折疊式自行車的結(jié)構(gòu)設(shè)計(jì)【說(shuō)明書+CAD+PROE】

折疊式自行車的結(jié)構(gòu)設(shè)計(jì)【說(shuō)明書+CAD+PROE】,說(shuō)明書+CAD+PROE,折疊式自行車的結(jié)構(gòu)設(shè)計(jì)【說(shuō)明書+CAD+PROE】,折疊式,自行車,結(jié)構(gòu)設(shè)計(jì),說(shuō)明書,仿單,cad,proe Optimizing a Hydraulic Regenerative Braking System for a 20" Bicycle Wheel Executive Summary With a growing concern of climate change and decreasing availability of fossil fuels, the U.S. Environmental Protection Agency (EPA) has been researching hydraulic hybrid transportation systems. For seven years, the EPA and ME450 students at The University of Michigan (U-M) have collaborated on projects developing Hydraulic Regenerative Braking Systems (HRBS) for bicycles. These systems conserve energy that is normally lost during friction braking. The bike's kinetic energy is used to drive hydraulic fluid into an accumulator via a pump, braking the vehicle. This stored energy is later released to accelerate the bike forward. This semester we have refined previous HRBS designs by optimizing the mechanical systems and improving safety. A key goal for our team was to build a functioning prototype 20" wheel that weighs less and has fewer moving parts than previous generations. Our team has made minimal changes to the extant hydraulic system, as the parts have been well-researched and recommended by our sponsor, David Swain of the EPA. Working with Mr. Swain, we created a list of customer requirements for this project. Table 1 below lists many of our key engineering specifications that were created to meet these requirements, as well as the final characteristics of the prototype. Our four categories for engineering specifications are safety, cost, weight, and functionality. Due to the conflicting nature of these specifications, it has been difficult to improve many of the bike's systems without adversely affecting others. Compromises have been necessary in order to create a feasible design. table 1：summary of key engineering specifications Characteristic Target prototype Front wheel assembly weight ≤30lbs 24.75lbs Bicycle load rating(rider weight) ≤160lbs ＞200lbs System pressure as limited by relief vale ≤4200psi ≤4200psi Bicycle deceleration target 3.4m/s2—2.6m/s2 not available Bicycle acceleration target 2.0m/s2—2.5m/s2 not available Number of moving/ rotating parts inside hub ＜11 7 Prototype cost ≤$1400 $1338 Many of the main hydraulic components have long acquisition lead times. To meet our goal of having a functional prototype by the end of the term, we expedited concept generation and selection so as to leave enough time to order and receive these parts. We created a detailed plan for the semester based on expected task requirements as well as these lead times. In reducing the weight of the prototype compared to previous designs, we have significantly reduced the number of gears, replaced the bulky fiberglass hub support system with a lightweight aluminum spoke system, and removed excess material from the internal support plate ("superbracket"). These modification choices were made from a broad number of concepts, based on a thorough analysis of the forces and torques required of each of the components. The main engineering obstacles to implementing these design improvements have been dealing with the nonstandard interface between metric and non-metric components, and determining the routing of the hydraulic circuit. 1 Abstract The U.S. Environmental Protection Agency (EPA) is researching hydraulic hybrid transportation systems in an effort to address the growing concerns about global climate change and insatiable fossil fuel demands. Hydraulic hybrid vehicles use regenerative braking to store energy in pressurized fluids. This energy is then released to assist in vehicle acceleration. For the past seven years, ME450 students at The University of Michigan (U-M) have been developing designs for hydraulic hybrid bicycle systems. This semester we refined the design of a hydraulic hybrid system enclosed in a 20" bicycle wheel, with a focus on decreasing weight, improving safety, and reducing the number of moving parts. 2 Introduction This section outlines the origins of the hydraulic hybrid bicycle system concept at the EPA as well as the driving force for its development. A brief outline of the project's scope for the Winter 2009 semester of ME450 is also presented below. 2.1 Background and Motivation Founded in 1970, the United States Environmental Protection Agency is a federal body tasked with correcting environmental damage and establishing guidelines to help protect the natural environment of the United States [1]. Research into clean energy, particularly for use in transportation, is the focus of several of the EPA's efforts [2]. In cooperation with Eaton Corporation, United Parcel Service, Ford, International, and the U.S. Army, the EPA has developed several hydraulic hybrid vehicles for the purposes of improving fuel economy and reducing environmental impact [3]. The primary concept of hydraulic hybrid technology is to capture and utilize the energy that would otherwise be lost during braking and use it to accelerate the vehicle. As the vehicle brakes, a hydraulic pump connected to the drivetrain pumps hydraulic oil into the high-pressure accumulators. During vehicle acceleration, the energy stored in the accumulators is released back into the drivetrain, as the fluid flows through a hydraulic motor. This significantly lowers the amount of fuel needed to accelerate back to normal operating speeds [3]. The result of this regenerative braking is a marked improvement in fuel economy - a feature that is not just better for the environment, but also reduces fuel costs for the owner. A diagram showing this hydraulic regenerative braking system (HRBS) is shown in Figure 1 on page 6. Figure 1: The hydraulic fluid's path in an HRBS [4] The use of bicycles for commuting reduces fossil fuel use, greenhouse gas emissions, roadway congestion, and vehicle miles traveled while increasing the user's physical health [5]. The EPA has demonstrated 20-40 percent fuel economy improvements by installing HRBS on vehicles with internal combustion engines [3]. The possibility of clean, efficient transportation with hydraulic assistance bears exploration. The EPA has been working with U-M students on hydraulic bicycle implementation since 2002, but the project has produced only one functional product. 