CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. provisional application number 62/599,136 filed on December 15, 2017 which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates to a supercharger and EGR pump system for a two stroke engine.

BACKGROUND OF THE INVENTION

[0003] There are many previously known automotive vehicles that utilize internal combustion engines to propel the vehicle. Furthermore, many of these vehicles include a supercharger which supplies pressurized air to the engine with the fuel.

[0004] While some superchargers merely provide intake air in a compressed state to the engine for mixture with fuel and ultimately combustion of that mixture, in other constructions EGR (exhaust gas recirculation) recirculates the exhaust gas into the supercharger for mixture with the fuel. The EGR that is intermixed with the air in the supercharger enhances the overall combustion of the fuel. This, in turn, reduces exhaust gas emissions.

[0005] One disadvantage of intermixing exhaust gas with the intake to the supercharger is that the exhaust gas contains acids, such as sulfuric acid and particulate matter such as soot. Water vapor may be included in exhaust gases from an engine as a result of the combustion process of fuel supplied to the engine. Generally, the water vapor is expelled to the environment through an exhaust system. However in an EGR application a portion of the exhaust is recirculated to the engine intake manifold. The water vapor may provide a carrier for particulate matter such as soot and may also react with other components of the exhaust to form an acidic composition. The EGR stream including the particulate matter and acidic composition may degrade the performance of a supercharger. Soot deposits may accumulate on the rotors and housing of the supercharger and lead to seizure of the rotors.

[0006] In a two stroke engine, such as an opposed piston engine a supercharger may be utilized to meter and augment a turbocharged intake air that is mixed with exhaust gas in an EGR application. As described above, soot and corrosive elements in the EGR stream may degrade the performance of the supercharger.

[0007] It is therefore desirable to provide an EGR pump with abrasion and corrosion resistance as well as a surface that resists accumulation of soot deposits. It is also desirable to provide a separate EGR pump that transports EGR gases and a separate supercharger that acts upon a clean air stream and mix the streams after the outlet of the supercharger to prevent degradation of the supercharger.

SUMMARY OF THE INVENTION

[0008] In one aspect there is disclosed a two stroke engine assembly that includes a two stroke engine including an intake port and an exhaust port. A turbo charger including a turbine is coupled to the exhaust port and a compressor is coupled to the turbine compressing a fresh air source to a compressed fresh air stream. A super charger is coupled to the compressed fresh air stream moving the compressed fresh air to a mixing plenum. An EGR pump is coupled to the exhaust port moving an EGR stream to the mixing plenum wherein the fresh air and exhaust gas are combined and then fed to the intake port of the two stroke engine.

[0009] In another aspect there is disclosed a two stroke engine assembly that includes a two stroke engine including an intake port and an exhaust port. A turbo charger including a turbine is coupled to the exhaust port and a compressor is coupled to the turbine compressing a fresh air source to a compressed fresh air stream. A super charger is coupled to the compressed fresh air stream moving the compressed fresh air to a mixing plenum. An EGR pump is coupled to the exhaust port moving an EGR stream to the mixing plenum wherein the fresh air and exhaust gas are combined and then fed to the intake port of the two stroke engine. A control system is linked with the EGR pump and supercharger. The control system provides a determined air and EGR charge and cylinder scavenging function for the two stroke engine to maintain an efficient operation of the engine and maintain engine outputs such as power and exhaust emissions within a specified range.

