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SECTION
4
BLADE BRAKE AND CLUTCH (BBC) SYSTEM
introduction
In 1982 the federal government mandated that all
consumer walk behind mowers with a cut of 63.5 cm
(25') or less be equipped with safety devices. There
are two primary criteria which these safety devices
must meet.
1.
A two step operation must be performed in order
2. The
blade must come to a stop within
3
seconds
One of the ways The Toro Company met these
requirements was with the Blade Brake and Clutch or
BBC System. This system uses a clutch on the engine
crankshaft so that the blade can freewheel on the
crankshaft. It also uses a brake
to stop the blade within
3 seconds of when the operator releases the control
bar. This system has the advantage of allowing the
operator to stop the blade without stopping
the engine.
The BBC system is somewhat complex, and will
therefore be broken down into 4 subsections:
BBC Control Box
BBC Bellcrank System
BBC Deck Mechanism
BBC Cable
to get the blade turning.
of the operator leaving the operator's position.
BBC CONTROL BOX
BBC Control
Box
Operation
The BBC control mechanism's purpose is to actuate
the deck mechanism.
It
does this by tensioning and
loosening the BBC cable. While this sounds simple
enough, keep in mind that the control mechanism must
also meet the federal government's '2-step'
blade
engagement procedure, and on many models must
also control traction.
First, let's take a look at normal operation of
the BBC
control box. See Figure
74.
The normal or 'at rest' position of the control bar is
indicated by the number 1 in the previous figure. In
order to engage the blade, the operator must first
'cock' the control
bar
down to position 2, then raise the
control bar to position 3 .
Notice that position
3 is approximately 12 cm
(5")
below
the handle. This distance between position
3
and the
handle is resewed for engagement of the transmission
on those models equipped with the self propel. On
units without self-propel the control bar
can be lifted to
Vacu-Power
ower
47
the handle without affecting operation
of the BBC
system.
GROUND
SPEED
Figure 74
After engagement of the blade, release of the control
bar causes
it
to drop to the number 1 position which
disengages the blade and, on self-propel models, the
transmission.
Next, let's take a look inside the control box at the
various components and identify their function. See
Figure 75 and the corresponding explanations that
follow.
d
Figure 75
BBC System
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