Field of the invention

The present invention relates to a device and a method for regulating load transfer between a number of wheelshafts in a bogie, according to the introduction to the independent claims.

Background to the invention

A bogie is a device situated under a vehicle and used to spread the vehicle's weight over a number of axles and thereby reduce the axle pressure, increase the load capacity and improve the vehicle's cornering. A truck or bus may have at least one bogie with two or more axles with pairs of wheels. One or more of the axles in a bogie may be driveshafts, or the bogie may comprise tag axles only. To increase the vehicle's operabiiity and steerability, e.g. when reversing or cornering, load transfers may be effected between ttie bogie's axles. The general procedure adopted for load transfers is that the driveshaft pressure is increased and the tag axle pressure is reduced, i.e. the load distribution among the bogie's axles is altered.

Legal requirements about when and how load transfers should take place are stated inter alia in EC97/27, which sets out requirements for different driveshaft pressure limits for different markets. The driveshaft pressure according to

EC97/27 is usually allowed to be overloaded by up to 30% of the maximum permissible pressure. The upper speed limit for load transfers is 30 km/h if the legal requirements of the country concerned conform to EC97/27.

There are various types of load transfer. In manual load transfers, the driveshaft pressure is usually overloaded permanently by up to 30% of the maximum permissible pressure, e.g. by the driver activating a switch. Another example of load transfer is so-called "optimal traction", which is usually active continually if the function is preselected. It does not overload the driveshaft, as a control unit ensures that the driveshaft pressure is below the legally required limit.

In manual load transfers, the load ratio is usually 60:40 between driveshaft and tag axle. In "optimal traction" this ratio may be altered to maximum permissible pressure. If for example the maximum pressure is close to 10 tonnes for the driveshaft, the pressure is set to 9.999 tonnes.

An example of load transfer is described in US 4,284,156, in which load transfers in a bogie are effected automatically, depending on the vehicle's load, by raising or lowering of one of the bogie's axles.

A practice known from US 5,052,713 is automatic regulation of pneumatic pressure in the suspension system according to the vehicle's speed. This avoids the driver's forgetting to reverse the load distribution when the vehicle reverts to higher speeds. On markets where EC97/27 applies, however, it is only

permissible to resort to overloading the driveshaft pressure at speeds of up to a maximum of 30 km h, which means that the vehicle necessarily loses speed when travelling uphill if such load transfers are resorted to. This may also limit the vehicle's steerability downhill, depending on how it is configured, since most drivers will then be unwilling to travel at only 30 km/h.

On markets where EC97/27 does not apply, there might therefore be no upper speed limit for load transfer. The driver is subject to substantial requirements in handling load transfers with up to 30% or more overload on the driveshaft, since the dynamics of the moving vehicle are altered. There may be a potential hazard if it takes place at high speeds. The "optimal traction" function increases wear on the tyres of the driveshaft, since it is active continually. The object of the invention is to propose an improved system for load transfer which increases the vehicle's operability and reduces its wear. Summary of the invention

The object described above is achieved by a device for regulating load transfer between wheelshafts in a vehicle's bogie in which at least one wheelshaft is powered. The vehicle further comprises a control unit adapted to regulating the load distribution between said wheelshafts. The device comprises at least one sensor unit adapted to measuring a road parameter which indicates a

characteristic of the road, and to generating a road parameter signal based thereon, and a processor unit adapted to comparing said road parameter with a predetermined threshold value KQ, , K _t within the category of the road parameter, and to generating a load distribution signal based on the result of that comparison. The device is further adapted to sending the load distribution signal to said control unit, which thereupon regulates the load distribution between the wheelshafts on the basis of that signal. According to another aspect, the object is achieved by a method for regulating the load distribution between wheelshafts in a vehicle's bogie in which at least one wheelshaft is powered. The method comprises:

- measuring a road parameter which indicates a characteristic of the road, and generating a road parameter signal on the basis thereof;

- comparing the road parameter with a predetermined threshold value within the category of the road parameter;

- generating a load distribution signal which indicates the result of that

comparison; and

- sending the load distribution signal to a control unit which controls the load distribution between the bogie's wheelshafts, whereupon the load distribution between the wheelshafts is regulated on the basis of that signal.

