* Advanced Brake System as of 2004
Ideas of Honda put in CBS, ABS and Combined ABS for motorcycles
From it's very beginning, Honda has been actively tackling with the issue of safety. Safety of motorcycles can be largely classified into two stages, active safety and passive safety. The brake in particular can be said to be very important in active safety.
The aim of developing the brake is to secure a high effect with good controllability. It is necessary to achieve the goal to heighten three areas; controllability, convenience and the sense of confidence for the average rider. With respect to controllability, at first the improvement of conventional brake systems can be cited, which will include the development of a disk brake system for motorcycles for the first time in the world and the development of sintered friction materials. In regards to convenience, the second area, we have begun the development of a combined brake system (CBS) ahead of others and are now tackling the task of an easier way of distributing braking force between the front and rear wheels. This is related to the improvement of controllability mentioned in the beginning. As for the enhancement of the sense of confidence, the third, we aimed at preventing wheel lock and came up with the anti-lock brake system (ABS). Furthermore, in docking CBS and ABS, we developed a combined ABS which enhanced the respective effects.
Positioning CBS, ABS and combined ABS as those contributing to the manufacture of motorcycles with the sense of confidence, Honda aims at adopting and expanding them to many more models as an advanced brake system.
Honda adopted a front wheel disk brake for mass-produced motorcycles for the first time in the world in 1969 and realized high braking performance required by the trend for larger size and higher speed motorcycles. Later on, the front and rear wheel interlocking brake systems (CBS) were mounted on mass-produced motorcycles, which were developed through participating in endurance races. Subsequently, advanced brake systems such as dual CBS, ABS and combined ABS were developed one after another and installed on mass-produced models.
To be cited as the first case of improvement in brake controllability is the front wheel disk brake system installed on the CB750FOUR in 1969. The disk brake system applied to mass-produced motorcycles for the first time in the world enabled the achievement of high braking performance, meeting with the trend at that time for larger size and higher speed motorcycles.
Honda started involvement with CBS through racing. The RCB1000, started in 1976 and won consecutive victories in endurance races, was equipped with a pedal brake CBS which worked effectively on the front and rear wheels simultaneously. The objective was to reduce rider fatigue while in a long competition lasting 24 hours.
This chronological table shows mass-produced models equipped with advanced brake systems. CBS was first installed on the GL1200 in 1982. In 1993, dual CBS was developed for more sporty models and installed on the CBR1000F. The use of CBS then expanded to a number of models. ABS, on the other hand, was installed for the first time on the ST1100 in 1992. It was combined with CBS in 1996 referred to as combined ABS. In 2003, a newly developed, compact and lightweight combined ABS was installed on the Silver Wing and paved the way for installation on many more models.
Honda paid attention to the operation of brakes unique to motorcycles; front and rear wheel independent brakes applied through levers and pedals in accordance with ever changing driving conditions from moment to moment. However, proper braking of front and rear wheels is required to stop efficiently in a shorter distance according to various road surfaces. Honda aimed at enabling ideal and easy operation of front and rear wheel brakes, which could be applied at anytime and by anybody. That is the purpose of CBS (combined brake system); front and rear wheel interlocked brake system.
The first thing to be considered in thinking about CBS, a front and rear wheel interlocked brake system, is the difference with automobiles. As compared with automobiles, the center of gravity is higher and the wheelbase is shorter, this makes the numerical value obtained by dividing the height of gravity center by the wheelbase larger than for automobiles. This fact makes the shift in the gravity center for motorcycles at time of braking greater than that of automobiles.
That is why the braking characteristics of the front and rear wheels largely differ in motorcycles. The front wheel brake causes the shift of gravity center to the front wheel in accordance with the extent of deceleration taking place, so a high
deceleration is obtained but the nosedive is large. The rear wheel brake, on the other hand, cannot yield deceleration larger than the front wheel, but the resulting nosedive is small.
The road surface conditions vary greatly by the pavement and weather conditions, whether fine or rainy, affects the riders ability to properly use the brakes of front and rear wheels to suit with driving conditions, making the most of features of respective brakes. CBS enables at anytime and for anybody to properly distribute braking force between the front and rear wheels in accordance with road surfaces.
In conventional motorcycle brakes, the right lever controlled the front wheel brake while the pedal (or the left lever) controlled the rear wheel brake. Honda aimed at simultaneous and effective application of the brake on the front and rear wheels by one operation. In the development of CBS, it has become necessary to assure that no sense of discomfort will be felt on braking characteristics and motorcycle body behavior by the riders accustomed to the conventional independent front and rear wheel brake application. Therefore, the following three points were aimed at in the development:
Honda's CBS can be largely classified into two types; Combi brake adopted for scooters, medium sized motorcycles and American custom models and dual CBS used by large sports and large tourers.
