Patent Application
20080078593
Referring to
In this example embodiment, the hybrid propulsion system also includes an energy conversion device 18, which may include a motor, a generator, among others and combinations thereof. The energy conversion device 18 is further shown coupled to an energy storage device 20, which may include a battery, a capacitor, a flywheel, a pressure vessel, etc. The energy conversion device can be operated to absorb energy from vehicle motion and/or the engine and convert the absorbed energy to an energy form suitable for storage by the energy storage device (i.e. provide a generator operation). The energy conversion device can also be operated to supply an output (power, work, torque, speed, etc.) to the drive wheels 16 and/or engine 24 (i.e. provide a motor operation). It should be appreciated that the energy conversion device may, in some embodiments, include only a motor, only a generator, or both a motor and generator, among various other components used for providing the appropriate conversion of energy between the energy storage device and the vehicle drive wheels and/or engine.
The depicted connections between engine 24, energy conversion device 18, transmission 14, and drive wheel 16 indicate transmission of mechanical energy from one component to another, whereas the connections between the energy conversion device and the energy storage device may indicate transmission of a variety of energy forms such as electrical, mechanical, etc. For example, torque may be transmitted from engine 24 to drive the vehicle drive wheels 16 via transmission 14. As described above energy storage device 18 may be configured to operate in a generator mode and/or a motor mode. In a generator mode, system 18 absorbs some or all of the output from engine 24 and/or transmission 14, which reduces the amount of drive output delivered to the drive wheel 16, or the amount of braking torque to the drive wheel 16. Such operation may be employed, for example, to achieve efficiency gains through regenerative braking, improved engine efficiency, etc. Further, the output received by the energy conversion device may be used to charge energy storage device 20. In motor mode, the energy conversion device may supply mechanical output to engine 24 and/or transmission 14, for example by using electrical energy stored in an electric battery.
Hybrid propulsion embodiments may include full hybrid systems, in which the vehicle can run on just the engine, just the energy conversion device (e.g. motor), or a combination of both. Assist or mild hybrid configurations may also be employed, in which the engine is the primary torque source, with the hybrid propulsion system acting to selectively deliver added torque, for example during tip-in or other conditions. Further still, starter/generator and/or smart alternator systems may also be used. The various components described above with reference to
From the above, it should be understood that the exemplary hybrid propulsion system is capable of various modes of operation. In a full hybrid implementation, for example, the propulsion system may operate using energy conversion device 18 (e.g., an electric motor) as the only torque source propelling the vehicle. This “electric only” mode of operation may be employed during braking, low speeds, while stopped at traffic lights, etc. In another mode, engine 24 is turned on, and acts as the only torque source powering drive wheel 16. In still another mode, which may be referred to as an “assist” mode, the alternate torque source 18 may supplement and act in cooperation with the torque provided by engine 24. As indicated above, energy conversion device 18 may also operate in a generator mode, in which torque is absorbed from engine 24 and/or transmission 14. Furthermore, energy conversion device 18 may act to augment or absorb torque during transitions of engine 24 between different combustion modes (e.g., during transitions between a spark ignition mode and a compression ignition mode).
Engine 24 includes combustion chamber 29 and cylinder walls 31 with piston 35 positioned therein and connected to crankshaft 39. Combustion chamber 29 is shown communicating with intake manifold 43 and exhaust manifold 47 via respective intake valve 52 and exhaust valve 54. While only one intake and one exhaust valve are shown, the engine may be configured with a plurality of intake and/or exhaust valves.
In some embodiments, intake valve 52 and exhaust valve 54 may be controlled by electric valve actuators (EVA) 55 and 53, respectively. Valve position sensors 50 may be used to determine the position of the valves such as for example, fully opened, fully closed, or another position in between.
In some embodiments, combustion cylinder 29 can be deactivated by at least stopping the supply of fuel supplied to combustion cylinder 29 for at least one cycle. During deactivation of combustion cylinder 29, one or more of the intake and exhaust valves can be adjusted to control the amount of air passing through the cylinder. In this manner, engine 24 can be configured to deactivate one, some or all of the combustion cylinders, thereby enabling variable displacement engine (VDE) operation.
Engine 24 is further shown configured with an exhaust gas recirculation (EGR) system configured to supply exhaust gas to intake manifold 43 from exhaust manifold 47 via EGR passage 130. The amount of exhaust gas supplied by the EGR system can be controlled by EGR valve 134. Further, the exhaust gas within EGR passage 130 may be monitored by an EGR sensor 132, which can be configured to measure temperature, pressure, gas concentration, etc. Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture within the combustion chamber, thus providing a method of controlling the timing of combustion by autoignition.
