Yanmar Tractors

[nova3930]

A JD/Yanmar dealership would be an interesting marriage since they share the same engines in the compact tractor segment. Of course, Yanmar’s iHMT is a much more advanced transmission than anything that JD offers so folks might gravitate towards the Yanmar’s due to the lower price and better transmission in the YT series.

What's the iHMT do for you? Probably my favorite feature of my 2420 is the power shift transmission on it.

 

[Tractorable]

What's the iHMT do for you? Probably my favorite feature of my 2420 is the power shift transmission on it.

In layman’s terms it puts power to the ground like a power shift and has infinitely variable speed like an HST. You can also toggle between speed/rpm settings with buttons on the loader control stick, and has cruise control.

 

[airbiscuit]

I also thought I read somewhere that you can remove the transmission without splitting the tractor.

 

[Cahaba Valley Farm]

Dealer is in Denton Texas. Lawn Land. The JD sign came down this week. Not sure if they are modifying for JD and Yanmar or replacing JD. This dealer is not carrying the heavy duty field tractors so much as the 75 and under HP tractors. It is a good store and purchased many items, sthil from them in the past.

I know about Lawn Land. That dealer has left me scratching my head more than a time or two. I'm not surprised that they are losing the JD brand, I'm surprised they were able to hold onto it as long as they did.

 

[Cahaba Valley Farm]

In layman’s terms it puts power to the ground like a power shift and has infinitely variable speed like an HST. You can also toggle between speed/rpm settings with buttons on the loader control stick, and has cruise control.

I would like to understand how it compares to Kubota's HST+

 

[mrgreenjeanstx]

I know about Lawn Land. That dealer has left me scratching my head more than a time or two. I'm not surprised that they are losing the JD brand, I'm surprised they were able to hold onto it as long as they did.

Not positive they are losing it yet. it is still early. they have both on the ground right now. We will see how it evolves and signs get replaced.

 

[Tractorable]

I would like to understand how it compares to Kubota's HST+

I’ll take a stab at it.

The Kubota HST+ has an additional transfer case in front of the HST which allows the operator to toggle between low and high range, within the primary range (L, M, H), using a lever on the dash as the tractor encounters different loads.

The Yanmar iHMT is similar in principle, but toggles electronically between pre-set speed/rpm settings using two buttons on the loader joy stick (mode A & B) as the tractor encounters different loads. The Yanmar uses a clutchless shuttle shift lever on the dash with a “gas pedal” on the floor (similar to driving an automatic vehicle) while the Kubota uses a sIngle HST pedal.

The iHMT puts more power to the ground and to the PTO than the HST, and once in gear you can inch around like with an HST.

 

[ptsg]

I’ll take a stab at it.

The Kubota HST+ has an additional transfer case in front of the HST which allows the operator to toggle between low and high range, within the primary range (L, M, H), using a lever on the dash as the tractor encounters different loads.

The Yanmar iHMT is similar in principle, but toggles electronically between pre-set speed/rpm settings using two buttons on the loader joy stick (mode A & B) as the tractor encounters different loads. The Yanmar uses a clutchless shuttle shift lever on the dash with a “gas pedal” on the floor (similar to driving an automatic vehicle) while the Kubota uses a sIngle HST pedal.

The iHMT puts more power to the ground and to the PTO than the HST, and once in gear you can inch around like with an HST.

The HST+ doesn't have another transfer case. It achieves the two speed change by adjusting the swash plate angle on the hydraulic motor, while the rocker pedal still control the swash plate angles on the hydraulic pump. Other brands use a fixed displacement hydraulic motor, hence why they don't have the two speed available. This concept has been around a long time ago on heavy equipment. Kubota simply applied it on a tractor.

The iHMT that Yanmar uses, is basically a scale down version of the Vario transmission that Fendt created. This transmission retains the mechanical power transfer instead of relying on a fluid power transfer like on a common HST, hence it has a lot less losses. It still has an hydrostatic drive but it doesn't actually drive the tractor directly.

 

[airbiscuit]

I finally spent some time to really understand how the IHMT/I-HMT transmission on the YT3 series(YT359/YT347) Yanmar tractors works and now I understand more clearly where the benefits come from and even why it makes hydrostatic noise at a stand-still. Hopefully I can shed some light on this for others as well. There is a good video on YouTube that shows the internal workings/cut-away of the transmission, with a factory rep explaining. I had to watch it a few times before it sunk in. Here, I'll borrow a picture from this video and another on the basic hydrostatic transmission workings to illustrate. See links for them at the end. Apparently this transmission is used in some military vehicles. Due to its efficiency in the working range, I'm predicting it could become the transmission of choice in the higher end hydrostatic tractor market. It's a pretty ingenious design.

