METHOD FOR STARTING AN ENGINE

Abstract

A method for starting an engine, comprising: Turn off the engine and during engine start, adjusting a transmission locking force in response to a timing of a first combustion event of a cylinder, wherein the actuator of the transmission is a torque converter lock-up clutch.

Description

Field of invention

[0001] The present invention relates to a system for improving engine starting. The method may be particularly suitable for engines that are frequently shut down and then restarted. General state of the art and brief description of the invention

[0002] Vehicle manufacturers have recognized that under some conditions it may be desirable to automatically start and stop a vehicle's engine. Turning off the engine can reduce fuel consumption, particularly when the vehicle is stationary for extended periods of time, such as in stop-and-go traffic. However, providing a desired amount of wheel torque to the driver shortly after an engine restart can be difficult due to torque management within a transmission. For example, if transmission clutches are in an open state during engine start-up, a wheel torque response delay may be perceived by the driver. Furthermore, the timing at which torque is transferred through the transmission will vary from start-up to start-up, leaving the driver with an impression of an inconsistent engine restart.

[0003] The inventors of the present invention have recognized the above-mentioned disadvantages and have developed a method for improving engine starting.

[0004] An embodiment of the present description includes a method of starting an engine, comprising: stopping the engine and, during an engine start, adjusting a transmission locking force in response to a timing of a first combustion event of a cylinder.

[0005] By adjusting transmission lockup force in response to an engine event during cranking, cranking uniformity and engine torque management can be improved. For example, transmission clutches can be adjusted based on the timing of a predicted engine first combustion event during engine restart to reduce torque transfer delay from an engine to a transmission. Furthermore, linking transmission clutch actuation to a more repeatable condition can reduce a driver's perception of an inconsistent engine restart.

[0006] From DE 10 2008 020 581 A1, an engine start detection in a hybrid electric vehicle is known, wherein a method for detecting ongoing combustion in the engine of a hybrid electric powertrain having a starter / generator drivingly connected to the engine, a transmission for driving a load, and an input clutch for opening and closing a drive connection between the electric machine and the transmission, comprising the steps of: using the starter / generator to generate torque and crank the engine, preparing the engine to effect combustion, generating torque capacity via the input clutch, wherein the clutch slips, and continuing to use the starter / generator until a sum of the crankshaft torque supplied by the starter / generator and the crankshaft torque supplied by the transmission is less than a torque limit for a predetermined period of time.

[0007] Furthermore, GB 2 403 523 A describes a method for controlling an engine and automatic transmission of a vehicle to reduce noise, vibration, and harshness problems during vehicle engine shutdown to improve fuel consumption. The method combines start / stop control of the vehicle engine with clutch control.

[0008] The present description can provide many advantages. In particular, the approach can improve engine cranking uniformity. Furthermore, the approach can improve the driver-requested wheel torque response time. The approach can further simplify a torque management system because torque transfer can be synchronized to an event that is more repeatable and easily identifiable.

[0009] The above advantages and other advantages and features of the present invention will be readily apparent from the following detailed description when considered alone or in conjunction with the accompanying drawings.

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

[0011] The advantages described herein will be more fully understood by reading an example of an embodiment, referred to herein as the detailed description, alone or with reference to the drawings. In the drawings: Fig. 1 a schematic diagram of an engine; Fig. 2 an exemplary vehicle system layout; Fig. 3 an exemplary diagram of relevant signals during a simulated engine start; Fig. 4 shows another exemplary diagram of relevant signals during a simulated engine start; Fig. 5 is a flowchart of an exemplary engine start routine; Fig. 6 is a flowchart of an exemplary transmission lock release routine and Fig. 7 is a flowchart of an exemplary transmission lock strategy routine. Detailed description

[0012] This description relates to the automatic starting of an engine coupled to a transmission. In a non-limiting example, the engine may be started as in Fig. 1. Furthermore, the engine may be part of a vehicle, as shown in Fig. 2 shown.

[0013] The engine can be started according to the Fig. 5-6 described procedures. The procedure of Fig. 5 can be used to transition the transmission torque control during engine start-up so that the response to a driver request is improved. The method of Fig. 6 describes the unlocking of a transmission during engine start-up, so that the driver experiences a smoother start. Thus, the Fig. 5-6 can be used during an engine start to improve the driver's perception of the vehicle starting process. Furthermore, Fig. 7 a transmission lock strategy for determining a transmission lock force during an engine stop. Fig. 3-4 show relevant signals during engine start-up according to the procedures of Fig. 5-6.

[0014] With reference to Fig. 1, an internal combustion engine 10 comprising several cylinders, one of which is in Fig. 1, is controlled by an electronic engine controller 12. The engine 10 includes a combustion chamber 30 and cylinder walls 32 with a piston 36 positioned therein and connected to a crankshaft 40. The combustion chamber 30 is shown communicating with an intake manifold 44 and an exhaust manifold 48 via a respective intake valve 52 and exhaust valve 54. Each intake and exhaust valve may be actuated by an intake cam 51 and an exhaust cam 53. Alternatively, the intake and / or exhaust valve may be actuated by an electromechanically controlled valve spool and armature assembly. The position of the intake cam 51 may be determined by an intake cam sensor 55. The position of the exhaust cam 53 may be determined by an exhaust cam sensor 57.

[0015] A fuel injector 66 is shown injecting fuel directly into the cylinder 30, known to those skilled in the art as direct injection. Alternatively, fuel may be injected to a port, known to those skilled in the art as port injection. The fuel injector 66 delivers liquid fuel proportional to the pulse width of the FPW signal from the controller 12. Fuel is delivered to the fuel injector 66 from a fuel system (not shown) that includes a fuel tank, a fuel pump, and a fuel rail (not shown). The fuel injector 66 receives operating power from a driver 68 responsive to the controller 12. In addition, the intake manifold 44 is shown communicating with an optional electronic throttle 62, which adjusts a position of the throttle plate 64 to control airflow from the air intake 42 to the intake manifold 44.In one example, a low-pressure direct injection system may be used, allowing fuel pressure to be increased to approximately 20-30 bar. Alternatively, a high-pressure dual-stage fuel system may be used to generate higher fuel pressures.

[0016] A distributorless ignition system 88, in response to the controller 12, delivers an ignition spark to the ignition chamber 30 via a spark plug 92. A UEGO (Universal Exhaust Gas Oxygen) sensor 126 is shown coupled to the exhaust manifold 48 upstream of a catalytic converter 70. Alternatively, a dual-state exhaust gas oxygen sensor may be substituted for the UEGO sensor 126.

