Control device for a gas generator for controlling a volume flow, as well as impact protection system and method for operating such a control device

Description

[0001] The invention relates to a control device for a gas generator for controlling the volume flow of a pressurized fluid for filling an airbag of a motor vehicle, comprising a valve arrangement. The valve arrangement includes a main valve with a main valve body having a through-hole and a main valve piston axially movable in the through-hole of the main valve body, as well as an electrically actuated pilot valve with a pilot valve piston and a pilot valve inlet bore. The main valve piston divides the through-hole into a control chamber, fluidically connected to the pilot valve via the pilot valve inlet bore, and a pre-chamber, fluidically connected to the gas generator. The main valve has a bypass channel that fluidly connects the pre-chamber and the control chamber.Within the main valve body, at least one drain bore branches off from the through-opening for draining the fluid into the airbag. By means of the fluid and depending on the position of the pilot valve piston, the main valve piston closes the at least one drain bore in a first operating position and opens the at least one drain bore in a second operating position. The invention further relates to an impact protection system for a motor vehicle with a gas generator for storing a fluid under pressure and an airbag. The gas generator is configured to supply the fluid to the airbag in response to an activation signal. The invention also includes a control device for controlling a volume flow of the fluid stored under pressure. The pre-chamber of the through-opening of the main valve is fluidically connected to a fluid outlet channel of the gas generator.Furthermore, the invention relates to a method for operating such a control device.

[0002] For many years, personal protective equipment, particularly impact protection systems designed as restraint systems, has been used in motor vehicles to protect occupants in the event of an accident. These systems aim to prevent injuries to the occupants or at least reduce their severity. Airbags are commonly used for this purpose. The airbag itself, which cushions the occupant in the event of a collision, is filled with a fluid, usually a gas. The airbag inflates within a short timeframe of 10 to 50 ms as the fluid flows in, creating a cushion between the occupant and parts of the vehicle's interior. This prevents the occupant from impacting hard interior components such as the steering wheel.

[0003] The fluid is regularly supplied in a gas generator at a high pressure between 50 bar and 1000 bar. The gas generator can be a so-called hot gas generator, in which the fluid is produced by a pyrotechnic combustion reaction, or a so-called cold gas generator, in which a pressurized fluid is already stored. A combined design as a hybrid gas generator is also possible.

[0004] The impact protection system typically activates shortly after the impact, meaning only after the collision has already occurred. However, impact protection systems are also being planned that use suitable sensors and signal analysis to detect a point in time when an impact is unavoidable. This point in time lies in the so-called pre-crash phase, and thus before the actual impact. The intention is to use this information to activate the impact protection system even before the impact, thereby providing even better protection for vehicle occupants against injury.

[0005] The use of two-stage or multi-stage gas generators is planned, particularly for this application. Here, a control device with a valve arrangement regulates the flow rate, delivering a specific volume of fluid in two or more successive phases and introducing it into the airbag. The corresponding opening and closing movements of the control device must occur within a few milliseconds and operate against high fluid pressures.

[0006] A control device and an impact protection system of the type mentioned above are disclosed, for example, in DE 10 2015 209 019 A1. The impact protection system for a motor vehicle comprises a gas generator for storing a gas under pressure and an airbag, as well as a control device for controlling the volume flow of the pressurized gas into the airbag. The control device comprises a main valve in whose main valve body a stepped through-hole is provided and a main valve piston axially guided in the through-hole of the main valve body and correspondingly stepped. The control device also includes an electrically actuated pilot valve with a pilot valve piston and a pilot valve inlet bore.The main valve piston divides the through-opening into a control chamber, fluidically connected to the pilot valve via the pilot valve inlet bore, and a pre-chamber, fluidically connected to the fluid outlet channel of the gas generator. The main valve has a bypass channel that fluidly connects the pre-chamber and the control chamber. Within the main valve body, a drain bore for releasing the gas into the airbag branches off from the through-opening. By means of the gas and depending on the position of the pilot valve piston, the main valve piston closes the at least one drain bore in a closed position and opens the at least one drain bore in an open position.

[0007] A disadvantage of such a control device, however, is that the fluid pressure actually building up in the control chamber deviates to a relatively large extent from the activation pressure required for the main valve piston to perform an opening and / or closing movement, and thus ultimately for opening and closing the drain bore. This results in a correspondingly long response time of the main valve piston.

