Method and system for starting an engine of a hybrid vehicle

Abstract

Methods and systems for starting an engine of a hybrid vehicle are provided. Systems and methods for operating an internal combustion engine coupled to a power split transmission are described. In one example, the internal combustion engine is started via generator rotation, and a torque output of the generator is adjusted to reduce noise that may be generated by completing gear clearance crossing.

Description

Technical Field

[0001] The present description relates to methods and systems for starting an engine of a hybrid vehicle. Background Art

[0002] A hybrid vehicle may include two or more propulsion sources. The propulsion sources may consist of an internal combustion engine, a first electric machine (e.g., a generator), and a second electric machine (e.g., a motor). During low torque demand conditions, the motor may be used as the sole propulsion source. In addition, the motor may assist the internal combustion engine during high torque demand conditions. During operating conditions where driver demand changes from a lower value to a higher value, the generator may assist in starting the internal combustion engine while the motor propels the vehicle. However, using the generator to start the engine may increase driveline noise. Therefore, it may be desirable to provide a method for starting the internal combustion engine of a hybrid vehicle in a manner that reduces the potential for driveline noise.

[0003] The above summary is provided to introduce a series of concepts further described in the detailed description in a simplified form. It is not meant to identify 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 disadvantages mentioned above or in any part of this disclosure. Summary of the invention

[0004] According to the present invention, a method for starting an engine includes: via a controller, rotating the engine to a speed greater than a threshold speed by transferring torque from a first motor to the engine through a planetary gear carrier gear set and a sun gear; and reducing the torque output of the first motor at a certain rate in response to the engine speed being greater than the threshold speed; and stopping reducing the torque output of the first motor at the rate in response to transferring torque from the engine through the sun gear to the first motor and to the planetary gear carrier gear set.

[0005] In one aspect of the present invention, the method includes combusting fuel in the engine while rotating the engine via the first electric machine.

[0006] In one aspect of the present invention, combusting fuel in the engine includes operating the engine with a spark timing retarded from a minimum spark advance for maximum torque generated at a particular engine speed and load.

[0007] In one aspect of the present invention, combusting fuel in the engine includes fully closing a throttle of the engine.

[0008] In one aspect of the present invention, reducing the torque output of the first electric machine includes adjusting the torque output of the first electric machine from a positive torque to a negative torque.

[0009] In one aspect of the present invention, the method includes charging a battery via the first electric machine in response to transferring torque from the engine to the first electric machine.

[0010] In one aspect of the present invention, the method includes advancing spark timing in response to transferring torque from the engine to the first electric machine.

[0011] According to the present invention, a system is provided, which has: an internal combustion engine; a power-split transmission connected to the internal combustion engine, the power-split transmission including two motors, a sun gear, a planetary gear carrier gear set and a ring gear; and a controller, the controller including: executable instructions stored in a non-volatile memory, the executable instructions causing the controller to rotate the internal combustion engine via a first motor of the two motors to start the internal combustion engine, and additional executable instructions to reduce the torque output of the first motor at a certain rate in response to the speed of the internal combustion engine exceeding a threshold speed; and additional instructions for further adjusting the torque output of the first motor in response to the clearance crossing between the sun gear and the planetary gear carrier gear set during engine starting.

[0012] According to an embodiment, the invention is also characterized by an additional instruction causing the controller to initiate combustion in the internal combustion engine.

[0013] According to an embodiment, the invention is also characterized by additional instructions that cause the controller to retard the ignition timing of the internal combustion engine during starting of the internal combustion engine and operate the internal combustion engine with the throttle of the internal combustion engine fully closed.

[0014] According to an embodiment, the invention also features additional instructions for adjusting control parameters of the proportional-integral-derivative controller to a first set of values ​​during engine starting.

[0015] According to an embodiment, the invention also features additional instructions for adjusting control parameters of the proportional-integral-derivative controller to a second set of values ​​in response to the speed of the internal combustion engine exceeding a threshold speed.

[0016] According to an embodiment, the invention further features additional instructions for adjusting control parameters of a proportional-integral-derivative controller to a third set of values ​​in response to backlash crossing between the sun gear and the planet carrier gear set.

[0017] According to an embodiment, the proportional-integral-derivative controller regulates the torque output of the first electric machine.

[0018] According to an embodiment, the invention also features additional instructions for propelling the vehicle via the second of the two electric machines.

[0019] According to the present invention, a method for operating an engine includes: rotating the engine by adjusting the torque of an electric motor based on the output of a proportional integral derivative (PID) controller operating with a first set of control parameters, via a controller, in response to an engine start request; adjusting the torque of the electric motor based on the output of the PID controller operating with a second set of control parameters, in response to the engine speed exceeding a threshold speed; and adjusting the torque of the electric motor based on the output of the PID controller operating with a third set of control parameters, in response to gear clearance crossing having occurred.

[0020] In one aspect of the invention, said second set of control parameters operates to reduce the rate of change of torque of said electric machine.

[0021] In one aspect of the invention, the method includes combusting fuel in the engine and operating the engine with a spark timing retarded from a minimum spark advance for maximum torque generated at a particular engine speed and load.

[0022] In one aspect of the invention, the gear backlash crossing is the first gear backlash crossing since the last engine stop.

