PLACE IN RETURN BOX to move this chockom from yam record.
TO AVOID FINES Mum on or Moro duo duo.

DATE DUE DATE DUE DATE DUE

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MSU Is An Affirmative Adlai/Equal Opportunity lnotltmlon
Wanna-9.1

ANALYSIS AND DESIGN OF
A HYBRID ELECTRIC VEHICLE BRAKING SYSTEM

By
Michael James Twork

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Mechanical Engineering

1993

ABSTRACT

ANALYSIS AND DESIGN OF
A HYBRID ELECTRIC VEHICLE BRAKING SYSTEM

By

Michael James Twork

The design, development and testing of the braking system of a hybrid electric vehicle for
the 1993 Ford/SAE/DOE competition are described. The main objective was to design a
system that would provide safe and reliable braking for the vehicle. This was
accomplished by modifying a braking system from a 1993 Geo Metro as well as by adding
an ABS unit. Regenerative braking effects are discussed. The system requirements are
presented and motivation is established for system modifications. The system provided
safe and reliable braking and was recognized by the competition organizers as the Most

Innovative Design in Mechanical Systems.

Dedicated to my wife, Kristi, and my daughter, Kali.

ACKNOWLEDGEMENTS

I would like to thank the Spartan Charge Team for all the blood, sweat and tears that we
shared on this project. I would like to thank Dr. John Gerrish and Dr. Gerald Park for their
tireless and fully committed support. I would like to thank the Mechanical Systems Team for
their efforts. Thanks to Denny Welch for his commitment to the project and to the team. I
would like to thank the College of Engineering for pursuing such an outstanding opportunity
for the students to learn through application. I would like to thank Ford Motor Company, The
Society of Automotive Engineers, The United States Department of Energy, and all other event
sponsors. Thank you to my family and friends for 15 months of understanding and
acceptance. Finally, I would like to thank my academic and thesis advisor, Dr. Clark

Radcliffe, for patience, encouragement, and guidance.

iv

TABLE OF CONTENTS

List of Tables ........................................................................................... vi
List of Figures ......................................................................................... vii
The Rev Competition .................................................................................. l
Braking System Specifications and Objectives ..................................................... 3
Braking System Design ................................................................................ 5
The Hydro / Mechanical System .................................................................. 5
Regenerative Braking ............................................................................. 11

The Anti-lock Braking System .................................................................. 12

HEV Braking Design Performance ................................................................. 15
References ............................................................................................. 18
Appendix A - Description of Events ................................................................ 19
Appendix B - Spartan Charge Awards 1993 HEV Challenge ................................... 20
Appendix C - Recommendations for Further Work .............................................. 22

LIST OF TABLES

 

Ember Title Pm
Table 1. SAE Friction Coefficient Classifications of Materials 9
Table 2. Summary of Spartan Charge Regenerative Testing 12
Table 3. Comparison of Mass, Wheel Base, and Track Width Between

the 1991 Corvette and the Spartan Charge 14
Table 4. Example Pedal Force Table 24
Table 5. Spartan Charge Brake System Parameters 25

LIST OF FIGURES

 

Number Title Page
Figure 1. A Typical Series Power Train Configuration for a Hybrid

Electric Vehicle 2
Figure 2. The Spartan Charge Hybrid Electric Vehicle 3
Figure 3. Pass/Fail Criteria for Vehicle Qualifying Brake Test. The Line

Corresponds to 0.425g Average Deceleration. 4
Figure 4. A Generic Hydro / Mechanical Braking System 6
Figure 5. Brake pedal Mechanical Advantage 8
Figure 6. An Adjustable Brake Bias Bar - Neutral Adjusted (left)

and Front Biased (right). 10
Figure 7. A Typical Regenerative Braking System 11
Figure 8. A Typical Anti-lock Bralcin g System 13
Figure 9. Comparison of an ABS Stop and a Skidding Stop 14
Figure 10. The Spartan Charge Braking System 15
Figure 11. Spartan Charge Brake Test Qualifying 16
Figure 12. How to Set the Bias Bar 24

vii

THE HEV COMPETITION

Hybrid electric vehicles (HEV) need to be proven as practical low emissions
vehicles. The goal of the 1993 Ford/SAE/DOE HEV Challenge was to encourage
development of HEV's and to demonstrate their practicality. The competition
determined the most practical and efficient student designed vehicle entry. Thirty
schools were chosen to compete from a field of 67 applicants. Michigan State
University was one of twelve schools that built a hybrid electric vehicle in the Ground-
up Class. The remaining 18 schools chose to convert Ford Escorts to hybrid electric
vehicles. The schools competed in static and dynamic events to evaluate design and

performance. Descriptions of the events are contained in Appendix A.

