Fuel Supply Apparatus
The present disclosure relates to a fuel supply apparatus. In particular, it relates to a
hydrogen supply apparatus for an electrochemical fuel cell. The invention also relates to
a fluid store for a fuel supply apparatus and a method of supplying a fuel.
A fuel supply apparatus is useful for supplying hydrogen as fuel to hydrogen-consuming
devices such as electrochemical fuel cells, which use the hydrogen to generate electrical
power. It is desirable to have a safe and controllable source of hydrogen.
A known type of fuel supply apparatus comprises a hydrogen gas supply apparatus that
releases hydrogen on demand by the reaction of a reactant fuel material, such as a
stabilized alkali metal material, contained within a reaction chamber, with an activation
fluid of aqueous solution or water supplied from a water chamber. As activation fluid is
fed into the reaction chamber, hydrogen gas is generated and can be draw off through
an outlet for consumption by the fuel cell. It is common for said apparatus to include a
pump and valves to control the flow of activation fluid into the reaction chamber.
It is important that the reaction within the fuel supply apparatus is easily controlled to
ensure sufficient hydrogen is generated to meet demand. It is also important that the
fuel supply apparatus is reliable and easy to manufacture.
In accordance with a first aspect of the invention there is provided a fuel supply
apparatus comprising;
a reaction chamber for hosting a reaction when a fuel generating fluid and a fuel
generating substance are brought together to generate fuel,
a plurality of discrete fuel generating fluid chambers, each chamber being separately
rupturable; and,
a heater assembly adapted to, when in use, selectively rupture the fuel generating fluid
chambers to supply the fuel generating fluid to the reaction chamber.
This is advantageous as the apparatus can activate the heater assembly to selectively
rupture the fluid chambers to provide the fuel generating fluid to the reaction chamber.
Preferably, the fuel generating fluid comprises an activation fluid and the fuel generating
substance comprises a fuel source. This is advantageous as the activation fluid and the
fuel source can react together in the reaction chamber to generate fuel when the
chambers are ruptured in use. Alternatively, the fuel generating fluid may comprise a
fuel source fluid and the second fuel generating substance may comprise a catalyst for
catalysing the fuel source fluid to generate fuel. This is advantageous as when the fuel
generating fluid chambers are ruptured, the fuel source fluid can flow to meet the catalyst
and generate fuel in the reaction chamber.
The heater assembly may comprise a plurality of heaters arranged such that each fuel
generating fluid chamber is associated with at least one heater for heating, and thereby
rupturing, said fuel generating fluid chamber.
The heaters may form part of the plurality of discrete fuel generating fluid chambers.
Alternatively, the heaters may be formed on part of the fuel supply apparatus and
arranged adjacent the plurality of discrete fuel generating fluid chambers and configured
such that they can be selectively activated. The fuel generating fluid chambers may
each be associated with at least one heater.
The discrete fuel generating fluid chambers may comprise a plurality of sealed bladders.
The bladders may be formed in a sheet, each bladder containing fuel generating fluid
and being separately rupturable. In particular, the sheet may be of at least two film
layers, the layers sealed together at localised portions to define the plurality of bladders.
The heater assembly may be printed onto the film sheet.
The heater assembly may include power receiving terminals for electrically connecting to
the fuel supply apparatus for receiving power therefrom.
The heater assembly may also be configured to heat the fuel generating fluid. A heated
fuel generating fluid may assist the reaction, for producing hydrogen for example. In
particular, the heaters may be configured to rupture the discrete chambers and vaporise
the fuel generating fluid therein.
The fuel supply apparatus may include a flow control device to control the rate at which
the fuel generating fluid is introduced to the reaction chamber. The flow control device
may comprise an absorbent layer between the discrete chambers and the reaction
chamber for controlling the rate at which the fuel generating fluid reaches the fuel source.
Each heater may have two terminals, a common terminal and an individual terminal,
wherein each of the common terminals are connected to a common shared conductor,
the heaters configured such that a heater can be activated by supplying power between
the shared conductor and its individual terminal.
The fuel generating fluid chambers and associated heaters may be arranged in a grid,
the grid comprising rows and columns, and including a shared conductor for each row
and a shared conductor for each column, the heaters connected to the shared conductor
for the row in which they are positioned and connected to the shared conductor for the
column in which they are positioned, the grid configured such that a particular heater can
be activated by supplying power between the shared conductors for its row and column.
