European Patent Office
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`(11) Publication number: 0 417 704 A1
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`(19)
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`(12) EUROPEAN PATENT APPLICATION
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`(51) Int. Cl.5: B60C 23/04
` (21) Application number: 90117410.2
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` (22) Application date: September 10, 1990
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`(30) Priority: September 12, 1989 DE
`3930480
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`(43) Publication date of application:
` March 20, 1991 Patent Gazette 91/12
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`(84) Named treaty nations:
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`Austria Belgium Switzerland Germany
`Denmark, Spain France Great Britain
`Greece Italy Liechtenstein Luxembourg
`Netherlands Sweden
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`(71) Applicant: Rainer Achterholt
` 7 Sportplatzweg
` Durach-Weidach, W-8968, Germany
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`(72) Inventor: Rainer Achterholt
`7 Sportplatzweg, Durach-Weidach W-8968,
`Germany
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`(74) Representative: Hans-Peter Brehm,
`holder of doctorate in chemistry, et al.
`Kern, Brehm & Partners, patent attorneys,
`73 Albert-Rosshaupter-Strasse
`Munich 70, Germany W-8000
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`(54) Valve cap generating a pressure reduction signal for air-filled tires
`
`(57) A valve cap able to be screwed onto a valve
`tube (6) of a tire valve generates a wirelessly
`transmittable pressure reduction signal when the
`pressure drops in the tire. Within the valve cap
`housing (1) a pressure chamber (48) and a
`reference chamber (44) are designed, able to be
`impinged on by the tire pressure to be
`monitored, which when the valve cap is screwed
`onto the tire valve, are able to be impinged on
`by a preset target pressure. Within the valve cap
`housing (1) on a circuit board (23), electrical
`and/or electronic components (24, 24’, 24”, 24’’’,
`25) of a transmitter are attached. A power
`supply source and a switching circuit are
`present, to which belongs at least one guide
`section (28) situated within the pressure
`chamber (48), which is situated at a small
`distance from the at-rest position of a membrane
`(40) able to be deployed out. An outward
`membrane movement evoked by a tire pressure
`drop closes a circuit and the transmitter circuit is
`supplied with current or voltage, and the
`transmitter delivers a temporally limited pressure
`drop signal.
`
`
`SCHRADER
`EXH. 1011
`Page 1011-1
`
`

`

` The invention relates to a valve cap generating
`a pressure reduction signal for an air-filled tire
`equipped with a valve. The valve cap is
`preferably for use with a passenger car that is
`operated at a target tire pressure of about 1.4 to
`3.0 bar. Modified embodiment forms are
`provided for bicycle tires, motorcycle tires and
`truck tires.
` Among the essential components of the new
`valve cap is a housing able to be screwed onto a
`valve tube of the tire valve. An operating
`component is provided, which, when the valve
`A valve cap with this design and function is
`known from German Patent Text 35 46 338.
`With the known valve cap, a housing section
`adjoining the pressure chamber is designed to
`be transparent. If the preferably colored
`membrane comes close to this transparent
`housing section, this is visually perceptible and
`indicates a pressure drop. To check the tire
`pressure, the driver of the vehicle must check
`each individual valve cap, which can be done
`only when the vehicle is stationary.
` The known method of functioning, which
`automatically produces a reference pressure
`and permanently stores it when a valve cap is
`screwed onto the tire valve, has proven to be
`especially simple, robust and reliable. A single
`embodiment form of the valve cap is usable at
`very varied tire pressures, because only a
`pressure difference is detected. Therefore the
`membrane can be designed to be thin and
`highly sensitive. Variations in tire pressure
`occurring when a passenger car is properly
`operated can amount to 0.3 bar or more. Such
`pressure variations do not alter the target
`pressure that serves as the reference basis
`within the reference chamber, and cannot impair
`the display and display accuracy of such a valve
`cap.
