WO2009080374A1

WO2009080374A1 - Power generation for circuitry on vehicle wheel

Info

Publication number: WO2009080374A1
Application number: PCT/EP2008/054688
Authority: WO
Inventors: Mihai Patrascu; Dennis Hohlfeld
Original assignee: Stichting Imec Nederland
Priority date: 2007-12-21
Filing date: 2008-04-17
Publication date: 2009-07-02

Abstract

An electrical power generator for powering circuitry (57) on a ve hicle wheel, has a first part for generating an energy field, a nd a second part which is movable relative to the energy field, e.g.a magnet (40) and coil s (30), to generate the electrical power, both the first and the second part being suitable for operation located on the wheel. The first part falls freely along a channel defi ning a circumferential path around the wheel, as the wheel rotates, so that the free falli ng part passes the othe r of the two parts to generate the electrical power. By having both parts mounted on the wheel, no sliding contacts or wireless power transmission are needed to conduct the power to the circuitry on the wheel, and relative alignm ent of the parts is easier to achieve and maintain in all conditions th an if one is mounted on a body of the vehicle. Rotational imbalance can be much reduced, for a given mass. It can be used for tire pressure monitoring systems.

Description

POWER GENERATION FOR CIRCUITRY ON VEHICLE WHEEL

Field of the invention

This invention relates to electrical power generators for powering circuitry mounted on a vehicle wheel, and to wheels or tires having such generators, and to tire pressure management systems (TPMS) having such generators.

Description of the Related Art

It is known to provide energy to circuitry in a vehicle wheel such as an aircraft or road vehicle. Such circuitry can be useful to monitor temperature, tire pressure, and so on. A tire pressure monitoring system (TPMS) requires electrical energy to operate circuitry such as that for acquiring sensor data, for processing and for making the outcome available to an end system and/or the user. Replacing or supplementing the battery by an energy harvesting or energy scavenging system is desired by the industry for reasons of maintenance, cost reduction and so on. By replacing the battery and integrating the TPMS either in the rim or the tire itself the system becomes operable over the lifetime of the tire. Thereby, added functionality can be generated such as tire identification and history logging (total distance, strong impacts, failure diagnosis, driver dynamics logging, etc.) At present, most TPMS-related research efforts concentrate on piezo-electric scavengers for converting mechanical into electrical energy, due to its solid state approach and relatively good conversion efficiency between the electrical and mechanical domains. In general, piezo-electric energy scavengers feature a high potential and small output current, which makes a considerable step-down conversion necessary. Typically, this conversion has a poor efficiency. Due to increased fabrication costs and limited applicability of piezo scavenging, other principles have been investigated. One of the possibilities is magnetic induction using coils. At least for wheels having pneumatic tires, it is known to mount a coil on the tire and have a magnet fixed to the vehicle body. However there are often difficulties in mounting to enable the tire to move with its suspension, or steering, and be removable, yet maintain a small spacing between the magnet and coil.

JP patent publication 2004187429 shows a generator for a tire inner pressure detection device. It has a long-length case wound with a coil. The interior of the case forms a slidable movement space wherein a permanent magnet can slidably move by the inertia relative to the case and is tethered by an elastic member. The generator generates power by the electromotive force of the coil generated from the movement of the permanent magnet relative to the coil when the case is displaced by being accelerated or decelerated in the longitudinal direction.

Summary of the Invention

An object of the invention is to provide improved apparatus or methods. According to a first aspect, the invention provides: An electrical power generator for powering circuitry on a vehicle wheel, the generator having: a first part (such as a magnet or electrostatic plates) for generating an energy field (such as a magnetic or electrostatic field), and a second part (such as coils or a dielectric) movable relative to the energy field to generate the electrical power, both the first and the second part being suitable for operation located on the wheel, a mounting for locating one or other of the first and second parts on the wheel and to constrain the respective part to move along a circumferential path around the same axis as that of the wheel, but to allow free fall continuously along the circumferential path as the wheel rotates, the other of the two parts being arranged adjacent to the circumferential path, so that in use the free falling part passes the other of the two parts to generate electrical power. By having both parts mounted on the wheel instead of on other parts of the vehicle, no sliding contacts are needed to conduct the power to the circuitry on the wheel, and relative alignment of the parts is easier to achieve and maintain in all conditions than if one is mounted on a body of the vehicle. This is particularly so if the wheel needs to be detachable, or has suspension, or is steerable for example. By allowing one of the parts to fall freely, the problem of the part causing rotational imbalance, resulting in disturbing vibrations, can be much reduced, for a given mass, compared to use of a tethered part. This reduction occurs partly because the path is circumferential rather than radial and thus oscillation is less likely. The reduction in rotational imbalance is because the part is free to fall along the path and so no rotation frequency dependent disturbance (force) is generated on the axis of the wheel. Free falling is not intended to mean free of any forces, as there will be centrifugal force from the mounting, and frictional drag forces from air or whatever other fluid might be present. Embodiments of the invention can have any other features added, some such additional features are set out in dependent claims and described in more detail below. Another aspect provides a tire pressure management system having the power generator. Another aspect provides a tire having the power generator. Another aspect provides a wheel having the power generator.

