Electric Brake system Proposal
School of Aerospace, Mechanical and Manufacturing Engineering
171577031115
AUTO1024 Management of Automotive Design and Development
Quality Function Deployment on an Electric Brake System
Milestone 3
LECTURER
Due Date: 03/06/2014
2014
1. Introduction
Advanced technologies have rapidly increased in the automotive industry in recent past particularly in sensor systems and braking systems. Traditional pneumatic brake systems in heavy goods vehicles are becoming less common, as electro-mechanism systems become more common due to their lower installation and component costs and increased availability. Introduction of electronic braking systems has set a platform for a broad variety of brake control systems with aim of improving safety and customer satisfaction. WABCO pioneered volume production of Electronic Braking System (EBS) in 1996. WABCO enhanced EBS to meet changing market needs. This is evident from increasing design innovations allowing tracking and control of the braking system such as brake assist, electronic force distribution, and electronic stability control (Grover et al., 2008).
2. Problem Definition
Honda recalled almost 250,000 vehicles with unexpected braking. The company asserted that it was no injuries or accidents related to the issue. According to the VSA (Vehicle Stability Assist), the recall was to check and rectify the problem the company identified in its electronic stability control system. The system was designed to detect when the vehicle was sliding. The system would then apply pressure to the brakes to correct the slide. Nevertheless, in some instances the brakes were deployed for no apparent reason.
It is vital for Honda Company to carry out an assessment of the EBS to identify all the known and potential modes of failure in the systems, parts or assemblies, their causes and consequences. The main issue here is to assess EBS failure by taking into consideration the needs and expectations of the customers (Diaz & Smith 2007).
Modes of failure occur according to the need function to three groups. They include partial function loss, complete function loss and wrong function. For every mode of failure, the analysis of possible effects occurs at a higher level such as system-wide level. This method is applicable for non-redundant systems. Quantitative reliability analysis deductively addresses several failure, creates a fault model, as well as comprising the analysis of the model.
From the control perspective, the system is a brake-by-wire. The measurement demand of decelerations is through a redundant sensor. Based on other parameters, the ECU (Electrical Control Unit) calculates the brake moment. Alternatively, the ECU brakes when a driver presses the brake pedal. The ECU incorporates more brake functions than pneumatic brake systems. EBS is among the most vital brake functions leading to a more stable vehicle. In the absence of an electronic intervention, there is little chance for the driver to respond (Li & Wang 2010).
Figure 1. Diagram of a Brake System
3. Scope
The braking system is a basic safety in vehicles. The brake has to offer deceleration capacity. The brake and clutch design is subject to uncertainties of the friction coefficients. In addition, the choice of the material with adequate friction coefficient and low wear relates directly with the useful life of the brake. It also involves the vehicle’s safety system. A vital consideration in the brake’s design is the materials’ working temperature. The scope focuses on the correct procedure steps to dealing with redundant systems with classical reliability approach. The scope begins from the definition of the system through function deployment and finishing with assessment. On the other hand, the requirements with relevant elements meet to fulfill the function at the interfaces. An interface is an effective tool of analyzing large, small, as well as complex system. It is vital in the development of preventive maintenance systems that are cost effective. It offers safeguard against repeating the similar mistakes in the future, and are vital to offer the comparison of the designs (Li & Wang 2010).
Figure 2. Electronic Brake System
4. Methodology
QFD is a tool for planning used to fulfill the expectations of customers. QFD is a closely controlled approach to the product engineering design and production, and it offers an in-depth assessment of the product. A company that implements QFD correctly can improve productivity, engineering knowledge, reduces costs, engineering changes and product development time. On the other hand, QFD focuses on the requirements or the expectations of the customer. Its application seeks to translate the expectations of the customer in terms of requirements into actions and directions. This happens in terms of engineering features, which allows deployment through part development, product planning, process planning, production planning and service.
QFD is a management tool that is team-based whereby the expectations of the customer drives the application process of product development. Conflicting requirements or characteristics recognition occur untimely in the process. Through implementing QFD, the company guarantees implementation to the customer’s voice on the final product.
