Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2002-01-16
2003-12-23
Lavinder, Jack (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C188S357000
Reexamination Certificate
active
06666530
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum booster apparatus and a brake apparatus including a vacuum booster.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 8-164840 discloses a vacuum booster apparatus provided with a vacuum booster. The vacuum booster comprises a first pressure chamber which is connected to an intake line of an engine at a position downstream of a throttle valve and a second pressure chamber which is selectively connectable to either the first pressure chamber or atmosphere. The vacuum booster boosts an operational force applied to a brake-operating member based on a difference between a pressure in the first pressure chamber and a pressure in the second pressure chamber. The vacuum booster apparatus also includes a throttle-opening-degree control apparatus which increases a negative pressure in the first pressure chamber by decreasing a degree of opening of the throttle valve. In the above-mentioned vacuum booster apparatus, when the negative pressure in the first pressure chamber becomes less than a predetermined negative pressure, the degree of opening of the throttle valve is decreased so as to maintain the negative pressure in the first pressure chamber at a pressure higher than the predetermined negative pressure. Accordingly, since the negative pressure in the first pressure chamber is maintained higher than the predetermined negative pressure whether or not the brake-operating member is being operated, a boost limit is prevented from being decreased. The boost limit is represented by a master cylinder pressure at a time when a boost action reaches a limit.
The above-mentioned engine having the throttle valve is a direct-injection-type gasoline engine in which gasoline is directly injected into cylinders. In this type of engine, a uniform combustion is performed when a load applied to the engine is large, that is, when an engine speed is high. On the other hand, when a load applied to the engine is not very large, that is, when the engine speed is medium or low, a stratified charge combustion is performed. In the uniform combustion, a combustion is achieved at a normal air-fuel ratio, that is, a stoichiometric air-fuel ratio. In the stratified charge combustion, an ultra lean burn occurs at a high air-fuel ratio of about 25 to 50. According to the ultra lean burn, a rate of fuel consumption is reduced which results in energy saving. When the engine load is medium or low, a necessary drive torque can be output even when the ultra lean burn occurs. Since, normally, the engine load is not very large when the brake operating member is being operated, the ultra lean burn is performed. In such the case, a degree of opening of the throttle valve is maintained at a relatively large degree so as to intake a large amount of air.
If the degree of opening of the throttle valve is maintained at a relatively large degree, the negative pressure in the first pressure chamber tends to be decreased. Accordingly, in the conventional vacuum booster apparatus, the degree of opening of the throttle valve is decreased when the negative pressure in the first pressure chamber is less than the predetermined negative pressure. When the degree of opening of the throttle valve is decreased, a state of combustion should be changed from the ultra lean burn to the uniform combustion. This is because an unstable combustion causing misfire occurs when the degree of opening of the throttle valve is decreased. Additionally, the change from a state of the ultra lean burn to a state of the uniform combustion is performed stepwisely (gradually). If an output torque is the same, an amount of injection of fuel, the degree of opening of the throttle valve and a degree of opening of a swirl port are considerably different between the state of the ultra lean burn and the state of the uniform combustion. Accordingly, when the state of the ultra lean burn is changed to the uniform combustion, these conditions are considerably changed, which results in deterioration of drivability. Similarly, the return from the state of the uniform combustion to the state of the ultra lean burn is performed stepwisely. As mentioned above, when the degree of opening of the throttle valve is decreased when the ultra lean burn is being performed, it is required to stepwisely or gradually change the ultra lean burn to the uniform combustion. This causes deterioration in a rate of fuel consumption. Accordingly, it is not preferable to decrease the degree of opening of the throttle valve so as to maintain a negative pressure in the first pressure chamber in a state in which the ultra lean burn is performed. Additionally, a frequency of such a change in the state of combustion should be as small as possible. On the other hand, when a braking operation is not being performed, there is a possibility that the uniform combustion is performed. In such a case, the rate of fuel consumption is not decreased by much even if the degree of opening of the throttle valve is decreased.
If the predetermined negative pressure at which the degree of opening of the throttle valve is decreased can be decreased, that is, if the predetermined negative pressure can be set closer to an atmospheric pressure, a frequency of the degree of opening of the throttle valve being decreased can be decreased. However, in such a case, the limit of boost is decreased. On the other hand, if the predetermined negative pressure is increased, that is, if the predetermined negative pressure is set closer to an absolute vacuum, the limit of boost can be increased. That is, the boosting function can be provided until an operational force applied to the brake-operating member is large. However, in such a case, the frequency of a degree of opening of the throttle valve being decreased is increased. Additionally, since the vacuum booster cannot reach the limit of boost even if the negative pressure is less than the predetermined negative pressure in a range where an operational force applied to the brake-operating member is small, the degree of opening of the throttle valve is decreased despite that the negative pressure is not required to be increased. As discussed above, in the above-mentioned vacuum booster apparatus, it is difficult to decrease a frequency of the degree of opening of the throttle valve being decreased while a necessary negative pressure is maintained in the first pressure chamber.
In the above-mentioned patent document, a vacuum booster apparatus which can decrease the frequency of the degree of opening of the throttle valve being decreased during a braking operation is also disclosed. This vacuum booster apparatus includes the above-mentioned vacuum booster and a throttle-valve-opening control apparatus. The throttle-valve-opening control apparatus increases a negative pressure in the first pressure chamber by decreasing the degree of opening of the throttle valve when the brake-operating member is continuously operated for a period longer than a predetermined period and when the negative pressure in the first pressure chamber is less than the predetermined negative pressure. In this vacuum booster apparatus, the degree of opening of the throttle valve is always decreased when the brake-operating member is continuously operated for a period longer than the predetermined period and when the negative pressure in the first pressure chamber is less than the predetermined negative pressure. However, when an operational force applied to the brake-operating member is small, the vacuum booster does not reach the limit of boost even if the braking operation continues for a long time and the negative pressure is small. In such a case, the negative pressure is not required to be increased. Additionally, when the operational force is large, the vacuum booster may reach the limit of boost even if the braking operation continues for only a short time. In such a case, the negative pressure should be increased. As discussed above, in the above-mentioned vacuum booster, the deg
Mizutani Yasuji
Nitta Hirofumi
Suzuki Motoshi
Lavinder Jack
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Williams Thomas J.
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