AU610185B2 - Automatic starting arrangement for an internal combustion engine - Google Patents

Description

?7 'u uuuiess ror service is care Of R. K. MADDERN and ASSOCIATES, Patent Attorneys.

King William Street, Adelaide, South Australia 5000.

345 Dated this 14th day o Jne, 18 May be signed by ANDREAS STIHL 18 Australian Patent Attorney. By its Patent Attorneys x R K MADDERN ASSOCIATES R S CATT Te Cmssioner ofPtet Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-62 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Application Number: Class Int. Class Lodged: Complete Specification Lodged: a Accepted: Published: Pribrity: Re~ae~d'rt:This docurn--i-t contains the Re~latEd *Art:ainendments made Under SSectin 49 and is correct foi TO BE COMPLETED BY AkPPLICANT Narfie of Applicant: ANDREAS STIHL Address of Applicant: Badstrasse 115, 7050 Waiblingen, Germany Ac ventorS tjrX.ichael Wissmann, Hans Nickel, and Jurgen Weber Address for Service: R K Maddern Associates, 345 King William Street, Adelaide, State of South Australia, Commrivmealth of Australia Complete Specification for the invention entitled: "AUTOMATIC STARTING ARRANGEMENT FOR AN INTERNAL COMBUSTION ENGINE" The following statement Is a full description of this invention, including the best method of performing it known to me us.

der Bevollmaechigte des/der eigentlichen Erfinder(s).

Paragraph 4-strike out if reverse side of sheet applicable.

Paragraph 4 aus zustreichen wenn Rueckseite zutrifft.

Signature(s) of declarant(s).

Untcrschrift(en) des/der Deklaranten.

(Note. No attestation or other signature is required).

Bemerkung. Beglaubigung der Unterschrift ist nicht benoctigt.

application.

Declared at Waib ingen this

M

a rz day of 24 1988 Firma Andreas Stihl l Hans Peter Stihi Drac3ln+ r 1- c'-

ABSTRACT

Simple and reliable starting of the internal combustion engine of a power tool, for example of a chain saw, is achieved ,by means of the automatic starting device. For this purpose, ,automatic operation of the choke flap is provided by means the vacuum produced, on starting, in part of the housing of the power tool. To achieve this, the throttle flap and *the choke flap arranged one behind the other in the intake channel of the carburettor are coupled in such a manner that '"the throttle flap remains in a partly open position until B "the choke flap reaches a pre-set opening angle. This produces an over-rich petrol/air mixture on starting of the cold engine, while, after the engine has started, sufficient air is supplied ,%p6r a short time to permit combustion of the over-rich mixture.

:The vacuum for operating the choke flap is expediently controlled as a function of the temperature of the power tool.

i_ I i:- The present invention relates to an automatic starting device for an internal combustion engine, in particular for the manually started engine of a power tool, such as, for example a chain saw.

Such an automatic starting device is known from d German Offenlegungsschrift DE-OS 34 45 839. It serves I for making it possible even for an unskilled user of a power tool to simply and reliably start the internal combustion engine, irrespective of the actual starting conditions. To achieve this, provision has been made for the choke flap to be automatically operated by the tt vacuum that is present in part of the housing of the power tool. The over-rich petrol/air mixture that is required for starting is obtained in this manner, such that the otherwise necessary manual operation of the choke flap is eliminated even under unfavourable starting conditions, in particular when the engine is cold.

Provision has been made in the known automatic starting device, by coupling the throttle flap with the choke flap by means of connecting rods, for the throttle flap to be partly opened, for example to the "half throttle" position, when the choke flap is closed. Since the choke flap is opened on starting by the vacuum in the housing of the power tool, the engine receives additional air through the still open throttle flap for a short time after starting, to permit combustion of the still over-rich -2mixture. The opening movement of the choke flap is coupled, by means of the connecting rods, with the closing movement of the throttle flap in such a manner that this closing movement of the throttle flap is simultaneous with the opening movement of the choke flap. In order to ensure nevertheless that the choke flap remains in the given opened position for a sufficient length of time to permit combustion of the over-rich mixture, the operating mechanism for the choke flap has been suitably designed to 1 0. result in the choke flap moving at different speeds: the ao opening movement of the choke flap is fast to begin with o 0 0 oo and later slows down, with the throttle flap being closed o oo during this slower phase. This control system requires accurately co-ordinated movements of the two flaps. The resulting difficulties in manufacture and adjustment oo of the components are accentuated by the provision of temperature control of the speed of the initial opening 0o 0o movement of the choke flap: the opening movement is to be slower when the engine is cold than when it is warm or hot. i o Accordingly, the object of the present invention is to simplify the design of the automatic starting device and to improve its operation.