Any of the additional features can be combined together and combined with any of the aspects. Other advantages will be apparent to those skilled in the art, especially over other prior art. Numerous variations and modifications can be made without departing from the claims of the present invention. Therefore, it should be clearly understood that the form of the present invention is illustrative only and is not intended to limit the scope of the present invention.

Brief Description of the Drawings :

How the present invention may be put into effect will now be described by way of example with reference to the appended drawings, in which:

Figures 1 to 3 show views of a first embodiment of the invention applied to a wheel having a tire, and Figures 4 to 6 show views of alternative embodiments.

Description of the Preferred Embodiments:

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun e.g. "a" or "an", "the", this includes a plural of that noun unless something else is specifically stated.

The term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

Additional features:

Some additional features are as follows:

The parts can be mounted on a rim of the wheel or a tire or both. On one hand, it is useful to have both parts on a tire so that the tire is self contained, can be monitored over time and need not be matched to a compatible wheel or vehicle. On the other hand, mounting the energy harvesting system on the rim alleviates the need to reinstall the system on each new tire. The energy field generating part can have a magnet for generating a magnetic field. An alternative is using electrostatic generation principles, by movement of a dielectric through an electrostatic field. The circumferential path can be in the form of a circumferential channel suitable for the part mounted to allow free fall to move along. The channel can be formed by inside walls of the tire to reduce a number of parts. Alternatively the circumferential channel can comprise a separate enclosed channel attached to the inside or outside of the tire or the rim of the wheel. This can be valuable to avoid a major redesign of the tire or to retrofit onto existing tires for example. A further alternative is to constrain the movement to circumferential movement by providing a bearing on the same axis as the wheel, and attached to the free falling part by a spoke. For a vehicle wheel this could be attached to the hub cap for example. The free falling part can be the first part for generating the energy field. The first part can be a permanent magnet shaped to roll or slide along the channel. The second part can comprise one or more conductive coils attached to the wheel adjacent to the circumferential path. The coils can be provided symmetrically on opposing sides of the path. The circuitry can comprise tire pressure monitoring circuitry. There can be multiple free falling parts, in different channels, or in the same channel, or a chain of coupled parts in one channel for example.

Issues for the example of a TPMS

A number of issues related to the electromagnetic and other conversion principles for TPMS are listed below:

1. Total weight needs to be very low, as vehicle weight is a critical factor; also. The undamped/unsuspended part of the vehicle decreases comfort and increases failures, maintenance, etc.

2. The magnetic field decreases dramatically with increasing distance between the field generator (magnet or coil) and the secondary coil; the magnetic field should therefore be limited and/or concentrated around the secondary coil;

3. The system should be EMC compatible, i.e. not influence nor be influenced by other sub-systems (rim, vehicle chassis, wheel axis, electronics, etc);

4. The system should not add any unbalance to the rotating parts, nor any noticeable inertia (for minimum consumption and maximum performance and comfort the tire and rim mass should be minimized, because T=J . d{omega}/dt, so torque T ~ inertia J);

5. General applicability without major vehicle adjustments is usually required (for a versatile system). The system should preferably fit on any type of car or other vehicle without major adjustments of the car or the tire itself, which should maintain its properties unchanged (elasticity, temperature resistant, etc);

6. The tire shape should not matter much for the TPMS system performance; and

7. The TPMS should be able to withstand the elevated temperatures of the vulcanization process required in tire fabrication integration within the tire if possible. 8. The system should be able to be inspected, diagnosed and repaired/replaced by a skilled mechanic, without special skills required. Figs 1-3: A first embodiment of the invention.

