Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2000-03-27
2001-04-10
Nguyen, Hoang (Department: 3748)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
C091S37600A
Reexamination Certificate
active
06212992
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to a vacuum type brake booster for a vehicle. More particularly, the present invention pertains to a vacuum type brake booster for a vehicle that is capable of compensating for deficiencies in the brake pedal depressing force during emergency braking.
BACKGROUND OF THE INVENTION
In recent years, results of analysis have indicated that oftentimes, when a driver hurriedly steps on the brake pedal because an obstruction has suddenly appeared in the path of his vehicle, i.e., during emergency braking, the stepping force which the driver applies to the brake pedal is relatively small compared to the stepping force required to produce a brake fluid pressure of a magnitude resulting in wheel lock. Consequently, the braking capability of the vehicle is not fully exerted. Thus, it has been proposed to install on a vehicle a device which determines on the basis of the brake pedal depression speed and the rate of increase in the master cylinder pressure whether the braking operation in progress is a normal braking operation or an emergency braking operation, and when it is determined that it is an emergency braking operation, the brake fluid pressure is automatically raised to a magnitude resulting in wheel lock.
Devices of various construction have been proposed for raising the brake fluid pressure to a magnitude that results in wheel lock upon emergency braking. One of these devices, described in Japanese Unexamined Patent Publication No. H7-251733, involves a vacuum type brake booster that is constructed so that its input-output characteristics can be switched by means of a control signal from outside between at least two different characteristics (a characteristic for normal braking and a characteristic for emergency braking). With the input-output characteristics of the vacuum type brake booster being switched from the characteristic for normal braking to the characteristic for emergency braking at times of emergency braking, it is possible to obtain the same result as when the driver steps on the brake pedal strongly.
With the vacuum type brake booster disclosed in Japanese Unexamined Patent Publication No. H7-251733, however, although when the booster is switched to the characteristic for normal braking a good brake pedal operation feeling is obtained because a reaction force is exerted on the input member of the booster by a reaction member in both the outward stroke and the return stroke of the input member, when the booster is switched to the characteristic for emergency braking, in the outward stroke of the input member a reaction is exerted on the input member by the reaction member but in the return stroke of the input member the reaction from the reaction member to the input member is cut off and consequently a good brake pedal operation feeling is not obtained.
A need exists therefore for a vacuum type brake booster for a vehicle in which a good brake pedal operation feeling is obtained both when the booster has been switched to a normal braking operation and when it has been switched to an emergency braking operation.
SUMMARY OF THE INVENTION
In light of the foregoing, one aspect of the present invention involves a vacuum servo unit for a braking system of a vehicle that includes a housing in which is defined a pressure chamber, a movable wall member disposed in the housing to divide the pressure chamber into a front chamber that is adapted to communicate with a negative pressure source and a rear chamber that is adapted to selectively communicate with atmosphere and the negative pressure source, and a movable power piston connected to the movable wall member. An input member is disposed in the movable power piston and is movable in the forward and backward directions with respect to the movable power piston upon actuation of the brake pedal. A valve mechanism is disposed in the movable power piston and is selectively changeable in response to movement of the input member in the forward and backward directions between a first state in which the rear chamber is in communication with the negative pressure source while communication between the rear chamber and atmosphere is cut off, a second state in which communication between the rear chamber and the negative pressure source is cut off and communication between the rear chamber and atmosphere is cut off, and a third state in which communication between the rear chamber and the negative pressure source is cut off and the rear chamber is in communicated with atmosphere. A first biasing member biases the input member towards a position in which the valve mechanism is in the first state, and an output member outputs as an output force a propulsion force generated by the movable power piston based on movement of the movable wall member. A reaction member transmits the propulsion force and the input force applied to the input member to the output member, and applies a reaction force corresponding to the output force outputted from the output member to the input member to move the input member in the backward direction with respect to the movable power piston. An actuator moves the input member with respect to the movable power piston to position the valve mechanism in the second state. The input member is urged in the backward direction with respect to the movable power piston by the first biasing member to a position in which the valve mechanism is in the first state during operation of the actuator upon a decrease of the input force applied to the input member, and the valve mechanism is maintained in the first state while the movable wall member continues to move in the backward direction with respect to the housing and the input force applied to the input member is being decreased. In addition, the input member is moved in the backward direction with respect to the movable power piston by the first biasing member with the valve mechanism being in the first state when the input force applied to the input member is completely removed during operation of the actuator, and the reaction member maintains application of the reaction force to the input member when the input force applied to the input member is larger than a preset value during operation of the actuator.
According to another aspect of the present invention, a vacuum servo unit for a braking system of a vehicle includes a housing in which is defined a pressure chamber, a movable wall member disposed in the housing for dividing the pressure chamber into a front chamber for communicating with a negative pressure source and a rear chamber for selectively communicating with atmosphere and the negative pressure source, a movable power piston connected to the movable wall member, and an input member disposed in the movable power piston for movement in forward and backward directions with respect to the movable power piston during actuation of the brake pedal. A valve mechanism is disposed in the movable power piston and includes a rearwardly facing air valve seat provided on the input member, a rearwardly facing first vacuum valve seat provided in the movable power piston, and a control valve having a movable portion and a portion fixed to the movable power piston. The movable portion of the control valve faces towards the air valve seat and the first vacuum valve seat. The control valve is biased in the forward direction by a first biasing member and is selectively changed between a first state in which the rear chamber communicates with the negative pressure source and communication between the rear chamber and atmosphere is cut off, a second state in which communication between the rear chamber and the negative pressure source is cut off and communication between the rear chamber and atmosphere is cut off, and a third state in which communication between the rear chamber and the negative pressure source is cut off and the rear chamber is in communication with atmosphere in response to a movement of the input member with respect to the movable power piston. A valve member is provided in the movable power piston for
Hirota Nobuyuki
Miwa Akihiko
Terasaki Yoichi
Tsubouchi Kaoru
Watanabe Minoru
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Nguyen Hoang
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