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