DE102012220290A1 - Method for controlled ventilation of fuel tank of hybrid car, involves taking charge of electrical energy storage device into account, and predicting low charge state of intermediate storage during start-up of engine drive unit - Google Patents

Abstract

The method involves allowing a pressure to prevail in a fuel tank of an automotive vehicle i.e. hybrid car, based on a current or foreseeable boundary condition. An internal combustion engine drive unit is arranged next to an electromotive drive unit that is supplied by electrical energy. A charge of an electrical energy storage device is taken into account. A ventilation of the volatile fuel components located in the fuel tank is carried out via an intermediate storage. A low charge state of the intermediate storage is predicted during start-up of the engine drive unit.

Description

The invention relates to a method for the controlled venting of a vehicle fuel tank, in which an overpressure can prevail, as a function of at least one current or foreseeable boundary condition. The state of the art is in addition to the DE 101 31 798 A1 on the DE 10 2007 030 523 A1 directed.

As is known, fuel tanks of motor vehicles must be at least occasionally ventilated, since it can come to the outgassing of volatile fuel constituents, in particular with greater heating of the fuel in the tank, but should not get into the environment. Therefore, the ventilation takes place via a temporary storage device, from which the cached fuel components are supplied to an internal combustion engine of the motor vehicle (which serves as the fuel cell stored in the tank) for incineration, which usually functions as a drive unit. This technology of temporary storage of volatile fuel components in motor vehicles, usually in so-called. Activated carbon filters is well known in the art. As is known, such activated carbon filters or intermediate storage must be flushed again and again in order to avoid a so-called "breakthrough" with which the volatile fuel constituents evaporating in the tank of the motor vehicle and cached in the activated carbon filter would escape unburned into the environment. Since flushing of the buffer for the operation of the internal combustion engine can be unfavorable under certain boundary conditions, various boundary conditions can be taken into account for the initiation or execution of such a flushing process. For this purpose, for example, the above-mentioned first DE 101 31 798 A1 directed.

In the above mentioned further DE 10 2007 030 523 A1 is a method for venting or venting a fuel tank of a motor vehicle in connection with a designated filling of the fuel tank at a gas station described, which may be in the tank pressure or negative pressure, which must be reduced in time before filling the tank. Basically, an overpressure in a fuel tank of a motor vehicle is advantageous because it reduces the outgassing tendency of the fuel in the tank. Overpressure in the fuel tank can also occur in hybrid vehicles, which in addition to a supplied from the fuel tank internal combustion engine drive unit from an electrical energy storage electromotive drive unit, occur and be desirable, since during the sole operation of the electric motor drive unit, of course, no flushing in the tank ventilation system envisaged intermediate storage tank ("activated charcoal filter") for volatile fuel constituents. Further, since the storage capacity of the activated carbon filter is limited to a reasonable degree, as far as possible venting of the fuel tank is avoided when operating the electric motor drive unit of a hybrid motor vehicle alone.

Coming back to the named DE 10 2007 030 523 A1 For example, in the method of venting a fuel tank described in connection with an intended filling of the fuel tank (at a gas station) by means of a positioning system, it is determined whether the motor vehicle is near a gas station. If yes, venting is performed. For this purpose, the motor vehicle has a navigation system or another, in particular satellite-supported position-determining device, wherein an electronic control unit can access information about the geographical positions of filling stations and compare the current position of the motor vehicle with these.

In view of the advantageous effects of a pressure prevailing in a fuel tank of a motor vehicle overpressure, which is of course limited in its height by the pressure resistance of the tank, which can only be demonstrated to a certain extent under reasonable pressure, it is intended to indicate when a venting of a vehicle fuel tank, in which an overpressure can prevail, is particularly advantageous in order to be able to interpret or program an electronic control device, which then implements a method according to the invention for controlled venting (= object of the present invention).

To solve this problem, the features of the independent claims 1 or 2 are proposed, which is based on the common idea to perform a venting of the tank when temporally shortly thereafter followed by an activated carbon filter (geng. Latch for volatile fuel components), carried out over the vent will, can be rinsed.

The first embodiment of a method according to the invention relates to the hybrid motor vehicles already briefly described above, which in addition to a supplied from the fuel tank internal combustion engine drive unit ("internal combustion engine") also have a supplied from an electrical energy storage electric motor drive unit. According to the invention, the state of charge of the electrical energy storage device is taken into account in the sole operation of the electromotive drive unit to the effect that venting via the said temporary storage device is then carried out if, due to a low charge State of charge of the electrical energy storage a commissioning of the internal combustion engine drive unit, during which a flushing of the buffer is possible, is predictable. In other words, in other words, it is checked whether the electromotive drive has switched over to the drive by the internal combustion engine for a short time and thus has to be started because the electrical energy store has almost been emptied. If yes, then the fuel tank is vented, as with a commissioning of the engine, which can be extremely limited in time, the activated carbon filter / cache can be rinsed again. A goal is thus to apply to the cache for as long periods as possible to a minimum extent with volatile fuel components or charged.

A second embodiment of a method according to the invention relates to any motor vehicle with a so-called "pressure tank", in which overpressure can prevail, as well as with a ventilation system of this fuel tank, in which a buffer for volatile fuel constituents is provided. Furthermore, the motor vehicle is equipped with a navigation system or the like, which knows a route ahead of the vehicle. However, the navigation system for the present invention need not be a satellite-assisted positioning system, but generally a suitable system or electronic control unit that knows a vehicle ahead route. For example, a route ahead may also be derived from repetitive "behavioral patterns", for example, if the vehicle is moved by the driver every working day early in the morning and at the end of the workday on a substantially identical route. Conventional navigation systems in which the road network is stored and in which the driver can directly or indirectly enter a destination, which he would like to reach or start from his current position, whereupon the navigation system proposes a suitable route, are of course the term "navigation system or the like ".

