Patent Application
20220020973
With roads becoming more and more congested, it would be desirable to develop alternative modes of travel, including such as aircraft that are easier and/or simpler to fly. In particular, electric vertical take-off and landing (eVTOL) vehicles are attractive because they do not require long runways and therefore can be deployed in and conveniently accessed in urban environments. Naturally, as such vehicles are prototyped and tested, various parts or components of such vehicles will be improved for better performance.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.
The invention can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer readable storage medium; and/or a processor, such as a processor configured to execute instructions stored on and/or provided by a memory coupled to the processor. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. Unless stated otherwise, a component such as a processor or a memory described as being configured to perform a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions.
A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
Various embodiments of a new battery system with cylindrical cells are described herein. In some embodiments, the battery system includes a plurality of cylindrical cells, including a first cylindrical cell and a second cylindrical cell, and an electrical tab that is connected to the first cylindrical cell and the second cylindrical cell using spot welding. The battery system also includes a battery management printed circuit board, where the electrical tab provides a connecting surface for a battery management signal between (1) the first cylindrical cell and the second cylindrical cell and (2) the battery management printed circuit board. As will be described in more detail below, the battery system with cylindrical cells described herein was developed as a second generation solution to an existing battery system (without cylindrical cells) used by an ultralight and overwater electric vertical take-off and landing (eVTOL) vehicle. As a result, the battery system with cylindrical cells is required to meet or otherwise have certain characteristics. Before describing the battery system with cylindrical cells it may be helpful to first describe the vehicle that it is used in and developed for.
The booms (108) provide a support for the outboard motors (e.g., 104) and also couple or otherwise connect the fuselage (110) and floats (e.g., 106a). They are not, however, wings, and all (or at least almost all) of the vertical lift to keep the vehicle airborne is provided by the motors. As such, motor and battery redundancy and reliability are important design considerations, as is battery weight (e.g., for vehicle range).
For safety, the exemplary vehicle is capable of taking off from and/or landing on water, if desired. To that end, the floats (106a) provide the necessary buoyancy to keep the vehicle afloat on water and permit water takeoffs and/or landing, if desired. For example, in some applications, it may be desirable to restrict the exemplary vehicle to overwater flight since it may be safer for the vehicle to crash in water as opposed to solid ground (e.g., the pilot is more likely to survive a crash over water). To prevent water intrusion into the floats (e.g., 106a), access panels (e.g., 152a) to access batteries and other components inside the floats are located on the top surface of the floats. If desired, the vehicle can alternatively take off from and/or land on land.
The eVTOL vehicle shown is an ultralight, relatively compact aircraft that weighs 250 lbs. without a pilot where the batteries collectively weigh ˜120 lbs. out of that total. The footprint of the vehicle is also relatively small to permit the vehicle to fit into a (standard) trailer (e.g., sideways, boom tips first) with a nose-to-tail length of ˜88 inches. As a result, the batteries (150a-150e) need to similarly be relatively light and relatively compact.
The following figure shows an initial version of the batteries with pouch cells.
To secure the battery system to the vehicle, the battery system has four feet (206) through which a bolt or other fastener (not shown) is screwed to secure the battery system to a shelf (not shown) in the float which all of the batteries sit on and are secured to.
In this example, a battery has the following dimensions:
Batteries that are designed for electric cars tend to have thousands of cells arranged in a single large, high voltage pack (e.g., 350V-600V) to maximize power output despite the relatively high weight (e.g., 1,054 lbs.). In contrast, the batteries described herein (which are designed for electric aircraft) have much lower voltages (e.g., on the order of 100V) designed to have multiple batteries for redundancy and safety (e.g., one battery per motor) instead of a single battery for the entire vehicle. Battery weight is also an important consideration in aircraft applications, and especially for the ultralight eVTOL vehicle described above. The (maximum) power delivery of the electric aircraft batteries described herein is also an important consideration for aircraft and especially for eVTOL vehicles during the power-hungry vertical take-offs and landings.
Electric car batteries also tend to use energy dense cells (e.g., cells with energy densities above 245 Wh/kg) to maximize electric car range but the downside of such cells is that such energy dense cells used limit or otherwise reduce the maximum power output. In contrast, maximum power output is an important consideration for electric aircraft and especially for eVTOL vehicles (e.g., vertical take-offs and landings are very power-hungry operations). In addition, due to the smaller, redundant, and lighter nature of batteries for electric aircraft, cells in electric aircraft batteries are expected to individually contribute a larger percentage of the power load and therefore are capable of high rate discharges.
Finally, electric car batteries tend to have cooling systems designed to keep the battery in some desired temperature range (e.g., 20° C.-40° C.) to maximize the lifetime of the battery. However, these cooling systems add weight and are much more undesirable in aircraft. As such, the aircraft batteries described herein do not operate with a cooler (e.g., the floats of the aircraft described above do not include cooling systems to cool the batteries during flight).