[0017] In one example, the catalyst 70 may include multiple catalyst blocks. In another example, multiple emission control devices may be used, each with multiple blocks. In one example, the catalyst 70 may be a three-way catalyst.

[0018] The controller 12 is in Fig. 1 as a conventional microcomputer including: a microprocessor unit 102, input / output ports 104, a read-only memory 106, a random access memory 108, a working memory 110, and a conventional data bus.The controller 12 is shown receiving, in addition to those signals already discussed, various signals from sensors coupled to the engine 10, 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 a force exerted by a foot 132; a manifold absolute pressure (MAP) measurement from a pressure sensor 122 coupled to the intake manifold 44; an engine position sensor from a Hall effect sensor 118 that senses the position of the crankshaft 40; a measurement of the mass of air entering the engine from sensor 120; and a measurement of throttle position from sensor 58. Barometric pressure may also be sensed (sensor not shown) for processing by the controller 12.In a preferred aspect of the present description, the engine position sensor 118 generates a predetermined number of equally spaced pulses per revolution of the crankshaft from which the engine speed (RPM - revolutions per minute) can be determined.

[0019] In some embodiments, the motor may be coupled to an electric motor-battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, a series configuration, or a variation or combination thereof. Furthermore, in some embodiments, other engine configurations may be used, for example, a diesel engine.

[0020] During operation, each cylinder in engine 10 typically experiences a four-stroke cycle: the cycle includes the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke. During the intake stroke, the exhaust valve 54 generally closes and the intake valve 52 opens. Air is introduced into the combustion chamber 30 via the intake manifold 44, and the piston 36 moves to the bottom of the cylinder to increase the volume within the combustion chamber 30. The position where the piston 36 is near the bottom of the cylinder and at the end of its stroke (e.g., when the combustion chamber 30 is at its largest volume) is typically referred to by those skilled in the art as bottom dead center (BDC). During the compression stroke, the intake valve 52 and the exhaust valve 54 are closed. The piston 36 moves toward the cylinder head to compress the air within the combustion chamber 30.The point at which piston 36 is at the end of its stroke and closest to the cylinder head (e.g., when combustion chamber 30 is at its smallest volume) is typically referred to by those skilled in the art as top dead center (TDC). In a process referred to herein as injection, fuel is introduced into the combustion chamber. In a process referred to hereinafter as ignition, the injected fuel is ignited by known ignition means such as spark plug 92, resulting in combustion. During the combustion stroke, expanding gases push piston 36 back to BDC. Crankshaft 40 converts piston motion into rotating shaft torque. 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.Note that the above is shown merely as an example and that intake and exhaust valve opening and / or closing times may vary to provide positive or negative valve overlap, late intake valve closing, or various other examples.

[0021] In one embodiment, the stop / start crank position sensor has both zero-speed and bidirectional capability. In some applications, a bidirectional Hall sensor may be used; in others, the magnets may be mounted on the target. Magnets can be placed on the target, and the "missing tooth gap" can potentially be eliminated if the sensor is capable of detecting a change in signal amplitude (e.g., using a stronger or weaker magnet to locate a specific position on the wheel). Furthermore, using a bidirectional Hall sensor or equivalent, the engine position can be maintained throughout shutdown, but an alternative strategy can be used during restart to ensure the engine is rotating in a forward direction.

[0022] Fig. 2 is a block diagram of a vehicle powertrain 200. The powertrain 200 may be driven by the engine 10. The engine 10 may be started using an engine starting system (not shown). Furthermore, the engine 10 may generate torque via a torque actuator 204, such as a fuel injector, throttle body, etc.

[0023] Engine output torque may be transferred to a torque converter 206 to drive an automatic transmission 208. Further, one or more clutches may be engaged, including a forward clutch 210, to propel a vehicle. In one example, the torque converter may be referred to as a component of the transmission. Further, the transmission 208 may include multiple gear clutches that may be engaged as needed to activate multiple fixed transmission ratios. The output of the torque converter may, in turn, be controlled by a torque converter lock-up clutch 212. For example, when the torque converter lock-up clutch 212 is fully disengaged, the torque converter 206 transfers engine torque to the automatic transmission 208 via fluid transfer between the torque converter turbine and the torque converter compressor wheel, enabling torque multiplication.In contrast, when the torque converter clutch 212 is fully engaged, the engine output torque is transferred directly to an input shaft (not shown) of the transmission 208 via the torque converter clutch. Alternatively, the torque converter clutch 212 may be partially engaged, allowing the amount of torque transferred to the transmission to be adjusted. A controller may be configured to adjust the amount of torque transferred by the torque converter 212 by adjusting the torque converter clutch in response to various engine operating conditions or based on a driver-based engine operating request.

[0024] Torque output from the automatic transmission 208 may, in turn, be transmitted to the wheels 216 to propel the vehicle. Specifically, the automatic transmission 208 may transmit input drive torque at the input shaft (not shown) in response to a vehicle driving condition before transmitting output drive torque to the wheels.

[0025] Furthermore, a frictional force may be applied to wheels 216 by applying wheel brakes 218. In one example, wheel brakes 218 may be applied in response to the driver pressing their foot on a brake pedal (not shown). In the same way, a frictional force on wheels 216 may be reduced by releasing wheel brakes 218 in response to the driver removing their foot from a brake pedal. Furthermore, the vehicle brakes may apply a frictional force to wheels 216 as part of an automated engine shutdown procedure.

[0026] A mechanical oil pump 214 may be in fluid communication with the automatic transmission 208 to provide hydraulic pressure to engage various clutches, such as the forward clutch 210 and / or the torque converter lock-up clutch 212. The mechanical oil pump 214 may be operated in accordance with the torque converter 212 and may be driven, for example, by the rotation of the engine or the transmission input shaft. Thus, the hydraulic pressure generated in the mechanical oil pump 214 may increase with engine speed and may decrease with engine speed. An electric oil pump 220, also in fluid communication with the automatic transmission but operating independently of the drive power of the engine 10 or the transmission 208, may be provided to supplement the hydraulic pressure of the mechanical oil pump 214.The electric oil pump 220 may be driven by an electric motor (not shown) to which electrical power may be supplied, for example, by a battery (not shown).

[0027] A controller 12 may be configured to receive inputs from the motor 10 as shown in Fig. 1 in more detail, and accordingly control a torque output of the engine and / or the operation of the torque converter, transmission, clutches, and / or brakes. As an example, a torque output may be controlled by adjusting a combination of spark timing, fuel pulse width, fuel pulse timing, and / or air charge by controlling throttle opening and / or valve timing, valve lift, and boost for turbocharged or supercharged engines. In the case of a diesel engine, the controller 12 may control the engine torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. In all cases, engine control may be performed on a cylinder-by-cylinder basis to control the engine torque output.

