Improved method for lowering a vehicle undercarriage to a desired vertical position

Abstract

The present invention relates to a method for lowering the chassis of a vehicle to a desired vertical position, the vehicle including only two sets of running gear, namely a front set of running gear and a rear set of running gear, each wheel of the running gear set being associated with a parking brake, the method comprising the following successive steps: - when the chassis is in its high running position, activating the parking brake only for all wheels of one of the two running gear sets; - lowering the chassis to its low position resting on the ground; - activating the parking brake for all wheels of the other of the two running gear sets.

Description

[Technical field]

[0001] The present invention relates to the field of vehicles whose undercarriage is controllable so that it can be moved between an elevated driving position and a lowered position in which the undercarriage is supported on the ground.

[0002] The present invention preferably relates to a delivery vehicle having a cargo carrying space, and even more preferably to an urban delivery truck. [Background technology]

[0003] The feature of this type of vehicle being able to lower the undercarriage makes it possible to facilitate cargo loading and unloading operations: in fact, when the undercarriage assumes its low position supported on the ground, the cargo loading space is located as close as possible to the ground, and the handling of the cargo, in particular the handling required for its delivery, is advantageously simplified.

[0004] Such vehicles have a number of wheels and, associated with each wheel, a pivoting wheel suspension arm on the chassis. A suspension arm actuator is also associated with each wheel and is located between the suspension arm and the chassis. The actuator makes it possible to control the angular position of the arm relative to the chassis in order to vary the vertical position of the chassis.

[0005] When a vehicle has front and rear running gears, the kinematics of the suspension arms are not necessarily the same on each of these two running gears. Moreover, it is generally recommended that the lowering be performed with the parking brakes applied to each of the vehicle's wheels to prevent the vehicle from moving unnecessarily, especially when the vehicle is parked on an inclined road.

[0006] Therefore, when the chassis is lowered with the parking brakes applied on each wheel of the vehicle, high stresses can be induced in the running gear due to the different kinematics associated with the rotating suspension arms. Summary of the Invention [Problem to be solved by the invention]

[0007] There is therefore a need for improved methods for lowering the undercarriage of a vehicle, in particular to reduce the mechanical stresses observed in the running gear during descent. [Means for solving the problem]

[0008] To at least partially address this need, the present invention relates to a method for lowering a chassis of a vehicle with a controllable vertical position, the vehicle being designed such that the chassis can be moved between an elevated running position and a lowered position in which the chassis is supported on the ground, the vehicle also including a plurality of wheels, each wheel having associated therewith: - suspension arms carrying wheels pivotally mounted on the chassis; - a suspension arm actuator arranged between the suspension arm and the chassis, making it possible to control the angular position of the arm relative to the chassis in order to vary the vertical position of the chassis; The vehicle includes only two running gears, namely a front running gear and a rear running gear, and each wheel of the running gears is associated with a parking brake, and the method includes the following series of steps. - applying the parking brake only to all the wheels of one of the two running gears when the vehicle chassis is in a high running position; - lowering the chassis to its lower position supported on the ground; and - activating the parking brake on all of the wheels of the other of the two running gears.

[0009] This method, which is specific to the invention, allows the lowering of the chassis to its lowered position supported by the ground without generating stresses in the running gear by the sequential administration of the parking brake on the wheels. The lowering of the chassis can therefore be performed stress-free, regardless of the kinematics associated with each of the suspension arms, while ensuring that the vehicle remains stationary by the parking brake being applied to the wheels of one of the two running gears during this descent.

[0010] The present invention preferably comprises at least one of the following optional features taken individually or in combination.

[0011] Preferably, the method includes the step of detecting a steering angle of the wheels of the front running gear, said step of lowering the chassis being performed only if the detected steering angle is below a safe value.

[0012] In this regard, when the detected steering angle is greater than a safe value, manual or automatic steps are performed to correct the direction of the wheels of the front running gear.

[0013] Preferably, the step of safely loading the tires is performed after the chassis has been lowered to its low position where it is supported on the ground.

[0014] Preferably, said one of the two running gears, the wheels of which have their parking brakes activated when the chassis is in the high running position, corresponds to the rear running gear, alternatively it may be the front running gear without departing from the scope of the invention.

[0015] Preferably, a safety device is associated with each wheel and is capable of limiting the accidental lowering of the chassis, the device being capable of assuming an active state which on the one hand enables limiting the rotation of the suspension arm in a first direction leading to lowering of the chassis to a safe position of this arm, and on the other hand an inactive state which enables rotation of this arm in the first direction beyond the safe position, the method comprising a step of switching the safety device from the active state to the inactive state before the step of lowering the chassis.

[0016] Preferably, each wheel is associated with a device for preventing rotation of its suspension arm, and the method includes, after the step of lowering the chassis, the step of activating a device for preventing rotation of the suspension arm (28) associated with each of the wheels of the vehicle.

