Abstract:
A high pressure internal combustion engine having a triple thermal cycle system for improved cooling and combustion utilizing an annular volume surrounding the cylinder having a connecting passage to the combustion chamber allowing air to enter the volume on compression, and a water injection system for injecting water into the volume during initiation of combustion, the water spray changing to steam to drive the air into the combustion chamber during combustion, the air, steam and combustion gases mixing and improving the engine efficiency, the system being combinable with an injection system that conserves energy by pumping high pressure fluid only during the injection process.

Description:
This application is a continuation-in-part of our application of the same title, Ser. No. 09/590,156, filed Jun. 7, 2000 and claims the benefit of provisional application Serial No. 60/190,303, filed Mar. 17, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention of this application relates to the subject matter of our U.S. Pat. No. 5,042,441, issued Aug. 27, 1991 entitled “Low Emission Combustion System For Internal Combustion Engines,” and U.S. Pat. No. 5,081,961, issued Jan. 21, 1992 entitled, “Internal Combustion Engine With Rotary Exhaust Control.” The referenced patents describe opposed piston engines that are capable of generating enormous power densities by a design that can achieve ultra-high compression/combustion pressures of over 300 bars. When the opposed piston engine designs are associated with auxiliary super-charging or turbo-charging systems to create a five, ten and fifteen atmospheric boost, a tremendous thermal energy density per cycle can be achieved. 
     This ability to generate an unprecedented power density in an engine device provides the opportunity to incorporate internal co-generation using a Rankin cycle combined with an internal air cooling cycle with thermal recovery and regeneration in association with and coincident with the internal combustion cycle. This integration of cycles forms a total energy thermal cycle or a “triple cycle” operating system. 
     In a conventional internal combustion engine the operating cycle is usually associated with an energy balance made up of 30% thermal efficiency, 30% cooling energy rejection, 30% exhaust energy and 10% friction. 
     At very high levels of air charging, where the air charge is boosted at 5, 10 or 15 bars, the thermal energy to be rejected by cooling and exhaust reaches an intensity that threatens the integrity of the structural components of the engine. Normal cooling by transferring excess heat through cylinder walls to a cooling system is inadequate to prevent thermal stresses in the cylinder and exhaust components of the hyper-charged engine. 
     Conventional cooling technologies cannot manage the combined thermal stress and mechanical stress generated by the ultra high pressure and ultra high power density which the opposed piston engine designs, in particular, are capable of producing. 
     However, novel cooling techniques and controlled injection processes described in this application permit a controlled combustion and a regenerative and cogenerative cooling. 
     SUMMARY OF THE INVENTION 
     This invention relates to a controlled injection process and a combined cycle cooling process for internal combustion engines for minimizing thermal losses and mechanical losses in high pressure reciprocal engines. 
     In an engine of the general type, having an ultra high energy density, it is desirable to have a cooling system that has the capability to work in an internal regeneration/cogeneration mode, where thermal energy extracted during cooling is recovered as useful power. The “triple cycle” cooling system of this invention uses a regenerative air charge to cool the cylinder liner and a water injection to drive the air charge and cogenerate energy in a Rankin cycle. 
     In a preferred embodiment, the engine cylinder is surrounded by a cylindrical and concentric air-gap form an annular volume with a first mission to forming an insulating thermal barrier or air jacket. In the compression stroke a part of the compressed air invades this annular insulating volume. The compressed air absorbs a part of the heat transferred through the internal wall or liner of the cylinder. At the end of compression and coincident with the time of fuel injection, high-pressure, pure water is tangentially injected at the bottom of the air-gap. The high circular speed of convection and conversion to steam absorbs the rest of the excess thermal energy, transforming this heat into high-pressure, internally cogenerated steam. This steam pushes the heated air back into the combustion chamber of the engine. The compressed air, pre-heated and tangentially re-injected into the combustion chamber during the process of combustion, produces major improvements in completing combustion and increasing the thermal efficiency of the engine. The compressed air is followed by the injection of steam during the same combustion process, the final result being a combined working fluid formed from combustion gases, heat regenerating compressed air, and cogenerating steam. The total energy, triple thermal cycle has a potential for a maximum thermal efficiency of 80-90%. The super high turbulence produced by the tangentially re-injected, high-speed and high-pressure air, and the associated injected steam has a major effect in producing a super clean combustion, with ultra low or zero emission. 
