Commercial vehicles, which here means, for example, trucks, buses and similar commercial and utility vehicles and, in certain cases, even passenger cars, incorporate according to conventional technology a longitudinal chassis element. The chassis element supports vehicle components such as, for example, engine, driver's cab and a load-bearing element, e. g. in the form of a load platform or a superstructure. Also, the vehicle's wheel shafts are suspended in the chassis element.

With the object, for example, of improving the riding comfort for the driver and passengers in the vehicle and, in particular, reducing the amount of damage to cargo, especially when carrying fragile goods, the vehicle is equipped with sophisticated suspension systems. Such a suspension system comprises gas springs, e. g. two gas springs between at least one rear wheel shaft and the chassis element. Gas suspension systems are also designed to make it easy to raise and lower the chassis element and hence the loading height, i. e. the load surface of the load-bearing element, thereby facilitating loading and unloading. The loading height may be increased by supplying compressed gas to respective bellows of the springs, and the loading height may be reduced by releasing compressed gas from the bellows of the springs. Load handling and/or load-bearing element replacement are/is thus facilitated. On recent commercial vehicles the gas springs and hence the level of the load-bearing element can be regulated electronically. Such an electronic level loading system is called ELC (Electronic Level Control). The chassis height is monitored by sensors and the chassis height can be adjusted automatically as necessary. It is for example

possible to maintain the prevailing loading height despite increased load, by supplying further compressed gas. It is also possible to maintain the loading height during loading, by supplying compressed gas as required. Such an electronic level loading system also makes it possible to deliver different amounts of gas to the respective gas springs. Such an electronic level loading system thus makes it easy to raise, lower or slope the load surface of the load-bearing element.

Electronically controlled level loading systems incorporate pressure sensors designed to detect the gas pressure in the respective bellows. Information about the gas pressure in the respective gas springs of a wheel shaft and knowledge of the effective cross-sectional area of the respective bellows can be used to calculate the weight acting upon the wheel shaft. The suspension characteristics of a gas spring depend on the compressibility of the active medium and the design of the gas spring, particularly the design of the bellows. The compressible medium normally used in gas springs is air. At any given air pressure in the bellows, the bearing capacity of an air spring, i. e. the latter's ability to absorb weight, is different at different chassis heights, i. e. at different lengths of the bellows. This difference is used for calculating the weight acting upon the wheel shaft when the load surface of the load-bearing element supported by the chassis element is in an initial position coinciding with the level at which the load surface usually is with respect to the wheel shaft during driving, i. e. the level at which the load surface is during movement of the vehicle, according to previous technology. If the load surface has thus been raised or lowered at the time of loading, correct calculation of said weight entails having, according to previous technology, to raise or lower the load surface to the level at which the load surface normally is during movement of the vehicle. The weight which will act upon the wheel shaft is thus calculated on the basis of the respective air pressures in the bellows and the respective effective cross- sectional areas of the bellows when the load surface is at the level at which the load surface is during movement of the vehicle. The driver of the vehicle may control the electronically controlled level maintenance system via some kind of control device. The electronically controlled level maintenance system also incorporates a display means whereby the driver can obtain information about the weight acting upon the wheel shaft.

There are many regulations concerning vehicle traffic, especially heavy vehicle traffic, such as maximum weight of vehicle. Accordingly the driver of the vehicle is interested in obtaining information about the weight which will act upon the respective axles during movement of the vehicle when the vehicle is laden. Information on the respective weights acting upon the various axles and knowledge of the tare weights of the respective wheel shafts can be used to arrive at the total weight acting upon the road surface.

A disadvantage of the procedure described in connection with previous technology is that the driver of the vehicle may be forced to lower and raise the load surface a number of times in order to find out whether, when for example the maximum permissible weight acting upon the road surface is reached, the load surface at the time of loading is at a level which differs from the level at which the load surface is during movement of the vehicle.

