Method for controlling a hybrid powertrain

Abstract

A method of operating a powertrain (200), comprising the steps of: operating an electric machine (240) in a torque control mode in response to a transmission line pressure being sufficiently high to enable a torque converter clutch (212) to transmit a driver-demanded torque, and operating the electric machine (240) in a speed control mode in response to the transmission line pressure being too low to enable the torque converter clutch (212) to transmit the driver-demanded torque.

Description

[0001] The present description relates to a method for operating a powertrain. The method is particularly useful for powertrains that include a torque converter and an electric machine.

[0002] A parallel hybrid powertrain may include an internal combustion engine, a powertrain disconnect clutch, and an electric machine. The internal combustion engine and electric machine may be selectively operated in response to vehicle operating conditions. If the internal combustion engine is stopped, it may be restarted by the electric machine when the powertrain disconnect clutch is closed. However, closing the powertrain disconnect clutch to start the internal combustion engine may cause a torque disturbance in the vehicle powertrain because it may be difficult to accurately estimate the torque transmitted through the powertrain disconnect clutch. Additionally, powertrain inefficiencies may reduce vehicle fuel efficiency if the torque converter clutch is fully open during vehicle launch.

[0003] For example, documents WO 2013 / 077401 A1 and DE 11 2012 003 350 T5 show a drive train of a hybrid vehicle with an electric motor in the drive train, wherein, as part of a start-up control when the vehicle starts moving, the speed of the internal combustion engine is increased by means of the electric motor. To avoid a torque surge when the electric motor is engaged, the engagement device for the electric motor is brought into a slipping state by controlling the hydraulic pressure before the engagement clutch of the internal combustion engine is brought into the slipping state. Furthermore, document DE 11 2010 000 430 T5 shows a drive train of a hybrid vehicle with an electric motor in the drive train. To avoid torque surges, an attempt is made here to estimate the transmitted torque of the engagement clutch and to adjust the target speed accordingly before the engagement clutch is actually closed.

[0004] The present invention is based on the object of allowing efficient starting of the drive train even with limited hydraulic pressure for the converter clutch.

[0005] According to the invention, the stated object is achieved by a method according to claim 1. Preferred embodiments of the invention are the subject of the dependent claims.

[0006] Thus, to mitigate the above-mentioned disadvantages, the present inventors have developed a method of operating a powertrain comprising the steps of: operating an electric machine in a torque control mode in response to a torque converter clutch torque capacity available at a transmission line pressure being greater than a driver demanded torque, and operating the electric machine in a speed control mode in response to the torque converter clutch torque capacity available at the transmission line pressure being less than the driver demanded torque.

[0007] By operating an electric machine in a speed control mode when transmission line pressure is low, it may be possible to suppress driveline torque disturbances through the electric machine and provide a desired driver-requested torque. Additionally, by operating the electric machine in a torque control mode when transmission line pressure is higher, it may be possible to lock a torque converter clutch to improve driveline efficiency while providing at least a portion of the driver-requested torque through the electric machine.

[0008] The present description can provide several advantages. In particular, the approach can improve powertrain efficiency while providing a desired driver-requested torque. Additionally, the approach can improve vehicle drivability by improving vehicle launch. Furthermore, the approach can improve engine starting.

[0009] The foregoing and other advantages and features of the present description will be readily understood from the following detailed description taken alone or in conjunction with the accompanying drawings.

[0010] It should be understood that the foregoing summary is provided to introduce, in a simplified form, a selection of concepts further described in the detailed description. It is not intended to identify key features or essential features of the claimed subject matter, the scope of which is defined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages mentioned above or in any part of this disclosure.

[0011] The advantages described here will be better understood when reading an example of an embodiment, referred to here as the Detailed Description, either on its own or with reference to the drawings. They show: Fig. 1 a schematic diagram of an internal combustion engine, Fig. 2 an example vehicle powertrain configuration, Fig. 3 an example control block diagram and Fig. 4 a flowchart for a method for operating a vehicle powertrain.

[0012] This description relates to the operation of a hybrid vehicle powertrain to provide driver-requested torque. The vehicle powertrain may consist of an internal combustion engine, a driveline integrated starter / generator (DISG), or an electric machine and transmission, as described in the Fig. 1 - 2. The drive train can be operated by a control system as shown in Fig. 3 is shown. Fig. 4 shows an example method of operating the vehicle powertrain to improve powertrain efficiency and vehicle drivability.

