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The Design of High Frequency Solenoid and Controller

for Unit Injector

Jae-Ou Chae, Sang-Man Lee, Jae-Won Hwang, l-Jin Yang, Seok-Chae Chang, Han-Joo Kal, Alexander

A.Martynchenko, Balin Andrei

Inha University

Young-Sik Jeong

Seoul National University

CJ.Park, J.K.Lee, B.C.Shin

Doowon Precision Industry Co, Ltd

Contact address

Combustion Lab. Department of Mechanical Engineering, INHA University, #253

Younghyun-Dong Nam-Gu Inchon 402-751, KOREA

TEL : 82-32-860-7314 FAX : 82-32-865-6525

ABSTRACT

Nowadays, we meet stringent demands on low air pollution of the Diesel engines. Environmental Protection Agency(EPA)

regulates the amoun t of NOx, Particula te, HC and CO at all driving conditions. To overcome the future emiss ions regulations , many

researchers submit two solutions about injection control to solve this problems. One is the common-rail type injection system. The other is

unit injection system. H owever, most rese archers agree that electronically controlled unit i njector has been developed to meet the future

emissions regulations realizing high injection pressure and precise control of SOI(Start Of Injection) and injection quantity. In order to

control start and end of injection, each unit injector contains a time- controlled high speed solenoid valve. Thus, the fuel injection quantity

is determine d by the time interval between closing a nd opening o f the solenoid valve. This s tudy introduces the desi gn method of

solenoid which is in stalled in u nit injector. As a res ult, it is known that there are important parameters to optimize solenoid performance.

The parameters are inductance, stroke, input voltage, coil resis tance, load and switching tim e.

Keywords : Unit injector, Rising time, Waiting time, Optimal inductance

INTRODUCTION

To satisfy the future severe emissions regulations for diesel

engine with low particulate and .NOx levels, both the engine combustion

system and the Fuel Injection Equipment(FIE) should be improved. For

the FIE, high injection pressure and variable injection timing as a function

of engine speed, load and intake temperature are very important

parameters. BOSCH is developing two different solutions;

1) Electronically controlled unit injector and sin gle cylinder

pump system.

2) High pressure inline pumps with control sleeve and

electronic control.The new generation of electronic diesel fuel injection system

with special sol enoid valves presents

a compli cated mechanical/electrical system. It involves a combination of

mechanical motion, hydraulic pressure wave propagation, and the

transient magnetic and electrical processes which interact with others.

In this paper, the coupled dynamic behavior of the new system is

studied based on a research type unit injector system developed by

INHA university, Korea. A general physical model which includes other

structure type such as the electronic pump-pipe-injector system and the

distributor pump system is established. Traditional mathematical

models for conventional mechanical injection system or conventional

solenoid valves are not suitable for the new type of injection system.

An atte mp t is the refore ma de to develo p

97142(Abstract Code 11 )

P A C I F I C C O N F E R E N C E O N A U T O M O T I V E E N G I N E E R I N G Ball, Indonesia, November 16 -21, 1997


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solenoid operated Unit lnjector(UI : Fig. 1)for diesel engines and to inject

more exactly into the combustion chamber at high press ure. These new

injectors have the size of conventional diesel injectors with small but are

more powerful and ultra-fast solenoids(switching time less than 3

ms)l ocated on the nozzle. To provide fast openin g and closing of the

nozzle, a multiobjective optimization method is used to select the design

variables of the injector. The mathematical model used for optimization

is developed with the help of experimental results obtained from the

solenoid force measurement at transient conditions. The optimization

result did show good dynamic performance of the injector, despite the

use of a small size solenoid actuator. The fast progress observed in

recent years in the field of electronic fuel injection(such as Unit injector

or Common-rail system)with solenoid operated injectors for internal

combustion engines, was mainly made in the gasoline supplied spark-

ignition engine s. In ideal engines, the hydraulic control of injectors by

the high pressure fuel injection pump is still dominating. There are

attempts to introduce solenoid actuators to control the fuel injection

process, but until now there are not many of these systems available for

commercial us e. The reason i s the requirement for very fast operation of

diesel injectors to inject a closely controlled fuel during a very short timein hostile conditions of the engine combustion chamber. When trying to

