Patent Publication Number: US-8118122-B2

Title: Method and system for monitoring signal integrity in a distributed controls system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/982,453, filed on Oct. 25, 2007 which is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure pertains to control systems for hybrid powertrain systems. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Known hybrid powertrain architectures can include multiple torque-generative devices, including internal combustion engines and non-combustion machines, e.g., electric machines, which transmit torque through a transmission device to an output member. One exemplary hybrid powertrain includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving tractive torque from a prime mover power source, preferably an internal combustion engine, and an output member. The output member can be operatively connected to a driveline for a motor vehicle for transmitting tractive torque thereto. Machines, operative as motors or generators, can generate torque inputs to the transmission independently of a torque input from the internal combustion engine. The machines may transform vehicle kinetic energy transmitted through the vehicle driveline to energy that is storable in an energy storage device. A control system is operative to monitor various inputs from the vehicle and the operator and provides operational control of the hybrid powertrain, including controlling transmission operating state and gear shifting, controlling the torque-generative devices, and regulating the power interchange among the energy storage device and the machines to manage outputs of the transmission, including torque and rotational speed. A control system can monitor input and control signals and execute algorithms to verify and secure operation of the powertrain. 
     SUMMARY 
     A powertrain system includes an engine, a transmission and a torque generating machine connected to an energy storage device. The transmission is operative to transfer power between the engine and the torque generating machine and an output member. A method to monitor integrity of a signal generated and communicated in the control system includes establishing a distributed control module system comprising a first control module operatively connected to the engine, a second control module operatively connected to the torque generating device, a third control module operatively connected to the transmission device, and a hybrid control module operative to command operation of the first, second, and third control modules. A communications link is established to transmit the signal between the first control module, the second control module, the third control module and the hybrid control module and a user interface. Integrity of each of the first, second, third, and hybrid control modules is monitored. The signal is generated in an originating control module comprising one of the first, second, third and hybrid control modules. Integrity of the signal within the originating control module is verified. The signal is transmitted via the communications link to a receiving control module comprising one of the first, second, third and hybrid control modules that is not the originating control module. Integrity of the transmitted signal within the receiving control module is verified. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of an exemplary hybrid powertrain, in accordance with the present disclosure; 
         FIGS. 2 and 3  are schematic diagrams of an exemplary architecture for a control system and hybrid powertrain, in accordance with the present disclosure; and 
         FIGS. 4 and 5  are schematic flow diagrams of a control scheme, in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,  FIGS. 1 and 2  depict an exemplary electro-mechanical hybrid powertrain. The exemplary electro-mechanical hybrid powertrain in accordance with the present disclosure is depicted in  FIG. 1 , comprising a two-mode, compound-split, electro-mechanical hybrid transmission  10  operatively connected to an engine  14  and torque machines comprising first and second electric machines (‘MG-A’)  56  and (‘MG-B’)  72 . The engine  14  and first and second electric machines  56  and  72  each generate mechanical power which can be transferred to the transmission  10 . The power generated by the engine  14  and the first and second electric machines  56  and  72  and transferred to the transmission  10  is described in terms of input and motor torques, referred to herein as T I , T A , and T B  respectively, and speed, referred to herein as N I , N A , and N B , respectively. 
     The exemplary engine  14  comprises a multi-cylinder internal combustion engine selectively operative in several states to transfer torque to the transmission  10  via an input member  12 , and can be either a spark-ignition or a compression-ignition engine. The engine  14  includes a crankshaft (not shown) operatively coupled to the input member  12  of the transmission  10 . A rotational speed sensor  11  monitors rotational speed of the input member  12 . Power output from the engine  14 , comprising rotational speed and engine torque, can differ from the input speed N I  and the input torque T I  to the transmission  10  due to placement of torque-consuming components on the input member  12  between the engine  14  and the transmission  10 , e.g., a hydraulic pump (not shown) and/or a torque management device (not shown). 
