Propulsion Question: Mini EX vs Tractor

[Henro]

In my search for a Mini Ex to replace my 3PH backhoe, questions keep popping into my mine...

Just wondering how different the hydraulic system on a Kubota mini ex is from my Kubota HST tractors.

It seems like my tractor manuals specify Kubota UDT or SUDT(my choice) but my limited exposure to Kubota mini ex manuals indicates they just seems to mention a regular type of hydraulic oil, with no mention of SUDT or UDT.

So I am wondering if this is an indication that the hydraulic systems on the mini ex may be different, perhaps simpler, than the HST tractors. And therefore perhaps more durable?

Do not know enough to properly ask the question at this point...

 

[Bulldog]

Think of it like this. Every function on the mini is done by hydraulics. It doesn't have a transmission, it has hydraulic drives. It doesn't require sudt2 fluid because it doesn't have a trans, only a hydraulic system. With that said if you want it to perform as it should don't just grab the cheap fluid and dump it in, use premium fluid.

I use the same fluid in mine as I do in my tractors and it works fine.

 

[Henro]

I would never go cheap. But the transmissions in my HSD tractors are mechanical range changes, and the HSD provides the variability in speed.

Thinking more about it, I guess the excavators must also have HSD pumps, if that is what you call them.

would like to hear something from someone who knows for sure though.

 

[Bulldog]

I would never go cheap. But the transmissions in my HSD tractors are mechanical range changes, and the HSD provides the variability in speed.

Thinking more about it, I guess the excavators must also have HSD pumps, if that is what you call them.

would like to hear something from someone who knows for sure though.

The engine in a excavator does nothing but drive a hydraulic pump. Depending on the size of the machine it may have multi stage pumps but they all work alike. Any speed changes to drive motors or any other function on the machine is from either increasing or decreasing flow.

 

[RCW]

Henro -

I don’t have a mini-ex, but I did stay at a Holiday Inn Express once several years ago.....

From my basic understanding, the mechanics of an HST transmission are very different from an hydraulic pump.

As Bulldog mentions, absent the HST transmission and it’s plates with very tight tolerances, ability to generate heat from drive horsepower requirements, etc., some things change.

A diesel train locomotive engine drives an electrical generator. An excavator engine drives hydraulic pump(s).

If Bulldog doesn’t own an excavator, he’s operated and maintained them.

I trust his perspective for preventive maintenance. Over the years, he and I are often in the minority over how routine service could/should be done. I feel I’m in good company if he agrees with me.

I’ve often surmised the shared HST transmission/hydraulics drove the SUDT2 requirements.

Absent the HST, or a transmission at all in the case of an excavator, any “good” trans/hydraulic fluid works, as long as it meets manufacturer specifications.

I might be all wet, just my perception.

 

[Henro]

As I mentioned, I do not have a clue so I am thinking out loud. But since functions move at different speeds, at first thought I was thinking that there was some similarity to a HST.

BUT my three point back hoe functions move at different speeds, depending on where I position the control levers. And the pump runs at whatever speed The pto is turning at.

so I am now thinking the excavator may be a simpler setup, more like my 3PH backhoe, where speed relates to the amount of fluid shifted from the power circuit so to speak.

But then why not do the same on tractors? My guess, again, is perhaps it is a functional, but less efficient, way to make movement happen...

 

[North Idaho Wolfman]

An HST (hydrostat) tractor and a hydraulic drive motor on an excavator do not work anywhere near the same.
It would take a lot of explaining as to how they are different mechanically.
Simplified answer:
A tractor uses a hydraulic pump in addition to and HST unit to run hydraulic functions, where and excavator uses only hydraulic pumps to drive hydraulics and hydraulic motors for the tracks.

One reason that tractors don't use the same hydraulic drive motors is speed.
A HST has a much greater ability at both speed and power via gearing.
Where a hydraulic motor is limited in speed.

 

[Henro]

An HST (hydrostat) tractor and a hydraulic drive motor on an excavator do not work anywhere near the same.
It would take a lot of explaining as to how they are different mechanically.
Simplified answer:
A tractor uses a hydraulic pump in addition to and HST unit to run hydraulic functions, where and excavator uses only hydraulic pumps to drive hydraulics and hydraulic motors for the tracks.

One reason that tractors don't use the same hydraulic drive motors is speed.
A HST has a much greater ability at both speed and power via gearing.
Where a hydraulic motor is limited in speed.