[0023] In one aspect of the invention, the method includes operating the engine with the throttle fully closed before the gear lash cross-over occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Advantages described herein will be more fully understood by reading examples of embodiments referred to herein as detailed descriptions when read alone or with reference to the accompanying drawings, in which:

[0025] Figure 1 It is a schematic diagram of the engine;

[0026] Figure 2 is a schematic diagram of a hybrid vehicle powertrain;

[0027] Figure 3 Shown according to Figure 4 A graph of an example engine starting sequence of a method of;

[0028] Figure 4 A flow chart illustrating an example method for starting an engine of a hybrid vehicle;

[0029] Figure 5 shows a block diagram of an example PID controller for a generator;

[0030] Figure 6 Gear backlash is shown; and

[0031] Figure 7 The transmission torque transfer and transmission twist angle in the case of gap crossing are shown. DETAILED DESCRIPTION

[0032] This specification relates to starting a hybrid vehicle. A hybrid vehicle may include Figure 1 The internal combustion engine may be included in a drive train including a Figure 2 The power split transmission shown in FIG. The power split transmission may include a motor and a generator. The transmission system may be as follows Figure 3 To reduce powertrain noise during engine starting, follow the instructions in Figure 4 The method shown in FIG. 1 is used to start the engine. Figure 5 A proportional / integral / derivative (PID) controller is shown in Figure 2 to adjust the generator torque. Figure 6 and Figure 7 The gear backlash of a gear set and its effect on the torque transfer through the gear set is shown.

[0033] A hybrid vehicle may include a power split transmission. The power split transmission may be comprised of gears including a planetary gear set. The power split transmission may also be configured such that a power source (e.g., an internal combustion engine and an electric motor) coupled to the power split transmission is continuously coupled to gears within the power split transmission. To reduce the likelihood of gear locking, clearance space may be provided between the gears. However, if torque is delivered to the engine via the gears to initiate the engine starting process and the engine subsequently begins delivering torque to the gears, the gear teeth may generate noise when the direction of torque delivery changes. Therefore, it may be desirable to provide a method for starting an engine of a hybrid vehicle that may reduce the likelihood of gear noise during engine starting.

[0034] The inventors of this article have recognized the above-mentioned problems and have developed a method for starting an engine, which includes: rotating the engine to a speed greater than a threshold speed via a controller by transferring torque from a first motor to the engine through a planetary gear carrier gear set and a sun gear; and reducing the torque output of the first motor at a certain rate in response to the engine speed being greater than the threshold speed; and stopping reducing the torque output of the first motor at the rate in response to transferring torque from the engine through the sun gear to the first motor and to the planetary gear carrier gear set.

[0035] By reducing the torque of the motor that rotates the engine through the planetary gear set during engine cranking in response to the engine speed exceeding a threshold speed, the possibility of generating noise when gear backlash crossing occurs during engine starting can be reduced. Specifically, the torque generated by the motor for cranking the engine can allow the engine speed to meet a specific speed (e.g., warm engine idle or cold engine idle) for a short period of time. Once the specific speed is reached, the torque output by the motor can be reduced at a certain rate, which can slow down the relative speed difference between the two gear sets during the time period when the engine torque output can increase. The lower speed difference between the gears can reduce the noise that may be generated when the speed of the gear coupled to the engine increases above the speed of the gear mechanically coupled to the motor.

[0036] The present description may provide several advantages. Specifically, the method may reduce driveline noise during engine starting. Additionally, the method may provide greater vehicle starting repeatability. Additionally, the method may reduce driveline wear.

[0037] The above advantages and other advantages and features of the present specification will be readily apparent from the following detailed description when taken alone or in conjunction with the accompanying drawings.

[0038] refer to Figure 1 Internal combustion engine 10 (also referred to as “engine”), comprising a plurality of cylinders, is controlled by electronic engine controller 12 . Figure 1 One of the cylinders is shown in FIG. 1 . The controller 12 receives Figure 1 and Figure 2 The controller 12 also uses various inputs (e.g., sensors) to receive signals. Figure 1 and Figure 2 The actuators shown regulate engine and powertrain operation based on received signals and instructions stored in the memory of controller 12 .

[0039] Engine 10 is comprised of cylinder head 35 and cylinder block 33, which includes combustion chamber 30 and cylinder wall 32 in cylinder 31. Piston 36 is positioned therein and reciprocates via connection with crankshaft 40. Combustion chamber 30 is shown communicating with intake manifold 44 and exhaust manifold 48 via respective intake valve 52 and exhaust valve 54. Each intake valve and exhaust valve may be operated by intake cam 51 and exhaust cam 53. The position of intake cam 51 may be determined by intake cam sensor 55. The position of exhaust cam 53 may be determined by exhaust cam sensor 57. Intake valve 52 may be selectively activated and deactivated by valve activation device 59. Exhaust valve 54 may be selectively activated and deactivated by valve activation device 58. Valve activation devices 58 and 59 may be electromechanical devices.

[0040] Direct fuel injector 66 is shown positioned to inject fuel directly into combustion chamber 30, which is known to those skilled in the art as direct injection. Port fuel injector 67 is shown positioned to inject fuel into an intake port of combustion chamber 30, which is known to those skilled in the art as port injection. Direct fuel injector 66 and port fuel injector 67 deliver liquid fuel in proportion to a pulse width provided by controller 12. Fuel is delivered to direct fuel injector 66 and port fuel injector 67 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail (not shown).

[0041] In addition, the intake manifold 44 is shown to be in communication with the turbocharger compressor 162 and the engine air intake 42. In other examples, the turbocharger compressor 162 can be a supercharger compressor. The shaft 161 mechanically couples the turbocharger turbine 164 to the turbocharger compressor 162. The optional electronic throttle 62 (also referred to as a "throttle") adjusts the position of the throttle plate 64 to control the airflow from the turbocharger compressor 162 to the intake manifold 44. Since the inlet of the throttle 62 is in the boost chamber 45, the pressure in the boost chamber 45 can be referred to as the throttle inlet pressure. The throttle outlet is in the intake manifold 44. In some examples, the throttle 62 and the throttle plate 64 can be positioned between the intake valve 52 and the intake manifold 44, so that the throttle 62 is an intake port throttle. The compressor recirculation valve 47 can be selectively adjusted to a plurality of positions between fully open and fully closed. Wastegate 163 may be adjusted via controller 12 to allow exhaust to selectively bypass turbine 164, thereby controlling the speed of turbocharger compressor 162. Air filter 43 cleans air entering engine air intake 42.