A practical, low emissions vehicle is needed in North America to break
dependence on foreign oil and to reduce pollutants that are harmful to the environment.
Electric vehicles have long been considered the next step in the automotive evolution
because of their environmental friendliness, however, they are not yet feasible for
general use because present battery technology limits vehicle range to 40 miles or less.
California has recently passed legislation mandating that in 1998 at least two percent of
all vehicles sold in that state must be emission free or have emission free capabilities
(Kobe 1993). This percentage increases to five percent in 2001 and ten percent in
2003. Major metropolitan areas will eventually be zoned as emission free zones, where
only vehicles with emission free capabilities may travel. Hybrid Electric Vehicles
combine electric vehicle operation with an auxiliary internal combustion power source
to give both emission free capabilities over a limited range and vehicle ranges of about

400 miles using auxiliary power.

Page 1

Page 2

The Hybrid Electric Vehicle is a compromise between pure electric and pure
internal combustion powered vehicles as it incorporates the benefits of both. Figure 1
shows a typical series power train configuration for a hybrid electric vehicle. The
vehicle can operate in pure electric mode while in emission free zones. In hybrid mode,
in outlying areas, the APU can be used to extend vehicle range. The internal
combustion engine, which is not directly coupled to the wheels, can be run at its
optimal rate for efficiency and emissions because it is used to generate electricity. This
electricity is either used to power the electric motor or to recharge the batteries,

extending the range of the vehicle.

 

 

 

 

attcry
‘ Pack
Internal
COHIDUSIIOII was Alternatorl i I Motor - Em
Eninc Controller -— Motor

Figure 1. A Typical Series Power Train Configuration for a Hybrid Electric Vehicle

Michigan State University's entry to the HEV Challenge, "Spartan Charge"
(Fig. 2), provided a unique opportunity to design and implement the vehicle's braking
system. The braking system design objectives are presented. The design constraints
and preliminary decisions regarding the braking system are examined. The three major
elements of the system are discussed. After a general model of each element is
presented, the modifications and implementation of each is detailed. The final, fully
integrated system is then reviewed. Finally, the competition performance of the vehicle

braking is presented followed by Challenge results.

Page 3

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1. |IOI""".r
'.n'“” . r (15' ‘ ‘1-

 

Figure 2. The Spartan Charge Hybrid Electric Vehicle

BRAKING SYSTEM SPECIFICATIONS AND OBJECTIVES

The braking system design objective was safe and reliable braking for the
vehicle. Within the scope of the competition, the vehicle was expected to have similar
braking performance to present production vehicles, which require a maximum pedal
effort in the range of 300 to 550 Newtons (Posa, 1993) to generate 0.7g. HEV
Challenge rules required the vehicle to brake at a rate of at least 0.425g. The HEV
Challenge vehicles would be tested during vehicle qualifying on a pass/fail basis

(Figure 3) to establish their ability to meet the deceleration specification.

Regenerative braking in electric and hybrid electric vehicles converts the inertia
of the moving vehicle, through rotational inertia at the drive axle, to electric power by
operating the electric motor as a generator. This energy is routed into the vehicles'
batteries, slows the vehicle, and conserves some of the energy normally lost to
coulomb friction upon braking. Regenerative braking increases the available braking

effort of the entire system and the efficiency of the vehicle. Regenerative braking

Page 4
increases the range of the Chrysler TEVan by 8 percent on the SAE C-cycle

(Riezenman, 1992). The more energy that can be recovered through regenerative
braking, the less that needs to be generated from the internal combustion engine, which
means lower emissions and increased efficiency. It also means increased range and
better acceleration. A design goal for the Spartan Charge power train was to realize

regenerative braking and to test its effects on the overall braking system performance.

