Suspension assembly for suspending a cabin of a truck or the like vehicle

The invention relates to a suspension assembly (1) for suspending a cabin (2) of a truck or the like vehicle. The assembly comprises a plurality of spring members (4a-d) arranged between the cabin (2) and a chassis of the vehicle, and a torsion bar (5) extending between at least two of said spring members (4a-d) so as to increase the roll stiffness of the assembly. The assembly further comprises an actuator (6) with which a torsion angle of the torsion bar (5) can be adjusted allowing active roll stabilization of the cabin (2).

The invention relates to a suspension assembly for suspending a cabin of a truck or the like vehicle. Such a suspension assembly is generally referred to and will hereinafter be referred to as ‘a secondary suspension assembly’, in contrast to ‘a primary suspension assembly’, used for suspending the vehicle wheels.

Typically, a secondary suspension assembly comprises a number of spring members arranged between the cabin and a chassis of the vehicle. To enhance driving comfort, the spring members preferably have a relatively low spring stiffness. This, however, may cause the cabin to experience rather large displacements during use, such as large roll motions when negotiating bends. The latter may affect the vehicle's steering behaviour. To reduce this problem, known suspension assemblies are equipped with a torsion bar, connecting a left and right side spring member so as to increase the overall roll stiffness of the assembly. The torsion bar may furthermore serve to guide vertical movements of the cabin and to facilitate tilting forward thereof, to provide access to components lying underneath the cabin, such as a motor.

To effectively decrease aforementioned roll motions, the torsion bar should have a relatively high torsion stiffness. This, however, may affect the driving comfort, for instance in situations where the left and right wheels of the vehicle are excited asymmetrically.

Therefore, a need exists for an improved secondary suspension assembly, which on the one hand provides for enhanced roll behaviour and steering behaviour and at the other hand provides for acceptable driving comfort.

To that end, an assembly according to the invention is characterized in that an actuator is provided with which a torsion angle of the torsion bar can be adjusted. Accordingly, the torsion bar can be used for active roll stabilisation by counteracting any roll motions of the cabin. As a consequence, the suspension members and the torsion bar can each have a relatively low stiffness, now that large cabin displacements caused by such low stiffnesses can be effectively suppressed. The low stiffnesses will prevent high frequent disturbances from exciting the cabin and as such enhance the driving comfort.

According to one aspect of the invention, the actuator can be arranged near an end of the torsion bar. Alternatively, the actuator may be positioned somewhere halfway, interconnecting two parts of the torsion bar. The position of the actuator can thus be freely varied, enabling efficient use of space. In case where the actuator is of the hydraulic type, its position may for instance be chosen so as to minimize the length of hydraulic supply and return lines, which will benefit its dynamic behaviour, e.g. its response time.

According to another aspect of the invention, the torsion bar can be coupled to the cabin by means of one or more ball joints. These ball joints can adapt their orientation to misalignments and/or deformations of the torsion bar, thereby allowing the torsion bar to pivot smoothly during use, without excessive frictional forces and/or excessive deformation stresses in the respective components.

According to yet another aspect of the invention, the actuator can be a hydraulic actuator. Such hydraulic actuator can be fed by a hydraulic supply circuit with a reservoir, a pump and control means for controlling the flow rate to and from the actuator or the pressure levels in the actuator. The pump may be driven by the combustion motor of the truck. Alternatively, the pump can be driven by a separate motor, for instance an electric motor. Such separate motor allows the actuator to be operated completely independent from the combustion motor, thus allowing active roll stabilisation to be in action when the combustion motor is shut off, and vice versa. By switching the motor on and off strategically, energy can be saved while an acceptable level of driving comfort can be maintained.

According to another aspect of the invention, the assembly may comprise a stabiliser bar, arranged to have its torsion axis extend substantially parallel to that of the torsion bar. Such stabiliser can provide for residual roll stiffness when the active roll stabilisation is deactivated. It furthermore can guide the cabin in vertical direction and help to stabilize it in the horizontal plane. It may also facilitate tilting forward of the cabin.

