Priority

[0001] This application is a continuation of U.S. Provisional Application No. 61/620533, filed April 5, 2012.

Field

[0002] The present teachings relate to supercharges for internal combustion engines.

Background

[0003] The air charge in a normally aspirated engine is limited by what the engine's cylinders can contain at atmospheric pressure. The air charge can be increased by forced induction, which is the process of pressurizing an engine's intake air. A supercharger is a compressor adapted to this purpose.

[0004] One type of supercharger is a Roots-type blower. A Roots-type blower is a rotary blower having two rotors with meshing lobes. The rotors turn within a chamber having an inlet and an outlet. Air from the inlet becomes trapped in spaces bounded by adjacent rotor lobes. These spaces are referred to as transfer volumes. Air trapped within a transfer volume is displaced from the inlet toward the outlet. Eventually, the transfer volume opens onto the outlet. Air becomes excluded from the transfer volume as its defining lobes mesh with lobes of the opposite rotor. Meshing forces air through the outlet and prevents transfer volumes from carrying air to the inlet.

[0005] Roots-type blowers were introduced in the 1860's as ventilating devices for blast furnaces. By the 1930s Roots-type blowers were used as supercharges. Early Roots-type blowers used rotors with two-lobes having little or no helix angle. The inlet was radial with respect to the rotors and the outlet was also radial, being directly opposite from the inlet. Early Roots-type blowers had relatively poor thermal efficiency. Significant improvements have since been made and have led to much wider use of superchargers in automotive applications. The improvements have included three and four lobed rotors, providing the rotors with a helical twist, and changing the blower porting. The changes in porting included forming the inlet through an axial end of the blower housing (102). Some of these improvements have sought to optimize the transfer seal time.

[0006] For rotary blowers in general, the transfer seal time is the period of rotor turn, expressed as an arc measurement in degrees or radians, that a transfer volume is effectively sealed from both blower inlet and outlet. Effectively sealed from both blower inlet and outlet means the transfer volume does not communicate directly with either the inlet or outlet port or indirectly via unrestricted communication with other transfer volumes, but does not exclude leaks through imperfect seals. The transfer seal time has been treated as a single-valued design parameter.

[0007] US 5,078,583 (the '593 patent) describes an improved inlet port opening for a Roots-type blower. The background section notes that increasing the transfer seal time improves blower efficiency at low blower speeds while decreasing the transfer seal time improves blower efficiency at high blower speeds. The '593 patent proposes an inlet port opening shape that improves blower performance at high speeds without reducing performance at low speeds.

[0008] Past improvements in supercharger efficiency have led to widespread use of supercharges in the automotive industry. Superchargers consume power, but they enable the use of smaller engines and ultimately improve fuel economy. Superchargers still consume a significant amount of energy and fuel economy has always been a concern. Accordingly, there remains a long felt need for more efficient superchargers.

[0009] The inlet seal time is the period a transfer volume is in communication with the inlet. The inlet seal time generally includes the expansion time. The expansion time is the period over which a transfer volume is drawing due to the rotor lobes coming out of mesh. The inlet seal time also includes a dwell time. The dwell time is the period that a transfer volume is communicating with the inlet while fully out of mesh with the lobes of the opposite rotor and no longer drawing due to expansion of the transfer volumes.

Summary

[0010] One aspect of the present teachings is a rotary blower having an inlet adaptor to vary the inlet geometry and thereby vary the dwell time. An actuator is configured to move the inlet adaptor between a plurality of positions. In a first position, the inlet adaptor makes the dwell time comparatively large. Such positions provide the highest efficiencies at high blower speeds. In a second position, the inlet adaptor makes the dwell time comparatively small. Such positions provide the highest efficiencies at low blower speeds. In general there will be two inlet adaptors, one cooperating with the first rotor and the other cooperating with the second rotor. The inlet adaptors can be operated to make the blower more efficient across a range of operation in comparison to a blower that has fixed inlet geometry.

[0011] Another aspect of the present teachings is a rotary blower comprising a chamber having an inlet and an outlet. Within the chamber there are first and second rotors having meshing lobes. The rotors are operative to transfer fluid from the inlet to the outlet. An inlet adaptor is provided. The inlet adaptor is configured to be actuated to alter the inlet geometry and thereby alter the dwell time.

[0012] Another aspect of the present teachings is a rotary blower comprising a chamber having an inlet and an outlet, an inlet adaptor, and an actuator. Within the chamber there are first and second rotors having meshing lobes. The blower has transfer volumes, which are spaces defined in relation to adjacent rotor lobes. The transfer volumes have an inlet-facing side that spans the space between adjacent rotor lobes. The inlet adaptor has a shape, size, and position that make it effective to complete a seal of the inlet-facing side of each of the first rotor's transfer volumes for at least a moment in each rotation of the first rotor. The inlet adaptor is movable between a plurality of positions. The angular position at which the inlet adaptor completes the seals of the transfer volumes' inlet-facing sides varies with the inlet adaptor's position. The actuator is configured to move the inlet adaptor among the plurality of positions while the blower is operating. Generally, moving the inlet adaptor will vary the dwell time. Moving the inlet adaptor can also vary the transfer seal time.

