FAILURE DIAGNOSIS APPARATUS OF BRAKE SYSTEM AND FAILURE DIAGNOSIS METHOD OF BRAKE SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2012-236478, filed Oct. 26, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a failure diagnosis apparatus and a failure diagnosis method of a brake system including an electric vacuum pump for supplying negative pressure to a negative pressure chamber of a brake booster.

2. Related Art

In general, a negative pressure chamber of a brake booster of a brake system in a vehicle is supplied with negative pressure generated in an intake system of an engine. To obtain sufficient negative pressure in the negative pressure chamber of the brake booster, an electric vacuum pump is placed in parallel to a main negative pressure passage for supplying negative pressure from the intake system of the engine to the negative pressure chamber of the brake booster so that the negative pressure is supplied to the negative pressure chamber of the brake booster by this electric vacuum pump.

Regarding such a brake system, Patent Document 1 discloses a technique that a discharge passage is provided to connect a discharge side of a vacuum pump to an intake system of an engine, a check valve is placed in this discharge passage and a release passage is provided to communicate a part located between the check valve and the discharge side of the vacuum pump with atmosphere, and another check valve is placed in this release passage.

RELATED ART DOCUMENTS
Patent Documents

Patent Document 1: JP-A-8 (1996)-192737

SUMMARY OF INVENTION
Problems to be Solved by the Invention

In a brake system, as mentioned above, negative pressure is supplied by an electric vacuum pump to a negative pressure chamber of a brake booster. In case the electric vacuum pump does not operate normally, a desired negative pressure could not be created in the negative pressure chamber of the brake booster. This may cause a problem that the brake booster could not generate sufficient assist power to tread force on a brake pedal. Thus, it is necessary to determine the functional (operational) normality of the electric vacuum pump. However, there is no disclosure about failure diagnosis of the brake system in Patent Document 1.

The present invention has been made to solve the above problems and has a purpose to provide a brake system failure diagnosis apparatus and a brake system failure diagnosis method capable of diagnosing failures or malfunctions of a brake system under any circumstances.

Means of Solving the Problems

To achieve the above purpose, one aspect of the invention provides a failure diagnosis apparatus of a brake system including: a first passage connected to a negative pressure chamber of a brake booster and an intake system of an engine; a second passage branching off from the first passage; an electric vacuum pump provided in the second passage; a first check valve for preventing a fluid from flowing from the intake system to the negative pressure chamber through the second passage; and a second check valve for preventing the fluid from flowing from the intake system to the negative pressure chamber through the first passage and preventing a fluid from flowing the intake system and a discharge port of the electric vacuum pump toward an suction port of the electric vacuum pump through the first passage; and a determination unit configured to determine functional normality of the electric vacuum pump based on a detection result of at least one of a booster internal pressure detection unit for detecting internal pressure of the negative pressure chamber and a current value detection unit for detecting an operating electric current value of the electric vacuum pump and a detection result of a pipe internal pressure detection unit for detecting internal pressure of a pipe communicated with the discharge port of the electric vacuum pump.

According to this aspect, the functional normality of the electric vacuum pump can be determined by utilizing at least one of a correlativity between the internal pressure of the pipe communicated with the discharge port of the electric vacuum pump and the internal pressure of the negative pressure chamber and a correlativity between the internal pressure of the pipe communicated with the discharge port of the electric vacuum pump and the operating electric current value of the electric vacuum pump. Specifically, the functional normality of the electric vacuum pump can be determined by utilizing characteristics that the operating electric current value of the electric vacuum pump and the internal pressure of the negative pressure chamber of the brake booster vary according to different internal pressure of the pipe communicated with the discharge port of the electric vacuum pump. This enables the failure diagnosis of the brake system to be executed under any circumstances.

In the above aspect, preferably, the brake system further includes a changeover unit to change a connection target of the discharge port of the electric vacuum pump to either one of an intake-system-side passage communicated with the first passage and blocked off from atmosphere and an atmosphere-side passage blocked off from the first passage and communicated with atmosphere, and the pipe internal pressure detection unit is used to detect internal pressure of a pipe between the electric vacuum pump and the changeover unit.

