# US 10,865,721 B1 · Method and system for measuring and balancing cylinder air-fuel ratio

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- Number: US 10,865,721 B1
- Document ID: US10865721B1
- Status: Granted
- Kind: B1
- Application number: 16/680,249
- Filed: 2019-11-11
- Granted: 2020-12-15
- Earliest claimed: 2019-11-11
- Assignees: Ford Global Technologies, LLC
- Applicants: Ford Global Technologies, LLC
- Inventors: Joseph Lyle Thomas; Ross Dykstra Pursifull; Michael James Uhrich; William Charles Ruona; Giovanni Cavataio
- Web page: https://patentgrep.com/patent/US10865721B1

## CPC

- F01N 3/2066: {Selective catalytic reduction [SCR]}
- F02D 41/0085: {Balancing of cylinder outputs, e.g. speed, torque or air-fuel ratio}
- F01N 3/0842: {Nitrogen oxides}
- F01N 3/208: {Control of selective catalytic reduction [SCR], e.g. by adjusting the dosing of reducing agent}
- F02D 41/0042: {Controlling the combustible mixture as a function of the canister purging, e.g. control of injected fuel to compensate for deviation of air fuel ratio when purging}
- F02D 41/009: {using means for generating position or synchronisation signals}
- F02D 41/1402: {Adaptive control}
- F02D 41/1475: {Regulating the air fuel ratio at a value other than stoichiometry}
- F02D 41/1498: {measuring engine roughness}
- F02P 5/045: {combined with electronic control of other engine functions, e.g. fuel injection (in general F02D37/02)}
- F02P 5/1502: {using one central computing unit}
- F02P 5/1512: {with particular means concerning an individual cylinder}
- F01N 2610/02: the substance being ammonia or urea
- F01N 2610/1406: Storage means for substances, e.g. tanks or reservoirs
- F01N 2900/08: said parameters being related to the engine
- F01N 2900/1402: Exhaust gas composition
- F01N 2900/1622: Catalyst reducing agent absorption capacity or consumption amount
- F02D 41/027: {to purge or regenerate the exhaust gas treating apparatus}
- F02D 41/2467: {for injectors}
- F02D 2200/021: Engine temperature
- F02D 2200/1002: Output torque
- F02D 2200/101: Engine speed
- F02D 2250/18: Control of the engine output torque
- F02D 2250/36: Control for minimising NOx emissions
- Y02T 10/12: Improving ICE efficiencies
- Y02T 10/40: Engine management systems
- F01N: GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES (arrangements in connection with gas exhaust of propulsion units in vehicles B60K13/00; combustion-air intake silencers specially adapted for, or arranged on, internal-combustion engines F02M35/00; protecting against, or damping, noise in general G10K11/16)
- F02D: CONTROLLING COMBUSTION ENGINES (vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed B60K31/00; conjoint control of vehicle sub-units of different type or different function, road vehicle drive control systems for purposes other than the control of a single sub-unit B60W)
- F02P: IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES ({anti-pollution means for internal-combustion engines F02B17/00}; specially adapted for rotary-piston or oscillating-piston engines F02B53/12; {ignition of gas turbine plants F02C7/26; ignition of jet propulsion plants F02K9/95; starting of combustion engines F02N9/00}; ignition of combustion apparatus in general, glowing plugs F23Q; measuring of physical variables in general G01; controlling in general G05; data processing in general G06; electrical components in general see Section H; {ignition coils H01F38/12}; sparking plugs H01T13/00)
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

Methods and systems are provided for operating an engine to diagnose and compensate for cylinder imbalance in an engine. In one example, a method may include diagnosing a torque imbalance in a multi-cylinder engine by operating the engine at a lean air-fuel ratio (AFR) while an amount of ammonia stored in an selective catalytic reduction (SCR) system is greater than a threshold amount and a temperature of the engine is greater than a threshold temperature; and responsive to the diagnosed torque imbalance, adjusting fueling and spark timing for each cylinder, the adjustments based on an AFR offset of each cylinder determined while adjusting the lean AFR.