[0028] When idle-stop conditions are met, the controller 42 may initiate an engine shutdown by shutting off fuel and spark to the engine. To maintain a degree of torsion in the transmission, the controller may ground rotating elements of the transmission 208 to a housing of the transmission and thereby to the frame of the vehicle. As further described with reference to Fig. 7, the controller may engage one or more transmission clutches, such as forward clutch 210, and lock the engaged or engaged transmission clutches to the transmission housing and the vehicle frame. Clutch pressure may be varied (e.g., increased) to adjust the engagement state of a transmission clutch and provide a desired amount of transmission torsion. In one example, during engine shutdown, hydraulic pressure for clutch modulation may be provided by activating electric oil pump 220 if sufficient hydraulic pressure cannot be provided by mechanical oil pump 214.

[0029] Also, during engine shutdown, wheel brake pressure may be adjusted based on clutch pressure to assist in locking the transmission while reducing torque transmitted through the wheels. In particular, by applying the wheel brakes while locking one or more engaged transmission clutches, opposing forces may be applied to the transmission and, consequently, the powertrain, thereby maintaining the transmission gears in active engagement and retaining potential torsional energy in the transmission gear set without moving the wheels. In one example, wheel brake pressure may be adjusted to coordinate application of the wheel brakes without locking the engaged transmission clutch during engine shutdown. As such, by adjusting wheel brake pressure and clutch pressure, the amount of torsion retained in the transmission when the engine is shut down may be adjusted.

[0030] When restart conditions are met and / or a vehicle operator wishes to drive the vehicle, the controller 12 may reactivate the engine by resuming cylinder combustion. As further described with reference to Fig. 5-6, to drive off the vehicle, the transmission 208 can be unlocked and the wheel brakes 218 can be released to send torque back to the drive wheels 216. Clutch pressure can be adjusted to unlock the transmission, while wheel brake pressure can be adjusted to coordinate the release of the brakes with the unlocking of the transmission and driving off the vehicle.

[0031] With reference to Fig. 3 shows an exemplary curve of a simulated engine starting sequence by the method of Fig. 5. Time begins on the left side of the curve and increases toward the right side of the curve. The sequence shown represents a cranking of a non-limiting four-cylinder, four-stroke engine. In this example, the vertical marks between the cylinder position traces CYL. 1-4 represent top dead center or bottom dead center for the respective cylinder strokes. And there are 180 crankshaft degrees between each vertical mark.

[0032] The first curve from the top of the figure represents the position of cylinder number one. And specifically, the stroke of cylinder number one when the engine crankshaft is rotated. To the left of T0, the engine is stopped and at rest. At T0, the engine crankshaft begins to rotate due to torque provided by a starter motor. The strokes of cylinders 1-4 are labeled according to the engine position the engine occupied when the engine stopped. For example, cylinder number one is shown on an intake stroke when the engine stopped before time T0. After T0, the engine is rotating and cylinder number one enters the compression stroke, followed by the power and exhaust strokes. The cylinder cycle for cylinder number one then repeats. For a four-stroke engine, one cylinder cycle might be 720°, the same crankshaft interval for one complete cycle of the engine.The asterisk at label 300 indicates the first ignition event for the first combustion event after engine shutdown. Asterisk 308 represents the second combustion event for cylinder number one after engine shutdown and the fifth combustion event after engine shutdown. Ignition can be initiated by a spark plug or by compression. In this sequence, the valves of cylinder number one are open for at least part of the intake stroke to allow air into the cylinder. Fuel can be injected to the engine cylinders through port or direct fuel injectors. The fuel-air mixture is compressed and ignited during the compression stroke. Peak cylinder pressure can occur at top dead center of the compression stroke or during the power stroke.

[0033] It should be noted that the engine position at the time of engine stop may be determined by tracking the engine position while the ignition and fuel are deactivated. In one embodiment, when the engine is substantially stopped, the engine position is determined and stored in memory for retrieval during the next engine start. In another embodiment, the engine position may be determined at engine start, after the engine begins to rotate, by sensing camshaft and crankshaft positions.

[0034] The second cylinder position trajectory from the top of the figure represents the position and stroke for cylinder number three. Since the combustion order of this particular engine is 1-3-4-2, the second combustion event is initiated from engine stop at 302, as indicated by the asterisk. Star 302 represents the initiation of the first combustion event for cylinder number three after engine stop and the second combustion event after engine stop.

[0035] The third cylinder position trajectory from the top of the figure represents the position and stroke for cylinder number four. Star 304 represents the initiation of the first combustion event for cylinder number four after engine stop and the third combustion event from engine stop.

[0036] The fourth cylinder position trajectory from the top of the figure represents the position and stroke for cylinder number two. Star 306 represents the initiation of the first combustion event for cylinder number two after engine stop and the fourth combustion event from engine stop.

[0037] It should be noted that the first cylinder to combust an air-fuel mixture may vary depending on the engine stop position and the method for determining the engine position. In some embodiments, fuel may not be delivered to one or more engine cylinders until the engine position is determined. In other embodiments, fuel may be delivered before or as soon as the engine begins to rotate, regardless of the engine stop position.

[0038] The fifth trace from the top of the figure shows an example of the timing of adjusting an actuator of a transmission, specifically a transmission clutch, to adjust a locking force in response to a first combustion event of a cylinder. The high portion of the CLUTCH-1 signal to the left of vertical mark T1 indicates that a higher force is being applied to the transmission by clutch 1. The lower portion of the CLUTCH-1 signal at the end of the ramp after vertical mark T1 indicates that a lower force is being applied to the transmission by clutch 1. Thus, during an engine stop, a higher force is being applied to the transmission by clutch 1 and begins to decrease at vertical mark T1 in response to a timing of combustion event 300. The amplitude of the higher portion of CLUTCH-1 can be adjusted based on operating conditions to control the transmission locking force.

[0039] The CLUTCH 1 signal is varied at 310 to gradually reduce a locking force applied to the transmission so that Clutch 1 begins to release the rotating components of the transmission from the transmission housing and the vehicle chassis. For example, Clutch 1 may release a transmission shaft. The rate of change of the CLUTCH 1 signal may be proportional to the amount of torque applied to the transmission input shaft and to the force applied to the vehicle brakes. Further, the CLUTCH 1 rate of change may be varied according to operating conditions. For example, the rate of change of the CLUTCH 1 signal may decrease with transmission oil temperature. In another example, the rate of change of the CLUTCH 1 signal may decrease as the force applied to vehicle brakes during a transmission lockup increases.

