DE102008037803A1 - Device for increase of axle load of motor vehicle i.e. car, during brake applications, has outlet nozzle attached to combustion chamber of pyrotechnic systems, where systems are connected with common fuel tank - Google Patents

Abstract

The device has an outlet nozzle attached to a combustion chamber (20) of two pyrotechnic systems (14). The outlet nozzle is upwardly aligned in a direction of a vertical axis of a motor vehicle (10) i.e. car. The systems are connected with a common fuel tank (18). A pressure generation device is provided for conveying of fuel under pressure applications from the fuel tank to the combustion chamber of the systems. A heat shield (22) is attached to the combustion chamber. A flow control equipment controls a fuel flow from the fuel tank into the combustion chamber. An independent claim is also included for a method for triggering a device for increase of an axle load.

Description

The The invention relates to a device for increasing the wheel load a motor vehicle during braking according to the preamble of claim 1. The invention further relates to a method for triggering such a device.

The maximum achievable braking deceleration of motor vehicles is essentially limited by the coefficient of friction between the wheel and the ground. For a motor vehicle which is customary today, the braking distance which can be achieved under optimum conditions carries, for example, a deceleration from a speed of 100 km / h to 0 km / h at approximately 36 m. Even if the braking system could produce higher forces, this value should not be undershot due to the friction limitation with conventional brakes. However, the braking force between the vehicle and the ground does not only depend on the friction coefficient. Another factor here is the wheel load, so the force acting on the braking wheel in the direction of the vehicle's vertical axis. This force is usually given by the vehicle weight and the axle positions and therefore not changeable. However, it is possible, in particular in emergency braking, to generate recoil forces by means of pyrotechnic devices which increase the wheel load and thus also the maximum possible braking force. For this purpose, the DE 25 00 351 A1 an emergency emergency braking device for motor vehicles, which comprises a plurality of missile systems. These can on the one hand produce a direct braking effect by exerting a repulsive force against the direction of travel of the vehicle. However, if the direction of the recoil force also has a component in the direction of the vehicle vertical axis, such a device also increases the wheel load of the vehicle, which increases the braking forces.

A similar emergency brake system is in the DE 21 32 657 disclosed. This includes a z. B. mounted on the vehicle axles rocket, which is triggered by a particularly deep depressions of the brake pedal via a multiple switch. The repulsive force of the missiles is directed substantially upward, so that the wheel load is increased on all four wheels of the motor vehicle.

Finally, the reveals DE 10 2004 054 544 B3 a device for increasing the deceleration of a motor vehicle at full braking, which also includes pyrotechnic devices, which are arranged on the stub axles of the front axle. The repulsive force of the pyrotechnic devices is directed vertically upwards, so as to increase the contact pressure on the road surface during the burning of the pyrotechnic devices.

such Devices have the disadvantage that the used pyrotechnic propellants usually flammable, though not very explosive. Such propellant sets So in an accident, a significant additional risk. About addition, it is disadvantageous that said devices usually over a particularly deep passage of the brake pedal can be activated. A separate check whether actually an emergency situation exists, does not take place. As such pyrotechnic Propellants are usually not refillable, so any triggering of such devices is too complicated Maintenance, but it is undesirable To avoid tripping. Also from safety-technical Aspects are the known triggering concepts by pyrotechnic devices not optimal. In particular no check if the device is at a given time triggered without endangering other road users can be.

At the asymmetric burning of such pyrotechnic devices In addition, there may be yawing and rolling moments on the vehicle, which further affect the tracking stability and in the worst case, an accident even more unfavorable can shape.

Of the The present invention is therefore based on the object, a device to increase the wheel load of a motor vehicle during braking with provide a pyrotechnic system in which the safety risks are minimized by the pyrotechnic system. It is still the task of the invention, a method of triggering such Device to provide, which is a triggering of the device only with an actual need for emergency braking ensures.

These The object is achieved by a device having the features of the patent claim 1, and by a method having the features of the claim 14 solved.

A Such device for increasing the wheel load of a motor vehicle comprises at least two pyrotechnic systems, each with one Combustion chamber and one of the combustion chamber associated outlet nozzle. The outlet nozzle is in the direction of the vehicle vertical axis directed upward so that the recoil forces generated by the system are directed downwards and therefore the wheel load and thus the increase the maximum producible braking force.