[0017] The safety device preferably comprises a jack having a cylinder mounted on the undercarriage and a piston mounted on the suspension arm, or vice versa, the jack defining a first chamber communicating with first and second fluid passages through the cylinder, the first passage and the second passage being spaced apart from each other in the sliding direction of the piston in the cylinder, whereby the second passage is located as close as possible to the bottom of the first chamber defined by the cylinder, the second passage communicating with a first fluid duct provided with a safety valve, the safety valve being an open position in which the safety device is deactivated to allow fluid to be evacuated from the first chamber through the second passage when the piston moves towards the bottom of the first chamber due to the rotation of the suspension arm in said first direction; - a closed position in which the safety device is activated, such that when the piston moves towards the bottom of the first chamber due to the rotation of the suspension arm in said first direction, the piston is locked in a safety position a short distance from the bottom of the first chamber, in which position fluid is compressed between the piston head and the safety valve.

[0018] By this design of the safety device used in the method according to the invention, a simple, reliable and compact solution is obtained, which makes it possible to prevent the undercarriage from being lowered to the ground by mistake. Indeed, in case of failure of the actuator associated with one of the wheels, the weight of the undercarriage and the load of the vehicle cause the suspension arm to rotate in a first direction. The unintended rotation of the suspension arm causes the piston of the safety device to move towards the bottom of the first chamber of the jack. When the piston head reaches the first fluid passage formed through the cylinder, the safety valve associated with the second fluid passage is in the closed position reflecting the activated state of the safety device, so that the fluid can no longer leave the first chamber of the jack. This locks the piston in a safety position a short distance from the bottom of the first chamber, which lock stops the suspension arm from rotating by mistake. The suspension arm then remains advantageously held in the safety position, preventing contact between the undercarriage and the ground by the pressure of the fluid between the piston head of the safety device and the safety valve in the closed position. Finally, it is noted that this design is at the same time advantageous in that the safety devices can be remotely controlled from the driver's seat, for example to facilitate the procedure of lowering the undercarriage.

[0019] Other advantages and features of the present invention will appear in the following non-limiting detailed description.

[0020] The detailed description of the invention is provided with reference to the accompanying drawings. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic side view of a vehicle with its chassis in an elevated driving position. [Diagram 2] FIG. 2 is a view similar to the previous one, but with the undercarriage in a lowered position supported on the ground. [Diagram 3] FIG. 3 is a bottom view of the vehicle shown in FIGS. 1 and 2. [Figure 4] FIG. 2 is a more detailed side view of a portion of the vehicle with the chassis in an elevated driving position in the first preferred embodiment. [Diagram 5] FIG. 5 is a diagram of a safety device for preventing the risk of the undercarriage being inadvertently lowered to the ground, the safety device being associated with the wheel shown in FIG. 4 and shown in an active state assumed with the undercarriage in the high running position of FIG. [Figure 6] A view similar to Figure 4, but with the wheel suspension arm in a safe position.Figure 6' is a schematic side view of a vehicle in the event of failure of an actuator associated with one of the rear wheels of the vehicle. [Figure 7] 7 is a view similar to FIG. 5 showing the safety device in the activated state which it assumes when the suspension arm occupies its safe position of FIG. 6; [Figure 8] FIG. 7 is a view similar to FIG. 6, but with the chassis in its lowered position supported on the ground. [Figure 9] 9 is a view similar to FIG. 7 showing the safety device in the inactive state which it assumes when the undercarriage occupies its lowered, supported position of FIG. 8; [Figure 10] FIG. 5 is a view similar to FIG. 4, where the vehicle is according to the second preferred embodiment. [Figure 11] 11 shows a safety device associated with the wheel shown in FIG. 10, the safety device being shown in an activated state assumed with the chassis in the high drive position of FIG. 10. [Figure 12] FIG. 2 is a schematic diagram of another embodiment in which safety devices associated with the wheels of a vehicle cooperate with each other to ensure the anti-roll function; [Figure 13] FIG. 13 is a schematic view similar to FIG. 12, in which the safety device also integrates an impact absorbing function. [Figure 14] FIG. 5 is a view similar to FIG. 4, in which the safety device and the actuator are integrated in the same assembly, and the actuator may also integrate the shock absorber. [Figure 15] FIG. 2 is a perspective view of one of the wheels of a vehicle according to an improved embodiment. [Figure 16] FIG. 6 is a view similar to FIG. 5, in which the safety device integrates the additional function of preventing rotation of the wheel suspension arm. [Figure 16a]FIG. 17 is a view similar to FIG. 16, in which the safety device is presented in an alternative form. [Figure 17] FIG. 1 shows a vehicle with its chassis in a lowered position supported on a convex ground surface. [Figure 18] FIG. 13 is a view similar to FIG. 12, in which the safety device integrates the additional function of preventing rotation of the wheel suspension arm. [Figure 19] FIG. 1 is a schematic side view of a vehicle with its chassis in an elevated driving position. [Figure 20] 3A-3C are schematic diagrams illustrating the various steps of the method for lowering the undercarriage, as shown in the previous figures, in a preferred embodiment of the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 1 to 3, there is shown a type of vehicle 1 which includes a chassis 2 having a controllable vertical position. The vehicle 1, which in this case is preferably an urban delivery truck, in effect has a chassis 2 which can be raised to a high running position as shown in Figure 1 and lowered to a low position supported on the ground 4 as shown in Figure 2. Nevertheless, the vehicle 1 may include other vehicles, preferably road transport vehicles.

