Note: Descriptions are shown in the official language in which they were submitted.
CA 02195995 2000-O1-OS
IMPROVED BATTERY-POWERED LAWN CUTTING SYSTEM
BACKGROUND OF THE INVENTION
This invention relates to electric lawnmowers.
More particularly, this invention relates to battery-
powered lawnmowers having removable, rechargeable
batteries and a rotating cutting blade.
Electric lawnmowers are known which operate on
AC line current. These lawnmowers typically have a plug
attached to the handle that is suitable for connection
with an AC power cord. A primary disadvantage of such
prior art lawnmowers is that the cord is unwieldy and
cumbersome, requiring the operator to constantly
manipulate or move the cord to keep it out of the way of
the cutting blade. Also, the cord may be cut by the
rotating cutting blade, leading to a short circuit.
To avoid the problems of such so-called "cord
electric" lawnmowers as described above, cordless
battery-electric lawnmowers have been developed. Such
lawnmowers typically have one or more large rechargeable
batteries disposed on the mower chassis along with the
electric motor. The batteries are typically recharged
by connecting a battery recharger to the lawnmower, or
by an on-board charger connected to a conventional
household outlet via an extension cord.
A major disadvantage of such prior art
"cordless electric" lawnmowers is that they are
difficult to maneuver and push due to the weight of the
batteries. The batteries must typically be very large
for the lawnmower.to run a sufficient length of time to
mow the average size lawn. In a typical prior art
battery-electric lawnmower, the batteries will operate
the lawnmower from 30 to 90 minutes before the batteries
have to be recharged. For a lawnmower having batteries
that operate for 30 to 90 minutes before recharging, the
lawnmower generally weighs about 55 to 80 pounds. Such
lawnmowers are difficult to maneuver and to push uphill.
WO 96105719 219 5 9 9 5 PCTIU595102765'
_2_
Such lawnmowers may be impossible to use by weaker
people.
Although it is possible to reduce the weight
of the lawnmower by reducing the size of the batteries,
such weight reduction also reduces the length of
lawnmower operating time between recharges. As a
practical matter, a prior art lawnmower which operates
for less than 25 minutes between recharges would be of
limited utility since many lawns require more than 25
minutes to cut.
The electrical and power components of a
battery-powered lawnmower of prior art devices may be
damaged under certain circumstances. For example, if
the battery is frequently allowed to discharge too much,
irreparable--damage may result to the battery. Also,
high current conditions may occur during the operation
of the lawnmower which may damage the electrical
components.
Another problem with prior art lawnmowers is
that grass clippings may accumulate between the inner
sidewall of the lawnmower chassis and the rotating
cutting blade. This accumulation may result in jamming
of the lawnmower. One prior art technique for reducing
the likelihood of such jamming was to form the outer
edge of the cutting blade at an angle, so that the
leading edge of the cutting blade ends in a point that
presumably moves through any accumulated grass clippings
on the inner sidewall of the mower housing. This
solution is unsatisfactory, however, because it reduces
the amount of lift at the end of the cutting blade,
where it is most needed to achieve a proper cut and for
proper mulching. The so-called °lift" is created by a .
lift section on the cutting blade behind the lead
cutting edge of the blade. However, when the outer edge
of the blade is tapered, the surface area of the lift
section at the end of the blade is substantially
reduced, thereby reducing the lift created by the
rotating cutting blade. Also, the tapering of the outer
edge of the blade allows grass clippings to escape more
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readily through the clearance between the lawnmower
chassis and the cutting path of the blade, which is
undesirable for mulching..
SUMMARY OF THE INVENTION
A vegetation cutting system is disclosed that
uses a lawnmower having an electric motor, at least one
removable, rechargeable battery pack adapted to being
connected in circuit with the electric motor, a chassis
or housing for supporting the electric motor, a
plurality of wheels interconnected with the chassis to
allow the mower to be moved, a handle interconnected -
with the chassis, and a rotary cutting means, such as a
cutting blade, interconnected with a rotatable motor
shaft of the motor. The vegetation cutting system also
includes a means for recharging the battery, which may
be disposed on the cutting apparatus or provided as a
separate unit.
The cutting system may also include a circuit
that shuts off the lawnmower if the battery voltage
falls below a preset level, if the lawnmower current _
exceeds a second preset level when the cutting blade
encounters excessive load, such as too heavy grass, or
if the lawnmower current exceeds a third preset level- _
such as when the cutting blade becomes jammed to the
extent that it cannot rotate. In any case, the
lawnmower may be restarted by disengaging and then re-
engaging the deadman handle.
The cutting system may also include a second
battery and a wire harness which allows the single
charger output to charge both batteries simultaneously.
Each battery pack may include a diode to prevent one _
charged battery pack from dumping its charge into the
other battery pack when both battery packs are-being
charged simultaneously by the recharges. The diode in
each battery pack also has a second function; it
prevents a spark or fire if someone accidentally shorts
the two exposed charging terminals that are in the
battery pack charging connector. The short may
W096/05719 ~ ~ ~ ~ ~ 9 5 PCTIU595I02765_
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otherwise occur when a screwdriver orother conducting
object is accidentally placed in contact with both pins
of the same charging connector.
