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Electrohydraulic Injector for a Diesel Engine Control System
Copyright © IFAC Pneumatic Wanaw, Poland 1980
a. Hydraulic Compon~nta
ELECTROHYDRAULIC INJECTOR FOR A DIESEL ENGINE CONTROL SYSTEM M. Bielecki*, Z. Kryszewski*,
J.
Sawicki* and Z. Moczulski**
*Institute of Control Engineering, Technical University of Poznan, ul, Piotrowo 3A, 60965 Poznan, Poland **Research and Development Cent er for Marine and Railway Diesel Engines at Engineering Works H. Cegielski, Poznan, ul Dzierzyfl.skiego 2231229 60965 Poznan, Poland
Abstraet. An electrohydraulic injector for medium power Diesel engines is described in the paper. The injector which is used as an element of electronic engine control system, consists of an electromagnetically controlled valve, a hydraulic servo and an actuator determining the fuel dose, supposed a high pressure fuel source is provided. In the first part of the paper the principle of operation as well as the schemes and diagrams of the electrical and mechanical parts of the injector are presented. Also certain characteristic curves are given. In the second part some optimization procedures and their implementations are described e.g. the control signals are optimized with respect to their shape. Also an extension of the problem with respect to certain parameters of the device is mentioned. Keywords. Control equipment; Diesel engine control; hydraulic amplifiers; optimal control; bang-bang control; electric actuators; solenoids; direct digital control; flow control.
INTRODUCTION
of opening and closing of valves, the injection advance angle, etc., remain approximately constant or uncontrollable.
It is a well known fact, that the processes of air supply, fuel injection and exhaust gases removal in large classical Diesel engines are controlled by mechanical elements like camshafts, inlet and outlet valves, injection pumps, fuel injectors etc. Also the rotational speed and the load of Diesel engines are usually controlled by mechanical centrifugal governors. The main feature of this system is that the most important parameters, as the instants
In recent years some attempts in order to introduce electronic controllers and remote control devices in oil engines can be observed. They have many advantages but require of course other input and output elements than classical controllers. In particular the principle of operation of the injectors results from the fact that the fuel pressure remain. 157
M. Bielecki et al.
158
approximately constant and the fuel dose is to be controlled by an electri c si gnal. In the following paper a new electrohydraulic injector and its electronic actuator deeigned as output of a digital controller, are described. Also some optimization procedures concerning the control signal and the parameters of the injector are presented. The whole system is a result of cooperation between the Institute of Control Engineering of the Technical University of Poznan and the Research and Development Center of Marine and Railway Diesel Engines at Engineering Works H.Cegielski - Poznan.
BLOCK DIAGRAM OF THE ENGINE CONTROL SYSTEM As mentioned above different electronic devices are already used in Diesel engines instead of mechanical controllers. Some of them were patented, above all in the United States, in the Federal Republic of Germany and
command
!!>peed del'iation desired
$J)eed
Setting and comparison unil
-
si9nal
Digital controller
-
pulse signal
in France. Also the injector, described in the paper, together with the digital control system was patented in different countries, e.g. in the United States /U.S.Pat. No 4176624/. The block diagram of the system is shown in Fig. 1. The main part of the system is a digital controller at which the preset values of speed and of some other parameters which are to be controlled, can be selected. There are several transducers producing the input signals for the controller, but the most important is the speed/pulse converter coupled to the main shaft of the engine. The output signals of the controller after a digital-to-analogue conversion are applied via special drivers to the electromagnetic injectors, as well as to the valve actuators and to the load control actua_ tore. The injection process is then influenced by two parameters of the controller output signal: the starting point and the duration of the pulse, corresponding to the advance angle and to the fuel dose.
actuating current
Electronic
fuel
dose
Electro -
actuator
r---- hydraUlic
Speed-
spfled
>----.-
injectors
pulses conYllrfer
Fig. 1.
The block diagram of the engine control system.
