US3675033A

US3675033A - Device for starting and stopping a diesel engine

Info

Publication number: US3675033A
Application number: US83502A
Authority: US
Inventors: Gilbert Richard; Gerard Moronval
Original assignee: Automobiles Peugeot SA; Renault SAS
Current assignee: Automobiles Peugeot SA; Renault SAS; Regie Nationale des Usines Renault
Priority date: 1969-03-31
Filing date: 1970-10-23
Publication date: 1972-07-04
Anticipated expiration: 1989-07-04

Abstract

Device for starting and stopping a combustion engine of the Diesel type comprising a three-position switch having a stable position in which the heater plug circuit and the engine starter circuit are open, a second stable position in which, assuming that the engine is insufficiently warm, the heater plug circuit is closed, the starter circuit remaining open, and an unstable position in which the starter circuit is closed. Means are provided to indicate to the driver when the switch can be placed in the unstable position. The heater plug circuit is automatically opened at the end of a given period of time which depends on the surrounding temperature irrespective of whether the user has or has not placed the switch in the unstable position and actuated the engine starter.

Description

[451 July4, 1972 [54] DEVICE FOR STARTING AND STOPPING A DIESEL ENGINE [72] Inventors: Gilbert Richard, Giromagny; Gerard Moronval, La Garenne, both of France [73] Assignees: Automobiles Peugeot, Paris; Regie Nationale Des Usines Renault, Billancourt, France 221 Filed: 0ct.23, 1970 21 Appl.No.: 83,502

3,275,836 9/1966 Vancha .L ..290/38 3,371,656 5/1968 Stauffer et al... ....123/179 H 3,450,977 6/1969 Krauss ....l23/179 H 3,167,659 1/1965 Cromwell ..290/38 3,009,067 11/1961 Janeczko et al. ..290/38 3,163,769 12/1964 Keuchen et a1..... ..290/38 3,485,226 12/1969 Arendt et a1 ..123/179 H Primary ExaminerG. R. Simmons Attarney-Bums, Doane, Swecker & Mathis [5 7] ABSTRACT Device for starting and stopping a combustion engine of the Diesel type comprising a three-position switch having a stable position in which the heater plug circuit and the engine starter circuit are open, a second stable position in which, assuming that the engine is insufficiently warm, the heater plug circuit is closed, the starter circuit remaining open, and an unstable position in which the starter circuit is closed. Means are provided to indicate to the driver when the switch can be placed in the unstable position. The heater plug circuit is automatically opened at the end of a given period of time which depends on the surrounding temperature irrespective of whether the user has or has not placed the switch in the unstable position and actuated the engine starter.

12 Claims, 3 Drawing Figures PATENTEnJuL 4 1972 SHEET 20F 3 PATENTEDJUL 4 I972 SHEET 3 OF 3 DEVICE FOR STARTING AND STOPPING A DIESEL ENGINE The present invention relates to a control device for starting engines of the Diesel type and the like and more particularly engines driving automobile vehicles and the like.

One of the known methods employed for starting a Diesel engine comprises heating the engine by passing during a variable period of time an electrical current in heater plugs before actuating the starter. The device supplying power to the heater plugs must be so designed that the current can in no case be maintained in the plugs permanently and especially after the engine has started. Thus this device is usually controlled by a control or pull-rod which the driver puts in an unstable position and must maintain in this position during the entire heating period.

This is why in automobile vehicles equipped with a Diesel engine it is necessary to provide starting means which distinctly differ from those normally employed for petrol engines. Consequently, constructors are obliged to manufacture facia panels which are different for a given vehicle depending on whether the vehicle receives a Diesel engine or a petrol engine. Moreover, the driver of the vehicle equipped with a Diesel engine must effect several inconvenient operations in succession on separate elements to start the engine of the vehicle.

The object of the present invention is to remedy these drawbacks and to provide an arrangement in which a Diesel engine is started with the same control element as with a petrol engine, the user simply effecting the same movements as for starting a normal petrol engine.

The invention provides a device for starting and stopping a combustion engine of the Diesel type or the like, comprising a source of electrical current, a heating circuit, a supply circuit for a starter, at three-position switch of known type having a first stable position in which said two circuits are open, a second stable position in which, assuming that the engine is cold or insufficiently warm, the heating circuit is closed, the supply circuit for the starter remaining open, and a third un stable position in which the supply circuit of the starter is closed, means for indicating to the user at which moment the switch can be placed in the third position, and means for automatically cutting off the supply to the heating circuit at the end of a given period of time which is a function of the surrounding temperature, irrespective of whether the user has or has not placed the switch in the third position and actuated the starter.