SUMMARY OF THE INVENTION The object of the present invention is to eliminate the aforesaid problems. What is particularly intended is an arrangement whereby it is possible to reliably calculate the weight which will act upon at least one wheel shaft of a commercial vehicle during loading even if the level of the load- bearing element is at a height which differs from the height at which the load-bearing element is during movement of the vehicle.

This object is achieved with the arrangement indicated in the introduction which has the features defined in the characterising part of claim 1.

With such an arrangement whereby the weight which will act upon the wheel shaft is calculated on the basis of both the pressure in the space of the first suspension means and the length of the space of the first suspension means in the longitudinal direction (x) when the load surface is in the second position, the load surface need not be in said first position, which may be the level at which the load surface is with respect to the respective shaft during driving, i. e. during movement of the

vehicle, in which position the space in the first suspension means has a known length in the longitudinal direction (x), when said weight is calculated. Said weight is thus calculated as a function of both the pressure in and the position of the suspension means, and no lowering or raising of the load surface to said first position is necessary in order reliably to calculate said weight. The suspension means may incorporate a bellows which defines said space of the suspension means. The suspension means may also have a known bearing capacity at a certain length of the space in the longitudinal direction (x), i. e. when the bellows is in a certain position, the suspension means has a certain bearing capacity. Said first and second sensor means are each adapted to send their respective signal to the calculation unit, thus providing the calculation unit with information about the prevailing pressure of the fluid in the bellows and the prevailing length of the bellows. It should be noted that when the load surface is in said second position it may be below or above the position at which the load surface is in said first position. The load surface may also slope in said second position. Some kind of display means is connected to the calculation unit so that, for example, the driver of the vehicle can obtain information about said weight. It should be noted that the driver of the vehicle is primarily interested in obtaining information about the weight which will act upon the road surface via said wheel shaft. The calculation unit may thus also be adapted to use the tare weight of the wheel shaft to calculate, as a next step, said total weight.

According to one embodiment of the invention, said fluid comprises a compressible medium, preferably some kind of gas, e. g. air.

According to a further embodiment, at any given pressure of the fluid in said space, the bearing capacity of said suspension means is different at different lengths of said space in the longitudinal direction (x) and the calculation unit is adapted to take into account a pertinent compensation factor which is related to said difference in bearing capacity with respect to said difference in length of the space in the longitudinal direction (x) in the situation where the load surface is in said second position and in the situation where the load surface is in said first position at said detected pressure when it calculates said weight.

According to a further embodiment, the calculation unit incomprises a first memory unit in which various compensation factors are stored, and each compensation factor relates to a certain difference in bearing capacity with respect to a certain difference in length of the space in the longitudinal direction (x) between the situation where the load surface is in said second position and the load surface is in said first position at a certain pressure. Said compensation factors may be arrived at empirically. The calculation unit can thus retrieve said compensation factors from said first memory unit.

According to a further embodiment of the invention, the calculation unit is adapted to calculate the prevailing bearing capacity of said fluid in said space at said detected pressure on the basis of said first parameter when the load surface is in said second position, and to calculate the difference in bearing capacity of said fluid in said space between the situation where the load surface is in said second position and the situation where the load surface is in said first position, and said difference in bearing capacity forms said pertinent compensation factor. It should be noted that the length of said space in the longitudinal direction (x) when the load surface is in said first position is known and is stored in the calculation unit. Said calculation unit may incorporate an algorithm for calculating said pertinent compensation factor.

According to a further embodiment, the calculation unit comprises a second memory unit in which information is stored about the bearing capacity of said fluid at different lengths of said space in the longitudinal direction (x) and different pressures of the fluid. The calculation unit is further adapted to use said stored information in the memory unit when it calculates/retrieves said pertinent compensation factor. Thus there are stored values for the bearing capacity of the fluid at different lengths of the space in the longitudinal direction (x) with respect to different pressures.