[0023] The undercarriage 2, also referred to as the "body", supports or defines a cargo carrying space 6. For example, this space 6 is defined by the undercarriage 2 at its bottom, as close to the ground as possible in the position of the low supported undercarriage.

[0024] In the high travel position, the ground clearance G1 of the chassis 2 remains moderate in order to limit the vertical travel distance required to reach the lower ground supported position taken for unloading the cargo. Typically, this ground clearance G1 is less than 500 mm, preferably between 150 mm and 500 mm.

[0025] The vehicle 1 includes only two running gears, namely a front running gear 8 and a rear running gear 10. Each of the two running gears is equipped with only two single wheel assemblies, each of the wheels being individually articulated on the chassis 2 by a suspension arm, which will be described below. Nevertheless, the design could be more complicated if each wheel were associated with a single suspension arm in this case. Indeed, there could be, for example, a front running gear in which the two wheels are on the same axle, the axle itself being articulated by generally two "pushed" or "pulled" suspension arms per wheel, mounted on the top and bottom of the axle to generate a parallelogram kinematics. Thus, each of the wheels could be articulated on the chassis 2 by at least one suspension arm in a "pushed" or "pulled" configuration, either individually or in pairs.

[0026] Thus, the front unit 8 includes a front left wheel R1 and a front right wheel R2, while the rear unit 10 includes a rear left wheel R3 and a rear right wheel R4.

[0027] The loading space 6 has an expanded rear cantilever area. In fact, this leads to the observation that the vertical projection of the center of gravity 12 of the loaded vehicle, as shown in FIG. 3, is located behind the intersection 14 between the two diagonals connecting the centers 16 of the treads 20 of the front and rear wheels R1-R4. In other words, the center of gravity 12 of the loaded vehicle is located behind the midpoint of the wheelbase between the two running gears 8, 10. In this case, the term "loaded vehicle" means that the loading space 6 is entirely occupied by cargo, all of which has the same weight per unit area.

[0028] The longitudinal distance of the centre of gravity 12 to the midpoint of the wheelbase, corresponding to the intersection 14 between the diagonals, is approximately 50 cm to 1 m, and may be up to 2 m. In this regard, it is noted that the vehicle 1 has a longitudinal direction referenced by "L" in the figures, as well as a lateral direction referenced by "T". Referring now to FIG. 4, an assembly is shown between one of the wheels of the vehicle and the chassis 2. In this case, the assembly is the left rear wheel R3, but it will be understood that the assembly is the same or similar for each of the four wheels R1 to R4. Therefore, only the assembly of wheel R3 will be described below.

[0029] It should first be noted that wheel R3 has a rim 22 as well as a tire 24 disposed about the rim. It is the tire 24 that defines the tread 20. The rim 22 is articulated about a wheel axis of rotation 26 on a suspension arm 28 having a generally rectangular shape. Wheel R3 is articulated at one of the vertices of arm 28. Arm 28 is pivotally mounted at another of the vertices on chassis 2 about an arm axis of rotation 30 that is parallel or substantially parallel to wheel axis of rotation 26.

[0030] At the third vertex of the suspension arm 28, one end of an actuator 32 of the suspension arm is articulated. This articulation is made about an actuator axis of rotation 34 parallel to the axes 26, 30. At its opposite longitudinal end, the actuator 32 is carried on the chassis 2 or is likewise articulated thereon. This actuator 32 makes it possible to control the angular position of the suspension arm 28 relative to the chassis 2 in order to vary the vertical position of the chassis as desired.

[0031] The actuator 32 is in this case of the airbag type. It is the control of its internal pressure that makes it possible to adjust its longitudinal spacing between the arm 28 and the chassis 2, which spacing determines the angular position of the arm 28. This pressure is regulated by a control unit 33 of the vehicle, which unit can be common for the four wheels, but which can supply different control signals according to the wheels.

[0032] In Fig. 4, the angular position of the suspension arm 28 is such that it forms an angle A1 with respect to the chassis 2, this angle A1 being determined in a side view between a perpendicular or normal line to the chassis and an imaginary line connecting the two axes 26, 30. The angle A1 assumed during travel of the vehicle is, for example, approximately 90°, but it can of course be smaller or larger. In addition, the suspension arm 28 is preferably damped, so that the value of the angle A1 varies during the damping phases encountered during travel.

[0033] To achieve this damping of the suspension arm 28, a damper 36 of any design known to those skilled in the art is provided. Both ends of the damper 36 are articulated on the arm 28 and on the undercarriage 2 about axes that are likewise parallel to the axes 26, 30 and 34.

[0034] Finally, the assembly is completed by a safety device, referenced 40 in Figure 4, which is capable of limiting the accidental lowering of the chassis 2 to the ground 4 by assuming an active state in which it limits the rotation of the suspension arm about the axis 30 in a first rotational direction S1, which corresponds to the clockwise direction in Figure 4. It is substantially in this rotational direction that the arm 28 lowers the chassis 2 towards the ground 4.