[0010] In a further aspect there is disclosed a two stroke engine assembly that includes a two stroke engine including an intake port and an exhaust port. A turbo charger including a turbine is coupled to the exhaust port and a compressor is coupled to the turbine compressing a fresh air source to a compressed fresh air stream. A super charger powered by an electrically assisted variable speed drive is coupled to the compressed fresh air stream moving the compressed fresh air to a mixing plenum. An EGR pump powered by an electric motor is coupled to the exhaust port moving an EGR stream to the mixing plenum wherein the fresh air and exhaust gas are combined and then fed to the intake port of the two stroke engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is view of an EGR pump super charger showing the components;

[0012] Figure 2 is a schematic representation of a two stroke opposed piston engine system including an independently controlled EGR pump and supercharger;

[0013] Figure 3 is a schematic representation of a control system of the Figure 2;

[0014] Figure 4 is a schematic representation of a two stroke opposed piston engine system including a jointly driven EGR pump and supercharger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Referring to figure 1 there is shown a schematic representation of a portion of an EGR pump 10. In one aspect, the EGR pump 10 includes a Roots device 12 that may include radial inlet and outlet ports 14, 16. A housing 18 of the EGR pump 10 may be formed of material able to tolerate high temperatures, such as cast iron or steel. Rotors 20 having a cycloidal profile whose sliding action limits the accumulation of soot may be disposed in the housing 18.

[0016] The EGR pump 10 may be integrated with the engine’s pressurized oil circulation system to lubricate and cool the EGR pump 10. The housing may include oil ports 22. The EGR pump 10 may also be integrated with the engine’s coolant circulation system to cool the EGR pump 10. The circulation of engine oil and/or engine coolant near the pump’s bearings and seals may manage EGR pump component temperatures.

[0017] As shown in the figures, the transmission 24 may include housing members 26, 28 that link the roots device 12 with a drive member. The housing members 26, 28 include through bores formed therein that allows attachment to the roots device 12 or drive member.

[0018] In one aspect, the rotors may be formed of aluminum providing a strong and lightweight material. However, in an EGR application various components of the EGR gases may degrade such a rotor or soot deposits may accumulate on the surface of the rotors. To combat accumulation of soot, a hard coating may be applied to the rotor surface. The coating may include a smooth surface finish to prevent nucleation and propagation of soot on the surface of the rotors. Various coatings such as may be applied to the rotors, housing or other components. The coatings may be applied by electroplating, CVD, plasma deposition or other coting methods. The smooth surface of the coating will prevent accumulation of soot.

[0019] In another aspect, the rotor and housing may be formed of a steel composition such as stainless steel. The steel material may be less prone to thermal expansion when exposed to the elevated temperatures of an EGR gas and allow for less stringent tolerances when assembling the supercharger. Additionally, the stainless steel components may be resistant to the corrosive components of an EGR gas such acids, water, NOx, soot or other components of an EGR gas.

[0020] Referring to Figure 2, there is shown a representation of a two stroke engine system 40 including a two stoke engine 42. Various two stroke engines may be utilized. In one aspect, the engine 42 may be an opposed piston two stoke engine, with two pistons per cylinder working in opposite reciprocating action. Ports are formed in the cylinder walls and act as valves. The intake ports are at one end of the cylinder and the exhaust ports are at the other end of the cylinder. The ports are opened by the piston motion.

[0021] Exhaust gas 44 from the engine 42 maybe routed to a turbo charger including a turbine 46 and a compressor 48. The turbine 46 receives exhaust gases 44 from the engine 42 and drives the compressor 48 to compress intake air delivered to the engine 42. Another portion of the exhaust gas is routed to the EGR pump 10 as previously described above. The EGR pump 10 may be a low flow device driven by a drive member such as an electric motor 50. The electric motor 50 may be linked with a control system 51 that regulates the flow of EGR gas to the engine 42. The EGR gas may be routed from the EGR pump 10 to an EGR cooler 52 to lower a temperature of the gas stream and then may be routed to a mixing plenum 54.

