Abstract:
A supercharger cooling system provides a path for coolant from an air/coolant heat exchanger to a supercharger intercooler and then loops around the supercharger housing proximal to a hot outlet end of the supercharger and back to the heat exchanger. The heat exchanger may be a dedicated air/coolant heat exchanger or be a vehicle radiator. The intercooler is sandwiched between the supercharger and intake manifold and cools the flow of hot compressed air from the supercharger into the intake manifold. The supercharger cooling loop cools the bearings and seals, the forward ends of the male and female rotors, and the male and female rotor gears. The cooling loop is preferably located between the supercharger rotors and the rotor drive gears to form a barrier to heat. A dedicated pump cycles the coolant flow and restrictions control the flow of coolant to the supercharger.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation In Part of U.S. patent application Ser. No. 12/567,679 filed Sep. 25, 2009, which application is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to supercharger cooling and in particular to cooling a hotter end of a supercharger including two or more rotating rotors. 
     Modern roots supercharger have improved efficiency by having an axial inlet at an inlet end and timing gears at an opposite end. Unfortunately, the opposite end is hotter than the inlet end exposing the timing gears to such heat reduced gear and lubricant life. 
     Twin screw type superchargers draw air into the rear of the supercharger and compress the air as it travels from the rear to the front of the supercharger between supercharger rotors. According to the ideal gas law, the air traveling through the supercharger is heated proportional to the compression of the air inside the supercharger and is thus hotter at the front of the supercharger then at the rear of the supercharger. Further, no supercharger is 100 percent efficient, and although screw type superchargers are more efficient than roots-type superchargers, they remain approximately 70 to 80 percent efficient, which means that if the ideal temperature increase is 100 degrees, the actual temperature increase in 20 to 30 percent greater (in terms of absolute temperature). This temperature variation from the front and the rear of the supercharger results in a corresponding unequal heating of supercharger components, and as a result, unequal expansion of the supercharger components and an accompanying variation in clearances (for example, rotors, cases, front plate, gears, bearings, and the like) between supercharger components. The rotor bearing are interference fit, and when the end cover becomes hot enough, the bearing may rotate in the bearing seats, damaging the seats, and causing the rotors to contact and destroy the supercharger. 
     When the front plate expands from heat, gears positioned by the front plate experiences an increased gear clearance. Correct gear positions are critical in a twin screw supercharger because the gear positions determine the location of the male and female rotors and their separation. Excessive gear clearance may also result in rotor contact, and proper operation of the supercharger requires that the rotors remain in phase with each other throughout the operating temperature range of the supercharger, which is between 100° F. and 450° F. 
     A possible solution to the variation of clearances with temperature is to increase rotor to rotor clearance to compensate for the temperature variation over the entire temperature range of supercharger operation. Unfortunately increasing the clearances in a twin screw type supercharger reduces supercharger efficiency. Further, increasing gear clearance results in noisy supercharger operation which is often objectionable to a driver, and accelerates wear of the gears. 
     Further, the rotors of twins screw type superchargers are generally made from aluminum. The aluminum rotors generally have 0.003 inches to 0.004 inches of clearance and thus controlling the expansion of the rotors, regardless of the clearances between gears, has been an issue with the twin screw type superchargers for decades. Greater than ideal clearances have been incorporated into the supercharger designed to deal with rotor expansion. Unfortunately these large clearances reduce supercharger efficiency resulting in hotter air charges, lower output, and higher power requirement for operating the supercharger. Further, should the rotors contact each other due to excessive expansion, the supercharger is generally destroyed. 
     The front (output) or discharge side of the supercharger is the hottest and rotor contact always occurs towards the front of the supercharger. The rear (inlet) or intake is ingesting cooler ambient air so there is generally no rotor contact at the rear end of the supercharger. And, the higher the temperatures inside the supercharger, the more severe the rotor contact and the farther the contact reaches from the rear to the front of the supercharger. 
     The rotors fore and aft shafts and bearings support and stabilize the positions of the rotors. Unfortunately, the front plate having a higher temperature expands more than the rear plate which is closer to ambient air temperature. This temperature imbalance accompanied by the expansion imbalance causes the front of the rotors to separate more than the rear of the rotors. The rotor gears are attached to the front of the rotors and as a result experienced increased gear lash as the fronts of the rotors separate. Both the gear lash and the rotor expansion move the rotors outward closer to the supercharger case and the timing change from the excess gear lash results in circumferentially excess movement of one rotor or in relation to the other. 
