Method and system for starting an engine

Abstract

The present disclosure provides "Methods and systems for starting an engine". Systems and methods for operating a hybrid powertrain or driveline including an engine and a belt-driven starter / generator are described. In one example, a clutch is positioned between the engine and the belt-driven starter / generator to reduce the likelihood that the belt-driven starter / generator will exceed the rated speed of the belt-driven starter / generator.

Description

Technical Field

[0001] This specification relates to methods and systems for operating the powertrain of hybrid vehicles. The methods and systems are particularly useful for hybrid vehicles that include a drive-driven starter / generator. Background Technology

[0002] Hybrid powertrains or drivetrains may include a belt-driven starter / generator (BISG) to charge the vehicle's battery, provide propulsion to the vehicle, and start the vehicle's engine. The BISG may have a rated positive output torque (e.g., the maximum torque provided by the BISG to propel the vehicle) and a rated negative output torque (e.g., the maximum torque absorbed by the BISG from the powertrain or drivetrain to decelerate the vehicle and / or charge an energy storage device). The BISG may also have a rated speed (e.g., the maximum or threshold rotational speed of the BISG that should not be exceeded). If the BISG is matched with a large-displacement engine, the BISG may not have sufficient output torque to rotate the engine at a starting speed (e.g., 250 RPM) during engine start-up. However, a pulley ratio that is not 1:1 can be placed between the BISG and the engine to provide a mechanical advantage to the BISG, allowing it to rotate the engine at a starting speed. However, the pulley ratio may cause the BISG speed to be significantly higher than the engine speed, meaning that if the engine operates at higher speeds, the BISG speed may exceed the rated BISG speed. Therefore, it may be desirable to provide a way to start the engine via the BISG without exceeding the rated speed of the BISG at higher engine speeds. Summary of the Invention

[0003] The inventors have recognized the above-mentioned problems and have developed a method for operating a power transmission system, comprising: closing the BISG control clutch via a controller in response to the BISG torque being non-zero and the BISG speed being less than a threshold speed; and opening the BISG control clutch via a controller in response to the BISG torque being zero or the BISG speed being greater than the threshold speed.

[0004] By engaging the BISG control clutch in response to a non-zero BISG torque and a BISG speed below a threshold speed, the starter engine can be rotated, providing propulsion torque to the powertrain via the BISG, and the battery can be charged via the BISG at a speed below the threshold speed (e.g., the BISG's rated speed). Furthermore, by disengaging the BISG control clutch in response to a zero BISG output torque or a BISG speed above the threshold speed, the engine can be operated at high speeds without exceeding the BISG's rated speed. Moreover, by disengaging the BISG control clutch when the BISG output torque is zero, the BISG can rotate freely without being bound by the engine speed, thereby reducing the likelihood of BISG degradation.

[0005] This specification offers several advantages. In particular, the method allows a smaller BISG to start a large-displacement engine without exceeding its rated speed. Furthermore, the method reduces BISG degradation. Additionally, the method can improve vehicle operation during periods of BISG-controlled clutch degradation.

[0006] The advantages and other advantages and features of this specification will become apparent from the following specific embodiments, either alone or in conjunction with the accompanying drawings.

[0007] It should be understood that the above overview is provided to introduce some concepts further described in the detailed description in a simplified form. This is not intended to represent key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to embodiments that address any shortcomings mentioned above or in any part of this disclosure. Attached Figure Description

[0008] The advantages described herein will be more fully understood by reading, either alone or with reference to, the examples referred to herein as specific embodiments, in which:

[0009] Figure 1 This is a schematic diagram of an engine;

[0010] Figure 2 This is a schematic diagram of the powertrain of a hybrid vehicle;

[0011] Figure 3A and Figure 3B An example BISG control clutch configuration is shown;

[0012] Figure 4 An example BISG operation sequence is shown; and

[0013] Figure 5A method for operating an engine including a BISG is described. Detailed Implementation

[0014] This manual pertains to operating the engine and the BISG that can be selectively connected to the engine. The engine can be... Figure 1 The type shown. Engines and BISGs can be included in, for example... Figure 2 In the powertrain of the hybrid vehicle shown, the BISG can selectively engage the clutch with the engine via BISG control. Figure 3A and Figure 3B Two different BISG control clutch configurations are shown. Figure 4 An example operating sequence for the BISG clutch is shown. Figure 5 A method for operating the BISG control clutch is shown.

[0015] refer to Figure 1 The internal combustion engine 10 (which includes multiple cylinders, one of which is in) Figure 1 (As shown in the diagram) Controlled by the electronic engine controller 12. Controller 12 from... Figures 1 to 3B The various sensors shown receive signals and use them based on the received signals and instructions stored in the memory of controller 12. Figures 1 to 3B The actuator shown is used to adjust engine operation.

[0016] Engine 10 comprises a cylinder head 35 and a cylinder block 33, which include a combustion chamber 30 and cylinder walls 32. A piston 36 is located in the cylinder block and reciprocates via a connection to a crankshaft 40. A flywheel 97 and a ring gear 99 are coupled to the crankshaft 40. An optional starter 96 (e.g., a voltage-driven (operating at less than 30 volts) motor) includes a pinion shaft 98 and a pinion 95. The pinion shaft 98 can selectively advance the pinion 95 to engage the ring gear 99. The starter 96 can be mounted directly to the front or rear of the 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 basic state when not engaged with the engine crankshaft. The combustion chamber 30 is shown communicating with an intake manifold 44 and an exhaust manifold 48 via corresponding intake valves 52 and exhaust valves 54. Each intake and exhaust valve can be operated 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 valve 52 can be selectively activated and deactivated by a valve activation device 59. The exhaust valve 54 can be selectively activated and deactivated by a valve activation device 58. The valve activation devices 58 and 59 can be electromechanical devices.

[0017] Fuel injector 66 is shown positioned to inject fuel directly into cylinder 30, which is referred to by those skilled in the art as direct injection. Fuel injector 66 delivers liquid fuel in proportion to the pulse width from controller 12. Fuel is delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). In one example, a high-pressure two-stage fuel system may be used to generate higher fuel pressure.

