The present invention relates to an arrangement for suspension of a sprung vehicle cab on a vehicle frame according to the preamble of claim 1.

State of the art.

It is today usual for trucks and other heavy vehicles to have a cab which is resiliently suspended on the frame at three or four points.

In the great majority of cases, such vehicles are provided with a stabiliser whose function is to damp out the heterogeneous deflection movements which may occur at the various suspension points. A forward stabiliser of this kind incorporates a transverse torsion rod which has at each axial end a link arm extending in the longitudinal direction of the vehicle. Each link arm is directly or indirectly supported on the cab at one end and on the frame at the other end.

These supports are often of the sliding, ball or roller bearing type. Such bearings are advantageous because they do not absorb deflection energy which it is desired to transfer via stabilisers to the suspension on the other side. This is due to their not damping out any deflection movement and at the same time being almost free from losses at the time of the torsional rotation which occurs at the link arm fastening. Their rigid construction is disadvantageous, however, in that vibration from the frame is readily propagated to the cab, thereby disturbing the driver.

A customary alternative solution is to use rubber bushings. A rigid bushing causes little damping out of deflection movements and may therefore result in insufficient driver comfort. A soft bushing results in good damping which is favourable from the vibration and comfort point of view but often has inferior strength characteristics and also absorbs deflection energy, thereby risking impairing the stabiliser function. Intermediate degrees of bushing rigidity between these two extremes may risk causing oscillations excited by rear axle suspension, frame vibration or the like.

Objects of the invention.

The present invention has the object of providing an arrangement for suspension of a sprung vehicle cab on a vehicle frame whereby the disadvantages mentioned above are reduced so that maximum possible driver comfort from the springing point of view may be achieved without noise vibration from the frame being propagated to the cab.

This is achieved according to the invention by designing at least one of the stabiliser supports on the vehicle as indicated in the characterising part of patent claim 1. The result is a bushing which is soft in the longitudinal and transverse directions but rigid in the vertical direction.

The soft part provides damping out of longitudinal and transverse vibrations which may occur, for example, when hauling trailers or in so-called pothole driving, while the rigid part makes it possible for rolling movements in the cab to be damped by the stabiliser.

Further features and advantages of the invention are indicated in the attached description of an embodiment. The description refers to the attached drawings, in which the same numerical notations denote parts which correspond to one another.

List of drawings.

Figure 1 shows a schematic side view of the forward section of a truck.

Figure 2 shows a view of the cab forward suspension and springing arrangement.

Figure 3 shows a partly cut-away side view of a bushing forming part of the suspension. Figure 4 shows a section of the bushing along the line IV-IV in Figure 3.

Description of an embodiment.

A tiltable driver cab 1 is arranged on the truck depicted in Figure 1. The cab 1 is suspended on a vehicle frame 5 which mainly comprises two longitudinal parallel sidebeams (only the lefthand one is shown in Figure 1), which are connected to one another by a number of transverse beams (not depicted). An engine 6 is fastened to the truck frame 5 in a conventional manner. A fluid cooler 8 is arranged in the forward part of the cab 1 in order to convey coolant conventionally to the engine 6. To render the engine 6 readily accessible for

inspection and possible repair, the cab 1 is tiltable forwards relative to the frame 5.

Figure 1 also shows a suspension arrangement 9. Both the forward and rear ends of the cab 1 are resiliently suspended.relative to the frame 5. The rear end of the cab 1 is suspended in any conventional manner, e.g. by a pneumatic spring arrangement, which is therefore not described in further detail here.

The forward suspension arrangement 9 incorporates a cast bracket 10 fixed to the cab 1, a fastening portion 21 secured to the frame, a spring element 13 and a stabiliser 17.

The aforesaid forward cab suspension arrangement 9 is depicted most clearly in Figure 2 and is symmetrical about a vertical plane through the centre of the vehicle in its longitudinal direction, so only one part (the lefthand part) is shown.

The spring element 13, which incorporates an undepicted central shock-absorber and a pneumatic spring 14, connects the bracket 10 fixed on the cab 1 to the fastening portion 21 which is secured to the frame and which forms a vertical turret at the forward edge of the frame 5.

The stabiliser 17, which is depicted best in Figure 2, has the function of conventionally damping heterogeneous deflection movements of the spring element 13 and incorporates a torsion rod 18 which is arranged in the transverse direction of the vehicle between the two upper ends of the turret 21 and which has at each of its ends a link arm 19 which is fixed to it non rotatably and oriented in the longitudinal direction of the vehicle, being in this case directed rearwards. The rear part 20 of the link arm is supported rotatably in the lower part of the bracket 10 via a bushing 11 which permits some relative rotation between the link arm 19 and the bracket 10 about a horizontal pin which runs substantially transverse to the vehicle.

A bearing journal 25 is supported rotatably on the end portion of the torsion rod 18 but is secured against axial movement relative to the stabiliser 17, preferably by means of a conventional ball-bearing. The bearing journal 25 is secured by means of a clamping piece 35 and two screws 39 to the turret 21 fastened to the frame. This design is described in more detail in SE 92 03 909 - 8.

The spring element 13 has its upper end secured to the bracket 10 via a rubber bushing 16 and its lower end to the bearing journal 25 via a ball and socket joint 15.

The bushing 11 consists advantageously of a prefabricated unit as depicted best in Figures 3 and 4 and incorporates an outer sleeve 40 with a cylindrical shell surface directed inwards which is intended for pressing into a hole in the link arm 19. An advantageous method of manufacture may be to cast or forge the link arm 19 as a single piece and thereafter to drill a hole through its rear part 20 adapted to accommodating the bushing 11. The axial length of the outer sleeve 40 is not less than the axial length of the hole.