inject gaseous fuels in the diesel engines, some researchers employed

hydraulic control of injectors that required the use of a conventional

diesel fuel injection pump. A few years ago, an attempt was made at

Concordia university to develop solenoid operated injectors for direct

injection of natural gas in diesel engi nes. The results obtained proved

the feasibility of such concept. The injector design was modified recently

by introducing a small powerful solenoid into comm ercial ly availabl e

diesel injector, in order to reduce its size and weight and to make it

exchangeable with typical size injectors. In order to make its operation

fast enough, a special switching circuit was developed and a

mul tiobj ective optim ization method was applied to select the best design

variables providing fast opening and closing of the injector.

SOLENOID DESIGN

Response time consists of waiting time between voltage

occurring in wire and armature beginning to move and rising time

between beginning to move and end of move of armature. Input voltage

is described as follows

where we can easily know parameters of solenoids are conne cted with

current, displacement, magnetic flux, traction force and inductance.

Moreover, above parameters are all function of time.

OPTIMAL INDUCTANCE FOR SWITCHING TIME

This study suggests how to design optimal solenoid. Optimal s olenoid

equals op timal respons e time at given size. Definition of inductance is

To get optima l ind uctance, waiting time can be expressed

with equation(7)

also optimal waiting time and optimal winding number can be

expressed with equation[10],[11]

We can easily get the relationship at optimal situati on

This equation shows that in case of optimal operating condition of risingcurrent it is approximately seventy percent of maximum current atgiven wire diameter. General solution of differential equation ofdynamic can be obtained if we take into accou nt all main parametersof the solen oid. If we conside r dynamics, we could g et the exact value

hereas ma gnetic flux is a function of current. The waiting

me as follows

and current r ises as an exponential function below,

so

where "d" equals

Therefore optimal Inductance of waiting time is


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,so minimum rising time is

surge voltage is 120 -360V which is value of 10 -30 times of input

voltage (12V). Furtherm ore bias voltage gives rise to current at the

neighbor wire through the conducting wire. And the chip which

recognizes surge voltage as a input signal misbehaves, as a result it

is im poss ible to control .

EXPERIMENTAL METHOD

TEST BED - Fig. 2, 3 is solenoid test bed and solenoid formeasuring the dynamic characteristic of solenoid. This picture

shows that the solenoid attached strongly on the test bed. Size of

solenoid is 28mm x20mm, silicon steel thickness is 0.35mm, length

of core is 17mm, projected area which piled up 8mm x 20mm and

bobbin is made by the epoxy for better operation at the high

temperature. Spring supports armature and its force can be set as

wish. At the end of armature, lift sensor and permanent magnetic

were installed for measuring the lift of solenoid. Data which is

received from the lift sensor can be read on the oscilloscope directly

and saved in the diskette. Solenoid supporter and sensor s upporter

are made of nonmagnetic material. Armature is made of pure iron

for piling up problem. Solenoid stroke is adjusted by dial gauge.

SOLENOID SURGE - If the solenoi d is excited by the current, the

electricity energy changes to the magnetic energy and magnetic

energy is accumulated in the wire. At that time if current switches off,

accumulated magnetic energy damages the wire

CIRCUIT - In this study, puls e width modulation method was used

for control the current of solenoid. Fig. 4 shows sol enoid controller

and stable 12 or 24voltage source which was used after two high

pass filters. To protect the solenoid surge diode was connected

positive direction. Then it de creased 40% s olenoid s urge.

initial conditions are defined as follows

Therefore we can get easily rising time:

and we can get optimal inductance for rising time using above equations:

where

and inductance is


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EXPERIMENTAL RESULTS

COMPARISON OF EXPERIMENTAL DATA AND

SIMULATION DATA FOR RISING CURRENT AND LIFT - Fig. 5

shows experiment and simulation results of relationship between rising

current and armature movement. Both results are relatively well

matched in case of neglecting electrical noise. Also experimental data

shows that the last period of movement is little different with simulation

result. Because s imulation program neglects mechanical counterforce.

In program current saturation of solenoid is consid ered for precise

simulation result. The reason of current difference between simulation

and experiment is that program neglects all chips which were used in

circuit had natural inner resistance and PWM control is used as soon as

armature moves for power cons umption reduction.

