Patent Application
20050205019
The present invention relates to a switching mechanism and more particularly to a switching mechanism capable of switching between a two-stroke and a four-stroke operation of an engine as desired, wherein the switching mechanism is switchable between engagement with a first cam lobe for four-stroke operation and a second cam lobe for two-stroke operation.
Conventional internal combustion engines operate according to thermodynamic principles following either a two-stroke cycle or a four-stroke cycle which are commonly classified as a two-stroke engine or a four-stroke engine, respectively. Both types of engines can operate using a range of fuels including gasoline, diesel, alcohol and gaseous fuels. The fuel is typically introduced into the engine using a range of devices including carburetors and fuel injectors, for example. The fuel-air mixture can be ignited by a range of methods including spark ignition and compression ignition. Each engine cycle type has different merits and shortcomings with varying power density, fuel consumption, exhaust emissions, noise, vibration, engine size, weight, cost, etc.
For ordinary driving conditions, a typical vehicle is powered by an engine that is sized for the maximum performance requirement of the vehicle. For example, a passenger vehicle passing another vehicle on a hill may for a brief period utilize the maximum power of the engine. At virtually all other times, from low speed city driving to highway cruising, the power demand is a fraction of the available power. Over-dimensioned engines with large displacements are therefore constructed to meet only occasional power demands.
The situation for large displacement working vehicles is even more dramatic. Freight hauling tractor-trailers, delivery trucks, and other vehicles are designed with engines to accommodate full loads. When traveling empty, the power requirement is substantially diminished. Similarly, marine engines often must shift from high speed or power operation to low speed where the engine operates in idle for long periods of time. Unused displacement or over displacement results in over-sized, large engines with a multiplicity of cylinders, having a weight and complexity resulting in an unnecessary consumption of fuel and excess pollution.
Existing internal combustion engines are usually limited in their operation to two-stroke or four-stroke cycles. The engines have a fixed fuel distribution system, optimized for a limited range of operation. With fixed compression ratios and limited means of optimizing performance for all ranges of power, torque, and engine speed, fuel consumption is typically characterized by a specific fuel consumption curve with one point of minimum fuel consumption.
Although certain improvements to engine design have addressed these problems, for example, the use of a turbocharger for high performance operation, satisfaction of power demand is at the expense of optimized fuel consumption.
Existing internal combustion engines have used switchable cam followers to actuate valves from multiple cam profiles to provide for variations in valve lash between one cam profile to the next. In a conventional system where a rocker arm or a cam follower operate with only a single cam profile, common practice is the use of a hydraulic valve adjuster that is pressurized by lubrication oil and held in a filled position using an internal check valve. These hydraulic valve adjusters have been placed in the block, in the head or in the rocker arm or cam follower itself and are very universal in their application. It is, however, inadequate in valve trains where multiple cam profiles actuate the valves through the use of rocker arms or cam followers that by some means switch from one profile to another.
It would be desirable produce a switching mechanism for switching an engine from two-stroke to four-stroke operation wherein fuel efficiency, emissions efficiency, and power are maximized.
Consistent and consonant with the present invention, a switching mechanism for switching an engine from two-stroke to four-stroke operation wherein fuel efficiency, emissions efficiency, and power are maximized, has surprisingly been discovered.
The switching mechanism for switching an engine from one stroke type to another stroke type comprises:
The above, as well as other objects, features, and advantages of the present invention will be understood from the detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings, in which:
Referring now to
As clearly illustrated in
In operation, the engine is typically operated in a standard mode, one of the four-stroke and the two-stroke mode. For illustrative purposes, standard operation will be considered four-stroke operation. Operation of the valve 12 is controlled by the rocker assembly 18. As the cam shaft 36 rotates, a lobe 33 of the four-stroke cam surface 32 is caused to rotate through 360 degrees. As the lobe 33 of the four-stroke cam surface 32 passes under the follower roller 28, the rocker assembly 18 is caused to pivot about the rocker shaft 22. Thus, the distal end of the rocker arm 16 is caused to move downwardly causing the valve 12 to open. As the lobe 33 of the four-stroke cam surface 32 moves beyond the follower roller 28, the rocker arm 16 is caused to move upwardly and the valve 12 is caused to close. Operation of the valve 12 by the lobes 35 of the two-stroke cam surface 34 is the same as that described for the lobe 33 of the four-stroke cam surface 32.