Diesel engine
Electrohydraulic Injector
ELECTROHYDRAULIC INJECTOR AND ITS OPERATION
The injector is of servo-type and consists of the following main elements: the electromagnetic valve, the hydraulic amplifier and the fuel dosing actuator. The injector is supplied with fuel from a ~onstant pressure supply
16
31
32 15
f9 20
23 10
14 4
25
17
3 2
Fig. 2. Electrohydraulic injector.
159
system including a high pressure pump. The structure of the injector is shown in Fig. 2. It can be seen that a cylinder /3/ as well as the plunger 4 and the nozzle holder 2 are fastened to the lower part of the body 6 by the use of a sleeve nut. The plunger 4, which can move in the cylinder leans wi th its lower end against the upper part of the nozzle needle 1, settled in the nozzle holder 2. The lower part of the needle has a cone and is settled in the injection chamber seat 13 above the injection apertures. The nozzle needle together with the plunger is a difference set, whereas the diameter of the plunger is greater than the greatest diameter of the needle. The plunger has a hydraulic connection with the control slider 5. Its shoulders control the fuel flow, depending on the actual position of the slider. There are two perimetric channels 28 and ~O, formed by the shoulders, the third one 29 belongs to cylinder 18 of the valve /the slider can move inside the cylinder/. The channel 29 is situated with respect to the shoulders in such a way, that in the lower position of the slider one of the perimetric channels 28 together with the channel 29 connects chamber 14 of the plunger with the supply line 19, through ducts 21 and 22 as well as through the gland 9 and the check valve 10, which are connected in parallel. In the upper position one of its perimetric channels 30 together with channel 29 connects the plunger chamber 14 with the offtake line 24 through gland 9, lines 22 and 32, a store chamber, a second gland 11 and an overflow valve 12. The injection chamber 13 situated in the injector body 2 has a continuous connection
160
M. Bielecki et aZ.
to the constant pressure supply line 19, not depending on the position of the slider. The control slider is connected with the armature 7 being a part of the electromagnet 31, which is suppli~d with a current pulse from the controller via electronic actuator. If a current pulse flows through the coil 31 of the electromagnet, its armature 7 together with the slider are shifted to the upper position, where the fuel flow from the line 19 to chamber 14 of the plunger is cut off, and the fuel which was compressed in the chamber can be taken off to the line 24 through the gland 9, line 22, channels 29 and 30, line 32, store chamber 23, gland 11 and the overflow valve 12. The force resulting from the pressure drop in the chamber 14 of the plunger, at a constant pressure at the injection chamber 13, is then directed up, causing thus a lift of the needle 1 and an injection of the fuel through the apertures of the nozzle holder. The injection process lasts as long as the current pulse, supplying the coil. If the current flowing from the electronic actuator is interrupted, the armature 7 and the slider 5 will be displaced, becouse of the reaction of the return spring 8, and stopped at the lower extreme position, where the outlet is closed and the flow way from the supply line 19 to the chamber 14, through the line 21, channels 28 and 29, line 22 and through the parallel connection of the check valve and gland 9 is opened. The hydraulic force resulting from the difference of surfaces of the plunger 4 and needle 1,provided the pressures in the chamber 14 and in the injection chamber 13 are
equal, is directed down, causing thus the closing of the apertures and cutting off the fuel injection. The described cycle of the injector operation, including the opening and closing of the nozzle apertures, corresponding to the beginning and the end of the injection, repeats at a frequency equal to the number of the revolutions of the engine or to the half of it, for a four a two - or four-stroke engine respectively.
ELECTRONIC ACTUATOR FOR THE INJECTOR The diagram of the electronic actuator of the injector is shown in Fig. 3. According to the scheme the current flowing through the coil can be forced in order to accelerate the armature movement.
BOY
~~----~---------------------.
Supply Units
50Y
R2 f()().R
.
R1 2SJJ
Th2
'--------t Control Unit
Fig. 3.
Diagram of the electronic actuator.
