WO2018010799A1

WO2018010799A1 - Vehicle with steerable driven rear axle

Info

Publication number: WO2018010799A1
Application number: PCT/EP2016/066779
Authority: WO
Inventors: Markus WIKSTRÖM; Lars Persson
Original assignee: Volvo Truck Corporation
Priority date: 2016-07-14
Filing date: 2016-07-14
Publication date: 2018-01-18

Abstract

The present invention relates to a vehicle (10), comprising: a chassis (12); a steerable driven rear axle (22), wherein the steerable driven rear axle (22) is pivotally mounted, such that the steerable driven rear axle (22) may be rotated relative to the chassis (12) about a vertical axis (34); air suspension struts (36a-d) adapted to suspend the steerable driven rear axle (22); and steering actuators (44a-b) adapted to rotate the steerable driven rear axle (22) about the vertical axis (34). The present invention also relates to a method and kit for providing steering of a driven rear axle of a vehicle.

Description

Vehicle with steerable driven rear axle

TECHNICAL FIELD

The invention relates to a vehicle comprising a chassis and a steerable driven rear axle. The present invention also relates to a method for providing steering of a driven rear axle of a vehicle. The present invention also relates to a kit for providing steering of a driven rear axle of a vehicle. The invention can for example be applied in heavy-duty vehicles, such as trucks, buses and construction equipment.

BACKGROUND

There currently exist trucks with three driven rear axles ("tri-drive"), wherein the third axle is non-steered. However, this can make such a truck hard to manoeuvre.

DE2554993 A1 discloses a heavy vehicle having drive on all wheels. On one end of the vehicle is the steering axle with steerable wheels powered through cardan linkages. The vehicle also has two fixed axles driven in the normal way. In addition to the fixed axles is a further rigid axle on the same side of the fixed axle as the steering axle. This rigid axle pivots round an axis on the vehicle chassis. This can be achieved by the use of a mechanical or hydraulic steering device. DE2554993 A1 , however, does not detail how the mechanical or hydraulic steering device is embodied, or how the further rigid axle is suspended.

US5320192 discloses a rear wheel steering device comprising: a chassis; a rear axle housing for supporting a pair of rear wheels at both end portions of said rear axle housing along a width direction of said chassis; a pair of leaf spring devices connected to said rear axle housing along each side of said chassis in said width direction of said chassis through tightening devices disposed at a longitudinal direction of said chassis; a pair of rear wheel steering actuators disposed on said chassis for revolving said rear axle housing around a rotational center positioned on a central line of said chassis along said longitudinal direction of said chassis; a plurality of pairs of slider shackle links for respectively connecting both end portions of each of said leaf spring devices to said chassis; a pair of upper and lower rubber pad members for connecting said rear axle housing to each of said leaf spring devices; and compressive force applying means for applying a predetermined compressive force to said pair of upper and lower rubber pad members by said tightening devices in order to tighten said rear axle housing. However, the rear wheel steering device of US5320192 appears to be useful only for very small steering angles (during high speed). It also has a lot of bushings in the steering linkages which can generate play and inaccuracy.

US5479999 relates to an automatic powered, self-tracking system for the rear axles of large vehicles. US5479999 discloses (figures 10a-b in US5479999) a four-bag per axle suspension system with torsion rods angled inwardly from the axle to a stabilizer bar. A rigid T-shaped bar attaches between frame members and extends downwardly between two laterally adjacent pair of air bags to provide a stable wall member against which laterally operating axle-pivoting mechanisms are mounted. The bottom support of each air bag is provided with an upwardly extending wall member against which said mechanisms act when actuated to move the bottom support of its respective air bag. The bottom support of each air bag ultimately connects to its associated axle via torsion rods. In this way, movement of bottom support causes a corresponding movement of its associated axle. However, it appears not possible to have this four air-bag suspension solution in a tri-drive installation, since it is not possible to have a prop shaft between the axles. Also, it seems like it only supports smaller steering angles of the axle.

SUMMARY

An object of the invention is to provide an improved vehicle comprising a steerable driven rear axle, which may overcome or at least alleviate at least some of the aforementioned drawbacks.

According to a first aspect of the invention, the object is achieved by a vehicle according to claim 1 .

