Longitudinal member for heavy truck

Abstract

The invention relates to a longitudinal member for a heavy-duty truck, the longitudinal member (1) comprising a front end (6) provided with a hinge element (10) for hingedly attaching the longitudinal member to a heavy-duty truck body (2) and a rear end (8) comprising an attachment element (12) for non-permanently attaching the longitudinal member to the heavy-duty truck body (2), the longitudinal member comprises a front portion (14) extending from a front end (6) of the longitudinal member to an intermediate region (16) and a rear portion (18) extending from the intermediate region (16) of the longitudinal member to a rear end (8). The product (PF) of the wall thickness (tF) of the front portion (14) multiplied by the yield strength (YsF) of the material of the front portion (14) is greater than the product (PR) of the wall thickness (tR) of the rear portion (18) multiplied by the yield strength (YsR) of the material of the rear portion (18).

Description

[0001] This application is a divisional application of a Chinese patent application named "Longitudinal Member for Heavy Goods Vehicles" with an application number of 201780034299.4. The patent application 201780034299.4 is a national application that entered the Chinese national phase from an international application (PCT / IB2017 / 053275) filed under the Patent Cooperation Treaty on June 2, 2017. Technical Field

[0002] The present invention relates to a longitudinal member for the structure of a heavy goods vehicle. This type of longitudinal member includes a front end and a rear end. The front end is intended to be oriented towards the front of the heavy goods vehicle structure and is provided with a hinge element for hingedly attaching the longitudinal member to the heavy goods vehicle body. The rear end is intended to be oriented towards the rear of the heavy goods vehicle structure, and the rear end includes an attachment element for non-permanently attaching the longitudinal member to the heavy goods vehicle body. The longitudinal member includes a front portion and a rear portion. The front portion extends from the front end of the longitudinal member to the intermediate region of the longitudinal member, and the rear portion extends from the intermediate region of the longitudinal member to the rear end of the longitudinal member.

[0003] The present invention also relates to a heavy goods vehicle structure including such a longitudinal member and a method for manufacturing such a longitudinal member. Background Art

[0004] In conventional motor vehicles, longitudinal members, also known as side rails, are arranged to protect the passenger compartment and its passengers in the event of an impact by absorbing a portion of the energy of the impact and by preventing deformation of the floor structure of the passenger compartment (beneath which the longitudinal members extend).

[0005] To this end, the longitudinal member can include a deformable portion and an undeformable portion. The deformable portion extends from the end of the longitudinal member where the impact occurs and is arranged to crush or buckle along its axis to absorb energy. The undeformable portion extends from the end of the front portion opposite to the end where the impact occurs and is arranged to remain undeformed under the influence of the impact. In the case of a frontal impact, the deformable portion is arranged in front of the passenger compartment and extends, for example, in a space arranged to accommodate the vehicle's engine, while the undeformable portion extends beneath the passenger compartment to prevent deformation of the floor structure. In the case of a rear impact, the deformable portion extends behind the passenger compartment, for example, beneath the storage space of the vehicle, and the undeformable portion extends beneath the passenger compartment. In other words, the longitudinal member is arranged such that the impact is applied to the deformable portion, while the undeformable portion extends away from the impact point.

[0006] This arrangement is advantageous because motor vehicles include spaces in front of and behind the passenger compartment that can be used to absorb energy through the deformation of the longitudinal members without causing deformation of the passenger compartment that could harm the vehicle's passengers.

[0007] This behavior of the longitudinal member can be obtained by forming a deformable part with a malleable material and an inflexible part with a high-strength part.

[0008] However, such an arrangement is not suitable for a frontal impact on a heavy goods vehicle or truck in which the cab extends at the front of the vehicle. In fact, in such a case, providing a deformable part arranged such that the impact is applied to the deformable part will cause the cab where the driver and possibly passengers are seated to be crushed during the impact. Thus, if the above longitudinal member is arranged in a heavy goods vehicle, the above longitudinal member will be dangerous for the vehicle occupants.

[0009] In view of this problem, the longitudinal member in a heavy goods vehicle is generally arranged to have a more continuous behavior, in which the energy absorption is evenly distributed over the entire length of the longitudinal member. In other words, the entire longitudinal member deforms in the case of an impact, such that the deformation of the space where the occupants are seated is reduced.

[0010] However, such a solution is still not satisfactory, because in the case of a frontal impact, the space where the occupants are seated will still deform, which may cause harm to the occupants. Summary of the Invention

[0011] One object of the present invention is to overcome the above drawbacks by providing a longitudinal member for a heavy goods vehicle, which has a satisfactory behavior in the case of an impact.

[0012] To this end, the present invention relates to a longitudinal member of the aforementioned type, wherein the product of the wall thickness of the front part and the yield strength of the material of the front part is greater than the product of the wall thickness of the rear part and the yield strength of the material of the rear part. Thus, the longitudinal member according to the present invention allows the energy of the impact to be absorbed by the deformation of the rear part of the longitudinal member (i.e., away from the impact point and away from the space where the vehicle occupants are seated), while the said space is kept protected by the front part of the longitudinal member which is substantially undeformed during the impact. More specifically, the rear part of the longitudinal member is arranged, for example, below the rear space of the cab, which is usually a storage space and is not used to accommodate passengers when the vehicle is in motion. Thus, this longitudinal member improves the protection of the vehicle occupants in the case where the cab is impacted.

[0013] The specific features of the longitudinal member are recited in claims 2 to 12.