Brake Test Pass/Fail Criteria Curve

 

 

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Hm Alhvabh

 

 

 

 

 

 

 

hlflal Vehicle 8'0“ (tall)

Figure 3. Pass/Fail Criteria for Vehicle Qualifying Brake Test. The
Line Corresponds to 0.425g Average Deceleration.

An Anti Lock Braking System (ABS) increases safety and maneuverability
during braking by regulating the hydraulic pressure to the wheel(s) which prevents
skidding. It would also improve the merit of the braking system design. The goal was

to integrate an ABS unit into the braking system to increase the safety of the vehicle.

The design constraints of the project were the timing, financial, and reliability.

The time frame of the project at Michigan State University encompassed 15 months

Page 5
from student organization to the competition. Off-the-shelf components could

significantly reduce design and manufacture time of some of the hardware. The
financial constraints on the project were severe. Every component on the vehicle
needed to be bought with donated funds or donated directly as a gift-in-kind. The
braking system reliability was critical. Custom components could seriously
compromise the reliability of the system. Ideally, an existing braking system could be
transplanted onto the Spartan Charge vehicle. A 1993 Geo Metro was purchased for its
California Emissions engine. It was more economical to purchase the entire vehicle
than to buy the engine, instrumentation and controls on individual bases. The braking
system from the Metro represented a fully tested and functional system that was
available immediately and that would not further deplete funds. The Metro braldng
system became the foundation for the Spartan Charge braking system.

BRAKING SYSTEM DESIGN

The Spartan Charge braking system consisted of three major elements.
Conventional hydro / mechanical brakes represented the foundation of the entire system
and were assembled predominantly from Geo Metro components. The regenerative
braking system included the drive motor, inverter, transmission and battery pack. The
Anti Lock Braking System (ABS) included a hydraulic pump unit, electronic control
module, and wheel speed sensors.

W
The Metro system represented a typical hydro / mechanical system. A generic

hydro / mechanical system model will be presented to establish a foundation for further

Page 6
discussion. Optimal effort bias will be defined for the Spartan Charge vehicle. Finally,

the modifications to the Metro system will be detailed.

A hydro / mechanical braking system operates by allowing the driver to control
braking force through a pedal control. The driver applies a force to the brake pedal,
which creates a pressure in the hydraulic lines. This pressure forces brake pads against
a brake rotor which is part of the wheel hub. The friction created slows down the
vehicle. Figure 4 shows a hydro / mechanical system with disc brakes in the front and
drum brakes in the rear.

Wheel / Brake Brake Wheel Hydrallic Hydradlc Brake Brake Brake Wheel /
re Drun ‘ -- - Cyllnde Line Line Caliper Pads Rotor Tue
Master
Rear Pedal Cylinder Front
Wheel / Brake Brake Wheel Hydraulic Hydradlc Wheel /
Tire Drum . ‘ ‘ cylinder line Line Caliper Pads Rotor Tue

Figure 4. A Generic Hydro/ Mechanical Braking System

The deceleration rate a vehicle with adequate braking is clearly limited by the
adhesion of the tires to the road surface. The maximum vehicle deceleration obtainable
occurs when all four wheels are on the verge of locking up or skidding. While it is
difficult to obtain simultaneous lock up of all four wheels, this theoretical condition can
be used to establish the maximum braking efforts. The forces required to create wheel

lock up are defined as the braking capacities and represent the maximum force that the

Page 7
system can use, while the optimal effort bias is defined as the ratio of the front brake

capacity to the rear brake capacity. The optimal ratio is described by;

Ff... _ urmg(b +cur)/WB _ 5. 8kN _ 62%

EfiorL Bias = - —
Fr... urmg(a - cur) / W3 3. 6kN 38%

 

 

where
Fr. = optimal braking force at the front axle;
E... = optimal braking force at the rear axle;
= mass of the vehicle (1360 kg);
g = gravity (9.81 m/ 32);
W3 = wheel base of vehicle (272 cm);
[4, = coefficient of friction between the tire and the road (0.7 - wet asphalt);

a = the distance from the front axle to the vertical projection of the center
of gravity (130.5 cm);

b = the distance firm the rear axle to the vertical projection of the center
of gravity (141.5 cm);

6 = the height of the center of gravity (37.6 cm).

