Abstract:
The hybrid powertrain includes an internal combustion engine, a regenerative brake/motor and an electric energy storage device such as a battery. Preferably the internal combustion engine is a diesel engine with programmable injection events and programmable intake and exhaust valve events. The regenerative brake/motor is capable of operating as both an electric generator and as an electric motor. The battery receives electric energy from the regenerative brake. In additional to supplying electricity to the motor, the battery drives the engine accessories. The battery also supplies electric energy to keep the exhaust aftertreatment systems (Lean NOx, NOx absorber, PM Filter) at optimal temperature to improve conversion efficiency. A powertrain controller schedules the energy distribution and driving forces associated with both the diesel engine and the motor to maximize the vehicle fuel economy and to minimize the vehicle exhaust emissions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/355,546, filed on Feb. 8, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to internal combustion engines for use in hybrid powertrains to improve fuel economy and to reduce exhaust emissions.  
         BACKGROUND OF THE INVENTION  
         [0003]    The recent development of hybrid powertrains in the automotive industry has demonstrated encouraging results for reductions in fuel consumption and exhaust emissions. A vehicle with a hybrid powertrain usually includes an internal combustion engine, an electric generator, an electric motor, a battery and other equipment. In series hybrid vehicles, the generator is driven by the mechanical output of the internal combustion engine. The output of the generator is then combined with the output of the battery to drive the electric motor, such that the mechanical output of the motor drives the vehicle. In contrast, the parallel hybrid vehicle includes an internal combustion engine, a regenerative brake/motor and an electric energy storage device such as a battery and other equipment. PHVs are usually driven directly by the mechanical output of the internal combustion engine. However, when the vehicle must be accelerated or decelerated at a rate that cannot be accomplished by the internal combustion engine alone, or if the drive efficiency of the engine would be degraded if only the internal combustion engine were used, the regenerative brake/motor, which is mechanically connected to the internal combustion engine, operates as an electric motor (on acceleration) or as a regenerative brake (on deceleration) to meet the required rate of acceleration or deceleration through the combined output of the internal combustion engine and the regenerative brake/motor.  
           [0004]    The internal combustion engine of hybrid powertrain has narrow operating range. In series hybrid vehicles, the internal combustion engine is not mechanical connected to the driving wheels. In parallel hybrid vehicles, the regenerative brake/motor provides rapid acceleration or deceleration. Therefore, the internal combustion engine used in hybrid powertrains can be optimized for better fuel economy and less exhaust emissions compared to conventional internal combustion engines.  
           [0005]    Examples of hybrid vehicle and their operating modes have been described in detail in several patents: For example, in U.S. Pat. No. 5,656,921, a parallel hybrid vehicle is disclosed having power sources from a SI engine and an electric motor. It employs fuzzy logic rules to adjust the entries in the tables determining the power splitting between the SI engine and the electric motor. The performance measure used to adjust the entries is given by the weighted ratio between the battery current and fuel flow rate. In U.S. Pat. No. 5,943,918, granted to Reed and U.S. Pat. No. 6,164,400 granted to Jankovic, a hybrid powertrain is described which uses power delivered by both the internal combustion engine and the electric motor. A shifting schedule was developed for a multiple ratio transmission to establishing a proportional relationship between accelerator pedal movement and the torque desired at the wheel. U.S. Pat. No. 6,223,106 granted to Toru Yano et al. and U.S. Pat. No. 6,318,487 granted to Yanase et al. each describe a hybrid vehicle control system operable to prevent the battery from being overcharged during regenerating braking. U.S. Pat. No. 5,725,064, describes a control system operable to open the intake and exhaust valves to reduce the pumping loss when the vehicle is operating in reverse or its electric motor driving mode without using a clutch device to disconnect the internal combustion engine from the transmission. Finally, U.S. Pat. No. 6,266,956 describes an exhaust emission control system for a hybrid car using a separate combustion device to heat the catalyst and to provide hydrocarbons as the reducing agent to the lean NOx catalyst.  
           [0006]    The primary focus of the above patents is the drivability of the hybrid vehicle. Unfortunately, little efforts have been applied to the development and integration of the internal combustion engines to optimize the benefits of the hybrid powertrain for lower cost, better fuel economy and lower exhaust emissions, especially, for the heavy-duty diesel engines for the urban and on-highway truck and bus applications.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention relates to advanced development of internal combustion engines for hybrid powertrain applications and its exhaust emissions controls for urban and on-highway vehicles. The hybrid powertrain includes a diesel engine, a regenerative brake/motor and an electric energy storage device such as a battery. The regenerative brake/motor is capable of operating as both an electric generator as a result of the regenerative braking to decelerate the vehicle and an electric motor. The battery supplies electric energy to and receives electric energy from the regenerative brake/motor. A powertrain controller schedules the driving forces supplied from at least one of the internal combustion engine and the electric motor.  
