US3457461A

US3457461A - Piezoelectric igniter for gaseous fuels or the like

Info

Publication number: US3457461A
Application number: US703587A
Authority: US
Inventors: Leo Steinke; Wilhelm Wiest
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1967-02-22
Filing date: 1968-02-07
Publication date: 1969-07-22
Anticipated expiration: 1986-07-22
Also published as: FR1555988A; GB1221070A; DE1629892A1; AT284324B

Description

July 22, 1969 L. STEINKE ET AL PIEZOELECTRIC IGNITER FOR GASEOUS FUELS OR THE LIKE 2 Sheets-Sheet 1 V20o 460 66o eo V1000 1o- 0 l 1 l :Y

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L. STEINKE EVAL PIEZOELECTRIC IGNITER FOR GASEOUS FUELS OR THE LIKE Filed Feb. '7, 1968 A 'Il-"3%.

2 Sheets.sheet 2 NVENOPS: e0 SUVA/kf Alum f ffy@ By me A TrOle/WSV United States Patent O im. ci. Fisq 3/00 U.S. Cl. 317-81 14 Claims ABSTRACT F THE DISCLOSURE A piezoelectric igniter for use in lighters or gas ranges comprises a housing accommodating a reciprocable striking member which can be biased by a rst spring to move toward an anvil and to thus cause one or more piezoelectric elements to impart to the anvil a blow and to cause the anvil to stress a return spring which'causes the anvil to recoil and to impart a blow to the piezoelectric element. Each blow brings about a change of mechanical stress in the piezoelectric element resulting in a potential difference high enough to cause the discharge of sparks across a spark gap which is electrically connected with the piezoelectric element. The spark gap is adjacent to a burner and a valve opens to admit gaseous fuel to the burner in response to depression of a kno-b which` causes the first spring to store energy prior to propelling the striking member toward the anvil.

The piezoelectric element or elements can be connected with the striking member or they may be installed in the housing adjacent to the anvil in the path of movement of the striking member.

CROSS-REFERENCE TO RELATED APPLICATION The piezoelectric igniter of our present invention coristitutes a modification of the igniter which is disclosed in the copending application Ser. No, 703,760, filed Feb. 7, 1968, by Leo Steinke et al. and assigned to the same assignee.

BACKGROUND OF THE INVENTION The present invention relates to piezoelectric igniters, and more particularly to improvements in piezoelectric igniters which may be utilized for ignition of flammable gaseous fuels iii gas ranges, table lighters or the like.

U.S. Patent No. 3,200,295 discloses a piezoelectric 1gniter for use in lighters wherein a change in mechanical stressing of a piezoelectric element causes the discharge of a single spark across a spark gap. The spark gap is adjacent to a burner and the discharge of a spark. causes ignition of pressurized gaseous lighter fuel. Such igniters are satisfactory for ignition of readily flammable gases ibut are not suited for use in gas ranges which burn certain types of less readily flammable gaseous fuels, such as butanenatural gas and others. If the combustible mixture adjacent to the spark gap is too lean or too rich, a single spark is often insufficient to insure ignition.

Another piezoelectric igniter is disclosed in Austrian Patent No. 241,008. This igniter comprises a lever which can transmit to the piezoelectric element a stress in the range of 300v-500 kp. A drawback of such igniters is that they are too bulky and too complicated for use in certain types of appliances. Furthermore, the stresses transmitted to the piezoelectric element vary within a wide range and their magnitude depends on the skill and strength of the manipulator so that they a-re not reliable for ignition of certain gaseous fuels.

ACC

SUMMARY OF THE INVENTION It is an object of our invention to provide a piezoelectric igniter which is equally useful and reliable for ignition of readily flammable as well as hard-to-ignite substances, particularly for ignition of various types of gaseous fuels including pressurized gaseous lighter fuel, butane and natural gas.

Another object of the invention is to provide a piezoelectric igniter which can be connected with a spark gap to produce several series or sequences of sparks and to thus insure reliable ignition of `less readily ammable fuels.