[0035] 4 is likewise articulated at two opposite ends on the chassis 2 and on the suspension arm 28 about axes of rotation 42, 44 parallel to axes 26, 30 and 34. In this case, the safety device 40 is distinct from the buffer 36, but these two items of equipment may advantageously be integrated as will be explained below.

[0036] 5, the safety device 40 is shown in more detail, still in its active state preventing the undercarriage from being inadvertently lowered to the ground. The safety device 40 comprises a hydraulic jack 46 having a cylinder 48 articulated on the suspension arm 28 about a rotation axis 42 and a piston 50 articulated on the undercarriage 2 about an axis 44, or vice versa. A piston head 52 delimits, on the left and right, a first oil chamber 54 and a second oil chamber 56. The first chamber 54 is likewise defined by a first chamber bottom 58, while the second chamber 56 is also defined by a second chamber bottom 60, through which the rod of the piston 50 passes.

[0037] The first chamber 54 communicates with a first oil passage 62 made transversely through the cylinder 48. The first chamber 54 also communicates with a second oil passage 64 made through the cylinder 48, this second passage being located closer to the bottom 58 of the first chamber and in any case closer to this bottom 48 than the first passage 62. In fact, the two passages 62, 64 are spaced apart from each other in the sliding direction 66 of the piston in the cylinder. The second passage 64 communicates with a first oil duct 68, while the first passage 62 communicates with a second oil duct 70 connected to the end of the first duct 68. Upstream of this connection, the first duct 68 is equipped with a safety valve 72, which can be manually operated but is preferably a solenoid valve controlled by the control unit 33.

[0038] The second chamber 56 communicates for a part with a third oil passage 74 made transversely through the cylinder 48, this third passage being preferably located near the bottom 60 of the second chamber. The third passage 74 communicates with an end of a third oil duct 76 belonging to a fluid circuit 78, which will be described below. In fact, downstream of the safety valve 72 in the direction of the oil flow going from the second passage 64 to this safety valve 72, the first fluid duct communicates not only with the second duct 70 connected to the first passage 62, but also with the other end of the third oil duct 76 belonging to the fluid circuit 78. The fluid circuit 78 is completed by a tap on the third duct 76, between its two ends, which leads to an oil tank 80 equipped at its top with an air reserve 82.

[0039] In the active state of the safety device 40 shown in FIG. 5, the valve 72 is held in a closed position. In this state, oil cannot pass through the second passage 64 because the valve 72 is closed. However, oil can circulate freely between the two chambers 54, 56 via the first opening 62, the second duct 70, the third duct 76 and the third passage 74. The piston 50 can therefore accompany the movement of the shock absorber during travel by the movement of the piston head 52 between the first and third passages 62, 74. In particular, in this active state of the safety device 40, the piston 50 can stop its movement in the direction 66 to prevent the undercarriage from lowering too much and therefore from colliding unintentionally with the ground during travel. More specifically, in case of failure of the actuator associated with the wheel R3, the weight of the undercarriage 2 and the load of the vehicle will cause the suspension arm 28 to rotate about the axis 30 in a first direction S1, which is represented diagrammatically by an arrow in FIG. 6. Unintentional rotation of the suspension arm 28 causes the piston head 52 to move towards the bottom 58, discharging oil from the first chamber 54 via the first passage 62, through the ducts 70, 76 and the third passage 74 towards the second chamber 56.

[0040] When the piston head 52 reaches the first passage 62 formed through the cylinder 48, oil can no longer escape from the first chamber 54 through this same passage 62 because the piston head blocks passage 62, just as oil cannot escape through the second passage 64 due to the closure of the safety valve 72. Thus, the piston 50 is locked in a safety position some distance from the bottom 58 by the pressurization of oil between the piston head 52 and the valve 72, as shown in FIG.

[0041] This locking of the piston 50 in the safety position advantageously stops the suspension arm 28 from accidentally rotating in the direction S1 relative to the chassis 2. This arm 28 is then held in the safety position shown in Figure 6, which locally provides a non-zero ground clearance G2 to prevent accidental contact with the ground. In this angular position of the arm 28, the arm 28 forms this angle A2 with the perpendicular to the chassis 2, which angle A2 is obviously smaller than the angle A1 described above with reference to Figure 4.

[0042] It should be noted that in case of failure of the actuator associated with one of the rear wheels R3, the chassis 2 has a tendency to tilt with respect to the ground 4, as shown diagrammatically in FIG. 6′. The rear cantilever must also avoid contact with the ground 4. Therefore, the ground clearance G2 provided locally at the rear wheel R3 by its safety device must be sufficient to maintain a non-zero ground clearance G3 at the rear end of the rear cantilever of the vehicle. In addition, the theoretical value of G2 for maintaining a non-zero ground clearance G3 may in fact be increased to take into account the dynamic movement of the vehicle during travel under such a condition of failure of the actuator of the rear wheel. For example, the theoretical value of G2 may be increased by 10, 40 or 60%, and this increase is therefore taken into account in the design of the safety device associated with the wheel. Similar logical thinking is applied to prevent the risk of the front cantilever of the vehicle coming into contact with the ground during failure of the actuator associated with the front wheel.