[0008] Therefore, a first object of the invention is to provide a control device for a gas generator for controlling the volume flow of a pressurized fluid for filling an airbag of a motor vehicle, which ensures a rapid response of the main valve piston and thus a rapid opening and closing of the drain bore. A second object of the invention is to provide an impact protection system for a motor vehicle with a control device in which a rapid response of the main valve piston and thus a rapid opening and closing of the drain bore is ensured. A third object of the invention is to provide a method for operating a control device by which a rapid response of the main valve piston and thus a rapid opening and closing of the drain bore is enabled.

[0009] The first problem is solved according to the invention by the features of claim 1. Advantageous embodiments and further developments of the invention are set out in the dependent claims and the following description.

[0010] Accordingly, a control device for a gas generator for controlling a volume flow of a pressurized fluid for filling an airbag of a motor vehicle comprises a valve arrangement, wherein the valve arrangement includes a main valve with a main valve body having a through-hole and a main valve piston axially movable in the through-hole of the main valve body, as well as an electrically actuated pilot valve with a pilot valve piston and a pilot valve inlet bore. The main valve piston divides the through-hole into a control chamber fluidically connected to the pilot valve via the pilot valve inlet bore and a pre-chamber fluidically connected to the gas generator, wherein the main valve has a bypass channel that fluidically connects the pre-chamber and the control chamber.Within the main valve body, at least one drain bore branches off from the through-hole for draining the fluid into the air bag, wherein, by means of the fluid and depending on a position of the pilot valve piston, the main valve piston closes the at least one drain bore in a first operating position and releases the at least one drain bore in a second operating position.

[0011] According to the invention, the valve arrangement for reducing the response time of the main valve piston includes a means for controlling a fluid pressure in the control chamber, wherein the means for controlling a fluid pressure is configured to bring or maintain the fluid pressure in the control chamber at a pressure which lies within a predetermined tolerance range around an activation pressure of the main valve piston.

[0012] The invention is based on the premise that particularly rapid filling of the airbag, and thereby the most precise possible filling with a predetermined fluid quantity in the individual phases, depends in particular on the respective activation time of the main valve piston. Furthermore, the invention is based on the premise that the fluid pressure actually building up in the control chamber of the main valve until the next opening or closing movement of the main valve piston, and in particular the degree of deviation from the respective activation pressure of the main valve piston required to carry out the corresponding movement, have a significant influence on the activation time of the main valve piston.Therefore, the invention provides a means for controlling the fluid pressure in the control chamber, wherein the means is configured to bring or maintain the fluid pressure in the control chamber at a pressure which is within a predetermined tolerance range around the activation pressure of the main valve piston, in particular approximately corresponding to the activation pressure of the main valve piston.

[0013] The embodiment according to the invention has the advantage that it provides a control device that ensures a rapid response of the main valve piston and thus a rapid opening and closing of the drain bore.

[0014] Essentially, the electrically controlled pilot valve regulates the movement and thus the position of the main valve piston, and consequently, in particular, the volume flow into the airbag. Preferably, the pilot valve is designed as a solenoid valve. Furthermore, the pilot valve can be designed as a normally closed pilot valve and include a compression spring that biases the pilot valve piston into a closed position, i.e., a position in which the pilot valve piston seals the pilot valve inlet bore. Alternatively, the pilot valve can be designed as a normally open pilot valve. In this case, the pilot valve is actively held closed by energizing it and opened by removing the energizer. Advantageously, a compression spring is provided to bias the pilot valve into a defined open position.

[0015] The activation pressure of the main valve piston is the theoretical pressure required to move the main valve piston. This includes movement towards both the first operating position and the second operating position. For movement towards the first operating position, the activation pressure of the main valve piston is the minimum pressure within the control chamber necessary to move the main valve piston into the first operating position. For movement towards the second operating position, the activation pressure of the main valve piston is the maximum pressure within the control chamber required to move the main valve piston into the second operating position.

[0016] Furthermore, the activation pressure value can vary, particularly depending on the fluid pressure provided by the gas generator at the respective time, and decrease accordingly if the fluid pressure provided by the gas generator decreases, especially over the period of filling the air bag.

[0017] The pressure that lies within a specified tolerance range around the activation pressure of the main valve piston is a pressure that is preferably as close as possible to the activation pressure of the main valve piston, without exactly matching it. In particular, this refers to the pressure that is as close as possible to the activation pressure, but just short of causing movement of the main valve piston.

[0018] The specified tolerance range defines the limits within which the fluid pressure in the control chamber is adjusted or maintained around the activation pressure of the main valve piston. Depending on the operating position of the main valve piston, this can be either an upper or a lower limit. Thus, when the main valve piston is in the first operating position, the specified tolerance range defines an upper limit; when the main valve piston is in the second operating position, the specified tolerance range defines a lower limit.

[0019] The volumetric flow rate of the fluid, in particular a gas, is defined by the volume of the fluid that flows through a specific cross-section per unit of time (V / t).

