Method for operating a pneumatic positioning system of a motor vehicle and control unit for carrying out the method

Abstract

Method for operating a pneumatic actuating system (7) of a motor vehicle, wherein the pneumatic actuating system (7) has an air reservoir (8) in which a system pressure prevails, wherein the pneumatic actuating system (7) pneumatically actuates a transmission (3) of the motor vehicle and a starting clutch (4) of the motor vehicle depending on the system pressure prevailing in the air reservoir (8) and depending on a switching position of switching valves (11, 12) of the pneumatic actuating system (7), characterized in that when the starting clutch (4) or the transmission (3) is actuated, a changing conductivity of a switching valve (11, 12) actuated to actuate the starting clutch (4) or the transmission (3) is determined and taken into account in a further actuation of the switching valve (11, 12).

Description

[0001] The invention relates to a method for operating a pneumatic actuating system of a motor vehicle according to the preamble of claim 1. Furthermore, the invention relates to a control unit configured for carrying out the method and a corresponding computer program product.

[0002] It is common practice for motor vehicles, such as trucks or other commercial vehicles, to have a pneumatic actuation system. This system provides pneumatic control for various vehicle components, such as the transmission and the starting clutch. A pneumatic actuation system in a motor vehicle has an air reservoir containing a specific system pressure. Depending on this pressure, the system uses switching valves to pneumatically control the transmission and the starting clutch. Knowing the system pressure in the air reservoir is crucial for the proper functioning of the pneumatic actuation system.

[0003] From DE 10 2009 045 090 A1, a method for operating a pneumatically or hydraulically actuated, automated starting clutch of a transmission is known, which is actuated for opening and closing by a pneumatic or hydraulic clutch actuator. The tightness of the pneumatic or hydraulic clutch actuator and / or the reservoir pressure of a pneumatic or hydraulic pressure accumulator interacting with the clutch actuator are automatically checked during transmission operation under defined operating conditions.

[0004] Based on this, the present invention aims to create a novel method for operating a pneumatic actuator system of a motor vehicle. Furthermore, a corresponding control unit and a computer program for carrying out the method are to be provided.

[0005] From a process engineering perspective, this problem is solved starting from the preamble of claim 1 in conjunction with its characterizing features. A control unit and a computer program product are also the subject of the further independent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0006] According to the invention, a method for operating a pneumatic actuating system of a motor vehicle is proposed, in which the pneumatic actuating system has an air reservoir in which a system pressure prevails. Depending on the system pressure prevailing in the air reservoir and depending on a switching position of switching valves of the pneumatic actuating system, the pneumatic actuating system pneumatically controls a transmission of the motor vehicle and a starting clutch of the motor vehicle.

[0007] It is intended that when the starting clutch or the transmission is controlled, a change in the conductivity of a switching valve controlled to actuate the starting clutch or the transmission is determined and taken into account in further control of the switching valve.

[0008] The invention thus proposes a novel, simple, and reliable method for operating a pneumatic actuator system in a motor vehicle, which maintains consistent control performance for the drivetrain components actuated by the actuator system throughout its service life. By appropriately adapting the pneumatic conductance, the mass flow through the switching valve can be accurately determined even if the conductance of the switching valve changes. Drivetrain components can therefore be operated with consistent ease of use throughout the service life of the pneumatic actuator system.

[0009] Following further training, the controlled switching valve of the pneumatic positioning system is energized at a defined constant system pressure for a defined constant actuation time, and the position of the actuated piston of a pneumatic actuator cylinder is measured. Depending on the position of the piston before or at the beginning of the defined constant actuation time, and depending on the position of the piston after or at the end of the defined constant actuation time, a change in the position of the piston during the actuation time is determined. The position change of the piston determined in this way is compared with at least one previously determined position change of the piston determined in the same manner. If a deviation exists between the determined position changes of the piston, it is concluded that the conductivity of the switching valve has changed.The changed conductivity of the switching valve is ultimately taken into account during a further actuation of the switching valve.

