Patent Application
20130033224
Electric vehicle energy storage systems are normally recharged using direct contact conductors between an alternating current (AC) source such as is found in most homes in the form of electrical outlets; nominally 120 or 240 VAC. A well known example of a direct contact conductor is a two or three pronged plug normally found with any electrical device. Manually plugging a two or three pronged plug from a charging device to the electric automobile requires that conductors carrying potentially lethal voltages be handled. In addition, the conductors may be exposed, tampered with, or damaged, or otherwise present hazards to the operator or other naïve subjects in the vicinity of the charging vehicle. Although most household current is about 120 VAC single phase, in order to recharge electric vehicle batteries in a reasonable amount of time (two-four hours), it is anticipated that a connection to a 240 VAC source would be required because of the size and capacity of such batteries. Household current from a 240 VAC source is used in most electric clothes dryers and clothes washing machines. The owner/user of the electric vehicle would then be required to manually interact with the higher voltage three pronged plug and connect it at the beginning of the charging cycle, and disconnect it at the end of the charging cycle. The connection and disconnection of three pronged plugs carrying 240 VAC presents an inconvenient and potentially hazardous method of vehicle interface, particularly in inclement weather.
In order to alleviate the problem of using two or three pronged conductors, inductive charging systems have been developed in order to transfer power to the electric vehicle. Inductive charging, as is known to those of skill in the art, utilizes a transformer having primary and secondary windings to charge the battery of the vehicle. The primary winding is mounted in a stationary charging unit where the vehicle is stored and the secondary winding is mounted on the vehicle
To maximize efficiency, it is important that the secondary winding on the vehicle be aligned with the primary winding in the stationary charging unit. The present invention relates to inductive proximity charging. More particularly, the invention relates to a system and for assisting the operator with positioning the vehicle so that the secondary winding thereon is in close proximity and aligned with the stationary primary winding for efficient inductive charging of the vehicle.
Inductive charging systems are well known in the prior art. For example, the Partovi US patent application publication No. 2009/0096413 discloses an inductive charging system in which includes a base unit containing a primary coil and mobile device including a secondary winding. To assist with alignment of the mobile device and the base unit, a plurality of alignment magnets are provided behind each coil. The magnets behind the primary and secondary coils are arranged in pairs, respectively, with the poles of each pair being opposite so that the magnets will attract and thus align the coils.
While the prior devices operate satisfactorily, they are not suitable for use in vehicle charging systems. First, the magnets add unnecessary weight to the vehicle coil which decreases the efficiency of the vehicle. Second, the magnets are not strong enough to reposition the vehicle or base unit relative to one another. Third, the magnets generate eddy currents which lead to heating and power loss. While eddy currents may be reduced by providing the magnets in two or more sections with a gap in between, this further increases the cost of the magnets.
The present invention was developed in order to overcome these and other drawbacks of the prior alignment techniques by providing an alignment apparatus which assists the operator of a vehicle in positioning the vehicle so that the secondary coil mounted thereon is in close proximity to and aligned with the stationary primary coil in the base unit for maximum inductive energy transfer to a battery charger on the vehicle.
Accordingly, it is a primary object of the invention to provide a method and apparatus for aligning a vehicle with an inductive charging system. The apparatus includes a transformer having a stationary primary coil and a secondary coil mounted on the vehicle. A plurality of alignment coils are equally spaced in the vicinity of the secondary coil. When the primary coil is energized, it generates a magnetic field which induces voltage in the alignment coils as a function of the proximity of each alignment coil to the central axis of the primary coil. The alignment coils are connected with a controller which generates an output signal corresponding to the position of the vehicle relative to the primary coil. The output signal is utilized to communicate information, via a display or the like, which is used by the operator of the vehicle to position the vehicle so that the secondary coil and primary coils are axially aligned.
The alignment coils each have the same diameter which is significantly less than the diameter of the secondary coil. The alignment coils are arranged symmetrically within the vicinity of the secondary coil and have axes which are parallel to the axis of the secondary coil.
A voltage sensor is connected with each alignment coil for measuring the voltage induced in each alignment coil by the primary coil. The voltage sensors are connected with a comparator within the controller. The comparator measures the voltage differential between the voltage sensors to generate a directional signal relative to the axis of the secondary coil. The directional signal contains information which is communicated either wirelessly to an external display or directly to a display within the vehicle to provide a visual indication to the vehicle operator of the direction that the vehicle must be moved in order to bring the vehicle secondary coil into alignment with the stationary primary coil.
The alignment system according to the invention can also be used to determine the presence of foreign metal objects within the inductive poles of the primary and secondary coils. This enables the charging system to be disabled when foreign metal objects are present in order to eliminate the risk of fire or injury resulting from overheating such objects during the charging process.
Other objects and advantages of the present invention will become apparent from a study of the following specification when read in conjunction with the accompanying drawing, in which:
Referring first to
The system for positioning the vehicle to align the vehicle secondary coil 8 with the stationary primary coil 6 will be described with reference to
The alignment coils are symmetrically arranged in the vicinity of the secondary coil. In a preferred embodiment shown in
In an alternate embodiment, the alignment coils may be arranged externally of the secondary coil. In either embodiment, the alignment coils are eqully spaced from each other in a symmetrical arrangement relative to the secondary coil as will be developed in greater detail below.
Referring now to
Preferably, an even number of alignment coils are provided, with the coils on opposite sides of the secondary coil being paired. Thus, in the embodiment shown in
As noted above, the charging station 2 is connected with a power source 12. The power source is preferably a 220 volt AC supply operating at between 50 and 60 Hz. For operation of the alignment system according to the invention, the primary coil 6 is initially energized by the power source and charging station at a reduced voltage so that the magnetic field 10 is produced which is symmetric about the axis of the primary coil. The alignment cols are arranged in the secondary coil so that the magnetic flux produced by the stationary primary coil 6 induces a voltage in each alignment coil which is proportional to its proximity to the center of the primary coil. The voltage sensors 20 measure the relative amount of voltage induced in each alignment coil, and the comparator determines the direction of misalignment based on the voltage differential in the opposed pairs of coils. For example, if the vehicle mounted secondary coil 8 is positioned relative to the stationary primary coil 6 as shown in
It will be appreciated that the alignment system according to the invention may be provided with only a single pair of opposed alignment coils if only two-direction misalignment information is desired. Additional pairs of alignment coils may be provided for more precise alignment information.
The inductive charging system may complement a conventional conductive charger. The controller 16 is operable to control both types of charging as well as operation of the alignment system. A transfer switch (not shown) on the controller is operable to isolate the charging sources to prevent the user from simultaneously using both inductive and conduction recharging systems.
While the preferred forms and embodiments of the present invention have been illustrated and described, it will be readily apparent to those skilled in the art that various changes and modifications may be made without deviating from the inventive concepts set forth above.
