# US 8,751,174 B2 · Method for determining the size of a leak

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- Number: US 8,751,174 B2
- Document ID: US8751174B2
- Status: Granted
- Kind: B2
- Application number: 12/531,159
- Filed: 2008-03-14
- Published: 2011-12-15
- Granted: 2014-06-10
- Earliest claimed: 2007-03-14
- Assignees: Audi AG
- Applicants: Armin Koehler; Ludger Hoelscher; Uwe Finis
- Inventors: Armin Koehler; Ludger Hoelscher; Uwe Finis
- Web page: https://patentgrep.com/patent/US8751174B2

## CPC

- F02M 25/0818: {having means for pressurising the evaporative emission space}
- F02M: SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF

## Abstract

A method for determining the size of a leak in the liquid-containing tank device of a vehicle, in particular of a motor vehicle, the liquid influencing the pressure in the tank device by evaporation, with the following steps: generating a first pressure as a reference pressure in the tank device at a first instant, detecting a first pressure characteristic up to a second instant, generating a second pressure at a third instant, the first pressure and the second pressure being chosen to be different, detecting a second pressure characteristic up to the fourth instant, determining the pressure gradient of the first pressure characteristic at the second instant and of the pressure gradient of the second pressure characteristic at the third instant, determining the first pressure difference of the pressure at the second instant from the reference pressure, determining the second pressure difference of the pressure at the third instant from the reference pressure, computing the size of the leak depending on the determined pressure gradient and the pressure differences, and the assumption that the evaporation rate is constant in the tank device, and that a leak rate is established which is proportional to the square root of the respective pressure difference.

## Claims

### Claim 1

A method for determining the cross sectional area of a leak in the liquid-containing tank device of a vehicle, in particular of a motor vehicle, the liquid influencing the pressure in the tank device by evaporation, with the following steps:
generating a first pressure as a reference pressure in the tank device at a first instant (t1),
detecting a first pressure characteristic up to a second instant (t2),
generating a second pressure at a third instant (t4), the first pressure and the second pressure being chosen to be different,
detecting a second pressure characteristic up to the fourth instant (t5),
determining the pressure gradient of the first pressure characteristic at the second instant (t2) and of the pressure gradient of the second pressure characteristic at the third instant (t4),
determining the first pressure difference of the pressure at the second instant (t2) from the reference pressure,
determining the second pressure difference of the pressure at the third instant (t4) from the reference pressure,
computing the cross sectional area of the leak depending on the determined pressure gradient and the pressure differences, based on an equation:
A
=
⁢
(
V
p
⋆
α
⋆
ρ
2
⋆
R
⋆
T
)
⋆
1
Δ
⁢
⁢
p
4
⋆
{
{
(
dp
/
dt
)
4
-
(
dp
/
dt
)
2
}
(
1
+
Δ
⁢
⁢
p
2
Δ
⁢
⁢
p
4
)
}
,
wherein
A is the cross sectional area of the leak,
V is the volume of the tank device,
p is the density of a gas flowing through the leak,
α is a flow characteristic that designates the leak as an orifice plate,
R is the universal gas constant,
T is the temperature of the gas flowing through the leak,
Δp2 is the first pressure difference,
Δp4 is the second pressure difference,
(dp/dt)2 is pressure gradient of the first pressure characteristic at the second instant, and
(dp/dt)4 is the pressure gradient of the second pressure characteristic at the third instant,
assuming that the evaporation rate is constant in the tank device, and that a leak rate is established which is proportional to the square root of the respective pressure difference.

### Claim 2 (depends on 1)

The method according to claim 1, wherein ambient pressure is generated as the first pressure.

### Claim 3 (depends on 2)

The method according to claim 2, wherein a negative pressure is generated as the second pressure.

### Claim 4 (depends on 2)

The method according to claim 2, wherein the first pressure is produced by opening a ventilation valve of the tank device.

### Claim 5 (depends on 2)

The method according to claim 2, wherein the second pressure is produced by opening a regeneration valve which establishes a connection to the intake manifold of an internal combustion engine which has a tank device.

### Claim 6 (depends on 2)

The method according to claim 2, wherein the second and/or the fourth instant are chosen such that the pressure gradient determined at the time adequately describes the pressure characteristic.

### Claim 7 (depends on 1)

The method according to claim 1, wherein a negative pressure is generated as the second pressure.

### Claim 8 (depends on 7)

The method according to claim 7, wherein the first pressure is produced by opening a ventilation valve of the tank device.

### Claim 9 (depends on 7)

The method according to claim 7, wherein the second pressure is produced by opening a regeneration valve which establishes a connection to the intake manifold of an internal combustion engine which has a tank device.

### Claim 10 (depends on 7)

The method according to claim 7, wherein the second and/or the fourth instant are chosen such that the pressure gradient determined at the time adequately describes the pressure characteristic.

### Claim 11 (depends on 1)

The method according to claim 1, wherein the first pressure is produced by opening a ventilation valve of the tank device.

### Claim 12 (depends on 11)

The method according to claim 11, wherein the second pressure is produced by opening a regeneration valve which establishes a connection to the intake manifold of an internal combustion engine which has a tank device.

### Claim 13 (depends on 11)

The method according to claim 11, wherein the second and/or the fourth instant are chosen such that the pressure gradient determined at the time adequately describes the pressure characteristic.

### Claim 14 (depends on 1)

The method according to claim 1, wherein the second pressure is produced by opening a regeneration valve which establishes a connection to the intake manifold of an internal combustion engine which has a tank device.

### Claim 15 (depends on 14)

The method according to claim 14, wherein the second and/or the fourth instant are chosen such that the pressure gradient determined at the time adequately describes the pressure characteristic.

### Claim 16 (depends on 1)

The method according to claim 1, wherein the second and/or the fourth instant are chosen such that the pressure gradient determined at the time adequately describes the pressure characteristic.