Patent Application
20080287255
This invention pertains generally to control systems for powertrain control systems employing electro-mechanical transmissions.
Powertrain architectures comprise torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to a vehicle driveline. One such transmission includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, typically an internal combustion engine, and an output member for delivering motive torque from the transmission to the vehicle driveline. Electrical machines, operatively connected to an electrical energy storage device, comprise motor/generators operable to generate motive torque for input to the transmission, independently of torque input from the internal combustion engine. The electrical machines are further operable to transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain system, including controlling transmission gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange between the electrical energy storage device and the electrical machines.
The exemplary electro-mechanical transmissions are selectively operative in fixed gear modes and continuously variable modes through actuation of the torque-transfer clutches, typically employing a hydraulic circuit to effect clutch actuation. A fixed gear mode occurs when rotational speed of the transmission output member is a fixed ratio of rotational speed of the input member from the engine, typically due to actuation of one or more torque-transfer clutches. A continuously variable mode occurs when rotational speed of the transmission output member is variable based upon operating speeds of one or more electrical machines. The electrical machines can be connected to the output shaft via actuation of a clutch, or by direct connection. Clutch actuation and deactivation is typically effected through a hydraulic circuit.
Engineers implementing powertrain systems having electro-mechanical transmissions are tasked with implementing control schemes to monitor system states and control operation of various systems and actuators to effectively control powertrain operation. Such a system is described hereinafter.
In accordance with an embodiment of the invention, a method and an apparatus are provided to control operation of a powertrain system comprising a torque transmission device operative to transmit torque input from a plurality of torque-generative devices.
The method is directed to determine operating conditions for a powertrain comprising an internal combustion engine and first and second electrical machines and an electro-mechanical transmission selectively operative to transmit torque therebetween. The method comprises determining an operating cost for operating the first and second electrical machines of the hybrid transmission effective to meet an operator torque request when the engine is operating in an engine-off operating state. The operating costs can be compared to operating costs for other operating states in an optimization routine. Determining the torque output for operating the first and second electrical machines comprises executing a predetermined system equation effective to determine motor torque outputs from each of the first and second electrical machines based upon the selected parametric value for the input torque and the operator torque request.
An aspect of the invention comprises the method intended to be executed in a control system for a hybrid powertrain system including the internal combustion engine and an electro-mechanical transmission. The control system preferably comprises a distributed control module architecture comprising a plurality of signally connected control modules including a hybrid control module, an engine control module, a transmission control module, and, a power inverter control module. The transmission is selectively operative in a plurality of fixed gear modes and continuously variable modes through selective actuation of a plurality of torque-transfer clutches.
These and other aspects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments.
The invention may take physical form in certain parts and arrangement of parts, an embodiment of which is described in detail and illustrated in the accompanying drawings which form a part hereof, and wherein:
Referring now to the drawings, wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same,
The exemplary hybrid powertrain system is configured to execute the strategic control scheme for controlling the engine depicted in
The transmission 10 utilizes three planetary-gear sets 24, 26 and 28, and four torque-transmitting devices, i.e., clutches C170, C262, C373, and C475. An electro-hydraulic control system 42, preferably controlled by transmission control module (‘TCM’) 17, is operative to control actuation and deactivation of the clutches. Clutches C2 and C4 preferably comprise hydraulically-actuated rotating friction clutches. Clutches C1 and C3 preferably comprise comprising hydraulically-actuated stationary devices grounded to the transmission case 68.
There is first electrical machine comprising a motor/generator 56, referred to as MG-A, and a second electrical machine comprising a motor/generator 72, referred to as MG-B operatively connected to the transmission via the planetary gears. Transmission output shaft 64 is operably connected to a vehicle driveline 90 to provide motive output torque, TO to vehicle wheels. Each clutch is preferably hydraulically actuated, receiving pressurized hydraulic fluid from a pump, described below, via an electro-hydraulic control circuit 42.
