GB2514258A

GB2514258A - Leaf spring assembly for a vehicle

Info

Publication number: GB2514258A
Application number: GB1407619.4A
Authority: GB
Inventors: Vishweshwar Ram
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2014-04-30
Filing date: 2014-04-30
Publication date: 2014-11-19
Also published as: GB201407619D0

Abstract

The invention relates to a leaf spring assembly 40 for a vehicle comprising at least one leaf spring 12 configured to support an axle on a frame 14 of the vehicle. The leaf spring assembly 40 comprises at least one damper 42 of which both ends 48, 50 are connected to the leaf spring, the damper therefore being configured to damp deformations of the leaf spring and limit the rotational movement of the axle. The damper can be a hydraulic damper and may be positioned beneath the leaf spring. The leaf spring assembly may be configured as a mono-leaf spring, where the leaf spring 12 is the only leaf spring. The leaf spring assembly may also comprise of a second damper (60 fig. 7) located on the opposite side of the leaf spring from the first damper. The damper acts to limit the tendency of the axle to wind-up during breaking or acceleration forces (Tb, Ta fig. 1) sometimes called axle-wrap.

Description

Leaf Spring Assembly for a Vehicle The invention relates to a leaf spring assembly according to the preamble of patent claim 1.

Such a leaf spring assembly for a vehicle can be found in US 2012/0133090 Al. The leaf spring assembly comprises at least one leaf spring configured to support at least one axle on a frame of the vehicle. In other words, the axle can be supported on the frame via the leaf spring. The leaf spring serves for guiding the axle so that loads such as torques and forces are transmitted from the axle to the leaf spring assembly during operation of the vehicle. For example, the vehicle is a utility vehicle such as a truck.

The leaf spring is a highly stressed part of a suspension system of the vehicle since the leaf spring is subjected to different driving dynamic load conditions. For example, braking torques, accelerating torques, driving torques, lateral forces and cornering forces act upon the leaf spring.

Therefore, it is an object of the present invention to provide a leaf spring assembly of the kind indicated in patent claim 1, in which leaf spring assembly loads acting upon the leaf spring during operation of the vehicle can be kept particularly low.

This object is solved by a leaf spring assembly having the features of patent claim 1.

Advantageous embodiments with expedient and non-trivial developments of the invention are indicated in the other patent claims.

In order to provide a leaf spring assembly of the kind indicated in the preamble of patent claim 1, in which leaf spring assembly loads acting upon the leaf spring during operation of the vehicle can be kept particularly low, according to the present invention, the leaf spring comprises at least one damper, wherein both ends of the damper are connected to the leaf spring, the damper being configured to damp deformations of the leaf spring. It was found that a leaf spring, in particular a mono or single leaf spring, tends to wind up in case of braking conditions and accelerating conditions of the vehicle. Thus, the leaf spring tends to deform during operation of the vehicle which results in high stress of the leaf spring. These deformations of the leaf spring can be damped and absorbed by the damper thereby keeping the stress of the leaf spring particularly low.

Further advantages, features, and details of the present invention derive from the following description of preferred embodiments as well as from the drawing. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respective indicated combination but also in any other combination or taken alone without leaving the scope of the invention.

Figs. 1 and 2 serve for illustrating the background of the invention.

The drawing shows in: Fig. 1 a schematic side view of a leaf spring assembly for a vehicle, the leaf spring assembly comprising a leaf spring mounted on a frame of the vehicle, wherein the leaf spring is shown in an undeformed state; Fig. 2 a schematic side view of the leaf spring assembly according to Fig. 1, wherein the leaf spring is shown in a deformed state; Fig. 3 a schematic side view of a leaf spring assembly for a vehicle, wherein the leaf spring assembly comprising at least one leaf spring configured to support at least one axle on a frame of the vehicle, wherein the leaf spring assembly comprises at least one damper and wherein both ends of the damper are connected to the leaf spring, the damper being configured to damp deformations of the leaf spring; Fig. 4 a further schematic side view of the leaf spring assembly according to Fig. 3; Fig. 5 a schematic perspective view of the leaf spring assembly according to Figs. 3 and 4; Fig. 6 a schematic side view of the leaf spring assembly according to Fig. 3; Fig. 7 a schematic side view of a second embodiment of the leaf spring assembly according to Fig. 3; and Fig. 8 a further schematic side view of the leaf spring assembly according to Fig. 7, wherein the leaf spring is shown in a deformed state.