According to this configuration, the functional normality of the electric vacuum pump can be determined separately from variations in the negative pressure of the intake system by changing over the connection target of the discharge port of the electric vacuum pump to the atmosphere-side passage and utilizing the detection result of the internal pressure of the pipe between the electric vacuum pump communicated with atmosphere and the changeover unit. Therefore, correct failure diagnosis of the brake system can be performed even under any circumstances with large variations in negative pressure of the intake system. Further, the failure diagnosis of the brake system can be performed in both systems, one being established when the discharge port of the electric vacuum pump is connected to the intake-system-side passage and the other being established when the discharge port is connected to the atmosphere-side passage.

Another aspect of the invention to achieve the above object provides a failure diagnosis method of a brake system including: a first passage connected to a negative pressure chamber of a brake booster and an intake system of an engine; a second passage branching off from the first passage; an electric vacuum pump provided in the second passage; a first check valve for preventing a fluid from flowing from the intake system to the negative pressure chamber through the second passage; and a second check valve for preventing the fluid from flowing from the intake system to the negative pressure chamber through the first passage and preventing a fluid from flowing the intake system and a discharge port of the electric vacuum pump toward an suction port of the electric vacuum pump through the first passage; and wherein the method includes determining functional normality of the electric vacuum pump based on a detection result of at least one of internal pressure of the negative pressure chamber and an operating electric current value of the electric vacuum pump and a detection result of internal pressure of a pipe communicated with the discharge port of the electric vacuum pump.

In the above aspect, preferably, the brake system further includes a changeover unit to change a connection target of the discharge port of the electric vacuum pump to either one of an intake-system-side passage communicated with the first passage and blocked off from atmosphere and an atmosphere-side passage blocked off from the first passage and communicated with atmosphere, and the detection result of internal pressure of the pipe communicated with the discharge port of the electric vacuum pump is a detection result of internal pressure of a pipe between the electric vacuum pump and the changeover unit.

Effects of the Invention

According to the brake system failure diagnosis apparatus and the brake system failure diagnosis method of the invention, it is possible to diagnose failures of a brake system under any circumstances.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view of a brake system and a failure diagnosis apparatus thereof in Example 1;

FIG. 2 is a block diagram showing a control system of the brake system and the failure diagnosis apparatus in Example 1;

FIG. 3 is a flowchart showing one example of a failure diagnosis method of the brake system in Example 1;

FIG. 4 is one example of a map diagram showing engine negative pressure and pump electric current value;

FIG. 5 is a determination graph based on a pump electric current value in a case where a detection result of engine negative pressure is about −40 kPa;

FIG. 6 is one example of a map diagram showing engine negative pressure and ultimate negative pressure;

FIG. 7 is a determination graph based on a ultimate negative pressure in a case where a detection result of engine negative pressure is about −40 kPa;

FIG. 8 is a flowchart showing another example of the failure diagnosis method of the brake system in Example 1;

FIG. 9 is a flowchart showing another example of the failure diagnosis method of the of the brake system in Example 1;

FIG. 10 is a schematic configuration view of a brake system and a failure diagnosis apparatus thereof in Example 2;

FIG. 11 is a flowchart showing one example of a failure diagnosis method of the brake system in Example 2;

FIG. 12 is one example of a map diagram showing engine negative pressure and pump electric current value;

FIG. 13 is one example of a map diagram showing engine negative pressure and ultimate negative pressure;

FIG. 14 is a flowchart showing another example of the failure diagnosis method of the brake system in Example 2;

FIG. 15 is a flowchart showing another example of the failure diagnosis method of the brake system in Example 2;

FIG. 16 is a schematic configuration view of a brake system and a failure diagnosis apparatus thereof in a modified example;

FIG. 17 is a schematic configuration view of a brake system and a failure diagnosis apparatus thereof in another modified example; and

FIG. 18 is a schematic configuration view of a brake system and a failure diagnosis apparatus thereof in another modified example.

DESCRIPTION OF EMBODIMENTS

A detailed description of an embodiment of a failure diagnosis apparatus and a failure diagnosis method of a brake system embodying the present invention will now be given referring to the accompanying drawings. FIG. 1 is a schematic configuration view of the brake system and the failure diagnosis apparatus thereof in Example 1. FIG. 2 is a block diagram showing a control system of the brake system and the failure diagnosis apparatus in Example 1. In the following explanation, a term “negative pressure” represents a lower pressure than atmospheric pressure, an expression “the negative pressure is high” means that a difference from atmospheric pressure is large and an expression “the negative pressure is low” means that the difference from atmospheric pressure is small.