[0043] The safety device 40 may alternatively assume an inactive state, shown in Figures 8 and 9, in which the valve 72 is in an open position. In this state, which is assumed in order to intentionally lower the chassis 2 to the ground, oil can be extracted from the first chamber 54 via the second passage 64 located near the bottom 58, even after the piston head has passed the first passage 62.

[0044] This allows additional travel distance of the piston 50 beyond the first passage 62 , accompanied by additional rotation of the arm 28 , to enable the chassis 2 to reach the ground 4 .

[0045] When the chassis 2 reaches the ground, the arm 28 is in an angular position such that it forms an angle A3 with a perpendicular to the chassis 2, this angle A3 shown in FIG. 8 being obviously smaller than the angle A2 described above in relation to FIG.

[0046] 10 and 11, a second preferred embodiment is shown in which the safety device 40 is integrated in the shock absorber 36, or vice versa. In other words, a single assembly fulfills both the safety and shock absorber functions, this assembly being articulated at its ends at two points on the suspension arm 28 and on the undercarriage 2, about axes 42 and 44, respectively. To obtain this assembly fulfilling two functions, the jack of the shock absorber is formed by the jack 46 of the safety device 40, or vice versa.

[0047] The second embodiment uses the same features as the first embodiment, for which an instrument is added in the fluid circuit 78. In fact, the third duct 76 of this circuit is equipped with a loop 84 arranged between the tap of the tank 80 and the connection of the duct 76 to the third passage 74. This loop 84 integrates an element for fulfilling a buffering function. For this purpose, the loop 84 integrates, in the main duct 90a, a first non-return valve 86a associated with the compressed fluid through opening 88a. The loop also has a duct 90b for bypassing the compressed fluid through opening 88a, this duct 90b being equipped with a second non-return valve 86b associated with the expanded fluid through opening 88b.

[0048] With this arrangement, the second check valve 86b allows the flow of oil in the opposite direction to the first check valve 86a. Thus, during the cushioning phase, oil passes through the main duct 90a, while during the rebound phase, oil passes through the bypass duct 90b. During the compression phase, oil passes through the compressed fluid through-opening 88a, which is adjusted to ensure energy dissipation and cushioning by wire-drawing of the oil. Similarly, in the expansion, the cushioning is determined by the passage of oil through the other through-opening 88b. As a result, differentiated cushioning is obtained in compression and rebound by ensuring that the two openings 88a, 88b have different flow cross-sections.

[0049] According to another embodiment shown in figure 12, the safety devices 40 on different wheels of the vehicle can cooperate in pairs to provide an anti-roll function. Figure 12 shows the cooperation of the devices 40 for the two wheels R3, R4 of the rear running gear, but the same or similar cooperation can be adopted for the two wheels of the front running gear.

[0050] More specifically, the end of the third duct 76 of the safety device 40 associated with the left rear wheel R3 no longer communicates with the third passage 74 of the jack 46 of this device 40, but with the third passage 74 of the jack 46 belonging to the safety device 40 associated with the right rear wheel R4 laterally opposite the left rear wheel R3. Therefore, when the piston 50 of the right rear wheel R4 descends into its cylinder 48 according to the rotation of the suspension arm of this wheel R4, the oil of the first chamber 54 of the jack associated with the wheel R4 is discharged towards the second chamber 56 of the jack associated with the other wheel R3. At the same time, the oil of the first chamber 54 of the jack associated with the wheel R3 is discharged towards the second chamber 56 of the jack associated with the wheel R4. Therefore, the piston 50 of the jack associated with the wheel R3 also descends, preventing or limiting unwanted rolling movements of the vehicle.

[0051] Such a function is all the more important when the safety device 40 also integrates a cushioning function, as shown in Figure 13. According to an alternative embodiment, shown in Figure 14, applicable to all modes and all embodiments described, an actuator 32 in the form of an airbag is integrated in an assembly incorporating the safety device 40, which can also incorporate a cushioning function, in the sense described with respect to Figures 10 and 11.

[0052] To achieve this, the longitudinal axis 92 of the airbag merges with the axis of the jack 46 of the safety device 40. In addition, a longitudinal end of the airbag 32 is fixed to the cylinder 48, while its opposite longitudinal end is pivotally mounted on the chassis 2 about the axis of rotation 44. The rod of the piston 50 is then pivotally mounted on the suspension arm 28 about the axis of rotation 42. With this particular arrangement, the bearing surface of the airbag 32 remains permanently centered on the cylinder 48, more specifically on the bottom 60 of the second chamber of the jack. The airbag 32 therefore remains permanently aligned with the jack 46, which ensures optimal transmission of mechanical forces between the chassis 2 and the suspension arm 28, regardless of the angular position of the suspension arm 28.

[0053] Now referring to FIG. 15, an improved embodiment of one of the wheels is shown. It is wheel R3, but all of the wheels of the vehicle can be made in this way. This wheel R3 includes, in addition to the rim 22 and the tire 24 defining the tread 20, a reinforcement 96 arranged radially around the rim. The reinforcement 96 is intended to abut the inside of the tire's tread 20 in case of loss of pressure, thus preventing direct contact between the tire 24 and the rim 22. The reinforcement 96 is designed to be rigid so as not to collapse under the weight of the vehicle, thus helping to prevent the risk of the chassis accidentally lowering to the ground in case of loss of pressure in the tire, for example due to a puncture.