           [0008]    The present invention also features a turbocharged diesel engine with capabilities of multiple fuel injection events and rate shaping, variable valve timing, an exhaust aftertreatment system, engine braking, and battery powered accessories, such as water pump and cooling fan etc.  
           [0009]    The electric motor is used to supply supplemental torque to the drivetrain during acceleration and peak torque operating conditions and further acts as the sole power source during low load conditions. The electric motor will also serve as a regenerative brake during the vehicle decelerations. The regenerating brake, in combination with the engine exhaust brake or compression release brake, will provide sufficient retarding power to maintain a proper vehicle speeds on a down slope road. The electricity generated by the regenerating brake will be used to charge the battery.  
           [0010]    The powertrain controller schedules fuel delivery to the diesel engine, monitors the battery power, and schedules the battery power delivery to the electric motor. The diesel engine is calibrated so that the combined power of the drivetrain will deliver sufficient power to the wheels and maintain drivability of the vehicle. Since the engine speed can be measured, the desired engine torque is equal to the engine power divided by engine speed Likewise, the desired motor torque is equal to the power desired from the electric motor divided by the electric motor speed. The power at the wheels is approximately equal to the sum of the power delivered from each of the power sources. The desired power at the wheels is the sum of the desired engine power and the desired electric motor power.  
           [0011]    This strategy requires a fuel-scheduling map for steady state and transient operations of the diesel engine, as well as the functional relationship maps between the diesel engine and the electric motor. The fuel injection system of the diesel engine has multiple injection event capability such as, for example, pilot injection, main injection, post injection, and rate shaping capabilities, (i.e., triangle, boot, square etc.). The fuel schedule map will specify the injection timing, rate shaping, injection pressure and quantity for best engine fuel economy, emission control, and drivability.  
           [0012]    One aspect of the present invention is to power the engine accessories with the battery of the hybrid powertrain. The accessories of current diesel engines are driven by the engines crankshaft which reduces its power output and fuel economy. The present invention uses the battery power, which is generated during the vehicle deceleration, to drive various engine accessories such as, for example, the cooling fan, water pump, engine control module, alternator, air compressor, power steering pump, and air conditioning compressor, etc.  
           [0013]    Another aspect of the present invention is to apply the variable valve timing capability of the diesel engine to reduce the pumping work during the electric motor only mode, to perform cylinder cut-out, and to re-circulate EGR internally by delaying the exhaust valve closing and/or by early intake valve opening to reduce exhaust emissions (variable intake valve closing for increased compression ratio and/or Miller cycle operation).  
           [0014]    A further aspect of the invention is to use the battery power to heat the catalytic converter to increase the catalyst efficiency. Efficiency of the after treatment device such as, for example, an NOx absorber and active lean NOx, are temperature dependent. The converter efficiency is decreased during partial load operation and at start up of the engine due to lower exhaust temperature. By externally heating the catalyst through a battery-powered heater, the catalyst maintains at its optimal conversion efficiency to reduce exhaust emissions.  
           [0015]    The fourth aspect of the invention is to open the exhaust valve during the compression stroke to perform compression release braking in combination with the regenerative braking of the electric motor to control vehicle speed and to prevent overcharge of the battery.  
           [0016]    The fifth aspect of this invention to use motor assisted turbocharger during acceleration to improve the turbo charger responsiveness. The motor is powered the battery of the hybrid powertrain.  
