Pneumacs

ACTIVE SUSPENSION CONTROL SYSTEM

Project: ASCS

Team Members:

Rudha Ben-Yuhmin

Michael Thai Duc Le

Tommy Chang Patrick O’Neill

San Jose State University Department of Mechanical and Aerospace Engineering

ME 195A

Dr. Ji Wang December 20, 2001

1

ABSTRACT:

In what follows is a description of an active suspension control system designed

for use with a modified 1949 Studebaker Pickup truck. The idea to develop this project

comes from the desire to have a suspension system that is more flexible and responsive.

Most current suspension systems have limited flexibility and can only perform

adequately, with flexibility in mind team Pneumacs set out to develop an effective

solution. Through the use of conventional air spring technology and an array of integrated

system monitoring electronics, Pneumacs has created a flexible control system to

augment suspension during extreme conditions. All goals set forth by the team have been

successfully achieved and a completed working prototype is ready for field-testing.

2

ACKNOWLEDGMENTS: This Project would not have been possible without the help and support of key

individuals within the University and industry; a listing in no specific order follows:

San Jose State University MAE Department, Dr. Ji Wang, SJSU Central Shops,

R. Brindos, T. Cargile, J. Wright, P. Buttitta, SJSU Mat E Dept., SJSU CE Dept.,

B. Miller, P. Laverty, C. Pritence, J. Mosey, G. Brooks, B. Whitaker, SJSU EE

Dept.

CONTACT INFORMATION

CONTACT NAME PHONE NUMBER COMPANY NAME OR INDUSTRY SPONSORED

1 Firestone 1-800-888-0650 Manufacturing of air bags and pneumatics

2 Paul Gibson (President) 1-800-888-0650 Firestone

3 Donald Foulke (Marketing) 1-800-888-0650 Firestone NA

4 Kevin Brown (Head Engineer) 1-800-888-0650 Firestone NA

5 Gram Brooks (Controls Group) Ext. 8765 Firestone YES

6 Bob Keller (President) 408-727-5756 Nor-Cal Controls

7 Ray Rawn (Engineer) 559-994-9301 Nor-Cal Controls NA

8 James Martin (Tech) 408-727-5756 Nor-Cal Controls

9 Chuck (Owner) 916-483-0110 Aftermarket (Airride & Valving)

10 Patti Buttitta (Owner) 707-431-1257 Buttitta Design YES

11 Paul Rohrer (Rep) 1-800-995-3070 x44 Schaevitz Sensors (LDVT,RDVT) NA

12 Dennis Hartwig/ Zane Cullen (707) 586-8696 Creative Concepts NA

13 13 Steve Litt (716) 684-0001 PCB Accelerometers YES

14 J. Mosey/G. Henesian (408) 943-9600 SMC (Pneumatic Valving) YES

15 Paul, Dave, Roy Brizio (650) 952-7637 Roy Brizio’s Street Rods, Inc. YES

16 Steve South Bay Driveline

17 Don Better Built Transmissions

3

TABLE OF CONTENTS:

ABSTRACT: ..................................................................................................................1

ACKNOWLEDGMENTS:.............................................................................................2

NOMENCLATURE:......................................................................................................4

INTRODUCTION: .........................................................................................................7

THE SOLUTION:..........................................................................................................9

ANALITICAL ANALYSIS/VALIDATION TESTING................................................21

DISCUSSION:.............................................................................................................47

CONCLUSION/SUGGESTIONS: ............................................................................48

REFERENCES:..........................................................................................................49

APPENDIX: .................................................................................................................50

4

NOMENCLATURE:

1. UCL = Upper control limit.

2. LCL = Lower control limit.

3. ECU = Electronic control unit.

4. Control Volume = extended reservoir attached to air spring

5. π = 3.14159

6. Spring K = A constant of proportionality in linear spring rate

7. M = Magnification factor for optimizing control volumes

8. R = Universal gas constant

9. T = Temperature

10. C = Damping coefficient for shock absorber modeling

11. LF/RF = Left/Right front locations

12. LR/RR = Left/Right rear locations

13. ω = Angular frequency (radians/sec)

5

EXECUTIVE SUMMARY: The concept of an active suspension control system (ASCS) is derived

from the inflexibility of a conventional steel sprung automotive suspension

systems. Classic systems are often designed for a narrow range of operating

conditions and cannot be easily modified. An active suspension system has the

flexibility of real-time modifiable mechanical assemblies, which in our case are

electronically monitored and actuated, giving it a means of accounting for broad

dynamic behaviors. Implementation of an, air-spring type, active suspension

system is the topic of the report herein. Results consist of a completed custom

vehicle that houses a simple active on/off suspension control implemented

through the use of extended control volumes. The interface of electronics with

mechanical subsystems is one of the key attributes of the system design. Each

control component is made modular for expandability and flexibility. The entire

control circuit is designed as a star type network around a centralized

microcontroller.

Project Scope: To design and build an active suspension system, activated

by position sensors, intended to enhance chassis characteristics

during hard cornering, braking and loaded applications.

Project Objectives: 1. Model and document system design.