Said device and method make it possible to regulate load distribution when really necessary. According to an embodiment, if load distribution is considered necessary, e.g. to enable the vehicle to travel uphill or downhill, a load distribution signal is generated for the driveshaft pressure to be increased on one of the bogie's wheelshafts. This increases the vehicle's operability primarily at high speeds and specifically in slippery or treacherous road conditions, including winter conditions. When the road has levelled out, the load distribution between the bogie's axles may subsequentiy be returned to an initial state. The axle pressure is kept, according to an embodiment, within the limits for maximum driveshaft pressure, which means that the driveshaft pressure can be increased even when the vehicle is maintaining high speed. The vehicle's ability to travel both uphill and downhill at higher speeds is thereby enhanced. As the function is only activated when really necessary, instead of being constantly active, wear on the vehicle's tyres is thus minimised.

The advantages of the invention increase if the vehicle is unladen or the pressure on the driveshaft is below the maximum limit.

Axle pressure means the amount of pressure which an axle of the vehicle exerts on the carriageway. There are regulations, e.g. EC 97/27, which indicate how high the driveshaft pressure and the tag axle pressure are allowed to be.

Preferred embodiments are described in the dependent claims and the detailed description.

Brief description of the drawings

The invention is described below with reference to the attached drawings, in which:

Figure 1 illustrates schematically a device according to an embodiment of the invention.

Figure 2 illustrates schematically a vehicle with a bogie as seen from below.

Figure 3 illustrates schematically the load distribution when travelling uphill according to an embodiment of the invention.

Figure 4 illustrates schematically the load distribution when travelling downhill according to an embodiment of the invention.

Figure 5 is a flowchart for the method according to an embodiment of the invention. Detailed description of preferred embodiments of the invention

Figure 1 depicts schematically a device according to the invention for regulating the load distribution between wheelshafts 5, 7 in a bogie of a vehicle. The device comprises at least one sensor unit adapted to measuring a road parameter which indicates a characteristic of the road, and to generating a road parameter signal on the basis thereof. If several different kinds of road parameters are to be measured, the device is preferably provided with respective sensor units adapted to measuring them. The device comprises also a processor unit adapted to comparing said road parameter with a predetermined threshold value KQ, , T within the category of the road parameter, and to generating a load distribution signal based on the result of that comparison. The device is further adapted to sending that signal to a control unit in the vehicle which is adapted to regulating the load distribution between said wheelshafts, whereupon the control unit regulates the load distribution between the wheelshafts 5, 7 on the basis of that signal.

According to an embodiment, the control unit comprises one or more preset limit values for the load distribution signal. Various modes for the load distribution between the wheelshafts may then be activated depending on how the load distribution signal relates to the limit value or values. One mode comprises for example setting a certain pressure on the driveshaft.

Figure 1 depicts the device as a separate unit from the control unit. According to another embodiment, the device is integrated in the control unit, and the load distribution signal is an internal signal in the control unit. The device comprises according to another embodiment an indicating unit situated in and visible on the vehicle's instrument panel. The indicating unit indicates when load transfers are activated, e.g. by a text message, by a computer window which opens or by an acoustic or lamp signal. According to an embodiment, these indications disappear after a predetermined period of time in order to reduce the number of disturbing impressions upon the driver. The device preferably comprises an activation unit so the driver can switch off and on the automatic load transfer according to the invention. Figure 2 depicts schematically the device in a vehicle 1 as seen from below. The vehicle is here depicted with a forward axle 3 with a pair of wheels 2, and a bogie which comprises two wheelshafts 5, 7 and their respective pairs of wheels 4, 6. According to the invention, at least one of the bogie's wheelshafts 5, 7 is powered. The bogie's other wheelshafl or wheelshafts 5, 7 may be further driveshafts and/or tag axles. In the text below, the bogie's wheelshaft on which the driveshaft pressure is increased/decreased in response to the load distribution signal is referred to as the "powered axle". It is possible, however, that the bogie may comprise more than one powered axle. The vehicle 1 further comprises a control unit adapted to regulating the load distribution between said wheelshafts 5, 7. The load distribution may be regulated by using one or more means 8, 9 associated with the bogie's wheelshafts to increase/reduce the pressure on wheelshafts in order to achieve a certain load distribution between the