[0042] Distributorless ignition system 88 provides spark ignition to combustion chamber 30 via spark plug 92 in response to controller 12. Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled to exhaust manifold 48 upstream of catalyst 70. Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor 126.

[0043] Exhaust gas may be processed via catalyst 70. In one example, catalyst 70 may include multiple bricks and a three-way catalyst washcoat. In another example, multiple emission control devices, each having multiple bricks, may be used.

[0044] The controller 12 Figure 11 is shown as a conventional microcomputer including: a microprocessor unit 102, input / output ports 104, read-only memory 106 (eg, non-transitory memory), random access memory 108, keep alive memory 110, and a conventional data bus. Controller 12 is shown receiving various signals from sensors coupled to engine 10 in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor 112 coupled to cooling sleeve 114; position sensor 134 coupled to driver demand pedal 130 (e.g., human / machine interface) for sensing force applied by human vehicle driver 132; position sensor 154 coupled to brake pedal 150 (e.g., human / machine interface) for sensing force applied by human vehicle driver 132; measurement of engine manifold pressure (MAP) from pressure sensor 122 coupled to intake manifold 44; engine position sensor from engine position sensor 118 sensing position of crankshaft 40; measurement of air mass entering the engine from sensor 120; and measurement of throttle position from sensor 68. Barometric pressure may also be sensed (sensor not shown) for processing by controller 12. In a preferred aspect of the present description, engine position sensor 118 produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined.

[0045] The controller 12 may also receive input from a human / machine interface 11. A request to start an engine or vehicle may be generated by a human and input to the human / machine interface 11. The human / machine interface 11 may be a touch screen display, buttons, key switches, or other known devices.

[0046] During operation, each cylinder within 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, exhaust valve 54 is closed and intake valve 52 is opened. Air is introduced into combustion chamber 30 via intake manifold 44, and piston 36 moves to the bottom of the cylinder so as to increase the volume within combustion chamber 30. The position where piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when combustion chamber 30 is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC).

[0047] During the compression stroke, intake valve 52 and exhaust valve 54 are closed. Piston 36 moves toward the cylinder head so as 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 smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means, such as glow plug 92, resulting in combustion.

[0048] During the expansion stroke, the expanding gases push piston 36 back to BDC. Crankshaft 40 converts piston movement into rotational power of the rotating shaft. Finally, during the exhaust stroke, exhaust valve 54 opens to release the combusted air-fuel mixture to exhaust manifold 48, and the piston returns to TDC. It should be noted that the above is shown only as an example, and the intake and exhaust valve opening and / or closing timings may be varied, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0049] Reference now Figure 2 , an example of a transmission 200 is shown. The transmission 200 includes an engine 10 and a torque actuator 218. The torque actuator 218 may be a throttle, a fuel injector, a camshaft actuator, an ignition system, or other actuator that can adjust the engine torque. The engine 10 delivers power to a transmission 244 via a crankshaft 40. In the depicted example, the transmission 244 is a power split transmission (or a transaxle) that includes a planetary gear set 202 that includes one or more rotating gear elements. The transmission 244 also includes a generator 204 and an electric motor 206. The generator 204 and the electric motor 206 may also be referred to as motors because they may each operate as a motor or a generator. Torque may be output from the transmission 244 to propel the vehicle 250 using the traction wheel 216 via a power transfer gear 210, a torque output shaft 219, and a differential and axle assembly 266. Braking torque may be provided via friction or a main brake 217.

[0050] Generator 204 and electric motor 206 are electrically coupled to electrical energy storage device 275 so that each of generator 204 and electric motor 206 can be operated using electrical energy from electrical energy storage device 275 (e.g., a high voltage battery). In some examples, an energy conversion device such as inverter 271 can be coupled between the battery and the motor to convert the DC output of the battery to an AC output for use by electric motor 206. Due to the mechanical characteristics of planetary gear set 202, generator 204 can be driven by the power output element (on the output side) of planetary gear set 202 via mechanical connection 222.

[0051] Electric motor 206 may be operated in a regenerative mode, i.e., as a generator, to absorb kinetic energy from the vehicle and / or the engine and convert the absorbed kinetic energy into an energy form suitable for storage in electrical energy storage device 275. Additionally, electric motor 206 may be operated as a motor or generator as needed to augment or absorb torque provided by engine 10, such as during transitions between different operating modes of engine 10.

[0052] Planetary gear set 202 includes ring gear 242, sun gear 243 and planetary gear carrier gear set 246. The planetary gears included in planetary gear carrier gear set 246 can be directly connected to sun gear 243 and ring gear 242. The ring gear and the sun gear can be coupled to each other via planetary gear carrier gear set 246. Crankshaft 40 of engine 10 is mechanically coupled to planetary gear carrier gear set 246, and sun gear 243 is mechanically coupled to generator 204. Ring gear 242 is mechanically coupled to power transmission device 210 including one or more meshing gear elements 260. Electric motor 206 drives gear element 270 and generator 204 is coupled to sun gear 243. In this way, planetary gear carrier gear set 246 (and therefore the engine and generator) can be coupled to the wheels of the vehicle and electric motor 206 via one or more gear elements.

[0053] The hybrid propulsion system or driveline 200 can be operated in various modes, including a full hybrid mode, in which the vehicle is driven solely by the engine 10 and the generator 204, or solely by the electric motor 206, or a combination thereof. Alternatively, an auxiliary or mild hybrid example can also be employed in which the engine 10 is the primary power source and the electric motor 206 selectively increases torque during certain conditions, such as during a driver demand tip-in event (e.g., application of a driver demand pedal).