     The exemplary transmission  10  comprises three planetary-gear sets  24 ,  26  and  28 , and four selectively engageable torque-transferring devices, i.e., clutches C 1   70 , C 2   62 , C 3   73 , and C 4   75 . As used herein, clutches refer to any type of friction torque transfer device including single or compound plate clutches or packs, band clutches, and brakes, for example. A hydraulic control circuit (‘HYD’)  42 , preferably controlled by a transmission control module (hereafter ‘TCM’)  17 , is operative to control clutch states. Clutches C 2   62  and C 4   75  preferably comprise hydraulically-applied rotating friction clutches. Clutches C 1   70  and C 3   73  preferably comprise hydraulically-controlled stationary devices that can be selectively grounded to a transmission case  68 . Each of the clutches C 1   70 , C 2   62 , C 3   73 , and C 4   75  is preferably hydraulically applied, selectively receiving pressurized hydraulic fluid via the hydraulic control circuit  42 . 
     The first and second electric machines  56  and  72  preferably comprise three-phase AC machines, each including a stator (not shown) and a rotor (not shown), and respective resolvers  80  and  82 . The motor stator for each machine is grounded to an outer portion of the transmission case  68 , and includes a stator core with coiled electrical windings extending therefrom. The rotor for the first electric machine  56  is supported on a hub plate gear that is operatively attached to shaft  60  via the second planetary gear set  26 . The rotor for the second electric machine  72  is fixedly attached to a sleeve shaft hub  66 . 
     Each of the resolvers  80  and  82  preferably comprises a variable reluctance device including a resolver stator (not shown) and a resolver rotor (not shown). The resolvers  80  and  82  are appropriately positioned and assembled on respective ones of the first and second electric machines  56  and  72 . Stators of respective ones of the resolvers  80  and  82  are operatively connected to one of the stators for the first and second electric machines  56  and  72 . The resolver rotors are operatively connected to the rotor for the corresponding first and second electric machines  56  and  72 . Each of the resolvers  80  and  82  is signally and operatively connected to a transmission power inverter control module (hereafter ‘TPIM’)  19 , and each senses and monitors rotational position of the resolver rotor relative to the resolver stator, thus monitoring rotational position of respective ones of first and second electric machines  56  and  72 . Additionally, the signals output from the resolvers  80  and  82  are interpreted to provide the rotational speeds for first and second electric machines  56  and  72 , i.e., N A  and N B , respectively. 
     The transmission  10  includes an output member  64 , e.g. a shaft, which is operably connected to a driveline  90  for a vehicle (not shown), to provide output power to the driveline  90  that is transferred to vehicle wheels  93 , one of which is shown in  FIG. 1 . The output power at the output member  64  is characterized in terms of an output rotational speed N O  and an output torque T O . A transmission output speed sensor  84  monitors rotational speed and rotational direction of the output member  64 . Each of the vehicle wheels  93  is preferably equipped with a sensor  94  adapted to monitor wheel speed, the output of which is monitored by a control module of a distributed control module system described with respect to  FIG. 2 , to determine vehicle speed, and absolute and relative wheel speeds for braking control, traction control, and vehicle acceleration management. 
     The input torque from the engine  14  and the motor torques from the first and second electric machines  56  and  72  (T I , T A , and T B  respectively) are generated as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (hereafter ‘ESD’)  74 . The ESD  74  is high voltage DC-coupled to the TPIM  19  via DC transfer conductors  27 . The transfer conductors  27  include a contactor switch  38 . When the contactor switch  38  is closed, under normal operation, electric current can flow between the ESD  74  and the TPIM  19 . When the contactor switch  38  is opened electric current flow between the ESD  74  and the TPIM  19  is interrupted. The TPIM  19  transmits electrical power to and from the first electric machine  56  through a first motor control module (‘MCP-A’)  33  using transfer conductors  29 , and the TPIM  19  similarly transmits electrical power to and from the second electric machine  72  through a second motor control module (‘MCP-B’)  34  using transfer conductors  31  to meet the torque commands for the first and second electric machines  56  and  72  in response to the motor torques T A  and T B . Electrical current is transmitted to and from the ESD  74  in accordance with whether the ESD  74  is being charged or discharged. 
