KEVOS® MAKEOS · Hydraulics
Hydraulic Motor Drive Sizing
What motor displacement, flow and pump power does this hydraulic drive need for the load torque and speed?
Sizing a hydraulic motor drive through an optional gear reduction: motor torque and speed, the displacement needed at the available pressure difference with mechanical efficiency, the flow with volumetric efficiency, hydraulic and pump input power, and, for a chosen motor size, the actual pressure needed (using the same relations as the hydraulic motor tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load torque | N·m | Torque needed at the load. |
| Load speed | rpm | Speed of the load. |
| Reduction between motor and load (1 = direct) | Gear reduction between the motor and the load. | |
| Gear efficiency | % | Efficiency of the gear reduction. |
| Pressure difference available | bar | Pressure difference across the motor available from the system (relief setting minus line losses and back pressure). |
| Motor mechanical efficiency | % | Mechanical (torque) efficiency of the motor. |
| Motor volumetric efficiency | % | Volumetric efficiency of the motor. |
| Pump overall efficiency | % | Overall efficiency of the pump. |
| Chosen motor displacement (0 = required) | cm³/rev | Displacement of a catalogue motor you are considering. |
Method and formulas
- Motor torque = T_L ÷ (i η_G); motor speed = n_L × i.
- Displacement needed V = 20π T ÷ (Δp η_m) cm³/rev (from T = V Δp η_m ÷ 20π).
- Flow Q = V n ÷ (1000 η_v) L/min; hydraulic power = Q Δp ÷ 600 kW; pump input = hydraulic ÷ η_pump.
- Example: 2000 N·m at 40 rpm through 4:1 needs 199.69 cm³/rev and 33.633 L/min.
Limitations
- Running efficiencies; starting torque efficiency is lower (check breakaway).
- Speed must lie within the motor’s rated range.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a hydraulic motor for a winch, wheel or conveyor drive
- Check whether a chosen motor has enough torque at the pressure available
- Size the pump for the drive
Who it is for
- Hydraulic engineers
- Machine designers
- Mobile equipment designers
What you get
- Motor torque and speed
- Displacement and flow
- Pressure needed and pump power
Interpreting the result
- A larger reduction allows a smaller, faster motor; check the motor’s minimum smooth speed for slow drives.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3418–3425. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
