Torque Determination

Torque, rather than horsepower, is crucial for selecting the right hydraulic motor. In most cases, the desired speed is already known, so the focus should be on determining the necessary torque.

Torque is the most critical factor in a Automotive Lift Repair Florida hydraulic motor system, far outweighing speed or horsepower. If the motor lacks sufficient torque to start or operate the load at maximum speed, the system won’t function properly, regardless of horsepower availability.

Once a Automotive Lift Repair Florida hydraulic motor is tentatively selected, you can calculate the required horsepower based on speed and torque. If the horsepower exceeds what the pump can provide, you’ll need to reduce the speed while maintaining the required torque.

Load Torque: This is the twisting or turning force needed to start and/or operate the load at its maximum rated speed. The hydraulic motor must provide this torque. You can estimate the required torque using several methods:

Torque Estimation by Measurement

Breakaway Torque: For small machines, breakaway torque can be measured with a torque wrench or a long lever with weights until the load shaft starts to turn. Calculate torque by multiplying the lever arm length (in feet) by the weight needed to start the shaft. This torque measurement, in foot-pounds, helps determine if the hydraulic motor can handle the load.

Electric Motor Substitution: Temporarily coupling an Automotive Lift Repair Florida electric motor to the load shaft and measuring the motor’s line current while running can help determine running torque. By referring to the motor’s torque/current performance curve, you can estimate the running torque and select a hydraulic motor that matches this requirement. Ensure the electric motor speed approximates the load’s maximum running speed.

Torque Estimation by Comparison

This method involves comparing the new machine to an existing one with similar functions, where torque and speed (or horsepower) are known. For instance, if the new machine produces twice as many parts per hour or processes larger parts, it will require proportionally more horsepower. If the new machine needs to handle larger parts at twice the existing rate, it may require four times the horsepower.

Compare horsepower to find torque by dividing horsepower by speed.

Caution: When comparing Automotive Lift Repair Florida hydraulic motors to electric motors, especially if high starting torque is needed, ensure the hydraulic motor’s starting torque meets or exceeds that of the electric motor.

Torque Estimation by Calculation

For new designs where direct measurement or comparison isn’t possible, torque and horsepower must be calculated:

Once horsepower output is calculated, adjust for friction losses in gearboxes and bearings to estimate the horsepower required from the hydraulic motor. Similarly, adjust for speed changes through gearboxes or chains to determine the input speed for the hydraulic motor.

Example Calculations:

– Winch: For a winch with a 20” diameter drum lifting a 15,000 lb load at 3 ft/sec, the mechanical horsepower is:

– Drilling Machine: The manufacturer usually provides HP and recommended speed specifications, which can be adjusted for friction and speed changes to determine input requirements.

– Vehicle Wheel Motor: Calculate the total drawbar pull to overcome road conditions and use the wheel radius to find wheel torque. Convert travel speed into wheel RPM and select a hydraulic motor to meet these specifications.

Automotive Lift Repair Florida Torque Determination

Despite advancements in predictive maintenance technologies, accurately determining the remaining bearing life of a pump or motor remains challenging.

On the other hand, deteriorating efficiency is easier to detect as it usually manifests through increased cycle times, indicating that the machine is slowing down. When this happens, quantifying the efficiency loss is often unnecessary. If the machine’s performance becomes unacceptable due to slow cycle times, the pump or motor is replaced.

However, in some situations, it is useful or even necessary to quantify the actual efficiency of the pump or motor and compare it to its original efficiency. Understanding hydraulic pump and motor efficiency ratings is crucial for this purpose.

Efficiency Categories

Hydraulic pumps (and motors) are typically described using three efficiency categories: volumetric efficiency, mechanical/hydraulic efficiency, and overall efficiency.

Theoretical flow is determined by multiplying the pump’s displacement per revolution by its driven speed. For example, a pump with a displacement of 100 cc/rev driven at 1000 RPM has a theoretical flow of 100 liters/minute. If the pump delivers 90 liters/minute at 207 bar (3000 PSI), its volumetric efficiency is 90% (90 / 100 x 100).

Volumetric efficiency is often used in the field to assess pump condition based on internal leakage due to wear or damage. However, without comparing it to theoretical flow, the actual flow measurement alone is not very informative.

A mechanical/hydraulic efficiency of 100% would imply that no torque is needed to drive the pump when delivering flow at zero pressure, which is not practically achievable due to mechanical and fluid friction.

For instance, the theoretical drive torque for the Automotive Lift Repair Florida pump can be calculated. If it is 329 Newton meters but the actual drive torque measured is 360 Nm, the mechanical efficiency is 91% (329 / 360 x 100).

Overall Efficiency: This is the product of volumetric efficiency and mechanical/hydraulic efficiency. For the pump example, if volumetric efficiency is 90% and mechanical efficiency is 91%, the overall efficiency is 82% (0.9 x 0.91 x 100). Typical overall efficiencies for various hydraulic pumps are listed in Table 1.

Automotive Lift Repair Florida System designers use the pump manufacturers’ volumetric efficiency to calculate the actual flow delivered by a pump with a given displacement and pressure. This efficiency is crucial for evaluating pump condition based on increased internal leakage.

When calculating volumetric efficiency from actual flow testing, it’s important to note that internal leakage paths within the pump are generally constant. Testing at less than full displacement can skew efficiency calculations unless leakage is accounted for and adjustments are made.

For example, a variable displacement pump with a maximum flow rate of 100 liters/minute tested at full displacement might show a volumetric efficiency of 90% (90 liters/minute flow).