Transmission chapter 5

Transmission Hydraulics and Orifice Functionality

• Separator Plate Gaskets and Orifices:

  • Large holes in a separator plate gasket align with structural bolt locations.

  • Smaller drilled holes in the separator plate matching gasket openings serve as calibrated hydraulic orifices.

• Fluid Restriction Mechanics and Metaphors:

  • Faucet Analogy: An orifice regulates fluid volume similarly to a manual water faucet controlling flow.

  • Highway Analogy: An orifice acts like constricting a five-lane highway filled with traffic down to a single lane. Fewer vehicles pass through per unit of time.

  • Hydraulic Effect: In a fluid-filled circuit, an orifice creates a localized restriction (analogous to orange construction barrels on a road). While fluid eventually reaches the target component, the time required to build operating pressure increases.

• Modifying Orifice Dimensions:

  • Drilling an orifice to expand its size from $0.001\,\text{in}$ to $0.010\,\text{in}$ dramatically increases fluid velocity through the passage.

  • Operational Effect: Fluid reaches the engaging component faster, resulting in a noticeably firmer shift.

  • Irreversibility Warning: Once an orifice in a separator plate is enlarged, it cannot be reduced back down.

Transmission Diagnostic Logic: Cause and Effect Relationships

• Line Pressure Principles:

  • Line pressure is the primary working hydraulic pressure for the entire transmission assembly, generated directly by the fluid pump.

  • Direct Effect: Increasing line pressure increases working pressure across every circuit, causing all shifts to become inherently firmer.

• Accumulator Spring Dynamics:

  • Accumulators serve as hydraulic shock absorbers designed to cushion and soften gear engagements.

  • Replacing a stock accumulator spring with a softer spring allows the accumulator piston to stroke faster and more easily.

  • Direct Effect: A faster accumulator stroke reduces fluid absorption during engagement, directly yielding a firmer shift feel.

• Hydraulic Circuits versus Electrical Circuits:

  • Electrical systems route power through numbered circuits (e.g., circuit $1$, $2$, $5$, or $7$ powering an air conditioning compressor).

  • Hydraulic systems route pressure through named channels ("worm tracks") cast into the valve body and mating transmission case.

  • Major named hydraulic circuits include Supply, Main, Drive, Reverse, and Governor circuits.

Fundamentals of Electromagnetism in Transmission Control

• Transition to Electronic Controls:

  • Modern electronically controlled transmissions operate under the same mechanical and hydraulic principles as older hydraulic units, substituting wired electronic components in place of purely mechanical controls.

• Constructing an Electromagnet:

  • Required Components: A conductive wire coil (such as copper) wrapped around a ferrous metal core (such as a steel roofing nail or magnetite).

  • Mechanism: Passing electric current through the copper conductor generates an invisible magnetic field around the wire. Placing a steel core within this field magnetizes the core material; longer exposure yields higher magnetization.

  • Bench Example: Tightly wrapping copper wire around a steel roofing nail and connecting the leads to a $9\,\text{V}$ battery creates a functional electromagnet capable of lifting steel items like paper clips.

• Permanent Magnets versus Electromagnets:

  • Permanent Magnets (e.g., a magnetic pocket screwdriver): Retain a fixed magnetic strength without external power, cannot be turned off, and permanently lose strength if cracked or broken.

  • Electromagnets: Can be instantly switched ON or OFF and allow dynamic strength adjustments by altering the volume of current passed through the conductive coil.

Solenoid Structure and Hydraulic Valve Operation

• Anatomy of a Shift Solenoid:

  • Coil Assembly: Composed of a long length of fine, multi-stranded copper wire tightly wound into a continuous coil.

  • Plunger / Actuator: A movable internal pin or piston constructed from steel or ferrous metal.

  • Return Spring: An internal spring that biases the plunger when de-energized ("everything has a spring").

  • Metering Ball: A small ball component resembling a hydraulic check ball used to open or seal fluid ports.

• Solenoid Operational Metaphor:

  • Solenoids function as electronically operated doors.

  • Venting (Door Open): Allows fluid to discharge freely through the orifice, preventing pressure accumulation.

  • Applying (Door Closed): Blocks the discharge port, trapping fluid within the bore to build working pressure.

• Solenoid-to-Valve Hydraulic Interaction:

  • Solenoids are mounted directly at the face of a hydraulic valve bore within the valve body.

  • Energizing the solenoid shuts the venting port, trapping hydraulic fluid inside the bore against the end face of the valve spool.

  • As trapped fluid pressure builds and overcomes return spring resistance, the hydraulic valve strokes inside its bore. Pressure is modulated electronically via computer signals rather than driver-operated mechanical linkages.

Solenoid Failure Modes

• 1. Electrical Failures:

  • Causes: Open circuits, short circuits, disconnected harness plugs, broken wiring, or rodent damage (e.g., chipmunks chewing through wires).

  • Impact: Current cannot pass through the copper coil, preventing magnetic field creation. The plunger remains stationary in its resting state.

• 2. Mechanical Failures:

  • Causes: Broken internal return springs or physical binding caused by foreign debris wedged inside the plunger chamber (e.g., clutch friction material).

  • Impact: The plunger physically jams, preventing movement regardless of magnetic field activation.

• 3. Hydraulic Failures:

  • Causes: Hardened, torn, or leaking rubber O-ring seals fitted around the solenoid body inside the valve body bore.

  • Impact: Fluid continuously leaks past the defective seal, creating a constant artificial vent. Hydraulic pressure fails to build, preventing the control valve from stroking.

• Universal Symptom of Solenoid Failure:

  • All three failure modes produce identical functional symptoms: the associated control valve fails to stroke or strokes sluggishly, causing delayed shifts, soft engagement, low pressure, or complete gear loss.

Solenoid Classifications and Electrical Resistance

• Simple On/Off Solenoids:

  • Binary operation operating strictly in two states: fully ON or fully OFF.

  • The hydraulic port is either fully open or fully closed, offering no middle ground for dynamic pressure control.

• Pulse Width Modulated (PWM) Solenoids:

  • Toggles rapidly between open and closed states to achieve partial opening positions (e.g., $75\%$, $50\%$, $25\%$, or $10.5\%$ open).

  • Fuel Injector Metaphor: Operates like an engine fuel injector, which pulses to supply heavy fuel flow during sub-zero cold starts and reduces fuel volume when warm.

  • Allows dynamic adjustments to shift timing and firmness tailored precisely to throttle position and driving demands.

• External Case-Mounted Solenoids:

  • Certain Asian vehicle manufacturers (e.g., Honda and Toyota) bolt solenoid packs directly to the exterior of the transmission case rather than internally on the valve body.

• Electrical Resistance Specifications:

  • Pulse Width Modulated solenoids possess substantially lower internal electrical resistance than basic On/Off solenoids.

  • Low resistance allows high-frequency switching and rapid current flow without inductive lag or excessive heat buildup.

Pulse Width Modulation Signal Metrics

• Duty Cycle:

  • Definition: The percentage of active (ON) time versus total cycle time ($\text{Duty Cycle} = \frac{\text{Time}_{\text{ON}}}{\text{Time}_{\text{Total}}} \times 100$).

  • Example: Equal duration of ON and OFF states represents a $50\%$ duty cycle.

  • A $100\%$ duty cycle means the solenoid is continuously energized and fully open.

  • Voltage Modulation: PWM chops average voltage. Toggling a $12\,\text{V}$ power source at a $50\%$ duty cycle produces an effective average output of $6\,\text{V}$.

  • LED Controller Analogy: Connecting an LED light directly to a $12\,\text{V}$