ACTUATION MECHANISM USING SOLENOID
Field of invention
The present invention relates to a circuit arrangement, particularly, the present invention relates to a circuit arrangement for power saving and heat reduction of solenoid/actuators, more particularly, the present invention relates to a circuit arrangement for controlling the power supply to a solenoid from a direct current (DC) power source.
Background of invention
Solenoid/Actuators are available with a variety of electrical specification, operating stroke and force. Solenoid valves are electromechanical valves that are controlled by stopping or running an electrical current through a solenoid, in order to change the state of the valve. A solenoid is a coil of wire that is magnetized when electricity runs through it. The solenoid valve makes use of this solenoid in order to activate a valve, thus controlling water flow, airflow and other things with electricity. Solenoid valves are usually found in automotive starter systems, industrial air hammers and electric bell assemblies. These are also used on several other machines that require power in order to make a specific part move.
Starter solenoid is a part of an automobile ignition system. Also called a starter relay, the starter solenoid receives a large electrical current from the car battery and a small electrical current from the ignition switch. When the ignition switch is turned on (when the key is turned to start the car), the small electrical current provides signal to the starter solenoid to relay the large electrical current to the starter motor. Similarly, Auto choke solenoid is used in automobile for better start ability and improved fuel economy of vehicle. Existing manual choke system has the following drawbacks:
1. It remains sticky which affects the fuel economy.
2. There is a tendency of a rider to forget the release of choke after vehicle start.
3. Choke should be need base, not always.
Further, the solenoids are used in vehicles for closing and opening of various valves such as Canister purge valve, Fuel injectors, hand clutch, auto gear changer, auto lead opener CNG / LPG solenoid and bi starter valve ( auto choke ) on carburetor. In all the above
mentioned electrical systems, electrical power is derived from the battery, alternator or magneto. Currently, each of the solenoid is connected in parallel to the battery via a separate switch.
A solenoid assembly made up of following elements: Cylindrical Coil wound on nylon bobbin, Sleeve, Ferromagnetic Plunger, spring, Plunger stopper and a Case for magnetic return path. Electric supply produce electromagnetic force in coil, which cause movement of plunger against the stationary spring located between plunger stopper and moving plunger.
Solenoid takes a high inrush current at the start and it declines as plunger closes, in full close position solenoid is held energized by a low holding current flowing through coil until solenoid is de-energized.
Current generate heat and if total heat generated by solenoid exceeds its ability to dissipate that heat, it will soon overheat and fail. The coil temperature rise and consequently ultimate temperature of solenoid increase. Unless the ultimate temperature exceeds Class "A", 105° C rating of insulation, the application will be satisfactory. The solenoid temperature can be lowered by mounting a surface such as Aluminum plate which will conduct heat away. Over heating of solenoid leads following problems:
(a) Solenoid fails as bobbin, outer shell material can melt & plunger stuck.
(b) Loosening of the magnetic force.
(c) Not useful where the fuel with low fire point is used.
The pull in force of solenoid decreases rapidly as voltage decreases below rated voltage. From a low voltage stand point solenoid size selection should allow for adequate force at some arbitrary low voltage level. This will ensure adequate solenoid force even during period of low voltage and will prevent failure to pull in and consequent coil burn out. Design practice varies but low voltage levels are usually set at 85% to 90% of rated voltage.
A solenoid designed to operate on Alternating current can also be operated on direct current. A solenoid operating on AC draws high inrush current when solenoid is open. This current characteristic of an AC solenoid is extremely important; the high inrush current provides a high initial force which is usually desirable to overcome the load on the solenoid.
On the other hand, when solenoid is held closed the current is at low holding level. This low holding current generates very little heat, so the solenoid remains cool.
When a solenoid is operated on DC, the current flow is constant regardless of open or close operation. The inrush and holding current are same. Because of this constant current feature of direct current (DC), a compromise between pull in force & holding force is needed, specially, if enough current is provided to give same pull in force and current is reduced to a level at which over heating of solenoid can be eliminated at holding position. Satisfactory performance of solenoid under DC power depends upon how pull in force and overheating are balanced. Figure 1 shows a solenoid existing in prior art. As shown in shows solenoid without protection since there is flow of continuous current, high current will generate more heat than solenoid can dissipate. The coil wire insulation burns. The bobbin melts & coil shorts out if being continuously on for more than 10 minutes. Applying too heavy load to solenoid will hold the plunger open in the same way.
