METHOD AND DEVICE FOR TANDEM- OR MULTIPLE-AXLE DRIVE FOR A VEHICLE

Abstract

A wheel suspension system and a method for controlling the system. The wheel suspension system includes a first axle provided with wheels and a second axle provided with wheels. The first axle is connected to a first driveshaft portion via a first differential 6a and the second axle is connected to a second driveshaft portion via a second differential 6b. The system further includes angular speed sensors designed to detect the rotational speed of the axles, and/or the rotational speed of the respective wheels. The angular speed sensors are connected to an electronic control unit (ECU) which is designed to calculate a difference between the angular speed of the first and second axles, and/or a difference between the angular speed of the respective wheels by the use of input data from the angular speed sensors. The speed difference can be used as an indication of different wheel radius of the wheels. The system includes a coupling, e.g. a dog clutch arrangement, arranged in the driveshaft and positioned between the first and second drive shaft portions for changing the first and second drive shaft portions between being drivingly connected and disconnected.

Claims

1. A control method for a wheel system including a multi-drive axle for a vehicle, the wheel system comprises at least two driven axles whereof each axle is provided with a pair of wheels and connected to a driveshaft via differentials, the driveshaft comprising a coupling positioned between each differential so as to divide the driveshaft into different driveshaft portions which can change between being drivingly connected and disconnected to the driveshaft, the wheel system further comprising angular speed sensors designed to detect the angular speed of the wheels connected thereto, the control method comprising the steps of: controlling the coupling to be disconnected such that each drive shaft portion is drivingly disconnected from at least one further drive shaft portion, detecting angular speed of the wheels connected thereto by the angular speed sensors while the driven axles are drivingly disconnected; using the detected angular speed of the wheels connected thereto in order to calculate a difference between the angular speed of the respective wheels of the driven axles; comparing the angular speed difference detected between wheels with reference values; and using the comparison of the angular speed difference to be an indication of different wheel radius and triggering a warning signal and/or a control action in case the angular speed difference is outside an allowable value.

2. A control method according to claim 1, wherein it is used for a wheel system comprising a lifting mechanism acting on a driven rear axle for being able to shift the position of the wheels on that axle between being in a working position in contact with the ground surface and being lifted up to be in a resting position above a ground contact level, the method comprising the following steps which may precede the steps of claim 6: lowering the liftable axle from an up-lifted resting position, in which the wheel pair of the liftable axle is above a ground contact level, to a lowered working position, in which the wheels are in contact with the ground, while the coupling is disconnected such that the liftable axle is drivingly disconnected from the other axles; maintaining the coupling disconnected to keep the driven axles drivingly disconnected at least until it is indicated that the detected angular speed values from the angular speed sensors, indicating the angular speed of the wheel pairs, are stabilized.

3. A control method according to claim 2, wherein if the angular speed difference is outside a critical upper limit, and in dependence of further parameters such as load and vehicle speed, the liftable axle is controlled to be drivingly disconnected from the other axles.

4. A control method according to claim 1, wherein if a calculated angular speed difference between the angular speed of the driven axles exceeds a “change warning limit”, then it is indicated that a change of position of the tires from one axle to another should be performed.

5. A control method according to claim 1, wherein if a calculated angular speed difference between the angular speed of the driven axles exceeds a “check warning limit”, then it is indicated that a manual check of the conditions of the tires should be performed.

6. A control method according to claim 1, wherein an angular speed is detected by wheel speed angular sensors for a wheel on each side of the axles for all axles being connectable to the driveshaft in the wheel system and the angular speed for each one of wheels are used in order to calculate an angular speed difference between the axles.

7. A control method according to claim 1, wherein the detected angular speed of the wheels used in order to calculate an angular speed difference between the angular speed of the first and second axles and/or a difference between the angular speed of the respective wheels of the first and second axles are taken when at least two of the following conditions are fulfilled: the turning radius of the vehicle is above a prescribed limit; the speed variations of the vehicle are below a prescribed limit; the tire pressure difference between different wheels is within a prescribed limit; the load distribution between the different axles is within a prescribed limit; the wheels are not being controlled by an anti-block braking system or a wheel slip control system while the angular speed is detected; the braking force on the measured wheels is below a prescribed value; the driving torque on the measured wheels is below a prescribed value; the tire temperature, or tire temperature difference, is within a prescribed limit; the axle differentials should be free; the measuring time point is selected by predicting an upcoming driving sequence.

