Background Heavy vehicles, e. g. trucks, often have a cab which is springingly suspended with respect to the vehicle's frame at three or four different points.

Heavy vehicles of the abovementioned kind often have a driver's cab which is suspended on the vehicle's frame and tiltable relative to the vehicle's frame. The cab is tiltable to provide access to the engine for servicing and repairs as necessary. The rear edge of the cab is suspended, for example, by means of a conventional air spring arrangement.

Such vehicles are often provided with an anti-roll bar whose purpose is to damp out the various kinds of springing movements which may occur at the various suspension points. In such cases, a forward anti-roll bar incorporates a transverse torsion bar which has at each of the axial ends a link arm which is directed in the longitudinal direction of the vehicle. Each link arm is directly or indirectly supported via bearings with respect to the cab at one end and to the frame at the other end.

The types of bearings used for the purpose are plain, ball and roller bearings. These bearings afford advantages in that they do not absorb springing energy which it is desired be transferred via the anti-roll bar to the suspension of the other side of the vehicle. This is because not only do they not damp out any springing movements but they are also almost free from losses during the torsional rotation which occurs at the link arm fastening. However, their rigid structure does entail disadvantages such as

their readily propagating vibrations from the frame to the cab which adversely affect the driver.

A usual alternative solution is to use rubber bushings. Bushings are used in anti-roll bars to prevent propagation of vibrations from the frame to the cab. Such a bushing results in little damping of springing movements and therefore cannot provide sufficient springing comfort. A softer bushing provides good damping, which is advantageous from the vibration and comfort points of view, but has inferior strength characteristics and also absorbs spring energy, with consequent risk of impairment of anti-roll bar function. A bushing with rigidity intermediate between the two kinds just mentioned may risk causing natural oscillations excited by front axle springing, frame oscillations or the like.

An example of a bushing for an anti-roll bar is referred to in SE 502 395 C2, which refers to a device for suspending a sprung driver's cab with respect to a vehicle frame, incorporating an anti-roll bar which comprises two link arms oriented substantially in the longitudinal direction of the vehicle. The link arms are supported with respect to the cab or the frame by means of a bushing with different rigidities in mutually perpendicular radial directions. The bushing incorporates an elastic means with two vertically diametrically opposite elastic units between casings arranged on the link arms and the cab/frame respectively so as to create a respective hollow space in the longitudinal direction of the vehicle. The design of the elastic means is such that its spring constant in the vertical direction of the vehicle is at least eight times greater than the spring constant in the longitudinal direction of the vehicle.

A problem with bushings of that kind is that the spring constant of the bushings in the vehicle's transverse direction is determined by the elastic means which also determines the spring constant in the vehicle's vertical and longitudinal directions respectively.

Another problem with bushings of that kind is that the elastic means is fixed at its ends situated in the vehicle's transverse direction, which means that the elastic means is subject to shearing forces when the cab is tilted for access to the engine.

Brief description of the invention The problem that the spring constant of the bushings in the vehicle's transverse direction is determined by the elastic means which also determines the spring constant in the vehicle's vertical and longitudinal directions respectively is solved according to the invention by providing a bushing arrangement incorporating not only a separate bushing unit which absorbs the vertical and longitudinal movements relative to the vehicle, but also at least one further bushing unit, preferably two other separate bushing units, to absorb the lateral movements relative to the vehicle, whereby the design of at least one of the forward suspensions of the cab is according to the invention. The bushing unit which absorbs the vertical and longitudinal movements relative to the vehicle is arranged to slide on a spindle in the transverse direction of the vehicle, so that the at least one further bushing unit, preferably the two other separate bushing units, absorbs/absorb all the lateral movements relative to the vehicle.

The bushing and hence the resulting springing are soft in the vehicle's longitudinal and transverse directions but rigid in the vehicle's vertical direction, so the soft portion provides damping of longitudinal and transverse vibrations, while the rigid portion enables rolling movements of the cab to be damped by the anti-roll bar.

The features of the bushing which are stated in claim 1 result in the advantage of changing the characteristics of the bushing arrangement in the vehicle's lateral direction without affecting the characteristics in the vehicle's longitudinal and vertical directions, which means that the bushing can be set for different lateral rigidity independently of the vertical and longitudinal rigidity.

The problem of the elastic means being fixed at its ends situated in the vehicle's transverse direction and being thereby subject to shearing forces when the cab is tilted for access to the engine is solved by the features in the dependent claims whereby the bushing is supported, resulting in the advantages that the cab can be tilted without causing considerable wear of the bushings (which means that the service life of the

bushings may be lengthened) and that the design of the bushing means that more rubber can be incorporated in the bushing, thereby also lengthening its service life.

