Interlock braking system for motorcycles

An interlock braking system for motorcycles comprising a brake pedal, a single master cylinder which generates a braking pressure according to an external force applied to the brake pedal, first and second brake mechanisms connected to the master cylinder for applying first and second braking forces according to the braking pressure to the front and rear wheels, respectively, and an anti-lock mechanism for changing the braking pressure according to rotational speeds of the front and rear wheels to prevent the wheels from becoming locked. In this manner, the interlock braking system effectively avoids the occurrence of a wheel-lock condition when braking the front and rear wheels of a motorcycle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to an interlock braking system for 
motorcycles. More particularly, the invention relates to an interlock 
braking system for motorcycles having front and rear wheel brake units 
connected to a single master cylinder which generates pressure when force 
is exerted on a brake pedal. 
2. Description of Relevant Art 
An interlock brake system for motorcycles having front and rear wheel brake 
units connected to a master cylinder which generates pressure when force 
is applied to a brake pedal has been generally known. In such a system, 
the generated pressure serves as a driving force to drive each of the 
brake units for braking both the front wheel and the rear wheel 
simultaneously, thereby simplifying the braking operation. 
In such an interlock braking system, however, because braking of the front 
and rear wheels is effected by operation of the brake pedal as set forth 
above, one of the wheels is likely to become locked when driving in 
slippery areas, such as on an icy road surface. Thus, such wheel lock 
phenomenon has been a serious problem with respect to known systems. 
The present invention effectively overcomes such problem attendant 
conventional interlock braking systems for motorcycles. 
SUMMARY OF THE INVENTION 
The present invention provides an interlock braking system for motorcycles 
comprising a brake pedal; a single master cylinder which generates a 
braking pressure in accordance with the magnitude of force externally 
exerted on the brake pedal; first and second braking mechanisms connected 
to the master cylinder for applying first and second braking forces to the 
front and rear wheels, respectively, in accordance with such braking 
pressure; and an anti-lock mechanism for changing such braking pressure in 
response to the rotational speed of each of the front and rear wheels to 
prevent locking of the wheels. 
It is an object of the present invention to provide an interlock braking 
system which effectively avoids a wheel-lock condition when braking the 
front and rear wheels in a motorcycle wherein front and rear wheel brake 
units are connected to a single master cylinder which generates pressure 
when force is exerted on a brake pedal. 
Another object of the present invention is to provide an interlock braking 
system in the aforesaid type of motorcycle whereby the possibility of the 
aforesaid wheel-lock condition occurring is minimized. 
It is a further object of the present invention to provide an interlock 
braking system in the aforesaid type of motorcycle wherein the braking 
operation can be performed with relatively substantial freedom and 
flexibility. 
The above and further objects, features and advantages of the present 
invention will become apparent from the following detailed description of 
preferred embodiments of the invention, when read in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
With reference to FIGS. 1 through 3, there is shown a master cylinder 1 
having an upper cylinder bore 2 and a lower cylinder bore 3 both formed in 
the interior of master cylinder 1, with a control piston 4 and an 
actuating piston 5 being slidably fitted in the cylinder bores 2 and 3, 
respectively. The control piston 4 partitions the cylinder bore 2 into an 
upper oil pressure control chamber 6 and a lower oil supply chamber 7, and 
is normally biased downwardly by a spring 8 which is disposed in a 
compressed manner within the chamber 6. The actuating piston 5 partitions 
the cylinder bore 3 into an upper oil pressure output chamber 9 and a 
lower oil supply chamber 10, and from the upper surface thereof is 
upwardly projected a piston rod 11 which extends through a partition wall 
12 formed between the upper and lower bores 2 and 3 and is in abutting 
engagement with the lower surface of the control piston 4. The actuating 
piston 5 is subjected to a biasing force of a spring 13 disposed in a 
compressed manner within the oil supply chamber 10 and that of the spring 
8 through the piston rod 11, whereby actuating piston 5 is normally urged 
to its lower limit position as shown. The lower surface of the actuating 
piston 5 is in abutting engagement with the upper end of a push rod 14, 
the lower end of push rod 14 being connected through a pin 17 to an arm 
member 57 which is integrally pivotable with a brake pedal 16. The brake 
pedal 16 is pivotably attached to the vehicle body frame through a pivot 
shaft 15. 