[0013] In various aspects of the present teachings, the lobes of a rotor can have ends that sweep a surface proximate the inlet. The inlet adaptor can have a face parallel to and proximate that swept surface. The inlet adaptor can be restricted to movements that maintains that parallelism and proximity. This type of restriction is consistent with the purpose of maintaining the inlet adaptor within a group of positions in which the inlet adaptor can form sealing relationships with the rotor lobes. The dwell time varies among the inlet adaptor's possible positions. For making this configuration, it is convenient to use a rotor with lobes that have flat ends lying in a single plane perpendicular to the rotor axis and proximate the inlet. The surface swept by the lobe ends and the inlet adaptor face are then flat and the restriction on the inlet adaptor's movement maintains the inlet adaptor face in a plane parallel the swept surface.

[0014] In many aspects of the present teachings, the inlet adaptor can be mounted to pivot about the axis of rotation of a rotor. This configuration maintains the angle of attack between the rotor lobes and the inlet adaptor's leading edge even as the inlet adaptor is moved to vary the dwell time. Typically, there are two rotors and two inlet adaptors with the second mounted to pivot about the axis of rotation of the second rotor. The two inlets adaptors are geared in a manner that synchronizes their movements, whereby a rotation of one inlet adaptor causes an equal magnitude counter rotation of the other inlet adaptor.

[0015] Other aspects of the present teachings include a method of operating a rotary blower provided with an inlet adaptor. The method comprises operating the blower at low speed. Increasing the blower speed. Actuating the inlet adaptor to decrease the dwell time. Reducing the blower speed. Actuating the inlet adaptor to increase the dwell time. This method uses the inlet adaptor to improve blower efficiency at both high and low blower speeds.

[0016] Further aspects of the present teachings include a method of operating a rotary blower provided with an inlet adaptor. The method comprises improving the blower efficiency at a first rate of operation by actuating the inlet adaptor to increase the inlet opening time and improving the blower efficiency at a second rate of operation that is lower than the first rate by actuating the inlet adaptor to decrease the inlet opening time.

[0017] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present teachings.

Brief Description of the Drawings

[0018] Fig. 1 illustrates an exemplary rotary blower in accordance with the present teachings.

[0019] Fig. 2 illustrates the rotary blower of Figure 1 with the bearing plate removed.

[0020] Fig. 3 is an exploded view of the bearing plate, the inlet adaptor, and the actuator of Figure 1. [0021] Fig. 4 is a view of the bearing plate of Figure 3 from its chamber-facing side with the inlet adaptor in its first (most open) position.

[0022] Fig. 5 is the same view as Figure 4, but with inlet adaptor in its second (most closed) position.

[0023] Fig. 6 is a view of the bearing plate of Figure 3 from outside the blower with the inlet adaptor in its first position.

[0024] Fig. 7 is the same view as Figure 6, but with the inlet adaptor in its second position.

Detailed Description

[0025] Figures 1 through 7 illustrate an exemplary rotary blower 100, which is a supercharger. Blower 100 can be an axial-inlet radial-outlet Roots-type blower. Blower 100 includes meshing rotors 101 contained within a chamber 106 of a housing (102) 102. Housing (102) 102 can include a bearing plate 104 bolted to one side proximate an inlet 107 of chamber 106. An opening 103 through housing (102) 102 can provide access to an outlet 108 of chamber 106. An opening 105 in bearing plate 104 can provide access to an inlet 107 of chamber 106. The geometry of inlet 107 can be modified by an inlet adaptor 120 mounted to bearing plate 104. Opening 105 can be sized to minimally obstruct inlet 107 even when inlet adaptor 120 has made inlet 107 as large as it can be.

[0026] The two rotors 101 shown by the Figures are individually rotor 101 a and rotor 101 b. Rotors 101 a and 101 b and corresponding structures are in most respects mirror images except that rotors 101 a and 101 b are out of phase. For repeated elements, an "a" following a reference number indicates an element on the side of rotor 101 a while a "b" following a reference number indicates a corresponding elements on the side of rotor 101 b. A reference number without a letter applies to both "a" and "b" elements.

[0027] The inlet adaptors 120a and 120b shown by the Figures are not quite symmetrical. Inlet adaptor 120b can be actuated directly, while inlet adaptor 120a can be actuated via inlet adaptor 120b. In general, inlet adaptors 120 can be provided in pairs and the dwell times of transfer volumes 1 12b associated with rotor 101 b can be varied in conjunction with the dwell times of transfer volumes 1 12a associated with rotor 101 a.

[0028] The rotors 101 a and 101 b can each have four lobes 109 arranged symmetrically about their respective axes 1 10a and 1 10b. Lobes 109 can have ends 1 14 that are flat and proximate inlet 107. Lobes 109 can have a profile that does not change along the lengths of the rotors 101 except for a twist that gives the lobes 109 a helical shape. From the perspective of end 1 14a and beginning from that end, the rotor 101 a in the example shown by Figure 1 twists 160 degrees in the counterclockwise direction. Lobes 109b of rotor 101 b twist by the same, but in the opposite direction. The rotors 101 will be configured to turn in the opposite direction from the twists of their lobes 109. For the example shown by Figure 1 , rotor 101 a will be configured to turn in the clockwise direction, while rotor 101 b will be configured to turn in the counterclockwise direction. When rotors 101 of the twisted lobe variety are turning in normal operation, lobe ends 1 14 proximate inlet 107 lead their opposite ends.