In one embodiment, the cutting apparatus
includes a -retaining means, such as a battery receptacle
that is integral with the chassis, having an attachment
means to which the battery pack is attached, or having
an opening therein into which the battery pack is
placed. Both the battery pack and the retaining means
have mating quick connect/disconnect terminals to allow
the battery pack to be quickly attached or inserted into
the.receptacle opening, and quickly removed and
replaced. A unique, multipart telescoping groove is
provided to readily guide the battery terminals into
engagement with the mating rn,?ck connect/disconnect
terminals. The battery pack has a handle, preferably
connected to its upper portion, so that the battery pack
may be readily lifted out of, or otherwise detached
from, the retaining means.
A battery recharging means may be connected to
the battery pack via a plug in the battery pack, or the
battery pack may be lifted from the lawnmower and either
connected to a recharging means or placed in a
receptacle opening within a battery recharging means. A
removable safety key is provided that blocks the
recharging plug on the battery pack during lawnmower
operation to prevent the lawnmower from being operated
while the installed battery pack is being recharged.
The installed safety key also prevents the battery pack
from being replaced without first removing the key.
The battery recharging means may include one
or more receptacle openings, each of the openings being
adapted to receive a battery pack. An alarm circuit may
be provided on the battery that emits an alarm signal ,
.when the voltage of the battery falls below a
predetermined level. A second alarm system may be
included which would provide an audible or visual signal
when the key is still in place.
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The present invention also comprises a method
of cutting grass with a battery-powered lawnmower.
According to the method of the present invention, the
cutting apparatus is operated using a first removable,
rechargeable battery or battery pack until the first
battery is discharged to a selected level. The first
battery is then electrically disconnected from the
electric motor of the cutting apparatus and removed, and
the cutting apparatus continues to operate to cut the
grass using a second battery as a power source. The
first battery may remain in place for recharging, or it
may be removed and placed into or connected to a
separate recharging unit. In a preferred embodiment,
the first battery is removed and replaced by a second
battery which has been fully charged by the battery
recharger.
Once the second battery has been discharged to
a selected level, it is electrically disconnected from
the electric motor. The second battery is preferably
disconnected by removing it and replacing it with either
the recharged first battery or with a third battery,
which is then electrically connected to the electric _.
motor. The discharged second battery is then
electrically connected with the recharger by either
attaching thedischarged second battery to the recharger
or by placing the discharged second battery within an
opening in the recharger housing. The operation of the
cutting apparatus is then continued, using either the
recharged first battery or the third battery.
If the method described above is used with at
least two batteries, the cutting apparatus may be
substantially continuously operated for an extended
period of time to cut almost any size lawn. At the same
time, the weight and size of the cutting apparatus are
reduced since the cutting apparatus only carries with it
a single battery at a time. When the cutting system is
used with two such batteries, the cutting apparatus may
be continuously operated for twice as long, even without
recharging.
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In one embodiment, the recharger is a so-
called "quick charge" recharger that recharges a battery
to SO% of its maximum level within a short period of
time. With this type of recharger, almost all lawns may
be cut using two or three batteries - only one of which
need be disposed on the cutting apparatus at any given
time. A second battery could optionally be carried on
the cutting apparatus to be used when the first battery
becomes discharged.
The invention also has several other important
features, including a cutting blade that lessens the
likelihood of jamming while still lifting the grass for
cutting, a unique height adjustment assembly, and a
handle attachment that enables the handle to be
tightened down as well as loosened for lawnmower
storage.
Another feature of the invention is that a
mulcher or aide-discharge mower can be achieved with a
simple attachment change. The mulcher plug and side
discharge chute each contain an attached magnet. When
either attachment is in place on the chassis, the magnet
closes a reed switch located within the chassis
enclosure, allowing mower operation. If neither
attachment is in place, the mower cannot be operated.
This safety feature protects an operator or bystander by
preventing operation when the operator's hand could be
in the blade area, and protects the operator or
bystanders from thrown objects.
It is a feature and advantage of the present
3D invention to provide a battery-powered lawn cutting
system that may be operated for an extended period of
time to cut virtually any size of lawn.
It is yet another feature and advantage of the
present invention to provide a battery-electric cutting ,
apparatus that is relatively lightweight and easy to
maneuver when compared to prior art devices.
It is yet another feature and advantage of the
present invention to provide a battery-electric lawn
cutting system that is adaptable to being used with
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small lawns or with Large=lawns simply by increasing the
number of removable, rechargeable batteries in the
system.
It is yet another feature and advantage of the
present invention to provide a battery-electric cutting .
apparatus in which an unusable battery may be easily
replaced by a non-skilled person.
These and other features and advantages of the
present invention will be apparent to those skilled in -
10, the art with the following detailed description of the
preferred embodiments and the drawings, in which:
BRIEF DESCRI TION OF THE DRAWINGS -_
Figure 1 is a perspective view of the
vegetation cutting system according to the present
invention.
Figure 2 is a side view of a lawnmower
according to the present invention.
Figure 3 is a cross-sectional side view of a
lawnmower according to the present invention.
Figure 4 is an exploded side cross-sectional
view depicting a safety key being removed.
Figure 5 is a cross-sectional end view of the
battery slide mount, taken along line 5-5 of Figure 4.