[0010] According to an advantageous further development, with the starting clutch closed, at least one switching valve serving to control the starting clutch is actuated in the opening direction of the starting clutch for a defined constant actuation period at a constant system pressure, and the position of the actuated piston of the pneumatic actuator cylinder of the starting clutch is measured. Depending on the position of the actuating piston before or at the beginning of the defined constant actuation period and depending on the position of the actuating piston after or at the end of the defined constant actuation period, a change in the position of the actuating piston during the actuation period is determined and compared with at least one previously determined change in the position of the actuating piston.If a deviation exists between the measured position changes of the actuating piston, this indicates a change in the conductivity of the switching valve controlling the starting clutch. This change is then taken into account during subsequent actuation of the switching valve to operate the starting clutch. Consequently, the starting clutch can be operated with consistent control accuracy throughout the entire service life of the pneumatic actuating system, enabling position or torque control of the starting clutch while maintaining consistent comfort.

[0011] In a further advantageous embodiment, a control pressure of the respective control cylinder is determined for the position of the actuating piston before or at the beginning of the actuation period and for the position of the actuating piston after or at the end of the actuation period, depending on a force characteristic of the actuating piston or the actuating cylinder. The pneumatic conductance of the switching valve is then calculated based on the position of the actuating piston before or at the beginning of the defined actuation period and the corresponding control pressure, based on the position of the actuating piston after or at the end of the defined actuation period and the corresponding control pressure, based on the length of the defined constant actuation period, and based on the level of the defined constant system pressure. The force characteristic of the actuating piston is known and stored in the control system.Depending on the force characteristic curve, actuating pressures can be assigned to the respective positions of the actuating piston, which are then incorporated into the calculation of the pneumatic conductance of the switching valve. The force characteristic curve could, for example, be the clutch release force characteristic of a starting clutch designed as a diaphragm spring clutch.

[0012] Furthermore, claim 6 specifies a control unit for operating a pneumatic actuator system of a motor vehicle, which is adapted to carry out the method according to the invention. The control unit can, for example, be designed as a transmission control unit.

[0013] The solution according to the invention can also be embodied as a computer program product which, when running on a processor of a control device, instructs the processor by means of software to carry out the associated process steps relating to the invention. In this context, a computer-readable medium on which a computer program product described above is stored and retrievable is also part of the subject matter of the invention.

[0014] The invention is not limited to the specified combination of features of the dependent or suffixed claims. Furthermore, it is possible to combine individual features, even those apparent from the claims, the subsequent description of embodiments, or directly from the drawings. References in the claims to the drawings by means of reference numerals are not intended to limit the scope of protection of the claims.

[0015] To illustrate the invention, a drawing with exemplary embodiments is attached to the description. This drawing shows: Fig. 1 a block diagram of a motor vehicle with a pneumatic actuating system; Fig. 2. A first diagram to illustrate details of the procedure for operating the pneumatic actuating system of the motor vehicle; and Fig. 3 a second diagram to illustrate details of the procedure for operating the pneumatic actuation system of the motor vehicle.

[0016] Fig. Figure 1 shows a highly schematic diagram of a motor vehicle which has a drive unit 1 , a downforce 2 and one between the drive unit 1 and the downforce 2 manual transmission 3 The motor vehicle also includes a starting clutch. 4 , which are located between the drive unit 1and the gearbox 3 is switched on. The operation of the drive unit 1 is controlled by an engine control unit 5 controlled and / or regulated. The operation of the gearbox. 3 as well as the starting clutch 4 is controlled by a transmission control unit 6 controlled and / or regulated according to Fig. 1. Replace the engine control unit for this purpose. 5 with the drive unit 1 and the transmission control unit 6 with the gearbox 3 Data from. Furthermore, the engine control unit is replaced. 5 and the transmission control unit 6 exchange data with each other.

[0017] Fig. Figure 1 shows a highly schematic representation of the components of a pneumatic positioning system. 7 of the motor vehicle. The positioning system 7 includes an air reservoir 8 , which is powered by a pump 13 It can be filled with compressed air. Starting from the air reservoir. 8are different pneumatic actuators, namely pneumatic actuator cylinders 9 , 10 supplied with compressed air, namely depending on the switching position of switching valves 11 , 12 .