I admit I had some reservations about going with it, really due to the newness, but I went with it due to the Yanmar name and quality and it was explained to me that the transmission can be much more easily pulled and serviced if required, through the bolted plate in the rear housing. Also, I wanted the speed control of a hydrostatic transmission, but didn't like the fact that they substantially heat up when pulling heavy loads. I've previously experienced this when pulling a harrow or plow for a couple of acres, albeit with a smaller unit. With the YT359, I have not noticed the transmission heat up really, but it is not an apples-to-apples comparison. I'll leave that to someone who has two comparable size units to try. Based on my understanding of the transmission though, the IHMT should remain cooler. No issues so far, but I'm only at 230 hours. Much of that has been reasonably heavy loader work.

Let's start with a bit about a standard hydrostatic transmission. Take a look at this diagram taken from Mekanizmalar's video on YouTube. This shows a single wheel load and an electric motor, but it illustrates the concept well. You might want to open this and the second picture in separate windows to refer to while reading.


View attachment 556801


This transmission uses an axial piston pump, to the left side with the red handle on its swash plate and an axial piston motor to the right with a fixed plate, powering the wheel to the far right. The connection between the two is purely hydraulic. Instead of an electric motor shown to the far left, the power source would be the compact tractor's diesel engine. This would power the axial piston pump, which sends pressurized fluid along the red line to the axial piston motor, powering the load.

With the swash plate tilted as shown and when the diesel engine turns the pump, each of the pistons rotates around the central shaft, compressing and elongating (due to the swash-plate angle), drawing in fluid from the return side (blue) and pumping it out on the high-pressure side (red). The more the swash-plate is tilted using the red ball handle, the faster the pump moves fluid and the faster the wheel turns. The swash-plate gives infinite speed adjustability. If the swash-plate is tilted perfectly vertically, no compression or elongation happens and no pumping occurs. Also, the tractor can't move, as the hydraulic motor is hydrostatically locked. If the swash plate is tilted in the opposite direction, the pump pumps backwards and drives the wheel in reverse.

The highest efficiency of a standard hydrostatic drive is when it is pumping very little fluid, as low hydraulic flow-rates produce low friction energy loss. This corresponds to the tractor moving, but at a virtual stand-still. The faster you go, the more the transmission pumps. Pumping fluid generates heat, wasted heat, which only makes things worse because you have to get rid of that heat. It also lessens the life of the fluid. Ideally, you want to pump as little as possible.

Now suppose we could get the zero-pumping state of the transmission to correspond with some non-zero speed? If we set this speed at the typical working speed of the tractor for each gear, then when working at this speed we have optimal efficiency (no pumping). This appears to be what Yanmar aimed for with the IHMT. Also, when working slightly away from this optimal speed, we still would minimize the amount of pumping, because only the amount of pumping needed to create the speed offset would be required.

With the workings of a normal HST transmission in mind, it will be easier to explain how the IHMT works. Here is a screenshot from the IHMT YouTube video; Daniel is the guy's name. This is the actual unit used in the YT359/YT347.

View attachment 556802


We can first make correspondences to similar pieces of the normal hydrostatic transmission. The hydraulic motor output of the transmission, connected to the wheels would be where Daniel's left hand is (our right, yellow arrow). There's a lighter blue flange hidden by his hand you can see elsewhere in the video that looks like it bolts to a gear. That gear would be connected to the wheels through the three-speed range gearbox. The white arrow shows the fixed plate of the motor side. This is a complement to the light blue pump side variable swash plate that is shown by the red arrow to the left. The silver round body he is pointing to is connected directly to the diesel motor output. It actually houses the pistons for both the pump side (light blue arrow) and the motor side (light green arrow). The pump and one side of the motor always spin together at the same rate as the diesel motor.

Now suppose you set the swash plate to vertical. No fluid would be pumped, so the motor and pump would be hydrostatically locked together, just like in the case with the standard hydrostatic transmission at zero speed. However, here the tractor is moving, as the output is spinning exactly at the motor's speed. With no pumping, the efficiency should be essentially the same as a gear tractor. Changing the swash plate angle from vertical in either direction will start the pump pumping to either add or subtract from the ideal "no-pumping" speed. I assume that Yanmar designed the system so that this no-pumping speed is in the middle of the speed range for that gear, but I'm not sure if there is a good reason to bias that toward the slow or fast side of the range. Yanmar, if you are reading, you might want to consider a dash light indicating hydrostatic lock or some kind of efficiency metric that could be aimed for while working. It would allow us to maximize fuel efficiency.

... it was explained to me that the transmission can be much more easily pulled and serviced if required, through the bolted plate in the rear housing​

 

[Cahaba Valley Farm]

It still has an hydrostatic drive but it doesn't actually drive the tractor directly.

This is where I get lost understanding the concept of this.

This transmission retains the mechanical power transfer instead of relying on a fluid power transfer like on a common HST, hence it has a lot less losses.

Well said, it seems like this design would be superior to straight hydrostat but if so why is Yanmar is the only manufacturer using it?

If there is anyone who has a YT347 or YT359 I would like to know what your experience has been with this transmission.