[0040] It should be noted that, alternatively, a reduction in the locking force applied by Clutch 1 to the transmission may be timed relative to the timing of the first combustion events in cylinders 2-4. Furthermore, the timing of the CLUTCH 1 signal adjustment need not coincide with the exact timing of a particular cylinder's first combustion event. Rather, the timing of the CLUTCH 1 signal adjustment may be relative to the timing of a cylinder's first combustion event. Thus, the CLUTCH 1 signal may begin to change before or after a cylinder's first combustion event, but the start timing of the change is relative to a cylinder's first combustion event.

[0041] In one example, combustion timing of a first combustion event of a cylinder may be determined based on the engine stop position. As in Fig. 3, it may be determined that cylinder 1 may be the first cylinder to combust since it is the first cylinder to complete intake and compression strokes. Alternatively, cylinder 2 may be the first cylinder to combust an air-fuel mixture if fuel can be injected into a cylinder holding an air charge. Thus, based on the engine stop position and engine configuration (e.g., direct fuel injector or port fuel injection), it may be determined which cylinder is capable of a first combustion event. Furthermore, since the order of combustion of an engine is known, the first combustion events after engine stop can be determined based on the first combustion event after engine stop for other cylinders.

[0042] The sixth curve from the top of the figure shows timing of the adjustment of another actuator of a transmission, specifically a transmission clutch, to adjust a locking force in response to a first combustion event of a cylinder. Analogous to the CLUTCH 1 signal, the high portion of the CLUTCH 2 signal to the left of vertical mark T2 indicates that a greater force is being exerted on the transmission by clutch 2. The lower portion of the CLUTCH 2 signal at the end of the change after 312 indicates that a lower force is being exerted on the transmission by clutch 2. Thus, a greater force is being exerted on the transmission by clutch 1 during an engine stop, and it begins to decrease at vertical mark T2 in response to timing of combustion event 300. The amplitude of the higher portion of CLUTCH 2 can be adjusted based on operating conditions to control the transmission locking force.

[0043] The CLUTCH-2 signal reduces the locking force exerted by clutch-2 on the transmission after the CLUTCH-1 signal begins reducing the locking force exerted by clutch 1 on the transmission. Thus, the CLUTCH-1 and CLUTCH-2 signals may be sequenced relative to a cylinder's first combustion event after engine shutdown. Furthermore, the rates of change of changes 310 and 312 may be different, as shown in Fig. 3. Clutch change rates can vary from clutch to clutch based on the position of the clutch in the transmission as well as the input torque applied to the transmission input shaft.

[0044] The CLUTCH-1 and CLUTCH-2 signals are representative of control signals for locking and unlocking a transmission. In some embodiments, only a single clutch may lock a transmission, while in other embodiments, three or more clutches may lock a transmission. Thus, for some transmissions, only one CLUTCH-1 signal may be asserted. Furthermore, the CLUTCH-1 and CLUTCH-2 signals are not necessarily intended to correspond to a first gear clutch and a second gear clutch, but rather to any two clutches that operate to lock a transmission when exerted. In other examples, transmission clutches may be released simultaneously. Furthermore, in some examples, two or more clutches may be released at the same release timing or rate.

[0045] Now with reference to Fig. 4 shows another exemplary curve of a simulated engine starting sequence by the method of Fig. 5. The time starts on the left side of the curve and increases towards the right side. Analogous to Fig. 3, the sequence shown represents a start-up of a non-limiting four-cylinder, four-stroke engine. In this example, the vertical marks represent top dead center or bottom dead center for the respective cylinder strokes. And between each vertical mark are 180 crankshaft degrees.

[0046] The first curve from the top of the figure represents the position of cylinder number one. And specifically, the stroke of cylinder number one when the engine crankshaft is rotated. To the left of T0, the engine is stopped or at rest. At T0, the engine crankshaft begins to rotate due to torque provided by a starter motor. The strokes of cylinders 1-4 are labeled according to the engine position the engine occupied when the engine stopped. For example, cylinder number one is shown on an intake stroke when the engine stopped before time T0. After T0, the engine is rotating and cylinder number one enters the compression stroke, followed by the power and exhaust strokes. The cylinder cycle for cylinder number one then repeats.

[0047] The asterisk at label 400 indicates the first firing event for the first combustion event after engine shutdown. In this example, cylinder number two is the first cylinder to combust an air-fuel mixture. Such a firing sequence is available for a direct injection engine. The asterisk 408 represents the second combustion event for cylinder number two after engine shutdown, and it is the fifth combustion event after engine shutdown. In this sequence, the valves of cylinder number two are closed and air is trapped in the cylinder during engine shutdown. Fuel is injected into cylinder number two while the engine is stopped. The fuel and air mixture are thereafter ignited during the compression stroke. In some examples, a cylinder's air-fuel mixture may be ignited in a compression stroke before engine rotation.

[0048] Since the combustion order of this particular engine is 1-3-4-2, the second combustion event after engine shutdown is initiated at 402, as indicated by the asterisk. Asterisk 402 represents the initiation of the first combustion event for cylinder number one after engine shutdown and the second combustion event after engine shutdown. Asterisk 406 represents the initiation of the first combustion event for cylinder number four after engine shutdown and the third combustion event after engine shutdown. Asterisk 406 represents the initiation of the first combustion event for cylinder number two after engine shutdown and the fourth combustion event after engine shutdown.

[0049] The fifth curve from the top of the figure shows an example timing of the adjustment of an actuator of a transmission, in particular a transmission clutch, to adjust a locking force in response to a first combustion event of a cylinder. The high portion of the CLUTCH-1 signal, to the left of mark 412, indicates that a greater force is being exerted on the transmission by clutch 1. The lower portion of the CLUTCH-1 signal indicates that a lesser force is being exerted on the transmission by clutch 1. Thus, a greater force is being exerted on the transmission by clutch 1 during an engine stop and is reduced at mark 412 in response to the timing of combustion event 402. The amplitude of the higher portion of CLUTCH-1 can be adjusted based on operating conditions to control the transmission locking force, as shown in Fig. 7, as an example.

[0050] The CLUTCH 1 signal is gradually decreased so that Clutch 1 begins to release the rotating components of the transmission from the transmission case and the vehicle chassis. For example, the CLUTCH 1 signal can release a transmission shaft.