According to the invention it is now provided that the at least two pyrotechnic systems are connected to a common fuel tank. In contrast to common solid or liquid fuel rockets, the fuel is thus no longer di held directly in or on the combustion chamber. By connecting the at least two pyrotechnic systems with a common fuel tank, a symmetrical admission of fuel to the two combustion chambers is guaranteed in each case, so that the forces acting on the motor vehicle as a result of triggering the pyrotechnic systems are also symmetrical. The occurrence of yawing or rolling moments, which could affect the tracking stability of the motor vehicle in such a release, is thus excluded. This advantageously ensures that such a device does not cause any additional stability risks.

Prefers Furthermore, a pressure generating device is provided, which the fuel pressurized from the fuel tank to the Is able to promote combustion chambers.

In order to is the use of liquid and gelatinous fuels which is not explosive at standard pressure and only by pressurizing into an ignitable Pass state. This is advantageously the security Such a device significantly increased because it, for example in an accident in which the device is not triggered will not ignite or even explode the fuel supplies can come. In the pressure generating device it is preferably a further, smaller pyrotechnic Institution, as they are z. B. also in the triggering of airbags Application finds. Such a device combines a fast Pressurization of the pyrotechnic system with low safety risks in case of an accident.

Thereby, that the fuel is not, as in solid systems already in the combustion chamber is held, is beyond a regulated fuel supply to the combustion chamber possible. So is in a further embodiment of the invention, a flow control device for controlling a flow of fuel from the tank to the associated one Combustion chamber provided so that is both a regulation of thrust as well as turning off the device after achieving the desired Braking effect possible.

Around when triggering the device other vehicle components not to be damaged by the resulting high temperatures, is in a further embodiment of the invention, each Combustion chamber associated with a heat protection panel.

In In a particularly preferred embodiment, two pyrotechnic Systems are provided, each in the vicinity of a front wheel of the motor vehicle are arranged. This is a symmetrical application of force achieved the front wheels of the motor vehicle, so that when triggered the Device no yawing or rolling moments are generated. Also one undesirable triggering of the device is at risk thus the traffic safety of the motor vehicle does not, since it by the symmetrical application of force to the front wheels is not can lead to a breakout of the car from the track.

The Connection of the pyrotechnic systems is preferably carried out a sill stump of the motor vehicle and / or on a cross member. Out Prior art devices are in contrast usually directly on the suspension or comparable Components attached. By determining the invention Device on a sill stump or cross member the load on the suspension when triggered significantly reduced the pyrotechnic systems. Recoil forces The pyrotechnic systems are used directly in supporting components of the Motor vehicle initiated, allowing a higher load of the motor vehicle through the pyrotechnic systems without overloading dynamic components.

In Another embodiment of the invention is provided that the outlet nozzles the pyrotechnic systems in each case an outlet opening open, wherein at least one of the outlet openings is arranged in the vehicle longitudinal direction in front of an A-pillar. When triggering the pyrotechnic systems is thus out View of the driver of the exhaust jet mostly obscured by the A-pillar, so it does not cause glare the driver or another distraction, in one with the trigger accompanying dangerous situation would be undesirable comes. Alternatively, such an outlet opening in the Be arranged area of a B-pillar. The application of force takes place with respect to the vehicle longitudinal axis more uniform, so not only the wheel load the front wheels, but also to a considerable extent is increased at the rear wheels. The distribution the braking forces is thus advantageously symmetrical over the whole vehicle.

In order to enable a visually appealing integration of the device in a motor vehicle, it can further be provided that the outlet openings of the respective pyrotechnic systems can each be closed with a film element. Such a film element is either demolished or burned when the pyrotechnic systems are triggered by the exhaust gas jet of the combustion chambers. The wheel load increasing effect is not affected. In contrast to other design options, such as cover flaps, there is no complicated mechanism for releasing the off necessary openings. Such cover films continue to protect the outlet nozzles and combustion chambers in their non-use state against the ingress of dirt, spray and the like.

In Another embodiment of the invention is a control device for delivering control signals to the respective pressure generating means and flow control devices of the pyrotechnic systems provided. Such a control device is preferably designed so that it can be connected to a vehicle bus. This is the integration a device according to the invention with existing Safety systems of the motor vehicle possible. Especially can provide data from driver assistance systems and brake assist systems and the like are transmitted to the control device, so as to ensure the triggering of the device only in actual dangerous situations, which is an emergency stop necessary, done.

preferably, has a device according to the invention for increasing the wheel load of a motor vehicle during a braking process a thrust of a maximum of about 6 kN per pyrotechnic system. The burning time The pyrotechnic system should be about 1.5 to 2 seconds. The occurring at such shear forces and burning times Loads on the suspension and suspension remain essentially manageable, so no damage are to be expected. The forces, however, are high enough at a common car in about a doubling of To achieve braking force.