As a result of the coupling of the throttle flap with the choke flap by means of the connecting rods, according to the present invention, the throttle flap is -3- 1 mechanically locked in its pre-set open position, for example in the "half-throttle" position, while the choke flap swings through a pre-set angle. This ensures that sufficient air is supplied to the engine during the starting process to ensure combustion of the over-rich mixture. This locking can be easily achieved by a suitable design of the connecting rods. In addition, the partial opening of the intake channel by the throttle flap being opened depending on the travel of the choke flap improves 10. starting of the engine when it is already warm or hot.

oi Since locking is released via the connecting rods as soon o 40 o 0 0 as the choke flap has reached a pre-set opening angle, the o 0 00 ~throttle flap can be operated by means of a throttle oo~ lever, in the conventional manner, after starting, i.e.

0 15. with the engine running, without throttle flap and choke 0 0 flap interacting with each other.

0 0 In order that the invention may be clearly understood 0.0 and readily carried into effect, a preferred embodiment will be described by way of example only with reference to the accompanying representations wherein:- 0° Fig. 1 is a schematic partial view of a chain saw, partially sectioned to show schematically the components of the carburettor that are essentials of the present invention; Fig. 2 is a schematic view of an axial section through the intake channel of the carburettor and the operating device for the throttle flap and the choke flap, in side elevation; -4o o00 0000 0000 010000 0 0 0 0 0 0 000 00 0 0 0 0 00 O 00 o aO o o oo Fig. 3 is a view in direction of the arrow III in Fig. 2; Figs. 4 to 6 show different positions of the operating device for throttle flap and choke flap shown in Fig. 2; Fig. 7 is a longitudinal section through a control unit with valves and a throttle, for controlling the operating device; and Fig. 8 shows part of the control unit in Fig. 7, 10. with the throttle in a different position.

Fig. 1 is a schematic side elevation of a section of a chain saw i. The housing 2 of the chain saw comprises a two-stroke internal combustion engine with a carburettor 3 and a cylinder 4. The piston moving in the cylinder 15. drives a crankshaft (not shown here) running in a crankshaft housing 5, and, by means of a pinion, drives a saw chain (not shown here) circulating along a guide rail 7. Two grips 8 and 9 are attached to the housing 2. A throttle control lever 10 is swivel mounted on a shaft 6 in the rear holding grip 9. The internal combustion engine is started manually by a pull-cord (not shown here), in the conventional manner. The throttle lever 10 operates, via throttle operating rods 11, the throttle flap 12 which is swivel-mounted in the intake channel 13 of the carburettor and is spring loaded in direction of the arrow, i.e. in its closing direction, 'IpSiPlipp I '4 0 0 0 0 )eel 00000 0 0 0 0 00 0 o a O 0 00 000 oooo 00 0 o o o by a spring (not shown here). Air flows through the intake channel 13 into the cylinder 4, in direction of the arrow 14. A choke flap 15 is swivel-mounted in the intake channel 13 in front of the throttle flap 12 as seen in direction of the air flow 14 and is spring loaded in direction of the arrow, i.e. in the sense opposite to that of the throttle flap 12, corresponding to the closing direction of the choke flap 15, by a spring (not shown here). The choke flap 15 can be opened against the spring 10. force by an operating device 16 comprising bellows 17. A rod 18 is guided axially in the bellows 17 and is attached to the top of belows 17. Rod 18 engages via a connecting link 19, a lever 20 that is fixed to the shaft of the choke flap 15. The throttle flap 12 is coupled to the choke flap 15 through a four-joint linkage 28, as described in greater detail in the following, with reference to Figs. 2 and 3.

