Can someone explain "dual power" on TC45DA

[Z-Michigan]

I test drove a TC45DA this past weekend. I believe these all have HST, but in any case the one I drove did. I notice that the HST has a lever for hi/lo range, and then a button for turtle or rabbit within either range ("dual power" I believe is what NH calls this). I got to drive it for 10 minutes or so and got some feel for the difference, but I'm wondering if someone can explain how the "dual power" works mechanically. I assume that the hi/lo lever is actually switching between two gears in the system. Given that dual power is just an electric switch, is it simply changing something in terms of how the HST responds to the foot pedals? Basically I am wondering if this is a smart and efficient engineering design or if it is more of a fuel-wasting gimmick to create 4 speeds out of 2. I note that the competition in this size range is generally providing a 3-range HST with a lever for all 3 ranges, so I'm assuming that they have 3 distinct gears in the HST system. (And just to clarify, I understand that the HST itself has no gears internally - but I believe the ranges are different gears just as you would get from the range lever on a gear drive tractor, e.g. an 8x8 gear with two ranges and 4 speeds in each range.)

 

[DocHeb]

You're correct, the TC45DA has HST.

JInman will hopefully provide the technical explanation (changing angles of swashplates, and all that...). He's done excellent explanations in the past.

I'll give you a great practical summary: No gimmicks - it's great. Running around the yard in Low Rabbit, dropping into Low Turtle to drive into a dirt pile with the loader, back to Rabbit - all with a simple thumb push. No need for more "gears" than what that machine has.

Just remember that with HST the "go pedals" are not like gas pedals - if you need more torque you let up on the pedal, and if you want more speed without increasing torque you push down on the pedal.

 

[jinman]

Chris, thanks for your confidence in my ability to explain the New Holland HST on the TC45DA and other class III Boomers. As you stated, it works very well and is in no way a "gimmick."

Z-Michigan, you are exactly right about the transmission ranges. The ranges are nothing more than a two or three-speed geared transmission. The input to that geared transmission is the HST transmission. What NH has done with the dual power is to give you a way of changing gears that is easy as pressing a button and can be done on-the-fly. I don't know of any other CUTs that can change gears without coming to a complete stop.

The HST transmission is nothing more than a pump and a motor. The more fluid the pump provides, the faster the motor turns. When you press on the HST pedal, you change the amount of fluid going to the motor. This is done by a variable component inside the pump. It's called a swashplate. When you change the swashplate's angle, the pump's output changes.

The other side of the HST is the motor. In most HSTs, that motor just responds to the input fluid. What NH decided to do was to make a two-speed hydraulic motor. The motor has a swashplate just like the pump, but it is a driven swashplate instead of a pump swashplate. When you press the rabbit-turtle switch, the angle of the motor's swashplate changes and provides two speeds as input to that two-speed geared transmission, effectively four speeds are now available.

For some additional detail, the motor's actual change is either to put it's swashplate at 15º or 9º. This is accomplished with hydraulic fluid pressure. When you press the button, it sends a signal to a solenoid that opens a valve, allowing pressure to change the motor's swashplate.

If there is an electrical failure, the transmission switches to the turtle mode. You would have only two ranges, but you will not be disabled. I've had a wire come off and I can attest to this happening. It will not disable the tractor, only limit the number of gears. I would recommend that anyone with a dual-power HST tranmission become familiar with where the solenoid valve is. It's easy to find under the left side of the operator's platform. The connector can get snagged by brush and pulled loose. In 1200 hours, it has happened to me once. I just stopped, plugged the wire back in, and was on my way in a matter of a few seconds. Reconizing the symptoms took longer than the fix.

I don't think you can call this a gimmick. It's a great feature and I would venture to say that all those who have it love it. It raises my productivity up a notch. I don't think I could easily adjust to another tractor without it.

 

[Z-Michigan]

Thanks, Jim. I have 100 times more understanding now. I have a basic understanding of how a simple HST works and how the swashplate works - although I have to say that there is precious little online explaining HST in technical terms. (Wikipedia has some info if you look under "combine harvester" and "swashplate motor".)

 

[jimg]

I don't know of any other CUTs that can change gears without coming to a complete stop.