     In addition to loss of efficiency and damage to the supercharger, the increased temperatures shorten the life of supercharger seals. 
     The front case of the supercharger contains the oil used to lubricate the gears and bearings. Friction from the rotating gears, bearings, and seals heat the oil, and higher supercharger rpm, greater boost, and higher air temperature at the front of the supercharger, further contribute to higher oil temperature. These effects combine to make controlling the temperature of the twin screw supercharger extremely difficult. 
     A possible solution to cooling the supercharger is to provide a pressurized flow of engine oil to the supercharger gears. Unfortunately, this approach requires external lines to provide a source of pressurized oil to the supercharger, and external drain lines from the supercharger to the engine oil pan to drain the oil from the supercharger, which create potential oil leaks. Further, additional heating of engine oil raises oil temperature and affects oil flow reducing the cooling affect of the oil. 
     Thus, a need remains for cooling the front (output) end of a screw type supercharger. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing a supercharger cooling system which provides a path for coolant from an air/coolant heat exchanger to a supercharger intercooler and then loops around the supercharger housing proximal to a hot outlet end of the supercharger and back to the heat exchanger. The heat exchanger may be a dedicated air/coolant heat exchanger or be a vehicle radiator. The intercooler is sandwiched between the supercharger and intake manifold and cools the flow of hot compressed air from the supercharger into the intake manifold. The supercharger cooling loop cools the bearings and seals, the forward ends of the male and female rotors, and the male and female rotor gears. The cooling loop is preferably located between the supercharger rotors and the rotor drive gears to form a barrier to heat. A dedicated pump cycles the coolant flow and restrictions control the flow of coolant to the supercharger. 
     In accordance with one aspect of the invention, there is provided a system for circulating engine coolant generally at 160 degrees Fahrenheit to 200 degrees Fahrenheit to the hot front (outlet end) of the supercharger. The cooling provided reduces the temperatures of the rotor bearings, seals, and gears. Providing the coolant flow to the outlet end wall of the supercharger provides a barrier to heat thereby improving performance and reduces wear and failures. 
     In accordance with another aspect of the invention, there is provided a system for circulating engine coolant through the outlet end wall of the supercharger. The outlet end wall includes seats for the outlet end rotor bearings and separates the rotor drive gears from the hot compressed air in the outlet end of the supercharger. Preventing overheating of the outlet end wall maintains proper rotor centerdistance thereby improving performance and reduces wear and failures. 
     In accordance with yet another aspect of the invention, there is provided the a system for circulating engine coolant through the outlet end wall of the supercharger. The outlet end wall separates the outlet end wall from the hot compressed air in the outlet end of the supercharger. Cooling the outlet end wall provides a barrier to heat reaching the rotor drive gears and lubricating oil inside the discharge side cover which lubricates the rotor drive gears. Such cooling improves lubrication and extends the life of the lubricating oil. 
     In accordance with still another aspect of the invention, there is provided the a system for circulating engine coolant through a supercharger housing proximal to the outlet end wall of the supercharger. Cooling the housing proximal to the outlet end wall provides a barrier to heat reaching the rotor drive gears and lubricating oil inside the discharge side cover which lubricates the rotor drive gears. Such cooling improves lubrication and extends the life of the lubricating oil. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1A  is a side view of a supercharged engine according to the present invention. 
         FIG. 1B  is a top view of the supercharged engine according to the present invention. 
         FIG. 1C  is a front view of the supercharged engine according to the present invention. 
         FIG. 2A  is a side view of a supercharger, intercooler, and intake manifold according to the present invention. 
         FIG. 2B  is a top view of the supercharger, intercooler, and intake manifold according to the present invention. 
         FIG. 3  is a cross-sectional view of the supercharger, intercooler, and intake manifold according to the present invention taken along line  3 - 3  of  FIG. 2B . 
         FIG. 4  shows the supercharged engine, a heat exchanger, and coolant lines according to the present invention. 
         FIG. 5  is a front view of a supercharger outlet end wall and intercooler coolant flow according to the present invention. 