RELATIONSHIP BETWEEN STROKE AND RISING

CURRENT ACCORDING TO THE TIME VARIATION - Fig. 6 shows

the stroke, current and magnetic flux according to wire diameter andwinding number. In this figure, high current means fast moving of

armature and fast operated solenoid means high power requirement to

move.

STROKE AND TRACTION FORCE ACCORDING TO

TIME VARIATION - Fig. 7 shows stroke, current and traction force

according to the time with 12V and 24V. As is seen in the figure,

applying 24V reduced rising time about 0.15ms compared with 12V.

About the tracti on force , onl y ma gne tic fil ed was con sidered in the

calculation. But usually in the real case, the inertia of armature and

spring force which vary according to the position should be taken into

consideration. The armature movement equation is described by

In the figure, traction force at armature starting point indicates 90N

as a preforce. Power consumption can be calculated easily by

integration of s quare current times resis tance. As armatur e almost

reaches core, the traction force decrease under the preforce. This

phenomenon is caused by reduction of current due to rising

inductance but in spite of reduced current armature continues to

move under the influence of ine rtia force.

SWITCHING TIM E OF SOLENOID WITH DIFFERENT

WIRE DIAMETER AND WINDING NUMBER - Fig. 8 shows

stroke, current and switching time with different wire diameters and

winding numbers. In this figure, wire diameter has a little affect on

current but little on the switching time of the solenoid for a given

winding number. But winding number do affect switching time and

also size of sole noid for a same wire diam eter, if we ignore other

factors this relation has great meaning about the design of

solenoid.

EFFICIENCY OF SOLENOID AND INSTANT

ACCELERATION - Fig. 9 shows efficiency and instant acceleration

with switching time. This figure can be used to determine optimum

solenoid for each case. All electronic energy can not be converted

to kinetic energy of solenoid when electronic field excite magneticfield. Here define efficiency of solenoid as follows.

Both cases 0.8mm x 48 and 0.6mm x 80 are good in

efficiency. But comparing of efficiency between two the former is

better if consider switching time. In real situation case 0.8mm

x48type shows higher current than simulation result due to current

saturation. So despite slow switching time we can conclude that

case 0.6mm x 80 which current saturation do not occur has better

efficiency in view of solenoid efficiency.


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CONCLUSIONS

1. The simulated res ult are well matched with experimental result i f

neglect the PWM control.

2. Rising time increased according to increase of winding number

at the same wire diameter and rising current decreased according

to increasing of inductance.

3. Waiting time and rising current increased according to preforce

increasing but r ising time decreased.

4. Generally, fast solenoid mean high rising current and high power

need to operate.

5. Response time is affected by winding number of wire rather than

wire diameter

REFERENCES

1. Hiroyuki Kano "Contribution of Optimum Desig n for Nozzle

Configurati on to Spray Formation" SAE 900824, 1990

2. T. Kato "Spray characteristics and Combustion improvement

of Dl diesel engine with high pressure fuel injection" SAE

890265, 1989

3. S.Shundoh "The effect of injection parameters and swirl on

diesel combustion with high pressure fuel injection" SAE

910489, 1989

4. S.Shundoh "NOx Reduction for Diesel combustion using pilot

injection with high pressure injection" SAE 920461, 1 992

5. S.Shundoh "Reduction particulate and NOx emissions by

using multiple injection in a Heavy duty D.I. Diesel engine"

SAE 940897, 1994

6. S.Shundoh "Prediction -A Measure to influe nce exhaust quality

and noise in diesel engi ne" Pro ceeding s ASME, 1989

7. Gerhard Stumpp "Fuel injection equipm ent for Heavy duty

diesel engine for U.S. 1991/1994 emission Limit" SAE

890851, 1989

8. VWIiam G.Wolbe r "An Overview of Automotive control

actuator SAE 840306, 1984 9. Pierre Lauvin "Electronical ly controlled high press ure unit

injector system for diesel engi ne" SAE 911819, 1991

10. Ronald K. Jurgen (Editor in Chief), Automotive Electronics

Handb ook, McGraw -Hill, Inc., (1995, pp. 10.1-10.34.Fi gure

1. Var ious solenoids

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