wheelshafts. It is thus possible to achieve a load transfer between the

wheelshafts such that a desired pressure on a driveshaft 5, 7 of the bogie is reached.

Load transfers between the wheelshafts are limited according to an embodiment in that a driveshaft is at most allowed to be subject to a certain driveshaft pressure max which is determined inter alia by law on different markets. According to an embodiment, the maximum driveshaft pressure is variable by an air suspension system of the vehicle and its setting can be altered at a workshop.

To know when it is appropriate to increase/decrease the driveshaft pressure, the road parameters which indicate characteristics of the road are measured progressively as the vehicle travels along it. Examples of situations where it is appropriate to increase the driveshaft pressure are where the vehicle has to travel uphill or downhill or negotiate a bend and/or travel at low road temperatures. The characteristics of the road may thus for example be its gradient, radius of curvature or temperature. Various embodiments are described below and it should be noted that they may be used individually or in combination. For example, several different road parameters may be measured simultaneously and result jointly or individually in one or more load distribution signals.

Figure 3 illustrates the vehicle travelling up a hill with a gradient a. According to an embodiment, the road parameter comprises the road's gradient a and said threshold value takes the form of a gradient threshold value KQ. The processor unit is then adapted to generating a gradient signal if the road gradient a exceeds KQ, in which case the gradient signal will so indicate. The gradient signal may then be converted, according to an embodiment, to a load distribution signal for the driveshaft pressure to be increased on one of the bogie's wheelshafts. The load distribution signal is sent to the control unit which thereupon, according to an embodiment, increases the driveshaft pressure up to the maximum permissible pressure P _max . According to another embodiment, the load distribution signal activates in the control unit a certain mode whereby the driveshaft pressure is thereupon regulated. In Figure 3, the bogie's forward wheeishaft 5 is the powered axle, marked "D". The driveshaft pressure is represented by an arrow and "P". The bogie's other axle 7 in the diagram is a tag axle marked "S".

Figure 4 illustrates a vehicle travelling down a hill with a gradient a. In the diagram, the bogie's rear wheeishaft 7 is the powered axle, marked "O". The driveshaft pressure is represented by an arrow and "P". Increased driveshaft pressure downhill enhances the vehicle's steerability even at high speeds. For increased driveshaft pressure to have some greater effect downhill, the powered axle should preferably be the bogie's rear axle 7, which is further away from the foremost axle. Where the road gradient is to be measured, the sensor unit preferably comprises a sensor for the purpose, e.g. an inclinometer. According to another embodiment, the processor unit is adapted to measuring the time t from when the road gradient a exceeds KQ, and if such is the case for longer than a predetermined time to the processor unit is adapted to generating a load distribution signal for the driveshaft pressure to be increased on one of the bogie's wheelshafts. Thus only when the gradient exceeds KQ for a certain time is the driveshaft pressure increased. There is thus assurance that no bad transfer will take place on short hills.

After the hill has levelled out, there is no longer need for an increase in the driveshaft pressure. The processor unit is then preferably adapted to generating a gradient signal if the road gradient a is equal to or less than the threshold value Kg, in which case the gradient signal will so indicate. The gradient signal may then be sent to the control unit as a load distribution signal for the driveshaft pressure to be returned to an initial state.