The throttle control rod 11 is connected, through a slot-and-pin guide 11A with a control member 11B fixed 20. to the shaft of the throttle flap 12. The centre lines of shafts 21 and 22 are situated at approximately the level of the longitudinal centre line of the intake channel 13. The control member 11B fixed to shaft 22 is provided, at its ring-shaped end that sits on the shaft 22, with a tab 23 pointing radially outward and being bent at its extreme end to form a catch 24. Catch 24

I

0 0 o 0 0 0 00 00 0000 0 00 o 0ooo0 0 00 0 0 0 o o o o 0 extends in axial direction of shaft 22 beyond a plane in which a lever 25 can swing that is swivel-mounted on shaft 22. This lever 25 is connected through a connecting rod 26 with a lever 27 that is swivel-mounted on shaft 21 of the choke flap 15. The two levers 25 and 27, and the crnnecting rod 26 that connects them, together with the shafts 21 and 22, form the four-joint linkage 28 that connects with each other the two flaps 12 and 15. The lever 20 that operates the choke flap 15 is provided, at 10. its approximately ring-shaped end 20A that is fixed to the shaft 21, with two tabs 29 and 30 pointing radially outward and being bent at their ends to form the catches 31 and 32 that extend, in axial direction of the shaft 21, beyond the plane in which the lever 27 can swing. The 15. control levers 11 and 20 as well as the four-joint linkage 28 are situated at the side of the housing of the carburettor 3 (see Fig. which also carries an end stop 33 for the lever 27. The two shafts 21 and 22 protrude out of the housing of carburettor 3 to accommodate the levers 20, 25, and 27, and the control member 11B.

The control lever 20 is provided with an extension protruding into the path of movement of a shoulder 11C of the operating rod 11, which is bent at right angles at this spot (Figs. 2 and 3).

Figs. 2 and 4 show the position of the operating device 16, the control member 11B, and the control lever -7- I; -LL b-r *1 with the linkage 28 with the engine at standstill.

The movements on starting of the engine are explained with reference to Figs. 5 and 6. In the standstill state (Fig. the bellows 17 are fully extended, such that their axial dimension is largest in this case. The choke is in its closed position under the spring loading applied in direction of the arrow. The throttle flap 12 is likewise spring loaded in the closing direction shown by the arrow, but is in half-open position, 1 0. corresponding to an opening angle of approximately 300.

The throttle flap is held in this position by the fourjoint linkage 28, whose joint 28A connecting the connecting rod 26 with the lever 27 is in a position raca0 0 beyond the dead centre position in the anti-clockwise sense, with lever 27 resting against the end stop 33. The o 0: four-joint linkage is in a quasi-stable state because of this angle at joint 28A and because lever 27 rests against 00 0 the end stop 33. Accordingly, the catch 24 of the control member 11B, which is in contact with lever 25 of the fourjoint linkage 28 under the spring force acting on the throttle flap 12, cannot move the throttle flap 12 out of the half-open position shown in Fig. 4 and into the closed position.

When the engine is started a vacuum is produced in the bellows 17, as described in detail below, and the bellows contract to the intermediate position shown in -8- I*II~BCLI L Fig. 5. The lever 20 is rotated in the clockwise sense by means of rod 18 and the coupling member 19, against the force of the spring acting on the choke flap 15, resulting in the choke flap 15 being opened. The four-joint linkage 28 remains for the time being in its initial position, such that also the opened position of the throttle flap 12 remains initially unchanged, until the catch 31 of the control lever 20 comes into contact with the lever 27 of the four-joint linkage 28. The latter position is shown in 10. Fig. .lo With increasing vacuum in the bellows 17 the control lever 20 of the choke flap 15 moves further in the @0 clockwise sense, with the catch 31 acting on lever 27 o a of the four-joint linkage and rotating it in the clockwise sense such that lever 27 moves away from its end stop 33. The joint 28A passes through its dead-centre position in which connecting rod 26 and lever 27 are in the extended position. The control member 11B can now rotate in the clockwise sense under the action of the spring acting on the throttle flap 12, moving relative to the throttle operating rod 11 because of the action of the pin-and-slot guide 11A, and rotating the lever 25 by means of the catch 24.

