Understanding FMR, RR, RP, FMD, and FMU in Vehicle Dynamics
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Understanding Vehicle Dynamics: FMR, RR, RP, FMD, and FMU
FMR (Force Moving Resistance): Power required to move machines on a surface, such as through a cut or haul road. The factors determining FMR are:
FMR = RR + RP
Rolling Resistance (RR)
RR (Rolling Resistance): The force opposing the ground at the turn of a vehicle's wheels. To move, the vehicle must counteract this force.
RR = rr x factor pbv
Several factors contribute to RR, the most important being:
A. Internal Friction
Internal friction produced in the powertrain, from the engine to the tires or tracks. Mechanical components like bearings create resistance to movement.
B. Tire Flexion
Flexion of tires increases resistance due to sidewall and tread deformation during spinning. The extent of this distortion depends on design, inflation, tire pressure, and the surface. (Tires with highlights and low relief).
C. Weight on Wheels
The weight on wheels is the sum of the vehicle's empty weight (tare) and the load being carried.
GVW (Gross Vehicle Weight) = TARE + LOAD
Approximately 20 kg/ton is needed for each ton of weight to move a tire machine on a hard, level surface.
Slope Resistance (RP)
RP (Resistance to Progression): The force of gravity a vehicle must overcome when ascending a slope. The magnitude of this force depends on the vehicle's total weight.
When ascending an adverse slope, more power is required in addition to RR. A downhill or favorable slope provides assistance, known as Help of Pending.
The resistance (or assistance) due to the slope equals the PBV (Percent Base Value) multiplied by the slope's inclination, expressed as a percentage per metric tonne (1000 kg).
Drawbar Pull (FMD)
FMD (Force Maximum Drawbar): Determined by two factors: power and speed.
Power
The rate of work execution over time. It's a constant value for a given machine.
Traction Power = Speed * (kg)
Shooting tractive force of the propelled wheels in kg.
Usable Drawbar Pull (FMU)
FMU (Force Maximum Usable): Depends on the grip of the wheels on the ground, varying with weight on wheels and the type of soil the machine moves on.