QFD helps to recognize new quality technology, as well as the job roles to fulfill the operations. The tool offers a historical reference to enhance the future technology and curb design errors. QFD is mainly a graphically oriented matrix applied as the basis for making decisions that affect the phase of the development cycle of the product. QFD results measurement depends on the number of engineering and design changes, costs, quality and the time to market. On the other hand, QFD enables the design phase in concentrating on the requirements of the customer; thus, spending less time on modifications and redesign. The time saved has been projected at one-half to one-third of the time spend for modification and redesign using conventional means. This implies decreased development costs and additional income since the products go into the market faster.
5. Research Concept/Expected outcomes
The present study concept is to understand the underlying incorporation of “Voice of the customer” in EBS design. Voice of customer is the first and most important matrix in generating “House of Quality” in a product. It documents all requirements as expressed by the customer directly into the product conceptual design and final production. Next is the “Voice of the Company’ which outlines the technical features of the Electronic brake system that must be aligned with the VO-1. The company achieves VO-1 through representation of efforts analysis of the final EBS model based on what it does to ensure customers’ needs are satisfied. The expected outcomes of advanced innovations of the EBS production team is to generate QFD matrices that directly or indirectly meets customer’s identified specifications. The first matrix is the Inter-relation, which defines the impacts of VO-1 on VO-2 (identified customer requirements and technical features of EBS). The second QFD outcome derived from correlation analysis of the EBS technical features (the roof of the “House of Quality”). On the right-end of the EBS design “House of Quality” (Planning Matrix) the customer’s expectations will drive the final EBS model targets Matrix that focused on sales point hence targeted competitive advantage.
6. Data/ research
Quality Function Deployment (QFD) method defines logical and systematic product quality analysis with aim of ensuring “Voice of the customer” is incorporated into the product throughout the product design stages (Veža and Grubić 2003). As illustrated by Japanese scholar Dr. Yoji Akao, the original developer of this method in 1966, who blended his creations in quality assurance and quality control spots with function deployment employed in value engineering (Bossert 1990).
The aim of the EBS is to maximize the braking safety costs; for example, through optimizing the wheel brake lining wear. WABCO considered the existing regulations when developing EBS, but their top priority was to offer user advantages and safety. Thus, vehicles that have EBS exceed the legal requirements. A high level of safety made possible by EBS is due to a number of factors: the shorter response time to braking, the timing of pressure build-up for the front and rear axle brakes, the elements of the rear and front axles braking systems, and that brake wear is constantly monitored (Li & Wang 2010).
The design of EBS permits greater flexibility for vehicle manufacturers when constructing the system. Concerning range, full systems, or subsystems, and cutoff redundancy electrical interfaces, demands that are most complex exists. EBS has an incorporated brake management function that constantly manages the brake endurance when the brake pedal is activated based on optimum vehicle delay. This function is vital in delay control. The application of delay control adopts the level of braking pressure to the desired braking rate of the driver. On the other hand, the control logic determines the amount of braking based on the rotation speed of the wheel, whether to decrease, increase or maintain braking pressure. While the vehicle is in motion, the electronic control system determines if the wheels of the vehicle are in a stable zone.
The speed sensors in the EBS determine the wheel’s slip ratio. The EBS needs two pieces of information: rotation speed of the wheel and the car speed. Sensors allow positioning of every wheel to determine their speeds. However, there exists no specific sensor to evaluate the vehicle’s forward motion. Instead, the measurement of speed from all the wheels is used to estimate the overall speed of the vehicle. There are also brake force modulators in the EBS. Brake force application takes place hydraulically, thus, the EBS can modulate the quantity of brake fluid entering each wheel by electrically actuated valves. In addition, the ECU receives input from the speed sensors to determine the wheel’s slip rotation, and then applies the brake force modulators to offer an appropriate quantity of force to maintain the slip rotation in every wheel within a predefined range.
The project purpose is focused on including customer’s perspectives and requirements at all design stages of EBS in order to achieve quality of the final product at competitive cost.
