Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-03-15
2001-11-27
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S114300, C303S116100, C303S119100, C060S547100, C060S534000, C060S545000
Reexamination Certificate
active
06322164
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a braking system for a vehicle, and more particularly to techniques for controlling a relationship between a brake operating force and a fluid pressure in a brake cylinder while a brake is operated by a vehicle operator.
BACKGROUND ART
In a braking system, some elements are generally disposed in series between a brake operating member
900
and a vehicle wheel
902
, for braking the vehicle upon operation of the brake operating member
900
by a vehicle operator, as schematically shown in FIG.
43
. That is, there are disposed in series a brake operating mechanism
904
, a booster
906
, a master cylinder
908
, a braking friction member
912
and a rotor
914
.
The brake operating mechanism
904
is adapted to transmit to the booster
906
an operating force F which has been applied to the brake operating member
900
. The booster
906
is adapted to boost the force received from the-brake operating mechanism
904
, while utilizing a pressure, and transmit the boosted force to the master cylinder
908
. As shown in
FIG. 44
, the booster
906
is able to boost the input force at a so-called “servo ratio” until a boosting limit has been reached, and is unable to boost the input force after the boosting limit has been reached. The master cylinder
908
has a pressurizing piston, which converts the output force of the booster
906
into a fluid pressure. The brake cylinder
910
has a brake piston, which converts the fluid pressure received from the master cylinder
908
into a force. The braking friction member
912
is forced by the output force of the brake cylinder
910
, onto the rotor
914
(brake rotor, brake drum, etc.) rotating with the vehicle wheel
902
to be braked, and cooperates with the rotor
914
to brake the wheel
902
, for thereby providing deceleration G of the vehicle body.
The braking system is required to cause the fluid pressure generated in the brake cylinder, to be as high as possible with a given brake operating force. This requirement is derived from an arrangement to reduce brake squeal and vibration. For instance, the arrangement employs a braking friction member made of a material which has a low friction coefficient or a large amount of compressive strain. This arrangement results in reducing a braking effect as represented by a ratio of the vehicle body deceleration G to the brake operating force F, as indicated in FIG.
45
. To prevent the reduction in the braking effect due to the above arrangement, the brake cylinder is required to generate a fluid pressure as high as possible with a given brake operating force.
An example of an arrangement to increase the fluid pressure in the brake cylinder is to reduce the diameter of the pressurizing piston of the master cylinder. However, this arrangement results in reduction in the volume for pressing the pressurizing piston, which increases the required operating stroke of the pressurizing piston, causing another problem that the longitudinal dimension of the master cylinder is increased. Another example of the arrangement to increase the fluid pressure in the brake cylinder is to increase the servo ratio of the booster. This arrangement results in lowering the boosting point of the booster, as indicated in
FIG. 46
, so that the braking effect varies to a great extent while the operating force F is relatively small, causing another problem that the brake operating feel is deteriorated.
In summary, there is a limitation in an attempt to increase the fluid pressure in the brake cylinder with a given brake operating force, as long as the attempt relies on the master cylinder or booster. Thus, there has been a problem of difficulty to control as desired the relationship between the brake operating force and the fluid pressure in the brake cylinder.
DISCLOSURE OF THE INVENTION
The present invention was made in the light of the background art described above. It is an object of the present invention to provide a braking system capable of controlling the relationship between the brake operating force and the fluid pressure in the brake cylinder, by using another hydraulic pressure source in addition to the master cylinder and the booster.
The above object may be achieved by a braking system according to any one of the following modes of this invention, each of which is numbered like the appended claims, so as to indicate possible combinations of features in the two or more modes of the invention:
(1) A braking system characterized by comprising:
a brake operating member operated by an operator of a motor vehicle;
a master cylinder for generating a fluid pressure based on an operation of the brake operating member;
a brake including a brake cylinder which is connected through a primary passage to the master cylinder and which is activated by the fluid pressure supplied through the primary passage, to restrain rotation of a wheel of the motor vehicle; and
a pressure increasing device for generating the fluid pressure in the above-indicated brake cylinder, which is higher than the fluid pressure in the above-indicated master cylinder, the pressure increasing device including
(a) a fluid flow control device which is disposed in the above-indicated primary passage and which has a plurality of selectively established states including a first state for permitting flows of a working fluid in opposite directions between the master cylinder and the brake cylinder, and a second state for inhibiting at least the flow of the fluid from the brake cylinder toward the master cylinder,
(b) a hydraulic pressure source connected through an auxiliary passage to a portion of the primary passage between the fluid flow control device and the above-indicated brake cylinder,
(c) a hydraulic pressure source control device for commanding the above-indicated the hydraulic pressure source to deliver the working fluid when the fluid pressure in the above-indicated brake cylinder is required to be higher than the fluid pressure in the above-indicated master cylinder during operation of the above-indicated brake operating member, and
(d) a pressure changing device for changing the fluid pressure in the above-indicated brake cylinder to a level higher than that in the above-indicated master cylinder, depending upon an operating force of the above-indicated brake operating member.
This braking system has an advantage that a relationship between the brake operating force and the fluid pressure in the braking cylinder can be controlled by a hydraulic pressure source provided in addition to the master cylinder and a booster, so that the fluid pressure generated in the brake cylinder can be easily controlled to be as high as possible for a given value of the brake operating force.
This advantage results in reduction in the required capacities of not only the master cylinder and booster but also the braking friction members, making possible to effect, for example, a braking effect characteristic control for controlling the braking effect characteristic, and a brake assisting control for emergency brake application so as to compensate for insufficiency of the brake operating force, without increasing loads on components of the braking system other than the hydraulic pressure source.
Unlike a braking system wherein the fluid pressure in the brake cylinder is determined irrespective of the brake operating force, this braking system in which the fluid pressure in the brake cylinder is determined depending upon the brake operating force permits the brake operating force to be reflected on the fluid pressure in the brake cylinder, so that the fluid pressure in the brake cylinder can be easily optimized in relation to the brake operating force.
The “hydraulic pressure source” in the present braking system may be a hydraulic pressure source provided for the braking system, or a hydraulic pressure source which is used for some other purpose, for example, a hydraulic pressure source provided for a power steering system. Further, the “hydraulic pressure source” may be a hydraulic pressure source of a type w
Isono Hiroshi
Itoh Kenji
Noguchi Noboru
Ohnuma Yutaka
Sakamoto Shigeru
Oberleitner Robert J.
Oliff & Berridg,e PLC
Sy Mariano
Toyota Jidosha & Kabushiki Kaisha
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