The battery system shown in
As described in Table 2, the cylindrical cells used in battery system 300 have a number of advantages over the pouch cells used in the battery system in
Also, the pouch cells are less robust (e.g., externally) compared to the cylindrical cells. Whereas cylindrical cells already have a hard, metal cylindrical case which protects cylindrical cells from punctures or other damage, pouch cells are in a flexible or bendable wrapper that can be pierced or otherwise damaged. As a result, pouch cells require additional and/or external protection which in turn increases the total weight of the battery system. And even without taking the additional weight to protect the softer pouch cells into account, each pouch cell weighs 14 g more than each cylindrical cell.
The energy density of cylindrical cells is also higher (i.e., better) than pouch cells at 230 Wh/kg to 221 Wh/kg. In aircraft applications, additional weight reduces range or flight time and so a battery cell with a higher energy density is more desirable.
The nickel-based chemistry of the cylindrical cells also means that cylindrical cells have better stability than pouch cells at high discharge rates and temperatures. In other words, cylindrical cells have a wider charging and discharging operating temperature range compared to pouch cells.
In this example, the battery system (300) includes 63 cylindrical cells (e.g., 302a-302c) which are held in place by an open frame comprising two end plates (304a and 304b). Structurally, the rigid external case of the cylindrical cells is leveraged or otherwise taken advantage of to provide structural support for the battery system as a whole. For example, this exposed frame would not work with cells that are floppy and/or not rigid. In some embodiments, there are no (e.g., additional) structural elements connecting or linking the two end plates beyond the cylindrical cells.
Electrically, the cylindrical cells are arranged or otherwise connected in a 3-in-parallel, 21-in-series (3p21s) arrangement where groups of three cylindrical cells (e.g., 302a-302c) first are electrically connected together in parallel and then the 21 groups of three cylindrical cells are connected together in series.
The two end plates (304a and 304b) include access channels or cutouts (306) which provide access to the positive and negative terminals of the cylindrical cells. An electrical tab (the position of which is indicated by dashed outlines 308a and 308b) fits into the cutouts (e.g., 306) and is connected to the positive or negative terminals of the cylindrical cells using spot welding (at least in this example). To preserve the readability of the drawing, electrical tabs are not shown throughout this drawing. Using spot welding to connect the cylindrical cells to the electrical tab is attractive because it is relatively cheap and simple (e.g., spot welding equipment costs on the order of tens of thousands of dollars). It is also suitable for lower voltage (e.g., low hundreds of volts) and/or a power architecture which uses many smaller batteries (see, e.g.,
The battery system also includes a battery management printed circuit board (not shown here to preserve the readability of the diagram) where the electrical tab (e.g., 308a and 308b) provides a connecting surface for a battery management signal between cylindrical cells (e.g., 302a-302c) and the battery management printed circuit board. For example, this connection may be monitored and/or used by the battery management system to measure or generate health and/or state information about (as an example) those cylindrical cells (e.g., information specific to a group of three in-parallel cylindrical cells) or all of the cylindrical cells (e.g., as a whole or collectively).
In contrast, the battery-holding holes, which are represented by dashed circles (e.g., 342), have circular cross sections that do not go through the end plate entirely except where they overlap with the cutouts (e.g., 340). This provides a lip or shelf to hold the cylindrical cells in place while still providing access to the positive and negative terminals of the cylindrical cells.
Returning briefly to
The example battery system described in
To minimize the dimensions of the electrical tabs and/or other wiring or connections (which is desirable), each electrical tab (e.g., 406a and 406b) connects cylindrical cells from multiple rows as well as multiple groups of two in-parallel cylindrical cells. To help keep the dimensions of the electrical tabs small, each cylindrical cell alternates direction (e.g., going from left to right along each row). As a result, exemplary electrical tab 406a is connected to the positive terminals of cylindrical cells 402a and 402b (which are in different rows) and the negative terminals of cylindrical cells 402c and 402d (which are also in different rows) where cylindrical cells 402a and 402b form one group of in-parallel cells and cylindrical cells 402c and 402d form another group of in-parallel cells.
In the case of electrical tab 406b, cylindrical cells from four different rows are connected. In that example, cylindrical cells 402e and 402f form one group of in-parallel cells and cylindrical cells 402g and 402h form another group of in-parallel cells.
Thus, each electrical tab (e.g., 406a and 406b) is used to create both an in-parallel connection (e.g., connecting one group's negative terminals to each other and the other group's positive terminals to each other) as well as an in-series connection (e.g., the connection between the first group's positive terminals and the other group's negative terminals). Compared to the example battery system (300) described in
Whereas the battery system embodiment described in
Another difference is that electrically, battery system 400 has a higher voltage. For example, if a single cylindrical cell has a nominal voltage of 3.6V, then the total voltage produced by battery system 400 is 3.6 V×36=129.6 V, which is higher than battery system 300 in
Returning briefly to the example vehicle shown in
In such an application (and even in other applications or usage scenarios), it is desirable if vehicle charging time could be reduced or otherwise improved. For a fleet of on-demand personal transportation vehicles, this would increase the duty cycle or up time of each vehicle and permit more people to be supported or flown given the same number of vehicles. Even for a single, dedicated user, faster charging times would be attractive, for example, for longer and/or intercity trips. With the battery embodiments described above, one limitation to improving charging time is that the batteries generate significant heat during flight that needs to be dissipated before charging can begin (i.e., the batteries need to be cooled to an acceptable charging temperature before charging can begin).