[0051] In this example, a reduction in the locking force applied by CLUTCH-1 to the transmission is timed relative to the timing of a first combustion event in cylinder number one, even though cylinder number two is the first cylinder to combust an air-fuel mixture. Furthermore, the timing of the CLUTCH-1 signal adjustment is shown to coincide with the timing of the CLUTCH-2 signal, but the timing of the CLUTCH-1 and CLUTCH-2 signals need not coincide with a first combustion event of a particular cylinder.

[0052] The sixth trace from the top of the figure shows timing of the adjustment of another actuator of a transmission, specifically a transmission clutch, to adjust a locking force in response to a first combustion event of a cylinder. Analogous to the CLUTCH-1 signal, the high portion of the CLUTCH-2 signal, to the left of mark 414, indicates that a greater force is being applied to the transmission by clutch 2. The lower portion of the CLUTCH-2 signal indicates that a lesser force is being applied to the transmission by clutch 2. Thus, during an engine stop, a greater force is applied to the transmission by clutch 1 and is reduced at marks 412 and 414 in response to the timing of combustion event 402. The amplitude of the higher portion of the CLUTCH-1 and CLUTCH-2 signals can be adjusted based on operating conditions to control the transmission locking force.

[0053] The CLUTCH-1 and CLUTCH-2 signals are representative of control signals for locking and unlocking a transmission. In some embodiments, only a single clutch may lock a transmission, while in other embodiments, three or more clutches may lock a transmission. Thus, for some transmissions, only the CLUTCH-1 signal may be valid. Furthermore, the CLUTCH-1 and CLUTCH-2 signals are not necessarily intended to correspond to a first gear clutch and a second gear clutch, but rather to any two clutches that operate to lock a transmission when applied.

[0054] Now with reference to Fig. 5, a flowchart of an exemplary engine start-up routine is shown. At 502, routine 500 determines operating conditions. Operating conditions may include, but are not limited to, engine temperature, ambient air temperature, barometric pressure (e.g., an indication of altitude), engine crankshaft position, engine camshaft position, torque converter input speed, torque converter output speed, vehicle brake pressure, humidity, transmission oil temperature, transmission oil pressure, engine position, and fuel type. The engine position at stop may be retrieved from memory or by interpreting engine position sensor information while the engine is stopped. Routine 500 proceeds to 504 after determining the operating conditions.

[0055] At 504, routine 500 judges whether or not an engine start request has been made following an engine stop. An engine start request may be made by a driver's action (e.g., changing the position of an actuator such as a brake pedal or accelerator pedal) or by a controller that automatically requests engine start in response to operating conditions (e.g., low battery charge, an air conditioning request, a traffic signal change, a preceding vehicle moving away from the stopped vehicle). If routine 500 judges that an engine start request has been made, routine 500 proceeds to 506. Otherwise, routine 500 proceeds to the exit.

[0056] At 506, routine 500 engages a starter motor and begins rotating the vehicle engine to start. Further, fuel injection and a spark are initiated at 506. Fuel injection and spark may be delivered sequentially to engine cylinders according to engine positions and the order of combustion in engine cylinders. Alternatively, the engine may be directly cranked by injecting fuel into a cylinder and igniting an air-fuel mixture with a spark. In direct-start applications, routine 500 may determine the first engine combustion event by predicting that the first cylinder to receive fuel will be the first cylinder to combust an air-fuel mixture after an engine stop. Routine 500 proceeds to 508 after the engine starter motor is engaged or after a direct crank is initiated.

[0057] At 508, routine 500 tracks engine position as the engine rotates and predicts the engine position of a first combustion event after engine shutdown. Engine position is tracked using position information acquired from crankshaft and camshaft position sensors.

[0058] Furthermore, the camshaft and crankshaft sensors can be used to update an engine position stored in memory from the last engine stop. For example, if, as in Fig. 3, a four-cylinder engine with cylinder number one stopping in an intake stroke, routine 500 may determine that cylinder number one will be the first cylinder to combust an air-fuel mixture after the engine stops because cylinder number one has a fresh air charge that may be mixed with fuel injected into cylinder number one via an intake port or directly. Thus, routine 500 may judge or predict that cylinder number one will be the first cylinder to combust an air-fuel mixture. Further, routine 500 may determine the engine crankshaft position at which combustion will begin since the engine controller adjusts spark timing. In another example, routine 500 may predict the location of a peak cylinder pressure based on the cylinder air charge and spark timing of cylinder number one.Thus, routine 500 may determine the timing of events related to the first combustion event in cylinder number one since engine shutdown.

[0059] The timing or predicted timing of events related to the first combustion event of cylinder number one may be used at 512 as reference timing for adjusting a transmission actuator, such as a transmission clutch or a transmission pressure control valve. Similarly, since the order of combustion is known for the engine, events related to the first combustion events in cylinders 2-4 may also be determined and / or predicted. In other examples, the output of a sensor may be used to determine an event of a cylinder related to a first combustion event in the cylinder. For example, a pressure transducer may be used to monitor the cylinder pressure in cylinder number one. The first time the pressure in cylinder number one exceeds a threshold pressure since an engine shutdown may be used to identify a first combustion event in cylinder number one.Thus, an event related to the first combustion event in an engine cylinder may be predicted and tracked based on engine position information, or it may be detected by a transducer. In another example, an ion detector may determine an engine event. Routine 500 proceeds to 510 after tracking engine position and events related to first combustion events in engine cylinders.

[0060] At 510, routine 500 judges whether the engine is in a position related to a first combustion event in an engine cylinder. In one example, routine 500 may track engine position and predict an event related to a first combustion event of an engine since the engine was stopped. In another example, routine 500 may track engine position and predict an event related to a first combustion event of a particular engine cylinder. If routine 500 judges that the engine is in a position corresponding to a first combustion event of a cylinder or a position of a predicted first combustion event, routine 500 proceeds to 512. Otherwise, routine 500 returns to 508.

[0061] At 512, routine 500 begins by adjusting a transmission actuator to reduce a locking force applied to the transmission. In one example, the force applied by a gear clutch may be reduced to reduce the transmission locking force. By reducing the transmission locking force, a portion of the torque input to the transmission may be directed to the transmission output and vehicle wheels. As indicated by Fig. 3-4, the rate of release and timing of the transmission coupling may be related to the amount of torque on the transmission input shaft as well as the amount of force applied to the vehicle brakes. Furthermore, in another example, the timing of a reduction in force applied to one clutch locking the transmission relative to a first combustion event of an engine cylinder may be varied from a reduction in force applied to another clutch locking the transmission. Depending on the system configuration, the type of transmission actuator that is adjusted may vary. For example, in one example, a position of a valve actuator that supplies oil to a transmission clutch may be adjusted. In another example, a solenoid that controls the line pressure of oil in the transmission may be adjusted.Furthermore, the voltage or current provided to an oil pump that sends oil to the transmission may be varied when routine 500 judges that the engine is in a position related to a first combustion event of a cylinder. The method of . Fig. Figure 6 provides further details on how transmission actuators may be controlled during a transmission lock release. Routine 500 proceeds to 514 after the transmission actuators are adjusted.

