Abstract:
A supercharger clutch system has a clutch housing ( 52 ) in which a clutch pack ( 84 ) is disposed to transmit torque from an input, such as a pulley ( 66 ), to one of the timing gears ( 58 ). The clutch pack ( 84 ) is disposed within a cage ( 92 ), having a spring seat member ( 98 ) adjacent thereto. A set of springs ( 104 ) biases the seat member and the clutch cage ( 92 ) to engage the clutch pack ( 84 ). On the opposite side, axially, of the clutch pack there is a piston ( 76 ) including a portion ( 80 ) surrounding the clutch cage ( 92 ) and engaging the seat member ( 98 ). The piston ( 76 ) and the clutch housing ( 52 ) define a pressure chamber ( 106 ) which, when pressurized, causes movement of the piston in a direction compressing the springs ( 104 ) and disengaging the clutch pack. With the invention, the clutch system can be operated by engine lubrication oil, while still achieving rapid engagements (short response time), wherein the rate of engagement can be modulated to suit vehicle operating conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE DISCLOSURE 
     The present invention relates to a rotary blower, such as a supercharger for supercharging an internal combustion engine. More particularly, the invention relates to a supercharger having a fluid pressure operated clutch assembly adapted to transmit torque from an input to the supercharger rotors. 
     Although the present invention may be used advantageously with superchargers having various rotor types and configurations, such as the male and female rotors found in screw compressors, it has been developed for use with a Roots Blower supercharger, and will be described in connection therewith. 
     As is well known to those skilled in the art, the use of a supercharger to increase or “boost” the air pressure in the intake manifold of an internal combustion engine results in an engine having greater horsepower output capability than would occur if the engine were normally aspirated, (i.e., if the piston would draw air into the cylinder during the intake stroke of the piston). However, the conventional supercharger is mechanically driven by the engine, and therefore, represents a drain on engine horsepower whenever engine boost is not required. For the above and other reasons, it has been known for several years to provide some sort of engageable/disengageable clutch assembly disposed in series between the input (e.g., a belt driven pulley) and the blower rotors. 
     The assignee of the present invention has sold superchargers commercially including such clutch assemblies which operate electromagnetically. Unfortunately, the ON-OFF characteristics of electromagnetic clutches produce a transient load torque on the engine. For example, as the electromagnetic clutch is engaged, the result will be a “droop” in engine speed which will likely be perceived by the driver and maybe manifested as an undesirable slowing down of the vehicle. 
     It is also known to provide a fluid pressure operated clutch assembly in which the clutch pack is spring biased toward a disengaged condition, and is moved toward an engaged condition in response to axial movement of a fluid pressure actuated piston member. In other words, the known supercharger clutch is of the “pressure-applied, spring-released” type. Although a supercharger with such a clutch arrangement can operate in a generally satisfactory manner, once the clutch is in either the engaged or the disengaged condition, the known arrangement does involve certain disadvantages during “transient” conditions, i.e., as the clutch assembly changes from the disengaged condition to the engaged condition, or vice versa. By way of example, a known supercharger clutch assembly of the pressure applied, spring released type requires a fairly long piston travel in order to achieve engagement of the clutch pack (or very high apply pressure), thus requiring substantial flow of fluid to accomplish the required piston movement. 
     Although such a high flow requirement is not a problem, once the engine has reached normal operating temperature, it frequently occurs that engagement of the clutch assembly is required soon after “cold engine start up”, while the engine oil is still cold. As a result, the known pressure applied, spring released system will have substantially longer time of engagement when the engine is cold than when the engine is warm, By way of example only, a typical engagement or release response time, as specified by the vehicle manufacturer, would be in the range of about 0.10 seconds. A substantially longer response time would result in the well known “turbo lag” feeling wherein the operator depresses the accelerator, but then there is a time lag before engine boost becomes noticeable, as is inherent in a turbo-charger type of engine boost system. On the other hand, response time should not be so fast (when engaging) and so sudden as to result in a large torque spike being imposed upon the engine. 
     Another disadvantage associated with the pressure-applied type of supercharger clutch is that the oil pressure typically used is the engine lubrication oil circuit. As a result, the fluid pressure available to engage the clutch may be only in the range of about 20 psi., and even that very low pressure may not be available on a sufficiently consistent and predictable basis to be relied upon for engagement of the supercharger clutch, especially within the specified response time. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved supercharger and clutch assembly which overcome the above-described disadvantages of the prior art. 