Example 1
Configuration and Operation of Brake System and Failure Diagnosis Apparatus Thereof

A brake system 1 and a failure diagnosis apparatus thereof in this example include, as shown in FIGS. 1 and 2, a brake pedal 10, a brake booster 12, a master cylinder 14, a negative pressure sensor 16, an electric vacuum pump 18 (“electric VP” in the figures), a first check valve 20, a second check valve 22, an ECU 24, a pressure detection unit 26, and a shunt resistor 28.

The brake booster 12 is provided between the brake pedal 10 and the master cylinder 14 as shown in FIG. 1. This brake booster 12 generates assist power at a predetermined boost ratio to the tread force of the brake pedal 10.

The brake booster 12 is internally partitioned by a diaphragm (not shown) into separate chambers; a negative pressure chamber (not shown) connected to the master cylinder 14 and a variable pressure chamber (not shown) for introducing atmosphere. The negative pressure chamber of the brake booster 12 is connected to an intake pipe 32 of an engine through a first passage L1. Specifically, the first passage L1 is connected to the negative pressure chamber of the brake booster 12 and the intake pipe 32. Accordingly, the negative pressure chamber of the brake booster 12 is supplied, through the first passage L1, with the negative pressure generated in the intake pipe 32 according to an opening degree of a throttle valve 34 during running of the engine. Herein, the intake pipe 32 is one example of an “intake system” of the invention.

The master cylinder 14 boosts oil pressure of a brake main unit (not shown) by activation of the brake booster 12 to generate a braking force in the brake main unit. The negative pressure sensor 16 is one of constituent components of the failure diagnosis apparatus of the brake system 1 and is arranged to detect the negative pressure in the negative pressure chamber of the brake booster 12. The negative pressure sensor 16 is one example of a “booster internal pressure detection unit” of the invention.

The electric vacuum pump 18 is provided in a second passage L2 as shown in FIG. 1 and has a suction port 18a connected to the negative pressure chamber of the brake booster 12 through the second passage L2 and the first passage L1 and a discharge port 18b connected to the first passage L1 via the second passage L2. Herein, the second passage L2 is branched off from the first passage L1 at a point between the first check valve 20 and the second check valve 22 in the first passage L1 and is connected to the first passage L1 downstream of the electric vacuum pump 18.

The electric vacuum pump 18 is further connected to the ECU 24 via a motor and a relay as shown in FIG. 2. In this manner, activation of the electric vacuum pump 18 is controlled by the ECU 24. To be concrete, the pump 18 is started to operate in response to an activation start signal from the ECU 24 to supply negative pressure to the negative pressure chamber of the brake booster 12 from the suction port 18a via the second passage L2 and the first passage L1. The electric vacuum pump 18 stops to operate in response to an operation stop signal from the ECU 24 to stop supplying negative pressure to the negative pressure chamber of the brake booster 12 from the suction port 18a via the second passage L2 and the first passage L1.

The first check valve 20 is provided in the first passage L1 in a position between a joint part with the second passage L2 and the brake booster 12. The second check valve 22 is provided in the first passage L1 in a position closer to the intake pipe 32 than the first check valve 20 and between the joint part with the second passage L2 and the intake pipe 32. These first check valve 20 and second check valve 22 are each configured to be opened only when the negative pressure on the side of the intake pipe 32 is higher than the negative pressure on the side of the negative pressure chamber of the brake booster 12 to allow a fluid to flow only in a direction from the side of the negative pressure chamber of the brake booster 12 to the side of the intake pipe 32. Specifically, the first check valve 20 prevents air from flowing from the intake pipe 32 to the negative pressure chamber of the brake booster 12 through the second passage L2. Further, the second check valve 22 prevents air from flowing from the side of the intake pipe 32 to the side of the negative pressure chamber of the brake booster 12 through the first passage L1 and also prevents air from flowing from the side of the intake pipe 32 and the side of the discharge port 18b of the electric vacuum pump 18 toward the side of the suction port 18a of the pump 18 through the first passage L1. In this manner, the brake system 1 in Example 1 can contain negative pressure in the negative pressure chamber of the brake booster 12 by the first check valve 20 and the second check valve 22.

The ECU 24 is one of the constituent components of the failure diagnosis apparatus of the brake system 1 and is configured by a microcomputer, for example, including a ROM for storing control programs, a readable/writable RAM for storing calculation results and others, a timer, a counter, an input interface, and an output interface. This ECU 24 is connected to the negative pressure sensor 16, the electric vacuum pump 18, the pressure detection unit 26, the shunt resistor 28, and others as shown in FIG. 2. The ECU 24 is also used as a “determination unit” of the invention.