           [0017]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereafter. However, it should be understood that the detailed descript and specific examples, while indicating preferred embodiments of the present invention, are intended for purposes of illustration only since various changes and modifications within the fair scope of the present invention will become apparent to those skilled in this art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a schematic representation of a conventional hybrid vehicle;  
         [0019]    [0019]FIG. 2 is a schematic of a hybrid powertrain according to the present invention with integration of various engine and vehicle components;  
         [0020]    [0020]FIG. 3 is a schematic of an alternative hybrid powertrain equipped with clutch and with integration of the engine and vehicle components;  
         [0021]    [0021]FIG. 4 is a schematic of an internal combustion engine for use in hybrid powertrain applications;  
         [0022]    [0022]FIG. 5 is an illustration of the catalyst conversion efficiency of a hybrid powertrain;  
         [0023]    [0023]FIG. 6 illustrates the capabilities of a diesel engine fuel injection system;  
         [0024]    [0024]FIG. 7 illustrates the valve lift of variable valve actuation system associated with the internal combustion engine of the present invention;  
         [0025]    [0025]FIG. 8 is a schematic of the ECU.;  
         [0026]    [0026]FIG. 9 is an operating diagram of steady state torque map for a hybrid vehicle;  
         [0027]    [0027]FIG. 10 is an operating diagram of transient operating control of a hybrid vehicle with motor assisted turbocharger;  
         [0028]    [0028]FIG. 11 is a flow chart of a control strategy for a heavy-duty hybrid vehicle;  
         [0029]    [0029]FIG. 12A is a flow chart for the regenerative brake control; and  
         [0030]    [0030]FIG. 12B is a flow chart for catalyst temperature and valve timing control.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    A schematic of a conventional serial hybrid powertrain is shown in FIG. 1. The numeral  10  designates a turbocharged diesel engine for use in a vehicle drivetrain. A motor/regenerative brake is shown at  20 . Both diesel engine  10  and motor/regenerative brake  20  are connected to a multiple ratio transmission  30 . Transmission  30  is mechanically connected to a pair of vehicle driving wheels  40 . A battery  50  serves as an energy storage device which is electrically connected to motor/regenerative brake  20 . An electronic controller unit  60  controls the overall drivetrain.  
         [0032]    Referring to FIG. 2, the conventional drivetrain of FIG. 1 is shown to be modified to incorporate the features of the present invention. Specifically, FIG. 2 shows an integrated internal combustion engine  10 A with the hybrid powertrain. Engine  10 A is shown to include various controllable systems including a fuel injection system  11 , a throttle system  12 , an engine retrading mechanism  13 , an aftertreatment system  14 , a turbocharger  15 , an intake/exhaust valve actuation system  16  for cylinder cutout and variable valve timing, in addition to power-operated accessories  17 . Likewise, ECU  60 A is shown to include several control functions including a vehicle control function  61 , an engine control function  62 , a transmission control function  63 , a motor-generator brake control function  64 , and a battery control function  65 .  
         [0033]    [0033]FIG. 3 shows an alternative configuration for the integrated internal combustion engine  10 A within the hybrid powertrain. Specifically, a clutch device  70  is placed in between internal combustion  10 A engine and motor  20 .  
         [0034]    [0034]FIG. 4 shows more details of the integration of the internal combustion engine and the hybrid powertrain. The clean air passes through an air filter  100  to a compressor  102 . Compressor  102 , which is driven by a turbine  105 , increases the pressure of the air. Air is cooled when it passes through a charge air cooler  104  to increase the air density before entering the intake manifold  106 .  
         [0035]    The energy of the exhaust air is used to drive turbine  105  with variable geometric nozzles  108 . A high-speed motor  110 , which is powered by battery  50  of the hybrid powertrain, will be used to increase turbine&#39;s responsiveness at part load operating condition and during acceleration.  
         [0036]    Harmful pollutants, such as NOx and particulate matters (PM), are removed from the exhaust gas before the discharging to the ambient. The efficiency of the after treatment system is temperature dependent. The conversion efficiency is lowered due to low exhaust temperature during low speed and part load and start up operating conditions. An electric heater  112  is used to heat the after treatment system at its optimum conversion temperature at all engine-operating conditions. Battery  50  of the hybrid powertrain provides the power to electric heater  112 . The conversion efficiency comparison with and without electric heat is shown in FIG. 5.  
         [0037]    The engine coolant is circulated to cool the engine by a water-pump  114 . Hot coolant flows to a radiator  116 , which is cooled by a fan  118 . Instead of being driven by the engine crankshaft, water pump  114  and cooling fan  118  are powered by battery  50  of the hybrid powertrain.  
         [0038]    The capability of diesel engine fuel injection system  11  is shown in FIG. 6. It has the multiple injection and rate shaping capabilities. The pilot injection reduces the combustion noise and the NOx emissions. The first post injection reduces PM emissions with minimum fuel economy penalty. The second post injection provides hydrocarbon species for catalytic converter to reduce NOx emissions.  
         [0039]    Valve actuators associated with valve actuation mechanism  16  provide variable timing capabilities and its valve lift profile is shown in FIG. 7. The Valve actuators change the opening and closing timing of the intake and exhaust valves, as well as to reopen the valves. By reopening the intake and exhaust valves, it will reduce the pumping loss during the motor only operating mode of the hybrid powertrain. By pre-opening the intake valve during the exhaust blow down stroke, a small portion of the exhaust gas discharges to the intake manifold. This portion of the exhaust gas will be readmitted to the cylinder to mix with fresh air. It is called internal exhaust gas recirculation. It reduces the NOx formation during diesel engine combustion process. Another EGR configuration is to reopen the exhaust valve during the intake stroke. The exhaust gases will reentry from the exhaust manifold to the cylinder due to higher pressure of the exhaust manifold.  