The The invention further relates to a method for triggering an initially described device for increasing the Wheel load, in which when applying a triggering criterion by means of the pressure generating device fuel under pressure is conveyed into the combustion chamber. The triggering criterion can in the simplest case, the exceeding of a Threshold for the pressure exerted by a brake pedal Braking force and exceeding a minimum braking time include. The triggering is so in this case only triggered by the behavior of the driver of the motor vehicle. Now it is known that in dangerous situations of car drivers often too low braking forces are used, it is particularly advantageous if the triggering criterion for the triggering of the device mentioned the trigger signal a brake assist system includes. Thereby can advantageous to include further data in the triggering decision, which of existing driver assistance and brake assistance systems are provided. For example, this can also be done Distance warning signals from radar devices, ultrasonic devices, Lidareinrichtungen or the like belong.

Farther it is advantageous to prevent triggering of the device, if a safety system already present in the vehicle is a pedestrian collision has detected. Here is, for example, a coupling with systems to activate an active hood imaginable. This can be advantageous be ensured that in the case of such an accident no Accident involved in the exhaust stream of the pyrotechnic system device.

in the Below is the invention and its embodiments with reference to the drawing be explained in more detail. Hereby show:

1 the distribution of power on a braking vehicle without a device for increasing the wheel load,

2 the distribution of power on a braking vehicle with a supporting device for increasing the wheel load,

3 a plot of the dependence of braking distance and braking deceleration on the force exerted by a device according to the invention,

4a and 4b a schematic representation of the arrangement of a device according to the invention in a motor vehicle and

5a and 5b a schematic detail views of the arrangement of a device according to the invention in a motor vehicle in a side and a front view.

1 shows the distribution of forces on a braking motor vehicle 10 , which has no device for increasing the wheel load. On the wheels initially weighed the weight of the vehicle, which varies depending on the center of gravity of the motor vehicle 10 distributed to the components F _{Z, V} for the front wheels and F _{z, H} for the cattle wheels. During a braking process, an additional pitching moment acts on the vehicle, so that the front wheels are more heavily loaded by an additional force component F _{Z, braking} caused by this pitching moment. The force action in the z-direction on the rear wheels is accordingly reduced by the same contribution F _{z, brake} . The effect of the vehicle brakes is on the slip friction of the wheels relative to the road in accordance with F _X = μ · F _Z in a against the direction of movement of the vehicle 10 acting force implemented. The coefficient of friction μ in this case represents the slip friction coefficient of the wheels relative to the road surface. The slip friction coefficient μ or the coefficient of sliding friction in the case of blocked vehicle wheels therefore represents the left-hand side mit factor for the maximum possible braking distance. From material-technical conditions of this slip friction coefficient μ is set under ideal conditions to a maximum value of about 1.1. The delaying forces F _{x, V} for the front wheels and F _{X, H} for the rear wheels ultimately result in a braking deceleration a _x = F _x / m, where m indicates the vehicle mass. This braking acceleration acts at the center of gravity 12 of the vehicle 10 ,

Since, as explained, the coefficient of friction μ of the wheels relative to the roadway can not be increased further for technical reasons, the only way to achieve a further shortening of the braking distance is to increase the forces F _Z , which are in the direction of the vehicle vertical axis to the vehicle wheels Act. Such an increase can be achieved by a device according to the invention.

2 shows the distribution of force on a braking vehicle, which has such a device. By igniting a pyrotechnic propellant whose exhaust jet is directed in the direction of the vehicle vertical axis upward, now acts an additional force on the front wheels of the vehicle 10 , In addition to the weight F _{Z, V} on the front wheels and the additional force F _Z generated by the pitching moment during braking _{, braking} on the front wheels increases the total force on the front wheels to the recoil force of the pyrotechnic device F _{Z, Boost} . Thus, the decelerating force F _X acting on the vehicle results as F _X = μ · (F _Z + F _{Z, Boost} ).