Figure 6 is an end cross-sectional view of the
key-connector assembly according to the present
invention.
Figure 7 is a diagrammatical view of the
telescoping groove that receives the battery's quick
disconnect terminals.
Figure 8 is a top view of the lawnmower
chassis, shown in partial section.
Figure 9 is an exploded top view depicting the
battery being slid into the battery receptacle.
Figure 1D is a bottom view of a lawnmower
according to the present invention.
Figure 11 is a side exploded view depicting
the height adjustment lever in two different positions,
taken along line 11-11 of Figure 8.
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Figure 12 is an exploded side view depicting
the height adjustment assembly.
Figure 13 is an end view of a lawnmower blade
according to the present invention, taken along line 13
13 of Figure 10.
Figure 14 is a cross-sectional side view of
the cutting blade, taken along line 14-14 of Figure 10.
Figure 15 is a cross-sectional side view of
the cutting blade, taken along line 15-15 of Figure 10.
Figure 16 is a side view of the lawnmower,
depicting the folded handle.
Figure 17 is a cross-section end view
depicting the handle attachment assembly.
Figure 18 is a schematic diagram of a control
circuit according to the present invention.
Figure 19 depicts a wire harness that may be
used to simultaneously charge two batteries.
Figure 20 is a schematic diagram of an alarm
circuit that may be used in the present invention.
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DESCRIPTION OF THE PREFER_R~D EMBODIMENT
Figure 1 is a perspective view depicting the
major components of the vegetation cutting system
according to the present invention. The system depicted -
in Figure 1 preferably includes a battery-powered
lawnmower 10 and either a trickle battery recharger 12
or a stand-alone battery recharger 14.
Lawnmower 10 includes a lawnmower chassis 16
that provides support to a power unit consisting of an
electric motor 18 (Fig. 3), a control circuit 20
(Fig. 18), a removable rechargeable battery pack 22
(Fig. 3) and an integrally-formed receptacle 24 (Fig. 3)
which retains battery pack 22 in a substantially fixed
position. Battery pack 22 comprises two 12 volt
batteries connected in series. Of course, a single
battery could be used; the terms "battery" and "battery
pack" are used interchangeably herein. Receptacle 24 is
integrally formed with lawnmower shroud 25. Motor 18 is
connected to control circuit 20 by a pair of wires 138
and 192 (Figs. 8 and 18).
Although it may be desirable to retain battery
22 in place by providing receptacle 24 with an opening
for receiving battery pack 22, other means could be used
to retain battery pack 22 in a fixed position. For
example, the battery retaining means could comprise a
frame that, along with the quick connect/ disconnect
electrical terminals discussed herein, acts as a
retainer member to hold the battery in place. In the
alternative, the battery retaining means could include
one or moremechanical connectors that keep the battery
in a substantially fixed position. The retaining means
could also consist of the electrical terminals alone.
Referring again to Figure 1, lawnmower 10 may
include a mulching attachment 26 which prevents the
discharge of cut grass. Of course, the mulching
attachment may be replaced by a chute to allow side
discharge of the cut grass, or by a bagging attachment.
Chassis I6 is supported by four rotatable wheels 28,
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which allow the lawnmower to be moved from one place to
another.
The movement of the lawnmower is controlled by
the operator using a handle assembly 30. Handle
assembly 30 has a first end 32 that is interconnected
with chassis 16, and an opposed second end 34 disposed
away from the chassis. Handle assembly 30 may be folded
by loosening a pair of thumbscrews 36, and by loosening
a second pair of thumbscrews 38 affixed to chassis 16.
Interconnected with handle assembly 30 is an
elongated bail handle 40 that is moved and gripped by
the operator during operation of the lawnmower. Bail
handle 40 may be replaced by one or more pushbuttons.
Interconnected with elongated handle 40 is a push button
switch 42, with handle 40 and switch 42 together
comprising the so-called "deadman~~ switch. A wire 44 is
interconnected with handle 40, and enables the lawnmower
to be stopped when bail handle 40 is released.
As best shown in Figures 1 through 3,
removable battery 22 has a handle 46 attached to its
upper end. Handle 46 is positioned or biased toward the
quick connect/disconnect terminals to allow the battery
to be readily inserted and removed from chassis 16
without binding. As more fully discussed below, a
safety key 48 engages a surface 50 (Fig. 3) on battery
22 such that the removal of battery 46 also results in
the removal of safety key 48.
Safety key 48 and its uses are best understood
in connection with Figures 3, 4 and 6. In Figures 3, 4
and 6, safety-key 48 has an outer housing 52, a lower
member 54, and a bolt 56 that connects housing 52 and
lower member 54. Safety key 48 also includes a flexible
handle or rope 58 that may be pulled by the operator to
remove the kay from the control circuit, or used to hang
the key for-storage.
As best shown in Figure 6, safety key 48
includes a conductive element 60 that completes an
electrical circuit between a pair of terminals 62 and 64
disposed on lawnmower chassis 16. Terminals 62 and 64
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are connected to a circuit board 65 that contains
control circuit 20 (Fig. 18). When safety key 48 is
removed, the circuit is broken and no power flows to
motor 18.
As best shown in Figures 3 and 4, safety key
48 also includes a protruding, engagement member or
flange 66 that engages a surface 50 on battery pack 22.
