Hybrid Vehicle Coasting Torque Control via Disconnect Clutch
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Solution Overview
Problem
Hybrid electric vehicles experience inconsistencies in compression braking during coasting due to the presence of an electric machine, leading to unpredictable behavior and varying magnitudes of negative torque, which can affect the driving experience.
Innovation Solution
A system that includes an engine, an electric machine, and a disconnect clutch, where a controller programs the clutch to disengage and alter the electric machine's torque in response to a tip-out of the accelerator pedal, simulating engine compression braking by varying the braking torque based on vehicle speed, and re-engages the clutch when the battery state of charge exceeds a threshold to maintain consistent coasting torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electric machine is present in the powertrain to provide propulsion power, then the vehicle gains hybrid electric power capability, but inconsistencies in compression braking occur during vehicle coasting
Solution Approach 1:
The disconnect clutch acts as an intermediary component that selectively couples or decouples the engine from the electric machine. During coasting events, the clutch disengages to isolate the engine compression braking from the drivetrain, preventing inconsistent braking forces from being transmitted to the wheels. This mediator approach allows the hybrid powertrain to maintain propulsion capability while eliminating compression braking inconsistencies during coasting.
Solution Approach 2:
The powertrain is segmented into separate functional modules (engine, electric machine, disconnect clutch) that can operate independently. The disconnect clutch enables the engine to be isolated from the electric machine and drivetrain during specific operating conditions such as coasting, allowing each component to function optimally without interfering with the others. This segmentation resolves the contradiction by enabling the engine to provide compression braking only when needed while the electric machine handles propulsion.
2Reliability
If the disconnect clutch disengages the engine from the electric machine during coasting, then compression braking inconsistencies are eliminated, but the engine cannot provide immediate propulsion power
Solution Approach 1:
The disconnect clutch dynamically adjusts its engagement state based on real-time operating conditions. The control system monitors vehicle speed, accelerator pedal position, and coasting detection to determine when to engage or disengage the clutch. During coasting, the clutch disengages to ensure consistent braking; during acceleration requests, the clutch engages to enable immediate engine propulsion. This dynamic adaptation resolves the contradiction between braking consistency and propulsion response.
Solution Approach 2:
The control system uses feedback from various sensors (accelerator pedal position, vehicle speed, coasting detection) to continuously monitor operating conditions and adjust the disconnect clutch state accordingly. When coasting is detected (accelerator released, vehicle decelerating), the system feedback triggers clutch disengagement. When propulsion is needed (accelerator depressed), the feedback triggers clutch engagement. This closed-loop feedback mechanism ensures both compression braking consistency and rapid propulsion response.
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
The system provides a consistent overall negative torque during coasting, simulating engine compression braking and ensuring a smooth driving experience by supplementing or substituting engine compression torque with electric braking, thereby reducing inconsistencies in hybrid electric vehicles.
Implementation Method 1
command braking torque in the electric machine in response to the tip-out of the accelerator pedal
Implementation Method 2
The battery is electrically connected to the electric machine for storing electric power generated by the electric machine
Data Source
AI summary
A hybrid vehicle is provided that includes an engine, a reversible electric machine capable of generating and providing electric power, and a clutch for selectively engaging the engine to the electric machine. While the vehicle is traveling, an operator of the vehicle may release (“tip-out”) the accelerator pedal, indicating a desire for a reduction in speed and/or acceleration of the vehicle. If the clutch is engaged during the tip-out, the at least one controller is programmed to disengage the clutch and alter a commanded torque to the electric machine in response to the tip-out of the accelerator pedal to simulate compression braking of the engine. If the vehicle is operating in an electric-only mode of propulsion during the tip-out, and if a state-of-charge of the battery is relatively high, the controller is programmed to activate the engine and provide compression torque to the driveline in response to the tip-out.