Powertrain Matching John Bucknell DaimlerChrysler Powertrain Systems Engineering What is Powertrain Matching? Selecting the right engine and gearing for a given application Not just performance, but giving the driver the expected response to pedal inputs In automotive applications delves deeper into transmission shift schedules as fuel economy is heavily impacted A little side story to get you in the right mindset which illustrates the difference between motorheads and everyone else The Story of Power and the Power Paradigm (the early life of Electronic Throttle Control at Chrysler) The Beginning Driver Pedal Driver pushes on Pedal to move vehicle Pedal formerly known as Gas Pedal, and before that, Accelerator Pedal Driver Intent Relates to Pedal Position Speed up Driver Intent a lot Speed up a little Maintain speed Foot off Pedal Slow down Floored Pedal Position Driver Intent Driver Intent is essentially acceleration rate (+ or -) Since pedal position is related to driver intent, pedal position is related to desired vehicle acceleration. Vehicle Acceleration Acceleration Relates to Pedal Position Foot off Pedal Floored Pedal Position Vehicle Acceleration Newton’s First Law: F=ma Vehicle mass is constant (ignoring fuel usage, washer solvent spray, and any fluid leaks) So, Force is proportional to acceleration Force Applied to Vehicle Force Relates to Pedal Position Foot off Pedal Floored Pedal Position Where Does the Force Come From? Engine produces some torque, at a speed: Tengine, engine Transmission: Ttrans Tenginentrans trans engine ntrans Ignoring Losses, of Course Where Does the Force Come From? Axle: Taxle Ttransnaxle Tenginentransnaxle trans engine axle naxle ntransnaxle Ignoring Losses, of Course Where Does the Force Come From? Tire: Fvehicle Taxle Tenginentransnaxle TireDiamet er TireDiamet er 2 2 TireDiamet er Vvehicle axle 2 Ignoring Losses, of Course Interesting, but not the end of the Story. Where Does the Force Come From? Note: Tengine Ttrans Taxle engine trans axle Where Does the Force Come From? Power- the rate at which work is done: Power is Force times Velocity (linear) Power Force Velocity FV Power is Torque times Rotational Speed (rotary) Power Torque Rotational Speed T Where Does the Force Come From? Engine produces power: Pengine Tengineengine Where Does the Force Come From? Transmission: Ptrans Ttranstrans engine Tenginentrans ntrans Tengineengine Ptrans Pengine Ignoring Losses, of Course Where Does the Force Come From? Axle: Paxle Taxle axle trans Ttransnaxle naxle Ttranstrans Paxle Ptrans Pengine Ignoring Losses, of Course Where Does the Force Come From? Tire: Pvehicle FvehicleVvehicle Taxle TireDiamet er axle 2 TireDiamet er 2 Taxle axle Pvehicle Paxle Ptrans Pengine Ignoring Losses, of Course Where Does the Force Come From? Power is conserved: Pengine Ptrans Paxle Pvehicle POWER IS ABSOLUTE Torque is relative (depends on gear ratio) Ignoring Losses, of Course Where Does the Force Come From? The force comes from engine power: Pengine Fvehicle Vvehicle At a given vehicle velocity, force, and therefore acceleration, depends on power produced by the engine Force Applied to Vehicle Force Relates to Pedal Position Foot off Pedal Floored Pedal Position Engine Power Engine Power Relates to Pedal Position Foot off Pedal Floored Pedal Position Engine Power Relates to Pedal Position 100 Power Demanded (% of max power) 90 80 70 60 50 40 30 20 10 0 -10 100 75 -20 -30 50 -40 0 25 25 50 75 Vehicle Speed (% of max speed) 0 100 Pedal Position (%) Implications of the Power Paradigm Powertrain Control Vehicle Performance Engine Performance Optimization Criteria Powertrain Control Should provide the power level demanded by the driver as efficiently as possible Efficiency could be based on: minimum fuel consumption minimum emissions best NVH some combination of these or other considerations Should use the best combination of: engine speed (gear ratio) throttle position (ETC) spark advance fuel flow rate EGR rate cylinder deactivation variable valve timing active manifold external charge motion devices Powertrain Control Example Example: minimize fuel consumption at a driver commanded power level