Technical field

[0001] The present disclosure relates generally to electrically driven mining vehicles. Specifically, it relates to a method and system for controlling a traction speed of an electrically powered mining vehicles during downhill driving.

Background

[0002] When an electrically powered vehicle moves downhill, the electrical motor functions as a generator, converting kinetic energy from the vehicle into electric energy while slowing down the vehicle. The electric energy can be used to charge a battery of the vehicle. This is known as regenerative braking. Regenerative braking is thus a form of motor braking which is unique to electrically powered vehicles.

[0003] One advantage with regenerative braking is that it limits the dependence on conventional friction brakes. Friction brakes are associated with several problems, one being overheating. Overheating is especially dangerous in a mining environment where service is not readily available.

[0004] During regenerative braking, the battery can only receive the generated electric energy until it is fully charged. One problem associated with regenerative braking is consequently that, when the battery is fully charged, the electric vehicle may lose its ability to motor brake because the battery cannot receive any more charge. In mining environments, mining vehicles often travel long distances downhill leading to a lot of regenerated energy. In fact, it is not uncommon for a mining vehicle to have a fully charged battery when reaching a low-end position in a mine. This presents a risk, as the vehicle would then be fully dependent on the frictional brakes during at least part of the downhill travel.

[0005] An additional problem during downhill driving is overspeed. Overspeed is a condition where the motor rotation speed of the vehicle is forced to a state beyond a design limit of the vehicle, which may cause damage to the vehicle. When the vehicle battery becomes fully charged, and the ability to motor brake is unavailable, the risk of entering into an overspeed condition increases.

[0006] Thus, there is a need for solutions for sustainable regenerative braking for mining vehicles, i.e., solutions that are accessible also following a long downhill travel of the mining vehicle.

[0007] An object of the present disclosure is to overcome at least some of the problems outlined above and to provide a solution for controlling the speed of a mining vehicle in order to sustain regenerative braking.

[0008] This and other objects are achieved by means of a computer-implemented method, a computer program product, a traction control system, and a mining vehicle as defined in the appended claims. The term exemplary is in the present context to be understood as serving as an instance, example or illustration.

[0009] In a first aspect of the disclosure there is provided a computer-implemented method for controlling a traction speed of a mining vehicle during downhill driving. The mining vehicle comprises a traction control system, an electrical drive system comprising a traction motor and at least one inverter, and an electric energy storage. The method comprises setting a braking torque of the traction motor and determining an available charge power of the electric energy storage; when the available charge power is below a first predetermined value: calculating a reference rotation speed of the traction motor based on the available charge power and the set braking torque; and controlling the traction speed of the mining vehicle by controlling the rotation speed of the traction motor toward the reference rotation speed.

[0010] Controlling the traction speed toward a reference rotation speed allows the vehicle to be slowed down during downhill driving without exceeding the available power of the battery, that is, the power the battery can receive before it is fully charged. Thus, a set level of motor braking is always available, without exceeding the available power of the batter and overspeed can be avoided.

[0011] The reference rotation speed is a calculated rotation speed. The reference rotation speed is specifically calculated such that, if the rotation speed of the traction motor is controlled towards the reference rotation speed, the set motor brake is maintained, and the battery is not charged to an undesired level. The undesired level relates to the battery being fully charged, or close to fully charged.

[0012] In some examples, controlling the rotation speed comprises controlling an output direct current of the at least one inverter.

[0013] When electric power is generated by the electrical motor, the magnetic field in the motor slows the motor down. By controlling the output direct current of the at least one inverter it is thus possible to control how much electric power is generated in the motor and thus how much the magnetic field will slow the motor down. Using existing components of the motor in the vehicle for controlling the rotation speed, and thus the traction speed, is efficient and cost effective. Furthermore, controlling the rotation speed by controlling output direct current is a method which provides high precision and control over the resulting traction speed.

[0014] In some examples, the rotation speed of the traction motor is not allowed to exceed the reference rotation speed.

[0015] Thus, rotation speed is maintained at a level whereby a set motor brake is maintained and whereby available charge power is maintained below a predetermined value.

[0016] In some examples, determining the available charge power comprises requesting the available charge power from a battery management system, BMS, of the mining vehicle. Utilizing existing systems of the vehicle such as the BMS is efficient and cost effective. [0017] In some examples, the available charge power is obtained from the BMS at scheduled and/or regular intervals. In some examples, the available charge power is obtained from the BMS at predetermined time intervals when it is determined that the vehicle is in downhill driving.

[0018] In some examples, the available charge power is based on at least one of a state of charge, SoC, of the electric energy storage and a temperature of the electric energy storage. Both the SoC and the temperature provides information of how much power the battery may receive.