[0018] This shows Fig. 1. An example: a control cylinder 9 with a piston 9a for pneumatic control of the starting clutch 4 as well as a pneumatic actuator cylinder 10 with a piston 10a for the pneumatic control of a switching element of the transmission 3 , using the actuating cylinder 9 a switching valve 11 and with the actuator cylinder 10 a switching valve 12 interacts. According to Fig. 1 is simply a switching valve 11 for controlling the actuator cylinder 9 and only one switching valve 12 for controlling the actuator cylinder 10shown. It should be noted that this is for the control of the actuator cylinder. 9 the starting clutch 4 and for controlling the actuator cylinder 10 a switching element of the transmission 3 Several switching valves may be provided in each case.

[0019] According to Fig. 1 is the actuator cylinder 9 , which controls the starting clutch 4 It serves as a position sensor 9b assigned, with the help of which the positions of the actuating piston are determined. 9a of the actuator cylinder 9 can be measured.

[0020] So that the pneumatic positioning system 7 For it to function properly, it is important to check the system pressure p sys within the air reservoir 8 to know. Is the system pressure p sys within the air reservoir 8 For example, if the voltage is too low, it can potentially cause problems in the gearbox. 3a circuit may not be executed correctly. For example, if the system pressure p sys within the air reservoir 8 If the level is too high, components of the gearbox may be damaged. 3 They may be damaged. Therefore, it is important to maintain the system pressure p. sys within the air reservoir 8 to know. This way the system pressure p can be... sys either determined by suitable methods or by means of at least one in the pneumatic positioning system 7 The pressure sensor is positioned to determine the pressure.

[0021] The invention now relates to details for operating the pneumatic positioning system. 7 , with the help of which a conductance value of a switching valve 11 , 12 of the positioning system 7 can be adapted.

[0022] This will be discussed below with regard to the control of the starting clutch. 4 This will be explained in more detail. It is intended that the switching valve11 of the pneumatic positioning system 7 at a constant system pressure p sys for a defined constant actuation time or pulse duration and the position of the actuated piston is determined. 9a of the actuator cylinder 9 is measured using measuring equipment.

[0023] Depending on the position of the actuating piston 9a before or at the beginning of the defined constant actuation time and depending on the position of the actuating piston 9a After or at the end of the defined constant actuation time, a change in the position of the actuating piston occurs. 9a determined during the actuation period. The change in position of the actuator piston thus determined. 9a is determined by at least one previously determined change in the position of the actuating piston in the same way. 9a compared.

[0024] The change in position of the actuating piston, previously determined in the same way 9awas preferably done in a new condition of the switching valve 11 determined, i.e., in a state where the switching valve 11 It shows no wear. This determined change in the position of the actuating piston. 9a in the new condition of the switching valve 11 is finally transferred to a control unit, preferably the transmission control unit. 6 stored in non-volatile memory. This has the advantage that the information about the determined change in position of the actuator piston is retained. 9a in the new condition of the switching valve 11 the data remains stored even when the control unit is switched off and is available upon subsequent activation of the control unit, and can be taken into account in the method according to the invention.

[0025] Is there a discrepancy between the determined position changes of the actuating piston? 9a , then it can be concluded that the conductivity of the switching valve 11has changed, since the switching valve 11 of the pneumatic positioning system 7 at the same constant system pressure P sys was controlled with the same defined pulse duration. The changed conductivity of the switching valve 11 Finally, upon further activation of the switching valve, 11 This takes into account a consistent control quality for regulating the system using the switching valve. 11 and the actuator cylinder 9 This enables the controlled starting clutch.

[0026] For this purpose, the position of the actuating piston is determined. 9a before or at the beginning of the defined actuation period, as well as for the position of the actuating piston 9a after or at the end of the defined actuation period, depending on a so-called force characteristic of the actuating piston. 9a or the actuator cylinder 9 Each requires a corresponding actuating pressure from the respective actuating cylinder. 9 determined.

[0027] Fig. Figure 2 shows an example of such a force characteristic curve. 14 , which here is the clutch release force characteristic of the starting clutch designed as a diaphragm spring clutch 4 The diagram shows the actuating pressure p plotted against the position or actuating path s.

