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In a failure diagnostic system for a fuel vapor processing apparatus, a processing flow path comprising a vapor line, a canister and a purge line is closed with a vapor control valve and a purge control valve. The interior of the processing flow path is reduced in pressure or pressurized by rotating

In a failure diagnostic system for a fuel vapor processing apparatus, a processing flow path comprising a vapor line, a canister and a purge line is closed with a vapor control valve and a purge control valve. The interior of the processing flow path is reduced in pressure or pressurized by rotating an air pump of a pump module in a forward or reverse direction. An electronic control unit (ECU) closes the vapor control valve and the purge control valve to close the processing flow path after stop of the engine and, when the fuel temperature detected by a temperature sensor is lower than a predetermined value, reduces the internal pressure of the processing flow path through an air pump, then checks air-tightness of the interior of the processing flow path based on behavior of a vapor pressure detected by a pressure sensor. The ECU closes the processing flow path and, when the fuel temperature detected is not lower than the predetermined value, pressurizes the interior of the processing flow path through the air pump, then checks air-tightness of the processing flow path based on behavior of a vapor pressure subsequently detected.

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What is claimed is: 1. A canister included in a fuel vapor processing apparatus for processing fuel vapor generated in a fuel tank and incorporating, in a casing, an adsorbent for adsorbing the fuel vapor, wherein the canister comprises a diagnosing function part for the fuel vapor processing appar

What is claimed is: 1. A canister included in a fuel vapor processing apparatus for processing fuel vapor generated in a fuel tank and incorporating, in a casing, an adsorbent for adsorbing the fuel vapor, wherein the canister comprises a diagnosing function part for the fuel vapor processing apparatus, the diagnosing function part being integrally mounted nearly centrally of the casing so that the canister has a center of gravity located nearly centrally of the canister, wherein the diagnosing function part is a pump module for changing the internal pressure of the casing; wherein the casing is in the shape of a generally U-shaped cylindrical body having a first end portion through which the fuel vapor is introduced in and discharged out of the canister and a second end portion which is able to communicate with atmosphere, and the casing includes a valley portion positioned nearly centrally, and the pump module is mounted in the valley portion. 2. The canister according to claim 1, wherein an insertion hole is formed in the bottom of the valley portion, and an engaging portion to be inserted and engaged into the insertion hole is formed in a lower end of the pump module. 3. The canister according to claim 1, wherein the pump module comprises a pump, a check valve disposed on an air inlet side of the pump, and a solenoid valve disposed on an air outlet side of the pump. 4. A canister included in a fuel vapor processing apparatus for processing fuel vapor generated in a fuel tank and incorporating, in a casing, an adsorbent for adsorbing the fuel vapor, wherein the canister comprises a diagnosing function part for the fuel vapor processing apparatus, the diagnosing function part being integrally mounted nearly centrally of the casing so that the canister has a center of gravity located nearly centrally of the canister, wherein the diagnosing function part is a pump module for changing the internal pressure of the casing, wherein the pump module is connected to a fuel vapor processing apparatus which is disposed correspondingly to an engine mounted on a vehicle and wherein fuel vapor generated in the fuel tank is trapped by the canister and a fuel component contained in the trapped fuel vapor is purged to an intake passage in the engine, the pump module being used for changing the internal pressure of the fuel vapor processing apparatus and for diagnosing a failure of the fuel vapor processing apparatus based on behavior of the pressure detected at this time, wherein the pump module comprises: a pump for reducing or increasing pressure in the fuel vapor processing apparatus; a connection port connected to the fuel vapor processing apparatus; an air port including a first end and a second end, the first end being opened to the atmosphere; an orifice passage including a first end and a second end, the first end being connected to the connection port, the second end being connected to the pump, with an orifice being provided in an intermediate position of the orifice passage to calculate a reference value in failure diagnosis; a pressure detecting means for detecting an internal pressure of the fuel vapor processing apparatus and that of the orifice passage; and a change-over valve for changing from a state of communication to a cut-off state or vice versa between the connection port and the air port; and the orifice is disposed in a vertex direction in a mounted state of the pump module on the vehicle and is located at a higher position than an opening/closing portion of the change-over valve. 5. The canister according to claim 4, further comprising a case and wherein the change-over valve comprises an actuator and a valve body, the orifice is disposed between the actuator and the valve body in the change-over valve, and the change-over valve can be mounted in the case while being rotated about an extension line extending in a movable direction of the valve body. 6. A failure diagnostic system for a fuel vapor processing apparatus, using the pump module in the canister according to claim 5. 7. The canister according to claim 4, further comprising a case, the case having a plurality of mounting holes for mounting the pump module to the vehicle, and wherein the change-over valve comprises an actuator and a valve body, the orifice is disposed between the actuator and the valve body in the change-over valve, and at the time of mounting the pump module in the vehicle by utilizing the plural mounting holes, the change-over valve can be mounted in the case while being rotated about an extension line extending in a movable direction of the valve body, thereby disposing the orifice in the vertex direction and at a higher position than the opening/closing portion of the change-over valve. 8. A failure diagnostic system for a fuel vapor processing apparatus, using the pump module in the canister according to claim 4. 9. A canister included in a fuel vapor processing apparatus for processing fuel vapor generated in a fuel tank and incorporating, in a casing, an adsorbent for adsorbing the fuel vapor, wherein the canister comprises a diagnosing function cart for the fuel vapor processing apparatus, the diagnosing function part being integrally mounted nearly centrally of the casing so that the canister has a center of gravity located nearly centrally of the canister, wherein the diagnosing function part is a pump module for changing the internal pressure of the casing, wherein the pump module is connected to a fuel vapor processing apparatus which is disposed correspondingly to an engine mounted on a vehicle and wherein fuel vapor generated in the fuel tank is trapped by the canister and a fuel component contained in the trapped fuel vapor is purged to an intake passage in the engine, the pump module being used for reducing the internal pressure of the fuel vapor processing apparatus and for diagnosing a failure of the fuel vapor processing apparatus based on behavior of the pressure detected at this time, the pump module comprising: a case; a vacuum pump installed in the case to develop a negative pressure in the fuel vapor processing apparatus; a connection port formed in the case and connected to the fuel vapor processing apparatus; an air port formed in the case and including a first end and a second end, the first end being opened to the atmosphere; an orifice passage formed in the case and having a first end and a second end, the first end being connected to the connection port, the second end being connected to the vacuum pump, with an orifice being provided in an intermediate position of the orifice passage to calculate a reference value in diagnosis; and a change-over valve for changing from a state of communication to a cut-off state or vice versa between the connection port and the air port, the change-over valve being mounted in the case while being rotated about an extension line extending in a movable direction of a valve body of the change-over valve, thereby disposing the orifice in a vertex direction and at a higher position than an opening/closing portion of the change-over valve.