8. A computer comprising a computer program for performing the steps of claim 1 when the program is run on the computer.

9. A non-transitory computer readable medium carrying a computer program for performing the steps of claim 1 when the program product is run on a computer.

10. An electronic control unit (ECU) for controlling a wheel system, the electronic control unit (ECU) being configured to perform the steps of the method according to claim 1.

11-15. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings:

[0049] FIGS. 1A-1B show a tractor for a tractor-trailer combination with a wheel suspension system according to a first embodiment the invention;

[0050] FIGS. 2A-2B show a truck with a wheel suspension system according to a second embodiment the invention,

[0051] FIGS. 3A-3D show schematic views of different embodiments of the wheel suspension system according to the invention, and

[0052] FIGS. 4A-4b show flow charts illustrating a control method for a wheel suspension system according to the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0053] FIGS. 1A and 1B shows a tractor 100 and a wheel suspension system 1 for the tractor 100. The tractor 100 is provided with a driver's cabin 101 and a trailer connecting platform 102 for connecting a trailer to be towed by the tractor. The tractor 100 is provided with a pair of front wheels 103 a, b and the wheel suspension arrangement 1 is arranged in the rear part of the tractor 100. The tractor 100 further comprises a propulsion unit 104, e.g. an ICE, connected to a gear box 105 which in turn is connected to a drive shaft 5 to provide a propulsive force to the tractor. The wheel suspension arrangement 1 comprises a first driven axle 2 and a second driven axle 3. The first driven axle is provided with a first pair of driven wheels 4a, 4b and the second driven axle 3 is provided with a second pair of driven wheels 4c, 4d. The first driven axle 2 is connected to a first portion 5a of the drive shaft 5 via a first differential 6a and the second driven axle 3 is connected to a second portion 5b of the drive shaft 5 via a second differential 6b. The first drive shaft portion 5a and the second drive shaft portion 5b are separated by a coupling 7. The wheel suspension system further comprises a first angle speed sensor 8a for detection of the angle speed of the first wheel 4a, a second angle speed sensor 8b for detection of the angle speed of the second wheel 4b, a third angle speed sensor 8c for detection of the angle speed of the third wheel 4a and a fourth angle speed sensor 8d for detection of the angle speed of the fourth wheel 4a.

[0054] The wheel suspension system further comprises an electronic control unit (ECU) which can either be a separate control unit for the wheel suspension system 1, or be a part of a larger control system for the tractor 100. The electronic control unit (ECU) is connected to the angle speed sensors 8a-d in order to receive input signals for control of the wheel suspension system 1.

[0055] FIGS. 2A and 2B shows a cargo truck (or load carrying truck) 200 and a wheel suspension system 1 for the cargo truck 200. The cargo truck 200 is provided with a driver's cabin 201 and a load compartment 202 for carrying a load. The cargo truck 200 is provided with a pair of front wheels 203 a, b and the wheel suspension arrangement 1 is arranged in the rear part of the cargo truck 200. The cargo truck 200 further comprises a propulsion unit 204, e.g. an ICE, connected to a gear box 205 which in turn is connected to a drive shaft 5 to provide a propulsive force to the cargo truck 200.