[0028] Before or at the beginning of the defined actuation period, the actuator piston 9a of the actuator cylinder 9 the position s1, whereby in this case the actuating cylinder 9 The pressure p1 prevails, preferably ambient pressure or atmospheric pressure.

[0029] After or at the end of the defined actuation time, the actuator piston 9a of the actuator cylinder 9 the position s2, to which, according to the force characteristic curve 14 The pressure p2 belongs.

[0030] For the two positions s1 and s 2 of the actuating piston 9a of the actuator cylinder 9Accordingly, the corresponding actuating pressures p1 and p2 are determined before or after, or at the beginning or end of the defined actuation period, depending on the respective force characteristic curve.

[0031] Depending on the above positions s1, s2 of the actuating piston 9a Depending on the actuating pressures p1 and p2 determined from the force characteristic curve, as well as depending on the length of the defined, constant actuation time and the level of the constant system pressure, the pneumatic conductance of the switching valve can then be determined. 11 preferably calculated according to the following formula and adapted accordingly: C = p 2 ∗ ( ( l M A X − s 2 ) ∗ A + V 0 ) − p 1 ∗ ( ( l M A X − s 1 ) ∗ A + V 0 ) R S ∗ T ∗ t O N ∗ p S Y S ∗ ρ ∗ ψ where C is the pneumatic conductance of the switching valve 11 is, where p sys the system pressure is, where t ON the length of the defined control time duration, where s1 is the position of the actuator piston. 9abefore or at the beginning of the defined actuation time and p1 is the corresponding actuating pressure, where s2 is the position of the actuating piston. 9a after or at the end of the defined control time duration and p2 is the corresponding actuating pressure, where l MAX a maximum adjustment range of the adjustment cylinder 9a is, where A is the area of ​​the control box 9a is, where V0 is a filling volume of the actuator cylinder 9 before or at the beginning of the defined activation period, where p is the air density, where T is the air temperature, where R S is the specific gas constant of air and where ψ is the flow function of the switching valve. 11 is.

[0032] By adapting the pneumatic conductance of the switching valve 11 can the mass flow through the switching valve 11 also calculated correctly and during the control of the starting clutch 4This must be taken into account if the conductivity of the switching valve changes due to wear. 11 is present. Consequently, the starting clutch cannot be used. 4 over the entire lifespan of the pneumatic positioning system 7 actuated with a constant control quality, whereby a position or torque control of the starting clutch 4 which is achievable while maintaining the same level of comfort.

[0033] When determining the actuator cylinder 9 via the switching valve 11 The supplied air mass is preferably according to Fig. 3 between a control of the switching valve 11 in a supercritical range 15a with constant mass flow and control of the switching valve 11 in a subcritical range 15b with non-constant mass flow. As shown in the diagram of the Fig. 3 can be taken from the mass flow through the switching valve 11in the subcritical range 15b approximated by an ellipse.

[0034] The air mass m1 in the actuator cylinder 9 The position of the actuating piston s1 depends on the position in the actuating cylinder. 9 prevailing pressure, depending on the volume of the actuating cylinder 9 and is determined depending on the air temperature. The air mass in the actuator cylinder 9 The position of the actuating piston s1 is preferably calculated according to the following equation: m 1 = p 1 ∗ V 1 R S ∗ T where m1 is the air mass in the actuator cylinder 9 is, where p1 is the one in the actuating cylinder 9 prevailing pressure at position s1, where V1 is the volume of the actuating cylinder. 9 is, where T is the air temperature, and where R S is a specific gas constant of air.

[0035] Accordingly, the air mass in the actuator cylinder is 9 at the actuating piston position s2 preferably calculated according to the following equation: m 2 = p 2 ∗ V 2 R 2 ∗ T where m2 is the air mass in the actuator cylinder 9 is, where p2 is the one in the actuating cylinder 9 prevailing pressure at position s2, where V2 is the volume of the actuating cylinder. 9 is, where T is the air temperature, and where R S is a specific gas constant of air.