## Claims

### Claim 1

A method comprising:
diagnosing a torque imbalance in a multi-cylinder engine while operating the engine at a lean air-fuel ratio (AFR), in response to determining that an amount of ammonia stored in an selective catalytic reduction system is greater than a threshold amount and a temperature of the engine is greater than a threshold temperature; and
responsive to the torque imbalance, adjusting fueling based on an AFR offset of each cylinder determined while adjusting the lean AFR.

### Claim 2 (depends on 1)

The method of claim 1, wherein diagnosing the torque imbalance in the multi-cylinder engine includes:
operating the engine at the lean AFR while determining a cylinder torque produced by each cylinder of the multi-cylinder engine;
averaging the cylinder torque produced by each cylinder to determine a mean cylinder torque; and
identifying the torque imbalance responsive to the cylinder torque produced by one or more cylinders being outside of a threshold deviation from the mean cylinder torque.

### Claim 3 (depends on 2)

The method of claim 2, wherein determining the cylinder torque produced by each cylinder includes measuring a crankshaft acceleration produced by each cylinder.

### Claim 4 (depends on 1)

The method of claim 1, wherein determining the AFR offset of each cylinder while adjusting the lean AFR includes:
commanding a series of lean AFRs while monitoring a torque output of each cylinder at each lean commanded AFR in the series of lean AFRs; and
determining the AFR offset of each cylinder based on a change in the torque output of the corresponding cylinder between two consecutive lean commanded AFRs in the series of lean AFRs and a difference between the consecutive lean commanded AFRs.

### Claim 5 (depends on 4)

The method of claim 4, wherein determining the AFR offset of each cylinder based on the change in the torque output of the corresponding cylinder between two consecutive lean commanded AFRs in the series of lean AFRs and the difference between the consecutive lean commanded AFRs includes mapping a ratio of the change in the torque output and the difference between the consecutive lean commanded AFRs to a torque-AFR function.

### Claim 6 (depends on 4)

The method of claim 4, wherein adjusting the fueling includes adjusting a fuel injection amount of each cylinder based on the corresponding AFR offset of each cylinder.

### Claim 7 (depends on 1)

The method of claim 1, wherein diagnosing the torque imbalance includes learning fuel injector offsets before operating the engine at the lean AFR, the threshold temperature is above a temperature for releasing entrained fuel from a crankcase of the engine, and a source of the torque imbalance includes an air distribution difference between one or more cylinders of the multi-cylinder engine.

### Claim 8 (depends on 1)

The method of claim 1, wherein the first threshold amount is a threshold amount of ammonia for NOx conversion by the selective catalytic reduction system while operating the engine at the lean AFR.

### Claim 9 (depends on 1)

The method of claim 1, further comprising:
responsive to the amount of ammonia stored in the selective catalytic reduction system being less than the threshold amount, storing additional ammonia at the selective catalytic reduction system; and
waiting until the amount of amount of ammonia stored in the selective catalytic reduction system is greater than the threshold amount before diagnosing the torque imbalance.

### Claim 10 (depends on 1)

The method of claim 1, further comprising:
transitioning the engine to operating at stoichiometry responsive to the amount of ammonia stored in the selective catalytic reduction system decreasing below the threshold amount while operating the engine at the lean AFR.

### Claim 11

A method, comprising:
storing at least a threshold amount of ammonia in a selective catalytic reduction (SCR) system; and
balancing torque output of each cylinder of a multi-cylinder engine based on an offset of each cylinder determined while commanding engine operation at a series of lean air-fuel ratios (AFRs), in response to determining that the stored ammonia amount is at least the threshold amount;
wherein exhaust gas from the engine remains above a first temperature threshold and below a second temperature threshold during the balancing.