[0022] The air from the compressor 48 may be routed to a charge air cooler 56 to adjust the temperature of the compressed air before introduction to a supercharger 58. In one aspect, the supercharger may be a high flow low differential pressure supercharger that acts as a positive displacement pump. The supercharger 58 may be utilized to meter the fresh air to the engine 42 as will be discussed in more detail below. The supercharger may be driven by a drive mechanism 60. The drive mechanism 60 may include a belt or chain that is linked with a crank shaft of the engine 42. The drive mechanism may also include an electrically assisted variable speed (EAVS) drive or an electric drive having a motor which may include a transmission or gear box. The EAVS drive may include an electric motor and planetary gear set that is coupled to the drive shaft of the supercharger 58. The EAVS drive mechanism allows for a variable flow of the supercharger independent of the engine speed ln this manner, the EGR flow and fresh air flow may be controlled independently by electrically controlled mechanisms.

[0023] Referring to Figure 3, the depicted system includes a control system 51 for controlling the amount of air moved by the supercharger 58 and the amount of EGR gas moved by the EGR pump 10. The control system 51 includes sensors 53 capable of sensing conditions and of sending signals, such as temperature, pressure, speed, air flow, mass flow or volumetric flow. The control system 51 also includes a control unit 55 which includes a computer processor, communication ports, memory, and programming. The control unit 55 may be a portion of an engine control unit (ECU). The control unit 55 may provide signals to control the speed of the electric motor 50 and the supercharger drive 60. The control system 51 provides a determined air and EGR charge and cylinder scavenging function for the two stroke engine 42 to maintain an efficient operation of the engine and maintain engine outputs such as power and exhaust emissions within a specified range.

[0024] The fresh air discharged from the supercharger 58 and the EGR gases from the EGR cooler 52 are mixed in the mixing plenum 54. In one aspect, the EGR gases are mixed after the supercharger 58 or with the discharge gas from the super charger to prevent degradation of the supercharger 58.

[0025] Referring to Figure 4, there is shown a representation of a two stroke engine system 140 including a two stoke engine 142. Various two stroke engines may be utilized. In one aspect, the engine 142 may be an opposed piston two stoke engine, with two pistons per cylinder working in opposite reciprocating action. Ports are formed in the cylinder walls and act as valves. The intake ports are at one end of the cylinder and the exhaust ports are at the other end of the cylinder. The ports are opened by the piston motion.

[0026] Exhaust gas 144 from the engine 142 maybe routed to a turbo charger including a turbine 146 and a compressor 148. The turbine 146 receives exhaust gases 144 from the engine 142 and drives the compressor 148 to compress intake air delivered to the engine 142. Another portion of the exhaust gas is routed to the EGR pump 1 10 as previously described above. The EGR pump 1 10 may be a low flow device. The EGR gas may be routed from the EGR pump 110 to an EGR cooler 152 to lower a temperature of the gas stream and then may be routed to a mixing plenum 154.

[0027] The air from the compressor 148 may be routed to a charge air cooler 156 to adjust the temperature of the compressed air before introduction to a supercharger 158. In one aspect, the supercharger may be a high flow low differential pressure supercharger that acts as a positive displacement pump. The supercharger 158 may be utilized to meter the fresh air to the engine 142 as will be discussed in more detail below. The supercharger may be driven by a drive mechanism 160. The drive mechanism 160 may include a belt or chain that is linked with a crank shaft of the engine 142. The drive mechanism may also include an electrically assisted variable speed (EAVS) drive or an electric drive having a motor which may include a transmission or gear box. The drive mechanism may also be linked with the EGR pump 1 10 to drive both the supercharger 158 and the EGR pump 1 10. The EGR gases from the EGR pump may be routed to the EGR cooler 152 or a portion may enter a bypass conduit which includes a bypass valve 164 that is controlled to provide a specified portion of EGR gas to the EGR cooler 152.

[0028] The fresh air discharged from the supercharger 158 and the EGR gases from the EGR cooler 152 are mixed in the mixing plenum 154. In one aspect, the EGR gases are mixed after the supercharger 158 or with the discharge gas from the super charger to prevent degradation of the supercharger 158.

[0029] The separation of the low flow EGR pump from the high flow supercharger provides an economical system that separates the two streams such that the high flow supercharger does not suffer damage from EGR gas.