         FIG. 6  is a cross-sectional view of the supercharger outlet end wall taken along line  6 - 6  of  FIG. 5 . 
         FIG. 7A  is a front view of a coolant channel cover according to the present invention. 
         FIG. 7B  is an edge view of the coolant channel cover according to the present invention. 
         FIG. 8  shows the supercharged engine, a heat exchanger, and coolant lines according to the present invention. 
         FIG. 9  shows a cutaway view of the supercharger housing proximal to the outlet end wall showing a coolant path according to the present invention. 
         FIG. 10  shows a cross-sectional view of the supercharger housing proximal to the outlet end wall taken along line  10 - 10  of  FIG. 9  showing a coolant path according to the present invention. 
         FIG. 11  shows a cross-sectional view of a single piece supercharger housing and outlet end wall proximal to the outlet end wall taken along line  6 - 6  of  FIG. 5  showing a coolant path according to the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A side view of a supercharged engine  10  according to the present invention is shown in  FIG. 1A  and a top view of the supercharged engine  10  is shown in  FIG. 1B . The supercharged engine  10  includes a screw compressor type supercharger  12  attached to an intake manifold  20  through an intercooler  22 . The screw compressor type supercharger  12  compresses air received through a throttle body  16  and provides the compressed air to the supercharged engine  10  through the intercooler  22  and intake manifold  20 . The screw compressor type supercharger  12  is driven by a belt  14  connecting a crankshaft pulley to a supercharger pulley. 
     A side view of the screw compressor type supercharger  12  according to the present invention is shown in  FIG. 2A  and a top view of the screw compressor type supercharger  12  is shown in  FIG. 2B . A supercharger pulley  18  is attached to the screw compressor type supercharger  12  at a front (outlet) end  12   a  of the supercharger and the throttle body  16  is attached at a rearward end  12   b . While the supercharger is shown as having the outlet end to the front, belt drives may also be provided to position the inlet end of the supercharger to the front and the supercharger driven from the rear, and such variations are intended to come within the scope of the present invention. The supercharger includes a housing  13  having a length L, an inlet end wall  51  behind the housing  13 , and the outlet end wall  47  ahead of the housing  13 . 
     A cross-sectional view of the screw compressor type supercharger  12  taken along line  3 - 3  of  FIG. 2B  is shown in  FIG. 3 . A first rotor  24  and a second rotor  26  are rotatably housed in a housing  13  of the screw compressor type supercharger  12 . The rotors  24  and  26  are turned by the pulley  18  and draw ambient air  28  through the throttle body  16  and through the rear (inlet) end  12   b  and into the screw compressor type supercharger  12 . The ambient air is compressed as it passes through the screw compressor type supercharger  12  by the rotors  24  and  26 . The compressed air  29  is pumped through compressed air passage  30  and through the intercooler  22  and the intake manifold  20  into the engine  10 . 
     The power produced by a supercharging internal combustion engine  10  is generally increased by increasing the supercharger  12  boost pressure. Increasing the boost pressure necessarily results in increased temperature of the compressed air  29  being pumped into the engine  10 . Such temperature increase is proportional to the absolute pressure increase (the Ideal Gas Law) and further increased by less than 100 percent supercharger efficiency. The hot air flowing through the supercharger further heats mechanical components and lubrication oil of the supercharger. The air flow is heated as it passes from the inlet end  12   b  to the outlet end  12   a , and as a result, the components near the front  12   a  of the supercharger  12  experience significantly greater temperature rise than near the rear  12   b . Such heating of elements near the front  12   a  of the supercharger  12  has resulted in reduced performance, wear to components, and mechanical failures. 
     The supercharged engine  12 , a heat exchanger  45 , and coolant lines  40   a ,  40   b , and  40   c  according to the present invention are shown in  FIG. 4 . Increased pressure (i.e., boost) often requires intercooling to prevent detonation. The air to liquid coolant intercooler  22  is popular for many installations because of the compact size and the elimination of a cooling air flow through the intercooler required by air to air intercoolers. The intercooler  22  is conveniently mounted between the supercharger  12  and the intake manifold  20 . The circulating liquid coolant is cooled by air  43  in a radiator  45  which is generally mounted in the front of the car. The line  40   a  carries the coolant  41  from a heat exchanger coolant outlet  45   b  on the heat exchanger  45  to an intercooler coolant inlet  22   a  on the intercooler  22  through a pump  44 . The line  40   b  carries the coolant  41  from an intercooler coolant outlet  22   b  on the intercooler  22  to a supercharger coolant inlet  12   a  on the supercharger  12 . The line  40   c  carries the coolant  41  from a supercharger coolant outlet  12   b  on the supercharger  12  back to a heat exchanger coolant inlet  45   a  on the heat exchanger  45  to complete the cycle. 