Reversal to an initial state results in a decrease in the pressure on the bogie's driveshaft which was previously subject to increased pressure. According to an embodiment, the load distribution between the bogie's wheelshafts is returned to a normal state. A normal state for a bogie with two axles comprising a driveshaft and a tag axle may for example mean a 60:40 load distribution between them. This means the driveshaft being subject to about 60%, and the tag axle about 40%, of the total pressure on the bogie. Another example of normal state might be a 50:50 load distribution between the bogie's driveshaft and tag axle. The load distribution between the wheelshafts has according to an embodiment a dynamic relation to the road gradient. For example, the driveshaft pressure will be maximum if the road has a large gradient, and if the road has a smaller gradient the driveshaft pressure may be less than P _ma x. According to an embodiment, the processor unit is adapted to measuring the time t from when the road gradient a is equal to or less than the threshold value KQ, and if such is the case for longer than a predetermined time , the processor unit is adapted to generating a load distribution signal for reversal of the driveshaft pressure. According to this embodiment, only when the road has for example levelled out for a certain time after a hill is the load distribution in the bogie thus reversed. Altering the bogie's load distribution unnecessarily often is thus avoided. When for example a climb is immediately followed by a downhill run, the increased pressure on the driveshaft is preferably maintained if the vehicle is so configured that this results in better controllability of the driveshaft pressure. The powered axle is then preferably the bogie's rear axle. According to another embodiment, the road parameter comprises the road's radius of curvature r, said threshold value takes the form of a threshold value K, for that radius of curvature and the processor unit is adapted to generating a load distribution signal for the driveshaft pressure to be increased on one of the bogie's wheelshafts if the radius of curvature r exceeds the threshold value Kr. According to an embodiment, the device comprises map data and GPS so that it can keep track of the vehicle's location relative to the map and thus know when a bend is coming and its radius of curvature r. The driveshaft pressure can then be increased before the bend, resulting in the possibility of safer cornering. The vehicle's lateral acceleration may also be used to determine the road's radius of curvature, in which case the sensor unit comprises one or more lateral

acceleration sensors.

After the bend, the driveshaft pressure has preferably to be returned to an initial state. The processor unit is adapted according to an embodiment to generating a load distribution signal for the driveshaft pressure to be returned to an initial state if the radius of curvature r is equal to or less than the threshold value Kr. The signal is sent to the control unit, which reverses the driveshaft pressure. It is also possible here to use GPS and map data to know when the bend ends and hence to reverse the driveshaft pressure. GPS and map data can also be used to determine the road s topography and hence its gradient. According to another embodiment, the road parameter comprises the road's temperature T, said threshold value takes the form of a temperature threshold value K _T and the processor unit is adapted to generating a load distribution signal for the driveshaft pressure to be increased on one of the bogie's wheelshafts 5 when the temperature of the road is below the threshold value K _T . An increase in the driveshaft pressure can thus be effected already before any risk of the vehicle becoming unstable, e.g. because of slippery road surface at low outdoor temperatures. The processor unit is preferably also adapted to generating a load distribution signal for the driveshaft pressure to be returned to an initial state if the l o road temperature T is equal to or exceeds the threshold value K _T . The driveshaft pressure is thus reversed when there is no risk of the vehicle becoming unstable because of the state of the road in cold weather.

According to an embodiment, ad transfer with increased driveshaft pressure is 15 only possible if the vehicle's speed does not exceed a predetermined level, e.g.

60 km/h. This makes it possible to reduce the risk that the driver might not be able to manage the vehicle because of its altered dynamics at high speeds.