     It is a more specific object of the present invention to provide an improved supercharger and clutch assembly which accomplishes the above-stated object, and which has both a variable and a controllable engagement and disengagement response time, thus avoiding both transient overloading of the engine and a time lag upon engagement. 
     It is a further object of the present invention to provide such an improved supercharger and clutch assembly which operates in a consistent manner, substantially independent of variables such as engine oil temperature. 
     The above and other objects of the invention are accomplished by an improved rotary blower of either the backflow or compression type comprising a housing assembly including a main housing and a clutch housing, the main housing defining a blower chamber. Blower rotor assemblies are disposed in the blower chamber for effecting transfer of volumes of fluid in response to rotation of an input shaft. One of the blower rotor assemblies is operably mounted on a rotor shaft and has an input hub portion disposed adjacent the input shaft. A clutch assembly is disposed in the clutch housing and in driven relationship with the input shaft, and in driving relationship with the input hub portion, the clutch assembly being selectively operable between an engaged condition, operable to transmit torque from the input shaft to the input hub portion, and a disengaged condition. 
     The improved rotary blower is characterized by the clutch assembly including a first set of clutch disks fixed for rotation with the input shaft and a second set of clutch disks fixed for rotation with the input hub portion. A biasing means normally biases the first and second sets of clutch disks toward the engaged condition. A piston member cooperates with the clutch housing to define a pressure chamber, the piston member being axially moveable, in response to the presence of relatively high pressure fluid in the pressure chamber to a position releasing the biasing means and permitting the clutch assembly to move to the disengaged position. A valve means is operably associated with the clutch housing and is operable to communicate the pressure chamber to a source of relatively low pressure fluid in response to an electrical input signal having a first condition, and to a source of relatively high pressure fluid in response to the electrical input signal having a second condition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an intake manifold assembly having disposed therein a supercharger of the type which may utilize the present invention. 
     FIG. 2 is a front plan view of the supercharger shown schematically in FIG.  1 . 
     FIG. 3 is an enlarged, fragmentary, axial cross-section taken on line  3 — 3  of FIG. 2, and showing primarily the clutch assembly of the present invention, in its engaged condition. 
     FIG. 4 is an enlarged, fragmentary, axial cross-section taken on line  4 — 4  of FIG. 2, and showing primarily the control valve assembly for controlling the clutch assembly of the present invention. 
     FIG. 5 is an enlarged, fragmentary, axial cross-section similar to FIG. 3, and on approximately the same scale, illustrating an alternative embodiment of the clutch assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, which are not intended to limit the invention, FIG. 1 is a schematic illustration of an intake manifold assembly, including a Roots blower supercharger and bypass valve arrangement of the type which is now well known to those skilled in the art. An engine, generally designated  10 , includes a plurality of cylinders  12 , and a reciprocating piston  14  disposed within each cylinder, thereby defining an expandable combustion chamber  16 . The engine includes intake and exhaust manifold assemblies  18  and  20 , respectively, for directing combustion air to and from the combustion chamber  16 , by way of intake and exhaust valves  22  and  24 , respectively. 
     The intake manifold assembly  18  includes a positive displacement rotary blower  26  of the backflow or Roots type, as is illustrated and described in U.S. Pat. Nos. 5,078,583 and 5,893,355, assigned to the assignee of the present invention and incorporated herein by reference. The blower  26  includes a pair of rotors  28  and  29 , each of which includes a plurality of meshed lobes. The rotors  28  and  29  are disposed in a pair of parallel, transversely overlapping cylindrical chambers  28   c  and  29   c , respectively. The rotors may be driven mechanically by engine crankshaft torque transmitted thereto in a known manner, such as by means of a drive belt (not illustrated herein). The mechanical drive rotates the blower rotors at a fixed ratio, relative to crankshaft speed, such that the blower displacement is greater than the engine displacement, thereby boosting or supercharging the air flowing to the combustion chambers  16 . 
     The supercharger or blower  26  includes an inlet port  30  which receives air or air-fuel mixture from an inlet duct or passage  32 , and further includes a discharge or outlet port  34 , directing the charged air to the intake valves  22  by means of a duct  36 . The inlet duct  32  and the discharge duct  36  are interconnected by means of a bypass passage, shown schematically at  38 . If the engine  10  is of the Otto cycle type, a throttle valve  40  preferably controls air or air-fuel mixture flowing into the intake duct  32  from a source, such as ambient or atmospheric air, in a well known manner. Alternatively, the throttle valve  40  may be disposed downstream of the supercharger  26 . 
