Measuring and testing – Tire – tread or roadway – Tire inflation testing installation
Patent
1991-05-06
1992-08-04
Woodiel, Donald O.
Measuring and testing
Tire, tread or roadway
Tire inflation testing installation
200 6122, 200 6125, 340442, B60C 2304
Patent
active
051348802
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention starts from a tire pressure monitor for motor vehicles according to the generic category of the main claim.
For high vehicle speeds of over 160 km/h, tire and vehicle manufacturers specify increased tire pressures in order to guarantee driving safety. If it is desired to make allowance for this, the switching threshold of the pressure switch fixed to the wheel must be set to the maximum pressure required. This leads to a loss in comfort at low speeds (German Offenlegungsschrift 3,243,845). If allowance is not made for this and the tire-pressure sensor is set to the tire pressure specified in the lower speed range at full load, at high speeds the requisite higher tire pressure will not be monitored, but on the contrary a safety which is absent will be falsely indicated by the tire-pressure monitoring device.
It is known from German Offenlegungsschrift 2,626,475 to provide the diaphragm of the reference-pressure chamber of a tire-pressure monitor with a solid piston against whose end face the tube of the tire to be monitored bears and which, when air pressure in the tire is sufficient, presses in the diaphragm against the pressure in the reference-pressure chamber to such an extent that an electrical contact is closed in the reference-pressure chamber. Furthermore, it is mentioned there that centrifugal forces on the piston of the diaphragm, when speed increases, advantageously reduce the force exerted on the diaphragm by the tire pressure so that, at higher speeds, the tire pressure must be increased in order to keep the switching contact closed. It is disadvantageous in this solution that the piston used as an additional mass for the diaphragm is covered by the tube of the tire so that the centrifugal forces acting upon it become effective only partly and in a completely indeterminable manner on the reference-pressure chamber for increasing the switching threshold. Furthermore, it is disadvantageous that this additional mass is securely riveted to the diaphragm in the centre of the same and thereby not only weakens the diaphragm but in addition, through the stiffening at the riveted point, affects the pressure-dependent and centrifugal force-dependent deformation of the diaphragm in a very variable and unpredictable manner. With this solution, therefore, it is not possible to increase the switching threshold to a reproducible extent at a certain speed relative to rest, since the speed-dependent increase in the switching threshold cannot be predetermined in this known embodiment.
With the present solution, the aim is to develop a tire-pressure monitor in which the additional mass is formed and arranged on the diaphragm of the reference-pressure chamber in such a way that the elasticity of the diaphragm is not thereby impaired and the switching threshold is increased as a function of speed by a predeterminable amount relative to rest.
The tire-pressure monitor according to the invention, having the characterizing features of the main claim, has the advantage that the additional mass, which is flexible compared with the rigid, preferably metallic diaphragm, no longer affects the elasticity and the strength of the diaphragm and in addition, by specific proportioning, permits a reproducible increase in the switching threshold as a function of the speed of the wheel. Thus, at high speeds of the vehicle, a signal is triggered by the tire-pressure monitoring device whenever the vehicle exceeds the maximum speed permissible for the existing tire pressure. The monitored minimum pressure in the tire is consequently increased in a defined manner as speed increases. A further advantage is that the characteristic curve of the threshold value, increasing as a function of speed, of the tire-pressure monitor, due to the centrifugal forces acting on the additional mass, progressively rises as speed increases. It is thus possible, over the entire speed range, to keep the threshold value at a sufficient distance above the pressure value at which the tire would be destroyed under full load (so-called d
REFERENCES:
patent: 5040562 (1991-08-01), Achterholt
patent: 5065134 (1991-11-01), Schmid et al.
Robert & Bosch GmbH
Striker Michael J.
Woodiel Donald O.
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