In some applications where stroke is extremely large, solenoid inrush current is higher than holding current. The constant current characteristic of DC supply alone is not enough to overcome the heating problem of solenoid at holding condition.
US patent 4,081,499 titled "Carburetor with electric heating type auto choke device", consist of electrical bimetal material, when supply is connected to bimetallic material through switch it get deflected and convert into flap movement with the help of proper linkage. For this, flap is used to control flow of air & the movement of flap is controlled by means of linkage means bimetallic strip or flap. Disadvantages of mechanism described in US patent 4,081,499: (a) This mechanism is not reliable because of bimetallic strip, (b) No consistency.
US patent 7,128,036 describes auto choke controller is device maintains good start ability through hot wax type auto choke, comprises a heater in wax, wax is expanded/contracted by ON/OFF operation of the heater; so that a valve is opened/closed gradually in response to the expansion/contraction of the wax. Disadvantages of mechanism described in US patent 7,128,036:
(a) Poor response time
(b) Less life.
Objects of the present invention:
The main object of the present invention is to provide a circuit arrangement.
Another object of the present invention is to provide a circuit arrangement for controlling
the power supply to a solenoid/ actuators from a direct current (DC) power source.
Still another object of the present invention is to provide a circuit arrangement which
overcomes at least one of the problem associated with the prior art.
Yet another object of the present invention is to provide circuit arrangement which saves
power and eliminates heating problem in solenoids.
One more object of the present invention is to provide protection and increased life cycle
of solenoids in automobiles.
A further object of the present invention is to provide better start ability system which
contributes in fuel economy.
Summary of the invention:
Present invention overcomes existing problems of heating and excess power consumption by solenoids used in vehicles. The present invention also helps in increasing the total operation cycles of the product by providing an actuation mechanism which has protection means and support to fuel economy.
Brief description of the drawings:
Figure 1 illustrates a solenoid existing in prior art.
Figure 2 illustrates the block diagram of the circuit arrangement for actuation mechanism
using solenoid according to the present invention.
Figure 3 shows the detailed circuit arrangement according to the present invention.
Figure 3 (a) shows current direction when switch S1 is turned ON.
Figure 3(b) shows current direction when switch S1 is turned OFF.
Figure 3(c) shows the circuit arrangement of the present invention with totem pole circuit
for better noise immunity.
Figure 3(d) shows the details of driver current wave form comparison.
Figure 4 shows the comparison in performance of circuit arrangement for actuation
mechanism using solenoid as a power saver.
Figure 5 shows the comparison in performance of circuit arrangement for actuation
mechanism using solenoid in heat reduction.
Figure 6 describes actuation mechanism using solenoid of the present invention.
Figure 7 illustrates circuit arrangement for actuation mechanism using solenoid according
to an embodiment of the present invention.
Figure 8 illustrates a configuration used for the proto trial in automobile.
Detailed description of the present invention:
Accordingly, the present invention provides a circuit arrangement comprising:
(a) a direct current (DC) power source;
(b) a solenoid coil coupled the DC power source;
(c) a current controller comprising:
(i) a switching means
(ii) a low resistance path to a ground;
(iii) a high resistance path to a ground;
(d) a timer circuit comprising an input and an output; input of the timer circuit is
coupled to the power source and output of the timer circuit is coupled to the
switching means;
said switching means being configured to connect the low resistance path to the coil for a predetermined amount of time as determined by an output of the timer circuit and thereafter connect the high resistance path to the coil.
In an embodiment of the present invention the timer circuit is selected from the group comprising resistance- capacitive (R-C) timer circuit, IC-555 timer circuit, inverter gate timer circuit.
In another embodiment of the present invention the switching means is selected from the group comprising MOSFET, FET, transistors, insulated-ate bipolar transistor (IGBT).
In still another embodiment of the present invention the high resistance path of the current controller comprises a parallel connection of the resistors.
In yet another embodiment of the present invention the timer circuit is coupled to the current controller through a totem pole circuit.
Also, the present invention provides a circuit arrangement comprising:
a direct a direct current (DC) power source coupled to a parallel connection of a solenoid coil and a timer circuit; and
a current controller is in series connection with the timer circuit and solenoid; said current controller comprising:
a switching means
a low resistance path to a ground;
a high resistance path to a ground; wherein the switching means being configured to connect the low resistance path to the coil for a predetermined amount of time as determined by an output of the timer circuit and thereafter connect the high resistance path to the coil.