[0018] Furthermore, intake manifold 44 is shown communicating with turbocharger compressor 162 and engine intake port 42. In other examples, compressor 162 may be a supercharger compressor. Shaft 161 mechanically connects turbocharger turbine 164 to turbocharger compressor 162. Optional electronic throttle 62 adjusts the position of throttle plate 64 to control airflow from compressor 162 to intake manifold 44. The pressure in boost chamber 45 may be referred to as throttle inlet pressure because the inlet of throttle 62 is within boost chamber 45. Throttle outlet is in intake manifold 44. In some examples, throttle 62 and throttle plate 64 may be located between intake valve 52 and intake manifold 44, such that throttle 62 is an intake manifold throttle. Compressor recirculation valve 47 may be selectively adjustable to multiple positions between fully open and fully closed. The exhaust valve 163 can be adjusted via controller 12 to allow exhaust gas to selectively bypass turbine 164, thereby controlling the speed of compressor 162. Air filter 43 cleans the air entering engine intake 42.

[0019] Distributorless ignition system 88 provides an ignition spark to combustion chamber 30 via spark plug 92 in response to controller 12. Universal exhaust oxygen (UEGO) sensor 126 is shown as being coupled to exhaust manifold 48 upstream of catalytic converter 70. Alternatively, dual-state exhaust oxygen sensor may replace UEGO sensor 126.

[0020] In one example, converter 70 may include multiple catalyst bricks. In another example, multiple emission control devices (each with multiple bricks) may be used. In one example, converter 70 may be a ternary catalyst.

[0021] Controller 12 in Figure 1The controller 12 is shown as a conventional microcomputer, which includes: a microprocessor unit 102, an input / output port 104, a read-only memory 106 (e.g., non-transitory memory), a random access memory 108, a keep-alive memory 110, and a conventional data bus. The controller 12 is shown to receive various signals from sensors coupled to the engine 10, in addition to those previously discussed, including: engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 114; a position sensor 134 coupled to an accelerator pedal 130 for sensing forces applied by a human driver 132; a position sensor 154 coupled to a brake pedal 150 for sensing forces applied by a human driver 132; a measurement of engine manifold pressure (MAP) from a pressure sensor 122 coupled to an intake manifold 44; an engine position sensor from a Hall effect sensor 118 for sensing the position of the crankshaft 40; a measurement of the mass of air entering the engine from a sensor 120; and a measurement of the throttle position from a sensor 68. Atmospheric pressure can also be sensed (by a sensor not shown) for processing by controller 12. In a preferred aspect of this specification, engine position sensor 118 generates a predetermined number of equidistant pulses per revolution of the crankshaft, based on which engine speed (RPM) can be determined.

[0022] The controller 12 can also receive input from the human-machine interface 11. A request to start the engine or vehicle can be generated via input from the user to the human-machine interface 11. The human-machine interface can be a touchscreen display, buttons, push-button switches, or other known devices.

[0023] During operation, each cylinder in engine 10 typically undergoes a four-stroke cycle: the cycle includes an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. During the intake stroke, generally speaking, the exhaust valve 54 is closed and the intake valve 52 is open. Air is introduced into combustion chamber 30 via intake manifold 44, and piston 36 moves to the bottom of the cylinder to increase the volume within combustion chamber 30. The position of piston 36 near the bottom of the cylinder and at the end of its stroke (e.g., when combustion chamber 30 is at its maximum volume) is generally referred to by those skilled in the art as bottom dead center (BDC).

[0024] During the compression stroke, intake valve 52 and exhaust valve 54 are closed. Piston 36 moves toward the cylinder head to compress the air within 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 minimum volume) is commonly referred to by those skilled in the art as top dead center (TDC). Fuel is introduced into the combustion chamber during what is hereinafter referred to as injection. The injected fuel is ignited by a known ignition device, such as spark plug 92, resulting in combustion.

[0025] During the expansion stroke, the expanding gas pushes piston 36 back to the BDC. Crankshaft 40 converts the piston movement into rotational torque on the rotating shaft. Finally, during the exhaust stroke, exhaust valve 54 opens to release the combusted air-fuel mixture into exhaust manifold 48, and piston returns to the TDC. It should be noted that the above is only shown as an example, and the opening and / or closing timing of the intake and exhaust valves can vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0026] Figure 2 It is a block diagram of a vehicle 225 including a powertrain or transmission system 200. Figure 2 The power transmission system includes Figure 1 The engine 10 is shown in the diagram. The powertrain 200 is shown as including a vehicle system controller 255, an engine controller 12, an electric motor controller 252, a transmission controller 254, an energy storage device controller 253, and a brake controller 250. The controllers can communicate via a controller area network (CAN) 299. Each of the controllers can provide information to the other controllers, such as torque output limits (e.g., the torque output of a control device or component that should not be exceeded), torque input limits (e.g., the torque input of a control device or component that should not be exceeded), torque output of control devices, sensor and actuator data, and diagnostic information (e.g., information about a deteriorated transmission, information about a deteriorated engine, information about a deteriorated electric motor, and information about a deteriorated brake). Furthermore, the vehicle system controller 255 can provide commands to the engine controller 12, the electric motor controller 252, the transmission controller 254, and the brake controller 250 to fulfill driver input requests and other requests based on vehicle operating conditions.

[0027] For example, in response to the driver releasing the accelerator pedal and the vehicle speed, the vehicle system controller 255 can request a desired wheel torque or wheel power level to provide a desired vehicle deceleration rate. The desired wheel torque can be provided by the vehicle system controller 255 requesting a first braking torque from the motor controller 252 and a second braking torque from the brake controller 250, the first torque and the second torque providing the desired braking torque at the wheel 216.

[0028] In other examples, the division of the control powertrain system can be related to... Figure 2 The components can be divided in different ways as shown. For example, a single controller can replace the vehicle system controller 255, engine controller 12, electric motor controller 252, transmission controller 254, and brake controller 250. Alternatively, the vehicle system controller 255 and engine controller 12 can be a single unit, while the electric motor controller 252, transmission controller 254, and brake controller 250 are independent controllers.

[0029] In this example, the powertrain 200 can be powered by the engine 10 and the electric motor 240. In other examples, the engine 10 can be omitted. The engine 10 can be... Figure 1 The engine starting system shown is started via BISG 219 or via a drivetrain starter / generator (ISG) 240, also known as a drivetrain starter / generator. The speed of BISG 219 can be determined via an optional BISG speed sensor 203. The drivetrain ISG 240 (e.g., a high-voltage (operating at a voltage greater than 30 volts) motor) can also be referred to as a motor, generator, and / or generator. Furthermore, the torque of engine 10 can be adjusted via torque actuators 204 such as fuel injectors, throttle valves, etc.

