Patent Publication Number: US-2022213852-A1

Title: Egr pump system with overhung rotors

Description:
FIELD OF THE INVENTION 
     The invention relates to exhaust gas recirculation (EGR) pumps and control of EGR pumps. 
     BACKGROUND OF THE INVENTION 
     There are many previously known automotive vehicles that utilize internal combustion engines such as diesel, gas or two stroke engines to propel the vehicle. In some constructions EGR (exhaust gas recirculation) recirculates the exhaust gas into the engine for mixture with the cylinder charge. The EGR that is intermixed with the air and fuel to the engine enhances the overall combustion of the fuel. This, in turn, reduces exhaust gas emissions. 
     By including a separate EGR pump an increase in fuel economy may be achieved in comparison to prior art systems that may use a turbocharger to drive an EGR flow with the addition of costly EGR valves. Additionally, a separate EGR pump provides full authority of the EGR flow rate. In a diesel application, a separate EGR pump may allow for removal of an EGR valve and replace a complicated variable geometry turbocharger with a fixed geometry turbocharger optimized for providing a boosted air charge. The separate EGR pump may provide reduced engine pumping work and improved fuel economy. 
     One disadvantage of intermixing exhaust gas is that the exhaust gas contains 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. Soot deposits may accumulate on various components degrading performance. 
     It is therefore desirable to provide an EGR pump that resists accumulation of soot deposits. It is also desirable to provide a separate EGR pump that transports EGR gases to prevent degradation of the additional components such as a supercharger or turbocharger. 
     Various portions of EGR pumps may be exposed to exhaust gases at elevated temperatures. For example the rotors associated with the pump may contact exhaust gases at temperatures such as from 220 to 300 C. In such a scenario, the high temperature may demagnetize the components of the electric motor causing a loss of torque. Additionally, the high temperature may adversely affect the mechanical components of the EGR pump such as varying the heat treatments and properties of the materials. 
     It is therefore desirable to reduce heat transfer from the EGR pump rotors to the electric motor that drives the EGR pump. There is therefore a need in the art to thermally isolate rotors of an EGR pump from an electric motor that may drive the pump such that the motor does not overheat. 
     Further, it is desirable to cool and lubricate the various components of the EGR pump for safe and long operation in an EGR environment. 
     SUMMARY OF THE INVENTION 
     In one aspect there is disclosed, an exhaust gas recirculation pump system for an internal combustion engine that includes an EGR gas source and an electric motor assembly. A roots device is coupled to the electric motor. The roots device includes a housing defining an internal volume wherein the housing includes a radial inlet port receiving the EGR gas source and an outlet port expelling the EGR gas from the housing. Rotors are disposed in the internal volume and connected to the electric motor. A transmission housing is attached to the housing. The transmission housing includes journals formed therein receiving bearings that support the rotors on only a single end of the rotors. 
     In another aspect, there is disclosed an exhaust gas recirculation pump system for an internal combustion engine that includes an EGR gas source and an electric motor assembly. A roots device is coupled to the electric motor. The roots device includes a housing defining an internal volume wherein the housing includes a radial inlet port receiving the EGR gas source and an outlet port expelling the EGR gas from the housing. Rotors are disposed in the internal volume and connected to the electric motor. A transmission housing is attached to the housing. The transmission housing includes a lip seal disposed therein. The lip seal is movable in response to a pressure differential to contact an oil slinger or rotor sealing a rotor cavity from a bearing cavity. 
     In a further aspect, there is disclosed an exhaust gas recirculation pump system for an internal combustion engine that includes an EGR gas source and an electric motor assembly. A roots device is coupled to the electric motor. The roots device includes a housing defining an internal volume wherein the housing includes a radial inlet port receiving the EGR gas source and an outlet port expelling the EGR gas from the housing. Rotors are disposed in the internal volume and connected to the electric motor. A transmission housing is attached to the housing. The transmission housing includes journals formed therein receiving bearings that support the rotors on only a single end of the rotors. The bearings include a spacer assembly positioned in a bearing bore between the bearings. The spacer assembly includes an inner spacer spaced radially from an outer spacer. 