[0020] Through the overflow channel of the main valve, which fluidically connects the pre-chamber and the control chamber, the fluid can flow, in particular, from the valve chamber into the control chamber, whereby a certain volume flow can flow through the overflow channel mainly depending on a pressure difference between the valve chamber and the control chamber.

[0021] When the gas generator is activated and pressurized fluid is supplied, the fluid pressure in the pre-chamber rises and moves the main valve piston into the second operating position, where it opens at least one outlet port. Fluid flows into the control chamber via the overflow channel, thus exerting fluid pressure on the main valve piston from the control chamber as well. Due to the pressure conditions in the control chamber and the valve chamber, and depending on the geometric design of the main valve body, corresponding forces act on the main valve body from both chambers, causing the main valve piston to move accordingly in the event of an imbalance of forces.

[0022] In an advantageous embodiment, the activation pressure depends on the fluid pressure provided by the gas generator at the respective time, wherein the activation pressure preferably decreases accordingly with a decrease in the fluid pressure provided by the gas generator over the period of filling the air bag.

[0023] In a further advantageous embodiment, the means for controlling a fluid pressure is designed to bring or maintain the fluid pressure in the control chamber at the respective pressure which lies within a predetermined tolerance range around the respective activation pressure of the main valve piston.

[0024] In a further advantageous embodiment, the means for controlling the fluid pressure is designed as an electrical control device that supplies the pilot valve with a control signal in pulse-width modulated form. Depending in particular on the duty cycle, i.e., the ratio between the pulse duration and the period of the control signal, this causes a corresponding alternating and brief opening and closing of the pilot valve, more precisely the pilot valve inlet bore, over a specific period. For example, during the brief opening phases, a corresponding volume flow of fluid can be discharged from the control chamber via the pilot valve inlet bore, thus reducing the fluid pressure in the control chamber. In this way, the fluid pressure in the control chamber can be maintained at a specific pressure that deviates only slightly from the activation pressure of the main valve piston.This significantly reduces the activation time of the main valve piston for the next opening or closing movement, or ensures a fast response of the main valve piston.

[0025] In a further advantageous embodiment, the means for controlling the fluid pressure is a pressure reducer arranged on and / or in the main valve. The pressure reducer advantageously comprises a valve with an inlet side and an outlet side and a pressure sensor, wherein the pressure sensor detects the pressure prevailing in the control chamber, and wherein at least the valve is arranged, for example, in a bore in the main valve body or in the main valve piston, particularly in the overflow channel. The valve is expediently arranged with its outlet side adjacent to the control chamber. The pressure reducer ensures, in particular, that a specific fluid pressure, which deviates only slightly from the activation pressure of the main valve piston, is not exceeded in the control chamber.As the pressure in the control chamber increases, the valve is gradually closed until the desired fluid pressure is reached and the valve is completely closed. Alternatively or additionally, the means for controlling the fluid pressure can also be a pressure compensator or a flow control valve located on and / or in the main valve.

[0026] In a further advantageous embodiment, the pressure reducer comprises a valve with an inlet side and an outlet side, wherein the valve is arranged in a bore in the main valve body or in the main valve piston and with its outlet side adjacent to the control chamber, and wherein the valve is designed such that the fluid pressure in the control chamber, which lies within a predetermined tolerance range around the activation pressure of the main valve piston, is not exceeded.

[0027] The pressure reducer is preferably designed such that, in the event of a pressure increase in the control chamber, the valve is gradually closed further and further, and that when the fluid pressure in the control chamber is reached, which lies within a predetermined tolerance range around the activation pressure of the main valve piston, the valve is essentially completely closed.

[0028] The means for controlling the fluid pressure can also be expediently designed as a combination of a pressure reducer and / or a pressure balance and / or a flow control valve with an electrical control device that supplies the pilot valve with a control signal in pulse width modulated form.

[0029] In a further advantageous embodiment, the overflow channel is designed as a piston bore in the main valve piston. Through the piston bore, the fluid can flow from the valve chamber into the control chamber and thus to the opposite side of the piston, whereby a specific volume flow rate can flow through the piston bore, particularly depending on a pressure difference between the valve chamber and the control chamber.

[0030] In a further advantageous embodiment, the main valve piston has a first pressure-acting surface facing the control chamber and a second pressure-acting surface facing the pre-chamber, the first pressure-acting surface being larger than the second pressure-acting surface. The different sizes of the pressure-acting surfaces of the main valve piston can be achieved, for example, by different diameters of the main valve piston in the control chamber region and in the pre-chamber region. A force equilibrium results from the area ratios of these diameters of the main valve piston, provided that the fluid pressure in the control chamber is correspondingly lower than the fluid pressure in the pre-chamber. The main valve piston can thus switch, i.e., be activated, at the latest when the fluid pressure in the control chamber and in the pre-chamber is equal, and in particular move into the first operating position in which it closes the at least one drain bore.

