Controlling weight allocation between truck axles

1. A truck vehicle comprising:

a chassis comprising a chassis frame;

a speed sensor for providing data indicative of the speed of the vehicle, at least as between a first predetermined speed, a second predetermined speed and a third predetermined speed;

steerable right and left front wheels suspended from the chassis frame;

a tandem axle suspended from the chassis frame rearward of the front wheels and comprising a drive axle having drive wheels and a tag axle having non-drive wheels;

a load apportioning mechanism for apportioning the sum total of weight borne by the tandem axle between the drive axle and the tag axle; and

a controller for receiving the data indicative of the speed of the vehicle from the speed sensor and controlling the load apportioning mechanism to apportion a desired percentage of the sum total of weight borne by the tandem axle as between the drive axle and tandem axle based at least in part on the speed of the vehicle as follows:

when the data indicative of the speed of the vehicle indicates that the speed of the vehicle is less than the first predetermined speed (first speed range), the controller apportions a first predetermined maximum allowable load to the drive axle, with a lesser load on the tag axle;

when the data indicative of the speed of the vehicle indicates that the speed of the vehicle is equal to or greater than the first predetermined speed, but less than the second predetermined speed (second speed range), the controller apportions a second predetermined load, which is less than the first predetermined load, to the drive axle, with a lesser load on the tag axle which is greater than the load on the tag axle in the first speed range; and

when the data indicative of the speed of the vehicle indicates that the speed of the vehicle is equal to or greater than the second predetermined speed (third speed range), the controller apportions the second predetermined load to the tag axle, with a lesser load on the drive axle.

2. The truck vehicle as set forth in claim 1 in which the controller further receives signals indicative of the ride height of the vehicle, and the controller controls the mechanism to apportion a desired percentage of the sum total of weight as between the tandem axle and the tag axle simultaneous with maintaining the ride height of the vehicle within a predetermined ride height range regardless of the apportionment of weight between the drive axle and the tag axle.

3. The truck vehicle as set forth in claim 1 in which the second predetermined load is the maximum load allowed by for vehicles.

4. The truck vehicle as set forth in claim 1 in which both the ride height of the vehicle and the apportionment of load as between the drive axle and the tag axle are controlled by inflating and deflating gas bags.

5. The truck vehicle as set forth in claim 4 in which the gas bags comprise one or more gas bags disposed between the chassis frame and the load for apportionment of the load as between the drive axle and the tag axle and one or more gas bags disposed between the chassis frame and the drive axle for adjustment of the ride height of the vehicle.

6. The truck vehicle as set forth in claim 2 in which the truck vehicle further comprises a ride height sensor which sends a signal to the controller indicative of the height of the drive axle from the road on which the vehicle is travelling, which signal is processed by the controller to keep the height of the drive axle of the vehicle within the predetermined height range.

7. The truck vehicle as set forth in claim 1 further comprising a fifth wheel supported on the chassis frame in overlying relation to the tandem axle, and further including a trailer coupled to the fifth wheel for towing by the truck vehicle with weight of the trailer bearing on the fifth wheel contributing to the sum total of weight borne by the tandem axle.

8. The truck vehicle as set forth in claim 1 in which the drive axle is forward of the tag axle.

9. The truck vehicle as set forth in claim 1 in which the controller comprises a control strategy for actively controlling the mechanism during operation of the vehicle to apportion a percentage of the sum total of weight borne by the tandem axle relative to the drive axle to a percentage within a percentage range between a minimum percentage load and a maximum percentage load with the sum of the apportioned percentages always equaling 100%.

10. The truck vehicle as set forth in claim 2 in which the respective load percentages apportioned to the drive axle and to the tag axle by the controller are functions of load borne by the drive axle, load borne by the tag axle, and slip of at least one wheel of the drive axle.

11. The truck vehicle as set forth in claim 10 in which the controller operates the mechanism to control the respective percentages apportioned to the drive axle and to the tag axle as a function of a load control range for load borne by one of the axles of the tandem axle and as a function of a drive axle wheel slip control range for at least one wheel of the drive axle.

12. The truck vehicle as set forth in claim 11 in which the controller operates the mechanism to cause the percentage apportioned to the drive axle to increase and the percentage apportioned to the tag axle to decrease when load borne by the drive axle is less than an upper limit of a load control range for load borne by the drive axle and wheel slip is greater than an upper limit of the drive axle wheel slip control range and to cause the percentage apportioned to the drive axle to decrease and the percentage apportioned to the tag axle to increase when load borne by the tag axle is less than an upper limit of load control range for load borne by the tag axle and wheel slip is less than a lower limit of the drive axle wheel slip control range.

13. A method for controlling a load apportioning mechanism to apportion the sum total of weight borne by a tandem axle of a vehicle between a drive axle and a tag axle of the tandem axle, the vehicle comprising a chassis frame, steerable right and left front wheels suspended from the chassis frame, and a tandem axle suspended from the chassis frame rearward of the front wheels and comprising a drive axle having drive wheels and a tag axle having non-drive wheels, the method comprising,

providing a controller for receiving data indicative of the speed of the vehicle from the speed sensor and controlling the load apportioning mechanism to apportion a desired percentage of the sum total of weight borne by the tandem axle as between the drive axle and tandem axle based at least in part on the speed of the vehicle as follows:

when the data indicative of the speed of the vehicle indicates that the speed of the vehicle is less than the first predetermined speed (first speed range), the controller apportions a first predetermined maximum allowable load to the drive axle, with a lesser load on the tag axle;

when the data indicative of the speed of the vehicle indicates that the speed of the vehicle is equal to or greater than the first predetermined speed, but less than the second predetermined speed (second speed range), the controller apportions a second predetermined load, which is less than the first predetermined load, to the drive axle, with a lesser load on the tag axle which is greater than the load on the tag axle in the first speed range; and

when the data indicative of the speed of the vehicle indicates that the speed of the vehicle is equal to or greater than the second predetermined speed (third speed range), the controller apportions the second predetermined load to the tag axle, with a lesser load on the drive axle.

14. The method as set forth in claim 13 comprising, controlling the mechanism to cause the respective percentages apportioned to the drive axle and to the tag axle as functions of load borne by the drive axle, load borne by the tag axle, and slip of at least one drive wheel of the drive axle.

15. The method as set forth in claim 14 comprising, controlling the mechanism to cause the respective percentages apportioned to the drive axle and to the tag axle to be maintained within an axle load control range for one of the drive axle and the tag axle and to maintain drive axle wheel slip for at least one wheel of the drive axle within a drive axle wheel slip control range.

16. The method as set forth in claim 15 comprising, controlling the mechanism to cause the percentage apportioned to the drive axle to increase and the percentage apportioned to the tag axle to decrease when load borne by the drive axle is less than an upper limit of a drive axle load control range for load borne by the drive axle and wheel slip is greater than an upper limit of the drive axle wheel slip control range and to cause the percentage apportioned to the drive axle to decrease and the percentage apportioned to the tag axle to increase when load borne by the tag axle is less than an upper limit of a tag axle load control range for load borne by the tag axle and wheel slip is less than a lower limit of the drive axle wheel slip control range.