The project scope is limited to Quality Function Deployment of the Electronic braking system. The objective is to assess the EBS on:
Customer perspectives
Technical requirements
Technological capacity
Cost benefit analysis using the House of Quality matrices
7. Design Analysis
To gain insights on “House of Quality”, views of customers or users of the EBS product and technical persons involved in the design and production of EBS were analyzed as follows:
Voice of customer: Primary requirements for EBS (VO-1)
Brakes Well Comfortable Environmental friendly Quiet Looks Good Durable
Engages quickly No fatigue while braking Recyclable Quiet Braking Complimentary colors Maintains consistent braking throughout product lifespan
Confident breaking under all conditions Easy to control while in use Safe Materials Quiet when not in use Easy to maintain its appearance High performance
Voice of the Company: Electronic brake system technical features (VO-2)
The EBS quality characteristics were tailored to meet VO-1 (Customer needs) using a qualitative approach (QFD). The identified customer requirements were converted into measurable design elements as illustrated on the hierarchical affinity diagram bellow:
Demanded Quality EBS Quality features Measurement %
Brakes Well Efficiency 4.0
Compressibility 2.2
Stiffness 0.8
Durable Low effort braking 1.2
Easy to control brake power 2.7
Withstands deceleration force 2.8
Absolute QC 12.0%
Relationship matrix or WHATs and HOWs
Figure SEQ Figure * ARABIC 3 L-shaped structuring diagram
The matrix is two-dimensional. For each customer requirement, the level of inter-relationship has four to five scales that must be determined from technical features (2). Therefore, use of (3) in “House of Quality” is the core of establishing weak points of the EBS during design and production followed by remedial actions to eliminate the weaknesses in the design.
Correlation Matrix
The premise of (4) is to correlate technical features (2) that either support (+) or do not support (-) each other. For example, improvement of “i” technical feature directly results to (+) improvement or (-) deterioration of technical feature “j”. It also answers the question of “what” is the degree of improvement or deterioration (1, 2, 3 etc.).
This makes it possible for the QFD team to establish EBS design elements that may contribute towards customer satisfaction, or elements that require further innovations in order to attain optimal trade-off between involved EBS technical features.
Planning Matrix:
From Correlation matrix (4), customer survey gave responses for each identified requirement. The coefficient of responses to each identified requirement quantifies their relative importance. Thus the Planning matrix was used in determining the whether the customer’s identified requirements (1) will help in generating enough perception to warrant competitiveness of the final EBS product.
(6) House of Quality
The Basic “House of Quality” above for the EBS is the foundation of decision making regarding future innovations of the product to ensure greater customer satisfaction as a quality requirement. The EBS customer requirements, technical features, subsequent structural analysis are presented in the following diagrams.
Central to EBS QFD is converting the VO-1 into Voice of engineer (VO-2). House of Quality is used in achieving the quality demands. House of Quality is a special matrix with the following elements:
Demanded quality – explained earlier referring to independent quality expressions by customers VO-1, and further categorized and structured into affinity diagram VO-2.
Importance – establishing quality using qualitative survey for purposes of improving design quality
Competitors – The design improvement activities focused on competing models. However, braking components are difficult to be singled out by customers, therefore, specific car models were used in customer survey to identify competing EBS vendors
Amalgamation of Quality demand, product characteristics, and competition matrices
Prioritizing targeted EBS component specifications with aim of beating competitors (see the following chart)
Figure SEQ Figure * ARABIC 4 House Of Quality
The exterior walls represent customer requirements. The second floor/ceiling contains product technical characteristics, interior walls defines the interrelationships between customer requirements and technical characteristics. The roof is the interrelation matrix between the EBS design characteristics, the foundation of the house show the prioritized or targeted quality design features aimed at beating competition.
8. Discussion (of Analysis)
The objective of this project was to review the high-level requirements for deployment of EBS that meets customer satisfaction. To achieve the high-level technical requirements, a logical and systematic QFD process was followed driven by business strategies that trade off technological capacity and requirements against comfort and durability.
Durability and cost braking were of greater importance to the customer and hence assigned metric values of 4 and 5 respectively. The aim of the QFD analysis was to decide whether the EBS, as it currently exists on the market should remain unchanged, improve the design, or innovate it to make it more competitive. This was achieved using a scale-up factor ratio or target value that rates inclusion of customer perspectives to boost its competitiveness.
