Tire pressure sensor for motor vehicles

• US 5,065,134 A
• Filed: 06/04/1990
• Issued: 11/12/1991
• Est. Priority Date: 12/04/1987
• Status: Expired due to Fees

• Current Assignee: Dr. Ing. H.C.F. Porsche Ag
• Original Assignee: Dr. Ing. H.C.F. Porsche Ag, Robert Bosch GmbH
• Inventors: Burkard, Johannes, Schmierer, Wolfgang, Hettich, Gerhard, Schmid, Hans-Dieter
• Primary Examiner(s): Crosland, Donnie L.
• Assistant Examiner(s): Hofsass, Jeffery A.
• Application Number:
  US07/477,953
• Time in Patent Office: 526 Days
• Field of Search: 340/442, 340/445, 340/626, 340/448, 200/61.22, 200/61.25
• US Class Current: 340/442
• 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

The tire pressure sensor (13) for monitoring vehicle tires is fastened radically relative to the wheel axis at the circumference of a wheel rim and includes a reference pressure chamber (20) with a contact pin (22) which cooperates with an electrically conductive diaphragm (21) closing the reference pressure chamber (20) toward the tire. An added mass (30) is fastened freely at the diaphragm center for raising the switching threshold of the tire pressure sensor (13) as a function of speed and is dimensioned in such a way that the switching threshold is raised by a desired pressure differential (Δp) relative to the switching threshold p_o at standstill at a predetermined radius r of the diaphragm (21), a predetermined rotational radius R of the diaphragm (21) and a predetermined rotational speed v of the diaphragm (21). The required added mass (m) results from the equation m=f(Δp, r², R, v²), advantageously m=(π/4)r² {[R/v² ]Δp - p.a}k wherein p is the material density of the diaphragm, a is the diaphragm thickness and the factor k is between 1.1 and 1.5.

Claims

1. A tire pressure sensor for a vehicle, said vehicle having a plurality of vehicle wheels, each of said vehicle wheels having a wheel axis and a wheel rim on which a tire is mounted, said tire having a tire pressure and a running surface said tire pressure sensor comprising a pressure switch which is mounted on the circumference of the wheel rim of one of the vehicle wheels and which extends radially relative to the wheel axis, said pressure switch being actuable by the tire pressure and being provided with an electrically conductive diaphragm responding to and communicating with the tire pressure in the tire, said electrically conductive diaphragm being arranged parallel to the running surface of the tire, said diaphragm being provided with an added mass for increasing a switching threshold of the tire pressure sensor as a function of speed of the vehicle, said diaphragm having a contact, which is contacted by a contact surface, on a central area of the diaphragm for closing an electric circuit, when the tire pressure in the tire is large enough, wherein the state of the electric circuit is to be monitored without the use of wires by a signal generator, which is mounted in the vehicle and said signal generator includes an evaluating circuit;

furthermore the added mass (30, 30a) is fastened at the diaphragm center, is free so as not to impede the motion of the diaphragm and is determined by a functional relationship between the variables Δ

p, r², R and v² so as to be large enough to increase the switching threshold by a desired pressure differential Δ

p compared with the threshold value p_o at a stationary state, at a predetermined radius r of the diaphragm, at a predetermined rotational radius R of the diaphragm, and at a predetermined rotational speed v of the diaphragm.

2. The sensor as defined in claim 1, wherein the added mass m (30, 30a) is determined by the equation (6)

3. The improvement as defined in claim 1, further comprising a centric projection (31, 31a) provided on the diaphragm (21), said added mass (30, 30a) being attached to the centric projection.

4. The improvement as defined in claim 1, wherein the increase of the switching threshold at a driving speed of 130 km/h amounts to at least 5% compared to a threshold value p_o in the stationary state.

5. The improvement as defined in claim 1, wherein the added mass is fastened to the diaphragm (21) with a spot weld (32).

6. The improvement as defined in claim 3, wherein the added mass is fastened to the diaphragm (21) with a spot weld (32).