- #1
Frangelo
- 18
- 0
Hello,
I'm trying to compare efficiency of different hydraulic motors by looking at unit of output per unit of input, viz:
[itex]\frac{rpm × torque}{pressure × flow}[/itex]
I'm a bit flummoxed by one set of motor specs, for Eaton Duraforce motors, which is attached below.
these motors seem to have variable displacement, but operate at a constant pressure.
From the spec sheet, it looks like these motors operate at constant torque with a given pressure, irrespective of displacement (or rpm). that is, the spec sheet does not suggest that torque varies with respect rpm as I've seen on other spec sheets.
this leads me to the dubious proposition that the motor produces more power (rpm x torque) with constant pressure and lower flow.
For example, on the Duraflow 55, it says minimum displacement is 18.3 cm3 / rev.
and at minimum displacement rpm is 4700. So flow in lpm is (18.3 x 4700)/1000 = 86 lpm.
the chart also indicates that at "continuous pressure" of 250 bar (3625 psi) torque is constant at 218nm (161 ft pounds). It doesn't suggest that it is related to any particular displacement.
At maximum displacement, rpm decreases to 4100 rpm, and flow increase to (54.8 x 4700)/1000 = 258 lpm.
But if torque remains constant and RPM decreases, then power output decreases as well.
In other words decreased flow x constant pressure results in higher power output. So I'm clearly doing something wrong.
Perhaps I am misunderstanding what the top line of chart means?
Does "rated size displacemenet" measured in "cm3/rev" mean the amount of fluid required for each revolution of the motor? Or perhaps it means something else?
Any advice much appreciated.
I'm trying to compare efficiency of different hydraulic motors by looking at unit of output per unit of input, viz:
[itex]\frac{rpm × torque}{pressure × flow}[/itex]
I'm a bit flummoxed by one set of motor specs, for Eaton Duraforce motors, which is attached below.
these motors seem to have variable displacement, but operate at a constant pressure.
From the spec sheet, it looks like these motors operate at constant torque with a given pressure, irrespective of displacement (or rpm). that is, the spec sheet does not suggest that torque varies with respect rpm as I've seen on other spec sheets.
this leads me to the dubious proposition that the motor produces more power (rpm x torque) with constant pressure and lower flow.
For example, on the Duraflow 55, it says minimum displacement is 18.3 cm3 / rev.
and at minimum displacement rpm is 4700. So flow in lpm is (18.3 x 4700)/1000 = 86 lpm.
the chart also indicates that at "continuous pressure" of 250 bar (3625 psi) torque is constant at 218nm (161 ft pounds). It doesn't suggest that it is related to any particular displacement.
At maximum displacement, rpm decreases to 4100 rpm, and flow increase to (54.8 x 4700)/1000 = 258 lpm.
But if torque remains constant and RPM decreases, then power output decreases as well.
In other words decreased flow x constant pressure results in higher power output. So I'm clearly doing something wrong.
Perhaps I am misunderstanding what the top line of chart means?
Does "rated size displacemenet" measured in "cm3/rev" mean the amount of fluid required for each revolution of the motor? Or perhaps it means something else?
Any advice much appreciated.