The device operates in the following way. The switching on the thyristor Th 1 initiates a discharge of the
161
Electrohydraulic Injector
forcing capaci tor C1; a powerful current pulse flows through the injector coil. If the capacitor is already discharged, the current energizing the coil takes a lower value; it flows through resistor R1 /holding current/. As Th 2 switches on, the current is interrupted by a positive charge from capacitor C2, blocking the thyristor Th 1. The current and the armature displacement vs. time curves can be seen in Fig. 4. i(t)
x,
Fig. 4. Effect of current forcing. The use of the forcing current makes possible to reach a high speed of the armature, required if the injector is to be opened in a few miliseconds.
speed of operation without reboundings. This total optimization problem can be simplified if its decomposition into two problems is provided /Hielecki,Sawicki, 1977,1979/. The optimization algorithm was found using certain basic principles of the optimal control theory /the "bang-bang" principle/, when the calculations were done by the use of an analog computer. This algorithm can be used not only for an analog model of the electromagnet, but also for a real solenoid-armature system, the more the operating time measurement is here not required. In a fact, the algorithm was found without taking into consideration the current "kick" but, as the experiments have shown, it remains actual if the "kick" is applied. The external circuit should be therefore designed in such a way, that the first pulse gives a higher current than the second one /Fig. 5/. The current "kick" together wi th the "bang-bang" control mode, resul t in a very quick, no-reboundings operation. ift)
SOME OPTIMIZATION PROCEDURES The most important property of the electromagnet should be its sufficient rapidity. On the other hand, if the energizing pulse is too high, some reboundings can appear /Fig. 4/, which impair the behaviour of the injector hydraulic system. A very important and difficult problem is therefore not only the optimization of the solenoid parameter values, such as the number of turns and the spring constant, but also the choice of a proper current pulse shape, in order to assure the highest
t
t, 1({t)
t...t~ I I
I -- - - - - -
-,._..,jI_-----~1.....
t o Fig. 5.
Optimal control principle
The electronic optimal control circuit can be obtained after some modifications of the actuator from Fig. 3.
M. Bielecki et aZ.
162
mOPERTIES OF THE DESIGNED INJECTOR The characteristic curve of the injector /the fuel dose per one injection vs. duration of the control pulse, at fuel supply pr.ssure equal to 60 MPa/ is shown in Fig. 6. tJ["".,I/inil 1100
: Q
'00
"
700
I
IJ
CONCLUSIONS The application of the described injector together with an electronic control system enables to obtain new properties of Diesel engines; their parameters can be optim1zed more effectively than it they are controlled by mechanical governors and tradi tional injection pumps. For example the injection regularity even at the lowest engine speed ranges and a good constancy of the injection moment can be a chi eved.
I1
600
Also some additional advantages resulting partially from the new injection technics schould be mentioned: the reduction of fuel consumption, of toxicity and of the engine noise level.
I If
500
I
11
-lOO
I
11
JOO
j
I
REFERENCES
1
1OO
0
,11 1
2
,
-I
$
6
ti[,m-l
Current puI!IC duration
Fig.6.
Injector characteristic curv••
During test. a sufficient repeatability of particular doses was observed, .specially for greater doses. The portion of maximum to minimum dose was about 2011, beeing a very important advantage if compared wi th purely mechanical systems. Some irregularities and nonlinearities can result probably from a residual rebounds of the armature, disturbing the hydraulic control of the needle movement. It must be noted that certain limited varia tions of the holding current wi thin the assumed limits of 1% of the rated value, do not influence the charaCteristic curve of the injector.
Bielecki, M., and Sawicki, J. /1977/. Optimization of an electromagnetic control unit. Foundations of Control Engineering, vol.2 No 2. Bielecki, M. /1979/. A hybrid implementation of the no-rebounding, time optimal control for an electromagnetic actuator. Foundations of Control Engineering,vol.4 No 2. U.S.Pat. No. 4 176 624, Diesel Engine with Electronic Control, Dec. 1979.
a. Hydraulic Compon~nta
ELECTROHYDRAULIC INJECTOR FOR A DIESEL ENGINE CONTROL SYSTEM M. Bielecki*, Z. Kryszewski*,
J.