[0030] The BISG is mechanically connected to the engine 10 via belt 231. The BISG can be connected to the crankshaft 40 or the camshaft (e.g., Figure 1 (51 or 53). When powered via energy storage device 275 or low-voltage battery 280, the BISG can operate as a motor. The BISG can operate as a generator supplying power to energy storage device 275 or low-voltage battery 280. The bidirectional DC / DC converter 281 can transfer electrical energy from high-voltage bus 274 to low-voltage bus 273 and vice versa. Low-voltage battery 280 is electrically connected to low-voltage bus 273. Energy storage device 275 is electrically connected to high-voltage bus 274. Low-voltage battery 280 selectively supplies electrical energy to starter motor 96.

[0031] Engine output torque can be transmitted via dual-mass flywheel 215 to the input or first side of powertrain disengagement clutch 235. Disengagement clutch 236 can be electrically or hydraulically actuated. The downstream or second side 234 of disengagement clutch 236 is shown as mechanically coupled to ISG input shaft 237.

[0032] The ISG 240 can be operated to provide torque to the powertrain 200 or, in regenerative mode, convert powertrain torque into electrical energy for storage in the energy storage device 275. The ISG 240 is electrically connected to the energy storage device 275. The ISG 240 has a higher specific energy density than... Figure 1The starter 96 or BISG 219 shown has a higher output torque capacity. Furthermore, the ISG 240 directly drives or is directly driven by the powertrain 200. There is no belt, gear, or chain connecting the ISG 240 to the powertrain 200. Instead, the ISG 240 rotates at the same rate as the powertrain 200. The energy storage device 275 (e.g., a high-voltage battery or power source) can be a battery, capacitor, or inductor. The downstream side of the ISG 240 is mechanically coupled to the pump wheel 285 of the torque converter 206 via shaft 241. The upstream side of the ISG 240 is mechanically coupled to the disengagement clutch 236. The ISG 240 can provide positive or negative torque to the powertrain 200 via operation as a motor or generator, as instructed by the motor controller 252.

[0033] Torque converter 206 includes turbine 286 to output torque to input shaft 270. Input shaft 270 mechanically connects torque converter 206 to automatic transmission 208. Torque converter 206 also includes torque converter bypass lock-up clutch 212 (TCC). When TCC is locked, torque is transmitted directly from pump wheel 285 to turbine 286. TCC is electrically operated by controller 12. Alternatively, TCC can be hydraulically locked. In one example, the torque converter may be referred to as a component of the transmission.

[0034] When the torque converter lock-up clutch 212 is fully disengaged, the torque converter 206 transmits engine torque to the automatic transmission 208 via fluid transfer between the torque converter turbine 286 and the torque converter pump impeller 285, thereby doubling the torque. In contrast, when the torque converter lock-up clutch 212 is fully engaged, the engine output torque is transmitted directly to the input shaft 270 of the transmission 208 via the torque converter clutch. Alternatively, the torque converter lock-up clutch 212 can be partially engaged, thereby enabling adjustment of the amount of torque transmitted directly to the transmission. The transmission controller 254 can 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 driver-based engine operation requests.

[0035] The torque converter 206 also includes a pump 283, which pressurizes fluid to operate the disengagement clutch 236, the forward clutch 210, and the gear clutch 211. The pump 283 is driven via a pump wheel 285, which rotates at the same speed as the ISG 240.

[0036] Automatic transmission 208 includes a gear clutch (e.g., gears 1-10) 211 and a forward clutch 210. Automatic transmission 208 is a stepped transmission. Gear clutch 211 and forward clutch 210 can be selectively engaged to change the ratio of the actual total revolutions of the input shaft 270 to the actual total revolutions of the wheels 216. Gear clutch 211 can be engaged or disengaged by adjusting the fluid supplied to the clutch via shift control solenoid valve 209. Torque output from automatic transmission 208 can also be transmitted to wheels 216 via output shaft 260 to propel the vehicle. Specifically, automatic transmission 208 can transmit input drive torque at input shaft 270 in response to vehicle driving conditions before transmitting output drive torque to wheels 216. Transmission controller 254 selectively engages or disengages TCC 212, gear clutch 211, and forward clutch 210. Transmission controller also selectively disengages or deactivates TCC 212, gear clutch 211, and forward clutch 210.

[0037] Furthermore, friction can be applied to wheel 216 by engaging friction wheel brake 218. In one example, friction wheel brake 218 may engage in response to the driver pressing his foot on the brake pedal (not shown) and / or in response to a command within brake controller 250. Additionally, brake controller 250 may apply brake 218 in response to information and / or requests from vehicle system controller 255. Similarly, friction to wheel 216 can be reduced by disengaging wheel brake 218 in response to the driver releasing his foot from the brake pedal, brake controller command and / or vehicle system controller command and / or information. For example, vehicle brakes may apply friction to wheel 216 via controller 250 as part of an automated engine stop process.

[0038] In response to a request to accelerate vehicle 225, the vehicle system controller 255 may obtain a driver-demanded torque or power request from the accelerator pedal or other device. Vehicle system controller 255 then allocates a portion of the requested driver-demanded torque to the engine and the remainder to the ISG or BISG. Vehicle system controller 255 requests engine torque from engine controller 12 and ISG torque from motor controller 252. If the sum of the ISG torque and engine torque is less than the transmission input torque limit (e.g., a threshold that should not be exceeded), the torque is delivered to torque converter 206, which then transmits at least a portion of the requested torque to transmission input shaft 270. Transmission controller 254 selectively locks torque converter clutch 212 and engages gears via gear clutch 211 in response to a shift schedule and TCC lock-up schedule that may be based on input shaft torque and vehicle speed. In some cases, when it may be desirable to charge energy storage device 275, charging torque (e.g., negative ISG torque) may be requested while a non-zero driver-demanded torque is present. The vehicle system controller 255 can request an increase in engine torque to overcome the charging torque, thereby meeting the driver's torque requirements.