The end position reached in this manner is shown in Fig. 6. The throttle flap 12 is now clos"., and the choke flap 15 is in the fully opened position in which it -9is held by the operating device 16. The throttle flap 12 can now be further opened as desired, by means of the throttle lever 10 and the throttle operating rod 11 (Fig.

such that the engine can operate under full throttle.

The two flaps 12 and 15 cannot interact with each other while the engine is in an operating state. When the throttle flap 12 has been opened by operating the throttle lever 10 and thereby the throttle rod 11, the choke flap is held in its open position also by the throttle oo 10. operating rod 11 which, with its shoulder 1lC (Fig. 2), o rests against the projection 20B of the control lever o such that the latter cannot swing back. The right angle bend of the operating rod 11 with the shoulder 11C also o permits "emergency starting" of the engine in conjunc ion with the projection 20B of the control lever 20: If the engine has stalled inadvertently by the petrol/air mixture being over-rich, both flaps 12 and 15 can be moved by operating the throttle lever and the throttle operating rod 11, from their closed position into the open position, thus permitting a new start.

0 Normal pressure returns to the bellows 17 when the engine is stopped, and the control lever 20 for the choke flap 15 is rotated anti-clockwise by connecting rod 18 and the coupling member 19, under assistance by the spring acting on the choke flap. The catch 32 of the control lever 20 acts on the lever 27 of the four-joint linkage 28, such that the joint 28A passes again through the dead-centre position, and the state shown in Fig. 4 is re-established.

mom Since the autoi the foregoing ensur the throttle flap 1 depending on a pre-s flap 15, sufficient the initially over- In order to pei 16, the bellows 17 control unit 35 loc 10. Vacuum and pres bellows 17. On star S" in the crankshaft h o a' line 34, resulting 17.

15. Figs. 7 and 8 0 a 0 0 o S0, section or in parti, It comprises a hous 38, and a partition 000o 38, and a partition atic starting device described in es that, during the starting process, 2 remains in its half-open position, set travelling angle of the choke air is fed to the engine to burn rich petrol/air mixture.

rmit controlling the operating device are connected via a line 34 to a ated in the crankshaft housing 5 (Fig.

sure are alternatingly supplied to the ting of the engine a vacuum is produced ousing 5, and thereby suction in the in vacuum being applied to the bellows show the control unit 35 in longitudinal al longitudinal section, respectively.

ing 36 consisting of a trough 37, a lid wall 39. The lid 38 is provided with *a~ 0811 two connecting sockets 40 and 41. The connecting socket serves for connecting the section 34A of the line 34 leading to the crankshaft housing 5, while the line section 34B leading to the bellows 17 is connected to connecting socket 41, as is shown in Fig. 1, and schematically in Fig. 7. The trough 37 together with the partition wall 39 form a chamber 42 serving as air reservoir and being connected to the external atmosphere -11control lever carried by the shaft of the choke flap and being operated by the vacuum in part of the housing of the power tool through a line comprising a non-return valve and a thermostatically controlled throttle, and with a /2 flU I I E- a r e sa:T-nr i~~ii« in- iiiii 11 I :l 00 i op 00 P0 00 0 Oi: 4 0 8+~ Lar 1 Lr through a venting bore 43. The external opening of the venting bore 43 is located in a recess 44 of the wall of the housing and is covered there by a screen The bore 40A of the connecting socket 40 leads into a chamber 46 formed by the lid 38 of the housing and the partition wall 39, and being connected with chamber 42 by two bores 47 and 48 which are closed, on standstill of the engine, by a mushroom-shaped non-return valve 49. The non-return valve 49 is made of a rubber-elastic material and is provided with a stem 49A by which it is inserted in a bore 50 of the partition 39, being located between the bores 47 and 48. The top part 49B of the stem 49A forms a seal on the upper edge of the bore in the partition wall 39. The upper part 49B is integral 15. with the ring-shaped valve flap 49C which covers the two bores 47 and 48, and whose edge lies, under elastic prestressing, on the partition wall 39. The valve stem 49 is provided near its lower end with a thickened part 49D of spherical shape. On assembly, the valve 49 is inserted by its stem 49A into the bore 50, and is held there in its closud position by the thickened part 49D. Accordinglyr assembly is very simple.