     Controlling the temperature of the combustion by the air and steam injection, the formation of nox and other pollutants is virtually eliminated. 
     Even the friction loss of the piston is transformed as heat in the cylinder liner and is then, by thermal combustion, transferred back to the working fluid and recovered by the internal cooling air of regeneration and the steam of cogeneration. 
     The fuel injection and the water injection are preferably accomplished by a novel concept of a sequential, common rail injection system. The injection system advantageously works in conjunction with the total energy, triple thermal cycle to minimize both thermal and mechanical losses in high pressure engine systems, or in other systems where high pressure, hydraulic pumping systems result in losses in overall engine efficiency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a partial cross-sectional view of an engine cylinder in an opposed piston engine. 
     FIG. 1B is a cross-section of the engine cylinder of FIG. 1A taken on the lines  1 B— 1 B in FIG.  1 A. 
     FIG. 2A is a partial cross-sectional view of an engine cylinder of an opposed piston engine. 
     FIG. 2B is a cross-section of the engine cylinder of FIG. 2A taken on lines  2 B— 2 B in FIG.  2 A. 
     FIG. 3 is a schematic illustration of a sequential, common rail injection system adapted for a conventional engine. 
     FIG. 4 is the sequential, common rail injection system of FIG. 3 adapted to an opposed piston engine. 
     FIG. 5 is a schematic illustration of a sequential, common rail injection system having a controlled injection cutoff. 
     FIG. 6 is a schematic illustration of the sequential, common rail injection system having a controlled injection cutoff with a pressure amplifier module. 
     FIG. 7 is a schematic illustration of a sequential, common rail injection system having a controlled injection cutoff with a pressure amplifier module and gas-hydraulic pumping module. 
     FIG. 8 is a cross-sectional view of a conical injector with a hollow, conical spray. 
     FIG. 9 is a cross-sectional view of the injector of FIG. 8 with a wider conical spray. 
     FIG. 10 is a cross-sectional view of the injector of FIG. 9 with a pulse injector spray. 
     FIG. 11A is a schematic illustration of an improved sequential, common rail injection system adapted for a conventional engine with an open fuel return valve. 
     FIG. 11B is a schematic illustration of the improved sequential, common rail injection system of FIG. 11A with a closed fuel return valve. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The triple thermal cycle system for internal combustion engines is described with reference to its preferred implementation as an opposed piston engine of the type described in the referenced patents. Referring to FIG.  1 A and FIG. 1B, a cross-sectional view of the combustion chamber portion of an opposed piston engine  100  is shown. The engine  100  has two pistons  101  and  102  in a single engine cylinder  103 . The cylinder is formed with a structural housing having an inner sleeve or liner  104  encircled by an air gap envelope  105 . The inner sleeve or liner  104  is a thermally conductive structural member that separates the piston cylinder from the annular volume that forms a cooling jacket. 
     In the embodiment of FIG.  1 A and FIG. 1B, the engine  100  is provided with two opposed fuel injectors  106  and two water injectors  108 , shown schematically. The opposed pistons  101  and  102  are shown approaching top dead center with a circular crown  110  of the piston  101  forming the perimeter of an inner combustion chamber  111 . The circular crown  110  of piston  101  is shown penetrating a recessed combustion chamber  112  in the opposite piston  102 . 
     By this conjunction, the crown  110  separates the peripheral volume  113  from the central volume  114 . During the progression of the two pistons toward the top dead center of the piston cycle, the perimeter air in the peripheral volume  113  is forced through the crown  110  to the central volume  114  through tangential ports  115  and flared injection passages  107 . The tangential orientation of the ports  115  and passages  107  creates a turbulent, high-speed, spiral air movement in the central combustion chambers  111  and  112 . 
     During the process of compression, a part of the air between the pistons  101  and  102  is transferred from the cylinder  103  to penetrate the air gap  105  where it compresses and absorbs part of the heat transferred from the cylinder liner  104 . 
     At the end of the compression stroke of the pistons, the substantially simultaneous injection of fuel by the fuel injectors  106  and water injectors  108  is commenced. 