According to the first aspect, there is provided a vehicle, comprising: a chassis; a steerable driven rear axle, wherein the steerable driven rear axle is pivotally mounted, such that the steerable driven rear axle may be rotated relative to the chassis about a vertical axis; air suspension struts adapted to suspend the steerable driven rear axle; and steering actuators adapted to rotate the steerable driven rear axle about the vertical axis.

The invention is based on the understanding that by suspending the driven rear axle using air suspension struts and steering the driven rear axle with steering actuators, for example hydraulic cylinders, steering can readily be provided to existing (standard) driven rear axles with existing (standard) hubs and brakes. Also, it gives the possibility to have a mechanically driven and steered axle in a multi axle configuration on a rear air suspension installation. Furthermore, the present solution is relatively uncomplex. Also, no steering knuckles/king pins or reaction rods are required. The air suspension struts may comprise a left pair of air suspension struts attached to the chassis and further attached to the steerable driven rear axle via a left air spring member, and a right pair of air suspension struts attached to the chassis and further attached to the steerable driven rear axle via a right air spring member.

"Left" may be construed as arranged on the left hand side of the vehicle, and

"right" may be construed as arranged on the right hand side of the vehicle.

The steering actuators may comprise a left steering actuator attached to the left air spring member and a right steering actuator attached to the right air spring member. By attaching the steering actuators to the air spring members, the steerable driven rear axle does not have to be modified.

Alternatively, the left and right steering actuators may be attached (directly) to the steerable driven rear axle.

The left steering actuator may further be attached to the chassis via a left bracket extending downwards from the chassis, wherein the right steering actuator is further attached to the chassis via a right bracket extending downwards from the chassis.

Each steering actuator may be configured to operate in a direction parallel or substantially parallel to the longitudinal axis of the vehicle. This may allow the steerable driven rear axle to move in an optimal way when the air suspension struts are active.

Each steering actuator may be a hydraulic cylinder.

A maximum steering angle of the steerable driven rear axle may be in the range of approximately 10 °- 12 °, though for wide vehicles even larger angles are possible.

The steerable driven rear axle may be pivotally mounted to a midpoint of a V-stay attached to the chassis. Hence, existing solutions (like the V-stay) may beneficially be used in conjunction with the present invention, which reduces the need for special constructions or modifications.

Each air suspension strut may comprise an air spring and a shock absorber. This, again, is a construction which is generally known per se.

The vehicle may further comprise a prop shaft connected to the steerable driven rear axle, for mechanically driving the steerable driven rear axle. The arrangement of the present steerable driven rear axle makes it easy to connect the prop shaft, which in turn allows the steerable driven rear axle to be positioned behind another driven rear axle.

The vehicle may further comprise an axle lift adapted to raise the steerable driven rear axle relative to the chassis. The arrangement of the present steerable driven rear axle makes it easy to fit such an axle lift. The vehicle may further comprise a declutch device adapted to declutch the steerable driven rear axle, to (temporarily) make it non-driven.

The vehicle may be a tri-drive vehicle. To this end, the vehicle may further comprise two non-steerable driven rear axles, wherein the steerable driven rear axle may be arranged behind the two non-steerable driven rear axles (as seen in the forward driving direction of the vehicle). Alternatively, the steerable driven rear axle may be arranged in front of the two non-steerable driven rear axles. In yet another alternative, the vehicle may comprise one non-steerable driven rear axle, wherein the steerable driven rear axle is arranged behind the non-steerable driven rear axle, and wherein the vehicle further comprises another steerable driven rear axle arranged in front of the non-steerable driven rear axle. The "another" steerable driven rear axle may be arranged in the same way as the previously discussed steerable driven rear axle, i.e. suspended by air suspension struts and steered/rotated by steering actuators such as hydraulic cylinders, etc.

According to a second aspect of the present invention, there is provided a method for providing steering of a driven rear axle of a vehicle, wherein the driven rear axle is pivotally mounted such that the driven rear axle may be rotated relative to a chassis of the vehicle about an axis perpendicular to the driven rear axle, which method comprises: attaching air suspension struts on one hand to the chassis, and on the other hand to the driven rear axle via air spring members; attaching hydraulic cylinders to at least one of the driven rear axle and the air spring members for rotating the driven rear axle about said axis; and connecting the hydraulic cylinders to a hydraulic steering system. That is, the hydraulic cylinders may for example be attached either (directly) to the driven rear axle or to the air spring members. This aspect may exhibit the same or similar features and technical effects as the first aspect, and vice versa. The method is applicable both when building a new vehicle and when "retrofitting" steering to a driven rear axle of an existing vehicle.