The fuel supply apparatus may include a fuel generating fluid chamber pressurisation
assembly for applying pressure to the fuel generating fluid in the chambers. The
pressurisation assembly may comprise a bias member to physically press against the
chambers, a mount to stretch a film sheet in which the chambers are formed, or the
chambers themselves may be filled such that the fluid pressure elastically stretches a
film sheet in which the chambers are formed. Applying pressure to each chamber is
advantageous as it aids the efficient ejection of the fuel generating fluid from the
chamber once it is ruptured.
The fluid supply apparatus may include a controller configured to monitor the demand for
fuel and, in response to the monitored demand, rupture at least one fuel generating fluid
chamber.
The fuel supply apparatus may be a hydrogen fuel supply apparatus. The fuel
generating fluid may be water or an aqueous solution. The reaction chamber may
include the fuel generating substance. The fuel generating substance may comprise a
stabilized alkali metal material. The fuel generating substance may be solid, powdered,
granulated or other dry form.
According to a further aspect of the invention, we provide a fluid store for use with the
fuel supply apparatus of the first aspect of the invention, the fluid store comprising a
plurality of discrete fuel generating fluid chambers, each fuel generating fluid chamber
containing fuel generating fluid and being separately rupturable.
The discrete fuel generating fluid chambers may comprise a plurality of sealed bladders
formed on a sheet, each bladder containing a fuel generating fluid, such as an activation
fluid, and being separately rupturable. In particular, the sheet may be of at least two film
layers, the layers sealed together at localised portions to define the plurality of bladders.
This is advantageous as the flexible sheet can be arranged in various configurations to fit
within a fuel supply apparatus.
The fluid store may include a heater assembly comprising a plurality of heaters, each fuel
generating fluid chamber associated with at least one heater.
The heater assembly may be printed onto the film sheet.
The heater assembly may include power receiving terminals for electrically connecting to
a fuel supply apparatus for receiving power therefrom.
The heaters may also be configured to heat the fuel generating fluid. In particular, the
heaters may be configured to rupture the chambers and vaporise the fluid therein.
According to a further aspect of the invention, there is provided a method of supplying a
fuel for use in a fuel cell, the method including the steps of;
providing a plurality of discrete fuel generating fluid chambers, each fluid
chamber containing fuel generating fluid and being separately rupturable;
providing a fuel generating substance which, in combination with the fuel
generating fluid can generate a fuel; and
rupturing at least one fuel generating fluid chamber to transfer the fuel generating
fluid to the fuel generating substance for generating the fuel.
A description is now given, by way of example only, with reference to the accompanying
drawings, in which;
figure 1 shows a diagrammatic view of an exemplary embodiment of a fuel supply
apparatus of the invention;
figure 2 shows one of the fuel generating fluid chambers shown in figure ;
figure 3 illustrates an embodiment of an array of fuel generating fluid chambers;
figure 4 illustrates a further embodiment of an array of fuel generating fluid
chambers;
figure 5 illustrates a still further embodiment of an array of fuel generating fluid
chambers; and
figure 6 illustrates an exemplary embodiment of the method of the invention.
A diagrammatic view of an embodiment of a section of a fuel supply apparatus 100 is
shown in Figure 1. The apparatus of this exemplary embodiment uses the reaction
between a fuel generating fluid (an activation fluid) and a fuel generating substance (a
fuel source). The apparatus 100 includes a reaction chamber 101 containing the fuel
source 102, which can be activated with an activation fluid to generate fuel. In this
embodiment, the fuel source 102 comprises sodium borohydride, although any other fuel
source 102 (hydrogen generating or otherwise) could be used. The apparatus 100
further comprises a plurality of discrete fuel generating fluid chambers 103a-d each
containing activation fluid and therefore referred to hereafter as activation fluid
chambers. In this embodiment, the activation fluid is water, although it could be any
other suitable fluid. A heater assembly comprising a plurality of heaters 104a-d is
provided. The heaters 104a-d can be selectively activated to rupture the activation fluid
chamber 103a-d with which they are associated. Once ruptured, the activation fluid can
flow from its chamber to react with the fuel source 102. Thus, in this example, the
aqueous activation fluid will react with the sodium borohydride and generate hydrogen
for fuelling an electrochemical fuel cell.