In the figures the same elements or elements having the same function are indicated with the same reference sign.

Fig. 1 shows a leaf spring assembly 10 for a vehicle, in particular, a utility vehicle. The leaf spring assembly 10 is configured as a mono leaf spring assembly comprising one single leaf spring 12. The leaf spring 12 extends at least substantially in the longitudinal direction of the vehicle and is configured to support at least one axle on a frame 14 of the vehicle. The frame 14 comprises two longitudinal members from which a longitudinal member 16 can be seen in Fig. 1.

The leaf spring assembly 10 comprises two mounting brackets 18 and 20 by means of which the leaf spring 12 is attached to the longitudinal member 16. Moreover, a mounting assembly 22 is provided by means of which the axle can be mounted on the leaf spring 12 so that the axle is mounted on the longitudinal member 16 via the leaf spring 12.

Furthermore, a damper 24 is provided. On one end, the damper 24 is connected to the leaf spring 12 via the mounting assembly 22. On the other end, the damper 24 is mounted on the longitudinal member 16. For example, the damper 24 is designed as a hydraulic damper and comprises a cylinder 26 and a piston which cannot be seen in Fig. 1. The piston is arranged inside the cylinder 26 and translationally movable in relation to the cylinder 26. The damper 24 further comprises a piston rod 28 connected to the piston so that the piston rod 28 moves along the piston in relation to the cylinder 26. The damper 24 further comprises a damping fluid in the form of a damping liquid contained in the cylinder 26. The damping fluid serves for damping the movement of the piston rod 28 in relation to the cylinder 26 thereby damping movements of the axle in relation to the frame 14.

The leaf spring assembly 10 further comprises a lever element 30 which is pivotably connected to the leaf spring 12 on one side and the mounting bracket 20 on the other side. This means the lever element 30 is rotatably mounted on the mounting bracket 20 on one side and the leaf spring 12 on the other side so that the lever element 30 is rotatable in relation to the mounting bracket 20 and in relation to the leaf spring 12.

The leaf spring 12 is a highly stressed part in a suspension system of the vehicle since the leaf spring 12 is subjected to different driving dynamic load conditions, e.g. braking torques, accelerating torques, driving torques, lateral forces and cornering forces. In Fig. 1, a braking torque Tb acting upon the leaf spring 12 is illustrated by a directional arrow. Moreover, an accelerating torque acting upon the leaf spring 12 is illustrated by the directional arrow Ta.

In case of multiple leaf springs, each leaf spring carries a proportional amount of load and is stressed equally and provides enough support to the vehicle in case of eventual failure.

The tendency of each leaf spring to wind up during braking condition is minimal in case of the multiple leaf springs.

In case of a mono leaf spring assembly, however, the leaf spring 12 is the only leaf spring. The leaf spring 12 has a middle portion 32 and respective end portions 34 and 36.

In the middle portion 32, the leaf spring 12 is thicker than in the respective end portions 34 and 36. The single leaf spring 12 has atendencyto wind up in case of braking conditions and accelerating conditions since the leaf spring 12 is not supported by any other leaf spring and because of the great length of the single leaf spring 12.

Fig. 1 shows the leaf spring 12 in an undeformed state. Fig. 2 shows the leaf spring 12 in a deformed state in which the leaf spring 12 is wound up due to the braking torque Tb acting upon the leaf spring 12 during a braking condition of the vehicle.

If the leaf spring 12 winds up during braking condition, the leaf spring 12 can reach a state of high stress which increases the chances of breaking or failure. Thus, it is an object to stop and dampen the longitudinal braking and accelerating loads acting upon the leaf spring 12 by restricting the motion of the leaf spring 12 during braking conditions and accelerating conditions.