[0014] The present invention also relates to a heavy goods vehicle structure, which includes a heavy goods vehicle body and a heavy goods vehicle cab attached to the body by at least one longitudinal member as described above.

[0015] The specific features of the heavy goods vehicle structure are recited in claims 14 to 16.

[0016] The present invention also relates to a method for manufacturing a longitudinal member as described above, which comprises the following steps:

[0017] - providing a front blank and a rear blank,

[0018] - joining the front blank to the rear blank to obtain a member blank; and

[0019] - hot pressing the member blank into the shape of a longitudinal member, the longitudinal member comprising a front portion and a rear portion, such that the product of the wall thickness of the front portion and the yield strength of the material of the front portion is greater than the product of the wall thickness of the rear portion and the yield strength of the material of the rear portion.

[0020] The specific features of the method are recited in claims 18 to 22. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other aspects and advantages of the present invention will become apparent after reading the following description given by way of example and with reference to the accompanying drawings, in which:

[0022] - Figure 1 is a perspective view of a longitudinal member according to the present invention,

[0023] - Figure 2 is a side view of a heavy goods vehicle structure according to the present invention in normal use of the heavy goods vehicle,

[0024] - Figure 3 is Figure 2 a side view of the heavy goods vehicle structure of

[0025] - Figure 4 is Figure 2 a side view of the heavy goods vehicle structure of DETAILED DESCRIPTION

[0026] In the following description, the terms "rear portion" and "front portion" are defined according to the normal direction of the vehicle in which they are installed. The term "longitudinal" is defined according to the front-rear direction of the vehicle.

[0027] With reference to Figure 1 , a longitudinal member 1 or a longitudinal beam for a heavy goods vehicle will be described. Such a heavy goods vehicle, also known as a truck or lorry, is a vehicle having a weight of 3.5 tons or more. The structure of such a heavy goods vehicle includes: a body 2 carrying wheels and means for attaching, for example, a lorry trailer, and a cab 4 attached to the body 2 by one or more longitudinal members 1 as described in more detail subsequently.

[0028] When the longitudinal member 1 is installed in a vehicle, the longitudinal member 1 extends in the longitudinal direction between a front end 6 and a rear end 8. The front end 6 is provided with a hinge element 10 which is arranged to attach the longitudinal member 1 to the vehicle body 2 in a hinged manner, as will be described later. The rear end 8 is provided with an attachment element 12 which is arranged to attach the longitudinal member 1 to the vehicle body 2 in a non-permanent manner, as will be described later.

[0029] The longitudinal member includes a front portion 14 extending between the front end 6 of the longitudinal member 1 and an intermediate region 16 of the longitudinal member 1 and a rear portion 18 extending between the intermediate region 16 and the rear end 8. Thus, the front portion 14 and the rear portion 18 are adjacent to each other and are separated by the intermediate region 16.

[0030] According to Figure 1 the embodiment shown, the front portion 16 includes a first portion 20 extending along a first longitudinal axis A between the front end 6 and an opposite end 22 and a second portion 24 having an elbow shape extending from the opposite end 22 to the intermediate region 16. This means that the first portion 14 mainly extends along the first longitudinal axis A outside the elbow-shaped second portion 24 of the first portion 14. The rear portion 18 extends from the intermediate region 16 to the rear end 8 along a second longitudinal axis B different from and parallel to the first longitudinal axis A. The elbow shape of the second portion 24 joins the first portion 20 of the front portion 14 to the rear portion 18 and includes an inclined portion 26 inclined between the first longitudinal axis A and the second longitudinal axis B and extending between the opposite end 22 and the intermediate region 16. This shape of the longitudinal member is given by way of example, and the longitudinal member 1 may have other shapes, such as a straight shape in which the first longitudinal axis and the second longitudinal axis coincide.

[0031] According to Figure 1 the embodiment shown, the longitudinal member 1 has a U-shaped cross-section in a plane perpendicular to the first longitudinal axis A and the second longitudinal axis B. Thus, the longitudinal member 1 includes a bottom 28 and two branches 30 perpendicular to the two sides of the bottom 28 and extending on the two sides of the bottom 28. The U opens towards the passenger compartment 4, meaning that the branches 30 extend between the bottom 28 and the passenger compartment 4.

[0032] In the same plane perpendicular to the first longitudinal axis A and the second longitudinal axis B, the wall thickness of the bottom 28 is equal to the wall thickness of the branches 30, and the thickness may vary in the longitudinal direction.

[0033] The length of the front portion 14 measured in the longitudinal direction is greater than the length of the rear portion 18 measured in the longitudinal direction. More specifically, the length of the front portion 14 is substantially equal to the length of the space arranged to accommodate occupants in the passenger compartment 4, and the length of the rear portion 18 is proportional to the amount of energy absorbed by the rear portion 18 in the event of an impact, as will be described later. For example, the length of the front portion 14 is between 80 cm and 130 cm, and the length of the rear portion 18 is between 30 cm and 60 cm.

[0034] The front part 14 and the rear part 18 are arranged such that the wall thickness t of the front part 14 F multiplied by the yield strength Ys of the material of the front part 14 F the product P F is greater than the wall thickness t of the rear part 18 R multiplied by the yield strength Ys of the rear part 18 R the product P R . In other words, the front part 14 and the rear part 18 are arranged so as to conform to the following formula: P F = t F * Ys F , P R = t R * Ys R and P F > P R .