2. Analyze component structures.

3. Fabricate prototype assemblies.

4. Develop controller algorithm to satisfy design criteria.

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5. Implement and test system design.

7. Develop an engineering report.

Deliverables: 1. Frame and component Pro/E model.

2. Pneumatic/Electronics schematics.

3. Finite Element Analysis documentation.

4. Computer control program source code.

The design of the ASCS is to be a prototype system. The end result will be a functional

active suspension control system. This will enable filed testing for verification and proof

of concept, aiding in its development for future production.

7

INTRODUCTION:

Pneumacs is a team of five Mechanical Engineering students who have

committed themselves to graduating with a sense of success. Their success will

come from the completion of the “Senior Design Project”. Pneumacs’ project is a

challenging task, consisting of building a vehicle and implementing an Active

Suspension Control System (ASCS). Automotive icons such as Studebaker,

Chrysler, Mercedes, General Motors and Land Rover have inspired this concept-

car that sprang form a love of classic styling and the engineering desire to build

better automobiles. A Studebaker pickup will sport the appearance, only the skin,

on a later model GM suspension and powertrain. The modified 1970’s GM A/G

chassis is fitted with four independently actuated AirRide™/Firestone™

pneumatic springs, while power comes from a precisely tuned GM (four-bolt

main) 350/350 combination. The chassis’ characteristics will be monitored by

position sensors, reported to an on board electronic control unit (ECU) which will

apply a control algorithm to assist in handling capabilities. Pneumacs feels this is

a viable solution to the dilemma: how does one achieve superior ride quality

while maximizing handling capabilities? The solution is to have real time monitor

and control over chassis characteristics, enabling computer controls to adjust for

varying road conditions.

Pneumacs is composed of two Design specialists, and three Mechatronics

specialists. The Design side works concurrently with the Mechatronics side to

develop appropriate sensor locations and control theories based on overall

design parameters. Dr. J. Wang, a university professor who is heavily involved

8

with control system theory and fuzzy logic control, supports Pneumacs as well.

The team is a well-rounded group of motivated mechanical engineers who see a

clear solution to a design problem. The organization of the group is designed to

keep individuals informed and productive; delegation of tasks is based on

individual expertise and background, while all team members contribute to

manufacturing from plans generated by the elected lead engineer. Some of the

individual strengths of Pneumacs are: mathematical modeling, Pro/E CAD,

manufacturing, programming, electronics and circuit analysis. These added

personal attributes augment a developed core mechanical engineering

education.

The process of developing the hybrid vehicle mentioned above took a little

planning and a lot of luck. The chassis, donated by Jack Wright, gives a solid

foundation on which to start construction. The body was nostalgic and followed

the popular retro-look of new millennium automobile manufacturers; it was

donated by Tom Cargile.

Thanks Tom

9

THE SOLUTION: Research:

Conventional suspension systems that are currently being used on most

automobiles consist of shock absorbers, springs, and struts. Although these

systems are rugged and reliable, they have a lot of limitations such as poor ride

quality and poor traction in turns on Sport Utility Vehicles/trucks. These

limitations can only be eliminated by the more advanced active suspension

systems. Currently Mercedes, Cadillac and Land Rover are the only

manufacturers that offer Active Suspension Systems. A brief description of an

active suspension system follows.

Active Suspension Systems:

Active suspension systems use computers to collect data from onboard

sensors, the computer controls valving to fill or vent air/oil from pneumatic or

hydraulic cylinders at each wheel of the car. They permit vehicles to lean into

their turns instead of the natural tendency of leaning away from the turn, while

continuously adjusting the system according to road conditions. These systems

are highly popular with performance and sport vehicles. There is a growing

demand for active suspension system for SUV/trucks. Active suspension

systems improve road handling, stability, traction, as well as comfort and safety.

10

Mercedes’s ABC system:

• Active Body Control(ABC):– Used in model CL500– Uses 13 on-board sensors and 2 ECU(Electronic

Control Unit), with hydraulic servos located on each of the 4 coil springs.

– Mercedes modeled its system as “Slow Active”.– Only controlling Low-frequency disturbances, cutoff at

5 hertz.– Traditional shock absorbers will handle High-

frequencies.– Controlling rate is 10 milliseconds/cycle.

11

Cadillac’s CVRSS•Continuously Variable Road-Sensing Suspension.

•Offered in Deville Concours and Seville STS models.

•The system uses a series of sensors to actuate hydraulic shock absorbers at all four corners.

•Improving road feel and dampening.

12

Land Rover’s ACE•Active Cornering Enhancement.

•The first Active Suspension for Sport Utility Vehicle.

•Offered in the Land R.over Discovery Series II

•Utillizing a hydraulic system to replace the more traditional front and rear anti-roll bars.

•Apply torque to the body via two piston/lever configurations.

•Has the capability to handle up to 1.0 G lateral acceleration in250 miliseconds

13

Position Sensors Technology:

Laser Triangulation:

Laser triangulation sensors are non-contact linear displacement sensors.