     The pump  44  may be a mechanical pump or an electric pump. When an electric pump is used the pump may be controlled, for example using a pulse width modulated power signal, to provide the required coolant flow  41  to the supercharger  12 . 
     Two restricted flows  41   a  and  41   b  connect the line  40   b  to the line  40   c . The restricted flow  41   a  passed through a fixed restriction  48  and the flow  41   b  passes through a variable restriction  49  to control the amount of coolant  41  flowing through the supercharger  12 . The variable restriction  49  may be thermostatically controlled and is preferably controlled based on supercharger  12  temperature. 
     A front view of a supercharger outlet end wall  47  and coolant flow  41  according to the present invention is shown in  FIG. 5  and a cross-sectional view of the supercharger outlet end wall  47  and discharge end cover  59  taken along line  6 - 6  of  FIG. 5  is shown in  FIG. 6 . As the boost is increased, the temperature of the compressed air  30  pumped into the engine  10  also increases, particularly at the outlet end  12   a  of the supercharger (see  FIG. 2A ). The outlet end wall  47  is in contact with the hot compressed air  30  causing the temperature of the outlet end wall  47 , the bearings  52  and  53 , the shaft seals  54  and  55 , the rotor drive gears  50   a  and  50   b , and lubricating oil inside the discharge end cover  59  to increase under high boost, reducing performance and increases wear and failures. 
     The outlet end wall  47  is generally made of aluminium and includes seats  52   a  and  53   a  for the bearings  52  and  53 . Because of the high thermal expansion of aluminum, outlet end wall  47  does not maintain the centerdistance of the gears  50   a  and  50   b  and the rotors  24  and  26  when the hot compressed air  30  heats the outlet end wall  47  to high operating temperatures. The gears  50   a  and  50   b  are made of steel having a coefficient of thermal expansion different from the outlet end wall  47  and as a result the gear mesh of the gears  50   a  and  50   b  is affected by the expansion of the outlet end wall  47 . The supercharger inlet end wall is also made of aluminium but is continuously cooled by the inlet air  28  at ambient temperature, and as a result, the outlet ends  24   a  and  26   a  of the rotors  24  and  26  do not maintain the same rotor centerdistance as the inlet ends. Heat is also generated by the rotor drive gears  50   a  and  50   b , the pulley  18 , the bearings  52  and  53  and the seals  54  and  55 . 
     Some of the heat is further transferred to oil in the space  57  between the discharge end cover  59  and the outlet end wall  47 . The oil is continuously thrown against neighbouring walls, and additionally, a number of mounting bosses spaced around the interior of the discharge end cover  59  tend to collect the oil in the top half of the discharge end cover  59  delaying the oil from running down into the oil sump, resulting in the hot oil heating the discharge end cover  59 . The lubricating quality of the oil may be reduced when the oil is heated excessively resulting in wear to the gears  50   a  and  50   b.    
     The supercharger cooling system according to the present invention cools the outlet end wall  47  thereby effectively cooling the bearing seats  52   a  and  53   a , the bearings  52  and  53 , and the seals  54  and  55 , and creating a barrier to heat from the hot compressed air  30  reaching the gears  50   a  and  50   b . As a result, the rotor centerdistance in the outlet end  12   a  remains very close to the rotor centerdistance in the inlet end  12   b , and proper gear mesh is maintained, thereby improving performance and reducing wear and failures. Additionally, reducing expansion allows the rotor to rotor centerdistance to be kept small for optimum performance and safe operation. 
