Power Split Transmission for Street Sweeper Creep Drive
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Solution Overview
Problem
Street sweepers and similar specialty vehicles face challenges in power management, as they need to split engine power between work equipment and vehicle propulsion efficiently, especially at varying speeds, which is difficult with commercial on-highway truck chassis that are not capable of creeping drive without auxiliary engines.
Innovation Solution
A power split and variable speed transmission system that distributes power between work equipment and vehicle propulsion using a planetary gear set and a hydraulic machine, allowing for efficient power distribution and variable speed creep drive without an auxiliary engine, by routing engine power through a hydraulic work circuit and PTO port, and using the hydraulic machine as a pump during creep drive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a commercial on-highway truck chassis is used for street sweeper applications, then the vehicle can achieve high-speed travel for job site changing and water refilling, but the vehicle cannot achieve creeping drive at low speeds without auxiliary engines
Solution Approach 1:
The power transmission path is segmented into multiple controllable elements: a hydrostatic transmission system for the drive wheels, a mechanical PTO system for work equipment, and a planetary gear set for torque distribution. This segmentation allows independent control of creep drive and work equipment operation, resolving the contradiction between speed range and system complexity.
Solution Approach 2:
The single chassis engine is made multi-functional by using it to simultaneously power both the hydrostatic transmission (for vehicle propulsion at variable speeds including creep) and the mechanical PTO (for work equipment). This eliminates the need for auxiliary engines while expanding the vehicle's operational versatility.
2Use of energy by moving object
If engine power is split between work equipment and vehicle propulsion, then fuel efficiency can be improved, but power distribution control becomes challenging due to significant differences in power demands
Solution Approach 1:
A planetary gear set is introduced as a mechanical intermediary between the engine and the two power paths (hydrostatic transmission and PTO). It automatically distributes torque based on the relative speeds and loads of the two outputs, simplifying power distribution control while maintaining fuel efficiency through optimized engine operating points.
Solution Approach 2:
The system uses dynamic control elements including a variable displacement hydraulic pump for the PTO and a hydrostatic transmission with variable flow control for the drive wheels. These dynamic elements allow continuous adjustment of power distribution ratios to match varying operational requirements, making power management easier and more efficient.
3Power
If dual engines are used to meet opposite power demands, then work equipment can run at full power while vehicle moves slowly, but vehicle cost and complexity increase
Solution Approach 1:
The power transmission is segmented into two independent but coordinated paths: a hydrostatic transmission path for vehicle propulsion and a mechanical PTO path for work equipment. This segmentation allows a single engine to simultaneously satisfy opposite power demands (high torque at low speed for work equipment, low torque at variable speed for propulsion) without requiring dual engines.
Solution Approach 2:
A hydrostatic transmission system using hydraulic fluid power is employed to replace the need for a second engine. The hydraulic system can deliver high torque at low speeds for work equipment while the same engine provides variable speed propulsion through the hydrostatic drive, eliminating engine complexity while satisfying all power demands.
4Speed
If hydraulic motor is used for creep drive, then variable speed creep drive can be achieved, but energy waste increases
Solution Approach 1:
The patent replaces the hydraulic motor-based creep drive with a hydrostatic transmission system that uses a variable displacement pump and motor arrangement. This mechanical-hydraulic combination achieves variable speed creep drive more efficiently by allowing the engine to operate at optimal points while providing precise speed control through hydraulic flow regulation, reducing energy waste compared to direct hydraulic motor drive.
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
Enables efficient power distribution between work equipment and vehicle propulsion, achieving variable speed creep drive capabilities at lower costs and higher fuel efficiency, reducing energy waste, and allowing for retrofitting of on-highway truck chassis into single-engine street sweepers without additional motors.
Implementation Method 1
the torque split is achieved through a planetary gear set, in which the ring gear is as input, the sun gear as first output connecting to a hydraulic machine and the carrier as second output connecting to driveline
Implementation Method 2
The hydraulic machine is routed to provide additional hydraulic power to the work equipment in a work mode. At given pressure, changing the displacement of the hydraulic machine will change its torque.
Data Source
AI summary
A power split and creep drive system for street sweeper or like specialty vehicle having a single engine is disclosed. The system intends to retrofit and convert on-highway truck chassis into specialty vehicles capable of performing work function and moving at creeping speed, such as a street sweeper. It includes a hydraulic work circuit or power-take-off (PTO) port, a planetary gear set, a hydraulic system comprising pumps and motors to drive the working devices and balance the demand between propulsion and work function such as sweeping. The planetary gear set includes an input shaft connecting to a transmission output shaft of the chassis, a first output shaft connecting to a hydraulic machine, and a second output shaft to vehicle propulsion drive shaft.