3 shows a plot of the achievable deceleration in m / s ^-2 and the possible braking distance in meters against the thrust force of such a pyrotechnic device in N. The braking distance refers to a conventional middle class vehicle, which at a slip friction coefficient of 1.1 between the wheels and the road decelerates from a speed of 100 km / h. The braking distance without an additional pyrotechnic device is approximately 36 m, with a delay of 10 m / s ^{-2 is} achieved. As can be seen from the above equation, the possible deceleration increases substantially linearly with the thrust force with the pyrotechnic device. To shorten the braking distance to 20 m, a thrust of about 23,500 N would be necessary. This corresponds to an additional load of the front wheels by a weight of 2.25 t. In order not to overload the suspension, suspension and the like, therefore, a compromise between thrust of the pyrotechnic device and load limits of the installed components must be found. In a design of the pyrotechnic device to a total thrust force of 6 kN per front wheel, so a total of 12 kN, already a reduction of the braking distance can be achieved by about 30%. For common middle-class vehicles such additional load by pyrotechnic device corresponds approximately to a doubling of the dynamic wheel load of the front wheels. Such stresses are in the manageable area, through the use of such a pyrotechnic device thus no damage can be expected.

In 4 is the arrangement of a pyrotechnic system to increase the wheel load on the front wheels of a motor vehicle 10 shown. 4a shows a schematic longitudinal section through the car 10 , The system 14 is in an area behind the front wheels 16 of the motor vehicle and arranged with a in the representation of 4 unrecognizable longitudinal member of the motor vehicle body connected. The system 14 includes a combustion chamber 20 , where the combustion chamber 20 from a heat protection panel 22 is surrounded to spare when triggering the device adjacent components.

The system 14 is with a fuel tank 18 which also has a second pyrotechnic system, which is on the other side of the motor vehicle 10 mounted in the same position with respect to the vehicle longitudinal axis, supplied with fuel.

4b shows a plan view of the arrangement, from which it can be seen that the pyrotechnic systems 14 in the area of the fenders 24 of the motor vehicle 10 are arranged, wherein the positioning in the direction of the vehicle longitudinal axis is such that the systems 14 directly in the area behind the A-pillars 26 are mounted. When the systems are triggered 14 escaping gases are thus not directly in the driver's field of vision, which means that the driver is less distracted and can concentrate better on the current emergency situation. At the top are the combustion chambers of the systems 14 through protective caps 28 Covered in the form of films, which should prevent the ingress of dirt and the like and at the same time by flush termination with the outer skin of the motor vehicle 10 provide an aesthetically pleasing appearance.

In 5 the arrangement of a schematically illustrated pyrotechnic device is shown again in detail, wherein 5a a view on the vehicle side and 5b represents a view from the vehicle front. The combustion chamber 20 the pyrotechnic system is via a holding element 30 at the sill stump 32 of the motor vehicle 10 established. An additional connection can also be made on the arranged in this area vehicle cross member. Also in the area of the sill stump 32 is the fuel tank 18 arranged, which over a line 34 connected to the combustion chamber.

Another, not shown, fuel line connects the fuel tank 18 with a second, arranged on the other side of the vehicle pyrotechnic system.

The tank contains another propellant 36 , the pressurization of the tank contents and its associated promotion in the combustion chambers 20 the pyrotechnic systems used in triggering the pyrotechnic device. The propellant 36 has taken on its own, no significant thrust, it essentially corresponds to common airbag propellant charges. The endangerment of this propellant itself is therefore minimal. The one in the tank 18 held fuel is preferably a gel-like fuel, which is ignitable only when pressurized, and therefore does not pose a personal safety risk in accidents. Such fuels are known from military applications, especially rocket engines with variable thrust. Natural fuels can be carried out both monergol and diergol.

Around a secure release of the invention One device is still not possible here shown control unit provided. About this control unit the pyrotechnic device can be connected to a vehicle bus be, and so with other components of various already existing Driving safety systems communicate. For the trigger In such a device several concepts are conceivable. In the simplest Case, the triggering of pyrotechnic systems is easy depending on maximum brake pedal position and a Minimum braking time possible. So that is the brake force increase by Increase in wheel load initiated when the Driver automatically triggers an emergency stop. However, it is known that in dangerous situations of motor vehicle drivers often exerted insufficient braking forces become. For this reason, so-called Brake assistance systems introduced, which automatically Recognize dangerous situations and situational appropriate braking forces exercise. A coupling of the invention Device with such a brake assist system would the performance of the invention Improve device accordingly. It can continue doing so be checked by the brake assist system, whether the braking force of a conventional braking in the respective Situation is sufficient to bring the vehicle to a stop in time. Only if this was not the case, then would the Device according to the invention by the brake assist system triggered. A combination of the invention Device is also possible with an autonomous braking system. Such a system includes distance warning, for example in shape radar sensors or in the form of lidar or camera detection of the surrounding traffic. If the assistance system detects that Clash with an obstacle imminent, so can it without the driver's intervention, a full stop and, if the appropriate Braking force is desired, a triggering of the invention System.

