Machine element or mechanism – Engine starters – Automatic
Reexamination Certificate
1998-12-17
2001-05-29
Hannon, Thomas R. (Department: 3682)
Machine element or mechanism
Engine starters
Automatic
C192S066220
Reexamination Certificate
active
06237432
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a starter for a motor vehicle combustion engine.
The invention is more particularly concerned with a starter of the type including an electric motor the drive shaft of which has helical splines for rotating a drive bush which is part of an overrunning clutch that can slide axially on the drive shaft between a rest position at the rear and a front position in which a pinion of the overrunning clutch meshes with a toothed ring on the flywheel of the internal combustion engine, and of the type in which the pinion is coupled axially to the drive bush with which it is constrained to rotate by a rotation enabling device of the drive bush relative to the pinion when the rotation speed of the pinion is greater than that of the drive bush.
BACKGROUND OF THE INVENTION
In conventional starters a freewheel device is disposed between the pinion and the drive bush. The main function of the freewheel is to prevent the pinion driving the electric motor of the starter at too high a speed, likely to damage it, when the internal combustion engine starts.
The freewheel device with rollers also damps sudden vibrations in the torque transmitted between the drive bush and the pinion.
This type of freewheel device using rollers offers very high performance, especially if the excessive speed of the pinion relative to the drive bush continues for a long period, which happens in particular if the driver does not de-energise the starter immediately after the internal combustion engine starts.
This phenomenon is occurring all the more frequently now that the passenger compartments of modern vehicles are increasingly better insulated from the acoustical point of view, this soundproofing blocking perception by the driver of the starting of the internal combustion engine, generally by listening for variations in the sound of the engine.
More recent electronically controlled starters include means for detecting starting of the internal combustion engine and for controlling the starter contactor in such a way as to return the overrunning clutch to its rest position by means of a lever on which the contactor acts.
Thus starters of the above kind use electronic control modules for their electric motor which automatically de-energise the electric motor of the starter and simultaneously return the drive bush to its rest position at the rear in which the pinion no longer meshes with the flywheel of the internal combustion engine.
The “freewheel” phase of operation is therefore of extremely short duration and is independent of the reaction time of the vehicle driver.
A prior art freewheel design, in particular of the type using rollers, is therefore overengineered for its purpose, in particular in relation to the short time for which it operates.
A freewheel of the above kind is therefore too bulky, too heavy and too costly for its function.
Completely eliminating the freewheel device has already been proposed, but eliminating the freewheel also eliminates the damping function, which is to the detriment of the mechanical durability of the starter and its operating noise level, which results in particular from the fact that the resisting torque imposed by the internal combustion engine varies greatly over one rotation of the crankshaft because of the cyclic forces compressing the gases present in the cylinders of the engine.
U.S. Pat. No. 3,666,958 to Ruhle et al. also proposes an inertial overrunning clutch design in which the coupling ring has a conical surround the section of which decreases in the direction towards the drive bush. During starting the enlarged conical drive bush acting on the elastic coupling ring engages with the conical surround. In the above device a compression spring bears against the pinion and against a stop ring fixed to the armature shaft.
In the above design the compression spring has a double role: to pre-stress the two cones and to return the overrunning clutch to its rest position and retain it there. Accordingly, in the operative position, the spring develops a maximal force that increases the residual torque during freewheel operation although a low force is required to avoid transmitting excessive overspeed to the armature.
DISCUSSION OF THE INVENTION
An aim of the invention is to overcome the drawbacks just mentioned by proposing a starter for a motor vehicle internal combustion engine of the type in which the pinion is rotationally coupled to the drive bush by a rotation enabling device of the drive bush relative to the pinion when its rotation speed is greater than that of the drive bush, wherein the device between the drive bush and the pinion includes complementary front and rear friction surfaces respectively carried by the pinion and the drive bush, the pinion is mounted to be mobile axially relative to the drive bush to which it is coupled and the two friction surfaces are pressed elastically into contact with each other with a predetermined force so that the drive bush can rotate relative to the pinion when the rotation speed of the overrunning clutch is greater than that of the drive bush.
In accordance with other features of the invention:
the friction surfaces are two complementary frustoconical surfaces;
the rear frustoconical friction surface is convex and extends axially towards the rear from the front end of the drive bush and in that the complementary front friction surface is concave and extends axially towards the front from the rear end of the drive pinion;
the average diameter of the friction surfaces is substantially equal to the diameter of the primitive cylinder of the pinion;
at least one of the two friction surfaces is covered with a friction lining;
the rotation enabling device between the pinion and the drive bush includes radially oriented front and rear abutment surfaces respectively carried by the drive bush and the pinion and between which are mounted spring means compressed axially to urge the two friction surfaces into contact with each other;
the front abutment surface or the rear abutment surface is an inside radial flange that is part of a connecting cap another inside radial flange of which is opposite an outside radial shoulder on the drive bush or on the pinion;
the drive bush is moved axially from the rear towards the front by one end of a lever received axially in a radial groove in the drive bush.
Further features and advantages of the invention will appear more clearly on reading the following detailed description which is given with reference to the accompanying drawings.
REFERENCES:
patent: 2921473 (1960-01-01), Fellows
patent: 3666958 (1972-05-01), Ruhle et al.
patent: 3905245 (1975-09-01), Mortensen
patent: 4260903 (1981-04-01), Mazzorana
patent: 4261452 (1981-04-01), Barrows
patent: 4330713 (1982-05-01), Greenwood
patent: 4777836 (1988-10-01), Giometti
patent: 5046373 (1991-09-01), Zabrowski et al.
patent: 5050441 (1991-09-01), Giometti
patent: 5237882 (1993-08-01), Giometti
patent: 5241871 (1993-09-01), McKnight, III et al.
patent: 0 732 498 (1996-09-01), None
Hannon Thomas R.
Hansen Colby
Morgan & Finnegan , LLP
Valeo Equipement Electriques Moteur
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