Naveed Ashraf

The Measurement and Analysis of the Disc/Pad Interface Dynamic Centre of Pressure and its Influence on Brake Noise.

This paper discusses the measurement of the dynamic centre of pressure (CoP) of a brake pad during a normal braking event using a modified 12-piston opposed calliper. The modifications allow the centre of pressure to be controlled both radially and along the length of the pad, inducing a leading or trailing centre of pressure as desired. The technique is unique in its design and implementation. Both the centre of pressures of the in-board and out-board pads are recorded simultaneously with varying pressures and speeds. The results, which include pressure and force maps, show the position of the centre of pressure to vary considerably during a braking event, both radially and axially along the pad. The CoP offset is related to the calliper mounting geometry which is subsequently compared to the effective “spragging angle” and the generation of brake noise. It is seen that by inducing a leading offset noise may be generated and subsequently eliminated if a trailing centre is then induced. The results suggest that by careful selection of the backplate abutment friction level the CoP may be controlled to always fall within the “stable envelope” region and so resist noise generation.

An Investigation of the Pad/Disc Dynamic Centre of Pressure using a 12 Piston Opposed Caliper

Pressure-sensitive film embedded into the body of a pad friction compound is a unique technique used to measure the dynamic center of pressure at the pad/disc interface during a normal braking operation. This paper uses of a modified 12 piston opposed caliper where the initial center of pressure may be varied both along the pad and radially. Results show a very definite movement of the center of pressure towards the center of the pad as the brake pressure is increased. In addition it is seen that a leading center of pressure (CoP) will result in noise whereas a trailing CoP gives a quiet brake. Equally a CoP towards the inner edge of the pad increases noise propensity whereas towards the outer edge a quiet brake. The results also show little influence on the CoP with disc speed.

Measurement of the dynamic centre of pressure of the disk/pad interface during a braking operation

This paper demonstrates the influence of the trailing end of the piston, or inboard, pad on the propensity of a brake to generate audible squeal. The unique technique was employed to measure the dynamic CoP at the pad/disk interface during a normal braking operation. This novel technique uses an embedded pressure sensitive film within the pad. The paper also presents the co-planar analysis of the pad/caliper contact regions and its influence on the position of the disk/pad CoP. The analysis shows how the trailing end of the piston pad influences the position of the CoP and goes on to explain why the centre moves as the pad abutment vibrates against the abutment. The paper includes additional work with a 12-piston opposed caliper where the initial CoP may be varied both along the pad and radially. Results show a very definite movement of the CoP as the brake pressure is increased.