Patent Application
20090308198
1. Field of the Invention
This invention relates generally to an apparatus for starting an internal combustion engine, and, in particular, to a start-stop engine cranking system.
2. Description of the Prior Art
An electrical starting motor is used to crank and start an engine in an automotive vehicle. Under normal driving conditions, the engine continues to run after it is cranked by a starting motor. To improve fuel economy, a stop-start engine cranking system turns the engine off after the vehicle stops for a predetermined period, and automatically restarts the engine in response to the vehicle operator's depressing the accelerator pedal, which indicates a desire to accelerate the vehicle. These actions occur without need to turn the ignition key either on or off.
In one version of a stop-start engine cranking system a pinion is permanently engaged with a ring gear, which is driveably connected to the engine. The starting motor does not include an overrun clutch, but, instead, the overrunning clutch is located on the engine flywheel or drive plate, where the engine ring gear is located.
When the engine misfires while attempting to start the engine by cranking it, a large torsion load is transmitted from engine to the starting motor through the ring gear and the starting motor pinion. This torsion load can cause damage to the ring gear and starting motor, or significantly reduce the service life of the ring gear and starting motor. Repair of the ring gear requires a long period and large cost.
A need exists in the industry for a technique to protect the ring gear and starting motor if the engine should misfire or another overload torque condition occurs while the engine is being cranked by a starter motor in a stop-start engine cranking system.
A cranking system starter system for a start-stop cranking system includes an electric motor, an engine crankshaft, a pinion, a ring gear engaged with the pinion and driveably connected to the crankshaft, and a one-way clutch, which alternately opens and closes a drive connection between the pinion and the starter motor and functions as a torque limiter.
A method for operating an engine cranking system includes the steps of securing a ring gear to an engine crankshaft, driveably connecting a pinion to the ring gear, locating a torque limiter one-way clutch in a drive path between the pinion and a starter motor, operating the starter motor, and transmitting torque produced by the starter motor through the one-way clutch, pinion and gear to the crankshaft.
To protect the ring gear and starting motor, an integral pinion and one-way clutch are arranged in series in a drive path between the starter motor and the engine crankshaft. The one-way clutch is engaged while cranking the engine and disengages when a negative torque is applied to the crankshaft by the misfiring engine.
In this way, the integrated one-way clutch releases the drive connection between the starter pinion and motor and the starter shaft. The release avoids damage to the assembly and repair costs.
Yet the system improves fuel economy by permitting the engine to be shut off when the engine idles for a period of predetermined length and by automatically starting the engine in response to a demand for increased wheel torque.
The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art.
The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:
Referring now to
Shaft 16 is supported for rotation on a bearing 22, which is secured to a starter housing 24, and another bearing 26, located at the right-hand side of pinion 12.
The ring gear 18 is formed on a flywheel 28, which is driveably connected to a crankshaft 30 of an engine 32 with a OWC (not shown).
One-way clutch 20 includes a set of clutch actuation elements 34, preferably in the form of rollers or balls, spaced mutually about an axis 36. Each clutch element 34 is located in a annular space, which is bounded by an outer surface 38 formed on pinion 12 and having a slight radial incline, and an inner cylindrical surface 40 formed on shaft 16. Either the inner surface 40 or outer surface 38 is formed with inclined ramps, each ramp extending toward surfaces 38, 40 and spaced angularly about axis 36 from the other ramps.
The depth of each space, i.e., the radial distance between surfaces 38, 40, decreases along each ramp 38 such that each clutch element 34 engages surfaces 38, 40 when the element 34 moves toward the shallow end of the respective space. Each clutch actuating element 34 disengages surfaces 38, 40 when the clutch actuating element moves to the deeper end of the respective space.
A spring 48, located in each of the annular spaces between surfaces 38, 40, urges a clutch actuating element 34 along its respective ramp 38 and away from the clutch engagement position.
Each of the rollers 34 alternately ascends and descends a respective ramp 38, in response to the force of the respective spring 48, the direction of torque carried by pinion 12 and shaft 16, and the relative rotary speed of the pinion and shaft about axis 32.
