Accessory Drive Arrangement

Technical Field

This invention relates generally to a drive arrangement and more particularly to a power take-off system for driving engine accessories and the like.

Background Art

Conventional power take-offs for driving accessories of an internal combustion engine, such as pumps thereof, normally include a plurality of intermeshing spur gears driven by the crankshaft of the engine. The gears are suitably designed to provide the desired torque and horsepower to the pumps and to minimize the standout dimension of the integrated drive system, i.e., the distances separating the axes of rotation of the various gears from each other and from the rotational axis of the crankshaft. Since the various gears must necessarily mesh at their toothed peripheries, drive systems of this type cannot be packaged as compactly as desired.

Although chain and belt drive systems have also been used for this purpose, they tend to provide even larger standout dimensions. In particular, the axes of rotation of the various pulleys and sprockets of these systems are disposed at even greater distances relative to each other. In addition to exhibiting relatively large standout dimensions, some conventional drive systems of the above type may tend to increase shaft and bearing loads and create related

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problems in proportion to increases in the standout dimensions.

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure of Invention

In one aspect of the present invention, a drive arrangement comprises a rotary first shaft, at least two rotary first members secured on the first shaft, a rotary second shaft disposed in parallel relationship relative to the first shaft, at least one rotary second member secured on the second shaft and extending into nested relationship between the first members, and endless flexible drive means for transmitting rotary motion between the first and second members.

In another aspect and commercial application of this invention, the first shaft is connected to the crankshaft of an engine and the second shaft is connected to an accessory of the engine, such as a pump thereof.

Brief Description of the Drawing

Other objects and advantages of this invention will become apparent from the following description and accompanying drawing wherein:

Figure 1 schematically illustrates a drive arrangement embodiment of the present invention interconnected between an engine and an accessory of the engine; Figure 2 is a side elevational view of the

drive arrangement, taken in the direction of arrows II- II in Figure 1; and

Figure 3 is a side elevational view illustrating a conventional chain and sprocket drive system.

Best Mode of Carrying Out the Invention

Figure 1 illustrates a drive arrangement 10 interconnected between an internal combustion engine 11 and an engine accessory 12, such as a fan, implement, lube, or scavenge pump. Drive arrangement 10 provides a power take-off from a rotary output or crankshaft 13 of the engine for driving, the pump at the desired torque and horsepower levels. It will be understood by those skilled in the art that the drive arrangement has other power take-off applications, such as a final wheel drive for driving the wheels of a tractor or other land vehicle.

In the embodiment illustrated in Figure 1, drive arrangement 10 comprises a rotary first shaft 14, suitably connected to the crankshaft through a standard coupling. The shaft has at least two and preferably three rotary first members 15, 16, and 17 secured in longitudinally spaced relationship thereon. In the vehicle application illustrated, shaft 14 is further connected in a suitable manner to an input shaft of a conventional transmission 18. A rotary second shaft 19 has its rotational axis disposed in parallel relationship relative to the rotational axis of shaft 14 and has at least one and preferably two rotary members 20 and 21 secured thereon.

Rotary members 20 and 21 extend radially outwardly from shaft 19 into overlapping or nested

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relationship between a respective pair of first members 15-17. The rotary members preferably nest as compactly as physically possible without interference and with consideration being given to various design parameters, such as the desired drive ratio. An endless flexible drive means 22 surrounds the rotary members to transmit rotary motion from rotary members 15-17 to rotary members 20 and 21.

In the preferred embodiment of this invention, each of the rotary members constitutes a drive sprocket and drive means 22 constitutes a common chain, either of the block, roller, or silient type. In a roller-chain drive system of the type shown in Figure 1, for example, an efficiency approaching 100% can be realized with no slippage and no initial tension. As shown, a separate chain may be employed with each sprocket with the parallel single chains being suitably assembled on common pins to all strands to provide a relatively high horsepower capacity. The Axial dimension required for the drive arrangement (the axial distance along shafts 14, 19) can be minimized by using an inverted-tooth "silent" chain, such as the Morse "Hy-Vo" or its equivalent. This type of chain renders it unnecessary to space the overlapping sprockets as far apart as the chains of Figure 1 which require such spacing to clear side plates employed therewith. The inverted-tooth "silent" chain enables the sprockets associated therewith to be placed as close together as manufacturing and assembly tolerances (or concern over windage losses) will permit. The design parameters for the drive arrangement, such as the size of the sprockets and

number of teeth employed thereon, will depend on the particular application under consideration. For example, sprocket wheels with fewer than sixteen teeth may be employed for relatively low-speed applications, whereas sprocket wheels having eighteen to twenty-four teeth are normally desirable for high-speed applications. When the two sets of sprockets 15-17 and 20, 21 have the same diameters and the same number of teeth, a 1:1 drive ratio will result. As is well known to those skilled in the arts relating hereto, such drive ratio may be greater or less than unity, depending on the relative sizes and number of teeth employed on the respective .- sprocket sets. As the ratio differs from unity, it may prove desirable to change the shaft having the larger number of sprockets so that sprocket wear is made as uniform as possible. The larger number of sprockets should be those with the smaller number of teeth. In addition, the distance or standout dimension S (Figure 1) between shafts 14 and 19 can be selectively varied depending on the application under consideration and the degree of compactness required in the overall accessory drive system. It is preferred to employ at least three first- sprockets 15- 17 and at least two second sprockets 20, 21 to avoid any bending across the width of chain 22 and any adverse loads on shafts 14, 19 and the support bearings therefor. It should be further understood that rotary members 15, 16, 17, 20, and 21, although preferably chain-driven sprockets, could constitute pulleys employed with suitable belt drives or the like,

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especially toothed belts of the type known in the art as "timing" belts. However, in most power transmission applications, such as that illustrated in Figure 1, chain drives are preferred due to their high efficiency, long service life, and zero slippage capabilities. Other desired functions and design criteria for the chain drive can be found in Marks' Standard Handbook for Mechanical Engineers, Eighth Edition.

Industrial Applicability

Drive arrangement 10 has particular application to land vehicles, isuch as tractors and the like, to function as a power take-off from the engine's crankshaft to drive accessories of the engine. For example, the unitized and modular accessory drive system may comprise an alternator, air conditioning compressor, and pumps for the fan, implement, transmission, and scavenge systems. In certain track-type tractor applications, the unit is isolation-mounted on the right side of the vehicle's main frame, below the operator's compartment, and powered-off the engine flywheel by a U-joint-coupled accessory drive shaft, generally shown in Figure 1. The unitized design of the accessory drive system tends to simplify engine-torque divider removal with a floor plate in the operator's compartment providing ready access to the drive system components for servicing purposes. As discussed above, applicant's unique drive system, wherein sprockets 15- 17, 20, and 21 are disposed in nested relationship, provides for the transmission of high engine torque and horsepower to input shaft 19 for pump 12 while yet

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minimizing the standout dimension S between shafts 14 and 19 (Figure 1). Figure 3 illustrates a conventional chain drive arrangement C wherein a substantially larger standout dimension S' is required for similar applications.

Other aspects, objects, and advantages of this invention can be obtained from a study of the drawing, the disclosure, and the appended claims.