     Water injected into the air gap  105  by the water injectors  108  is instantly converted to steam, driving the compressed air through the circular crown into the  110  central volume  114  cooling the cylinder  103 , and particularly the cylinder liner  104  which absorbs a part of the thermal energy of combustion, cutoff 
     The fuel injected into the central volume  114  is turbulently mixed with compressed air squished from the peripheral volume  113  and driven from the air gap  105  by the co-generated steam through constricted passages in the form of tangential ports  115  and injection passages  107  in the piston crown  110 . 
     The result is a “triple thermal cycle” of energy recovery wherein the thermal energy of combustion is recovered by the cycled air to the air gap envelope, the cogeneration of the Rankin cycle in converting injected water to steam in the air gap envelope and the primary combustion in the central combustion chambers  111  and  112 , which is supplemented by the air cooling and steam cooling cycles for the mechanical work output. Additionally, since the primary friction losses result from the piston/cylinder contact which converts friction to heat. This thermal energy is also recovered by the air cooling and water-steam conversion cooling in the air gap envelope since the heat of friction is transferred. Virtually all energy generated in the engine is compounded in the development of an effective maximum power output. 
     Referring now to the alternate embodiment of FIG.  2 A and FIG. 2B, the opposed piston engine  200  is configured and operated in the same manner as the engine  100  of FIG.  1 A and FIG. 1B, but with two additional fuel injectors  109 , as schematically illustrated in FIG.  2 B. Notably, the tangential ports  115  are replaced by injector passages  107  as previously described. 
     Referring to FIG. 3, a “common rail sequential injection system” is shown and designated generally by the reference numeral  300 . The injection system  300  includes a hydraulic pump  301  that receives a liquid, which is fuel or water, depending on the system implemented, from a reservoir  302 . The hydraulic pump  301  pumps the liquid to the electro-hydraulic valve  303 , which has a body  304  with a solenoid actuator  305  attracting armature plate  306  connected to the spool or poppet valve  307 . A return bypass conduit  309  with supply conduits  310  and  311  form a low pressure supply circuit for circulating the liquid around at low pressure with minimum expended energy, so long as the valve  307  is open. 
     At the proper moment of injection, the electro hydraulic valve  307  is energize closing the bypass conduit  309 . The high pressure liquid is conducted through conduit  312 , check valve  313 , toward the injector  314 , for example, which is electronically opened for injection under the command of the electronic control module  321 . 
     The level of the injection pressure is measured and controlled by the transducer  315 , informing the electronic control module  321 , which in turn controls the output of the pump  301  for maintaining a constant injection pressure only during the injection time. During the rest of the time, the pump  301  operates as a fluid circulating pump. 
     At the end of the injection of the injector  314 , the electro-hydraulic valve  303  is de-energized simultaneously with the closing of the injector  314 . The check valve  313  conserves the pressure in the rail  322 , when the electro-hydraulic valve  303  is discharging the liquid through the bypass circuit of conduits  309 ,  310  and  311 , and the open valve  303 , eliminating the energy consumption between the injections. 
     When the injectors  316 ,  317 ,  318 , etc. must inject, the electro-hydraulic valve  303  is sequentially energized repeating the same process of sequential injection. 
     The engine  321  is driving the encoder  320  which is the timing trigger for the actions of the electronic control module  321 . 
     In the embodiment of FIG. 4, the engine  400  is of the opposed piston type as shown in FIGS. 1A and 2B, with two or four injectors, the specific embodiment of FIG. 4 showing four injectors  314 ,  316 ,  317  and  318  arranged around the engine cylinder  402  for tangential injection into the combustion chamber  401 , as schematically illustrated. 
     The fundamental difference from the sequential common rail injection system depicted in the FIG. 3, is that all four injectors are injecting in a continuous overlapped injection: 
     1. - - - - - - - - - - - - - - - - - - - - - - - - - 
     2. - - - - - - - - - - - - - - - - - - - - - - - - 
     3. - - - - - - - - - - - - - - - - - - - - - - - 
     4. - - - - - - - - - - - - - - - - - - - - - - 
     with no more than a 3-5 degree interval between injections and no more than 30 degree total injection time. 
     During each injection cycle the injection process is sequentially divided by the four injectors which inject fuel in this embodiment into the single combustion chamber  401 . 