Thanks NIW. That is the conclusion I deduced after thinking about it, I think... Makes sense.

 

[UpNorthMI]

Thanks NIW. That is the conclusion I deduced after thinking about it, I think... Makes sense.

Compared to a tractor the excavator seems so slow for travel, mine has 2 speeds but sometimes I have to travel over a mile from my barn to where I’m working, it’s a very slow journey ....lol

slow travel is 1.8 mph
Fast travel is 3.1 mph

When it comes to clearing stumps and digging the excavator out performs a tractor backhoe by many times.

Excavator just takes regular hydraulic oil, my dealer recommends ISO 46 in Michigan or Kubota all season hydraulic excavator oil

 

[Geoz67]

I have a U17 and it uses hydraulic oil (ISO 46). It has a tiny 900 cc 3 cylinder engine and as it was said before the engine basically only drives the hydraulic pump. Propulsion is also via hydraulically driven motors.

I would take the ex over a back hoe any day, I just move around a lot while using the ex. I'd add that digging is not the only thing I use it for, it's amazing how many jobs around the property need an extra (hydraulic) arm. The ex isn't fast but that's not the point: I can move while I use the arm. To a degree at least, on the U17 the hydraulics are not strong enough to move too many rams at the same time.

Hope that helps.

 

[Henro]

The engine in a excavator does nothing but drive a hydraulic pump. Depending on the size of the machine it may have multi stage pumps but they all work alike. Any speed changes to drive motors or any other function on the machine is from either increasing or decreasing flow.

I forgot to say thanks for the input Bulldog. What you said is what I was thinking.

I assume the hydraulic pump on a small excavator has constant output for a given rpm, and the speed of the hydraulic motors is controlled by diverting some of the flow to the motors. Just like we can adjust a tractors loader speed by feathering the control valve.

 

[Henro]

Henro -

I don’t have a mini-ex, but I did stay at a Holiday Inn Express once several years ago.....

From my basic understanding, the mechanics of an HST transmission are very different from an hydraulic pump.

As Bulldog mentions, absent the HST transmission and it’s plates with very tight tolerances, ability to generate heat from drive horsepower requirements, etc., some things change.

A diesel train locomotive engine drives an electrical generator. An excavator engine drives hydraulic pump(s).

If Bulldog doesn’t own an excavator, he’s operated and maintained them.

I trust his perspective for preventive maintenance. Over the years, he and I are often in the minority over how routine service could/should be done. I feel I’m in good company if he agrees with me.

I’ve often surmised the shared HST transmission/hydraulics drove the SUDT2 requirements.

Absent the HST, or a transmission at all in the case of an excavator, any “good” trans/hydraulic fluid works, as long as it meets manufacturer specifications.

I might be all wet, just my perception.

RCW...my perception is the same.

But I never stayed at a Holiday Inn Express. We have slept in our Ford van a few times in the distant past though...LOL. Until it got too old to trust over any distance...

 

[SidecarFlip]

If my memory serves me right, you had a Subaru when I was there???? I remember you drove like a manic too.....

 

[Bulldog]

I forgot to say thanks for the input Bulldog. What you said is what I was thinking.

I assume the hydraulic pump on a small excavator has constant output for a given rpm, and the speed of the hydraulic motors is controlled by diverting some of the flow to the motors. Just like we can adjust a tractors loader speed by feathering the control valve.

I don't know at what size mini (if any) you can get into the priority controls like the big machines have. On large excavators you can select where you want different strength and/or speed depending on what you are doing. Example, you can slow the swing and add more digging force or any number of combinations. This is where a multi stage pump comes into play. In easy terms you have hydraulic power in reserve that you can select where to apply it.
On a mini it's pretty much up to the operator and feathering the controls like you said. The good thing about a mini is because of the simple design it eliminates expensive electronics.

Bottom line a mini will out work a tractor mounted hoe 10-1. Only draw back is travel speed in my opinion. I try to haul mine as close to the work as I can because it's so slow but when you get there it's amazing what can be done with a small machine. Hope this helps.

 

[Geoz67]

The U17 is pretty small and only has a manual throttle, no auto speed or other options.
However, it tows nicely behind the car on a medium sized trailer.

 

[Henro]

If my memory serves me right, you had a Subaru when I was there???? I remember you drove like a manic too.....