[0039] In response to a request to decelerate vehicle 225 and provide regenerative braking, the vehicle system controller may provide a negative desired wheel torque based on vehicle speed and brake pedal position. The vehicle system controller 255 then allocates a portion of the negative desired wheel torque to the ISG 240 (e.g., desired powertrain wheel torque) and the remainder to the friction brake 218 (e.g., desired friction brake wheel torque). Furthermore, the vehicle system controller may notify the transmission controller 254 that the vehicle is in regenerative braking mode, causing the transmission controller 254 to change gear 211 based on a unique shift plan to improve regenerative efficiency. The ISG 240 supplies negative torque to the transmission input shaft 270, but the negative torque provided by the ISG 240 may be limited by the transmission controller 254, which outputs a negative torque limit for the transmission input shaft (e.g., a threshold that should not be exceeded). Additionally, the negative torque of the ISG 240 may be limited by the vehicle system controller 255 or the motor controller 252 based on the operating conditions of the energy storage device 275 (e.g., constrained to a negative threshold torque below a threshold). Any portion of the desired negative wheel torque that cannot be provided by the ISG 240 due to the transmission or ISG limits can be allocated to the friction brake 218, such that the desired wheel torque is provided by a combination of the negative wheel torque from the friction brake 218 and the ISG 240.

[0040] Therefore, torque control of various powertrain components can be monitored by the vehicle system controller 255, which provides local torque control for the engine 10, transmission 208, motor 240 and brake 218 via the engine controller 12, motor controller 252, transmission controller 254 and brake controller 250.

[0041] As an example, engine torque output can be controlled by adjusting a combination of spark timing, fuel pulse width, fuel pulse timing, and / or air charging by controlling the throttle opening and / or valve timing, valve lift, and boost of a turbocharged or supercharged engine. In the case of a diesel engine, controller 12 can control engine torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charging. In all cases, engine control can be performed on a cylinder-by-cylinder basis to control engine torque output.

[0042] The motor controller 252 can control the torque output and electrical energy generation from the ISG 240 by adjusting the current flowing into and out of the field windings and / or armature windings of the ISG, as is known in the art.

[0043] The transmission controller 254 receives the transmission input shaft position via position sensor 271. The transmission controller 254 can convert the transmission input shaft position into input shaft speed by differentiating the signal from position sensor 271 or by counting multiple known angular distance pulses within a predetermined time interval. The transmission controller 254 can receive the transmission output shaft torque from torque sensor 272. Alternatively, sensor 272 can be a position sensor or a torque and position sensor. If sensor 272 is a position sensor, the controller 254 can count shaft position pulses within a predetermined time interval to determine the transmission output shaft speed. The transmission controller 254 can also differentiate the transmission output shaft speed to determine the transmission output shaft acceleration. The transmission controller 254, engine controller 12, and vehicle system controller 255 can also receive additional transmission information from sensor 277, which may include, but is not limited to, pump output line pressure sensors, transmission hydraulic sensors (e.g., gear clutch fluid pressure sensors), ISG temperature sensors, BISG temperature sensors, and ambient temperature sensors.

[0044] The brake controller 250 receives wheel speed information via wheel speed sensor 221 and receives braking requests from vehicle system controller 255. The brake controller 250 can also receive braking requests directly or via CAN 299 from... Figure 1The brake pedal sensor 154 shown receives brake pedal position information. The brake controller 250 can provide braking in response to wheel torque commands from the vehicle system controller 255. The brake controller 250 can also provide anti-lock braking and vehicle stability braking to improve vehicle braking and stability. Thus, the brake controller 250 can provide the vehicle system controller 255 with wheel torque limits (e.g., a threshold of negative wheel torque that should not be exceeded) so that negative ISG torque does not lead to exceeding the wheel torque limits. For example, if the controller 250 issues a negative wheel torque limit of 50 N-m, the ISG torque is adjusted to provide less than 50 N-m (e.g., 49 N-m) of negative torque at the wheels, taking into account transmission gearing.

[0045] therefore, Figure 1 and Figure 2 The system provides a system comprising: an engine; a transmission starter / generator (ISG) connected to a crankshaft of the engine via a belt; a clutch configured to selectively connect the shaft of the ISG to the shaft of the engine; and a controller including executable instructions stored in a non-transitory memory to perform the following operations: closing the clutch via the controller in response to the output torque of the ISG or a commanded output torque not being equal to zero and the rotational speed of the ISG being less than a threshold rotational speed. The system further includes additional instructions to open the clutch via the controller in response to the output torque of the ISG or a commanded output torque being equal to zero or the rotational speed of the ISG being greater than the threshold rotational speed. The system further includes additional instructions to reduce the output torque of the ISG in response to the rotational speed of the ISG being within a predetermined speed of the threshold rotational speed when the clutch is closed. The system further includes additional instructions to adjust the rotational speed of the ISG to the engine speed multiplied by the pulley ratio before closing the clutch. The system further includes additional instructions to limit the engine speed to less than the rated speed of the ISG in response to clutch deterioration. The system also includes a starter and additional instructions for starting the engine via the starter during engine starting in response to clutch deterioration.

[0046] Now for reference Figure 3AA sketch of a first example position of the BISG control clutch is shown. In this example, engine 10 is shown with eight cylinders that rotate crankshaft 40. BISG control clutch 302 is directly coupled to crankshaft 40 and engine crankshaft pulley 310. BISG control clutch 302 can be fully open to disengage crankshaft 40 from engine crankshaft pulley 310. Alternatively, BISG control clutch 302 can be fully closed to engage crankshaft 40 to engine crankshaft pulley 310. Engine crankshaft pulley 310 is coupled to BISG pulley 312 via belt 231. BISG pulley 312 is directly coupled to BISG shaft 350. The ratio of BISG pulley 312 to engine crankshaft pulley 310 can provide BISG 219 with a mechanical advantage in rotating engine 10. When BISG control clutch 302 is fully closed, the pulley ratio can also allow BISG 219 to rotate faster than crankshaft 40. BISG control clutch 302 can be adjusted according to the following parameters: Figure 5 The method in Figures 1 to 3A Operating within the system.

[0047] Now for reference Figure 3B A sketch of a first example position of the BISG control clutch is shown. In this example, engine 10 is shown with eight cylinders that rotate crankshaft 40. BISG control clutch 304 is directly coupled to BISG shaft 350 and BISG pulley 312. BISG control clutch 304 can be fully open to disengage BISG shaft 350 from BISG pulley 312. Alternatively, BISG control clutch 304 can be fully closed to engage BISG shaft 350 to BISG pulley 350. Engine crankshaft pulley 310 is coupled to BISG pulley 312 via belt 231. BISG pulley 312 is directly coupled to BISG shaft 350. The ratio of BISG pulley 310 to engine crankshaft pulley 312 can provide BISG 219 with a mechanical advantage in rotating engine 10. When BISG control clutch 304 is fully closed, the ratio can also allow BISG 219 to rotate faster than crankshaft 40. BISG control clutch 304 can be adjusted according to... Figure 5 The method in Figures 1 to 3A Operating within the system.