The bore 41A of the connecting socket 41 leads into a chamber 51 formed by a recess in the lid 38 and likewise being closed by the partition wall 39. Chamber 51 is connected with the air reservoir chamber 42 through a -12- 1 L -I r- 4II 4 I 9 441 suction throttle system 52 and two bores 53 and 54, vwhi-h, on standstill of the engine, are closed by a non-return valve 55 being designed and arranged the same as the valve 49 described in the foregoing.

The suction throttle system 52 comprises a chamber 56 formed by a trough-like recess of the partition wall 39 and being closed by part of the lid 38. A bore 57 connects chamber 56 with chamber 51. The mouth of bore 57 is widened by a recess in the lid 38, in which a sealing ring 58 is located. Opposite the mouth of bore 57 there is a bore 59 passing through the partition wall 39 likewise being provided with a sealing ring 60 in a recess of the partition wall, at its end facing chamber 56. Each of the sealing rings 58 and 60 is in contact with one of two slightly curved bimetal disks 61, 62, being held in position by an S-shaped ieaf spring 63. Coaxial bores '1A and 62A are provided in the bimetal disks 61 and 62, respectively, which together form a throttle bore 64. A connection channel 65 is recessed, at one side of the chamber 56, in the wall of the chamber formed by the lid 38 and the partition wall 39. This connecting channel forms a bypass to the throttle bore 64 when the bimetal disks 61 and 62 are in their operating position (Fig. 8).

The suction throttle system 52 is a thermostatic regulator sensing the temperature in the region of the cylinder 4 of the chain saw (Fig, 1) j -13- "AUTOMATIC STARTING ARRANGEMENT FOR AN INTE'NIKu COMBUSTION

ENGINE"

The following statement Is a full description of this invention, including the best method of performing it known to me. us.

1 0 00 0000 0000oooo oo000 0 00 o oo 000 o0 0 000 000000 0 00 0 0 0 0 ooo0 0 00 0 00 o o00 o oo 0000o oo o oo0 o ooo o 0 The control unit 35 applies a vacuum to the bellows 17 when the engine is running, and supplies air again when the engine has stopped.

Fig. 7 shows the position of valves 49 and 55 and of the suction throttle system 52 with the engine at standstill and at a temperature corresponding to ambient temperature. When the engine is started a vacuum is produced in the crankshaft housing 5 and, thereby, via the line section 34A in chamber 46, causing the valve flap 49C of valve 49 to be lifted and thus establishing a connection between chambers 46 and 42. Air is sucked out of the bellows 17 through bores 41A and 57, the throttle bore 64, the air reservoir chamber 42, and through the bores 47, 48, and 40A to the crankshaft housing 5, in 15. direction of the arrows shown. The venting bore 43 leading from the external atmosphere into the air reservcir chamber 42 is suitably dimensioned to ensure that the pressure in chamber 42 cannot drop to the vacuum in chamber 46, such that the suction air stream that is required for evacuating the bellows 17 is maintained. When the engine is still cold, the flow velocity is relatively low because of the effect of the throttle bore 64, such that the choke flap 15 is opened only relatively slowly by the operating device 16 (Figs. 2 to The two bimetal disks 61, 62 are actuated by different temperatures: when the temperature in the region of the cylinder 4 rises to a -14iiil..~L-~ YII-C1~- certain value the bimetal disk dimensioned for this temperature, for example the upper disk 61, inverts its concavity, such that a bypass to the bore 61A is established through channel 65 to the bore 62A of the other disk 62, and a larger volume of air can be sucked out through chamber 42. When the temperature rises further, the second bimetal disk 62, that reacts to the higher temperature, inverts its concavity. Accordingly, both bimetal disks 61, 62 have inverted their concavity into face to face position, against the force of the leaf spring 63, when the chain saw has reached, in the region of the cylinder 4, the higher operating temperature of the thermostatically controlled suction throttle system 52.