The solution to this (with the battery embodiments described above) is to open the access panels (e.g., 152a in
In this application, the batteries are accessed from above because the access panels (e.g., 152a in
The swappable battery system is held in place using slide-in brackets (506a) in the float, vertical guide rails (508a) on the exterior of the case (502a), and retaining clips (510a) which are separate from the slide-in brackets (506a) and case (502a) and are used to secure the case (502a) to the slide-in brackets (506a). (The following figures describe in more detail how these components are used to hold the swappable battery system in place.)
It is noted that the slide-in brackets (506a) and case (502a) have any asymmetry which may make it easier to distinguish which side of the case contains the battery management system and/or PCB if it is not apparent from a particular drawing. The cylindrical cells are much heavier than the battery management system and/or PCB and so to properly secure the heavier cylindrical cells, the slide-in brackets (506a) are aligned with and/or placed beneath the heavier cylindrical cells inside the case. As a result, the slide-in brackets (506a) on the heavier side of the case (516a), which in this view is facing the viewer and does not have the PCB, extend almost fully to the edge of the heavier side of the case (516a). In contrast, on the lighter side of the case (514a), which in this view is facing away from the viewer and has the PCB, the slide-in brackets (506a) do not extend fully to the lighter side (514a) and so the case appears to protrude more (e.g., from the slide-in brackets) on that side.
In this example, the battery system (500a) also includes a display (512a) which presents or otherwise displays information associated with the management, health, and/or state of the battery system. Older versions of the battery system did not have a display. To make the display easily visible when the swappable battery system is in the float, the display is located on the top surface of the case. Naturally, the display may be used when the battery is outside of the float (e.g., on a charging rack being charged, after charging while awaiting insertion into a float, etc.). In this example, the display is coupled to a battery management system in the case which collects, measures, and/or generates information about the battery. Some examples of information from the battery management system which is displayed by display (512a) include battery charge (e.g., percent charged), battery temperature, error codes from the most recent flight. This information may, for example, let a technician know which batteries are near or at end-of-life, which ones are fully charged, which ones are sufficiently cooled (e.g., for performance and/or to extend the lifetime of the battery it may be desirable to swap in batteries that are at or below some desired temperature), etc.
The top of the case also includes screw terminals (e.g., positive terminals 517a and negative terminals 518a) to electrically connect the power supply from the battery to the vehicle. For example, a float may include 5 power cables, one for each of the batteries in that float. The ends of the power cables may be inserted into and/or otherwise coupled to screw terminals (517a and 518a) to supply power from that battery to the vehicle. Naturally, in some other embodiments, other types of interfaces and/or connectors may be used. Other screw terminals may be associated with other signals (e.g., control signals to the battery management system from the flight controller, data signals from the battery management system to the flight controller, etc.).
The following figures show how the exemplary battery system shown here (500a) is inserted or otherwise connected to the vehicle.
As described above, even with improvements, it is estimated that it will take ˜40 minutes to cool and charge a battery if the battery were to remain within the float when charged on the ground. With the swappable battery system example described above, it is possible for all 10 of the batteries to be swapped out for fully charged batteries in less time than it would take to cool and charge the batteries in the float, even with improvements (e.g., less than ˜40 minutes). As described above, for applications in which the vehicle is part of a fleet of autonomous vehicles to transport people (and even applications where a single user owns or uses a given vehicle), it is desirable to reduce down time.
Another benefit is that the features shown here which make it easier to swap batteries in and out may also lighter, less expensive, and/or less complex than components or structures that would be required (as an example) to support liquid cooling of batteries. For example, it would require ˜20 lbs. of dielectric oil to cool 10 batteries and with an ultralight vehicle this is a significant increase in weight.
In some embodiments, the access panels (e.g., 602) on the top of the float double as the lid or handle for each swappable battery pack. For example, a technician would first unlock or otherwise unlatch the access panel by inserting and turning a key or lever which relieves the downward pressure on the panel against the float and then electrically and physically decouple the swappable battery pack from the vehicle by pulling straight up on a handle that would be on the top of the access panel so that there is no need to remove wires in this case. Once the appropriate locks, latches, and/or connectors have been unlocked or released, a technician grabs a handle (not shown) on the access panel and removes the battery, as well as the access panel. A fully charged battery with its attached access panel is then inserted into the float.
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.