     The TPIM  19  preferably includes a hybrid control module (hereafter ‘HCP’)  5  and the pair of power inverters and respective motor control modules  33  and  34  configured to receive the torque commands and control inverter states therefrom for providing motor drive or regeneration functionality to meet the commanded motor torques T A  and T B . The power inverters comprise known complementary three-phase power electronics devices, and each includes a plurality of insulated gate bipolar transistors (not shown) for converting DC power from the ESD  74  to AC power for powering respective ones of the first and second electric machines  56  and  72 , by switching at high frequencies. The insulated gate bipolar transistors form a switch mode power supply configured to receive control commands. There is typically one pair of insulated gate bipolar transistors for each phase of each of the three-phase electric machines. States of the insulated gate bipolar transistors are controlled to provide motor drive mechanical power generation or electric power regeneration functionality. The three-phase inverters receive or supply DC electric power via DC transfer conductors  27  and transform it to or from three-phase AC power, which is conducted to or from the first and second electric machines  56  and  72  for operation as motors or generators via transfer conductors  29  and  31  respectively. 
       FIGS. 2 and 3  are schematic block diagrams of the distributed control module system of the control system. As used herein, the term ‘control system’ is defined as the control modules, wiring harnesses (not shown), communications links, sensors and actuators that monitor and control operation of the powertrain system. The control system monitors sensor inputs and commands outputs for controlling the actuators. The distributed control module system comprises a subset of overall vehicle control architecture, and provides coordinated system control of the exemplary hybrid powertrain described in  FIG. 1 . The control system includes the distributed control module system for synthesizing information and inputs, and executing algorithms to control actuators to meet control objectives, including objectives related to fuel economy, emissions, performance, drivability, and protection of hardware, including batteries of ESD  74  and the first and second electric machines  56  and  72 . The distributed control module system includes an engine control module (hereafter ‘ECM’)  23 , the TCM  17 , a battery pack control module (hereafter ‘BPCM’)  21 , and the TPIM  19 . The HCP  5  provides supervisory control and coordination of the ECM  23 , the TCM  17 , the BPCM  21 , and the TPIM  19 . A user interface (‘UI’)  13  is preferably signally connected to a plurality of devices through which a vehicle operator controls, directs, and commands operation of the electro-mechanical hybrid powertrain. The devices include an accelerator pedal  113  (‘AP’), an operator brake pedal  112  (‘BP’), a transmission gear selector  114  (‘PRNDL’), and a vehicle speed cruise control (not shown). The transmission gear selector  114  may have a discrete number of operator-selectable positions, including the rotational direction of the output member  64  to enable one of a forward and a reverse direction. The user interface  13  can comprise a single device, as shown, or alternatively can comprise a plurality of user interface devices directly connected to the individual control modules (not shown). 
     The aforementioned control modules communicate with other control modules, sensors, and actuators via a communications link comprising a local area network (hereafter ‘LAN’) bus  6 , in this embodiment. The LAN bus  6  allows for structured communication between the various control modules. The specific communication protocol utilized is application-specific. The LAN bus  6  and appropriate protocols provide for robust messaging and multi-control module interfacing between the aforementioned control modules, and other control modules providing functionality including e.g., antilock braking, traction control, and vehicle stability. Multiple communications buses may be used to improve communications speed and provide some level of signal redundancy and integrity. Communications between the MCP-A  33  and the HCP  5  and between the MCP-B  34  and the HCP  5  is preferably effected using direct links preferably comprising serial peripheral interface (hereafter ‘SPI’) buses  37 . Communication between individual control modules can also be effected using a wireless link, e.g., a short range wireless radio communications bus (not shown). 
     The HCP  5  provides supervisory control of the hybrid powertrain, serving to coordinate operation of the ECM  23 , TCM  17 , MCP-A  33 , MCP-B  34 , and BPCM  21 . Based upon various command signals from the user interface  13  and the hybrid powertrain, including the ESD  74 , the HCP  5  determines an operator torque request, an output torque command, an engine input torque command, clutch torque(s) for the applied torque-transfer clutches C 1   70 , C 2   62 , C 3   73 , C 4   75  of the transmission  10 , and the motor torques T A  and T B  for the first and second electric machines  56  and  72 . The HCP  5  sends commands to specific control modules to effect control of the engine  14 , transmission  10  and the first and second electric machines  56  and  72 . 