This state is shown in Fig. 8, where the leaf spring 63 has been omitted for the sake of simplicity. With both bim(t.al disks in the shown position, a bypass to both bores 61A, 62A, i.e. to the entire throttle bore 64, has been established through the channel 65, such that the flow velocity produced by the suction, and therefore the speed at which the bellows 17 are evacuated, increases considerably. Accordingly, the opening speed of the choke flap 15 is increased in two steps, corresponding to two temperature limits in the region of the cylinder 4.

Excessive over-richness of the petrol/air mixture during starting is prevented in this manner, depending on the higher temperature of the power tool.

I starting, to permit combustion of ll the still over-rich starting, to permit combustion of the still over-rich -2- I SI I rrrr~ i ;i o 04« a o 00 0 a oe o a0 0 0 0000

O

S 6 *l I W i G 1

M

When the engine is stopped the pressure in the crankshaft housing 5 increases again to the normal value, and valve 49 closes the connection between chambers 42 and 46. This produces suction in direction towards the bellow 17 in which there is still a vacuum: air flows from the air reservoir chamber 42 through the suction throttle system 52, and, as the case may be, through the bypass channel 65 into the bore 57, and from there through line section 34B into the bellows 17. Air supply to the bellows is accelerated by valve 55 opening as a result of the pressure difference between chambers 51 and 42, such that air from the chamber 42 can also flow through bores 53 and 54 in direction toward the bellows 17. The venting bore 43 makes possible the desired rapid air supply to the bellows 17, by ensuring that a sufficient quantity of air or sufficient pressure, respectively, is present in the air reservoir chamber 42. This ventilation of chamber 42 through the venting bore 43 also prevents the accumulation of liquid in chamber 42, that may leak from the crankshaft 20. housing when valve 49 is opened.

Since the non-return valve 49 can be designed to open when the pressure difference between chambers 42 and 46 reaches a certain value, it is also possible to work with a higher vacuum for a given rotational speed of the engine, which improves the operational reliability of the automatic starting device. A further advantage offered by -16- I ithe control unit 35 is that its design is simple and reliable in operation, and that no narrow tolerances have to be observed in its manufacture, such that the entire automatic starting device is very economical to manufacture.

The bellows may be replaced by a different pressuredependent device, such as, for example, a pneumatic or pneu.catic-hydraulic actuating cylinder, whose piston would have to be provided with a connecting rod for coupling it to the control lever 1a e c 0 47

Claims (5)