` Additionally, a number of tire pressure
`checking devices has become known, which
`operate with wireless signal transmission,
`wherein within the tire, or on the rim, a radio
`frequency or high-frequency transmitter is
`attached (see such as DE-PSn 24 41 430, 26 17
`448, 29 15 227 or DE-OS 31 08 998). For the
`most part these known devices require
`engagements into, or alterations of, the wheel
`rim. In part, an electrically conducting
`membrane, or one provided with an electrically
`conducting coating, is moved out, to close or
`open an electrical contact, which activates the
`transmitter. With DE-OS 36 05 661, an alarm
`device has been proposed for attachment to an
`air-filled tire, which is equipped with a
`
`cap is screwed onto the valve tube, opens the
`tire valve. Within the valve cap housing, a
`pressure chamber able to be impinged on by the
`tire pressure to be monitored, is designed, as
`well as a reference chamber, which, when the
`valve cap is screwed onto the tire valve, is able
`to impinged on by a preset tire pressure. The
`two chambers are separated from each other by
`a membrane, which assumes a position
`extending out into the pressure chamber, when
`the pressure to be monitored drops under the
`target pressure.
`transmitter, a power supply source and a
`pressure detection means, wherein the alarm
`device is able to be screwed on the valve shaft
`of the tire. Serving as a pressure detection
`means, is a membrane prestressed by a spring,
`which, when tire pressure is higher or lower than
`permitted, activates a switch, whereupon the
`transmitter is activated. Doubts exist as to
`whether this proposal can be implemented or
`already has been implemented.
` Despite a multiplicity of known proposals for
`tire pressure checking devices with wireless
`signal transmission, such devices have until now
`have been practically implemented and
`marketed only to a minor extent. Often the
`reliability of the known devices under the tough,
`varying conditions of a motor vehicle tire leave
`something to be desired, and/or the known
`devices are too costly and too expensive.
` Based on this, the task of the present
`invention consists in producing a simply
`designed and cost-effectively-produced valve
`cap of the type named at the outset, which –
`while maintaining the advantages named above
`– makes it possible to wirelessly transmit signals
`reliably and free of distortion.
` According to a further goal of the invention, the
`valve cap equipped with a transmitter and a
`power source should exhibit small dimensions,
`be able to be secured solely by being screwed
`onto the tire valve, and possess low weight, to
`avoid any substantial out-of-balance condition of
`an air-filled tire equipped with this valve cap.
` According to a further goal, the valve cap
`should be simply designed and consist of as few
`components as possible, prefabricated and able
`to be manipulated independent of each other,
`from which, using automated mass production,
`the completed valve cap is able to be
`assembled.
` According to still another goal of the invention,
`the new valve cap should be suited for repeated
`us without replacing the power source and/or
`
`SCHRADER
`EXH. 1011
`Page 1011-2
`
`

`

`other alterations, and ensure a multi-year
`service life.
` Based on a valve cap that generates a
`pressure reduction signal, with the features
`named initially, the invention-specific solution to
`this problem and goals is characterized in that
`within the valve cap housing a printed circuit is
`present, to which electrical and/or electronic
`components of a transmitter are attached,
`which, when power is supplied, generates one
`or more signal frequencies, which are able to be
`transmitted wirelessly to a receiver placed
`adjacent to the air-filled tire. Serving as the
`power supply is a battery accommodated on or
`in the housing, and a mechanical switching
`circuit, open as a rule, to which is assigned a
`guide section situated within the pressure
`chamber, which is placed at a small distance
`from the at-rest state of the membrane. If the tire
`pressure to be monitored drops relative to the
`target pressure stored in the reference chamber,
`this causes the membrane to extend out, which
`closes the switching circuit, whereupon a circuit
`is closed which activates the circuit of the
`transmitter. The transmitter exhibits a sequential
`control, which, after short-duration signal
`transmission, stops this signal transmission and
`again switches the transmitter into a state of
`readiness.
` This combination of figures produces a simply
`designed, reliably operating valve cap with small
`dimensions, which wirelessly transmits a signal
`to a receiver, which is preferably accommodated
`in the area of the wheel suspension. One
`practical embodiment form of this valve cap has
`a length (in the direction of the valve axis) of
`about 20 mm and a diameter of about 20 mm
`and weighs less than 10 g. This valve cap can
`be equipped with a lithium battery which delivers
`a nominal voltage of 3 V and possesses a
`capacity of mAh; this battery performance
`suffices – due to the limited signal transmission
`duration – for at least 500 to 1000 alarm pulses.