[0048] Now for reference Figure 4 This shows an example graph illustrating the vehicle's operating sequence. The operating sequence can be achieved via... Figure 1 and Figure 2 The system and Figure 5 The method is used in conjunction with other techniques. The vertical lines from time t0 to t10 represent the times of interest during the sequence. Figure 4 The curves in the graphs are time-aligned and occur simultaneously.

[0049] Figure 4The first graph from the top is a curve of engine speed versus time. The vertical axis represents engine speed, and engine speed increases in the direction of the arrow on the vertical axis. The horizontal axis represents time, and time increases from the left to the right of the graph. The solid line 402 represents engine speed. The dashed horizontal line 450 represents the threshold engine speed. When the engine speed is higher than the threshold 450, the BISG control clutch may not engage or close, thus not exceeding the BISG's rated speed. When the engine speed is lower than the threshold 450, the BISG control clutch can close.

[0050] Figure 4 The second graph from the top is a graph of the BISG torque request state versus time. When trace 404 or trace 406 is at a higher level near the vertical axis arrow, BISG torque (e.g., positive or negative) is requested and the BISG torque has a magnitude greater than zero. When trace 404 or trace 406 is at a lower level near the horizontal axis, no BISG torque is requested and the magnitude of the BISG torque is zero. The horizontal axis represents time, and time increases from the left to the right of the graph. Solid line 404 represents a negative BISG torque request, whereby when solid line 404 is at a higher level near the vertical axis arrow, the BISG charges the battery or energy storage device. Dashed line 406 represents a positive BISG torque request, whereby when dashed line 406 is at a higher level near the vertical axis arrow, the BISG provides torque to rotate the drivetrain. Dashed line 406 follows solid line 404 when only solid line 404 is visible.

[0051] Figure 4 The third graph from the top is a graph of the BISG control clutch operating state versus time. The solid line 408 represents the BISG control clutch operating state; when line 408 is higher near the vertical axis arrow, the BISG control clutch is fully engaged to transmit torque. When line 408 is lower near the horizontal axis, the BISG control clutch is fully open and it does not transmit torque. The horizontal axis represents time, and time increases from the left to the right of the graph.

[0052] At time t0, the engine stops (e.g., does not rotate) and no BISG torque is requested. The BISG controls the clutch to fully engage, preparing for engine start. Near time t1, an engine start request is made by a person or autonomous driver (not shown), and the engine rotates at a rotational start speed via the starter motor or ISG. In other examples, the engine can be started via rotational starting via the BISG.

[0053] At time t1, the engine speed begins to increase and the engine starts. The engine rotates under its own power via the combustion of air and fuel. Since no BISG torque is requested and the BISG torque is zero, the BISG clutch fully disengages shortly after the engine begins to accelerate.

[0054] Between time t1 and time t2, the engine speed stabilizes below the threshold of 450 rpm and the BISG torque is zero. Therefore, the BISG clutch is commanded to disengage. By disengaging the BISG clutch, the engine's rotational inertia decreases, and wear on the BISG bearing may be reduced.

[0055] At time t2, a request for battery charging is made by the BISG. This request can be made via a system controller (not shown). The BISG control clutch engages in response to the BISG's request for battery charging. By engaging the BISG control clutch, torque can be transmitted from the engine or drivetrain to the BISG, allowing the BISG to convert the torque into electrical energy for storage in the battery. The magnitude of the torque requested from the BISG is greater than zero (not shown). The engine speed remains below a threshold of 450 rpm.

[0056] At time t3, the BISG's request to charge the battery is cancelled, and in response to the cancellation of the BISG's request and the commanded BISG torque being zero, the BISG controls the clutch to fully disengage. The engine speed remains below the threshold of 450.

[0057] At time t4, the request for the BISG to provide propulsion torque to the drivetrain is asserted. The request for the BISG to provide propulsion torque can be made in response to high driver torque demand (not shown). In response to the BISG's request to provide propulsion torque and the BISG output torque value being greater than zero (not shown), the BISG controls the clutch to engage. By engaging the BISG-controlled clutch, the torque generated via the BISG can be supplied to the drivetrain to accelerate the vehicle.

[0058] At time t5, the BISG's request to provide propulsion torque to the drivetrain is cancelled, and in response to the cancellation of the BISG's request to provide propulsion torque and the commanded BISG torque being zero, the BISG control clutch BISG fully disengages. The engine speed remains below the threshold of 450.

[0059] At time t6, the engine stops rotating and the BISG controls the clutch to fully engage in preparation for engine start. The BISG torque request state is not active. Near time t7, an engine start request is made via a person or autonomous driver (not shown), and the engine rotates at a rotational start speed via the starter motor or ISG. In other examples, the engine may be started via rotation via the BISG.

[0060] At time t7, the engine speed begins to increase and the engine starts. The engine rotates under its own power via the combustion of air and fuel. Since no BISG torque is requested and the BISG torque is zero, the BISG clutch fully disengages shortly after the engine begins to accelerate.

[0061] Between time t7 and time t8, the engine speed stabilizes above the threshold of 450 rpm and the BISG output torque is zero. Therefore, the BISG clutch is commanded to disengage. By disengaging the BISG clutch, the engine's rotational inertia decreases, and wear on the BISG bearings may be reduced.

[0062] At time t8, a request for battery charging from the BISG is made. However, since the engine speed is greater than the threshold 450 rpm, the BISG control clutch remains fully open. By keeping the BISG control clutch open, the BISG's rated speed (e.g., the BISG speed that should not be exceeded) can be kept below this limit, thereby reducing the likelihood of BISG degradation. In other words, the BISG can rotate freely while the engine is running at high speeds, thus preventing BISG degradation. When the BISG control clutch is fully open, torque is not transmitted from the engine to the BISG. Therefore, even if the BISG torque request is triggered, the BISG will not charge the battery. A request for battery charging from the BISG can be made via the controller in response to the battery's state of charge (not shown).