In this embodiment, each activation fluid chamber 103a-d is associated with one
heater 104a-d. The activation fluid chambers are formed in a film sheet 105 comprising
two film layers, such as a double skinned polyester film. The layers are sealed together
at localised regions 106 to define the activation fluid chambers 103a-d. The
chambers 103a-d thus take the form of bladders or pockets in the film sheet 105 that are
filled with activation fluid. The bladders 103a-d may be arranged side by side with
borders of sealed film around them, as shown in figure 1, or they may be directly
adjacent one another without borders and an internal separating wall or a narrow sealed
strip to separate the discrete chambers. The chambers may be arranged in repeated
geometric pattern such as a grid, or randomly over the sheet or any other arrangement.
Further, the sheet 105 may be arranged in a substantially flat configuration, or it may be
folded, multiple folded or rolled or arranged in any suitable shape. Several sheets 105
may be provided.
The fuel source 102 may be arranged in a strip or over an area that may correspond to
the arrangement of the sheet 105. Alternatively, the apparatus 100 may include
channels to direct the activation fluid released from the chambers 103a-d to the reaction
chamber or through the reaction chamber for reacting with the fuel source 102. In the
embodiment of figure 1, an activation fluid flow control device 107 is shown to control the
rate at which the activation fluid is introduced to the fuel source 102. This may be useful
to achieve a steady release of hydrogen fuel and avoid spikes in reaction rate, fuel
pressure and/or heat generation. The activation fluid flow control device 107 comprises
an absorbent layer between the bladders 103a-d and the fuel source 102. When the
activation fluid is released from the bladders 103a-d it is absorbed by the absorbent
layer 107 and subsequently released into contact with the fuel source 102 at a steady
rate as it permeates through the layer 107. Thus, the selective rupturing of the
bladders 104a-d provides a primary means for controlling the flow of activation fluid and
the activation fluid flow control device 107 provides a secondary means. The rupturing of
a bladder 104a-d releases a predetermined amount of the total activation fluid available
and the activation fluid flow control device 107 controls the rate at which that
predetermined amount is introduced to the fuel source 102.
Other means to control the flow of activation fluid may be used, such as flow restrictors,
valves or using smaller (and perhaps more numerous) activation fluid chambers.
Alternatively, an activation fluid flow control device 107 may not be provided at all.
The heaters 104a-d may be formed on the outside surface of the activation fluid
chambers 103a-d. Alternatively the heaters may be formed on an internal surface or
within the chambers. The heaters 104a-d include connections to receive power for
activating the heaters 104a-d. The sheet 105 may include the connections at a
predetermined location such that power providing terminals (not shown) in the
apparatus 100 can contact when assembled. Arrangements of the connections are
discussed in more detail below.
The heaters may be printed or affixed to an inner surface of a layer of the bladder 103ad,
in contact with the activation fluid, or printed or affixed to an outer surface of a layer of
the bladder. The heater may extend into the bladders 103a-d. Further, the heater may
be formed on part of the apparatus and the chambers 103a-d may be arranged such that
they are mounted against an associated heater.
The activation fluid in the bladders 103a-d may be stored therein under pressure exerted
by the resilience of the sheet 105. Thus, when the associated heater 104a-d melts
through the bladder, the activation fluid is forcefully ejected from the ruptured bladder
103a-d. Alternatively or in addition, a chamber pressurisation assembly may be used to
urge the activation fluid to leave the activation fluid chamber 103a-d when it is punctured.
In this embodiment, the chamber pressurisation assembly 08 comprises a foam layer
arranged to contact and exert a physical pressure on the chambers 103a-d (the layer
108 is shown spaced from the chambers 103a-d in Figure 1 for clarity). Alternatively, the
chamber pressurisation assembly 108 may comprise a plurality of surfaces that
sandwich the chambers 103a-d. The surfaces may be resilient or rigid and may
comprise surfaces (or in part comprise surfaces) of the apparatus 100 or reaction
chamber 101 . The chamber pressurisation assembly 108 may alternatively comprise
means to stretch the sheet 105, such as mounts or clamps that retain the sheet 105
under tension.