In the leaf spring assembly 10 according to Figs. 1 and 2, the mono leaf spring 12 is subjected to high compression and tension when it winds up during braking and accelerating load conditions. For example, the leaf spring 12 is designed as a parabolic mono leaf spring. In order to provide a good ride and comfort, a soft suspension is used, the soft suspension having a little stiffness only. Said soft suspension can be achieved by using a mono leaf spring layout especially for low tonnage vehicles. The leaf spring 12 is not only used as an energy absorbing element in case of road undulations and tire excitations providing vertical compliance, but also as a supporting member which is connected to the axle at the centre and to the mounting brackets 18 and 20 at both ends.

The great length of the leaf spring 12 is used to provide a particularly good load distribution over the length. However, this results in increasing the tendency to wind up in case of braking and accelerating load conditions during which the leaf spring 12 is highly stressed.

As can be seen from Figs. 1 and 2, the leaf spring assembly 10 comprises a so-called wind up stopper 38 which is attached to the longitudinal member 16 on one end and free on the other hand. The wind up stopper 38 extends in the vertical direction of the vehicle towards the bottom and protrudes beyond the longitudinal member 16 towards the leaf spring 12. The wind up stopper 38 is configured to reduce the deformations of the leaf spring 12 when the leaf spring 12 winds up. For this purpose, the motion of the leaf spring 12 in the vertical direction of the vehicle is restricted by the wind up stopper 38 since the leaf spring 12 comes into contact with the wind up stopper 38 when the leaf spring 12 winds up. This can be seen in Fig. 2.

The wind up stopper 38 may reduce or restrict the deformations of the leaf spring 12.

However, the wind up stopper 38 does not reduce the loads acting upon the leaf spring 12 so the leaf spring 12 is still highly stressed. Moreover, the wind up stopper 38 does not absorb the loads. Thus, the wind up stopper 38 does not reduce the stress of the leaf spring 12.

If braking torques and accelerating torques act upon the leaf spring 12, the leaf spring 12 is deflected and bands thereby absorbing the energy. Because of axle twist, the tendency to wind up is further increased and once the loads are relieved, the leaf spring 12 is released which can affect the stability and performance of the vehicle.

The vertical damper 24 helps absorb the energy and loads acting upon the leaf spring 12 in the vertical direction of the vehicle due to bumps, rebound and cross articulation condition so that bouncing effects can be reduced. However, the vertical damper 24 does not absorb energy of the leaf spring 12. Moreover, the vertical damper 24 does not restrict the motion of the leaf spring 12 during braking conditions or accelerating conditions which cause the wind up movement. When axle tramp or axle twist occurs during braking conditions or accelerating conditions, the vertical damper 24 moves along with the axle. In this condition, the vertical damper 24 does not provide a damping effect by absorbing the spring loads.

Thus, it is desirable to provide a mechanism by means of which loads due to braking, accelerating and driving during different driving conditions can be absorbed and damped by restricting the motion of the leaf spring 12. Thereby, the wind up motion of the leaf spring 12 and, thus, the loads and stresses can be reduced.

Figs. 2 to 6 show a first embodiment of a leaf spring assembly 40 which is configured as a mono leaf spring assembly in which loads acting upon the single leaf spring 12 and stresses of the leaf spring 12 can be kept particularly low.

As can be seen from Fig. 3, the leaf spring assembly 40 comprises a damper 42 which extends at least substantially in the longitudinal direction of the vehicle. Moreover, the damper 42 is arranged beneath the leaf spring 12 with respect to the vertical direction of the vehicle. For example, the damper 42 is configured as a hydraulic damper. The damper 42 comprises a cylinder 44 and a piston not shown in Fig. 3. The piston is movably arranged inside the cylinder 44 so that the piston can move translationally in relation to the cylinder 44. The damper 42 further comprises a piston rod 46 connected to the piston so that the piston rod 46 can move along with the piston in relation to the cylinder 44. The damper 42 further comprises a damping fluid in the form of a damping liquid contained in the cylinder 44. The damping fluid serves for damping the movement of the piston rod 46 in relation to the cylinder 44.