In fact, battery pack 22 may be provided with a ridge or
flange 68 to retain key flange 66 in place. When
battery 22 is being removed, the upward motion of
surface 50 causes flange 66 disposed thereon to also
move in an upward direction, thereby displacing key 48.
When the key has been removed, the lawnmower will not
operate. In the alternative, battery pack 22 may be
provided with the engagement member, which engages the
key to displace the key when the battery is removed.
Another purpose of key 48 is to block battery
pack recharges plug 70 (Fig. 3), into which a battery
recharges may otherwise be connected. Recharges plug 70
may be disposed on the battery, or it may be disposed on
shroud 25 or chassis 16. Key 48 has a surface 72 which
blocks recharges plug 70. It is desirable to block
recharges plug 70 when the lawnmower is being operated
to prevent the lawnmower from being operated while the
battery pack is being recharged. However, once key 48
is removed, a charger may be plugged into receptacle 70
while the battery pack is still in place. Key flange 66 -
extends a sufficient distance over battery receptacle 24
to prevent battery pack 46 from being.inserted while key
48 is in place.
Another important feature of the present
invention comprises the manner in which the battery is
readily placed and removed from the battery receptacle,
as well as the quick connect/disconnect terminals used
to connect the removable battery pack to the lawnmower
electrical system. These features are best understood
in connection with Figures 3 through 5, 7 and 9. As
best shown in Figures 4, 7, and 9, the battery is
mounted to the lawnmower chassis by providing one or
219 5 9 9 5 p~rtJS95/0276~
-12 --
more projections 74 on battery 22, which are received in
a groove 76 provided in lawnmower chassis 16. A top
view of groove 76 is shown in Figure 9. As best shown
in Figures 4 and 7, groove 76 preferably includes three
tapered sections 78, 80, and 82. First tapered section
78 has a first set of three tapered sidewal k 78a, 78b
and 78c, each of sidewalls 78a, 78b and 78c forming a
first angle-with longitudinal axis 77 of groove 76 that
is between 0 to 5', with one-half degree being
10. preferred. -also, second tapered section 80 has three
tapered sidewal k SOa, SOb and 80c, each of which forms
a second angle with respect to longitudinal axis 77 of
groove 76 of between 1 to 45', with 2' being preferred.
Similarly, third tapered section 82 has a third set of
sidewalls 82a, 82b and 82c, each of which forms a third
angle with respect to longitudinal axis 77 of between 0
to 5', with one-half degree being preferred.
The purpose of tapered groove 76 and tapered
sections 78 through 82 is to facilitate the placement
and removal of battery 22. The multipart tapered groove
has a tendency to guide battery projections 74 into
groove 76, thereby facilitating the electrical
connection,between the battery connectors and the
chassis connectors. The sidewalls of second tapered
section 80 form a larger. angle to the longitudinal axis
than the other tapered sidewalls to increase the size of
the upper end of groove 76 to facilitate battery
placement.
These electrical connectors are best shown in
Figures 4 and 5. In Figures 4 and 5, battery pack 22
has a pair of electrical connectors 84 and 86 which
engage connectors 88 and 90, respectively, on the
lawnmower chassis. Each of electrical connectors 84
through 90 may be a resilient or spring type of
connector, and may have a protruding ridge that engages
a mating protruding ridge on the opposed connector.
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Chassis connectors S8 and 90 are connected to
control circuit 20 by cables 92 and 94, respectively.
Similarly, battery connectors 84 and 86 are connected to
battery pack 22-by cables 96 and 98, respectively.
The lawn cutting system according to the
present invention may be used to cut virtually any size
of lawn, if two or more removable batteries are used.
The number and/or size of the batteries that are
included in the system are dictated by cost factors and
by the length of time the operator wants to run the
lawnmower continuously. For example, the operator may
have a small lawn and, thus, be able to cut the entire -
lawn in 20 to 30 minutes. In that case, the operator -
would only require a single battery, which will run the
lawnmower from about 15 to 40 minutes.
At additional expense, the user may purchase a
system, or upgrade a previously-purchased single
battery system, to include two or more batteries. With
such a system, the operator rune the lawnmower with a
first battery until the first battery discharges to a
predetermined level. The first battery is then placed
in the battery recharger, as depicted in Figure 1. A
second, recharged battery, which may have been connected
to the battery recharger, is then inserted into
receptacle 24 of chassis 16 (Fig. 1) and the operation
of the lawnmower is continued. When the second battery
has discharged to a predetermined level, the second
battery is electrically disconnected from motor 18 and
is removed from the battery receptacle. The second
battery is then electrically connected to recharger -
(Fig. 1). Thereafter, either the recharged first
battery or a third battery is placed into the battery
receptacle so that operation of the lawnmower is
continued. It may be desirable to use a quick-charge
recharger to enable the first battery to be recharged to
approximately 80% of full charge within a short period -
of time.
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ding the above-described system with two or
more batteries enables the_lawnmower to be substantially
continuously operated for an extended period of time.
Since statistics indicate that most lawns may be cut in
20 to 60 minutes, it is apparent that a cutting system
that uses two or more batteries - each permitting 15 to -
40 minutes of cutting - would enable the majority of
lawns to be cut with substantially continuous operation.