     The total time of the energized electro-hydraulic valve  303  is the 30-degree phase in which time individual injectors are sequentially energized, activated and de-activated. The rest of the 330 degrees of the total cycle time (two stroke engine), or 690 degree cycle (four stroke engine) the high pressure pump  301  is de-activated by the de-energized electro-hydraulic valve  303 , which opens the by-pass circuit of conduits  309 ,  310  and  311  with the pump  301  operating as a low pressure circulating pump. 
     This de-activation of the common rail pump  301  in the time of non-injection produces a significant reduction of the energy lost by conventional common rail injection systems. 
     The sequential common rail injection system can also be used for water injection for an internal cogeneration cycle for conventional or ultra high-pressure opposed piston engines. Similar applications can involve the injection of other liquids such as alcohols, hydro ammonia, liquid natural gas, hydrogen alone or in combination with other petroleum fuels. 
     The fundamental principles of our invention can be applied to all existing and new engines, in any and all potential combinations, without departing from the spirit of the invention. 
     Referring now to FIG. 5, the components of the sequential, common rail injection system  500  are illustrated with an exemplar injector  314  from the arrangement of FIG.  3 . The injector  314  has an injector body  505  connected by a liquid supply line  504  to an electro-hydraulic valve  501 . The electro-hydraulic valve  501  has a solenoid  502  and an actuatable discharge valve spool  503 , and is connected to the injector  314  by supply line  504 . The electro-hydraulic discharge valve  507  has a solenoid  506  and an actuatable discharge valve spool  508  connected to bypass line  510  and discharge line  509  for timely relief of pressure in the liquid supply line  504 . 
     In operation the modular sequential injection system starts the injection by a command from the electronic control module  321  that is triggered by the cycle timing encoder  320 . The electronic command causes the energizing of solenoid  305  closing the valve  303  thereby pressurizing the common rail  322 ; energizing solenoid  502 , which opens valve  501 , pressurizing the injector  314  through line  504  connected to injector housing  505 ; and, energizing solenoid  506  closing the valve  507  preventing flow through bypass line  510 . 
     The modular sequential injection system  500  stops the injection process by a command from the electronic control module  321  by de-energizing the solenoids  305 ,  502 , and  506 . The common rail pressure system is thereby relieved by the opening of valves  305  and  507  and the closing of valve  503 . The electro-hydraulic valve  301  will be relaxed until the next sequential injection of the companion injectors  316 ,  317 , and  318 , schematically illustrated in FIG.  5 . The check valve  313  conserves the pressure in the common rail  322  until the next injection. To prevent over-pressurization of the common rail, a pressure relief valve  511  in return line  512  limits rail pressure to a preset maximum pressure. The sequentially operated injectors  316 ,  317 , and  318  repeat the same operation as described for injector  314 . 
     In FIG. 6, the sequential, common rail injection system designated generally by the reference numeral  600  and operable with an engine system described in FIG. 3, includes a supplemental pressure amplification module  606 . 
     In the supplemented common rail injection system  600 , there is included an electro-hydraulic valve  601  having a balanced valve spool  603  connecting common rail  322  with feed lines  604  and  605  to the pressuring amplification module  606 . The pressure amplification module  606  is provided with a large piston  607 , biased by a compression spring  608 , acting on a plunger  609 , biased by a compression spring  610 . The plunger  609  pumps the high pressurized fuel through the feed line  611  in the injector  612 . The feed line  613  is connected with the discharge valve  615  which is provided with a solenoid  614  and activated valve spool  616 . 
     A bypass connection line  617  with a check valve  618  supplies the fuel to the cylinder chamber  321  of the pressure amplification module  606  and the connecting line  613  to the discharge valve  615 . The other injectors  619 ,  620  and  630  shown schematically in FIG. 6 are similarly constructed and operated. 
     In operation the supplemented modular sequential injection system  600  starts the injection by a command from electronic control module  321  that is triggered by the cycle timing encoder  320 . The electronic command causes the energizing of solenoid  305  to close the valve  305  and pressurize the common rail  322 ; the energizing of solenoid  602  to open the valve  601 ; and the energizing of solenoid  614  to close the discharge valve  615 . The pressure of the common rail  622  acts through the valve  601  over piston  607  and coupled plunger  609  amplifying the injection pressure of the fuel in the cylinder  621  in the ratio of the area of the piston  607  over the area of the plunger  609 . 