Ari additional object of the invention is to provide an igniter wherein the piezoelectric means is invariably subjected to predictable mechanical stresses and wherein such stresses suice to insure ignition of nearly all types of gaseous fuels.

Another object of the invention is to provide a piezoelectric igniter which occupies little room, which comprises a small number of simple and inexpensive parts, and which can be manipulated by semiskilled or unskilled persons.

An ancillary object of the invention is to provide a piezoelectric igniter which invariably produces at least two sparks and wherein the interval between the discharge of initial and secondary sparks can be selected with a view to insure reliable ignition of less flammable gaseous fuels.

A concomitant object of the invention is to provide a t piezoelectric igniter which can be installed in conventional fuel-consuming apparatus, such as gas ranges, table lighters and many others.

The improved piezoelectric igniter comprises piezoelectric means comprising one or more piezoelectric elements, a spark gap electrically connected in circuit with the piezoelectric means and preferably placed adjacent t0 a valve lfor a burner, resilient return means disposed at one side of the piezoelectric means, an anvil located between the resilient means and the piezoelectric means, striking means disposed at the other side of the piezoelectric means, and biasing means operative to propel the striking means toward the anvil so that the piezoelectric means imparts to the anvil a blow and undergoes a first change in mechanical stress resulting in a potential difference between the sides of the spark gap and the discharge of one or more sparks across the spark gap to ignite a readily flammable gaseous fuel which ows through the valve no later than at the time the piezoelectric means strikes against the anvil. The blow imparted to the anvil by piezoelectric means causes the resilient means to store energy and to cause the anvil to recoil or rebound and to impart to the piezoelectric means a blow so that the latter undergoes a second change in mechanical stress resulting in the discharge of one or more additional sparks across the spark gap and in ignition of less readily flammable gases.

The piezoelectric means can be coupled to the striking means to share the movement of such striking means under the action of biasing means. Alternatively, the piezoelectric means may be installed in a housing between the anvil and the striking means so that the striking means first imparts a blow to the piezoelectric means and. the latter immediately transmits the blow to the anvil and causes the latter to recoil.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved igniter itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

3 BRIEF DESCRIPTION OF THE DRAWING FIG. l is a schematic view of essential elements of a piezoelectric igniter which embodies one form of our invention;

FIG. 2a is a diagram showing the voltage curve when the igniter is disconnected from a spark gap;

FIG. 2b shows the voltage curve when the igniter is connected with a spark gap;

FIG. 3 is an axial sectional view of an igniter for use in gas ranges, the striking member being shown in starting position;

FIG. 4a is a similar axial sectional view and shows one position of the anvil of the igniter subsequent to release of the striking member;

FIG. 4b shows the anvil of the igniter in another position subsequent to release of the striking member;

FIG. 5 is an axial sectional view of a piezoelectric igniter for use in a lighter, the actuating member of the igniter being shown in starting position;

FIG. 6a is a similar sectional view but showing the actuating member in depressed position and the striking member in its normal position; and

FIG. 6b shows the actuating member in released position and the striking member in depressed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates schematically the essential components of our igniter. A housing 18 is connected with the ground and accommodates a reciprocable actuating member or knob 10 which can stress a biasing means here shown as a helical spring 11. The spring 11 can propel a striking member 12 against the upper end of one of two stacked piezoelectric elements 13. These piezoelectric elements are connected in parallel and their adjoining poles are connected with an electrode 14 which is further connected with one side of a spark gap 15. The other side of the spark gap 1'5l is grounded. The lower piezoelectric element 13 abuts against a reciprocable back support or anvil 16 which can be propelled upwardly by a helical return spring 17 connected to the ground by way of the housing 18. The spring constant of the spring 11 is 0.1 kp./mm. and the spring constant of spring 17 is 0.6 kp./mm. The mass of the striking member 12 is 45 grams and the mass of the anvil 16 is also 45 grams.

