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DE-102016206582-B4 - Pneumatic control

DE102016206582B4DE 102016206582 B4DE102016206582 B4DE 102016206582B4DE-102016206582-B4

Abstract

Method (200) for controlling an actuating force (F_act) provided by means of a pneumatic actuating device (120), wherein the actuating device (120) comprises a cylinder (125) and a piston (130) displaceably closing the cylinder (125), wherein a mass flow of air at a predetermined pressure into the cylinder (125) can be controlled by means of a valve (155), and wherein the method (200) comprises the following steps: sensing (205) a position (150) of the piston (130) in the cylinder (125); determining (235) a mass flow of air into the cylinder (125); determining (210) a pneumatic pressure in the cylinder (125) based on the mass flow and the position (150); determining (220) an actuating force (F_act) provided at the piston (130) based on the pressure and an effective piston area; and control (225) of the actuation of the valve (155) depending on the provided actuation force (F_act) and a desired actuation force (F_should), wherein the mass flow rate is determined by means of a characteristic map (300) based on the actuation of the valve (155) and a pressure ratio that exists between the pressure of a compressed air source (170) connected to the valve (155) and a pressure in the cylinder (125) and wherein two characteristic maps (300) are specified which correspond to different wear states of the valve (155), and interpolation is performed between mass flow values of both characteristic maps (300) depending on the operating time of the valve (155).

Inventors

  • Alain Tierry Chamaken Kamde
  • Wilhelm Moser

Assignees

  • ZF FRIEDRICHSHAFEN AG

Dates

Publication Date
20260513
Application Date
20160419

Claims (8)

  1. Method (200) for controlling an actuating force (F_act) provided by means of a pneumatic actuating device (120), wherein the actuating device (120) comprises a cylinder (125) and a piston (130) displaceably closing the cylinder (125), wherein a mass flow of air at a predetermined pressure into the cylinder (125) can be controlled by means of a valve (155), and wherein the method (200) comprises the following steps: sensing (205) a position (150) of the piston (130) in the cylinder (125); determining (235) a mass flow of air into the cylinder (125); determining (210) a pneumatic pressure in the cylinder (125) based on the mass flow and the position (150); determining (220) an actuating force (F_act) provided at the piston (130) based on the pressure and an effective piston area; and control (225) of the actuation of the valve (155) depending on the provided actuation force (F_act) and a desired actuation force (F_soll), whereby the mass flow rate is determined by means of a characteristic map (300) based on the actuation of the valve (155) and a pressure ratio that exists between the pressure of a compressed air source (170) connected to the valve (155) and a pressure in the cylinder (125) and whereby two characteristic maps (300) are specified which correspond to different wear states of the valve (155), and interpolation is performed between mass flow rate values of both characteristic maps (300) depending on the operating time of the valve (155).
  2. Procedure (200) according to Claim 1 , wherein the pressure prevailing in the cylinder (125) is determined iteratively on the basis of a pressure dynamics equation.
  3. Procedure (200) according to Claim 2 , whereby a change in pressure is determined using the pressure dynamics equation based on the mass flow rate and a change in position (150).
  4. Procedure (200) according to one of the Claims 2 or 3 , where the pressure dynamics equation for increasing x is: p ˙ = 1 A ( x − x m i n ) [ A x ˙ p + m ˙ R s T ] and for falling x: p ˙ = 1 A ( x max − x ) [ A x ˙ p + m ˙ R s T ] ; where p is the pressure in the cylinder (125), A is the effective piston area (130), R s is the specific gas constant of air, m is the mass of air in the cylinder (125), T is the air temperature, x is the position (150) of the piston (130) in the cylinder (125), x min is the minimum position and x max is the maximum position (150) of the piston (130) in the cylinder (125).
  5. Method (200) according to one of the preceding claims, wherein the actuating device (120) controls the engagement or disengagement of a gear stage in a manual transmission (105) and the desired actuating force (F_should) is selected depending on the gear stage.
  6. Method (200) according to one of the preceding claims, wherein a correction factor (k) is determined on the basis of a difference between the determined actuating force (F_act) and the desired actuating force (F_soll) and the actuating of the valve (155) is adjusted by the correction factor in a subsequent control.
  7. Control device (198) for a pneumatic actuating device (120), wherein the actuating device (120) comprises a cylinder (125) and a piston (130) which slidably closes the cylinder (125), and wherein the control device comprises: a scanning device for scanning a position (150) of the piston (130) in the cylinder (125); an interface to a valve (155) for controlling a mass flow of air of a predetermined pressure into the cylinder (125); a processing device which is configured to carry out a method (200) according to one of the preceding claims and to actuate the valve (155) in order to match an actuating force (F_act) provided by the actuating device (120) to a desired actuating force (F_soll).
  8. Control system (100), comprising the control device according to Claim 7 , the actuating device (120) and the valve (155).