A laser beam is reflected off a target surface, and the returning beam is received

and focused onto a CCD sensing array. The CCD array detects the peak value of

the light and determines the position based on the beam spot. The sensor

produces an analog signal in the range of –10V to +10V that is proportional to the

distance measured. Price of laser sensors can be quite high.

Rotary Hall Effect Sensors:

The Hall effect sensor detects the presence of a magnetic field, yielding a

true or false output. The devices typically latch onto the last pole detected; e.g.,

North Pole yields logic high and South Pole yields logic low. Hall effect sensors

are good for building shaft encoders; mount a small magnet on a wheel that

rotates by the sensor and the sensor will register one transition each time the

magnet swings by.

14

Ultrasonic Sensors:

Ultrasonic Position sensors are non-contact distance transducers. The

ultrasonic sensors measure the time it takes for a sound wave to travel from the

sensors to the target and back. The ultrasonic sensors output analog signal and

are very easy to use, but ultrasonic sensors have a deadband of 6 inches in front

of the sensors where it cannot measure the distance.

Rotary Encoders/Potentiometers:

Linkage arm can be attached to a potentiometer to measure the angular

displacement. The angular displacement is then used to determine the amount of

linear motion.

15

Mechanical/Structural manufacturing:

With the skeleton of the vehicle secured it was easy to decide on the

internal powertrain. The motor was designed and built under the tutelage of

professor Robert Miller of Santa Rosa Junior College 1996. The design was a

high torque motor capable of rally type driving demands, the block is a ’77 GM 4-

bolt main with a full roller valve train with estimated power output at a

conservative 390hp/400 ft-Lbs torque. This type of power plant must be followed

by an appropriate transmission capable of withstanding the abuse of 400+ ft-lbs

of torque. For this a GM TH350 was selected. The stock transmission was

modified per professor Phil Laverty’s instructions by fly cutting the two main

clutch pistons to allow for extra stets of steal/clutch assemblies. Valve body

modification was made to achieve a fully manual semi-automatic transmission.

Power is transmitted to the road through a late model GM limited slip differential

with steel axils, built by The Rear End Shop in Santa Rosa California. The brake

system has been fully restored to factory specs using Bendix brake parts and the

suspension bushings, tie rod ends and ball joints were replaced with PST Poly-

graphite type components. The front lower and rear control arms are boxed for

stiffness, and the conventional springs are now AirRide’s Shock Wave® (front)

and F9000 (rear) air springs for flexibility and system controllability.

The mating of the body and chassis took considerable calculation and

finesse. These modifications were accompanied by a steep learning curve for fist

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time builders and took long hours to justify. The fist step was to strip the El

Camino body from the GM A/G body chassis and remove the Studebaker body

from its out dated frame for the body graft. A trial fit was done to locate wheel

wells and mounting points. Noted in the trial fit were necessary modifications for

body alignment.

Figure 1. Trial fit of body/frame alignment

Next the frame was marked and modified in a cut and weld procedure. Step one

was to identify a linear region of the frame that would not be adversely affected

by modification. The center section of the frame was chosen and a 4-foot section

was modified. Fist the fame was leveled and then cut.

Figure 2. First frame modification cut

17

Then a five inch section was removed from the length and the section was

relocated five inches inward of its original location.

Figure 3. shortened and narrowed modification, re-enforced for structural integrity Once the frame was complete the suspension and brakes were rebuilt

.

Figure 4. Boxed suspension components and brake rebuild

The critical component of the control system could then be installed making the

frame a true rolling chassis.

18

Figure 5. AirRide air springs front and rear

Figure 4: Workspace and rolling chassis

19

Figure 5: Secure Lab and brainstorming area room 123

By securing the lab and workspace above we could facilitate a working

environment conducive to a developing project. Now that phase one of the

chassis rebuild was complete, attention to the body and appearance of the

vehicle could be addressed. A considerable amount of body and metalworking

was completed, making the means for a finished looking product.

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Figure 6. Body and paintwork

With the vehicle taking shape it was necessary to look into the more analytical

aspects of the design project. Consulting vendors at SMC and other local

pneumatic supply houses we were able to narrow down our pneumatic system

design. The pneumatics were the fist parts of the project that needed to be

secured to ensure proper testing of all system components, be accomplished

before manufacturing and assembly of the entire system.

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ANALITICAL ANALYSIS/VALIDATION TESTING

Human Whole Body Vibration Resonance Occurs Between 4 & 8 Hz.WBV

Resonance has been linked to severe lower-back pain, lumbar disk

degeneration, and kidney problems.Recent studies have indicated that females

exposed to WBV can possibly have added risk factors such as miscarriages and

other gynecological disorders. With this in mind we set forth to build a system

that was controlled by conventional shock absorbers for any vibrations above a

five Hertz cutoff frequency. This enabled us to be concerned with only low

frequency responses of the chassis and control system. By designing our spring

damper assemblies for a slightly underdamped effect we ensured that vibrations

would be attenuated sufficiently above the five Hertz range.

Figure 12: Simplified model and frequency response Bode Diagram

m

k cx

1

GROUND

x2

22

Mathematic Modeling of Theoretical Design:

By generating simplified physical models we were able to develop

operating principles that could aid us in the development of theoretical system

control parameters.

