Abstract:
An internal combustion engine that propels a vehicle has a fuel injection system for injecting fuel into engine cylinders at desired injection control pressure. A control system controls activation and de-activation of a hydraulic actuator for an engine brake. A processor processes data to develop data for desired injection control pressure. Transitional injection control pressure data is used as desired injection control pressure during a transition time interval that commences with de-activation of the engine brake caused by the relief of pressure of the control fluid for allowing resumption of positive power flow from the engine for propelling the vehicle and that ends after the processor has determined the existence of a predetermined correlation between the transitional injection control pressure data and data indicating pressure of the control fluid.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to internal combustion engines for propelling motor vehicles, and particularly to a transitional fueling strategy for fueling an engine as an engine brake that had previously been activated to slow the engine is being deactivated so that the engine can return to delivering positive power for propelling a vehicle. 
   BACKGROUND OF THE INVENTION 
   Various devices can be associated with an internal combustion engine that powers a motor vehicle to brake the engine by itself. Such engine brakes can be useful in larger vehicles like highway trucks. A known technique for retarding an internal combustion comprises augmenting engine back-pressure. One way of doing this comprises restricting the exhaust gas flow from the engine. In a conventional camshaft engine, a valve that is disposed in the exhaust system, sometimes called an exhaust brake, can be operated to restrict the exhaust gas flow. In an engine that has variable valve actuation, the individual cylinder exhaust valves may be actuated in a manner that creates the desired restriction. 
   It is known the use hydraulic control fluid for operating an engine brake. When the brake is to be applied (activated), fluid under pressure is delivered to an actuator for the brake to operate the brake. When the brake is to be released (de-activated), the fluid is dumped from the actuator to relieve the applied pressure and allow the brake to release. 
   Certain diesel engines have fuel injection systems that utilize hydraulic fluid under pressure to force fuel into engine combustion chambers. The hydraulic fluid is supplied to a respective fuel injector at each engine cylinder. When a valve mechanism of a fuel injector is operated by an electric signal from an engine control system to inject fuel into the respective cylinder, the hydraulic fluid is allowed to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber. 
   A running engine experiences a transition in operation when an engine brake is released and the engine returns to delivering positive power for propelling a vehicle. If fueling is not suitably controlled during the transition, the transition may not be as smooth as desired. A rough transition is evidenced by engine misfire and the consequent generation of excess smoke in the engine exhaust. 
   It has been observed that a contributing factor to engine roughness during such transitions is the rate at which the engine brake releases. If the hydraulic fluid that is activating the brake is not dumped sufficiently fast from the actuator, cylinder misfires and extra exhaust smoke may result. For example, delayed release of a brake acting on engine exhaust valves can cause them to stay open longer than desirable, potentially causing misfires and extra smoke in the exhaust. Hence it is generally desirable to dump the hydraulic fluid as rapidly as possible so that engine braking can promptly end in anticipation of a return to positive power delivery. But during dumping, fueling must be controlled in a way that can accommodate the more rapid brake de-activation. 
   Commonly owned U.S. Pat. No. 6,807,938 of the inventors discloses a strategy for limiting fueling after de-activation of an engine retarder that had previously been activated to brake an engine. While limiting and/or delaying fueling during the transition can provide some improvement, it is believed that further improvement would be desirable during such transitions. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a new and improved fueling strategy for fueling an engine during such a transition. The transitional strategy can provide smoother transitions from the beginning of engine brake de-activation until the resumption of positive power flow from the engine through the vehicle powertrain to the vehicle drivetrain. Consequently, the potential for misfire, and resulting generation of smoke in the exhaust, is significantly reduced. 
   The invention can be embodied in an engine control system by a devoted transitional algorithm that temporarily interrupts a main fuel control algorithm during such a transition. 
   The invention allows the use of a dump valve that can more rapidly dump the hydraulic control fluid from the engine brake actuator, while in doing so, providing control of engine fueling that is appropriate for such faster dumping of the control fluid. 
   One general aspect of the present invention relates to an internal combustion engine that propels a vehicle and comprises a fuel injection system for injecting fuel into engine cylinders at a desired injection control pressure, a fluid-operated device that uses pressure of a control fluid for activating an engine brake to increase engine back pressure, and a control system that controls the pressure of the control fluid and comprises a processor that processes data to develop data for desired injection control pressure. 
   During activation of the brake, the processor develops desired injection control pressure data from a main ICP-determining strategy, and upon the control system requesting de-activation of the brake, develops desired injection control pressure data from a transitional ICP-determining strategy instead of the main ICP-determining strategy during a transition time interval that commences in response to the de-activation request. 
   The transition time interval continues while pressure of the control fluid acting on the device is being relieved to allow resumption of positive power flow from the engine to propel the vehicle. 
   The transition time interval ends after the processor has determined the existence of a predetermined correlation between transitional injection control pressure data from the transitional ICP-determining strategy that is being used as desired injection control pressure data and data indicating pressure of the control fluid acting on the device. 