[0054] Preferably, in the design of the safety device 40, the possibility of undercarriage collapse caused by loss of tire pressure can also be taken into account. The ground clearance G2 locally provided by the safety device at the wheel is therefore preferably greater than the maximum amplitude of the collapse of the wheel following a tire pressure loss that may be due to deflation or a puncture. Similarly, the principle defined above with respect to FIG. 6' is also applicable to a situation of cumulative failure of the actuators associated with one of the wheels, the loss of pressure at this wheel leading to rolling on the reinforcement 96. In other words, the principle ensures that the value of the ground clearance G2 locally provided by the safety device at the rear wheel R3, subtracted from the value of the maximum amplitude of the collapse of the wheel following a tire pressure loss, is sufficient to maintain a non-zero ground clearance G3 at the rear end of the rear cantilever of the vehicle. In this case again, similar conditions are presented for the front wheels.

[0055] With reference to figure 16, a third preferred embodiment is shown, in which each wheel is associated with a device for preventing rotation of the wheel suspension arms, this device for preventing rotation being integrated in this case with the safety device 40. The device takes the form of a shut-off valve 98, preferably a solenoid valve controlled by the control unit. A manually operated shut-off valve may also be envisaged without departing from the scope of the invention. The shut-off valve 98 is arranged in the fluid circuit 78, on the third duct 76 near its connection with the first and second ducts 68, 70.

[0056] When the shut-off valve 98 is in the shut-off position and the safety valve 72 also assumes its closed position, no fluid communication is possible between the two chambers 54, 56 of the jack 46. As a result, when these two valves 72, 98 are closed, the piston 50 remains locked in its position in the cylinder 48. In other words, the piston 50 can no longer move in the sliding direction 66, regardless of the direction of movement. The locking of the position of the piston 50 prevents the suspension arm from rotating in both rotational directions relative to the undercarriage. This function is particularly advantageous when the undercarriage 2 is in its lowered position supported on an uneven ground 4. Such a situation is shown diagrammatically in FIG. 17, which shows that the front part of the undercarriage 2 is in contact with the ground, while the rear part of the undercarriage 2 remains a little off the ground due to the convex nature of the road. In this situation, there is a risk that the center of gravity of the vehicle will shift, for example as cargo is unloaded. This shift in the centre of gravity may result in the chassis 2 tilting unintentionally, e.g. reducing the initial spacing J between the chassis 2 and the convex road 4. Such unwanted tilting presents risks to people located close to the front of the chassis of the vehicle, e.g. the risk of their feet being crushed between the ground and this front part of the chassis approaching the ground.

[0057] However, such risks to people located near the vehicle are avoided by a shut-off valve 98 preferably provided in the safety device 40 of each wheel.

[0058] It should be noted that the shut-off valve 98 may be located at another location on the third duct 76, for example near the third oil passage 74 through the cylinder 48, as shown in FIG. 16a.

[0059] Moreover, this principle of locating the shutoff valve 98 to prevent rotation of the suspension arm also applies when the safety device 40 integrates the damping function described with reference to Fig. 11. In this case, the shutoff valve 98 can be located upstream or downstream of the loop 84 without departing from the scope of the invention.

[0060] This principle of arranging the shut-off valve 98 to prevent rotation of the suspension arm is also applicable if the safety device 40 integrates an anti-roll function, as shown diagrammatically in FIG.

[0061] By way of example, at least one embodiment is provided in which a safety device associated with each wheel integrates several of the additional functions described above, or even all of them, namely a buffer function, a roll stop function, a function for integrating an actuator, and a function for preventing rotation of the suspension arm by preventing translational movement of the piston.

[0062] Moreover, it should be noted that in the context of the present invention relating to a method for lowering the undercarriage of a vehicle, the safety device disclosed above remains optional and, moreover, when such a safety device is provided on one or more wheels of the vehicle, its design may differ from that disclosed in the various embodiments described above, in particular the safety device does not necessarily integrate a jack.

[0063] Other preferred features are described below which may be expressly combined with the features described above.

[0064] 19, a vehicle 1 is shown whose chassis 2 is in a running configuration, i.e. in a high running position, defining a ground clearance G1. Here, the uniqueness of the vehicle lies in the fact that the kinematics associated with each of the four wheels are identical. More specifically, these identical kinematics allow an identical or substantially identical longitudinal offset of the chassis 2 relative to the ground 4 when the chassis is lowered.

[0065] By means of this design, lowering the chassis to its low position supported on the ground does not generate stresses in the running gear 8, 10, even when all of the wheels are locked by the parking brake during this descent.

[0066] For each of the four wheels R1 to R4 (only two wheels R1 and R3 are visible in the side view of FIG. 19), in the high running position of the chassis, the following characteristics are observed: - the suspension arm 28 has an arm length "LB" defined between the two rotation axes 26, 30; - the arm rotation axis 30 has a first vertical distance "DV1" relative to the ground; the wheel axis of rotation 26 has a second perpendicular distance "DV2" relative to the ground that is smaller than the first perpendicular distance, The wheel includes a tread 20 having a wheel diameter "D".

