On-­‐Road Measurements of Powertrain Losses that Reduce Fuel Efficiency Tom Johnson Powertrain Items Discussed
Engine output/Individual engine cylinders
Torque converter
Automatic and hybrid transmission throughput and internal losses
Differential losses
Wheel bearing drag
Brake drag
Tire rolling resistance
Aerodynamic drag
Estimating Fuel Economy Loss
Test Vehicle: 1994 Chevrolet Suburban
Vehicle Condi@ons Firestone Steeltex Tires 32 psi 350 V8 4 speed Automa@c Trans 3.42 Rear Axle Ra@o 2WD Selected “Flat” Asphalt Road Transducers Flexplate with Telemetry and RPM Rear DriveshaO with Telemetry and RPM HR Wheel Torque Transducers Wheel Speed Slip Rings Hot Wire Anemometer Air Speed Al@meter Engine Torque
Telemetry Slip Ring Engine Cylinder Variability
Engine Torque
Torque Converter/Transmission Input
Converter Torque = Engine Power– Transmission Input Power Condi@ons: Stall Clutch on/off Gear Selec@on Speed Driving Schedule Fluid Temperature Spin Losses Pump Transducer Etc. Hybrid Motor/Transaxle
Driveshaft
Transmission Loss = Input shaO power– DriveshaO power(RWD) Transmission and Axle Efficiency
Transmission 60 MPH Converter Clutch Locked 98% 30 MPH Converter Clutch Open 72% Rear Axle Low Torque Steady Speed
99% Halfshaft Axle Shaft
Wheel Torque Transducers
Aerodynamic, Tire, Brake, Bearing Forces
Aerodynamic
Forces
Constant speed, Rear drive
vehicle Direction of travel
Rear
Front
Driven Axle
Drive
Torque
Rolling Axle
Losses
RWD Wheel Torque Constituents
Rear Drive Torque Four Tire Rolling Resistance Components Total Vehicle Aerodynamic Drag Vehicle Frontal Area Component Tire Rota@onal Windage Components Two Front Brake Drag Components Two Front Bearing Drag Components Front Drag Torque Front Wheel Bearing Drag Components Front Brake Drag Components ***Determine each individual item, and then subtract it from the measured drive torque Bearing + Brake Drag
Brake Drag Disk Brake Drag is not a constant value High just aOer brake release Asympto@cally drops Can be forced to zero by removing calipers, pads, or pinching brake lines Drum brake drag can be adjusted to zero Wheel Bearing Drag
Ball Bearing Rolling Element Drag is usually very low, and oOen can be ignored Roller Bearing Rolling Element is usually also low enough to be ignored Bearing Seal Drag is usually high enough to cause significant Fuel Economy Reduc@on Bearing Seal Drag is usually high enough to cause significant Fuel Economy Reduc@on Wheel Bearing Drag Demonstra@on Measurement Techniques Residual Front (or Rear) Torque when Brake Drag is Eliminated Measure off Vehicle with Test Stand like Demonstra@on Measure During Bearing Development Assume front and rear bearing proper@es are similar (usually wrong) Front Drag Torque
Stabilized Drag Torque lb-ft
Observation
Left
Right
Total
1
2
3
4
5
6
7
8
9
10
6.0
5.5
4.0
4.0
4.3
3.5
3.7
3.7
5.2
3.8
4.5
4.5
4.8
5.2
5.3
4.3
4.7
4.5
6.0
6.3
10.5
10.0
8.8
9.2
9.6
7.8
8.4
8.2
11.2
10.1
Mean
4.4
5.0
9.4
Cons@tuents Disk Brake Drag Spindle Bearing Drag Four Ball Rolling Elements Four Seals Front Axle ShaOs Two Roller Elements Two Seals RWD Wheel Torque Constituents
Rear Drive Torque Four Tire Rolling Resistance Components Total Vehicle Aerodynamic Drag Vehicle Frontal Area Component Tire Rota@onal Windage Components Two Front Bearing Drag Components Two Front Brake Drag Components Front Drag Torque Front Wheel Bearing Drag Components Front Brake Drag Components ***Determine each individual item, and then subtract it from the measured drive torque Non-Driven Tire Rolling Resistance
F = Crr N F = Rolling Resistance Force Crr = Rolling Resistance Coefficient N = Normal Force (Weight) Note that no rolling resistance torque is present. Non-Driven Wheel Torque Transducers
Do not Respond to Tire Rolling Resistance!
At a constant speed, the driven
wheel torques include torque to
overcome tire rolling resistance
from all four tires.
RWD Wheel Torque Constituents
Rear Drive Torque Four Tire Rolling Resistance Components Total Vehicle Aerodynamic Drag Vehicle Frontal Area Component Tire Rota@onal Windage Components Two Front Bearing Drag Components Two Front Brake Drag Components Front Drag Torque Front Wheel Bearing Drag Components Front Brake Drag Components ***Determine each individual item, and then subtract it from the measured drive torque Vehicle Aerodynamic Drag
Theore@cal Drag, Fd = ½ρ v2CdA A is Frontal Area v is vehicle Velocity ρ is Air Density Cd is Drag Coefficient Vehicle Air Speed
Kanomaxx 6332d Probe 0962-­‐00
0.1 to 50 m/s
Uni-­‐direc@onal Determining Aerodynamic Drag
Fd, is measured using the high resolu@on wheel torque transducer data. A, frontal area, can be usually obtained from Manufacturer, or it can be measured using several different techniques. v, velocity, is usually measured at various values for regression curve fits, but must be measured from air speed, not vehicle speed. ρ, air density, can be determined from air temperature and standard tables Cd, coefficient of drag, is calculated from the data, once other terms are considered. It can include wheel rota@on effects, which are small, and follow the same formulas as vehicle speed. Aerodynamic Drag and Tire Rolling Resistance
Approximating Fuel Consumption
Average Speeds (for Window S@cker MPG): City – 21.2 mph Highway -­‐ 48.3 mph The percent of Horse Power absorbed at the average speed is roughly equal to the percent of fuel consumed at that speed Estimating Fuel Economy Contribution
Chassis Fuel Efficiency Losses
Power Delivered to the Rear Corners of the Vehicle City Schedule (21.2 MPH) Total
100% Aerodynamics Brakes and Front Bearings
Tire Rolling Resistance Highway Schedule (48.3 MPH) Total
100% Aerodynamics Brakes and Front Bearings
Tire Rolling Resistance Torque lb-­‐O
Percent 82
22
9.4
50.6
27% 11% 62% 175.3 115.3 9.4
50.6 66% 5% 29% Questions?