Powertrain Matching

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Powertrain Matching

• John Bucknell
• DaimlerChrysler
• Powertrain Systems Engineering
• September 30, 2006

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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

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A little side storytoget you in the right
mindset which illustrates the difference
between motorheads and everyone else
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The Story of Powerand the Power Paradigm(the
early life of Electronic Throttle Control at
Chrysler)
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The Beginning
Pedal
Driver

• Driver pushes on Pedal to move vehicle
• Pedal formerly known as Gas Pedal, and before
  that, Accelerator Pedal

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Driver Intent Relates to Pedal Position
Speed up a lot
Speed up a little
Driver Intent
Maintain speed
Foot off Pedal
Floored
Slow down
Pedal Position
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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.

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Acceleration Relates to Pedal Position
Vehicle Acceleration
Foot off Pedal
Floored
Pedal Position
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Vehicle Acceleration

• Newtons First Law
• Fma
• Vehicle mass is constant (ignoring fuel usage,
  washer solvent spray, and any fluid leaks)
• So, Force is proportional to acceleration

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Force Relates to Pedal Position
Force Applied to Vehicle
Foot off Pedal
Floored
Pedal Position
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Where Does the Force Come From?

• Engine produces some torque, at a speed
• Transmission
• Ignoring Losses, of Course

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Where Does the Force Come From?

• Axle
• Ignoring Losses, of Course

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Where Does the Force Come From?

• Tire
• Ignoring Losses, of Course
• Interesting, but not the end of the Story.

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Where Does the Force Come From?

• Note

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Where Does the Force Come From?

• Power- the rate at which work is done
• Power is Force times Velocity (linear)
• Power is Torque times Rotational Speed (rotary)

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Where Does the Force Come From?

• Engine produces power

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Where Does the Force Come From?

• Transmission
• Ignoring Losses, of Course

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Where Does the Force Come From?

• Axle
• Ignoring Losses, of Course

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Where Does the Force Come From?

• Tire
• Ignoring Losses, of Course

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Where Does the Force Come From?

• Power is conserved
• POWER IS ABSOLUTE
• Torque is relative (depends on gear ratio)
• Ignoring Losses, of Course

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Where Does the Force Come From?

• The force comes from engine power
• At a given vehicle velocity, force, and therefore
  acceleration, depends on power produced by the
  engine

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Force Relates to Pedal Position
Force Applied to Vehicle
Foot off Pedal
Floored
Pedal Position
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Engine Power Relates to Pedal Position
Engine Power
Foot off Pedal
Floored
Pedal Position
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Engine Power Relates to Pedal Position
Acceleration
Constant Speed
Deceleration
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Implications of the Power Paradigm

• Powertrain Control
• Vehicle Performance
• Engine Performance Optimization Criteria

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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

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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

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Specific Fuel Consumption vs. Speed MAP
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Engine Power vs. Speed MAP
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Specific Fuel Consumption vs. Speed MAP
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Engine Power vs. Speed MAP
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BSFC vs. Speed MAP with Constant Power Lines
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Powertrain Control Example

• Any combination of MAP and rpm along the 100 hp
  line will satisfy the drivers 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

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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

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Simulated Vehicle Performance with Different
Transmissions
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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

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Engine Optimization Example Which Engine
Performs Better in a Vehicle?
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Engine Optimization Example Which Engine
Performs Better in a Vehicle?
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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

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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

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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

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