The operation is as follows:

In order to produce a series of sparks across the spark gap 15, the user depresses the knob 10 to stress the spring 11 which causes the striking member 12 to impart to the upper piezoelectric element 13 a blow with an energy of 0.04 mkp. The thus produced pressure impulse is transmitted to the anvil 16 which compresses the return spring 17. The spring 17 recoils and propels the anvil 16 upwardly so that the latter strikes against the lower piezoelectric element 13 with an energy of about 0.03 mkp. to thus produce in the piezoelectric means a second pressure impulse.

During each such pressure impulse, there develops in the elements 13 a change in mechanical stress including an initial rise and a subsequent decrease in mechanical stress. If the spark gap is disconnected from the piezoelectric elements 13, the potential diierence u varies in a manner as indicated by the curve shown in FIG. 2a.

Such potential difference is measured at the electrode 14 and is substantially proportional to the pressure in piezoelectric elements 13. Due to relatively high potential difference and also due to internal and insulation resistance of the igniter, the potential diiference goes over into negative during reduction of stresses in piezoelectric elements 13. This is indicated by such portions of the curve shown in FIG. 2a which extend below the abscissa. Time t (in microseconds) is measured along the abscissa and the potential difference u in kilovolts is measured along the ordinate. The self-discharge is compensated for in opposite direction. The peak of the initial voltage impulse is at about 10 kilovolts. The second voltage impulse develops with a delay of about 0.1-1 millisecond and its shape is similar to that of the initial or primary impulse. However, the peak of the second impulse is lower because the energy with which the anvil 16 strikes against the lower piezoelectric element 13 is less than that with which the striking member 12 imparts a blow to the upper piezoelectric element.

When the spark gap 15 is electrically connected in circuit with the piezoelectric elements 13, the potential difference varies in a manner as indicated by the curve shown in FIG. 2b. The voltage required to produce an initial spark is about 10 kilovolts. Such voltage is reached when the striking member 12 imparts a blow to the upper piezoelectric element 13, i.e., the discharge of a spark across the gap 15 takes place in response to initial compressive stress upon the piezoelectric elements and the voltage collapses in immediate response to generation of the spark. A potential difference of opposite polarity develops in response'to decreasing mechanical stress upon the piezoelectric elements 13 to produce a secondary arc discharge across the'spark gap 15 which is ionized during initial or primary discharge. Due to the fact that the spark gap 15is ionized during the initial discharge of a spark, a voltage of at least .7 kilovolt suices to eifect a secondary-discharge. The same procedure is repeated when the anvil 16 imparts a blow to the lower piezoelectric element 13.

Ou-r invention is based on the -recognition that less flammable gases can be readily ignited by employing a spark gap in combination with an igniter which can elect secondary discharges of sparks over an intervel of 0.1-1 millisecond following the initial discharge. The two pressure impulses which develop in response to biasing of the spring 11 and subsequent release of the striking member 12 follow each otherwith a delay of between 0.5-1 millisecond. Each pressure impulse brings about two rapidly following spark discharges, one in response to. a rise and the other in response to a decrease in mechanical stressing of the piezoelectric elements 13. The electrical energy, which is converted into heat energy at the spark gap 15, is doubled by employing a pair of parallel-connected piezoelectric elements.