[0013] With reference to Fig. 1 it should be noted that the internal combustion engine 10 is provided with several cylinders, one of which is Fig. 1, is controlled by an electronic engine controller 12. The internal combustion engine 10 includes a combustion chamber 30 and cylinder walls 32 with a piston 36 disposed therein and connected to a crankshaft 40. A flywheel 97 and a ring gear 99 are coupled to the crankshaft 40. A starter 96 includes a pinion shaft 98 and a gear 95. The pinion shaft 98 can selectively advance the gear 95 to engage the ring gear 99. The starter 96 can be mounted directly in front of or behind the internal combustion engine. In some examples, the starter 96 can selectively supply torque to the crankshaft 40 via a belt or chain. In one example, the starter 96 is in a base state when it is not engaged with the internal combustion engine crankshaft. The combustion chamber 30 is connected to the engine crankshaft via an intake valve 52 orAn exhaust valve 54 communicates with an intake manifold 44 and an exhaust manifold 48. Each intake and exhaust valve can be actuated by an intake cam 51 and an exhaust cam 53. The position of the intake cam 51 can be determined by an intake cam sensor 55. The position of the exhaust cam 53 can be determined by an exhaust cam sensor 57. The intake cam 51 and the exhaust cam 53 can be moved relative to the crankshaft 40.

[0014] A fuel injector 66 is positioned as shown to inject fuel directly into the cylinder 30, known to those skilled in the art as direct injection. Alternatively, fuel may be injected into an intake manifold, known to those skilled in the art as port fuel injection. The fuel injector 66 delivers liquid fuel proportional to the pulse width of the signal from the controller 12. Fuel is supplied to the fuel injector 66 by a fuel system (not shown) that includes a fuel tank, a fuel pump, and a fuel rail (not shown). Additionally, the intake manifold 44 is shown in communication with an optional electronic throttle 62 that adjusts a position of the throttle plate 64 to control airflow from the air intake 42 to the intake manifold 44. In one example, a two-stage high-pressure fuel system may be used to produce higher fuel pressures.In some examples, the throttle 62 and the throttle plate 64 may be positioned between the intake valve 52 and the intake manifold 44 such that the throttle 62 is a manifold throttle.

[0015] A distributorless ignition system 88 provides an ignition spark to the combustion chamber 30 via a spark plug 92 in response to the controller 12. A universal exhaust gas oxygen (UEGO) sensor 126 is coupled, as shown, to the exhaust manifold 48 upstream of a catalyst 70. Alternatively, a dual-state exhaust gas oxygen sensor may replace the UEGO sensor 126.

[0016] In one example, the catalyst 70 may include multiple catalyst blocks. In another example, multiple emission control devices, each including multiple blocks, may be used. In one example, the catalyst 70 may be a three-way catalyst.

[0017] The control device 12 is in Fig. 1 as a conventional microcomputer comprising a microprocessor unit 102, input / output ports 104, a read-only memory 106, a random access memory 108, a latch 110, and a conventional data bus.As shown, controller 12 receives various signals from sensors coupled to engine 10 in addition to the signals discussed above, including: engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling jacket 114, a position sensor 134 coupled to an accelerator pedal 130 to measure the force exerted by a foot 132, an engine manifold pressure (MAP) measurement from a pressure sensor 122 coupled to intake manifold 44, an engine position sensor from a Hall effect sensor 118 that senses the position of crankshaft 40, a measurement of air mass entering the engine from a sensor 120, and a measurement of throttle position from a sensor 58. Barometric pressure may also be sensed for processing by controller 12 (sensor not shown).In a preferred aspect of the present description, the engine position sensor 118 generates a predetermined number of equally spaced pulses for each revolution of the crankshaft from which the engine speed (RPM) can be determined.

[0018] In some examples, the internal combustion engine may be coupled to an electric motor / battery system in a hybrid vehicle, as in Fig. 2. Furthermore, in some examples, other internal combustion engine configurations may be used, such as a diesel engine.

[0019] During operation, each cylinder within the internal combustion engine 10 typically undergoes a four-stroke cycle: the cycle includes the intake stroke, the compression stroke, the power stroke, and the exhaust stroke. During the intake stroke, the exhaust valve 54 generally closes and the intake valve 52 opens. Air is introduced into the combustion chamber 30 via the intake manifold 44, and the piston 36 moves to the bottom of the cylinder to increase the volume within the combustion chamber 30. The position where the piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 is at its largest volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, the intake valve 52 and the exhaust valve 54 are closed. The piston 36 moves toward the cylinder head to compress the air within the combustion chamber 30.The point at which piston 36 is at the end of its stroke and closest to the cylinder head (e.g., when combustion chamber 30 is at its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC). In a process referred to below as injection, fuel is introduced into the combustion chamber. In a process referred to below as ignition, the injected fuel is ignited by known ignition means such as spark plug 92, resulting in combustion. During the power stroke, expanding gases push piston 36 back to BDC. Crankshaft 40 converts piston motion into rotational torque of the rotating shaft. Finally, during the exhaust stroke, exhaust valve 54 opens to discharge the combusted air-fuel mixture to exhaust manifold 48, and the piston returns to TDC.It should be noted that the above is presented merely as an example and that the opening and / or closing times of the intake valve and the exhaust valve may vary to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0020] Fig. 2 is a block diagram of a vehicle powertrain 200 and a vehicle 290. The powertrain 200 may be driven by the internal combustion engine 10. The internal combustion engine 10 may be connected to a Fig. 1 or via a DISG 240. Furthermore, the internal combustion engine 10 may generate or adjust torque through a torque actuator 204 such as a fuel injector, throttle, camshaft, valve lifter, etc.

