Tire-pressure sensors having batteries for power supply are known for motor vehicles. These sensors are located in the tire and include a sensor element whose output signal is encoded and transmitted by a transmitter to the receiver in the vehicle. One problem with these sensors is the power supply, usually a battery having a short lifetime. The toxic substances of which batteries are made are equally critical from the standpoint of possible disposal.
The present invention relates to a power supply device for a tire-pressure sensor, including a generator which is corotational with the tire (i.e., fixedly mounted on the wheel or tire or valve) in which an electric voltage is generated by electromagnetic induction. This has the following advantages:
An advantageous embodiment is characterized in that
An advantageous embodiment is characterized in that the geometric change in the magnetic circuit is achieved by a change in the air gaps.
Another advantageous embodiment is characterized in that the magnetic circuit contains at least one permanent magnet. This makes it possible to generate a magnetic field easily and without expending energy.
An advantageous embodiment is characterized in that the magnetic circuit
An advantageous embodiment is characterized in that the movable core moves along a guide.
Another advantageous embodiment is characterized in that a restoring spring is mounted on the movable core for returning the movable core to its starting position after a relative change in position.
Another advantageous embodiment is characterized in that the movable core is mounted on a plate spring which allows a one-dimensional change in position of the movable core, i.e., the movable core can move along a curved path.
Another advantageous embodiment is characterized in that the movable core is mounted on a torsion bar which allows a two-dimensional change in position of the movable core, i.e., the movable core can move over a two-dimensional surface.
In all these embodiments mentioned last, inexpensive production is possible due to the use of field-tested components.
Another advantageous embodiment is characterized in that the size of the relative change in position is limited by at least one stop.
An advantageous embodiment is characterized in that the stationary core contains a coil in which the induced voltage is generated. Since the coil is mounted on the stationary core, the coil feeder lines do not move while the generator is in operation.
Another advantageous embodiment is characterized in that the relative change in position is caused by an acceleration and/or a change in acceleration of the tire.
An advantageous embodiment is characterized in that an electric current is generated by the electric voltage, resulting in a charge buildup in an energy storage mechanism (capacitor, battery, . . . ).
While driving, sizeable accelerations occur in the wheels of motor vehicles. This includes centrifugal acceleration, which may be very high (up to approximately 400 g; g=gravitational acceleration), and other accelerations in the tangential direction as well as in the transverse direction of the vehicle. These accelerations are shown in
In addition,
Essentially only centrifugal acceleration occurs at a constant driving speed on an ideally planar road surface. In reality, however, there are constant up and down movements and small lateral movements of the wheels due to minor or major irregularities in the road surface, resulting in changes in acceleration (e.g., in a tangential direction and transversely thereto). These changes in acceleration may be converted to electric power using the generator according to the present invention, i.e., used to generate electric power. The following changes in acceleration occur, for example:
1) centrifugal acceleration superimposed on twice the acceleration due to gravity plus a dynamic component in the radial direction:
az=az0+azg(t)+azd(t),
where
The contribution azg(t)=2*g*sin(ω*t) is very easily understandable due to the fact that gravitational acceleration g (in a fixed coordinate system) always points in the same direction, but the direction of the centrifugal acceleration acting on the generator is always changing in the same fixed coordinate system.
2) Changes in tangential acceleration occur, for example, in acceleration or deceleration of the vehicle and due to irregularities in road surface:
at=at0+atd(t), where at0≈0.
3) Transverse acceleration occurs, for example, when cornering or again due to irregularities in road surface:
aq=aq0+aqd(t), where aq0≈0.
Three embodiments of the generator are described below.
This embodiment is shown in
Movable core 307 moves along a guide 308. The movement is limited by upper stop 305 and lower stop 311, the fastening of the stops on the housing being labeled as 312. The return of the movable core to the starting position is accomplished by restoring spring 310.
If the movable core is moved up and down (due to changes in acceleration), then the magnetic flux through coil 300 changes (due to the change in magnetic circuit geometry and thus the change in magnetic resistance), so that a voltage U is induced in the coil. For effective operation, there should preferably be a small air gap between the poles. An upper stop and a lower stop prevent the spring from being overextended. Magnetic flux φb is induced in the coil.
This embodiment is shown in
400=coil,
401=stationary core,
402=(small) air gap,
403=upper stop,
404=movable core having seismic mass m,
405=plate spring,
406=permanent magnet, and
407=lower stop.
Acceleration a0 acts on the core having mass m, which is vibratingly mounted, and thus force F=m*a0 acts on the core, resulting in deflection. The vibrating part is composed of the permanent magnet and a core made of a magnetically conductive material (e.g., iron or ferrite). Due to the movement of the core, there is a time-dependent magnetic flux through the coil and thus an induced voltage U=n*d(φb)/dt. In the position of the movable core depicted in
This embodiment is shown in
500=coil,
501=stationary core,
502=movable core,
503=permanent magnet,
504=torsion bar.
This embodiment is almost identical to that depicted in
Number | Date | Country | Kind |
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10301192.7 | Jan 2003 | DE | national |