Thus the calculation unit first uses said first parameter and said stored information to arrive at the pertinent bearing capacity of the fluid in said space at said detected pressure. This bearing capacity value is compared with what the bearing capacity of the fluid would have been if the load surface

had been in said first position at the prevailing fluid pressure, thereby obtaining said pertinent compensation factor.

As compared with mechanical springs, gas springs behave in a less linear manner, i. e. plotting the relationship between applied force and resulting deformation does not produce a straight line.

This relationship is called the spring characteristic of the spring.

According to a further embodiment, said compensation factor is adapted to take into account said non-linear spring characteristic. It should be noted, however, that within certain lengths of the space in the longitudinal direction (x) the relationship between length and applied force is linear.

Within that range the compensation factor is adapted to take into account said linear relationship.

According to a further embodiment, said first sensor means comprises at least one first position sensor adapted to detect the distance between the load surface and at least said first wheel shaft, and the calculation unit is adapted also to use said known distance for deriving said first parameter.

The position sensor may be situated at many different locations, whether on the load surface or on the chassis element. The position sensor is adapted to send a signal to the calculation unit, which can use information about the distance detected to derive the first parameter, which is related to the length of the space in the longitudinal direction (x) when the load surface is in said second position.

Alternatively, said first sensor means may comprise at least one ultrasonic sensor arranged adjacent to the space of said first suspension means, said ultrasonic sensor being adapted to detect the length of the space of said first suspension means in the longitudinal direction (x). The calculation unit receives direct information about the length of the space in the longitudinal direction (x) via a signal from the ultrasonic sensor.

A suspension means is arranged adjacent to each wheel of said first wheel shaft. The vehicle thus also incorporates a second suspension means arranged between said first wheel shaft and said chassis element, and said second suspension means also comprises a space which extends in a longitudinal direction (x) and which contains a fluid, said second suspension means together with

said first suspension means being adapted to enable the load surface to assume said first position and said second position as a result of a fluid also being supplied to or released from said space of said second suspension means, while said space of said second suspension means also has in the longitudinal direction (x), when the load surface is in said second position, a length which differs from the length which said space of said second suspension means has in the longitudinal direction (x) when the load surface is in said first position. If the respective spaces of the suspension devices have the same length in the longitudinal direction (x) and the load is evenly distributed on the load surface, said first parameter and said second parameter for the first suspension means may be assumed to apply also for the second suspension means, whereupon the calculation unit calculates the weight which will act upon the first wheel shaft on the basis of said first parameter and said second parameter of the first suspension means. However, the load surface may slope in such a way that the space has in the longitudinal direction (x) of the first suspension means a length which differs from the length of the space in the longitudinal direction (x) of the second suspension means. Moreover, the load may be unevenly distributed on the load surface. According to an advantageous embodiment, the first sensor means is also adapted to detect a first parameter which is related to the length of the space in the longitudinal direction (x) of said second suspension means when the load surface is in said second position, and the second sensor means is also adapted to detect a second parameter which is related to the pressure of said fluid in said space of said second suspension means when the load surface is in said second position and said load is arranged on said load surface, and the calculation unit is adapted to calculate the weight which will act upon said first shaft, on the basis of the respective first and second parameters of said first and second suspension means.

The vehicle may incorporate a third suspension means and a fourth suspension means which are arranged between a second of said wheel shafts and said chassis element, in which case said third and fourth suspension means each comprise a respective space which extends in a longitudinal direction (x) and contains a fluid, said third and fourth suspension means together with at least said first suspension means being adapted to enable the load surface to assume said first position and said second position as a result of a fluid also being supplied to or released from said spaces of said