10. device being associated with the choke flap and engaging a control lever carried by the shaft of the choke flap and being operated by the vacuum in part of the housing of the power tool through a line comprising a non-return valve and a thermostatically controlled throttle, and with a manually operated throttle control lever being coupled with a control member carried by the shaft of the throttle flap, f q+ 20. characterised by the throttle flap and the choke flap being coupled by the connecting linkage in such a manner MAon4(C.(,Y fockell that the throttle flap isamaintaine in its partly open position until the choke flap reaches a certain pre-set opening angle. 2. Automatic starting device according to claim I, characterised by the connecting linkage being a four- joint linkage capable of being swung beyond a dead-centre -18- .I 1 position by means of the control lever being fixed on the shaft of the choke flap, and being held by an end stop in its end position corresponding to the pre-set partly open position of the throttle flap, and by locking the throttle flap in this position. 3. Automatic starting device according to claim 2, characterised by the four-joint linkage comprising two levers each being rotatably mounted on one of the shafts of the choke flap and throttle flap and being connected to each other by a coupling rod. 4. Automatic starting device according to claim 3, characterised by the dead-centre position of the four-joint linkage being defined by the in-line position of one of the levers and the coupling rod. Automatic starting device according to claim 3 or 4, characterised by said control lever fixed to the shaft of the choke flap being provided with first and second catches for engaging the lever of the four-joint linkage that is rotatably mounted on the same shaft, the first catch being provided for releasing the locked end position of the four- joint linkage when the control lever is rotated, said first catch being positioned at a certain distance from said lever of the four-joint linkage when the choke flap is in the closed position, which distance corresponds to the pre-set opening angle of the choke flap up to which the throttle flap is maintained in its partly open position. -19- 6. Automatic starting device according to claim characterised by the second catch of the control lever of the choke flap limiting the swivel movement of said O- iAe -pour foinvft 'oif ((&kc1ge leverAwhen the choke flap is in the fully open position. 7. Automatic starting device according to any one of the preceding claims, characterised by the throttle flap and the choke flap being capable of being rotated, in opposite senses, into their closed position, under the action of a spring force. 8. Automatic starting device according toA ne of the claims 3 to 7, characterised by the control member for the throttle flap being provided with a catch being in contact, under the spring force acting in the closing direction of the throttle flap, with that lever of the four-joint linkage that is rotatably mounted on the shaft of the throttle flap. o 9. Automatic starting device according to any one of the preceding claims, characterised by the operating o o 0 device for the control lever of the choke flap, to which vacuum is applied from the crankshaft housing of the power tool, being controlled via a control unit being arranged S in -he connecting lineAbetween the crankshaft housing and Sai'd coA-iU( unif the operating deviceA and- comprising a non-return valve and an air reservoir chamber that is connected through the non-return valve with a chamber to which the vacuum can be applied, and from which chamber air is supplied to the operating device after the vacuum has ceased to exist. Automatic starting device according to claim 9, characterised by the thermostatically controlled throttle being a suction throttle system connecting a bore in the housing of the control unit with the air reservoir chamber, and by that section of the connecting line that leads to the operating device being connected to the bore ii the housing.

11. Automatic starting device according to claim characterised by the bore in the housing leading into a suction throttle chamber and by its mouth being 4 coaxial with a bore that connects the said suction pot 5. throttle chamber with the air reservoir chamber, and u ca o by the suction throttle system comprising two curved bimetal disks located within the suction throttle chamber a o and being arranged opposite each other and each being O pre-stressed towards one of the two walls of the suction o P 1 0. throttle chamber through which pass the bores, and which in one of their end positions are in contact with seals o placed around the mouth of the corresponding bore, and by each of said bimetal disks being provided with a central bore to form a throttle bore, and by a bypass channel being provided in one side wall of the chamber and being opened, as a function of temperature, as a partial or full bypass to the throttle bore, by one of said bimetal disks, or by both bimetal disks in their other end position that is reached after a certain temperature limit has been exceeded. -21- .t

12. Automatic starting device according toAone of claims 9 to 11, characterised by the air reservoir chamber being connected with the external atmosphere through a venting passageway.

13. Automatic starting device according to any one of the claims 10 to 12, characterised by the bore in the housing, to which the line section leading to the operating device is connected, being widened to form a chamber in the region between the suction throttle system and the connection socket for the line section, and with a Qb said chamber being connected through a non-return valve a° a with the air reservoir chamber. ft s 014 Q 0r e6 4 O~r

14. Automatic starting device according to claim 13, characterised by the non-return valves being made of an elastomeric material and each comprising a stem and a head part adjoining a ring-shaped valve flap 5. covering the bores provided in the corresponding wall of the housing, between which bores there is another bore for taking up the stem, with said head part being located cano/Ger at one end of said bore and with a widening of the stem being located at the other end of said another bore, and by the valve being pre-stressed in said bore by said head part and widening. Automatic starting device for an internal combustion engine substantially as hereinbefore described -22- I-e c and illustrated in the accompanying drawingst Dated this 14th day of June, 1988. ANDREAS STIHL, By its Patent Attorneys, R.K. MADDERN ASSOCIATES Kvvt o 0 A A A 0 0 004$ $A A f~ A A A 4$ A A A A 14 -23-