303D: Powershift & Automatic Trans Control & Shifting

Question 1

What is the purpose of the transmission scavenging pump and the torque converter scavenging pump?

Answer 1

Remove leakage oil from transmission/torque converter preventing overheating from excessive buildup of oil

303D Pg. 7

Question 2

What is the purpose of the transmission priority valve?

Answer 2

Ensures that oil pressure is available for steering clutch and brake functions before transmission functions.

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Question 3

What does transmission clutch modulation refer to?

Answer 3

The gradual buildup of clutch pressure, resulting in a controlled slippage to prevent harsh shifting and shift shock.

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Question 4

What are the three circuits used in the hydraulic system of a powershift transmission?

Answer 4

• Clutch application
• Torque converter charging
• Transmission lubrication

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Question 5

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

Answer 5

Shift selector valve

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Question 6

The function of the clutch pressure regulator valve is to:

Answer 6

Limit clutch application pressure
100-500 psi

303D Pg. 3

Question 7

The transmission circuit that receives oil flow after the clutch application circuit has been satisfied, is the:

Answer 7

Torque converter charging circuit

303D Pg. 4

Question 8

Maximum oil pressure within the torque converter is controlled by:

Answer 8

Torque converter relief valve

303D Pg. 4

Question 9

Torque converter outlet oil flow is cooled and filtered before it is directed into the:

Answer 9

Transmission lubrication circuit

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Question 10

Some transmissions are equipped with a scavenging pump whose function is to:

Answer 10

Remove leakage oil from the transmission case and return it to the reservoir

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Question 11

Oil flow for transmission control system operation is supplied by:

Answer 11

Charging pump. Typically driven at engine speed.

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Question 12

The two factors that influence the point at which an automatic transmission will shift are:

Answer 12

• Machine ground speed
• Operator’s demand for power

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Question 13

The function of the governor circuit in an automatic transmission is to:

Answer 13

Provide a hydraulic signal that is proportional to machine ground speed.

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Question 14

The hydraulic governor in an automatic transmission operates by balancing the centrifugal force of the governor flyweights against:

Answer 14

Governor pressure

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Question 15

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)

Answer 15

False

Accomplished by adjusting shift signal valve spring force. Lower spring force = earlier shift.

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Question 16

The function of the modulator circuit in an automatic transmission is to:

Answer 16

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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Question 17

If a clutch releases much more quickly than the next clutch is applied during a shift, the result is:

Answer 17

• Engine rpm flare up
• Momentary freewheeling of the machine until the next clutch is fully applied

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Question 18

Momentary engine lugging and slowing of machine speed during shifting indicates that:

Answer 18

The releasing clutch did not fully release before the next clutch applied

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Question 19

The shift selector of an electronically shifted automatic transmission consists of a number of switches that sends __ signals to the ECU that indicate ____.

Answer 19

Voltage signals to the ECU that indicate the speed and direction desired by the operator

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Question 20

What component of an electronic automatic shift control system performs the same function as the governor in hydraulically controlled systems?

Answer 20

Speed sensor

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Question 21

What are four functions of the ECU in an electronically controlled shift system?

Answer 21

• Control upshifts and downshifts
• Control clutch modulation
• Provide diagnostic information
• Provide a warning to the operator when a malfunction occurs

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Question 22

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:

Answer 22

Shift solenoids

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Question 23

What typically drives the transmission charging pump?

Answer 23

An engine accessory drive or torque converter impeller

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Question 24

What limits working pressure in the torque converter?

Answer 24

Torque converter relief valve

50 - 125 psi

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Question 25

What is the term that refers to the gradual buildup of clutch application pressure to give a controlled amount of slippage?

Answer 25

Clutch Modulation

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Question 26

What is the function of the priority valve in a powershift transmission?

Answer 26

Ensures oil pressure is available for steering clutch and brake functions before transmission functions.

Normally closed pressure control valve

303D Pg. 9

Question 27

What are the four main clutch components in a typical transmission?

Answer 27

• Steel Reaction Discs
• Friction Discs
• Pistons
• Return Springs

303D Pg. 11

Question 28

Why must care be taken when towing machinery equiped with a powershift or automatic transmission?

Answer 28

Pressure lubricated, so there is no transmission lubrication when the engine is not running.

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Question 29

What is used in an automatic transmission to control the rate of clutch release?

Answer 29

An orifice which restricts the oil flow back to the transmission sump.

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