`The valve cap is simply designed and consists
`of a few prefabricated, independently
`manipulated components, from which, by
`automated mass production, the completed
`valve cap can be assembled. Preferably the
`transmitter generates two signal frequencies
`with frequencies that differ, which are irradiated
`at a preset pulse sequence. To each of the
`transmitters or valve caps a correspondingly
`tuned receiver is assigned, with the maximum
`distance between transmitter and receiver
`preferably amounting to less than 1000 mm.
`Under these conditions, a false alarm resulting
`
`from outside transmissions and/or interference
`with other receivers can be virtually precluded.
`The various tires of a motor vehicle can be
`equipped with the same embodiment form of a
`valve cap, because the assignment to the
`particular wheel is made via the particular
`receiver. Advantageous configurations and
`further developments of the invention are
`gleaned from the subordinate claims.
` The basic, mechanical-structural design of the
`invention-specific valve cap to move a
`membrane if the pressure drops sufficiently in
`air-filled tires is known from DE-PS 35 46 338.
`To avoid repetitions, with this reference the
`content of that document – if helpful and
`required – will also be become a part of the
`present documents. When the valve cap is
`screwed on to the valve tube of a tire valve, a 3-
`stage seal is created. In a first stage, a tightly-
`sealed connection is made between the valve
`tube and the open housing end of the valve cap.
`For this, within the open housing end, a
`compressible sealing element can be present,
`and/or the valve cap housing consists of plastic,
`which tightly and in securely sealed fashion
`adjoins the outer threading of the valve tube. In
`a second stage, when the screwing process is
`continued, the operating part present on the
`valve cap presses against the tire valve tappet,
`displaces it against its elastic pressure and
`opens the tire valve. Thereupon a pressurized
`medium flows from the tire into the interior
`housing space of the valve cap and impinges
`both on the reference chamber and the pressure
`chamber at the current tire pressure, which
`corresponds to a preset target tire pressure.
`When the process of screwing on continues, the
`reference chamber is closed in pressure-tight
`fashion. As practical experience has shown, the
`reference chamber remains closed in pressure-
`tight fashion for months, and maintains the
`target pressure once preset.
` According to one viewpoint of the present
`invention, the reference chamber is designed
`within a container closed on one side, the
`container opening of which is closed by the
`membrane. This container is delimited by a floor
`and a circumferential wall, which exhibits a front
`surface. The inner container space is impinged
`on with pressure, via at least one channel made
`within the circumferential container wall, which
`starts at the front surface of the circumferential
`container wall and ends in the interior container
`space. This container is held within the housing
`so as to shift, and when the valve cap is
`screwed onto the tire valve tube, the front
`
`SCHRADER
`EXH. 1011
`Page 1011-3
`
`

`

`container surface is compressed against a seal,
`which is securely attached within the valve cap
`housing. By this means, the interior container
`space and thus the reference chamber, are
`securely closed.
` When the valve cap of the tire valve is
`unscrewed, the application pressure between
`the front container surface and the seal is
`canceled. An elastic member accommodated
`within the valve cap provides for separation
`between the seal and front container surface, so
`that the reference chamber again can be
`impinged on, if necessary with another target
`pressure.
` The transmitter provided according to the
`invention consists in essence of a digital circuit
`and an oscillatory circuit, the coil of which is
`designed as a transmitting antenna. According
`to an essential viewpoint of the present
`invention, a sequential control of the digital
`circuit is provided, such that after a brief-
`duration signal transmission, this signal
`transmission is again interrupted and the
`transmitter switched into a readiness state.
` For this, the digital circuit can preferably
`exhibit, as essential functional groups, an RC
`generator, a starter device (trigger), a
`modulation circuit, a multi-stage frequency
`divider and a power amplifier capable of being
`switched on and off. The RC generator
`(oscillator) delivers various signal frequencies,
`the particular frequency of which is determined
`by the components of resistance (R) and
`condenser (C). The circuit is designed so that,
`via various feedbacks from the frequency
`divider, the corresponding functional groups of
`the digital circuit are guided so that through the
`closing of the connecting device, the circuit is
`initiated and a complete signal transmission is
`carried out. If this has been done, then the
`power amplifier and the RC oscillator are
`switched off, which results in a very substantial
`reduction of the power drawn from the battery.