[0056] The wheel suspension arrangement 1 comprises a first driven axle 2, a second driven axle 3 and a third driven 10. The first driven axle is provided with a first pair of driven wheels 4a, 4b, the second driven axle 3 is provided with a second pair of driven wheels 4c, 4d and the third driven axle 10 is provided with a third pair of driven wheels 4e, 4f. The first driven axle 2 is connected to a first portion 5a of the drive shaft 5 via a first differential 6a, the second driven axle 3 is connected to a second portion 5b of the drive shaft 5 via a second differential 6b and the third driven axle 10 is connected to a third portion 5c of the drive shaft 5 via a third differential 6c. The first drive shaft portion 5a and the second drive shaft portion 5b are separated by a coupling 7 and the second drive shaft portion and the third drive shaft portion are separated by a second coupling 11. The wheel suspension system 1 further comprises first to fourth angle speed sensors 8a-d arranged to the first to fourth wheels 4a-d as disclosed in the arrangement in FIGS. 1A and 1B and also a fifth angle speed sensor 8e for detection of the angle speed of the fifth wheel 4e and a sixth angle speed sensor 8f for detection of the angle speed of the sixth wheel 4f.

[0057] The wheel suspension system further comprises an electronic control unit (ECU) which can either be a separate control unit for the wheel suspension system 1, or be a part of a larger control system for the cargo truck 200. The electronic control unit (ECU) is connected to the angle speed sensors 8a-f in order to receive input signals for control of the wheel suspension system 1.

[0058] To be noted, the wheel suspension system 1 disclosed in FIG. 1B could also be used for the cargo truck 201 in FIG. 2A. Likewise, the wheel suspension system 1 disclosed in FIG. 2B could also be used for the tractor 201.

[0059] In FIGS. 3A-3D are disclosed different embodiments of the wheel suspension system 1 which can be used for example in a tractor 100 or a load carrying truck 200. In FIG. 3A is disclosed a wheel suspension system 1 similar to the one described in FIG. 1B but with the difference that this system has been provided with an axle lifting mechanism 9 working on the first axle 2. The axle lifting mechanism 9 may thus be used to control the first axle 2 to be positioned in a lowered position in which the first wheel pair 4a, b are in contact with the ground and a second raised position in which the first wheel pair 4a, b are lifted up above the surface level.

[0060] In FIG. 3B is disclosed a wheel suspension system 1 similar to the one described in FIG. 2B but with the difference that this system has been provided with an axle lifting mechanism 9 working on the first axle 2. The axle lifting mechanism 9 may thus be used to control the first axle 2 to be positioned in a lowered position in which the first wheel pair 4a, b are in contact with the ground and a second raised position in which the first wheel pair 4a, b are lifted up above the surface level.

[0061] The arrangement shown in FIG. 3C differs from the arrangement in FIG. 3B in that a further axle lifting mechanism 9 has been added and adapted for lifting the second axle 3.

[0062] FIG. 3D shows an arrangement which differs from the arrangement disclosed in FIG. 3B in that the third wheel pair 3e, f connected to the third axle 10 not are able to be connected to and powered to the drive shaft 5. Hence, these wheels can be non-driven or powered by another power source.

[0063] FIG. 4A shows a flow chart of a method according to the invention. The method may for example be used for control of the wheel suspension system 1 for the tractor 100 in FIG. 1A or the wheel suspension system 1 for the load carrying truck 200 in FIG. 2A or for any of the other wheel suspension systems 1 described in FIGS. 3A to 3D.

[0064] In the first step, S1, in FIG. 4A, it is checked that the wheel axles for which the angular speed will be measured are disconnected from each other. In case of a tandem axle as shown in FIG. 1 the coupling 7 is controlled to be disconnected such that a first drive shaft portion 5a, comprising a first differential 6a connected to the first driven axle 2, is drivingly disconnected from the second drive shaft portion 5b, comprising a second differential 6b connected to a second driven axle 3. In this state may thus the first and second axles 2, 3 rotate without influencing the speed of each other. In general will this mean that one axle, e.g. the second axle 3, is totally disconnected from the powertrain and the drive shaft 5 and can rotate freely independent of the propulsion unit 104, 204, e.g. an internal combustion engine (ICE), while the other axle, e.g. the first axle 2, is connected to the propulsion unit 104, 204. However, both axles 2, 3 could be disconnected from the powertrain. In case there is a third driven axle 10 present, e.g. as shown in FIG. 2, could also this axle 10 be disconnected from the other axles 2, 3 by disengaging a second coupling 11 for allowing the axles 2, 3, 10 to rotate independent of each other. In case there are further driven axles present these axles could of course also be set to rotate freely.

