Method of making a vehicle transmission case
A skid steer loader comprising an improved loader main frame and including an operator's compartment designed to present a low profile vehicle particularly suitable for low clearance applications. The loader main frame includes a center compartment partially defined by a pair of longitudinally extending, laterally spaced side beams. The engine for the vehicle is mounted at the rear of the center compartment and is acoustically enclosed by structural elements of the frame. A seat pan mounted on the side beams overlies the engine and transmission and separates the operator compartment from the center compartment. At a forward end of the center compartment an elongated transmission case forms a partial bottom wall and also encloses the chain and sprocket drive system of the vehicle. The side walls of the transmission case are displaced from the side walls of the frame, enabling the operator to straddle the case, thus reducing height requirements for both the operator compartment and the overall vehicle. Uprights secured to the side beams of the main frame at respective outer rear portions thereof partially enclose the rear portion of the center compartment and boom loader arms are secured to upper pivotal mountings provided on the uprights. Respective front ends of the loader arms are arcuately proportioned to extend forward of the wheels of the vehicle. An improved attachment mounting means incorporating a single mid-plane cylinder is provided between respective outer ends of the loader arms, the loader arms also carrying attachment means for implements used with the vehicle. A low profile overhead guard specially fabricated encloses the operator compartment and completes the assembly. This is a division of application Ser. No. 654,256, filed Feb. 2, 1976, U.S. Pat. No. 4,055,262. PAC FIELD OF THE INVENTION This invention pertains to the art of skid steer loaders and more particularly to a main frame for an improved loader adapted to provide an improved operator's module and to incorporate a low profile particularly suitable for low clearance applications. PAC BACKGROUND OF THE INVENTION Skid steer loaders are vehicles possessing a high degree of maneuverability which are propelled and maneuvered by driving the wheels on one side of the vehicle at a different speed and/or in a different direction from those on the other side of the vehicle so as to achieve a turning motion. In the case where the wheels on one side are driven forwardly and those on the opposite side reversely, the loader will turn on its axis or, in other words, spin in its tracks. However, the operator's compartment of such vehicles are typically constricted, with the operator surrounded by the working elements of his machine and buffeted by engine and transmission noise. Typically, the skid steer loader's high levels of maneuverability are put to best use in operation wherein the loader's steering abilities easily enable it to negotiate around obstacles such as struts, columns and supports encountered in an enclosed environment and used to support the structure in which the loader is working. However, in many instances, particularly in agricultural applications, the requirements of the job include a necessity for a machine which has the ability to work under conditions of low clearance as well as conditions requiring high maneuverability. Such low clearance applications requiring a low profile vehicle suggest a further encroachment of the operator's space. Further, the necessity of providing a protective enclosure for the machine operator has heretofore limited the low clearance capability of such skid steer loaders. Heretofore low vehicle clearance has been achieved only at a sacrifice in load capability and power, and with additional encroachment on the operator's compartment. PAC DESCRIPTION OF THE PRIOR ART The prior art vehicles generally present an upright box-like structure of uniform body width wherein all structural members are located inside the inner face of the wheels mounted on the vehicle. A skid steered loader having such a body construction and employing a hydrostatic drive comprising two independent variable speed transmissions, one mounted on each side for driving their respective sets of wheels, is disclosed in U.S. Pat. No. 3,635,365 entitled "Tractor Vehicle with Hydrostatic Drive Means" by James J. Bauer which issued Jan. 18, 1972 to the assignee of the present invention. The design of that vehicle is also the subject of U.S. Pat. No. Des. 224,588 entitled "Self-Propelled Loader Vehicle" by the same inventor, issued Aug. 8, 1972 also assigned to the assignee of the present invention. Efforts to improve the mobility of a skid steer loader vehicle also involved body design. For example, it is known that a skid steer loader should preferably have a wheel base shorter than the center-to-center distance between the wheels on opposite sides of the loader to reduce tire wear and resistance to skid turns. Further, proper weight distribution in a skid steer vehicle improves mobility. Thus the engine is located in the rear and partially counterweights the loader bucket in front. An earlier attempt to change the body design of the vehicle is disclosed in U.S. Pat. No. 3,895,728 entitled "Tractor Vehicle Having Material Handling Subframe" by John F. Heggen which issued July 22, 1975 to the assignee of the present invention. Although the frame described in the above patent was designed to isolate the loader and skid steering forces of the vehicle from the drive components, no consideration was given to improving the operator's compartment of such vehicle or designing such frame for low clearance applications. An early effort to change the profile of the skid steer loader is shown in U.S. Pat. No. Des. 231,482, entitled "Self-Propelled Loader Vehicle" by James J. Bauer, issued April 23, 1974, and assigned to the assignee of the present invention. This latter vehicle represents a scaled down version of a larger vehicle with some design modifications. The rear loader uprights and the boom arms project outwardly from the side frames to overlie the wheels of the vehicle, but an offset knee must be provided at the front end of the boom arms to accommodate power cylinders mounted on each loader arm for operating the loading bucket. Further, the operator enclosure becomes a fairly narrow, high enclosure, severly restricting side-to-side movement of the operator. Further, the load carrying capacity of such vehicle is severely limited since it remains primarily a scaled down version of a larger model. The present invention represents a substantial innovative advance over the prior art in that a vehicle having a mid-range operating capacity (800 lbs. load capability) presents a wider and lower profile specially suited for low