The main purpose of the two types is the same; to increase the deceleration obtained on appllication of the pedal brake (or the left lever), which was previously relatively lower during the application of the rear wheel brake alone. To achieve the purpose, it was made possible to apply the brakes simultaneously on the front and rear wheels by operation of the pedal (or the left lever). In case of dual CBS, furthermore, it was made possible to apply the brakes simultaneously on the front and rear wheels when the right lever was operated, to reduce nosedive.
A number of small scooters are equipped with mechanical drum brakes. The mechanical Combi Brake is a system designed for small scooters. On application of the left lever, the brakes will work simultaneously on the front and rear wheels through the equalizer. On input of low power, however, the front wheel brake efficacy is checked to bring nosedive closer to the former level caused by operation of the left lever. Thanks to the system, a high degree of deceleration is effectively obtained through a single operation of the left lever.
Fluid pressure type Combi Brakes were developed for large scooters, medium-sized touring bikes and American custom cruisers. Hydraulic pressure created by application of the pedal (or the left lever) is conveyed simultaneously to the front and rear wheel brakes. Similar to mechanical Combi Brakes, they are equipped with delay valves to cut hydraulic pressure to assure no brake will work on the front wheel at input of low power. The hydraulic pressure type Combi Brake is similarly effective to the mechanical Combi Brake; a high degree of deceleration can be effectively obtained by operation of the pedal (or the left lever) only.
The above figure shows the force distribution characteristics of the Combi Brake of a certain model, to front and rear wheels. The axis of abscissa represents the braking force of the front wheel while the axis of ordinate the braking force of rear wheel. The curve connecting blue points indicates an ideal braking force distribution characteristics in case of a single rider while the same connecting red points the ideal braking force distribution characteristics in case of maximum loading.
The maximum deceleration on a road surface having a friction coefficient occurs immediately before the simultaneous lock of the front and rear wheels. Individual points denote ideal braking force distribution on a road surface µ. Ideal braking force distribution characteristics are obtained by connecting points of ideal braking force distributions of respective friction coefficients. On a road surface with friction coefficient (µ) of 0.2 in case of single rider (green circle), for example, the figure shows that it is better if the braking force on the rear wheel was made larger than the front wheel. In case of 1.0 (yellow circles), on the other hand, it will be better if the distribution on front wheel brake was increased.
The riders will make either higher or lower distribution from the ideal braking force distribution characteristics. Making higher distribution will indicate that braking force distribution on rear wheel is larger while making lower distribution will show the braking force distribution on front wheel is larger.
The dark blue line denotes the braking power distribution characteristics into the front and rear wheel on operation of pedal (or the left lever) of the Combi Brake. Being positioned above the ideal braking force distribution characteristic diagram, the braking force distribution on rear wheel is larger. On operation of the right lever, braking force will take place on the front wheel only so that the distribution will be on the green line of front wheel braking force line.
Honda has further advanced Combi Brake, which will work simultaneously on the front and rear wheels by operation of the pedal (left lever) only, to develop dual CBS for application to much larger sports models. Based on the front double disk brake and rear disk brake, this not only brakes the front and rear wheels at the same time by applying the pedal, but also applies braking force on the rear wheel when the right lever is operated. The dual CBS enabled to efficiently decelerate and reduce nosedive.
In the dual CBS, the hydraulic pressure generated on operation of the right lever will act on the pistons on both ends of "three-pot" calipers on the left and right of the front. The braking force generated then will move the calipers on the left to generate new hydraulic pressure on the secondary master cylinder.
The hydraulic pressure will act on the pistons on both ends of three-pot calipers through the proportional control valve, PCV, having the function of pressure reduction, to general braking force on the rear wheel. Furthermore, the hydraulic pressure generated by operation of the pedal will act on the piston in the middle of three-pot calipers in the fore and aft. Similarly to the lever brake, the braking force generated on the front calipers on the left will generate hydraulic pressure in the secondary master cylinder, which will act on the pistons on both ends of the rear calipers. As the result, braking force higher than the time of lever operation will be generated on the rear wheel since all three pistons of the calipers are actuated.
Because of these mechanisms, the dual CBS turns out to be CBS also when the lever is operated unlike the case of Combi Brake. In addition to it, distribution characteristics different from the time of operating pedal will be obtained.
The above figure shows the braking force distribution characteristics of dual CBS. The characteristics of pedal brake lies on the ideal braking force distribution characteristic diagram at the time of maximum loading, similarly to the case of Combi Brake.