[0035] This means that the load corresponding to the onset of plasticity of the rear part 18 is lower than the load corresponding to the onset of plasticity of the front part 14. In other words, when a load higher than a given threshold is applied to the longitudinal member 1, the rear part 18 forms a deformable part, while the front part 14 remains undeformed when the load is applied to the longitudinal member 1. This behavior of the longitudinal member 1 is satisfactory in the case of an impact on the front of a heavy goods vehicle, as will be described subsequently.

[0036] For example, the wall thickness t of the front part 14 F is substantially between 0.6 mm and 3 mm. For example, the yield strength Ys of the material of the front part 14 F is substantially between 960 MPa and 1550 MPa. The wall thickness t of the front part 14 F and the yield strength Ys F are, for example, constant over the entire length of the front part measured in the longitudinal direction. In another embodiment, the wall thickness t of the front part 14 F and the yield strength Ys F vary over the entire length of the front part measured in the longitudinal direction. In this case, the minimum wall thickness and the minimum yield strength are considered to determine the product P F .

[0037] Such a yield strength of the front part 14 can be obtained using a press-hardened steel component having a high tensile strength, for example a tensile strength greater than 1200 MPa.

[0038] The composition of such steel may contain, for example, in weight %, 0.15% ≤ C ≤ 0.5%, 0.5% ≤ Mn ≤ 3%, 0.1% ≤ Si ≤ 1%, 0.005% ≤ Cr ≤ 1%, Ti ≤ 0.2%, Al ≤ 0.1%, S ≤ 0.05%, P ≤ 0.1%, B ≤ 0.010%, with the balance being iron and inevitable impurities resulting from processing.

[0039] According to another preferred embodiment, the steel composition contains, for example, in weight %, 0.20% ≤ C ≤ 0.25%, 1.1% ≤ Mn ≤ 1.4%, 0.15% ≤ Si ≤ 0.35%, ≤ Cr ≤ 0.30%, 0.020% ≤ Ti ≤ 0.060%, 0.020% ≤ Al ≤ 0.060%, S ≤ 0.005%, P ≤ 0.025%, 0.002% ≤ B ≤ 0.004%, with the balance being iron and inevitable impurities resulting from processing. Within this composition range, the tensile strength of the press-hardened component is between 1300 MPa and 1650 MPa.

[0040] According to another preferred embodiment, the steel composition contains, for example, in weight %, 0.24% ≤ C ≤ 0.38%, 0.40% ≤ Mn ≤ 3%, 0.10% ≤ Si ≤ 0.70%, 0.015% ≤ Al ≤ 0.070%, Cr ≤ 2%, 0.25% ≤ Ni ≤ 2%, 0.015% ≤ Ti ≤ 0.10%, Nb ≤ 0.060%, 0.0005% ≤ B ≤ 0.0040%, 0.003% ≤ N ≤ 0.010%, S ≤ 0.005%, P ≤ 0.025%, with the balance being iron and inevitable impurities resulting from processing. Within this composition range, the tensile strength of the press-hardened component is greater than 1800 MPa.

[0041] Such steel has very high mechanical properties, which makes it suitable for forming the front part 14 of the longitudinal member 1, since the front part 14 extends below the space of the passenger compartment where the passengers are seated and participates in the non-deformability of this space, as will be described later. The microstructure of such steel contains a large fraction of martensite.

[0042] For example, the wall thickness t of the rear part 18 R is substantially between 0.6 mm and 3 mm. For example, the yield strength Ys of the material of the rear part 18 R is substantially between 350 MPa and 950 MPa. For example, the wall thickness t of the rear part 18 R and the yield strength Ys R are constant over the entire length of the front part measured in the longitudinal direction. In another embodiment, the wall thickness t of the rear part 18 R and the yield strength Ys RVaries over the entire length of the rear portion measured in the longitudinal direction. In this case, the highest wall thickness and the highest yield strength are considered to determine the product P R .

[0043] Such a yield strength of the rear portion 18 can be obtained by using a press-hardened steel part having a low tensile strength, for example, a tensile strength greater than 350 MPa and less than 800 MPa.

[0044] The composition of such a steel may contain, for example, in weight %: 0.04% ≤ C ≤ 0.1%, 0.3% ≤ Mn ≤ 2%, Si ≤ 0.3%, Ti ≤ 0.08%, 0.015% ≤ Nb ≤ 0.1%, Al ≤ 0.1%, S ≤ 0.05%, P ≤ 0.1%, Cu, Ni, Cr, Mo less than 0.1%, and the balance being iron and unavoidable impurities resulting from processing. The microstructure of such a steel contains a low fraction of martensite or even no martensite. In any case, the fraction of martensite in the microstructure of the front portion 14 is greater than the fraction of martensite in the microstructure of the rear portion 18.

[0045] The bending angle of the rear portion 18 is, for example, greater than 75°, preferably greater than 80°, which imparts good ductility characteristics to the rear portion 18. The bending angle is determined according to the VDA-238 bending standard on a 60x60 mm 2 press-hardened part. The bending force is applied by a sharp punch with a radius of 0.4 mm. The spacing between the rollers and the punch is equal to the thickness of the part being tested, with a 0.5 mm clearance added. The appearance of cracks is detected because it coincides with a load reduction in the load-displacement curve. The test is interrupted when the load reduction exceeds 30 N of its maximum value. After unloading and thus after the specimen rebounds, the bending angle (a) of each sample is measured. Five samples are bent in each direction (rolling direction and transverse direction) to obtain the average value a of the bending angle A .

