Horsepower rating vs pulling power - 3039R vs 3046R

[Dave81]

Hi, I have a tractor question that I can't find the answer to.

I'm wondering if engine hp and torque affects pushing or pulling power with an HST in the same tractor class? I know engine hp increases pto hp but does not affect loader capacity. Does this mean that engine hp and torque does not change pulling or pushing capacity either because the tractor is hydrostatic drive?

For example, would a 3046R plow heavy snow (with chains and ballast - no traction loss) better than a 3039R? Thanks for the help.

 

[ovrszd]

Yes...

 

[jeff9366]

I'm wondering if engine hp and torque affects pushing or pulling power with an HST in the same tractor class? I know engine hp increases pto hp but does not affect loader capacity.

I not a fluid drive expert but I will take a stab at answering anyhow, partly to clarify in my own mind and hopefully learn from others.

FEL is moved by lift cylinders being pumped full of hydraulic fluid. For more lift, more cylinder volume is required. Pretty simple.

Does this mean that engine hp and torque does not change pulling or pushing capacity either because the tractor is hydrostatic drive?

Hydrostatic drive is much more complex because of inclusion of swash plates. Max torque in an HST transmission comes as tractor starts from rest. As throttle opens tractor speed increases but torque decreases. The reason HST transmissions cannot propel tractors very fast is because they run out of torque. Tractor HST transmissions require multiple ranges.
(In contrast to non-fluid CVT transmissions which have only one setting.)

"Hydrostatic transmissions with fixed or variable hydraulic pumps and fixed or variable motor combinations provide an extended range of motor speeds and torques."

I love moldboard plowing with an HST. Tractor barely notices plow sucking into the ground.


MORE: explanation of Hydraustatic operation - Google Search

 

[ovrszd]

Let's not complicate this.

Your question was, would a 3046R plow snow better than a 3039R? Yes.

 

[Dave81]

Thanks for the responses. I think that loader lift capacity is determined by the amount of pressure to the cylinders, which is limited by the pump and unaffected by engine hp. I'm wondering if maybe pressure to the drive is also pump limited, and therefore drive/pushing/pulling power is also unaffected by engine hp?

 

[Dave81]

Let's not complicate this.

Your question was, would a 3046R plow snow better than a 3039R? Yes.

I would think so, especially for gear drive tractors, just not sure about HST.

 

[jeff9366]

I think that loader lift capacity is determined by the amount of pressure to the cylinders, which is limited by the pump and unaffected by engine hp.

I do not believe that is correct. Pump hydraulic flow in volume per unit of time determines potential power. No power until a restriction, which determines pressure.

I wonder if pressure to the drive is also pump limited, and therefore drive/pushing/pulling power is also unaffected by engine hp?

I believe not, due to the characteristics of HST transmissions, particularly dynamic swash plates, which vary torque transmission.

Tractor engine power is transmitted directly to the HST pump and motors when transmission is engaged.

 

[Egon]

The larger the pump output volume the more HP required. Pump size/output volume is not required for ultimate pressure but the rate at which things happen depends on the flow rate.

If the are PD more horsepower will move more fluid.

 

[TSO]

I would say.... Probably.

The limitation here is the overall hydraulic system relief. If both machines (and in truth the HP difference is minor and most likely negligible) have the same system relief setting, then at the end if the day they will probably pull the same.

However, the slightly higher HP may help the pump recover to make output more quickly... In the instance where you put the machine under a heavy load and bog down the engine.

 

[Dave81]

Thanks for all the comments.

TSO, that is exactly what I'm trying to understand. I would think the extra hp would turn the pump with more force if needed, but if the pump and hydro transmission are the same, how much benefit is there really. Probably noticeable if using the tractor to the limit. Thanks for the comment.