If three batteries are used in the system, a lawn of
almost any size may be cut. At the same time, the
weight and size of the lawnmower is reduced since it is
necessary to carry only a single, relatively small
battery on the lawnmower at one time.
The present invention also includes a unique
control circuit that shuts down the electric lawnmower
under several predetermined conditions. In each case,
however, the lawnmower may be restarted by releasing
deadman handle 40 (Fig. 1), and thereafter moving
deadman handle 40 again, after pushing button 42, so
that handle 40 is gripped along with handle end 34 by
the operator to restart the lawnmower.
The first predetermined condition which
results in the shutdown of the lawnmower is that the
battery pack output voltage has dropped to a
predetermined level. Assuming that the battery output
voltage is normally 24 volts, the predetermined low
voltage level may be approximately l6 to 19 volts, with
18 volts being preferred. The purpose of this feature
is to prevent deep discharging of the batteries, thereby
avoiding harm to the batteries.
The second predetermined condition under which
the lawnmower is abut down occurs when electric motor 18
is continuously drawing 32 to 38 amps of current, with
amps being preferred, for more than 3 seconds. This
35 predetermined condition will typically occur if the
operator is mowing through heavy or thick grass so that
the load on the motor forces the motor current to go
very high. The purpose of the 3 second delay feature is
to prevent the motor from being turned off only when a
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temporary heavy load condition occurs, such as a small
but thick clump of grass, or when the current surges
upon starting the motor. This shutdown feature prevents
the electrical components in the lawnmower from becoming
too warm, and prevents the rapid discharge of the
battery.
The third predetermined condition leading to
shutdown is that the motor is drawing 50 amps or more of
current at any time after the motor is started. This
feature is disabled during lawn mower start-up due to
the normal, high in-rush current that occurs during
start-up. Thereafter, however, current to the motor -
will be turned off when the motor current exceeds
approximately 50 to 60 amps, with 50 amps being
preferred. The motor current will exceed 50 amps if the .,
cutting blade is stalled, such as when the blade is
jammed with a stick or a cord.
Figure IS is a schematic diagram of the
control circuit for shutting down the lawnmower when the
above-discussed predetermined conditions occur. In
Figure 18, the low battery voltage shutdown circuit
comprises resistor 100, resistor 102, and comparator
104. Resistor 105 is a pull-up resistor for comparators -
104 and 144. Comparator 104 has two inputs; the
negative input is set at 12 volts, and the positive
input is divided down by the resistor network consisting
of resistors 100 and 102. The voltage at node 106,
between resistors 100 and 102, is two-thirds of the
present battery voltage. Once the battery voltage drops
down to about 18 volts, the voltage at node 106 will
become 12 volts. As soon as the voltage at node 106
drops below 12 volts, the output of comparator 104 goes
low, thereby providing a low signal to the base of
transistor 108. Transistor 108 is thus turned OFF.
When transistor 108 is OFF, current flows from the 12
volt source connected to line 110 through resistor 112
and charges up capacitor 114. Once capacitor 114 is
sufficiently charged, capacitor 114 will begin to drive
current through zener diode 116 into the gate of SCR .
VVO 96105719 219 5 9 9 516 _ p~~gg510176~
118, thereby turning ON SCR 118. When SCR 118 is turned
ON, current is drawn away from diode 124, so that all
the current through line I22 passes through reaistar 120
and SCR 118 instead of through relay 128. Relay 128 is
thereby turned OFF, which removes current from the
electric motor. SCR 118 will continue to conduct as
long as the 24 VDC supply is connected to line 122. The
operator of the lawnmower must then release bail handle
40 (Fig. 1)_ to return SCR 118 to its original OFF state.
SCR 118 will remain OFF unless the original low battery
voltage condition recurs afterrestart, at which time
SCR 118 will again be turned ON to remove current from
the electric motor.
To insure that the user is able to restart the
lawnmower after the lawnmower has been stopped by the
low voltage circuit, even if the low battery voltage
condition still exists, capacitor 114 is discharged
through transistor 130 to prevent SCR 118 from being
immediately turned ON again after the restart. As soon
as transistor 126 is turned OFF, current will flow
through resistor 132 to the base of transistor 130,
thereby turning ON resistor 130 and shorting out
capacitor 114.
This restart circuit operates each time the
motor is stopped for any type of shutdown, whether the
shutdown is caused by a low battery voltage or by an
overcurrent condition. Capacitor 114 is discharged
completely so that upon restart, the condition that
caused the shutdown does not prevent the lawnmower from
being restarted. Of course, if the condition causing
the shutdown still exists after restart, the lawnmower
will again shut down after a very short period of time. ,
Even if the shutdown is caused by a low battery voltage,
the lawnmower may be restarted at least briefly even
though the-battery voltage still is below the cutoff
level. The lawnmower will continue to operate if the
battery voltage has rebounded to an acceptable level
above approximately 18 volts.
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The battery undervoltage shutdown feature is
delayed for a period of approximately 3 seconds by the
RC timing circuit consisting of resistor 112 and
capacitor 114. Capacitor 114 must charge up to the
threshold voltage of zener diode 116 before the motor
current will be shut off due to a low battery voltage.
