This invention generally relates to transmissions for marine and land vehicles and machines and more particularly to transmission housings used to house the components of transmissions. More specifically, the invention pertains to transmission fluid dipsticks used in connection with a transmission to determine levels of transmission fluid available for operation of the transmission. Another aspect of the invention relates to internal lugs that are circumferentially spaced on an internal surface of the transmission housing for securing in place components of a transmission. In addition, the invention pertains to injection additional cooled transmission fluid into the transmission housing.
Dipsticks for Transmission Housings
Automatic transmissions comprise a series of gears, shafts, clutches, valves and hydraulic controls housed within a transmission housing or casing. The transmission is connected at its front end to an engine crankshaft and flexplate via a torque converter. At its back end, the transmission is connected to an output shaft, which transmits rotary power generated by the engine and transmission to wheel axles, via a universal joint, in the case of an automobile transmission. Such similar transmission arrangements are available for marine vehicles and machinery that include transmissions in combination with engines to generate rotary power.
In such transmissions, an oil pan is mounted and sealed to a bottom of the housing, and provides a reservoir for automatic transmission fluid used to operate the transmission. An oil pump, which is typically positioned toward a front of the transmission housing, is in fluid communication with the oil pan and an interior of the housing via a series of fluidic channels and one or more valve bodies. The oil pump supplies the transmission fluid (oil) under pressure to actuate the various clutches inside the housing in order to transmit power from the engine to the axles and wheels.
To insure that a sufficient amount of transmission fluid is present in the transmission oil pan, the transmission includes a fluid level detection device that is manually inserted either through the transmission housing or the oil pan to detect a level of transmission fluid in the oil pan. The most commonly used device is a dipstick, which is inserted through an access port disposed on a side of the transmission housing and extends into the oil pan. Such a dipstick includes a handle fixed to a thin metal strip that has been stamped with fluid level markings. The metal strip passes through the access port, which includes a raised aperture on the housing and a guide tube positioned at the aperture and fixed to the transmission housing. As indicated above, the access port is typically positioned on a side of the housing (for an automobile, that is the passenger side or driver side) and the dipstick is long enough to allow the top of the dipstick to be positioned at a location that is accessible by hand and convenient for checking.
A less common placement of the dipstick is at the oil pan instead of dipstick passing through the transmission housing. In order to obtain an accurate reading of the transmission fluid level the access port is positioned relatively low on the oil pan. This leaves the dipstick vulnerable to damage as the bottom of the vehicle is exposed and unprotected to road debris. The dipstick and or guide tube can easily snag road debris and become dislodged or ripped from the access port, which then drains the transmission fluid from the oil pan, potentially causing catastrophic failure of the transmission. When the dipstick tube is installed in the transmission housing, it is in a protected area that lies between the transmission housing and the floorboard/firewall of the vehicle so damage from road debris rarely occurs.
Another reason tubes are rarely attached to the oil pan involves servicing of the transmission. Transmissions are serviced (maintained) by removing the oil pan, cleaning and flushing the inside of the transmission, and then changing the oil filter. When the guide tube is attached to the oil pan, the oil pan cannot be easily removed because the dipstick and/or the guide tube hangs up or attaches to parts or areas in the engine compartment. This makes servicing more difficult and time consuming. Conversely, the dipstick and guide tube do not have to be removed during services when attached to the transmission housing; and, a technician simply unbolts and removes the oil pan to perform the required maintenance. Accordingly, the dipstick has been predominantly and traditionally positioned along one of the two sides (primarily the passenger side) of the transmission housing.
However, this traditional placement of the dipstick is not without some shortcomings. More specifically, in competitive or modified vehicles that incorporate original equipment manufacturer (OEM) transmissions, the position of the transmission and transmission housing relative to the engine, engine compartment and/or firewall may be different as compared to OEM vehicles for which the OEM transmission was designed. In addition, after market manufacturers of transmission housings that are used in competitive and modified vehicles generally follow the OEM specifications of the transmission housings and have maintained the traditional placement of the dipstick and guide tube on the passenger side of a vehicle. Accordingly, access to the dipstick may be compromised and difficult to reach.
Internal Lugs for Transmission Housings
The Hydra-Matic 400 transmission, manufactured by General Motors®, and its transmission housing are oftentimes used in competitive vehicles, for example, drag racing vehicles and off-road desert racing vehicles. The transmission housing includes lugs (also sometimes referred to as splines or teeth) that are spaced apart equidistance on an internal surface of the housing. These lugs interconnect with lugs of a transmission component to minimize rotational movement of the component relative to the transmission housing.
While the lugs on the housing are spaced generally circumferentially on the internal surface of the housing, the lugs do not expand the entire internal circumference of the housing. That is, a gap is disposed between two end lugs wherein the gap is larger than the spacing between consecutive lugs. This gap is represented by the square 40 shown in FIG. 5, which is a drawing of the subject invention including lugs at the location of the gap. This gap was provided for ease and speed of manufacturing of the transmission.