According to a further aspect of the invention, active roll stabilisation may be based on various control strategies. According to one control strategy, the roll motions may be suppressed completely, so as to keep the cabin substantially horizontally or at least parallel to the road surface. Such control strategy may greatly facilitate the steering behaviour of the truck. According to an alternative control strategy, the roll motions may be controlled to keep the cabin substantially in parallel with the chassis of the truck. Such control strategy helps to provide the driver with a realistic feeling of the actual truck and/or cabin motions and as such may help in achieving safe driving behaviour.

Additionally or alternatively the control strategy may depend on the driving conditions. For instance, when driving straight forward, at relatively high speeds, the cabin is likely to experience little roll motions. Accordingly, the active roll control may be switched off and energy may be saved. When driving at relatively low speeds, the cabin is more likely to experience roll motions, which may for instance be induced by road turns and/or a bumpy road surface. In such case, the active roll control may be switched on to its fullest. Other control strategies and/or combinations thereof are conceivable.

Further advantageous embodiments of an assembly according to the invention and a truck provided therewith are set forth in the dependent claims.

FIGS. 1 and 2schematically show a truck10comprising a chassis3and a cabin2which is mounted onto the chassis3via a suspension assembly1according to the invention. The suspension assembly1comprises, at least in the illustrated embodiment, four spring members4A-D, arranged near the corners of the cabin2. These spring members4A-D may for instance be construed as air springs.

The assembly1further comprises a torsion bar5which extends between the front spring members4A, B, an actuator6for adjusting a torsion angle of said torsion bar5, measurement means Sifor measuring a roll parameter of the cabin2, and a control unit30for controlling the actuator6based on data received from the measurement means Si. It is noted that the term “bar” should be interpreted broadly and not be limited to a straight bar.

As best seen inFIGS. 3 and 4, the torsion bar5comprises a midsection11which with two angled arms15L, R is pivotally connected to brackets13of the chassis3. The torsion bar5is further pivotally connected to an upper end of the two front spring members4A, B via suitable brackets14, and pivotally connected to the cabin2via suitable brackets12. The latter connection may for instance make use of ball joints20, as schematically shown inFIG. 5. Such ball joints20can absorb any misalignment which may be present between the brackets12and the midsection11due to for instance manufacturing inaccuracies and/or deformation of said components during use. Thus, jamming and accompanying high frictional forces and excessive wear can be prevented. Instead, the torsion bar5can pivot smoothly during use, which is beneficial for the cabin's overall driving comfort.

The actuator6may be mounted in the midsection11of the torsion bar5, as schematically shown inFIG. 2. Alternatively, the actuator6may be arranged at the junction of the midsection11with one of the arms15R, as shown inFIGS. 3 and 4. In the illustrated embodiment, the actuator6is configured as a rotation actuator having a stationary house16and a rotary part18. The house16is fixated to the arm15R by means of for instance a bushing17, a flange19and suitable fastening means. The rotary part18is fixated to an end21of the midsection11by means of for instance a spline. Said end21and the rotary part18are rotatably supported in the arm15R by means of bearings22(seeFIG. 4). The other end of the midsection11is fixated to the other arm15L.

The suspension assembly1functions as follows. During use, when driving over an irregular road surface or when taking turns, the cabin2will be subject to roll motions (i.e. rotations around a longitudinal axis L of the truck10, seeFIG. 2). These roll motions can be detected by the measurement means Si, which to that end may for instance be arranged to sense lateral and/or roll displacement, velocity and/or acceleration of the cabin2. Based on these data, the control unit30may control the actuator6to adjust a torsion angle of the torsion bar5so as to at least partly counteract said roll motions. Depending on a selected control strategy, the actuator6may be controlled to suppress the roll motions completely, so as to keep the cabin2substantially horizontal, or at least parallel to the road surface. This may contribute to good, i.e. direct steering behaviour. According to an alternative control strategy, the actuator6may be controlled to keep the cabin2parallel to the chassis3. This may provide a driver of the truck10with realistic feedback of the actual roll angle. Of course, other control strategies are possible.