pedal position indicates driver wants 100 hp delivered (based on power required vs. pedal position and vehicle speed) need to find engine speed and MAP (throttle position) for best fuel consumption assume Electronic Throttle Control Specific Fuel Consumption vs. Speed & MAP 0.80 0.75 0.70 0.70 0.65 0.65 0.60 0.60 0.55 0.55 0.60 0.50 0.50 0.45 0.40 20 BSFC (lb/hp-hr) 0.45 0.41 6000 5000 4000 70 3000Eng ine S2000 peed (rpm) 1000 80 90 0100 a) 30 P40 k ( AP50 M 60 Engine Power vs. Speed & MAP 300.00 250.00 350 200.00 300 250 150.00 Power (bhp) 200 100.00 75.00 25.00 100 150 100 50 10.00 0 6000 50.00 90 80 70 5000 25.00 60MAP (k 50Pa) 10.00 40 30 10.00 pm) r ( d 3000 pee S e in 2000 Eng 1000 200 4000 Specific Fuel Consumption vs. Speed & MAP 100 90 0.41 0.60 80 70 60 0.45 50 0.50 40 0.55 0.60 0.65 0.70 30 20 0 1000 2000 3000 Engine Speed (rpm) 4000 5000 6000 Engine Power vs. Speed & MAP 100 90 300.00 25.00 80 250.00 200.00 70 150.00 60 100.00 75.00 50 50.00 40 25.00 10.00 30 10.00 10.00 20 0 1000 2000 3000 4000 5000 6000 BSFC vs. Speed & MAP with Constant Power Lines 100 90 300.00 25.00 0.41 0.60 80 250.00 200.00 70 150.00 60 100.00 0.45 75.00 50 0.50 50.00 40 0.55 0.60 25.00 10.00 0.65 0.70 30 10.00 10.00 20 0 1000 2000 3000 Engine Speed (rpm) 4000 5000 6000 Powertrain Control Example Any combination of MAP and rpm along the 100 hp line will satisfy the driver’s power requirement Low rpm and high MAP gives best BSFC Ideally, efficient CVT sets engine speed (1900 rpm, set MAP to 90 kPa) Conventional transmissions with discreet gear ratios must pick gear ratio for combination of rpm and MAP for lowest BSFC at a vehicle speed Vehicle Performance Best possible vehicle acceleration if engine runs at peak power (not at peak torque) requires efficient CVT to change transmission ratio vs. vehicle speed to maintain peak power engine speed Transmission that allows the engine to provide the highest average power over an acceleration event will give best vehicle acceleration more transmission gears improves vehicle acceleration by keeping engine speed in range that makes more power Simulated Vehicle Performance with Different Transmissions 160 140 Vehicle Speed (mph) 120 100 100% Efficient CVT 80 90% Efficient CVT 4 Speed Automatic 60 40 20 0 0 10 20 30 Time (s) 40 50 60 Engine Performance Optimization Criteria Typically engine program goals are a peak torque value and a peak power value Assuming different sets of engine hardware could meet the program goals, only one set of hardware will perform the best in a vehicle The best performing vehicle will have the highest average power delivered to the wheels during an acceleration event, which is dependent on transmission capability Engine Optimization Example: Which Engine Performs Better in a Vehicle? 450 400 Torque (lb-ft), Power (bhp) 350 300 engine A engine B 250 200 150 100 Peak Torque (lb-ft) Average Torque (1200-5600rpm) (lb-ft) Peak Power (bhp) Average Power (1200-5600rpm) (bhp) 50 0 1000 1500 2000 2500 3000 3500 4000 Engine Speed (rpm) 4500 engine A 400 362 350 234 5000 engine B 400 351 350 231 5500 6000 Engine Optimization Example: Which Engine Performs Better in a Vehicle? Average Power from x rpm to 5600 rpm (bhp) 360 340 320 300 engine A engine B 280 260 240 220 200 1000 1500 2000 2500 3000 3500 4000 Engine Speed (rpm) 4500 5000 5500 6000 Engine Optimization Example Engine A & Engine B both meet program objectives Which one is better? It depends on the transmission Engine B will perform better if transmission keeps engine speed above 3200 rpm during an acceleration event This is true for any of the typical vehicle performance metrics: 5 sec. Distance 0-60 time 1/4 mile time Summary The Story of Power Pedal Position relates to driver demanded power output The Power Paradigm Power is Absolute Powertrain (engine/transmission) matching is crucial to maximize vehicle performance Closing Remarks Powertrain Matching makes best use of your engine potential Torque & Power shaping can give optimal performance for a given set of gearing Optimal gearing can make your car faster for no changes in engine performance Copyright © 2011 John Bucknell. All rights reserved.