Vehicle Speed & Boost by Gear

High-power front-wheel-drive (FWD) platforms—such as the Volkswagen Golf GTI and Jetta 1.8T—suffer from severe mechanical traction limitations in lower gears. Delivering peak turbocharger boost (> 1.3 bar) and 400 Nm of engine torque in 1st or 2nd gear overwhelms street tire adhesion, causing violent wheel hop, differential failure, and excessive front tire wear.

Bosch ME7.5 solves this challenge through an internal **Gear Detection Algorithm (Gangerkennung) that mathematically determines the currently engaged mechanical transmission gear from engine speed and vehicle velocity. By linking this gear observer to the maximum cylinder filling ceiling (LDRXN), an engineer can implement progressive Boost-by-Gear (gangabhängige Ladedruckbegrenzung)** to optimize launch traction without sacrificing high-speed top-end acceleration.

code

┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│                     GEAR RATIO DETECTION & BOOST-BY-GEAR PIPELINE                                │
├──────────────────────────────────────────────────────────────────────────────────────────────────┤
│                                                                                                  │
│   [ Engine Speed: N_mot (G28 Crank Sensor) ]                                                     │
│   [ Vehicle Road Speed: vfzg (G22 Hall Sensor / CAN ABS Frame 0x1A0) ]                           │
│   [ Clutch Switch: B_kuppl == 0 (Pedal Released) ]                                               │
│                                  │                                                               │
│                                  ▼ Ratio Calculation                                            │
│   ┌─────────────────────────────────────────────────────────────────────────┐                    │
│   │ Transmission Ratio Quotients: R_gear = N_mot / vfzg                     │                    │
│   │ • Gear 1: R ≈ 135 rpm/(km/h) ──► Selected Gear = 1                      │                    │
│   │ • Gear 2: R ≈  78 rpm/(km/h) ──► Selected Gear = 2                      │                    │
│   │ • Gear 3: R ≈  52 rpm/(km/h) ──► Selected Gear = 3                      │                    │
│   │ • Gear 4: R ≈  39 rpm/(km/h) ──► Selected Gear = 4                      │                    │
│   │ • Gear 5: R ≈  30 rpm/(km/h) ──► Selected Gear = 5                      │                    │
│   │ • Gear 6: R ≈  25 rpm/(km/h) ──► Selected Gear = 6                      │                    │
│   └──────────────────────────────┬──────────────────────────────────────────┘                    │
│                                  │                                                               │
│                                  ▼ Active Gear State: gangi                                      │
│   ┌─────────────────────────────────────────────────────────────────────────┐                    │
│   │ Gear-Dependent Maximum Engine Load Selector:                            │                    │
│   │ • 1st Gear: Clamped to 0.55 bar boost (rl = 115%) -> Zero Wheelspin      │                    │
│   │ • 2nd Gear: Clamped to 0.85 bar boost (rl = 145%) -> Max Traction Hold   │                    │
│   │ • 3rd Gear: Ramped to 1.25 bar boost (rl = 185%) -> Forward Thrust Surge │                    │
│   │ • 4th-6th: Full 1.50 bar boost (rl = 215%) -> Maximum Top-End Power!     │                    │
│   └─────────────────────────────────────────────────────────────────────────┘                    │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

58.1. Transmission Ratio Calculation & Algorithmic Gear Identification

Manual transmissions (02J 5-speed and 02M 6-speed) have no physical gear position sensors inside the selector forks. ME7.5 identifies gear state mathematically:

Rtransmission =Nmotvfzg

When the clutch is engaged (B_kuppl = 0) and road speed exceeds 5 km/h, the firmware compares this continuous quotient against calibrated ratio windows defined by the scalar array NVQUOT1 through NVQUOT6 with a tolerance band DNVQ:

|Nmotvfzg - NVQUOTi | ≤ DNVQi ⟹ gangi = i

If the clutch pedal is depressed (B_kuppl = 1) or the ratio falls outside all calibrated windows (clutch slipping or transmission in neutral), ME7.5 assigns internal gear index gangi = 0 (Neutral/Transition).