     Disposed within the bypass passage  38  is a bypass valve  42  which is moved between an open position and a closed position by means of an actuator assembly, generally designated  44 . The actuator assembly  44  is responsive to fluid pressure in the inlet duct  32  by means of a vacuum line  46 . Therefore, the actuator assembly  44  is operative to control the supercharging pressure in the discharge duct  36  as a function of engine power demand. When the bypass valve  42  is in the fully open position, air pressure in the duct  36  is relatively low, but when the bypass valve  42  is fully closed, the air pressure in the duct  36  is relatively high. Typically, the actuator assembly  44  controls the position of the bypass valve  42  by means of suitable linkage. Those skilled in the art will understand that the illustration herein of the bypass valve  42  is by way of generic explanation and example only, and that, within the scope of the invention, various other bypass configurations and arrangements could be used, such as a modular (integral) bypass or an electronically operated bypass, or in some cases, no bypass at all. 
     Referring now primarily to FIGS. 2 and 3, the blower  26  includes a housing assembly generally designated  48 , which includes a main housing  50  (shown only fragmentarily in FIG,  3 ), which defines the chambers  28   c  and  29   c . The housing assembly  48  also includes an input housing  52 , also referred to hereinafter as a clutch housing. Disposed axially between the main housing  50  and the clutch housing  52  is a bearing plate  54  through which extends a forward end of a rotor shaft  56 , on which is mounted the rotor  28 . 
     As is well known to those skilled in the art of superchargers, a timing gear  58  is pressed onto the forward end of the rotor shaft  56 , and in the subject embodiment, the timing gear  58  includes an input hub  60 . Journalled within the forward end (left end in FIG. 3) of the input hub  60  is a reduced diameter portion  62  of an input shaft  64 . Disposed about a forward end of the input shaft  64  is an input pulley  66 , by means of which torque is transmitted from the engine crankshaft (not shown) to the input shaft  64 . It should be noted that the input pulley  66  is shown only fragmentarily in FIG.  3 . The input pulley  66  surrounds a reduced diameter portion  68  of the clutch housing  52 , and disposed radially between the input shaft  64  and the portion  68  is a bearing set  70 . 
     The clutch housing  52  defines a relatively smaller internal diameter  72 , also referred to hereinafter as a cylindrical surface  72 , and a relatively larger internal diameter  74 , also referred to hereinafter as a cylindrical surface  74 . The cylindrical surfaces  72  and  74  comprise a clutch chamber which will hereafter also bear the reference “74”. Disposed within the clutch chamber  74  is a clutch assembly, generally designated  75 , including a clutch piston  76 , including a reduced diameter portion  78  which is in sealing engagement with the smaller cylindrical surface  72 , and a larger cylindrical portion  80  which is in sealing engagement with the cylindrical surface  74 . 
     A splined drive member  82  is in driven engagement with the input shaft  64  by any suitable means, such as a press-fit relationship. Surrounding the drive member  82  is a clutch pack, generally designated  84 , including a set of internally splined clutch disks  86 , which are in splined engagement with the drive member  82 . Interleaved with the disks  86  is a set of externally splined clutch disks  88 , which are in splined engagement with internal splines defined by a cylindrical portion  90  of a clutch housing or cage  92 . The clutch cage  92  also includes a relatively smaller cylindrical portion  94  which is in a splined relationship with the input hub  60 , such that there can be relative axial movement therebetween, for reasons which will become apparent subsequently. Therefore, whenever the clutch pack  84  is engaged, input torque is transmitted from the input pulley  66  through the input shaft  64  to the splined drive member  82 , and from there through the clutch pack  84  to the clutch cage  92 , and then through the timing gear  58  to the rotor shaft  56 . 
     Disposed about the cylindrical portion  94 , and in a press-fit relationship thereto, is a bearing set  96 , and surrounding the bearing set  96  is a spring seat member  98  (also referred to hereinafter as a release plate), the outer periphery of the member  98  being in engagement with a rearward shoulder surface  100  of the cylindrical portion  80  of the clutch piston  76 . The purpose of the above relationship of the spring seat member  98  and the clutch piston  76  will be described subsequently. 