Figure 2 shows a plan view of an embodiment of one of the activation fluid
chambers 103a. It will be appreciated that all or some of the activation fluid
chambers 103a-d may have the same configuration. The activation fluid chamber 103a
contains activation fluid and includes a heater 104a printed onto an external surface of
one of the layers of the film sheet 105. The heater 104a comprises a resistive heater
element 200a and two connections 201a, 202a for receiving electrical power to cause the
heating of the heater element 200a. The heater element 200a comprises a serpentine
resistive track in this embodiment, although the heater element 200a could take other
forms. The heater element 200a may be configured to act over a small point of the
chamber 103a or over its entire surface or an area in between. It may be arranged to
locally heat the film sheet to melt a hole in it to release the activation fluid. Alternatively,
it may be arranged to heat the activation fluid so that the internal pressure in the
chamber 103a causes it to rupture and release the activation fluid. It will be appreciated
that the arrangement of the heater element 200a will affect how the activation fluid is
released, i.e. the release rate and state of the activation fluid, which can be selected to
suit the intended use of the apparatus 100. Thus, the heater may be arranged to heat
(possibly above 100°C) the activation fluid sufficiently to partially or completely vaporise
it such that it flows to the reaction chamber 101 as a vapour or gas.
The connections 201a, 202a may be connected to terminals in the apparatus which
apply an electric current to the connections to heat the heater and rupture the chamber
103a. The electric current may be applied as a pulse. The profile of the pulse affects the
size of the hole melted into the sheet 105. A short pulse creates a smaller hole while a
longer pulse creates a larger hole. The size of the hole will affect the rate at which the
activation fluid leaves the chamber 103a.
Figure 3 shows an exemplary arrangement of four activation fluid chambers 103a-d side
by side in a strip. The heater elements 300a-d are represented as a box. Each heater
element includes a pair of connections 201 a-d, 202a-d which may each connect to
corresponding terminals in the apparatus 100. A controller (not shown) associated with
the apparatus can therefore selectively apply power to the terminals to activate one or
more of the heaters elements 300a-d and thus selectively rupture each of the chambers
103a-d.
Figure 4 shows an exemplary arrangement of four activation fluid chambers 403a-d side
by side in a strip. In this embodiment, the connections are arranged differently. Each
heater includes a common terminal connection 401 a-d and an individual terminal
connection 402a-d. The arrangement includes a shared connection 410, which is
connected to the common terminal connections 401 a-d of each heater element 400a-d.
The shared connection terminates at point 4 1, which in this embodiment is located on
the first chamber 403a in the strip. The individual connections 402a-d of each of the
heater elements 400a-b is present on each of the chambers 103a-d. Thus, to rupture
each of the chambers 403a-d, the controller applies power across the shared connection
410 and one or more of the second individual connections 402a-d depending on which of
the chambers 403a-d it is rupturing.
Figure 5 shows an exemplary arrangement of nine activation fluid chambers 503a-i each
with an associated heater 500a-i in a grid. The connection arrangement comprises a
shared connection 520, 521 , 522 for each of the rows 523, 524, 525 of chambers and
heaters. The connection arrangement further comprises a shared connection 530, 531 ,
532 for each of the columns 533, 534, 535 of chambers and heaters. The shared
connections terminate at points 526, 527, 528 and 536, 537, 538 for connection to
terminals of the apparatus 100. Each heater element has two connections, one of which
is connected to the shared connection for the row it is in and the other is connected to
the shared connection for the column it is in. Thus, heater element 500a is connected to
shared connections 520 and 530. Heater element 500b is connected to shared
connections 520 and 531, and so on, to heater element 500i, which is connected
between shared connections 522 and 532. Thus, to rupture a particular chamber 503ad,
the controller applies power to the termination points of the shared connections that
correspond to the row and column in which the heater element is located. Thus, to
rupture chamber 503e, which lies in the second row and the second column, the
controller applies power between the second row shared connection 521 and the second
column shared connection 531.