third and fourth suspension means, and the respective spaces of said third and fourth suspension means each also have in the longitudinal direction (x) when the load surface is in said second position a length which differs from the length which the respective spaces of said third and fourth suspension means each have in the longitudinal direction (x) when the load surface is in said first position. According to an advantageous embodiment, the first sensor means is also adapted to detect a first parameter which is related to the lengths of the respective spaces of said third and fourth suspension means in the longitudinal direction (x) when the load surface is in said second position, and said second sensor means is also adapted to detect a second parameter which is related to the pressure of said fluid in the respective spaces of said third and fourth suspension means when the load surface is in said second position and said load is arranged on said load surface, and the calculation unit is adapted to use the respective first and second parameters of said third and fourth suspension means to calculate the weight which will act upon said second wheel shaft. It should be noted that the vehicle may comprise more than two wheel shafts. For example, the vehicle may comprise five wheel shafts. It should also be noted that more than two suspension means of the aforesaid type may be arranged between the respective wheel shafts and the longitudinal chassis element. For example, four suspension means of the aforesaid type may be arranged between the respective wheel shafts and the longitudinal chassis element. To calculate the weight which will act upon a wheel shaft, said first sensor means may be adapted to detect a respective first parameter which relates to the lengths of the respective spaces of the four suspension means of the wheel shafts in the longitudinal direction (x) when the load surface is in the second position, and said second sensor means be adapted to detect the respective pressures in the respective spaces of the four suspension means of the wheel shafts when the load surface is in the second position and a load is arranged on the load surface, in which case the calculation unit uses the respective first and second parameters of the four suspension means of the wheel shafts to calculate the weight which will act upon the wheel shafts.

The invention also relates to a commercial vehicle incorporating an arrangement according to any one of claims 1 to 14.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be explained by describing a preferred embodiment with reference to the attached drawings.

Fig. 1 depicts a side view of a heavy vehicle, Fig. 2 depicts a suspension system of a vehicle, Fig. 3 depicts an arrangement according to the invention, adapted to be applied to the vehicle in Fig. 1.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Fig. 1 depicts a commercial vehicle 1 with a load-bearing element which comprises a load surface 2. The vehicle 1 incorporates a longitudinal chassis element 3, and the load surface 2 is supported by the chassis element 3. The vehicle 1 comprises a first rear wheel shaft 4 and a second rear wheel shaft 5. The first rear wheel shaft 4 and the second rear wheel shaft 5 comprise two sets of wheels 6,7, but only one wheel 6,7 respectively is depicted on each of the wheel shafts 4,5.

As may be seen in Fig. 2, a first suspension means 8 is arranged between the first rear wheel shaft 4, adjacent to the first wheel 6 of the first rear wheel shaft 4 and the chassis element 3. A second suspension means 9 (not depicted in Fig. 2, but depicted in Fig. 3) is arranged between the first rear wheel shaft 4, adjacent to the second wheel (not depicted) of the first rear wheel shaft 4 and the chassis element 3. A third suspension means 10 is arranged between the second rear wheel shaft 5, adjacent to the first wheel 7 of the second rear wheel shaft 5 and the chassis element 3. Moreover, a fourth suspension means 11 (not depicted in Fig. 2, but depicted in Fig. 3) is arranged adjacent to the second wheel (not depicted) of the second rear wheel shaft 5 and the chassis element 3.

As depicted in Fig. 3, the respective suspension means 8, 9,10,11 each comprise a respective space 12,13,14,15 which extends in a longitudinal direction (x) and contains a compressed gas. The

suspension means 8,9,10,11 are of the air springs type, so the compressible medium is air. Each of the respective spaces 12,13,14,15 of the air springs is defined by a bellows. The air springs 8,9,10,11 form part of an electronically controlled level loading system of the commercial vehicle 1 (the level loading system will not be explained in more detail in this patent application). The chassis element 3 and hence the load surface 2 can be raised by supplying compressed air to the respective air springs 8,9,10,11. Compressed air is supplied to the respective air springs 8,9,10,11 from a pressure tank 16 via a valve device 18. The pressure tank 16 is also connected to a compressor 17 of the vehicle 1 via the valve device 18. The chassis element 3 and hence the load surface 2 can be lowered by releasing compressed air from the respective bellows 12,13,14,15.