Your memory is half right. We have had Subarus for probably two decades. But I never really drove cars in this country like you remember. Motorcycles, when young, were a different story though...

Now in Europe, especially Germany, when we were traveling for three weeks quite a while ago, the rental car started to shimmy in the front end at 115 MPH. So we cruised at 110 MPH on the highways. Got used to it. When the speed limit dropped to 80 MPH for construction zones or something, we felt like we became snails...

Moral of the story? I guess if I buy a mini ex the speed will suit me in my old age...

 

[ruger1980]

A hydrostatic transmission is nothing more than a variable displacement axial piston hydraulic pump coupled to an axial piston hydraulic motor which can be fixed or variable displacement. The engine drives the pump which drives the motor which in then drives the mechanical section of the driveline.

Most excavators use a variable displacement axial piston hydraulic pump supplying a main control valve with various spools to operate each function. These systems are much more complicated than the usual HST.

The oil used in the excavator is generally only used ion the hydraulic system whereas the HST in most tractors the lube is in a combined sump and must lubricate the mechanical transmission as well. Tractor fluids are designed to lubricate transmissions and differentials while also having friction modifiers for wet brakes and transmission clutch packs.

 

[SidecarFlip]

Your memory is half right. We have had Subarus for probably two decades. But I never really drove cars in this country like you remember. Motorcycles, when young, were a different story though...

Now in Europe, especially Germany, when we were traveling for three weeks quite a while ago, the rental car started to shimmy in the front end at 115 MPH. So we cruised at 110 MPH on the highways. Got used to it. When the speed limit dropped to 80 MPH for construction zones or something, we felt like we became snails...

Moral of the story? I guess if I buy a mini ex the speed will suit me in my old age...

I remember you drove to a beer garden somewhere in or around Pittsburgh and your wife was hollering at you to slow down. I was in the backseat and it was a Subaru station wagon. I remember you were impressed with the power. Your wife wasn't impressed. I also remember how good her Sushi was. Never had that good of Sushi anywhere else, ever and I'm not a fan but it was excellent. Those were the days and I remember you had power and we didn't and that is when I bought the diesel standby genset. You remember right?

 

[lugbolt]

most excavators are entirely hydraulic

The engine drives several hydraulic pumps and that is all it does, drives the pump(s). Those pumps send oil to various valves which direct oil to one or more hydraulic motors and a bunch of hydraulic cylinders.

The systems are so vastly different in every aspect that a different type fluid is specified, specific to running the functions of an excavator or skid steer (SSV or SVL). This is also a very good reason to think about tossing just any fluid into your expensive equipment.

In a very simplified explanation, When you move for instance the forward/reverse travel levers on a mini-ex, all you're really doing it directing low pressure oil thru valves. The valves then send oil at low pressure to actuate the travel pump, which sends high pressure and high volume oil to the travel motor(s). So a low pressure system controls a high pressure system. Some of this stuff runs up to 6500 psi. If direct acting valves were used like on a tractor, or U17 or K008 (I think those are the only two direct acting mini's) you'd be wore out in about an hours' time. Also, because of the volume of fluid needed to run much larger cylinders and motors, you'd have very little control over slow speed hydrualic functions. Enter the pilot system. It reduces (drastically) the amount of effort that the operator needs to use but still allows the system to use high pressure and volume to make the end functions work satisfactorily and without much physical effort from the operator so he can run it all day and not get tired. A lot of times on excavactors the pumps are in a 'neutral' position, with very very little oil being moved if none of the hydraulic functions are being asked for. But when you move a lever, to, say, crowd the stick, pilot pressure is sent to the main pump's actuator, depending on how far you move the lever, to control oil flow to the stick cylinder. Kind of a confusing system? Wait until you have to work on one. You'd be wise to get a hydrualic engineering degree. Then you can work on them with confidence. But the dealer ain't paying an engineer no better than any other mechanic so there you go. One of many challenges facing the industry.

 

[SidecarFlip]

Buddy has a Yanmar Mini-Ex and I let him use my shop to change a travel motor. Those things are a mass of hoses, hard pipes and stuff under the panels. but If I was ever to get one, I'd get a Yanmar. His is basically bulletproof unless he does something stupid with it. A small Mini-Ex digs circles (literally) around any 3 point BH ever made., Why I'd never buy a rear mount backhoe attachment. For what they cost new, you can buy a nice used mini-ex.