The optimal braking effort that could be applied to the front wheels of Spartan Charge
is 5.8kN. The vehicle braking can not be Optimized if the system can not create 5.8kN
at the front wheels. A similar analysis for the Metro yielded an effort bias of 77/23
with the front braking capacity at 4.8kN. Effort bias ratios are usually in the range of
65/35 to 75/25 because most vehicles are front heavy (Newcomb, 1975). Spartan
Charge was slightly rear heavy and had a low center of gravity, which caused the

optimal effort bias to fall below the normal range.

The hydro / mechanical system required some modifications to compensate for
the 450kg increase in mass and a 21% increase in front braking capacity from the Metro
to the Spartan Charge. To maintain system reliability, simple changes were preferred.
The four modifications to the hydro / mechanical system were: the elimination of the

vacuum powered brake booster", increasing the brake pedal mechanical advantage;

(1)

Page 8
increasing the friction coefficient of the brake pads; and adding an adjustable bias bar.

The net result of these modifications along with change in mass, wheel base and center

of gravity from the Metro to Spartan Charge yielded a predicted pedal effort of 533N.

Vacuum powered brake boosters use vacuum from an internal combustion
engine to reduce pedal efforts. Since hybrid electric vehicles have the capability to run
in a pure electric mode, the internal combustion engine would not always be available
as a source of vacuum. Alternate sources of vacuum and other types of boosters were
investigated, however, each would have hampered the vehicle efficiency. As a result,

the vacuum powered brake booster was eliminated from the system.

 

 

 

 

A
M i n .._4':_..
i F
——>

 

Figure 5. Brake Pedal Mechanical Advantage

The brake pedal mechanical advantage is the ratio of the pedal lever arm to the
master cylinder push rod lever arm (Figure 5).. The mechanical advantage of the brake
pedal could be altered to increase the brake effort available while keeping the pedal
force constant. The mechanical advantage of the Metro brake pedal was 4.1:]. The
input force at the brake pedal is multiplied by the mechanical advantage, and the

resulting force acts on the master cylinder push rod. Increasing the mechanical

Page 9
advantage, however also increases the pedal travel, which is generally undesirable. A

Tilton pedal assembly, with a mechanical advantage of 6.2:1, was identified to replace
the Metro pedal which increased the braking effort available by 51 percent.

The friction coefficients could be increased on the pads and shoes and would
result in increased braking performance. The relationship between the hydro /
mechanical braking effort available at the front wheels and the friction coefficient of the
brake pads is described by (2).

may R.

Rm” (2)

 

Flair:

where
Ff... = the effort available from the front hydro / mechanical brakes;

Fm = the actuating force of the caliper piston;
u = the coefficient of friction between the disc brake rotor and the brake

Pad;
R. = the effective radius of the brake pads;
Rroll = the rolling radius of the tires.

Table 1 summarizes the SAE method of labeling friction materials. A two digit code is
stamped on the pad or shoe with the first digit representing the normal, or cold,

coefficient of fiiction, and the second digit representing the hot coefficient of fiiction.

TABLE 1. SAE Friction Coefficient Classifications of Materials

 

 

 

 

 

 

 

 

 

CLASS FRICTION COEFFICIENT
D 0.15 < It < 0.25
E 0.25 <11 < 0.35
F 0.35 < 1.1 < 0.45
G 0.45 < p. < 0.55
H 0.55 < 1.1

 

The Metro stock pads were classified E, with both cold and hot coefficients of friction

between 0.25 and 0.35. A classification of PG would correspond to a cold friction

Page 10
coefficient between 0.35 and 0.45 and a hot friction coefficient between 0.45 and 0.55.

Ferodo Automotive Products Incorporated makes after market pads for the Metro that
have a friction coefficient that is classified as GG.

