Bumper structure subassembly including a cushioning element associated with an impact sensor
Technical Field
The present invention claims priority from french application 1901863 filed on 25/2/2019, the disclosure (text, drawings and claims) of which is incorporated herein by reference.
The invention relates to a bumper structure subassembly including a cushioning element associated with an impact sensor. The invention also relates to a bumper structure comprising such a subassembly.
Background
In the field of motor vehicles, the evolution of legislation is increasingly tending to limit the aggressiveness of vehicles with respect to other road users (in particular with respect to pedestrians).
Thus, there is a need for motor vehicles that can provide a satisfactory response to impacts that occur at the front bumper locations of these vehicles and that have different impact areas and impact forces (e.g., pedestrian impacts and repairable impacts, which correspond to impacts of lateral portions of the bumper with rigid obstacles at a certain speed (typically less than 20 km/h).
In the case of an impact of a pedestrian with the front bumper of a motor vehicle, in order to limit the physical injuries sustained at the position of the leg of the pedestrian, it is necessary to absorb the kinetic energy of such a slight and limited impact, which is generally reflected in the architecture of the vehicle by the addition of a cushioning element made of foam mounted longitudinally between the bumper cover and the transverse beam of the metal bumper reinforcement.
Moreover, at the time of such an impact, the pedestrian tends to be thrown toward the vehicle hood: the femur of the pedestrian impacts the front of the hood, while the head of the pedestrian impacts the area between the middle and the rear of the hood.
In order to absorb the kinetic energy of this secondary impact, the hood is made of a material that can deform under the effect of this impact.
The engine compartment of some types of vehicles, in particular passenger cars, is heavily clogged by rigid components, such as in particular the powertrain and the radiator, the distance between the powertrain and the radiator and the bonnet proving insufficient to be able to deform the bonnet sufficiently and absorb the impact.
In order to overcome this problem, it is known to provide on this type of vehicle a component which is able to automatically raise the hood in the event of a collision of a pedestrian with the front bumper being detected by means of a special impact sensor coupled to the electronic control unit.
Such an impact sensor is described in international application document WO2012/113362a1, said impact sensor comprising: an elastically deformable flexible hollow conduit received in a recess provided on a rear surface of the cushioning element; and two pressure sensors respectively mounted on both end portions of the duct, the two pressure sensors being capable of detecting a pressure change inside the duct, the pressure change being caused by deformation of the cushion member upon impact between an object and a front bumper of a vehicle.
The analysis of the signals transmitted by these sensors enables the electronic control unit to determine the type of crash that has just occurred and thus to control the lifting of the hood in the event of a collision with a pedestrian.
Unfortunately, in the event of a repairable impact, the lateral ends of the beam of the bumper reinforcement tend to shear the duct, which requires the entire replacement of the impact sensor, the relatively high cost of which can account for 5% of the total cost of the repair damage caused by such an impact.
Disclosure of Invention
The object of the invention is therefore to improve the situation.
To this end, the invention provides a bumper structural subassembly for a motor vehicle, comprising: a cushion element for being longitudinally mounted between the bumper cover and the transverse beam of the bumper reinforcement; and an impact sensor comprising an elastically deformable pipe and two pressure sensors mounted on two ends of the pipe, respectively, the two pressure sensors being capable of detecting pressure changes inside the pipe, the pipe comprising at least one main section housed in a transverse groove provided on a rear surface of the cushioning element; characterized in that said duct comprises two end segments, which extend transversely on either side of said main segment and are respectively housed in two respective cavities provided respectively inside two lateral end portions of said cushioning element, which extend transversely on either side of said groove.
This configuration makes it possible to avoid that the end of the beam intended to be positioned facing the two lateral end portions of the cushioning element may come into direct contact with the pipe in the event of a repairable impact, so as to prevent any shearing of the pipe.
As a result, after such a collision, the undamaged impact sensor 40 can be reassembled on a new damping element 30, which can significantly reduce the total repair effort.