### Claim 12 (depends on 11)

The method of claim 11, wherein balancing the torque output of each cylinder of the multi-cylinder based on the offset of each cylinder determined while commanding engine operation at the series of lean AFRs includes:
operating the engine at a first lean AFR in the series of lean AFRs; and
identifying an air imbalance in one or more cylinders by comparing a first individual cylinder torque produced by each cylinder while operating the engine at the first lean AFR to a mean cylinder torque produced while operating the engine at the first lean AFR.

### Claim 13 (depends on 12)

The method of claim 12, wherein balancing the torque output of each cylinder further includes:
responsive to identifying the air imbalance in the one or more cylinders, operating the engine at a second lean AFR in the series of lean AFRs;
determining a second individual cylinder torque produced by each cylinder while operating the engine at the second lean AFR; and
determining a torque-AFR slope of each cylinder based on a torque difference between the first individual cylinder torque and the second individual cylinder torque and a difference between the first lean AFR and the second lean AFR.

### Claim 14 (depends on 13)

The method of claim 13, wherein balancing the torque output of each cylinder further includes:
determining a first observed AFR and a second observed AFR of each cylinder by mapping the torque-AFR slope of each cylinder to a torque-AFR function;
determining the offset of each cylinder by comparing the first observed AFR and the second observed AFR of each cylinder to the first lean AFR and the second lean AFR; and
adjusting a fuel injection amount of each cylinder based on the determined offset of the cylinder.

### Claim 15 (depends on 11)

The method of claim 11, wherein the first threshold temperature is a light-off temperature of the SCR system, the second threshold temperature is a threshold for reducing heat-related degradation of the SCR system, and the threshold amount of ammonia is calibrated to reduce NOx emissions during commanding engine operation at the series of lean AFRs.

### Claim 16

A system, comprising:
a spark ignition engine including a plurality of cylinders;
a selective catalytic reduction (SCR) device coupled in an exhaust passage of the engine; and
a controller with computer readable instructions stored in non-transitory memory that, when executed during engine operation, cause the controller to:
operate in a lean imbalance testing mode responsive to determining that at least a threshold amount of ammonia is being stored in the SCR device; and
identify a cylinder air imbalance based on a torque produced by each of the plurality of cylinders relative to a mean torque produced by all of the plurality of cylinders while operating in the lean imbalance testing mode.

### Claim 17 (depends on 16)

The system of claim 16, wherein to operate in the lean imbalance testing mode, the controller includes further instructions stored in non-transitory memory that, when executed, cause the controller to:
operate the engine at a series of lean air-fuel ratios; and
determine the torque produced by each of the plurality of cylinders at each lean air-fuel ratio in the series of lean air-fuel ratios.

### Claim 18 (depends on 17)

The system of claim 17, wherein the controller includes further instructions stored in non-transitory memory that, when executed while operating in the lean imbalance testing mode, cause the controller to:
for each of the plurality of cylinders, determine an air-fuel ratio offset by mapping a change in the torque produced by the cylinder between consecutive lean air-fuel ratios in the series of lean air-fuel ratios to a relationship of torque and air-fuel ratio.

### Claim 19 (depends on 18)

The system of claim 18, wherein the controller includes further instructions stored in non-transitory memory that, when executed, cause the controller to:
adjust a fuel injection amount of each cylinder based on the air-fuel ratio off-set determined for the corresponding cylinder; and
after adjusting the fuel injection amount, perform torque balancing between cylinders based on the torque produced by each of the plurality of cylinders relative to the mean torque produced by all of the plurality of cylinders using spark timing adjustments.

### Claim 20 (depends on 16)

The system of claim 16, further comprising an evaporative emissions system, including a fuel vapor storage canister coupled to a fuel tank, the fuel vapor storage canister coupled to an intake passage of the engine via a purge line with a canister purge valve disposed therein, and wherein operating in the lean imbalance testing mode is further responsive to the canister purge valve being fully closed and a temperature of the engine being greater than a threshold.