[0029] Rotors 101 can be mounted on bearings to turn within chamber 106 about their axes 1 10. Cylindrical structures 1 13 in bearing plate 104 can receive ends 1 1 1 of rotors 101. As rotors 101 turn, their lobes 109 can sweep cylindrical volumes. The swept volumes can be parallel, aligned, and overlapping. The collective sweep of the two rotors 101 , including the sweep of lobes 109, fits narrowly within chamber 106. The fit is narrow enough for chamber 106 to form sealing relationships with lobes 109, but wide enough to avoid impeding rotors 101 even when their shapes are altered by thermal expansion that is normal for supercharger operation. Timing gears (not shown) coordinate the movements of rotors 101 a and 101 b, keeping them slightly spaced apart but still close enough to form sealing relationships.

[0030] Housing (102) 102 forms sealing relationships with top lands 1 18 of lobes 109 at the periphery of chamber 106. Housing (102) 102 forms sealing relationships with the lobe ends opposite bearing plate 104 at one end of chamber 106. Inlet adaptors 120 form sealing relationships with lobe ends 1 14. Housing (102) 102 also forms sealing relationships with lobe ends 1 14. In the example shown by Figure 1 , a raised area 135 of bearing plate 104 is a part of housing (102) 102 that forms sealing relationships with the lobe ends 1 14. Housing (102) 102 determines a shape for inlet 107 of chamber 106. That shape is modified by inlet adapter 120. Lobe ends 1 14 can be flat and can lie within a single plane that is perpendicular to the rotor axes 1 10. This orientation can facilitate placing inlet adapters 120 and raised area 135 in sealing relationships with lobe ends 1 14.

[0031] Inlet adaptor 120 can include a sealing member 139 located on chamber-facing side 136 of bearing plate 104 and a supporting member 140 located on the outer side 137 of bearing plate 104. Bearing plate 104 can have a recess 138 for receiving and supporting sealing member 139. Recess 138 can include a rim 142. In cooperation with blower housing (102) 102, rim 142 can trap the perimeter of sealing member 139. Sealing member 139 can be sized to fit rim 142 in such a way as to form a sealing relationship with side 143 and periphery 144 of rim 142. The thickness of sealing member 139 can allow it to form sealing relationships with lobe ends 1 14 and recess 138.

[0032] The supporting member 140 can be connected to sealing member 139 by posts 141. Posts 141 can move within a slot 129 formed in bearing plate 104. Slot 129 can be positioned to be masked from chamber 106 by sealing member 139 throughout the range of the motion of the inlet adaptor 120. (See Figures 4 and 5). Sealing member 129 can fit closely against bearing plate 104 within recess 138 in part to seal off slots 129. Bearing plate 104 can be provided with bearings to support sealing member 139 and facilitate its movement.

[0033] The shape of leading edge 123a of sealing member 139a can conform to leading edges 124a of lobes 109a. Likewise, leading edge 123b of sealing member 139b can conform to leading edges 124b of lobes 109b. This shape can be shown to contribute to maximizing the open area of inlet 107. It will be appreciated in light of the disclosure that it is desirable for the inlet area to be as large as possible subject to the limits on inlet opening time.

[0034] The supporting member 140 can hold sealing member 139 against bearing plate 104 and thus can facilitate maintaining a narrow separation between sealing member 139 and lobe ends 1 14. The separation is sufficiently narrow for lobe ends 1 14 to enter sealing relationship with sealing member 139 during their rotational cycle.

[0035] Chamber facing side 136 of bearing plate 104 can include raised area 135. Raised area 135 can be positioned and shaped to form sealing relationships with lobe ends 1 14 just at or slightly before top lands 1 18 reach upper cusp 131. Raised area 135 can maintain the seal until the leading transfer volume 1 12 of the pair to either side of lobe 109 begins its expansion phase. Raised in this context can simply be not recessed. Raised area 135 can be flush with sealing member 139.

[0036] Supporting members 140 can surround and rotate about structures 1 13 formed in bearing plate 104 for receiving rotor ends 1 1 1. This configuration can restrict the movements of inlet adaptors 120 to rotations about axes 1 10 of rotors 101. Supporting members 140 can further include meshing teeth 122. Meshing teeth 122 can coordinate the movements of inlet adaptors 120a and 120b so that rotation of adaptor 120a can cause an equal and opposite rotation of adaptor 120b. In the example shown by Figure 1 , the adaptors 120 are free to rotate through 30 degree arcs. Rotation in one direction can be limited by the length of rim 142. Rotation in the opposite direction can be limited by the interference of inlet adaptor supporting members 140 with one another.

[0037] An actuator 127 can be mounted to the outer side 137 of bearing plate 104. Actuator 127 can have a gear 128 that can mesh with teeth 130 formed in supporting member 120b. The actuator 127 can move inlet adapter 120b among a plurality of positions. There can be at least three distinct positions in order to provide a broad selection of dwell times. The actuator 127 can be configured to move inlet adapter 120a as well. The movements of the inlet adapters 120a and 120b can be synchronized or linked. For example, the movements of inlet adapters 120 can be linked and coordinated by meshing teeth 122.

[0038] During operation of blower 100, air becomes trapped in transfer volumes 1 12. In the example shown by Figure 1 , air is trapped in transfer volumes 1 12 beginning at the moment leading edge 124 of the trailing lobe 109 of the pair defining the transfer volume 1 12 reaches the trailing edge 123 of inlet adaptor 120. At that moment, trailing lobe 109 enters a sealing relationship with inlet adaptor 120. Top lands 1 18 of both the leading and trailing lobes 109 are then in sealing relationships with chamber 106. The dimensions of the space in which the air is initially trapped define the transfer volume 1 12.