In use, the apparatus 100 includes the fuel source 102 and activation fluid contained
within the chambers 103a-d, 403a-d, 503a-d. The apparatus 100 is connected to a fuel
cell, which requires a supply of hydrogen fuel from the apparatus 100. As hydrogen is
required, which may be detected by maintaining a pressure within the apparatus (which
will fall as hydrogen is drawn off by the fuel cell), the controller may selectively rupture
the chambers 103a-d, 403a-d, 503a-d to release a quantity of activation fluid for reacting
with the fuel source 102. In the present embodiment, the heater elements 200a-d, 300ad,
400a-d, 500a-i are activated sequentially as hydrogen is required. Thus, a pulse of
power is applied, in turn, to each chamber to melt a hole in its surface and release the
activation fluid therein. In other embodiments, several chambers may be ruptured
simultaneously depending on the demand for fuel. In the embodiment of Figure 1, the
activation fluid is received by the activation fluid flow control device 107, which absorbs
the activation fluid and releases it at a slower rate to which it was received from the
ruptured chamber 103a-d. The activation fluid can then react with the fuel source 102, or
be channelled to the reaction chamber 101 to react with the fuel source 102 and
generate the hydrogen fuel.
In a further embodiment, the controller is configured to apply sufficient energy to the
heaters to rupture the chamber and vaporise the activation fluid therein. The activation
fluid thus travels to the fuel source 102 and reacts therewith as a vapour or gas. This
may make the reaction more efficient. Further, the power level supplied to the heater
may be controlled to effect heating of the activation fluid and then rupturing of the
chamber. For example, a first power level may be applied to heat the activation fluid
followed by a higher power level (which may be a spike in power) which ruptures the
chamber.
The arrangement of activation fluid in discrete, separately rupturable chambers is
advantageous as it allows the controller to control the amount of activation fluid that is
released by rupturing only the relevant number of chambers.
The bladders may be formed of multiple layers of film, which may encapsulate the fuel
generating substance between certain layers and the heaters and connections between
other layers. The conductors for the heaters may be arranged to extend in the borders
between the bladders. The heaters may act on a single point on the bladder or multiple
points, which can be used to control the rate of release of fuel generating fluid. The
heaters may be destroyed on actuation and rupture of the bladder or they may be
reusable. The size and number of the bladders can be used to control the rate of fuel
generation and thus suit the power requirements of a particular application.
In a further embodiment (not shown), the fuel generating fluid comprises a fuel source
fluid, such as sodium borohydride solution. The fuel generating substance, which may
be located within the reaction chamber, comprises a catalyst, such as ruthenium,
rhodium, nickel or platinum. Thus, in this embodiment, rather than a reaction between
the fuel generating fluid and the fuel generating substance, the fuel generating substance
catalyses the generation of fuel from the fuel generating fluid. Accordingly, in use, the
sodium borohydride solution is released from the fuel generating fluid chambers and
meets the catalyst in the reaction chambers, which catalyses the generation of hydrogen
fuel from the sodium borohydride solution. It will be appreciated that other fuel
generating fluids in combination with other catalysts may be used.
Figure 6 shows a flow chart illustrating an exemplary embodiment of the invention. Step
601 illustrates providing a plurality of discrete fuel generating fluid chambers, each fluid
chamber containing fuel generating fluid and being separately rupturable. Step 602
illustrates providing a fuel generating substance which can generate fuel in combination
with the fuel generation fluid. Step 603 illustrates rupturing at least one fuel generating
fluid chamber to transfer the fluid to the fuel generating substance for generating the fuel.
It will be appreciated that features described in regard to one example may be combined
with features described with regard to another example, unless an intention to the
contrary is apparent.
Claims
1. A fuel supply apparatus comprising;
a reaction chamber for hosting a reaction when a fuel generating fluid and a fuel
generating substance are brought together to generate fuel,
a plurality of discrete fuel generating fluid chambers, each chamber being
separately rupturable; and,
a heater assembly adapted to, when in use, selectively rupture the fuel
generating fluid chambers to supply fuel generating fluid to the reaction chamber.
2. A fuel supply apparatus as defined in claim 1, in which the fuel generating fluid
comprises an activation fluid and the fuel generating substance comprises a fuel source,
wherein the reaction between the activation fluid and the fuel source generates fuel.
3. A fuel supply apparatus as defined in claim 1 or 2, in which the heater assembly
comprises a plurality of heaters arranged such that each fuel generating fluid chamber is
associated with at least one heater for heating, and thereby rupturing, said fuel
generating fluid chamber.
4. A fuel supply apparatus as defined in claim 3, in which the heaters form part of
the plurality of discrete fuel generating fluid chambers.
5. A fuel supply apparatus as defined in claim 3, in which the heaters are formed on
part of the fuel supply apparatus, the heaters configured such that they can be
selectively activated and arranged adjacent the plurality of discrete fuel generating fluid
chambers.