The brake system 1 configured as above can adjust the negative pressure in the negative pressure chamber of the brake booster 12 by supplying the negative pressure generated in the intake pipe 32 to the negative pressure chamber of the brake booster 12 through the first passage L1. The brake system 1 can also adjust the negative pressure in the negative pressure chamber of the brake booster 12 by operating (activating) the electric vacuum pump 18 to supply the negative pressure to the negative pressure chamber of the brake booster 12 through the second passage L2 and the first passage L1.

The pressure detection unit 26 is for example a pressure sensor to detect the internal pressure in the intake pipe 32 which is a pipe communicated with the discharge port 18b of the electric vacuum pump 18. This pressure detection unit 26 is one of the constituent components of the failure diagnosis apparatus of the brake system 1. The pressure detection unit 26 is one example of a n “pipe internal-pressure detection unit” of the invention. Instead of the pressure detection unit 26, a pressure estimation unit (not shown) for estimating the internal pressure of the intake pipe 32 may be used.

Herein, the brake system 1 in Example 1 includes, as one of the constituent components of the failure diagnosis apparatus, the shunt resistor 28 serving as a resistor to detect an operating electric current value of the electric vacuum pump 18, between the motor and the relay. The information of detection results obtained by the shunt resistor 28 is transmitted to the ECU 24. This shunt resistor 28 is one example of a “current value detection unit” of the invention.

Failure Diagnosis Method of Brake System

The failure diagnosis method of the brake system 1 configured as above will be explained below. In the failure diagnosis method of the brake system 1 of this example, the functional normality of the electric vacuum pump 18 is determined from a correlativity between a detection result of the negative pressure in the intake pipe 32 (hereinafter, also referred to as “engine negative pressure”) and a detection result of an operating electric current value of the electric vacuum pump 18 (hereinafter, also referred to as a “pump electric current value”) and also a correlativity between the detection result of the engine negative pressure and a detection result of an ultimate (final) negative pressure in the negative pressure chamber of the brake booster 12 (hereinafter also simply referred to as a “ultimate negative pressure”). That is, the ECU 24 determines the functional normality of the electric vacuum pump 18 by using characteristics that the pump electric current value and the ultimate negative pressure vary according to different engine negative pressure.

The engine negative pressure is detected by the pressure detection unit 26 or the aforementioned pressure estimation unit (not shown), the pump electric current value is detected by the shunt resistor 28, and the ultimate negative pressure is detected by the negative pressure sensor 26.

A concrete example of the failure diagnosis method of the brake system 1 of this example will be explained below. The first explanation is given to the case of determining the functional normality of the electric vacuum pump 18 based on both the correlativity between the detection result of engine negative pressure and the detection result of pump electric current value and the correlativity between the detection result of engine negative pressure and the detection result of ultimate negative pressure. At that time, the ECU 24 periodically executes a control routine shown in FIG. 3 at a predetermined time interval. The failure diagnosis method of the brake system 1 which will be explained below is supposed to be performed under a condition that a system detection condition is established by turn-on of an ignition switch of a vehicle or the like.

Upon start of the processing of the routine shown in FIG. 3, the ECU 24 first activates (turns ON) the electric vacuum pump 18 (step S1) and detects the engine negative pressure by the pressure detection unit 26 (step S2). The ECU 24 decides a determination value used to determine the functional normality of the electric vacuum pump 18 based on the detection result of engine negative pressure (step S3). To be concrete, based on the detection result of engine negative pressure, a predetermined lower limit and a predetermined upper limit of the pump electric current value and a determination value of the ultimate negative pressure are decided. For this purpose, herein, for example, map diagrams shown in FIGS. 4 and 6 which will be mentioned later are used. The ECU 24 then determines whether or not the pump electric current value is equal to or higher than the predetermined lower limit (step S4). If YES in step S4, the ECU 24 determines whether or not the pump electric current value is equal to or lower than the predetermined upper limit (step S5).

If YES in step S5, the ECU 24 determines whether the brake pedal 10 is additionally depressed (i.e., whether the brake is turned ON) (step S6). If YES in step S6, the ECU 24 terminates this routine immediately.