Giving rise to our variation of the extended reservoir accumulator volume.

r

EQUILIBRIUM POSITION (SETPOINT)

XP = 65 PSIG

P

LBAG

LRES

r

NORMALLY OPENSOLENOID VALVE

1/2 LBAG

P = 65 PSIGUCL

LCL

AIRBAGVOLUME

EXTENDEDVOLUME

PISTON

23

Our extended volume concept relies upon a microcontroller actuated solenoid valve

located between the air spring and the reservoir, to “extend” the air spring volume.

Changing the effective volume of the air spring causes a corresponding change in its

spring rate. Closing the solenoid valve at the UCL and LCL retards oscillation amplitudes

beyond these positions

X

F2

L2P2

EQUILIBRIUM POSITION(SETPOINT)

X

F1

L1

P1

F1P1 π⋅ r

2⋅ L1⋅

L1 x−F2

P2 π⋅ r2

⋅ L2⋅

L2 x−

Restoring Force for Air Spring plus Extended Volume Restoring Force for Air Spring Alone

24

F1(x)

F2(x)

RE

ST

OR

ING

FO

RC

E (

LB

F)

PISTON DISPLACEMENT (INCHES)

XUCL

F1 (UCL)

F2(UCL)

SOLENOID VALVECLOSURE POINT

xF2 UCL( )d

dM

xF1 UCL( )d

d⋅ F 1 UCL( ) F 2 UCL( )

25

The extended volume reservoir length is a function of the upper control limit, air

spring length, and the spring rate magnification factor M

L res UCL L bag, M,( )L bag

2UCL−

M 1−( )⋅:=

Lres

r

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With theoretical concepts of our design taking shape, we decided to

build and test some of the theories in the lab. First we developed a plan on how

the pneumatic subsystem would be positioned in the vehicle and then tested our

hypothesis

Figure 9: Pneumatic Schematic

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We used a testing apparatus to measure information from our sensors and

air springs. This data would be used to verify theoretical projections and optimize

hardware constraints that governed the manufacturing of the control volumes

Figure 10: Testing apparatus and pneumatic supply system

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Excel Data sheets:

Airspring test data compiled during static force-displacement testing performed

4/18/2002 Airspring Type: Front No Extended Volume Small Extended Volume: ~ 45 in3 Pressure at Setpoint: 65 PSI Pressure at Setpoint: 65 PSI

Displacement Force Displacement Force inches lbf inches lbf -1.00 530 -1.00 570 -0.75 620 -0.75 620 -0.50 690 -0.50 700 -0.25 790 -0.25 780 0.00 900 0.00 900 0.25 1080 0.25 1100 0.50 1260 0.50 1220 0.75 1420 0.75 1360 1.00 1640 1.00 1520

Medium Extended Volume: ~ 144 in3 Large Extended Volume: ~ XXX in3 Pressure at Setpoint: 65 PSI Pressure at Setpoint: 65 PSI

Displacement Force Displacement Force inches lbf inches lbf -1.00 600 -1.00 650 -0.75 685 -0.75 700 -0.50 740 -0.50 760 -0.25 800 -0.25 810 0.00 900 0.00 900 0.25 1080 0.25 1080 0.50 1180 0.50 1140 0.75 1290 0.75 1230 1.00 1380 1.00 1300

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1 0.5 0 0.5 1

500

1000

1500

2000

Empirical ValuesTheory

Air Spring: Theory vs. Empirical

displacement from setpoint (inches)

rest

orin

g fo

rce

(lbf

)

Restoring Force vs. Displacement from Setpoint: 65 PSI S.P. Pressure

400

600

800

1000

1200

1400

1600

1800

-1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25

inches

lbf

No Extended Volume

Small Extended Volume: ~ 45 in3

Medium Extended Volume: ~ 144 in3

Large Extended Volume: ~ XXX in3

Poly. (Medium Extended Volume: ~ 144 in3)

Poly. (Small Extended Volume: ~ 45 in3)

Poly. (No Extended Volume)

Poly. (Large Extended Volume: ~ XXX in3)

30

With the conceptual data processed and approved by the team an overall

design of the system was sought after. Through the use of solid modeling

software (Pro/E) we were able to generate an accurate representation of the

physical relationship of critical components within the confines of our system

design.

Pro Engineer Solid Modeling:

Figure 7. Complete chassis full assembly solid model

31

We were able to achieve an extraordinary degree of accuracy in the

model, making mass properties and special locations of critical components

straightforward and easy.

Figure 8. Solid modeling with cab

32

With the validation of the theoretical design it was important to develop a

definite on the hardware that was to be used. Through industry contacts at SMC,

Aftermarket and Nor Cal Controls, we were able to secure the necessary valving

and associated fittings that would comprise our pneumatic system

AIR SPRINGS

CONTROL VOLUME CONTROL VOLUME

LR Position Sensor

EXHAUST

INPUT

ECU

RR Position Sensor

RF Position Sensor LF Position Sensor

Compressor

Dryer

33

From the diagram above we can see the location of each wheel from above. At

each location there exists a wheel pneumatic modular assembly. This assembly

consists of two normally closed solenoid valves, an air spring with inlet and

exhaust ports of 3/8” and a normally open solenoid connected to our extended

reservoir. The control algorithm is designed to close the valve between the

control volume and the air spring in the event that a displacement outside of a

predefined envelope is sensed. The other two valves are primarily for input and

exhaust during the initialization and ride height establishment portion of the

control software.

