Interacción entre la Remodelación Isquemia y el Crecimiento Generado por Tensiones

In order to check the transferability of simulation results to the real experiments and get an impression of the brake force distributions (BFD) practically realized by the C-ABS brake-by-wire system of the test motorcycle (Honda CBR 600 RR), the simulated BFD are qualitatively compared to randomly captured BFD from real riding experiments in the form of BFD diagrams. It is important to note, that the entry of data points from the experiments is derived from brake pressure measurements under the assumption of constant friction characteristics of the brake pad / disk combinations, undeformable tire contours, and an unsprung chassis. Moreover, the excess brake torque needed to decel- erate the wheel’s spinning inertia is not considered, which may altogether lead to devia- tions from the actual BFD. However, a qualitative comparison is still valid, despite these limitations. The simplified calculation for the entry of measured data into the BFD diagram is explained along with parameters of the brake system in appendix A.3.3.

Simulated Brake Force Distributions

Figure 3.18 presents the 9 different cases of simulated BFD. While rear only braking coincides for both the maximal and partial braking experiment (cases 4 and 9) and includes the rolling resistance force at the front wheel, the partial braking experiments with ax = 0.5g remain left of the respective line of constant deceleration level and the maximal braking maneuvers are found right of it. It is important to note, that this line starts at a value of 0.6 (instead of 0.5) on the axis of the relative front brake force (x-axis) of the graph, since the front braking cases with clutch engaged and a driving force at the rear (cases 3 and 8) require a prolongation of the diagram in negative verti- cal direction. As a side note, the rear wheel driving force, which is based on keeping constant the initial driving torque at the rear wheel, is sinking for the partial deceleration in case 3, while it is growing for the maximal deceleration in case 8. On one hand, the tire rolling radius increases with decreasing roll angles, which leads to a diminution of driving force for the constant torque. On the other, the rear wheel is unloaded due to the deceleration, leading to lower rolling resistance. Since its initial value is covered in the driving torque and the rear wheel is almost completely unloaded due to the high decel- eration in case 8, this effect is dominating and leading to the increase in driving force.

Figure 3.18: Simulated brake force distributions of the 9 different cases. Markers indicate the beginning of the braking process. Further explanation is given in the running text.

While the ideal BFD (cases 1 and 5) nicely follows the “airfoil-like” shape of the ideal BFD curves, starting with a roll angle of λ0 = 35° and ending with straight conditions,

the rear-oriented Cornering Adaptive BFD (case 6) operates firmly above, at the rear wheel’s friction limits, and all front braking BFD (cases 2, 3, 7, and 8) stay firmly be- low the ideal reference curves.

Real Brake Force Distributions in Maximal Straight Braking

The real BFD obtained for maximal straight braking with the test motorcycle are com- pared against the ideal BFD curve in Figure 3.19. Even the sole activation of the front brake initially leads to a rather quick build-up of brake force at the rear wheel. After a first ABS-intervention, be it due to dynamic over-braking or for reasons of rear wheel lift-off mitigation respectively pitch control, the rear brake force is kept at an almost constant low level. After only 0.3 to 0.4 seconds of braking, also the front brake force has settled, delivering a smooth braking control with a clearly front wheel oriented BFD and achieving a mean deceleration of 0.75g in the presented example. The distinctively high values occur after halting the vehicle, before releasing the brake again.

The sole activation of the rear brake leads to an even sharper increase in rear brake force, but starts to involve also the front brake with more modest increase rates after about 0.2 s of braking. After about 0.6 s of braking, the BFD has settled at its operation point. It remains clearly rear wheel oriented, but through application of the front brake

1 2 3 4 5 6 7 8 9 10 0 10 20 30 40 50 60 70 80 90 100 bb-eq, cases 1+5 bb-rr, case 6 ft, cases 2+7 ft, eng., cases 3+8 rr, cases 4+9

3.6 Effectiveness Comparison of BSTAM and Standard Chassis

already allows to achieve a mean deceleration of 0.59g in the example, which is about the typical deceleration level reached by average riders153.

