1. Field of the Invention
The present invention relates generally to an device for collecting and treating vaporized fuel in a fuel tank without releasing the fuel vapor into the atmosphere. More particularly, the present invention pertains to a testing apparatus that tests for malfunctions concerning the sealing of a fuel vapor treating device, which is provided with a canister for collection of fuel and a purging means for appropriate purging of the fuel into an intake passage of an engine.
2. Description of the Related Art
A fuel vapor treating device typically mounted on a vehicle, collects and treats vaporized fuel in a fuel tank without releasing the fuel vapor into the atmosphere. As shown in FIG. 17, a typical apparatus has a canister 73 that draws in and collects fuel vaporized in a fuel tank 71 through a vapor line 72. The canister 73 is filled with an adsorbent 74 comprised of activated carbon or the like. A purge line 75, extending from the canister 73, is connected to an intake passage 77 of an engine 76. The canister 73 first adsorbs the vaporized fuel drawn in through the vapor line 72. The canister 73 collects fuel and discharges only the residual gas, from which fuel components (particularly hydrocarbon, HC) have been extracted, into the atmosphere through a hole 78. The fuel collected in the canister 73 is purged into the intake passage 77 by way of the purge line 75 during operation of the engine 76. A purge control valve 79, provided in the purge line 75, adjusts the flow rate of the fuel conveyed through the purge line 75 in accordance with the requirements of the engine 76.
In this typical treating device damage or disconnection of the vapor line 72 may lead to a degradation in the airtightness, or sealing, of the treating device. This may result in insufficient treatment of the vaporized fuel.
Japanese Unexamined Patent Publication 6-108930 describes an apparatus that tests for malfunctions such as those described above. As shown in FIG. 18, a testing apparatus used for fuel vapor treating devices includes a fuel tank 81, a canister 82, a vapor line 83, and a purge line 84. A purge vacuum switching valve (VSV), or purge control valve 85, provided in the purge line 84, adjusts the flow rate of the fuel passing through the purge line 84. An electronic control unit (ECU) 86 controls the purge control valve 85 during operation of the engine 76. A vapor control valve 87, provided in the vapor line 83, controls the flow of vaporized fuel directed toward the canister 82 from the fuel tank 81. A difference in pressure between the fuel tank 81 side and the canister 82 side of the vapor control valve 87 opens the valve 87 and causes the vaporized fuel to flow therethrough toward the canister 82. The testing apparatus includes a pressure sensor 88 which separately detects the interior pressure in the tank side of the vapor control valve 87 and the canister side of the vapor control valve 87. That is, a three-way valve 89, connected to the pressure sensor 88, includes a port connected to the vapor line 83 at the side of the fuel tank 81 and another port connected to the vapor line 83 at the side of the canister 82. The pressure sensor 88 selectively detects the tank pressure and the canister pressure when the ECU 86 switches the side which the three-way valve 89 is connected to in accordance with its requirements. The ECU 86 determines whether there is a malfunction in either the tank side or the canister side based on the detected value of the tank pressure and the canister pressure.
However, accurate detection of the interior pressure in the canister side is obstructed in the testing apparatus described in the above publication when a malfunction occurs in the purge control valve 85. For example, when a valve body of the control valve 85 adheres to a casing or other parts in a closed state, the interior pressure of the canister side may be detected inaccurately since the pressure is detected under the assumption that the valve body is opened. Or, for example, when the valve body of the control valve 85 adheres to the casing or other parts in an opened state, the interior pressure of the canister side may be detected inaccurately since the pressure is detected under the assumption that the valve body is closed. Such erroneous detection of the interior pressure in the canister side may hinder appropriate testing concerning the sealing in the canister side that is conducted by the ECU 86.