Brief description of the drawings The invention will now be explained in more detail below with reference to the attached drawings in which: Figure 1 depicts schematically a view of a forward suspension and springing arrangement for a cab for a heavy vehicle, Figure 2 depicts schematically a perspective view of a bushing arrangement with three bushing units according to a first embodiment of the invention, Figure 3 depicts schematically a cross-section of a bushing arrangement of the first embodiment of the invention depicted in Figure 1, Figure 4 depicts schematically a cross-section of a bushing arrangement according to a second embodiment of the invention, and Figure 5 depicts schematically a cross-section of a bushing arrangement according to a third embodiment of the invention.

Description of preferred embodiments Figure 1 depicts schematically a view of a forward suspension and springing arrangement for a cab 1 for a heavy vehicle. The cab 1 of a heavy vehicle, e. g. a truck, is usually suspended on a vehicle frame 3 which mainly comprises two longitudinal parallel side-members. The latter are tied together by a number of transverse members, and an engine is fastened to the frame 3 in a conventional manner. To render the engine readily accessible for inspection and repairs as necessary, the cab 1 according to

the invention is tiltable forwards relative to the frame 3. The front edge of the cab 1 is springingly suspended relative to the frame 3 in the manner according to the invention.

The rear edge of the cab 1 is suspended in a conventional manner, e. g. by means of an air spring arrangement. The forward suspension arrangement comprises a bracket 2 secured to the cab 1, a fastening portion 4 fastened to the frame, a spring element 6 and an anti-roll bar 8.

The arrangement is symmetrical about a vertical plane through the middle of the vehicle in its longitudinal direction, so only one (the left) portion is depicted.

The spring element 6, which comprises an undepicted central shock-absorber and an air spring 10, connects the bracket 2 secured to the cab 1 to the fastening portion 4 which is fastened to the frame and which forms part of the vertical turret 12 at the front edge of the frame 3.

The purpose of the anti-roll bar 8 is to damp in a conventional manner various kinds of springing movements of the spring element 6, and said anti-roll bar incorporates a torsion rod 14 which is arranged in the vehicle's transverse direction between the two upper ends of the turret 12 and which has at each of its own ends a link arm 16 which is oriented in the vehicle's longitudinal direction and, in this case, directed rearwards, and is arranged for rotation jointly with the torsion rod 14. The rear portion 18 of the link arm is supported for rotation with respect to the lower portion of the bracket by means of a bushing arrangement 20 which allows relative rotation between the link arm 16 and the bracket 2 about a horizontal spindle which extends substantially transversely relative to the vehicle.

A pivot pin 22 is supported for rotation with respect to the end portion of the torsion rod 14 but is secured against axial movement relative to the anti-roll bar 8, preferably by means of a conventional ball bearing. The pivot pin 22 is secured to the turret 12 which is fastened to the frame. The spring element 6 is secured at its upper end to the

bracket 2 by means of a rubber bushing 24 and at its lower end to the pivot pin 22 by means of a ball bearing.

The bushing arrangement 20 for the anti-roll bar 8 takes with advantage the form of a prefabricated unit which is best illustrated in Figures 3,4 and 5 and is described in detail below. The bushing arrangement 20 comprises inter alia an outer casing 28 with a cylindrical shell surface facing outwards which is intended to be pressed into a hole in the link arm 16. A suitable manufacturing method may be to cast or forge the link arm 16 integrally and thereafter to drill through its rear portion 18 a hole appropriate to accommodating the bushing arrangement 20.

The invention thus relates to a bushing arrangement for an anti-roll bar 8 in the suspension of a sprung driver's cab 1 with respect to a vehicle frame 3, with the anti- roll bar 8 being supported for rotation with respect to both the cab 1 and the frame 3, which anti-roll bar 8 comprises two link arms 16 oriented substantially in the vehicle's longitudinal direction and each situated on their respective sides of a longitudinal vertical plane through the middle of the vehicle, which link arms 16 are firmly connected together by means of a transverse torsion rod 14, with each of the link arms 16 being supported by at least one vehicle portion in the form of either the driver's cab 1 or the vehicle frame 3 to allow relative rotation between the link arm 16 and the vehicle portion about a spindle 58 oriented substantially in the vehicle's transverse direction, with the link arm 16 being supported on the vehicle portion by means of a first bushing unit 34 with different rigidities in mutually perpendicular radial directions relative to said spindle 58, with the bushing arrangement further comprising at least one bushing unit 30, 32 arranged to damp movements in the longitudinal direction of said spindle 58 oriented substantially in the vehicle's transverse direction. The bushing unit 34 which absorbs the vertical and longitudinal movements relative to the vehicle is arranged to slide on said spindle 58 in the vehicle's transverse direction, so that the at least one further bushing unit 30, 32, preferably the two other separate bushing units 30,32, absorbs/absorb all the lateral movements relative to the vehicle.

