8-Speed Transmission with Low-Range Mode for Towing and Fuel Economy
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Solution Overview
Problem
Light trucks face a trade-off between towing capability and highway fuel economy due to existing axle ratios, with steeper ratios improving launch capability but reducing fuel economy when unloaded, and current transmissions have excessive gear steps and inefficiencies.
Innovation Solution
A transmission design using simple planetary gear sets with specific beta ratios and additional low-range and overdrive ratios, along with a kinematic arrangement of clutches and brakes, to provide a wide speed ratio span with smaller step sizes, enhancing towing capability and fuel economy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If steeper axle ratios are used to improve towing capability, then vehicle launch capability when loaded is improved, but highway fuel economy deteriorates when the vehicle is unloaded
Solution Approach 1:
The transmission system dynamically adapts its gear ratios through multiple forward speeds (8 speeds) and a low-range mode, allowing the vehicle to optimize between towing capability and fuel economy based on operating conditions. The system transitions between different gear sets and ranges to match the dynamic needs of the vehicle.
Solution Approach 2:
The invention changes the gear ratio parameters across 8 forward speeds plus a low-range mode, providing a wide speed ratio span. This includes varying the step sizes between gears, with smaller steps in overdrive ratios for fuel economy and appropriate steps in lower gears for towing capability.
2Adaptability or versatility
If multiple axle ratios are provided to accommodate different towing needs, then adaptability to different conditions is improved, but device complexity increases at the vehicle assembly plant
Solution Approach 1:
The transmission system provides multiple functions within a single device: 8 forward speeds for various driving conditions, a low-range mode for 4x2 and 4x4 vehicles, and reverse gear. This multi-functionality replaces the need for multiple axle ratio options, simplifying assembly while maintaining adaptability.
Solution Approach 2:
The system dynamically switches between different gear sets and a low-range mode to provide adaptability for different towing and driving conditions, eliminating the need for multiple static axle ratio configurations at the assembly plant.
3Speed
If 8-speed transmissions are designed with traditional gear ratios, then speed ratio span is increased, but gear mesh losses increase compared to six-speed transmissions
Solution Approach 1:
The invention carefully selects gear ratios across 8 speeds with optimized step sizes. The overdrive ratios use small step sizes to minimize speed differences between gears, reducing gear mesh losses and improving fuel economy while maintaining a wide overall speed ratio span.
4Force
If a very low ratio is added to the transmission to improve low-range capability, then towing capability is improved, but the transmission complexity increases
Solution Approach 1:
The transmission is segmented into two epicyclic gearing assemblies: a first assembly with four planetary gear sets for main gear ratios, and a second assembly with additional planetary gear sets for the low-range mode. This segmentation allows the low-range capability to be added as a distinct functional module.
Solution Approach 2:
The transmission uses nested planetary gear sets where the second epicyclic gearing assembly is integrated with the first assembly. The planetary gear sets are arranged in stages, with later gear sets building upon the foundation of earlier ones, creating a compact structure that provides low-range capability without excessive complexity.
Data Source
AI summary
A multiple speed transmission includes an input and output; a first, second, third and fourth planetary gear sets, each gear set including a sun gear, a ring gear, a carrier, and pinions supported on the carrier and meshing with the sun gear and the ring gear; a first epicyclic gearing assembly including the first gear set, the second gear set, a first clutch, a first brake, a second brake, and first, second, third and fourth rotating members, said first clutch being operable to couple said first rotating member to the input, said first brake being operable to hold said fourth rotating member against rotation, and said second brake being operable to hold said second rotating member against rotation; and a second epicyclic gearing assembly including the third gear set, the fourth gear set, a second clutch, a third clutch, a third brake, and fifth, sixth, seventh and eighth rotating members, the third rotating member being secured to the eighth rotating member, said second control clutch being operable to couple said fifth rotating member to the input, said second control clutch being operable to couple said seventh rotating member to the input, said third brake being operable to hold the seventh rotating member against rotation, and said sixth rotating member being secured for rotation to the output.