The electronically controlled level loading system also makes it possible to deliver different quantities of air to the respective air springs 8,9,10,11, thus making it possible to cause the load surface to slope. A control unit of the level loading system receives signals from various sensors such as position sensors, thereby making it possible to monitor and adjust the level of the load surface 2.

The load surface may be in a first position which may be that in which the load surface normally is during movement of the vehicle, i. e. during driving. For such purposes as loading, the load surface can be raised, lowered and/or sloped to a second position, a so-called loading position, to facilitate the arrangement of a load on the load surface 2 when the vehicle is standing still, by compressed air being supplied to or released from the respective bellows 12,13,14,15 of the air springs 8,9,10,11. As previously mentioned, loading can thus be facilitated, e. g. the load surface 2 of the vehicle 1 can be adapted to the level of a loading bay from which loading takes place. In the second position, the length of each of the respective spaces 12,13,14,15 of the air springs 8,9,10,11 in the longitudinal direction (x) differs from the length of the respective spaces 12,13,14,15 in the longitudinal direction (x) in the first position.

The state of the art for vehicles incorporating level loading systems of the aforesaid type has made it necessary to have the load surface assume the first position, which is normally the level at which the load surface is during driving, in order to obtain information about the weight which will act

upon the respective wheel shafts during movement of the vehicle. If during loading the load surface is at a level which differs from the level at which the load surface is during driving, the driver wishing to obtain correct information about said weight thus has to cause the load surface to assume the first position, whereupon the weight which acts upon the respective wheel shafts is calculated on the basis of the pressure of the air in the respective bellows and the effective cross- sectional area of the respective bellows when the load surface is in the first position.

Fig. 3 depicts an arrangement 19 according to an embodiment of the invention which is intended to be applied to the vehicle in Fig. l, which vehicle 1 incorporates an electronically controlled level loading system. The arrangement 19 makes it possible to have the load surface 2 remain in the second position, which in this case is the loading position, and to calculate the weight which will act upon the respective wheel shafts 4,5.

The arrangement 19 comprises a first sensor means which incorporates a first position sensor 20 for the first wheel shaft 4, and a second position sensor 21 for the second wheel shaft 5, and these position sensors are situated on the load surface 2. Alternatively, the first sensor means may comprise respective ultrasonic sensors 22,23,24,25 arranged adjacent to the respective spaces 12,13,14,15 of the air springs 8,9,10,11. The arrangement 19 also comprises a second sensor means which incorporates respective pressure sensors 26,27,28,29 arranged adjacent to the respective spaces 12,13,14,15 of the air springs 8,9,10,11. The arrangement 19 further comprises a calculation unit 30 and a first memory unit 31. Alternatively, the calculation unit 30 may incorporate a second memory unit 32. The function of the calculation unit 30, the memory unit 31 and the memory unit 32 will be described later on in the description. It should be noted that the calculation unit 30 may be integrated in the control unit of the level loading system of the vehicle in Fig. l, and so the first memory unit 31 and the second memory unit 32 may be a memory unit of the control unit of the level loading system. It should further be noted that the position sensors 20,21 and/or the ultrasonic sensors 22,23,24,25 may take the form of sensors of the level loading system. The pressure sensors 26,27,28,29 may also take the form of sensors of the level loading system.