In the piston 4 are longitudinally formed oil holes 18 and 19 for 
establishing communication between the oil supply chamber 7 and the oil 
pressure control chamber 6, while in the piston 5 is longitudinally formed 
an oil hole 20 for establishing communication between the oil supply 
chamber 10 and the oil pressure output chamber 9. The pistons 4 and 5 are 
provided on the respective upper surfaces thereof with elastic sealing 
cups 21 and 22 for opening and closing the oil holes 18 and 20, 
respectively. Seal members 23 and 24 are disposed on the lower side of the 
partition wall 12 and on a lower portion of the piston 5, respectively, to 
ensure that the portion between the cylinder rod 11 and the inner wall of 
the cylinder bore 3 is oil tight. 
An oil tank 25 is formed in the interior of the master cylinder 1, and 
communicates through an oil hole 26 formed in the upper portion thereof 
with an oil path 28 which leads to a reservoir 27 as will be described in 
greater detail hereinbelow. An actuating oil is supplied from the 
reservoir 27 through the oil path 28 to the master cylinder 1 so as to 
fill same. The oil pressure control chamber 6 is also charged with the 
actuating oil from the reservoir 27 through a normally open valve 29, an 
oil path 30 and an oil hole 31. On the other hand, the oil supply chamber 
7 normally communicates with the oil tank 25 through an oil path 32. While 
the piston 5 is not in operation, the oil pressure output chamber 9 and 
the oil supply chamber 10 are also in communication with the oil tank 25 
through oil paths 33 and 34, respectively. 
The oil pressure output chamber 9 of the master cylinder 1 is connected to 
a front wheel-side caliper 37 through an oil hole 35 formed in the side 
wall thereof and also through an oil path 36, and is also connected to a 
rear wheel-side caliper 39 through an oil path 38 branched from the oil 
path 36. To the respective axles 40a and 41a of a front wheel 40 and a 
rear wheel 41 are respectively fixed brake disks 42 and 43. The calipers 
37 and 39 are mounted so as to surround the brake disks 42 and 43, 
respectively, and are each provided in a known manner with a hydraulic 
cylinder, a piston fitted in the hydraulic cylinder and a pair of brake 
pads. 
The actuating oil in the reservoir 27 is held substantially at atmospheric 
pressure. As described hereinabove, the reservoir 27 communicates with the 
oil tank 25 of the master cylinder 1 through the oil path 28 and the oil 
hole 26 to supply the actuating oil to the oil tank 25, and also 
communicates with the oil pressure control chamber 6 of the master 
cylinder 1 through the normally open valve (solenoid valve) 29, the oil 
path 30 and the oil hole 31 to supply the actuating oil to the chamber 6. 
The reservoir 27 is further connected to an accumulator 46 through a 
hydraulic pump 44 and an oil path 45. From the oil path 45 is branched an 
oil path 47 at a portion of oil path 45 between the hydraulic pump 44 and 
the accumulator 46. The oil path 47 joins the oil path 30 through a 
normally closed valve (solenoid valve) 48. 
Proximal the brake disks 42 and 43 of the front and rear wheels 40 and 41 
are disposed revolution sensors 49 and 50 for detecting rotational speeds 
of the front and rear wheels 40 and 41, respectively. Output signals from 
the revolution sensors 49 and 50 are fed to a signal processing unit 53 
through conductors 51 and 52, while control signals are provided from the 
signal processing unit 53 to the normally open valve 29 and also to the 
normally closed valve 48 through conductors 54 and 55, respectively, to 
energize or de-energize the solenoids of the valves 29 and 48 to thereby 
switch such valves from each other. 
As shown in FIG. 3, the master cylinder 1 is fixed substantially 
perpendicularly to a substantially centrally positioned frame of the 
vehicle body through a bracket 56. On the other hand, the reservoir 27, 
the normally open valve 29 and the normally closed valve 48 are integrated 
as a single unit 58 mounted substantially parallel to the vehicle body 
frame. 