Figure 3.19: Comparison of ideal and maximal (ABS controlled) real BFD of the Honda CBR 600 RR test motorcycle in three subsequent straight braking maneuvers from

v0 ≈ 28 m/s ≈ 100 km/h to standstill using front, rear or both brakes (achieving deceleration

levels of ax ≈ 0.75g, 0.59g, and 0.81g, respectively, on a test track with 0.7% downward slope). Data points are marked every 0.1 s of the measurement, starting in the origin of the diagram and following the direction of the curved arrows.

Finally, for the combined actuation of both brakes, also the advanced rise in rear brake force is to be observed, with a sharp increase of the front brake force between 0.2 and 0.3 s of braking. After less than 0.5 s, the BFD has settled. With only two exceptions for ABS respectively pitch control, it remains nicely on the ideal BFD curve, delivering an average deceleration of 0.81g in the presented example. It has to be noted, that the experiment was conducted on a slight downward slope of 0.7% and that higher decel- erations are achieved with the unmodified base vehicle with a curb mass of only 197 kg compared to 29 kg more of the BSTAM prototype vehicle.

Real Brake Force Distributions in Maximal and Partial Corner Braking

Figure 3.20 illustrates the real BFD achieved for two corner braking experiments on a constant radius of R = 50 m. The first is a maximal braking maneuver, using both brakes. Its BFD exhibits great similarities to that for maximal straight braking (cf. Fig- ure 3.19), especially in the initial phase of brake force build-up. However, an imaginary hull curve is resembling the simulated ideal BFD for the maximal corner braking exper- iment presented in Figure 3.18 (case 1), however, staying below in both brake forces and hence also deceleration level (7.6 m/s² in the experiment vs. simulated 9.5 m/s²).

Besides the more challenging initial conditions of the experiment, this is mostly due to the fact that the real brake system needs to keep a certain safety margin to the absolute physical limits in order to maintain stability as well as the idealizing simplifications of the model calculation. This BFD was chosen as the reference for “state of the art corner braking” experiments with the standard chassis.

Figure 3.20: Comparison of ideal BFD curves with two real BFD of the Honda CBR 600 RR test motorcycle in corner braking experiments on a constant radius turn with R = 50 m. The first experiment is maximal braking with both brakes (v0 ≈ 18.6 m/s ≈ 67 km/h, ay,0 ≈ 6.9 m/s², λ0 ≈ 35°, ax ≈ 7.6 m/s² ≈ 0.77g) and the second is partial front braking (v0 ≈ 18.3 m/s ≈ 66 km/h, ay,0 ≈ 6.7 m/s², λ0 ≈ 30°, achieving a mean deceleration of ax ≈ 6.1 m/s² ≈ 0.62g). Data points are marked every 0.1 s of the measurement, starting in the origin of the diagram and following the direction of the curved arrows.

The second is a partial front braking experiment. Also the BFD achieved in this case resembles strongly to that in straight running (cf. Figure 3.19). After the initial phase with a quick rise in rear brake force, it also settles towards a clearly front wheel oriented BFD with almost constant rear wheel contribute. A mean deceleration of 6.1 m/s² is achieved at slightly milder initial conditions than for the simulations, aiming at just 0.5g ≈ 4.91 m/s² of deceleration. A qualitative comparison to the simulated BFD (cf.

Figure 3.18, cases 5 and 7) suggests a transferability of the conclusions from the simula- tions towards the experiment, since the real BFD still comes close to the “front only” simulated one (case 7). However, improvements on the BST effect are to be expected through combined application with the rear brake in the sense of a tendency towards a more “ideal” BFD (case 5). – Since this BFD was easy to reproduce with high repeata- bility and before the background, that the BST effect and improvements thereon are most relevant for partial braking, this BFD was chosen the reference for experiments to compare BSTAM with the standard chassis.