     Seated against a forward surface of the bearing plate  54  is a plurality (of which two are shown in FIG. 3) of spring support members  102 , each member  102  being surrounded by a coil compression spring  104 , the forward end of each spring  104  being seated against the spring seat member  98 . Disposed axially between the radially extending portion of the clutch housing  52  and the forward surface of the clutch piston  76  is an annular pressure chamber  106 . Whenever relatively high pressure is communicated to the pressure chamber  106 , the clutch piston  76  is moved rearwardly (to the right in FIG. 3) to a position in which the springs  104  are sufficiently compressed that the member  98  is disposed in contact with the forward end (left end in FIG. 3) of each of the support members  102 . Thus, the members  102  also serve as travel “stops” for the springs  104  and the seat member  98 . 
     As is used herein, the term “relatively high” pressure will be understood to mean high relative to the low pressure, or sump (reservoir) pressure which would be present in the pressure chamber  106  whenever the chamber  106  is drained, i.e., is communicated to a case drain region, such as that surrounding the timing gear  58  (and the other timing gear, not shown herein). However, it is also one important aspect of the invention that the “relatively high” pressure used to disengage the clutch pack  84  is preferably a pressure of only about 10 to 20 psi. (gauge). As was mentioned in the BACKGROUND OF THE DISCLOSURE, it is desirable to be able to operate the supercharger clutch using only the engine lubrication oil, for which the pressure would typically be about 20 psi. at the “end” of its flow path, which is where the supercharger clutch would be disposed. 
     When the piston  76  is moved to the right from the position shown in FIG. 3, the spring seat member  98  is also moved rearwardly, compressing the springs  104 , as mentioned previously. With the springs  104  somewhat compressed, the clutch cage  92  is moved somewhat to the right in FIG. 3, and the loading of the clutch pack  84  is relieved sufficiently such that no substantial torque will be transmitted from the input shaft  64  to the clutch cage  92 . In other words, no substantial input torque will be transmitted to the timing gear  58  or to the rotor shaft  56 . Preferably, the unloading of the clutch pack  84  is sufficient to eliminate any “clutch drag”, the presence of which would somewhat diminish the benefit of being able to de-clutch the supercharger. 
     In order to engage the clutch pack  84 , and therefore, to drive the rotors of the supercharger, it is necessary to reduce the fluid pressure in the pressure chamber  106  from the relatively high pressure to a relatively low pressure (which could be sump or reservoir pressure). In the subject embodiment, the spring rate of the springs  104  has been selected such that, when the pressure in the chamber  106  is reduced to the relatively low pressure, the springs  104  will bias the seat member  98  forwardly (to about the position shown in FIG. 3) which, in turn, biases the bearing set  96  and the clutch cage  92  forwardly. Such forward movement of the radially extending wall of the clutch cage  92  will compress the clutch pack  84  against a radially extending lip  108  of the drive member  82 . 
     Clutch Controls 
     It will be apparent to those skilled in the art that the time of engagement of the clutch assembly of the present invention is determined indirectly by the net force compressing the clutch pack  84 . The compression force is determined by the fluid pressure in the pressure chamber  106 , as it decreases from the relatively high pressure to a relatively low pressure. In connection with the development of the present invention, it has been determined that it is an important aspect of the present invention to be able to modulate the rate of engagement of the clutch pack  84 , in accordance with various vehicle and engine operating parameters, i.e., to reduce the pressure in the chamber  106 , to a desired level, and therefore engage the clutch pack more rapidly or more slowly, depending upon various predetermined conditions. For example, when the engine is operating under a “part throttle” condition, it is desirable to achieve a longer time of engagement, whereas when the engine is operating under a “full throttle” condition, it is acceptable to engage the clutch pack more rapidly. 
     Referring now primarily to FIG. 4, there is illustrated a control valve assembly, generally designated  110 , of the type which may be used to control the pressure in the chamber  106 . It will be understood by those skilled in the art, that the invention of this application is not limited to any particular type or configuration of control valve, or to any particular control logic. What is essential to the present invention is merely that the clutch assembly include some sort of control valving which is capable of modulating the pressure in the chamber  106  between the relatively high and relatively low pressures to achieve engagement and disengagement of the clutch pack  84  within the specified response times. 
     Disposed in threaded engagement with the clutch housing  52  is a fitting  112  (see also FIG.  2 ), which is connected to a source of fluid pressure, such as the engine lubrication fluid, as was described previously. The clutch housing  52  also defines a chamber  114  in which is disposed the control valve assembly  110  The housing  52  also defines an axial passage  116  communicating with a transverse passage  118 , which is in open communication with the pressure chamber  106 . 