Sawicki* and Z. Moczulski**
*Institute of Control Engineering, Technical University of Poznan, ul, Piotrowo 3A, 60965 Poznan, Poland **Research and Development Cent er for Marine and Railway Diesel Engines at Engineering Works H. Cegielski, Poznan, ul Dzierzyfl.skiego 2231229 60965 Poznan, Poland
Abstraet. An electrohydraulic injector for medium power Diesel engines is described in the paper. The injector which is used as an element of electronic engine control system, consists of an electromagnetically controlled valve, a hydraulic servo and an actuator determining the fuel dose, supposed a high pressure fuel source is provided. In the first part of the paper the principle of operation as well as the schemes and diagrams of the electrical and mechanical parts of the injector are presented. Also certain characteristic curves are given. In the second part some optimization procedures and their implementations are described e.g. the control signals are optimized with respect to their shape. Also an extension of the problem with respect to certain parameters of the device is mentioned. Keywords. Control equipment; Diesel engine control; hydraulic amplifiers; optimal control; bang-bang control; electric actuators; solenoids; direct digital control; flow control.
INTRODUCTION
of opening and closing of valves, the injection advance angle, etc., remain approximately constant or uncontrollable.
It is a well known fact, that the processes of air supply, fuel injection and exhaust gases removal in large classical Diesel engines are controlled by mechanical elements like camshafts, inlet and outlet valves, injection pumps, fuel injectors etc. Also the rotational speed and the load of Diesel engines are usually controlled by mechanical centrifugal governors. The main feature of this system is that the most important parameters, as the instants
In recent years some attempts in order to introduce electronic controllers and remote control devices in oil engines can be observed. They have many advantages but require of course other input and output elements than classical controllers. In particular the principle of operation of the injectors results from the fact that the fuel pressure remain. 157
M. Bielecki et al.
158
approximately constant and the fuel dose is to be controlled by an electri c si gnal. In the following paper a new electrohydraulic injector and its electronic actuator deeigned as output of a digital controller, are described. Also some optimization procedures concerning the control signal and the parameters of the injector are presented. The whole system is a result of cooperation between the Institute of Control Engineering of the Technical University of Poznan and the Research and Development Center of Marine and Railway Diesel Engines at Engineering Works H.Cegielski - Poznan.
BLOCK DIAGRAM OF THE ENGINE CONTROL SYSTEM As mentioned above different electronic devices are already used in Diesel engines instead of mechanical controllers. Some of them were patented, above all in the United States, in the Federal Republic of Germany and
command
!!>peed del'iation desired
$J)eed
Setting and comparison unil
-
si9nal
Digital controller
-
pulse signal
in France. Also the injector, described in the paper, together with the digital control system was patented in different countries, e.g. in the United States /U.S.Pat. No 4176624/. The block diagram of the system is shown in Fig. 1. The main part of the system is a digital controller at which the preset values of speed and of some other parameters which are to be controlled, can be selected. There are several transducers producing the input signals for the controller, but the most important is the speed/pulse converter coupled to the main shaft of the engine. The output signals of the controller after a digital-to-analogue conversion are applied via special drivers to the electromagnetic injectors, as well as to the valve actuators and to the load control actua_ tore. The injection process is then influenced by two parameters of the controller output signal: the starting point and the duration of the pulse, corresponding to the advance angle and to the fuel dose.
actuating current
Electronic
fuel
dose
Electro -
actuator
r---- hydraUlic
Speed-
spfled
>----.-
injectors
pulses conYllrfer
Fig. 1.
The block diagram of the engine control system.