According to one feature of the invention, the supply of power to the heater plugs is effected through a pulse control circuit also employed for shifting a closing valve in the fuel conduit.

According to another feature of the invention, said means for cutting off the supply to the heating circuit are independent of the indicating means and are controlled by the battery charging circuit which includes a generator, a regulator and its associated automatic switch.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawings.

in the drawings:

FIGS. 1 and 2 show schematically two embodiments of the starting device according to the invention, and

FIG. 3 shows a third embodiment of the invention in which the cutting off means are independent of the indicating means.

Reference will firstbe made to FIG. 1. Note that the same reference numerals designate equivalent elements in the three Figures.

The whole of the starting device for a Diesel engine is supplied with power by the battery 1 of the vehicle and the actuating element actuated by the user is a lever 2, which may be constituted by a key conventionally employed with a petrol engine. This lever 2, which has a rotary contact 3 in the form of a circular sector, can occupy three positions a first stable position or "off" position, in which the rotary contact 3 bears against only a single fixed contact 4 permanently connected to the battery;

a second stable position or "on position, in which the rotary contact 3 interconnects the contact 4 and a second fixed contact 5;

a third unstable position or starting" position, in which the rotary contact 3 interconnects the contacts 4 and 5 and a third fixed contact 6; return means (not shown) bias the lever or key 2 to the aforementioned second position.

The contact 5 is connected to a coil 7 of a first relay 8 actuating a reversing switch 9 which interconnects the

contacts

10 and 11 when no voltage is applied to the coil 7 and interconnects the contacts 12 and 13 when a voltage is applied to the coil 7.

A pulse control circuit, brought into action by the shifting of the reversing switch 9, is constituted by two

reversing switches

14 and 15 and an electromagnet 16. The magnetic circuit of the electromagnet closes on a ferrite element or permanent magnet and the moving part 16a actuates, by its movement, the two reversing switches 14 and 15.

Apart from its action on the

reversing switches

14 and 15, the electromagnet 16 also actuates a closing valve 17 in a conduit 18 of the fuel supply circuit of the vehicle.

When stationary, the reversing switch 14 is on a contact 19 connected to the contact 13 and the reversing switch 15 is on a grounded contact 20. In operation, the reversing switch 14 is placed on an insulated contact 21 and the reversing switch 15 is placed on a contact 22 connected to the fixed contact 11. The reversing switch 14 is connected to a coil 23 of a second relay 24 for bringing into action the heating. The coil 23 is grounded through a bimetallic strip 25, a contact 26 having a delayed opening, a resistor 27 and a contact 28 which is closed when the engine stops and opens when the engine reaches a given speed. The contact 28 can be actuated by any known means, as an alternator, regulator oil pressure or other means.

The second relay 24 causes, when voltage is applied across the coil 23:

the closure of a switch 29 termed a maintaining switch, which interconnects the contacts 30 and 31 connected in parallel with the

reversing switch

14, 19, 21;

the switching of a reversing switch 32 which opens the connection 33-34 between the electromagnet 16 and ground and interconnects the contacts 35-36 closing the circuit between the contact 13 and the electromagnet;

the closure of a switch 37 which interconnects the

contacts

38 and 39 and supplies power to the heater plugs 40 through a ballast resistor 41.

A bimetallic strip 42 is connected in parallel to the resistor 41 and is heated by the latter. Its contact 43 is opened when it is cold and closes at the end of a period of time which is the longer as the surrounding temperature is lower, this time being such that the heating of the engine by the heater plugs 40 is sufiicient. The return of the current to ground is through a heating resistance 44 heating the bimetallic strip 25, through the contact 26, the resistor 27 and the contact 28.

Connected in parallel through the

resistors

44 and 27, is an indicator lamp 45 which indicates the closure of the contact 43 and consequently indicates to the driver that the heating is sufficient and that the starter can be actuated.

In addition, an indicator lamp 46 between the switch 37 and the ground could indicate that voltage is applied across the heater plugs.

Closure of the starting contact 6 causes power to be supplied to the coil of a relay 47 controlling a starter 48 and power to be supplied to a coil 49 which is coaxial with the coil 23 of the relay 24. The outputs of the

coils

47 and 49 are permanently grounded.