With the pneumatic portion of the system in full production an

accompanying electronics design was necessary being that the valves were all

electronically actuated. The input (feedback loop) of the control system also

consisted of electronic position sensors that needed an adequate mounting

location. With this in mind we developed the outlines of an electrical

schematic.(see figure below). The electronics are powered by the vehicles

battery supply and are all networked to the main ECU through high speed

Category five Ethernet connections. If the ECU receives a signal that is outside

of the desired operating range the control solenoid will close and the vehicle will

attain a increased spring rate.

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Figure 14: Electrical wiring schematic

LR CONTROL

INPUT

INPUT

REAR CONTROL MODULE

LF CONTROL MODULE

LR Position Sensor

EXHAUST

INPUT

ECU

RR Position Sensor

RF Position Sensor LF Position Sensor

Compressor

LF CONTROL MODULE

150 psi PRESSURE SWITCH

CONTROL VALVES

RR CONTROL

EXHAUST

35

Once the big picture of how the system electrical would be managed it

was necessary to incorporated the electronic interface to the microcontroller.

Each wheel has its own control module consisting of a terminal block control

switches (MOSFET) and low pass filter. These modules are then networked to

the main microcontroller. This design is simple and effective making

troubleshooting easier and maintenance and replacement as simple as plug and

play. The schematic of the module board layout can be seen in the schematic

below.

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Algorithm Development:

The algorithm for this project was broken down into two sections, the main

loop and the initialization loop. The main loop will be used to control the vehicle ‘s

suspension system with the manipulation of the extended volume. The

initialization loop is used to reset the vehicle to its geometric set points.

When the user turns on the microcontroller and started the program, the

program will first check to see if the initialization switch is turned on or not. Once

the Initialization process is verified, the program will execute the codes for the

initialization process, which loads in its own parameters such as set points and

offsets. Then the program will continuously monitor each sensor per wheel and

maintain the position within the lower and upper control limit while the

initialization switch is on. If the position of the wheel is outside of the envelope,

then the program instruct the system to either pump or deplete air appropriately.

In order to detect and combat against air leakage or adverse conditions

such as parking up hill or loaded vehicle, we developed an Average Scheme,

which was aimed to detect and correct these situations. The detail for the main

loop, initialization and average scheme will be discuss in the following

programming and flowchart section.

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Programming and Flowchart:

Overall System:

As described in the previous section, the overall system is consists of two major

subprograms, initialization and the main loop. The detail of each loop is

explained as follow:

Initialization Loop:

As the microcontroller is turned on, the program will check to see if the

initialization switch is turned on, and will execute the codes within the

Initialization loop. The purpose of the Initialization is to reset the current position

of each wheel to the preloaded set points for the Initialization process, which

might be different than that of the Main loop’s set points and offsets. Then it will

continue to take reading of sensors for each wheel and compare with the set

points and offsets. If the position of the wheel travels outside of the upper control

limit, which is the set point plus the offset, then the program will instruct the

system to deplete air (dump) out of the system through the solenoid valves. If the

situation is reverse and the wheel travel below the lower control limit, then the

microcontroller will instruct the system to pump more air into the bag and

maintain the position within the envelope. This process will continue until the

Initialization switch is turned off and the system will go into the Main loop, which

is our controlled system.

The purpose of the Initialization loop is to allow the user to adjust the height of

the vehicle to its preload set points after indicator lights turned on. Indicators

38

lights indicate that there is a leak in the system or the wheel ‘s average position

is outside of the geometric set point of more than one-sixteenth of an inch.

Main loop:

Once the Initialization switch is turned off, the system will execute codes

for the main loop, which is similar to Initialization loop. The microcontroller will

load in the main loop’s set points and offsets, and then will check and compare

sensor of each wheel versus the set point and offset for that particular wheel. If

the position of the wheel travels outside of the upper or lower control limit, which

is the set point plus the offset for upper control limit and minus the offset for lower

control limit, then the microcontroller will instruct the solenoid to disconnect or

close the extended volume from the airbag. At this point, the vehicle will be riding

just on the airbag system, which is stiffer than its original configuration that

includes the airbag and the extended volume. A detailed flowchart is included to

clarify the system.

In order to detect any leakage in the system or to accommodate heavy

loading and uphill parking condition, an Average Scheme was included in our

main loop, which is described in the next section.

Average Scheme:

The Average Scheme was developed to further ensure that our system

can accommodate a wide range of condition such as heavy loading and uphill

parking, as well a detection device for any leakage. At the end of our main loop,

the current position of each wheel is recorded for the duration of ten minutes. At

the end of the ten minutes sampling, the program will sum up the recorded

39

position in the ten minutes sampling and take the average, which is the total

position divided by the number of samples for ten minutes. The average position

is then will be used to compare against the set point for that particular wheel, and

if it is within one-sixteenth of an inch, then the set point will be replaced by the

average position value. However, if the average position is outside of the one-

sixteenth envelope of the set point, then an LED light will be turned on to indicate

the user of the situation, and the set point remain unchanged.