     The ECM  23  is operatively connected to the engine  14 , and functions to acquire data from sensors and control actuators of the engine  14  over a plurality of discrete lines, shown for simplicity as an aggregate bi-directional interface cable  35 . The ECM  23  receives the engine input torque command from the HCP  5 . The ECM  23  determines the actual engine input torque, T I , provided to the transmission  10  at that point in time based upon monitored engine speed and load, which is communicated to the HCP  5 . The ECM  23  monitors input from the rotational speed sensor  11  to determine the engine input speed to the input member  12 , which translates to the transmission input speed, N I . The ECM  23  monitors inputs from sensors (not shown) to determine states of other engine operating parameters including, e.g., a manifold pressure, engine coolant temperature, ambient air temperature, and ambient pressure. The engine load can be determined, for example, from the manifold pressure, or alternatively, from monitoring operator input to the accelerator pedal  113 . The ECM  23  generates and communicates control signals to control engine actuators, including, e.g., fuel injectors, ignition modules, and throttle control modules, none of which are shown. 
     The TCM  17  is operatively connected to the transmission  10  and monitors inputs from sensors (not shown) to determine states of transmission operating parameters. The TCM  17  generates and communicates actuator control signals to control the transmission  10 , including controlling the hydraulic circuit  42 . Inputs from the TCM  17  to the HCP  5  include estimated clutch torques for each of the clutches, i.e., C 1   70 , C 2   62 , C 3   73 , and C 4   75 , and rotational output speed, N O , of the output member  64 . Other actuators and sensors may be used to provide additional information from the TCM  17  to the HCP  5  for control purposes. The TCM  17  monitors inputs from pressure switches (not shown) and selectively actuates pressure control solenoids (not shown) and shift solenoids (not shown) of the hydraulic circuit  42  to selectively actuate the various clutches C 1   70 , C 2   62 , C 3   73 , and C 4   75  to achieve various transmission operating range states, as described hereinbelow. 
     The BPCM  21  is signally connected to sensors (not shown) to monitor the ESD  74 , including states of electrical current and voltage parameters, to provide information indicative of parametric states of the batteries of the ESD  74  to the HCP  5 . The parametric states of the batteries preferably include battery state-of-charge, battery voltage, battery temperature, and available battery power, referred to as a range P BAT     —     MIN  to P BAT     —     MAX . 
     A brake control module (hereafter ‘BrCM’)  22  is operatively connected to friction brakes (not shown) on each of the vehicle wheels  93 . The BrCM  22  monitors the operator input to the brake pedal  112  and generates control signals to control the friction brakes and sends a control signal to the HCP  5  to operate the first and second electric machines  56  and  72  based thereon. 
     Each of the control modules ECM  23 , TCM  17 , HCP- 5 , MCP-A  33 , MCP-B  34 , BPCM  21 , and BrCM  22  is preferably a general-purpose digital computer comprising a microprocessor or central processing unit, storage mediums comprising read only memory (‘ROM’), random access memory (‘RAM’), electrically programmable read only memory (‘EPROM’), a 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 of the control modules has a set of control algorithms, comprising resident program instructions and calibrations stored in one of the storage mediums and executed to provide the respective functions of each computer. Information transfer between the control modules is preferably accomplished using the LAN bus  6  and SPI buses  37 . The control algorithms are 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 to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the actuators, using preset calibrations. Loop cycles are executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing operation of the hybrid powertrain. Alternatively, algorithms may be executed in response to the occurrence of an event. 
     The exemplary hybrid powertrain selectively operates in one of several states that can be described in terms of engine states comprising one of an engine-on state (‘ON’) and an engine-off state (‘OFF’), and transmission operating range states comprising a plurality of fixed gears and continuously variable operating modes, described with reference to Table 1, below. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Engine 
                 Transmission Operating 
                 Applied 
               