FIGS. 3, 4a and 4b illustrate the details of a piezoelectric igniter whichcan be utilized in a gas range or the like to effect ignition of flammable gaseous fuels. This igniter comprises an elongated tubular housing 20 which resembles a cylinder or cartridge and has one of its ends closed by an end wall 20a. The housing 20 is grounded and accommodates a cylindrical anvil 21, an elastic diskshaped cushion 23 of rubber or the like which is interposed between the lower end face of the anvil and the bottom wall 20a and which can be attached to the anvil, and a helical return spring 22 which operates between the bottom wall 20a and an external annular shoulder of the anvil. The upper end face of the anvil 21 has a cylindrical recess 21a which accommodates the lower end portion of a cylindrical sleeve 24 of insulating material. The sleeve 24 surrounds two stacked piezoelectric elements 25 which are connected in parallel. The high-voltage electrode 26 which is placed between the adjoining ends of the piezoelectric elements 25 extends into a radial nipple 24b of the sleeve 24, and such nipple extends radially through an axially parallel slot 20b of the housing 20. The sleeve 24 has an external ring-shaped projection or collar 24a which is guided in the housing 20. The collar 24a forms part of an anchoring device and cooperates with a ringshaped spring 27 which is engage-d by several inwardly extending projections 20c of the housing 20. The collar 24a further serves as an abutment for the lowermost convolution of a helical resettingspring 28 which biases a striking member 29 upwardly to the starting position shown in FIG. 3. FIG. 4a shows this striking member 29 in its other end position when it imparts a blow to an extension or cap 25a at the upper end of the upper piezoelectric element 25. The lower end face of the striking member 29 has a recess 29b which accommodates one or more convolutions of the resetting spring 28. The upper portion of the striking member 29 is provided with a substantially disk-shaped ilange or head 29a of frustoconical outline which can be engaged by the lower end portions or hooks 30a of severalequidistant elastic retaining claws 30 which serve to yieldably retain the striking member 29 in the starting position shown in FIG. 3. The claws 30 are integral with a mounting ring 33 which is ixedly secured in the upper endof the housing 20.

The biasing means for the striking member 29 comprises a helical spring 31 having a lower end convolution which abuts against the head 29g. The upper convolutions of the spring 31 extend into a depressible actuating member or knob 32 which is guided in the top end wall of the housing 20 and extends into the space between the claws 30. The mounting ring 33 --and its claws 30 preferably consist of synthetic thermoplastic material. Cams 30h provided on the claws 30 immediately above the respective end portions 30a can be engaged by the lower end face of the knob 32 to thus disengage the end portions 30a from the flange or head 29a when the spring 31 stores suicient energy to propel the striking member 29 against the cap 25a.

When the knob 32 is depressed (see FIGS. 4a, 4b) it engages the cams 30b and causes the end portions 30a to move radially outwardly so that the striking member 29 undergoes strong acceleration in response to the bias of spring 31 which is stressed during initial depression of theA knob 32. The bias of the spring 31 is much stronger than the bias of resetting spring 28 so that the latter cannot prevent rapid acceleration of the striking member 29 and the transmission of a strong blow to the cap 25a. The pressure impulse propagates itself lthrough the piezoelectric elements 25 and causes a downward movement of the anvil 21 which stresses the return spring 22. This is shown in FIG. 4a. The anvil 21 recoils because the return spring 22 expands and propels the anvil upwardly so that the latter strikes against an extension or cap 25b of the lower piezoelectric element 25. This is shown in FIG. 4b. The anvil 21 then produces a second pressure impulse. The knob 32 is released upon completed rebounding of the anvil 21 so that the resetting spring 28 returns the striking member 29 to the starting position of FIG. 3. The lower end portions 30a of the claws 30 engage and retain the ilange 29a to hold the striking member 29 in such starting position. The manner in which the potential difference varies in response to depression of the knob 32 is the same as described in connection with FIGS. 2a and 2b.

The igniter of FIGS. 5, 6a and 6b comprises a prismatic or block-shaped housing 40 of rectangular cross-sectional outline which is adapted to be installed in the decorative case or outer shell of a table lighter. The upper portion 40a of the housing resembles a hollow cylinder and the lower end of the housing 40 is closed by a grounded bottom wall 41 of metallic material. The housing 40 consists of synthetic plastic material. The upper side of the end wall 41 is engage-d by the lowermost convolution of a helical biasing spring 42 located below an assembly 43 including a metallic striking member 44, an insulating sleeve 46, and a piezoelectric element 45 in the sleeve 46. The

parts

45, 46 are received in a recess of the striking member 44 and the sleeve 46 is threadedly connected with the striking member. The sleeve 46 overlies the top face of the piezoelectric element 45 and carries a centrally located cap or extension 47 which can transmit blows to and by the element 45. An external projection or collar 46a of the sleeve 46 is engaged from below by the topmost convolution of the spring 42. In addition, the collar 46a can slide along the internal surface of the housing 40 to prevent tilting of the assembly 43.