One of the most difficult parts of the programming is to minimize the overall

system time per loop to less than 0.02 second. Since our vehicle ‘s cycle time is 0.2

second (from 5 hz), our program cycle time must be at least ten time faster or less than

0.02 second in order to allow us ten data points per vehicle’s cycle, otherwise the data

obtained is not a true representation of the system. This was proven to be very difficult

since our processor is at 2 Mhz. After some extensive streamlining twenty-five different

version of our program, from eliminating all for and if-then loop, we were able to obtain

our system time at 0.018 second, which is faster than what needed.

5 Hz Sinusoid (Normalized)

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

time (seconds)

Nor

mal

ized

Am

plitu

de

0.02 secsampling time

40

The above diagram indicates a visual representation of the averaging scheme

used herein

Figure 15: Algorithm flow chart

Start

Is SwitchOn?

InitializeSwitch

ExtendedReservoir Off

Is Wheel InLimits?

Adjust Height

Main Loop

Is SensorIn Range?

Sum InputValues

DisconnectExtendedVolume

Is Amountof Data

reached?

AverageSensor Inputs

Is AverageWithin

Limits?

FlashWarning LED

ReplaceSetpoint With

Average

True

False

False

True

False

False

FalseTrue

TrueTrue

41

Sample programming (Interactive C)

void main() { int i,m,k,samples; long avg0,avg1,avg2,avg3,setpoint0,setpoint1,setpoint2,setpoint3; long offset0,offset1,offset2,offset3; float sum1,sum2,sum3,sum0; setpoint0=100L; /* Declare setpoints and Offset per wheel*/ setpoint1=100L; setpoint2=100L; setpoint3=100L; offset0=10L; offset1=10L; offset2=10L; offset3=10L; sum0=0.0; sum1=0.0; sum2=0.0; sum3=0.0; samples=327; /* Enter number of Samples */ init_expbd_servos(1); /* Turn on servos on as indicators*/ while(!stop_button()) { for(k=0;k<=samples;k++){ reset_system_time(); /* Reset System time to get system time later */

for complete code see appendix.

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PROTOTYPE PRODUCTION:

With the majority of the project planned it was time to start prototype

production and the assembly of our ASCS. Things don’t always go as planned,

but for the most part the equipment generated met or exceeded expectations.

Figure 17: Front and Rear sensor mounting hardware and sensor

Figure 16: Pneumatic supply plumbing

43

Figure 17: Two rear and one front air Spring

Figure 17: First test setup

A

B

C

D

44

As can be seen in figure 17 the testing of each assembly phase was

critical in ensuring that the system had no leaks and operated to the desired

specifications. The arrow pointing to “A” indicates the microcontroller location, “B”

is the FL Sensor location, “C” is the test valve assembly which was later replaced

by the actual valve assembly. “D” is the Control Volume and two different sizes

are noted here.

Figure 18: Engine installation and pneumatics finalization

With the engine mounted and the sensors, valving and control volumes in their

final positions the vehicle begins to take shape. “A” represents the final control

volume, “B” is the LF control module and “C” is the valving final location, it was a

tight fit but putting the valves inside the frame rails made mounting the body

more efficient.

A

B

C

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The rear of the system was put in place and mounting of the body panels

began shortly after.

Figure 18: Rear pneumatic system with centralized control module box

Figure 19: Driving prototype Assembly 5/10/2002

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Figure 20: Final Prototype Assembly

With many nights of long working hours the team was able to put a

prototype together that met all their second semester goals. The finished

prototype can level itself under dissimilar weight distributions in the initialization

portion of the control program. On the control side of the program the computer

establishes a set point and an offset in which to create the envelope. Once the

suspension travels outside of this range the control volume is removed from the

air spring volume and a stiffer spring is had. The overall projet works well and

looks like expected.

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DISCUSSION: The project scope initially may have been above and beyond the capabilities of the

team and therefore had to be pared down over the mid-semester break. This was a setback

from the initial timeline projections but the simplification of goals made the results you

have seen more realizable. The overall operation of the control system works as it was

designed. The scope of the project has been met and final assembly of the prototype is

complete. Some of the major issues that we encountered were electronics related. The

method we were using to actuate the high current driven solenoid valves from the low

current microcontroller, consisted of the implementation of a MOSFET. The issues we

developed was a common ground problem, and a residual charge buildup due primarily to

the use of manual override circuitry within the control modules. This residual charge

made the system react non-uniformly and erratic. The solution to this problem was a pull

up resistor between the gat and drain of the MOSFET to ensure that the gate would be

pulled down to reference voltage if the microcontroller was not powered. This fixed the

problem and the final results were pleasing. The only other concern is the size of the

supply compressor, under initialization mode the compressor lags behind the system flow

and there is a considerable delay in response time. To combat this issue installation of a

belt driven compressor will be necessary.