On the other hand, if the brake pedal 10 is not additionally depressed, the ECU 24 determines whether a predetermined time has passed from the time when the electric vacuum pump 18 is started to operate (step S7). Herein, the predetermined time is a time required until the negative pressure in the negative pressure chamber of the brake booster 12 reaches a target negative pressure value.

If YES in step S7, the ECU 24 determines whether or not the ultimate negative pressure is equal to or less than the determination value (step S8). Specifically, the ECU 24 determines whether or not the ultimate negative pressure is equal to a predetermined negative pressure value (the determination value in FIG. 6) or whether or not the ultimate negative pressure is higher than the predetermined negative pressure value (the determination value in FIG. 6).

If YES in step S8, the ECU 24 determines that the function of the electric vacuum pump 18 is normal (step S9). In other words, if the ultimate negative pressure is equal to or higher than the predetermined negative pressure value, the ECU 24 determines that the function of the electric vacuum pump 18 is normal.

On the other hand, if the pump electric current value is less than the predetermined lower limit in step S4 (S4: NO), if the pump electric current value is larger than the predetermined upper limit in step S5 (S5: NO), or if the ultimate negative pressure is larger than the determination value (the ultimate negative pressure is lower than a predetermined negative pressure value) in step S8 (S8: NO), the ECU 24 determines that the function of the electric vacuum pump 18 is abnormal (step S10).

A concrete example of the failure diagnosis method of the brake system 1 of this example mentioned above will be explained below. This example uses a map diagram shown in FIG. 4, for example, showing the engine negative pressure (a horizontal axis in FIG. 4) and the pump electric current value (a vertical axis in FIG. 4). Further, this example uses a map diagram shown in FIG. 6, for example, showing the engine negative pressure (a horizontal axis in FIG. 6) and the ultimate negative pressure (a vertical axis in FIG. 6).

For the engine negative pressure of about −40 kPa, for example, a normal range of the pump electric current value ranges from a lower limit of about 4.3 A to an upper limit of about 5.0 A from FIG. 4 and a determination value of the ultimate negative pressure is thus about −90.5 kPa from FIG. 6. When a detection result of the engine negative pressure is about −40 kPa, therefore, if the detection result of the pump electric current value is within the normal range (in a range of about 4.3 A or more and about 5.0 A or less) shown in FIG. 4 as indicated in FIG. 5 and the detection result of the ultimate negative pressure is equal to the determination value (about −90.5 kPa) shown in FIG. 6 as indicated in FIG. 7 or if the negative pressure is higher than the determination value shown in FIG. 6 (the negative pressure is a value on a line representing the determination value in FIG. 6 or a value located below the line representing the determination value in FIG. 6), the ECU 24 determines that the electric vacuum pump 18 is functioning normally. A vertical axis in FIG. 5 represents the engine negative pressure and a vertical axis in FIG. 7 represents the engine negative pressure and the ultimate negative pressure.

On the other hand, in the case where the detection result of the pump electric current value is out of the normal range shown in FIG. 4 or in the case where the detection result of the ultimate negative pressure shows that the negative pressure is lower than the determination value shown in FIG. 6 (the negative pressure is a value above the line representing the determination value in FIG. 6), the ECU 24 determines that the electric vacuum pump 18 is functioning abnormally.

Moreover, the failure diagnosis method of the brake system 1 of this example may be configured to determine the functional normality of the electric vacuum pump 18 only from the correlativity between the detection result of engine negative pressure and the detection result of pump electric current value as shown in FIG. 8. At that time, the ECU 24 periodically executes the control routine shown in FIG. 8 at predetermined time intervals.

Upon start of the processing of the routine in FIG. 8, the ECU 24 first activates (turns ON) the electric vacuum pump 18 (step S11) and detects the engine negative pressure (step S12). The ECU 24 then decides a determination value used to determine the functional normality of the electric vacuum pump 18 based on the detection result of engine negative pressure (step S13). To be concrete, based on the detection result of engine negative pressure, a predetermined lower limit and a predetermined upper limit of the pump electric current are decided. If the pump electric current value is equal to or higher than the predetermined lower limit (step S14: YES) and if the pump electric current value is equal to or lower than the predetermined upper limit (step 15: YES), the ECU 24 determines that the function of the electric vacuum pump 18 is normal (step S16). On the other hand, if the pump electric current value is less than the predetermined lower limit (step S14: NO) or if the pump electric current value is larger than the predetermined upper limit (step S15: NO), the ECU 24 determines that the function of the electric vacuum pump 18 is abnormal (step S17).