The Ferodo pads had a cold friction coefficient of 0.534 and a hot friction
coefficient of 0.513. According to (2), these pads would increase the available braking
effort at the front wheels by 67 percent. Consultants from Robert Bosch Corporation
cautioned against expecting drastically increased performance based solely on friction
coefficients because the properties of friction materials can change drastically with
rising temperatures (Posa 1993). With this in mind, a conservative interpretation of the

Ferodo data was taken and a factor of safety of 1.2 was introduced into all brake

performance predictions.

 

 

PEDAL FORCE

Figure 6. An Adjustable Brake Bias Bar - Neutral Adjusted (left)
and Front Biased (right).

An adjustable bias bar is a mechanism that allows the vehicle's hydro /

mechanical effort bias to be tuned. A bias bar distributes the pedal force to the front

Page 11
and rear master cylinder push rods (Fig. 6) for a near neutral adjustment and a front

biased adjustment. The bias bar in the Spartan Charge vehicle was set up for dual
master cylinders. One master cylinder is dedicated to the front brakes and one to the
rear brakes. This type of a split system has the added advantage that the front and rear
master cylinder bores can be chosen independently to complement the needed line
pressures to achieve the braking capacities at each axle. Finally, the adjustable bias bar
was instrumental in tuning the hydro / mechanical system correctly to support and

utilize regenerative braking.
B . E l'

Regenerative braking operates the electric portion of the power train in reverse
(Fig. 7). The torque from the wheels is transferred through the transmission to create
electrical power at the electric motor, used as a generator during regenerative braking
mode. This electrical power is routed to the batteries by the inverter, or motor
controller. Each of the components in Figure 7 already exists within the power train of

the vehicle, so no additional components needed to be purchased.

Front
Wheel

Axle
, ectrc

Battery
I Tranemlsslon Pack

Generator

 

       
 

Trans /
- le
Figure 7. A Typical Regenerative Braking System

Regenerative braking increased the range of the Spartan Charge by 6 to 15% on

individual tests, depending on the driving environment. These tests were run

Page 12
approximately one month before the competition and include urban and highway

driving environments. Table 2 summarizes the regenerative braking test results.

Table 2. Summary of Spartan Charge Regenerative Testing

 

 

 

 

 

Drive Total Total Regenerated Average
Cycle Kilometers KWH KWH Range Increase
Urban Drives 44 4.352 0.667 15.3 %
_Ll_i9hway Drives 83 7.082 0.430 6.1 %
Total 127 1 1.434 1.097 9.6 %

 

 

 

 

 

 

The optimal or maximum regenerative effort that the power train could create
depends on the breakdown (maximum) torque of the electric motor. This maximum
torque for the Spartan Charge was 54.6 Nm. First gear of the transmission is 3.42 and
the rolling radius of the tires is 0.28m. This results in a maximum regenerative effort
of 662.4N, or 11.5% of the front braking capacity. Regenerative braking will make
vehicles more efficient, so auto makers will try to recapture as much energy through
regenerative braking as they can. Coupled with the modifications to the hydro /
mechanical system, the addition of regenerative effort could produce forces large
enough to result in wheel lock up. ABS will be necessary on hybrid electric vehicles
that employ regenerative braking to prevent brake lock up and to compensate for the

changing front / rear brake effort encountered with regenerative braking.

D!’-]lEl°S

An Anti-lock Braking System prevents wheel lock up by sensing the wheel
speeds and appropriately regulating hydraulic pressure. The elements shown inside the
shaded region of Figure 8 are components of the ABS system, while those outside are

Page 13
part of a hydro / mechanical system. The four wheel speed sensors continuously

monitor the wheel speeds. If the speed of any wheel is 5% lower than another wheel
during braking, then the pump unit regulates the pressure in the hydraulic line leading
to that wheel's brake hardware to prevent that wheel from locking up. If the ABS
electronic control module senses a wheel or wheels skidding during braking, then it
pulsates the pressure in the hydraulic lines. Pulsating the pressure alternately reduces
braking to prevent wheel lock up, and then quickly increases the braking effort near

capacity again to optimize braking.