[0063] At time t9, the BISG's request to charge the battery is cancelled. The BISG controls the clutch to remain fully open and the engine speed to remain above the threshold 450. The BISG's request to charge the battery can be cancelled in response to vehicle operating conditions (such as battery state of charge and road gradient). The engine speed remains above the threshold 450.

[0064] At time t10, the engine speed decreases to zero. The BISG control clutch fully engages in response to the engine speed reaching zero. The BISG torque request is not activated.

[0065] In this way, the BISG control clutch can selectively open and close fully in response to vehicle operating conditions. Opening the BISG control clutch can reduce the likelihood of BISG degradation.

[0066] Now for reference Figure 5 The flowchart illustrates a method for operating the powertrain of a hybrid vehicle. Figure 5 The method can be incorporated Figures 1 to 3B In the system and can cooperate with the system. Furthermore, Figure 5At least a portion of the method can be incorporated as executable instructions stored in non-transitory memory, while other portions of the method can be executed by a controller that changes the operating state of devices and actuators in the physical world.

[0067] At 502, Method 500 determines the operating condition. The operating condition may include, but is not limited to, engine speed, BISG torque, ISG torque, driver-demanded torque, the presence or absence of BISG control clutch deterioration, engine load, ambient temperature, ambient pressure, vehicle speed, and BISG speed. Method 500 proceeds to 504.

[0068] At point 504, method 500 determines whether BISG control clutch deterioration exists. In one example, if the BISG control clutch is commanded to open and the BISG speed equals the engine speed multiplied by the pulley ratio between the engine crankshaft and the BISG shaft, then method 500 can determine that the BISG control clutch is deteriorated. Furthermore, if the BISG control clutch is commanded to close and the BISG speed is not equal to the engine speed multiplied by the pulley ratio between the engine crankshaft and the BISG shaft, then method 500 can determine that the BISG control clutch is deteriorated. If method 500 determines that BISG control clutch deterioration exists, the answer is yes and method 500 proceeds to point 540. Otherwise, the answer is no and method 500 proceeds to point 506.

[0069] At 540, method 500 determines whether to request engine start-up and starting. The request can be made in response to vehicle operating conditions or via input from a human driver to the human / machine interface. If method 500 determines that engine start-up and starting are requested, the answer is yes and method 500 proceeds to 542. Otherwise, the answer is no and method 500 proceeds to 544.

[0070] At 542, method 500 is via a starter (e.g., Figure 1 96) or ISG (e.g., Figure 2 240) Rotation of the starter engine. The starter engine is rotated by power supplied by an electric motor, allowing combustion to begin within the engine. Furthermore, method 500 supplies fuel and a spark to the engine, enabling it to begin burning fuel and rotate under its own power. Therefore, when the BISG control clutch deteriorates, the engine can be started via an electric motor other than the BISG. After the engine is started, method 500 proceeds to 544.

[0071] At 544, method 500 limits or prevents the BISG speed from exceeding a threshold speed. Furthermore, method 500 can limit or prevent the amount of torque requested by the BISG from exceeding a threshold torque amount. For example, when there is BISG control clutch deterioration, method 500 can prevent the engine speed from exceeding a threshold speed (e.g., 7500 RPM) to reduce the likelihood of the BISG exceeding its rated BISG speed. In one example, the engine speed is limited by limiting the opening amount of the engine throttle. Additionally, the amount of fuel injected into the engine can be prevented from exceeding a threshold amount to limit the engine speed to below the threshold speed. Therefore, if the BISG control clutch cannot disengage, the BISG speed will not exceed the rated BISG speed because the engine speed is limited and the BISG is belt-connected to the engine. On the other hand, if the BISG control clutch cannot disengage, the torque requested by the BISG can be prevented from exceeding a threshold torque amount, so that the BISG does not unnecessarily accelerate and / or discharge the battery. By limiting the requested BISG torque, the actual amount of torque generated by the BISG can be limited. Method 500 proceeds to exit.

[0072] At 506, method 500 determines whether an engine start request is needed or whether the engine is off (e.g., not burning fuel and not rotating). In one example, if the engine speed is zero and fuel is not being injected into the engine (e.g., the fuel injectors are commanded to be off), then method 500 can determine that the engine is off and not burning fuel. If a person provides input to the human / machine interface, then method 500 can determine that an engine start request is needed. If method 500 determines that an engine start request is needed or that an engine stop request is needed, the answer is yes and method 500 proceeds to 530. Otherwise, the answer is no and method 500 proceeds to 508.

[0073] At 530, method 500 fully engages the BISG control clutch. The BISG control clutch engagement allows the BISG to rotate and start the engine for engine starting. After the BISG control clutch is engaged, method 500 proceeds to 516.

[0074] At point 516, method 500 maintains the current state of the BISG-controlled clutch. Therefore, if the BISG-controlled clutch is engaged, it remains engaged. If the BISG-controlled clutch is disengaged, it remains disengaged. Method 500 proceeds to disengage.

[0075] At 508, method 500 determines whether the BISG-controlled clutch is engaged. In one example, the operating state of the BISG-controlled clutch is indicated by the value of a variable in the controller's memory. For example, if the BISG-controlled clutch is fully engaged, the variable's value is 1. If the BISG-controlled clutch is disengaged, the variable's value is zero. If method 500 determines that the BISG-controlled clutch is fully engaged, the answer is yes and method 500 proceeds to 520. Otherwise, the answer is no and method 500 proceeds to 510.

[0076] At 510, method 500 determines whether the rotational speed of the BISG is less than a threshold speed (e.g., the BISG's rated or maximum rotational speed that should not be exceeded) and whether the absolute value of the requested BISG output torque or commanded BISG torque is greater than a threshold torque (e.g., the maximum torque with a zero torque value, or alternatively, another torque value less than 10 Nm). The BISG speed can be determined via a speed sensor or by multiplying the engine speed by the pulley ratio between the engine and the BISG. Method 500 checks the relationship between the current BISG speed and the threshold speed to ensure that the BISG speed does not exceed the BISG's rated speed before engaging or disengaging the BISG control clutch, thus avoiding BISG overspeed. Furthermore, method 500 checks whether the requested or commanded BISG torque is greater than the threshold torque by a certain amount to ensure that the BISG control clutch remains open unless the desired BISG torque (positive or negative) is expected. If method 500 determines that the BISG's rotational speed is less than the threshold speed and if the absolute value of the requested BISG output torque is greater than the threshold torque, the answer is yes and method 500 proceeds to 512. Otherwise, the answer is no and method 500 proceeds to 516.