`By this means, the circuit is switched back again
`to readiness and is ready for a new signal
`transmission, even if the connecting device
`continues to remain closed. A signal is again
`emitted only after the membrane has been reset
`and the connecting device has been opened,
`and when a tire pressure drop has again been
`detected, is again closed.
` Preferably the transmission signal is irradiated
`at comparatively long-wave frequencies in the
`kHz range. In this range, interference by outside
`signal sources is not likely to be expected.
`Nonetheless, the transmitted signal can be sent,
`
`free of interference, to the receiver(s) preferably
`situated no more than 1000 mm distant in the
`area of the vehicle wheel.
` To increase recognition between transmitter
`and receiver, and to preclude as much as
`possible false alarms due to outside signals, the
`transmission signal preferably consists of two
`differing frequencies (9.6 kHz and 10.4 kHz, for
`example), which are generated alternately over
`an interval of 10 to 20 milliseconds. The total
`duration of a transmitted signal preferably is only
`a few seconds, such as 1 to 3 seconds, and,
`especially preferred, about 1.6 seconds. Under
`these conditions, the capacity of the lithium
`battery indicated suffices for at least 500 to 1000
`alarm impulses, i.e. for the entire expected
`service life of the valve.
` The entire transmitter with all of the electrical
`and/or electronic components is preferably
`designed as a module. The components,
`including two chips, one RC generator and a
`number of condensers and resistors, are
`situated on a circuit board, which forms a printed
`circuit. In one practical embodiment form, a
`round printed circuit with a diameter of about 17
`mm suffices to admit all of the components. This
`board with the components is protected in the
`interior of a plastic housing, on the outer
`circumference of which the transmission coil is
`accommodated in a groove, which is configured
`as a wire winding. The entire signal generation
`device, including the reference chamber with a
`connecting device, transmitter and battery,
`preferably constitutes a signal integrated
`component. This entire component is held so as
`to slide within the valve cap housing. On this
`combined component, short and stable
`electrically conducting connections can be
`implemented. Assembly of the valve cap is
`facilitated, because all of the small and/or
`sensitive components of the transmitter as well
`as the sensitive membrane are on a single,
`prefabricated component.
` To each valve cap with its transmitter, a
`separate receiver is assigned. Typically a part
`of each receiver is a ferrite rod with a receiver
`antenna and a known receiver circuit. The
`receiver circuit obtains its power supply from the
`power supply source of the vehicle. The outputs
`of the receiver circuit are connected via
`connection lines with a display device on the
`dashboard or the like of the vehicle. Part of the
`display device is an electronic evaluation device,
`which assigns the impulses deriving from one
`specific transmitter-receiver to the pertinent
`wheel display. Additionally, the display device
`
`SCHRADER
`EXH. 1011
`Page 1011-4
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`

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`generates to the impulses obtained from the
`receiver its warning signal, detectable visually
`and/or acoustically, which also remains after the
`signal frequencies cease being sent, until the
`vehicle operator has deleted or reset the
`warning display.
` After the transmission of an alarm pulse, the
`valve cap is again ready to transmit a new alarm
`pulse, after the membrane has returned to its at-
`rest state. This can especially be done by
`unscrewing of the valve cap from the tire valve,
`because then the access to the reference
`chamber is opened, and the pressure can be
`equalized or the target pressure can be reset.
` The electrical and/or electronic components
`and parts in the invention-specific valve cap are
`supplied with power or current from a power
`supply source, preferably a round cell battery.
`As a rule the digital circuit of the transmitter is in
`a state of readiness. This circuit is connected
`with a mechanical connecting device that as a
`rule is open, to which belongs a guide section,
`which is located within the pressure chamber
`and there is situated in fixed fashion at a small
`distance from the at-rest position of the
`membrane. A sufficient reduction of the pressure
`in the tire, and thus also in the pressure
`chamber, causes the membrane to move out,
`directed into the pressure chamber. This
`movement of the membrane generates an
`electrically conducting connection between this
`guide section and another contact of the
`connecting device, whereupon a circuit is
`closed, which activates the transmitter circuit.