     In another aspect, there is disclosed an exhaust gas recirculation pump system for an internal combustion engine that includes an EGR gas source and an electric motor assembly. A roots device is coupled to the electric motor. The roots device includes a housing defining an internal volume wherein the housing includes a radial inlet port receiving the EGR gas source and an outlet port expelling the EGR gas from the housing. Rotors are disposed in the internal volume and connected to the electric motor. A transmission housing is attached to the housing. The transmission housing includes journals formed therein receiving bearings that support the rotors on only a single end of the rotors. The housing includes a bushing attached thereon. The bushing is positioned to support an inner diameter of a hole bored in the rotor only during a deflection of the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of an EGR system including an engine and EGR pump; 
         FIG. 2  is a perspective view of an EGR pump, electric motor and transmission assembly; 
         FIG. 3  is a perspective view of an EGR pump and transmission assembly; 
         FIG. 4  is a partial sectional view of an EGR pump and transmission assembly; 
         FIG. 5  is a partial sectional view of an EGR pump and transmission assembly showing an oil path; 
         FIG. 6  is a partial sectional view of an EGR pump and transmission assembly showing an oil path; 
         FIG. 7  is a partial sectional view of an EGR pump and transmission assembly detailing an angled inlet; 
         FIG. 8  is a partial perspective sectional view of an EGR pump and transmission assembly showing an oil path; 
         FIG. 9  is a partial perspective sectional view of an EGR pump detailing rotor profiles and a back flow port; 
         FIG. 10  is a perspective view of a rotor; 
         FIG. 11  is a partial sectional view of a rotor; 
         FIG. 12  is a perspective view of a rotor; 
         FIG. 13  is a partial sectional view of a rotor housing including a bushing; 
         FIG. 14  is a partial perspective sectional view of an EGR pump and transmission assembly showing bearings and a spacer assembly; 
         FIG. 15  is a perspective view of a spacer assembly; 
         FIG. 16  is a partial sectional view of an EGR pump and transmission assembly showing an oil path to a spacer assembly and a lip seal; 
         FIG. 17  is a partial sectional view of an EGR pump and transmission assembly showing a lip seal in a normal unsealed state; 
         FIG. 18  is a partial sectional view of an EGR pump and transmission assembly showing a lip seal in a sealed state. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a diagram of an EGR system including an EGR pump  10 . The EGR system includes an engine  12  having an intake manifold  14  and an exhaust manifold  16 . A portion of the exhaust gases  17  from the exhaust manifold  16  are routed to an EGR cooler  18  to adjust a temperature of the EGR stream  17 . The stream  20  exiting the EGR cooler  18  is next routed to the EGR pump system  10 . The gas stream is then routed to the intake manifold  14  of the engine  12  and combined with fresh air. It should be realized that a turbo charger may also be used and a portion of the exhaust gases may be used to drive the compressor of the turbo charger and the boost air from the turbo charger may be routed to the intake manifold. 
     Referring to  FIGS. 2-4 , there is shown an exhaust gas recirculation pump (EGR pump) system  10 . The EGR pump system  10  includes an electric motor  21  having a housing. A roots device  22  is coupled to the electric motor  21 . The Roots device  22  includes a housing  24  that defines an internal volume  26 . Rotors  28  are disposed in the internal volume  26  and are connected to the electric motor. The rotors are supported on only a single end and are over hung or cantilevered. The electric motor  21  may be linked with the rotors  28  by a transmission assembly  30 . 
     In one aspect, for diesel applications, the EGR pump system  10  enables higher engine efficiency by reducing engine pumping losses by enabling the use of a high-efficiency turbo with a lower exhaust backpressure in comparison to prior designs. The EGR pump system  10  provides more accurate EGR flow rate control for better combustion and emissions management. The EGR pump system  10  may provide cost benefits in comparison to a traditional EGR system by eliminating structures such as an EGR valve, variable geometry turbocharger and an intake throttle associated with such designs. 
     The function of the EGR pump system  10  is to deliver exhaust gas from an engine&#39;s exhaust manifold  16  to its intake manifold  14  at a rate that is variable and that is controlled. In order to pump exhaust gas, the EGR pump system  20  may use a Roots device  22  coupled to an electric motor  21  such as a 48V electric motor. The electric motor  21  provides control of EGR flow rate by managing the motor speed and in turn the pump speed and flow rate of exhaust gas. 
     Referring to  FIGS. 3-4 , the exhaust gas recirculation pump system  10  includes a housing  24  that defines an internal volume  26  that receives the rotors  28 . The housing  24  includes a generally elliptical shape that accommodates the lobes  44  of the rotors  28 . The housing  24  includes a housing end face  34  linked with a housing side wall  36 . The portion of the housing  24  opposite the end face  34  is open. The housing  24  includes radial inlet and outlet ports  38 ,  40  formed therein. The inlet port  38  and the outlet port  40  include an angled geometry  42  best shown in  FIGS. 3 and 7 . In the depicted embodiments, the angled geometry  42  is in the shape of a parallelogram. The parallelogram shape provides a gradual or regulated release of the carrier volume of exhaust gas to the outlet port  40 . This results in reduced pulsations and potential noise, vibration and harshness (NVH). 