[0054] The vehicle can be driven in a first engine start mode, which can be referred to as an "engine" mode, in which the engine 10 operates with the generator 204 (which provides a counter torque to the planetary gear set and allows a net planetary output torque for propulsion of the vehicle) and is used as the dominant power source and torque for powering the traction wheel 216. In this mode, the generator 204 can generate electricity, and the generated electricity can also be applied by the drive motor 206 to propel the vehicle. This can result in no net power being delivered from the engine power to the energy storage device 275 or the high-voltage accessories. If the drive motor 206 does not use the generator power, this generator power will have to be used by the high-voltage accessories or to charge the high-voltage battery. All power generated by the engine is consumed in the power split system. During the "engine" mode, fuel can be provided from the fuel tank to the engine 10 via the direct fuel injector 66, so that the engine can be rotated and fueled to provide torque for propulsion of the vehicle. Specifically, the engine power is delivered to the ring gear 242 of the planetary gear set 202, thereby delivering power to the traction wheel 216. Alternatively, the engine may be operated to output more torque than required for propulsion, in which case additional power may be absorbed by generator 204 (in a generating mode) to charge electrical energy storage device 275 or to provide electrical power to other vehicle electrical loads.

[0055] In another example, the hybrid propulsion system can be driven in a second engine starting mode, which can be referred to as an "assist" mode. During the assist mode, the engine 10 is operated and used as the dominant torque source for powering the traction wheels 216, and the electric motor 206 is used as an additional torque source for cooperating with the engine 10 and supplementing the torque provided by the engine. During the "assist" mode, as in the engine-only mode, fuel is supplied to the engine 10 so that the engine is rotationally fueled and torque is provided to the vehicle wheels.

[0056] In yet another example, the hybrid propulsion system or driveline 200 may be driven in an engine off mode, which may be referred to as an electric-only mode, in which the battery-powered electric motor 206 is operated and used as the sole source of power for driving the traction wheels 216. To this end, during the engine off mode, no fuel may be injected into the engine 10, regardless of whether the engine is rotating. For example, during braking, when no load is requesting engine power, or when propulsion is not required, such as when the vehicle is stopped at a traffic light, etc., the "engine off" mode may be employed. Specifically, the motor power is delivered to the gear element 270, which in turn drives the meshing gear element 260, thereby driving the traction wheels 216. The generator 204 rotates so that all rotations of the gears 242 are balanced and the ring gear 242 has a net zero speed, thereby allowing the engine not to rotate.

[0057] During the engine off mode, based on vehicle speed and driver demand torque, the vehicle can be operated in a first electric-only mode, where the vehicle is propelled by the electrical energy storage device 275 via the electric motor 206, while the engine is not rotating and not fueled, or the vehicle can be operated in a second electric-only mode, where the vehicle is propelled by the electrical energy storage device 275 via the electric motor 206, while the engine is rotating without fueling. During the second electric-only mode, the generator 204 applies torque to the planetary gear set 202 through the sun gear 243. The planetary gear carrier gear set 246 provides a counter torque to the generator torque, and thus directs the torque to the engine 10 to rotate the engine 10. In this example, the motor 206 is supplied with the counter torque provided by the planetary gear carrier gear set 246 (or alternatively, the vehicle momentum when the vehicle speed is reduced), and thus the torque from the motor to the wheels is reduced.

[0058] The shifter 290 may receive input from the human vehicle driver 132 to select an operating mode of the transmission 244. The shifter 290 may be placed in one of a plurality of positions or states as indicated by the PRNDL. When the shifter 290 is moved to the "P" position, the driver may request the transmission 244 to be in park. When the shifter 290 is in the "R" position, the driver may request the transmission 244 to be in reverse. When the shifter 290 is in the "N" position, the driver may request the transmission 244 to be in neutral. When the shifter 290 is in the "D" position, the driver may request the transmission 244 to be in drive. When the shifter 290 is in the "L" position, the driver may request the transmission 244 to be in low gear. Note that the low selection in the power split system is not a gear selection. Instead, it reduces the vehicle speed by generating more regenerative braking torque and / or turning the unfueled engine to generate torque on the wheels, thereby simulating engine braking when the driving demand pedal is fully released. The position of the shifter 290 may be determined via a shifter position sensor 291 .

[0059] therefore, Figure 1 and Figure 2A system is provided, comprising: an internal combustion engine; a power split transmission coupled to the internal combustion engine, the power split transmission comprising two electric machines, a sun gear, a planetary gear carrier gear set and a ring gear; and a controller, the controller comprising: executable instructions stored in a non-transitory memory, the executable instructions causing the controller to rotate the internal combustion engine via a first electric machine of the two electric machines to start the internal combustion engine, and additional executable instructions to reduce the torque output of the first electric machine at a certain rate in response to the rotation speed of the internal combustion engine exceeding a threshold speed; and additional instructions for further adjusting the torque output of the first electric machine in response to the clearance crossing between the sun gear and the planetary gear carrier gear set during engine starting. In a first example, the system also includes additional instructions causing the controller to initiate combustion in the internal combustion engine. In a second example that may include the first example, the system also includes additional instructions causing the controller to retard the ignition timing of the internal combustion engine during starting of the internal combustion engine and operate the internal combustion engine with the throttle of the internal combustion engine fully closed. In a third example, which may include one or both of the first and second examples, the system further includes additional instructions for adjusting the control parameters of the proportional-integral-derivative controller to a first set of values ​​during engine starting. In a fourth example, which may include one or more of the first to third examples, the system further includes additional instructions for adjusting the control parameters of the proportional-integral-derivative controller to a second set of values ​​in response to the speed of the internal combustion engine exceeding a threshold speed. In a fifth example, which may include one or more of the first to fourth examples, the system further includes additional instructions for adjusting the control parameters of the proportional-integral-derivative controller to a third set of values ​​in response to the clearance crossing between the sun gear and the planetary gear set. In a sixth example, which may include one or more of the first to fourth examples, the system includes: wherein the proportional-integral-derivative controller adjusts the torque output of the first motor. In a seventh example, which may include one or more of the first to sixth examples, the system further includes additional instructions for propelling the vehicle via the second motor of the two motors.

[0060] Reference now Figure 3 , shows an example graph predicting an engine start sequence. The engine start sequence may be initiated via Figure 1 and Figure 2 system and Figure 4 The vertical line from time t0 to t3 represents the relevant time during the sequence. Figure 3 The graphs in are time aligned and occur simultaneously.