Diesel engine
Electrohydraulic Injector
ELECTROHYDRAULIC INJECTOR AND ITS OPERATION
The injector is of servo-type and consists of the following main elements: the electromagnetic valve, the hydraulic amplifier and the fuel dosing actuator. The injector is supplied with fuel from a ~onstant pressure supply
16
31
32 15
f9 20
23 10
14 4
25
17
3 2
Fig. 2. Electrohydraulic injector.
159
system including a high pressure pump. The structure of the injector is shown in Fig. 2. It can be seen that a cylinder /3/ as well as the plunger 4 and the nozzle holder 2 are fastened to the lower part of the body 6 by the use of a sleeve nut. The plunger 4, which can move in the cylinder leans wi th its lower end against the upper part of the nozzle needle 1, settled in the nozzle holder 2. The lower part of the needle has a cone and is settled in the injection chamber seat 13 above the injection apertures. The nozzle needle together with the plunger is a difference set, whereas the diameter of the plunger is greater than the greatest diameter of the needle. The plunger has a hydraulic connection with the control slider 5. Its shoulders control the fuel flow, depending on the actual position of the slider. There are two perimetric channels 28 and ~O, formed by the shoulders, the third one 29 belongs to cylinder 18 of the valve /the slider can move inside the cylinder/. The channel 29 is situated with respect to the shoulders in such a way, that in the lower position of the slider one of the perimetric channels 28 together with the channel 29 connects chamber 14 of the plunger with the supply line 19, through ducts 21 and 22 as well as through the gland 9 and the check valve 10, which are connected in parallel. In the upper position one of its perimetric channels 30 together with channel 29 connects the plunger chamber 14 with the offtake line 24 through gland 9, lines 22 and 32, a store chamber, a second gland 11 and an overflow valve 12. The injection chamber 13 situated in the injector body 2 has a continuous connection
160
M. Bielecki et aZ.
to the constant pressure supply line 19, not depending on the position of the slider. The control slider is connected with the armature 7 being a part of the electromagnet 31, which is suppli~d with a current pulse from the controller via electronic actuator. If a current pulse flows through the coil 31 of the electromagnet, its armature 7 together with the slider are shifted to the upper position, where the fuel flow from the line 19 to chamber 14 of the plunger is cut off, and the fuel which was compressed in the chamber can be taken off to the line 24 through the gland 9, line 22, channels 29 and 30, line 32, store chamber 23, gland 11 and the overflow valve 12. The force resulting from the pressure drop in the chamber 14 of the plunger, at a constant pressure at the injection chamber 13, is then directed up, causing thus a lift of the needle 1 and an injection of the fuel through the apertures of the nozzle holder. The injection process lasts as long as the current pulse, supplying the coil. If the current flowing from the electronic actuator is interrupted, the armature 7 and the slider 5 will be displaced, becouse of the reaction of the return spring 8, and stopped at the lower extreme position, where the outlet is closed and the flow way from the supply line 19 to the chamber 14, through the line 21, channels 28 and 29, line 22 and through the parallel connection of the check valve and gland 9 is opened. The hydraulic force resulting from the difference of surfaces of the plunger 4 and needle 1,provided the pressures in the chamber 14 and in the injection chamber 13 are
equal, is directed down, causing thus the closing of the apertures and cutting off the fuel injection. The described cycle of the injector operation, including the opening and closing of the nozzle apertures, corresponding to the beginning and the end of the injection, repeats at a frequency equal to the number of the revolutions of the engine or to the half of it, for a four a two - or four-stroke engine respectively.
ELECTRONIC ACTUATOR FOR THE INJECTOR The diagram of the electronic actuator of the injector is shown in Fig. 3. According to the scheme the current flowing through the coil can be forced in order to accelerate the armature movement.
BOY
~~----~---------------------.
Supply Units
50Y
R2 f()().R
.
R1 2SJJ
Th2
'--------t Control Unit
Fig. 3.
Diagram of the electronic actuator.
