, and between the exterior surface of the tube and the interior surface of the cooling chamber; and an impeller for circulating water through the cooling flow-path.
The tube may be stationary with respect to the engine body.
The impeller may be mounted on the open end of the output shaft.
The exterior surface of the tube may be spaced from the interior surface of the cooling chamber by 2 mm or more.
The preferred features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the invention.
Embodiments of the invention will be described, by way of example, with reference to the following drawings, in which:
Common reference numerals are used throughout the figures to indicate similar features.
Embodiments of the present invention are described below by way of example only. These examples represent the best ways of putting the invention into practice that are currently known to the Applicant although they are not the only ways in which this could be achieved. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.
The cooling fluid flows from the heat exchanger 12 back to the rotor interior 10 to complete the closed circuit. The cooling circuit may be pressurized by gasses blowing past the rotor side seals and accordingly a pressure relief valve 13 may be provided to limit the pressure within the cooling circuit.
An oil injector 14 is provided to inject oil into the cooling fluid to lubricate the working parts in the interior of the rotor. Since the cooling circuit is a closed loop, the oil circulates continuously and is only lost via leakage at the side seals of the rotor into the combustion chamber. The oil creates a film over the side plates which is then burnt in the combustion process. Previous cooling systems have used a total loss lubrication system which is both expensive to run and environmentally unfriendly. The closed-loop arrangement mitigates these disadvantages. In an embodiment the oil injector is a high-pressure injector capable of injecting oil into the pressurized cooling system without utilizing a pressurized reservoir. As explained above, the cooling system may be pressurized to 1 bar. A low-pressure injector could be utilized by also pressurizing the reservoir.
Where a non-pressurized oil reservoir is utilized the vent of the pressure release valve may be fluidly connected to the oil reservoir such that air exiting through the pressure release valve passes through the oil reservoir on its path to atmosphere. Oil suspended in the released cooling gasses is collected in the oil reservoir before the gasses are vented to atmosphere. This arrangement allows recycling of the oil, thereby reducing oil use.
The rotor 21 is provided with at least one opening 22 such that a flow path is open from a first side to a second side of the rotor to allow the flow of fluids through the rotor 21 parallel with the output shaft 20. In an example, the at least one opening 22 may be semi-circular in shape with a 20 mm radius. Openings 23 are also defined in the first 25 and second 26 side plates such that fluids can enter the interior of the rotor 21, flow through the at least one opening 22 in the rotor 21, and exit through the other side plate. The side plate openings 23 are positioned within the path traced by the rotor side seals during rotation of the rotor 21 such that they do not disrupt the seal created by those seals. This leads to the ‘lemon’ shape of opening seen in the figures. In a typical example, the opening has dimensions of 95 mm and 65 mm on the long and short axis.
A centrifugal fan 27 is mounted on the output shaft 20 such that it is driven by and rotates with the output shaft 20. The opening 23 in the first side plate 26 forms a flow path from the rotor interior to the center, inlet, of the centrifugal fan 27. An annular outlet flow path 28 is defined at the exterior of the fan 27 to collect the output from the fan 27. As will be appreciated, the flow path 28 is shown as a continuous annulus in
The direct mounting of the fan 27 on the output shaft 20 removes a requirement for a geared or belt connection to drive the fan 27. This direct connection has improved mechanical efficiency, thereby improving engine power output. Due to the direct mounting of the fan 27 it rotates at the same speed as the output shaft 20 and cannot be geared to provide a higher speed and hence greater output. The limitation in fan speed, and associated reduction in output, has previously been thought to prevent direct mounting of the fan.
A fan capable of providing sufficient output when rotating at typical output shaft speeds has now been designed, thereby allowing this mounting. In an example embodiment, a suitable fan may be centrifugal fan, 160 mm in diameter with forwarding curving blades of 10 mm height. In further embodiments the fan diameter may be larger than 160 mm. In an example, the fan should be capable of providing an airflow with a dynamic pressure of 12″ water gauge (48 kPa).