[0065] When it is assured in in the first step S that the wheel axles 2, 3 10 for which the angular speed will be measured may rotate independently of each other, the second step S2 will follow, in which the angular speed is detected or measured, e.g. by the use of angular speed sensors 8a-f for each one of the wheels 4a-f A suitable occasion for performing the angular speed measurements in the second step S2 is when there is no torque applied to the driven wheels 4a-f, neither propulsive nor braking torque, and the respective axles are allowed to rotate freely with a minimum of propulsive force or braking torque from the powertrain or other axles. In this aspect could it be advantageously to perform the angular speed measurements when all axles and wheels are disconnected from the powertrain in order to reduce the risk for slip and/or spin of driven wheels 4a-f and thus being able to measure a correct value of the angular speed of the respective axles and/or wheels.

[0066] In the next step S3, the detected angular speed of the relevant axles 2, 3, 10, and/or the wheels 4a-f connected thereto, is used in order to calculate an angular speed difference between the angular speed of the axles 2, 3 10 and/or a difference between the angular speed of the respective wheels 4a-f of the wheels.

[0067] The calculated angular speed difference between the different axles and/or wheels in the third step S3 is used in the next step S4 to be compared with reference values to establish a comparison of the speed differences. Depending on which kind of angular speed sensors, e.g. angular speed sensors for each wheel or for the respective axles, and what features that are desired to control may different values be set as reference values, e.g. for certain features is it enough with the relative speed while for other features may the absolute speed also be of interest.

[0068] In the fifth step S5 the comparison of the angular speed difference of the individual driven wheels 4a-f or driven axles 2, 3, 10 is used as an indication of different wheel radius. An indication of different wheel radius could for example also be used as indication of differences in the circumference of the wheels, rolling radius or other parameters being related to the wheel radius. Based upon a detected difference in the angular speed may different alerts be displayed or control actions performed depending on the magnitude of the difference and/or driving conditions and vehicle characteristics. For example, critical values can be set for the angular speed differences above which different driven axles may not be drivingly connected. The different control actions could have different limits depending on a selected mode (e.g. working/transport) or detected/selected road conditions (e.g. paved/mud/gravel/ice) and have defined levels in a look-up table for different scenarios. Hence, an appropriate alert or control action will be output from the ECU when the angle speed difference has been estimated and compared with predefined values.

[0069] A speed difference between a pair of axles or between individual wheels may also be used as an indication of the status of the tires, e.g. wear and tire pressure, and could for example alert a driver to check the tire status or change the tires. Hence, the result of the measurements of the angular speed could be either a direct control signal to the wheel suspension system (or to some part of the vehicle) or to alert a driver of a status or feature to be checked.

[0070] In FIG. 4B is described certain steps which can be added to the control method described in FIG. 4A for a vehicle comprising a liftable axle. The steps included therein, preparatory step 1 (P1) and preparatory step 2 (P2), can be performed before the control method described in FIG. 4A is performed.

[0071] In the first preparatory step P1 an axle, e.g. the first axle 2, is lowered from an up-lifted resting position by a lifting mechanism 9 acting on the first axle 2 to a lowered position in contact with the ground. The lifting mechanism is designed to be able to shift the position of the first and second wheels 4a, 4b connected to the first axle 2 between being in a working position in contact with the ground surface and being lifted up to be in a resting position above a ground contact level. The lowering is made while keeping a coupling 7 disconnected such that the first axle 2 is drivingly disconnected from the second axle 3.

[0072] In the next step, the second preparatory step P2 the coupling 7 is maintained disconnected to keep the driven axles 2, 3 disconnected at least until it is indicated that the detected angular speed values from the angular speed sensors 8a, 8b, indicating the angular speed of the first axle 2 and/or its wheel pairs 4a, 4b, are stabilized. A stabilized speed may for example be decided to be reached when the angle speed sensors 8a, 8b indicates similar speed values and speed fluctuations as other angular speed sensors 8c-f. When the speed is considered to be stabilized may the method proceed as described in FIG. 4A.

[0073] 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 can be made within the scope of the appended claims.