[0036] The volume in the actuator cylinder 9 The values ​​at the actuating piston position s1 and at the actuating piston position s2 are preferably calculated according to the following equations: V 1 = A ∗ ( l M A X − l s 1 ) V 2 = A ∗ ( l M A X − l s 2 ) where A is the piston area of ​​the actuating cylinder 9 is, where l MAX a maximum actuation range of the actuator cylinder 9 is, where l s1 an actuation path of the actuator cylinder 9 to position s1 and where l s2 an actuation path of the actuator cylinder 9 to position s2.

[0037] Regarding the air masses determined above in the actuator cylinder9 Finally, taking into account the volume and the duty cycle of the switching valve, one arrives at the following conclusion. 11 , the air density and the flow function of the switching valve 11 Regarding the formula for calculating the pneumatic conductance of the switching valve 11 : m 2 − m 1 = ( p 2 ∗ ( ( l M A X − s 2 ) ∗ A + V 0 ) − p 1 ∗ ( ( l M A X − s 1 ) ∗ A + V 0 ) ) R S ∗ T m ˙ = ( m 2 − m 1 ) t O N = c ∗ p S Y S ∗ ρ ∗ ψ C = ( p 2 ∗ V 2 − p 1 ∗ V 1 ) R S ∗ T ∗ t O N ∗ p S Y S ∗ ρ ∗ ψ C = p 2 ∗ ( ( l M A X − s 2 ) ∗ A + V 0 ) − p 1 ∗ ( ( l M A X − s 1 ) ∗ A + V 0 ) R S ∗ T ∗ t O N ∗ p S Y S ∗ ρ ∗ ψ where C is the pneumatic conductance of the switching valve 11 is, where p sys the system pressure is, where t ON the length of the defined control time duration, where s1 is the position of the actuator piston. 9a before or at the beginning of the defined actuation time and p1 is the corresponding actuating pressure, where s2 is the position of the actuating piston. 9a after or at the end of the defined control time duration and p2 is the corresponding actuating pressure, where l MAX a maximum adjustment range of the adjustment cylinder 9ais, where A is the area of ​​the control box 9a is, where V0 is a filling volume of the actuator cylinder 9 before or at the beginning of the defined activation period, where p is the air density, where T is the air temperature, where R S is the specific gas constant of air and where ψ is the flow function of the switching valve. 11 is.

[0038] When the actuator cylinder is activated 9 for controlling the starting clutch 4 will be the actuator cylinder 9 via the switching valve 11 Air mass supplied depends on mass flow rate via the switching valve 11 determined, whereby the mass flow rate via the switching valve 11 from the one in the air reservoir 8 prevailing first pressure p sys , from which in the actuator cylinder 9 prevailing second pressure p, from a maximum mass flow rate via the switching valve 11 and the conductance of the switching valve 11is dependent on the actuator cylinder 9 via the switching valve 11 The supplied air mass m is preferably calculated according to the following equations: m = ∫ m ˙ ∗ d t m ˙ = ψ M A X ∗ 1 − ( ( p p s y s ) − b 1 − b ) 2 ψ M A X = C ∗ p s y s ∗ ρ ∗ ( T 0 T ) where m the actuator cylinder 9 via switching valve 11 supplied air mass, where ṁ is the mass flow through the switching valve 11 is, where p sys the one in the air reservoir 8 prevailing pressure is, where p is the pressure in the actuating cylinder 9 prevailing pressure, where b is a critical pressure ratio of the switching valve 11 is, where ψ MAX the maximum mass flow through the switching valve 11 is, where C is a pneumatic conductance of the switching valve. 11 is, where p is the air density, where T0 is the absolute air temperature under standard conditions, and where T is the current air temperature.

[0039] According to the formulas above, the following result is obtained via the switching valve 11 in the actuator cylinder 9 starting from the air reservoir 8 flowing air mass from the integration of the mass flow across the switching valve 11 The equation for calculating the mass flow rate through the switching valve 11 is finally combined with the adapted pneumatic conductance of the switching valve. 11 corrected, thereby correcting the starting clutch 4 over the entire lifespan of the pneumatic positioning system 7 can be operated with consistent comfort.