In the construction as described hereinabove, if the brake pedal 16 is 
pushed pivotally downwardly (in the direction of arrow .alpha. in FIG. 1), 
the actuating piston 5 is subjected to a force transmitted from the push 
rod 14, so that it slides upwardly (in the direction of arrow .beta. in 
FIG. 1), thus causing the control piston 4 to slide in the same direction 
through the piston rod 11 against the biasing force of the springs 8 and 
13. At this time, the actuating piston 5 closes the oil path 33 to thereby 
cut off communication between the oil pressure output chamber 9 and the 
oil tank 25, so that the actuating oil within the oil pressure output 
chamber 9 is compressed and increases in pressure. This increased pressure 
is transmitted through the oil hole 35 and oil paths 36, 38 to the front 
and rear wheels 37 and 39, thereby actuating the calipers 37 and 39 to 
generate braking forces. At this time, moreover, the oil supply chamber 10 
of the master cylinder 1 slides while maintaining a constant capacity, and 
thus does not generate a resisting force to the oil pressure against the 
sliding motion of the actuating piston 5. In this case, the biasing force 
of the springs 8 and 13 and a reaction force against the actuating piston 
5 caused by the increase in oil pressure of the oil pressure output 
chamber 9 are offset by the pushing force of the push rod 14, so that it 
is not necessary to take such forces into consideration. 
On the other hand, the capacity of the oil supply chamber 7 increases with 
the sliding motion of the control piston 4, but by virtue of a negative 
pressure generated along with such sliding motion, the actuating oil in an 
amount corresponding to the capacity increase is absorbed and charged from 
the oil tank 25 into the chamber 7 through the oil path 32, while the 
capacity of the oil pressure control chamber 6 decreases by an amount 
corresponding to the capacity increase of the oil supply chamber 7. 
However, the actuating oil corresponding to the capacity in question is 
returned to the reservoir 27 through the oil hole 31, oil path 30 and 
normally open valve 29, so that the sliding motion of the control piston 4 
does not cause a resisting force to the oil pressure. 
The braking forces generated against the front and rear wheels 40 and 41 
are substantially equal if the cylinder bores of the calipers 37 and 39 
are the same, so that both change in a linear relation such as indicated 
by the broken line A in FIG. 4. 
In the event that either or both of the front and rear wheels 40 and 41 are 
likely to become locked due to an excessive braking force, i.e., when a 
deceleration value detected by the revolution sensors 49 and 50 and 
computed by the signal processing unit 53 exceeds a predetermined value, 
the signal processing unit 53 generates control signals to close the 
normally open valve 29 and open the normally closed valve 48. On the other 
hand, the accumulator 46 is normally filled with oil pressurized by the 
hydraulic pump 44, and thus upon such switching operation of the valves 29 
and 48 this pressurized oil flows into the oil pressure control chamber 6 
through the oil path 47, valve 48, oil path 30 and oil hole 31 and acts on 
the upper surface of the control piston 4, i.e., a downward reaction force 
is exerted thereon. This reaction force acts as a downward force on the 
actuating piston 5 through the piston rod 11. As a result, the oil 
pressure of the oil pressure output chamber 9 is decreased to mitigate the 
braking forces exerted on the front and rear wheels 40 and 41, to thereby 
avoid a wheel-lock condition. 
The vehicle body as thus mitigated in braking force is accelerated by 
virtue of an inertia force acting thereon, i.e., the speed of rotation of 
the front and rear wheels is increased. When an acceleration value 
computed on the basis of rotational speeds detected by the revolution 
sensors 49 and 50 exceeds a predetermined value, the signal processing 
unit 53 again generates control signals to open the normally open valve 29 
and close the normally closed valve 48. At this time, the control oil in 
the oil pressure control chamber 6 becomes equal to atmospheric pressure, 
so that the downward reaction force which has been exerted on the control 
piston 4 is removed, thus allowing the actuating piston 5 to move upwardly 
and increase the oil pressure of the oil pressure output chamber 9 for 
recovery of the braking force. 
Thereafter, if a vehicular deceleration value again exceeds the 
predetermined value, the foregoing mitigation and recovery of the braking 
force is again performed and the foregoing anti-lock operation is 
repeated. In the range wherein vehicular deceleration values do not reach 
the aforesaid predetermined value, the foregoing mitigation of the braking 
force is not performed and corresponding forces are applied until the 
vehicle body comes to a stop. 
When the vehicle body comes to a stop and the treading force applied to 
brake pedal 16 is removed, the pistons 4 and 5 are moved downwardly by the 
biasing force of the springs 8 and 13, so that the oil pressure in the oil 
pressure output chamber 9 decreases and returns to atmospheric pressure. 
If vehicular deceleration values never exceed the predetermined value from 
the time the brake pedal 16 is depressed until the vehicle body comes to a 
stop, it is not necessary for the aforesaid anti-lock function to be 
performed, and thus the foregoing mitigation and recovery of the braking 
force is not performed. 