The characteristics at the time of using the right lever brake, on the other hand, exist on the underside along the ideal braking force distribution characteristics in case of a single rider, which indicates the braking force is distributed rather largely on the front wheel. As the braking force on the front wheel is increased, the braking force on the rear wheel increases at first, then goes down after passing the peak. Such unique distribution characteristics are obtained from the characteristics of PCV exclusively of motorcycles with the function of pressure reduction.
When both the pedal and lever are used, the distribution is in the region lying between the two braking force distribution characteristics, depending on the manner of distribution. This will make it easy to obtain a distribution closer to the ideal braking force distribution.
The above figure compares the deceleration generated by combination of operation of the lever and pedal on completed vehicles between the one equipped with conventional brake and that equipped with dual CBS. The directional axis diagonally to the right (blue) indicates lever input while the directional axis diagonally to the left (red) shows pedal input and the direction along the axis of ordinate (yellow) represents the deceleration generated by combination of respective inputs.
The figure on the left shows the deceleration generated by the combined operation of lever and pedal in the conventional brake system. It can be seen that both of the values of input and generated deceleration are low in the single operation by pedal input while high deceleration generated by the combination with lever input takes place in a partly limited input distribution area surrounded by green.
The figure on the right shows the deceleration generated by dual CBS. It can be seen that the operation of pedal alone enables to yield high input and high deceleration and that the area in which high deceleration can be generated is expanded. This means that riders can generate high deceleration much more easily.
Honda is now using two types of ABS for motorcycles, ABS using circulating type modulator widely used in automobiles and ABS used exclusively by motorcycles with modulators driven directly by motors. There are cases of using those two types of ABS
as they are for the conventional brake system and of using them in combination with CBS as combined ABS, aiming at installation of ABS on many models.
For the combined ABS for large scooters, circulating type modulators partially improved for motorcycles were adopted for "Combi brake".
For large tourers, combined ABS capable of giving higher braking force was completed, combining modulators directly driven by motors with dual CBS.
Combined ABS combining "Combi brake" and circulating type modulators. In this system prepared in one body with the electric control unit (ECU), a motor-driven pump generates hydraulic pressure and pressure is controlled by the solenoid valve. The system is characterized by a simple construction, which enables a unit to control brakes on the front and rear wheels.
Combined ABS for large sports and tourers are the brake systems combining dual CBS with ABS modulators driven directly by motor, which were developed exclusively for the purpose. The ABS modulators will control hydraulic pressure by directly lifting up and down the position of the piston with a motor. A modulator controls the brake hydraulic pressure of one wheel. The modulators are installed one each on the front and rear wheel.
The above figure compares the control of two types of ABS. The red line at the bottom denotes the changes in brake hydraulic pressure while the black line on top represents motorcycle body speed, and the blue line indicates wheel speed.
With the increase in hydraulic pressure, wheels start decelerating by the braking force. However, when wheel speed drops down excessively against motorcycle body speed, that is, wheels are nearing lock conditions, the modulators will lower hydraulic pressure receiving a signal from the ECU. As the wheel speed gets close to motorcycle body speed, the hydraulic pressure will be raised once again. This is repeated time and again in one second.
Hydraulic pressure fluctuation is smaller in the ABS directly driven by a motor, so that wheel speed is much smoother and finely controlled. As the result, the pitching of the motorcycle body is reduced.
Advanced brake systems developed by Honda so far, CBS and ABS, were merged as combined ABS to enable to produce a greater effect.
The figure below shows a comparison of maximum deceleration generated by operation of the pedal alone in a model between the conventional brake and the advanced brake systems. The deceleration generated by the pedal operation in the conventional brake system is approximately 0.4G (1G = 9.8m/s2). As against to it, the deceleration is increased in CBS by about 1.7 times by obtaining braking force of the front wheel. In case of combined ABS, furthermore, the deceleration is increased as much as approximately 2.3 times.
A survey was conducted to find out how the advanced brake system of Honda was actually evaluated by users in the market. The following graph shows the satisfaction of users of four models sold in ten countries in Europe equipped with CBS and combined ABS. It can be seen that as many as 87.5% of users have a positive opinion about the advanced brake system.
Honda's advanced brake system has rapidly increased in the latter half of 1990s. The aggregate throughout the world exceeded the mark of 1.5 million units in 2003. Approximately 50% of the models are now equipped with these advanced brake systems in Japan, America and Europe.
Honda aims at increasing the application of advanced brake systems to many more models in the future. The required performance and costs vary greatly by categories of motorcycles. Therefore, a proper system must be introduced according to the need. Ceaseless efforts are made for that purpose. For examples, there are systems adapted to the excellent kinetic characteristics of more sporty models and the development of more light and compact ABS. It is required, however, to overcome a variety of tasks for the realization of such goals.
Honda will strive for the development and expansion of advanced brake systems from the viewpoint of positively tackling with improving performance.