In one more embodiment of the present invention the input of the timer circuit is coupled to. one or more sensors for sensing parameters of an automobile engine.
Accordingly, the present invention provides a circuit arrangement or mechanism for actuation of solenoid. The circuit arrangement comprises a direct current (DC) power source for supplying power to a solenoid coil. The circuit arrangement of the present invention comprises a timer circuit. The timer circuit had an input and an output. The input of the timer circuit is coupled to the direct current (DC) power source and the input of the timer circuit is in parallel connection with the solenoid coil. The output of the timer circuit coupled to a current controller in series connection. The current controller is in series
connection with the solenoid coil. The current controller comprises a low resistance path, a high resistance path and a switching means. The switching means being configured to connect the low resistance path to the solenoid coil for a predetermined time as decided or determined by output of the timer circuit and thereafter connect the high resistance path to the solenoid coil.
In other words the timer circuit provides the output signal, after a predetermined time, to the switching means to disconnect the between low resistance path from solenoid and connect the high resistance path to the solenoid coil. Therefore, during activation, when the solenoid coil requires high inrush current the resistance to current flow is lower because the low resistance path to ground is connected to the solenoid coil. After a predetermined time (decided by timer circuit), when the coil is energized, the switching means connect the high resistance path to the solenoid coil and a low current flow through the solenoid coil. Therefore, solenoid coil can be saved from overheating.
The timer circuit can be configured to provide an output after a predetermined time delay which can be decided depending upon the tome required by the coil to get energized.
According to an embodiment of the present invention the timer circuit can be resistance-capacitance based timer circuit. However, any suitable timer circuit can be used which can be configured to provide an output signal after a predetermined time to the switching means to turn it ON or OFF. The timer circuit can be selected from the group comprising resistance- capacitive (R-C) timer circuit, IC-555 timer circuit, inverter gate timer circuit.
According to an embodiment of the present invention, the switching means can be a metal-oxide-semiconductor field-effect transistor (MOSFET). However, any other suitable switching means can be used which can be configured to turn ON and OFF depending upon the output received from the timer circuit. The switching means can be selected from the group comprising metal-oxide-semiconductor field-effect transistor (MOSFET), field-effect transistor (FET), transistors, insulated-ate bipolar transistor (IGBT).
In other words any switching means can be used which can be configured to connect the high resistance path to the solenoid coil upon receiving the output from the timer circuit. The high resistance path can be a parallel connection of resistances. The high resistance path when connected with solenoid coil makes a series connection with the solenoid coil.
According to an embodiment of the present invention the timer circuit can be coupled to the current controller through a totem pole circuit.
The present invention is described with reference to the figures and specific embodiments; this description is not meant to be construed in a limiting sense. Various alternate embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such alternative embodiments form part of the present invention.
Figure 2 illustrates a simplified block diagram for the circuit arrangement for the low power actuation mechanism using solenoid. As can be observed from figure 2, the circuit arrangement comprises a solenoid coil, a current controller circuit and a timer circuit. Current controller circuit limits the flow of extra current during ON time of solenoid. For predetermined time, current controller allows actual current required by the solenoid to go in active state, after this predetermined time is over current controller switch to low power mode and only predetermined current required to hold solenoid in active state is sourced by the current controller.
Figure 3 shows a detailed circuit arrangement according to the present invention. As shown in figure 3, the circuit arrangement comprises timer circuit and current controller or current switch circuit.
Here in the present invention the function of timer circuit is to turn ON solid state switch in the current switch circuit, for a predetermined time delay which is decided by resistnaces Rl, R2, and capacitance C1.
As shown in figure 3, the timer circuit is resistance- capacitance (RC) based timer circuit. The timer circuit comprises resistors (Rl, R2) and capacitor (C1). The timer circuit can also be provided with diode Dl. As shown in figure 3 the timer circuit can also be provided with a transistor (Ql). The output of the transistor is given to a switch (S1) which is a MOSFET via Resistors (R3, R6) acts as a Load for Transistor (Ql) and also serves as Gate to source resistor along with resistor (R3).