[0046] The front portion 14 and the rear portion 18 may have the same wall thickness. However, according to one embodiment, the wall thickness t F of the front portion 14 is greater than the wall thickness t R of the rear portion 18.

[0047] According to one embodiment, the front portion 14 and the rear portion 18 are coated with a zinc-based coating (i.e., zinc forms the main part of the coating) or an aluminum-based coating (i.e., aluminum forms the main part of the coating). The coating may contain, for example, zinc, aluminum (about 3.7%) and magnesium (about 3%).

[0048] The above longitudinal beam 1 is formed by joining a flat front blank made of the material of the front portion 14 to a flat rear blank made of the material of the rear portion 18 to form a member blank and hot-pressing the blank to form a longitudinal member.

[0049] The flat front blank has the wall thickness of the front part 14 and is made of the material of the front part 14. The flat rear blank has the wall thickness of the rear part 18 and is made of the rear part 18. In order to join the front blank to the rear blank, the blanks are placed side by side such that their adjacent ends are in contact with each other. This placement is arranged such that the front blank and the rear blank do not overlap, meaning that the component blank does not include a region having two layers (one layer formed by the front blank and the other layer formed by the rear blank). Then, the adjacent ends of the front blank and the rear blank are joined together, for example by welding. More specifically, the welding is, for example, a laser welding step.

[0050] Forming the component blank into a longitudinal member is, for example, a hot stamping step or a hot press forming step, during which the component blank obtains a U-shaped cross-section and during which the second part 24 having an elbow shape is formed. After hot stamping, the obtained longitudinal member causes P F to be greater than P R .

[0051] Then the obtained longitudinal member can be plated by applying a zinc-based coating or an aluminum-based coating.

[0052] Then the hinge element 10 is attached to the front end 6 of the longitudinal member, and then the attachment element 12 is attached to the rear end 8 of the longitudinal member. The hinge element 10 is formed, for example, by two tabs protruding from the bottom wall 28 of the longitudinal member 1, each tab extending in a continuum of one branch 30. The tabs are provided, for example, with holes for rotatably receiving corresponding pins provided on the vehicle body 2. The attachment element 12 is formed by any means adapted to cooperate in a non-permanent manner with a corresponding locking element provided on the vehicle body 2. According to the embodiment shown in the figure, the attachment element 12 is formed, for example, by a plate carrying parallel loops 31 that define a longitudinal housing arranged to receive a corresponding locking element provided on the vehicle body in the form of a shaft, as Figure 2 shown. Alternatively, the hinge element 10 and / or the attachment element 12 can be made integral with the longitudinal member 1 and can be obtained during the forming step of the component blank.

[0053] The above-mentioned longitudinal member is part of the floor structure of the passenger compartment and is attached, for example, by the free ends of the branches 30 to a floor panel arranged to enclose the U-shaped cross-section of the longitudinal member. Thus, the longitudinal member 1 extends below the floor structure. According to one embodiment, the floor structure includes two longitudinal members 1 attached to both sides of the floor panel. This means that the floor structure includes two parallel longitudinal members extending along the left and right sides of the passenger compartment below the floor panel.

[0054] The front part 14 of the longitudinal member 1 extends below the front space 32 of the carriage 4, where the driver's and passengers' seats are located, while the rear part 18 of the longitudinal member 1 extends below the rear space 34 of the carriage 4, which provides storage space. According to the embodiment shown in the figure, the rear part 18 also extends over the engine compartment 36 (shown in dashed lines in Figures 2 to 4 ), which is attached to the vehicle body 2. The second part 24 of the front part 14 is arranged to allow the height of the longitudinal beam 1 relative to the vehicle body 2 and the engine compartment 36 to be changed, so that the engine compartment 36 can be accommodated below the rear space 34 of the carriage 4, as shown in Figure 2 .

[0055] As previously mentioned, the longitudinal member 1 is attached to the vehicle body 2 by means of a hinge element 10 and an attachment element 12. Such a vehicle body 2 is arranged to carry, in addition to the carriage, the wheels of the vehicle, the engine compartment 36, and a goods trailer, for example by means of a device for attaching the goods trailer to the vehicle body. The vehicle body 2 is formed from a metal chassis including the necessary means for attaching the above elements. The metal chassis is made of steel, for example, and its wall thickness is in the range of 8 mm to 15 mm. Therefore, the vehicle body 2 has a high tensile strength and is suitable for withstanding large impacts without deformation of the metal chassis.

[0056] The vehicle body 2 includes at least one complementary hinge element 38, which is arranged to cooperate with the hinge element 10 of the longitudinal member 1, so that the longitudinal member is hinged to the vehicle body 2 by its front end 6. The complementary hinge element 38 is formed by a pin, for example, which is rotatably inserted into the corresponding holes of the tabs forming the hinge element 10 of the longitudinal member 1. The axis of rotation extends transversely (i.e., in the vertical direction of the longitudinal direction). When two longitudinal members 1 are provided on the carriage, the vehicle body 2 includes two complementary hinge elements 38, and each of the two complementary hinge elements 38 cooperates with one hinge element 10.