The 35 amp shutdown circuit will now be
described. This shutdown circuit includes a feedback
resistor 136, which is connected in series to high
current line 138. A small RC timing circuit, consisting
of resistor 140 and capacitor 142, filters the feedback
signal passing through resistor 136. The filtered
feedback signal then is applied to the negative input of
comparator 144, wherein the signal is compared to a
voltage set point determined by resistors 146 and I48.
In the present embodiment, the voltage at node 152 is
0.35 volts, which corresponds to 35 amps through the
motor. If the voltage at node 152, between resistor 140
and capacitor 142, ever exceeds 0.35 volts, the output
of comparator 144 will go low, thereby removing current
from the base of transistor 108. Transistor 108 will
then turn OFF, thereby allowing capacitor 114 to charge
up. The remainder of the circuit operates in the same
manner as the undervoltage circuit described above,
including the 3 second delay.
The operation of the 50 amp shutdown circuit
will now be described. The 50 amp shutdown circuit uses
the same filtered feedback signal used in the 35 amp
shutdown circuit discussed above. The filtered feedback
signal is input to the positive input of comparator 154,
and is compared to a voltage determined by resistors 156
and 158. In the present case, the voltage at node 160
is 0.5 volts (which corresponds to 50 amps through the
motor), so that if the voltage at the positive input of -
, comparator 154 is ever greater than 0.5 volts, then the
output of comparator 154 will go high. When the output
of comparator 154 goes high, current will flow from the
12 VDC source through resistor 162, through resistor
164, and into the gate of SCR 118 to turn ON SCR 118.
W 0 96105719 219 5 9 9 5 -18 - P~'~159SI0276~
When SCR lI8-is turned ON, current is removed from the
base of transistor 126, and relay 128 is turned OFF.
The turning OFF of relay 128 removes current from motor
18 (Fig. 3). Since zener diode 116 is not part of this
circuit, the motor will turn off immediately without any
3 second delay.
The 50 amp shutdown circuit does contain a
1-1/2 second delay during lawnmower start-up to prevent
the lawnmower from being shut off due to the high
in-rush current that normally occurs during start-up.
This delay circuit operates as follows. The RC time
constant voltage determined by resistor 166 and
capacitor 16B is applied to the positive input of a
comparator 170. A voltage determined by resistors 172
and 174-is applied to the negative input of comparator
170. Once the RC time constant voltage applied to the
positive input of comparator 170 rises above the
constant voltage determined by resistors 172 and 174,
the output of comparator 170 goes high. This occurs
approximately 1-1/2 seconds after mower start-up. In
essence, comparators 154 and 170 must both have high
outputs for-a sufficient voltage to be applied to the
gate of SCR 118 to shut off the electric motor.
The control circuit also includes a voltage
regulator 176 that is used to convert 24 volts to 12
volts. Resistor 178 prevents a current surge from
damaging the_circuits. Capacitor 180 filters out
switching noise. Flyback diode 182 prevents damage to
voltage regulator 176 if switching noise appears on the
24 volt line; it ensures that the output aide of the
regulator can never be a higher voltage than the input
side. Capacitor 184 filters out switching noises from
the 12 volt line.
Current is provided to motor 18 through a
quick connect/disconnect connector 186, through circuit
breaker 188, through safety key contacts 62 and 64, and
through line 192. After passing through motor 18, the
current travels through line 138 and through relay
contacts 194, which are the contacts for relay 128.
WO 96105719 2 1 9 5 9 9 5
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Line 210 is connected to the negative side of the
battery through feedback resistor 136.
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Power passes through contacts 62 and 64 into
line 198. If bail switch 200 on the lawnmower handle is
in the STOP position, the motor is shorted since lines
198 and 202 are connected together through switch 200.
If the bail switch is in the RUN position, as when the
bail handle is being gripped by the operator, power
passes from line 198 through line 204 and into line 206.
If reed switch 208 is closed, power then passes to line
196 to voltage regulator 176 through diode 178. Reed
switch 208 (Fig. 83 senses whether a side discharge
chute, a mulching attachment, or a bagging attachment is
attached to the lawnmower. The reed switch is closed
only when such an attachment is in place. Flyback diode
211 helps protect relay contacts 194 during shutoff by
providing an alternate path for motor current flow.
Surge resistor 213 protects transistor 126 during
shutoff by providing an alternate path for relay current
flow.
As depicted in Figure 8, reed switch 208 is
disposed inside the cutting area of lawnmower chassis
16, on an inner side of chassis sidewall 209. A magnet
211 is affixed to attachment 26 and is disposed on the
opposite, outer side of sidewall 209. Reed switch is
closed in response to magnet 211, even though sidewall
209 is disposed between the magnet and the reed switch.
Figure 20 depicts an optional alarm circuit
that may be used in the present invention, to warn the
operator that key 48 is in place when the mower is not
being used. In Figure 20, alarm circuit 290 includes a
diode 292, a capacitor 294, and an indicator 296.
Indicator 296 is shown as a buzzer, but other audible or
visual indicators may be used.
When the lawnmower is turned on and bail
switch 200 is in the STOP position, no alarm signal is
generated. After bail switch 200 is placed in the RUN
position and the lawnmower is running, capacitor 294 is
charged, and stays charged until bail switch 200 goes to
the STOP position. Thereafter, capacitor 294 discharges
W096/05719 2 i 9 5 9 9 ~ p~~gg5/01765
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through indicator 29b, resulting in the generation of an
alarm signal.
