Session 4.1: Reliability Block Diagram

Session 4 takes place in the RAM module and focuses on setting up and generating reliability analyses from the MADE model, including RBD, Reliability Allocation, Failure Rate Prediction (MIL-HDBK-217F), Markov Analysis, and Hardware Fault Tree.

Session 4.1 Outline

• 4.1.1: Reliability Block Diagrams
• 4.1.2: Create RBD groups
• 4.1.3: Generate RBD Analysis
• 4.1.4: Generate RBD Report

4.1.1 Discussion: Reliability Block Diagrams

Reliability Block Diagrams are models showing reliability dependencies between items. The blocks (subsystems, components, parts) are derived from system model items.

Types of RBD groupings in MADE:

• Series Grouping
• Parallel Grouping
• Complex Group (Decomposition)
• Complex Group (Event Space)
• Standby Redundancy Grouping
• K/N Redundancy Grouping
• Exclusion Grouping

Series Group represents a collection of items in which all items must function in order for the series group to function.

• Exponential Distribution: R(t) = ∏ Ri(t)
• Weibull Distribution: R(t) = ∏ Ri(t)
• Group equation: R = R1 × R2 × R3 ... = ∏ Ri

Parallel Group represents a collection of items in which some items must be functioning in order for the group to function.

• Group equation: R = R1 + R2 + R3 - R1R2 - R1R3 + R1R2R3
• General form: R = 1 - ∏(1 - Ri)

Complex Group (Decomposition Method) represents a collection of items which cannot be decomposed into a combination of distinct series or parallel groups. It consists of items with the key item in a functioning state.

Complex Group (Event Space) represents a collection of items which cannot be decomposed into a combination of distinct series or parallel groups. It consists of items with can be mirrored to configure the system.

Standby Redundancy Group represents a combination of redundant items that provide greater system reliability. It consists of a fraction which indicates the cold standby (numerator) and the total number of redundant items (denominator).

K/N Redundancy Group represents a collection of items operating under constant, identical load. It consists of a fraction which indicates the functioning items (numerator) and the total number of redundant items (denominator). All items are assumed to have the same failure rate — the lowest failure rate of the group is used if they are not identical in the model.

Exclusion Group is used to disregard selected items from reliability analysis.

Exercise 4.1.2: Create RBD Groups

To apply a Series RBD grouping:

1. Right-click Vehicle System in Project Explorer viewer
2. Select RBD Model
3. Select all items in the RBD Model editor
   • Method 1: Shift + Select
   • Method 2: Select and drag
4. Select the Series Group icon from the icon menu, or Group > Series Group from the right-click menu
5. Review reliability of series group and individual subsystems

Note: Within the RBD group, components and subsystems can be rearranged by clicking and dragging. Reliability is computed considering maintenance actions effectiveness factor (discussed in Session 5).

Continue to apply RBD groupings to items in the Driveline Subsystem:

1. Right-click Driveline Subsystem in Project Explorer & select RBD Model
2. Create Series Group #1 including: Half Shaft Rear, Planetary Gearbox Rear, Wheel Resistance Rear & Wheel Rear
   • Select the group and using the Properties window, rename the Series group to Rear wheel configuration
3. Create Series Group #2 including: Half Shaft Front, Planetary Gearbox Front, Wheel Resistance Front & Wheel Front
   • Rename the Series group to Front wheel configuration
4. Create a Parallel group for Series Groups 1 & 2
   • Rename the Parallel group to Wheel configuration
5. Create a Series group for remaining items and include the Parallel group
6. Review reliability of top series group and individual sub-groups

Create the following RBD groupings on the Diesel Engine subsystem:

1. Right-click on the Diesel Engine subsystem in Project Explorer and select RBD Model
2. Create a K/N Redundancy Group including: Air Filter, Primary Fuel Filter & Secondary Fuel Filter
   • Set Functioning items / No. of Redundant Items (Properties viewer): 2/3
3. Create an Exclusion Group and place the Governor in the Exclusion Group

Discussion 4.1.3: Generate RBD Analysis

RBD Analysis uses RBD Groups (Session 4.1) and reliability information (Session 4.3). Outputs include:

• Reliability — Calculated based on the distribution type, e.g. R = e^(-λt) for Exponential
• MTTF — Calculated based on Part Failure Rate
• Inherent Availability — Based solely on reactive maintenance: Ai = MTTF / (MTTF + MTTR)
• Operational Availability — Based on preventative maintenance & logistic delay
• General Reliability & Distribution Type parameters
• Dynamically updates based on changes to the system & reliability parameters
• Maintenance effectiveness factor is considered when computing revised Reliability and Availability metrics

Exercise 4.1.3: Generate RBD Analysis

To determine the reliability of the Control Unit component:

1. From the menu bar, select Analyses > RBD Analysis
2. Expand the tree and select the Control Unit
3. Verify that Control Unit reliability is 0.9999089

Discussion 4.1.4: Generate RBD Report

This report summarizes the RBD Models, including Failure Rates, Groups, MTTR, and other reliability/availability information. It allows the ability to choose the Reliability Metrics to report: Baseline / Revised / Both.

Report is divided into sections:

• Cover Page & Glossary
• Poor Performers
• Reliability & Availability
• Item Properties
• RBD Diagrams

Exercise 4.1.4: Generate RBD Report

1. Select Reports > Report Wizard from the main menu
2. Select Reliability Block Diagram Report then select Next
3. Select Vehicle System check box in the System Hierarchy section (or select all)
4. Select the Include screenshot of diagrams check box
5. Select Poor Performers Threshold of 0.9999999
6. Select Revised and Baseline under Included Reliability Metrics
7. Select Generate

Session 4.1 Summary

• 4.1.1: Reliability Block Diagrams
• 4.1.2: Create RBD Groups
• 4.1.3: Generate RBD Analysis
• 4.1.4: Generate RBD Report