 

 

   

 
 

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Figure 8. A Typical Anti-lock Braking System

An Anti-lock Braking System (ABS) was desirable because it could increase
safety and performance. Figure 9 compares the braking performance of two vehicles.
The first vehicle has ABS and the second vehicle, which does not have ABS, is
assumed to be in a skid. Both vehicles had an initial speed of 100 km/h. The skidding
vehicle takes 25% more distance to stop compared to the vehicle with an ABS system

(Emig, 1992). It is important to note that the vehicle without ABS is still traveling at

Page 14
over 45km/h at the same point where the vehicle with ABS has stopped. The vehicle

with ABS decelerated 25% faster than the skidding vehicle.

 

 

 

 

100
80 — e
w/ ABS w/out ABS

E? 6‘“ ‘
r 4o— -
m

20 _ Initial Velocity = 100km/h q

0 r l L L
0 20 40 60 80 100

Distance (meters)

Figure 9. Comparison of an ABS Stop and a Skidding Stop

The ABS system for the 1991 Chevrolet Corvette, manufactured by Bosch,
closely matched the weight, track width, and wheel base of the Spartan Charge vehicle.
Table 3 compares the key parameters of the two vehicles. A unit was donated by
Bosch and consisted of a hydraulic pump unit and electronic control module. Bosch
did not manufacture the wheel speed sensors for the system, consequently an alternate

source had to be located.

Table 3. Comparison of Mass, Wheel Base, and Track Width Between
the 1991 Corvette and the Spartan Charge

 

 

 

1991 Corvette Spartan Charge % Dltterence
Mass 1465 59 1360 K9 -7%
Wheel Base 245 cm 272 cm +10 %

 

 

Track Width 153 cm 165 cm +7 °/o

 

 

 

 

 

Page 15
The wheel speed sensors from the Corvette were not available and not suitable

for the rear drum brakes of the Geo. A search was undertaken to reach the Corvette
engineer responsible for the ABS unit to seek advice. The phone conversations led to
NDH Integral Bearing Systems, who were experimenting with ABS for smaller cars.
NDH had reu'ofitted a 1991 Geo Metro with ABS. NDH was eager to get involved and
donated custom, integral bearing sensors for the rear and the pulse wheels and sensors

for the front.

HEV BRAKING DESIGN PERFORMANCE

The braking system underwent a transformation from the fundamental Metro
system to the final competition system. Figure 10 shows the fully integrated braking
system. All the components from each of the three elements have been included and are
functional. The predicted pedal effort of the system is 533N, which falls into the upper
end of the 300 to 550N range of the automotive standard.

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Page 16

The braking system achieved and surpassed the required system specifications
and objectives. Spartan Charge passed vehicle qualifying, including the pass / fail
brake test, on the first attempt. The vehicle stopped from an initial velocity of 72km/h
in 41 meters, in a safe and controlled manner, for a deceleration rate of 0.497 3. Figure
11 shows the pass / fail curve again with the Spartan Charge braking performance
included. The vehicles were allowed to try as many times as necessary to qualify, so
the driver did not approach the braking capacities on the first, and only, qualifying

attempt.

Spartan Charge Qualifying Brake Performance

 

 

 

 

100
3
i so-
i so-
.5
0)
“i *°'
r
é
! zo-«
I: 04

 

Initial Speed (In. In)

Figure 11. Spartan Charge Brake Test Qualifying

Spartan Charge was one of two vehicles in the Ground-up Class with

regenerative braking. Test runs yielded as much as an 18 percent increase in range

Page 17
during urban driving and an average increase in range of 9.6% for both highway and

urban driving. Regenerative braking can account for as much as 11.5% of the front

braking capacity and greater percentages under gentler braking conditions.

Spartan Charge was the only vehicle at the competition with an Anti Lock
Braking System. The ABS was necessary because of the increase in available braking
effort from regenerative braking. It was a testimonial to the team's dedication to safety

and engineering.

The braking system clearly fulfilled the main objective of providing safe and
reliable braking. The Spartan Charge braking and power train system was recognized
by the competition organizers as the Most Innovative Design in Mechanical Systems.
Clearly, the ABS (braking) and the regenerative braking (braking and power train)
contributed to Spartan Charge receiving this award as it was the only vehicle with both

capabilities.