Moreover, the failure diagnosis method of the brake system 1 of this example may be configured to determine the functional normality of the electric vacuum pump 18 only from the correlativity between the detection result of engine negative pressure and the detection result of ultimate negative pressure shown in FIG. 9. At that time, the ECU 24 periodically executes the control routine shown in FIG. 9 at predetermined time intervals.

Upon start of the processing of the routine shown in FIG. 9, the ECU 24 first activates (turns ON) the electric vacuum pump 18 (step S21) and detects engine negative pressure (step S22). The ECU 24 then decides a determination value of ultimate negative pressure based on the detection result of engine negative pressure (step S23). In the case where the brake pedal 10 is not additionally depressed (the brake is not turned ON) (step S24: NO) and a predetermined time has passed from the time when the electric vacuum pump 18 is started to operate (step S25: YES), if the ultimate negative pressure is equal to or lower than the determination value (step S26: YES), the ECU 24 determines the function of the electric vacuum pump 18 is normal (step S27). In other words, if the ultimate negative pressure is equal to or higher than the predetermined negative pressure value, the ECU 24 determines the function of the electric vacuum pump 18 is normal. On the other hand, if the ultimate negative pressure is larger than the determination value (if the ultimate negative pressure is lower than the predetermined negative pressure value) (step S26: NO), the ECU 24 determines that the function of the electric vacuum pump 18 is abnormal (step S28).

According to the present example, as explained above, the functional normality of the electric vacuum pump 18 is determined by use of at least one of the correlativity between the internal pressure of the intake pipe 32 and the internal pressure of the negative pressure chamber of the brake booster 12 and the correlativity between the internal pressure of the intake pipe 32 and the operating electric current value of the electric vacuum pump 18. Specifically, the ECU 24 determines the functional normality of the electric vacuum pump 18 by utilizing the characteristics that the pump electric current value and the ultimate negative pressure vary according to different engine negative pressure. Therefore, even when the engine negative pressure varies according to a running condition of an engine, it is possible to determine the functional normality of the electric vacuum pump 18. Accordingly, the failure diagnosis of the brake system 1 can be performed under any circumstances.

Example 2

In Example 2, a brake system 2 and a failure diagnosis apparatus thereof are configured as shown in FIG. 10. The brake system 2 differs from the brake system 1 in that a changeover valve 30 is provided in the second passage L2 and connected to the discharge port 18b of the electric vacuum pump 18. The changeover valve 30 is a changeover unit to change a connection target of the discharge port 18b of the electric vacuum pump 18 to either one of an intake-system-side passage LA and an atmosphere-side passage LB. Herein, the intake-system-side passage LA is a passage communicated with the first passage L1 and blocked from atmosphere and the atmosphere-side passage LB is a passage blocked from the first passage L1 and communicated with atmosphere. The activation of the changeover valve 30 is controlled by the ECU 24.

The changeover valve 30 is configured to connect the discharge port 18b of the electric vacuum pump 18 to the intake-system-side passage LA during non-energization (non-operation) and alternatively connect the discharge port 18b of the pump 18 to the atmosphere-side passage LB during energization (operation). Concrete examples of the changeover valve 30 may include an electromagnetic type three-way valve and others.

In the brake system 2, different from the brake system 1, the pressure detection unit 26 detects the internal pressure of a pipe (a part of the second passage L2) (hereinafter, also referred to as “discharge-port negative pressure”) between the discharge port 18b of the electric vacuum pump 18 and the changeover valve 30.

In the failure diagnosis method of the brake system 2 of this example, as shown in FIG. 11, the changeover valve 30 is first changed to communicate with atmosphere (step S31). Specifically, the changeover 30 changes the connection target of the discharge port 18b of the electric vacuum pump 18 from the intake-system-side passage LA to the atmosphere-side passage LB. While the discharge port 18b of the pump 18 is connected to the atmosphere-side passage LB in this way, the processing in steps S32 to S41 is executed. The details of the processing in steps S32 to S41 are the same as those of the processing in steps S1 to S10 shown in FIG. 3, Specifically, the ECU 24 determines the functional normality of the pump 18 from the correlativity between a detection result of the discharge-port negative pressure and a detection result of the pump electric current value and the correlativity between the detection result of the discharge-port negative pressure and a detection result of the ultimate negative pressure.