[0062] At 514, routine 500 judges whether or not the engine is being cranked. In one example, routine 500 judges that the engine is being cranked when the engine speed exceeds a threshold speed. If routine 500 judges that the engine is being cranked, routine 500 proceeds to 516. Otherwise, routine 500 proceeds to 518.

[0063] At 516, routine 500 disengages the engine starter. In some examples, the starter pinion may be retracted when the engine speed reaches a threshold speed. Furthermore, the starter may include a one-way clutch so that the starter speed is not increased by the accelerating engine. Routine 500 ends after the engine starter disengages.

[0064] At 518, routine 500 adjusts the position of transmission actuators. In one example, routine 500 may increase the force applied to lock the transmission because it judged at 514 that the engine has not yet started. The transmission actuators may be adjusted to positions or states they occupied prior to an adjustment at 512. In another example, the transmission actuators may be adjusted to positions or states intermediate between the states the actuators occupied when the engine stopped and the positions they were adjusted to at 512. Routine 500 proceeds to 520 after the transmission actuators are adjusted.

[0065] At 520, routine 500 adjusts the engine actuators. In one example, routine 500 may increase an amount of fuel injected into the engine cylinder to improve the likelihood of engine cranking. Furthermore, routine 500 may adjust spark timing and cylinder air volume to improve the likelihood of engine cranking. Routine 500 returns to 508 after the engine actuators are adjusted to improve the likelihood of engine cranking.

[0066] Now with reference to Fig. 6, a flowchart of an exemplary transmission lock release routine is shown. At 602, routine 600 determines the transmission lock force. In one example, the transmission lock force may be determined by the routine of Fig. 7, a value stored in a controller's memory is read. In an alternative example, the transmission lockup force may be determined from oil pressure supplied to one or more transmission clutches. In particular, the oil pressure supplied to a clutch is read with a pressure transducer. The clutch oil pressure may be converted to a force by inputting the measured oil pressure into a function that describes the clutch force in response to clutch oil pressure. Routine 600 proceeds to 604 after determining the transmission lockup force.

[0067] At 604, routine 600 determines an amount of torque transferred to the transmission. In one example, the amount of torque transferred to the transmission may be determined based on engine speed. Specifically, engine speed may be input in a function that describes torque converter output torque as a function of input speed. The transmission input torque is determined by querying a lookup table that relates engine speed to torque converter output torque, which corresponds to a transmission input torque. Routine 600 proceeds to 606 after determining the transmission input torque.

[0068] At 606, routine 600 determines the vehicle braking force. In one example, the vehicle braking force may be determined by using a value stored in the memory of a controller through the routine of Fig. 7. In an alternative example, the braking force may be determined from the oil pressure supplied to the vehicle brakes. Specifically, the oil pressure supplied to the vehicle brakes is read with a pressure transducer. The brake oil pressure may be converted to a force by inputting the measured oil pressure into a function that describes a braking force in response to oil pressure. Routine 600 proceeds to 608 after determining the vehicle braking force.

[0069] At 608, routine 600 reduces the transmission lockup force. In one example, the timing of the release of the transmission lockup force may be determined by querying one or more two-dimensional tables containing empirically determined clutch release timings. In another example, the clutch release rate may be determined by querying one or more two-dimensional tables containing empirically determined clutch release rates. Data in the two-dimensional tables may be retrieved by indexing the two-dimensional tables with a transmission input torque as determined at 604 and a braking force as determined at 606. The output of the two-dimensional table defines the transmission clutch release timing or the clutch release rate.

[0070] It should be noted that while the force applied to the transmission lockup clutches is reduced, the transmission remains locked. Furthermore, during a first condition (e.g., when a vehicle is stopped on an incline), the transmission lockup torque is set to a first magnitude such that torque is not transferred from the engine to the vehicle wheels until a first engine speed is reached (e.g., an engine speed at which the torque converter torque output exceeds the transmission lockup torque). During a second condition (e.g., when a vehicle is stopped on a flat road), the transmission lockup torque is set to a second magnitude, the second magnitude being less than the first magnitude, such that torque is not transferred from the engine to the vehicle wheels until a second engine speed, the second engine speed being less than the first engine speed. In some examples, as described with reference to Fig. As discussed in Figure 7, the transmission lockup torque may be adjusted in response to the vehicle braking force. Furthermore, as the vehicle braking force is increased, the transmission lockup force may be decreased. Thus, in some examples (e.g., when vehicle brakes are released after the transmission lockup torque is released), the transmission lockup torque may be reduced and released at a higher rate than when the transmission lockup torque is set at a higher level.

[0071] Additionally, the transmission lockup force may be reduced in response to the fuel supplied to the engine. For example, if a lower octane fuel is supplied to the engine, the lockup release rate may be reduced, thus increasing the transmission lockup duration. It may be desirable to increase the transmission lockup duration when there is a higher potential for engine misfiring. Alternatively, the release timing may be increased, thus increasing the transmission lockup. Similarly, the transmission lockup force release rate may be adjusted for altitude. For example, the release rate may be reduced as altitude increases. Similarly, the transmission lockup release rate or timing may be adjusted for other engine and / or transmission conditions (e.g., transmission temperature, engine temperature). Routine 600 proceeds to 610 after determining the transmission clutch release timing.

[0072] At 610, routine 600 adjusts the clutch oil pressure. In one example, the pressure of oil delivered to the transmission clutches may be reduced by adjusting a duty cycle of a solenoid. In particular, the duty cycle of a solenoid valve may be reduced to lower the oil pressure delivered to the transmission clutches. By lowering the oil pressure delivered to the transmission clutches, the transmission lock-up force is reduced. In one example, the pressure of oil delivered to the clutches may be feedback-controlled such that if the initial demand does not result in the desired clutch oil pressure, the control command (e.g., duty cycle) is further reduced so that the actual clutch oil pressure equals the desired clutch oil pressure. Routine 600 proceeds to exit after the clutch oil pressure is adjusted.