According to a third aspect of the present invention, there is provided a kit for providing steering of a driven rear axle of a vehicle, wherein the driven rear axle is pivotally mounted such that the driven rear axle may be rotated relative to a chassis of the vehicle about an axis perpendicular to the driven rear axle, which kit comprises: four air suspension struts adapted to be attached on one hand to the chassis, and on the other hand to the driven rear axle via air spring members; two hydraulic cylinders adapted to be attached to one of the driven rear axle and said air spring members for rotating the driven rear axle about said axis; and a hydraulic steering system connectable to the two hydraulic cylinders. That is, the hydraulic cylinders are adapted to be attached either (directly) to the driven rear axle or to the air spring members. This aspect may exhibit the same or similar features and technical effects as any of the previous aspects, and vice versa. The kit may be used to modify or upgrade an existing vehicle by making the driven rear axle steerable.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings:

Fig. 1 is a schematic side view of a vehicle according to an embodiment of the present invention.

Figs. 2a-b are partial perspective views illustrating a steerable driven rear axle of the vehicle of fig. 1 .

Figs. 3a-c are schematic top views of vehicles with various tri-drive configurations according to embodiments of the present inventions.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Fig. 1 illustrates a vehicle 10 according to an embodiment of the present invention.

The vehicle 10 is a truck. The truck may be heavy duty or medium duty. The truck could be a tractor or a truck with some superstructure(s) such as a platform, a tanker, a freight compartment, etc. Alternatively, the vehicle 10 could be a heavy or medium bus, a wheel loader, etc.

The vehicle 10 comprises a chassis 12, a cab 14, an engine 16, a hydraulic steering system 18, a steerable front axle 20, and three driven rear axles 22, 24a-b (tri- drive; 8x6 or 8x8). The three driven rear axles 22, 24a-b are mechanically driven by the engine 16. The foremost two driven rear axles 24a-b are non-steerable, whereas the rearmost driven rear axles 22 behind the two non-steerable driven rear axles 24a-b is steerable, see also fig. 3a. The hydraulic steering system 18 is adapted to steer the steerable driven rear axle 22. The steerable driven rear axle 22 may comprise a casing, a differential, two half-shafts, brakes, wheel hubs, one or two wheels on each side, etc. A prop shaft 26 is connected to the steerable driven rear axle 22 for mechanically driving the steerable driven rear axle 22. Furthermore, the steerable driven rear axle 22 may be equipped with at least one of an axle lift 50 and a declutch mechanism 52, as schematically illustrated in fig. 1 .

With further reference to figs. 2a-b, the steerable driven rear axle 22 is pivotally mounted to a midpoint 28 of a V-stay 30 attached to left and right rails 32a-b of the 5 chassis 12. In this way, the steerable driven rear axle 22 may be rotated relative to the chassis 12 about a vertical axis 34. The axis 34 is also perpendicular to the steerable driven rear axle 22.

The steerable driven rear axle 22 is suspended by four air suspension struts 36a- d. Each air suspension strut 36a-d comprises an air spring 38 and a shock absorber 40.

10 The air spring 38 and shock absorber 40 are axially aligned. There are two air suspension struts arranged on each side of the steerable driven rear axle 22. Namely, the air suspension struts 36a-d comprise a left pair of air suspension struts 36a-b attached to the chassis 12 and further attached to the steerable driven rear axle 22 via a left air spring member 42a, and a right pair of air suspension struts 36c-d attached to the chassis 12

15 and further attached to the steerable driven rear axle 22 via a right air spring member 42b, as illustrated in figs. 2-3. The air spring members 42a-b are attached to the underside of the steerable driven rear axle 22. Each air spring member 42a-b may be a beam. Each pair of air suspension struts comprises a front air suspension strut 36a;36c ahead of the steerable driven rear axle 22 and a rear air suspension strut 36b;36d behind the steerable

20 driven rear axle 22. Furthermore, each air suspension strut 36a-d is attached at its upper end to the chassis 12, for example by means of a bushing, and at its lower end to the respective air spring member 42a;42b, for example by means of a ball joint. The bushing may for example be made of rubber or synthetic rubber. The bushings and ball joints allow for a certain amount of movement so that the steerable driven rear axle 22 can be

25 rotated.