A connection 50 having a diode 51 is also provided between the starting circuit and the contact 26 which grounds the coil 23 and the

bimetallic strips

42 and 25.

The device according to the invention operates in the following manner:

When the engine is stationary, the various component parts are in the positions shown in FIG. 1 and the closing valve 17 closes the fuel conduit 18.

To start the engine, the driver must first place the lever 2 in the normal operating position in which the contacts 4 and 5 are interconnected by the sector 3. The following operations are then automatically carried out:

current is supplied to the coil 7 of the first relay 8;

the reversing switch 9 is switched to close the connection 12-13; current is supplied to the coil 23 of the second relay 24 through the reversing switch 14;

the switch 37 supplying current to the heater plugs 40 and to the indicator 46 is closed; the reversing switch 32 is switched to interconnect the

contacts

35 and 36. The electromagnet 16 then has a voltage applied thereto and its armature 16a moves in a direction which opens the valve 17 in the fuel conduit 18 and shifts the

reversing switches

14 and 15. It is therefore a brief pulse which passes through the electromagnet 16 since the return to ground is interrupted by the passage of the switch to the contact 22, which justifies the expression "pulse control circuit" to designate this arrangement;

closure of the switch 29 which maintains the supply of power to the coil 23 notwithstanding the switching of the switch 14 to the insulated contact 21.

At the end of a variable period of time which depends on the surrounding temperature and can be, for example 45 seconds for an outside temperature of 20 C., the heat given off by the ballast resistor 41 causes the contact 43 to be closed which simultaneously supplies current to the heating resistance 44 of the bimetallic strip and the indicator 45. The driver is then informed that he can actuate the starter and he has for this the time necessary for the resistor 44 to heat the bimetallic strip 25 until it opens the contact 26.

To actuate the starter, the driver shifts the lever 2 to the unstable position which sends current by way of the contact 6 to the relay 47 of the starter 48. During this, the coil 49 also has voltage applied thereto and this guarantees that the switch 37 controlling the supply of power to the heater plugs 40 is maintained in the closed position, even if the starter operates when, or after, the contact 26 opens.

Further, as the current passes through the diode 51 it brings both ends of the resistance 44 to the same potential which prevents it from heating and thus delays the start of the time delay produced by the bimetallic strip 25 to the moment when the action on the starter ceases, should the engine fail to be started or a new starting must be attempted.

Thus it is clear that the time delay produced by the second bimetallic strip 25 is neutralized while the starter is actuated.

The presence of the diode 51 constitutes a safety measure and precludes any risk of accidentally supplying power to the relay 47 through the elements 37-42-43-44-26-50-47.

If the engine starts, the contact 28 opens and interrupts the return to ground of the coil 23 and the relay 24 returns to its position of rest and cuts off the supply of power to the plugs 40. The presence of the switch or reversing

switch

14, 19, 21 between the

switch

9, 12, 13 and the coil 23 of the maintaining circuit closed by the switch 29, 30, 31, is not theoretically essential, but this arrangement constitutes an additional safety measure should the contact 28 accidentally close or fail to open. Indeed, without this safety measure, the coil 23 could have voltage applied thereto and the heating circuit supplied with power while the engine runs normally which, bearing in mind the high power consumption of the plugs 40, might result in the destruction of the plugs and a rapid discharging of the battery.

If the driver does not actuate the starter during the period of the heating of the bimetallic strip 25, the contact 26 opens at the end of a predetermined period of time, for example of the order of 40 seconds, and cuts off the return to ground of the coil 23 which returns the relay 24 to its position of rest and cuts off the supply of power to the plugs 40.

When the engine is stopped by bringing the lever 2 to the off position, the coil is no longer supplied with power and the switch 9 opens the connection between 12 and 13 and closes the connection between 10 and 11. A current in the opposite direction to the current for starting is sent to the pulse control circuit through 10-11-22-15-16-33-34, which has for effect to shift the moving part 16a in the direction to close the valve 17 in the fuel conduit 18. Simultaneously, the reversing

switches

14 and 15 are returned to their

contacts

19 and 20 respectively. The current is then cut off in the whole of the circuit.

In the embodiment shown in FIG. 2, the main elements having the same reference numerals as those shown in FIG. 1 are identical and perform the same function.