Figure 2 depicts schematically a perspective view of a bushing arrangement 20 with three bushing units according to a first embodiment of the invention. The bushing arrangement 20 comprises two lateral bushing units 30,32, at least one of which may be replaceable, and, arranged between them, an intermediate bushing unit 34. Each of the lateral bushing units 30 and 32 respectively incorporates a lateral bushing 36 and 38 respectively and an intermediate disc 40 and 42 respectively, preferably made of steel, connected to the lateral bushings 36 and 38 respectively. The intermediate bushing unit 34 comprises an outer casing 28, preferably made of steel, an inner casing 44 arranged within and substantially concentric to the outer casing 28 and preferably made of steel, and an intermediate bushing 46 which is arranged between the outer casing 28 and the inner casing 44 and which connects the outer casing 28 to the inner casing 44. Said intermediate bushing 46 may be made integrally, preferably of rubber.

Alternatively, said intermediate bushing 46 may comprise two or more parts. For example, the intermediate bushing 46, as viewed along an axis A-A running transverse to the outer casing 28 and passing through the cross-sectional centre of the inner casing 44, may comprise an inner intermediate bushing portion 48 arranged outside and connected to the inner casing 44, first and second stiffening portions 50 and 52 respectively each arranged outside and connected to the inner intermediate bushing portion 48 on their respective sides of the inner casing 44, first and second outer intermediate bushing portions 54 and 56 respectively which are not only arranged outside and connected to the first and second stiffening portions 50 and 52 respectively but are also arranged inside and connected to the outer casing 28. The stiffening portions 50,52 are preferably made of plastic or metal, e. g. steel, whereas the elastic bushing portions 36,38, 46,54, 56 are preferably made of rubber. The fastening between the various portions is preferably effected by solid vulcanisation. The drawing also shows a spindle 58 in tubular form, preferably made of steel, which is situated inside the inner casing 44 so that the inner casing 44 and hence the whole intermediate bushing unit 34 can rotate about this spindle 58. The spindle 58 is firmly attached to the bracket 2 which is fastened to the cab. The intermediate bushing unit 34 which absorbs the vertical and longitudinal movements relative to the vehicle is arranged to slide on said spindle 58 in the vehicle's longitudinal direction so that the at least one

further bushing unit 30, 32, preferably the two other separate bushing units 30, 32, absorbs/absorb all the lateral movements relative to the vehicle.

Figure 3 depicts schematically a cross-section of a bushing arrangement of the first embodiment of the invention depicted in Figure 2. The bushing arrangement 20 comprises two lateral bushing units 30,32 and, arranged between them, an intermediate bushing unit 34. Each of the lateral bushing units 30,32 respectively incorporates a lateral bushing 36 and 38 respectively and an intermediate disc 40 and 42 respectively, preferably made of steel, connected to the lateral bushings 36 and 38 respectively. The intermediate bushing unit 34 comprises an outer casing 28, preferably made of steel, an inner casing 44 arranged inside and substantially concentric to the outer casing 28 and preferably made of low-friction material, and an intermediate bushing 46 which is arranged between the outer casing 28 and the inner casing 44 and which connects the outer casing 28 to the inner casing 44. Said intermediate bushing 46 may be made integrally, preferably made of rubber. Alternatively, said intermediate bushing 46 may comprise two or more parts. The intermediate discs 40,42 of the lateral bushing units abut against both the link arm 16 and the outer casing 28 of the intermediate bushing unit. The drawing also shows a spindle 58 in tubular form, preferably made of steel, which is situated inside the inner casing 44, whereby the inner casing 44 and hence the whole intermediate bushing unit 34 can rotate about this spindle 58. The spindle 58 is firmly attached to the bracket 2 which is fastened to the cab. The intermediate bushing unit 34 which absorbs the vertical and longitudinal movements relative to the vehicle is arranged to slide on said spindle 58 in the vehicle's longitudinal direction so that the at least one further lateral bushing unit 30,32, preferably the two other separate lateral bushing units 30,32, absorbs/absorb all the lateral movements relative to the vehicle.