[0021] The engine output torque may be transmitted to an input side of a dual-mass flywheel 232. The engine speed, as well as the input position and speed of the dual-mass flywheel, may be determined by an engine position sensor 118. The dual-mass flywheel 232 may include springs and separate masses (not shown) to dampen driveline torque disturbances. The output side of the dual-mass flywheel 232 is shown as being mechanically coupled to the input side of a disconnect clutch 236. The disconnect clutch 236 may be electrically or hydraulically actuated. A position sensor 234 may be disposed on the disconnect clutch side of the dual-mass flywheel 232 to measure the output position and speed of the dual-mass flywheel 232. The downstream side of the disconnect clutch 236 is shown as being mechanically coupled to the DISG input shaft 237.

[0022] The DISG 240 may be operated to provide torque to the powertrain 200 or to convert powertrain torque into electrical energy to be stored in the electrical energy storage device 275. The DISG 240 has a higher output torque capacity than the Fig. 1. Further, the DISG 240 directly drives the powertrain 200 or is directly driven by the powertrain 200. The electrical energy storage device 275 may be a battery, a capacitor, or an inductor. The downstream side of the DISG 240 is mechanically coupled to the impeller 285 of the torque converter 206 via a shaft 241. The upstream side of the DISG 240 is mechanically coupled to the disconnect clutch 236. The torque converter 206 includes a turbine 286 for outputting torque to the input shaft 270. The input shaft 270 mechanically couples the torque converter 206 to an automatic transmission 208. The torque converter 206 also includes a torque converter bypass lock-up clutch 212 (TCC). Torque is transferred directly from the impeller 285 to the turbine 286 when the TCC is locked.The TCC is hydraulically actuated by controller 12 by adjusting the position of a control valve. In one example, the torque converter may be referred to as a component of the transmission. The speed and position of the torque converter turbine may be determined by a position sensor 239. In some examples, 238 and / or 239 may be torque sensors or combined position and torque sensors.

[0023] When the torque converter clutch 212 is fully disengaged, the torque converter 206 transfers engine torque to the automatic transmission 208 through fluid communication between the torque converter turbine 286 and the torque converter impeller 285 (e.g., via a hydraulic torque path), enabling torque multiplication. Conversely, when the torque converter clutch 212 is fully engaged, the engine output torque is transferred directly through the torque converter clutch to an input shaft (not shown) of the transmission 208 (e.g., via the friction torque path). Alternatively, the torque converter clutch 212 may be partially engaged, allowing the amount of torque transferred directly to the transmission to be adjusted.The controller 12 may be configured to adjust the amount of torque transmitted by the torque converter 212 by adjusting the torque converter lock-up clutch in response to various engine operating conditions or based on the driver-based engine operating request.

[0024] The automatic transmission 208 includes gear clutches (e.g., gears 1 - N, where N is a natural number between 4 and 10) 211 and a forward clutch 210. The gear clutches 211 and the forward clutch 210 can be selectively engaged to propel a vehicle. The torque output from the automatic transmission 208 can, in turn, be transmitted to wheels 216 to propel the vehicle via an output shaft 260. In particular, the automatic transmission 208 can transmit input torque to the input shaft 270 in response to a vehicle driving condition before transmitting output torque to the wheels 216.

[0025] Furthermore, a frictional force may be applied to wheels 216 by applying wheel brakes 218. In one example, wheel brakes 218 may be applied in response to the driver pressing their foot on a brake pedal (not shown). In other examples, controller 12 or a controller coupled to controller 12 may control the application of wheel brakes. Similarly, a frictional force acting on wheels 216 may be reduced by releasing wheel brakes 218 in response to the driver removing their foot from the brake pedal. Furthermore, vehicle brakes may apply a frictional force to wheels 216 by controller 12 as part of an automated engine stop procedure.

[0026] A mechanical pump 214 may supply pressurized transmission fluid to the automatic transmission 208, providing hydraulic pressure for engaging various clutches, such as the forward clutch 210, the gear clutches 211, the engine disconnect clutch 236, and / or the torque converter lock-up clutch 212. The mechanical pump 214 may be operated in accordance with the torque converter 206 and may be driven, for example, by the rotation of the engine or the DISG via the input shaft 241. Accordingly, the hydraulic pressure generated in the mechanical pump 214 may increase as the engine speed and / or the DISG speed increases and decrease as the engine speed and / or the DISG speed decreases.