A seal ring 50, secured to shaft 16 by a snap ring 52, closes the annular space and seals it against entry of contaminants and the loss of lubricant located in the space.
The system 10 further includes a source 54 of electric power, an armature 56 of the starter motor 14, a switch 58 for opening and closing a connection between power source 54 and armature 56, and a controller 60 for changing the state of switch 58. The position of an accelerator pedal 62, i.e., the extent to which the pedal is displaced by the vehicle operator, is represented by a signal 64 produced by a position sensor 66. Controller 60 receives signal 64 as input and determines from that signal whether the operator is causing the engine to idle or is demanding an increase in wheel torque. The controller 60 alternately turns off engine if the engine 32 remains in idle mode for a predetermined period and restarts the engine when a demand for wheel torque is present.
In normal operation, when switch 58 is closed to crank and start the engine 32, the clutch actuating elements 34 move against the force of springs 48 radially into engagement with surfaces 38, 40, the OWC 20 engages, and a drive connection among starter motor 14, shaft 16, pinion 12, ring gear 18 and crankshaft 30 is produced causing starter motor 14 to drive pinion 12 about axis 32 and the engine crankshaft 30 to rotate about its axis at a speed that corresponds to the speed reduction produced by the engagement of pinion 12 with ring gear 18. Thus, positive torque is transmitted from the armature 56 of starter motor 14 to the crankshaft 26.
After the speed of crankshaft 30 reaches a speed at which engine combustion can be sustained, combustion of an air-fuel mixture occurs in the combustion chambers of the engine, either in response to a spark produced by spark plugs controlled by an engine ignition system, in the case of a gasoline engine, or spontaneously, in the case of a diesel engine.
After sustainable engine ignition occurs, controller 60 opens switch 58, which opens the connection to the electric power source 54, causing the starter motor 14 to produce no torque. Consequently, the clutch elements 34 move away from engagement with surfaces 38, 40 due to the force of springs 48, the OWC 20 disengages, and the drive connection opens allowing pinion 12 and starter shaft 16 to rotate independently of crankshaft 30.
Occasionally, an engine misfire or an engine back-rock occurs while cranking the engine 32. The misfire or back rock creates a large magnitude of negative torque and causes a large reverse impact load to be transmitted in the direction from ring gear 18 toward starter pinion 12. That negative torque exceeds the predetermined torsion limit. Thus slip occurs between clutch actuating elements 34 and inner surface 40. The slippage causes the OWC 20 to disengage and makes OWC 20 working as a torque limiter. When a misfire or engine back-rock occurs, therefore, the slipping OWC 20 opens the drive connecting between pinion 12 and ring gear 28, and the large negative torque cannot be transmitted from the engine crankshaft 30, ring gear 18, starter pinion 12 to starter motor 14. Thus, the disengaged OWC 20 prevents damage of the stop-start cranking system 10 due to the negative torque and impact torsion load that would have been applied to system 10 from engine 32.
Referring now to the modular, integral pinion and torque limiter for the engine starter shown in
As
In normal operation, when switch 58 is closed to crank and start the engine 32, the clutch elements 34 move against the force of springs 48 radially into engagement with surfaces 38, 76, the OWC 20 engages, and a drive connection among starter motor 14, shaft 16, sleeve 72, pinion 12, ring gear 18 and crankshaft 30 is produced causing starter motor 14 to drive pinion 12 about axis 32 and the engine crankshaft 30 to rotate about its axis at a speed that corresponds to the speed reduction produced by the engagement of pinion 12 with ring gear 18. Thus, positive torque is transmitted from the armature 56 of starter motor 14 to the crankshaft 26.
After the speed of crankshaft 30 reaches a speed at which engine combustion can be sustained, combustion of an air-fuel mixture occurs in the combustion chambers of the engine, either in response to a spark produced by spark plugs controlled by an engine ignition system, in the case of a gasoline engine, or spontaneously, in the case of a diesel engine.
After sustainable engine ignition occurs, controller 60 opens switch 58, which opens the connection to the electric power source 54.
In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.