As can be seen from Fig. 3, both ends 48 and 50 of the damper 42 are connected to the leaf spring 12 via respective mounting brackets 52 and 54. For example, the mounting brackets 52 and 54 are made of sheet metal and attached to the leaf spring 12.

The damper 42 is a so-called helper damper mounted underneath the leaf spring 12. For example, the damper 42 is applicable for either parabolic or semi-elliptical mono leaf spring systems, the damper 42 providing longitudinal damping absorbing loads acting upon the leaf spring 12 during braking conditions and accelerating conditions thereby reducing the wind up movement of the leaf spring 12 by restricting the motion of the leaf spring 12. Thus, stresses of the leaf spring 12 can be reduced which results in an increased life of the leaf spring 12.

The one end 48 of the damper 42 is mounted on the mounting bracket 52 which is mounted underneath the leaf spring 12 substantially at the spring centre. The other end of the damper 42 is mounted on the mounting bracket 54 which is in turn mounted on a round eye 56 at the rear end of the leaf spring 12. The damper 42 mounted on the leaf spring 12 moves along with the leaf spring 12 during different ride conditions of the vehicle. The damper 42 and the mounting brackets 52 and 54 can be seen in Figs. 4 and 5.

As shown in Fig. 6, the leaf spring 12 winds up during the braking condition along with the longitudinally mounted damper 42 underneath the leaf spring 12. The leaf spring 12 winds up since the braking torque Tb acts upon the leaf spring 12 and the entire momentum of the moving vehicle tends to rotate the axle in a forward turning direction. During this condition, the damper 42 undergoes a compression since the piston rod 46 is pushed into the cylinder 44. Thereby, energy from the leaf spring 12 is absorbed by the damper 42 thereby providing enough resistance to the motion of the leaf spring 12. When the brakes of the vehicle are released, the leaf spring 12 releases the absorbed energy by returning back to its normal position shown in, for example, Fig. 3. In this process, the damper 42 provides resistance to the motion of the leaf spring 12 so that the energy released by the leaf spring 12 is absorbed again while the leaf spring 12 unwinds. Thus, the damper 42 simultaneously acts along with the leaf spring 12 during braking conditions and accelerating conditions of the vehicle when the leaf spring 12 winds up and unwinds.

Thereby, the damper 42 absorbs loads acting upon the leaf spring 12 and restricts the motion of the leaf spring 12 by undergoing compression and expansion cycles. In Fig. 6, a compression stroke of the damper 42 is shown and designated with 58.

The damper 42 not only serves for dampening and absorbing the loads acting upon the leaf spring 12 but also is used as a connecting and supporting link member which additionally takes loads and distributes them to other members of the suspension. The damper 42 adapts to the dynamic behaviour of the leaf spring 12 and helps reduce the wind up motion of the leaf spring 12 by restricting its motion thus reducing the high stressed developed in case of extreme wind up situations during braking and accelerating conditions.

If the leaf spring 12 eventually breaks in a front portion or rear portion, the damper 42 acts as a safety device which holds the leaf spring 12 together thereby avoiding a sudden drop down of the vehicle at, for example, the front. The helper damper is easy to install via the mounting brackets 52 and 54 and can be provided as an add-on after-market installation component.

Figs. 7 and 8 show a second embodiment of the leaf spring assembly 40. The second embodiment comprises a second damper 60, wherein both ends 62 and 64 of the second damper 60 are connected to the leaf spring 12, the second damper 60 being configured to damp deformations of the leaf spring 12. Moreover, the second damper 60 is arranged above the leaf spring 12. This means the second damper 60 is arranged on a side of the leaf spring 12, said side facing away from the first damper 42. With respect to the longitudinal direction of the vehicle, the damper 42 is arranged in a rear portion 66 of the leaf spring 12. Thus, the second damper 60 is arranged in a front portion 68 of the leaf spring 12. The second damper 60 also comprises a cylinder 70, a piston movably arranged in the cylinder 70, a piston rod 72 connected to the piston and a damping fluid in the form of a damping liquid. Hence, the working principle of the damper 60 corresponds to the working principle of the damper 42. For example, the damper 60 is configured as a hydraulic damper.