` It is possible to manufacture the movable
`membrane itself from an electrically conducting
`material, and to use it as a movable contact of
`the connecting device. True, difficulties can arise
`in combining sufficient electrical conductivity
`with the desired elasticity and mechanical
`strength and durability of membrane material.
` Alternatively, it is possible to provide a non-
`conducting membrane material of plastic or
`rubber with the desired elastic properties with an
`electrically conducting coating. In isolated cases,
`this coating can impair the sensitivity, durability
`and/or the response behavior of the membrane.
`Additionally, it is possible to select a membrane
`of plastic or rubber material that is optimal as
`regards its elastic and mechanical properties,
`and to coat this membrane on its surface that
`adjoins the guide section with a thin, electrically
`conducting plastic foil. This electrically
`conducting plastic foil may, for example, be a
`conducting polycarbonate foil filled with carbon
`black (which is sold by Bayer AG under the
`
`trade name MA-Krofol). A layer thickness of this
`polycarbonate foil of about 35 is sufficient and
`well suited. This electrically conducting plastic
`foil is preferably stamped out in a circular shape
`and has an edge-fixed terminal lug, which is
`connected in electrically conducting fashion with
`the attachment contact of the connecting device.
`Preferably this electrically conducting plastic foil
`is equipped with a number of notches projecting
`radially from the foil center point, not extending
`to the foil edge; for example, two notches that
`cross at right angles are well suited. Thanks to
`these notches, the presence of this electrically
`conducting plastic foil lying directly on the
`membrane and clamped on its edge, does not
`interfere with outward membrane motion.
` According to another alternative preferably
`provided in the present instance, in the center of
`the membrane a small electrically conducting
`metal plate or metal ring is attached, which is
`connected via a thin metallic wire with the
`transmitter circuit. The presence of this small
`metal plate or metallic ring does not hinder
`outward membrane motion and forms a simple
`and robust movable contact of the connecting
`device.
` In each instance a mechanically movable
`connecting device is produced, which exerts
`virtually no counter pressure to membrane
`outward motion. The sensitivity and response
`behavior of the membrane is not impaired by
`integration of the membrane into an electrical
`switching device. Rather, a mechanical switch is
`created which operates virtually without counter
`pressure, which operates safely and reliably on
`a turning wheel even when severe and
`alternating forces are in operation. Trials with
`the invention-specific valve caps have shown
`that this configuration of the membrane and the
`connecting device detects a drop in tire pressure
`of at least 0.2 bar in reliable and reproducible
`fashion, and thereupon activates the transmitter.
`An outward membrane motion of a few tenths of
`a millimeter is sufficient to close the circuit and
`supply the transmitter circuit with power or
`voltage.
` In this case, the guide section situated within
`the pressure chamber can preferably consist of
`a metal bow-shape, which is attached at
`opposite locations on the section of the
`circumferential container wall projecting out over
`the membrane, and is aligned essentially
`parallel to the membrane. This metal bow-shape
`is placed a few tenths of a mm distant from the
`membrane, or from the plastic foil supported by
`the membrane, or from the small metal plate
`
`SCHRADER
`EXH. 1011
`Page 1011-5
`
`

`

`supported by the membrane. Placement of the
`guide section parallel to, and at a small distance
`from, the membrane, does not take up much
`structural height, and provides a fast and reliably
`responding switch.
` In what follows, a preferred embodiment form
`of an invention-specific valve cap is explained
`with reference to a figure; the latter, employing a
`schematic depiction, shows an invention-specific
`valve cap.
` The valve cap depicted in the figure exhibits a
`housing 1 closed on one side, with a cover 2
`and a cylindrical circumferential wall 3, which
`makes a graded transition into a sheath section
`4 tip-stretched in a single piece, on the inner
`circumference of which an inner threading 5 is
`formed. This sheath section 4 forms the open
`end of the valve cap, which can be screwed onto
`a tire valve, of which, in the present instance,
`only a valve tube 6 and a spring-loaded valve
`tappet 7 are depicted in sectional fashion. The
`valve tube 6 is provided with an adapted outer
`threading. The entire valve cap housing 1
`preferably consists of impact-resistant plastic.
