Transcript Powertrain Matching

Powertrain Matching
John Bucknell
DaimlerChrysler
Powertrain Systems Engineering
September 30, 2006
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  Tenginentrans
trans 
engine
ntrans
Ignoring Losses, of Course
Where Does the Force Come From?

Axle:
Taxle  Ttransnaxle   Tenginentransnaxle 
trans
engine
axle 

naxle ntransnaxle 
Ignoring Losses, of Course
Where Does the Force Come From?

Tire:
Fvehicle 
Taxle 

Tenginentransnaxle 

 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 
 FV 

Power is Torque times Rotational Speed
(rotary)
Power  Torque Rotational Speed 
 T 
Where Does the Force Come From?

Engine produces power:
Pengine  Tengineengine
Where Does the Force Come From?
 Transmission:
Ptrans  Ttranstrans
 engine 
 Tenginentrans

 ntrans 
 Tengineengine
Ptrans  Pengine
Ignoring Losses, of Course
Where Does the Force Come From?
 Axle:
Paxle  Taxle axle 
 trans 
 Ttransnaxle 

 naxle 
 Ttranstrans
Paxle  Ptrans  Pengine
Ignoring Losses, of Course
Where Does the Force Come From?
 Tire:
Pvehicle  FvehicleVvehicle
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
25.00
M
60 AP
(k
50Pa)
10.00
40
30
200
5000
10.00
4000
)
rpm
ed (
Spe
e
n
i
2000
Eng
1000
3000
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
300.00
90
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
300.00
90
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
Q&A