[0039] Air can remain trapped in transfer volumes 1 12 for a period or rotation, which is by definition the transfer seal time. Eventually, the trap opens. In the example shown by the Figures, the trap opens when the top land 1 18 of the leading lobe 109 reaches a position where it no longer has a sealing relationship with chamber 106 along its entire length. From that angular position and through a subsequent period, the transfer volume 1 12 ceases to be physically bounded all about its perimeter. It is nevertheless convenient to refer to these inter-lobe regions as transfer volumes throughout the rotations of rotors 101. In the example shown by Figure 1 , there are eight transfer volumes 1 12. Four of these are spaces between adjacent lobe pairs 109a and four are spaces between adjacent lobe pahs 109b.

[0040] The outlet 108 can have an approximately triangular shape. The base 132 of the triangular shape can be opposite from the inlet 107. The apex 133 of the triangular shape can meet the upper cusp 131. The cusps can be defined as locations where the portion of the chamber 106 that follows the shape of one cylinder meets the portion of the chamber 106 that follows the shape of another cylinder. In the example shown by Figure 1 , there are two cusps: upper cusp 131 and lower cusp 145. Upper cusp 131 can be located on the same side as outlet 108. Sides 134 of the outlet 108 can be shaped to match the curvature of top lands 1 18. The shape of side 134a can conform to lands 1 18a and the shape of side 134b can conform to lands 1 18b.

[0041] When tp lands 1 18 of leading lobe 109 pass sides 134 of outlet 108, transfer volume 1 12 begins to communicate directly with outlet 108. Transfer volume 1 12, however, can begin communication with outlet 108 before then. Communication with outlet 108 can begin when the top land 1 18 of the leading lobe 109 passes over cusp 131 , creating an indirect path to outlet 108. In the example shown by Figure 1 , due to the direction of rotor rotation, this path first opens proximate inlet 107. The indirect path can pass over the leading lobe 109 and through one or more transfer volumes 1 12 that are more advanced in the rotational cycle. An indirect path that opens prior to direct communication with outlet 108 is called a blowhole. A blowhole occurs in a blower 100 of the type shown in the example of Figure 1 if the lobe twist is sufficient. A blowhole can slow the rate at which the pressure within a transfer volume 1 12 equalizes with the outlet pressure, which provides advantages including reduced noise and increased blower efficiency.

[0042] Blowers can be provided with other blowholes other than the type that results from high lobe twist in an axial inlet-radial outlet Roots-type blower, including blowholes that allow flow through the periphery of chamber 106 and blowholes controlled by valves. Such blowholes can create ambiguity as to the transfer seal time. In such cases, the transfer seal time is defined according to the direct and indirect opening paths from inlet 107 to outlet 108 described above. These paths have in common that they are entirely within chamber 106 and are entirely through spaces within the sweep of rotor lobes 109.

[0043] As rotors 101 continue to turn, lobe 109 of one rotor 101 begins to mesh with lobes 109 on the opposite rotor 101. Meshing of lobes 109 drives air from transfer volumes 1 12 to outlet 108. With further rotation, the leading lobe 109 of a pair defining a transfer volume 1 12 enters into a sealing engagement with a first and then a second of the lobes 109 of the opposite rotor 101 . The lobe pair defining the transfer volume 1 12 becomes fully meshed with a lobe 109 of the opposite rotor 101. For rotors with twisted lobes, full mesh initially occurs proximate inlet 107. The area of full mesh then migrates toward outlet 108. Meshing divides transfer volume 1 12 into two spaces sealed from one another by lobes 109. As the area of full mesh migrates from the inlet end, the divided portion of the transfer volume space that is further from the inlet 107 shrinks while the portion proximate the inlet 107 grows. Transfer volume 1 12 can open to inlet 107 just as the divided space proximate inlet 107 begins to grow.

[0044] The transfer seal time for the blower 100 in the example of Figure 1 is the amount of rotor turn from the point at which leading edge 124 of a trailing lobe 109 of an adjacent pair reaches trailing edge 123 of inlet adaptor 120 to the point at which top land 1 18 of the leading lobe 109 of the pair passes over upper cusp 131 adjacent bearing plate 104. At the limit of clockwise rotation of inlet adaptor 120a, which is the first position, the transfer seal time is at a minimum, zero in the example, and the dwell time is at a maximum, 30 degrees in this example. Through operation of actuator 127, inlet adaptor 120a can be adjusted to a new more anti-clockwise position. A corresponding adjustment of inlet adaptor 120b can occur through the mesh of gear teeth 122. In the new position, the dwell time is reduced. Movement of inlet adaptor 120 changes the geometry of inlet 107 and can decrease the dwell time down to a minimum, which is zero in this example. The inlet seal time varies to the same extent as the dwell time. The transfer seal time varies to an equal and opposite extent with the following caveat.

[0045] When inlet adaptor 120a rotates in the counter clockwise direction, it can vacate a portion of recessed area 138 on bearing plate 104. As the leading lobe 109 passes over this vacated area, air trapped within the transfer volume 1 12 can leak past the leading lobe 109 through a path between the lobe end 1 1 1 and bearing plate 104. The leak can be to a transfer volume 1 12 more advanced in its rotational cycle and already in communication with outlet 108. Depending on the thickness of sealing member 139, this leak path can be significant and operate as a blowhole. Such a blowhole can be beneficial provided it does not open until the transfer volume 1 12 is out of communication with the inlet 107. Inlet adaptor 120 can span the distance between adjacent lobes 109 such that it seals off transfer volumes 1 12 on the inlet side for at least a moment in each rotor's rotation. It can be shown that this geometry assures that at any given time at least one rotor lobe 109 is in a sealing relationship with sealing member 129 and therefore prevents such a blowhole from forming before transfer volume 1 12 is out of communication with inlet 107.

