Chapter 18 · Ignition, Knock Control, Dwell & Oxygen Sensing

Knock Control & BTS

Piezo knock filtering, retard dynamics, the ATR model and BTS enrichment.

Calibration symbols

TABGBTS DWKREC DWKSTE KFLBTS TABG_W DLBTS KRMX ATR BTS G61 G66

ECUs covered

06A906032LP

Size

11 symbols · 1 diagram · ~714 words

Piezo knock filtering, retard dynamics, the ATR model and BTS enrichment.

To extract maximum brake torque from the 1.8T 20V engine without catastrophic pre-ignition or piston crown erosion, Bosch ME7.5 utilizes a dual-layered closed-loop protection architecture: Cylinder-Selective Acoustic Knock Control (KR) for combustion stability, and the Physical Exhaust Gas Temperature Model (ATR) paired with Component Protection (BTS) for turbine and valve thermal survivability.

18.1. Piezoelectric Knock Sensing & Frequency Bandpass Filtering#

The 1.8T engine utilizes two broadband piezoelectric accelerometer knock sensors bolted to the cylinder block:

G61 (Knock Sensor 1, Cylinders 1 & 2): Input on Pins 106 (+) and 107 (-).
G66 (Knock Sensor 2, Cylinders 3 & 4): Input on Pins 100 (+) and 99 (-).

1. Acoustic Resonance Frequency Calculation#

When end-gas detonation occurs, pressure shockwaves resonate within the combustion chamber at characteristic frequencies determined by the speed of sound in hot combustion gas (c_s \approx 900\text{ m/s}) and the cylinder bore diameter (D_{\text{bore}} = 81.0\text{ mm}):

$f_{\text{knock}} =\frac{1.841 \times c_s}{\pi \times D_{\text{bore}}} =\frac{1.841 \times 900\text{ m/s}}{\pi \times 0.081\text{ m}}\approx \mathbf{6.51\text{ kHz}}$

The second radial harmonic occurs at approximately 13.2\text{ kHz}. The internal Bosch CC460 / HIP9011 signal conditioning processor filters the raw AC waveform through a configurable bandpass filter centered on 6.8\text{ kHz}, discarding extraneous mechanical valvetrain, alternator, and transmission gear noise.

2. Knock Measurement Gate (`KRW`)#

The ECU does not listen continuously. It opens an evaluation window per cylinder:

Gate Open: 10\text{° ATDC} (after peak firing pressure initiates).
Gate Close: 50\text{° ATDC} (before exhaust valve opening).

3. Dynamic Reference Noise Adaptation (`KRMX`)#

The integrator integrates the rectified voltage signal across the gate. The ECU maintains a rolling average of background engine noise (KRMX). A combustion event is classified as "knock" only if its integrated peak voltage exceeds the reference baseline by a calibrated threshold ratio (K_{\text{thresh}}\approx 1.4\dots 1.8).

┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│                   CYLINDER-SELECTIVE KNOCK RETARD & DECAY DYNAMICS                               │
├──────────────────────────────────────────────────────────────────────────────────────────────────┤
│ Ignition Angle                                                                                   │
│      ▲                                                                                           │
│ Base ┼────────────────────────┐                             ┌─────────────────── Base Advance    │
│      │                        │                             │                                    │
│      │       Knock Event!     │ DWKSTE (-3.0°)              │ DWKREC (+0.75° / 20 cycles)        │
│      │      ┌────────────┐    ▼                             ▲                                    │
│      │      │            │    ┌─────────────────────────────┘                                    │
│      │      │            │    │ Hold Dwell Window                                                │
│      │      ▼            │    │                                                                  │
│ Ret  ┼───────────────────┴────┴─────────────────────────────────────────► Engine Cycles          │
│      │◄───── Normal ─────►│◄─── Retarded ────►│◄────── Recovery ───────►│                        │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

4. Knock Retard Step & Recovery Parameters#

DWKSTE (Knock Retard Step): When knock is detected on a cylinder, the ECU immediately retards ignition timing for that specific cylinder by 3.0\text{° KW} on the next firing stroke.
WKRMX (Maximum Retard Limit): Caps maximum cumulative individual cylinder knock retard to -12.0\text{° KW} (dwkrz_x).
DWKREC (Advance Recovery Rate): If no knock is detected over a calibrated hold interval (e.g. 20–40 engine revolutions), timing advances back toward the base map in small increments of +0.75\text{° KW} per step.

18.2. Modeled Exhaust Gas Temperature (`ATR`) & Component Protection (`BTS`)#

On the 06A906032LP (and all standard 150/180 PS ME7.5 platforms), there is no physical thermocouple sensor in the exhaust manifold. Instead, Bosch implements the Abgastemperaturmodell (ATR) to calculate real-time exhaust gas temperature (tabg_w at RAM 0x38148C).

Factors Governing Modeled EGT#

$\text{EGT}_{\text{modeled}} = f(N_{\text{mot}}, \ r_l, \ \lambda_{\text{actual}}, \ \Delta ZW_{\text{retard}}, \ T_{\text{ambient}})$

Ignition Retard Thermal Penalty: When knock control retards spark timing (dwkrz), late combustion causes the flame front to exit into the exhaust manifold, rapidly increasing exhaust temperatures by 30\text{°C} to 80\text{°C}.

Bauteileschutz (BTS — Component Protection Fueling)#

BAUTEILESCHUTZ (BTS) THERMAL ENRICHMENT THRESHOLDS

Symbol	Flash Address	Factory Val	High-Perf Tuned	Functional Purpose
TABGBTS	0x01956A	920 °C	950 °C	Modeled EGT activation threshold
KFLBTS	0x0194A2 (16x12)	Lambda ~0.82	Lambda 0.75–0.78	Rich fueling target vs RPM & Load
DLBTS	0x019574	0.05 lambda	0.03 lambda	Transient delta step enrichment

Calibration Rules for Upgraded Turbochargers#

Never Disable BTS: Raising TABGBTS to an impossible value (e.g. 1200\text{°C}) to force an engine to run leaner for a dyno pull will cause turbine housing cracking, wastegate flap warping, and exhaust valve burning.
Set TABGBTS to Inconel Limits: For factory K03/K04 turbochargers equipped with Inconel 713C turbine wheels, continuous operating temperatures must remain below 950\text{°C} (1742\text{°F}). Setting TABGBTS = 950 °C allows maximum power under brief acceleration while instantly commanding cooling enrichment (\lambda = 0.77) during sustained top-speed runs.