[0057] Therefore, the hinge element 10 and the complementary hinge element 38 form a hinge 39, which hinges the front end of the longitudinal member 1 to the front end of the vehicle body 2, so that between the normal use position shown in Figure 2 and the tilted position shown in Figure 3 , the carriage 4 is hinged to the vehicle body 2 at its front by means of two longitudinal members 1. Such tilting of the carriage 4 is conventional in heavy goods vehicles in order to gain access to the engine compartment 36 for maintenance or repair operations, since, as previously mentioned, the engine compartment 36 extends below the rear space 34 of the carriage 4.

[0058] A hinge 39 formed by a hinge element 10 and a complementary hinge element 38 is arranged to break when an external load equal to or greater than a predetermined load is applied to the front end 6 of the longitudinal member 1 in the longitudinal direction. The predetermined force is an example of a force substantially equal to 80 kN and corresponds to the minimum external load applied to the longitudinal member in the longitudinal direction in the case of a frontal impact (a part of the energy of which needs to be absorbed).

[0059] The vehicle body 2 further includes at least one locking element 40 which is arranged to cooperate with the attachment element 12 of the longitudinal member 1 such that the longitudinal member is non-permanently attached to the vehicle body 2 through its rear end 8. The locking element 40 is formed by any means adapted to cooperate with the attachment element 12 for attaching the longitudinal member 1 through its rear end 8 in a locked position such that when the locking element 40 is in the locked position, the rear end 8 of the longitudinal member 1 does not move relative to the vehicle body 2, so that the passenger compartment cannot move to its tilted position. According to Figures 2 to 4 the illustrated embodiment, the locking element 40 is in the form of a shaft, for example, which is introduced into a loop 31 forming the attachment element 12.

[0060] The locking element 40 can also be moved to an unlocked position, in which the attachment element 12 does not cooperate with the locking element 40, such that when the locking element 40 is in the unlocked position, the passenger compartment can move to its tilted position. According to a variant, the attachment element 12 can be moved between an unlocked position and a locked position. The locking element 40 can, for example, be translated in the longitudinal direction in the unlocked position such that the shaft can be removed from the loop 31, as Figure 3 illustrated. When two longitudinal members 1 are provided on the passenger compartment, the vehicle body 2 includes two locking attachments 40, and the two locking attachments 40 each cooperate with one attachment element 12.

[0061] The attachment element 12 and the locking element 40 together form a locking attachment that connects the rear end of the longitudinal member 1 to the vehicle body 2. Such a locking attachment is also conventional in heavy goods vehicles and allows preventing the passenger compartment from moving to its tilted position during normal use of the vehicle (for example, in the case of an emergency brake or in the case of an impact).

[0062] For this purpose, the locking attachment formed by the attachment element 12 and the locking element 10 is arranged to resist an external load applied to the longitudinal member 1 in the longitudinal direction in the case of a frontal impact. Resisting means that the locking attachment does not break in the case of an impact, and the immovable connection provided by the locking attachment remains in the locked position of the locking attachment after the impact. The locking attachment is, for example, capable of resisting an external load greater than 80 kN and up to a force of 140 kN.

[0063] The vehicle body 2 may further include means (not shown) for moving the carriage 4 between a normal use position and a tilted position when the locking attachment is in the unlocked position. Such means are formed, for example, by one or more piston means arranged between the vehicle body 2 and the carriage 4.

[0064] The behavior of the longitudinal member in the case of a frontal impact on the above-described heavy truck structure will now be described.

[0065] In the case of a frontal impact, for example when the heavy truck hits a wall or another vehicle, the impact occurs at the front end of the heavy truck, particularly at the front end 6 of the longitudinal member 1.

[0066] When the external load applied to the longitudinal member due to the impact is equal to or exceeds a predetermined load that requires energy absorption, the hinge 39 breaks while the locking attachment remains, as Figure 4 shown. Thus, the longitudinal member 1 becomes a deformable structure capable of deforming between its front end 6 and its rear end 8, and it remains attached to the vehicle body 2.

[0067] Since the front portion 14 forms a substantially non-deformable structure, the energy of the impact is transmitted to the rear portion 18 of the longitudinal member 1 without deforming the front portion 14. Specifically, when the front portion 14 includes a second portion 24 having an elbow shape, the second portion 24 does not deform and does not bend the rear portion 18 out of its second longitudinal axis B. As Figure 4 shown, since the longitudinal member does not deform during the impact, the front space 32 remains intact during the impact and the driver and passengers are protected.

[0068] Since the rear portion 18 forms an extensible part of the longitudinal member 1, the energy transmitted from the front portion 14 of the longitudinal member 1 to the rear portion 18 of the longitudinal member 1 causes the rear portion 18 to deform along its second longitudinal axis B. The deformation of the rear portion is more specifically a buckling of the rear portion 18 along the second longitudinal axis B. This deformation causes the rear portion 18 to be crushed or buckled along its longitudinal axis and form a folded portion 42. Since the end of the second portion 24 of the front portion 14 is formed by the intermediate portion 16 and is also located on the second longitudinal axis B, the deformation remains along the second longitudinal axis B. The folded portion 42 allows part of the impact energy to be absorbed, thus reducing the impact on the carriage. The deformation of the rear portion 18 of the longitudinal member causes the walls of the carriage 2 to deform around the rear space 34 of the carriage, as Figure 4 the folded portion 44 shown. Thus, the walls around the rear space 34 also participate in energy absorption.

[0069] The deformation of the carriage in the rear space 34 is not dangerous for the occupants of the carriage because the rear space 34 is not used to accommodate these passengers.