[0077] At 512, method 500 adjusts the rotational speed of the BISG shaft to the rotational speed of the BISG pulley (e.g., engine speed multiplied by the pulley ratio between the engine crankshaft and the BISG shaft). Method 500 can operate the BISG in motor mode to match the BISG shaft speed with the BISG pulley speed. The BISG speed can be increased by increasing the amount of current flowing to the BISG. The BISG speed can be decreased by decreasing the amount of current flowing to the BISG. By adjusting the BISG shaft speed to the BISG pulley speed, the BISG control clutch can be closed without causing large torque disturbances to the engine and / or drivetrain. Method 500 proceeds to 514.

[0078] At 514, method 500 fully engages the BISG control clutch. The BISG control clutch can be commanded to engage electrically or hydraulically. By fully engaging the BISG control clutch, torque can be transferred from the engine to the BISG, and vice versa. Method 500 proceeds to 516.

[0079] At 520, method 500 determines whether the rotational speed of the BISG is within a predetermined speed of the threshold rotational speed. Furthermore, method 500 determines whether the requested output torque of the BISG is within a predetermined torque of the threshold torque. If either condition is true, the answer is yes and method 500 proceeds to 522. Otherwise, the answer is no and method 500 proceeds to 516.

[0080] At 522, method 500 reduces the absolute value of the BISG's output torque. Reducing the absolute value of the BISG's output torque prevents large changes in drivetrain torque when the BISG-controlled clutch disengages. In this way, drivetrain torque disturbances are reduced. Method 500 proceeds to 524.

[0081] At 524, method 500 determines whether the rotational speed of the BISG is greater than a threshold. In one example, the threshold speed is the rated speed of the BISG (e.g., the speed of the BISG that should not be exceeded (20,000 RPM)). Furthermore, method 500 determines whether the absolute value of the requested output torque or the commanded output torque of the BISG exceeds a threshold (e.g., zero, or alternatively, less than 10 N-meters of torque). The BISG speed can be determined via a speed sensor, and the requested BISG output torque can be determined based on a value stored in the controller's volatile memory. If method 500 determines that the rotational speed of the BISG is greater than the threshold or the absolute value of the requested BISG output torque is greater than the threshold torque amount, the answer is yes and method 500 proceeds to 526. Otherwise, the answer is no and method 500 proceeds to 516.

[0082] At 526, Method 500 fully engages the BISG control clutch. The BISG control clutch can be fully engaged electrically or hydraulically via a controller. Engaging the BISG control clutch allows the engine speed to increase without exceeding the BISG's rated speed. Furthermore, when the BISG output torque is low, engaging the BISG control clutch can reduce BISG bearing degradation and lower engine inertia to save fuel. Method 500 proceeds to 516.

[0083] In this way, the BISG control clutch can be selectively opened and closed to improve drivetrain performance and efficiency. Furthermore, it can reduce the likelihood of BISG degradation.

[0084] therefore, Figure 5A method provides a powertrain operation method comprising: determining, via a controller, that the torque of a belt-driven starter / generator (BISG) is not zero and the BISG speed is less than a threshold speed; in response to the BISG torque being not zero and the BISG speed being less than the threshold speed, engaging a BISG control clutch via the controller; determining, via the controller, that the BISG torque is zero; determining, via the controller, that the BISG speed is greater than the threshold speed; and engaging the BISG control clutch via the controller in response to the BISG torque being zero or the BISG speed being greater than the threshold speed. The method includes the BISG control clutch being located between an engine crankshaft and an engine pulley. The method includes the BISG control clutch being located between a BISG shaft and a BISG pulley. The method further includes determining that the BISG speed is greater than the threshold speed by multiplying the engine speed by the pulley ratio. The method further includes engaging the BISG control clutch during engine starting. The method includes the BISG torque being zero when there is no request for battery charging via the BISG and when no propulsion torque is provided via the BISG. The method includes the BISG torque being non-zero when the BISG is charging the battery or when the BISG is providing propulsion torque. The method also includes charging the battery via the BISG when the torque of the BISG is not zero.

[0085] Figure 5 The method also provides a powertrain operation method, comprising: determining via a controller that the torque of a belt-driven starter / generator (BISG) is not zero and the BISG speed is less than a threshold speed; in response to the BISG torque being not zero and the BISG speed being less than the threshold speed, closing the BISG control clutch via the controller; determining via the controller that the BISG torque is zero; determining via the controller that the BISG speed is greater than the threshold speed; in response to the BISG torque being zero or the BISG speed being greater than the threshold speed, opening the BISG control clutch via the controller; determining via the controller that the BISG control clutch is deteriorating; and in response to the deterioration of the BISG control clutch, preventing the engine speed from exceeding the threshold speed via the controller. The method includes wherein preventing the engine speed from exceeding the threshold speed includes adjusting engine airflow via a throttle valve. The method includes wherein preventing the engine speed from exceeding the threshold speed includes adjusting engine fuel flow via a fuel injector. The method further includes starting the engine via the BISG when the BISG control clutch is not deteriorated. The method further includes starting the engine via a starter motor other than the BISG when the BISG control clutch is deteriorated. The method further includes reducing the output torque of the BISG in response to the BISG speed being within a predetermined speed of the threshold speed.

[0086] It should be noted that the example control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein can be stored as executable instructions in non-transitory memory and can be executed by a control system including controllers in conjunction with various sensors, actuators, and other engine hardware. The specific routines described herein can represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreaded, etc. Thus, the various actions, operations, and / or functions shown can be executed in the order shown, in parallel, or in some cases omitted. Similarly, the processing order is not necessarily necessary to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the shown actions, operations, and / or functions can be repeatedly executed according to the specific strategy used. Furthermore, at least a portion of the described actions, operations, and / or functions can be graphically represented as code to be programmed into the non-transitory memory of a computer-readable storage medium in the control system. When the described actions are executed by executing instructions in conjunction with one or more controllers in a system including various engine hardware components, the control actions can also change the operating state of one or more sensors or actuators in the physical world.

[0087] This concludes the instruction manual. Those skilled in the art will conceive of many changes and modifications upon reading this manual without departing from its spirit and scope. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating with natural gas, gasoline, diesel, or alternative fuels can benefit from this manual.