clearance, agricultural applications with little sacrifice in operating capacity, and substantial increase in operator compartment space. Further substantial innovative advances have been made to accomplish the low profile of the present vehicle without sacrificing any substantial operating capacity and with marked improvement in operator comfort as summarized below. PAC SUMMARY OF THE INVENTION The present invention comprises an improved main frame for a skid steer loader vehicle, the main frame comprising a center compartment partially defined by a pair of longitudinally extending, laterally spaced side beams. At the rear of the center compartment the main frame integrates a number of structural elements therefor to provide an acoustic enclosure for the engine for dissipating engine noises. Operator comfort is enhanced by substantially reduced noise levels for the loader in the operative mode. The improved acoustic enclosure for the engine reduces noise levels substantially, making the improved loader one of the quietest in the industry. A cross plate is welded between the longitudinally extending laterally spaced side beams at respective rear bottom portions to form a partial floor at the rear of the main frame. A front wall having an inwardly turned top flange is secured between the side beams at respective front portions thereof. A transmission case presenting an elongated, substantially narrow, profile is mounted at a forward end of the side beams to form a partial floor at the front of the main frame for a center compartment of the main frame. Skid steering forces as well as the normal loader forces are largely isolated from the drive components associated with and contained in the case. The interior compartment formed receives the engine at a rear portion thereof. The main frame substantially surrounds the center compartment in laterally spaced relation. Protruding from the case at respective front and rear ends thereof are the stub axles for the vehicle. Brackets mounted on the stub axles secure the case to the side beams of the main frame. Housed within the transmission case is the chain and sprocket drive for each set of wheels for the vehicle. Bolted to the outside of the transmission case are a pair of hydraulic motors which drive their respective set of wheels through the chain and sprocket drive contained within the transmission case. The transmission case is oil filled to lubricate the drive for the vehicle. The mounting of the drive motors on the outside of the case permits a relatively long, narrow configuration for the case enabling a re-design of the operator's compartment which substantially increases the amount of leg room in the operator's space by permitting the operator to straddle the transmission case. New fabrication methods for the transmission case include the manufacture of separate halves of the transmission case with the housings for the stub axles mounted in phase for boring. The housings for the stub axles are bored as mounted on the transmission case with the axle shafts thereafter rotatably mounted in the housings, the separate halves of the transmission case being assembled after the axle housings are bored. This technique substantially reduces welding distortion produced by mounting pre-bored stub axles in place after the transmission case is assembled. The chain drive for the vehicle has also been modified to improve the reliability of the vehicle. The new drive sprocket arrangement places the sprocket driving the rear wheel of each set of wheels at the outer end of the output shaft of the drive motor. The inner sprocket, mounted on the shaft between the outer sprocket and the drive motor, drives the front wheel of the set. Thus the rear chain offers substantial resistance to forces exerted on the vehicles under loading conditions. Torsional forces exerted on the vehicle under loading conditions are substantially greater for the front wheels. By mounting the chains for the front wheels on the inner sprockets moments for the cantilever mounted engine output shaftsare balanced, with the greater forces exerted on the front wheels equalized by the longer moment arms for the rear wheels. The engine is rubber mounted on the bottom cross plate provided at the rear of the center compartment. Suitably secured to the engine are dual axially aligned variable displacement pumps which drive the motors mounted on the transmission case. Mounted between an operator compartment and the engine is a hydraulic reservoir for the pumps. A pair of uprights are fabricated from plate material and are mounted at the rear of the side beams to structurally support loader arms mounted at upper pivotal mountings on each side. In the preferred embodiment the uprights are disposed outwardly of the main frame to lie behind the wheels mounted on the axles secured to the main frame of the vehicle. With the uprights of the loader vehicle lying behind the wheels of the vehicle, the loader arms, of necessity, must overlie the wheels of the vehicle. Accordingly, the front end of each loader arm has been arcuately proportioned to overlie the front wheels of the vehicle and to receive the outer end of the loader bucket thereon. To achieve this configuration the tilt cylinder for the loading bucket must be mounted inboard of the loader arms and the present invention incorporates a single mid-plane bucket tilt cylinder replacing the two cylinders mounted co-planar with the loader arms in the prior art. The improved transmission case, as well as the outboard mounted loader arms, provides a wider, lower prifile for the operator's compartment and permits a substantial reduction in the height of the overhead guard for the vehicle without reducing overall compartment height and a substantial increase in compartment width. Further innovative advances have been achieved in the fabrication of the overhead guard of the vehicle. The overhead guard comprises stamped halves appropriately folded. When the required halves have been formed they are assembled and welded in place to provide a completed guard for the vehicle with minimal assembly time. Mounting means are provided for the overhead guard to absorb energy for protection under roll-over conditions and to vibrationally isolate the operator compartment under normal vehicle operating conditions. The advantage recited above, as well as many others, will become more apparent to the reader in the detailed description set forth below when said description is viewed in conjunction with the drawings provided which are described as follows.
Clark Equipment Company
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B62D B62D E02F B60R B62D B60P B62D Y10T E02F B60R
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James L. James J. Larry E. Lonnie D. Thomas M.
Werner Bauer Albright Hoechst Sagaser