The transmission 10 receives input torque from the torque-generative devices, including the engine 14 and the MG-A 56 and MG-B 72, and referred to as ‘TI’, ‘TA’, and ‘TB’ respectively, as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (ESD) 74. The ESD 74 is high voltage DC-coupled to transmission power inverter module (‘TPIM’) 19 via DC transfer conductors 27. The TPIM 19 is an element of the control system described hereinafter with regard to
Referring now to
The HCP 5 provides overarching control of the hybrid powertrain system, serving to coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Based upon various input signals from the UI 13 and the powertrain, including the battery pack, the HCP 5 generates various commands, including: an operator torque request (‘TO
The ECM 23 is operably connected to the engine 14, and functions to acquire data from a variety of sensors and control a variety of actuators, respectively, of the engine 14 over a plurality of discrete lines collectively shown as aggregate line 35. The ECM 23 receives the engine torque command from the HCP 5, and generates a desired axle torque, and an indication of actual input torque, TI, to the transmission, which is communicated to the HCP 5. For simplicity, ECM 23 is shown generally having bi-directional interface with engine 14 via aggregate line 35. Various other parameters that may be sensed by ECM 23 include engine coolant temperature, engine input speed, NE, to shaft 12 which translates to transmission input speed, NI, manifold pressure, ambient air temperature, and ambient pressure. Various actuators that may be controlled by the ECM 23 include fuel injectors, ignition modules, and throttle control modules.
The TCM 17 is operably connected to the transmission 10 and functions to acquire data from a variety of sensors and provide command signals to the transmission. Inputs from the TCM 17 to the HCP 5 include estimated clutch torques (TCL
The BPCM 21 is signally connected one or more sensors operable to monitor electrical current or voltage parameters of the ESD 74 to provide information about the state of the batteries to the HCP 5. Such information includes battery state-of-charge, battery voltage and available battery power, referred to as a range PBAT
Each of the aforementioned control modules is preferably a general-purpose digital computer generally comprising a microprocessor or central processing unit, storage mediums comprising read only memory (ROM), random access memory (RAM), electrically programmable read only memory (EPROM), high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O) and appropriate signal conditioning and buffer circuitry. Each control module has a set of control algorithms, comprising resident program instructions and calibrations stored in ROM and executed to provide the respective functions of each computer. Information transfer between the various computers is preferably accomplished using the aforementioned LAN 6.
Algorithms for control and state estimation in each of the control modules are typically executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by one of the central processing units and are operable to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the respective device, using preset calibrations. Loop cycles are typically executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.
The exemplary two-mode, compound-split, electro-mechanical transmission operates in several fixed gear operating modes and continuously variable operating modes, described with reference to
The various transmission operating range states described in the table indicate which of the specific clutches C1, C2, C3, and C4 are engaged or actuated for each of the operating range states. A first mode, i.e., Mode 1, is selected when clutch C170 is actuated in order to “ground” the outer gear member of the third planetary gear set 28. The engine 14 can be either on or off. A second mode, i.e., Mode 2, is selected when clutch C170 is released and clutch C262 is simultaneously actuated to connect the shaft 60 to the carrier of the third planetary gear set 28. Again, the engine 14 can be either on or off. For purposes of this description, Engine Off is defined by engine input speed, NE, being equal to zero revolutions per minute (RPM), i.e., the engine crankshaft is not rotating. Other factors outside the scope of the invention affect when the electrical machines 56, 72 operate as motors and generators, and are not discussed herein.
The control system, shown primarily in
The first and second modes of operation refer to circumstances in which the transmission functions are controlled by one clutch, i.e., either clutch C162 or C270, and by the controlled speed and torque of the electrical machines 56 and 72, which can be referred to as a continuously variable transmission mode. Certain ranges of operation are described below in which fixed gear ratios are achieved by applying an additional clutch. This additional clutch may be clutch C373 or C475, as shown in the table, above.
When the additional clutch is applied, fixed ratio operation of input-to-output speed of the transmission, i.e., NI/NO, is achieved. The rotations of machines MG-A and MG-B 56, 72 are dependent on internal rotation of the mechanism as defined by the clutching and proportional to the input speed measured at shaft 12. The machines MG-A and MG-B function as motors or generators. They are independent of engine to output power flow, thereby enabling both to be motors, both to function as generators, or any combination thereof. This allows, for instance, during operation in Fixed Ratio 1 that motive power output from the transmission at shaft 64 is provided by power from the engine and power from MG-A and MG-B, through planetary gear set 28 by accepting power from ESD 74.