A concrete example of the aforementioned failure diagnosis method of the brake system 2 will be explained below. The following example uses a map diagram shown in FIG. 12, for example, showing the discharge-port negative pressure (a horizontal axis in FIG. 12) and the pump electric current value (a vertical axis in FIG. 12). Further, this example uses a map diagram shown in FIG. 13, for example, showing the discharge-port negative pressure (a horizontal axis in FIG. 13) and the ultimate negative pressure (a vertical axis in FIG. 13).

For the discharge-port negative pressure of 0 kPa, for example, a normal range of the pump electric current value ranges from a lower limit of about 5.75 A to an upper limit of about 6.75 A from FIG. 12 and a determination value of the ultimate negative pressure is about −83 kPa from FIG. 13. When the discharge port 18b of the electric vacuum pump 18 is connected to the atmosphere-side passage LB and the discharge-port negative pressure is 0 kPa, therefore, if the detection result of the pump electric current value is within the normal range (in a rage of about 5.75 A or more and about 6.75 A or less) shown in FIG. 12 and the detection result of the ultimate negative pressure is equal to or higher than the determination value (about −83 kPa) shown in FIG. 13 (i.e., if the negative pressure is a value on the determination value in FIG. 13 or a value located below the determination value in FIG. 13), the ECU 24 determines that the function of the electric vacuum pump 18 is normal.

On the other hand, when the detection result of the pump electric current value is out of the normal range shown in FIG. 12 or when the detection result of the ultimate negative pressure is lower than the determination value shown in FIG. 13 (a value located above the determination value in FIG. 13), the ECU 24 determines the function of the electric vacuum pump 18 is abnormal.

As above, the failure diagnosis method of the brake system 2 shown in FIG. 11 is configured to make determination of the functional normality of the electric vacuum pump 18 by changing over the connection target of the discharge port 18b of the electric vacuum pump 18 to the atmosphere-side passage LB, irrespective of the running status of an engine. Accordingly, it is possible to determine the functional normality of the electric vacuum pump 18 under stable conditions not affected by variations in engine negative pressure.

Moreover, the failure diagnosis method of the brake system 2 of this example can also make determination of the functional normality of the electric vacuum pump 18 only from the correlativity between the detection result of the discharge-port negative pressure and the detection result of the pump electric current value as indicated in FIG. 14. At that time, the ECU 24 periodically executes the control routine shown in FIG. 14 at predetermined time intervals.

Upon start of the processing in the routine shown in FIG. 14, the ECU 24 first causes the changeover valve 30 to communicate with atmosphere (step S51). Specifically, the changeover valve 30 changes the connection target of the discharge port 18b of the electric vacuum pump 18 from the intake-system-side passage LA to the atmosphere-side passage LB. While the discharge port 18b of the pump 18 is connected to the atmosphere-side passage LB in this way, the processing in steps S52 to S58 is executed. The details of the processing in steps S52 to S58 are the same as those in the processing in steps S11 to S17 in FIG. 8. The ECU 24 makes determination of the functional normality of the electric vacuum pump 18 from the correlativity between the detection result of the discharge-port negative pressure and the detection result of the pump electric current value.

Moreover, the failure diagnosis method of the brake system 2 of this example also may be configured to determine the functional normality of the electric vacuum pump 18 only from the correlativity between the detection result of the discharge-port negative pressure and the detection result of the ultimate negative pressure as shown in FIG. 15. At that time, the ECU 24 periodically the control routine shown in FIG. 15 at predetermined time intervals.

Upon start of the processing of the routine shown in FIG. 15, the ECU 24 first causes the changeover valve 30 to communicate with atmosphere (step S61). Specifically, the changeover valve 30 changes the connection target of the discharge port 18b of the electric vacuum pump 18 from the intake-system-side passage LA to the atmosphere-side passage LB. While the discharge port 18b of the pump 18 is connected to the atmosphere-side passage LB in this way, the processing in steps S62 to S69 is executed. The details of the processing in steps S62 to S69 are the same as those in the processing in steps S21 to S28 in FIG. 9. The ECU 24 makes determination of the functional normality of the electric vacuum pump 18 from the correlativity between the detection result of the discharge-port negative pressure and the detection result of the ultimate negative pressure.

