Evaporated fuel processing device

Abstract

 An evaporated fuel processing device comprises a canister including a canister case accommodating an adsorbent material and a volume compensator means to keep the adsorbent material in a compact state. According to the invention, said volume compensator means comprises at least one resilient body including one or more gas-filled cells and said resilient body is arranged inside the canister case.

Description

Field of the invention

[0001] The present invention generally relates to an evaporated fuel processing device, in particular for an internal combustion engine of an automotive vehicle, comprising an evaporative canister.

Background of the invention

[0002] There are three main sources of polluting gases from an internal combustion engine: engine exhaust, crankcase and fuel supply systems. In the fuel tank, the hydrocarbons that are continually evaporating from the fuel constitute a significant contributing factor to air pollution.

[0003] To control the air pollution resulting from these emissions, governments establish quality standards and perform inspections to ensure that standards are met. Standards have become progressively more stringent, and the equipment necessary to meet them has become more complex. Emissions from the fuel tank are reduced by an evaporated fuel processing device, a part of which is an evaporative canister of activated carbon capable of holding fuel vapour entering the canister via a tank port. The evaporative canister acts as a storehouse. When the engine is running, the adsorbent is regenerated by purging the vapours from the evaporative canister through the purge port into the combustion chamber, where they are burnt. During this regeneration, fresh air enters the canister through an atmospheric port, usually situated on the opposite side of tank and purge ports.

[0004] To prevent fuel vapours from passing to easily around loose adsorbent particles, it is desirable to provide and to keep the adsorbent in a relatively packed or compact state. Thermal volume variations are also of great concern, as these canisters may be used in a very large range of temperatures, e.g. from -40°C to +120 °C. Chemical expansion and contraction due to adsorption/desorption cycles or mechanical effects, such as vibrations or shock, also tend to degrade the packing of the adsorbent material. Therefore, canisters generally also comprise volume compensators including e.g. a compacting plate and springs to keep a sufficient pressure on the adsorbent by axially sliding inside the canister.

[0005] Hence, the shape and the size of the cross section of such a compacting plate will be determined by the inner cross section of the canister case, whereas at least part of the shape of the canister will be determined by the fact that this compacting plate must slide inside the canister case, generally along a longitudinal axis. Such a configuration therefore severely reduces the freedom in designing the canister case, which is nevertheless an important aspect for an optimum integration e.g. in the engine compartment of a car.

[0006] As this compacting plate is usually inserted in the canister case after the adsorbent material has been filled in, the canister case should present a cover portion with a sufficient size and an appropriate shape to permit the placing of the volume compensator, thereby further reducing the freedom of shape of the canister.

[0007] A further disadvantage of these volume compensators is that they are composed of multiple parts giving rise to higher manufacturing costs. Moreover, these parts must be assembled, at least partially during the manufacture of the canister itself, which leads to additional assembly costs.

[0008] Other disadvantages are due to the fact that these compensators, as they are slidably, but nevertheless sealingly inserted in the canister, they must be designed as to prevent chocking or jamming inside the canister under all operating conditions. Further manufacturing constraints, such as narrow tolerance and additional sealing means, therefore arise from the need for sufficient mechanical reliability of such a device.

Object of the invention

[0009] The object of the present invention is hence to provide an improved evaporated fuel processing device which provides for an efficient volume compensation while allowing significantly greater freedom in designing the shape of such a device.

[0010] This object is achieved by an evaporated fuel processing device as claimed in claim 1.

General description of the invention

[0011] In order to overcome the abovementioned problems, the present invention proposes an evaporated fuel processing device comprising a canister including a canister case accommodating an adsorbent material and a volume compensator means to keep said adsorbent material in a compact state. According to the invention, said volume compensator means comprises at least one resilient body including one or more gas-filled cells and said at least one resilient body is arranged inside said canister case.

[0012] During operation of such a device, temperature variations inside the canister cause the gas-filled cell(s) of the resilient body to expand or to contract and thereby compensate for thermal and chemical volume variations of the adsorbent material. In a device according to the invention, the adsorbent is therefore efficiently kept in a sufficiently compact state to ensure an optimal fuel vapour adsorption and desorption function.

[0013] A major advantage of a volume compensator means of the present invention is a considerably larger freedom in designing the shape of the canister case, because the flexible volume compensator means does not require specifically designed cover and body parts in order to accomplish its function. In fact, the shape of the canister no longer depends on volume compensation considerations and therefore may be chosen to optimise the overall fuel adsorption capacity of the device and/or to best meet space constraints inside the engine compartment.

[0014] Another important advantage of such a device is an improved reliability over prior art solutions, because the volume compensation is done without interaction of a number of mechanical parts with narrow manufacturing tolerances and stringent assembly procedures.

[0015] Furthermore, another benefit is due to the one-part design of the volume compensator, combining ease of manufacturability and lack of tedious assembly steps, and hence reduced manufacturing and assembly costs.

[0016] Although the shape of the resilient body is not limiting, in a preferred embodiment of the invention, the resilient body is a spheroid, i.e. having a roughly spherical shape. Such a resilient spheroid presents several advantages, the most important being an optimal three-dimensional pressure development within the canister case to allow for a sufficiently uniform compacting of the adsorbent. A further advantage of this embodiment is that the risk of jamming inside the canister during the insertion of the volume compensator is reduced, especially if more than one resilient body is being used to compensate for thermal volume variations.

[0017] In a further preferred embodiment of the invention, the resilient body comprises an elastomeric outer envelope defining a gas-filled chamber, such as an elastomeric ball.