According to preferred features of the subassembly which can be employed individually or in combination:
-said pressure sensor is also housed inside said cavity;
-the cavity is covered with a material thickness of at least 20 mm;
-the material thickness is between 30mm and 40 mm;
-said cavity has a cross-sectional profile substantially corresponding to the cross-sectional profile of said pressure sensor;
-the cushioning element is constituted by a block of foam made of expanded polypropylene and having a thickness of between 20kg/m3And 80kg/m3A density of (d) in between; and/or
-the pipe has a circular cross-section with a thickness between 0.8mm and 1.2 mm.
According to a second aspect, the invention also relates to a bumper structure for a motor vehicle, comprising a bumper cover, a bumper reinforcement comprising a transverse beam, and such a subassembly, the cushioning element of the subassembly being mounted longitudinally between the bumper cover and the beam.
According to a preferred feature of the bumper structure, the bumper element extends transversely over an intermediate length between the length of the hood and the length of the beam, the groove itself extending transversely over a length less than the length of the beam such that each end of the groove is spaced transversely from a respective end of the beam by a predetermined distance.
Advantageously, the predetermined distance is between 10mm and 40 mm.
Drawings
The invention will be better understood from a reading of the detailed description of an embodiment of the invention given below as an illustrative but non-limiting example and the accompanying drawings, in which:
figure 1 is a view of a front bumper structure of a motor vehicle according to the invention;
figure 2 shows an enlarged cross-sectional view of a subassembly consisting of a damping element and an impact sensor, in a cross-sectional position at the position of a main section of the pipe (which is housed in a groove provided on the rear surface of the damping element);
figure 3 is an enlarged cross-sectional view of the subassembly of figure 2, in a cross-sectional position at the position of the end segment of the duct (which is housed in a cavity provided inside the respective end of the damping element, respectively); and
Fig. 4 shows an enlarged cross-sectional view of the subassembly of fig. 2, in a cross-sectional position at the location of the pressure sensor (which is housed in a cavity provided inside a respective end of said damping element, respectively).
Detailed Description
An orthogonal coordinate system XYZ is defined with respect to the vehicle, comprising three axes perpendicular two by two, namely:
-an axis X defining a longitudinal horizontal direction, coinciding with the general direction of movement of the vehicle;
an axis Y defining a transverse horizontal direction, defining a horizontal plane XY with the axis X, an
An axis Z, defining a vertical direction, perpendicular to the horizontal plane XY.
In the following description, the terms "front" and "rear" are used, by convention, to define the relative position of an element with respect to another element, according to the general direction of movement of the vehicle.
Fig. 1 shows a front bumper structure 1 of a motor vehicle, comprising: a bumper cover 10 forming a front end portion of the vehicle; a bumper reinforcement 20 constituting a front end portion of a vehicle chassis; and a cushion member 30 longitudinally installed between the bumper cover 10 and the bumper reinforcement 20.
The bumper cover 10 extends over the entire width of the vehicle while being integrally connected to the body of the vehicle by means of a plurality of fixing points, not shown, due to being made of a thin metal plate or a molded plastic resin.
The bumper reinforcement 20 is mainly constituted by a hollow metal beam 21 extending transversely over a length less than that of the bumper cover 20, and by two identical lateral metal absorbers 22, each of which is integral with a respective lateral end portion of the beam 21, these absorbers being intended to be fixed to the front end portions of two lateral longitudinal beams of the vehicle.
The beam 21, as usually obtained by forming or extrusion, is designed to transmit to the lateral absorber the forces encountered in an impact with the front of the vehicle. The beam may comprise an inner reinforcing metal plate extending transversely and serving to improve the mechanical properties of the beam.
Since the mechanical stiffness provided is less than that of the beam 21 and of the vehicle lateral longitudinal beams, the two lateral absorbers 22 are designed to be crushed in the event of a repairable impact and thus to absorb the energy of this impact, so as to avoid any damage to these lateral longitudinal beams.
Due to the construction of the foam blocks of polyurethane, polypropylene or expanded polystyrene, the damping element 30 has a mechanical stiffness which is less than the mechanical stiffness of the bumper reinforcement 20 (in particular less than the mechanical stiffness of the two lateral absorbers 22 of said bumper reinforcement).
