Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-02-11
2001-08-21
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S113400, C188S358000
Reexamination Certificate
active
06276763
ABSTRACT:
This application is based on Japanese Patent Application No. 10-35033 filed Feb. 17, 1998, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to techniques for diagnosing a booster of a braking system for an automotive vehicle.
2. Discussion of the Related Art
JP-A-4-56669 discloses an example of a known technique for diagnosing a vacuum booster of a vehicle braking system, for any abnormality. This known diagnosing technique is based on a fact that the vacuum booster becomes inoperative to perform a normal boosting function when a negative pressure of a negative pressure source to which the vacuum booster is connected has been raised above a predetermined upper limit. According to the known diagnosing technique, a pressure switch is used to either mechanically or electrically detect that the negative pressure of the negative pressure source has exceeded the upper limit.
A study of the present inventors has revealed that when the vacuum booster is abnormal, the input and the output of the booster do not have a predetermined or known nominal relationship, and that this fact can be utilized to effect a diagnosis of the booster for any abnormality.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a method by which a brake booster can be diagnosed for any abnormality, based on the fact that the input and output of the booster do not have or meet a nominal relationship therebetween when the booster is abnormal.
It is a second object of this invention to provide a braking system capable of diagnosing its booster for any abnormality, based on the above fact.
The first object may be achieved according to any one of the following modes (1)-(5) of this invention, while the second object may be achieved according to any one of the following modes (6)-(33). Each of these modes of the invention is numbered like the appended claims, and depends from the other mode or modes, where appropriate, so as to indicate possible combinations of elements or features in preferred forms of the present invention:
(1) A method of diagnosing a booster of a braking system for an automotive vehicle, the braking system including a brake operating member operated with a brake operating force, a master cylinder for producing a hydraulic pressure on the basis of an input force received from the booster as a result of boosting of the brake operating force by the booster, and a wheel brake cylinder which is activated by the hydraulic pressure produced by the master cylinder, to brake a wheel of the automotive vehicle, the method comprising the steps of: (a) detecting an input and an output of the booster; and (b) determining that the booster is abnormal, if the detected input and output do not meet a predetermined nominal relationship therebetween.
The present method permits highly reliable diagnosis of the booster for any abnormality thereof on the basis of the relationship of the detected input and output of the booster, regardless of a cause for the abnormality.
The booster to be diagnosed by the present method may be not only a vacuum booster activated by a negative air pressure source, but also a hydraulic booster activated by a hydraulic pressure source, more specifically, a high-pressure source whose pressure is higher than the atmospheric pressure. Generally, the vacuum booster has a negative-pressure chamber connected to a negative pressure source, and a variable-pressure chamber which is selectively communicated with the negative-pressure chamber and the atmosphere, and includes a power piston which is operated on the basis of a pressure difference of the negative-pressure and variable-pressure chambers, so as to boost a brake operating force which acts on a brake operating member of the braking system. On the other hand, the hydraulic booster is generally adapted such that a power piston is operated to boost the brake operating force, on the basis of the pressure in a power chamber which is selectively communicated with the high-pressure source and a low-pressure source.
The input of the booster may be selected from among various parameters, such as the brake operating force acting on the brake operating member, an axial force acting on the input rod of the vacuum or hydraulic booster, the pressure in the variable-pressure chamber of the vacuum booster, and a pressure in the power chamber of the hydraulic booster. The brake operating force acting on the brake operating member may be detected either directly, or indirectly on the basis of the operating stroke of the brake operating member. Similarly, the axial force acting on the input rod of the booster may be detected either directly, or indirectly on the basis of the operating stroke of the input rod.
The output of the booster may be selected from among various parameters, such as an axial force acting on the power piston or output rod of the booster, an axial force acting on the pressurizing piston of the master cylinder, a pressure in a pressurizing chamber of the master cylinder, a pressure in a fluid passage connected to the pressurizing chamber, a pressure in the wheel brake cylinder, and a deceleration value of the automotive vehicle braked by braking of the wheel by the wheel brake cylinder.
(2) A method according to the above mode (1), wherein the input and the output of the booster are substantially concurrently detected by respective sensors, and the booster is determined abnormal if the detected input and output do not meet the predetermined nominal relationship.
(3) A method according to the above mode (1), wherein one of the input and output of the booster is detected as a first physical quantity by a switch which generates two signals one of which indicates that the first physical quantity is smaller than a predetermined value and the other of which indicates that the first physical quantity is not smaller than the predetermined value, the other of the input and output being substantially continuously detected as a second physical quantity by a sensor when the first physical quantity has become equal to the predetermined value, and wherein the booster is determined to be abnormal, if the second physical quantity detected by the sensor deviates from a nominal value thereof corresponding to the predetermined value of the first physical quantity.
Generally, a switch for digitally detecting that a certain physical quantity has become equal to a predetermined value has a higher degree of operating reliability and is simpler in construction and available at a lower cost, than a sensor for substantially continuously detecting a certain, physical quantity. In this sense, the method according to the above mode (3) is more reliable than the method according to the above mode (2), and a diagnosing device adapted to practice the method according to the mode (3) is simpler in construction and easier to manufacture, than a diagnosing device adapted to practice the method according to the mode (2).
(4) A method according to the above mode (3), wherein the first physical quantity is the input of the booster while the second physical quantity is the output of the booster.
Some braking system employs a sensor for substantially continuously detecting the output of the booster, for a purpose other than a diagnosis of the booster. In this type of braking system, the sensor is preferably used for diagnosing the booster. It is also noted that where the sensor for detecting one of the input and output of the booster is available, the use of another sensor for detecting the other of the input and output is not essential for diagnosing the booster, that is, the use of a switch for detecting a threshold value of this input or output is sufficient for diagnosing the booster. The use of the sensor and the switch indicated above makes it possible to reduce an increase in the constructional complexity and cost of manufacture of the braking system, which increase arises from the provision of the diagnosing device for effecting the dia
Isono Hiroshi
Nitta Hirofumi
Suzuki Motoshi
Kenyon & Kenyon
Schwartz Christopher P.
Toyota Jidosha & Kabushiki Kaisha
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