`On the gradation between the circumferential
`wall 3 and sheath section 4, a pressure plate 10
`is guided so as to shift, from which, in a single
`piece, an operating part 12 that is roughly flush
`with the central longitudinal axis of the valve cap
`projects. When the valve cap is screws onto a
`tire valve, this operating part 12 comes in
`contact with the valve tappet 7 and presses it
`down against its spring loading, so that from the
`tire valve that is thereupon opened, the interior
`of the valve cap is impinged on by the current
`tire pressure. In the pressure plate 10, at least
`one channel 11 is made, via which a pressurized
`medium connection is made between the open
`tire valve and the interior of the valve cap. As
`indicated in the drawing, on the outer
`circumference of pressure plate 10, a round-
`running groove can be made, in which a seal 13
`such as an O ring, is placed, which seals the
`pressure plate 10 vis-à-vis the circumferential
`inner wall of housing 1. Alternatively, a seal –
`not depicted – could be provided, which acts in
`concert with valve tube 6 of the tire valve.
` Adjacent to pressure plate 10, a sheath 20 is
`situated to as to slide within housing 1. On its
`outer circumference, this sheath 20 exhibits a
`groove 21, and on its inner circumference a
`projecting shoulder 22. On this shoulder 22 a
`circuit board is supported, on which the electrical
`and/or electronic components 24, 24’ 24’’, 24’’’
`of a transmitter are located. As part of this
`transmitter, a transmitter coil 25 is configured as
`
`a wire winding, which is accommodated within
`the groove 21 on the outer circumference of
`sheath 20. Additionally, in the inner space of
`sheath 20 a round cell battery 26 is
`accommodated.
` Adjacent to sheath 20, a container 30 is
`placed so as to slide within the valve cap
`housing 1. This container 30 consists of a
`container floor 31 and a circumferential
`container wall 32, which exhibits a front surface
`35. On the inner circumference of
`circumferential container wall 32, a membrane
`40 is clamped, in the center of which a small
`metal plate 41 is attached. A reference chamber
`44 is created, which is delimited by membrane
`40, the container floor 31 and the circumferential
`container wall 32. In circumferential container
`wall 32, a channel 36 is made, which starts at
`the front surface 35 of circumferential container
`wall 32 and ends in reference chamber 44.
`Through this channel 36, the reference chamber
`44 can be impinged on by the target tire
`pressure. On the inner side of the housing cover
`2, an annular seal 45 is attached, which exhibits
`a sealing surface 46 parallel to the front surface
`35. Provided that the front surface 35 adjoins
`this sealing surface 46 under application
`pressure, the channel 36 is locked and the
`reference chamber 44 is closed pressure-tight.
` Adjoining reference chamber 44, a pressure
`chamber 48 is designed, which is delimited by
`the membrane 40, a section of the
`circumferential container wall 32 projecting over
`membrane 40, and a plate 47. An elastic
`member 49, such as a cup spring or a
`compressible rubber ring is placed between
`plate 47 and housing cover 2. Pressure
`impinges on pressure chamber 48 via at least
`one notch in the front surface 35 – not depicted
`– or via a transverse borehole 33 in the section
`of circumferential container wall 32 projecting
`out over the membrane. A non-lockable flowing
`medium connection exists between pressure
`chamber 48 and the opened tire valve.
` Preferably the container 30 is permanently
`connected with sheath 20, and the two together
`form a single signal generation device with a
`pressure detection part and transmitter part.
` Within pressure chamber 48 there is a guide
`section 28, which is placed at a small distance
`from the at-rest position of membrane 40. This
`guide section 28 is connected via a first line with
`the transmitter circuit. A small metal plate 27
`attached to membrane 40 is connected via a
`second line with the transmitter circuit.