   Another general aspect relates to a method for controlling injection control pressure at which fuel is injected into cylinders of an internal combustion engine that propels a vehicle during a transition time interval that commences with de-activation of an engine brake by the relief of pressure of a control fluid that had been acting on a device which had been braking the engine. The method comprises developing transitional injection control pressure data for use as desired injection control pressure and using the transitional injection control pressure data, to the exclusion of injection control pressure data from other sources, as the desired injection control pressure data that controls injection control pressure during the transition time interval. The transition time interval ends after the existence of a predetermined correlation between the transitional injection control pressure data and data indicating the pressure of control fluid acting on the device has been determined. 
   Still another general aspect relates to a control system for controlling pressure at which a fuel injection system injects fuel into engine cylinders of an internal combustion engine that propels a vehicle during a transition time interval commencing with de-activation of an engine brake by the relief of pressure of a control fluid that had previously been acting on the device to cause increased engine back pressure. 
   The control system comprises a processor for establishing desired injection control pressure and for causing the relief of pressure of the control fluid acting on the device to deactivate the brake. The processor processes various data to develop transitional injection control pressure data for use as desired injection control pressure data to the exclusion of injection control pressure data from other sources during the transition time interval and to develop data that determines the end of the transition time interval. The processor also processes certain data that includes at least indicated pressure of control fluid acting on the device and engine speed data in accordance with maps to select from the maps data values that are further processed to project a length of time for the transition time interval and to signal the end of the transition time interval upon pressure of control fluid acting on the device and transitional injection control pressure having maintained a predetermined correlation for the projected length of time. 
   The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a general schematic diagram of an exemplary embodiment of software strategy for fueling an internal combustion engine and that includes a transitional fueling strategy in accordance with principles of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a portion of a fuel control strategy embodied in an exemplary internal combustion engine control system  10 . The particular engine is a diesel engine that has a fuel injection system controlled by the fuel control strategy and an engine brake that is activated by pressure of a hydraulic control fluid. Activation and de-activation of the engine brake are controlled by requests from a portion of control system  10  not specifically shown in  FIG. 1 . When the brake is being applied (activated), the control system causes hydraulic control fluid under pressure to be delivered to a hydraulic actuator. When the brake is to be released (de-activated), the control system causes the hydraulic control fluid to be dumped from the actuator, relieving the pressure in the actuator and allowing the brake to de-activate. 
   The engine comprises cylinders forming combustion chambers in which fuel injected by fuel injectors ignites in hot air that has entered through an intake system and been compressed by pistons that reciprocate within the cylinders. The combusting mixture powers the engine, and hence propels the vehicle. Gas resulting from combustion is exhausted through an exhaust system. The fuel injectors are under the control of the fuel control strategy of system  10 . 
   Control system  10  comprises one or more processors that process various data to develop data for controlling various aspects of engine operation including controlling pressure of hydraulic fluid for operating the fuel injectors and the timing of operation of valve mechanisms in the fuel injectors. The engine comprises a hydraulic system that supplies hydraulic fluid, with control system  10  controlling the hydraulic fluid pressure for operating the fuel injectors, which is also sometimes called injection control pressure or ICP. 
   When a valve mechanism of a fuel injector is operated by an electric signal from system  10  to inject fuel into the respective cylinder, the hydraulic fluid at a desired ICP is enabled to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber. Fuel injectors of this general type are disclosed in various prior patents. 
   The fuel control strategy is part of the overall engine control strategy and is implemented by algorithms that are repeatedly executed by the processor, or processors. Certain algorithms form a main ICP-determining strategy  12  that develops data values for ICP that control ICP under most engine operating conditions. Those data values are processed as a command input to a virtual feedback controller  14  in control system  10  in closed-loop control of injection control pressure. 
   Data values for ICP processed as command inputs by controller  14  may be considered as desired ICP. A data value for indicated ICP, as measured or estimated in any suitably appropriate way, is a feedback input to controller  14 . The feedback input is subtracted from the command input to create a data value for an error signal that is used by the controller to secure correspondence of ICP to desired ICP. 
     FIG. 1  shows that a switch  16  controls the delivery of the data values for ICP from strategy  12  to controller  14 . In a first state, switch  16  passes the data values from strategy  12  so that they are used as desired ICP. In a second state, switch  16  passes the data value for a parameter ICP_VRE_OFF that is developed as a data value for desired ICP by a transitional ICP-determining strategy that develops data values for transitional ICP that is used as desired ICP to control ICP during a transition time interval that commences upon a request to de-activate the engine brake. 
   The state to which switch  16  operates is controlled by a parameter ICP_VRE_OFF_LATCH from a latch  18 . When the data value for ICP_VRE_OFF_LATCH changes from a logic “0” to a logic “1”, switch  16  changes from the first state to the second state. When the data value for ICP_VRE_OFF_LATCH changes back from a logic “1” to a logic “0”, switch  16  changes from the second state back to the first state. 
   Latch  18  is set by a parameter FL_VRE_TRANSO and reset by a parameter ICP_VRE_OFF_RESET. Setting of latch  18  places switch  16  in the second state. Resetting of latch  18  places switch  16  in the first state. When the engine brake is being activated, desired injection control pressure data from strategy  12  is being passed by switch  16  to the command input of controller  14 . 
