Power plants – Pressure fluid source and motor – Coaxial impeller and turbine unit
Reexamination Certificate
2002-06-13
2004-08-03
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Coaxial impeller and turbine unit
C060S352000, C060S358000
Reexamination Certificate
active
06769248
ABSTRACT:
REFERENCE TO RELATED APPLICATION
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
This invention has to do with a fluid coupling for use on diesel engine-driven mobile equipment such as wood chippers, rock crushers, road surface grinders (also known as scarifiers or road millers), and the like comminuting mills. This comminuting mill equipment is typically used in conjunction with feedstock conveyors, or in the case of the road surface grinder, used in conjunction with a method to move the grinder along the road to be ground. For controlling the speed and connecting and disconnecting the mills and engines, there are four types of clutch in common use. Three types can be engaged and disengaged with the engine running: a mechanical clutch, a hydraulically operated mechanical clutch, and a fluid coupling. One type must be engaged with the driver stopped and it is usually disengaged with the driver running: a mechanical torque limiter. The feedstock conveyors, or driving mechanisms of road grinders, are typically driven separately by hydraulic motors via hydraulic pumps that are mounted on and powered by the diesel engine, the conveyors being controlled by a manual control valve remotely operated by the operator of the mobile equipment. Heretofore, with a mechanical clutch, the conveyors have been run at a constant speed that may be set by the operator or at a speed that is directly proportional to engine speed. Because the hydraulic pumps and motors are positive displacement; if a jam develops in the mill, the operator operates the control valve to the reverse position, the feedstock conveyor stops and backs up for several seconds at the same speed as it goes forward, and then when the operator observes that the mill is cleared, the operator manually puts the valve into forward position and the conveyor returns to a normal forward feeding rate. A problem with this combination of a mechanical clutch and a manually operated conveyor or road grinder is that the operator's reaction time is slow, compounded because the operator has much equipment to operate simultaneously, and therefore, it is relatively easy to jam a mill to a complete stop. If such a quick and immediate stop occurs, the diesel engine, especially certain susceptible components, such as turbochargers, can be expected to be damaged, often requiring repairs before restart.
These problems of damage to the diesel engine and its susceptible components are generally tolerable when the diesel engines being used are only up to 300 hp. However, the problems that result from a quick and immediate stop are exacerbated as the diesel engine sizes increase to the current levels of 1000 to 1500 HP and as the new electronically controlled fuel systems are introduced that measurably increase the power ratings of diesel engines without significantly changing the physical size and without significantly changing the physical strength of the engines.
Mechanical clutches have been widely used in such diesel engine driven mobile equipment applications. A mechanical clutch mechanism, such as manufactured and supplied by Twin Disc, Inc. of Racine, Wis., is mounted onto the flywheel housing of a diesel engine. In such a manually operated mechanical clutch, a lever is used to operate the clutch pack and requires an operator to be next to the diesel engine and clutch housing while engaging and disengaging the clutch. This arrangement functions reasonably well except when a very hard object or a large amount of feedstock is fed into the comminuting mill, for example, a hammer mill, and the hammer mill becomes overloaded and jams. In this case, the belts driving the hammer mill slip and wear, the bearings become overloaded, and the diesel engine stops almost instantaneously. This damages the bearings, the belts, the clutch, the diesel engine, and the turbocharger for the diesel engine.
As a mechanical clutch is used over time, the surfaces of the clutch plates wear and the linkage needs to be adjusted to make certain the clutch can be fully disengaged at one end of the clutch lever throw and fully engaged at the other end of the clutch lever throw. If the clutch cannot be fully disengaged, then a considerable amount of power can still be transmitted and the clutch plates will get very hot and possibly become severely damaged. If the clutch cannot be fully engaged, then the clutch will slip at high-power conditions and wear rapidly. Because lever activated mechanical clutches require the operator to be situated very close to the diesel engine, clutch, sheave and belts or other load equipment when the lever is actuated to engage and/or to disengage the load equipment, if the high-powered mechanical equipment breaks, parts may be thrown about and pose grave risk to the operator. Hydraulically operated mechanical clutches that use a lever operated master hydraulic cylinder and a slave hydraulic cylinder to operate the clutch permit the operator to be further removed, but the rest of the problems remain.
Another version of an hydraulically actuated mechanical clutch is one wherein the mechanical clutch pack is compressed and thereby engaged by means of hydraulic pressure, and the hydraulic pressure is controlled by an electronic controller, such as manufactured by Power Transmission Technology, Inc., of Ohio. In normal operation, the electronic controller, which is remote from the clutch, can be manually given a signal to engage, and the controller causes hydraulic pressure to act, engaging the clutch. Similarly, a manual signal to the controller can cause the hydraulic pressure to be released, and the clutch pack is released and almost no power is transmitted through the clutch. Under abnormal conditions such as a jam that develops over several seconds, the electronic controller, essentially a dedicated digital computer based controller, can sense a decrease in speed, and the controller can release the clutch pack and attempt to reengage the clutch a series of times. After a preset number of attempts to reengage the mill wherein the speed of the output shaft of the clutch does not increase to engine speed, the electronic controller will decide that the mill is jammed, and the controller can cause the clutch pack to remain released. In summary, this type of electronically controlled, hydraulically actuated mechanical clutch (a) in the case of a jam that develops over several seconds, can separate the engine from the mill when the mill is jammed, saving the engine and its susceptible components from damage, but, in the case of an instantaneous jam, cannot separate the engine from the mill fast enough to avoid stopping the engine and damaging susceptible components, and (b) can sense when there is too much wear of the clutch parts to assure full engagement, and can separate the engine from the mill in this case, or once separated, can maintain separation of the engine from the mill. However, this type of hydraulically actuated mechanical clutch suffers from the problem of all mechanical clutches: From time to time and depending upon operator care and the types of duty to which the mill is subjected, the transmission must be disassembled and the worn clutch plates must be replaced.
For lower power equipment, below perhaps 300 hp, mechanical clutches do not wear much during normal engagement and normal disengagement. However, as the power transmitted increases to the current levels of 1000 to 1500 hp, the wear of mechanical clutches during normal engagement and normal disengagement increases to the point that it is noticeable and is a concern. Due to the wear during normal engagement and normal disengagement, and due to the possibility of shearing shafts and couplings during a quick engagement event and throwing these parts about, it is common practice for manufacturers of all sizes of mechanical clutches to provide signs to be mounted on the equipment and visible to the operators, that the clutches must be engaged when the engine is operating at idle speed, and not above idle
Abrams Gerald L.
Giberson Melbourne F.
Simonelli Mark T.
Wiesinger, Jr. Frederick C.
Leslie Michael
Look Edward K.
Polster Lieder Woodruff & Lucchesi L.C.
Turbo Research, Inc.
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