■ The ideal of street vest is a friction material whose μ does not change.
Even if the ultimate purpose of braking is to stop, "deceleration" is also important for drivers who enjoy driving.The brakes stepped on at the entrance of the corner are exactly the purpose of controlling the posture of the car body and preparing for the next acceleration.Therefore, the driver's expectations and operations, such as how much deceleration should be aimed at and how much force should be pressed on the pedal, must be directly linked to accurate deceleration.It can be said that deceleration that is different from the image not only impairs the "effectiveness" but is sometimes even dangerous.
So what influences the relationship between pedaling force and deceleration?Brake pads ultimately fulfill that function.In the same vehicle, the braking force can be conceptually considered to be proportional to [brake pressure x friction coefficient (μ)].If the μ is constant, the strength of the braking force is proportional only to the driver's pedaling force, so the driver's controllability is improved and the driving feeling of the human and horse can be obtained.However, unfortunately, the coefficient of friction is not always constant, and changes due to heat generation due to vehicle speed and deceleration are unavoidable.Therefore, in order to enjoy the effect synchronized with the driver's sensibility, it is important not only to increase or decrease μ, but also to reduce the way of change as much as possible.

■ How does ❝μ❞ change with deceleration and deceleration time?
For street sports brake pads, the characteristics of friction materials are carefully evaluated by rigorous bench tests.We continuously collect data more than 400 times from the new state to the normal use process.Among them, please see the raw data (Ⓐ) of the test that can evaluate the original performance of the pad after the break-in is finished. Eight types of μ with different decelerations are plotted from three types of speeds of 50 km, 100 km, and 130 km to stop.This pad has a target value of μ of 3, a maximum of 8, a minimum of 0.42, and a width of 0.462, which is within a small error of ± 0.378%.In other words, even with continuous braking regardless of vehicle speed or pedaling force, the fluctuation range of the change in μ is small, and a stable effect is obtained.

■ Braking, mastering controllability at that moment.
Next, let's take a closer look at Figure A (Ⓑ). The plot in Fig. A is the average value of each test, but in reality, the change is repeated from the occurrence of μ to the stop. It is a waveform that connects the moments when μ is generated over time.Theoretically, it is easy to speculate that a horizontal waveform of μ will give a more stable effect, but with that characteristic, the driver feels that the effect is not so good even if he steps on it.In human sensibility, as the deceleration progresses as shown in the figure, the deceleration is linear with respect to the pedaling force when the waveform rises toward the right shoulder.
For example, when entering a blind corner, even though the vehicle has decelerated sufficiently, the R becomes tighter toward the back, and when the pedal is further depressed, the μ waveform decelerates quickly if it rises to the right.On the contrary, when R is larger than the prediction, the pedal can be loosened and the speed can be recovered instantly.It can be said that it is an excellent characteristic from the viewpoint of safety.The best way to achieve control at will is to make a gentle, upward-sloping change in μ.

■Deceleration = negative acceleration, a numerical value of how much deceleration per unit time.The unit is m / sec² or G.For example, when a car running at 100km / h (≈27.8m / s) is stopped in 5 seconds, the deceleration is 27.8 ÷ 5 = 5.56m / sec² (about 0.56G).

■ Focus not only on the stability of μ, but also on its “transient characteristics”.
Now, let's grasp what happens to the braking force if you continue to step on with a constant pedaling force in the actual driving scene from the human sense side (Ⓒ).

In this graph, the red line (μ) and the black line (vehicle speed) are shown so that the relationship between deceleration can be intuitively imagined by the change of μ. Needless to say, the figure on the left, in which there is little change in μ and the deceleration method is constant, is excellent.In the other figures, a sudden change in μ occurs, and even if the pedaling force is constant, the deceleration method is not constant.Therefore, it is necessary to correct the unexpected deceleration.
In this way, in order to obtain the "deceleration at will" that is synchronized with the human sensibilities that we aimed for, the process of change in μ and the angle of upward movement in the figure are important.If the angle is steep, the effect will suddenly rise, and if it is too loose, it will not work.Stability of μ is absolute due to the influence of pedaling force, vehicle speed, braking time, temperature, etc., but among them, the driver's sensibility and the amount of change and how to make changes without deviation.In other words, it is indispensable to develop a friction material that identifies the "transient characteristics of μ", and it can be said that it is an important means for enjoying "deceleration".