               
                 Description 
                 State 
                 Range State 
                 Clutches 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 M1_Eng_Off 
                 OFF 
                 EVT Mode 1 
                 C1 70 
                   
               
               
                 M1_Eng_On 
                 ON 
                 EVT Mode 1 
                 C1 70 
               
               
                 G1 
                 ON 
                 Fixed Gear Ratio 1 
                 C1 70 
                 C4 75 
               
               
                 G2 
                 ON 
                 Fixed Gear Ratio 2 
                 C1 70 
                 C2 62 
               
               
                 M2_Eng_Off 
                 OFF 
                 EVT Mode 2 
                 C2 62 
               
               
                 M2_Eng_On 
                 ON 
                 EVT Mode 2 
                 C2 62 
               
               
                 G3 
                 ON 
                 Fixed Gear Ratio 3 
                 C2 62 
                 C4 75 
               
               
                 G4 
                 ON 
                 Fixed Gear Ratio 4 
                 C2 62 
                 C3 73 
               
               
                   
               
            
           
         
       
     
     Each of the transmission operating range states is described in the table and indicates which of the specific clutches C 1   70 , C 2   62 , C 3   73 , and C 4   75  are applied for each of the operating range states. A first continuously variable mode, i.e., EVT Mode  1 , or M 1 , is selected by applying clutch C 1   70  only in order to “ground” the outer gear member of the third planetary gear set  28 . The engine state can be one of ON (‘M 1 _Eng_On’) or OFF (‘M 1 _Eng_Off’). A second continuously variable mode, i.e., EVT Mode  2 , or M 2 , is selected by applying clutch C 2   62  only to connect the shaft  60  to the carrier of the third planetary gear set  28 . The engine state can be one of ON (‘M 2 _Eng_On’) or OFF (‘M 2 _Eng_Off’). For purposes of this description, when the engine state is OFF, the engine input speed is equal to zero revolutions per minute (‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gear operation provides a fixed ratio operation of input-to-output speed of the transmission  10 , i.e., N I /N O . A first fixed gear operation (‘G 1 ’) is selected by applying clutches C 1   70  and C 4   75 . A second fixed gear operation (‘G 2 ’) is selected by applying clutches C 1   70  and C 2   62 . A third fixed gear operation (‘G 3 ’) is selected by applying clutches C 2   62  and C 4   75 . A fourth fixed gear operation (‘G 4 ’) is selected by applying clutches C 2   62  and C 3   73 . The fixed ratio operation of input-to-output speed increases with increased fixed gear operation due to decreased gear ratios in the planetary gears  24 ,  26 , and  28 . The rotational speeds of the first and second electric machines  56  and  72 , N A  and N B  respectively, are dependent on internal rotation of the mechanism as defined by the clutching and are proportional to the input speed measured at the input member  12 . 
     In response to operator input via the accelerator pedal  113  and brake pedal  112  as captured by the user interface  13 , the HCP  5  and one or more of the other control modules determine torque commands to control the torque actuators to meet the operator torque request at the output member  64  for transference to the driveline  90 . The torque actuators preferably include a plurality of torque generative devices, e.g., the engine  14  and the first and second electric machines  56  and  72  and a torque transferring device comprising the transmission  10  in this embodiment. The HCP  5  determines the operator torque request, an output torque command from the transmission  10  to the driveline  90  and actuator controls including an input torque command from the engine  14 , clutch torques for the torque-transfer clutches C 1   70 , C 2   62 , C 3   73 , C 4   75  of the transmission  10  and motor torque commands for the first and second electric machines  56  and  72  based upon operator commands from the user interface  13 . 
       FIG. 4  shows an embodiment of an architecture to control and manage signal flow in a powertrain system including torque actuators comprising multiple torque generating devices and a torque transferring device to control and manage torque transfer and power flow. The architecture is described with reference to, but not limited by, the powertrain system described hereinabove. The flow of signals through the control modules controls the torque generating devices and the torque transferring device. In operation, the operator inputs to the accelerator pedal  113  and the brake pedal  112  are monitored to determine the operator command comprising the operator torque request (‘To_req’). Operation of the engine  14  and the transmission  10  are monitored to determine the input speed (‘Ni’) and the output speed (‘No’). A strategic optimization control scheme (‘Strategic Control’)  310  determines a preferred input speed (‘Ni_Des’) and a preferred engine state and transmission operating range state (‘Hybrid Range State Des’) based upon the output speed and the operator torque request, and optimized based upon other operating parameters of the hybrid powertrain, including battery power limits and response limits of the engine  14 , the transmission  10 , and the first and second electric machines  56  and  72 . The strategic optimization control scheme  310  is preferably executed by the HCP  5  during each 100 ms loop cycle and each 25 ms loop cycle. 
     The outputs of the strategic optimization control scheme  310  are used in a shift execution and engine start/stop control scheme (‘Shift Execution and Engine Start/Stop’)  320  to change the transmission operation (‘Transmission Commands’) including changing the operating range state. This includes commanding execution of a change in the operating range state if the preferred operating range state is different from the present operating range state by commanding changes in application of one or more of the clutches C 1   70 , C 2   62 , C 3   73 , and C 4   75  and other transmission commands. The present operating range state (‘Hybrid Range State Actual’) and an input speed profile (‘Ni_Prof’) can be determined. The input speed profile is an estimate of an upcoming input speed and preferably comprises a scalar parametric value that is a targeted input speed for the forthcoming loop cycle. The engine operating commands are based upon the input speed profile and the operator torque request during a transition in the operating range state of the transmission. 