[0061] from Figure 3 The first graph from the top of is a graph of engine speed versus time. The vertical axis represents engine speed, and engine speed increases in the direction of the vertical axis arrow. Dashed trace 302 represents the target or requested engine speed. Dashed dotted trace 303 represents the filtered target or requested engine speed. The filtered target engine speed is the target engine speed value that has passed through a low pass filter. Solid trace 304 represents the measured or actual engine speed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph.

[0062] from Figure 3 The second graph from the top of is a graph of generator torque versus time. The vertical axis represents generator torque, and when trace 306 is above the horizontal axis, the generator torque is positive (e.g., delivering torque to rotate a gear in a planetary gear carrier gear set). When trace 306 is below the horizontal axis, the generator torque is negative (e.g., absorbing torque from the planetary gear carrier gear set to charge the traction battery). The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph. Trace 306 represents the generator torque.

[0063] from Figure 3 The third graph from the top of FIG. 3 is a graph of engine intake manifold pressure versus time. The vertical axis represents engine intake manifold pressure, and engine intake manifold pressure increases in the direction of the vertical axis arrow. Trace 308 represents engine intake manifold pressure. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph.

[0064] from Figure 3 The fourth graph from the top is a graph of engine ignition timing versus time. The vertical axis represents engine ignition timing, and when trace 310 is above the horizontal axis, the engine ignition timing is advanced from the minimum ignition advance for the maximum torque generated at a specific engine speed and load (e.g., MBT ignition timing). When trace 310 is below the horizontal axis, the engine ignition timing is retarded from the MBT ignition timing. Trace 310 represents engine ignition timing. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph.

[0065] from Figure 3 The fifth graph from the top is a graph of the rate of change of generator speed versus time. The vertical axis represents the rate of change of generator speed, and the rate of change of generator speed increases in the direction of the vertical axis arrow. Trace 312 represents the rate of change of generator speed. The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph.

[0066] from Figure 3The sixth graph from the top is a graph of the PID contribution to the PID controller versus time. The vertical axis represents the PID contribution value. Trace 314 represents the proportional contribution to the PID controller output (e.g., K p ·e(t)). Trace 316 represents the integral contribution to the PID controller output (eg, K i ·∫e(t)dt). Trace 318 represents the derivative contribution to the PID controller output (e.g., K d ·de(t) / dt). The horizontal axis represents time, and time increases from the left side of the graph to the right side of the graph.

[0067] At time t0, the engine is off (eg, not spinning and not burning fuel) and the engine torque is zero. The intake manifold pressure is increased and the ignition timing is set to a retarded value. The generator speed change rate is zero and the PID contribution to the PID controller output is zero.

[0068] At time t1, an engine start is requested (not shown), so the target engine speed increases. As the torque of the generator increases, the filtered target engine speed begins to increase, and the actual or measured engine speed begins to increase. The generator begins to rotate the engine shortly after time t1. The PID controller is loaded with a first set of PID control parameters (e.g., K p1 , K i1 and K d1 )(not shown) to control the generator torque during engine acceleration. The derivative contribution to the PID controller output moves from a zero value to a positive value.

[0069] Between time t1 and time t2, the engine speed increases and the generator torque increases, and then begins to decrease. The intake manifold pressure remains high and the ignition timing is unchanged. The generator speed change rate increases, and then decreases.

[0070] At time t2, the actual engine speed or measured engine speed exceeds the filtered target engine speed, so the PID control parameter switches to a different value (eg, K p2 , K i2 and K d2)(not shown). In this example, this causes the contributions of P, I, and D to the PID controller output to deviate from zero and move in a negative direction. The output of the PID controller reduces the generator output torque. In addition, as the generator output torque decreases toward zero in response to the change in the PID control parameters, the rate of change of the generator speed decreases. Reducing the generator output torque can reduce the possibility of torque disturbances during gear clearance crossing, which may occur when a gear driven by a gear coupled to the generator begins to drive a gear coupled to the generator. The engine intake manifold pressure begins to be evacuated, and the engine ignition timing remains retarded.

[0071] Between time t2 and time t3, the engine speed continues to increase and then levels off. As the gear backlash crossover begins to approach, the generator torque is adjusted to decrease at a lower rate. The intake manifold pressure continues to decrease, and the ignition timing remains retarded. The low intake manifold pressure and retarded ignition timing can allow the engine to generate very little torque to spin the engine so that the engine start does not cause the planetary carrier gear set to overspeed the sun gear. Continue to adjust the P, I, and D contributions.

[0072] At time t3, transmission gear lash crossing occurs. The P, I and D control parameters are changed again so that the generator can respond as needed during the engine operating conditions. Once gear lash crossing has occurred, the engine throttle can be opened and the ignition timing can be advanced to increase the engine torque output. However, because the engine generates little torque during the transmission gear lash crossing and because the generator torque output is low, the noise that may be caused by gear meshing during gear lash crossing may have been reduced. The generator begins to apply load to the engine and generate charge shortly after time t3.

[0073] In this way, noise caused by gear meshing after gear backlash crossing can be reduced. In some examples, the engine intake manifold pressure, ignition timing, and generator torque can be adjusted in open loop based on the time since the last engine start request or the actual number of cylinder cycles, as shown. However, adjusting these vehicle operating conditions via a PID controller as described herein can provide a more repeatable and robust engine start.

[0074] Reference now Figure 4 , a flow chart showing a method for starting an engine of a hybrid vehicle utilizing a power split transmission. Figure 4 The method can be incorporated into Figure 1 and Figure 2 In addition, Figure 4At least portions of the method may be incorporated as executable instructions stored in a non-transitory memory, while other portions of the method may be executed via a controller that transforms operating states of devices and actuators in the physical world.