Referring again to FIG. 1, a proportioning valve 65 is disposed in an 
intermediate position of the oil path 38 connecting between the master 
cylinder 1 and the rear wheel-side caliper 39. Assuming that upon 
depression of the brake pedal 16 a pressure is produced within the oil 
pressure output chamber 9 of the master cylinder 1 as previously noted, 
then in the range below the foregoing predetermined pressure at which the 
proportioning valve 65 starts operating, the pressures transmitted to the 
front and rear wheel-side calipers 37 and 39 are substantially equal and 
the braking forces acting on the front and rear wheels 40 and 41 are also 
substantially equal, and thus such braking forces change along line 
segment O - P in FIG. 4. 
When the pressure generated in the oil pressure output chamber 9 exceeds 
the foregoing predetermined level at which the proportioning valve 65 is 
operated, the pressure acting on the rear wheel-side caliper 39 is 
decreased in a certain ratio with respect to the pressure generated in the 
oil pressure output chamber 9, i.e., the pressure acting on the front 
wheel-side caliper 37, and the rear wheel braking force is decreased in 
the same ratio with respect to the front wheel braking force, both 
changing along line segment P - Q in FIG. 4. 
It will thus be understood that in accordance with the present embodiment 
of the invention it is possible to distribute the braking oil pressure in 
a ratio such as indicated by a bent line B (O-P-Q) in FIG. 4, so that by 
adjusting the aforesaid predetermined value and distribution ratio it is 
possible to attain performance closely resembling a curved line D shown in 
FIG. 4. If the distribution ratio of the braking oil pressure to the front 
and rear wheels 40 and 41 by the proportioning valve 65 is made 
approximately coincident with a ratio at which if a wheel-lock condition 
occurs both the front and rear wheels 40 and 41 are locked simultaneously, 
the probability of occurrence of wheel lock can be kept to a minimum. Even 
if the possibility of a wheel-lock condition should increase, the 
foregoing anti-lock function operates to effectively avoid the wheel-lock 
condition. 
Moreover, because braking forces are proportional to the cylinder areas of 
the front and rear wheel-side calipers 37 and 39, instead of employing the 
proportioning valve 65, the calipers may be constructed so that their 
cylinder bore ratio coincides with the braking force distribution ratio to 
the front and rear wheels 40 and 41. In this case, the front and rear 
wheel braking forces change in a relation such as indicated by a straight 
line C in FIG. 4. 
A front wheel brake device 70 as shown in FIG. 1 comprises a master 
cylinder 73 which generates pressure upon operation of a brake lever 72 
attached to a handle 71 of the motorcycle, a caliper 75 connected to the 
master cylinder 73 through an oil path 74, and a brake disk 76 fixed to 
the axle 40a of the front wheel 40. If a large braking force is required 
in the righthand area from point (a) in FIG. 4, the front wheel brake 
device 70 can be operated independently, and consequently a substantial 
amount of freedom and flexibility is imparted to the braking operation. 
Further, the front wheel brake device 70 can also be utilized when pushing 
the motorcycle by hand or stopping it on an upward slope. 
Referring generally to FIG. 4, front and rear wheel braking forces are 
plotted along the axis of abscissa and that of ordinate, respectively, 
shown in the range of approximately 0.1 g to approximately 1.0 g (g being 
a gravitational acceleration) as a total of front and rear wheel 
decelerations, in which D is an ideal braking force distribution curve, 
i.e., an ideal front and rear wheel braking force distribution curve at a 
friction coefficient .mu. ranging from 0.1 to 1.0. 
The dashed straight line A shows the case where the braking force 
distributed to the front wheel and to the rear wheel is almost equal, in 
which the rear wheel braking is likely to become excessive. On the other 
hand, according to the bent line B showing the relation of braking force 
distribution ratios in the case of adopting the proportioning valve 65 as 
the braking force distribution mechanism or a straight line C showing the 
relation of braking force distribution ratios in the case where instead of 
employing the valve 65 the size of the rear wheel-side brake unit is set 
to be smaller than that of the front wheel-side brake unit, the front and 
rear wheel braking forces scarcely involve excess or deficiency until 
point (a) is reached, which is an intersecting point with the ideal curve 
D, i.e., in the lefthand area from point (a). Thus, an ideal distribution 
ratio can substantially be maintained. 