[0073] Now with reference to Fig. 7, a flowchart of an example transmission lock routine is shown. At 702, routine 700 determines engine stop conditions. Engine stop conditions may include, but are not limited to, atmospheric pressure, engine temperature, cam position, ambient temperature, and throttle position. In some examples, a trailer attached signal may inhibit automatic engine stop if it is determined that a trailer is attached to a vehicle. In other examples, trailer mass may be estimated based on applied braking force and stopping distance during a vehicle stop. In other examples, trailer mass may be estimated from F=m a during vehicle acceleration by solving for m based on vehicle acceleration and estimated torque produced by the engine. Routine 700 proceeds to 704 after engine operating conditions are determined.

[0074] At 704, routine 700 determines the vehicle pitch. In one example, the vehicle pitch may be determined by an inclinometer. For example, if a vehicle is parked on a substantially flat surface, an inclinometer outputs a first voltage. If the vehicle is parked on a hill, the inclinometer outputs a second voltage, where the second voltage is greater than the first. In another example, the vehicle pitch may be determined using a global positioning system. Routine 700 proceeds to 706 after the vehicle pitch is determined.

[0075] At 706, routine 700 determines the vehicle braking force. In one example, routine 700 determines the vehicle braking force according to the following equations: Vehicle_Brake_Force=r⋅m⋅g⋅sin Θ

[0076] Where Vehicle_Brake_Force is a wheel torque, r is a tire rolling radius, m is the vehicle mass, g is a gravity constant, and sin θ is the sine of the angle of the vehicle relative to a horizontal plane. In some examples, the vehicle braking force may be increased by a factor (e.g., 1.2) to account for increases in vehicle mass or other variables, thereby increasing the force applied to the brakes when the engine stops. Further, the mass term m may include the vehicle mass plus an estimated trailer mass. In some examples, the vehicle braking force is stored in memory for use when the engine is restarted and the vehicle is driven away.

[0077] At 708, routine 700 determines the transmission lockup force. The transmission lockup force applied at engine stop is determined based on the vehicle's drive-away strategy. Specifically, if vehicle brakes are released before lockup clutches, the transmission lockup force is adjusted based on the following equation. Trans_tie_clutch_torq=r⋅m⋅g⋅sin Θ

[0078] Where Trans_tie_clutch_torq is the transmission lock-up clutch torque, and where r, m, g, and sin θ are as described above. Furthermore, the mass term m may include the vehicle mass plus any estimated trailer mass. Thus, if the wheel brakes are to release before the transmission lock-up clutches, then the transmission lock-up clutches are set to a force that will hold the vehicle stationary when the wheel brakes are released. In some examples, a multiplier may increase the transmission lock-up clutch force above that of the above equation to further limit the possibility of vehicle movement during a vehicle brake release.

[0079] In another example, when the vehicle wheel brakes are released after the transmission lock-up clutches, the force exerted on the transmission lock-up clutches can be expressed by the following equation: Trans_tie_clutch_torq≥r⋅m⋅g⋅sin Θ−T_brake

[0080] Where Trans_tie_clutch_torq, r, m, g, and sin θ are as described above, and T_brake is the force applied to vehicle brakes. Furthermore, the mass term m may include the vehicle mass plus any estimated trailer mass. Thus, according to this equation, less force may be applied to the transmission lock-up clutches if the vehicle brakes are released after transmission lock-up. However, as indicated by the greater-than symbol, in some examples, the transmission lock-up clutch force is increased above the vehicle holding force (e.g., r m g sin θ).

[0081] In some examples, the transmission locking force may be adjusted with respect to altitude. For example, the transmission locking force may increase with altitude. The altitude adjustment may be implemented as a function whose output is multiplied by the transmission locking force to provide a height-modified transmission locking force. Similarly, the transmission locking force may be adjusted with respect to other engine and / or transmission conditions (e.g., transmission temperature, engine temperature).

[0082] Thus, during a first condition (e.g., when a vehicle is stopped on an incline), the transmission lock-up torque is set to a first magnitude such that torque is not transferred from the engine to the vehicle wheels until a first engine speed is reached (e.g., an engine speed at which torque converter torque output exceeds the transmission lock-up torque). During a second condition (e.g., when a vehicle is stopped on a flat road), the transmission lock-up torque is set to a second magnitude, the second magnitude being less than the first magnitude, such that torque is not transferred from the engine to the vehicle wheels until a second engine speed is reached, the second engine speed being less than the first engine speed. In this way, the transmission lock-up force is set to a first magnitude during a first engine and vehicle stop.During a second engine and vehicle stop following the first engine and vehicle stop, the transmission lockup force is set to a second magnitude that is greater or less than the first magnitude. Routine 700 proceeds to 710 after the transmission lockup force is determined.

[0083] At 710, routine 700 adjusts the clutch oil pressure to lock the transmission at the desired transmission locking force. In one embodiment, a duty cycle of a signal that affects the transmission clutch oil pressure is adjusted to vary the clutch oil pressure and the transmission locking force. In one embodiment, the duty cycle is provided to an electric pump to control the pressure of oil supplied to the transmission. In another embodiment, the duty cycle is provided to a solenoid to control the clutch oil pressure. In one embodiment, the oil pressure may be increased by increasing the duty cycle of a signal applied to an electric pump that supplies oil to transmission clutches. In other embodiments, an analog signal may be provided to a pump that controls the clutch oil pressure in response to a voltage level.In each example, a transfer function relates the actuator duty cycle to a force applied to the transmission clutches. In this way, the requested or desired lockup torque is applied to the transmission clutches. In some examples, routine 700 also stores the transmission lockup force in memory so that the lockup force can be released as desired during engine restart. Routine 700 proceeds to the exit after the clutch fluid pressure is adjusted.

[0084] Thus, the procedures of Fig. 5-7 provides a method for starting an engine, comprising: stopping the engine and, during engine start-up, adjusting a transmission locking force in response to a timing of a first combustion event of a cylinder. The method also includes where the cylinder is a first cylinder to combust an air-fuel mixture since the engine stop. In one example, the method applies where the actuator of the transmission is a clutch. The method also includes adjusting the clutch by varying a pressure of oil supplied to the clutch. The method also includes where the actuator of the transmission is a torque converter lock-up clutch. The method also applies where the clutch is a gear clutch. The method also applies where the actuator is further adjusted during start-up in response to a temperature of the transmission.The method also applies where the actuator continues to be adjusted during engine start-up in response to altitude. The method involves further adjusting the actuator during engine start-up in response to fuel type.

[0085] The procedures of Fig. 5-7 also provide for starting an engine, comprising: stopping an engine; adjusting at least one actuator of a transmission to control a transmission lock-up force during the engine stop; and during an engine start, adjusting the at least one actuator of the transmission to decrease the transmission lock-up torque in response to a timing of a first combustion event of a cylinder of the engine since the engine stop. The method includes where the at least one actuator is a clutch. The method includes where the at least one actuator is adjusted in response to a trailer coupled to a vehicle. In one example, the method applies where the at least one actuator is a torque converter lock-up clutch. The method further applies where the clutch is adjusted by varying a pressure of oil supplied to the clutch. The method further includes where the clutch is a gear clutch.The method includes further adjusting the at least one actuator in response to altitude during engine start-up.