     A tactical control scheme (‘Tactical Control and Operation’)  330  is repeatedly executed during one of the control loop cycles to determine engine commands (‘Engine Commands’) for operating the engine, including a preferred input torque from the engine  14  to the transmission  10  based upon the sensor inputs comprising output speed, the input speed, and the operator torque request and the present operating range state for the transmission. A clutch torque (‘Tcl’) for each clutch is estimated in the TCM  17 , including the presently applied clutches and the non-applied clutches, and a present engine input torque (‘Ti’) reacting with the input member  12  is determined in the ECM  23 . A motor torque control scheme (‘Output and Motor Torque Determination’)  340  is executed to determine the preferred output torque from the powertrain (‘To_cmd’), which includes motor torque commands (‘T A ’, ‘T B ’) for controlling the first and second electric machines  56  and  72  in this embodiment. The preferred output torque is based upon the estimated clutch torque(s) for each of the clutches, the present input torque from the engine  14 , the present operating range state, the input speed, the operator torque request, and the input speed profile. The first and second electric machines  56  and  72  are controlled through the MCP-A  33  and MCP-B  34  to meet the preferred motor torque commands based upon the preferred output torque. 
     Securing and monitoring signal integrity to effect torque security is described hereinbelow with reference to the hybrid powertrain system shown in  FIGS. 1 ,  2 ,  3 , and  4 , and resides in the aforementioned distributed control modules in the form of executable algorithms and calibrations. The architecture can be applied to powertrain systems having multiple torque generating devices, including, e.g., an electro-mechanical powertrain system having an engine and a single electric machine, a hybrid powertrain system having multiple electric machines, and hydraulic-mechanical hybrid powertrain systems. Controlling and managing the torque and power flow includes monitoring control system hardware, algorithms, and signal integrity. 
     Torque security of the hybrid powertrain system can be achieved by executing integrity tests of the control system which include monitoring hardware integrity of the control system, including the wiring harnesses (not shown), communications links, sensors and actuators that monitor and control operation of the powertrain system. Torque security can be achieved by monitoring integrity of algorithms and memory devices, securing and monitoring signal integrity during communications within a control module and communications between the control modules, monitoring integrity of the individual control modules and processors, and executing remedial actions. Torque security in the presence of an observed fault can include limiting an actuator command signal. This can include maximum and minimum limits on actuator command signals, and maximum rates of change on actuator command signals. Specifically, motor torque commands T A  and T B  can be limited to maximum and minimum motor torques, and changes in the motor torque commands T A  and T B  can be limited to effect a maximum rate of change in output torque, e.g., 0.2 g. 
     Securing and monitoring signal integrity is preferably accomplished by individually securing the control modules and securing the serial communications links between the control modules. The distributed control module system of the embodiment preferably includes each of the torque actuators controlled by a separate control module. This embodiment includes the ECM  23  that monitors sensors and control actuators of the engine  14 , the TCM  17  that monitors sensors and control actuators of the transmission  10 , the MCP-A  33  that monitors sensors and control actuators of the first electric machine  56 , and the MCP-B  34  that monitors sensors and control actuators of the second electric machine  72 . The HCP  5  monitors inputs from and commands operation of the ECM  23 , TCM  17 , MCP-A  33  and MCP-B  34 . The control modules communicate the signals using the LAN bus  6  and the SPI bus  37 . Each of the ECM  23 , MCP-A  33 , MCP-B  34  and TCM  17 , is responsible for closed loop monitoring and self-security based on secured commands received from the HCP  5 . 
     Securing and monitoring integrity of the signal includes monitoring processor integrity for each of the control modules. The processor integrity can be determined using diagnostics software that monitors data internal to the control module, and rationalizing it in one of the loop cycles. When an inconsistency between monitored data and rationalized data is detected, the inconsistency is recorded as a mismatch or a fault in a fault maturation algorithm, e.g., an X of Y routine wherein a matured fault is detected when X faults are observed out of immediately preceding Y observations of the signal. An example is detecting a matured fault when more than half the immediately preceding observations are mismatches occurring between the monitored data and the rationalized data. When the fault maturation algorithm achieves a threshold number of mismatching observations in the immediately preceding observations, the fault has matured, indicating signal corruption and a requirement for remedial action. The remedial action can be actuator-specific or across the entire control system, and places the powertrain in a torque-safe state. The remedial action will also include storing an OBD compliant code for subsequent retrieval. A diagnostic may preliminarily identify a fault pending, meaning an inconsistency has been detected but the fault maturation algorithm has not reached its threshold. The hardware integrity can be further determined using diagnostics software that monitors the sensors and actuators of the control system. 