The top portion 40a of the housing 40 accommodates a cylindrical anvil 48 which is connected with a highvoltage electro-de 49. The latter extends from the housing 40. A return spring 51 biases the anvil 48 downwardly, and this spring 51 also serves as a means for resetting a depressible actuating member or knob 52 which is slidable on and surrounds the portion 40a of the housing 40. When the spring 51 is free to expand, it maintains the anvil 48 in abutment with one or more internal projections or stops 50 of the housing portion 40a. These stops 50 may form a continuous internal collar in the housing portion 40a. The knob 52 has two elastic claws or tongues 53 which are located diametrically opposite each other, and the lower end portion of each claw 53 is provided with an inwardly extending hook 54. These hooks extend through longitudinally extending slits 55 of the housing 40 and abut against the top face of the collar 46a on the sleeve 46 in the starting position of the knob 52. Each of the claws 53 is further provided with a cam 56 which cooperates with a cam 57 on the housing 40 to move the respective hook 54 radially outwardly in response to depression of the knob 52. This is shown in FIGS. 6a and 6b When the user depresses the knob 52, the end portions 54 of its claws 53 moves the assembly 43 downwardly because the end portions 54 bear against the top face of the collar 46a. The spring 42 is compressed and stores energy. As the knob 52 continues to 4move downwardly toward the end wall 41, the cams 56 of the claws 53 engage the cam or cams 57 on the housing 40 and cause the end portions 54 to move apart and to be disengaged from the collar 46a. This is shown in FIG. 6a. The assembly 43 is released and is propelled upwardly in response to expansion of the spring 42 which causes the cap 47 to strike against the underside of the anvil 48. The piezoelectric element `45 receives a pressure impulse and causes the anvil 48 to move upwardly against the opposition of the return spring 51 which stores energy. This is shown in FIG. 6b. The anvil 48 recoils and its lower end face imparts to the cap 47 a blow to produce in the piezoelectric element 45 a second pressure impulse. Such second impulse lags behind the initial impulse by a predetermined interval. When the user releases the knob 52, the spring 51 expands fully and returns'the parts to the positions shown in FIG. 5, i.e., the end portions 54 of the claws 53 come to rest on the top face of the collar 46a. The potential difference which develops in response to depression of the knob 52 varies in the same way as described in connection with FIGS. 2a and 2b. The electrode 49 is connected with one side of a spark gap (not shown) which is adjacent to the orifice of a fuel valve 70 for a burner 74.

Readily tiammable gaseous fuels are ignited in response to the first series of first spark discharges which develop when the piezoelectric means receives a blow from the striking member (FIGS. 3, 4a and 4b) or when the piezoelectric means strikes against the anvil (FIGS. 5, 6a and 4b). Ignition of hard-to-ignite gaseous fuels invariably takes place in response to the secon-d 'series of spark discharges which develop when the anvil recoils. As explained hereinbefore, the second series of discharges follows the rst series with a certain time lag. The duration of discharges can be extended in a well known manner by placing the spark gap in series with a resistor or with an inductance. For example, the resistor may comprise .an anti-interference cable of high ohmic resistance of the type often used in internal combustion engines.