2.2 Project Description The goal of this project is to develop a hydraulic regenerative braking system for a children's 20" bicycle. Due to the difficult nature of scaling down a hydraulic system, and the comparative ease of scaling upwards, the intent of using a 20" bicycle is to analyze the weight, force, and torque issues inherent to the HRBS on a small scale. The EPA has been working on HRBS bicycles with ME450 students for the past seven years. Previous ME450 teams have worked on fitting these systems in 26" and 20" bicycle wheels. The primary focus of our work on the HRBS is refining the existing designs by improving safety, reducing weight, ensuring functionality, and lowering cost. We are designing an HRBS for a 20" wheel. Notably, one of the main goals is to reduce the device weight to 30 lbs without sacrificing mechanical robustness or safe pressure containment. We plan to retain the majority of the hydraulic components from past designs, as this technology has been well-researched and documented by David Swain and previous teams. By focusing on reducing moving parts, decreasing weight, and improving safety, we are further developing the understanding and implementation of HRBS technology through the fabrication of a functional prototype. 3 Information Search To gain a better understanding of hydraulic hybrid systems, our team surveyed a broad collection of information including research papers, previous ME450 reports, and EPA resources. This section of the report discusses the information we found regarding hydraulic hybrid vehicle technology. Hydraulic systems are used in a variety of applications such as machinery, braking systems, and energy storage. They are often used because of their ability to transfer large forces and convert kinetic energy into potential energy efficiently. To safely utilize this technology, many precautions must be taken to prevent high-pressure systems from rupturing. The EPA, U-M, and companies such as Eaton and Ford have been developing hydraulic hybrid systems for transportation applications including cars, trucks, and bicycles. Hydraulic hybrid bicycle technology has been pioneered through a partnership between the EPA and U-M. For seven years, ME450 students at U-M have been researching, designing, and building hydraulic hybrid bicycle systems using HRBS. These systems require improvements in safety, functionality, and performance. 4 Project Requirements & Engineering Specifications To outline the specifications for this project, we began by defining our customer requirements. We then translated these requirements into engineering specifications. This section of the report details these requirements and the resulting specifications. 4.1 Customer Requirements The customer requirements for this term, as outlined by our sponsor David Swain, are continuations of the past two semesters with an added emphasis on three major underlying themes-safety, performance, and cost- to guide the formation of our engineering specifications. Table 1 on page 11 shows a listing of our customer's requirements, as grouped by the three major themes and their relative importance in each. 4.2 Engineering Specifications When translating the customer requirements into engineering specifications, cost and safety translated directly. However, performance split into weight and functionality, as we find both categories of high enough importance to be separate. The resultant engineering specifications are described in the following list. 5 Concept Generation To effectively generate a broad collection of concepts, we began by decomposing the main subsystems of the HRBS. After breaking down the subsystems, we listed the main components of each. Each team member then created a list of concepts for each of the components. We then met as a team to build on one another's ideas and we created a master concept list 5.1 Functional Decomposition Based on the unique history and relative complexity of our project, we followed a slightly different concept generation process than most teams. We began by decomposing the bicycle HRBS into five functional subsystems. These subsystems are hydraulics, powertrain, hub, superbracket, and user interface. Each of these subsystems contained at a minimum two major components. Figure 3 is a functional decomposition tree showing which components fall under which subsystem. Figure 3: Functional decomposition tree outlining main components of each subsystem After completing the functional decomposition, we generated concepts for each of the subsystem components. By individually creating concepts and analyzing them as a team, we were able to attack each design problem from multiple angles. 