[0027] An electric pump 215 may also be provided to increase transmission line pressure when the DISG is rotating at speeds less than, for example, 300 rpm. The electric pump 215 may be selectively operated by the controller 12 in response to the DISG speed. Accordingly, the mechanical pump 214 may supply transmission line pressure when the DISG speed is greater than a threshold speed while the electric pump 215 is not activated. However, when the DISG speed is less than the threshold speed, the electric pump 215 may be activated to supply transmission line pressure.

[0028] The controller 12 may be configured to receive inputs from the internal combustion engine 10, as described in further detail in Fig. 1, and accordingly control engine torque output and / or operation of the torque converter, transmission, DISG, clutches, and / or brakes. For example, engine torque output may be controlled by adjusting a combination of spark timing, fuel pulse width, fuel pulse timing, and / or air charge by controlling throttle opening and / or valve timing, valve lift, and boost for turbocharged or supercharged engines. In the case of a diesel engine, controller 12 may control engine torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. In all cases, engine control may be performed on a cylinder-by-cylinder basis to control engine torque output.The controller 12 may also control the torque output and electrical energy generation from the DISG by adjusting the current flowing to and from the field and / or armature windings of the DISG, as is known in the art.

[0029] When engine stop conditions are met, controller 12 may initiate engine shutdown by shutting off fuel and ignition to the engine. However, in some examples, the engine may continue to rotate. Further, to maintain an amount of torsion in the transmission, controller 12 may ground rotating elements of transmission 208 to a housing 259 of the transmission and thus to the frame of the vehicle. In particular, controller 12 may engage one or more transmission clutches, such as forward clutch 210, and lock the engaged transmission clutch(es) against the transmission housing 259 and the vehicle. A transmission clutch pressure may be changed (e.g., increased) to adjust the engaged state of a transmission clutch and provide a desired amount of transmission torsion.When restart conditions are met and / or a vehicle operator wishes to start the vehicle, the controller 12 may reactivate the internal combustion engine by resuming cylinder combustion.

[0030] Wheel brake pressure may also be adjusted during engine shutdown based on transmission clutch pressure to assist in locking the transmission while reducing the torque transmitted through the wheels. In particular, by applying the wheel brakes 218 while locking one or more engaged transmission clutches, opposing forces may be applied to the transmission and consequently to the driveshaft, thereby keeping the transmission gears actively engaged and retaining potential torsional energy in the gear train without moving the wheels. In one example, wheel brake pressure may be adjusted to coordinate the application of the wheel brakes with the locking of the engaged transmission clutch during engine shutdown.By adjusting the wheel brake pressure and the clutch pressure, the amount of torsion held in the transmission when the combustion engine is switched off can be adjusted.

[0031] The system from the Fig. 1 and Fig. 2 provides a vehicle system comprising: an electric machine, a torque converter in mechanical communication with the electric machine, the torque converter having a torque converter clutch, and a controller having non-transitory instructions executable to schedule the torque transfer capacity of the torque converter clutch in response to a driver demanded torque and a transmission line pressure.The vehicle system further includes adjusting the torque transferred between a torque converter impeller and a torque converter turbine in response to the driver requested torque and the designed torque transfer capacity of the torque converter clutch (e.g., an amount of torque that a torque converter clutch can transfer across a torque converter clutch at a pressure at which the transmission fluid is supplied to a torque converter clutch actuator).

[0032] The vehicle system further includes a powertrain-integrated starter / generator in mechanical communication with the torque converter, wherein adjusting the torque transferred between the torque converter impeller and the torque converter turbine includes adjusting the speed of a powertrain-integrated starter / generator. The vehicle system further includes determining the torque transferred via a hydraulic torque path between a torque converter impeller and a torque converter turbine in response to the driver-requested torque and the torque capacity of the torque converter clutch. The vehicle system further includes additional commands to operate the electric machine in a speed control mode in response to the torque converter clutch capacity being less than the driver-requested torque.

[0033] Fig. Figure 3 shows a control block diagram for operating a vehicle powertrain. The block diagram can be applied to the Fig. 1 and Fig. 2 can be used. The block diagram can be replaced by the Fig. 4 procedures can be implemented.

[0034] The driver demand torque is input to a torque converter hydraulic torque path determination block 302 and a torque converter clutch capacity planner block 304. In one example, the driver demand torque is based on the position of an accelerator pedal and represents a desired torque at the torque converter impeller. Alternatively, the driver demand torque may be vehicle wheel torque, which may be converted to torque converter turbine torque by considering gear ratios and driveline torque losses (e.g., wheel torque may be scaled by transmission gear ratios, and driveline losses may be added to wheel torque to provide torque converter impeller torque). The transmission line pressure is also input to the torque converter clutch capacity planner block 304.The transmission line pressure is a regulated pressure of the mechanical pump 214, as shown in . Fig. 2. If the mechanical pump output is at a high level, the transmission fluid is regulated to a line pressure lower than the pump outlet pressure. If the mechanical pump output is at a lower level, the transmission fluid may be at a line pressure that is the pressure output by the mechanical pump.

