303D: Powershift & Automatic Trans Control & Shifting Flashcards
What is the purpose of the transmission scavenging pump and the torque converter scavenging pump?
Remove leakage oil from transmission/torque converter preventing overheating from excessive buildup of oil
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What is the purpose of the transmission priority valve?
Ensures that oil pressure is available for steering clutch and brake functions before transmission functions.
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What does transmission clutch modulation refer to?
The gradual buildup of clutch pressure, resulting in a controlled slippage to prevent harsh shifting and shift shock.
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What are the three circuits used in the hydraulic system of a powershift transmission?
- Clutch application
- Torque converter charging
- Transmission lubrication
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In a basic hydraulic shift control system, transmission speed and direction changes are made by the:
a) clutch pressure regulator valve
b) torque converter pressure relief valve
c) shift selector valve
d) lubrication pressure relief valve
Shift selector valve
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The function of the clutch pressure regulator valve is to:
Limit clutch application pressure
100-500 psi
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The transmission circuit that receives oil flow after the clutch application circuit has been satisfied, is the:
Torque converter charging circuit
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Maximum oil pressure within the torque converter is controlled by:
Torque converter relief valve
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Torque converter outlet oil flow is cooled and filtered before it is directed into the:
Transmission lubrication circuit
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Some transmissions are equipped with a scavenging pump whose function is to:
Remove leakage oil from the transmission case and return it to the reservoir
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Oil flow for transmission control system operation is supplied by:
Charging pump. Typically driven at engine speed.
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The two factors that influence the point at which an automatic transmission will shift are:
- Machine ground speed
- Operator’s demand for power
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The function of the governor circuit in an automatic transmission is to:
Provide a hydraulic signal that is proportional to machine ground speed.
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The hydraulic governor in an automatic transmission operates by balancing the centrifugal force of the governor flyweights against:
Governor pressure
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Some automatic transmissions allow the adjustment of automatic shift points. This is normally accomplished by replacing the shift signal valves with ones of differing areas. (T/F)
False
Accomplished by adjusting shift signal valve spring force. Lower spring force = earlier shift.
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The function of the modulator circuit in an automatic transmission is to:
Alter the shift points in relation to the operator’s demand for power.
Wide-Open Throttle: Low modulation pressure = Delayed shifts
Closed Throttle: High modulation pressure = Early shifts
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If a clutch releases much more quickly than the next clutch is applied during a shift, the result is:
- Engine rpm flare up
- Momentary freewheeling of the machine until the next clutch is fully applied
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Momentary engine lugging and slowing of machine speed during shifting indicates that:
The releasing clutch did not fully release before the next clutch applied
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The shift selector of an electronically shifted automatic transmission consists of a number of switches that sends __ signals to the ECU that indicate ____.
Voltage signals to the ECU that indicate the speed and direction desired by the operator
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What component of an electronic automatic shift control system performs the same function as the governor in hydraulically controlled systems?
Speed sensor
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What are four functions of the ECU in an electronically controlled shift system?
- Control upshifts and downshifts
- Control clutch modulation
- Provide diagnostic information
- Provide a warning to the operator when a malfunction occurs
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Output devices in an automatic transmission that are responsible for speed and direction changes as well as the application and release of torque conveter lockup clutches are:
Shift solenoids
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What typically drives the transmission charging pump?
An engine accessory drive or torque converter impeller
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What limits working pressure in the torque converter?
Torque converter relief valve
50 - 125 psi
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What is the term that refers to the gradual buildup of clutch application pressure to give a controlled amount of slippage?
Clutch Modulation
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What is the function of the priority valve in a powershift transmission?
Ensures oil pressure is available for steering clutch and brake functions before transmission functions.
Normally closed pressure control valve
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What are the four main clutch components in a typical transmission?
- Steel Reaction Discs
- Friction Discs
- Pistons
- Return Springs
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Why must care be taken when towing machinery equiped with a powershift or automatic transmission?
Pressure lubricated, so there is no transmission lubrication when the engine is not running.
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What is used in an automatic transmission to control the rate of clutch release?
An orifice which restricts the oil flow back to the transmission sump.
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