[0075] At 402, method 400 determines vehicle operating conditions. Vehicle operating conditions may include, but are not limited to, vehicle state (e.g., started / deactivated), engine operating state, battery system operating state, motor operating state, brake system operating state, transmission shifter position, driver demand torque, brake torque, and vehicle operating mode. Method 400 may determine vehicle operating conditions via sensors as described herein. Method 400 proceeds to 404.

[0076] At 404, method 400 determines whether an engine start is requested. An engine start may be requested via operator input or based on vehicle operating conditions. For example, an engine start may be requested when the battery state of charge is low and when the vehicle operator starts the vehicle. Additionally, an automatic engine start may be requested in response to increased driver demand torque, low battery state of charge, the amount of time since the last engine start, etc. If method 400 determines that an engine start is requested, the answer is yes, and method 400 proceeds to 406. Otherwise, the answer is no, and method 400 proceeds to exit.

[0077] At 406, method 400 enables engine throttle and ignition control. The controller may look up the requested throttle opening and ignition timing from a table or function stored in the controller memory. The table or function may be indexed or referenced by vehicle operating conditions. The values ​​in the table or function may be empirically determined during an engine start procedure that monitors engine emissions and combustion stability.

[0078] It may be desirable to start the engine with low intake manifold pressure and ignition retarded from the MBT ignition timing so that the engine does not increase the speed difference between the gears of the power split transmission during engine starting. If the engine generates a lot of torque, the engine may cause one gear to change from being a driven gear to being a driving gear, thereby shifting the gear backlash through, as described with respect to Figure 6 Thus, method 400 may minimize engine torque output during engine starting and acceleration prior to a first gear backlash crossing since a most recent engine stop.

[0079] For example, during an engine warm start, the engine throttle may be fully closed and the ignition timing may be retarded from the MBT ignition timing to reduce engine torque. The engine ignition timing retardation may be limited and the throttle opening may be minimized to provide a desired level of combustion stability so that engine emissions and noise may meet metrics. On the other hand, during an engine cold start, the throttle may be opened a small amount and the ignition may be retarded less from the MBT ignition timing than during an engine warm start. Method 400 adjusts the throttle opening and ignition timing in response to the engine temperature and the ambient air temperature. Method 400 proceeds to 408.

[0080] At 408, method 400 installs a first set of PID controller control parameters into the PID controller. The first set of PID control parameters can ensure that the actual engine speed closely follows the desired engine speed during engine acceleration. The first set of control parameters can include a variable K p1 The first scaling factor or gain (eg, a scalar real number) represented by K p1 The value of may depend on vehicle components and vehicle performance criteria. The first set of control parameters may also include the variable K i1 The first integral scaling factor or gain (eg, a scalar real number) represented by K i1 The value of may depend on vehicle components and vehicle performance criteria. The first set of control parameters may also include the variable K d1 K represents the first derivative scaling factor or gain (e.g., a scalar real number). d1 The values ​​of may depend on vehicle components and vehicle performance criteria. The PID controller is populated with these values ​​and the PID controller adjusts the generator torque. Method 400 proceeds to 410.

[0081] At 410, method 400 determines a target engine operating speed or target speed. In one example, the target speed can be empirically determined based on engine emissions, ambient temperature, engine temperature, vehicle operating mode, and time since engine start. Specifically, the engine can be started while monitoring engine emissions and combustion stability. A table or function may include empirically determined target engine speed values ​​for engine starting. Method 400 may index or reference the table or function based on vehicle operating conditions, and the table or function outputs a target engine speed. In some examples, method 400 may pass the target engine speed through a first-order low-pass filter to generate a filtered target engine speed. The filtered target engine speed may provide a smooth engine speed transition, which may be desirable from a user's perspective. Method 400 proceeds to 412.

[0082] At 412 , method 400 initiates an engine start. The engine start may initiate the engine start by positioning a throttle to a requested throttle position, initiating engine spark timing, activating an engine fuel pump, etc. Method 400 proceeds to 414 .

[0083] At 414, method 400 adjusts the generator torque. Engine starting may include adjusting the generator torque in response to the target engine speed or alternatively the filtered target engine speed. The open loop feedforward torque value and the feedback torque value generated via the PID controller may be combined to generate the generator torque request. In one example, the generator torque request may be generated via a feedforward torque value such as Figure 5 The controller shown in generates the generator torque demand. Therefore, the commanded generator torque can be expressed by the following equation:

[0084] GTq=FF+PID

[0085] Wherein GTq is the requested or commanded generator torque, FF is the requested feed forward torque, and PID is the generator torque adjustment determined via the PID controller applying the first set of PID control parameters. The generator is commanded to the requested generator torque. The generator may be commanded via commanding an inverter. Method 400 proceeds to 416.

[0086] At 416, method 400 determines whether the engine speed is greater than the target engine speed, or alternatively, determines whether the engine speed is greater than the filtered target engine speed. If yes, the answer is yes, and method 400 proceeds to 418. If no, method 400 returns to 414.

[0087] At 418, method 400 installs a second set of PID controller control parameters into the PID controller, the second set of PID controller control parameters being different from the first set of PID control parameters. The second set of PID control parameters may ensure that the rate at which the actual engine speed changes is less than a threshold rate. This may allow the transmission to approach a gear backlash crossover at a lower rate, thereby reducing the likelihood of generating objectionable transmission noise. The second set of control parameters may include a variable K p2 K represents a scaling factor or gain (e.g., a scalar real number). p2 The value of may depend on vehicle components and vehicle performance standards. The second set of control parameters may also include the variable K i2 K represents the integral scaling factor or gain (e.g., a scalar real number). i2 The value of may depend on vehicle components and vehicle performance standards. The second set of control parameters may also include the variable K d2 K represents the derivative scaling factor or gain (e.g., a scalar real number). d2The values ​​of may depend on vehicle components and vehicle performance criteria. The PID controller is populated with these values ​​and the PID controller adjusts the generator torque. Method 400 proceeds to 420.