Figure 4 depicts schematically a cross-section of a bushing arrangement according to a second embodiment of the invention. The bushing arrangement 20 comprises two lateral bushing units 60,62 and, arranged between them, an intermediate bushing unit 34. Each of the lateral bushing units 60 and 62 incorporates a lateral bushing 64 and 66 respectively and an intermediate disc 68 and 70 respectively, preferably made of steel, connected to the lateral bushings 64 and 66 respectively. The intermediate

bushing 34 comprises an outer casing 28, preferably made of steel, an inner casing 44 arranged inside and substantially concentric to the outer casing 28 and preferably made of low-friction material, and an intermediate bushing 46 which is arranged between the outer casing 28 and the inner casing 44 and which connects the outer casing 28 to the inner casing 44. Said intermediate bushing 46 may be made integrally, preferably of rubber. Alternatively, said intermediate bushing 46 may comprise two or more parts.

The difference as compared with the embodiment according to Figure 3 is that the intermediate discs 68,70 of the lateral bushing units abut against the link arm 16 on the latter's outside as viewed in the radial direction of the intermediate discs 68,70. The advantage is of having space for more intermediate bushing material as compared with the situation according to the first embodiment of the invention. The disadvantage is that the link arm 16 has to be machined. The drawing also shows a spindle 58 in tubular form, preferably made of steel, which is situated inside the inner casing 44 so that the inner casing 44 and hence the whole intermediate bushing unit 34 can rotate about this spindle 58. The spindle 58 is firmly attached to the bracket 2 which is fastened to the cab. The intermediate bushing unit 34 which absorbs the vertical and longitudinal movements relative to the vehicle is arranged to slide on said spindle 58 in the vehicle's transverse direction so that the at least one further lateral bushing unit 60,62, preferably the two other separate lateral bushing units 60,62, absorbs/absorb all the lateral movements relative to the vehicle.

Figure 5 depicts schematically a cross-section of a bushing arrangement according to a third embodiment of the invention. The bushing arrangement 20 comprises two lateral bushing units 72,74 and, arranged between them, an intermediate bushing unit 34.

Each of the lateral bushing units 72 and 74 incorporates a lateral bushing 76 and 78 respectively and an intermediate disc 80 and 82 respectively, preferably made of steel, connected to the lateral bushings 76 and 78 respectively. The intermediate bushing 34 comprises an outer casing 28, preferably made of steel, an inner casing 44 arranged inside and substantially concentric to the outer casing 28 and preferably made of low- friction material, and an intermediate bushing 46 which is arranged between the outer casing 28 and the inner casing 44 and which connects the outer casing 28 to the inner

casing 44. Said intermediate bushing 46 may be made integrally, preferably of rubber.

Alternatively, said intermediate bushing 46 may comprise two or more parts. The difference as compared with the embodiment according to Figure 4 is that the intermediate discs 80, 82 of the lateral bushing units abut against the link arm 16 on the latter's inside as viewed in the radial direction of the intermediate discs 80,82. The advantage is of having space for more intermediate bushing material as compared with the situation according to the first embodiment of the invention. The disadvantage is that the link arm 16 has possibly to be machined. The drawing also shows a spindle 58 in tubular form, preferably made of steel, which is situated inside the inner casing 44 so that the inner casing 44 and hence the whole intermediate bushing unit 34 can rotate about this spindle 58. The spindle 58 is firmly attached to the bracket 2 which is fastened to the cab. The intermediate bushing unit 34 which absorbs the vertical and longitudinal movements relative to the vehicle is arranged to slide on said spindle 58 in the vehicle's transverse direction so that the at least one further lateral bushing unit 72,74, preferably the two other separate lateral bushing units 72,74, absorbs/absorb all the lateral movements relative to the vehicle.

According to the embodiment described above, the dead weight of the cab is borne by the spring element so that the bushing arrangement is only stressed by the dynamic forces which occur during rolling of the vehicle and by the road-induced vibrations which the bushing arrangement is intended to filter out and which are thus to be prevented from reaching the cab. According to the embodiments, the fastening of the anti-roll bar's link arm to the torsion bar is secured against relative movement with respect to the frame, while the other end is supported with respect to the cab. The opposite relationship is also possible. Also according to the embodiments, the link arm is directed rearwards, but it may also be turned so as to be directed forwards instead.

The lateral bushing units and the intermediate bushing unit which form part of the bushing arrangement may be connected together movably or immovably.