[0031] In a further advantageous embodiment, the valve arrangement includes a pressure sensor for detecting the fluid pressure prevailing in the control chamber. Preferably, the pressure sensor is arranged in the control chamber in order to detect the fluid pressure directly within the control chamber. In an embodiment of the means for controlling the fluid pressure as a pressure reducer arranged on and / or in the main valve, wherein the pressure reducer includes a pressure sensor, the pressure sensor is in particular formed by the pressure sensor of the pressure reducer.

[0032] In a further advantageous embodiment, the specified tolerance range is defined by a maximum permissible deviation from the activation pressure, wherein the specified tolerance range or the maximum permissible deviation is 30%, preferably 20%, preferably 10%. This enables a particularly fast response of the main valve piston.

[0033] The second problem is solved according to the invention by the features of claim 8.

[0034] The impact protection system according to the invention for a motor vehicle comprises a gas generator for storing a fluid under pressure and an airbag, wherein the gas generator is configured to supply the fluid to the airbag in response to an activation signal. The impact protection system has a control device according to the invention for controlling a volume flow of the pressurized fluid for filling the airbag, wherein the pre-chamber of the through-opening of the main valve is fluidically connected to a fluid outlet channel of the gas generator.

[0035] The advantages and preferred embodiments described for the control device according to the invention also apply accordingly to the impact protection system according to the invention.

[0036] Advantageously, the impact protection system further includes at least one sensor which, during an impact and / or in the time prior to an impact, detects parameters for calculating a likely impact trajectory and transmits them to a control unit which is specifically designed to determine the likely impact trajectory from the detected parameters and, based on this, the required volume flow of fluid into the airbag at each point in time during the impact trajectory.

[0037] The third problem is solved according to the invention by the features of claim 9.

[0038] The inventive method for operating a control device according to the invention comprises the following steps: Providing a pressurized fluid; and controlling the fluid pressure in the control chamber using the means to control a fluid pressure to a pressure within a predetermined tolerance range around the activation pressure of the main valve piston in order to reduce the response time of the main valve piston.

[0039] The advantages and preferred embodiments described for the control device according to the invention also apply accordingly to the method according to the invention.

[0040] In an advantageous embodiment, the activation pressure depends on the fluid pressure provided by the gas generator at the respective time; preferably, the activation pressure decreases accordingly with a decrease in the fluid pressure provided by the gas generator over the period of filling the air bag, wherein in the step of controlling the fluid pressure in the control chamber, the fluid pressure in the control chamber is brought to or held at the respective pressure which lies within a predetermined tolerance range around the respective activation pressure of the main valve piston.

[0041] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 shows a schematic longitudinal section of an impact protection system, Fig. 2 a schematic diagram showing various pressure profiles of the impact protection system. Fig. 1as a function of time, and Fig. 3 a flowchart of a method for operating the control device of the impact protection system from Fig. 1 .

[0042] Corresponding parts in all figures are always marked with the same reference symbols.

[0043] In Fig. 1A schematic sectional view illustrates an embodiment of an impact protection system 1. The impact protection system 1 for a motor vehicle comprises a gas generator 2, designed as a cold gas generator, for storing a gaseous fluid under pressure, and an airbag 3. The gas generator 2 is configured to supply the fluid to the airbag 3 in response to an activation signal. For this purpose, the gas generator 2 has a rupture disc-type closure element (not shown) for closing a fluid outlet channel 4 of the gas generator 2. In the event of an impact, the closure element is destroyed, allowing the pressurized fluid to escape from the gas generator 2.

[0044] The impact protection system 1 further comprises a control device 5 for controlling a volume flow of the pressurized fluid for filling the airbag 3, wherein the control device 5 includes a valve arrangement 6.

[0045] The valve arrangement 6 comprises a main valve 7 with a main valve body 8 having a through-opening 9 and a main valve piston 10 axially movable in the through-opening 9 of the main valve body 8.

