TIRE PRESSURE INDICATION DEVICE

Abstract: An arrangement for indicating vehicle tire pressure comprises a transmitter unit (6) which is connected to a pressure monitor (20) that communicates with the air in the tire and is constructed to generate electrically an acoustic signal when the tire pressure falls beneath a given pressure level. Mounted on the vehicle is a receiver unit (3) which detects the acoustic signals, and an indicating device (4) which indicates air leakage. The acoustic signal comprises a first signal of a first frequency and a second signal of a second frequency, this second signal being produced after a given time interval. The receiver unit on the vehicle will not indicate an air leakage until the two signals have been received at the correct frequencies and at the correct time intervals. The transmitter unit (6) is attached to the wheel rim and connected to the wheel air valve.

Description: i Tire Pressure Indication Device The present invention relates to an arrangement which generates a warning signal when the air pressure of a vehicle tire becomes excessively low. In view of the increasing density and higher speeds of present-day vehicle traffic, it is highly essential that the tire pressures of private cars and commercial vehicles lie within the limits intended. This is important from the aspect of safety, since an excessively low tire pres¬ sure may cause a vehicle to skid and lurch unexpected¬ ly and, in the mildest case, result in damage to the tire. Further, the optimum wear conditions and rolling resistance conditions are lost when the tire pressure deviates from the correct intended level, resulting in impaired tire and fuel economy. Several endeavours have been made to provide a tire pressure monitoring device. An example of one such device is disclosed in Swedish Published Specification 7410559-4. Only a few of these devices have progressed beyond the prototype stage, and all of the devices known hitherto have been impractical, not sufficiently reliable, too expensive or have been encumbered with some other character defect which reduces their ability to be used effi- ciently in practice, for one reason or another. The object of the present invention is to eliminate this problem and to provide an inexpensive and reliable tire pressure monitoring device. This problem is resolved in accordance with the inven¬ tion, by providing on each wheel a pressure monitor which monitors the air pressure in the wheel and delivers an electrically generated acoustic signal. Further advantageous developments of the invention are defined in the subordinate Claims. A number of advantages are obtained when the acoustic signal is generated eleciricaiiy. For instance, this enables pressure monitoring to be effected electrical- ly more readily, which affords greater precision and greater reliability. In addition, the monitoring device is supplied with energy from an independent source, and the tire air pressure need not be utilized to this end, for instance. With an electric, or per¬ haps it should be said electronic, acoustic signalling device there is less risk that the acoustic device will be rendered inoperative by dirt and similar contaminates and therewith malfunction. The use of an electronic sound generator enables a relatively high tone to be generated which falls well within the audible window beneath a car. A suitable frequency in this respect is one which lies between 2,000-6,000 Hz, or there may be alternatively used several different signals which lie within this frequency band. Essen¬ tially, the only sound which exists in this wavelength range beneath a car is wind noise, which is so much weaker than the inventive signal emitter as to obviate the risk of error indications, particularly when coded signals are not used. One advantage with the use of frequencies that lie within the aforesaid wavelength band is that the sensitivity of the human ear is greatest within this band. In other words, when a signal is generated which indicates that one of the tires of a vehicle has lost air, it is a simple matter for the driver of the vehicle to leave the vehicle, listen and ascertain which tire is involved. The inventive arrangement will preferably include a sound-receiving part which is fitted to the underside of the vehicle and which receives a signal from the air pressure monitoring unit fitted to the wheel. In one developed variant of the inventive concept, it is conceivable for the various wheels of the vehicle to be provided with sensors which are coded in mutual¬ ly different ways, such that an indication given within the vehicle will also indicate the wheel that is at fault. The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings, in which Figure 1 illustrates a car fitted with the inventive arrangement; Figure 2 is a perspective view of part of a wheel on the vehicle shown in Figure 1; Figure 3 is a block schematic illustrating the con¬ struction of receiver and transmitter; and Figure 4 is a pressure sensor. A microphone 2 is fitted