The Spartan Charge hybrid electric vehicle met all of its objectives, including
the mission to provide safe and reliable braking. This was accomplished by modifying
a Geo Metro braking system to support both regenerative braking and Anti Lock

Brakes. The braking system attained each of its objectives which are summarized here.

- Deceleration rate of 0.497 g,

- Predicted pedal effort of 533N,

- Functional regenerative braking yielding an average 9.6% increase in range,
- Functional Anti-lock Braking System.

The braking system helped set the Spartan Charge hybrid electric vehicle apart from the
other contestants. The braking and power train system was celebrated as the Most

Innovative Design in Mechanical Systems.

REFERENCES

1) Kobe, Gerry, "What if Electric Vehicles Don't Sell?", Chilton's Automotive Industries,
April 1993.

2) Posa, Ron, Personal Interview, Vehicle Brake Engineer, Robert Bosch Corporation,
February 1993.

3) Riezenman, Michael, "Pursuing Efficiency", IEEE Spectrum, November 1992.

WW

4) Newcomb,T.P., "Automobile Brakes and Braking Systems", Chapman and Hall,

unmarr-

c.1975.

5) Emig, Reiner, "Anti-lock Brake Systems for Commercial Vehicles", Automotive

Engineering, July, 1991.

Page 18

APPENDIX A

Description of Events

Description of Events

Emissions Event - This event was designed to measure vehicle exhaust emissions
and evaluate its ability to minimize the formation of regulated vehicle emissions.

Commuter Event - The goal of the commuter event was to evaluate the low speed
maneuverability and handling of the HEV under typical commuting conditions.

Range Event - The objective of the range event was to test the durability of the
vehicles and their overall range.

Acceleration Event - The acceleration event evaluated the ability of the vehicles to
accelerate from a standing start over a distance of 100 meters.

Efficiency Event - The efficiency event was designed to determine which vehicle
had the best distance per unit energy rating during the commuter, range, and emissions
events.

Engineering Design Event - The engineering design event evaluated the amount of
engineering effort each school put into constructing their vehicle.

Oral Presentation - The oral presentation event evaluated each team's ability to make
an informative and exciting presentation aimed at selling the benefits of their hybrid electric
vehicle.

Cost Assessment - The purpose of the cost assessment event was to quantify the
market value of each vehicle, including hardware and labor.

Technical Report - The objective technical report event was to evaluate each vehicle
design and operation strategy‘ .

Page 19

APPENDIX B

Spartan Charge Awards 1993 HEV Challenge

Spartan Charge Awards 1993 HEV Challenge

The competition consisted of not only static and dynamic events, for which points
were awarded, but also a series of engineering awards. The points awarded for the events
determined which school would win the competition, while the engineering awards were
monetary and were intended to recognize individual aspects, elements or systems of the

vehicles' designs.

Eight engineering awards were presented during the competition. Spartan Charge

was awarded the following;

- Best Styling

- Best Ergonomics

- Best Use of Materials

- Best Use of Electronics

- Most Innovative Design in Mechanical Systems

The citation for Most Innovative Design in Mechanical Systems was awarded based on the
braking system and the power uain. The remaining three engineering citations were

awarded to three different schools.

The competition events were intended to evaluate design and performance of the

vehicles. Spartan Charge placed in the following static and dynamic events;

- EMISSIONS EVENT (3rd Prize)
- ORAL PRESENTATION (3rd Prize)
- RANGE EVENT (3rd Prize)
— COMMUTER EVENT (2nd Prize)
- TECHNICAL REPORT (2nd Prize)
- DESIGN EVENT (2nd Prize)

Page 20

Page 21

The top five schools, along with their point totals, are listed below. The total points
available was 1000.

- 5th Place, Lawrence Technological University with 507 points,

- 4th Place, University of Tennessee with 550 points,

- 3rd Place, Michigan State University, with 676 points,

- 2nd Place, University of California at Davis, with 700 points,

- 1st Place, Cornell University, with 775 points.

APPENDIX C

Recommendations for Further Work

Recommendations for Further Work

Although the Spartan Charge Braking System performed well and was identified as
part of the Most Innovative Design in Mechanical Systems, many improvements can and
should be made. The following list contains items under three headings; the minimum or
Must Do Items, the Should Do Items, and finally the wishful, or Try To Do Items.