[0086] The procedures of Fig. 5-7 also provide a method for starting an engine, comprising: during a first condition: starting an engine while a transmission is in an operator-selected state; and during a second condition, different from the first condition: stopping an engine at a first engine position; starting the engine while the transmission is in a locked state; and reducing a locking force of the transmission in response to an occurrence of a first combustion event of a cylinder since the engine stop, the occurrence of a first combustion event being related to the first engine position. The method includes where the first condition is a first engine start after the engine has been stopped by an operator, and where a timing of reducing the locking force is predicted based on the first engine position.The method includes the second condition being an engine start after the engine has been stopped by the controller. The method also includes reducing the locking force by opening a clutch of the transmission.

[0087] The procedures of Fig. 5-7 also provide a method for starting an engine coupled to a transmission, comprising: stopping the engine; applying a locking force to the transmission during the engine stop; and reducing the locking force in response to an amount of torque applied to the transmission via a torque converter and an amount of force applied by a vehicle brake. The method includes starting the transmission by engaging at least two gear clutches, wherein the at least two gear clutches, when engaged, ground the transmission input shaft torque to a transmission housing, and wherein the locking force varies from engine stop to engine stop in response to vehicle operating conditions.In one example, the method includes reducing the locking force by an amount that releases the transmission from a locked state in response to torque transferred to the transmission via the torque converter and in response to force applied to the vehicle brake. The method also includes reducing a force applied to the transmission by one of the at least two gear clutches at a rate that is different from a rate of force applied to the transmission via a second clutch of the at least two gear clutches. The method also includes reducing a force applied to the transmission by one of the at least two gear clutches at a different timing than a timing at which a force is reduced to the transmission via a second clutch of the at least two gear clutches.The method further includes reducing the locking force by decreasing an oil pressure applied to a clutch. The method also includes adjusting the locking force in response to a temperature of the transmission. The method also includes adjusting the locking force in response to altitude. The method also includes adjusting the locking force in response to fuel type.

[0088] The procedures of Fig. 5-7 also provide a method for starting an engine coupled to a transmission, comprising: stopping the engine; locking the transmission during the engine stop; and reducing a locking force applied to the transmission in response to an operator input and vehicle braking force during an engine start after the engine stop. The method also includes where the operator input is a change in the position of a brake pedal or an accelerator pedal. The method includes where the reduction in the locking force is related to an amount of torque supplied by an input shaft of the transmission and an amount of force applied to vehicle brakes. The method further includes where the locking force is applied by at least one clutch. The method further includes where the clutch is a gear clutch.The method further includes varying the clutch by varying the oil pressure supplied to the gear clutch. The method further includes determining the torque supplied to the input shaft of the transmission based on a torque converter speed.

[0089] The procedures of Fig. 5-7 also provide a method for starting an engine coupled to a transmission, comprising: stopping the engine; applying a locking force to the transmission during the engine stop; restarting the engine in response to an operating condition, wherein the operating condition is other than an operator input; and reducing the locking force when a transmission input torque exceeds a threshold torque, wherein the threshold torque decreases with increasing force applied to a vehicle brake. The method further includes wherein the operating condition is a battery charge state. The method further includes applying the locking force by actuating a clutch. The method further includes adjusting the locking force in response to operating conditions.

[0090] The Fig. The routines described in Figures 5-7 may be executed by a controller substantially simultaneously during an engine start, or the routines may be executed independently, if appropriate.

[0091] As the average person skilled in the art understands, in the Fig.5-7 represent one or more of a variety of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. As such, various illustrated steps or functions may be performed in the illustrated sequence, in parallel, or in some cases may be omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages described herein, but is presented for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will readily recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy employed.

[0092] This concludes the description. Upon reading the description, many variations and modifications will become apparent to those skilled in the art without departing from the spirit and scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could advantageously utilize the present description.

Claims

[1] A method of starting an engine, comprising: Turn off the engine and during engine start, adjusting a transmission locking force in response to a timing of a first combustion event of a cylinder, wherein the actuator of the transmission is a torque converter lock-up clutch. [2] The method of claim 1, wherein the cylinder is a first cylinder that has been combusting an air-fuel mixture since the engine stop. [3] The method of claim 1, wherein the actuator of the transmission is a clutch. [4] The method of claim 3, wherein the clutch is adjusted by varying a pressure of the oil supplied to the clutch. [5] The method of claim 3, wherein the coupling is a toothed coupling. [6] The method of claim 1, wherein the actuator is further adjusted during cranking in response to a temperature of the transmission. [7] The method of claim 1, wherein the actuator is further adjusted during engine start-up in response to altitude. [8] The method of claim 1, wherein the actuator is further adjusted during engine cranking in response to a fuel type. [9] A method of starting an engine, comprising: Stopping an engine; Adjusting at least one actuator of a transmission to control a transmission locking force during engine stop; and during an engine start, adjusting the at least one actuator of the transmission to decrease the transmission lock-up torque in response to a timing of a first combustion event of a cylinder of the engine since the engine was stopped, wherein the at least one actuator is a torque converter lock-up clutch. [10] The method of claim 9, wherein the at least one actuator is a clutch. [11] The method of claim 9, wherein the at least one actuator is adjusted in response to a trailer coupled to a vehicle. [12] The method of claim 10, wherein the clutch is adjusted by varying a pressure of the oil supplied to the clutch. [13] The method of claim 10, wherein the coupling is a toothed coupling. [14] The method of claim 9, wherein the at least one actuator is further adjusted during engine start-up in response to altitude. [15] A method of starting an engine, comprising: during a first condition: Starting an engine while a transmission is in an operator-selected condition; and during a second condition, different from the first condition: Stopping a motor at a first motor position; Starting the engine while the transmission is in a locked state; and Reducing a locking force of the transmission in response to an occurrence of a first combustion event of a cylinder since the engine stop, wherein the occurrence of a first combustion event is related to the first engine position. [16] The method of claim 15, wherein the first condition is a first engine start after the engine has been stopped by an operator, and wherein a timing of reducing the locking force is predicted based on the first engine position. [17] The method of claim 15, wherein the second condition is engine starting after the engine has been stopped by the controller. [18] Method according to claim 17, wherein the locking force is reduced by opening a clutch of the transmission.

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