Around in case of a pedestrian impact pedestrian granting additional protection may continue be provided that the area of the hood with other sensors, For example, ultrasonic sensors is detected. Becomes a pedestrian caught by the vehicle and thrown into the area of the bonnet, so on the one hand, the active hood is triggered and the prevent others from triggering the pyrotechnic system, so that the pedestrian is not injured threaten the exhaust jet of pyrotechnic systems.

10

motor vehicle

12

main emphasis

14

systems

16

front wheels

18

fuel tank

20

combustion chamber

22

Heat protection panel

24

fender

26

A column

28

caps

30

retaining element

32

sill stub

34

management

36

propellant

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 2500351 A1 [0002]
• - DE 2132657 [0003]
• - DE 102004054544 B3 [0004]

Claims (17)

Device for increasing the axle load of a motor vehicle ( 10 ) during braking, with at least two pyrotechnic systems ( 14 ) each with a combustion chamber ( 20 ) and one each of the combustion chamber ( 20 ), wherein the outlet nozzle is directed upward in the direction of the vehicle vertical axis, characterized in that the at least two pyrotechnic systems ( 14 ) with a common fuel tank ( 18 ) are connected. Apparatus according to claim 1, characterized in that a pressure generating device ( 36 ) for conveying fuel under pressure from the fuel tank ( 18 ) to the combustion chambers ( 20 ) of at least two pyrotechnic systems ( 14 ) is provided. Apparatus according to claim 1 or 2, characterized in that a flow control means for controlling a fuel flow from the fuel tank ( 18 ) in the associated combustion chambers ( 20 ) is provided. Device according to one of claims 1 to 3, characterized in that each combustion chamber ( 20 ) a heat protection cover ( 22 ) assigned. Device according to one of claims 1 to 4, characterized in that the pyrotechnic systems ( 14 ) can each be arranged in the vicinity of a front wheel of the motor vehicle. Device according to one of claims 1 to 5, characterized in that the pyrotechnic systems ( 14 ) on a sill stub ( 32 ) and / or a cross member can be fixed. Device according to one of claims 1 to 6, characterized in that the outlet nozzles open into a respective outlet opening, wherein at least one of the outlet openings in the vehicle longitudinal direction in each case in front of an A-pillar ( 26 ) is arranged. Device according to one of claims 1 to 7, characterized in that the outlet nozzles in each case an outlet opening open, wherein at least one of the outlet openings in the region of a B-pillar is arranged. Apparatus according to claim 7 or 8, characterized in that the outlet openings with a film element ( 28 ) are closable. Device according to one of claims 1 to 9, characterized in that a control device for outputting control signals to the respective pressure generating devices ( 36 ) and flow control devices of the at least two pyrotechnic systems ( 14 ) is provided. Device according to claim 10, characterized in that the control device can be connected to a vehicle bus. Device according to one of the preceding claims, characterized in that the at least two pyrotechnic systems ( 14 ) have a maximum thrust of 6 kN. Device according to one of the preceding claims, characterized in that the at least two pyrotechnic systems ( 14 ) have a burning time of 1.5 s to 2 s. Method for triggering an axle load increasing device according to one of Claims 1 to 13, in which the fuel tank ( 18 ) of at least two pyrotechnic systems ( 14 ) is pressurized when a triggering criterion applies and a pressure in the fuel tank ( 18 ) received fuel into the associated combustion chambers ( 20 ) is promoted and ignited. Method according to claim 14, characterized in that that the triggering criterion is the exceeding of a Threshold for the pressure exerted by a brake pedal Braking force and exceeding a minimum braking time includes. Method according to claim 14 or 15, characterized that the trigger criterion is the trigger signal of a Brake assistance system includes. Method according to one of claims 14 to 16, characterized in that the triggering criterion is a distance warning signal a radar device, ultrasound device, lidar device or the like.