     The control valve assembly  110 , which will be described only briefly hereinafter, may be of the general type illustrated and described in U.S. Pat. No. 4,947,893, assigned to the assignee of the present invention, and incorporated herein by reference. The control valve assembly  110  includes a valve body  120  and disposed for axial movement therein, a valve spool  122 , the valve spool  122  being shown in FIG. 4 in a centered (or “neutral” position). The valve spool  122  is biased to the left in FIG. 4 by a compression spring  124 , and can be moved to the right in FIG. 4 by means of an electromagnetic coil  126  which, when energized, biases an armature assembly  128  to the right, moving the valve spool  122  to the right also. 
     In operation, with the coil  126  de-energized, the spring  124  biases the valve spool  122  to the left in FIG. 4, permitting communication of pressure from the chamber  114  through the valve assembly  110  to the axial passage  116 , thus pressurizing the chamber  106 , such that the piston  76  moves to the right in FIG. 3, disengaging the clutch pack  84 , in the manner described previously. The above-described arrangement whereby the coil  126  is de-energized to disengage the clutch pack  84  is preferred because, in a typical vehicle application, the supercharger is disengaged for a greater part of the total duty cycle than it is engaged. More importantly, it is considered desirable that an electrical failure result in the supercharger clutch being disengaged. 
     When it is desired to operate the supercharger, by engaging the clutch pack  84 , an appropriate electrical signal  130  is transmitted to the coil  126 , moving the valve spool  122  to the right of the position shown in FIG. 4, thus communicating the passage  116  (and therefore, the chamber  106 ) through the valve assembly  110  to a case drain region, illustrated generally as  132  in FIGS. 3 and 4. The decreasing pressure in the chamber  106  permits the springs  104  to bias the release plate  98  to the left, to the position shown in FIG. 3, as described previously, engaging the clutch pack  84 . The rate of engagement (response time) of the clutch pack is determined by the pressure in the chamber  106 , which in turn is controlled in response to changes in the electrical signal  130 , such that a “soft engagement” may be achieved when that is desirable, or a more rapid engagement may be achieved when that is need and is acceptable. Those skilled in the art will understand that in most supercharger installations, it is the engagement response time which is more critical, whereas the disengagement response time is typically less critical. 
     Referring now primarily to FIG. 5, an alternative embodiment of the clutch assembly  75  will be described, in which the same or similar elements bear the same reference numeral, and new, or substantially modified portions of elements bear reference numerals in excess of “132”. Whereas the embodiment of FIG. 3 is especially suited for applications in which axial length must be minimized, the embodiment of FIG. 5 is especially suited for applications in which the length is less of an issue, but overall diameter must be minimized. 
     In the FIG. 5 embodiment, the rearward end (right end in FIG. 5) of the input shaft  64  is either splined or press-fit within a reduced diameter portion  134  of the drive member  82 , with the bearing set  96  being disposed radially between the portion  134  and the input hub  60 . The clutch piston  76  includes a generally cylindrical portion  136  surrounding the central portion of the input shaft  64 , the portion  136  in turn being surrounded by a partition member  138  and by a bearing set  140 . The bearing set  140  is disposed against a shoulder  142  formed on the cylindrical portion  136 , such that axial movement of the piston  76  will result in axial movement of the bearing set  140 . Disposed about the bearing set  140 , and adjacent the clutch pack  84  is a wall portion  144 . 
     Surrounding the input shaft  64  is a single coil compression spring  146 , seated to bias the piston  76  to the right in FIG. 5, toward the engaged position, as shown. In the absence of relatively high pressure (as that term was explained previously) in the chamber  106 , the spring  146  will bias the piston  76  and, through the cylindrical portion  136 , will bias the bearing set  140  and wall portion  144  to apply sufficient loading to the clutch pack  84 . When the pressure in the chamber  106  is increased, the piston  76  is biased to the left in FIG. 5, overcoming the force of the spring  146 , and relieving the loading on the clutch pack  84  enough that the clutch assembly  75  operates in the disengaged condition. Within the scope of the present invention, the controls for the alternative embodiment of FIG. 5 could be substantially the same as for the primary embodiment of FIG. 3, to achieve the same sort of modulation of engagement and response time. 
     The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.