The engine, which has a combustion system suitable for both two-stroke and four-stroke operation, can be changed from one operating mode to another by changing from the operation of the valve 12 from once per revolution of the cam shaft 36 or crank to twice per revolution of the cam shaft 36. This is accomplished by switching the engine valve 12 from following the four-stroke cam surface 32 to following the two-stroke cam surface 34. The first locking pin 42 operates to lock and engage the follower arm 24 for four-stroke mode. The second locking pin 44 operates to lock and engage the follower arm 26 for two-stroke mode. The third pin 43 ensures proper alignment of the first locking pin 42 to engage the follower arm 24 for the four-stoke mode. The fourth pin 45 ensures proper alignment of the second locking pin 44 to engage the follower arm 26 for the two-stroke mode. In the embodiment shown, when one of the first locking pin 42 and the second locking pin 44 is engaged with the respective follower arm 24, 26, the other of the first locking pin 42 and the second locking pin 44 is disengaged from the respective follower arm 24, 26.
Engagement and disengagement of the first locking pin 42 and the second locking pin 44 is accomplished by a hydraulic pressure applied which is controlled by a solenoid valve based on a signal from an engine management system. A pressure fluid such as engine oil, for example, is supplied to the hollow portion of the rocker shaft 22. The pressure fluid enters the radial bore 38 and the pressure fluid chamber 40 and urges the first locking pin 42 and the third pin 43 to move against the force of the first return spring 46 and the second locking pin 44 and the fourth pin 45 to move against the force of the second return spring 48. In the embodiment shown, when it is desired to operate in the four-stroke mode, the pressure fluid causes the first locking pin 42 to move in a direction against the force of the first return spring 46 to engage the follower arm 24. The second locking pin 44 is likewise caused to move in a direction against the force of the second return spring 48 to disengage the follower arm 26. The split between the second locking pin 44 and the fourth pin 45 facilitates the disengagement of the follower arm 26. When it is desired to operate in the two-stroke mode, a flow or pressure of the pressure fluid is reduced and the force of the second return spring 48 causes the second locking pin 44 to move to the position shown in
Referring now to
The inner tappet 56 is maintained in contact with the four-stroke cam surface 62 by an inner tappet return spring 70. One end of an outer tappet return spring 72 urges the outer tappet 58 to maintain contact with the two-stroke cam surfaces 64 of the cam shaft 52. The other end of the outer tappet return spring 72 abuts a spring retainer 74.
Lateral holes 76 are formed in opposing sides of the inner tappet 56 and are aligned with a hole 78 formed in the valve plunger 60 and a hole 80 formed in the outer tappet 58. Locking pin return springs 82 are disposed in the holes 76 of the inner tappet 56. One end of each of the locking pin return springs 82 is received in a locking pin plunger 84. A locking pin 86 is disposed on a side of the locking pin plunger 84 opposite the locking pin return springs 82 and is slidingly received in the holes 76, 78, 80. A pair of locking pin retainers 88 prevent each of the locking pins 86 from sliding free of the outer tappet 58. Each of the locking pin retainers 88 has a central aperture 90 formed therein and is in communication with a pressure fluid source (not shown). A lubrication and lash adjustment aperture 92 is also formed in the outer tappet 58 and the valve plunger 60. As clearly shown in
In operation, the engine is typically operated in a standard mode, one of the four-stroke and the two-stroke mode. For illustrative purposes, standard operation will be considered four-stroke operation. Actuation of the valve stem 54 is controlled by the tappet assembly 50. As the cam shaft 52 rotates, a lobe 96 of the four-stroke cam surface 62 is caused to rotate through 360 degrees. As the lobe 96 of the four-stroke cam surface 62 rotates into the inner tappet 56, the inner tappet 56 is caused to move downwardly, thus causing the valve stem 54 to move downwardly and open a valve (not shown). As the lobe 96 of the four-stroke cam surface 62 moves beyond the inner tappet 56, the inner tappet 56 is caused to move upwardly, thus causing the valve stem 54 to move upwardly and close the valve. Downward movement of the valve stem 54 by a pair of lobes 98 of the two-stroke cam surface 64 is caused by the lobes 98 causing the outer tappet 58 to move downwardly, similar to that described for the lobe 96 of the four-stroke cam surface 62. The outer tappet return spring 72 causes the tappet assembly 50 to maintain contact with the lobes 96, 98 of the cam shaft 52 and return to the position shown in
The engine, which has a combustion system suitable for both two-stroke and four-stroke operation, can be changed from one operating mode to another by changing from the actuation of the valve stem 54 from once per revolution of the cam shaft 52 or crank to twice per revolution of the cam shaft 52. This is accomplished by switching the tappet assembly 50 from following the four-stroke cam surface 62 to following the two-stroke cam surface 64. In the embodiment shown, the locking pins 86 operate to unlock and disengage the valve plunger 60 from the outer tappet 58 for four-stroke mode. Conversely, the locking pins 86 operate to lock and engage the valve plunger 60 to the outer tappet 58 for two-stroke mode.