[0046] Furthermore, the valve arrangement 6 comprises an electrically actuated pilot valve 11 with a pilot valve piston 12 and a pilot valve inlet bore 13. The pilot valve piston 12 interacts with the pilot valve inlet bore 13 and closes or opens the pilot valve inlet bore 13 depending on its position. The pilot valve 11 also includes a stationary pole piece 14 and a movable armature 15, the armature 15 being coupled to the pilot valve piston 12. The armature 15 thus transmits its movement to the pilot valve piston 12. To induce the movement of the armature 15, the pilot valve 11 includes a coil 16, which is energized for this purpose. When the coil 16 is activated, a magnetic field is generated in the magnetic circuit, and a magnetic force is created between the armature 15 and the pole piece 14. This magnetic force moves the armature 15 and thus the pilot valve piston 12.

[0047] The main valve piston 10 of the main valve 7 divides the through-opening 9 into a control chamber 17, which is fluidically connected to the pilot valve 11 via the pilot valve inlet bore 13, and a pre-chamber 18, which is fluidically connected to the fluid outlet channel 4 of the gas generator 2. Furthermore, the main valve 7 has a bypass channel 19 designed as a piston bore in the main valve piston 10, which fluidically connects the pre-chamber 18 and the control chamber 17.

[0048] The main valve piston 10 has a first pressure-acting surface 20 facing the control chamber 17 and a second pressure-acting surface 21 facing the pre-chamber 18, the first pressure-acting surface 20 being larger than the second pressure-acting surface 21. The different sizes of the pressure-acting surfaces 20 and 21 of the main valve piston 10 can be achieved, for example, by different diameters of the main valve piston 10 in the region of the control chamber 17 and in the region of the pre-chamber 18. A force equilibrium results from the area ratios of these diameters of the main valve piston 10, provided that the fluid pressure in the control chamber 17 is correspondingly lower than the fluid pressure in the pre-chamber 18. The main valve piston 10 can thus switch, i.e., be activated and move into a first operating position, at the latest when the fluid pressure in the control chamber 17 and in the pre-chamber 18 is equal.

[0049] Within the main valve body 8, a drain bore 22 branches off from the through-opening 9 for draining the fluid into the air bag 3. By means of the fluid or the fluid pressure, and depending on the position of the pilot valve piston 12, the main valve piston 10 closes the drain bore 22 in a first operating position and opens the drain bore 22 in a second operating position.

[0050] To reduce the response time of the main valve piston 10, the valve arrangement 6 includes a means 23 for controlling the fluid pressure in the control chamber 17. The means 23 is configured to bring the fluid pressure in the control chamber 17 to or maintain a pressure that lies within a predetermined tolerance range of 30% around the activation pressure of the main valve piston 10. The means 23 for controlling the fluid pressure is designed as an electrical control device that supplies the pilot valve 11 with a control signal in pulse-width modulated form. Depending in particular on the duty cycle, i.e., the ratio between the pulse duration and the period of the control signal, this causes the pilot valve piston 12 to move several times over a specific period, thus resulting in a corresponding alternating and brief opening and closing of the pilot valve 11, more precisely, the pilot valve inlet bore 13.For example, during the short opening phases, a corresponding volume flow of fluid can be discharged from the control chamber 17 via the pilot valve inlet bore 13, thus reducing the fluid pressure in the control chamber 17. In this way, the fluid pressure in the control chamber 17 can be maintained within the specified tolerance range, and therefore at a pressure that deviates only slightly from the activation pressure of the main valve piston 10. This significantly reduces the activation time of the main valve piston 10 for the next opening or closing movement, ensuring a rapid response of the main valve piston 10.

[0051] The impact protection system 1 functions as follows: The pilot valve 11 is designed as a normally open pilot valve 11, meaning that the pilot valve piston 12 remains in any position when the coil 16 is de-energized. The pilot valve piston 12 can be moved into an open position without magnetic force or the required current. When current is applied, the pilot valve piston 12 is in a closed position.

[0052] After activation of the gas generator 2, the fluid pressure in the through-opening 9 and thus in the pre-chamber 18 increases. The pilot valve 11 closes, and the pilot valve piston 12 moves into a closed position. The fluid pressure is present at the second pressure-acting surface 21 of the main valve piston 10.

[0053] The main valve piston 10 is thereby pressed axially towards the control chamber 17. This initially opens the drain bore 22 and discharges fluid into the air chamber 3. Due to the back pressure on the main valve piston 10 in the pre-chamber 18, the fluid also flows through the overflow channel 19 into the control chamber 17. This increases the fluid pressure in the control chamber 17. Upon reaching the activation pressure, which in this case is the minimum pressure required to move the main valve piston 10 into its first operating position and thus into the closed position, the main valve piston 10 moves towards the pre-chamber 18 and the drain bore 22 is closed.