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CONCLUSION/SUGGESTIONS: The final presentation of our findings regarding the use and implementation of our

ASCS were all very positive. The future recommendations consist of changing the on

board compressor to a belt driven style that can handle the volumetric demands that the

system requires during the initialization period of the control program. Little hardware

modifications will be necessary other than re-torquing of suspension component and final

engine installation. The software is very robust and will serve as the foundation for any

expansion in the future. One of the parts that will be replaced is the microcontroller, the

HB is an educational evaluation style board, and a dedicated control microprocessor

would be desirable. Future field testing of the control system will consist of data

acquisition form an on board accelerometer and DAC system. This will enable further

analysis of the effectiveness of our design and will give insight into directions of

modification. This is a prototype and should be used as so. Testing is a must if production

is at all in its future. The experience of working in a large group has been enlightening

and will serve each group member in a different but equally important way. The overall

success of our project was merely a reflection of the efforts that the team made in

completing a solution to an engineering problem, effectively the outcome form our senior

project was exactly what the program has been designed to achieve. We would like to

especially thank Dr. Wang for his support and guidance down the unknown road of

product development in engineering.

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REFERENCES: 1.Engineering Mechanics Dynamics 2nd edition; pp. 458-518; A. Bedford, W. Fowler; ©

1999 Addison Wesley Longman, Inc. Menlo Park, CA. 2. Airstroke/Airmount Firestone Engineering Manual and Design Guide ©2000 Firestone

Industrial Products Company. 3. Air Ride Technologies 1999-2000 Catalog & Technical Manual; © 1999 Air Ride

Technologies Jasper, IN. 4.Linear Algebra and its Applications 2nd edition; David C. Lay; ©1999 Addison Wesley

Longman, Inc. Menlo Park, CA. 5. Theory and Design for Mechanical Measurements 3rd edition; R. Figliola, D. Beasley

©2000 John Wiley & Sons, Inc. New York. 6. Modern Control Engineering 3rd edition; Katsuhiko Ogata ©1997 Prentice-Hall, Inc.

Upper Saddle River, NJ.

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APPENDIX:

PNEUMACS PROJECT PROPOSAL 2001-2002

Project Title: Active Suspension Control System: ASCS

Faculty Advisor: Dr. Ji Wang Tel: (408) 924-4299 Fax: (408) 924-3995

e-mail: jiwang@email.sjsu.edu Engineering Team: 1. Duc Le Tel: (408) 623-1913 2. Michael Thai Tel: (408) 814-5735 3. Tommy Chang Tel: (408) 292-3605 4. Patrick O’Neill Tel: (408) 804-0240 5. Rudha Ben-Yuhmin Tel: (408) 293-8672 Project Scope: Design and build an active suspension, vibration isolation control system, activated by acceleration and position sensors intended

to enhance chassis characteristics during hard cornering, braking and loaded applications.

Project Objectives: 1. Model and document system design. 2. Analyze frame and component structures. 3. Fabricate prototype assemblies. 4. Develop controller algorithm to satisfy design criteria. 5. Implement and test system characteristics.

6. Document error analysis and project modifications. 7. Develop an engineering report. Deliverables: 1. Frame and component Pro/E model. 2. Wiring and sensor schematic. 3. Finite Element Analysis documentation. 4. Computer control program source code. Timeline: See attached pages. Resources: Student and Industry Sponsors Approval Signatures: Students: 1. 2.

3. 4. 5.

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TIMELINE:

Process 2001-2002

Month starting Aug. 2001 Aug Sept Oct Nov Dec Jan Feb Mar Apr/May

Feasibility Study/Project Organization

Interviews/Observations/Supply Location

Data Analysis/Pro-E Modeling/ Purchasing

Calculations/Comparative Analysis/ Programming

Prototype Production/ Implementation/Testing

Generating Reports/ Documentation/Modifications

Presentations/Graduation

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Following are the images of work that done during the project.

Rolling Chassis Studebaker Pickup Cab

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Body Modification and Metalwork.

Pneumatic test apparatus and controls table

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55

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Equipment information and Specifications Air Springs:

Air Ride Technologies Shockwave™ SKW1010 ’78-’81 front steer Camaro subframe Stud/Trunnion mounting $849.00 Note: This is a bolt on part and utilizes a Qa1 Hal 12 point rebound adjustable shock (center), with Air Ride’s patented sealing technology.

Firestone Airstroke® Actuators W02-358-9004 for rear air spring Sold by Air Ride Technologies as: F9000 Tapered Sleeve Airspring 1500 lbs@100psi $95.00 x4 for special leveling support.