With reference now to FIGS. 5 and 8 through 10, there is shown a second 
embodiment of the present invention. A brake pedal 316 is pivotably 
supported by an arm shaft 315, and on the arm shaft 315 are mounted two 
arms 357a and 357b so that the arms 357a and 357b are approximately 
90.degree. out of phase with each other as shown in FIG. 5, and pivot 
integrally with the shaft 315. Between the arm 357a and the shaft 315 is 
stretched a return spring 360. To an end portion of the arm 357a is 
pivoted the lower end of a push rod 314a which extends downwardly from an 
upright master cylinder 301a. To an end portion of the other arm 357b is 
pivoted an end portion of a push rod 314b extending from an actuator 301b 
which is mounted nearly horizontally. 
In this embodiment, the master cylinder 301a functions as a pressure 
generating mechanism which generates pressure when treading force is 
applied to the brake pedal 316, and as a mechanism for controlling the 
pressure generated in the master cylinder 301a there is separately 
provided the actuator 301b which is of substantially the same shape as the 
master cylinder 301a. Also provided is a proportioning valve 365 and a 
front wheel brake device 370, both of which constructions are similar to 
those of the first embodiment. 
In FIGS. 9 and 10 there is shown a motorcycle 500 having a front wheel 540, 
a rear wheel 541, front wheel brake disks 542a and 542b, a rear wheel 
brake disk 543, a handlebar 371, a fuel tank 502, a seat 503, an engine 
504 and a muffler 505, with a signal processing unit 353 being attached to 
motorcycle 500. 
The master cylinder 301a and the actuator 301b are fixed to the vehicle 
body frame. As clearly shown in FIG. 8, slidably disposed within the 
master cylinder 301a is an actuating piston 305 which is normally urged 
downwardly by the biasing force of a spring 313 disposed within an oil 
pressure output chamber 309. The piston 305 is adapted to slide through 
the push rod 314a, the upper end of which abuts the lower surface of the 
piston 305, and further through the arm 357a and arm shaft 315 when 
treading force is applied to the pedal 316. The oil pressure output 
chamber 309 and an oil supply chamber 310 both formed within the master 
cylinder 301a are normally filled with an actuating oil fed from a 
reservoir 327a mounted separately from the master cylinder 301a through a 
pipe 328a and oil paths 333 and 334. The oil pressure output chamber 309 
is connected through an oil path 336 to front and rear wheel-side calipers 
337 and 339. 
Slidably disposed within the actuator 301b is a control piston 304 which 
normally is held in the rightmost position in FIG. 8 by the biasing force 
of a spring 308 disposed within the oil pressure control chamber 306. As 
is the case with the master cylinder 301a, the control piston 304 is 
adapted to slide through the push rod 314b which is in abutting engagement 
at its tip end portion with the right end face of the piston 304, and 
further through the arm 357b and arm shaft 315 when treading force is 
applied to the brake pedal 316. 
Above the actuator 301b is separately disposed a unit 358 comprising an 
integrated combination of a reservoir 327b, a normally open valve 329 and 
a normally closed valve 348. The reservoir 327b communicates with an oil 
supply chamber 307 formed within the actuator 301b through a pipe 328b and 
an oil path 332, and supplies an actuating oil to the oil supply chamber 
307. When the actuator 301b is not in operation, the reservoir 327b 
communicates through the normally open valve 329 and a pipe 330 with an 
oil pressure control chamber 306 formed within the actuator 301b. Further, 
when the actuator 301b is in operation, i.e., when the normally open valve 
329 is closed and the normally closed valve 348 is open, the reservoir 
327b communicates with the oil pressure control chamber 306 in the 
actuator 301b through pipe 345, hydraulic pump 344, pipe 347, accumulator 
346, normally closed valve 348 and pipe 330. The hydraulic pump 344, 
driven by part of the vehicular engine power, is for pressurizing the 
actuating oil, and the resulting pressurized oil is normally stored in the 
accumulator 346. The reservoir 327b may be common to the other reservoir 
327a if desired. 
Operation of the second embodiment of the invention, wherein the master 
cylinder 301a as a source of oil pressure control and the actuator 301b 
for controlling the pressure generated in the master cylinder 301a are 
mounted separately, will be described hereinbelow. 