The function of the arrangement 19 will now be described. It is supposed that the load surface 2 is in the second position, which in this case is a loading position. It is further supposed that the lengths in the longitudinal direction (x) of the respective spaces 12,13,14,15 of the suspension means 8,9,10,11 when the load surface 2 is in the second position differ from the lengths of the respective spaces 12,13,14,15 in the situation where the load surface 2 is in the first position. It is also supposed that all the suspension means 8,9,10,11 are of the same design. During loading it is important to obtain information about the weight which will act upon the respective rear wheel shafts 4,5. The first position sensor 20 and the second position sensor 21 are designed to send signals to the calculation unit 30. The first position sensor 20 is designed to detect the distance between the load surface 2 and the first rear wheel shaft 4, and the second position sensor 21 is designed to detect the distance between the load surface 2 and the second rear wheel shaft 5. The calculation unit 30 is designed to use information about said distance and knowledge of the locations of the position sensors 20,21 to derive a first parameter which is related to the lengths in the longitudinal direction (x) of the respective spaces 12, 13,14,15 when the load surface is in the second position. Alternatively, the calculation unit 30 may receive information about the lengths in the longitudinal direction (x) of the respective spaces 12,13,14,15 when the load surface 2 is in the second position, via signals from the ultrasonic sensors 22,23,24,25. Signals from the pressure sensors 26,27,28,29 to the calculation unit 30 provide the calculation unit 30 with information about a second parameter which is related to the respective pressures of the air in the spaces 12,13,14,15. The fact that at any given pressure of the air in the space/bellows the bearing capacity of the air springs is different at different lengths in the longitudinal direction (x) of said spaces means that the calculation unit 30 has to take into account a respective pertinent compensation factor related to said difference in bearing capacity with respect to the respective difference in length in the longitudinal direction (x) of the spaces 12,13,14,15 in the situation where the load surface 2 is in the second position and the situation where the load surface 2 is in the first position at the respective detected pressures of the air in the spaces/bellows 12,13,14,15 when it calculates said weight. The memory unit 31 stores various compensation factors, and each compensation factor relates to a certain difference in bearing capacity with respect to a certain difference in the

length of the space in the longitudinal direction (x) between the situations where the load surface 2 is in said second position and the load surface 2 is in said first position at a certain pressure of the air in the bellows/space. The calculation unit 30 is designed to retrieve the respective pertinent compensation factor from the memory unit 31 and use the respective detected pressure and respective effective cross-sectional area of the bellows and the respective pertinent compensation factor to calculate the weight which will act upon the respective rear wheel shafts 4,5. It should be noted that the effective cross-sectional area is that which the respective bellows/spaces 12,13,14,15 have when the load surface 2 is in the first position.

The ensuing describes how the calculation unit 30 may alternatively be designed to calculate the weight which will act upon the respective rear wheel shafts 4,5.

The memory unit 32 stores information about the bearing capacity of the air springs 8, 9,10,11 at different lengths in the longitudinal direction (x) of the spaces 12,13,14,15 and different pressures of the air in the spaces 12,13,14,15. The calculation unit 30 uses the stored information and the respective first parameters of the suspension means 8,9,10,11 at the respective detected pressures of the air in the spaces 12,13,14,15 to calculate the prevailing bearing capacity of the respective suspension means 8,9,10,11. The next step is that the calculation unit 30 uses the information stored and knowledge of the lengths in the longitudinal direction (x) of the respective spaces 12,13,14,15 in the situation where the load surface 2 would be in the first position to calculate the bearing capacity of the respective suspension means 8,9,10,11 at the respective detected pressures of the air in the spaces 12,13,14,15. Thereafter the calculation unit 30 is designed to calculate a pertinent compensation factor for the respective suspension means 8, 9,10,11 by calculating the difference in bearing capacity of the respective air springs 8,9,10,11 between the situation where the load surface 2 is in the second position and the situation where the load surface 2 is in the first position. Finally, the weight which will act upon the respective rear wheel shafts 4,5 is calculated on the basis of the respective detected pressures of the air in the spaces 12,13,14,15 and the effective cross-sectional area of the respective spaces 12,13,14,15 and the respective pertinent compensation factors. It should be noted that the cross-sectional area is that which the respective bellows/spaces 12,13,14,15 have when the load surface 2 is in the first position.

Since in both of the situations described above the calculation unit 30 is designed to take into account the fact that at any given pressure of the air in the bellows 12,13,14,15 the bearing capacity of the air springs is different at different chassis heights, the load surface 2 need not be in the first position in order to calculate reliably the weight which will act upon the respective wheel shafts 4,5.

The invention is not limited to the embodiment described but may be varied and modified within the scopes of the ensuing patent claims.