Description

The invention relates to a pneumatic control system. In particular, the invention relates to the pneumatic control of a process in a manual transmission. In a mechanical transmission, such as in the drivetrain of a motor vehicle, different gears can be engaged. Engaging or disengaging a gear can be achieved using a pneumatic actuator, which comprises a cylinder and a piston movably mounted within the cylinder. The piston acts via a piston rod on an actuating element, the position of which determines whether the gear is engaged or disengaged. A compressed air source provides air at a predetermined, constant pressure. A valve allows air to be released from the compressed air source into the cylinder, increasing the pressure within the cylinder and exerting a force on the piston, which is then transmitted to the actuating element. The valve actuation can be controlled with varying degrees of force, allowing different mass flow rates of air to pass through the valve. Consequently, the piston in the cylinder moves faster or slower, and the force exerted on the actuating element is greater or lesser. It is desirable to control the actuating force provided by the piston as precisely as possible. If the actuating force is too great, the actuating element can move too quickly, potentially causing mechanical stress on the synchronizer mechanism of the transmission. Conversely, if the actuating force is too small, engaging or disengaging a gear can take longer than necessary, potentially reducing the transmission's shifting dynamics. DE 10 2007 022 126 A1 Disclosing a motor vehicle device with a control and/or regulation unit for controlling and/or regulating a piston-cylinder unit. The motor vehicle device includes a calculation module designed to determine at least one characteristic parameter of the piston-cylinder unit. DE 10 2012 220 496 A1 discloses a method for controlling an automated friction clutch which can be passively closed via a pressure spring and engaged and disengaged via a single-acting pneumatic actuator cylinder. DE 10 2006 058 913 A1 relates to a control device for a gearbox, wherein a double-acting actuating device is controlled by means of associated solenoid valves in such a way that different pressures are set on different sides of a piston. To control the actuation force, the pressure in the cylinder can be measured using a sensor. However, such a sensor is expensive and can be prone to failure. Known techniques for sensorless control of the actuation force do not always achieve sufficiently good results. Furthermore, for such a method, the valve actuation time often has to be determined experimentally, necessitating time-consuming calibration of the procedure. The invention is based on the objective of providing an improved technique for controlling the actuating force of a pneumatic actuator. The invention achieves this objective by means of the subject matter of the independent claims. Dependent claims describe preferred embodiments. An actuating device comprises a cylinder and a piston that slidably closes the cylinder. A valve allows the flow of air at a predetermined pressure into the cylinder to be controlled. A method for controlling an actuating force provided by the pneumatic actuating device includes the steps of sensing the position of the piston in the cylinder; determining the flow rate of air into the cylinder; determining the pneumatic pressure in the cylinder based on the flow rate and the position; determining the actuating force applied to the piston based on the pressure and the effective piston area; and controlling the actuation of the valve depending on the applied actuating force and a desired actuating force. The actuation force can be controlled more precisely, allowing for a good compromise between gentle, slow, and efficient, rapid actuation of a device via the piston. A pressure sensor to determine the pressure in the cylinder is not required. The pressure of the mass flow of air into the valve is assumed to be constant. This pressure, also called system pressure, can be determined by a sensor or estimated using a specific method. By determining the position of the piston relative to the cylinder, feedback can be provided, enabling improved control of the valve to achieve the desired actuation force. The mass flow rate is determined using a characteristic map based on the actuation of the valve and a pressure ratio is determined. The pressure ratio indicates the pressure of a compressed air source connected to the valve relative to the pressure in the cylinder (or vice versa). The characteristic map for the valve can be easily determined, for example, experimentally. Typically, several valves are used in a control device, such as the one used to control the transmission described above. These valves may be identical in design and therefore may all share the same characteristic map. Even larger or more complex control systems can thus be designed relatively easily