Engine 24 is also shown having fuel injector 65 coupled thereto for delivering liquid fuel in proportion to the pulse width of signal FPW from controller 48 directly to combustion chamber 29. As shown, the engine may be configured such that the fuel is injected directly into the engine cylinder, which is known to those skilled in the art as direct injection. Distributorless ignition system 88 provides ignition spark to combustion chamber 29 via spark plug 92 in response to controller 48. Universal Exhaust Gas Oxygen (UEGO) sensor 76 is shown coupled to exhaust manifold 47 upstream of catalytic converter 70. The signal from sensor 76 can be used to advantage during feedback air/fuel control in a conventional manner to maintain average air/fuel at stoichiometry during the stoichiometric homogeneous mode of operation.
In some embodiments, the engine may include a fuel vapor purging system for purging fuel vapors to the combustion chamber. As one example, fuel vapors originating in fuel tank 160 may be stored in fuel vapor storage tank 164 until they are purged to intake passage 43 via fuel purge valve 168. Fuel vapor purge valve 168 may be connected to controller 48. Furthermore, the position of the fuel vapor purge valve may be varied by the control system to provide fuel vapors to the combustion chamber during select operating conditions.
Controller 48 is shown in
In some embodiments, controller 48 can be configured to control operation of the various systems described above with reference to
Combustion in engine 10 can be of various types/modes, depending on operating conditions. In one example, spark ignition (SI) can be employed where the engine utilizes a sparking device, such as spark plug coupled in the combustion chamber, to regulate the timing of combustion chamber gas at a predetermined time after top dead center of the expansion stroke. In one example, during spark ignition operation, the temperature of the air entering the combustion chamber is considerably lower than the temperature required for autoignition. While SI combustion may be utilized across a broad range of engine torque and speed it may produce increased levels of NOx and lower fuel efficiency when compared with other types of combustion.
Another type of combustion that may be employed by engine 10 uses homogeneous charge compression ignition (HCCI), or controlled autoignition (CAI), where autoignition of combustion chamber gases occurs at a predetermined point after the compression stroke of the combustion cycle, or near top dead center of compression. Typically, when compression ignition of a pre-mixed air and fuel charge is utilized, fuel is normally homogeneously premixed with air, as in a port injected spark-ignited engine or direct injected fuel during an intake stroke, but with a high proportion of air to fuel. Since the air/fuel mixture is highly diluted by air or residual exhaust gases, which results in lower peak combustion gas temperatures, the production of NOx may be reduced compared to levels found in SI combustion. Furthermore, fuel efficiency while operating in a compression combustion mode may be increased by reducing the engine pumping loss, increasing the gas specific heat ratio, and by utilizing a higher compression ratio.
In compression ignition operation mode, it may be desirable to exercise close control over the timing of autoignition. The initial intake charge temperature directly affects the timing of autoignition. The start of ignition is not directly controlled by an event such as the injection of fuel in the standard diesel engine or the sparking of the spark plug in the spark ignited engine. Furthermore, the heat release rate is not controlled by either the rate or duration of the fuel-injection process, as in the diesel engine, or by the turbulent flame propagation time, as in the spark-ignited engine.
Note that autoignition is also a phenomenon that may cause knock in a spark-ignited engine. Knock may be undesirable in spark-ignited engines because it enhances heat transfer within the cylinder and may burn or damage the piston. In controlled compression ignition operation, with its high air-to-fuel ratio, knock does not generally cause degradation of the engine because the diluted charge keeps the rate of pressure rise low and the maximum temperature of the burned gases relatively low. The lower rate of pressure rise mitigates the damaging pressure oscillations characteristic of spark ignition knock.
In comparison to a spark ignition engine, the temperature of the charge at the beginning of the compression stroke typically may be increased to reach autoignition conditions at or near the end of the compression stroke. It will be appreciated by those skilled in the art that numerous other methods may be used to elevate initial charge temperature. Some of these include: heating the intake air (heat exchanger), keeping part of the warm combustion products in the cylinder (internal EGR) by adjusting intake and/or exhaust valve timing, compressing the inlet charge (turbo-charging and supercharging), changing the autoignition characteristics of the fuel provided to the engine, and heating the intake air charge (external EGR).
During HCCI combustion, autoignition of the combustion chamber gas may be controlled to occur at a desired position of the piston or crank angle to generate desired engine torque, and thus it may not be necessary to initiate a spark from a sparking mechanism to achieve combustion. However, a late timing of the spark plug, after an autoignition temperature should have been attained, may be utilized as a backup ignition source in the case that autoignition does not occur.
Note that a plurality of other parameters may affect both the peak combustion temperature and the required temperature for efficient HCCI combustion. These and any other applicable parameters may be accounted for in the routines embedded in engine controller 48 and may be used to determine optimum operating conditions. For example, as the octane rating of the fuel increases, the required peak compression temperature may increase as the fuel requires a higher peak compression temperature to achieve ignition. Also, the level of charge dilution may be affected by a variety of factors including both humidity and the amount of exhaust gases present in the intake charge. In this way, it is possible to adjust engine parameters to compensate for the effect of humidity variation on autoignition, i.e., the effect of water makes autoignition less likely.