[0018] The lack of inner partitioning walls in the case of a resilient body with only one gas-filled cell allows for larger volume variations. Hence the number of resilient bodies needed may be reduced while getting the same volume compensation efficiency. Therefore, in an especially preferred embodiment, the volume compensation is done by only one elastomeric ball.

[0019] In another advantageous embodiment, the resilient body comprises an elastomeric foam material, i.e. it is made of a large number of smaller gas-filled cells. While the presence of inner partitioning cell walls may reduce expansion and contracting capability of the resilient body, as already mentioned, these walls, on the other hand, increase the intrinsic three-dimensional stability of the resilient structure.

[0020] Volume compensators made of elastomeric foam material are also inexpensive and easy to handle.

[0021] The fuel adsorbing efficiency and/or the manufacturing process of the device may be further improved by varying the size and/or the number of resilient bodies used. As indicated above, there may be only one resilient body or ball with a relatively large size compared to the volume of adsorbent material, whereas the use of foam bodies is especially advantageous if a larger number of smaller bodies is to be used to achieve the volume compensation.

[0022] In the case of a single compensator, its position inside the canister is preferably chosen in order to uniformly distribute the pressure within the adsorbent. The volume compensation body is therefore advantageously centrally arranged inside the canister case.

[0023] In the case of a large number of compensation bodies, it may be convenient to introduce the bodies into the device at the same time as the adsorbent material. Depending on the relative size of the resilient bodies and the adsorbent particles it may even be favourable to combine them before filling the resulting mixture into the canister case.

[0024] Hence, in a further preferred embodiment, said resilient body is incorporated inside said adsorbent material, i.e. each resilient body is substantially surrounded by adsorbent particles, the main advantage being an increased ease of handling allowing the filling of the device either by its bottom or its top side.

[0025] Nevertheless, in another aspect of the invention such a resilient body may also be arranged between the inner walls of said canister case and said adsorbent material. Although, such a configuration may require some preassembly steps, the ease of shaping of such a body and its inherent elasticity do not substantially restrict the freedom in designing the shape of the canister as compared to the above-mentioned embodiments of the invention.

[0026] It may even be of particular interest to combine the latter configuration of wall supported bodies, e.g. attached to the inner side of a cover part, with resilient bodies, e.g. a resilient ball or a plurality of foam beads, incorporated inside said adsorbent.

[0027] In a further embodiment, the device further comprises supporting means to maintain said at least one resilient body in a predefined position inside the adsorbent chamber. This arrangement is of particular interest in the case of one or a small number of larger compensation bodies to control the position of each compensator within the canister case and thereby to optimise the path taken by the fuel vapours during adsorption and desorption cycles.

Detailed description with respect to the figures

[0028] The present invention will be more apparent from the following description of a non limiting embodiment with reference to the attached drawings, wherein

Fig. 1 is a partial cross-sectional view of a typical prior art evaporated fuel processing device and

Fig. 2 is a partial cross-sectional view of an advantageous embodiment of a device according to the invention.

In Fig. 1, the prior art canister case (1) defines an adsorbent chamber (3) containing adsorbent material, such as activated carbon, to temporarily store fuel vapours. To keep the adsorbent in a sufficiently compact state, volume compensation means are provided which generally comprise a compacting plate (4) and a spring (6). To prevent adsorbent material from passing between compacting plate (4) and the inner walls of the canister case (1) and thereby causing chocking or jamming of the plate inside the case, a foam layer (5) is applied to the compacting plate (4). After filling in the adsorbent material, the compacting plate (4) with its foam layer (5) and the spring (6), the canister case (1) is closed using cover (2).

[0029] Fig. 2 represents an embodiment of an evaporated fuel processing device of the invention, in which the canister case (1) is closed with a cover (2). In the adsorbent chamber (3) containing the adsorbent is arranged a resilient ball (7) whose elastomeric envelope encloses a gas-filled core (8). The correct position of the resilient ball (7) inside the canister is ensured using supporting pins or ribs (9), which extend from the inner walls of the canister case. The expansion and contraction of the ball (7) due to thermal variations keeps the adsorbent in a sufficiently compact state for an optimum operation. After insertion of the ball (7) and the adsorbent material, the cover (2) comprising a foam layer (11) and ribs (10) is placed on the canister case (1). The foam layer (11) supported by the ribs (10) are not only useful to compensate for variations in the filling height with adsorbent material, but also to pressurize the gas inside the resilient body during assembly of the device, thereby further enhancing its compacting effect on the adsorbent.

Claims

1. Evaporated fuel processing device comprising a canister including:

• a canister case accommodating an adsorbent material and

• a volume compensator means to keep said adsorbent material in a compact state,

characterized in that
said volume compensator means comprises at least one resilient body including one or more gas-filled cells, said at least one resilient body being arranged inside said canister case.

2. Evaporated fuel processing device according to claim 1, wherein said resilient body is a spheroid.

3. Evaporated fuel processing device according to any of the preceding claims, wherein said resilient body comprises an elastomeric outer envelope defining a gas-filled chamber.

4. Evaporated fuel processing device according to any of the preceding claims, wherein said resilient body comprises an elastomeric foam material.

5. Evaporated fuel processing device according to any of the preceding claims, wherein said resilient body is incorporated inside said adsorbent material.

6. Evaporated fuel processing device according to any of the preceding claims, wherein said resilient body is arranged between the inner walls of said canister case and said adsorbent material.

7. Evaporated fuel processing device according to one of the preceding claims, further comprising supporting means to maintain said at least one resilient body in a predefined position inside the adsorbent chamber.

Drawing