Automotive Tribology and Noise, Vibration & Harshness Assignment - Noise Vibration & Harshness

1. Introduction - Noise, vibration and harshness (NVH) causes many refinement issues for the automotive industry, therefore the ability to measure, model and analyse NVH problems is a desirable skill for automotive engineers.

In this individual assignment you will demonstrate the use of both CAE and analysis techniques in the analysis of noise, vibration & harshness (NVH), together with the experimental techniques that have been demonstrated in the lecture sessions.

2. Learning outcomes - Successful completion of this assignment enables you to demonstrate the following learning outcomes of the module:

1. Critically evaluate vehicle component behaviour and the influence of tribology and NVH on such systems.

2. Use CAE tools competently to design, simulate and critically analyse component behaviour.

3. Apply experimental techniques to analyse vibrating systems.

4. Present and interpret experimental and CAE results.

5. Communicate effectively and manage your own learning.

3. Tasks -

Automotive brake systems are susceptible to frictionally induced dynamic instabilities which can result in brake squeal. Dynamic instability can be related to the coefficient of friction between the brake pad and brake disc, with higher friction coefficients generally generating more instability. This can be demonstrated theoretically whereby two mode pairs will combine at a bifurcation point and will generate instability (Figure 1). You are to investigate mode-coupling phenomenon as a potential mechanism for brake noise.

3.1 Identification of system parameters -

You will be provided with a CAE model of the brake disc. Predict the free-free natural frequencies using Finite Element analysis (FEA) and compare to the measured values that have been provided to you. Investigate and explain any differences in the correlation between the predicted and measured values. Using the experimentally measured modal analysis data, identify values for modal damping and stiffness for the frequency peaks that are closest to your provided data.

To identify stiffness, you should assume that the entire component mass (m) vibrates at each natural frequency (ω). The stiffness (k) can be obtained from:

ω_n = √(k/m) (rad/s)

Modal damping at each frequency can be obtained from the half-power bandwidth method using the component Fourier response function (FRF).

3.2 Predicting instability -

You will be provided with a 2DoF Matlab model which is based upon a model originally proposed by Hoffmann et al (2002) as shown in Figure 2. Using this model and the parameters identified in section 3.1, you should investigate the modal coupling behaviour between the brake disc in-plane and out-of-plane modes of vibration. You should use the parameter variables that are close to the frequency of interest which will be provided separately. It is expected that you investigate and analyse the effect of changes to these parameter values.

Provided information:

• CAE disc model
• Disc FRF data
• Pad FRF data
• Baseline parameter values
• Matlab model

Parameters:

• K₁ =k₂ = stiffness (N/m)
• K₃ = Disc dynamic stiffness (N/m)
• m = disc mass (kg)
• a₁ = TBC
• a₂ = TBC
• µ = TBC

Note:

• Damping coefficients are not required, but you should comment on your findings from section 3.1
• For this coursework, the terms and parameters used in the model differ from that in the published paper - this is intentional.

Deliverables - You should produce a technical report on your findings following the guidance set out in the marking scheme. The total report should be equivalent to ~2000 words.

The report should contain as a minimum but is not limited to:

• Executive summary
• Aims & objectives
• Literature review
• Theory & analysis
• Results
• Discussion
• Conclusions
• References

Resources -

• Journal of Sound and Vibration.
• SAE Mobilus (SAE Technical papers).
• Proceedings of the IMechE, Part D: Journal of Automobile Engineering.
• Library search engine - Summon.

References - Norbert Hoffmann, Michael Fischer, Ralph Allgaier, Lothar Gaul, "A minimal model for studying properties of the mode-coupling type instability in friction induced oscillations", Mechanics Research Communications, Volume 29, Issue 4, 2002, Pages 197-205, ISSN 0093-6413.