Referring now to
Referring to Table 1 and again to
In response to an operator's action, as captured by the UI 13, the supervisory HCP control module 5 and one or more of the other control modules determine the operator torque request TO
Referring now to
The method comprises determining operating conditions for the exemplary powertrain, comprising determining a torque output and an operating cost for operating the first and second electrical machines of the hybrid transmission effective to meet an operator torque request when the engine is operating in an engine-off operating state. Determining the torque output for operating the first and second electrical machines comprises executing a predetermined system equation effective to determine motor torque outputs from each of the first and second electrical machines based upon the selected parametric value for the input torque and the operator torque request.
In overall operation, the method includes monitoring output of the transmission, typically NO, the operator torque request, TO
Referring now to
Referring now to
Referring now to
Referring now to
Referring now to
The parametric values of input torque TI=0 and input speed NI=0 are input to system equation 362, through line 246 for either of Mode 1 and Mode 2 to segment 260, which comprises an element of either of segments 266 for Mode 1 and segment 268 for Mode 2, and comprise an output from segment 240, described above. When the exemplary transmission is operated in one of the continuously variable modes Mode 1 or Mode 2, the speed relationship between MG-A, MG-B, NI and NO is defined as shown in Eq. 1, below:
wherein NI=0 comprises the input speed from engine 14, NO is the transmission output speed, NA and NB are the operating speeds for MG-A 56 and MG-B 72, and b11, b12, b21, b22, are known scalar values determined for the specific application in the specific operating range state. Therefore, the determined scalar values for b11, b12, b21, b22 are specific to each of Mode 1 and Mode 2. In this application, when the transmission output speed, NO is known, and NI=0, motor speeds NA and NB can be determined.
The torque relationship between MG-A, MG-B, NI and NO is defined as shown in Eq. 2, below:
wherein TI=0 is the input torque from engine b4, TO is the transmission output torque, TA and TB are the operating torques for MG-A 56 and MG-B 72, {dot over (N)}I and {dot over (N)}O represent time-rate changes in input speed and output speed of the engine 14, and d11, d12, d13, d14, d21, d22, d23, d24 are known scalar values determined for each operating range state, i.e., either of Mode 1 and Mode 2, of the application. In this application, when the transmission output torque TO
is substantially equal to the operator torque request TO
The system equation (Block 362) derived from Eqs. 1 and 2, provides the motor values for MG-A and MG-B is as follows in Eq. 3:
wherein a11, a12, a21, a22, b1, and b2 are known scalar values determined for the specific application, and for the specific mode of operation, i.e., Mode 1 or Mode 2.
The calculated parametric values for motor torques TA and TB which are output from Eq. 3 are input to the cost function (Block 364) to calculate a cost, PCOST, which is associated with the selected parametric values for TI=0 and NI=0.
The cost information used in the cost function 364 preferably comprises operating costs which are generally determined based upon factors related to vehicle driveability, fuel economy, emissions, and battery life for the determined torque range. Furthermore, costs in this invention are assigned and associated with only electrical power consumption associated with a specific operating point of the powertrain system for the vehicle. Lower operating costs are generally associated with lower battery power usage, and lower emissions for an operating point, and take into account a current operating range state of the powertrain system. The optimum operating cost (PCOST) can be determined by calculating a total powertrain system loss, comprising an overall system power loss and a cost penalty, such as can be associated with controlling battery state of charge. The overall system power loss comprises a term based upon losses in the electrical system (e.g. wire impedances and switching and solenoid losses), and heat losses. Other losses include electrical machine power losses and internal battery power losses. Other factors may also be considered, including factors related to battery life due to depth of discharge of the ESD 74, current ambient temperatures and their effect on state of charge of the battery. Operating costs are preferably developed relative to specific powertrain/vehicle applications during vehicle calibration pre-production. An exemplary method for determining engine power losses are described in commonly assigned U.S. Patent Application Publication Number 2005/0256633 A2, entitled C
It is understood that modifications in the hardware are allowable within the scope of the invention. The invention has been described with specific reference to the embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention.