[0035] If the DISG speed is also less than a threshold speed, the electric pump 215 can Fig. 2 to supply line pressure. The pressure from the electric pump 215 can be controlled by a separate regulator or by adjusting the power supplied to the electric pump 215.

[0036] The torque converter clutch capacity planner block 304 may be implemented as a function or table indexed according to the driver demand torque and the transmission line pressure. The torque converter clutch capacity planner block 304 outputs a desired torque converter clutch torque. The desired torque converter clutch torque is an amount of torque the torque converter clutch is to be set to transmit or output. For example, the desired torque converter clutch torque may be a torque-transmitting capacity of the torque converter clutch at the application force provided by transmission fluid supplied for operation of the torque converter clutch.When the driver-demanded torque is implemented as a torque at the torque converter impeller, the desired torque converter clutch torque is set to the driver-demanded torque if the transmission line pressure is high enough to enable the torque converter clutch to transmit the driver-demanded torque. If the transmission line pressure is insufficient to enable the torque converter clutch to transmit the driver-demanded torque, the desired torque converter clutch torque is set to the highest torque that the transmission line pressure allows the torque converter clutch to transmit.

[0037] In one example, transmission line pressure is used to index a table or function describing a torque converter clutch transfer function. The transfer function outputs an amount of torque the torque converter clutch will transfer at the pressure at which transmission fluid is supplied to the torque converter clutch. Values ​​describing the transfer function can be determined empirically. If the output from the torque converter transfer function is greater than or equal to the driver-requested torque, the desired torque converter clutch torque can be adjusted to the driver-requested torque.If the output from the torque converter transfer function is less than the driver-requested torque, the desired torque converter clutch torque can be set to the amount of torque the torque converter clutch transmits at the current transmission line pressure. The desired torque converter clutch torque is input to the torque converter hydraulic torque path torque determination block 302 and the pressure conversion block 308.

[0038] The pressure conversion block 308 converts the desired torque converter clutch torque into a pressure at which transmission fluid is to be applied to the transmission torque converter clutch actuator to transfer torque at the desired torque converter clutch torque across the torque converter clutch. In one example, the desired torque converter clutch torque indexes a transfer function that outputs a torque converter clutch actuator pressure that is supplied to the torque converter clutch 216. Values ​​in the transfer function can be determined empirically.

[0039] The torque converter hydraulic torque path torque determination block 302 outputs an amount of torque to be transferred on the hydraulic torque path (e.g., between the torque converter impeller and the torque converter turbine). The amount of torque to be transferred on the hydraulic torque path is the driver-requested torque minus the desired torque converter clutch torque when the powertrain is not in a regenerative braking mode.

[0040] A torque converter impeller speed determination block 306 outputs a desired torque converter impeller speed to an engine speed control block 310. The desired torque converter impeller speed is output from a transfer function or a table. The values ​​in the table or function are determined by the converter design and experimental data and are indexed by the amount of torque to be transferred on the hydraulic torque path and the torque converter turbine speed, since the torque transfer on the torque converter's hydraulic torque path is a function of the impeller speed and the turbine speed.

[0041] The engine speed control block 310 actuates the Fig. 2 is in a speed control mode. For example, the current supplied to the DISG 240 is controlled based on a desired DISG speed. The desired DISG speed is set to the desired torque converter impeller speed input from block 306 to block 310. Additionally, the disconnect clutch torque may be input as a feedforward torque setting at the desired DISG speed input to the engine speed control block 310.

[0042] The DISG 240 provides torque to the torque converter 206, which includes the impeller 285 and the turbine 286. The torque may be transferred from the impeller 285 to the turbine 286 via transmission fluid in a hydraulic torque path. The torque converter clutch 216 may also transfer torque across the torque converter 206 in a friction path. The turbine speed sensor 239 monitors the speed of the turbine 286 and provides an input to the torque converter impeller determination block 306.

[0043] Accordingly, the block diagram shows the control of the torque transmitted to the transmission input shaft via hydraulic and friction torque paths. The torque transmitted via the friction torque path is based on the transmission line pressure, so that the amount of torque transmitted via the friction torque path is close to the torque transmission limit of the friction torque path at the prevailing transmission line pressure.

[0044] Fig. 4 shows a method for operating a vehicle powertrain. The method of Fig. 4 can be executed as executable instructions stored in a non-volatile memory in the system from the Fig. 1 and Fig. 2 be implemented.