[0070] The longitudinal member 1 according to the present invention allows the protection of the passenger compartment 2 in the space where the occupants are seated, while allowing the absorption of energy in the unoccupied space by placing the ductile part of the longitudinal member away from the impact point, since the impact point is directly in front of the space where the occupants are seated in a heavy goods vehicle.

[0071] The longitudinal member is particularly suitable for meeting the requirements of Test A (or frontal impact test) of the ECE (Economic Commission for Europe) regulation ECE-R29 / 03.

[0072] The present invention provides the following technical solutions:

[0073] Solution 1. A longitudinal member (1) for a heavy goods vehicle structure, the longitudinal member comprising a front end (6) and a rear end (8), the front end (6) being intended to be oriented towards the front of the heavy goods vehicle structure, the front end (6) being provided with a hinge element (10) for hingedly attaching the longitudinal member to the heavy goods vehicle body (2), the rear end (8) being intended to be oriented towards the rear of the heavy goods vehicle structure, the rear end (8) comprising an attachment element (12) for non-permanently attaching the longitudinal member to the heavy goods vehicle body (2), the longitudinal member comprising a front part (14) and a rear part (18), the front part (14) extending from the front end (6) of the longitudinal member to an intermediate region (16), the rear part (18) extending from the intermediate region (16) of the longitudinal member to the rear end (8), characterized in that the product (P F ) of the wall thickness (t F ) of the front part (14) and the yield strength (Ys F ) of the material of the front part (14) is greater than the product (P R ) of the wall thickness (t R ) of the rear part (18) and the yield strength (Ys R ) of the material of the rear part (18).

[0074] Solution 2. The longitudinal member according to Solution 1, wherein the wall thickness (t F ) of the front part (14) is substantially between 0.6 mm and 3 mm, and the yield strength (Ys F ) of the material of the front part (14) is substantially between 960 MPa and 1550 MPa.

[0075] Solution 3. The longitudinal member according to Solution 1 or 2, wherein the wall thickness (t R ) of the rear part (18) is substantially between 0.6 mm and 3 mm, and the yield strength (Ys R ) of the material of the rear part (18) is substantially between 350 MPa and 950 MPa.

[0076] Solution 4. The longitudinal member according to any one of Solutions 1 to 3, wherein the wall thickness (t F ) of the front part (14) is greater than the wall thickness (t R ) of the rear part (18).

[0077] Solution 5. The longitudinal member according to any one of Solutions 1 to 4, wherein the longitudinal member is a press-hardened member.

[0078] Solution 6. The longitudinal member according to any one of Solutions 1 to 5, wherein the front part (14) is made of press-hardened steel, and the press-hardened steel contains, by weight%:

[0079] - 0.15% ≤ C ≤ 0.5%, 0.5% ≤ Mn ≤ 3%, 0.1% ≤ Si ≤ 1%, 0.005% ≤ Cr ≤ 1%, Ti ≤ 0.2%, Al ≤ 0.1%, S ≤ 0.05%, P ≤ 0.1%, B ≤ 0.010%, the balance being iron and inevitable impurities resulting from processing; or

[0080] - 0.20% ≤ C ≤ 0.25%, 1.1% ≤ Mn ≤ 1.4%, 0.15% ≤ Si ≤ 0.35%, ≤ Cr ≤ 0.30%, 0.020% ≤ Ti ≤ 0.060%, 0.020% ≤ Al ≤ 0.060%, S ≤ 0.005%, P ≤ 0.025%, 0.002% ≤ B ≤ 0.004%, the balance being iron and inevitable impurities resulting from processing; or

[0081] - 0.24% ≤ C ≤ 0.38%, 0.40% ≤ Mn ≤ 3%, 0.10% ≤ Si ≤ 0.70%, 0.015% ≤ Al ≤ 0.070%, Cr ≤ 2%, 0.25% ≤ Ni ≤ 2%, 0.015% ≤ Ti ≤ 0.10%, Nb ≤ 0.060%, 0.0005% ≤ B ≤ 0.0040%, 0.003% ≤ N ≤ 0.010%, S ≤ 0.005%, P ≤ 0.025%,%, the balance being iron and inevitable impurities resulting from processing.

[0082] Solution 7. The longitudinal member according to any one of Solutions 1 to 6, wherein the rear part (18) is made of press-hardened steel, and the press-hardened steel contains, by weight%: 0.04% ≤ C ≤ 0.1%, 0.3% ≤ Mn ≤ 2%, Si ≤ 0.3%, Ti ≤ 0.08%, 0.015% ≤ Nb ≤ 0.1%, Al ≤ 0.1%, S ≤ 0.05%, P ≤ 0.1%, Cu, Ni, Cr, Mo are less than 0.1%, the balance being iron and inevitable impurities resulting from processing.

[0083] Variant 8. The longitudinal member according to Variant 7, wherein the bending angle of the rear part (18) is greater than 75°.

[0084] Variant 9. The longitudinal member according to any one of Variants 5 to 8, wherein the fraction of martensite in the microstructure of the front part (14) is greater than the fraction of martensite in the microstructure of the rear part (18).

[0085] Variant 10. The longitudinal member according to any one of Variants 1 to 9, wherein the front part (14) and the rear part (18) are coated with a zinc-based coating or an aluminum-based coating.