approximately centrally beneath the vehicle illustrated in Figure 1. The microphone is connected to a receiver unit 3 which is mounted in the engine space of the vehicle and which, in turn, is connected to the electrical system of the car and also to an indicating device 4 mounted on the instrument panel of the car. As illustrated in Figure 2, a transmitter unit 6 is mounted on the inside of the wheel rim 5 and is con¬ nected by means of a cable 7 to a pressure monitor 8 fitted to the air valve 9 of the wheel. As shown in Figure 3, the transmitter includes a battery 10 which can be connected by the pressure monitor 8 to the electronic components of the trans- mitter unit, so that an acoustic signal or tone signal or several signals can be emitted in accordance with the invention. To this end, the transmitter unit includes an oscillator which supplies a sequence generator, which in turn activates a controlled tone generator and an amplifier connected downstream of the tone generator, this amplifier supplying a piezoelec¬ tric loudspeaker. It will be understood from the aforegoing that the transmitter unit is only active when the pressure monitor has reacted to an excessive- ly low tire pressure. Thus, no load is placed on the battery when the pressure in the tire 16 lies above a given threshold. As a result, the battery or batteries will have a long use time, which also enhances reli- ability in operation. The transmitter unit is con¬ structed conveniently to deliver a first tone, for instance a low tone, when a drop in tire pressure is sensed, and then to deliver a higher tone after a given period of time has lapsed. By varying the time interval or the frequencies of the respective differ¬ ent tones, a code can be established which may either be used to eliminate error indications deriving from other vehicles, by giving different vehicles different tones and different time intervals respectively, i.e. different codes. Alternatively, coding can be used to indicate the tire/wheel that is excessively low in pressure. Coding will also prevent other acoustic sources from causing fault indications. When fitted to the inside of the wheel, the transmit¬ ter unit is very well protected, even against theft, and will not impair the appearance of the vehicle. Further, the path travelled by the sound waves from the transmitter unit to the receiver unit is both short and unobstructed, so as to achieve a high degree of reliability. This position of the transmitter unit also screens the unit from other vehicles, thereby reducing the risk of error indication should the tires of other vehicles be punctured, for instance. The receiver unit illustrated in Figure 3 is also con¬ nected to a microphone 2 and to the vehicle electrical system. The receiver unit includes an amplifier which is connected to a filter, from where the signal or signals received are deiivereα to a signal processor, the output signals of which are compared in a down¬ stream compiler which compares the signals with in¬ serted or set values corresponding to tne coαe of tne transmitter unit. In turn, the compiler is connected to an indicator 4 mounted within the vehicle. The indicator may have the form of a lamp or an acoustic signalling device, or alternatively may comprise both lamp and acoustic device. Figure 4 illustrates the construction of the pressure monitor. The monitor comprises a cap 20, similar to a tire valve cap, in which there is moulded a metal sleeve 21 which is provided with an internal screw thread by means of which the cap can be screwed onto the valve. The cap is preferably manufactured from polyurethane. Projecting centrally of the screw thread is a valve opening pin 22 which functions to open the valve when the cap 20 is screwed onto the valve but which is then sealed by screwing the cap into abutment with the inner wall surfaces defining the screw- threaded opening against the valve wall. Provided in the upper part of the cap is a space 23 which is connected with the valve through a channel 24, and therewith also connected to the tire interior when the cap is screwed onto the valve. The space 23 also houses an electrically conductive membrane or dia¬ phragm 24 and a further electric contact 35, both of which are provided with connections which extend beyond the cap for connection to the transmitter unit. The membrane 24 is held raised from the contact 25, provided that the pressure in the tire, and therewith the pressure acting on the membrane 24, is sufficient¬ ly high. No current will be delivered to the trans- mitter unit. Should the pressure fall sufficiently, however, electric contact will be established and result in activation of the transmitter unit. The transmitter unit battery of the illustrated case is intended to be replaceable, although it will be understood that fully encapsulated transmitter units may also be used. Although the aforedescribed embodiment is at present considered to be the best that can be achieved, it will be understood that modifications and changes can be made without