Chapter 5: Speed Control System; How The Speed Control Works - MTD 830 Series Shop Handbook

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830-860 SERIES SELF-PROPELLED MOWERS

CHAPTER 5: SPEED CONTROL SYSTEM

How the speed control works

1. The red lever on the control panel applies ten-
sion to a cable. See Figure 5.1.
Red lever = speed control
Figure 5.1
2. The cable runs down into the crankshaft pulley
cover, where it pulls on an arm that rotates a
cam. See Figure 5.2.
Ramps
Figure 5.2
Bottom end of
speed control
cable
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3. The cam has a series of ramps that work against
ramps in the crankshaft pulley cover, forcing the
two sheaves of the crankshaft pulley together.
4. When the crankshaft pulley sheaves squeeze
together, the force the contact patch of the drive
belt further out on the pulley. The outer part of
the pulley travels at a higher linear speed than
the part closer to the crankshaft, shifting the
drive ratio in the direction of greater speed.
5. The belt does not stretch any significant amount.
When the engine end pulley effectively grows,
the tension on the belt increases.
6. The sheaves on the transmission pulley are
spring-loaded to react to the added belt tension.
See Figure 5.3.
Power ratio to wheels
Figure 5.3
Speed ratio to wheels