[0046] Actuator 127 can be implemented with many suitable mechanisms. Suitable mechanisms for actuator 127 can include hydraulic, mechanical, and electronic mechanisms. Examples of electronic actuation mechanisms can include solenoids and electric motors. An electric motor can turn a spindle that drives gear 128. A solenoid can turn gear 128 through rack and pinion gears.

[0047] Examples of hydraulic actuation mechanisms can include ones in which the actuator position is determined by a spring position in which the spring tension balances a hydraulic force. The hydraulic force is determined by the pressure of hydraulic fluid in an actuator chamber. In this example, the spring can deflect sufficiently to balance the hydraulic pressure, and the amount of deflection can determine the position of inlet adaptor 120. The position of inlet adaptor 120 can therefore be determined by the hydraulic fluid pressure in the actuation chamber.

[0048] The fluid pressure in the actuator chamber can be increased by operating a hydraulic pump. The flow into the actuator chamber is optionally controlled by a valve, as would be the case if one hydraulic pump provides the pressure for several independently controlled actuators. A valve or an orifice or both can limit the rate of fluid flow out from the actuator chamber. The actuation chamber pressure, and thus the inlet adaptor's position, can be changed by either increasing the flow rate into the actuation chamber, by increasing a pumping rate for example; or decreasing the flow rate out from the actuation chamber, by closing a valve for example.

[0049] Actuator 127 can be implemented with various types of control. Suitable control types can include electronic control, manual control, and autonomous control. Electronic control can be provided by an engine control unit programmed to control the actuator 127 or by a separate electronic controller with suitable instruction in memory. An electronic control unit can receive data relating to control parameters. One such control parameter can be the blower speed. The engine speed can often be a proxy for the blower speed and can be provided to the controller in place of the blower speed, or in addition to the blower speed when the two are independent. Other exemplary control parameters can include the intake manifold pressure, the engine torque, and the ambient temperature, and other suitable vehicle control parameters. The controller can be programmed with various suitable control methods. Examples of such control methods can include feed forward control algorithms, feedback control algorithms, and algorithms that use both types of control.

[0050] Autonomous control refers to control that is neither electronic nor manual. One example is a hydraulic system that can be responsive to the rate at which the blower is being driven. For example, a hydraulic pump can be coupled to an input shaft that can drive the rotors. The hydraulic pump can increase the flow rate of hydraulic fluid to an actuator chamber as the shaft speed increases. The outflow from the actuator chamber can be limited by an orifice or valve or both. The actuator chamber pressure at which the inflow and outflow rates balance can depend on the blower speed and can serve as a proxy for the actuator position and thus the position of inlet adaptor 120.

[0051] The exemplary autonomous system can implement a basic control method. The basic control method includes setting the inlet adaptor position according to the blower speed or a proxy therefor. The inlet adaptor can be set to increase the dwell time for high speed operation and to reduce the dwell time for low speed operation.

[0052] The effect of the dwell time on blower efficiency depends on the blower speed and the pressure drop across the blower 100. The pressure drop can be affected by blower speed and can be defined as a dependent variable. During the dwell period, two relevant processes can be occurring: (1 ) filling and (2) leakage. At the beginning of the dwell period, the transfer volume 1 12 is no longer drawing air due to expansion and has already been open to the inlet 107 for some time. Nevertheless, the transfer volume can still be filling as the dwell period begins, particularly if blower speed is high. Increasing the dwell time, can increase the amount of fill and therefore also increase the amount of air transported per cycle by each transfer volume 1 12.

[0053] During the dwell period, there is leakage from the outlet 108 to the transfer volume 1 12 through imperfect seals. At low blower speeds, there is more time per cycle for this leakage to take place in comparison to at high blower speeds. Viewed another way, at low blower speeds this leakage is greater in relation to the blower throughput than at high blower speeds. The leakage can be sufficient to cause a flow from the outlet 108 to the inlet 107, which decreases blower efficiency. Reducing the dwell time can reduce this leakage. There is therefore a trade-off between limiting leakage and allowing adequate fill time. It will be appreciated in light of the disclosure that this trade-off can be balanced to result in an optimum dwell time that varies with blower speed and inlet to outlet pressure drop. An inlet adaptor 120 can be used to set the dwell time to the optimal value when peak blower efficiency is required.

[0054] A control method according to the present teachings can be one that when high blower efficiency is desired sets the inlet adaptor 120 to a position in which the dwell time is comparatively small if blower speed is low and a position in which the dwell time is comparatively large if blower speed is high. Maximum efficiency is usually desirable at low blower speeds unless the engine is at idle. At high blower speeds, maximum efficiency may be desired only when high torque is required. For example, an internal combustion engine can have both high and low torque operating modes in which the engine is running at high speed. In the high torque mode, maximum supercharger efficiency will generally be desirable. In the low torque mode, maximum supercharger efficiency may or may not be desirable depending on such factors as engine configuration, engine tuning, whether the engine is at idle, and whether a gear shift is in progress. Accordingly, even where there is a unique inlet adaptor position 120 that maximizes blower efficiency and that position is a function of essentially the blower speed only; it may be desirable to consider factors other than the blower speed in deciding where to position or whether to reposition the inlet adaptor 120.