According to the invention (according to the second embodiment) a venting is carried out when the type of the preceding route allows flushing of the buffer. In other words, therefore, it is checked whether the buffer can be flushed in the short term because the internal combustion engine will be operated in operating points favorable for a flushing operation or because a flushing of the buffer can be predictably carried out on the basis of another boundary condition which can be anticipated based on the distance traveled ahead. In particular, it can be taken into account by or in an electronic control unit, which type of the preceding, d. H. Coming soon driving distance of the motor vehicle is, preferably taking into account the and compared to the current type of driving. This electronic control unit then controls a suitable tank vent valve or the like. Suitably, which establishes (or prevents) a connection between the fuel tank via the buffer to the environment. An advantageous or optimized ventilation strategy is thus designed by an electronic control unit such that, on the one hand, a break-through of the buffer is prevented as far as possible and, on the other hand, a foreseeable operating state of the internal combustion engine is impaired as little as possible by the flushing process.

For example, when driving on a highway, when the internal combustion engine is more heavily loaded, the volatile fuel storage buffer can be optimally purged. The same applies (in a somewhat weakened form) in general for cross-country journeys, d. H. when the motor vehicle is moved outside closed villages. On the other hand, in city traffic, due to the many load changes of the internal combustion engine taking place there, flushing of the intermediate storage unit can impair the smooth and even running of the internal combustion engine. Accordingly, it can be provided that with respect to the nature of the route ahead, a distinction is made between trips outside and within closed towns, and that when driving outside a village (as "current route") shortly before a foreseeable entrance to a village (as Travel distance ") is vented in a first step, the fuel tank and still completely rinsed in a subsequent second step, the buffer before being moved into a locality. The fact that an entry into a village is imminent can easily be ascertained with an electronic navigation system which knows the current position of the vehicle and the upcoming route, for example by means of a destination input previously entered by the driver of the motor vehicle.

Practically the same as for journeys outside or within localities applies, if a distinction is made with regard to the constant-running part of journeys. Constant travel is a driving state in which no significant load changes of the internal combustion engine and, in particular, no significant load reduction takes place or takes place, ie when the vehicle is driven by the internal combustion engine at a substantially constant speed. A low cruise share is emerging Consequently, by rapidly changing speeds and is far less suitable for a flushing process of the buffer (and therefore to avoid as far as possible) as a route with a high constant-rate share, on which preferably a rinsing process is performed. In particular, a distinction between free travel and stop-and-go traffic can be distinguished in this sense, with purging being avoided as long as possible in the stop-and-go traffic and preferably always carried out when evaluated by evaluating the appropriate data of a navigation system or Like. By an electronic control unit, a high probability of a free ride is detected. Whether a free ride or "stop-and-go traffic" (ie column traffic in traffic jams) is expected, can be easily determined with modern navigation systems, which continue to receive information about impending traffic congestion or traffic density and then first the tank be properly vented or not vented to then flush the buffer in case of venting can.

Furthermore, it can be provided in a tank ventilation system according to the invention that a venting of the tank is carried out before a predictable uphill, as in an uphill due to the decreasing ambient air pressure, an increased fuel output is expected in the fuel tank. Consequently, the aim is to keep the tank at ambient pressure before the start of the uphill drive, so that further pressure can build up again.

Generalizing the concrete case of uphill travel, a method according to the invention can consider, as a further boundary condition, the altitude above sea level and / or the ambient temperature, since both variables influence the outgassing tendency of the fuel in the tank. At a lower outgassing tendency, an overpressure can be held without hesitation in the fuel tank, while venting should take place at a higher output inclination for safety reasons, as long as this is possible with further consideration of the storage capacity of the intermediate store. Its storage capacity is particularly high when it can be reasonably quickly flushed due to the route ahead. As a further boundary condition for carrying out venting of the tank, the loading state of the buffer can also be taken into account directly if this is determined in a suitable manner. For example, various methods for measuring the loading state of an activated carbon filter are known to those skilled in the art; Alternatively, its load condition can also be estimated.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10131798 A1 [0001, 0002]
• DE 102007030523 A1 [0001, 0003, 0004]

Claims (2)

Method for the controlled venting of a vehicle fuel tank, in which an overpressure may prevail, depending on at least one current or foreseeable boundary condition, wherein the motor vehicle in addition to an supplied from the fuel tank internal combustion engine drive unit also has a supplied from an electrical energy storage electromotive drive unit, and wherein in sole operation of the electromotive drive unit, the state of charge of the electrical energy storage is taken into account that venting via a buffer for volatile fuel components in the fuel tank is then performed when due to a low state of charge commissioning of the internal combustion engine drive unit, during which a flushing of the buffer is possible , is predictable. A method for controlled venting of a vehicle fuel tank, in which an overpressure can prevail, via a volatile fuel constituent buffer and in response to at least one current or foreseeable constraint, wherein the motor vehicle is equipped with a navigation system or the like, which is a preceding route of the vehicle knows and a venting is then performed when the nature of the route ahead allows a flushing of the cache.