`
`SCHRADER
`EXH. 1011
`Page 1011-6
`
`

`

` When the valve cap is screws on a tire valve,
`first a pressure-tight seal is created between the
`outer threading on valve tube 6 and the inner
`threading 5 on sheath section 4 of valve cap
`housing 1. With additional screwing on, the
`operating part 12 presses down the valve tappet
`7 and the pressurized medium can flow from the
`open tire valve into the inner space of the valve
`cap. The pressurized medium impinges on both
`the reference chamber 44 and the pressure
`chamber 48 with the current tire pressure acting
`as the target pressure. With continued screwing
`on, the front surface of valve tube 6 strikes the
`underside of the pressure plate and the front
`surface 35 of container 30 is compressed
`against the annular seal 45 and the channel 36
`is closed. The reference chamber 44 is impinged
`on by the preset target pressure and closed. If
`thereupon the tire pressure to be monitored
`drops, then also the pressure in pressure
`chamber 48 also drops. The membrane 40
`moves into pressure chamber 48, and an
`electrically conducting contact is made between
`the guide section 28 and the small metal plate
`27, which together form a mechanically
`controlled, electrical switch. A current flows,
`which activates the circuit of the transmitter,
`whereupon it emits one or more temporally
`limited signal frequencies, until the digital circuit
`automatically interrupts the signal emission
`again.
` If the valve cap is thereupon screwed off the
`tire valve, then through spring force of the elastic
`member 49, the front surface 35 of container 30
`is separated from the annular seal 45, and
`pressure is equalized between pressure
`chamber 38 and reference chamber 33. The
`membrane reassumes its at-rest position, and
`the small metal plate 27 is separated from the
`guide section 28. The valve cap is again ready
`for use.
` One practical embodiment form of the valve
`cap depicted in the figure exhibits a length (in
`the direction of the valve axis) of about 20 mm
`and a diameter of about 20 mm, and, including
`the round cell battery, weighs less than 10 g.
`
`
`Claims
`
`
`1. Valve cap generating a pressure reduction
`signal for an air-filled tire equipped with a valve,
`with a housing (1) able to be screwed onto a
`valve tube (6) of the tire valve, in which a
`pressure chamber (48) able to be impinged on
`
`by the tire pressure to be monitored, as well as a
`reference chamber (44) is configured, which,
`when the valve cap is screwed onto the tire
`valve, is able to be impinged on by a preset
`target pressure, wherein the two chambers (44,
`48) are separated from each other by a
`membrane (40), which assumes a setting
`extended out into the pressure chamber (48)
`when the pressure to be monitored drops below
`the target pressure, and with an operating part
`(12) which, when the valve cap is screwed onto
`the valve tube (6), opens the tire valve,
`characterized in that
`within the housing (1) a circuit board (23) is
`present, on which the electrical and/or electronic
`components (24, 24’ 24”, 24’’’, 25) of a
`transmitter are attached, which, when power is
`supplied, generates one or more signal
`frequencies, which are able to be transmitted
`wirelessly to a receiver placed next to the air-
`filled tires;
`on or in the housing (1) a battery (26) and a
`mechanical connecting device (27, 28), which is
`open as a rule, is accommodated, to which a
`guide section (28) belongs, situated within the
`pressure chamber (48), which is situated at a
`small distance from the at-rest position of the
`membrane (40);
`a movement of the membrane creates an
`electrically conducting connection between this
`guide section (28) and an additional contact (27)
`connected with a circuit of the transmitter; and
`the transmitter (24, 24’, 24”, 24’’’; 25) exhibits a
`sequential control, which after a brief signal
`transmission, again interrupts this signal
`transmission and shifts the transmitter again into
`a state of readiness.
`
`2. Valve cap according to claim 1,
`characterized in that
`the reference chamber (44) is situated within a
`container (30), the opening of which is closed by
`the membrane (40); and
`pressure impinges on the interior of the
`container via at least one channel (36) made
`within the circumferential container wall (32),
`which starts at one front surface (35) of the
`circumferential container wall (32) and ends in
`the interior of the container.
`
`3. Valve cap according to claim 2,
`characterized in that
`the container (30) is held so as to slide within
`the housing (1); and
`the container front surface (35), when the valve
`cap is screwed on, is pressed onto the valve
`
`SCHRADER
`EXH. 1011
`Page 1011-7
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`tube (6) against a seal (45), w