[0045] At 402, method 400 determines the desired torque converter clutch torque. In one example, the desired torque converter clutch torque is set to the driver-requested torque when the transmission line pressure (e.g., the regulated transmission fluid pump output pressure) is sufficient to allow torque equal to the driver-requested torque to be transferred across the torque converter clutch.If the transmission line pressure is less than the transmission line pressure required to transmit the torque requested by the driver through the torque converter clutch, the desired torque converter clutch torque is set to a torque within a predetermined torque range of a maximum torque that the existing transmission line pressure allows to be transmitted through the torque converter clutch (for example, the transmission line pressure is determined at the existing torque converter clutch torque).

[0046] Accordingly, the torque converter clutch torque may be limited to a torque that the torque converter can transmit at the existing transmission line pressure when the transmission line pressure is applied to the torque converter clutch actuator. The torque converter clutch torque may be reduced to less than the driver-requested torque if the transmission is shifting or if the vehicle is starting from a stopped state, even if the transmission line pressure allows the driver-requested torque to be transmitted via the torque converter clutch. Furthermore, the torque converter clutch may be intentionally slipped during a shift, a vehicle launch, or during vehicle deceleration.In this way, the portion of driver-demanded torque delivered to the vehicle wheels via the torque converter clutch can be increased as the torque converter clutch torque capacity increases in response to transmission line pressure. Similarly, the portion of driver-demanded torque delivered to the vehicle wheels via the torque converter clutch can be decreased as the torque converter clutch torque capacity decreases in response to transmission line pressure.

[0047] Method 400 dictates the pressure of the transmission fluid supplied to the torque converter clutch at 404 to provide the desired torque converter clutch torque. In one example, the pressure of the transmission fluid supplied to the torque converter clutch is regulated by a pulse-width modulated solenoid valve. At 406, method 400 determines whether the desired torque converter clutch torque is less than (LT) the driver requested torque. If method 400 determines that the desired torque converter torque is less than the driver requested torque, the answer is yes, and method 400 continues at 420. Otherwise, the answer is no, and method 400 continues at 408.

[0048] At 408, method 400 determines whether the engine is starting. In one example, in response to an engine starting, method 400 may determine that engine rotation is accelerating from zero speed to idle speed. If method 400 determines that the engine is starting, the answer is yes, and method 400 continues at 410. Otherwise, the answer is no, and method 400 continues at 412.

[0049] At 410, method 400 adjusts the torque converter slip to less than a threshold amount of slip. For example, the transmission torque converter clutch may be pressurized to a pressure that provides less than 50 rpm of slip between the torque converter impeller and the torque converter turbine. Additionally, transmission line pressure may be supplied to the torque converter clutch during engine cranking to provide a low amount of slip at the prevailing transmission line pressure. Accordingly, transmission fluid may be supplied to the torque converter at a pressure regulated to the transmission pump output.Therefore, if the transmission line pressure is low due to low transmission input speed, the torque converter clutch torque can be set to the highest amount of torque available for transmission across the torque converter by the torque converter clutch at the existing transmission line pressure.

[0050] Supplying transmission fluid to the torque converter clutch at line pressure may reduce slip between the torque converter impeller and the torque converter turbine. Torque converter slip may be adjusted by operating the DISG in a speed control mode and adjusting the DISG speed relative to the torque converter turbine speed. The DISG is not mandated to follow a torque in speed control mode, however, the DISG torque may be adjusted so that the DISG follows a desired speed in DISG speed control mode. Method 400 continues at 430 after the transmission torque converter clutch slip is adjusted.

[0051] At 412, method 400 locks the torque converter clutch. The torque converter clutch may be locked once the transmission line pressure has increased to a sufficient level to lock the torque converter. Method 400 continues at 414 after the transmission torque converter has been locked.

[0052] At 414, method 400 operates the DISG in a torque control mode. The DISG may provide the entire amount of driver-requested torque or a fraction of the driver-requested torque (e.g., less than the driver-requested torque but not all of the driver-requested torque). The DISG is not required to follow a speed in torque control mode. Rather, the DISG torque is adjusted so that the DISG follows a desired torque in DISG torque control mode. If the engine is operating with the motor, the engine torque and the motor torque may be adjusted to provide the driver-requested torque. Method 400 exits after the motor is operated in a torque control mode.

[0053] At 420, method 400 determines whether the hybrid powertrain is in a regenerative braking mode (e.g., a mode where the vehicle's kinetic energy is converted to electrical energy by the DISG). In one example, method 400 may determine to operate the hybrid powertrain in a regenerative braking mode if the driver demand torque is less than a threshold torque while the vehicle speed is greater than a threshold vehicle speed. If method 400 determines to operate the powertrain in a regenerative braking mode, the answer is yes, and method 400 continues at 422. Otherwise, the answer is no, and method 400 continues at 426.

