# US 7,467,033 B2 · Control method for a vehicle powertrain with protection against low load conditions

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- Number: US 7,467,033 B2
- Document ID: US7467033B2
- Status: Granted
- Kind: B2
- Application number: 10/906,784
- Filed: 2005-03-07
- Published: 2006-09-07
- Granted: 2008-12-16
- Earliest claimed: 2005-03-07
- Assignees: Ford Global Technologies, LLC
- Inventors: Kenneth Miller; Paul Gartner; Carol Okubo; Douglas Martin; Edward Badillo
- Web page: https://patentgrep.com/patent/US7467033B2

## CPC

- B60W 20/11: using model predictive control [MPC] strategies, i.e. control methods based on models predicting performance {(utilising navigation and traffic information in the control strategy B60W20/12)}
- B60K 6/445: Differential gearing distribution type
- B60W 10/06: including control of combustion engines
- B60W 10/08: including control of electric propulsion units, e.g. motors or generators
- B60W 20/00: Control systems specially adapted for hybrid vehicles {(hybrid vehicle design, B60K6/00; electric vehicles B60L)}
- B60L 2260/12: of combustion engines
- Y02T 10/40: Engine management systems
- Y02T 10/62: Hybrid vehicles
- B60W: CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
- B60K: ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60L: PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES (arrangements or mounting of electrical propulsion units or of plural diverse prime-movers for mutual or common propulsion in vehicles B60K1/00, B60K6/20; arrangements or mounting of electrical gearing in vehicles B60K17/12, B60K17/14; preventing wheel slip by reducing power in rail vehicles B61C15/08; dynamo-electric machines H02K; control or regulation of electric motors H02P); SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES (electric coupling devices combined with mechanical couplings of vehicles B60D1/64; electric heating for vehicles B60H1/00); ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL (control or regulation of electric motors H02P); MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

A control method is disclosed for maintaining a calibrated minimum load for an engine in a vehicle powertrain with an engine. The possibility of engine misfire due to low engine loads is reduced. Further, undesired high temperature of an engine exhaust gas catalytic converter due to prolonged operation of the powertrain at low engine loads is avoided.

## Claims

### Claim 1

A method for controlling an engine in a powertrain for a hybrid electric vehicle, the vehicle having an internal combustion engine, at least one electric motor-generator, a battery, the battery and the motor-generator being electrically coupled, gearing establishing power flow paths from the engine and the motor-generator to a driven member connected drivably to vehicle traction wheels, and a controller for coordinating power distribution from the engine and the motor-generator in accordance with operating variables including a driver demand for power and battery state of charge, the method comprising the steps of:
calibrating a minimum load for the engine below which the engine fuel combustion tends to be unstable at a given engine speed;
determining an engine torque command by the vehicle system controller;
measuring engine load corresponding to the engine torque command;
calculating a minimum torque adder;
comparing the engine torque command at a given engine speed with a minimum engine torque that corresponds to the calibrated minimum engine load; and
adding the minimum torque adder to the minimum engine torque when the measured engine load is near the calibrated minimum load whereby engine fuel combustion stability is maintained.

### Claim 2 (depends on 1)

The method set forth in claim 1 wherein the minimum engine torque is computed at a given engine speed as function of operating variables including a calibrated engine speed and torque relationship, frictional torque losses, and the minimum torque adder.

### Claim 3 (depends on 1)

The method set forth in claim 1 wherein the minimum torque adder is increased with respect to time when the measured engine load is less than the calibrated minimum load, increases in the minimum torque adder being ended when the measured engine load is greater than the calibrated minimum load by a calibrated amount.

### Claim 4 (depends on 2)

The method set forth in claim 2 wherein the minimum torque adder is decreased when the measured engine load exceeds a calibrated upper limit whereby the measured load is maintained within a calibrated load limit band.

### Claim 5 (depends on 3)

The method set forth in claim 3 wherein the minimum torque adder is decreased when the measured engine load exceeds a calibrated upper limit whereby the measured load is maintained within a calibrated load limit band.

### Claim 6 (depends on 3)

The method set forth in claim 3 wherein the minimum torque adder is increased using a ramp and hold computation technique when the measured engine load is less than the calibrated minimum load until the measured engine load exceeds the calibrated minimum load.

### Claim 7 (depends on 3)

The method set forth in claim 3 wherein the minimum torque adder is increased using a proportional-integral computation technique when the measured engine load is less than the calibrated minimum load until the measured engine load exceeds the calibrated minimum load.

### Claim 8 (depends on 4)

The method set forth in claim 4 including the step of calculating a maximum value of the minimum torque adder whereby undesired battery charging is avoided.

### Claim 9 (depends on 4)

The method set forth in claim 4 wherein the minimum torque adder is decreased with respect to time using a ramp and hold computation technique when the measured engine load is greater than the calibrated minimum load limit band.

### Claim 10 (depends on 4)

The method set forth in claim 4 wherein the minimum torque adder is decreased with respect to time using a proportional-integral computation technique when the measured engine load is greater than the calibrated minimum load limit band.