Merely the pulse control circuit is slightly simplified. By so choosing the characteristics of the

relays

24 and 16 so that the period of operation of the relay 24 is less than the period of operation of the electromagnet 16, the reversing switch 32 of the first embodiment and its

contacts

33, 34, 35 and 36 can be dispensed with. The electromagnet 16 is then directly supplied with power by the reversing switch 14 whose contact 21a must be grounded. A diode 52 must then be added to preclude shorting by the grounding of the fixed contact 31 through the reversing switch 14 on the fixed contact 21a.

Apart from this slight difference in design, the operation of the device is in every way identical to that of the first embodiment.

In the embodiments described with reference to FIGS. 1 and 2, the thermal time delay is supplied with power under the control of a bimetallic strip at the same time as the means indicating to the user that the heating is sufi'rcient, so that in the event of failure of this bimetallic strip, the heating is not automatically interrupted, and this, bearing in mind the high power consumption of heater plugs, is liable to discharge the battery.

The device shown in FIG. 3 overcomes this drawback.

In FIG. 3, all the elements already described and shown in FIG. 1 are designated by the same reference numerals and will not be described in detail.

The description will therefore be limited to the part of the diagram which concerns the automatic stoppage of the heatmg.

The reference C designates in the diagram the batterycharging circuit having a generator 6 which may be a dynamo or, preferably, an alternator and the associated regulator 61. This regulator comprises, in the known manner, an automatic switch, or break switch, which connects the generator to the battery when the voltage of the generator exceeds that of the battery. A

double connection

62a, 62b between the generator and the regulator corresponds to the connection between the armature winding and the field winding respectively of the generator and regulator.

The coil 23 is connected in series with a thermal switch 63 having a bimetallic strip 64 and connected to the regulator 61. The heating resistance 65 of this switch is connected in the same way as a battery-charging indicator 66 in such manner as to be connected in parallel with the coil 23 after the closing of the contact 12, 13 and the switching of the switch 14. This battery-charging indicator is employed in the usual way, namely it lights up as soon as the switch 2 is switched to its second position and goes out when the regulator 60 furnishes a given current.

The device operates in the following manner When the switch 2 is switched to the fixed contact 5, the relays 8 and 24 and the moving parts are caused to operate in the manner described with reference to FIGS. 1 and 2.

The heater plugs 40 are supplied with power through the

switch

38, 37, 39 and the resistance 41 starts to heat the bimetallic strip 42 whose contact 43 is open at rest.

The resistance 65 is supplied with power through the

switch

12, 9, 13 and starts to heat the bimetallic strip 64 of the switch 63 which is closed at rest.

The period for opening the switch 63 is chosen to exceed the period of closure of the contact 43, these two periods being, for example, respectively of the order of 2 and 1 minute respectively. When the contact 43 is closed, the indicator 45 lights up and informs the driver that he can actuate the starter by placing the switch 2 on the fixed contact 6. The heating is maintained as long as the charging indicator 66 remains lit up, that is, as long as the engine has not been fully started. After the engine has been started, the switch 2 is released and returns to the fixed contact 5. As there is no longer a return to ground through the regulator 61, owing to the actuation of the automatic switch, the indicator 66 goes out and the coil 23 is no longer supplied with power and this results in the opening of the

switch

38, 37, 39 and the stoppage of the heating.

If the driver does not actuate the starter after the lighting up of the indicator 45, the switch having the bimetallic strip 64 heated by the resistance 65 opens after a predetermined period of time. As the coil 23 is no longer supplied with power the heating stops.

The starting device according to the invention enables a motor of the Diesel type which requires a prior heating, to be started in the same way as a normal petrol engine. However, a period of time necessary for the heating is allowed for between the two successive moments of the lever or key when the engine is cold. If the engine is warm, the period for heating is not necessarily allowed for and it is possible to pass from the off position directly to the starting position in which the heater plugs are in any case supplied with current. As mentioned in the description and explanation of the operation of the device, all the required operations are carried out automatically and all safety requirements are satisfied. In particular, a harmful prolonged supply of power to the heater plugs or the stoppage of this supply too soon after the user has actuated the starter, is avoided.

Further, with the arrangement shown in FIG. 3, the time delay governing the duration of the heating which must precede the starting of the engine and the time delay governing the stoppage of the heating in the case of non-starting, are independent. This precludes supplying power to the heater plugs for an excessive period of time in the event of failure of the bimetallic strip 42.

