Pneumatic control

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_soll), ; 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).

Description

[0001] The invention relates to a pneumatic control system. In particular, the invention relates to the pneumatic control of a process in a manual transmission.

[0002] 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.

[0003] 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.

[0004] DE 10 2007 022 126 A1 discloses a motor vehicle device with a control and / or regulating unit for controlling and / or regulating a piston-cylinder unit. The motor vehicle device has a calculation module that is designed to determine at least one characteristic parameter of the piston-cylinder unit.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] The mass flow rate is determined using a characteristic map based on the valve actuation and a pressure ratio. The pressure ratio specifies the pressure of a compressed air source connected to the valve relative to the pressure in the cylinder (or vice versa).

[0012] 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. By using the characteristic map, the mass of air in the cylinder can be determined simply and accurately at any given time.

[0013] It is particularly advantageous to determine the pressure in the cylinder iteratively based on a pressure dynamics equation. A differential equation can be used for this purpose, with a portion of the result serving as the new input for the determination in a subsequent iteration. This allows for rapid stabilization of the pressure readings and enables quick and accurate determination of the air pressure in the cylinder.

[0014] Using the pressure dynamics equation, a change in pressure can be determined based on the mass flow rate and a change in position. The determined absolute position of the piston can also be used as an input variable for the pressure dynamics equation. The pressure in the cylinder can then be determined by integrating the pressure change over time.

[0015] In a particularly preferred embodiment, the actuating device controls the engagement or disengagement of a gear in a manual transmission, with the desired actuating force being selected depending on the gear. In this way, the manual transmission can be controlled with exceptional sensitivity yet precision. A desired actuating force can be individually predefined for each gear, allowing for an optimal compromise between rapid and forceful or slow and gentle actuation for each gear.

[0016] Two characteristic curves are provided, corresponding to different wear states of the valve. For example, the first curve might correspond to a new valve. When determining the mass flow rate, interpolation between mass flow rates from both curves can be performed, depending on the valve's operating time and, if applicable, a projected service life. To do this, a first mass flow rate value can be determined using the first curve, and a second mass flow rate value using the second curve. A point between these determined mass flow rates can then be calculated based on the percentage of the valve's service life achieved, for example, using linear regression. The mass flow rate determined in this way can be used in the procedure described above. The valve's wear behavior can thus be modeled to achieve further improved determination or control results.

[0017] In yet another embodiment, a correction factor can be determined based on the difference between the specified actuation force and the desired actuation force, and the valve actuation can be adjusted by this factor during subsequent control. This allows for adaptive adjustment of the valve actuation, enabling, for example, automatic compensation of valve backlash—that is, mechanical play between an actuation device, particularly an electrical one, and a mechanical mass flow control mechanism. The correction factor is preferably applied by multiplying a specific output variable of the process by the correction factor. The valve can be controlled electrically via modulation.In the case of pulse frequency modulation (PFM), the output variable can include a frequency, and in the case of pulse width modulation (PWM), a pulse width or a pulse width ratio ("duty cycle").

[0018] A control device for the pneumatic actuating device described above comprises a scanning device for scanning a position of the piston in the cylinder; an interface to a valve for controlling a mass flow of air of a predetermined pressure into the cylinder; a processing device configured to perform the procedure described above; and to actuate the valve to match an actuating force provided by the actuating device to a desired actuating force.

[0019] The processing unit can be implemented, in particular, as a programmable microcomputer or microcontroller. The processing unit can also perform other control tasks, for example, further processes during gear changes in a manual transmission.

[0020] A control system comprises the control device described above, the actuating device and the valve.

[0021] The invention will now be described in more detail with reference to the attached figures, in which: Fig. 1 a control system for a manual transmission; Fig. 2. A flowchart of a procedure; and Fig. 3 an exemplary characteristic curve for the procedure of Fig. 2 represents.

[0022] Fig. Figure 1 shows a control system 100 for a manual transmission 105. The manual transmission 105 can be arranged, in particular, in the drivetrain of a motor vehicle. For example, the manual transmission 105 can comprise a main transmission 110 and a range group 115 and be configured for use in a commercial vehicle. An actuating device 120, comprising a cylinder 125 and a piston 130, is provided for engaging or disengaging a gear in the main transmission 110 or the range group 115. Essentially, any actuating device 120 can be used for the technology presented here, and not only one of those shown here as an example. The design of the manual transmission 105 can differ from the design described.