   The data value for ICP_VRE_OFF represents a transitional injection control pressure that is used as the command input to feedback controller  14  during a transition time interval that commences upon a request for de-activation of the engine brake. De-activation of the brake is signaled by a change in FL_VRE_TRANSO that causes latch  18  to be set, placing switch  16  in the second state and causing the data value for ICP_VRE_OFF to become the command input to controller  14  to the exclusion of the data value from strategy  12 . 
   The data value for ICP_VRE_OFF is obtained from a map  20  that contains data values for ICP_VRE_OFF each correlated with a data value representing a respective range of engine speeds within the overall engine speed range. A data value for indicated engine speed N is obtained from any appropriate source, such as a data link on which engine speed is regularly published, and forms an input to map  20 . Processing of indicated engine speed N yields a corresponding data value for ICP_VRE_OFF from map  20 . 
   Data for populating map  20  are obtained during engine development to provide proper fueling during the transition from brake de-activation to restoration of positive power flow from the engine through the vehicle powertrain to the vehicle drivetrain. Proper fueling during the transition promotes a smoother transition with reduced potential for both misfires and increases in exhaust smoke. 
   The data value for ICP_VRE_OFF is also used as an input to a logic function  22  that compares the data value for ICP_VRE_OFF with a data value for a parameter BCP that indicates pressure of hydraulic control fluid being applied to the actuator for the engine brake. This hydraulic control fluid, like the hydraulic fluid for ICP, may come from the engine hydraulic system, but at its own pressure and not necessarily at the same pressure being applied to the fuel injectors. The data value for BCP is obtained from any appropriate source, such as a pressure sensor that furnishes pressure data for publishing the data link. 
   Logic function  22  compares the data values for ICP_VRE_OFF and BCP in the following way. If the data value for BCP is less than the data value for ICP_VRE_OFF, then logic function  22  causes the data value of a parameter ICP_VRE_BCP_MIN to be a logic “1” state. If the data value for BCP is not less than the data value for ICP_VRE_OFF, then logic function  22  causes the data value of parameter ICP_VRE_BCP_MIN to be a logic “0” state. 
   The data value ICP_VRE_BCP_MIN controls the running of a timer  24 . As long as the data value for ICP_VRE_BCP_MIN is a logic “1”, timer  24  runs. Should the data value for ICP_VRE_BCP_MIN become a logic “0”, the timer is reset to zero, and can begin timing again from zero only when the data value for ICP_VRE_BCP_MIN once again becomes a logic “1”. 
   The elapsed time on timer  24 , represented by the parameter ICP_VRE_OFF_TMR is used as one input to another logic function  26  that compares the data value for ICP_VRE_OFF_TMR and the data value for a parameter ICP_VRE_OFF_TM. Logic function  26  compares the two data values in the following way. If the elapsed time on timer  24 , ICP_VRE_OFF_TMR, is less than the time set by ICP_VRE_OFF_TM, then logic function  26  causes the data value for ICP_VRE_OFF_RESET to be a logic “0”. If the data value for elapsed time on timer  24 , ICP_VRE_OFF_TMR, is equal to or greater than the time set by ICP_VRE_OFF_TM, then logic function  26  causes the data value for ICP_VRE_OFF_RESET to be a logic “1”. 
   The data value for ICP_VRE_OFF_TM is obtained from a map  28  that contains data values for ICP_VRE_TM each correlated with a respective pair of data values for engine speed and engine operating temperature representing a respective range of engine speeds and a respective range of engine operating temperatures. A data value for indicated engine operating temperature EOT as obtained from any appropriate source. The data values for indicated engine temperature EOT and indicated engine speed N form inputs to map  28 . Processing of indicated engine speed N and indicated engine temperature EOT yields a corresponding data value for ICP_VRE_OFF_TM from map  28 . Like map  20 , map  28  is also populated during engine development. 
   The purpose of map  28  is to set a duration for the transition time interval based on engine speed and engine temperature. For timer  24  to time during that time interval, function  22  requires that a predetermined relationship exist between pressure of control fluid being applied to the brake actuator and injection control pressure ICP. If the predetermined relationship exists throughout the duration of the time interval set by map  28 , then elapsed time on timer  24  will eventually reach the time established by map  28  whereupon function  26  will signal the end of the interval by resetting latch  18 . 
   The resetting of latch  18  returns switch  16  to the first state so that ICP data values from strategy  12 , and not ICP_VRE_OFF, will thereafter be supplied to the command input of virtual controller  14 . 
   During the transition time interval, the hydraulic control fluid being applied to the brake actuator can be dumped as rapidly as possible to promote fast cylinder exhaust valve closings. The transitional ICP will continue to control ICP until the transitional strategy assures that the pressure being applied to the brake actuator has been reduced to at least a level consistent with the transitional ICP without exceeding that level for some minimum amount of time that is a function of engine speed and engine temperature. In other words, the strategy assures that a predetermined correlation between the transitional ICP and the indicated control fluid pressure acting on the brake actuator continually exists for some minimum interval of speed- and temperature-based time before ICP data values from strategy  12  are allowed to re-gain control of virtual controller  14 . 
   While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.