[0054] In the next step, when the pilot valve 11 is opened, i.e., the pilot valve piston 12 is pushed into the open position, fluid flows out of the control chamber 17 via the pilot valve inlet bore 13, and the fluid pressure in the control chamber 17 decreases. Upon reaching the activation pressure, which is the pressure required to move the main valve piston 10 into the second operating position and thus into the open position, the main valve piston 10 moves towards the control chamber 17, and the drain bore 22 is opened, metering fluid to the drain bore 22 and subsequently into the air bag 3.

[0055] After the drain bore 22 opens, the means 23 for controlling the fluid pressure in the control chamber 17 causes the pilot valve piston 12 to move several times, thus resulting in a corresponding alternating and brief opening and closing of the pilot valve 11, more precisely the pilot valve inlet bore 13. In this way, the fluid pressure in the control chamber 17 is maintained within the specified tolerance range and thus at a pressure that deviates only slightly from the activation pressure of the main valve piston 10. This significantly reduces the activation time of the main valve piston 10 for the next closing movement and ensures a rapid response of the main valve piston 10.

[0056] The process of opening and closing the drain bore 22 is repeatable and is carried out in particular depending on the impact profile, thus enabling a controlled metering of the fluid into the airbag 3 adapted to the impact. In the embodiment shown here, the means 23 for controlling the fluid pressure only acts after the pilot valve 11 has been actively opened for the first time and the resulting opening of the main valve 7 or main valve piston 10. However, it is also possible for the means 23 to control the fluid pressure to act for the first time and / or additionally after one or each subsequent opening of the pilot valve 11 and the resulting opening of the main valve piston 10. Furthermore, it is possible for the means 23 to control the fluid pressure to act alternatively or additionally after the pilot valve 11 has been closed and the main valve piston 10 has closed.

[0057] Fig. 2shows a schematic diagram illustrating various pressure profiles of the impact protection system 1. Fig. 1 represents as a function of time t.

[0058] The pressure curve of the gas generator fluid pressure, i.e., the fluid pressure prevailing in and available from gas generator 2, is designated with reference numeral 31. A pressure curve of the control chamber fluid pressure, i.e., the fluid pressure prevailing in control chamber 17, is designated with reference numeral 32. The graph designated with reference numeral 33 represents the activation pressure required to initiate the main valve piston 10 to perform an opening and / or closing movement, and thus ultimately to open and close the drain bore 22. The activation pressure 33 is therefore the theoretical pressure within control chamber 17 required to move the main valve piston 10. This includes movement in the direction of both the first operating position and the second operating position.

[0059] In the following, the behavior of the impact protection system 1 or the corresponding pressure profiles without the means 23 for controlling the fluid pressure in the control chamber 17, i.e. the control chamber fluid pressure 32, is described first.

[0060] After the gas generator 2 is activated at time t1 and the pilot valve 11 is closed, the drain bore 22 is initially opened, and fluid flows from the gas generator 2 through the drain bore 22 into the air chamber 3 and through the overflow channel 19 into the control chamber 17. This causes the gas generator fluid pressure 31 to decrease, and the control chamber fluid pressure 32 to initially increase. At time t2, the control chamber fluid pressure 32 reaches the activation pressure 33, which moves the main valve piston 10 towards the pre-chamber 18 and closes the drain bore 22. Consequently, no more fluid flows through the drain bore 22 into the air chamber 3. However, fluid continues to flow through the overflow channel 19 into the control chamber 17, leading to a further increase in the control chamber fluid pressure 32.

[0061] In the next step, when the pilot valve 11 is opened at time t 3, i.e., the pilot valve piston 12 is pushed into the open position, fluid flows out of the control chamber 17 via the pilot valve inlet bore 13, gradually reducing the control chamber fluid pressure 32. However, only when the activation pressure 33 is reached at time t 4, and thus only after a relatively long period of time, does the main valve piston 10 move towards the control chamber 17 and the outlet bore 22 open, metering fluid into the air bag 3 via the outlet bore 22. Fluid also continues to flow out of the control chamber 17 through the still-open pilot valve inlet bore 13, leading to a further decrease in the control chamber fluid pressure 32.

[0062] At time t 5, the pilot valve 11 closes, causing the control chamber fluid pressure 32 to rise again. However, only when the activation pressure 33 is reached at time t 6, and thus only after a relatively long period of time, does the main valve piston 10 move towards the pre-chamber 18 and the drain bore 22 close.

[0063] At time t 7, the pilot valve 11 is opened again and the control chamber fluid pressure 32 decreases. When the activation pressure 33 is reached at time t 8, the main valve piston 10 moves towards the control chamber 17 and the drain bore 22 is opened, metering more fluid into the air bag 3 via the drain bore 22.