Steering actuators in the form of two hydraulic cylinders 44a-b are further provided to rotate the steerable driven rear axle 22 about the vertical axis 34. The hydraulic cylinders 44a-b are connected to the hydraulic steering system 18. There is one hydraulic cylinder arranged on each side of the steerable driven rear axle 22. Namely, the hydraulic

30 cylinders 44a-b comprise a left hydraulic cylinder 44a and a right hydraulic cylinder 44b.

One end of the left hydraulic cylinder 44a is attached to the underside of the left air spring member 42a, and the opposite end of the left hydraulic cylinder 44a is attached to a lower end of a left bracket 46a extending downwards from the chassis 12. Likewise, one end of the right hydraulic cylinder 44b is attached to the underside of the right air spring member

35 42b, and the opposite end of the right hydraulic cylinder 44b is attached to a lower end of a right bracket 46b extending downwards from the chassis 12. Both hydraulic cylinders 44a-b are oriented and configured to operate longitudinally, in a direction parallel to the longitudinal axis 48 of the vehicle 10.

In operation, the steerable driven rear axle 22 is rotated, and hence steered, by 5 the hydraulic steering system 18 actuating the hydraulic cylinders 44a-b. When the vehicle 10 is turning right, as shown in fig. 3a, the left hydraulic cylinder 44a is extended whereas the right hydraulic cylinder 44b is shrunk, whereby the steerable driven rear axle 22 is rotated anticlockwise. Likewise, when the vehicle 10 is turning left, the left hydraulic cylinder 44a is shrunk whereas the right hydraulic cylinder 44b is extended, whereby the 10 steerable driven rear axle 22 is rotated clockwise. The maximum steering angle a of the steerable driven rear axle 22 may for example be in the range of 10 °-12 °. The current steering angle of the steerable front axle 20 may be input to the hydraulic steering system 18, for coordinated steering of the steerable front axle 20 and the steerable driven rear axle 22. By steering the driven rear axle 22, the vehicle 10 may be easier to manoeuvre. 15 In an alternative tri-drive configuration shown in fig. 3b, the steerable driven rear axle 22 is arranged in front of the two non-steerable driven rear axles 24a-b. In operation, this steerable driven rear axle 22 is rotated clockwise when the vehicle 10 turns right, and anticlockwise when the vehicle 10 turns left.

In yet another alternative shown in fig. 3c, the vehicle 10 comprises only one non- 20 steerable driven rear axle 24c but two steerable driven rear axles 22, 22'; one 22' in front of the non-steerable driven rear axle 24c and one 22 behind the non-steerable driven rear axle 24c. The steerable driven rear axle 22' may be arranged in the same way as the steerable driven rear axle 22, albeit in operation they are rotated in opposite directions, as shown in fig. 3c.

25 The present steerable driven rear axle 22 can be added when building a new vehicle 10, wherein the air suspension struts 36a-d and hydraulic cylinders 44a-b are attached as detailed above, and wherein the hydraulic cylinders 44a-b are connected to the hydraulic steering system 18.

Steering can also be applied or retrofitted to a driven rear axle of an existing

30 vehicle, in order to modify or upgrade the existing vehicle. To this end, an upgrade kit may comprise the four air suspension struts 36a-d, the two hydraulic cylinders 44a-b, and the hydraulic steering system 18. When providing steering to the driven rear axle of such an existing vehicle, existing air springs and fixation brackets may be replaced by the air suspension struts 36a-d, which are attached to the chassis 12 and to the driven rear axle

35 22 via the air spring members 42a-b. New fixation brackets for the air suspension struts 36a-d may also be provided. Furthermore, existing shock absorbers and brackets are removed. Any stabiliser installation may also be removed or modified. Then existing reaction rods are replaced by the hydraulic cylinders 44a-b, which are attached to the air spring members 42a-b. The hydraulic steering system 18 is also mounted to the vehicle 10, and the hydraulic cylinders 44a-b are connected to the hydraulic steering system 18.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

For example, instead of being attached to the air spring members 42a-b, the hydraulic cylinders 44a-b could be attached directly to the steerable driven rear axle 22.

Claims

1 . A vehicle (10), comprising:

a chassis (12); and

a steerable driven rear axle (22), wherein the steerable driven rear axle (22) is pivotally mounted, such that the steerable driven rear axle (22) may be rotated relative to the chassis (12) about a vertical axis (34),

characterized by:

air suspension struts (36a-d) adapted to suspend the steerable driven rear axle (22); and

steering actuators (44a-b) adapted to rotate the steerable driven rear axle (22) about the vertical axis (34).