     Referring to  FIGS. 9-12 , the exhaust gas recirculation pump system  20  includes rotors  28  disposed within the housing  24 . The rotors  28  include a rotor shaft  43  having a plurality of lobes  44  formed thereon, the lobes  44  include a straight profile having a modified cycloidal geometry as disclosed in PCT application PCT/US16/47225 filed on Aug. 16, 2016, which is herein incorporated by reference. The modified cycloidal geometry includes a cycloid curve modified with at least two interpolated and stitched spline curves. The rotor lobe  44  profile further includes a flattened tip. The rotors  28  may be formed by a metal injection molding process. The rotors  28  include a rotor shaft  43  that extends to the lobe body  44  of the rotors. The rotor shaft  43  terminates at the lobe body  44  as the rotors  28  are supported on only a single end as described above. The lobe body  44  includes hollow cavities  46  formed therein corresponding to the inner portion of the three lobes  44  as well as along a direction of the rotor shaft  43 . The hollow cavities  46  are sealed by caps  48 . The hollow rotor lobe structure provides weight savings and improvements to the efficiency of the EGR pump. 
     Referring to  FIG. 13 , the housing  24  may include a bushing  90  attached or formed thereon. The bushing  90  may be formed of metal such as bronze, or another material such as a polymer or composite material. The bushing  90  may support the inner diameter  92  of a hole  94  bored into the rotor  28  to limit deflection of the rotors  28  in an overhung or cantilevered configuration. The bushing  90  may be easily replaceable and serviceable. 
     In an overhung configuration, there is concern that under a high pressure ratio condition, the rotors  28  could deflect and contact the housing  24 . The bushing  90  limits rotor deflection, while providing an interface for the rotor  28  to contact and still spin without galling, or causing other failure modes. In one aspect, the bushing  90  is positioned inside the rotor  28  with clearance. In this manner the bushing  90  only makes contact with the rotor  28  when a deflection occurs and acts as a protection against contact with the housing  24 . The bushing  90  may be installed over a stub shaft that is part of the housing  24  or a removable rear cover. 
     Referring to  FIGS. 4-8 , the transmission housing  25  includes journals  50  formed therein receiving bearings  52  that support the rotors  28 . The bearings  52  support the rotors  28  on only one end, such that the rotors  28  are overhung or cantilevered. In the depicted figures, two bearings  52  are positioned about the rotor shaft  42 . A spacer assembly  54  is provided in the bearings  52  to direct a load from an inner race of the bearing to an outer race. The bearings  52  in an EGR pump  10  require continuous oil flow for lubrication and heat dissipation. Oil flow can cause churning losses leading to pump inefficiency. By maintaining proper oil flow and improved oil drainage, the churning losses can be reduced, increasing pump efficiency. 
     The bearing arrangement  52  best shown in  FIG. 14-15  requires two bearings  52  with the spacer assembly  54 . The spacer assembly  54  includes an inner spacer  53  and an outer spacer  55  which are positioned in one bearing bore  57 . The bearings  52  are lubricated with oil that enters from an inlet port  61  formed in the transmission housing  25  and is directed to the spacers  53 ,  55 . The spacers  53 ,  55  provide bearing pre-load for proper operation. The bearing  52  and spacer assembly  54  arrangement allows continuously flowing oil into and out of the bearing bore  57  which has the spacer assembly  54 . The outer bearing spacer  55  includes notches  59 , allowing two-way oil flow. The center cavity drain  62  allows oil out of the bearing bore  57  without forced oil flowing though the bearings  52 . 
     Referring to  FIGS. 3-6 , the transmission housing  25  includes an oil cavity  56  formed therein. The oil cavity  56  is linked with an oil path  58  formed in the transmission housing  25 . The oil path  58  includes oil inlets  60  extending to oil outlets  62 . The oil inlets  60  and outlets  62  are coupled to an engine oil circulation system such that the oil path lubricates bearings  52  and a transmission assembly  30 . 
     The oil path  58  includes selected orifices  64  disposed therein providing a selectable amount of oil to the bearings  52  and transmission assembly  30 . In the depicted embodiment, selectable orifices  64  are positioned at each of the bearings  52 , at the oil inlet  60  and at a selected location of the transmission assembly  30 . 
     Referring to  FIGS. 16-18 , a lip seal  100  may be utilized to prevent the flow of oil vapor into the EGR pump rotor cavity  26  and is designed in such a way that the lip  116  is not contacting either an oil slinger  106  or rotor shaft  43  during normal operation (when exhaust cavity pressure is higher than oil sump pressure) to eliminate seal drag. During periodic events, such engine intake throttle closures, the EGR pump rotor cavity pressure will decrease causing the seal lip  116  to make contact and prevent backflow of oil vapors. 
