Overrun Gear Reduces Drag Losses in Vehicle Drive Device
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Solution Overview
Problem
Existing drive devices for motor vehicles face inefficiencies in overrun mode, leading to high drag losses and increased electrical load due to the need to restart the internal combustion engine, which results in high fuel consumption and prolonged reconnection times, especially in hybrid vehicles where the engine is decoupled during overrun phases.
Innovation Solution
The introduction of an overrun gear that is specifically designed to reduce the rotational speed of the internal combustion engine to idling speed or below in overrun mode, without decoupling the engine, using a gearbox with a unique gear ratio step that is only engaged in overrun mode, allowing for efficient energy recovery and reduced drag torque, and utilizing multiple overrun gears to maintain idling speed over a wide range of speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the transmission is shifted to a high gear in overrun mode to reduce drag torque, then fuel consumption is reduced, but the progressive ratio step becomes small which limits further drag loss reduction
Solution Approach 1:
The transmission system is segmented into two distinct functional modes: driving gears for propulsion with harmonic ratio steps, and an overrun gear for energy recovery with a specialized large ratio step. This segmentation allows the overrun gear to operate independently with optimized gear ratio (i6=0.45) that maximizes drag torque reduction without compromising driving performance.
Solution Approach 2:
The gear ratio parameter for the overrun gear is specifically changed to a large value (0.45) that is significantly different from the progressive ratio steps used in driving gears. This parameter change enables the internal combustion engine to rotate at much lower speeds during overrun, reducing drag torque by approximately 40% compared to conventional high-gear operation.
2Loss of energy
If the internal combustion engine is switched off during overrun phases to reduce drag losses, then fuel consumption decreases, but the electrical system load increases requiring redundant power supply
Solution Approach 1:
The previously harmful drag torque produced by the internal combustion engine during overrun is converted into a beneficial force by operating the engine at optimized low speeds through the overrun gear. The engine's rotational motion, which formerly represented energy loss, is now harnessed to drive the electric motor as a generator for efficient energy recovery, transforming drag losses into useful electrical energy.
3Loss of energy
If the clutch is disengaged to restart the internal combustion engine during overrun, then drag losses are reduced, but reconnection time increases affecting acceleration response
Solution Approach 1:
The internal combustion engine is kept rotating during overrun phases through the overrun gear, maintaining it in a ready state without complete shutdown. This preliminary action of keeping the engine running at low speeds eliminates the need for time-consuming restart and reconnection procedures, reducing reconnection time to approximately 2 seconds while still achieving significant drag loss reduction.
4Ease of operation
If the transmission uses conventional progressive ratio steps for harmonic gear engagement, then smooth drivability is achieved, but drag torque in overrun mode remains high
Solution Approach 1:
The transmission system dynamically adapts its gear ratio based on operational mode. During driving phases, conventional progressive ratio steps provide harmonic engagement and smooth drivability. During overrun phases, the system dynamically switches to the overrun gear with a large ratio step (0.45), optimizing for drag torque reduction. This dynamic adaptation allows the system to achieve both smooth operation and energy efficiency in their respective operating 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 solution enhances fuel efficiency and energy recovery in overrun and braking operations by minimizing drag losses and maintaining propulsion without engine decoupling, allowing for efficient kinetic energy utilization and reduced electrical load, while ensuring seamless transitions between overrun and drive modes.
Implementation Method 1
The transmission has at least one ratio step that provides an overrun gear... the ratio of the overrun gear is designed specifically for a strong reduction of the rotational speed of the internal combustion engine
Implementation Method 2
the motor vehicle is braked via the electric motor switched to operation as a generator
Data Source
AI summary
A drive device for a motor vehicle, having an internal combustion engine that outputs to a gearbox or transmission. A plurality of gear ratios steps provides shiftable driving gears from a starting gear to a highest driving gear. The gearbox has at least one gear ratio step that provides an overrun gear, which cannot be engaged in the traction mode, but only in an overrun mode, in which the vehicle drags the internal combustion engine.