When the brake pedal 316 is depressed to thereby allow the arm shaft 315 
and the arm 357a, both adapted to pivot integrally therewith, to move 
pivotally in a counter-clockwise direction in FIG. 8, the piston 305 in 
the master cylinder 301a is pushed by the push rod 314a and moves upwardly 
against the spring 309, thus increasing the pressure within the oil 
pressure output chamber 309. This increased pressure in the chamber 309 is 
transmitted to the front and rear wheel-side calipers 337 and 339 to 
actuate the calipers to generate required braking forces. 
On the other hand, the control piston 304 within the actuator 301b also 
moves to the left against the spring 308, but because at this time the oil 
pressure control chamber 306 is in communication with the reservoir 327b 
held at a pressure equal to atmospheric pressure by the action of the 
normally open valve 329, the actuating oil in the chamber 306 is returned 
to the reservoir 327b by the pumping action of the control piston 304. 
When the motorcycle undergoes an excessive braking force and consequently a 
wheel-lock condition is very likely to occur, the normally open valve 329 
is closed and the normally closed valve 348 is opened, so that the 
pressurized oil stored in the accumulator 346 flows into the oil pressure 
control chamber 306 of the actuator 301b and acts on the end face of the 
control piston 304, thus causing the latter to move to the right in FIG. 
8. Upon such rightward movement of the piston 304, the arm 357b pivots in 
a clockwise direction in FIG. 8 through the rod 314b, thus causing the arm 
357a adapted to pivot integrally with the arm shaft 315 to move pivotally 
in a clockwise direction through the arm shaft 315, so that the push rod 
314a undergoes a downward reaction force. Therefore, an upward force 
acting on the actuating piston 305 is diminished by an amount 
corresponding to such reaction force and the pressure within the oil 
pressure output chamber 309 also decreases in proportion thereto, whereby 
the front and rear wheel braking forces are mitigated to effectively avoid 
a wheel-lock condition. 
Thereafter, the motorcycle is again accelerated by virtue of an inertia 
force acting on the vehicle body, and when this acceleration exceeds the 
predetermined value, the valves 329 and 348 are switched from each other 
to again apply the brakes. Then, from the time when the possibility of 
wheel lock in braking is eliminated and until the motorcycle comes to a 
stop, braking forces are applied continuously without being mitigated. 
In the interlock braking system according to the second embodiment 
described hereinabove, the brake system and the control system serving as 
an anti-lock mechanism are provided separately. Therefore, the anti-lock 
mechanism can be easily attached to conventional interlock braking systems 
whenever required and the type of oil to be used in the control system can 
be selected independently of the oil used in the brake system with the 
result that maintenance is facilitated. Moreover, as can be seen from FIG. 
8, the entire system is rendered highly compact, and such reduction in 
size is particularly advantageous in motorcycles wherein the mounting 
space for such equipment is a limiting factor. Further, because the shape 
of the actuator 301b is substantially the same as that of the master 
cylinder 301a, the machining method for the actuator 301b is substantially 
the same as that for the master cylinder 301a, so that the number of 
machining steps, as well as the production costs, can be reduced. 
With reference now to FIGS. 6 and 7, there are shown exemplary arrangements 
of a master cylinder and an actuator with respect to an arm shaft in 
interlock braking systems according to third and fourth embodiments of the 
present invention. 
In FIG. 6, there is shown an arm shaft 615 to which are fixed two arms 657a 
and 657b extending in substantially the same direction, and disposed 
upright above these two arms is a master cylinder 601a and an actuator 
601b. Rods 614a and 614b extend downwardly from the master cylinder 601a 
and actuator 601b and are pivoted to the arms 657a and 657b, respectively. 
In FIG. 7, there is shown an arm shaft 715 to which is fixed a single arm 
757, and disposed upright above single arm 757 is a master cylinder 701a 
and an actuator 701b. Rods 714a and 714b extend downwardly from the 
master cylinder 701a and actuator 701b, respectively, and are pivoted to 
the arm 757 at different distances from the arm. 
The same effect as attained by the second embodiment of the invention 
described hereinabove with reference to FIG. 5 is also attained in 
accordance with the third and fourth embodiments shown in FIGS. 6 and 7. 
Although there have been described what are at present considered to be the 
preferred embodiments of the invention, it will be understood that the 
present invention may be embodied in other specific forms without 
departing from the spirit or essential characteristics thereof. The 
present embodiments are therefore to be considered in all respects as 
illustrative, and not restrictive. The scope of the invention is indicated 
by the appended claims rather than by the foregoing description.