machmeter62 said:
What is the differrence between the hydraulic shuttle and the GST trans? Is it the gear selection process?
Here a good description from the TractorSmart website:
"Hydrostatic Drive. Any hydraulic pump's sole purpose in life is to deliver
some amount (volume) of fluid to some other device, which in turn moves whatever is attached to that device, causing work to be performed. This can be either through linear motion (as in a hydraulic cylinder), or rotary motion (as in a hydraulic motor). If we want to control how quickly our device moves (or rotates), one way we can do that is to
vary the amount of oil that the pump sends to it. If our pump is delivering four gallons a minute, things will happen four times faster than if we only pump one gallon a minute. (Are you with me, so far?) Since we can control our pump's output, we can control the motor's speed. Now, unless we just want to go around in a circle all day long, we've got to figure out how to change
directions. No problem. (You knew that, didn't you?) Most hydraulic motors don't care whether they are turned clock-wise or counter-clockwise. (They probably don't even know the difference!) Since a hydrostatic transmission operates in what is called a closed loop system, consisting of the pump and motor units, we simply reverse the direction of flow from the pump, causing the motor to operate in the opposite direction. Oh, by the way, closed loop means that a fixed amount of system oil is trapped, or contained, within the pump/motor circuit. Assume that a certain hydro transmission is of a size that it contains 500 ml of oil within the closed loop. That volume remains constant, never changing regardless of tractor speed or direction. So, for any change that we make in the output volume and/or direction of flow of oil from the
pump section, a reaction
must occur in the
motor section, inducing a corresponding change in motor speed and/or direction. In reality, there is a certain amount of oil that is constantly escaping from and being replenished back into the closed loop section of the transmission. This is because a small amount of oil is allowed to flow all around the various components for lubrication and cooling purposes. The greatest advantage of a hydrostatic transmission is the ability to infinitely vary the ground speed and quickly change directions. It's like having a million speed transmission. If you need a travel speed of 1.200589 MPH, it is available. Another advantage is reliability. This transmission is, by way of design, pretty much self-protecting from operator abuse. Also, on foot pedal controlled transmissions, there is a built in safety factor in that you need only lift your foot from the pedal, to bring the tractor to a controlled stop. The only disadvantage of note is a slight loss of power at the PTO shaft. You must also remember to apply the parking brake should you park the tractor on a slope. Hydrostatic is, by far, the best choice for turf mowing applications or for any tasks that require constant speed and direction changes within a small area.
Glide Shift. This is a Kubota exclusive. It is best described as a manual shift transmission whereby gear selection is achieved without the necessity to operate the tractor's main clutch. It is very similar in design and function to the synchro-shift type. All of the gears in this transmission are synchronized. The major difference is found in the addition of one hydraulic clutch pack and a hydraulic shift cover that is mounted to the side of the transmission housing. Eight speeds are available, with forward and reverse (shuttle) for each speed. Stay with me as we go through a shifting sequence. Let's assume that we are in 2nd gear and wish to shift into 3rd. Without touching the clutch pedal, we simply move the shift lever from 2nd gear position into 3rd gear position. (Boy, that was easy!). What just happened was, we lined up some oil passages in the shift cover to redirect pressurized hydraulic oil to make the shift for us. The first thing that happened was that the hydraulic pressure that was holding the clutch pack squeezed together was allowed to escape, releasing the clutch. This causes the engine to stop driving the transmission. Next, oil (under pressure) is directed to the 2nd gear shift rail cylinder in a manner which places that rail in neutral. Then, oil pressurizes the 3rd gear shift rail cylinder to move 3rd gear into engagement. Oil is then directed to the clutch pack squeezing it together once again, to reconnect engine drive power to the transmission. The actual shift part of the sequence occurs very quickly, taking about 4/10ths of a second. Clutch pack re-engagement, however, is a time-controlled process in order to allow smooth shifting and eliminate jerkiness in the shifting process. Glide shift has been around for several years now with excellent reliability. It is a great choice if you will be doing a lot of front loader work, as well as working in larger fields. Using a front loader can be
very hard on main drive clutches. With glide shift the need for manual clutching is eliminated
."
