Engine balancer

Details Engine balancer Engine balancer

2000-01-12

2001-09-11

Argenbright, Tony M. (Department: 3747)

Internal-combustion engines

Vibration compensating device

Balancing arrangement

Reexamination Certificate

active

06286474

ABSTRACT:

TECHNICAL FIELD
This invention relates to an engine balancer having two weighted balance shafts for an internal combustion engine.
BACKGROUND OF THE INVENTION
Certain engine configurations, in particular in-line four cylinder engines, are known to generate second order vibration unbalance. To offset this unbalance, a balancer including a pair of balance shafts is integrated into the engine. The balance shafts are carried in a housing below the crankshaft and rotate in opposite directions at twice the crankshaft speed. A crankshaft gear or chain drives the first balance shaft, which in turn drives the second balance shaft through a pair of drive and timing gears.
A common concern of balancers is gear rattle noise, accentuated at engine idle when the crankshaft rotational velocity fluctuates between firing pulses of succeeding cylinders. The velocity fluctuation causes the meshing teeth of the balance shaft drive and timing gears to lose contact and impact adjacent teeth.
Gear rattle may be reduced by including drag-inducing elements to increase the drag torque on the second balance shaft, thereby reducing the speed differential between the first and second balance shafts. Drag-inducing elements, such as oil pumps, driving chains, and journal bearings, may reduce rattle but at the expense of fuel economy and system efficiency.
In addition, balance shaft gears generally only have a pair of teeth in contact at a given time so these contacting teeth must be able to withstand the impact of the one upon the other. Therefore the gears are usually steel that may be carburized, quenched, and tempered after the final machining of the teeth to provide sufficient strength. Such heat treatment has the potential for distorting the dimensions of the teeth.
SUMMARY OF THE INVENTION
The present invention provides a solution to the noise concern of balancer gear rattle at idle, in addition to several other potential benefits. The balancer drive system is gear-driven with an engine crankshaft helical spur gear driving a first balance shaft gear, which in turn drives a second balance shaft gear in a counter-rotating manner. The gear teeth are designed with sufficiently fine gear pitch, shallow pressure angle, and a high helix angle to yield an involute contact ratio of approximately three and a total contact ratio of approximately five. Therefore about five teeth are meshed at a given time, providing greater load sharing and less noise transmission.
In a preferred embodiment, the crankshaft helical spur gear is made from grey cast iron and drives the first balance shaft gear made from aluminum. The aluminum first balance shaft gear drives a grey cast iron, second balance shaft gear. The mixed material selection provides two key advantages. First, grey cast iron is more likely to have microscopic graphite flakes that provide damping properties to the gears thereby reducing noise vibrations. Second, modern engine blocks and balance shaft housings tend to be made from aluminum for mass efficiency. Aluminum thermally expands at a faster rate than ferrous based materials. If all the gears were made from ferrous material, the backlash between gears, and therefore gear rattle, would increase as the engine temperature increased. Including an aluminum gear provides partial thermal compensation to reduce backlash. The system is designed to take advantage of the benefits from both materials.
Due to the novel gear design and material selection, the balancer drive system may be all gear-driven with no drag-inducing chains. Also roller bearings for the balance shafts, which only require splash lubrication, may be employed instead of journal bearings, which require pressure lubrication.


REFERENCES:
patent: 4300493 (1981-11-01), Berti
patent: 5305656 (1994-04-01), Kamiya et al.
patent: 5535643 (1996-07-01), Garza
patent: 5657728 (1997-08-01), Diggs
patent: 5875753 (1999-03-01), Ishikawa

Affiliated with

Also associated with

Rating

Engine balancer does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Engine balancer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Engine balancer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2491733