The cushioning element 30 is advantageously constituted by a block of expanded polypropylene foam having a thickness of between 20kg/m3And 80kg/m3The density of (d) in between.
The cushion element 30 is designed to be crushed in the event of a pedestrian impact and thereby absorb the energy of the impact in order to avoid any damage to the bumper reinforcement 20.
As shown in fig. 1, the cushion element 30 extends transversely over an intermediate length between the length of the bumper cover 10 and the length of the beam 21 of the bumper reinforcement 20, which projects transversely from both sides of the beam.
Referring to fig. 2, it can be observed that the cushion member 30 has a groove 31 provided on a rear surface 30A thereof and extending laterally over a length slightly less than the length of the beam 21 of the bumper reinforcement 20.
The bumper structure 1 further comprises an impact sensor 40 comprising an elastically deformable duct 41 and two pressure sensors 42 mounted respectively on the two ends of the duct 41, said two pressure sensors being able to detect pressure variations inside the duct, said pressure variations being caused by the deformation of the cushioning element 30 upon impact between an object and the front bumper of the vehicle.
The two pressure sensors 42 are used for electrical coupling with an electronic control unit, not shown. The analysis of the signals transmitted by the two pressure sensors 42 and by other sensors, such as impact speed sensors, enables the control unit to determine the type of object (e.g. a pedestrian or an object (e.g. a pillar or a low wall)) that the vehicle has just collided with, in the event of a frontal impact. In the event of detection of a pedestrian impact, the control unit is thus able to trigger the automatic lifting device of the vehicle hood, which enables the vehicle hood to deform sufficiently in the event of a secondary impact with the head of the pedestrian, to ensure effective absorption of the kinetic energy of this impact.
The duct 41, advantageously made of cross-linked silicone, has a substantially uniform circular section over its entire length, advantageously with a thickness comprised between 0.8mm and 1.2 mm.
Preferably, the duct 41 has an inner diameter of between 7mm and 9mm and an outer diameter of between 9mm and 11 mm.
As shown on fig. 1 and 2, the main section 41A of the duct 41 is housed in a groove 31 provided on the rear surface 30A of the cushioning element 30 and extending transversely over a length less than the length of the beam 21 of the bumper reinforcement 20, so that each end of this groove 31 is transversely spaced from the respective end of the beam 21 by a predetermined distance, advantageously between 10mm and 40 mm.
The groove 31 has a U-shaped cross section with its semicircular bottom oriented towards the rear and its width being extremely slightly greater than the outer diameter of the duct 41.
With reference to fig. 1 and 3, it can be observed that the two end segments 41B of the duct 41 extend laterally on either side of a main segment 41A of the duct (which is housed in the groove 31) and are respectively housed in two respective cavities 32 provided respectively inside two lateral end portions 30B of the cushioning element 30, which extend laterally on either side of the groove 3.
This arrangement makes it possible to avoid that the end of the beam 21 may come into direct contact with the pipe 41 in the event of a repairable impact, so as to prevent any shearing of said pipe.
As a result, after such a collision, the undamaged impact sensor 40 can be reassembled on a new damping element 30, which can significantly reduce the total repair effort.
Advantageously, the cavities 42 have a cross-sectional profile substantially corresponding to that of said sensors, so as to allow easy insertion of each of the pressure sensors 42 through the respective cavity 42 by the operator when the impact sensors 40 are assembled on the damping element 30.
For optimum protection, the cavities 32 provided inside the two lateral end portions 30B of the cushioning element 30 are covered with a material thickness (for example foam) of at least 20mm, preferably between 30mm and 40 mm.
In addition, in order to avoid discontinuous coverage at the interface between the end of the duct 41 and the two pressure sensors 42 (which may constitute weak areas in the event of a repairable impact), these two pressure sensors 42 are advantageously also housed respectively inside two cavities 32, respectively inside the two lateral end portions 30B of the damping element 30.
According to an embodiment variant that is not shown, the characteristics of the duct of the impact sensor and/or the characteristics of the damping element are different.
In general, it is noted that the invention is not limited to the embodiments described and illustrated, but encompasses any implementation variant that can be reached by a person skilled in the art.