A pocket (shown in FIG. 5) is formed in the internal surface of the housing adjacent the lugs to support a component of the transmission housing adjacent to the set of lugs and the gap. During the course of manufacturing of the prior art Hydra-Matic 400 transmission housing, a core or plug is fixed relative to an external mold. This plug includes various projections, protrusions, recesses, voids, channels, etc., representing structural features of the housing that are positioned in mating relationship with matching features on the external mold. The external mold surrounds the plug to form the housing. After the housing is formed between the external mold and the plug, the external mold is removed. A protrusion forming the pocket actually extends forward to an end of the plug so the pocket on the housing extends to the end of the housing. In this manner, the plug can be removed from the formed transmission housing. However, if lugs were formed in the gap, the lugs would block the protrusion on the plug forming the pocket and the plug could not be removed. Accordingly, additional steps in the manufacturing process would be required if lugs were to be formed at the gap.
It is known that, at least with respect to the use of this transmission housing in competitive vehicles as described above, the existence of the gap compromises the structural integrity of the transmission housing. A snap ring is disposed within a slot aligned in each of the lugs, and moving transmission components bump or push against the support ring causing mechanical stress on the lugs. Two end lugs at the gap absorb additional stresses in the absence of the lugs at the gap. As the end lugs at the gap are exposed to additional stresses, they tend to crack or break first, especially in the above-described competitive vehicles. When the end lugs crack or break off this causes what may be characterized as a chain reaction, in which the next consecutive lug eventually breaks and so on until a sufficient number of lugs break destroying the locking interconnection between the transmission and the transmission housing.
As this problem with the Hydra-Matic 400 transmission is well-known to those skilled in the art, some after-market parts manufacturers make and sell parts such as intermediate tabs, supports or plates that are fixed to the internal surface at the gap between the two end lugs. This additional part better distributes the stresses along the lugs to prevent the lugs from breaking. Moreover, not all transmission housings include the above-described gap between the two end lugs. For example, the transmission housings for an Allison AT542 transmission, which have been manufactured at least as early as 1980, include lugs that are spaced equidistance apart and are positioned circumferentially 360° along an interior surface of the housing, and does not include the above-described gap. However, the transmission housing for the AT542, or any other transmission housing designed specifically for another transmission, obviously will not fit a Hydra-Matic 400 automatic transmission, which is an extremely popular transmission for competitive racing and off-road vehicles.
Injection of Cooled Transmission Fluid into Housing
Under extreme conditions, gear train parts of a transmission must transmit higher levels of power thru the transmission. The higher power levels result in more forces being applied to the various gear train parts. Higher forces create more load and friction on the parts. This breaks down the transmission fluid or lubricating oil causing great wear or galling of the parts eventually leading to failure. The loading caused friction also heats up the parts, which breaks down the lubricating properties of the transmission fluid thereby creating even more wear, heating, and friction in an endless downward spiral until the entire transmission fails.
In the OEM transmission applications, oiling and cooling is accomplished by taking pressurized transmission fluid from the torque converter and sending it out to an external cooler via a hose connected to a fitting on the side of the transmission housing. The transmission fluid returns from the cooler in a much cooler state and is injected back into the transmission case via a second hose and fitting in the side of the transmission case that is located near the first fitting and hose toward a front of the housing. This cooled transmission fluid is conducted thru the shafts and gears throughout the gear train. It eventually is sprayed out thru openings in the shafts, gears, clutches and drums and it drains down into the oil pan at the bottom of the transmission. This transmission fluid cools and lubricates the various parts inside the transmission and works adequately under normal transmission use.
In severe duty applications, not enough oil reaches the rear of the gear train to cool and lubricate the parts, because the cooled transmission fluid is introduced toward the front of the housing. General Motors® recognized this problem and in a next generation of transmissions called the 4L80E that succeeded the Hydra-Matic 400, the location of the return oil line was moved to a more central location. The intermediate (sometimes called the center) support housing which is the part that mates to the above-mentioned lugs inside the transmission case, has an additional oil passageway present that allows oil to be transmitted from the outside of the case to the inside gear train section. The 4L80E transmission has been manufactured since the 1990's.
In a effort to make the Hydra-Matic 400 live longer under extreme conditions, it is well-known in the industry (particularly the off-road racing industry) that an additional external oil cooling line may be plumbed into the intermediate support housing. Two companies that have been making this modification to the Hydra-Matic 400 for many years are Rancho Drivetrain Engineering in Temecula, Calif., and Gearworks in Las Vegas, Nev. This is accomplished by drilling and threading the additional oil hole duplicating the 4L80E arrangement. One shortcoming with this procedure is that the casting is very thin where the additional oil fitting is added, so care must be used in installing and properly supporting the extra oil line.