At power up when voltage (VCC) is applied, base Voltage of PNP Transistor (Ql) is nearly equal to Zero as the capacitance (C1) is not Charged and emitter voltage is equal to Supply Voltage. Hence transistor Ql is turned fully on which in turn Gives Gate voltage to S1. Slowly capacitor (C1) begins to charge through Resistor (Rl + R2) and in Time=(Rl+R2)*Cl, capacitor gets charged to applied Voltage (VCC) by which Base voltage of transistor Q1 becomes almost equal to Emitter voltage (VCC) which turns OFF transistor (Ql) and gate Voltage to Switch S1. Diode (Dl) provides Quick Discharging Path for capacitor C1 during Turn OFF. Time = (Rl + R2) *C1 is always kept Greater than the activation time of solenoid.
As can be noticed from figure 3, the current controller circuit or the current switch circuit comprises a switch (S1), a low resistance path to ground and a high resistance path (connection of resistors R4 and R5) to the ground. Function of the current controller circuit or current switch circuit is to switch solenoid from high current mode to low current mode depending on timer output or the input received from the timer circuit. Initially at power up switch (S1) is ON, due to which heavy current (In this case 1A max) flows through the solenoid coil (L1) depend on its resistance; after a predetermined time decided by Timer circuit (300ms to lSec). Switch is turned OFF which forces current to flow through resistor R5 and R4. This in turn reduces over all current to greater than or equal to holding current (in this case 250 mA max).
In circuit arrangement of the present invention diodes can be provides to protect electronic devices used in the circuit. As shown in figure 3, diode D2 is used to protect all used electronics from Back EMF generated from solenoid switching. Diode D3 along with resistor (R3) protects MOSFET (i.e. Switch S1).
Initially at power ON, as transistor (Q1) and Switch (S1) is turned ON current flow direction is as shown in figure (3a) and current is limited by coil resistance only.
For example here coil resistance is 12 Ohm therefore at supply voltage of 12V DC max coil Current equals 1A. But after a predetermined time Delay as Q2 and in turn S1 is turned OFF; Current flows from coil to ground via Resistors R4 and R5 (which are High wattage resistors) as shown in figure (3b). Thus total Current is limited by Current = VCC / [Coil resistance + (R4 // R5)]. The value of this current should be equal to or greater than holding current of the solenoid (which is nearly equal to 220mA).
For example here coil resistance is 120hm therefore at supply voltage of 12V DC max coil current is equal to (VCC / [Coil resistance + (R4 // R5)J).
Here holding current with safety is considered to be 220 to 250mA for coil resistance of 120hm and supply voltage of 12V. parallel connection of resistors (R4 // R5) can be replaced by a single high wattage resistor of 390hm. (R4 // R5) = 390hm.
Figure 3 (c) shows that a timer circuit can be coupled to the current controller circuit through a totem pole circuit. For better noise immunity totem pole circuit can be used to drive switch (S1). As shown in figure 3(c) totem pole output will ensure fast turn ON and turn OFF of MOSFET (S1) and better Noise immunity. As shown in figure 3(c) transistor Q2 and Q3 form totem pole and have complimentary symmetry pair with push pull operation, at power ON stage Ql and hence Q2 turns ON and provides gate Voltage to switch S1 here Q3 remains OFF and hence full Voltage is applied across Gate to source of MOSFET (Switch S1). As Ql turns OFF, Q2 also turns OFF and with LOW Voltage at base of Q3, Q3 turns ON and rapidly Discharge gate capacitance of Mosfet Switch S1 and Switch S1 turns OFF until next ON OFF operation.
Figure 3 (d)(i) shows waveform for standard solenoid which takes constant current through out the operation. A shown in figure 3 (d)(i) a current wave form during solenoid
operation, standard solenoid takes constant rated current through out operation where as cool Solenoid takes Constant rated Current for a predetermined time after which it switches in low current mode by which solenoid current is reduce by 70 %. Table 1 shows the data pertaining to Figure 3 (d)(i).
Table 1

(Table Removed)
Figure 3(d)(ii) shows the current waveform for cool solenoid. Table 2 shows the data pertaining to figure 3(d)(ii). Waveform for cool solenoid with driver circuit reduces current by 70% after complete activation.
Table 2

(Table Removed)
Note: Current Calibrated in terms of Voltage Scale: 1 Volt = 1 Ampere
Figure 4 shows performance graph of actuation mechanism using solenoid as a power saver as compared to standard solenoid. As shown in graph standard solenoid consumes approx.l2W continuous power without any actuation mechanism. By Addition of actuation mechanism solenoid consumes 12W power initially during activation; however after a predetermined time power consumption reduces to approx. 2.64W only. Therefore, total power saved by actuation mechanism solenoid valve is approx.9.36W. Hence, it is an effective power saver. Table 3(a) and 3(b) shows the data pertaining to figure 4.