2. A vehicle according to claim 1 , wherein the air suspension struts (36a-d) comprise a left pair of air suspension struts (36a-b) attached to the chassis (12) and further attached to the steerable driven rear axle (22) via a left air spring member (42a), and a right pair of air suspension struts (36c-d) attached to the chassis (12) and further attached to the steerable driven rear axle (22) via a right air spring member (42b).

3. A vehicle according to claim 2, wherein the steering actuators (44a-b) comprise a left steering actuator (44a) attached to the left air spring member (42a) and a right steering actuator (44b) attached to the right air spring member (42b).

4. A vehicle according to claim 1 or 2, wherein the steering actuators comprise a left steering actuator (44a) attached to the steerable driven rear axle (22) and a right steering actuator (44b) attached to the steerable driven rear axle (22).

5. A vehicle according to claim 3 or 4, wherein the left steering actuator (44a) is further attached to the chassis (12) via a left bracket (46a) extending downwards from the chassis (12), and wherein the right steering actuator (44b) is further attached to the chassis (12) via a right bracket (46b) extending downwards from the chassis (12).

6. A vehicle according to any proceeding claim, wherein each steering actuator (44a- b) is configured to operate in a direction parallel or substantially parallel to the longitudinal axis (48) of the vehicle (10).

7. A vehicle according to any proceeding claim, wherein each steering actuator is a hydraulic cylinder.

8. A vehicle according to any proceeding claim, wherein a maximum steering angle 5 of the steerable driven rear axle (22) is in the range of approximately 10°-12 °.

9. A vehicle according to any proceeding claim, wherein the steerable driven rear axle (22) is pivotally mounted to a midpoint (28) of a V-stay (30) attached to the chassis (12).

10

10. A vehicle according to any proceeding claim, wherein each air suspension strut (32a-d) comprises an air spring (38) and a shock absorber (40).

1 1 . A vehicle according to any proceeding claim, further comprising a prop shaft (26) 15 connected to the steerable driven rear axle (22) for mechanically driving the steerable driven rear axle (22).

12. A vehicle according to any proceeding claim, further comprising an axle lift (50) adapted to raise the steerable driven rear axle (22) relative to the chassis (12).

20

13. A vehicle according to any proceeding claim, further comprising a declutch device (52) adapted to declutch the steerable driven rear axle (22).

14. A vehicle according to any proceeding claim, further comprising two non-steerable 25 driven rear axles (24a-b).

15. A vehicle according to claim 14, wherein the steerable driven rear axle (22) is arranged behind the two non-steerable driven rear axles (24a-b).

30 16. A vehicle according to any preceding claim 1 -13, further comprising one non- steerable driven rear axle (24c), wherein the steerable driven rear axle (22) is arranged behind the non-steerable driven rear axle (24c), and wherein the vehicle (10) further comprises another steerable driven rear axle (22') arranged in front of the non-steerable driven rear axle (24).

35

17. A method for providing steering of a driven rear axle (22) of a vehicle (10), wherein the driven rear axle (22) is pivotally mounted such that the driven rear axle (22) may be rotated relative to a chassis (12) of the vehicle (10) about an axis (34) perpendicular to the driven rear axle, which method comprises:

attaching air suspension struts (36a-d) on one hand to the chassis (12), and on the other hand to the driven rear axle (22) via air spring members (42a-b);

attaching hydraulic cylinders (44a-b) to one of the driven rear axle (22) and the air spring members (42a-b) for rotating the driven rear axle (22) about said axis (34); and connecting the hydraulic cylinders (44a-b) to a hydraulic steering system (18).

18. A kit for providing steering of a driven rear axle (22) of a vehicle (10), wherein the driven rear axle (22) is pivotally mounted such that the driven rear axle (22) may be rotated relative to a chassis (12) of the vehicle (10) about an axis (34) perpendicular to the driven rear axle (22), which kit comprises:

four air suspension struts (36a-d) adapted to be attached on one hand to the chassis (12), and on the other hand to the driven rear axle (22) via air spring members (42a-b);

two hydraulic cylinders (44a-b) adapted to be attached to at least one of the driven rear axle (22) and said air spring members (42a-b) for rotating the driven rear axle (22) about said axis (34); and

a hydraulic steering system (18) connectable to the two hydraulic cylinders (44a- b).