[0067] Therefore, in order to avoid creating stresses in the running gear 8, 10 when the undercarriage is being lowered, the following instructions apply for the four wheels. the arm rotation axis 30 is offset longitudinally from the wheel rotation axis 26 in the same direction, in this case backwards, which leads to a "pushed" arm configuration, even if an opposite "pulled" arm configuration could also be envisaged without departing from the scope of the invention; - the arm lengths LB are the same or substantially the same, - the first vertical distances DV1 to the ground are the same or substantially the same, - the second vertical distance DV2 to the ground is the same or substantially the same, - the wheel diameters D are the same or substantially the same;

[0068] When all of these values ​​are not strictly identical, the deviation permitted is such that, when they are combined, the difference in the longitudinal offset given to the chassis between the lowest and highest offset between the four wheels does not exceed 5 cm, or even 2 or 3 cm.

[0069] In fact, this low offset deviation can be absorbed by moderate sliding of the tires on the ground during descent, even when all four wheels are locked by the parking brake, without causing harmful stresses on the running gear.

[0070] Nevertheless, various designs can be observed in which the kinematics associated with the four wheels are not necessarily all identical, for example the kinematics associated with the front wheels being different from the kinematics associated with the rear wheels. In this latter case, the different kinematics present a risk of producing unequal longitudinal offsets and thus considerable mechanical stresses in the running gear when the chassis is being lowered.

[0071] To solve this problem, the present invention proposes a method for lowering the undercarriage, applicable to all of the above-mentioned vehicles.

[0072] Figure 20 shows diagrammatically the various steps of such a method for lowering the chassis 2 of a vehicle, which is particularly suitable when, unlike the mode described with reference to figure 19, not all of the wheels have the same kinematics of movement during descent, but the method is nevertheless also applicable to this mode without departing from the scope of the invention.

[0073] The method starts with step E1, which waits to receive a command to lower the undercarriage. This command can be triggered by the operator, for example via a dedicated dashboard button or any other button linked to the vehicle's control unit 33.

[0074] When such a lowering command is received, step E2 consists in verifying that the wheels of the front gear do not have an excessive steering angle, since this would cause the vehicle to pivot while lowering the chassis. If the steering angle is therefore greater than a safe value, step E'2 is carried out in order to correct the direction until a suitable steering angle is obtained. This step E'2 can be performed automatically by the power steering system or manually by the operator by directly manipulating the steering wheels of the vehicle.

[0075] If the steering angle falls below a safe value, step E3 can be carried out, which consists of activating the parking brake only for the wheels R3, R4 of the rear drive unit, in this respect it is noted that the parking brake is not shown, but it may have any conventional configuration known to the person skilled in the art.

[0076] Once the parking brake has been activated for the rear running gear and kept deactivated for the front running gear, step E4 involves switching all of the safety valves 72 from their closed position to their open position in order to set the safety device 40 in an inactive state. Step E5 then consists of lowering the undercarriage 2 by controlling the actuators 32, always via the vehicle's unit 33. In addition, this unit 33 can be programmed to carry out all of the steps of the method automatically, i.e. sequentially, without intervention by the operator.

[0077] The lowering step E5 continues until the undercarriage 2 rests on the ground 4 in its low supported position. When the undercarriage is in the low supported position on the ground, a step E6 of safe loading of the tyres of the wheels can be performed in order to avoid an excessively weak grip of the vehicle on the ground. This optional step aims to ensure that the tyres are not completely unloaded after the undercarriage is supported on the ground. This step is for example carried out by lifting control of the undercarriage 2 via the actuators 32 in order to generate a small relative vertical movement between the undercarriage and the rotation axis of each wheel. This vertical movement does not usually exceed a few millimetres in order to avoid a loss of contact between the undercarriage 2 and the ground 4. Nevertheless, the loading of the tyres on the ground reinforces the overall grip of the vehicle in the low supported position of the undercarriage. The risk of the vehicle skidding is reduced, which is particularly advantageous when the undercarriage is lowered on a slope.

[0078] Once the lowering has been performed, a step E7 can be carried out, which consists of activating the parking brake on the wheels R1, R2 of the front running gear, the parking brake remaining activated on the wheels of the rear running gear. Once this parking brake has been activated on the front running gear, a final step E8 involves activating a device 98 for preventing rotation of the wheel suspension arms 28, in order to avoid the risk of unwanted movements of the undercarriage during loading / unloading operations of the cargo.

[0079] The order of some of these steps may nevertheless be reversed: for example, step E7 of applying the parking brake on the wheels R1, R2 of the front running gear may be performed after step E8 of activating device 98 to prevent rotation of wheel suspension arm 28, without departing from the scope of the invention. The same applies to steps E3 and E4 or to steps E2-E'2 and E3.