As well as improved mechanical efficiency, the direct mounting of the fan also provides a reduced physical size and simpler construction.
An outlet port 29 in the fan output flow path provides for a fluid connection through a heat exchanger and back to the opening in the second side plate 25, thereby providing a closed flow path as described with reference to
As seen in
As noted above, a pressure relief valve is provided in the cooling circuit to prevent the pressure increasing above a predetermined level, for example 1 bar which is bled off back into the oil reservoir and re-cycled into the closed cooling/lubrication circuit. The output shaft main seals 31, 32 also form part of the cooling circuit wall and this pressure limitation protects those seals from damage.
In use, as the engine starts up the output shaft 20 drives the fan 27 which circulates cooling fluid around the closed circuit. Blow past the side seals 30 increases the pressure in the cooling system. As the pressure in the cooling circuit increases blow-past reduces due to the reduced pressure difference between the combustion chambers and the cooling circuit. The fan circulates the gasses around the cooling circuit. The temperature of the gasses reduces from the combustion temperature due to heat transfer through the heat exchanger, and the gasses then transport heat from the rotor interior to the heat exchanger, thereby cooling the engine.
The output shaft 60 is at least partially hollow comprising a longitudinal cooling chamber 61 extending along the axis of the output shaft 60 from a first end 62 to a second closed end 63.
A water impeller 64 is attached to the open end 62 of the output shaft 60 to turn with that output shaft 60. A water pump housing 65 encloses the water impeller 64 and the open end 62 of the output shaft 60. The output shaft 60 is sealed to the engine body by a seal 66 to create a sealed chamber 67. In an example embodiment the water impeller is 50 mm in diameter. As will be appreciated, the diameter of the impeller may be selected according to the required circulation of the cooling system.
A tube 68 extends through the water pump housing 65 and into the cooling chamber 61 within the output shaft 60. The tube 68 is sized such that it is spaced from the interior of wall of the output shaft 60 to allow cooling fluid to flow between the tube 68 and the output shaft 60. That space is in fluid communication with the inlet to the impeller 64. The tube 68 is attached and sealed to the water pump housing 65 and so remains stationary with respect to the engine body, and does not rotate with the output shaft 60.
In an example embodiment the inner diameter of the cooling chamber is 20 mm. In further embodiments the diameter may be greater than 20 mm. In an example, the inner diameter of the tube 68 is 13 mm and the outer diameter is 15 mm. These dimensions, when used with a 20 mm diameter cooling chamber, provided a flow path around the outside tube having a height of 2.5 mm and extending around the circumference of the tube. In alternative embodiments different dimensions may be utilized.
An inlet to the tube 68 is provided for connection to the output of the impeller 64 via a heat exchanger to form a closed cooling path. The closed cooling path is typically filled with water to act as a cooling medium, but as will be appreciated other coolant fluids may be utilized.
In use the impeller 64 is rotated by the output shaft 60 and pumps fluid around the cooling circuit through the heat exchanger, into the center of the tube 68, and back through the output shaft 60 to the impeller 64 inlet.
The cooling circuit described in relation to
The cooling chamber is shown extending to approximately the center of the eccentric bearing, but as will be appreciated the length of the chamber may be selected to provide the required thermodynamic performance.
Two cooling systems have been described hereinbefore for cooling rotary engines. The two systems may be utilized alone or in combination.
As will be appreciated a more than one rotor, and associated chamber and components, may be arranged along the length of the output shaft. In such engines suitable openings between the rotor interiors may be provided to guide coolant flow through the rotors. Similarly, the opening in the output shaft may extend along an appropriate length to provide cooling to the shaft in the region of more than one rotor.
Any range or device value given herein may be extended or altered without losing the effect sought, as will be apparent to the skilled person.
It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages.
Any reference to ‘an’ item refers to one or more of those items. The term ‘comprising’ is used herein to mean including the method blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.
It will be understood that the above description of a preferred embodiment is given by way of example only and that various modifications may be made by those skilled in the art. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1220888.0 | Nov 2012 | GB | national |