[0088] At 420, method 400 determines whether the first gear backlash crossing has occurred since the engine speed was last less than a threshold speed. In one example, method 400 determines the presence or absence of the first gear backlash crossing according to the method described in U.S. Patent 8,733,183, which is hereby fully incorporated herein by reference for all intents and purposes. In other examples, gear backlash crossing can be estimated based on the speed difference of the transmission gears. If method 400 determines that the first gear backlash crossing has occurred since the engine speed was last less than a threshold speed, the answer is yes and method 400 proceeds to 422. Otherwise, the answer is no and method 400 returns to 418.

[0089] At 422, method 400 installs a third set of PID controller control parameters into the PID controller, the third set of PID controller control parameters being different from the first set of PID control parameters and the second set of PID control parameters. The third set of PID control parameters can ensure that the generator responds as needed when the engine is running. The third set of control parameters can include a variable K p3 K represents a scaling factor or gain (e.g., a scalar real number). p3 The value of may depend on vehicle components and vehicle performance standards. The third set of control parameters may also include a variable K i3 K represents the integral scaling factor or gain (e.g., a scalar real number). i3 The value of may depend on vehicle components and vehicle performance standards. The third set of control parameters may also include a variable K d3 K represents the derivative scaling factor or gain (e.g., a scalar real number). d3 The values ​​of may depend on vehicle components and vehicle performance criteria. The PID controller is populated with these values ​​and the PID controller adjusts the generator torque. Method 400 proceeds to 424.

[0090] At 424, method 400 adjusts engine throttle position and spark timing to base nominal values ​​based on engine operating conditions. The engine may be operated at or near MBT spark timing and throttle position that varies in response to driver demand torque. Method 400 proceeds to exit.

[0091] In this way, the torque of the generator can be adjusted during engine starting and shortly thereafter to reduce the possibility of noise generated by changes in torque transmitted through a set of gears. The method can adjust the generator torque and / or engine torque via adjusting PID control parameters or alternatively as a function of time. However, adjusting the torque via PID control parameters may be a more robust solution.

[0092] therefore, Figure 4 A method for starting an engine is provided, comprising: rotating the engine to a speed greater than a threshold speed via a controller by transferring torque from a first motor to the engine through a planetary gear carrier gear set and a sun gear; and reducing the torque output of the first motor at a certain rate in response to the engine speed being greater than the threshold speed; and stopping reducing the torque output of the first motor at the rate in response to transferring torque from the engine through the sun gear to the first motor and to the planetary gear carrier gear set. In a first example, the method also includes burning fuel in the engine while rotating the engine via the first motor. In a second example that may include the first example, the method includes: wherein burning the fuel in the engine includes operating the engine at an ignition timing that is retarded from the MBT ignition timing. In a third example that may include one or both of the first example and the second example, the method includes: wherein burning the fuel in the engine includes completely closing the throttle of the engine. In a fourth example that may include one or more of the first to third examples, the method includes: wherein reducing the torque output of the first motor includes adjusting the torque output of the first motor from a positive torque to a negative torque. In a fifth example, which may include one or more of the first to fourth examples, the method further includes: in response to transferring torque from the engine to the first motor, charging a battery via the first motor. In a sixth example, which may include one or more of the first to fifth examples, the method further includes: in response to transferring torque from the engine to the first motor, advancing ignition timing.

[0093] Figure 4The method also provides a method for operating an engine, comprising: rotating the engine via a controller, in response to an engine start request, based on the output of a proportional integral derivative (PID) controller operated with a first set of control parameters, by adjusting the torque of an electric machine; in response to the engine speed exceeding a threshold speed, adjusting the torque of the electric machine based on the output of a PID controller operated with a second set of control parameters; and in response to a gear clearance crossing having occurred, adjusting the torque of the electric machine based on the output of a PID controller operated with a third set of control parameters. In a first example, the method comprises: wherein the second set of control parameters operates to reduce the rate of change of the torque of the electric machine. In a second example that may include the first example, the method further comprises: burning fuel in the engine and operating the engine with an ignition timing retarded from the MBT ignition timing. In a third example that may include one or both of the first example and the second example, the method comprises: wherein the gear clearance crossing is the first gear clearance crossing since the last engine stop. The method of claim 19, further comprising operating the engine with the throttle fully closed before the gear clearance crossing has occurred.

[0094] Reference now Figure 5 , a block diagram of an example PID controller for regulating generator torque is shown. Figure 5 The PID controller shown in Figure 4 The method is applied to control gear clearance crossing after the most recent engine start.

[0095] Block diagram 500 includes a PID controller with a feedforward term. In this example, the feedforward term includes torque for battery charging and engine cranking torque. The engine cranking torque can be determined via a table or function in reference block 502. The table or function can be referenced via the time since the last engine start request and the engine temperature. The table or function in block 502 outputs the requested engine cranking torque. The requested engine cranking torque is added to the battery charging torque at summing point 504. The battery charging torque can be a zero value until the engine is running and gear clearance crossing has occurred. The output of summing point 504 is delivered to summing point 516.

[0096] At summing junction 506, the actual or measured engine speed is subtracted from the target engine speed or alternatively a low pass filtered target engine speed to generate an engine speed error. The engine speed error is delivered to blocks 508 through 512. At block 508, a proportional scalar or gain (e.g., real number) variable K is added to the target engine speed. pThe engine speed error (e) as a function of time is multiplied to generate a proportional component of the PID controller output. Block 508 outputs the proportional component of the PID controller to summing junction 514. At block 510, an integral scalar or gain (e.g., real number) variable K is converted to i The integral of the engine speed error (e) is multiplied by the integral of the engine speed error (e) to generate the integral component of the PID controller output. Block 510 outputs the integral component of the PID controller to summing junction 514. At block 512, a derivative scalar or gain (e.g., real number) variable K is d The derivative of the engine speed error (e) is multiplied to generate a derivative component of the PID controller output. Block 512 outputs the proportional component of the PID controller to summing junction 514. The PID control adjustment to the generator torque is output from summing junction 514 to summing junction 516 where it is added to the output of summing junction 504 to generate a generator torque request. The generator torque request can be sent to the generator or an inverter that controls the generator.