The challenge here is that a higher scale-up factor requires greater investment in terms of technical requirements (Voice of engineer) hence higher cost of the final product. One option considered in lowering the cost of final product at higher target value of 4 and 5 for cost and durability (Voice of customer) is selection of appropriate materials. Therefore, the measurable design elements in VO-2 were converted into target specifications with aim of overcoming market competition see excel chart bellow.
EMBED Excel.Sheet.8
Figure SEQ Figure * ARABIC 5 Prioritized EBS design activities to beat competition
To establish sale point of the new EBS design, QFD analysis promoted the best Voice of Customer in the final product that will beat competition. The No fatigue while braking and Engages quickly are the sales point with 8.3 and 12.2 demanded quality (See Correlation Matrix). The two customer requirements were acceptable because they show more positive interactions based on the competitive comparison (see Planning matrix).
The House Of Quality thus facilitated communication between strategic business operations, engineering design, and sales point (Xie & Goh 2003). For each technical descriptor, the level of technical difficulty required to achieve target value were considered. The values on House Of Quality (matrix 6) facilitated estimation that EBS model C meets or exceeds the customer’s requirements of comfort and durability (17.0%) at less cost. This was achieved by creating a new chart of HOWs (Technical requirements) and WHATs (customer requirements) as illustrated in the diagram bellow:
Figure 9 QFD Refinement chart.
The objective is to refine the House Of Quality to actionable level through prioritization of the technical descriptors (HOW MUCH). The innovative actions undertaken based on the target values are however subject to change if ultimate customer requirements are untenable or the QFD process failed to listen to the Voice of the Customer (WHYs). In the present case, Quick brake engagement and comfortable pedal lever (WHATs) had functional demanded weight of 2.0 and 2.0 for EBS Model C (HOWMUCH). These requirements translate to technical descriptors “conversion of kinetic Energy” and “electronic signal feedback” improvements 7.0 and 9.0 percent respectively (see Correlation matrix 4). This then answers the question of WHYs as follows: the QFD target is use of innovative technology in design of EBS model C that has higher efficiency in the braking process.
On the other hand, Voice of customer (VO-1) requires the braking system not only to have higher efficiency but also durable. Durability of the EBS is dependent on material capacity in terms of resistance to wear, heat, or any other physical damages. From the relationship matrix (3) the EBS product features (HOWs) listed long lifespan and light weight materials as technical descriptors for durability which can be achieved through material selection, adjustments of the mechanical system, and innovative electronic sensor system to improve signal transmission. Every purchaser requirements is collapsed to the next level through listing at least one primary, secondary and tertiary descriptors as shown on figure 8
Figure 8 Refinement of technical descriptors
It is important to note that, the changes in material used improve customer requirements by raising the competitiveness of the EBS model without necessarily affecting the product technical descriptors.
9. Conclusion
Quality Function Deployment particularly the “house of quality” is an effective approach in ensuring customers expectations are used in driving the design processes of a product. With this process, the problems associated to the EBS from the perspective of the customers will be highlighted. Even though QFD proves to be very effective in detecting EBS related problems, it does not suggest solutions for such problems. QFD is an efficient tool in which the expectations of the customer drive the process of EBS design. There are several advantages of QFD such as shorter EBS development cycle, significantly decreased initial costs, lesser engineering changes, consensus decisions, and environment teamwork. QFD forces the whole company to be continually certain of the requirements of the customer. Implementing QFD leads to a satisfied customer.
10. Recommended Actions
A number of matrices are used in analysis and structuring of data during QFD sessions. The present analysis of QFD for Electronic Break system (EBS) used six matrices as shown from Figure 1, integration of the quality analysis matrices forms a diagram similar to a design layout of a house hence the term “House of Quality”. It is structured as follows:
– Product targets
– Technical priorities
– Competitive technical benchmarks
Based on the QFD analysis results, two Electronic braking systems are recommended. The first focuses on the comfort of braking system while the second on durability. However, further analysis of the EBS from design, endurance, dynamic, and thermal analysis data to establish optimal durability that meets customer’s requirements. From such findings, better materials for the braking systems as well and functional environment of EBS will ensure both higher efficiency and durability.
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