[0023] In the illustrated embodiment, the actuating device 120 associated with the main transmission 110 comprises, in addition to the piston 130, a trailing piston 135. The piston 130 acts, for example via a piston rod 140 and an actuating element 145, on the respective transmission part 110, 115. If the pressure conditions inside the cylinder 125 are changed, the actuating device 120, by means of the piston 130, provides an actuating force that seeks to change a position 150, also designated x below, relative to the cylinder 125. The illustrated actuating device 120 with the trailing piston 135 is configured to move into one of three positions 150, which are marked 1, N, and 2. Position N can correspond to neutral, and the other two positions, 1 and 2, can each influence a gear engaged in the transmission 105.Positions 1 and 2 shown can each correspond to several gear steps, one of which can be selected depending on a further actuating device 120. The other actuating device 120 shown is configured to control one of two positions 150, designated H and L, on the area group 115.

[0024] In an exemplary manner, both actuating devices 120 shown are designed to be double-acting; however, single-acting versions are also possible. Each actuating device 120 is provided with at least one valve 155 to admit a volume flow of air into a chamber of the actuating device 120, which is slidably closed by means of the piston 130. The valves 155 are usually designed as 3 / 2-way valves. In the present embodiment, the actuating device 120 associated with the main gearbox 110 also has check valves 160 due to the use of the sliding piston 135; the function of these check valves will not be discussed further below.

[0025] One of the valves 155 is preferably configured to be electrically actuated. For this purpose, the valve 155 comprises a coil 165 which, when an electric current flows through it, deflects a flow element of the valve 155, thus enabling or preventing the flow of a mass flow through the valve 155. The valve 155 is preferably a switching valve that can only assume a fixed number (here two) of predetermined states. The coil 165 can be controlled by modulation to periodically open and close the valve 155, resulting in a predetermined average mass flow through the valve 155. In one embodiment, pulse frequency modulation is used for this purpose, in another, pulse width modulation. In another embodiment, not shown, the valve 155 can also comprise a continuous valve whose flow behavior is proportional to the current through the coil 165.

[0026] The valves 155 are supplied from a compressed air source 170, which is configured to provide air at a predetermined, constant pressure p1, also called system pressure. In the illustrated embodiment, the compressed air source 170 comprises a compressor 175, a pressure reducer 180, and an optional pressure accumulator 185. However, the compressed air used to supply the valves 155 can also be obtained from any other source.

[0027] The control of electrical currents through the individual coils 165, in order to actuate the respective valve 155, is effected by means of a processing unit 190. The processing unit 190 is connected to a scanning unit 192, which is provided on the actuating unit 120, to scan the position 150 of the piston 130 relative to the cylinder 125, wherein the position 150 is preferably determined analogously, i.e., continuously over the entire available travel. If digital scanning is used, a sufficiently large number of discrete positions 150 should be distinguishable in order to apply the technique presented here with good results. In the illustration of Fig. For better illustration, the scanning devices 192 and connections to the coils 165 are only shown at the actuating device 120, which is assigned to the area group 115.

[0028] An interface 195, in particular a separable electrical interface 195, can be provided between the processing device 190 and a coil 165 of a valve 155. The processing device 190, the scanning device 192 and the interface 195 together form a control device 198.

[0029] Fig. Figure 2 shows a flowchart of a method 200. The method 200 is preferably configured to run on the control device 198 and, in particular, on the processing unit 190, in order to control the provision of an actuating force by means of an actuating device 120. The depicted method 200 is preferably executed iteratively, with the result of one iteration being used as the input for a subsequent iteration. The method 200 is based on the idea that the change in pressure in the cylinder 125 over time can be expressed as a differential equation, which can also be called the pressure dynamics equation.

[0030] The following applies to the switching in the direction of smaller position values ​​x: p˙=1A(xmax−x)[Ax˙p+m˙RsT]

[0031] For switching towards larger position values ​​x, the following applies: p˙=1A(x−xmin)[Ax˙p+m˙RsT]

[0032] This includes: p the pressure in the cylinder 125 A the effective piston area of ​​the piston 130 R s the specific gas constant of air: 287.058 J kg⋅K m the mass of air located in cylinder 125 T is the temperature of the air in the cylinder 125 x the position 150 of the piston 130 in the cylinder 125 x min the minimum position 150 of the piston 130 in the cylinder 125 x max The maximum position 150 of the piston 130 in the cylinder 125.

[0033] The procedure 200 can be initiated in step 205, in which the position x of the piston 130 in the cylinder 125 of the actuating device 120 under consideration is determined. In this step, a derivative of the position 150 with respect to time can also be determined, which corresponds to a movement velocity of the piston 130 in the cylinder 125. In a subsequent step 210, the pressure dynamics of the actuating device 120 are determined, for which one of the equations mentioned above is used. This requires a mass flow rate flowing through the valve 155 or into the cylinder 125, which may have been determined in a previous iteration of the procedure 200 or may be set to a predetermined initial value.