[0097] Now turn to Figure 6 , portions of gears are shown to illustrate gear backlash and backlash crossing. The first gear 602 includes teeth 620. Similarly, the second gear 604 includes teeth 621. The teeth 620 of the first gear 602 mesh with the teeth 621 of the second gear 604. In this example, the second gear 604 is a driven gear that drives the first gear 602 such that the teeth 621 contact the teeth 620 at the contact area 650. To allow the gear teeth to mesh freely without locking, a small space or gap 606 can be provided between the meshing teeth as shown. This gap 606 can result in a "dead zone" in torque transfer when the direction of the torque applied to the gear changes. The gap 606 can be referred to as a "backlash". Backlash crossing can refer to a situation where movement occurs between the teeth to remove the backlash when the direction of torque transfer through the gear set changes. For example, in Figure 6 , the gap 606 is shown at its maximum extent. However, if a torque is applied to the first gear 602 such that the tooth surface 660 moves relative to and contacts the tooth surface 670, a gear play crossing event has occurred because the gap is now reduced to zero.

[0098] Now turn to Figure 7, shows a graph of driveline torque as a function of driveline twist angle θ. The vertical axis represents driveline torque, and driveline torque above the horizontal axis is positive (e.g., torque is added to the driveline) and driveline torque below the horizontal axis is negative (e.g., torque is removed from the driveline). The horizontal axis represents the twist angle of the driveline. Twist angles to the left of the vertical axis are negative angles, and twist angles to the right of the vertical axis are positive angles. It can be observed that for small positive and negative twist angles, no torque is transferred through the gear set. This condition exists during a backlash-travel event, and vehicle occupants may notice a change in driveline torque and / or audible noise generated when torque transfer begins and the teeth actively engage.

[0099] 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 programs disclosed herein can be stored as executable instructions in a non-transitory memory and can be implemented by a control system including a controller in combination with various sensors, actuators, and other engine hardware. The specific program described herein may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, etc. To this end, the various actions, operations, and / or functions shown may be executed in the order shown, executed in parallel, or omitted in some cases. Similarly, the processing order is not necessarily required 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 actions, operations, and / or functions shown may be repeatedly performed according to the specific strategy used. In addition, at least a portion of the described actions, operations, and / or functions may graphically represent the code in the non-transitory memory of the computer-readable storage medium to be programmed into the control system. When the described actions are performed by executing instructions in conjunction with one or more controllers in a system including various engine hardware components, the control actions may also transform the operating state of one or more sensors or actuators in the physical world.

[0100] This specification ends here. Without departing from the spirit and scope of the present description, those skilled in the art will think of many variations and modifications after reading the present description. For example, single cylinder, I3, I4, I5, V6, V8, V10 and V12 engines operating in natural gas, gasoline, diesel or alternative fuel configurations may advantageously use the present description.

Claims

1. A method for starting an engine, comprising: rotating the engine to a speed greater than a threshold speed via the transfer of torque from the first electric machine to the engine through the planetary carrier gear set and the sun gear, via a controller; and reducing the torque output of the first electric machine at a rate in response to the engine speed being greater than the threshold speed; as well as Reducing the torque output of the first electric machine at the rate is ceased in response to transferring torque from the engine through the sun gear to the first electric machine and to the planetary carrier gear set. 2 . The method of claim 1 , further comprising combusting fuel in the engine while rotating the engine via the first electric machine. 3 . The method of claim 2 , wherein combusting fuel in the engine comprises operating the engine at a spark timing retarded from a minimum spark advance for maximum torque generated at a particular engine speed and load. 4 . The method of claim 3 , wherein combusting fuel in the engine comprises fully closing a throttle of the engine. 5 . The method of claim 1 , wherein reducing the torque output of the first electric machine includes adjusting the torque output of the first electric machine from a positive torque to a negative torque. 6 . The method of claim 1 , further comprising charging a battery via the first electric machine in response to transferring torque from the engine to the first electric machine. 7 . The method of claim 1 , further comprising advancing spark timing in response to transferring torque from the engine to the first electric machine.

8. A system comprising: Internal combustion engines; a power split transmission coupled to the internal combustion engine, the power split transmission comprising two electric machines, a sun gear, a planetary carrier gear set, and a ring gear; as well as a controller comprising: executable instructions stored in a non-transitory memory, the executable instructions causing the controller to spin the internal combustion engine via a first electric machine of the two electric machines to start the internal combustion engine; and additional executable instructions for reducing the torque output of the first electric machine at a certain rate in response to the speed of the internal combustion engine exceeding a threshold speed; and additional instructions for further adjusting the torque output of the first electric machine in response to backlash crossing between the sun gear and the planetary gear carrier gear set during engine starting.

9. The system of claim 8, further comprising additional instructions that cause the controller to initiate combustion in the internal combustion engine.

10. The system of claim 9 further comprising additional instructions that cause the controller to retard ignition timing of the internal combustion engine and operate the internal combustion engine with a fully closed throttle during starting of the internal combustion engine.

11. The system of claim 8 further comprising additional instructions for adjusting control parameters of the proportional-integral-derivative controller to a first set of values ​​during engine starting.

12. The system of claim 11 further comprising additional instructions for adjusting control parameters of the proportional-integral-derivative controller to a second set of values ​​in response to the speed of the internal combustion engine exceeding the threshold speed.

13. The system of claim 12 further comprising additional instructions for adjusting control parameters of the proportional integral derivative controller to a third set of values ​​in response to the backlash crossing between the sun gear and the planet carrier gear set.

14. The system of claim 13, wherein the proportional integral derivative controller regulates torque output of the first electric machine.

15. The system of claim 14 further comprising additional instructions for propelling the vehicle via a second of the two electric machines.

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