Overrun Fuel Cut-Off Torque Control via Electric Machine
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Solution Overview
Problem
Conventional methods for controlling overrun conditions in motor vehicles do not effectively minimize fuel consumption during shifting operations, particularly during backshifting downhill, due to friction losses in the internal-combustion engine.
Innovation Solution
The method involves monitoring torque changes at the output of the internal-combustion engine and using an electric machine coupled with the crankshaft to maintain a predetermined rotational speed, preventing the engine from falling below a restoring speed by generating additional torque during gear changes or clutch operation, thus avoiding fuel reactivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the fuel feed is interrupted during overrun condition, then fuel consumption is reduced, but the internal-combustion engine rotational speed decreases due to friction losses during shifting operations
Solution Approach 1:
The electric machine acts as an intermediary between the transmission and the internal-combustion engine. During shifting operations, the electric machine generates compensating torque to counteract friction losses, thereby maintaining engine rotational speed without requiring fuel feed resumption. This mediator enables the system to benefit from both fuel savings and speed maintenance.
Solution Approach 2:
The system dynamically adjusts the restoring speed threshold based on detected shifting operations. When a gear change or clutch operation is detected, the control device temporarily raises the restoring speed threshold or extends the fuel cut-off duration, allowing the engine speed to drop further before triggering fuel resumption. This parameter adaptation optimizes fuel savings during transient operating conditions.
2Use of energy by moving object
If the restoring speed is set close to idling speed, then fuel consumption is reduced, but the engine may stall or operate unstable during shifting operations
Solution Approach 1:
The control device detects shifting operations in advance through gear shift signals, clutch operating signals, or converter activating signals. Upon detecting an imminent shift, the system proactively extends the fuel cut-off duration or adjusts the restoring speed threshold before the engine speed becomes critical. This preliminary action prevents engine instability while maintaining fuel savings during the actual shifting event.
Solution Approach 2:
The system continuously monitors engine rotational speed, torque at the transmission input, and shifting operation status. Based on this feedback, the control device dynamically adjusts the fuel feed resumption timing and restoring speed threshold. When friction losses during shifting cause excessive speed drop, the feedback mechanism triggers earlier fuel resumption or threshold adjustment, ensuring engine stability while optimizing fuel consumption under normal conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces fuel consumption by maintaining the internal-combustion engine's rotational speed above the restoring speed, even during transmission disengagement, thereby preventing unnecessary fuel feed resumption and saving additional fuel.
Implementation Method 1
an additional torque is generated by way of an electric machine coupled with the crankshaft of the internal-combustion engine and is transmitted to the crankshaft
Data Source
AI summary
A method controls an overrun operation in a motor vehicle, wherein, in the presence of predetermined switch-off conditions, an overrun switch-off of the internal-combustion engine takes place by interrupting the fuel feed, and wherein, when a predetermined restoring speed is reached or fallen below, the fuel feed is resumed. Starting from an operating state with an activated overrun switch-off, the transmission line between the output of the engine and the input of the transmission device is monitored as to whether a torque difference is occurring which is greater than or equal to a predetermined limit torque. In such a case, the internal-combustion engine is driven by an electric machine coupled with the crankshaft of the internal-combustion engine such that a rotational speed of the internal-combustion engine is adjusted to be greater than or equal to the restoring speed.