Mumhems

1) Increase the rear Braking Capacity (BC) to the point where rear lock up is achievable.
This is possible by

A) Larger Drums
B) Replace Drums with Appropriate sized Discs (would affect ABS)
C) Higher Friction Coefficients (heat transfer effects?)
D) Smaller Rear Master Cylinder Bore (present is 0.625 in. dia.)
E) Larger Wheel Cylinders
2) Tune for Optimal Effort Bias (when entire system is finalized)
A) Determine Regenerative Braking Effort Desired (ie 50%)
B) Adjust Braking Capacity Effort Bias (to incorporate regen effort)

C) Tune Hydro / Mechanical System with Adjustable Bias Bar

EXAMPLE
NOTE: These are LLQI actual Spartan Charge Parameters!

A) Regen Setting (R530: 50%, Gear Ratio (Gratio) = 3.5 (1st gear Transmission), The
Breakdown Torque of the Electric Motor (de) = 75 Nm, Rolling Radius of the Tires
(Rroll) = 25Cm

RsethdGratio _ 0.5 "‘ 75Nm * 3.5
Rroll 0.25m
Page 22

 

 

Re gen_ Efi‘ort = = 525N (3)

Page 23

B) The Braking Capacity Effort Bias (BCEB) is the Ratio of the Front Braking Capacity
(maximum amount of braking effort usable without the tire skidding) to the Rear. If the
Front Brake Capacity =5.25 kN and the Rear = 3.5 kN, then

5.25m _ 60%

BCEB = —— —
3.5kN 40% (4)

 

The Hydro/ Mechanical System Bias (HMSB) is the ratio of the front effort required from
the HMS (brake capacity minus regen effort) to the rear effort required from the HMS

5.25kN—O.525kN _ 57.5%

HMSB = — (5)
3.5kN 42.5%

 

 

(This is the bias at the wheels that the HMS should be tuned for.)
The Front HM Effort (FHMcffm-o= 4.725 kN, The Rear HME = 3.5 kN.

The Force needed (to reach BC) at the Front Master Cylinder (Ffmc) is the pressure needed
in the hydraulic line times the Master Cylinder Area (Afmc). This pressure is the piston
actuating force needed divided by the Piston Area (Afp). The actuating force is the required
effort at the tire times the rolling radius divided by four times the Effective Radius (Rfcff)
of the braking material surface. The same equation will work for the rear. Therefore

 

F H M efiortR rollAfmc
F fmc =
4AM” <6)
Rfeff = 3.5 Cm, Rreff = 9 Cm
Afp = 18.09 cm2 Arp = 2.01 cm2
Afmc = 1.96 CIII2 Anne = 0.694 CI'II2

AS a result, Ffmc = 914.2 N and ch = 839.2 N

The Adjustable Bias Bar (ABB) distributes the pedal force to the front and rear master
cylinders and should be adjusted (Figure 12) to reflect the ratio of the master cylinder
forces

922.9N _ 52.4%

ABB_ Bias = — —
838.9N 47.6% (7)

 

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‘——1 OO°/o
Rear 4— 52.1% Front
Pushrod Pushrod

—

 

 

 

 

 

 

 

Figure 12. How to Set the Bias Bar

3) Test, measure and document pedal force at maximum and intermediate stopping forces
(Table 4). Correlate with deceleration rates and other factors. (Shoot for pedal effort
below 100# to create 0.5g or more.)

Table 4. Example Pedal Force Table

 

 

 

 

 

 

 

 

 

Vinitial Stop Dist Fiedal Fiset g
72km 40m 100# 50% 0'5097L
50km 34m 70# 50% 0.28923_

 

4) Analyze the Brake Fluid Volume Necessary to Displace to Create the Brake Capacities
and Compare to Actual Volumes Displaced.

3.1119111112233111}.

1) Duct Air to the Front & Rear Brake Hardware.

2) Heat Transfer Analysis of All Brake Hardware.

3) Replace Front Discs w/ Vented Discs (may require custom calipers).

4) Test/Verify that ABS Works Properly.

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