Engagement and disengagement of the locking pins 86 is accomplished by a hydraulic pressure applied to the locking pins 86 by a solenoid valve under the control of an engine management system. A pressure fluid such as engine oil, for example from the pressure fluid source, is supplied through the apertures 90 to the locking pins 86. The pressure fluid causes the locking pins 86 to move inwardly and disengage the valve plunger 60 from the outer tappet 58 for four-stroke mode. The pressure fluid enters the radial bore apertures 90 and urges the locking pins 86 against the force of the locking pin return springs 82. Thus, when it is desired to operate in the four-stroke mode, the pressure fluid causes the locking pins 86 to move inwardly from the position shown in
A third embodiment of the invention is illustrated in
Referring now to
In operation, the cam follower and rocker arm assembly 110 facilitates a selection of either a four-stroke or a two-stroke operation of an internal combustion engine (not shown) by switching between engagement of the four-stroke follower arm 150 and the two-stroke follower arm 152. The cam follower and rocker arm assembly 110 also allows compliance with manufacturing tolerance variation by incorporating a hydraulic lash adjustment device, which includes the piston 116 and the spring 120, that is deactivated while switching between the four-stroke follower arm 150 and the two-stroke follower arm 152. In both
Under normal operating conditions, as illustrated, the internal combustion engine is running in the four-stroke mode which is determined by the engagement of the four-stroke follower arm 150 by the shuttle pin 142. The shuttle pin 142 and shuttle pin piston 140 are held in this position by due to the urging of the shuttle pin return spring 148. Thus, the actuation of the valve stem 112 will be controlled by the four-stroke follower arm 150. Pressurized oil is supplied to the hydraulic lash adjustment cavity 118 through the first oil supply conduit 130, via the second conduit 128. Control of the supply of pressurized oil can be accomplished using any conventional control method such as an on-board vehicle computer and control valve system, for example. The check valve 134 militates against backflow of the oil through the second conduit 128 to prevent depressurization of the hydraulic lash adjustment cavity 118 during operation.
When it is desired or required to switch to the two-stroke operation mode, pressurized oil is supplied to the shuttle pin cavity 122 through the second oil supplying conduit 136, via the third conduit 138. Control of the supply of pressurized oil can be accomplished using any conventional control method such as an on-board vehicle computer and control valve system, for example. The pressurized oil introduced to the shuttle pin cavity 122 urges the shuttle pin piston 140, the shuttle pin 142, and the shuttle pin return piston 144 against the force of the shuttle pin return spring 148 causing them to move against the force of the shuttle pin return spring 148. At a point in the travel of the shuttle pin 142, the groove 146 aligns with and communicates with the first conduit 124 and the exhaust orifice 126. This alignment, in essence allowing the shuttle pin 142 to act as a spool valve, allows depressurization of the hydraulic lash adjustment cavity 118 and deactivates the hydraulic lash adjustment device. Upon full travel of the shuttle pin piston 140, the shuttle pin 142, and the shuttle pin return piston 144, the four-stroke follower arm 150 is disengaged by the shuttle pin 142 and the two-stroke follower arm 152 is engaged by the shuttle pin 142. Communication between the groove 146, the first conduit 124, and the exhaust orifice 126 is also interrupted, thus allowing re-pressurization of the hydraulic lash adjustment cavity 118 to re-activate the hydraulic lash adjustment device to resume the function of taking up or compensating for clearances between the valve stem 112 and the rocker arm assembly 114.
To return to the four-stroke mode, the reverse of the above is accomplished. The oil supply to the shuttle pin cavity 122 is interrupted and vented, thus relieving the pressure and allowing the shuttle pin return spring 148 to cause the shuttle pin return piston 144, the shuttle pin 142, and the shuttle pin piston 140 to move in the shuttle pin cavity 122 in the direction of the force of the shuttle pin return spring 148. The groove 146 again aligns with and communicates with the first conduit 124 and the exhaust orifice 126 to allow depressurization of the hydraulic lash adjustment cavity 118 and deactivate the hydraulic lash adjustment device. Upon full travel of the shuttle pin return piston 144, the shuttle pin 142, and the shuttle pin piston 140, the four-stroke follower arm 150 is re-engaged by the shuttle pin 142 and the two-stroke follower arm 152 is disengaged by the shuttle pin 142. Communication between the groove 146, the first conduit 124, and the exhaust orifice 126 is also interrupted, thus allowing re-pressurization of the hydraulic lash adjustment cavity 118 to re-activate the hydraulic lash adjustment device.
From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.