[0055] In one aspect of the present teachings, there is provided a controller that monitors the current actuator position and adjusts the actuator position incrementally to approach a setpoint position. The setpoint position can be determined from a map (e.g., a lookup table) that provides the position as a function of the blower speed, or a proxy therefore such as an engine speed, and optionally other parameters such as intake manifold pressure and torque. Engine speed can vary quickly during events such as shifting. A strategy of incremental adjustment can prevent overly rapid or overly frequent changes to the inlet adaptor position. Various types of control methods can be implemented. For example the method can be of the proportional-integral-differential type. Such methods can select the rate of adjustment for the inlet adaptor position as a linear combination of the difference between the current inlet adaptor position and the setpoint position, the integral of that difference over a period, and the rate at which that difference is changing. The method can also include a filter so that all adjustments can be made in discrete steps of predetermined magnitude. Such a filter may be suitable when the inlet adaptors have only a finite number of positions or if the controller can register only a finite number of discrete inlet adaptor positions.

[0056] In many examples, the set point position can be the inlet adaptor position at which blower efficiency is maximized. The position of maximum efficiency depends primarily on the blower speed, but may be significantly affected by other factors. Such possible factors can include the pressure drop across the blower and the intake air temperature. While the pressure drop across the blower is a function of the blower speed, it can also be affected by other factors. If the blower is a supercharger with a drive mechanism allowing the blower speed to be varied independently of the engine speed, the engine speed can independently affect the pressure drop. In some cases, the supercharger intake is provided with a throttle. The position of such a throttle can also affect the pressure drop and thus the inlet adaptor position at which efficiency is maximized.

[0057] A blower 100 according to the present teachings may include, or be configured with, a bypass valve. Superchargers are commonly provided with bypass valves to avoid parasitic loss. A common supercharger bypass valve can operate autonomously by a vacuum actuator that can cause the bypass to open during engine idle. The actuator opens the bypass valve when throttle loads are low and closes the valve when throttle loads are high. When the bypass valve is open there is little or no pressure drop across the supercharger and this allows the supercharger to run with negligible parasitic loss under conditions for which forced induction is not beneficial. In another example, the bypass valve can be controlled through a solenoid that can allow for more selective control of the bypass valve. If a bypass valve is provided, the position of the bypass valve position can be a factor in selecting the inlet adaptor position.

[0058] In accordance with the many aspects of the present teachings, inlet adaptor 120 can have a first position in which the dwell time is at a maximum and a second position at which the dwell time is at a minimum. The second position can be configured to make the dwell time very small, e.g., 10 degrees or less, 5 degrees or less, or ideally about zero. Such small dwell times can be beneficial at low blower speeds. The present teaching allow these small dwell times to be used without sacrificing performance at high blower speeds. Movement of inlet adaptor 120 beyond the position at which the dwell time becomes zero is generally avoided even at very low blower speeds because it can result in sealing the transfer volume from the inlet while the transfer volume 1 12 is still drawing. Doing so, can limit the amount of air transported by each transfer volume 1 12 and can force the blower 100 to work against an internal vacuum.

[0059] The dwell time for a first transfer volume 1 12 begins when it and any other transfer volumes 1 12 in communication with the first transfer volume 1 12 cease to expand due to lobes 109 coming out of mesh. For the example of Figure 1 , this is the point at which top land 1 18 of trailing lobe 109 of the pair defining first transfer volume 1 12 passes lower cusp 145. Although lobes 109 of opposing rotor 101 will have fully withdrawn from first transfer volume 1 12 before then until this point is reached first transfer volume 1 12 is in communication with another transfer volume 1 12 that is earlier in the rotational cycle and still expanding.

[0060] It will be appreciated in light of the disclosure that actuating the inlet adapter 120 for the blower 100 in the example of Figure 1 beyond the position at which the dwell time is zero in an attempt to further reduce the inlet opening time would be ineffective aside from the problem of doing work against a vacuum. This is so because until the dwell period is reached transfer volume 1 12 is in communication with other transfer volumes 1 12 themselves communicating with inlet 107. Until this communications with other transfer volumes 1 12 ceases, inlet adapter 120 cannot be effective to seal transfer volume 1 12 from inlet 107. Communication with these other transfer volumes 1 12 ceases only when top land 1 18 of trailing lobe 109 passes lower cusp 145, which also marks the end of the expansion time and the beginning of the dwell time.

[0061] The first position of inlet adapter 120 can make the dwell time large and the transfer seal time very small, e.g., 10 degrees or less, 5 degrees or less, or ideally about zero. The transfer seal time runs from the end of the dwell time until transfer volume 1 12 begins communication with outlet 108. Large dwell times can be beneficial at high blower speeds. The present teaching allow very large dwell times to be used without sacrificing performance at low blower speeds. A large dwell time is facilitated by making the transfer seal time small, e.g., 10 degrees or less. For the blower in the example of Figure 1 , a transfer seal time of 10 degrees or less allows the dwell period to be continued until top land 1 18 of the leading lobe 109 of the pair defining transfer volume 1 12 is within 10 degrees of upper cusp 131. If the dwell time does not end until top land 1 18 is within 5 degrees of upper cusp 131 , this provides an even larger dwell time. Ideally, inlet adapter 120 allows the dwell time to be prolonged until top land 1 18 has reached or nearly reached upper cusp 131. This provides the longest dwell time that is possible without opening a path communicating inlet 107 with outlet 108.