[0054] At 422, method 400 operates the DISG in a torque control mode. For example, the DISG is not commanded to follow a speed in the torque control mode. Rather, the DISG torque is adjusted so that the DISG follows a desired torque in the DISG torque control mode. The DISG may be operated in a torque control mode by supplying current to the DISG based on a map or transfer function of the DISG that relates DISG current to DISG torque. The DISG current is adjusted to provide the desired DISG torque.

[0055] At 424, method 400 adjusts the desired DISG torque to the torque converter clutch torque. For example, a negative torque applied by the DISG to the powertrain is adjusted to the torque converter torque so that the DISG can convert the torque transmitted through the torque converter clutch into electrical energy and the torque converter slip is less than a threshold slip amount (e.g., less than 5 rpm slip). Method 400 exits after the DISG torque is adjusted.

[0056] At 426, method 400 determines the amount of torque to be transmitted through the hydraulic torque path. Specifically, method 400 determines the torque transmitted through the hydraulic torque path based on the torque difference between the torque transmitted through the torque converter clutch and the driver demanded torque. For example, the driver demanded torque minus the torque transmitted through the torque converter clutch (e.g., torque converter clutch capacity) equals the desired hydraulic path torque. Method 400 continues at 428 after the hydraulic path torque is determined.

[0057] At 428, method 400 adjusts the DISG speed to provide the desired hydraulic path torque. In one example, the DISG speed is adjusted in response to the torque converter turbine speed and the torque difference between the torque converter clutch torque and the driver demanded torque. For example, the torque converter turbine speed and a torque value representing the torque difference between the torque transmitted through the torque converter clutch and the driver demanded torque (e.g., the desired hydraulic path torque) are input to a torque converter model.The torque converter model outputs a desired torque converter impeller speed based on the output of a torque converter transfer function that relates the torque converter impeller speed to the torque converter turbine speed and the torque transferred through the hydraulic torque path. The difference between the desired torque converter impeller speed and the torque converter turbine speed is the torque converter slip. Method 400 continues at 430 after the desired torque converter impeller speed is determined.

[0058] At 430, method 400 operates the DISG in a speed control mode. In one example, the current supplied to the DISG is adjusted in response to the desired DISG speed. For example, the DISG current may be adjusted to operate the DISG at a predetermined speed (e.g., 800 rpm). The DISG torque or DISG current is not commanded to follow a desired DISG torque in speed control mode. Method 400 continues at 432 after the DISG enters the speed control mode.

[0059] At 432, method 400 outputs current to the DISG. The current supplied to the DISG may be based on an error between a desired DISG speed corresponding to the torque converter impeller speed and the actual DISG speed. If the difference between the actual DISG speed and the desired DISG speed increases, the DISG current setting may increase proportionally with the speed difference. If the difference between the actual DISG speed and the desired DISG speed decreases, the DISG current setting may decrease similarly proportionally with the speed difference.

[0060] Accordingly, the procedure looks like Fig. 4 proposes operating a powertrain comprising the steps of: operating an electric machine in a torque control mode in response to a torque converter clutch torque (e.g., the torque a torque converter clutch transmits across a torque converter) available at a transmission line pressure being greater than a driver demanded torque; and operating the electric machine in a speed control mode in response to the torque converter clutch torque available at the transmission line pressure being less than the driver demanded torque. In some examples, the electric machine may be operated in a speed control mode in response to starting an internal combustion engine. The method includes a case where the electric machine is a starter / generator integrated into the powertrain.The method further includes adjusting a torque converter impeller speed in response to a torque converter turbine speed and a difference between driver requested torque and torque transmitted by a torque converter via a torque converter clutch.

[0061] In some examples, the method further includes operating the electric machine in a torque control mode instead of the speed control mode in response to the powertrain operating in a regenerative braking mode. The method includes a case where the transmission line pressure is a regulated transmission pump outlet pressure and the DISG torque is adjusted in response to the torque converter clutch capacity. The method also includes a case where the transmission line pressure is applied to the torque converter clutch and further the torque converter clutch torque is adjusted to equal the driver requested torque. The method further includes adjusting the speed of the electric machine in response to the driver requested torque while the electric machine is operating in the speed control mode. In another example, the method Fig. 4 proposes operating a powertrain comprising the steps of: adjusting a torque converter clutch to transmit a first portion of a driver-requested torque to vehicle wheels; and adjusting the speed of a torque converter impeller in response to a difference between the driver-requested torque and the first portion of the driver-requested torque. The method includes a case where torque transmitted via a torque converter clutch and torque transmitted between the torque converter impeller and a torque converter turbine are equal to the driver-requested torque.The method further includes adjusting the slip of the torque converter to be maintained above a minimum threshold slip amount during engine cranking when the torque transferable by the torque converter via the torque converter clutch is greater than a driver requested torque.