5.2 Hydraulics The subsystem most refined by previous teams is hydraulics. This is also the subsystem with the longest lead-time items. As a result, many of our hydraulic 5.2 Hydraulics The subsystem most refined by previous teams is hydraulics. This is also the subsystem with the longest lead-time items. As a result, many of our hydraulic components including the pump, motor, high pressure accumulator, tubing & fittings, and low pressure reservoir till remain the same as those specified by previous teams. In addition to the systems used on previous generations, it is important to include a pressure relief system to prevent over-pressurizing the system. This can be achieved by including a variable pressure relief valve or a burst disc. The valves category is made up of a check valve preventing high pressure flow from entering the pump and a directional valve to start and stop the launch process. There are various types of check valves that respond better to different pressures. The directional valve could either be a two-way or a three-way electronic valve. There are different types of each of these valves that vary in their sealing method. Poppet valves seal quite well, leaking only a few drops per minute; spool valves can leak multiple milliliters per minute. 5.3 Powertrain & Packaging Powertrain decomposes into only two component categories, but it is very complicated due to the packaging constraints of a 20" bicycle wheel. In the past, the mechanical reduction was created using steel spur gears. We generated many concepts including plastic gears, phenolic gears, sprockets & chain, cogged belts, cables & pulleys, and friction rollers like those used to launch roller coasters. The second powertrain category is clutch mechanisms. A system is needed to disengage the pump and motor from the rotating hub when braking and launching are not engaged. Concepts to complete this task included electromechanical clutches (benchmark), mechanical clutches, roller clutches, and a custom clutch utilizing a linear actuator. 5.4 Hub The hub's main roles on the bike are to support the rim, to interface with the mechanical reduction, and to enclose the system's moving components. This hub rotates around the bike's axle, which is stationary. Previous teams have created hubs made of carbon fiber and fiberglass. We included these in our concept list as well as aluminum sheet metal, vacuum formed plastic, and spokes with a thin cover. We developed another concept by combining the spoke and vacuum form designs. In this design a rigid skeletal structure would be used to support the bicycle and a thin plastic cover would enclose the system. 5.5 Superbracket The superbracket subsystem is made up of the superbracket and the bike's axle. These components are rigidly connected together. The hub rotates on the axle and electric wiring exits the hub through the center of the axle. Designing the superbracket is a material selection and thickness optimization problem. The bracket needs to support the hydraulic and mechanical components and prevent the pump and motor's output/input shafts from being loaded radially. To meet these criteria we created a list of potential materials, including steel, aluminum, fiberglass, tooling board, wood, carbon fiber, and plastic. Along with material selection we have discussed methods of increasing the bracket's stiffness by using dimple dies, adding gussets, and adding angle iron reinforcements. 5.6 User Interface and Controls Previous designs incorporated a switch box for controlling the brake and launch functions. This box was mounted on the frame of the bike directly in front of the seat. While functional, this forces the rider to let go of the handlebars with at least one hand to activate either system. In the event of a system braking failure, the rider would have to quickly adjust his hand position to activate the hand brake on the handlebar. One concept that could potentially solve this problem is to integrate the switch and the preexisting hand brake. This could be done by splicing a toggle switch into the cable. A light squeeze on the hand brake could activate the HRBS, while a hard squeeze would be enough to engage the friction brakes. Another option, provided that the bike is equipped with front and rear brakes, is to leave the rear hand brake unmodified and splice a toggle switch into the front hand brake cable. The launch activation could potentially be switched via a toggle switch mounted on the handlebars, or a pushbutton mounted on the handlebars. If two switches are wired in parallel, there is the advantage that both switches must be activated for the launch to be triggered - this could be beneficial from a safety standpoint. 6 Conclusion This semester we designed and built a hydraulic regenerative braking system enclosed in a 20" bicycle wheel. We used hydraulic hybrid technology that was proven by the EPA and previous ME450 teams. Using the vast resources available to our team, we redesigned the mechanical and electrical systems on the bike. The hydraulic component specifications did not change from previous iterations of the bicycle. We reduced weight, improved safety, and increased functionality with our design and were motivated by those driving factors during manufacturing and assembly. We were able to meet the deadlines of our project by sourcing parts aggressively and scheduling proactively throughout the semester. In such a short design cycle, adherence to a methodical and thoughtful approach was necessary to avoid confusion and misguided efforts. It also allowed for each team member to have an intimate knowledge of the system and its components, resulting directly in a significant leap forward in the evolution of this project.