58.2. Calibrating Progressive Boost-by-Gear (`KFLDRXN` / `LDRXNZ`)

To implement boost-by-gear in production calibrations:

In factory European files (such as 06A906032DL / AUQ 180 PS), Bosch utilizes KFLDRXN (Kennfeld maximale Zylinderfüllung abhängig vom Gang), an 8 × 6 map indexed by engine RPM and physical gear number.
In North American files (such as 06A906032LP / AWP 180 PS), LDRXN is a single 16-point 1D curve, but the firmware contains a gear-scaling offset map LDRXNZ (Zusatzfüllung für Gang): LDRXNfinal = LDRXN(Nmot) · fgear(gangi)

Recommended Boost-by-Gear Calibration Profile (FWD 1.8T Golf GTI)

Gear Engaged · Transmission Ratio · Target Boost Pressure · Relative Engine Load (rl)
Gear Engaged	Transmission Ratio	Target Boost Pressure	Relative Engine Load (rl)	Wheel Torque Limit	Driver Experience
1st Gear	135 rpm/(km/h)	0.55 bar (8.0 psi)	115%	240 Nm	Dead-hook off the line; zero tire smoke
2nd Gear	78 rpm/(km/h)	0.85 bar (12.3 psi)	145%	305 Nm	Progressive tractive grip on street radials
3rd Gear	52 rpm/(km/h)	1.25 bar (18.1 psi)	185%	385 Nm	Violent mid-range torque pull
4th Gear	39 rpm/(km/h)	1.50 bar (21.8 psi)	215%	440 Nm	Peak turbocharger compressor output
5th Gear	30 rpm/(km/h)	1.50 bar (21.8 psi)	215%	440 Nm	Maximum aerodynamic push
6th Gear	25 rpm/(km/h)	1.45 bar (21.0 psi)	205%	420 Nm	Mild safety taper to limit EGT heat buildup

58.3. Custom C167 Assembly Patch: Discrete 6-Gear Multi-LDRXN Tables

For binaries where KFLDRXN is compiled out, a custom C167CR machine code patch is injected into free flash space (0x07F900) to intercept the raw load lookup:

code

; ==============================================================================
; C167 Machine Code Patch: Discrete 6-Gear LDRXN Load Mapping
; Intercepts call to LDRXN at 0x052A30
; ==============================================================================
patch_boost_by_gear:
    ; Note: Internal RAM 0x382040 accessed via DPP2 (0x00E0): 0x8000 | 0x2040 = 0xA040
    MOV     R4, [0xA040]          ; Read internal gear variable (gangi) via DPP2 (RAM 0x382040)
    CMP     R4, #0x0001
    JMPR    CC_EQ, load_gear_1
    CMP     R4, #0x0002
    JMPR    CC_EQ, load_gear_2
    CMP     R4, #0x0003
    JMPR    CC_EQ, load_gear_3

    ; Default for 4th, 5th, 6th gear -> Standard high-boost LDRXN curve
    MOV     R4, #0xF054           ; Flash address of base LDRXN (0x01F054)
    CALLS   0x00, 0x4812          ; Call 1D Table Interpolator
    RETS

load_gear_1:
    MOV     R4, #0xFA00           ; Address of custom 1st Gear Curve (Flash 0x01FA00)
    CALLS   0x00, 0x4812
    RETS

load_gear_2:
    MOV     R4, #0xFA20           ; Address of custom 2nd Gear Curve (Flash 0x01FA20)
    CALLS   0x00, 0x4812
    RETS

load_gear_3:
    MOV     R4, #0xFA40           ; Address of custom 3rd Gear Curve (Flash 0x01FA40)
    CALLS   0x00, 0x4812
    RETS