     More preferably, the flow  41  through the liquid coolant channel  46  circles around the outside radii of the seats  52   a  and  53   a  of the two bearings  52  and  53  to cool the seats  52   a  and  53   a , the bearings  52  and  53 , and the outlet end wall  47 . Cooling the outlet end wall  47  contributes to maintaining the centerdistance between the rotors and the gears, even under high boost conditions. Cooling the bearing seats  52   a  and  53   a  also helps to maintain an interference fit of the bearings  52  and  53  to the bearing seats  52   a  and  53   a . Cooling the outlet end wall  47  also provides a barrier to heat flowing from the hot compressed air flow  30  through the outlet end wall  47  and into the space  57  inside the discharge end cover  59 , thereby preventing or reducing heating of the gears  50   a  and  50   b  and the oil residing in the space  57 . 
     A front view of a coolant channel cover  56  is shown in  FIG. 7A  and an edge view of the coolant channel cover  56  is shown in  FIG. 7B . The coolant channel cover  56  includes an O-ring  56   a  circling it&#39;s outside edge for sealing outside the coolant flow  41  against a recess edge of the outlet end wall  47 . O-rings  46   a  (see  FIG. 6 ) provide a second seal between the outlet end wall  47  and the coolant channel cover  56  for sealing inside the coolant flow  41 . 
     The present invention reduces heating of the discharge end cover  59  because a rear face of the cooling channel cover  56  is directly cooled by the liquid coolant  41  in channel  46 . The oil in the space  57  is exposed to a front face of the cooling channel cover  56  and is cooled as the oil runs down the front face of the cooling channel cover  56 . 
     A supercharged engine  10 ′, the heat exchanger  24 , and coolant lines are shown in  FIG. 8 . The supercharged engine  10 ′ is similar to the supercharged engine  10  but does not include an intercooler. The heat exchanger coolant outlet  45   b  is connected to the supercharger coolant inlet  12   a.    
     In another embodiment, a liquid coolant channel between forward edges  24 ′ and  26 ′ of the rotors  24  and  26  respectively and the bearings  52  and  53  creates a barrier to heat from the hot compressed air  30  reaching the gears  50   a  and  50   b  improving performance and reducing wear and failures. A cutaway view of a second supercharger housing  13   a  proximal to the outlet end wall  47  showing a coolant path  60  through the housing  13   a  is shown in  FIG. 9  and a cross-sectional view of the supercharger housing  13   a  proximal to the outlet end wall  47  taken along line  10 - 10  of  FIG. 9  showing the coolant path  60  is shown in  FIG. 10 . The rotors include rotor shaft  24 ′ and  26 ′ connecting the rotors to the gears  50   a  and  50   b  and the coolant path  60  circles the rotor shafts. The coolant path  60  is centered a distance [[D]] D 1  or alternatively no portion of the supercharger coolant path is greater than a distance D 2 , from an outlet end wall portion of the supercharger, from the outlet end wall  47 . The distances D 1  and D 2  are preferably less than three inches and more preferably less than two inches. 
     A cross-sectional view of a single piece supercharger housing and outlet end wall  13 ′ taken along line  6 - 6  of  FIG. 5  showing the coolant channel  46  is shown in  FIG. 11 . The single piece supercharger housing and outlet end wall  13 ′ is a single piece, and is otherwise similar to the supercharger housing and the outlet end wall  47 . 
     Space in the engine compartment is often limited and an embodiment of the supercharger cooling system according to the present invention described below uses an existing engine cooling system to provide the desired cooling without adding significant additional parts. The existing engine cooling system includes a radiator mounted in the front of the car and a water pump. The water pump circulates the existing liquid coolant through the radiator and the engine. The water pump may also be used to circulate a part of the total coolant flow to the cooling channel  46  in the outlet end wall  47  to cool the supercharger. A parallel circuit comprising the lines  40   a , and  40   c  is connected to the existing vehicle cooling system with the line  40   a  connected to a higher pressure point and the line  40   c  to a lower pressure point. The amount of liquid coolant cycled through the cooling channel  46  is controlled by the two restrictions  48  and  49 . By altering the size of the two restrictions  8  and  9  each flow can be determined for optimum cooling performance. 
     While the above description focuses on a screw type supercharger, those skilled in the art will recognize that the present invention is equally applicable to a roots type supercharger and such cooling for a roots type supercharger is intended to come within the scope of the present invention. 
     The liquid coolant is often a water based coolant but may also be a Propylene glycol coolant or any other liquid coolant. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.