[0062] In some examples, the method includes a case where the torque transferable by the torque converter via the torque converter clutch is estimated based on the transmission line pressure, and wherein the first portion of the driver demanded torque is based on the torque converter clutch capacity at a transmission line pressure at the time the torque converter clutch is adjusted. The method includes a case where the torque converter clutch is adjusted to transfer the driver demanded torque via a torque converter in response to the transmission line pressure. The method also includes a case where the torque converter impeller speed is further adjusted in response to the torque converter turbine speed.The method includes a case where the torque converter impeller speed is adjusted via a starter / generator integrated into the powertrain.

[0063] As the average person will understand, this can Fig. 4 may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, or similar processing strategies. Various steps or functions discussed may be performed in parallel within the sequence discussed, or in some cases, omitted. Likewise, the order of processing is not required to achieve the objects, features, and advantages described herein, but is provided for ease of explanation and description. Although not explicitly explained, those of ordinary skill in the art will understand that one or more of the steps or functions discussed may be performed repeatedly, depending on the particular strategy employed.

[0064] This concludes the description. As those skilled in the art read it, numerous alterations and modifications will occur to them without departing from the spirit and scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 internal combustion engines operating on natural gas, gasoline, diesel, or alternative fuel configurations may advantageously utilize the present description. KEY TO SYMBOLS

[0065] Fig. 4 402 DETERMINING THE TORQUE CONVERTER CLUTCH TORQUE 404 PRESCRIBING THE TORQUE CONVERTER CLUTCH PRESSURE 406 TORQUE CONVERTER CLUTCH TORQUE < DRIVER REQUESTED TORQUE? NO NO YES YES 408 COMBUSTION ENGINE STARTED? 412 LOCKING THE TORQUE CONVERTER CLUTCH 410 SET THE TORQUE CONVERTER SLIP TO A VALUE LESS THAN THE THRESHOLD SLIP AMOUNT 414 OPERATING THE DISG IN TORQUE CONTROL MODE 420 IN REGENERATIVE BRAKING MODE? 422 OPERATING THE DISG IN TORQUE CONTROL MODE 424 ADJUSTING THE DISG TORQUE TO THE TORQUE CONVERTER CLUTCH TORQUE 426 DETERMINING THE TORQUE TRANSMITTED VIA THE HYDRAULIC TORQUE PATH 428 DETERMINING TORQUE CONVERTER SLIP 430 OPERATING THE ENGINE IN SPEED CONTROL MODE 432 ADJUSTING THE ENGINE SPEED TO PROVIDE A TORQUE DIFFERENCE BETWEEN THE TORQUE CONVERTER CLUTCH TORQUE AND THE TORQUE REQUIRED BY THE DRIVER

Claims

[1] A method of operating a powertrain (200) comprising the steps of: operating an electric machine (240) in a torque control mode in response to a transmission line pressure being sufficiently high to enable a torque converter clutch (212) to transmit a driver-demanded torque, and operating the electric machine (240) in a speed control mode in response to the transmission line pressure being too low to enable the torque converter clutch (212) to transmit the driver-demanded torque. [2] The method of claim 1, wherein the electric machine is a starter / generator integrated into the drive train (200) and wherein the electric machine is operated in speed control mode during starting of the internal combustion engine (10). [3] The method of claim 1, further comprising the step of: adjusting a torque converter impeller speed in response to a torque converter turbine speed and a difference between driver demanded torque and torque transmitted by a torque converter via a torque converter clutch (212). [4] The method of claim 1, further comprising the step of: operating the electric machine (240) in a torque control mode instead of the speed control mode in response to the powertrain (200) operating in a regenerative braking mode. [5] The method of claim 4, wherein the transmission line pressure is a regulated transmission pump outlet pressure and further adjusting the torque of the electric machine (240) in response to the lesser of the driver requested braking torque and the torque converter clutch torque capacity. [6] The method of claim 1, wherein the transmission line pressure is applied to the torque converter clutch (212) and further adjusting the torque converter clutch torque to equal the driver demanded torque. [7] The method of claim 1, further comprising the step of: adjusting the speed of the electric machine (240) in response to the driver demanded torque while the electric machine is operating in the speed control mode. [8] Method for operating a drive train (200), comprising the following steps: Adjusting a torque converter clutch (212) to transmit a first portion of a driver-requested torque to vehicle wheels (216), and Adjusting the speed of a torque converter impeller in response to a difference between the driver demanded torque and the first part of the driver demanded torque, characterized by , that the method further comprises the step of: estimating a torque transmittable by the torque converter via the torque converter clutch (212) based on a transmission line pressure. [9] The method of claim 8, wherein a torque transmitted via the torque converter clutch (212) plus a torque transmitted between the torque converter impeller and a torque converter turbine equals the driver requested torque. [10] The method of claim 8, further comprising the step of: setting the slip of the torque converter during starting of the internal combustion engine (10) to less than a threshold amount of slip when the torque transmittable by the torque converter via the torque converter clutch (212) is not less than a driver requested torque.

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