[0062] The range of motion for an inlet adaptor 120 can correspond to the dwell time when the inlet adaptor 120 is in the first position. As will be appreciated from the present disclosure, being able to vary the dwell time to a large degree allows blower efficiency to be improved over a wide range of operating conditions. A range that permits the dwell time to be reduced by at least half can be considered a large range. For a given maximum dwell time, an inlet adapter 120 that allows the dwell time to be reduced by at least three quarters provides a still larger range. Moreover, it can be shown that an inlet adapter 120 having the largest useful range of motion allows the dwell time to be reduced to zero or nearly zero.

[0063] The foregoing reflects the desire to make the dwell time adjustable over a substantial range of motion as possible. A substantial range is 20 degrees or more. In general, the range can be made at least 30 degrees. These ranges reflect the desire to provide the ability to increase the dwell time to an extent that provides a significant efficiency benefit over a range of blower speeds. The range that can be achieved may be limited by other aspects of the design of the blower 100. A typical upper limit on the dwell time range achievable using an inlet adapter 120 is 60 degrees or less. For a rotor 101 having lobes 109 with a high degree of twist, it can be shown that there is a relationship between the twist angle and how widely the dwell time can be varied. A large twist angle, which can otherwise facilitate achieving high blower efficiency, can limit the dwell time range to, for example, 40 degrees or less.

[0064] To avoid leaks, it is desirable to size inlet adaptor 120 to maintain a sealing engagement with each rotor lobe 109 until the trailing lobe 109 has reached a sealing engagement with the inlet adaptor 120. This requires that the inlet adaptor 120 be large enough to span the space between adjacent rotor lobes 109. Each transfer volume 1 12 needs to be sealed off on its inlet facing side from the arc of bottom lands 1 19 to the arc of top lands 1 18. Inlet adaptor 120 can seal over all or part of this radial extent. For example, inlet adaptor 120 can seal from a radial position R1 , which is above the arc of bottom lands 1 19, to the radial position R2, which is along the arc swept by top lands 1 18. In the example shown by Figure 1 , the seal from bottom lands 1 19 to the position R1 is made by raised area 135 of bearing plate 104. The inlet adaptor 120 can seal nearly the entire radial area of a transfer volume 1 12 whereby the additional inlet opening area created by moving the inlet adaptor 1 12 is as large as possible.

[0065] Having the inlet adaptor 120 span the distance between adjacent lobes 109 can create a relationship between the number of lobes per rotor 101 and the required inlet adaptor size. For a four lobe rotor 101 , the span is nearly 90 degrees. The required inlet adaptor span can be slightly less due to the finite width of the rotor lobes 109. For blower 100 in the example of Figure 1 , this limits the dwell time to about 30 degrees. If the number of rotor lobes 109 were increased to five, the required span would be reduced to 72 degrees and the dwell time could be increased to about 48 degrees.

[0066] The inlet adaptor 120 can be supported in such a way that it forms a sealing engagement with the lobe ends 1 14 without actually touching the lobes 109. Inlet adaptor 120 in the example of Figure 1 illustrates several optional mechanisms of support. One mechanism includes the extension of the inlet adaptor 120 beyond the top lands 1 18 so that the blower housing (102) 102 can support the perimeter of the inlet adapter 120. This support area can be useful for maintaining a minimum spacing between inlet adapter 120 and lobe ends 1 14 with relative precision. Another support mechanism can be bearing plate 104, which can be useful for limiting the spacing between the inlet adaptor 120 and the lobe ends 1 14. Another support mechanism can be the cylindrical structure 1 13 that can be provided to receive rotor end 1 1 1. Using that structure for support can facilitate limiting movements of the inlet adaptor 120 to rotations about rotor axis 1 10.

[0067] Another support mechanism can be one or more connections to a supporting member 140 positioned outside the bearing plate 104. The one or more connections can be made by one or more posts 141 or other connecting members that move in one or more slots 129 or other openings in the bearing plate 104. Any such openings can be positioned to be masked by inlet adaptor 120 regardless of the inlet adaptor's position. [0068] Positioning a part of inlet adaptor 120 outside bearing plate 104 can permit the implementation of certain functionality without interfering with forming the desired sealing relationships with lobe ends 1 14. Such functionality can include controlling the movement of inlet adaptor 120 and coordinating the movements of a pair of inlet adaptors 120.

[0069] Lobes 109 can have a helical twist. The twist angle can be large such that the transfer volumes 1 12 first communicate with the outlet 107 when the top land 1 18 of the leading lobe 109 passes over the upper cusp 131. The twist angle can be sufficiently large such that a small increase would cause top land 1 18 of the leading lobe 109 to pass over the upper cusp 131 before the trailing lobe 109 formed a sealing relationship with the inlet adaptor 120 in its first (most open) position. Such an increase would place the inlet 107 in direct communication with the outlet 108. A small increase is 10 degrees or less. The small increase can also be 5 degrees or less. Ideally, the twist angle is at a maximum and cannot be increased significantly without causing the inlet 107 to come into direct communication with the outlet 108 periodically when the inlet adaptor 120 is in the first position. Maximizing the twist angle in this manner can be shown to improve blower efficiency.