[0040] The method according to the invention can be converted into a conventional control process for the starting clutch. 4 to be integrated, in which the starting clutch 4 through the actuator cylinder 9 is controlled in the opening direction, for example during the opening of the starting clutch to execute a shift in the transmission 3Therefore, there is no separate control of the starting clutch. 4 required. This is advantageous because it then ensures the availability of the starting clutch. 4 is not restricted and the execution of the inventive method for adapting the conductance of a switching valve for a driver does not occur perceptibly in the background.

[0041] The invention further relates to a control unit for carrying out the method. This control unit is preferably a transmission control unit. 6 , comprising the means for carrying out the method. These means include hardware-related means and software-related means. The hardware-related means are data interfaces for exchanging data with the assemblies involved in carrying out the method according to the invention.

[0042] This is how the transmission control unit is replaced. 6 for example, data with the switching valve11 to activate the same signal for the defined activation duration. Furthermore, the transmission control unit receives... 6 a signal from the position sensor 9b , to adjust the position of the actuating piston 9a of the actuator cylinder 9 to determine.

[0043] The hardware components still consist of a processor for data processing and a memory for data storage. The force characteristic curve, for example, is stored in the memory. 14 of the actuating piston 9a or actuator cylinder 9 or the starting clutch 4 and the conductance of the switching valve 11 in the new condition of the switching valve 11 or the determined change in position of the actuating piston 9a in the new condition of the switching valve 11 deposited.

[0044] The software-related means consist of program modules for carrying out the method according to the invention. Reference symbol list 1 drive unit 2 Drive 3 gearboxes 4 Starting clutch 5 Engine control unit 6 Transmission control unit 7 Positioning system 8 air reservoir 9 actuator cylinders 9a Actuating piston 9b Sensor 10 actuator cylinders 10a Actuating piston 11 Switching valve 12 switching valve 13 Pump 14 Force characteristic curve 15 Mass flow 15a supercritical region 15b subcritical region QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102009045090 A1

[0003]

