Patent Application
20070137197
Engine downsizing has become an increasingly popular option for automotive manufacturers looking to reduce carbon dioxide emissions and improve fuel economy. Unfortunately, the torque produced by a smaller engine can be markedly less than that of a larger one, and while end consumers might accept the reduced emissions and improved fuel economy of a reduced-displacement engine, they still often demand the same driving performance of a larger-displacement engine.
One solution is to pair a reduced-displacement engine with a turbocharger. Turbochargers, which get their power from the flowing exhaust gases produced by internal combustion, are a thermodynamically efficient boosting system, but under some conditions may suffer from lag as the exhaust flow builds to the point where effective boost can be delivered. As engine specific outputs increase, this effect is magnified, limiting the downsizing and carbon dioxide reduction potential offered by conventional turbocharging. Vehicle manufacturers commonly adopt shorter transmission gear ratios to mitigate this effect; however, this generally has an opposite effect to engine displacement downsizing on carbon dioxide emissions performance.
Another option that overcomes the limitations of turbocharging is pairing a reduced-displacement engine with a supercharger mechanically driven by the engine's crankshaft. Although turbo lag may be overcome with the use of a supercharger, conventional superchargers typically have lower compressor efficiency than turbochargers, and cause significant parasitic losses when boost is not required, potentially harming fuel economy and increasing carbon dioxide emissions.
A supercharging system for an engine is provided that includes a generator having an electrical output. A power transmission mechanism includes a mechanical input operatively connected to the engine and a mechanical output operatively connected to the generator. A motor is operatively connected to generator and is powered by the electrical output. An air pump is operatively connected to and driven by the motor to provide charged air to the engine.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:
Referring to
In an embodiment, power transmission mechanism 16 comprises a fixed-ratio power transmission mechanism, whereby the rotational speed of mechanical output 20 is greater than the rotational speed of mechanical input 18, such as, for example, by a factor of thirteen (13). In a particular configuration, power transmission mechanism 16 is a traction-drive device that includes a planetary system having a sun member 26 operatively connected to generator 12 through mechanical output 20, at least one planetary member 28 drivingly interfaced with sun member 26, and an annulus 30 drivingly interfaced with the at least one planetary member 28 and operatively connected to the engine through mechanical input 18. In an embodiment, an elasto-hydrodynamic lubrication oil, such as an automatic transmission fluid (ATF) grade oil, is contained within power transmission mechanism 16 and creates a film between sun member 26, planet member 28 and annulus 30. The oil film exhibits a viscosity that is increasable under pressure created by the closely rotating components of the planetary system to transmit torque between sun member 26, planet member 28 and annulus 30. Compared to a conventional toothed gear system, a traction-drive device can achieve a relatively large gear-ratio. However, the interface between sun member 26, planetary member 28, and annulus 30 may be a geared interface, whereby torque is transmitted between the components by virtue of the meshed gears.
In an embodiment, mechanical input 18 includes a pulley that is mechanically linked to the engine crankshaft (not shown) by a belt, gear or chain, for example. In a particular configuration, the ratio between mechanical input 18 and the engine crankshaft is about 2.5:1. As shown in the following table, for example, power transmission mechanism 16 and mechanical input 18 may cooperate to significantly increase the speed of mechanical output 20 when compared to the engine speed.
Since generator 12 produces an electrical output that is generally proportional to its operating speed, a relatively small and inexpensive generator may be employed in supercharging system 10 given the relatively high operating speeds achieved by power transmission mechanism 16 and mechanical input 18.
Mechanical output 20 may include a spindle connected for rotation with sun member 26, which enables a generator rotor 32 to be drivingly supported on the spindle requiring the use of bearings. Generator 12 may be an induction electrical machine or a permanent magnetic electrical machine, for example, the latter including a magnetic field-containing feature, such as an Inconnel sleeve, to contain the magnetic field produced by the permanent magnet. When configured as a permanent magnet electrical machine, generator 12 may be at least 90% efficient over the required power range. While the efficiency of an induction electrical machine may be less than a permanent magnet electrical machine, it does not necessarily require a magnetic field-containing feature.
Referring still to
Supercharging system 10 also includes a power transmitting link 43 that may be configured to transmit direct current at various voltages between first and second power converters 40, 42. In an exemplary implementation of the invention, the required electrical power for driving air pump 24 with an efficiency of about 70% is approximately 12kW, assuming a maximum engine speed of about 6000 RPM. To support this power requirement, power transmitting link 43 may be configured to transmit approximately 300V of direct current at about 40 A when the engine is operating at around 6000 RPM. As will be appreciated, the power requirement may depend on the required engine torque-speed curve and the efficiency may not be a steady 70% across the entire curve. Operation of supercharging system at other engine speeds is summarized below:
When supercharger system 10 is configured with a centrifugal supercharger, an impeller 44 is rotatably secured to a shaft 46, which in turn supports a motor rotor 48 for rotation therewith. Unlike generator 12, motor 22 may require a pair of bearings 50 to support rotation of shaft 46, motor rotor 48 and impeller 44. Bearings 50 may be ball bearings, which can require a supply of engine oil for lubrication, or may be plain bearings, which may also require a supply of engine oil for lubrication, but are generally less expensive than ball bearings. Unlike conventional turbocharger applications that use ball bearings to reduce friction and the “spooling-up” time of the turbo impeller when there is relatively little energy in the engine exhaust stream, supercharging system 10 is operable to provide motor 22 with sufficient energy at relatively low engine speeds to allow plain bearings to be used without impacting performance of air pump 24. Moreover, bearings 50 do not need to withstand the relatively high temperatures of the turbocharger environment, since air pump 24 is not within the engine exhaust gas stream. Indeed, air pump 24 may included a plastic housing since it is not subjected to the temperatures of the engine exhaust stream.
As will be appreciated, the mechanical disconnect between the power generating component of supercharging system 10 (i.e., generator 12, power transmission mechanism 16, etc.) and the supercharging component of supercharging system 10 (i.e., motor 22, air pump 24, etc.) permits the supercharging component to be conveniently located at various locations within the engine bay, providing the vehicle manufacturer with greater flexibility in design. Moreover, the location of the power generating component may be farther removed from more traditional supercharger locations adjacent the supercharger component and the engine intake manifold.
Referring to
Referring to
In an embodiment, capacitor 70 may include an ultra capacitor bank configured to supply sufficient energy to “warm start” the engine (i.e., start the engine after the engine has been recently operating and then shut-down). In a particular implementation of the invention, motor-generator 18 will require about 80 A to crank the engine on a 12V power supply. Assuming the engine is not shut-down without at least 50V on capacitor 70, the current rating would be about 20 A (i.e., 80 A/50V×12V), well less than the 40 A capability of first power converter 40 during its normal duty cycle. In the above-described embodiment, the conventional vehicle 12V starter motor is still used to “cold start” the engine. However, capacitor 70 and first power converter 40 may be sized to supply the necessary current to motor-generator 12 to “cold start” the engine.
The embodiment illustrated in
The present invention has been particularly shown and described with reference to the foregoing embodiments, which are merely illustrative of the best modes for carrying out the invention. It should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Moreover, the foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.