         [0040]    In combination of the diesel engine&#39;s injection capabilities and the valve actuation capabilities, one or more cylinders can be cut out during part load or the motor only operating modes to maximize the fuel economy.  
         [0041]    [0041]FIG. 8 shows the inputs and outputs of electronic controller  60 A. The inputs to the electronic controller include the vehicle torque requirements, vehicle speed, engine speed, engine boost pressure and temperature, battery power level, transmission gear and motor torque level etc. The outputs include engine speed, torque, engine fueling map, motor torque, transmission gear and retarding power etc.  
         [0042]    [0042]FIG. 9 shows a steady state map with the engine torque output  130  from the diesel engine  10 A and the motor torque output  120  from electric motor  20 . The hybrid powertrain demonstrate that vehicle emissions can be effective reduced. For example, if the hybrid powertrain outputs 500 HP at 1200 engine rpm (in which the diesel engine outputs 300 HP at NOx emission level of 3.5 g/hp-hr and the electric motor outputs 200 hp) the hybrid powertrain emission will be equivalent to a 500 HP engine with NOx emission level of 2.1 g/hp-hr.  
         [0043]    [0043]FIG. 10 shows time sequences for the hybrid powertrain&#39;s is transient responses. Step  150  shows a torque command of a vehicle. A command increases torque demand at time t 1  and decreases at time t 5 . The motor output torque  160  reaches its maximum value at time t 2 . The engine output torque  170  reaches a specific value at time t 4 . The combined torque of the hybrid powertrain  180  reaches a specified value at time t 3 , which has shorter response time than the internal combustion engine alone. As seen, the hybrid powertrain also has fast response at the decrease of command torque.  
         [0044]    [0044]FIG. 11 is a flowchart showing the control strategy of the hybrid powertrain. The powertrain ECU  60 A in FIG. 3 read the vehicle torque requirement and the engine operating parameters, such as speed, fuel injection rate, boost pressure and temperature etc. in step  210 . The ECU  60 A calculates the engine torque output in step  220 . Step  230  compares the vehicle operating torque T veh  and the vehicle torque requirement T req . If T req  is less than T veh , then step  280  indicates that vehicle braking is required to reduce the powertrain torque output, and the motor brake regeneration is activated as indicated at step  270 . If the required torque T req  is larger than T veh , then step  240  indicates that the engine torque output is checked. If the engine torque T eng  is less than T req , the hybrid powertrain will switch to the motor/engine dual operating mode at step  250 . Otherwise, the hybrid powertrain will operate in the engine only mode at step  260 .  
         [0045]    The powertrain regenerating brake control flowchart is shown in FIG. 12A. The ECU  60 A reads a deceleration command input at step  310 , and calculates the deceleration torque requirement (based on vehicle speed and other operating parameters, engine brake torque, and the motor brake torque) at step  320 . If the required deceleration torque is greater than the motor regenerative brake torque, which is determined at step  330 , then engine braking will be activated in combination with the motor regenerating brake, as shown at step  340 . Otherwise, the vehicle will operate in the motor regenerating brake only mode at step  370 . During the engine braking mode, the engine brake noise will be checked in order to comply with local noise regulations, as indicated by step  350 . If the braking noise level is not acceptable, the engine valve timing can be varied to reduce the brake noise as shown in step  360 .  
         [0046]    [0046]FIG. 12B shows a control strategy related to catalyst temperature for reducing engine exhaust emissions. At step  400 , the operating parameters of the diesel engine are read. Thereafter, step  430  compares the exhaust gas temperature with the temperature required for effective catalyst operation. If the exhaust gas temperature is lower than the required temperature, the exhaust valve timing will be adjusted through variable valve actuation (VVA) device to increase the temperature, as indicated in step  410 . Step  440  determines the hydrocarbon concentration of the exhaust gas since a proper hydrocarbon concentration is required for effective NOx adsorption and lean NOx catalyst operations. If the hydrocarbon concentration is lower than specified, post injection or auxiliary exhaust manifold injection is required to add hydrocarbons into the exhaust gas stream in step  420 . The catalyst temperature is determined in step  450  for optimum emissions reduction performance. If the catalyst temperature is lower than the optimum performance temperature, a battery powered catalyst heater will be turned on to increase the catalyst temperature in step  460 .  
         [0047]    Although a particular control strategy is disclosed, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. All such modifications as well as equivalents thereof are to be included within the scope of the following claims.