An inner sleeve 41 of the bushing 11 is arranged substantially concentrically with the outer sleeve 40. The inner sleeve 41 is attached firmly to the bracket 10 fastened to the cab. In this embodiment it is pressed firmly onto an undepicted pin which is parallel to the torsion rod 18 and firmly connected to the bracket 10.

An elastic device 50 with two elastic parts 42,43 which are situated diametrically opposite one another is arranged between the sleeves 40,41 in the vertical direction. These elastic parts 42,43 consist of rubber elements 48 between which stiffening discs 44 are firmly vulcanised. The discs 44 may be of metal or plastic and their purpose is to increase the vertical rigidity. There are two diametrically opposite hollow spaces 45,46 between the sleeves 40,41 in the longitudinal direction of the vehicle. The inner sleeve 41 is provided with elastic portions 47 which extend into the hollow spaces 45,46 and are advantageously made of the same material as and integrally with the rubber elements 48. These elastic portions 47 constitute damping elements which prevent the sleeves 40,41 colliding with one another during relative movement in the longitudinal direction of the vehicle.

The inner sleeve 41 is preferably made of metal and has an elliptical axial cross-section with major axis substantially in the longitudinal direction of the vehicle to enable the rubber elements 48 and the stiffening discs 44 to be designed as similar to straight blocks as possible, i.e. with as large a radius of curvature as possible. This results in maximum pressure load on the rubber elements 48 with simultaneous minimisation of shear stress when the bushing is subjected to forces in the vertical direction. A certain degree of curvature is nevertheless desirable for optimum clamping.

As depicted in Figure 4, the rubber elements 48 extend further in the axial direction of the bushing than both the stiffening discs 44 and the outer sleeve 40, thereby preventing contact, which might otherwise cause noise, between the rigid parts 40,44 of the bushing and the bracket 10. The edges of the rigid parts 40,44 and the shape of the rubber elements 48 should be designed so as to minimise the risk of crack formation in the rubber elements 48 when stressed in the transverse direction of the vehicle.

Designing and arranging the bushing 11 as described above results in hard springing in the vertical direction and soft springing in the longitudinal and transverse directions.

The principle of providing a bushing with different rigidities in different directions is previously known, e.g. from SE 458 552, where it is used in wheel suspension, but it has never been applied in cab suspension in heavy vehicles in which other special requirements apply concerning space, fitting, assembly work and, above all, deflection characteristics with a view to achieving maximum driver comfort.

According to the inventive arrrangement, the soft part provides damping out of longitudinal and transverse vibrations. The spring constant, i.e. the ratio between force and spring travel, has to be such that the natural, angular frequency remains lower than the vibration frequencies which may occur in these directions. Such vibrations may be due to deflection movements of the front axle or to frame oscillations which might be excited by hauling trailers or so-called pothole driving. Such a spring constant results in so-called supercritical oscillations which are desirable from the damping point of view. Research in the case of one type of truck has aimed at the spring constant being such that the natural angular frequency remains below 7Hz.

At the same time, the bushing is rigid in the vertical direction. During so-called cab roll, i.e. when the cab springs differently on the right and left sides while the vehicle is in motion, the heterogenous vertical movements which occur will be transferred conventionally via the stabiliser to the suspension on the other side. The result is an evening out of spring travel on the two sides. The best way of achieving this is for the bushing to be as rigid as possible in the vertical direction, otherwise there is risk of cab movements being damped out by relative movement in the vertical direction between the sleeves, thereby losing stabiliser function.

In purely practical terms, it has proved difficult with rubber bushings of this type to achieve

differences of more than approximately 10/1 in the spring constants in different directions. The soft part is therefore given a certain maximum vertical spring constant. The bushing has also to be dimensioned to cope with the stress to which it is subjected. Bushing strength may be achieved by using a larger amount of rubber, but this-entails not only a larger space requirement but also a lower spring constant.

According to the embodiment described above, the dead weight of the cab is supported by the spring element 13, so the bushing 11 is only stressed by the dynamic forces which occur when the cab rolls. The bushing 11 should therefore be dimensioned without too much strength, thereby resulting in a sufficiently low spring constant in the longitudinal and transverse directions without the bushing being too soft or insufficiently strong in the vertical direction.

According to the embodiment depicted in the drawings, it is possible to obtain spring constants of the order of 3000 kN/m in the vertical directiion and 280 kN/m in the longitudinal direction, thereby achieving a ratio of a good 10/1 between rigidities. For optimum comfort this ratio should be at least 8/1.

Designing the bushing 11 as above also provides a further advantage in the form of a low torsional spring-constant in the rotational direction, which is desirable for minimising losses which make purely vertical springing slower. The stabiliser should not interfere with purely vertical and equilateral deflection, which will pass through the spring element 13.

The embodiment described above may not set any limits upon the invention, which may be employed in a multiplicity of alternative forms, e.g. the bushing need not necessarily be cylindrical or have a concentrically arranged inner sleeve, and the shape of the elastic device may be varied. Experiments have also shown that stiffening discs are not necessary for certain vehicles.

According to the embodiment, the stabiliser link arm fastening to the torsion rod is secured against movement relative to the frame, while the other end is supported by the cab. The opposite situation is of course also possible.

Also according to the embodiment, the link arm is directed rearwards, but the arrangement may of course be turned so that the link arm is directed forwards.