If the alarm circuit depicted in Figure 20 is
placed after key 48 and is not on the main circuit
board, the alarm signal will be generated whenever key
48 is in place.
Another important feature of the present
invention is the height adjustment assembly used to
adjust the height of the chassis to achieve different
cutting lengths. The height adjustment assembly is best
understood by reference to Figures 2, 8, and 10 through
12. In these figures, the height adjustment assembly
includes a lever arm 212 that may be placed in one of
the plurality of fixed positions by moving the lever arm
into one of slots 214. Slots 214 are best shown in -
Figure 11. These slots are formed in a retainer member
216.
Lever arm 212 is connected to a pivot arm 218
which pivots about a pivot 220. Pivot 220 is retained
in position by a bracket 222 affixed to the lawnmower
chassis. The opposite end of pivot arm 218 is connected
to an axle end 224a of axle 224. Axle 224 spans the
distance between opposed wheels 28a and 28b. As lever -
arm 212 is moved, pivot arm 218 pivots about pivot 222,
thereby raising or lowering axle 224 to thereby raise or
lower chassis portion 226 that engages axle 224. Wheel
28a is connected to axle end 224a.
The movement of axle 224 in response to the
movement of pivot arm 218 causes an opposed pivot arm
228 at the opposite end of axle 224 to also be pivoted
about its fixed-pivot 230. Pivot 230 is retained in
position by a bracket 232 that is interconnected with
the lawnmower chassis. The opposite end of pivot arm
228 is connected to an end 224b of axle 224. Therefore,
axle end 224b is also raised or lowered in response to
the movement of lever arm 212, to thereby raise or lower
one end of the lawnmower chassis.
WO 96105719 219 5 9 9 5 pCTlUS95/02765a
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Movement of lever arm 212 also results in the
raising or lowering of the opposite end of the lawnmower
chassis due to a link means that connects pivot arm 228
to a pivot arm 234, which in turn is interconnected with
a second wheel axle 236. The link means is best
depicted in Figures 8 and 12. As shown in Figures 8 and
12, the link mechanism includes a link arm 238 that is
interconnected between pivot arm 228 and pivot arm 234.
The link mechanism also preferably includes a resilient
member such as spring 240 (Fig. 12), interconnected
between one end of L-shaped pivot arm 228 and link arm
238 at point 242. In the alternative, spring 240 may be
connected between pivot arm 234 and link arm 238. The
purpose of spring 240 is to reduce the force required to
raise or lower the lawnmower-chassis.
As shown in Fig. 10, the height adjustment
mechanism also includes a fourth pivot arm 244 having a
fixed pivot-246. Pivot 246 is retained in position by a
bracket 248 that is connected to the lawnmower chassis.
The movement.of pivot arm 234 in response to the
movement of -link arm 238 results in the raising or
lowering of second wheel axle 236 that is interconnected
between pivot arms 234 and 244. Pivot arm 244 also has
a fixed pivot 235 that is retained in position by a
bracket 237 interconnected with the lawnmower chassis.
In response to the rotation of pivot arm 234
about pivot 235, wheel axle 236 is raised or lowered,
thereby raising or lowering that portion of the
lawnmower chassis that engages wheel axle 236.
Another important feature of the present
invention enables the lawnmower handle assembly to be
folded during non-use, while at the same time enabling .
the handle to be tightened down to the lawnmower chassis
without any movement or play between the lawnmower ,
,handle and the lawnmower chassis. This feature of the
present invention is best understood in connection with
Figures 16 and 17. As shown in these figures, the
handle assembly includes an upper section 252 and a
lower section 254. Sections 252 and 254 are
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interconnected by a pair of threaded thumbscrews 36
which are loosened to hold down the handle for storage.
The handle assembly also includes a pair of
threaded thumbscrews 38 which are disposed in respective
apertures within lawnmower chassis 16.
As best shown in Figure 17, each of
thumbscrews 38 is received in a channel 256. Each of
the thumbscrews 38 is also received in an aperture 39 of
handle section 254. Channel 256 preferably has a
substantially flat bottom wall 258 and two opposed
angled sidewalls 260 and 262. Sidewalls 260 and 262
form included angles of between 90' and 180' with
respect to bottom wall 258 of channel 256, with105'
being preferred.
Although Figure 17 depicts the preferred
configuration of channel 256, other channel shapes may
be used that achieve the same purpose of channel 256.
For example, the channel may be substantially V-shaped,
or it may have a concave shape. Indeed, any channel
shape that has two opposed non-parallel sidewalls, even
without a bottom wall, will achieve the purpose of the
channel according to the present invention as long as
the lower end of handle section 254 has a corresponding
shape. The included angle between the two non-parallel
sidewalls is between 0' and 90'.
The lower end of lawnmower handle section 254
has a corresponding shape to that of channel 256. That
is, the lower end of handle section 254 has angled side
254a that engages angled sidewall 260; side 254a has an
included angle with respect to flat handle wall 254c
that is between 90' and 135', with 105' being preferred.
Similarly, section 254b has a shape corresponding to .
angled sidewall 262, and forms an included angle of
between 90' and 135' with respect to flat handle wall -
254c, with 105' being preferred.