Shocks:

QA1 Hal 12 Point Rebound Adjustable Shock Absorbers Listed by Air Ride As: SHO-HAL-7012 5/8 eye/tie bar mounting Compressed height: 12.5” Ride height: 15.5”-16” Extended height: 18.75” $150.00

Compressor: Air Ride’s Black Max air compressor designed to handle 150psi and work on a 12V car battery system. Integral pressure cutoff valve located at outlet automatically shuts pump off when desired operating pressure is attained. ARC6000 $279.00 X 2 150PSI pressure switch $35.00

Fittings and air Lines: Due to increased air flow needs within the system, it will be necessary to move from traditional ¼”lines and NPT fittings to enlarged orifice designs utilizing SMC ½” lines with 3/8” NPTfittings. Estimated Cost: $200

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Solenoid Actuators:

A critical component in system control. Zero pressure differential operation required (direct acting) Port size: 19mm with 3/8” NPT, Orifice size: 10mm to 15mm for increased flow Voltage: 6-12 VDC with UL DIN connectors x12 normally closed

x8 normally open estimated cost: $200 Hall Effect Position Sensors:

RPT 5000 Hall-Effect Rotary Sensor by Electro Corporation With a non-contact sensor, ware and fatigue are not a concern. There are several designs that could be implemented with rotational or linear IC package designs. Honeywell is another company to consider. Estimated cost: $250-$350

Accelerometers:

The Honeywell RBA-500 is a perfect choice for our application With a 70g range it is well within our expected tolerance and outputs a frequency proportional to the acceleration sensed, this directly enables a digital integration into the control system. However the use of analog voltage varying accelerometers are not entirely out of the equation. Estimated cost: $200

Microcontroller:

This is another critical component of our control system, without the proper Microcontroller the computing capabilities of our system will be limited, resulting in poor control of the chassis’s low frequency vibrations. Products: Pic-Micro, Motorola, Atmel and Basic Stamp. Desired Specifications: 40-60 I/O Pins; 6-10 A/D converters; on-board timers; 8-12 bit capabilities and EEPROM or FLASH compatibility for program modifications. 30MHz for safe operation and enough RAM to facilitate real time Data Logging would be an excellent debugging feature. Estimated cost: $225

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Projected Budget Estimations

EQUIPMENT COST ENGINE & POWER TRAIN: Chevrolet 350ci, 350hp OHRV powerplant GM Toubo Hydra-Matic 350 modified manual shift automatic transmission Late model GM differential with limited slip traction control

5,500.00

400.00 800.00

SUSPENSION COMPONENTS AND MODIFICATIONS: Polyurethane suspension bushings, ball joints and tie rod ends Full break equipment assemblies, master cylinder, lines and fluids Wheels and tires

1,000.00 1,850.00 2,700.00

AIR SPRING SYSTEM: Pneumatic spring assemblies, mounting hardware and equipment Solenoid actuators, lines, tanks, compressors and regulators Electrical interface and manual control unit

2,500.00 1,300.00

400.00 TOOLS, SERVICES AND SUPPLIES: 110 MIG welder for fabrication and modification Paint, sanding equipment, autobody supplies/services Machine work fabrication costs and outsourcing

450.00

3,000.00 600.00

ELECTRONIC CONTROL SYSTEM: Position sensors, accelerometers and signal conditioning components Microcontroller, development software and associated electronics Wiring, power relays, connectors, batteries and misc. equipment

700.00 500.00 350.00

SUBTOTAL 21,850.00

EXPENSES TO DATE: Suspension brakes and frame modifications Engine, transmission, sifter, steering wheel, differential, instrument gages Autobody paint, supplies and equipment

-3,200.00 -6,700.00 -1,150.00

TOTAL 10,800.00

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Sponsorship Proposal

The following equipment list is an example of several areas that are cost sensitive and would greatly benefit from industry augmentation or donation. Because of the nature and scope of this project, it is necessary to ensure that adequate financial and equipment support is secured prior to full system development. With this in mind I would like to introduce the benefits of securing your Corporate and or Industry Sponsorship.

Corporate Sponsorship

• Enables a Corporation or Private Company to support a San Jose State University Mechanical Engineering Senior Design Project.

• Creates a climate for Industry and University collaboration. • Typically range from $500-$5000 depending on equipment or monetary support. • Will receive a Project Proposal and project description as well as a monthly

correspondence project update • Is invited to a formal Product Presentation/Demonstration in the Spring of 2002,

held in the SJSU College of Engineering Executive Briefing Cambers. • Is recognized in a formal Engineering Report regarding contribution information.

Industry Sponsorship

• All of the above and more… • Is designed to allow contributions of material and equipment to aid in the

completion of the ASCS Design Project. • Gives students the experience of dealing with outside vendors and suppliers. • Establishes a link between Industry and University Engineering Graduates. • Is recognized in a formal Engineering Report regarding contribution information.

This is a chance to be part of an inspirational design project that strives to achieve

success. I hope the information herein will give you confidence in the dedication Pneumacs has to building the best Senior Design Project of academic year 2001-2002. As project manager I personally assure that timely delivery of all information regarding project updates and proposed plans are achieved. Thank you for your interest and support, feel free to inquire further by phone or e-mail at rudi_tudi1976@hotmail.com Sincerely,

Rudha Ben-Yuhmin Pneumacs™ ASCS San Jose State University One Washington Square San Jose, CA 95192 (408) 293-8672

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REAR F9000 AIR-SPRING

FRONT ‘SHOCKWAVE’ AIR-SPRING

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FRONT (SHOCKWAVE) AIR SPRING