There is also load transfer when the load distribution is regulated so that the 20 driveshaft is overloaded by up to 30% of the maximum permissible driveshaft pressure P _max for the vehicle. Prevailing laws may then sometimes only allow the vehicle to be driven at up to a certain maximum speed, e.g. 30 km h. According to an embodiment, when the driveshaft pressure has already been increased because of the value of one or more road parameters but is equal to or below 25 Pmax. and the vehicle's speed does not exceed a predetermined threshold value, e.g. 30 km/h, the device is adapted to generating a further load distribution signal for the driveshaft pressure to be further increased. For example, the driveshaft might then be overloaded by up to 30% more than maximum permissible driveshaft pressure Pmax- This is advantageous when the vehicle loses speed, 30 e.g. uphill, despite a toad transfer having already taken place. A further load

transfer may then be effected so that the vehicle can gain still more grip on the road and thus hopefully avoid losing more speed. The invention comprises also a method for regulating the load distribution between wheelshafts in a vehicle's bogie in which at least one wheelshaft is powered. The method is illustrated in a flowchart in Figure 5 and comprises the steps of S1 ) measuring a road parameter which indicates a characteristic of the road, and generating a road parameter signal based thereon, S2) comparing the road parameter with a predetermined threshold value KQ, Kr, K _T within the category of the road parameter, S3) generating a load distribution signal which indicates the result of that comparison and S4) sending that signal to a control unit which controls the load distribution between the bogie's wheelshafts, whereupon the load distribution between them is regulated as a step S5) based on the load distribution signal.

According to an embodiment, the method comprises as road parameter the road's gradient a, said threshold value takes the form of a gradient threshold value KQ, and if the gradient exceeds KQ a gradient signal so indicating is generated. The gradient signal may then be sent to the control unit as a load distribution signal for the driveshaft pressure to be increased on one of the bogie's wheelshafts.

According to another embodiment, the method comprises measuring the time t from when the road gradient a exceeds the threshold value KQ, and if such is the case for longer than a predetermined time to a load distribution signal is generated for the driveshaft pressure to be increased on one of the bogie's wheelshafts. This makes it possible for the driveshaft pressure to be increased on hills with or without a time aspect.

According to another embodiment, the method, if the road gradient a is equal to or less than the threshold value KQ, comprises generating a gradient signal which so indicates. The gradient signal may then be sent to the control unit as a load distribution signal for reversal of the driveshaft pressure. According to a further embodiment, the method comprises measuring the time t from when the gradient a is equal to or less than the threshold value KQ, and if such is the case for longer than a predetermined time to a load distribution signal is generated for reversal of the driveshaft pressure. This makes it possible for the driveshaft pressure to be reversed with or without a time aspect after a vehicle reversing operation.

According to a further embodiment, the method comprises as road parameter the road's radius of curvature r, said threshold value takes the form of a threshold value Kf for the radius of curvature, and if the radius of curvature r exceeds the threshold value K a load distribution signal is generated for the driveshaft pressure to be increased on one of the bogie's wheelshafts. To make it possible for the driveshaft pressure to be returned to an initial state after the bend, the method, if the radius of curvature r is equal to or less than the threshold value K _f , comprises generating a load distribution signal for the driveshaft pressure to be returned to an initial state. This makes it possible to increase the driveshaft pressure when cornering. According to yet another embodiment, the method comprises as road parameter the road's temperature T, said threshold value takes the form of a temperature threshold value K _T , and if the temperature of the road is below K _T a load

distribution signal is generated for the driveshaft pressure to be increased on one of the bogie's wheelshafts. According to another embodiment, the method, if the road temperature T exceeds or is equal to K _T , comprises generating a load distribution signal for the driveshaft pressure to be returned to an initial state. This makes it possible for the driveshaft pressure to be increased in cold weather.

The invention relates also to a computer programme product comprising computer programme instructions to enable a computer system in a vehicle to perform steps according to said method when those instructions are run on said computer system. The invention comprises also a computer programme product in which the computer programme instructions are stored on a medium which can be read by a computer system.

The present invention is not confined to the embodiments described above.

Sundry alternatives, modifications and equivalents may be used. The aforesaid embodiments therefore do not limit the invention's scope which is defined by the attached claims.