     The EGR pump has forced oil lubrication of its bearings  52  and gears  66  and this oil should not enter the EGR loop of the engine. Sealing rings  108  are used to separate the high pressure exhaust in the rotor cavity  26  of the pump from the bearing/gear cavity  110 , but these rings  108  do not create a perfect seal. The exhaust pressures seen in the rotor cavity  26  are typically very high (up to 500 kPa absolute), and a certain amount of exhaust is allowed to leak past these sealing rings  108  into the bearing/gear cavity  110  (this is known as blowby). However, during some engine operating conditions that are much less frequent, the pressure in the rotor cavity  26  might decrease substantially enough to drive flow across the rings  108  in the opposite direction (i.e. closing engine intake throttle). Once in the rotor cavity  26 , the oil can mix with the EGR soot, causing fouling of the pump, intake manifold, and excess hydrocarbon emissions from the engine combustion. 
     The flexible lip seal  100  includes a base or substrate  112  formed of metal or another hard material that includes a flexible body  114  attached thereon. The body  114  may be formed of a rubber or polymer material with flexible properties such that the body  114  including a lip portion  116  is normally not contacting the rotating surface of the rotor shaft  43  or oil slinger  106 . By its shape and flexible properties, the lip portion  116  can be pushed away from these rotating surfaces by flow across the sealing rings  108  from the rotor cavity  26  towards the bearings  52 , as shown in  FIG. 17 . During this operation, the seal lip  116  does not make contact or seal, but also does not introduce drag or accumulate wear. 
     Then when an event occurs that results in lower rotor cavity pressure relative to the normal operating condition, such as closing the intake throttle, the change in the pressure differential is sufficient to flex the lip  116  of the seal  100  to touch the rotating shaft  43  or oil slinger  106  surfaces, thus creating a contact lip seal  100  that won&#39;t allow any oil or oil vapor past, as shown in  FIG. 18 . During this operation the seal will be well lubricated, and because this is not the normal operating condition for the engine the accumulated wear over time will be substantially less than if a conventional seal were used that is making contact or dragging all of the time. This arrangement allows the lip seal  100  to last on applications such as heavy duty diesel engines which require very long component life. 
     Referring to  FIGS. 2-5 , the exhaust gas recirculation pump system  20  includes a transmission assembly  30  that includes a drive gear  66  that is meshed with a driven gear  68 . The drive gear  66  is coupled to a drive shaft of the electric motor and to the rotor shaft  43 . The driven gear  68  is meshed with the drive gear  66  and is coupled to the other rotor shaft  43 . The transmission housing  25  includes angled transmission oil inlet  70  formed therein directing oil to the meshing of the drive gear  66  and the driven gear  68 . 
     Referring to  FIG. 6 , the transmission housing  25  includes journals  50  formed therein receiving bearings  52  that support the rotors  28 . The journals  50  formed on the transmission housing  25  include a plurality of bearing oil outlets  72  formed therein, with three shown in the depicted embodiment. The bearing oil outlets  72  allow oil to exit the bearings  52  to be routed to the oil outlet  62  formed in the transmission housing  25 . 
     Referring to  FIGS. 1-6 , the exhaust gas recirculation pump system  20  includes transmission housing or bearing plate  25  attached to the transmission housing  25 . The bearing plate  25  includes bearing plate inner and outer surfaces  76 ,  78 . The bearing plate inner surface  76  faces a rotor end face. The bearing plate  74  outer surface  78  includes the journals  50  formed therein receiving bearings  52  as described above. The bearing plate outer surface  78  includes the oil cavity  56  formed therein. 
     Referring to  FIGS. 2-4 , the exhaust gas recirculation pump system  20  includes an insulated coupling  82  joining a rotor shaft  42  to an electric motor shaft. The insulated coupling  82  reduces heat transfer from the housing  24  to the electric motor. In one aspect, the insulated coupling  82  is formed of PEEK or may be formed of other materials such as plastic composites or ceramic insulating type materials. 
     In one aspect, the insulated coupling  82  includes a disk shaped body  84  having a plurality of through holes  86 . Pins formed on the electric motor shaft are received in a portion of the through holes  86  and pins formed on the drive gear  66  of the transmission assembly  30  are received in another portion of the through holes  86 . The insulated coupling  82  connects the electric motor to the rotors  28  and reduces heat transfer. 
     Alternatively, the insulated coupling  82  may include a pentagonal body having an inner bore formed therein. The pentagonal body may include a flange formed on one end. The inner bore may be sized to receive an end of the rotor shaft which has a complementary shape and size. The outer shape of the pentagonal body may be received in a corresponding drive bore formed on the drive shaft of the electric motor. In this manner, the drive shaft is thermally isolated and coupled to the rotor shaft.