This invention relates to hydraulic systems for mobile vehicles and more particularly to an oil reservoir for hydraulic systems used to operate hydraulically actuated components of such mobile vehicles. While the invention has a wide variety of applications, one application where it provides particular utility is in mobile agricultural implements which are typically operated at a variety of attitudes relative to a horizontal plane.
One example of such an application is in a self-propelled windrower. In a prior art windrower disclosed in U.S. Pat. No. 3,469,381, a tubular beam of a horizontally disposed subframe of the windrower is used as an oil reservoir for the machine's hydraulic system. The use of a frame member as an oil reservoir has two basic advantages. The first is that the frame member acts as a large surface area heat sink for cooling the oil. Secondly, the necessity of providing an additional component for the reservoir function is avoided. One known means (described in more detail in connection with FIG. 4 hereinbelow) for venting an oil reservoir formed in a beam of the frame is to provide a pipe connected at one end to an opening in the top wall of the beam. The opposite end of the pipe is provided with a sintered metal porous plug for venting the reservoir while preventing contamination of the reservoir from the outside environment. It has been found that when such machines are used on hillside terrain such that the beam is disposed at an angle relative to a horizontal plane, the vent is subject to oil leakage when a hydraulic function such as raising and lowering the header of the windrower is actuated. The leakage occurs because this function requires the emptying of two single-action hydraulic cylinders into the reservoir and if the angle is sufficient, the outlet opening from the beam into the vent pipe is submerged. When the outlet opening is submerged in the oil and additional oil is injected into the reservoir, there is a rapid pressurization of the air space within the reservoir which acts to force oil through the porous metal vent to relieve the increased pressure.
Accordingly, it is an object of this invention to provide an improved oil reservoir which may be used over a wide range of dispositions or attitudes relative to a horizontal plane without being subject to expulsion of oil from the reservoir vent.
Another object of this invention is to provide an improved oil reservoir which can use a high oil level within the reservoir, without oil expulsion, even though the reservoir is subjected to a wide range of dispositions relative to a horizontal plane during operation.
Still another object of this invention is to provide an oil reservoir of the aforementioned type which requires less maintenance and reduces the risk of oil contamination because the need to add oil to the reservoir is substantially reduced or eliminated.
Still another object of this invention is to provide an oil reservoir of the aforementioned type which provides improved vehicle or machine appearance as the collection of dust and dirt on the machine is reduced with the reduced or eliminated oil leakage.