The actuator6may be a hydraulic rotation actuator, with for instance four chambers I-IV, as shown inFIG. 6. The actuator6is linked to a hydraulic supply circuit25, comprising a hydraulic reservoir26, a supply line27, a return line28and pumping means29for circulating hydraulic fluid between the reservoir26and the actuator6. The circuit25further comprises several valves31,32, sensors Piand aforementioned control unit30for controlling a pressure level in the actuator6.

In the illustrated embodiment, the valves include a fail-safe valve32, arranged to cut off any supply to and from the actuator6, in case of some failure in for instance the supply circuit25. The valves furthermore include a pressure control valve31, for controlling a pressure difference or anti-roll moment at the actuator side. The pressure control valve31may for instance be a proportional control valve31(as illustrated inFIG. 6) enabling the pressure to be controlled proportionally variable to an input command between a base pressure and a maximum pressure. To that end, the valve31may include a plunger that from an open centre position (as shown inFIG. 6) is operable in two directions. In the open centre position the pressure will be substantially equal in all actuator chambers I-IV. When displacing the plunger to the right, the pressure in the lower left chamber I and upper right chamber III will increase so as to generate a positive pressure difference and a positive (i.e. counter clockwise) anti-roll moment at the actuator side. By driving the plunger to the other side, a negative anti-roll moment will be generated. In either case, the magnitude of the generated pressure difference and anti-roll moment depends on the displacement stroke of the plunger. Thanks to the open centre position of the plunger, the transition from positive to negative pressure difference can be smooth. The open centre position furthermore allows for hydraulic fluid to be returned to the reservoir26, substantially without resistance, in case where no moment is required at the actuator side.

The pumping means29may be driven by the combustion motor of the truck10. Alternatively, a separate motor may be provided, for instance an electric motor35as shown inFIG. 6. Such motor35can be relatively compact and as such offers much design freedom as to potential built-in locations. It furthermore allows the active roll stabilisation to be switched on and off at desire, i.e. completely independent of the combustion motor. Thus, the active roll stabilisation may be active when the truck10is at rest and its combustion motor is shut off. This may for instance be advantageous in cases where the cabin2is used to sleep in. Also, the active roll stabilisation may be deactivated in cases where it is not needed, for instance when driving straight forward, over a relatively smooth road surface. Under such conditions, the cabin2is not likely to experience considerable roll motions. By switching off the motor35energy can be saved.

The decision to switch the motor35on or off may for instance be based on the velocity of the truck10, which can be readily measured with suitable sensors. As long as the velocity is relatively high, for instance above 60 km/hr, the driver is not likely to effect considerable steering actions and consequently roll disturbances are not likely to occur. Consequently, the roll stabilisation feature can be deactivated with relatively little risk and/or little loss in drive comfort. As the velocity drops below a certain threshold value, for instance below 50 km/h, the motor35may be switched on again. Of course these values are for illustrative purposes only. They should not be construed as limiting.

To provide the suspension assembly1with sufficient residual roll stiffness in case where the motor35and active roll stabilisation are switched off, the assembly1may be provided with a supplementary bar or stabiliser bar25, extending substantially parallel to the torsion bar5as schematically shown inFIG. 2. This stabilizer bar25preferably has a relatively low torsion stiffness and relatively high bending stiffness, which may for instance be achieved by providing the bar25with a C-shaped cross section. As such, the bar25will hardly affect the operation of the adjustable torsion bar5but will be able to stabilize the cabin2in the horizontal plane and guide vertical movements thereof. As the stabilizer bar25can absorb most of the external bending loads acting on the assembly1, the torsion bar5may be of relatively light design, with a relatively low torsion stiffness. This is beneficial for the high frequent driving comfort of the cabin2, which is predominantly determined by the torsion stiffness of the adjustable torsion bar5. It also allows the spring members4A-D to be levelled with a relative simple, conventional levelling system, instead of a more complex provision, wherein each member requires its own levelling system.