Figures 1 to 3 show views of a vehicle wheel showing some parts of an embodiment of the invention having a mobile, freely moving magnetic part 40 and one or more coils 30 attached to the tire. The magnetic part is an example of the first part for generating an energy field. The coils are an example of the second part movable relative to the energy field. The system could be mounted either on the tire 20 itself, or onto the rim 10. The magnet is free to slide or rotate within a partly or fully closed channel 50. The channel is an example of the mounting for locating the first part on the wheel, which constrains the free falling part to fall along a circumferential path. The coil or coils 30 is (are) mechanically attached to the rotatable wheel (for example either the rim or the tire) and coupled electrically to circuitry in the form of electronics for refining the power supply, and for carrying out various functions such as sensing, amplification, signal conditioning, radio transmission and so on. In embodiments of the invention, the magnets could be adjacent to the path, and the coils in the free falling part. In this case the circuitry would be in the free falling part, which could be feasible if it communicates by radio to the rest of the vehicle.

Figure 2 shows a view of the same embodiment. The forces on the magnet are illustrated to show the working principle: a certain vehicle speed corresponds to a typical angular velocity ω of the tire. Inside the channel, the magnet encounters a drag force, F_d which depends strongly on the angular velocity. When a local/global equilibrium of the dynamics exists, it is mainly formed by a relation between the drag component on the magnet and a gravitation force F_g on the magnet. This force has a radial component and a circumferential component. The circumferential component will oppose the drag force. In equilibrium, the wheel rotates and the magnet will be dragged up, thus increasing a radial angle α which represents how far from the vertical is a radius passing through the magnet. Depending on the drag, this angle may reach a constant value when the drag is balanced by the circumferential component. This should be smaller than 90 degrees, but even if it exceeds 90 or even 180 degrees, power generation can still occur. Each time the magnet passes (one of) the coil(s), a current is induced due to the electromagnetic coupling in the coil.

The magnet is constrained within a channel 50 which creates the circumferential path for the magnet, and may have sides and an outer runway 53 and an inner runway 51. These may enclose the channel entirely, or may leave an opening in the inner runway, since the magnet should always be impelled against the outer runway by gravity and the centrifugal force.

Figure 3 shows a cross section view of a tire 20 according to the same embodiment. It shows the channel inside the tire, though it could in principle be located on an outside surface of the tire. The runways 51 and 53 are shown above and below the channel.

The induction coil or coils are arranged on the sides of the channel, though they could be adjacent to the runways. The coils are coupled to circuitry 57. This circuitry can include power generator circuitry as well as functional circuitry. The circuitry can be located anywhere. It should communicate in some wireless fashion with the rest of the vehicle, such as by radio or optical communications.

This example addresses some of the issues described above as follows:

1. the total weight per scavenging system can be reduced down to a few hundred grams or down to a few tens of grams or below 10 or below 5 grams in some cases, of which the most weight does not contribute to rotational inertia and thus does not unbalance the tire;

2. the distance between the coil(s) and the magnet can be minimal, so the coupling will be increased and thus power conversion is more efficient even for small (and thus lighter) magnets.

3. due to the reduced magnet size, there will be no noticeable interaction with other external magnetic fields from the environment;

4. the additional inertia is very small due to the small magnet mass and it does not add to the rotational inertia of the wheel;

5. in the case that the system is mounted on the rim, only the wheel rims need to be serviced and the system can be easily mounted on most types of rims; 6. in the case of mounting onto/into the tire itself, servicing and/or replacement can take place once the tire is off the rim or when it is being replaced; 7. in the case of system attachment to the rim, the tire shape does not influence performance. If the system is put on the tire instead, at equilibrium the magnet angle is constant with respect to the wheel axis, so a deflated tire would not influence the magnet position, nor will it create any periodic disturbance, which could result in imbalance and thus unwanted vibrations. Figs 4 to 6: Some alternative embodiments.

The magnet being shaped as a sphere or cylinder suitable for rotating is not strictly necessary. Instead, an aerodynamically shaped magnet could also be used, which is hovering (instead of sliding) at higher velocities (as shown in Figure 4). Other shapes suitable for sliding can be envisaged. The shape may be optimized to reduce frictional drag forces. The cross sectional profile of the channel is shown as rectangular, but can be other shapes such as circular or elliptical for example. The channel can be formed of a material of similar flexibility to that of the tire, so that it deforms with the tire. Or the channel can be formed of moulded rubber, and moulded at the same time as making the tire. Alternatively it can be made separately and attached to the tire after manufacture, either inside or outside the tire.

