Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-08-31
2001-04-17
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
C092S13000R
Reexamination Certificate
active
06216580
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a booster as may be used in a brake of an automobile, and more particularly, to a reaction mechanism for booster which imparts reaction force to an operating rod which actuates the booster.
DESCRIPTION OF THE PRIOR ART
A brake booster is known in the art which comprises a valve body slidably disposed within a shell, a power piston mounted on the valve body, a constant and a variable pressure chamber defined across the power piston, a valve mechanism disposed in the valve body, an input shaft connected to a brake pedal serving as an operating rod and adapted to drive a valve plunger, which forms part of the valve mechanism, back and forth to thereby switch a flow path in the valve mechanism, and an output shaft driven forward as the valve body is driven forward to cause a piston of a master cylinder to be driven forward, thereby developing a braking liquid pressure.
A conventional reaction mechanism is provided with a reaction disc formed of rubber and disposed between the output shaft and the valve plunger so that when the brake booster is actuated, both the valve body and the valve plunger are brought into contact with the reaction disc simultaneously, part of a braking force applied to the output shaft being transmitted to the valve body while the remainder thereof is transmitted to the valve plunger, the braking reaction force transmitted to the valve plunger being sensed by a driver through the input shaft and the brake pedal.
A serve ratio of the brake booster can be changed by changing the ratio of the reaction force transmitted to the valve body and the reaction force transmitted to the valve plunger, and more specifically, the ratio of pressure-responsive areas of the both members. A high serve ratio is generally established in the brake booster so that a braking liquid pressure of an increased magnitude can be developed with a depression of the brake pedal with a reduced force. However, it is found that during a quick braking operation, a serve ratio of a predetermined magnitude cannot be obtained as a result of an operational lag of the brake booster, and it is difficult for a less powerful driver such as an aged person or woman to perform a quick braking operation.
More specifically describing the reason, when the brake pedal is depressed, a flow path in the valve mechanism is switched through the input shaft, whereby a pressure fluid is introduced into the variable pressure chamber to drive the power piston and the valve body forward. As the valve body is driven forward, the output shaft is also driven forward through the reaction disc, the forward movement of the output shaft developing a braking pressure. A reaction therefrom is applied to the output shaft, and the brake reaction applied to the output shaft is distributed between the valve body and the valve plunger in a manner mentioned above. However, the valve plunger which is connected to the brake pedal through the input shaft will be driven forward before the power piston and the valve body are driven forward by the pressure fluid which is introduced into the variable pressure chamber during a quick braking operation, and as a consequence, a major proportion of the braking reaction which is applied to the output shaft will be transmitted to the valve plunger. This results in a braking reaction of an abnormally high magnitude being transmitted to the driver. Consequently, when a quick braking operation is to be performed, the brake pedal must be depressed by overcoming the abnormal braking reaction which is transmitted. As compared with a normal braking operation in which the brake pedal is gradually depressed to achieve a high braking force, a braking force of an increased magnitude which is required for a quick braking operation cannot be obtained unless the brake pedal is depressed with a force which is much greater than in a normal braking operation.
SUMMARY OF THE INVENTION
In view of the foregoing, the invention provides a reaction mechanism for booster which enables a high output to be obtained with a reduced force of depression during a quick braking operation without degrading a normal operation feeling of the booster.
Thus, the invention relates to a booster including a valve body slidably disposed within a shell, a power piston mounted on the valve body, a constant and a variable pressure chamber defined across the power piston, a valve mechanism disposed in a valve body, an input shaft connected to an operating rod for driving a valve plunger, which forms a valve mechanism, back and forth to switch a flow path in the valve mechanism, and an output shaft which is driven forward as the valve body is driven forward. In accordance with the invention, there is provided pseudo-reaction imparting means which prevents the reaction applied to the output shaft during the operation of the booster from being transmitted to the valve plunger and which imparts a pseudo-reaction which depends on a travel of the input shaft to the operating rod. The pseudo-reaction imparting means is arranged such that a pseudo-reaction having a lower rate of increase is imparted to the operating rod when a travel of the operating rod is low, while a pseudo-reaction having a higher rate of increase is imparted to the operating rod when a travel of the operating rod is higher.
With the described arrangement, upon actuation of the booster, the reaction applied to the output shaft is prevented from being transmitted to the valve plunger, and accordingly, during a quick braking operation, if the valve plunger which is connected to the operating rod through the input shaft is driven forward before the power piston and the valve body are driven forward by pressure fluid introduced in the variable pressure chamber, the transmission of a reaction applied to the output shaft to a driver through a path including the valve plunger, the input shaft and the operating rod is prevented.
On the other hand, the pseudo-reaction imparting means transmits a pseudo-reaction which depends on a travel of the operating rod to the driver through the operating rod. In this manner, the transmission of an abnormally high reaction during a quick braking operation is prevented, and instead, a high output can be obtained with a reduced operating force in the same manner as in a usual operation.
As mentioned above, the pseudo-reaction imparting means imparts a pseudo-reaction having a lower rate of increase to the operating rod when a travel of the operating rod is low, and imparts a pseudo-reaction having an increased rate of increase to the operating rod when a travel of the operating rod is high. Accordingly, a similar operation feeling as in a usual operation can be obtained independently from a quick and a slow braking operation. By way of example, when an operating rod comprises a brake pedal, during an initial phase of the braking operation, an increase in the pseudo-reaction will be low if the brake pedal is depressed through an increased stroke, but after a braking force of certain magnitude is developed, the magnitude of pseudo-reaction will increase relative to the amount of depression of the brake pedal if it is small. The pseudo-reaction imparting means which exhibits such characteristic is effective in realizing such a normal operation feeling.
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Ikeda Masahiro
Kobayashi Kazuo
Satoh Tohru
Flynn ,Thiel, Boutell & Tanis, P.C.
Jidosha Kiki Co. Ltd.
Lopez F. Daniel
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