Table 3(a)

Table 3(b)

(Table Removed)
Figure 5 is the graph of temperature verses time for both solenoids i.e. standard solenoid & actuation mechanism using solenoid. For standard solenoid after 50 minutes net temperature rise is 80.4°C & net temperature rise of actuation mechanism using solenoid is 6 °C. As temperature rise of actuation mechanism using solenoid is less compared to standard solenoid, hence, the present invention reduces heat. Table 4 shows the data pertaining to figure 5.
Table 4

(Table Removed)
Figure 6 shows actuation mechanism using solenoid, which limits the flow of extra current during the ON time of solenoid.
In earlier design the stopper of solenoid was fixed in brass sleeve by caulking method due to which variation were observed in the operating stroke of solenoid & the cost of the brass sleeve was very high. So, in this design the stopper is insert molded with plastic sleeve material such as delrin, due to this there are no variations in operating stroke of solenoid & cost is approximately reduced by 50%.
Figure 6 shows solenoid with Driver Circuit here Supply goes directly to Electronic Commutation circuit and controlled output from electronic circuit goes to solenoid coil.
The circuit arrangement or mechanism of the present invention can be used as auto choke mechanism for automobile engine. In this mechanism solenoid actuate when there is a real need of a choke, decided by engine with the help of temperature sensor an electronic control unit. Thus an electric current is supplied to auto choke solenoid through an electronic control unit as per the demand of engine. As shown in figure 7, the input of the timer circuit can be coupled to one or more sensors for sensing parameters of an automobile engine. The timer circuit and current controller circuit form an electronic control unit (ECU). Figure 8 shows the auto choke solenoid valve in vehicle which is mounted on carburetor.
Some of the advantages of the present invention are as follows:
1. Low power consumption.
2. Coil life is increased due to less heating of solenoid.
3. Good performance makes this product a great value for many automation applications.
4. The stopper insert molded plastic sleeve help in controlling variations in operating
stroke of solenoid & economic.
The foregoing detailed description has described only a few of the many possible implementations of the present invention. Thus, the detailed description is given only by
way of illustration and nothing contained in this section should be construed to limit the scope of the invention.

We Claim:
1. A circuit arrangement comprising:
(a) a direct current (DC) power source;
(b) a solenoid coil coupled the DC power source;
(c) a current controller comprising:
(i) a switching means
(ii) a low resistance path to a ground;
(iii) a high resistance path to a ground;
(d) a timer circuit comprising an input and an output; input of the timer circuit is
coupled to the power source and output of the timer circuit is coupled to the
switching means;
said switching means being configured to connect the low resistance path to the coil for a predetermined amount of time as determined by an output of the timer circuit and thereafter connect the high resistance path to the coil.
2. A circuit arrangement as claimed in claim 1, wherein the timer circuit is selected from the group comprising resistance- capacitive (R-C) timer circuit, IC-555 timer circuit, inverter gate timer circuit.
3. A circuit arrangement as claimed in any one of the preceding claims, wherein the switching means is selected from the group comprising MOSFET, FET, transistors, insulated-ate bipolar transistor (IGBT).
4. A circuit arrangement as claimed in any one of the preceding claims, wherein the high resistance path of the current controller comprises a parallel connection of the resistors.
5. A circuit arrangement as claimed in any one of the preceding claims, wherein the timer circuit is coupled to the current controller through a totem pole circuit.
6. A circuit arrangement comprising
a direct a direct current (DC) power source coupled to a parallel connection of a solenoid coil and a timer circuit; and
a current controller is in series connection with the timer circuit and solenoid; said current controller comprising:
(i) a switching means
(ii) a low resistance path to a ground;
(iii) a high resistance path to a ground; wherein the switching means being configured to connect the low resistance path to the coil for a predetermined amount of time as determined by an output of the timer circuit and thereafter connect the high resistance path to the coil.
7. An auto choke mechanism comprising a circuit arrangement as claimed in any of the preceding claims, wherein the input of the timer circuit is coupled to one or more sensors for sensing parameters of an automobile engine.
8. A circuit arrangement substantially as herein described with reference to the accompanying drawings.