Figure 5 shows another alternative embodiment in which the channel is no longer needed. The free falling part in the form of the magnet is instead mounted on a mounting formed by a bearing 60 and a spoke 70. It is thus constrained to fall freely along a similar circumferential path in the same way as is achieved by the channel. The bearing and spoke can, in embodiments of the present invention, be located inside the tire. In other, easier embodiments, it can be fit to the outside of a tire, perhaps by fitting onto a hubcap, depending on the type of wheel. The coils can be located to the sides of the path, or on the side of the tread of the tire. In this example, the coils could alternatively or additionally be located on the rim (10) of the wheel rather than the tire. The spoke could in principle be implemented as a disc having the center of gravity below the wheel axis, with many magnets around its periphery.

Figure 6 shows another alternative embodiment. In this case there is no separate channel, but the inside of the tire 20 is used as to constrain the magnet to a circumferential path. The coils in this case are located on an inner surface of the tire. Alternatively, the coils could be part of a thin, additional flexible layer that is being glued inside the tire after the tire fabrication. The magnet could be shaped to cover more of the width of the tire. There may be less power generated if the magnetic part is much smaller than the width of the tire. But without a separate channel or a bearing and spoke, there is less to manufacture and less to wear out or become deformed in use.

The power generator can include power conversion circuitry such as AC/DC conversion and DC/DC conversion circuitry as needed. This can enable the voltage or voltages needed for the circuitry such as a pressure sensor, temperature sensor, acceleration sensor, control circuitry, signal amplifier circuitry, and radio transmitter circuitry to be supplied as desired according to the application. A power storage element such as a capacitor or rechargeable battery may be used to operate the circuitry even when the vehicle is not moving, and to smooth out pulses in the generated power. Other forms of power generation can be combined such as solar or thermal generators.

The power generator and other circuitry can be enclosed and sealed in a casing to protect it from external shocks, humidity, instantaneous temperature peaks and more. The circuitry can be arranged to condition sensing signals and output them at predetermined or arbitrary time intervals and in a predetermined format for example, to the control and monitoring circuitry on the vehicle Other variations can be envisaged within the scope of the claims.

Claims

Claims:

1. An electrical power generator for powering circuitry (70) on a vehicle wheel (10, 20), the generator having: a first part (40) for generating an energy field, and a second part (30) movable relative to said energy field to generate the electrical power, both the first and the second part being suitable for operation located on the wheel, a mounting (50, 51, 53, 60, 70) for locating one or other of the first and second parts on the wheel and to constrain the respective part to move along a circumferential path around the same axis as that of the wheel, but to allow free fall continuously along the circumferential path as the wheel rotates, the other of the two parts being arranged adjacent to the circumferential path, so that in use the free falling part passes the other of the two parts to generate the electrical power.

2. The power generator of claim 1, the parts being suitable for locating on a tire (20) of the wheel.

3. The power generator of claim 1 or 2, the energy field generating part having a magnet (40) for generating a magnetic field.

4. The power generator of any preceding claim, the circumferential path comprising a circumferential channel (50, 20) suitable for the free falling part to fall freely along as the wheel rotates.

5. The power generator of claim 4, the circumferential channel comprising a separate enclosed channel (50) for attaching to the wheel.

6. The power generator of any preceding claim, the free falling part being the first part for generating the energy field.

7. The power generator of claim 6, the first part being a permanent magnet.

8. The power generator of claim 7, the magnet being shaped to roll along the circumferential path.

9. The power generator of claim 7, the magnet being shaped to slide along the circumferential path.

10. The power generator of claim 7, the other of the two parts comprising one or more conductive coils (30).

11. The power generator of any preceding claim arranged to constrain the movement to circumferential movement by providing a bearing on the same axis as the wheel, and a spoke attaching the free falling part to the bearing.

12. A tire pressure monitoring system comprising tire pressure monitoring circuitry (57), and the power generator according to any preceding claim.

13. A tire having circuitry mounted on the tire, and having the power generator of any of claims 1 to 11.

14. The tire of claim 13, having the power generator of claim 4, the channel being formed by inside walls of the tire.

15. A wheel having circuitry (57) mounted on the wheel, and having the power generator of any of claims 1 to 12.