[0064] The pressure curves shown show that there is a certain time delay at each of the switching times of the pilot valve 11 at times t3, t5, and t7 between the opening or closing of the pilot valve 11 and the resulting opening or closing of the main valve 7. Such a time delay 34 therefore exists, for example, between the closing of the pilot valve 11 at time t5 and the resulting closing of the main valve 7 (only) at time t6, and is illustrated here by way of example. Fig. 2 marked.

[0065] In order to reduce the activation time of the main valve piston 10 for a closing movement in the present embodiment, or rather to ensure a rapid response of the main valve piston 10, the means 23 for controlling the fluid pressure in the control chamber 17 causes the pilot valve piston 12 to move several times at or from time t 4 onwards. This results in a corresponding alternating and brief opening and closing of the pilot valve 11, more precisely the pilot valve inlet bore 13. In this way, the control chamber fluid pressure 32 is maintained within the specified tolerance range around the activation pressure 33, and thus at a fluid pressure that deviates only slightly from the activation pressure 33 of the main valve piston 10. Fig. 2 The control chamber fluid pressure 32 resulting from time t 4 onwards, through the means 23 for controlling the fluid pressure in the control chamber 17, is represented by a solid line.

[0066] Out of Fig. 2It is evident that at time t 5, when the pilot valve 11 is (re)closed, the control chamber fluid pressure 32 reaches the activation pressure 33 of the main valve piston 10 with virtually no time loss, or, compared to the pressure profile without the means 23 for controlling the fluid pressure, with only a very small time loss. Thus, the main valve piston 10 responds at this time and closes the drain bore 22. This ensures a rapid response of the main valve piston 10 and therefore a rapid closing of the drain bore 22. The time delay 34, i.e., the time loss between the closing of the pilot valve 11 and the resulting closing of the main valve 7 or the main valve piston 10, is therefore almost completely eliminated.

[0067] The modified pressure profiles, which were adjusted accordingly over time, are not shown for the sake of clarity, but should be obvious to the expert based on the above explanations.

[0068] It should be noted again that in the embodiment shown here, the means 23 for controlling the fluid pressure only acts after the pilot valve 11 has been actively opened for the first time and the main valve 7 has opened as a result, at time t4. Of course, it is also possible for the means 23 to control the fluid pressure alternatively or additionally after one or more other switching times of the pilot valve 11 at times t1, t5, t7 and the resulting closing or opening of the main valve 7 at times t2, t6, t8.

[0069] Fig. 3shows a flowchart of a procedure 100 for operating the control device 5 of the impact protection system 1. Fig. 1 .

[0070] In step 110, the pressurized fluid is first supplied and, in particular, directed into the through-hole 9 and the control chamber 17 of the main valve 7. In step 120 (at or from time t4), the fluid pressure in the control chamber 17 is controlled, i.e., brought to or maintained, within a predetermined tolerance range around the activation pressure of the main valve piston 10 using the means 23 for controlling the fluid pressure. This reduces the response time of the main valve piston 10. Reference symbol list

[0071] 1 Impact protection system 2 Gas generator 3 Airbag 4 Fluid outlet channel 5 Control device 6 Valve assembly 7 Main valve 8 Main valve body 9 Through port 10 Main valve piston 11 Pilot valve 12 Pilot valve piston 13 Pilot valve inlet bore 14 Pole piece 15 Armature 16 Coil 17 Control chamber 18 Pre-chamber 19 Overflow channel 20 First pressure surface 21 Second pressure surface 22 Outlet bore 23 Means of controlling a fluid pressure 31 Gas generator fluid pressure 32 Control chamber fluid pressure 33 Activation pressure 34 Time delay 110 Provision 120 Control

Claims

1. Control device (5) for a gas generator (2) for controlling a volume flow of a fluid stored under pressure for filling an airbag (3) of a motor vehicle, having a valve assembly (6), comprising a main valve (7) having a main valve body (8) with a passage opening (9) and a main valve piston (10) axially movable in the passage opening (9) of the main valve body (8), and comprising an electrically actuable pilot valve (11) with a pilot valve piston (12) and a pilot valve inflow bore (13), wherein the main valve piston (10) divides the passage opening (9) into a control chamber (17) fluidically connected to the pilot valve (11) via the pilot valve inflow bore (13) and a prechamber (18) fluidically connectable to the gas generator (2), wherein the main valve (7) has an overflow channel (19), which fluidically connects the prechamber (18) and the control chamber (17) to one another, wherein, within the main valve body (8), at least one outflow bore (22) for discharging the fluid into the airbag (3) branches off from the passage opening (9), and wherein, by means of the fluid and depending on a position of the pilot valve piston (12), the main valve piston (10) closes the at least one outflow bore (22) in a first operating position and opens the at least one outflow bore (22) in a second operating position, characterized in that the valve assembly (6), for reducing a response time of the main valve piston (10), has a means (23) for controlling a fluid pressure in the control chamber (17), and in that the means (23) for controlling a fluid pressure is designed to move or to keep the fluid pressure in the control chamber (17) to / at a pressure which lies within a predefined tolerance range around an activation pressure (33) of the main valve piston (10).