[0086] Variant 11. The longitudinal member according to any one of Variants 1 to 10, wherein the intermediate region (16) extends at the end of the elbow part (24) of the first part (14) such that the front part (14) extends mainly along a first longitudinal axis (A) outside the elbow region (24) and the rear part (18) extends mainly along a second longitudinal axis (B), the first longitudinal axis (A) and the second longitudinal axis (B) being different and substantially parallel to each other.

[0087] Variant 12. The longitudinal member according to any one of Variants 1 to 11, wherein the longitudinal member is intended to extend under the floor structure of the heavy goods vehicle body.

[0088] Variant 13. A heavy goods vehicle structure comprising a heavy goods vehicle body (2) and a heavy goods vehicle load compartment (4), the heavy goods vehicle load compartment (4) being attached to the body (2) by at least one longitudinal member (1) according to any one of Variants 1 to 12, wherein the hinge element (10) at the front end (6) of the longitudinal member (1) is attached to a complementary hinge element (38) of the body (2) to form a hinge (39) that pivotally connects the load compartment (4) to the body (2), and wherein the attachment element (12) at the rear end (8) of the longitudinal member (1) is attached to a locking element (40) of the body (2) to form a locking attachment that non-permanently connects the load compartment (4) to the body (2).

[0089] Variant 14. The heavy goods vehicle structure according to Variant 13, wherein the hinge (39) is arranged to break under an impact applied substantially longitudinally to the front end (6) of the longitudinal member (1) under an external load greater than 80 kN, while the locking attachment is arranged to resist the impact when the attachment element (12) is attached to the locking element (40) such that the rear part (18) of the longitudinal member (1) can be crushed under the impact to absorb energy.

[0090] Solution 15. The heavy truck structure according to Solution 13 or 14, wherein the longitudinal member extends below the floor structure of the heavy truck structure.

[0091] Solution 16. The heavy truck structure according to Solution 15, wherein the carriage (4) is attached to the body (2) by at least two longitudinal members (1) extending on both sides of the floor structure of the carriage.

[0092] Solution 17. A method for manufacturing a longitudinal member according to any one of Solutions 1 to 12, comprising the following steps:

[0093] - Providing a front blank and a rear blank, - Joining the front blank to the rear blank to obtain a member blank; and

[0094] - Hot pressing the member blank into the shape of the longitudinal member, the longitudinal member comprising a front part (14) and a rear part (18), such that the product (P F ) of the wall thickness (t F ) of the front part (14) and the yield strength (Ys F ) of the material of the front part (14) is greater than the product (P R ) of the wall thickness (t R ) of the rear part (18) and the yield strength (Ys R ) of the material of the rear part (18).

[0095] Solution 18. The method according to Solution 17, wherein the member blank is hot pressed into a shape having a U-shaped cross section.

[0096] Solution 19. The method according to Solution 18, wherein the member blank is formed to include an elbow part (24).

[0097] Solution 20. The method according to any one of Solutions 17 to 19, wherein the front blank is joined to the rear blank by welding without overlapping the front blank and the rear blank.

[0098] Solution 21. The method according to Solution 20, wherein the welding is laser welding.

[0099] Solution 22. The method according to any one of Solutions 17 to 21, further comprising the steps of attaching a hinge element (10) to the front end (6) of the longitudinal member (1) and attaching an attachment element (12) to the rear end (8) of the longitudinal member (1).

Claims

1. A longitudinal member (1) for a heavy goods vehicle structure, the longitudinal member comprising a front end (6) and a rear end (8), the front end (6) being intended to be oriented towards the front of the heavy goods vehicle structure, the front end (6) being provided with a hinge element (10) for hingedly attaching the longitudinal member to the heavy goods vehicle body (2), the rear end (8) being intended to be oriented towards the rear of the heavy goods vehicle structure, the rear end (8) comprising an attachment element (12) for attaching the longitudinal member to the heavy goods vehicle body (2) in a non-permanent manner, the longitudinal member comprising a front portion (14) and a rear portion (18), the front portion (14) extending from the front end (6) of the longitudinal member to an intermediate region (16), the rear portion (18) extending from the intermediate region (16) of the longitudinal member to the rear end (8), characterized in that the product (P F ) of the wall thickness (t F ) of the front portion (14) and the yield strength (Ys F ) of the material of the front portion (14) is greater than the product (P R ) of the wall thickness (t R ) of the rear portion (18) and the yield strength (Ys R ) of the material of the rear portion (18).

2. The longitudinal member according to claim 1, wherein the wall thickness (t F ) of the front portion (14) is substantially between 0.6 mm and 3 mm, and the yield strength (Ys F ) of the material of the front portion (14) is substantially between 960 MPa and 1550 MPa.

3. The longitudinal member according to claim 1 or 2, wherein the wall thickness (t R ) of the rear part (18) is substantially between 0.6 mm and 3 mm, and the yield strength (Ys R ) of the material of the rear part (18) is substantially between 350 MPa and 950 MPa.

4. The longitudinal member according to any one of claims 1 to 3, wherein the wall thickness (t F ) of the front part (14) is greater than the wall thickness (t R ) of the rear part (18).

5. The longitudinal member according to any one of claims 1 to 4, wherein the longitudinal member is a press-hardened member.

