156 lines
8.0 KiB
Markdown
156 lines
8.0 KiB
Markdown
# Engine-Position Inputs
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## Purpose
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This module defines the dedicated crank and cam position-input class for
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NeoECU V1. It is separate from the generic digital-input module because engine
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timing needs bounded edge delay, jitter, and false-trigger behaviour.
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This is an architecture and schematic-design basis, not a released schematic.
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Final component values and qualified fault ratings require the selected sensor,
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harness, connector, and test results.
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## V1 timing and signal assumptions
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| Signal | V1 arrangement | Function |
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| --- | --- | --- |
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| Crank | Two events per crank revolution | 180-degree position events and speed estimation |
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| Cam | One event per 720-degree cycle | Four-stroke phase identification |
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The V1 speed limiter is 5,000 RPM. At that speed the interval between selected
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crank events is 6 ms; a four-event-per-revolution trigger would instead have a
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3 ms interval. V1 retains the two-event pattern. Moving to four events is a
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future trigger-wheel and firmware change, not a reason to alter this input
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class.
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The intended interface is a three-wire, active-low Hall sensor: the output is
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normally high and sinks current while active. Capture one defined edge per
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event, normally the falling edge, in an STM32H747 timer channel. Do not use
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both edges as independent position events unless firmware explicitly models
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the Hall-window geometry.
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`FEBI BILSTEIN 44421` is the selected cam sensor. It cross-references to EFI
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Automotive 144321 and OE references 1920.6T and 9629684380. It is a three-wire
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12 V Hall sensor with an open-drain output: supply it from `+12V_SENS`, connect
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its return to `SENSOR_GND`, and pull its signal high at the ECU. Confirm the
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physical connector pinout and output sink-current limit from the delivered part
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or its manufacturer documentation before assigning the connector pins and
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freezing `R_PULLUP`. The crank-sensor part number remains to be selected.
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## Electrical interface
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```text
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ECU
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+12V_SENS ------------------------+--------------------------> sensor supply
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SENSOR_GND ---------------------------------------------------> sensor return
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+12V_SENS -- R_PULLUP -- TRIG_x ---+-- connector -- sensor output
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+-- connector-side transient protection
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+-- R_DIV_TOP --+-- Schmitt buffer --> 3.3 V timer input
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+-- R_DIV_BOTTOM -- SENSOR_GND
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+-- C_FILTER ------ SENSOR_GND
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```
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- Supply the sensor from `+12V_SENS`; its rail generation, protection, current
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limit, and diagnostics belong to `POWER_ARCHITECTURE.md`.
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- Place the signal pull-up at the ECU, to `+12V_SENS`, rather than at the
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sensor or 3.3 V domain. A 4.7 kOhm footprint is a starting provision only.
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Select its value from the confirmed sensor sink-current rating, high/low
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thresholds, cable capacitance, and required edge time.
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- Protect the connector-side signal against the assigned positive and negative
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harness transients. The completed clamp, series impedance, divider, and
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Schmitt buffer must keep all intermediate nodes within their validated limits
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without back-powering the 3.3 V rail while the ECU is off.
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- Scale the high-level signal before the 3.3 V Schmitt buffer. The buffer
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provides defined logic thresholds and hysteresis; the STM32 pin is never
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exposed to the sensor-domain voltage.
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- The divider also supplies the resistance for the RC filter. Connect the
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configurable `C_FILTER` footprint from the divided signal to `SENSOR_GND`,
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in parallel with `R_DIV_BOTTOM`. Its effective series resistance is
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`R_DIV_TOP || R_DIV_BOTTOM`, so `tau = (R_DIV_TOP || R_DIV_BOTTOM) *
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C_FILTER`. Do not add a separate RC series resistor by default. Add one only
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if it has a separately demonstrated purpose, such as limiting residual-clamp
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current.
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- Populate 1 nF initially, with 470 pF and 2.2 nF alternatives available.
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Validate the selected value with the final harness and ignition operating; it
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must reject short interference without eroding legitimate-edge timing margin.
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- Use the automotive-qualified `SN74LVC2G17QDCKRQ1`, powered from
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`+3V3_MAIN`, as the two-channel non-inverting Schmitt buffer for crank and
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cam. Its inputs must only receive the protected, divided signal, never the
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raw 12 V harness node.
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## Connector, harness, shield, and layout
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Crank and cam use the dedicated **engine-sensors connector**, not the
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power/actuator connector. This preserves physical separation from coil,
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injector, starter, and other high-current wiring. The V1 connector plan is:
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| Connector group | Carries |
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| --- | --- |
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| Power/actuators | Battery and power returns, ignition, injector, and high-current outputs |
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| Engine sensors | Crank/cam supply, signals, sensor returns, thermistors, and analogue sensors |
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| Vehicle I/O/CAN | CAN, deadman, generic digital inputs, and generic 5 V logic outputs |
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Use a screened harness for each trigger sensor. Route the trigger signal as a
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twisted pair with `SENSOR_GND`; route its `+12V_SENS` supply in the same
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screened cable. The screen is an EMC structure, not a sensor return or circuit
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ground conductor.
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Terminate each screen at the ECU end only, at a dedicated `SHIELD_GND` bond
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with a short, broad connection to the enclosure/chassis structure near the
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power-entry region. Do not connect the screen to `SENSOR_GND`, `DGND`, or
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`+3V3_ANA`, and do not connect it at the sensor end. Final backshell and case
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bonding details depend on the selected connector and enclosure.
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Place transient protection at the connector. Keep the divider, filter, Schmitt
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buffer, and timer route on the quiet MCU side. Keep these paths away from the
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ignition high-voltage node, injector switching loop, and regulator hot loops.
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## False-trigger handling and validation
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Hardware filtering is the first defence. Firmware provides a second,
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independent plausibility check; it does not replace the hardware network.
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For every selected crank edge, firmware shall:
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1. timestamp the edge with the timer;
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2. reject an edge whose interval since the previous accepted edge is below a
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calibrated physical minimum; and
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3. reject an interval that implies an implausible acceleration from the recent
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accepted speed estimate.
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The threshold shall be derived from the maximum measured engine acceleration,
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the 5,000 RPM speed limit, timer resolution, and a conservative margin. It
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shall not be a fixed arbitrary debounce time. A rejected edge shall not update
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speed, position, dwell, injection scheduling, or the reference interval, so a
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spark-induced pulse cannot displace the next accepted timing event.
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Cam edges shall be checked against the expected crank phase. A missing or
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inconsistent cam event removes phase synchronisation and must lead firmware to
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the explicitly defined no-sync behaviour; it must never invent a phase from a
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single unexpected edge.
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Validate with the installed engine and final harness:
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- no false accepted crank/cam events during worst-case dwell and spark;
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- no missed genuine events at 5,000 RPM and during the maximum measured
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acceleration;
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- measured conditioning delay and jitter within the firmware timing budget;
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- correct rejection of injected short glitches without corrupting the following
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genuine event; and
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- sensor unplug, signal open/short, and sensor-supply fault behaviour as
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defined by the final selected parts.
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## Remaining inputs before schematic freeze
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1. Confirm the FEBI 44421 physical connector pinout and output sink-current
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limit from the delivered part or manufacturer documentation.
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2. Select and obtain the equivalent data for the crank sensor.
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3. Confirm connector family, pin assignment, cable length/construction, and
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enclosure/backshell method for the engine-sensors connector.
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4. Select protection components and final pull-up, divider, and filter values
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against the confirmed sensor and harness limits.
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5. Measure maximum real engine acceleration and establish the timer-based
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interval-plausibility limits in firmware.
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