[0070] Many aspects of the present teachings can be applicable to any rotary blower in which a larger inlet provides a higher efficiency at high rotation rates and a comparatively smaller inlet provides higher efficiency at comparatively lower rotation rates. Examples include Roots-type, scroll, screw, sliding vane, and flexible vane pumps and blowers. As the term is used here, the term blower encompasses pumps suitable for moving air. A Roots-type blower is any rotary blower 100 having two or more rotors 101 with meshing lobes 109 contained in a chamber 106 having an inlet 107 and an outlet 108 and functional to transfer fluid from inlet 107 to outlet 108 in discrete transfer volumes 1 12 defined by adjacent lobes 109 and chamber 106. The present teachings are particularly well adapted for superchargers. Moreover, power generation systems and vehicles can be made more efficienct by incorporating superchargers according to the present teachings.

[0071] The present teachings can also be applied to turbochargers, but are more likely to be applied to superchargers that are driven by a mechanical linkage to the crankshaft of the supercharged engine. Turbochargers are superchargers that are driven by an exhaust flow. The present teachings, however, are particularly useful when there is a mechanical linkage providing a fixed speed ratio between the supercharger and the supercharged engine. The mechanical linkage can be a direct drive, a belt drive, a gear drive, or a chain drive. These linkages generally provide a fixed relationship between the engine speed and the supercharger speed. Optionally, the speed ratio can be controlled with devices such as a clutch, a transmission, or an electric drive.

[0072] Chamber 106 is a void within housing (102) 102. Chamber 106 is bounded in part by housing (102) 102 and inlet adapter 120. Inlet 107 and outlet 108 are defined as two-dimensional surfaces on the perimeter of chamber 106. Inlet 107 and outlet 108 are locations where chamber 106 is unbounded. For a Roots-type blower, chamber 106 is defined to be limited to space within the sweep of rotors 101 and the additional space that is sufficiently close to that sweep for sealing relationships with the rotor lobes 109.. A sealing relationship generally requires gaps to be less than 1 millimeter Clearances between rotors 101 are typically less than 300 microns. Moreover, clearances between rotors 101 and chamber 106 are typically less than 150 microns. Reducing clearances can be shown to increase performance. To that end, very small clearances can be achieved by applying an abradable coating to rotors 101 or other blower components or both during manufacturing. A coating thickness can be about 100 microns. The coating thickness can be sufficiently thick to initially fill the clearance space entirely. Some of the coating will wear away during the blower break-in period.

[0073] Clearances can be provided to allow for thermal expansion and manufacturing tolerances. Accordingly, the seals and sealing relationships as those terms are used in the present disclosure refer to containment that is imperfect. A reasonably limited amount of leakage therefore does not negate the existence of a seal.

[0074] Superchargers to which the present teachings apply typically have operating speeds in the range from 1 ,000 to 20,000 rotations per minute (RPM). Their compression ratios are typically in the range from 1 : 1 to 1 :3. The operating speed and compression ratio are generally limited to prevent the outlet temperature from exceeding 150 °C. The number of lobes 109 per rotor 101 is usually four. Three or more lobes 109 per rotor 101 is desirable in terms of blower efficiency. Increases the number of lobes

109 per rotor 101 from three to four improves efficiency, but before the present teaching there was insufficient advantage to increase the number of lobes 109 to five or more. Increasing the number of lobes 109 per rotor 101 from four to five substantially increase the extent to which dwell time can be varied using inlet adapter 120. Accordingly, the present teachings make rotors 101 with five lobes 109 desirable. . The lobe twist is typically in the range from 60 degrees up to the maximum lobe twist less 20 degrees. The maximum lobe twist (TA _max ) for a Roots-type blower is a function of the lobe number (N), the distance from rotor axis to a top land (OD), and the distance between the rotor axes (CD).

, CD 2π\

TA _max = 2π— 2 sin — + —J

[0075] The maximum lobe twist can be reached only as the dwell time and the transfer seal time both approach zero. In Roots-type blowers, the lobe twist can be determined from the maximum lobe twist minus the desired maximum dwell time and the minimum transfer seal time. The minimum transfer seal time can be very small. The present teaching however show the desirability of being able to achieve a large maximum dwell time for when the inlet adaptor 120 is in its first position. The desire to be able to set this large dwell time constrains the lobe twist to be smaller than would be feasible if dwell time were fixed at a smaller value. For blower efficiency, it is desirable that the lobe twist be as large or nearly as large as possible subject to this constraint. This means that the lobe twist is desirably within 10 degrees of the maximum lobe twist less the dwell time when the inlet adaptor 120 is in its first position. [0076] While specific aspects have been described in the specification and illustrated in the drawings, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements and components thereof without departing from the scope of the present teachings, as defined in the claims. Furthermore, the mixing and matching of features, elements, components and/or functions between various aspects of the present teachings are expressly contemplated herein so that one skilled in the art will appreciate from the present teachings that features, elements, components and/or functions of one aspect of the present teachings can be incorporated into another aspect, as appropriate, unless described otherwise above. Moreover, many modifications may be made to adapt a particular situation, configuration or material to the present teachings without departing from the essential scope thereof. Therefore, it is intended that the present teachings not be limited to the particular aspects illustrated by the drawings , but that the scope of the present teachings include many aspects and examples following within the foregoing description and the appended claims.

Industrial Applicability

[0077] The present teachings provides improved supercharges that can be used to provide pressurized air to internal combustion engines.