     Monitoring integrity of a signal that is generated and communicated in the control system comprises actions to determine whether a received signal matches the generated signal. A signal can include an operator command signal, a sensor input signal and an actuator command and control signal. With reference to the embodiment described hereinabove, a signal can comprise an actuator command or control signal, including, e.g., motor torque commands for the first and second electric machines  56  and  72 , the input torque command to the engine  14 , and clutch torque commands for the clutches C 1   70 , C 2   62 , C 3   73 , and C 4   75  of the transmission  10 . The signal can include the sensor input signal, e.g., a signal from the rotational speed sensor  11  and the transmission output speed sensor  84  and resolvers  80  and  82 . The signal can include an operator command, e.g., an operator input to the accelerator pedal  113 , the operator brake pedal  112  and the transmission gear selector  114 . 
     When a signal is generated in an originating control module, the signal is verified within the originating control module prior to transmitting it. The signal is transmitted via one of the communications links to a receiving control module. The transmitted signal is verified in the receiving control module prior to using it for command or other operation in the receiving control module. The signal can include operator command signals including the operator inputs to the accelerator pedal  113 , the operator brake pedal  112 , the transmission gear selector  114  and the vehicle speed cruise control. The signal can include sensor input signals comprising states of operating parameters determined from sensor inputs. The signal can include actuator command and control signals. 
     Securing and monitoring integrity of the signal includes verifying first and second memory locations in a memory device of the originating control module, and verifying the signal by redundantly storing the signal at the first and second memory locations in a memory device. The redundantly stored signals at the first and second memory locations can be compared immediately prior to transmitting the redundantly stored signals. Securing and monitoring integrity of the signal includes transmitting the redundantly stored signals via the communications link to the receiving control module, which receives and stores the transmitted redundantly stored signals in first and second memory locations. The transmitted signal is verified in the receiving control module by comparing the transmitted redundantly stored signals stored in first and second memory locations within the receiving control module. Corruption of the signal within either the originating control module or the receiving control module can be determined when a difference between the redundantly stored signals is greater than a threshold, leading the control module to execute remedial action. 
     Monitoring integrity of a signal that is generated and communicated in the control system comprises actions to determine whether a received signal matches the original signal. A signal can include an operator command signal, a sensor input signal and an actuator command and control signal. With reference to the embodiment described hereinabove, a signal can comprise an actuator command or control signal, including, e.g., motor torque commands for the first and second electric machines  56  and  72 , the input torque command to the engine  14 , and clutch torque commands for the clutches C 1   70 , C 2   62 , C 3   73 , and C 4   75  of the transmission  10 . The signal can include the sensor input signal, e.g., a signal from the rotational speed sensor  11  and the transmission output speed sensor  84  and resolvers  80  and  82 . The signal can include an operator command, e.g., an operator input to the accelerator pedal  113 , the operator brake pedal  112  and the transmission gear selector  114 . 
     Securing and verifying integrity of a signal that is communicated from an originating control module to a receiving control module is preferably effected by using redundant data comprising primary and secondary signals, rationalizing the primary signal, executing a dual store function prior to storing the signal, creating and transmitting a message including the signal from an originating control module to a receiving control module using the communications bus, e.g., LAN bus  6 , or SPI bus  37 , and receiving and decoding the received message to primary and secondary signals. The primary and secondary signals can be compared prior to processing or execution at one of the actuators. 
       FIG. 5  shows signal flow to secure and verify integrity of an input signal to an originating control module, which comprises an input signal generated by a sensor signally connected to the originating control module in this depiction. Alternatively, the input signal in the originating control module can comprise one of an operator command signal and an actuator command and control signal. The input signal is generated ( 502 ) and is captured as a primary signal  504  and a redundant signal  504 ′. This can include the input signal from the sensor converted to a digital representation of the input from the sensor using an analog-to-digital converter (not shown) which may be interposed between the sensor and the originating control module. Diagnostics (‘Diagnostics’) are executed on both the primary signal and the redundant signal ( 506 ,  506 ′). Diagnostics can include limit checks that indicate when the signal is outside of a predetermined operating range for the signal, a rationality check of the signal, and other diagnostics check that can indicate corruption of the signal. If a corrupted signal is detected (‘Signal Fault’) in either or both the primary signal and the redundant signal, a default signal is generated (‘Defaulting’) ( 508 ,  508 ′) and communicated to a rationality check  510 . The default signal preferably comprises a predetermined signal that is recognizable in the control module as indicating the primary signal or the redundant signal has been corrupted. When a fault is not detected (‘No Fault’), the primary and/or the redundant signals are communicated to the rationality check  510 . The rationality check  510  compares the primary signal and the redundant signal and identifies a fault (‘Fault’) when there is a difference detected between the primary and redundant signals. When the rationality check  510  indicates that the primary signal is valid (‘Valid Signal’), the primary signal is communicated to a dual store function (‘Dual Store’)  511 . The dual store function  511  monitors and compares present contents in first and second memory locations  512 ,  512 ′ to verify integrity of the memory locations, preferably during each 6.25 ms loop cycle. When the dual store function  511  verifies integrity of the first and second memory locations, i.e., the present contents in the first and second memory locations are identical, the primary signal is stored as the primary signal in the first memory location (‘Store Primary Signal’) ( 512 ) and stored as a secondary signal in the second memory location (‘Store Secondary Signal’) ( 512 ′). The primary signal stored in the first memory location is subsequently communicated to a control path (‘Primary Signal To Control Path’). The secondary signal stored in the second memory location is subsequently communicated to a security path. (‘Secondary Signal To Security Path’). If there is a difference between the present contents of the memory locations, a fault (‘Fault’) is recorded indicating corruption of one of the first and second memory locations. 