An additional advantage of the last-mentioned arrangement is the fact that the automatic switch included in the regulator 61 is of much more precise operation than the previously provided manocontact 28.

We claim:

1. A device for starting and stopping a combustion engine of the Diesel type or the like, comprising a source of electric current, an engine starter, heater plugs, a heating supply circuit for the plugs, a supply circuit for the starter, a three-position switch of known type having a first stable position in which said two circuits are open, a second stable position in which, assuming that the engine is insufficiently warm, the heating circuit is closed, the supply circuit for the starter remaining open, and a third unstable position in which the supply circuit of the starter is closed, a second switch inserted in said heating supply circuit and controlled by a relay associated therewith and having a coil connected between said source of electric current and ground in series with a third switch, the closure of which is controlled when said three-position switch is placed in its second position and with a first delayed-opening contact for automatically opening the heating circuit at the end of a given period of time which is a function of the surrounding temperature, irrespective of whether the user has or has not placed the three-position switch in the third position and actuated the starter said first delayed-opening contact being controlled by temperature responsive delay means inserted in the heating circuit, said delay means being also provided for indicating to the user at which moment said three-position switch can be placed in the third position 2. A device as claimed in claim 1, wherein said temperature responsive delay means comprises a second contact, a first heating resistance for heating said first delayed-opening contact, a first bimetallic strip controlling said second contact, said first bimetallic strip and said first heating resistance being connected in parallel with said heater plugs, a second heating resistance connected in series in the heating circuit and having an operating time which is a function of the surrounding temperature, said second heating resistance being associated with and adapted to heat said first bimetallic strip.

3. A device as claimed in claim 2, wherein an indicator lamp is connected in parallel with said first resistance heating the first delayed-opening contact.

4. A device as claimed in claim 1, wherein a normallyclosed contact is connected in series with said coil of said relay, said normally-closed contact being adapted to open as soon as the engine has reached a given operating speed.

5. A device as claimed in claim 1, comprising means for neutralizing the operation of said first delayed-opening contact while the starter is being supplied with power.

6. A device as claimed in claim 5, wherein said second heating resistance has a low voltage terminal and the supply circuit for the starter has a fourth switch controlling operation of the starter, said neutralizing means comprising a diode connected between the supply circuit for the starter and the low voltage temtinal of said second heating resistance so as to put the two ends thereof at the same potential when the starter is supplied with power, and a second coil actuating said relay, a relay controlling said fourth switch being connected in parallel with said second coil.

7. A device as claimed in claim 1, comprising a pulse control circuit which has two stable positions and comprises a closing valvein a fuel supply conduit of the engine, an electromagnet having a moving part which actuates the closing valve, a first reversing switch and a second reversing switch which coact with said third switch so as to reverse the direction of current in said electromagnet, the third switch being a reversing switch and controlling the pulse control circuit.

8. A device as claimed in claim 7, comprising a safety circuit provided in the event of faulty operation of said normallyclosed contact and including said first reversing switch combined with said moving part and disposed between said third switch and said one coil of said relay and a by-pass circuit comprising a fifth switch controlled by said relay.

9. A device as claimed in claim 7, comprising a third reversing switch actuated by said relay and controlling supply of power to said electromagnet of said pulse control circuit.

10. A device for starting and stopping a combustion engine of the Diesel type or the like, comprising a source of electric current, an engine starter, heater plugs, a heating supply circuit for the plugs, a supply circuit for the starter, a three-position switch of known type having a first stable position in which said two circuits are open, a second stable position in which, assuming that the engine is insufficiently warm, the heating circuit is closed, the supply circuit for the starter remaining open, and a third unstable position in which the supply circuit of the starter is closed, a second switch inserted in said heating supply circuit and controlled by a relay associated therewith and having a coil connected between said source of electric current and ground in series with a third switch, the closure of which is controlled when said threeposition switch is placed in its second position and with a delayed-opening contact for automatically opening the heating circuit at the end of a given period of time which is a function of the surrounding temperature, irrespective of whether the user has or has not placed the three-position switch in the third position and actuated the starter, and temperature responsive delay means inserted in the heating circuit for indicating to the user at which moment said three-position switch can be placed in the third position, said delayed-opening contact being controlled independently from said indicating means by a battery-charging circuit which comprises a generator, a regulator and an associated automatic switch.

11. A device as claimed in claim 11, wherein said delayedopening contact comprises a bimetallic strip, a heating resistance for heating the bimetallic strip and connected in parallel with the bimetallic strip when the three-position switch is placed in its second position.