6. The longitudinal member according to any one of claims 1 to 5, wherein the front portion (14) is made of press-hardened steel, and the press-hardened steel contains, by weight %: -0.15% ≤ C ≤ 0.5%, 0.5% ≤ Mn ≤ 3%, 0.1% ≤ Si ≤ 1%, 0.005% ≤ Cr ≤ 1%, Ti ≤ 0.2%, Al ≤ 0.1%, S ≤ 0.05%, P ≤ 0.1%, B ≤ 0.010%, the balance being iron and inevitable impurities resulting from processing; Or - 0.20% ≤ C ≤ 0.25%, 1.1% ≤ Mn ≤ 1.4%, 0.15% ≤ Si ≤ 0.35%, ≤ Cr ≤ 0.30%, 0.020% ≤ Ti ≤ 0.060%, 0.020% ≤ Al ≤ 0.060%, S ≤ 0.005%, P ≤ 0.025%, 0.002% ≤ B ≤ 0.004%, the balance being iron and unavoidable impurities resulting from processing; Or - 0.24% ≤ C ≤ 0.38%, 0.40% ≤ Mn ≤ 3%, 0.10% ≤ Si ≤ 0.70%, 0.015% ≤ Al ≤ 0.070%, Cr ≤ 2%, 0.25% ≤ Ni ≤ 2%, 0.015% ≤ Ti ≤ 0.10%, Nb ≤ 0.060%, 0.0005% ≤ B ≤ 0.0040%, 0.003% ≤ N ≤ 0.010%, S ≤ 0.005%, P ≤ 0.025%, %, the balance being iron and unavoidable impurities resulting from processing.

7. The longitudinal member according to any one of claims 1 to 6, wherein the rear portion (18) is made of press-hardened steel, and the press-hardened steel contains, by weight %: 0.04% ≤ C ≤ 0.1%, 0.3% ≤ Mn ≤ 2%, Si ≤ 0.3%, Ti ≤ 0.08%, 0.015% ≤ Nb ≤ 0.1%, Al ≤ 0.1%, S ≤ 0.05%, P ≤ 0.1%, Cu, Ni, Cr, Mo less than 0.1%, the balance being iron and unavoidable impurities resulting from processing.

8. The longitudinal member according to claim 7, wherein the bending angle of the rear portion (18) is greater than 75°.

9. The longitudinal member according to any one of claims 5 to 8, wherein the fraction of martensite in the microstructure of the front portion (14) is greater than the fraction of martensite in the microstructure of the rear portion (18).

10. The longitudinal member according to any one of claims 1 to 9, wherein the front portion (14) and the rear portion (18) are coated with a zinc-based coating or an aluminum-based coating.

11. The longitudinal member according to any one of claims 1 to 10, wherein the intermediate region (16) extends at the end of the elbow portion (24) of the first portion (14) such that the front portion (14) extends mainly along a first longitudinal axis (A) outside the elbow region (24) and the rear portion (18) extends mainly along a second longitudinal axis (B), the first longitudinal axis (A) and the second longitudinal axis (B) being different and substantially parallel to each other.

12. The longitudinal member according to any one of claims 1 to 11, wherein the longitudinal member is intended to extend under the floor structure of the heavy goods vehicle.

13. A heavy-duty truck structure, comprising a heavy-duty truck body (2) and a heavy-duty truck carriage (4), wherein the heavy-duty truck carriage (4) is attached to the body (2) by at least one longitudinal member (1) according to any one of claims 1 to 12, wherein a hinge element (10) at the front end (6) of the longitudinal member (1) is attached to a complementary hinge element (38) of the body (2) to form a hinge (39) that hingedly connects the carriage (4) to the body (2), and wherein an attachment element (12) at the rear end (8) of the longitudinal member (1) is attached to a locking element (40) of the body (2) to form a locking attachment that non-permanently connects the carriage (4) to the body (2).

14. The heavy-duty truck structure according to claim 13, wherein the hinge (39) is arranged to break in the case of an impact applied substantially longitudinally to the front end (6) of the longitudinal member (1) under an external load greater than 80 kN, while the locking attachment is arranged to resist the impact when the attachment element (12) is attached to the locking element (40), such that the rear part (18) of the longitudinal member (1) can be crushed in the case of the impact to absorb energy.

15. The heavy-duty truck structure according to claim 13 or 14, wherein the longitudinal member extends below the floor structure of the carriage of the heavy-duty truck structure.

16. The heavy-duty truck structure according to claim 15, wherein the carriage (4) is attached to the body (2) by at least two longitudinal members (1) extending on both sides of the floor structure of the carriage.

17. A method for manufacturing a longitudinal member according to any one of claims 1 to 12, comprising the following steps: - providing a front blank and a rear blank, - joining the front blank to the rear blank to obtain a member blank; and - Hot press the blank of the component to form the shape of the longitudinal component, the longitudinal component including a front portion (14) and a rear portion (18), such that the wall thickness (t F ) of the front portion (14) multiplied by the yield strength (Ys F ) of the material of the front portion (14), the product (P F ) is greater than the wall thickness (t R ) of the rear portion (18) multiplied by the yield strength (Ys R ) of the material of the rear portion (18), the product (P R ).

18. The method according to claim 17, wherein the member blank is hot-pressed into a shape having a U-shaped cross-section.

19. The method according to claim 18, wherein the member blank is formed to include an elbow portion (24).

20. The method according to any one of claims 17 to 19, wherein the front blank is joined to the rear blank by welding without overlapping the front blank and the rear blank.

21. The method according to claim 20, wherein the welding is laser welding.

22. The method according to any one of claims 17 to 21, further comprising the steps of attaching a hinge element (10) to the front end (6) of the longitudinal member (1) and attaching an attachment element (12) to the rear end (8) of the longitudinal member (1).

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