[0080] Naturally, various modifications may be made by those skilled in the art to the invention described above, purely by way of non-limiting example, the scope of which is defined by the appended claims, in particular the various modes and the features of the various embodiments and alternatives may be combined without departing from the scope of the invention. [Explanation of symbols]

[0081] 1 vehicle 2 Chassis 4 ground 6 Cargo loading space 8 Front running gear 10 Rear running gear 12 Center of gravity 14 Crossing 16 center 20 Tread 22 Rims 24 Tires 26 Wheel rotation axis 28 Suspension arm 30 Arm rotation axis 32 Actuator, airbag 33 Control Unit 34 Actuator rotation axis 36 Buffer 40 Safety Devices 42 Rotation axis 44 Rotational Axis 46 Hydraulic Jack 48 Cylinder, bottom 50 Piston 52 Piston head 54 First Oil Chamber 56 Second Oil Chamber 58 Bottom of the first chamber 60 Bottom of the second chamber 62 First oil passage 64 Second oil passage 66 Sliding direction 68 First Oil Duct 70 Second Oil Duct 72 Safety valve 74 3rd oil passage 76 Third Oil Duct 78 Fluid circuit 80 Oil Tank 82 Air Reserve 84 Loop 86a First check valve 86b Second check valve 88a Compressed fluid through opening 88b Expansion fluid through opening 90a Main duct 90b Duct 92 Vertical Axis 96 Reinforcement 98 Shut-off valve

Claims

1. A method for lowering a vehicle chassis (2) with a controllable vertical position, said vehicle (1) being designed such that said chassis (2) can move between an elevated running position and a lower position in which said chassis is supported on the ground (4), said vehicle also comprising a number of wheels (R1-R4), associated with each wheel: a suspension arm (28) pivotally mounted on said chassis (2) and carrying a wheel; a suspension arm actuator (32) arranged between the suspension arm (28) and the chassis (2) and enabling the angular position of the suspension arm to be controlled relative to the chassis in order to vary the vertical position of the chassis; The vehicle comprises only two running gears, namely a front running gear (8) and a rear running gear (10), each wheel of the running gears being associated with a parking brake, and the method comprises the following sequence of steps, in the following order: activating the parking brake only for all of the wheels (R3, R4) of one of the two running gears (10) when the chassis (2) is in the high running position; lowering the chassis (2) to a low position supported by the ground (4); and activating the parking brake for all of the wheels (R1, R2) of the other (8) of the two running gears.

2. 2. The method according to claim 1, characterized in that it includes a step of detecting a steering angle of the wheels (R1, R2) of the front running gear (8) and that the step of lowering the chassis (2) is performed only if the detected steering angle is below a safe value.

3. 3. A method according to claim 2, characterized in that, when the detected steering angle is greater than the safety value, a manual or automatic step of correcting the direction of the wheels (R1, R2) of the front running gear (8) is performed.

4. 4. A method according to any one of claims 1 to 3, characterized in that after the chassis (2) has been lowered to a low position supported by the ground, a step of loading the tyres is carried out such that the tyres are not unloaded.

5. 5. The method according to claim 1, characterized in that the one (10) of the two running gears corresponds to the rear running gear, the wheels (R3, R4) of which have their parking brakes activated when the chassis (2) is in the high running position.

6. 6. The method according to claim 1, characterized in that a safety device (40) is associated with each wheel and is capable of limiting the accidental lowering of the chassis (2), said safety device being capable of taking an active state making it possible, on the one hand, to limit the rotation of the suspension arm (28) in a first direction (S1) leading to the lowering of the chassis to a safe position of said arm, and, on the other hand, an inactive state making it possible to rotate said arm (28) in said first direction (S1) beyond said safe position, and said method comprising a step of switching said safety device (40) from said active state to said inactive state before said step of lowering the chassis (2).

7. The method according to any one of claims 1 to 6, characterized in that each wheel (R1 to R4) is associated with a device (98) for preventing rotation of a suspension arm (28) and that the method comprises, after the step of lowering the chassis (2), a step of activating a device (98) for preventing rotation of the suspension arm (28) associated with each of the wheels (R1 to R4) of the vehicle.

8. The method is carried out with a respective safety device (40) including a jack (46) having a cylinder (48) mounted on the chassis (2) and a piston (50) mounted on the suspension arm (28), or vice versa, the jack defining a first chamber (54) communicating with a first fluid passage (62) and a second fluid passage (64) through the cylinder (48), the first fluid passage (62) and the second fluid passage (64) being spaced apart from each other in the sliding direction (66) of the piston in the cylinder, whereby the second fluid passage (64) is located as close as possible to the bottom (58) of the first chamber defined by the cylinder, the second fluid passage (64) communicating with a first fluid duct (68) provided with a safety valve (72), the safety valve (72) being an inactive open position of the safety device (40) to allow fluid to be exhausted from the first chamber (54) through the second fluid passage (64) when the piston (50) moves towards the bottom (58) of the first chamber due to the rotation of the suspension arm (28) in a first direction (S1) leading to a lowering of the chassis; 8. The method according to claim 1, in combination with claim 6, characterized in that when the piston (50) moves towards the bottom (58) of the first chamber due to the rotation of the suspension arm (28) in the first direction (S1), the piston (50) is locked in a safety position a short distance from the bottom (58) of the first chamber and assumes a closed position in an activated state of the safety device (40) such that in that position the fluid is compressed between the piston head (52) and the safety valve (72).

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