Measuring and testing – Internal combustion engine or related engine system or... – Compression
Reexamination Certificate
2001-08-24
2003-03-18
McCall, Eric S. (Department: 2855)
Measuring and testing
Internal combustion engine or related engine system or...
Compression
C073S116070
Reexamination Certificate
active
06532810
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
This invention was not made by an agency of the U.S. Government or under a contract with any agency of the U.S. Government.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates generally to belt drives and more particularly to a method and apparatus for protection from damage following failure of, for example, a toothed belt drive as utilized for example in timing belt applications. Timing belt failure may result in expensive damage and/or dangerous consequences, so that the detection of incipient belt failure in this application is very useful and important.
Toothed belt drives are commonly utilized for mechanical power transmission, particularly where a correct angular relationship or “timing” between a driving shaft and a driven shaft needs to be accurately maintained.
Vehicles utilizing internal combustion engines typically have a camshaft with spaced cams mounted on the camshaft for opening and closing engine valves in accordance with the requirements of the engine operating cycle. Some engines use a single camshaft whereas others utilize a plurality of camshafts, for example, two camshafts. The camshafts are typically driven by the engine crankshaft which also transmits the engine power through the vehicle transmission to the wheels.
A typical application for a toothed belt drive is, for example, in a four-stroke cycle automotive engine wherein a camshaft used for operating valves runs at one-half the angular velocity or, otherwise expressed, at one-half the revolutions per minute (rpm) of the crankshaft that drives it by way of the toothed belt and wherein the angular position relationship or timing of the camshaft and crankshaft needs to be maintained accurately.
Traditionally in the past, “link chains” or bicycle chain type timing chains, sometimes utilizing double side by side chains, have been used in car engines to couple the crankshaft to the camshaft, using a driven camshaft sprocket having twice as many teeth as a driving crankshaft sprocket. In some engines, a timing gear train has been used to drive the camshaft from the crankshaft.
Chains and gears are both capable of driving a camshaft while maintaining the required timing relationship between the camshaft and the crankshaft. However, the high cost of chain and gear drives and, to some extent, their operating noise level have more recently led to the widespread use of toothed belts for coupling the crankshaft and the camshaft in automotive engines, particularly in smaller engines. A toothed belt drive is quiet and well suited to driving the camshaft while maintaining the required timing relationship to the crankshaft. The same timing belt drive may also be used to drive, for example, a fuel injection pump, an ignition distributor, or some other accessory.
Examples of toothed belt and timing chain drives may be found in, for example, U.S. Pat. No. 5,463,898 entitled METHOD OF DETECTING TIMING APPARATUS MALFUNCTION IN AN ENGINE issued Nov. 7, 1995 in the name of Blander et al.; and U.S. Pat. No. 5,689,067 entitled DIAGNOSTIC METHOD AND APPARATUS FOR MONITORING THE WEAR OF AT LEAST AN ENGINE TIMING CHAIN issued Nov. 18, 1997 in the name of Klein et al., whereof the disclosure is herein incorporated by reference to the extent it is not incompatible with the present invention.
While a toothed timing belt drive offers advantages, the likelihood of belt failure is present. If a timing belt breaks in such an engine, the camshaft will very soon stop rotating, while the crankshaft will typically continue to turn for a time, either due to its rotational momentum and/or because it is coupled to the driving wheels which continue to turn because of the vehicle's momentum.
In some cases, repairing the engine following such a timing belt failure may merely require realigning the camshaft and the crankshaft into proper relationship and replacing the belt. Naturally, the vehicle will be inoperable until the belt is replaced, generally in a repair shop, and the operator may be stranded. Furthermore, since a broken timing belt can cause instant and total loss of power at an unexpected moment, a potentially hazardous traffic situation can result.
Furthermore, in a number of engines, such as those utilizing a high compression ratio, clearance space at the top of the cylinders may be very restricted such that the pistons can only move freely to the top of their stroke with valves in the closed position.
In such an engine, if the crankshaft is rotating and the camshaft stops so that a valve is held open by its cam, interference between a piston and a stopped valve can occur so that a piston can collide with the stopped valve. This generally leads to extensive damage, and possibly ruining the engine so that the cost of repair is no longer economically justifiable. The likelihood that the problem of valve/piston interference will occur in at least one cylinder of such an engine is generally very high upon loss of a timing belt.
When such interference occurs after timing belt breakage, damage may range from a bent valve, and/or a hole in a piston, damage to a cylinder head and/or a camshaft, a gouged cylinder head, to a completely ruined engine. Furthermore, if the car is being driven at the time of the belt failure, the engine may become locked by the collision of a piston with a valve so that the driving wheels may also become locked, thereby possibly creating a hazardous situation in traffic.
As was stated above, the problem of serious damage following timing belt failure is very likely to occur in high compression ratio engines. These include many high-performance engines and compression-ignition or “diesel” engines wherein the very high compression ratio needed for ignition generally leaves insufficient room for a piston to avoid hitting a valve held open by an inoperative camshaft. Despite the problems consequent on timing belt failure, car manufacturers continue to build such “interference engines” which exhibit the problem, apparently because a “free-running engine” with enough clearance results in lower performance. The problem represents a weak point in engine reliability and, given the usually catastrophic damage resulting from timing belt failure, is likely to result in lowering of customer confidence in the product. Utility type vehicles and other vehicles intended to provide dependable performance in remote areas are thereby made less reliable in a rather unpredictable manner.
The problem of serious damage caused by timing belt failure in automotive engines has been addressed to some extent by maintenance schedules for periodically replacing toothed timing belts in such engines at an interval based on the average life expectancy of such belts. For example, an extensive list of “interference engines”, that is, engines where serious damage is likely following timing belt failure, was made available by The Gates Rubber Company on the Internet at the address http://www.gates.com/interfer.html. Manufacturer's service manuals generally suggest periodic replacement of the belt as precautionary maintenance every 60,000 to 80,000 miles of driving or so.
One manufacturer is understood to provide a belt replacement warning light which indicates when a prescribed odometer mileage has been reached at which point presumably the belt has become less reliable. Nonetheless, failure may occur at any time before the prescribed mileage has been reached.
However, even periodic scheduled belt replacement can, at best, only reduce the average probability of belt failure: an individual belt may exhibit a shorter operating life than the average and, even with a new belt installed, initial failure remains a possibility, resulting in expensive damage to an engine. Generally, the timing belt in a typical automotive engine is not readily visible to the operator and regular inspection to ascertain the condition of a timing belt is inconveni
LandOfFree
Method and apparatus for detecting timing belt damage using... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for detecting timing belt damage using..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for detecting timing belt damage using... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3013894