deviating from the concept of the invention. For instance, the pressure sensor may be mounted in a special hole provided in a wheel rim to this end. The wheel rim may also be provided with transmitter unit attachment means. Further, it is not necessary to use a mechanical membrane as a pressure monitor, since an electronic pressure sensor may alternatively be used to monitor tire pressure, for instance. Admittedly, this will result in continuous current consumption, although it is probable that this consumption can be kept sufficiently low to achieve long-term reliability nevertheless, with the aid of modern technology. In this regard, it is possible to provide the transmitter unit with means which will indicate or signal in one way or another when it becomes necessary to replace the battery. It will also be understood that the pressure monitor may include further valve means which when the pres¬ sure monitor is screwed onto the existing tire valve will enable the tire to be inflated or topped-up without needing to remove the pressure monitor. It also lies within the scope of the invention for the pressure sensor 8 to be included in a unit which replaces the conventional air valve and therewith obviate the need for a double valve, instead of in- eluding the pressure sensor in a valve cap part of the kind illus¬ trated in Figure 4. The receiver unit is suitably not constructed to respond solely to a code comprising the tone heights and time intervals from the transmitter unit, but will be constructed to react solely to a given sound level, so as to reduce the risk of error indications caused, for instance, by other and closely proximate vehicles. Of course, several tones can be used, optionally simultaneously. It also lies within the scope of the invention to pro¬ vide the vehicle spare tire with a transmitter unit. The transmitter unit may be screwed or glued to the wheel rim. Instead of being fitted to an axially extending rim surface, the transmitter unit may be fitted to the inwardly facing surface of the rim, so as to prevent the transmitter unit from being torn from the rim by the centrifugal forces that are gener- ated at high vehicle speeds. The transmitter unit will conveniently be constructed to deliver an intermittent signal, for instance to deliver the aforesaid signals over periods of some seconds, whereafter the signal sequence is repeated after a lapse of one minute or one-half minute. This will maintain a long battery life. Because the code may include tone heights, time inter- vals and amplitudes, it is possible to eliminate false alarms even when the receiver is constructed to accept relatively large deviations in tone. Although a rela¬ tively wide band will increase the risk of wrong indication, a broad band is necessary because the Doppler effect generated as the wheels rotate will result in tone variation. Thus, the band width in detecting the code tones must be greater than the Doppler variation at the maximum speed of the vehicle.

Claims: Claims 1. An arrangement for indicating vehicle tire pres¬ sure, c h a r a c t e r i z e d in that the device includes a transmitter unit which is connected to a pressure monitor which communicates with the air in a vehicle tire and which is constructed to generate electrically an acoustic signal when the tire pressure falls beneath a given pressure level. 2. An arrangement according to Claim 1, c h a r a c t e r i z e d in that the arrangement includes vehi¬ cle-mounted acoustic signal detecting means. 3. An arrangement according to Claim 1 or 2, c h r -a c t e r i z e d in that the acoustic signal pro¬ duced is comprised of a first signal which has a first frequency and a second signal which has a second frequency and which is generated at a given time interval after the first signal; and in that the vehicle mounted arrangement is constructed so as to indicate air leakage only when both signals are re¬ ceived at the correct frequencies and at the correct time intervals. 4. An arrangement according to any one of the preced¬ ing Claims, c h a r a c t e r i z e d in that the transmitter unit and/or the pressure sensor is mounted to the wheel rim and connected to the air valve of the wheel. 5. An arrangement according to any one of the preced¬ ing Claims, c h a r a c t e r i z e d in that the acoustic signal lies in a frequency band of 1,000- 10,000 Hz, and particularly in the frequency band of 2,000-6,000 Hz. 6. An arrangement according to Claim 5, c h a r a c t e r i z e d in that the acoustic trans¬ mitter is mounted on the inside of the wheel rim. 7. An arrangement according to any one of the preced¬ ing Claims, c h a r a c t e r i z e d in that the pressure monitor is connected between the transmitter unit and its battery and is so constructed that no current will be supplied to the transmitter when the tire pressure lies at a sufficiently high level.

Inventors: SVENSSON LARS, SVENSSON, LARS
Applicants: SMITH GOERAN, SVENSSON LARS, SMITH, GOERAN
Application year: 1993
Main classification: B60C23
IPC codes: B60C23