     When the rationality check  510  indicates corruption of one or both of the primary and the redundant signals, or the dual store function  511  indicates corruption of the present contents of one the first and second memory locations  512 ,  512 ′ the control system identifies occurrence of the fault (‘Fault’). The control system determines whether the corrupted signal has matured (‘Mature Fault’) ( 514 ), and executes remedial action ( 516 ) to mitigate risks associated with the presence of the fault. A fault maturation algorithm can be executed, including, e.g., an X of Y routine wherein a fault has matured when X mismatched signals are observed out of immediately preceding Y signal observations. An example includes determining a fault has matured when more than half the immediately preceding observations indicate a corrupted signal. 
     Monitoring integrity of a signal transmitted over a serial bus includes detecting missing data, e.g., detecting loss of a message frame and taking a short term mitigation action and informing the receiving control module that no new data is available. Detecting missing data also includes detecting long term loss of communications to one of the control modules and taking a remedial action. 
     Monitoring integrity of algorithms and memory devices comprises verifying integrity of algorithmic code, calibrations and variable data stored in the storage mediums of the control modules including, e.g., ROM, RAM, and EPROMs. Results of the calculations executed in one of the algorithms are monitored and verified by monitoring functions that detect inconsistencies with torque security critical data stored in memory and transmitted over the serial data communications busses, i.e., CAN bus  6  and SPI bus  37 . Methodologies applied to detect the inconsistencies include utilizing an alive rolling counter and applying a protection value to signals that are transmitted over a serial data bus to detect corruption of data during transfer. Methods further include redundantly calculating signals and rationalizing the primary value with the redundant value. Methods further include back-calculating a signal and rationalizing the resultant with the original signal. Methods further include rationalizing an achieved torque value with actual commanded torque value. Monitor software can execute a detection algorithm in one of the loop cycles to detect signal inconsistency. When an inconsistency between a monitored signal and a rationalized signal is detected, the inconsistency is recorded as a mismatch count in a fault maturation algorithm, e.g., an X of Y routine wherein a fault has matured when X mismatched signals are observed out of immediately preceding Y signal observations. When a fault matures thus indicating a fault in the signal, the control system can execute remedial action to mitigate risks associated with the presence of the fault. 
     Torque security can include limiting an actuator command signal. This can include maximum and minimum limits on actuator command signals, and maximum rates of change on actuator command signals. Specifically, motor torque commands T A  and T B  can be limited to maximum and minimum motor torques, and changes in the motor torque commands T A  and T B  can be limited to maximum rate of change, e.g., 0.2 g. 
     Monitoring integrity of a signal transmitted over a serial bus includes detecting missing data, e.g., detecting loss of a message frame and taking a short term mitigation action and informing the receiving control module that no new data is available. Detecting missing data also includes detecting long term loss of communications to one of the control modules and taking a remedial action. 
     Securing and monitoring integrity of the signal includes monitoring integrity of the control modules, i.e., the digital computer comprising the microprocessor, storage mediums, high speed clock and related signal conditioning and buffer circuitry. This can be determined by executing test functions to detect inconsistencies in memory, in general purpose and special purpose registers, execution of instructions, program pointer errors, memory addressing errors, timing errors, and others. Test functions include detecting inconsistencies during system initialization, detecting inconsistencies during normal execution by running a check function in the background, detecting inconsistencies by executing a detection algorithm in one of the loop cycles. When a signal inconsistency is detected, the inconsistency is recorded and a remedial action taken to mitigate risks associated with presence of the fault. The processor integrity can be determined through an interaction between the HCP  5  and one of the other control modules using a seed and key process, where the monitored control module transmits a certain seed to the HCP  5 , and the HCP  5  responds with a key. The key is made up of results from a process that monitors the sequence of the functions executed in the HCP  5  and the seed. The monitored control module evaluates the key and determines if it is the expected key based on the seed that it sent to the HCP  5 . If the returned key does not match the expected key, an inconsistency is recorded as a fault count in a fault maturation algorithm, preferably an X of Y routine wherein a fault has matured when X mismatches are observed out of immediately preceding Y observations, thus indicating a corrupted signal. When inconsistencies persist long enough for the fault maturation algorithm to reach a predetermined threshold, indicating a corrupted signal, remedial action can be taken. Remedial action is executed to mitigate risks associated with the presence of the fault. 
     It is understood that modifications are allowable within the scope of the disclosure. The disclosure has been described with specific reference to the preferred 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 disclosure.