[0034] The change in pressure over time determined in step 210 is integrated over time in step 215 to determine the pressure prevailing in cylinder 125. This determined pressure can then be provided to step 210 for a subsequent iteration of procedure 200. In step 220, the applied actuating force F_act can be determined based on the effective area A of piston 130. The effective area A is a constant parameter of the actuating device 120 and can be assumed to be known.

[0035] In step 225, the provided actuating force F_act is regulated by determining a control variable for the valve 155 based on a difference between the determined actuating force F_act and a desired actuating force F_soll.

[0036] If the timing behavior or control play of the valve 155 does not allow, or only allows with difficulty, the control proposed here, the difference between the determined actuating force F_act and the desired actuating force F_soll can be used to determine a correction factor k. The control variable determined in step 225, which is used to set a current through a coil 165 of a valve 155, can be multiplied by the correction factor k in a subsequent iteration of the procedure 200 to achieve an improved control result.

[0037] In step 230, the specified control variable is converted to actuate the valve 155. For example, a desired voltage or electrical current through the coil 165 can be converted into an actuation frequency in the case of PFM or into a pulse width ratio in the case of PWM.

[0038] In step 235, a mass flow rate of air flowing through the valve 155 is determined based on the specified actuation. The mass flow rate is preferably determined using a two-dimensional characteristic map that maps two input variables to the output mass flow rate. One input variable corresponds to the actuation determined in step 230, and the other input variable is a ratio between the system pressure p1, supplied by compressed air source 170, and the pressure prevailing in the cylinder 125. This pressure ratio can be determined based on the pressure determined in step 215, given the system pressure p1. In another embodiment, the pressure ratio can also be derived from the specified actuation force. The provided mass flow rate is typically expressed in kg / s, thus indicating the mass of air flowing through the valve 155 per unit of time during the selected actuation.

[0039] Fig. Figure 3 shows an example characteristic map 300 for step 235 of procedure 200 of Fig. 2. A first input variable 305 relates to the actuation of the valve 155. This assumes a frequency-modulated control of the coil 165 of the valve 155, so the frequency in Hertz is specified as the first input variable 305. A second input variable 310 relates to the ratio of the pressure prevailing in the cylinder 125 and the system pressure p1, which is supplied by the compressed air source 170. Fig. 1 can be provided. The system pressure p1 is preferably in the denominator. As a ratio of two pressures, this quantity has no unit.

[0040] In the vertical direction, an output quantity 315 is applied, which corresponds to the mass flow rate of the air flowing through the valve 155. Since the system pressure p1 is constant and the pressure in the cylinder 125 is usually very small in comparison, the valve 155 is practically always operated in the supercritical range, resulting in a constant mass flow rate.

[0041] In a further embodiment, different characteristic maps 300 can be provided, which express different wear states of the valve 155. A first characteristic map 300 can, for example, relate to a new valve 155 and a second characteristic map 300 to a valve 155 at the end of its projected service life, for example, after an operating time of 2000 hours. Using the first characteristic map 300, a first mass flow rate can then be determined, and using the second characteristic map 300, a second mass flow rate can be determined. If the current operating time of the valve 155 is, for example, 200 hours, meaning the valve 155 has reached approximately 10 percent of its projected service life, a point can be determined between the two defined mass flow rates, the distance of which to the first mass flow rate is one-tenth and to the second mass flow rate is nine-tenths.This point then represents the mass flow rate, which was determined using the characteristic maps 300 as a function of the wear behavior of the valve 155. Reference sign 100 tax system 105 manual transmission 110 Main gearbox 115 Area Group 120 Actuating device 125 cylinders 130 pistons 135 trailing pistons 140 piston rod 145 Actuating element 150 position 155 valve 160 shut-off valve 165 Coil 170 Compressed air source 175 Compressor 180 pressure reducers 185 pressure accumulators 190 processing equipment 192 scanning device 195 interface 198 Control device 200 procedures 205 Determine position x 210 Pressure dynamics: Determining dp / dt 215 Integrating with time 220 Determine actuating force F_act 225 rules Convert 230 235 Determine mass flow 300 map 305 first input size 310 second input size 315 Initial size

Claims

[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 of 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); Determine (220) an actuating force (F_act) provided at the piston (130) on the basis of 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); 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). [2] Method (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] Method (200) according to claim 2, wherein a change in pressure is determined by means of the pressure dynamics equation on the basis of the mass flow and a change in position (150). [4] Method (200) according to one of claims 2 or 3, wherein the pressure dynamics equation for increasing x is: p˙=1A(x−xmin)[Ax˙p+m˙RsT] and for falling x: p˙=1A(xmax−x)[Ax˙p+m˙RsT]; where p is the pressure in the cylinder (125), A is the effective piston area (130), R s the specific gas constant of air, m the mass of air in the cylinder (125), T the air temperature, x the position (150) of the piston (130) in the cylinder (125), x min the minimum and x max 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).

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