When the motor35is switched on again, it may take some time before sufficient hydraulic pressure has built up for the actuator6to be able to deliver a certain anti-roll moment. This response time may be taken into account when deciding when to switch the motor25off and on. Also, the need for active roll stabilization may be anticipated by monitoring precursors of external roll disturbances, such as for instance the steering angle (assuming that a steering angle ushers a turn and a turn invokes roll disturbances). The motor35can then be restarted in an early stage, so as to allow the assembly1sufficient time to built up the necessary hydraulic pressure.

Alternatively, the hydraulic actuator6can be combined with a hydraulic circuit125according toFIG. 7. Like components have been denoted with like reference numerals, increased by 100. The circuit125differs from the one shown inFIG. 6in that the proportional pressure control 4/3 valve31has been replaced by two 3/2 valves, more particularly two proportional ‘closed centre’ pressure reduction valves131A, B for controlling the pressure difference at the actuator side. Such valve arrangement in rest or centre position supplies the actuator with hydraulic pressure and substantially closes off all return lines to a hydraulic fluid reservoir. In addition, the circuit125is provided with an accumulator140, a pressure controlled pressure relief valve142and a check valve143.

The circuit125ofFIG. 7is arranged to lower the pressure in the actuator chambers I-IV by having the pumping means129suction hydraulic fluid from the reservoir126into the high pressure zone H of the circuit125. With valves131A, B in the illustrated position, the pressure will be essentially equal in all actuator chambers I-IV. By switching over valve131B, hydraulic fluid in chamber II and IV will return to the reservoir causing the actuator106to rotate counter clockwise and generate a positive anti-roll moment. To generate a negative anti-roll moment the other valve131A is switched over. The pressure near the pumping means135and/or the accumulator140can be readily controlled by the motor135in cooperation with the pressure relief valve142. When the pressure in the high pressure zone H reaches a desired level, the motor135can be switched off. In such case, the check valve143prevents hydraulic fluid from returning to the reservoir126via the switched off pumping means129.

The circuit125according toFIG. 7offers several advantages. First of all, thanks to the accumulator140and the valves131A, B, in particular their closed centre configuration, a certain amount of hydraulic reserve can at all times be stored in the circuit125, even when the motor135is switched off. Thanks to such hydraulic reserve, the assembly1can have good response behaviour. It furthermore allows the use of smaller pumping means129. Also, thanks to the closed centre configuration of the valves131A, B, all actuator chambers I-IV will be connected to the high pressure zone H when the truck is driven straight ahead (corresponding to the state illustrated inFIG. 7). In this state, hydraulic fluid will be able to flow almost without resistance from one chamber to the other during rotational movements of the actuator (due to roll motions of the cabin2relative to the chassis3). Consequently, the delivered moment will be practically zero and the damping resulting from said rotational movement will be low. This will be beneficial for the driving comfort, as hardly any irregularities in the road surface will be transferred to the cabin2.

Furthermore, any other pressure peaks that may arise in the circuit125during use can be reduced or equalized by the buffering action of the accumulator140. This too is beneficial for the driving comfort. In addition, the closed centre configuration of the valves131A, B allows for a relatively simple fail safe valve132. Generally, such fail safe valve132will feature a safety mode in which hydraulic fluid is allowed to return to the reservoir126. Consequently, in case of any failure, the pressure in the circuit125can be prevented from becoming too high, thereby protecting the pumping means129from becoming damaged. With the closed centre configuration of the valves131A, B the aforementioned safety provision can be fulfilled by the pressure relief valve142, which will simply open to the reservoir126when the pressure in the high pressure zone H exceeds a certain, predetermined level. Alternatively or additionally, the motor135can be designed to switch off. As a consequence, the fail safe valve132no longer has to include the aforementioned open safety mode. Instead, it can be designed to be completely closed in said safety mode, which allows for a more simple design.

The invention is not in any way limited to the exemplary embodiments presented in the description and drawing. All combinations (of parts) of the embodiments shown and described are explicitly understood to be incorporated within this description and are explicitly understood to fall within the scope of the invention. Moreover, many variations are possible within the scope of the invention, as outlined by the claims