     The modular sequential injection by de-energizing all of the solenoids  305 ,  602  and  614  resulting in a pressure relaxation of the hydraulic pump  301  and a sharp pressure cutoff at the injector  612  by the opening of the discharge valve  615  and the closing of the electro-hydraulic valve  601  preserving the pressure in the common rail  322 . 
     The return of piston  607  by the compression spring  608  drives fuel from the top of the amplification module  606  through bypass line  617  and check valve  118  refilling injection cylinder  610  with a new charge as plunger  609  rises with piston  607 . The same sequence of operation is repeated with the other injectors  619 ,  620 , and  630 , schematically shown in FIG.  6 . 
     In the arrangement of the sequential, common rail injection system of FIG. 7, designed generally by reference numeral  700 , the system is modified as a self-injection system. Self injection is accomplished by inclusion of a gas-hydraulic pumping module  730  provided with a piston  701 , a compression spring  702 , and a hydraulic line  703  communicating with a fluid pumping chamber  731 . On the opposite side of the piston  701  from the fluid pumping chamber  731  is a gas pressurizing chamber  732  with a communicating passage  733  to the combustion chamber  734 , shown schematically in FIG.  7 . In this manner, the pressure in the combustion chamber is reflected in the gas pressurizing chamber  732  which act on the fluid in the fluid pumping chamber  731  by displacement of the piston  701  against the return spring  702 . 
     The hydraulic line  703  connects to the electro-hydraulic valve  704  provided with a solenoid  705  and actuatable valve spool  706  for controlling liquid passage to the pressure amplification module  708  through supply line  707 . The pressure amplification module is provided with a large piston  709 , biased by a spring  710 , acting over a plunger  711 , biased by a spring  712 , in the injection cylinder  735 . The injection cylinder  735  is connected by passage  713  to the injector  714  and by relief line  715  with the electro-hydraulic valve  717 . The electro-hydraulic valve  717  is provided with a solenoid  716  and an actuatable valve spool  718 . The valve  717  connects a fuel supply  720  to the injection cylinder  735  using a supply pump  719  for refilling the injector. 
     In operation injection starts upon processing a compression pressure signal received from the pressure transducer  725  which reflects the pressure in the combustion chamber  734 . At a predetermined optimized compression pressure, as coordinated with a trigger signal from the encoder  724 , the electronic control module  723  generates a command signal. The command signal causes the energizing of solenoid  705  opening electro-hydraulic valve  704  transmitting hydraulic pressure through line  707  over large piston  709  thereby amplifying the pressure produced by plunger  711  in the ratio of piston area over plunger area, for example, 10-15 times. Also, solenoid  716  is energized, closing electro-hydraulic valve  717  pressurizing the liquid in the injector module  708  and injector  714 . 
     The injected fuel starts the combustion process raising the combustion chamber pressure with a corresponding rise in the injection pressure, proportionally amplified 10-15 times. A dynamically shaped injection pressure profile evolves that is the definition of an ideal injection system. 
     The modular sequential injection system stops the injection process by de-energizing the solenoids  705  and  716 , which produces a sharp cut off of the injection and a gradual return of the large piston  709  and pumping piston  701  to their original position, recovering all of the energy accumulated in the amplification module during injection. In this manner the efficiency of the injection system is maximized. 
     Referring now to FIGS. 8-10, a preferred type of injector for use in the modular sequential injection system is shown. In FIG. 8, an injector, designated generally by the reference numeral  800  has a housing body in the form of a sleeve  801  having a nozzle  802  with a conical, outwardly displaceable valve  803 . The valve has a spiral stem portion  804  and guide vane portion  805 . The valve  803  is biased by a compression spring  806 , engaging a spring head  807 . The spring head  807  is connected to the end of the valve stem  820  by a split conical seating  808  in a recess on the spring head  807 . The end of the valve stem  820  has a magnetic element that cooperates with a sensor transducer  810  to indicate the valve position. 
     The stroke of the valve  803  is limited by a slotted bushing  811  contained within outer bushing  812 . The injector body  813  is provided with a fuel passage  814  and a supply port  815 . An electrical conduct  816  of the transducer  810  transmits a signal responsive to valve movement to the electronic control module for continuous diagnostic control. The injector  800  of FIG. 8 has a hollow conical spray pattern  818 , as shown. 