It should be noted that the failure diagnosis method of the brake system 2 may also be configured to determine the functional normality of the electric vacuum pump 18 without causing the changeover valve 30 to communicate with atmosphere, that is, by holding the discharge port 18b of the pump 18 connected to the intake-system-side passage LA though the changeover valve 30.

According to the present example as explained above, the functional normality of the electric vacuum pump 18 is determined by using at least one of the correlativity between the internal pressure of the pipe located between the discharge port 18b of the pump 18 and the changeover valve 30 and the operating electric current value of the pump 18 and the correlativity between the internal pressure of the pipe located between the discharge port 18b of the pump 18 and the changeover valve 30 and the internal pressure of the negative pressure chamber of the brake booster 12. In other words, the ECU 24 determines the functional normality of the electric vacuum pump 18 by utilizing the characteristics that the pump electric current value and the ultimate negative pressure vary according to different discharge-port negative pressure.

According to the present example, the connection target of the discharge port 18b of the electric vacuum pump 18 is changed to the atmosphere-side passage LB by the changeover valve 30, so that the discharge-port negative pressure becomes atmospheric pressure and is not affected by the engine negative pressure. This can make determination of the functional normality of the electric vacuum pump 18 separately from variations in engine negative pressure. Thus, the brake system 2 can be subjected to correct failure diagnosis even when the engine negative pressure largely varies.

According to the present example, the failure diagnosis of the brake system 2 can be achieved in both systems, one being established when the discharge port 18b of the electric vacuum pump 18 is connected to the intake-system-side passage LA and the other being established when the discharge port 18b is connected to the atmosphere-side passage LB.

MODIFIED EXAMPLES

One modified example may be configured as a brake system 3 shown in FIG. 16. This brake system 3 differs from the brake system 1 in that a third check valve 36 is provided in the second passage L2 on the side of the discharge port 18b of the electric vacuum pump 18. In this modified example, the third check valve 36 prevents air from flowing from the intake pipe 32 to the negative pressure of the brake booster 12 through the second passage L2.

Another modified example may be configured as a brake system 4 shown in FIG. 17. This brake system 4 differs from the brake system 2 in that the first check valve 20 is provided in the second passage L2 on the side of the discharge port 18b of the electric vacuum pump 18. In this modified example, the first check valve 20 prevents air from flowing from the intake pipe 32 to the negative pressure chamber of the brake booster 12 through the second passage L2.

In the above brake systems 3 and 4 of the modified examples, the first check valve 20 or the third check valve 36 is provided in the second passage L2 on the side of the discharge port 18b of the electric vacuum pump 18. Accordingly, even after the electric vacuum pump 18 is stopped to operate, the inside of the pump 18 and the inside of the second passage L2 are kept at negative pressure. This can provide an assist effect to operation of the electric vacuum pump 18 (an effect of reducing drive torque) at the time of restart of operation of the pump 18. The brake systems 3 and 4 of the modified examples can perform the failure diagnosis method similar to the failure diagnosis method of the brake systems 1 and 2 and provide the same effects as the brake systems 1 and 2.

Still another modified example may be configured as a brake system 5 shown in FIG. 18. This brake system 5 differs from the brake system 2 in that the first check valve 20 is provided in the second passage L2 on the side of the suction port 18a of the electric vacuum pump 18. In this modified example, the first check valve 20 prevents air from flowing from the intake pipe 32 to the negative pressure chamber of the brake booster 12 through the second passage L2. The brake system 5 of this modified example can perform the failure diagnosis method similar to the failure diagnosis method of the brake system 2 and provide the same effects as the brake system 2.

The above examples are mere examples and do not give any limitations to the invention. The present invention may be embodied in other specific forms without departing from the essential characteristics thereof

Reference Sings List

1 to 5: Brake system,
10: Brake pedal,

12: Brake booster,
14: Master cylinder,

16: Negative pressure sensor,
18: Electric vacuum pump (Electric VP),

18a: Suction port,
18b: Discharge port,

20: First check valve,
22: Second check valve,

24: ECU
26: Pressure detection unit,

28: Shunt resistor,
30: Changeover valve,

32: Intake pipe,
34: Throttle valve,

36: Third check valve,
L1: First passage,

L2: Second passage,
LA: Intake-system-side passage,

LB: Atmosphere-side passage

FAILURE DIAGNOSIS APPARATUS OF BRAKE SYSTEM AND FAILURE DIAGNOSIS METHOD OF BRAKE SYSTEM

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CPC

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Priority Claims (1)