6 . A fuel supply apparatus as defined in any preceding claim, in which the discrete
fuel generating fluid chambers comprise a plurality of sealed bladders formed in a sheet,
each bladder containing fuel generating fluid and being separately rupturable.
7. A fuel supply apparatus as defined in claim 6, in which the sheet is of at least two
layers, the two layers sealed together at localised portions to define the plurality of
bladders.
8. A fuel supply apparatus as defined in claim 6 or claim 7, in which the heater
assembly is printed onto the film sheet.
9 . A fuel supply apparatus as defined in claim 4 or claim 8, in which the heater
assembly includes power receiving terminals for electrically connecting to the fuel supply
apparatus for receiving power therefrom.
10. A fuel supply apparatus as defined in any preceding claim, in which the heater
assembly is configured to heat the fuel generating fluid as well as rupture the fuel
generating fluid chambers.
11. A fuel supply apparatus as defined in any preceding claim, in which the apparatus
includes a fluid flow control device to control the rate at which fuel generating fluid is
introduced to the reaction chamber.
12. A fuel supply apparatus as defined in claim 11, in which the fluid flow control
device comprises an absorbent layer between the fuel generating fluid chambers and the
reaction chamber.
13. A fuel supply apparatus as defined in any preceding claim, in which each heater
has two terminals, a common terminal and an individual terminal, each of the common
terminals being connected to a common shared conductor, wherein each one of the
heaters are configured to be activated by supplying power between the shared conductor
and its individual terminal.
14. A fuel supply apparatus as defined in any preceding claim, in which the fuel
generating fluid chambers and associated heaters are arranged in a grid, the grid
comprising rows and columns, and including a shared conductor for each row and a
shared conductor for each column, the heaters connected to the shared conductor for
the row in which they are positioned and connected to the shared conductor for the
column in which they are positioned, the grid configured such that a particular heater can
be activated by supplying power between the shared conductors of its row and column.
15. A fuel supply apparatus as defined in any preceding claim, in which the fuel
supply apparatus includes a fuel generating fluid chamber pressurisation assembly for
applying pressure to the fuel generating fluid in the chambers.
16. A fuel supply apparatus as defined in claim 15, in which the pressurisation
assembly comprises a bias member to physically press against the chambers,
17. A fuel supply apparatus as defined in claim 15, in which the pressurisation
assembly comprises a mount to stretch a film sheet in which the chambers are formed.
18. A fuel supply apparatus as defined in any preceding claim, in which the fluid
supply apparatus includes a controller configured to monitor the demand for fuel and, in
response to the monitored demand, rupture at least one fuel generating fluid chamber.
19. A fuel supply apparatus as defined in claim 1, in which the fuel supply apparatus
is a hydrogen fuel supply apparatus.
20. A fluid store configured to be used with the fuel supply apparatus of any one of
claims 1 to 19, the fluid store comprising a plurality of discrete fuel generating fluid
chambers, each fluid chamber containing fuel generating fluid and being separately
rupturable.
21. A fluid store as defined in claim 20, in which the discrete fuel generating fluid
chambers comprise a plurality of sealed bladders formed on a sheet, each bladder
containing fuel generating fluid and being separately rupturable.
22. A fluid store as defined in claim 2 1, in which the sheet is of at least two film
layers, the layers sealed together at localised portions to define the plurality of bladders.
23. A fluid store as defined in any of claims 20 to 22, in which the fluid store includes
a heater assembly comprising a plurality of heaters, each fuel generating fluid chamber
associated with at least one heater.
24. A method of supplying a fuel for use in a fuel cell, the method including the steps
of;
providing a plurality of discrete fuel generating fluid chambers, each fluid
chamber containing fuel generating fluid and being separately rupturable;
providing a fuel generating substance which, in combination with the fuel
generating fluid, can generate a fuel; and
rupturing at least one fuel generating fluid chamber to transfer the fuel generating
fluid to the fuel generating substance for generating the fuel.
25. A fuel supply apparatus as described herein and as illustrated in Figures 1 to 5 of
the drawings.
26. A fluid store as described herein and as illustrated in Figures 1 to 5 of the
drawings.
A method as described herein and as illustrated in Figure 6 of the drawings.