In one particular example, autoignition operation and combustion timing may be controlled by varying intake and/or exhaust valve timing and/or lift to, for example, adjust the amount of residual trapped gasses. Operating an engine in HCCI using the gas trapping method can provide fuel-efficient combustion with extremely low engine out NOx emissions.
However, the achievable HCCI window of operation for low engine speed and/or low engine load may be limited. That is, if the temperature of the trapped gas is too low, then HCCI combustion may not be possible at the next combustion event. If it is necessary to switch out of HCCI and into spark ignition mode during low load in which temperatures may fall too low, and then to return back into HCCI operation once conditions are acceptable, there may be penalties in engine emissions and fuel economy and possible torque/NVH disruption to the driver during each transition. Therefore, in one embodiment, a method that enables additional operation in HCCI or other limited combustion mode at high or low speeds and loads is described herein utilizing an alternative torque source, such as an energy conversion device/generator. Furthermore, extending the low load limit of HCCI operation, for one or more cycles, to obtain increased benefit from HCCI operation may be desirable.
While one or more of the above combustion modes may be used in some examples, still other combustion modes may be used, such as stratified operation, either with or without spark initiated combustion.
As discussed above, hybrid propulsion system 10 may be operated in a variety of different modes. Various inputs may be used to select from among the different modes, and/or to control operation of the hybrid propulsion system while operating in a given mode. Example inputs include engine speed, vehicle speed, requested torque, catalyst temperature, manifold pressure, air/fuel ratio, catalyst temperature and/or status of aftertreatment systems, throttle position, accelerator pedal position, requested power, adaptively-learned drive behavior, operating temperature conditions, humidity, etc., status of climate controls, PIP, state of charge (SOC) in hybrid-electric vehicle, etc.
Also, it should be understood that the hybrid drivetrain may be configured in a variety of different ways.
In the various exemplary systems and methods, it will often be desirable to employ camless valve control over the internal combustion engine. Electro-hydraulic, electromechanical and/or other electrically-actuated camless valve control systems may be employed. In these electrically-actuated camless systems (referred to generally herein as EVA systems), cylinder valve operation is not constrained mechanically by the position of the engine crankshaft. Accordingly, a variety of different valve modes may be employed, including timing/lift variations, in order to achieve various benefits during operation of the hybrid powertrain. EVA control may be employed during mode transitions when the engine is being turned on or off, and/or may be employed within various operating modes (e.g., electric-only operation), to improve fuel consumption, reduce NVH, optimize aftertreatment performance and provide other benefit.
Referring now to
Continuing with
Referring now to
Referring specifically to the figure, during electric-only mode (determination at 502), the method may include determining at 504 whether EVA control can be employed to achieve one or more net benefits. For example, while on one hand there may be a benefit to actively opening and closing cylinder valves during electric-only mode, at times it may be desirable to deactivate one or more cylinders, as shown at 506, to reduce the electrical load of the EVA valvetrain. Deactivation may be implemented in various different ways. Engine speed may be used as a factor to control EVA valve deactivation. For example, the deactivation at 506 may be implemented by holding intake valves open and exhaust valves closed at low engine speeds, or if engine speed is below a threshold, as shown at 508 and 510. This closing of the valves can minimize pumping losses in addition to lowering the electrical load on the EVA system. Additionally, or alternatively, all valves may be closed at high(er) speeds, as shown at 512 and 514. Such opening of the valves at low speeds may aid in reducing blow-by and heat transfer losses resulting from compression/recompression of the cylinder gases. Accordingly, holding all the valves closed through EVA actuation may be the most desirable operating mode to reduce friction at higher engine speeds.
EVA actuation may also be employed during mode transitions involving engine shutdown. Typically, as the engine comes to rest, torsional pulses are caused by the piston compressing and expanding air that is trapped in the cylinder. These pulses can be mitigated to the driveline through slipping of clutches or motor control, however there is little opportunity to mitigate pulse transmission to the vehicle body. Accordingly, engine shutdown events can produce degraded noise, vibration and harshness (NVH), also referred to as shutdown shake, a problem exacerbated in hybrid systems by the fact that the engine is often turned on and off repeatedly during operation of the vehicle.
Accordingly, the present disclosure provides a system and method for employing EVA valve control in a hybrid vehicle during engine shutdown events. An exemplary method is depicted in
Note that the example control and estimation routines included herein can be used with various engine and/or hybrid propulsion system configurations. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. Further, the described steps may graphically represent code to be programmed into the computer readable storage medium in controller 48.
It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-4, V-6, V-8, I-4, I-6, V-10, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