The device operates in the following way. The switching on the thyristor Th 1 initiates a discharge of the
161
Electrohydraulic Injector
forcing capaci tor C1; a powerful current pulse flows through the injector coil. If the capacitor is already discharged, the current energizing the coil takes a lower value; it flows through resistor R1 /holding current/. As Th 2 switches on, the current is interrupted by a positive charge from capacitor C2, blocking the thyristor Th 1. The current and the armature displacement vs. time curves can be seen in Fig. 4. i(t)
x,
Fig. 4. Effect of current forcing. The use of the forcing current makes possible to reach a high speed of the armature, required if the injector is to be opened in a few miliseconds.
speed of operation without reboundings. This total optimization problem can be simplified if its decomposition into two problems is provided /Hielecki,Sawicki, 1977,1979/. The optimization algorithm was found using certain basic principles of the optimal control theory /the "bang-bang" principle/, when the calculations were done by the use of an analog computer. This algorithm can be used not only for an analog model of the electromagnet, but also for a real solenoid-armature system, the more the operating time measurement is here not required. In a fact, the algorithm was found without taking into consideration the current "kick" but, as the experiments have shown, it remains actual if the "kick" is applied. The external circuit should be therefore designed in such a way, that the first pulse gives a higher current than the second one /Fig. 5/. The current "kick" together wi th the "bang-bang" control mode, resul t in a very quick, no-reboundings operation. ift)
SOME OPTIMIZATION PROCEDURES The most important property of the electromagnet should be its sufficient rapidity. On the other hand, if the energizing pulse is too high, some reboundings can appear /Fig. 4/, which impair the behaviour of the injector hydraulic system. A very important and difficult problem is therefore not only the optimization of the solenoid parameter values, such as the number of turns and the spring constant, but also the choice of a proper current pulse shape, in order to assure the highest
t
t, 1({t)
t...t~ I I
I -- - - - - -
-,._..,jI_-----~1.....
t o Fig. 5.
Optimal control principle
The electronic optimal control circuit can be obtained after some modifications of the actuator from Fig. 3.
M. Bielecki et aZ.
162
mOPERTIES OF THE DESIGNED INJECTOR The characteristic curve of the injector /the fuel dose per one injection vs. duration of the control pulse, at fuel supply pr.ssure equal to 60 MPa/ is shown in Fig. 6. tJ["".,I/inil 1100
: Q
'00
"
700
I
IJ
CONCLUSIONS The application of the described injector together with an electronic control system enables to obtain new properties of Diesel engines; their parameters can be optim1zed more effectively than it they are controlled by mechanical governors and tradi tional injection pumps. For example the injection regularity even at the lowest engine speed ranges and a good constancy of the injection moment can be a chi eved.
I1
600
Also some additional advantages resulting partially from the new injection technics schould be mentioned: the reduction of fuel consumption, of toxicity and of the engine noise level.
I If
500
I
11
-lOO
I
11
JOO
j
I
REFERENCES
1
1OO
0
,11 1
2
,
-I
$
6
ti[,m-l
Current puI!IC duration
Fig.6.
Injector characteristic curv••
During test. a sufficient repeatability of particular doses was observed, .specially for greater doses. The portion of maximum to minimum dose was about 2011, beeing a very important advantage if compared wi th purely mechanical systems. Some irregularities and nonlinearities can result probably from a residual rebounds of the armature, disturbing the hydraulic control of the needle movement. It must be noted that certain limited varia tions of the holding current wi thin the assumed limits of 1% of the rated value, do not influence the charaCteristic curve of the injector.
Bielecki, M., and Sawicki, J. /1977/. Optimization of an electromagnetic control unit. Foundations of Control Engineering, vol.2 No 2. Bielecki, M. /1979/. A hybrid implementation of the no-rebounding, time optimal control for an electromagnetic actuator. Foundations of Control Engineering,vol.4 No 2. U.S.Pat. No. 4 176 624, Diesel Engine with Electronic Control, Dec. 1979.