Just FYI the MF dynaqps transmission, a semi-power shift, allows clutchless shifting w/i a range (16x16). It looks pretty cool to me. I *think* it's available on all their 1500 series machines and for sure on the 1560. The down side is it seems to only be an option w/ a cab.

 

[dqdave1]

Jinman; Now if we can only convince CNH to put it on the class ii boomers!

 

[Z-Michigan]

The HST transmission is nothing more than a pump and a motor. The more fluid the pump provides, the faster the motor turns. When you press on the HST pedal, you change the amount of fluid going to the motor. This is done by a variable component inside the pump. It's called a swashplate. When you change the swashplate's angle, the pump's output changes.

The other side of the HST is the motor. In most HSTs, that motor just responds to the input fluid. What NH decided to do was to make a two-speed hydraulic motor. The motor has a swashplate just like the pump, but it is a driven swashplate instead of a pump swashplate. When you press the rabbit-turtle switch, the angle of the motor's swashplate changes and provides two speeds as input to that two-speed geared transmission, effectively four speeds are now available.

For some additional detail, the motor's actual change is either to put it's swashplate at 15º or 9º. This is accomplished with hydraulic fluid pressure. When you press the button, it sends a signal to a solenoid that opens a valve, allowing pressure to change the motor's swashplate.

If I understand correctly, in a normal HST the pedals will control the angle of the swashplate on the pump side of the HST (connected to engine) and the swashplate on the motor side of the HST (transmission/final drive) will have its swashplate at a fixed angle. In "dual power" it is possible to change the angle of both swashplates (pedals for pump side, turtle/rabbit switch for motor side). Now my understanding is that a swashplate motor transmits more power as the swashplate angle increases, up to the point where the swashplate can't be angled any more, which I presume is the limit of piston stroke. It seems like the variable motor-side swashplate in "dual power" is just another mechanism to reduce the amount of power transmitted. Am I missing something? Does the lower angle (9 degrees) of the swashplate function to mechanically increase torque, or does the swashplate/pump system operate only as a device to vary the amount of torque transmitted, like a friction clutch does?

 

[jinman]

Now my understanding is that a swashplate motor transmits more power as the swashplate angle increases, up to the point where the swashplate can't be angled any more, which I presume is the limit of piston stroke.

Exactly...The 15º angle is the turtle position and the 9º angle is rabbit. The increased angle supplies less speed/more torque and the lower angle is more speed/less torque.

It seems like the variable motor-side swashplate in "dual power" is just another mechanism to reduce the amount of power transmitted.

Yes, along with increasing the speed of the output. That's the same thing any gear-type transmission gear does, isn't it?

Am I missing something? Does the lower angle (9 degrees) of the swashplate function to mechanically increase torque, or does the swashplate/pump system operate only as a device to vary the amount of torque transmitted, like a friction clutch does?

You got that one backwards. The lower angle reduces the supplied torque and increases the speed of the output. The continuous variance is in the pump side controlled by continuous position of the foot pedal which supplies fluid based on high flow/low pressure or low flow/high pressure up to the limits of the relief valve pressure.

Now, you would think that all you would need is one gear and one HST range since the pedal is continuously variable down to zero and up to maximum, but that is not the case. There is leakage, heat, an other mechanical inefficiencies that make this not possible. The transmissions all will stall if you are trying to climb a steep hill in high range with a tiny pedal movement. I can tell you that there is a dramatic increase in torque when you shift from rabbit to turtle with the dual power switch. Like many other things, the HST works best when you are operating in the mid-range of torque and speed.

Did I fail to mention that you also need to keep the engine speed constant and 2000 or greater rpm for best operation? On an HST, you just set the engine speed for the job you are doing an leave it. There's no need for a variable throttle.

Hope this helps some with your understanding. It's best when you can feel all these effects through the seat of your pants. Nothing beats seat time.

 

[Z-Michigan]

Thanks again, Jim. I didn't realize that the swashplate angle affected both speed and torque, I thought it just varied the amount of power transmitted. Seems like other manufacturers should be copying this idea.

As for seat time - with no load on the tractor during my test drive, I could only tell the speed difference, not any torque difference.