### Claim 11

A method for controlling an engine in a powertrain for a hybrid electric vehicle, the vehicle having an internal combustion engine, at least one electric motor-generator, a battery, the battery and the motor-generator being electrically coupled, gearing establishing power flow paths from the engine and the motor-generator to a driven member connected drivably to vehicle traction wheels, a catalytic converter in an exhaust gas transfer system for the engine, and a vehicle system controller for coordinating power distribution from the engine and the motor-generator in accordance with operating variables including a driver demand for power and battery state of charge, the method comprising the steps of:
calibrating a minimum load for the engine below which the engine fuel combustion tends to be unstable at a given engine speed;
determining an engine torque command by the vehicle system controller;
measuring engine load corresponding to the torque command;
calculating a minimum torque adder;
comparing the engine torque command at a given engine speed with a minimum torque value that corresponds to the calibrated minimum engine load;
adding the minimum torque adder to the minimum engine torque to obtain an increased engine torque command when the measured engine load is near the calibrated minimum engine load whereby engine fuel combustion stability is maintained;
limiting the minimum torque adder to effect a calibrated maximum torque limit; and
limiting the duration of operation of the powertrain when the measured engine load is near the calibrated minimum load whereby excessive thermal damage to the catalytic converter is prevented.

### Claim 12 (depends on 11)

The method set forth in claim 11 wherein the minimum engine torque is computed at a given engine speed as a function of operating variables including a calibrated engine speed and torque relationship, frictional torque losses, and the minimum torque adder.

### Claim 13 (depends on 11)

The method set forth in claim 11 wherein the minimum torque adder is increased with respect to time when the measured engine load is less than the calibrated minimum load, increases in the minimum torque adder being ended when the measured engine load is greater than the calibrated minimum load.

### Claim 14 (depends on 13)

The method set forth in claim 13 wherein the minimum torque adder is decreased with respect to time when the measured engine load exceeds a calibrated high limit whereby the measured engine load is maintained within a calibrated load limit band.

### Claim 15 (depends on 14)

The method set forth in claim 14 including the step of calculating a maximum value of the minimum torque adder value whereby undesired battery charging is avoided.

### Claim 16

A method for controlling an engine in a powertrain for a vehicle, the vehicle having an internal combustion engine, gearing establishing power delivery from the engine to a driven member connected drivably to vehicle traction wheels, and a controller for coordinating power distribution to the traction wheels in accordance with operating variables including a driver demand for power, the method comprising the steps of:
calibrating a minimum load for the engine below which the engine fuel combustion tends to be unstable at a given engine speed;
determining an engine torque command by the vehicle system controller;
measuring engine load corresponding to the torque command;
calculating a minimum torque adder;
comparing the engine torque command at a given engine speed with a minimum engine torque that corresponds to the calibrated minimum engine load; and
adding the minimum torque adder to the minimum engine torque when the measured engine load is near the calibrated minimum engine load whereby engine fuel combustion stability is maintained.

### Claim 17 (depends on 16)

The method set forth in claim 16 wherein the minimum engine torque is computed at a given engine speed as a function of variables including a calibrated engine speed and torque relationship, frictional torque losses, and the minimum engine torque adder.

### Claim 18 (depends on 16)

The method set forth in claim 16 wherein the minimum torque adder is increased with respect to time when the measured engine load is less than the calibrated minimum load value, increases in the minimum torque adder being ended when the measured engine load is greater than the calibrated minimum load by a calibrated amount.

### Claim 19 (depends on 18)

The method set forth in claim 18 wherein the minimum torque adder is decreased with respect to time when the measured load value exceeds a calibrated upper limit whereby the measured load value is maintained within a calibrated load limit band.

### Claim 20

A method for controlling an engine in a powertrain for a vehicle, the vehicle having an internal combustion engine, gearing establishing at least one power flow path from the engine to a driven member connected drivably to vehicle traction wheels, a catalytic converter in an exhaust gas transfer system for the engine, and a controller for controlling power distribution to the traction wheels in accordance with operating variables including a driver demand for power, the method comprising the steps of:
calibrating a minimum load for the engine below which the engine fuel combustion tends to be unstable at a given engine speed;
determining an engine torque command by the vehicle system controller;
measuring engine load corresponding to the torque command;
calculating a minimum torque adder;
comparing the engine torque command with a minimum engine torque that corresponds to the calibrated minimum engine load;
adding the minimum torque adder to the minimum engine torque to obtain an increased engine torque command when the measured engine load is near the calibrated minimum engine load whereby engine fuel combustion stability is maintained;
limiting the torque adder to effect a maximum torque limit; and
limiting the duration of operation of the powertrain when the measured engine load is near the calibrated minimum load whereby excessive thermal damage to the catalytic converter is prevented.

### Claim 21 (depends on 20)

The method set forth in claim 20 wherein the minimum engine torque is computed at a given engine speed as a function of a calibrated engine speed and torque relationship, frictional torque losses, and the minimum torque adder.

### Claim 22 (depends on 20)

The method set forth in claim 20 wherein the minimum torque adder is increased with respect to time when the measured engine load is less than the calibrated minimum load, increases in the minimum torque adder being ended when the measured engine load is greater than the calibrated minimum engine load.

### Claim 23 (depends on 22)

The method set forth in claim 22 wherein the minimum torque adder is increased with respect to time using a ramp and hold computation technique when the measured load is less than the calibrated minimum engine load until the measured engine load exceeds the calibrated minimum engine load.

### Claim 24 (depends on 22)

The method set forth in claim 22 wherein the minimum torque adder is increased with respect to time using a proportional-integral computation technique when the measured engine load is less than the calibrated minimum engine load until the measured engine load exceeds the calibrated minimum engine load.

### Claim 25 (depends on 22)

The method set forth in claim 22 wherein the minimum torque adder is decreased with respect to time using a ramp and hold computation technique when the measured load is greater than a calibrated minimum load limit band.

### Claim 26 (depends on 22)

The method set forth in claim 22 wherein the minimum torque adder is decreased with respect to time using a proportional-integral computation technique when the measured load is greater than a calibrated minimum load limit band.