12. A device as claimed in claim 11, comprising a batterycharging indicator controlled by said automatic switch and connected in parallel with the heating resistance for heating the bimetallic strip.

Claims

1. A device for starting and stopping a combustion engine of the Diesel type or the like, comprising a source of electric current, an engine starter, heater plugs, a heating supply circuit for the plugs, a supply circuit for the starter, a three-position switch of known type having a first stable position in which said two circuits are open, a second stable position in which, assuming that the engine is insufficiently warm, the heating circuit is closed, the supply circuit for the starter remaining open, and a third unstable position in which the supply circuit of the starter is closed, a second switch inserted in said heating supply circuit and controlled by a relay associated therewith and having a coil connected between said source of electric current and ground in series with a third switch, the closure of which is controlled when said three-position switch is placed in its second position and with a first delayed-opening contact for automatically opening the heating circuit at the end of a given period of time which is a function of the surrounding temperature, irrespective of whether the user has or has not placed the three-position switch in the third position and actuated the starter , said first delayed-opening contact being controlled by temperature responsive delay means inserted in the heating circuit, said delay means being also provided for indicating to the user at which moment said three-position switch can be placed in the third position .

2. A device as claimed in claim 1, wherein said temperature responsive delay means comprises a second contact, a first heating resistance for heating said first delayed-opening contact, a first bimetallic strip controlling said second contact, said first bimetallic strip and said first heating resistance being connected in parallel with said heater plugs, a second heating resistance connected in series in the heating circuit and having an operating time which is a function of the surrounding temperature, said second heating resistance being associated with and adapted to heat said first bimetallic strip.

4. A device as claimed in claim 1, wherein a normally-closed contact is connected in series with said coil of said relay, said normally-closed contact being adapted to open as soon as the engine has reached a given operating speed.

6. A device as claimed in claim 5, wherein said second heating resistance has a low voltage terminal and the supply circuit for the starter has a fourth switch controlling operation of the starter, said neutralizing means comprising a diode connected between the supply circuit for the starter and the low voltage terminal of said second heating resistance so as to put the two ends thereof at the same potential when the starter is supplied with power, and a second coil actuating said relay, a relay controlling said fourth switch being connected in parallel with said second coil.

7. A device as claimed in claim 1, comprising a pulse control circuit which has two stable positions and comprises a closing valve in a fuel supply conduit of The engine, an electromagnet having a moving part which actuates the closing valve, a first reversing switch and a second reversing switch which coact with said third switch so as to reverse the direction of current in said electromagnet, the third switch being a reversing switch and controlling the pulse control circuit.

8. A device as claimed in claim 7, comprising a safety circuit provided in the event of faulty operation of said normally-closed contact and including said first reversing switch combined with said moving part and disposed between said third switch and said one coil of said relay and a by-pass circuit comprising a fifth switch controlled by said relay.

10. A device for starting and stopping a combustion engine of the Diesel type or the like, comprising a source of electric current, an engine starter, heater plugs, a heating supply circuit for the plugs, a supply circuit for the starter, a three-position switch of known type having a first stable position in which said two circuits are open, a second stable position in which, assuming that the engine is insufficiently warm, the heating circuit is closed, the supply circuit for the starter remaining open, and a third unstable position in which the supply circuit of the starter is closed, a second switch inserted in said heating supply circuit and controlled by a relay associated therewith and having a coil connected between said source of electric current and ground in series with a third switch, the closure of which is controlled when said three-position switch is placed in its second position and with a delayed-opening contact for automatically opening the heating circuit at the end of a given period of time which is a function of the surrounding temperature, irrespective of whether the user has or has not placed the three-position switch in the third position and actuated the starter, and temperature responsive delay means inserted in the heating circuit for indicating to the user at which moment said three-position switch can be placed in the third position, said delayed-opening contact being controlled independently from said indicating means by a battery-charging circuit which comprises a generator, a regulator and an associated automatic switch.

11. A device as claimed in claim 11, wherein said delayed-opening contact comprises a bimetallic strip, a heating resistance for heating the bimetallic strip and connected in parallel with the bimetallic strip when the three-position switch is placed in its second position.

12. A device as claimed in claim 11, comprising a battery-charging indicator controlled by said automatic switch and connected in parallel with the heating resistance for heating the bimetallic strip.