[0088] According to the present invention, a method of operating a power transmission system includes: closing the belt drive starter / generator (BISG) control clutch via a controller in response to the BISG torque being non-zero and the BISG speed being less than a threshold speed; and opening the BISG control clutch via a controller in response to the BISG torque being zero or the BISG speed being greater than the threshold speed.

[0089] According to one embodiment, the BISG control clutch is located between the engine crankshaft and the engine pulley.

[0090] According to one embodiment, the BISG control clutch is located between the BISG shaft and the BISG pulley.

[0091] According to one embodiment, the invention is further characterized in that the BISG speed is determined to be greater than the threshold speed by multiplying the engine speed by the pulley ratio.

[0092] According to one embodiment, the invention is further characterized in that the BISG control clutch is closed during engine starting.

[0093] According to one embodiment, the torque of the BISG is zero when there is no request for battery charging via the BISG and when no propulsion torque is provided via the BISG.

[0094] According to one embodiment, the torque of the BISG is not zero when the BISG is charging the battery or when the BISG provides propulsion torque.

[0095] According to one embodiment, the invention is further characterized in that the battery is charged via the BISG when the torque of the BISG is not zero.

[0096] According to the present invention, a power transmission system operation method includes: in response to the BISG torque being non-zero and the BISG speed being less than a threshold speed, closing the belt-driven starter / generator (BISG) control clutch via a controller; in response to the BISG torque being zero or the BISG speed being greater than the threshold speed, opening the BISG control clutch via a controller; and in response to the deterioration of the BISG control clutch, preventing the engine speed from exceeding the threshold speed via a controller.

[0097] According to one embodiment, preventing the engine speed from exceeding a threshold speed includes adjusting the engine airflow via the throttle valve.

[0098] According to one embodiment, preventing the engine speed from exceeding a threshold speed includes adjusting the engine fuel flow via a fuel injector.

[0099] According to one embodiment, the invention is further characterized in that the engine is started by rotating the BISG when the BISG control clutch is not deteriorated.

[0100] According to one embodiment, the invention is further characterized in that when the BISG control clutch deteriorates, the engine is started by rotating a starter motor other than the BISG.

[0101] According to one embodiment, the invention is further characterized in that, in response to the rotational speed of the BISG being within a predetermined speed of a threshold rotational speed, the output torque of the BISG is reduced.

[0102] According to the present invention, a system is provided comprising: an engine; a transmission starter / generator (ISG) connected to the engine via a belt; a clutch configured to selectively connect the shaft of the ISG to the shaft of the engine; and a controller including executable instructions stored in a non-transitory memory to perform the following operation: closing the clutch via the controller in response to the output torque of the ISG being non-zero and the rotational speed of the ISG being less than a threshold rotational speed.

[0103] According to one embodiment, the invention is further characterized by an additional command from the controller to open the clutch in response to the ISG output torque being equal to zero or the ISG speed being greater than a threshold speed.

[0104] According to one embodiment, the invention is further characterized by an additional command to reduce the output torque of the ISG in response to the ISG's rotational speed being within a predetermined speed of a threshold speed when the clutch is engaged.

[0105] According to one embodiment, the invention is further characterized by an additional instruction to adjust the speed of the ISG to the engine speed multiplied by the pulley ratio before engaging the clutch.

[0106] According to one embodiment, the invention is further characterized by an additional command to limit the engine speed to less than the BISG rated speed in response to clutch deterioration.

[0107] According to one embodiment, the invention is further characterized by a starter motor and an additional command for starting the engine via the starter motor during engine starting in response to clutch deterioration.

Claims

1. A method for operating a power transmission system, comprising: In response to the fact that the torque of the belt drive starter / generator is not equal to zero and the speed of the belt drive starter / generator is less than the threshold speed, the belt drive starter / generator control clutch is closed via the controller; as well as In response to the torque of the belt-driven starter / generator being equal to zero or the speed of the belt-driven starter / generator being greater than the threshold speed, the belt-driven starter / generator control clutch is opened via the controller.

2. The method of claim 1, wherein the belt-driven starter / generator control clutch is located between the engine crankshaft and the engine pulley.

3. The method of claim 1, wherein the belt-driven starter / generator control clutch is located between the belt-driven starter / generator shaft and the belt-driven starter / generator pulley.

4. The method of claim 1, further comprising determining that the belt-driven starter / generator speed is greater than the threshold speed by multiplying the engine speed by the pulley ratio.

5. The method of claim 1, further comprising closing the belt-driven starter / generator control clutch during engine startup.

6. The method of claim 1, wherein the torque of the belt-driven starter / generator is zero when there is no request for battery charging via the belt-driven starter / generator and when no propulsion torque is provided via the belt-driven starter / generator.

7. The method of claim 1, wherein the torque of the belt-driven starter / generator is not zero when the belt-driven starter / generator is charging the battery or when the belt-driven starter / generator provides propulsion torque.

8. The method of claim 1, further comprising charging the battery via the belt-driven starter / generator when the torque of the belt-driven starter / generator is not zero.

9. The method of claim 1, further comprising: In response to the deterioration of the belt-driven starter / generator control clutch, the controller prevents the engine speed from exceeding the threshold speed.

10. A system for starting an engine, comprising: engine; A belt-driven starter / generator is connected to the engine via a belt; A clutch configured to selectively connect the shaft of the belt-driven starter / generator to the shaft of the engine; and The controller includes executable instructions stored in a non-transitory memory to perform the following operation: closing the clutch via the controller in response to the output torque of the belt-driven starter / generator being non-zero and the rotational speed of the belt-driven starter / generator being less than a threshold speed.

11. The system of claim 10, further comprising an additional command via the controller to open the clutch in response to the output torque of the belt-driven starter / generator being equal to zero or the speed of the belt-driven starter / generator being greater than the threshold speed.

12. The system of claim 10, further comprising an additional command to reduce the output torque of the belt-driven starter / generator in response to the rotational speed of the belt-driven starter / generator being within a predetermined speed of the threshold speed when the clutch is engaged.

13. The system of claim 10, further comprising an additional instruction to adjust the speed of the belt-driven starter / generator to the speed of the engine multiplied by the pulley ratio before disengaging the clutch.

14. The system of claim 10, further comprising an additional command to limit the engine speed to less than the rated speed of the belt-driven starter / generator in response to deterioration of the clutch.

15. The system of claim 10, further comprising a starter and additional instructions for starting the engine via the starter during engine starting in response to deterioration of the clutch.

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