Pressure sensing device for tires of motor vehicles

Claim 1

A pressure sensing device for motor vehicle tires comprising: a hollow body having an internal wall defining a chamber, first and second spaced apart electrical contact means fixed within said chamber, a movable contact member movable within said hollow body between said first and second fixed contact means, first resilient means biasing said movable contact member toward a first travel limit position in which said movable contact member engages said first electrical contact means, means for adjusting the load of said first resilient means, a drive piston slidable in said hollow body to push said movable contact member away from said first travel limit position, a diaphragm having a central part and a peripheral edge located in said chamber, means sealingly securing said peripheral edge of said diaphragm to said wall of said chamber within said body of said device with said central part in contact with said drive piston, means for connecting said hollow body to a tire to communicate the interior of a tire with a part of said chamber located on a side of said diaphragm opposite said drive piston, said second electrical contact means being engaged by said movable contact member when, as a result of the thrust of said drive piston due to air pressure within said tire, said movable contact member reaches a second travel limit position opposite said first travel limit position, second resilient means biasing said movable contact member away from said second travel limit position and located so as to act only in a final portion of the travel of said movable contact member toward said second travel limit position, and means for independently adjusting the load of said second resilient means relative to the load of said first resilient means.