Claims

[1] Method for operating a pneumatic actuating system (7) of a motor vehicle, wherein the pneumatic actuating system (7) has an air reservoir (8) in which a system pressure prevails, wherein the pneumatic actuating system (7) pneumatically actuates a transmission (3) of the motor vehicle and a starting clutch (4) of the motor vehicle depending on the system pressure prevailing in the air reservoir (8) and depending on a switching position of switching valves (11, 12) of the pneumatic actuating system (7), characterized by , that when the starting clutch (4) or the transmission (3) is actuated, a change in the conductivity of a switching valve (11, 12) actuated to actuate the starting clutch (4) or the transmission (3) is determined and taken into account during a further actuation of the switching valve (11, 12). [2] Method according to claim 1, characterized by, that the switching valve (11, 12) of the pneumatic actuating system (7) is actuated at constant system pressure for a constant actuation time and the position of an actuated piston (9a, 10a) of a pneumatic actuating cylinder (9, 10) is measured, wherein, depending on the position of the actuating piston (9a, 10a) before or at the beginning of the defined constant actuation time and depending on the position of the actuating piston (9a, 10a) after or at the end of the defined constant actuation time, a change in the position of the actuating piston (9a, 10a) during the actuation time is determined and compared with at least one previously determined change in the position of the actuating piston (9a, 10a), and wherein, in the event of a deviation between the determined changes in the position of the actuating piston (9a, 10a), a change in the conductivity of the switching valve (11, 12) is inferred, which, upon further actuation of the The switching valve (11, 12) is taken into account. [3] Method according to claim 1 or 2, characterized by, that when the starting clutch (4) is closed, at least one switching valve (11) serving to control the starting clutch (4) is controlled in the opening direction of the starting clutch (4) for the constant control time while the system pressure is kept constant, and the position of the actuated piston (9a) of the pneumatic actuating cylinder (9) of the starting clutch (4) is measured,wherein, depending on the position of the actuating piston (9a) before or at the beginning of the defined constant actuation period and depending on the position of the actuating piston (9a) after or at the end of the defined constant actuation period, a change in the position of the actuating piston (9a) is determined during the actuation period and compared with at least one previously determined change in the position of the actuating piston (9a), and wherein, in the event of a deviation between the determined changes in the position of the actuating piston (9a), a change in the conductivity of the switching valve (11) for actuating the starting clutch (4) is inferred, which is taken into account in a further actuation of the switching valve (11). [4] Method according to any one of claims 1 to 3, characterized by, that for the position of the actuating piston (9a) before or at the beginning of the actuation period and for the position of the actuating piston (9a) after or at the end of the actuation period, depending on a force characteristic (14) of the actuating piston or the actuating cylinder (9) or the starting clutch (4), an actuation pressure of the respective actuating cylinder (9) is determined, and that depending on the position of the actuating piston (9a) before or at the beginning of the defined actuation period and the corresponding actuation pressure, depending on the position of the actuating piston (9a) after or at the end of the defined actuation period and the corresponding actuation pressure, and depending on the length of the constant actuation period and the level of the constant system pressure, the pneumatic conductance of the switching valve (11) is calculated. [5] Method according to any one of claims 1 to 4, characterized by , that the pneumatic conductance of the switching valve (11) is calculated according to the following formula: C = p 2 ∗ ( ( l M A X − s 2 ) ∗ A + V 0 ) − p 1 ∗ ( ( l M A X − s 1 ) ∗ A + V 0 ) R S ∗ T ∗ t O N ∗ p S Y S ∗ ρ ∗ ψ where C is the pneumatic conductance of the switching valve (11), where p sys the system pressure is, where t ON the length of the defined actuation time, where s1 is the position of the actuating piston (9a) before or at the beginning of the defined actuation time and p1 is the corresponding actuating pressure, where s2 is the position of the actuating piston (9a) after or at the end of the defined actuation time and p2 is the corresponding actuating pressure, where l MAX a maximum stroke of the actuating piston (9a), where A is the area of ​​the actuating piston (9a), where V0 is a filling volume of the actuating cylinder (9) before or at the beginning of the defined actuation time, where p is the air density, where T is the air temperature, where R S is the specific gas constant of air and where ψ is the flow function of the switching valve (11). [6] Control unit (6) for operating a pneumatic actuating system (7) of a motor vehicle, wherein the actuating system (7) has an air reservoir (8) in which a system pressure prevails, wherein the pneumatic actuating system (7) pneumatically actuates a transmission (3) of the motor vehicle and a starting clutch (4) of the motor vehicle depending on the system pressure prevailing in the air reservoir (9) and depending on the switching position of switching valves (11, 12) of the actuating system (7), characterized by , that the control unit (6) controls a switching valve (11, 12) used to actuate the starting clutch (4) or the transmission (3) and, when controlling the starting clutch (4) or the transmission (3), determines a change in the conductivity of the switching valve (11, 12) controlled to actuate the starting clutch (4) or the transmission (3) and takes this into account when further controlling the switching valve (11, 12). [7] Control unit (6) according to claim 6, characterized by, that the control unit (6) actuates at least one switching valve (11, 12) of the pneumatic actuating system (7) at constant system pressure for a constant actuation time to actuate the starting clutch (4) or the transmission (3), and measures the position of an actuating piston (9a, 10a) of a pneumatic actuator cylinder (9, 10) thereby actuated, that the control unit (6) determines a change in position of the actuating piston (9a, 10a) during the actuation time, depending on the detected position of the actuating piston (9a, 10a) before or at the beginning of the defined constant actuation time and depending on the detected position of the actuating piston (9a, 10a) after or at the end of the defined constant actuation time, and compares this change with at least one previously determined change in position of the actuating piston (9a, 10a), and that if there is a deviation between the determined changes in position of the actuating piston (9a,10a) detects a change in the conductivity of the switching valve (11, 12) and takes this into account during further actuation of the switching valve (11, 12). [8] Computer program product comprising program code means stored on a computer-readable data carrier to carry out all steps of a method according to any one of claims 1 to 5 when the computer program product is executed on a computer or on a corresponding computing unit, in particular a control unit according to claim 6 or 7.

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