When the improved igniter is used in a lighter or in connection with a burner in Igas range or the like, the

knob

32 or 52 may be coupled with and can open a fuel valve prior to discharge of the initial series of sparks. This is shown in FIG. 5 which illustrates an operative connection 71 (e.g. a link train, a gear train or a solenoid) serving to open the valve 70 in response to depression of the knob 52. The valve 70 is installed in a conduit 72 -which supplies gaseous fuel from a source 73 to the burner 74.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, -by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our constribution to the art and, therefore, such adaptations should and are intended to 4be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claims:

1. A piezoelectric igniter, particularly for flammable gaseous fuels, comprising piezoelectric means; a spark gap electrically connected in circuit with said piezoelectric means; resilient return means disposed at one side of said piezoelectric means; an anvil located between said return means and said one side of said piezoelectric means; striking means disposed at the other side of said piezoelectric means; and biasing means operative to propel said striking means toward said anvil so that said piezoelectric means imparts to said anvil a blow and undergoes a first change in mechanical stress resulting in a potential difference between the sides of and a spark discharge across said gap whereby said anvil Icauses said return means to storage energy and to propel the anvil against said piezoelectric means so that the latter undergoes a second change in mechanical stress resulting in renewed spark discharge across said gap.

2. An igniter `as defined in claim 1, wherein the masses of said anvil and said striking means and the characteristics of said biasing means and said return means are such that the interval between said first and second changes in mechanical stress is in the range of 0.1-1 millisecond.

3. An igniter as defined in claim 1, wherein the mass of said striking means at least approximates the mass of said anvil.

4. An igniter ras defined 'in claim 1, further comprising a housing for said anvil and said return means, said housing having an end wall and said return means comprising spring means located between said anvil `and said end wall.

5. An igniter as defined in claim 1, wherein said striking means comprises a metallic member and further comprising an insulating member connecting said piezoelectric means with said metallic member.

6. An igniter as defined in claim 5, wherein said insulating member comprises a sleeve which surrounds said piezoelectric means and is movaible with said metallic member.

7. An igniter as defined in claim 1, further comprising actuating means operative to cause said biasing means to store energy prior to propulsion of said striking means toward said anvil.

8. An igniter as defined in claim 7, wherein said actuating means is movable from a starting position and said return means is arranged to return said actuating means to starting position on completed propulsion of said anvil against said piezoelectric means.

9. An igniter as defined in claim 8, further comprising a housing for said anvil, said striking means and said biasing means, said actuating means comprising a reciprocable member movable with reference to said housing and said return means. comprising a spring interposed between said actuating means and said anvil.

10. An igniter as defined in claim 9, wherein said housing comprises a tubular portion for said anvil and said reciprocable -member of said actuating means is coaxial with and is slidably guided by said tubular portion.

11. An igniter as defined in claim 9, further comprising an insulating member surrounding said piezoelectric means and connected with said striking means, said sleeve having an external projection and said actuating means further comprising a. plurality of elastic claws engaging said projection in the starting position of said actuating means so las to move said sleeve and said striking means and to thus cause said biasing means to store energy in response to movement of said actuating means from starting position. v

12. An igniter as defined in claim 11, wherein said housing is provided with slits for said claws and with means for disengaging `said claws from said projection in response to a predetermined displacement of said actuating means from starting position so that said biasing means is free to dissipate energy and to propel said striking means toward said anvil.

13. An igniter as -defined in claim 12, wherein said claws consist of elastomeric material.

14. An igniter as defined in claim 1 for use in combination with a burner having valve means movable between open and closed positions to respectively permit and prevent passage of a gaseous fuel, wherein said spark gap is adjacent to said :valve means and further comprising actuating means for effecting propulsion of said striking means toward said anvil at the will of the user, said actuating means comprising means for opening said valve means prior to initial spark discharge across said gap so that said valve means discharges fuel at the time of initial spark discharge.

References Cited UNITED STATES PATENTS 3,200,295 8/1965 Owens et al 317-81 X 3,298,421 1/1967 Tezuka et al 317-81 X 3,408,153 10/1968 Ishiguro 317-81 X FOREIGN PATENTS 606,498 10/ 1968 Canada.

VOLODYMYR Y. MAYEWSKY, Primary Examiner U.S. Cl. X.R.