     In FIG. 9, the injector  900  has the identical components as that shown for the injector  800  of FIG. 8, but with a modified tip  901  of the valve  902  that co-acts with a modified chamber in the nozzle  903 . This generates a wider conical spray pattern  904  as shown. 
     In FIG. 10, the injector  1000  is operated in a multiple injection pattern to produce a series of conical injection patterns  1001 ,  1002  and  1003  during each injection cycle. 
     Referring now to FIGS. 11A and 11B, an improved sequential, common rail, injection system is shown. The system of FIGS. 11A and 11B limits the existence of high pressure in the common rail to only the angular time of each injection. During the remaining time between injections the pressure of the rail is reduced to the level of the minimum pressure of the intake in an open recirculation loop. 
     As previously noted, a conventional common rail system continuously maintains a constant high pressure for the 360° crank rotation of a two stroke cycle or the 760° rotation of a four stroke cycle. If a normal injection time for one injection is 30° of crank rotation for the time of pumping, then in this case, it will be necessary to have twelve cylinders in a two stroke or twenty-four cylinders in a four stroke engine, if all the fuel is to be injected into the cylinders without waste. However, if the number of cylinders is less than twelve or twenty-four for the respective engine cycles, the conventional common rail systems are expending or “wasting” a large amount of energy through a valve “waste gate” between the injections. The lost energy is proportional to the level of pressurization of the common rail and is directly reflected in higher specific fuel consumption. 
     The system of this invention totally eliminates these losses which become significant when the injection pressure is more than 1000-2000 bar. In the system described herein the common rail pressure between injections is relaxed and all the fuel at high pressure is injected into the appropriate cylinder for maximum efficiency and zero energy loss. 
     In FIG. 11A, the sequential, common rail system is shown and designated generally by the reference numeral  1100 . The sequential, common rail system has a primary high pressure pump  1111  that draws fuel through a fuel line  1112  from a fuel tank  1113  and pumps the fuel through the main supply line  1114  to an electro-hydraulic valve unit  1115 . In FIG. 11A, the poppet  1116  of the electro-hydraulic valve unit  1115  is in an open position with the valve poppet  1116  extended as shown. In this position, fuel returns to the fuel tank  1113  through passage  1117  and return line  1118 . In this mode of operation, no pressure is produced and the hydraulic circuit is in an open position. 
     Referring now to FIG. 11B, during the time of injection a servo valve  1119  in the electro-hydraulic valve unit  1115  is closed upon activation of a solenoid  1120  which displaces a spool poppet  1121 . In this position, an auxiliary pump  1122  supplies a hydraulic fluid, such as fuel from the fuel tank  1113 , through the servo valve  11   19  and passage  1138  to the differential plenum  1123  which acts on differential piston  1124  driving the piston against compression spring  1125  to retract the poppet  1116  and securely close the valve unit  1114 . A pressure limit valve  1126  with a return line  1127  limits the maximum pressure that the auxiliary pump  1122  can develop for actuating the main poppet  1116  on closure. Any liquid bled by the pressure limit valve  1126  is returned to the hydraulic fluid source, which in the preferred embodiment is the fuel tank  1113 . 
     In this mode of operation, the common rail  1128  is at its maximum pressure level, corresponding with the injection pressure for activating the first electronic injector  1129 . After injection of fuel into the corresponding cylinder  1130  of engine  1131  the valve unit  1114  is switched by de-energizing the solenoid  1120  thereby allowing the compression spring  1125  to return the poppet  1116  to an open position as shown in FIG.  11 A. In this manner, each of the four fuel injectors,  1129 ,  1132 ,  1133  and  1134 , are sequentially activated only during the angular injection time, here selected as 30°. It is understood that the actual angular time of injection can vary from engine to engine and in fact during engine operation, since injection time is controlled by an electronic control module  1135  with input from the encoder  1136  connected to the crank shaft of the engine  1131  and the signal supplied by the pressure sensing transducer  1137 . 
     While, in the foregoing, embodiments of the present invention have been set forth in considerable detail for the purposes of making a complete disclosure of the invention, it may be apparent to those of skill in the art that numerous changes may be made in such detail without departing from the spirit and principles of the invention.