The damper 60 is mounted on the leaf spring 12 via mounting brackets 74 and 76. For example, the mounting brackets 74 and 76 are made of sheet metal. By means of the second damper 60, the wind up motion of the leaf spring 12 can be restricted by absorbing loads acting upon the leaf spring 12 during braking and accelerating conditions.

The damper 60 also reduces a high stress build up at one end and at the other end of the leaf spring 12, the one end being fixed and mounted on the mounting bracket 18 and the other end being movable and connected to the mounting bracket 20 via the lever element 30.

Fig. 7 shows the leaf spring 12 in an undetormed state, wherein Fig. 8 shows the leaf spring 12 in a deformed state in which leaf spring 12 in wound up during braking conditions. During this condition, the two dampers 42 and 60 undergo a respective compression thereby absorbing the loads acting upon the leaf spring 12 and, thus, reducing the wind up motion at both ends of the leaf spring 12.

The damper 42 underneath the leaf spring 12 longitudinally damps by absorbing sudden impact shock loads, braking and accelerating torques, driving torques so that the wind up motion of the leaf spring 12 can be restricted. Moreover, the damper 42 helps reduce the stress of the leaf spring 12. The damper 42 also acts as a connecting and supporting link member mounted between the respective ends of the leaf spring 12 so that the damper 42 can take loads and distribute them to other members of the suspension thereby acting as a load sharing member.

The wind up stopper 38 shown in Fig. 1 and 2 can be avoided. Reducing the stress of the leaf spring 12 results in an increased life of the leaf spring 12. Moreover, the damper 42 and/or 60 acts as a safety device in case of an eventual breaking of the leaf spring 12.

Moreover, the damper 42 and/or 60 is easy to install. For example, the damper 42 and/or are applicable for both parabolic and semi elliptical mono leaf spring designs.

List of reference signs leaf spring assembly 12 leaf spring 14 frame 16 longitudinal member 18 mounting bracket mounting bracket 22 mounting assembly 24 damper 26 cylinder 28 piston rod lever element 32 middle portion 34 end portion 36 end portion 38 wind up stopper leaf spring assembly 42 damper 44 cylinder 46 piston rod 48 end end 52 mounting bracket 54 mounting bracket 56 eye 58 compression stroke damper 62 end 64 end 66 rear portion 68 front portion cylinder 72 piston rod 74 mounting bracket 76 mounting bracket Ta accelerating torque Tb braking torque

Claims

Claims A leaf spring assembly (40) for a vehicle, the leaf spring assembly (40) comprising at least one leaf spring (12) configured to support at least one axle on a frame (14) of the vehicle, characterised in that the leaf spring assembly (40) comprises at least one damper (42), wherein both ends (48, 50) of the damper (42) are connected to the leaf spring (12), the damper (42) being configured to damp deformations of the leaf spring (12).
2. The leaf spring assembly (40) according to claim 1, characterised in that the damper (42) is configured as a hydraulic damper.
3. The leaf spring assembly (40) according to any one of claims 1 or 2, characterised in that the damper (42) is arranged beneath the leaf spring (12) with respect to the vertical direction of the vehicle.
4. The leaf spring assembly (40) according to any one of the preceding claims, characterised in that the leaf spring assembly (40) is configured as a mono leaf spring assembly in which the leaf spring (12) is the only leaf spring (12).
5. The leaf spring assembly (40) according to any one of the preceding claims, characterised in that the leaf spring assembly (40) comprises at least one second damper (60), wherein both ends (62, 64) of the second damper (60) are connected to the leaf spring (12), the second damper (60) being configured to damp deformations of the leaf spring (12) and arranged on a side of the leaf spring (12), the side facing away from the first damper (42).