This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-080969 filed on Mar. 22, 2000, the entire content of which is incorporated herein by reference.
The present invention is directed to a vehicular brake control device which makes it possible to apply a brake fluid pressure to each of wheel cylinders irrespective of a brake pedal operation.
One of the prior art vehicular brake control devices of the kind, as is well known, includes a hydraulic pressure generation means which makes it possible to cause a master cylinder to generate a master cylinder pressure in response to a brake pedal depression force which is, for example, boosted by a booster, a hydraulic pressure supply means which supplies the master cylinder, as a brake fluid pressure, to a wheel brake cylinder of each of wheels, and a pressure application means which introduces a hydraulic pressure into a pressure application chamber in the hydraulic pressure supply means. In addition, the aforementioned known vehicular brake control device includes a control means which controls the pressure application means to automatically adjust the master cylinder pressure and which drives the hydraulic pressure supply means to control a braking force to be applied to each of the wheels. The hydraulic pressure generation means has a normally opened electromagnetic valve, as a pressure-maintaining valve, which establishes and interrupts a fluid communication between the master cylinder and each of the wheel cylinder and a normally closed electromagnet valve, as a pressure-decrease valve, which establishes and interrupts a fluid communication between the master cylinder and a reservoir.
In the foregoing conventional or prior art brake control device, when the master cylinder pressure is automatically increased, if the wheel cylinders are for front-wheels as driven wheels of an FR-vehicle under traction control, the pressure retaining valve is required to close which is provided between the master cylinder and each of such wheel cylinders in order to prevent an increase of the brake fluid pressure of each of the wheel cylinders.
However, if the pressure retaining valve malfunctions or has trouble remaining in its opened state, the wheel cylinder which is never increased in hydraulic pressure is pressurized. Thus, for example, despite traction control for starting or accelerating the vehicle, a problem occurs such as prevention of starting the vehicle due to the brake fluid application into the wheel cylinder, or so-called xe2x80x98brake dragxe2x80x99.
Thus, a need exists to provide a vehicular brake control device, for overcoming the aforementioned problem, which make it possible to detect a malfunction of an electromagnetic valve wherein its opened state remains unchanged or can not be shifted to its closed state.
The present invention has been developed to satisfy the request noted above and a first aspect of the present invention is to provide a vehicular brake control device which comprises:
a master cylinder which is capable of generating a brake fluid pressure in response to a brake pedal depression force;
hydraulic pressure control means for controlling a brake fluid pressure which is transmitted from the master cylinder to each of wheel cylinders of respective wheels;
pressure application means which is capable of automatically applying a hydraulic pressure to each of the wheel cylinders independent of brake pedal depression by way of the hydraulic pressure control means; and
control means for controlling a braking force of each of the wheels by driving the pressure application means and/or the hydraulic pressure control means,
the hydraulic pressure control means including a first electromagnetic valve which establishes and interrupts fluid communication between the master cylinder and each of the wheel cylinders and a second electromagnetic valve which establishes and interrupts fluid communication between a reservoir and each of the wheel cylinders,
the control means including pressure application check means which makes all the first electromagnetic valves of the respective wheels and all the second electromagnetic valves of the respective wheels closed and opened, respectively, at a predetermined timing and which initiates a pressure application check for judging whether or not automatic pressure application is made successfully by controlling the pressure application means,
the pressure application check means having an electromagnetic valve abnormal condition judging means which judges that the first electromagnetic valve of one of the wheel cylinders fails to be kept opened if a changing rate of the hydraulic pressure applied by the pressure application means increases after a fixed duration (KT1) has elapsed from the initiation of the pressure application check.
In accordance with a first aspect of the present invention, the first electromagnetic valve and the second electromagnetic valve are closed and opened, respectively, if a failure or malfunction is found in closing the first electromagnetic valve (i.e., the first electromagnetic valve fails to shift from its open position to its closes position), the brake fluid flows into the reservoir through the second electromagnetic valve, the consumed amount of the brake fluid at each of the wheel cylinders increases. Thus, the increasing speed of the hydraulic pressure becomes slower which is introduced by the pressure application means after initiation of the pressure application check, which results in that immediately when the reservoir is filled with the brake fluid the increasing speed of the hydraulic pressure changes drastically, which is introduced by the pressure application means. Therefore, if a speed change is found to be increased in the increasing speed of the hydraulic pressure which is introduced by the pressure application means within a fixed time duration (KT1), measured from the initiation of the pressure application, the electromagnetic valve abnormal judging means makes it possible to detect, with great accuracy, a failure or malfunction in closing the first electromagnetic valve.
A second aspect of the present invention is to provide a vehicular brake control device, as a limited version of the first aspect, wherein the pressure application check means judges, if the master cylinder pressure increases to a predetermined value (KP1) before a fixed time duration (KT2) elapses after the initiation of the pressure application check, that the pressure application means and the first electromagnetic valve of each of the wheels are in normal condition.
In accordance with the second aspect of the present invention, if the hydraulic pressure which is introduced by the pressure application is increased to a fixed value (KP1) until a fixed time duration (KT2) elapses after initiation of the pressure application check, it becomes possible to judge that the pressure application means and the first electromagnetic valve of each of the wheels are in good order or in normal condition.
A third aspect of the present invention is to provide a vehicular brake control device, as a limited version of the first aspect, wherein the pressure application check means includes pressure application abnormal judging means and pump regenerative voltage check means, the pressure application abnormal judging means judging temporarily that the pressure application means is abnormal if more than a fixed time duration (KT2) from the initiation of the pressure application check is required for the master cylinder pressure to increase to a predetermined valve (KP1), the pump regenerative voltage check means driving a pump for a short time duration in order to suck the brake fluid, after the temporal judgment, which enters the reservoir by way of the second electromagnetic valve of each of the wheel cylinders, the pump regenerative voltage check means judging that if the regenerative voltage of the pump after its driving is less than a predetermined value (KVP) the first electromagnetic valve of one of the wheel cylinders fails to be kept open.
In accordance with the third aspect of the present invention, if the master cylinder pressure requires a fixed time duration (KT2) measured from the initiation of the pressure application check for reaching a predetermined value (KP1), it is impossible to judge whether the pressure application means is abnormal or the first electromagnetic valve is in failure in its closing operation. Thus, the pressure application means is temporarily judged to be abnormal. Thereafter, if the pump regenerative voltage is found to be not greater than the predetermined value (KVP) after driving the pump for a short time duration, the brake fluid flows into the reservoir by way of the second electromagnetic valve due to a failure or malfunction in the first electromagnetic valve, which makes it possible to judge that the pump inertia force of the pump upon its termination is used to discharge the brake fluid and therefore the pump regenerative voltage lowers temporarily. Thus, in such a case, it can be judged that a failure or malfunction is found in closing the first electromagnetic valve of any one of the wheel cylinders.
A fourth aspect of the present invention is to provide a vehicular brake control device, as a limited version of the third aspect, wherein the pump regenerative voltage check means judges that if the regenerative voltage of the pump after its driving is not less than the predetermined value (KVP), each of the first electromagnetic valves is normal and the pressure application means is abnormal.
In accordance with the fourth aspect of the present invention, if the regenerative voltage of the pump after its driving is not less than a fixed value (KVP) the first electromagnetic valve is normal and the brake fluid fails to flow into the reservoir by way of the second electromagnetic valve. Thus, the foregoing pump inertia force is not used to discharge the brake fluid when the pump stops, i.e., the pump has no load, which makes it possible to judge that the first electromagnetic valve is normal and the pressure application means is abnormal.