~ The advantage of using angled sidewalls 260
and 262, and angled handle sides 254a and 254b, is that
the lower end of handle section 254 may be tightened
down by tightening thumbscrews 38 without there being
W096/05719 219 5 q ~ J -24- PCT~S9510276~
any play between handle sides 254a and 254b on the one
hand and channel sidewalk 260 and 262 on the other
hand_
During storage of the lawnmower, thumbscrews
38 are loosened but not removed. The lower end of
handle section 254 may then be displaced out of channel
256, thereby allowing handle section 254 to be
repositioned to promote folding of the handle assembly
for storage.
The present invention also includes a unique
cutting blade that provides sufficient lift for lifting
the grass to..be cut while at the same time minimizing
the likelihood of jamming due to the accumulation of cut
grass between. a chassis wall and the cutting blade.
The cutting blade according to the present
invention is beat understood by reference to Figures 10
and 13 through 15. In these figures, cutting blade 264
includes lead cutting edges 266, a pair of opposed outer
blade edges 268, and a pair of trailing, angled lift
edges 270. Lift edges 270 are part of respective lift
sections 272 that prevent clippings from escaping
between the blade cutting path and the inner sidewall of
the lawnmower chassis, and that impart movement to the
clippings for the purposes of mulching or ejection. The
lift sections also provide a sufficient pressure drop to
lift the grass for cutting. Lift sections 272 and lift
edges 270 are disposed opposite at least a portion of
lead cutting edges 266.
Blade 264 also includes a pair bf raised
reinforcing ribs 274 and flared supports 276. Ribs 274
and flared supports 276 both provide strength and
stability to the rotating cutting blade while creating
minimal wind resistance. Aa shown in Figure 10 and 15,
the flared supports are disposed on opposite sides of
hub 265, are non-perpendicular and non-coplanar with hub
265, and are substantially V-shaped. Blade 264 is
bolted to the output shaft of motor 18 at hub 265.
Outer blade edges 268 are disposed between
cutting edges 266 and trailing lift edges 270. Each of
R'O 96/05719 PGTIUS95~02765
-25-
outer blade edges 268.preferably has a rake angle 278
between cutting edge 266 and outer blade edge 268 that
ie less than 90', and is preferably between 75' to 85'.
About halfway between cutting edge 266 and lift edge
270, the rake angle is discontinued and may in fact be
reversed. Other rake angles may be used, as long as
included angle 267 between outer blade edge 268 and
blade longitudinal axis 264a is greater than 90' when
taken across the blade, and as long as outer blade edge
268 is non-linear. Included angle 267 is between 120'
and 95', with 105' to 95' being preferred. As depicted
in Figure 10, outer blade edges 268 may be substantially
V-shaped; however, other shapes may be used including a
concave shape, as long as the outer blade edges are non-
linear.
The purpose of rake angle 278 and included
angle 267 is to provide the cutting blade with points
282 which may readily move through any grass clippings
or debris that has accumulated between the blade end and
aidewall 284 of the lawnmower chassis. In some prior
art lawnmowers, the outer blade edge was substantially
straight, and perpendicular to the longitudinal axis of
the blade, which may result in jamming of the cutting
blade when the cutting blade encountered accumulated
debris between the blade ends and sidewall 284.
The reasonfor not continuing the rake angle
all the way to trailing lift edge 270 is that a
substantial portion of the lift surface would be removed
from the end of the blade, where it is needed the moat,
for lifting and moving grass and for preventing
clippings from escaping between the cutting path and the
chassis aidewall. By discontinuing or reversing the
rake angle, a substantial portion of the effective lift
surface is retained.
In the present invention, cutting points 282
are provided to move through any accumulated debris
without sacrificing a significant portion of the lift
sections. The rake angle and the lift angle enable the
cutting blade to move through any accumulated debris
2195995
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without jamming while at the same time creating
sufficient lift for proper grass cutting and mulching or
ejection.
The present invention also includes a unique
wire harness which enables two batteries to be
simultaneously charged, while at the same time
preventing a charged battery from discharging into an
uncharged battery.
This wire harness is depicted in Figure 19.
In Figure 19, wire harness 300 includes two-prong
connectors 302, 304 and 306, a pair of conductive wires
308 connected between connector 302 and connector 3D6,
and a pair of conductive wires connected between
connectors 304 and 306. Connector 302 is connected to a
first electrical connector on a first battery, connector
304 is connected to a second electrical connector on a
second battery, and connector 3D6 is connected to an
electrical connector on a battery recharger. Each of
the first and second batteries preferably has a blocking
diode to prevxnt current from leaving their respective
electrical connectors. The blocking diodes are
preferably disposed between their respective electrical
connectors and a respective battery terminal. This
feature prevents current from one of the batteries from
passing through wire harness 300 into the other battery,
in the event_that one of the batteries is more fully
charged than-the other. This feature also prevents a
spark or fire if the two pins of the same battery
electrical connector are accidentally shorted together.
While the preferred embodiment o~ the present
invention has been shown and described, alternate
embodiments will be apparent to those skilled in the art
and are within the intended scope of the present
invention. Therefore, the invention is to be limited
only by the following claims.
