Pneumatically operable switch unit for monitoring tire pressure

• US 4,435,625 A
• Filed: 03/02/1982
• Issued: 03/06/1984
• Est. Priority Date: 03/10/1981
• Status: Expired due to Fees

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Burkel, Rainer, Frenznick, Anton, Buchschmid, Emil, Danamps, Jean, Stradtmann, Gunther
• Primary Examiner(s): Scott, J. R.
• Application Number:
  US06/353,966
• Time in Patent Office: 735 Days
• Field of Search: 200/61.22, 200/61.25, 200/83 N, 200/83 Q
• US Class Current: 200/61.22
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver

Abstract

An insulating cup-shaped body (29) that is screwed into the rim (11) of a vehicle wheel prevents conduction of heat (generated by the brakes, for example) from heating the metallic body (16) that forms a reference pressure chamber closed off by a membrane (17) from the inflated interior of a vehicle tire. The membrane (17) is set slightly within the rim of the cup for protection during tire changes. The chamber and switch housing (16) and a spool (27) for the coil of a resonant circuit form a preassembled unit that is snapped into the insulating cup and cemented into place. The relatively large coil diameter adds to the economy of the device, permitting the use of a small capacitor. The temperature of the gas sealed in the reference pressure chamber (18) by closure of the filling bore with a steel ball (25) follows the temperature of the interior of the tire and reliably opens the resonant circuit if the tire pressure falls below a prescribed limit. The condition of the resonant circuit is sensed by a fixed miniature oscillator mounted on the axle.

Claims

1. A pneumatically operated switch unit for monitoring vehicle tire pressure comprising a metallic conducting switch housing (16) capable of being inserted into a bore in a vehicle tire rim, an electrically conducting membrane (17) with the periphery thereof fastened to said switch housing on the side of said switch housing facing into the tire interior, said membrane closing off a gas-filled reference pressure chamber of said switch housing into which chamber there extends a switch contact insulatedly mounted in said switch housing, by pass-through insulation means, in such a position that it makes contact with said membrane when gas pressure in said chamber is at a reference pressure value and the air pressure in said tire exceeds a predetermined threshold value and is put out of contact with said membrane when the pressure in said tire falls below said threshold value, and circuit elements constituting a resonant circuit with said switch contact when the latter is in contact with said membrane, said switch unit also incorporating the improvement which comprises the provision of:

a cup-shaped shell (29) of insulating material capable of withstanding temperature changes and gradients, externally threaded for being screwed into said bore in said tire rim with its open end facing the interior space of said tire, and within which said metallic switch housing (16) and said resonant circuit (22,23) are firmly secured, said metallic switch housing (16) electrically connecting said conducting membrane (17) with said resonant circuit elements and being held within said cup-shaped shell (29) in a position in which said metallic switch housing (16) and said conducting membrane (17) do not project beyond said bore into said tire interior.

2. A pneumatically operated switch unit as defined in claim 1, in which the rim of said cup-shaped shell (29) of insulating material extends beyond said membrane (17) towards said tire interior.

3. A pneumatically operated switch unit for monitoring vehicle tire pressure comprising a metallic switch housing capable of being inserted into a bore in a vehicle tire rim, an electrically conducting membrane with a ring-shaped fastening to said switch housing on the side of said housing facing into the tire interior, said membrane closing off a gas-filled reference pressure chamber of said switch housing into which chamber there extends a switch contact insulatedly mounted in said housing, by pass-through insulation means, in such a position that it makes contact with said membrane when gas pressure in said chamber is at a reference pressure value and the air pressure in said tire exceeds a predetermined threshold value and is put out of contact with said membrane when the pressure in said tire falls below said threshold value, and circuit elements constituting a resonant circuit with said switch contact when the latter is in contact with said membrane, said switch unit also incorporating the improvement which comprises the provision of:

a cup-shaped shell (29) of insulating material capable of withstanding temperature changes and gradients, externally threaded for being screwed into said bore in said tire rim with its open end facing the interior space of said tire, and within which said switch housing and said resonant circuit (22,23) are firmly secured, and

a hollow cylindrical body (27) within said cup-shaped shell, serving as a spool on which a coil (23) forming part of said resonant circuit is mounted, said resonant circuit also including a capacitor (22) located inside said cylindrical body (27) and connected between said coil and said switch contact.

4. A pneumatically operated switch unit as defined in claim 3, in which said switch housing and said cylindrical body are bonded together and form a cylindrical unit of constant outer diameter fitting the innter diameter of said cup-shaped shell capable of being preassembled for insertion in said cup.

5. A pneumatically operated switch unit as defined in claim 4, in which said cylindrical unit (28) is bonded by adhesive to said cup-shaped shell (29).

6. A penumatically operated switch unit as defined in claim 4, in which said cup-shaped shell (29) is provided with an internal bead (31) in its upper portion, and said switch housing (16) is provided with an internal groove, whereby said cylindrical unit can be pressed and snapped into position in said cup-shaped shell.

7. A pneumatically operated switch unit for monitoring vehicle tire pressure comprising a switch housing capable of being inserted into a bore in a vehicle tire rim, an electrically conducting membrane with a ring-shaped fastening to said switch housing on the side of said housing facing into the tire interior, said membrane closing off a gas-filled reference pressure chamber of said switch housing into which chamber there extends a switch contact insulatedly mounted in said housing, by pass-through insulation means, in such a position that it makes contact with said membrane when gas pressure in said chamber is at a reference pressure value and the air pressure in said tire exceeds a predetermined threshold value and is put out of contact with said membrane when the pressure in said tire falls below said threshold value, and circuit elements constituting a resonant circuit with said switch contact when the latter is in contact with said membrane, said switch unit also incorporating the improvement which comprises the provision of:

a cup-shaped shell (29) of insulating material capable of withstanding temperature changes and gradients, externally threaded for being screwed into said bore in said tire rim with its open end facing the interior space of said tire, and with in which said switch housing and said resonant circuit (22,23) are firmly secured,

said reference pressure chamber (18) being provided with a fill channel (24) bored through said switch housing (16) and equipped with a metal ball closure element (25), pressed into said channel to close it to maintain the gas filling of said chamber at the reference pressure.