2. Control device (5) according to Claim 1, characterized in that the activation pressure (33) is dependent on the fluid pressure provided by the gas generator (2) at the respective time.

3. Control device (5) according to Claim 2, characterized in that the activation pressure (33) correspondingly decreases with a decrease in the fluid pressure provided by the gas generator (2) over the time period for filling the airbag (3).

4. Control device (5) according to Claim 2 or 3, characterized in that the means (23) for controlling a fluid pressure is designed to move or to keep the fluid pressure in the control chamber (17) to / at the respective pressure, which lies within a predefined tolerance range around the respective activation pressure (33) of the main valve piston (10).

5. Control device (5) according to one of the preceding claims, characterized in that the means (23) for controlling the fluid pressure is designed as an electrical control device which applies an actuation signal in pulse-width-modulated form to the pilot valve (11).

6. Control device (5) according to one of the preceding claims, characterized in that the means (23) for controlling the fluid pressure is a pressure reducer arranged on and / or in the main valve.

7. Control device (5) according to Claim 6, characterized in that the pressure reducer comprises a valve with an inlet side and an outlet side, in that the valve is arranged in a bore in the main valve body (8) or in the main valve piston (10) and with its outlet side adjacent to the control chamber (17), and in that the valve is designed in such a way that fluid pressure in the control chamber (17), which fluid pressure lies within a predefined tolerance range around the activation pressure (33) of the main valve piston (10), is not exceeded.

8. Control device (5) according to Claim 7, characterized in that the pressure reducer is designed in such a way that, when there is a pressure increase in the control chamber (17), the valve is gradually increasingly closed, and in that, when the fluid pressure in the control chamber (17), which fluid pressure lies within a predefined tolerance range around the activation pressure (33) of the main valve piston (10), is reached, the valve is substantially completely closed.

9. Control device (5) according to one of the preceding claims, characterized in that the overflow channel (19) is designed as a piston bore in the main valve piston (10).

10. Control device (5) according to one of the preceding claims, characterized in that the main valve piston (10) has a first active pressure area (20) facing the control chamber (17) and a second active pressure area (21) facing the prechamber (18), wherein the first active pressure area (20) is larger than the second active pressure area (21).

11. Control device (5) according to one of the preceding claims, characterized in that the valve assembly (6) comprises a pressure sensor for detecting the fluid pressure prevailing in the control chamber (17).

12. Control device (5) according to Claim 11, characterized in that the pressure sensor is arranged in the control chamber (17), wherein the pressure sensor is designed to detect the fluid pressure directly in the control chamber (17).

13. Control device (5) according to one of the preceding claims, characterized in that the predefined tolerance range is defined by a maximum permissible deviation from the activation pressure, and in that the predefined tolerance range is 30%, preferably 20%, preferably 10%.

14. Impact protection system (1) for a motor vehicle having a gas generator (2) for storing a fluid under pressure and having an airbag (3), wherein the gas generator (2) is designed to provide the fluid for the airbag (3) in response to an activation signal, and having a control device (5) for controlling a volume flow of the fluid stored under pressure for filling the airbag (3) according to one of Claims 1 to 13, wherein the prechamber (18) of the passage opening (9) of the main valve (7) is fluidically connected to a fluid outlet duct (4) of the gas generator (2).

15. Method for operating a control device (5) according to one of Claims 1 to 13, wherein the method comprises the following steps: providing (110) a fluid stored under pressure; and controlling (120) the fluid pressure in the control chamber (17) using the means (23) for controlling a fluid pressure to a pressure which lies within a predefined tolerance range around the activation pressure of the main valve piston (10) in order to reduce the response time of the main valve piston (10).

16. Method according to Claim 15, wherein the activation pressure (33) is dependent on the fluid pressure (31) provided by the gas generator (2) at the respective time, the activation pressure (33) preferably correspondingly decreases with a decrease in the fluid pressure (31) provided by the gas generator (2) over the period for filling of the airbag (3), and wherein, in the step of controlling (120) the fluid pressure in the control chamber (17), the fluid pressure in the control chamber (17) is moved to or held at the respective pressure which lies within a predefined tolerance range around the respective activation pressure (33) of the main valve piston (10).