[0019] In some examples, the method may comprise determining an inclination of the ground at a position of the mining vehicle; and calculating the braking torque based on the determined inclination of the ground. This allows the reference rotation speed to be adapted depending on where the vehicle is and depending on characteristics of a surrounding environment of the vehicle. This provides a higher level of control and a more efficient use of energy.

[0020] In some examples, the position of the mining vehicle is one of a current position and an expected, future position along a travel route of the mining vehicle. This allows the reference rotation speed to not only be adapted depending on the current position, but also be adapted such that a suitable reference rotation speed to be set is already determined when the vehicle arrives at a downhill slope.

[0021] In some examples, determining the inclination comprises: obtaining data from a positioning system, the data comprising information relating to the inclination of the ground at the position of the mining vehicle.

[0022] Positioning systems in mining environment are commonly able to determine the position of objects in the mining environment with high precision. As such, these systems may be utilized to provide information related to the position of the vehicle. Information may be provided both to the vehicle from a remote system, or from the vehicle to a remote system. [0023] In some examples, the mining vehicle comprises at least two gears, and the method may comprise: determining which of the at least two gears is engaged; and setting the braking torque based on the determination. In some examples, the method may comprise, when the available charge power is below a second predetermined value being lower than the first predetermined value: preventing shifting to a higher gear.

[0024] The present system may be arranged to prevent the vehicle from reaching an unwanted state, for example a state where motor brake is unavailable.

[0025] Preventing shifting to a higher gear could for example comprise mechanically preventing shifting or communicating an alarm to a driver that shifting is not recommended.

[0026] In a second aspect of the disclosure there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to the first aspect.

[0027] In a third aspect of the disclosure there is provided a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the first aspect.

[0028] In a fourth aspect of the disclosure there is provided a traction control system for controlling a traction speed of a mining vehicle during downhill driving. The mining vehicle comprises: an electrical drive system comprising a traction motor, and at least one inverter, and an electric energy storage. The traction control system comprises means for communicating with the electrical drive system, processing circuitry; and a memory, wherein said memory contains instructions executable by said processing circuitry. The traction control system is operative for setting a braking torque of the traction motor and determining an available charge power of the electric energy storage. When the available charge power is below a first predetermined value the traction control system is further operative for calculating a reference rotation speed of the traction motor based on the available charge power and the set braking torque and controlling the traction speed of the mining vehicle by controlling the rotation speed of the traction motor toward the reference rotation speed.

[0029] In a fifth aspect of the disclosure there is provided a mining vehicle comprising: a traction control system according to the fourth aspect, an electrical drive system comprising a traction motor, and at least one inverter, and an electric energy storage.

Brief description of drawings

[0030] The disclosure is now described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 displays an example mining vehicle during downhill driving.

Fig. 2 displays an example electrical drive system and vehicle components.

Fig. 3 displays an example traction control system.

Fig. 4 displays an example method for speed control.

Description of embodiments

[0031] In the following, a detailed description of a computer-implemented method, a system, a computer program, a computer-readable medium and a mining vehicle is provided. In the figures, like reference numerals designate identical or corresponding elements throughout the figures. Optional features are displayed with dashed lines. It will be appreciated that these figures are for illustration only and do not in any way restrict the scope of the present disclosure.

[0032] With reference to Fig. 1 there is displayed a vehicle 10. The vehicle 10 is a mining vehicle 10 arranged for travelling in a mining environment. The mining environment may be, but is not limited to, an underground mine or a surface mine, e.g., an open pit mine. The mining environment may be an area adjacent to or in connection to a mine. As such, the mining environment could be seen as any area where the mining vehicle may normally travel during operation. The vehicle 10 in Fig.l is exemplified as a loader. The loader is arranged to load blasted rock into a mining truck at a blasting site. To this end, the loader comprises a bucket 11 into which blasted rock may be loaded and subsequently emptied into e.g., a mining truck. In an alternative embodiment, the vehicle 10 may also be exemplified as a mining truck arranged for transporting blasted rock from the blasting site and through the mining environment. The vehicle 10 may be operated by an operator sitting inside the vehicle 10, operated by a remote operator or autonomously operated. It will be understood that the exemplary mining vehicle 10 is not limiting to the scope of the disclosure, and that other types of mining vehicles are encompassed by the present disclosure. Examples of mining vehicles include loaders, dumpers, trucks, excavators, drill rigs, haulers.

[0033] The mining vehicle 10 is driven by means of an electrical drive system 20. Turning to Fig. 2, the electrical drive system 20 generally comprises a traction motor 21 and an inverter 22. The electrical drive system 20 is connected to the battery 30 via the inverter 22 at one end, and to a gear box 40 at another end.

[0034] Turning back to the downhill scenario of Fig. 1, the mining vehicle 10 may travel long distances downhill when travelling within the mining environment. The mining vehicle must at all times maintain the ability to brake and come to a full stop if needed. To this end, the vehicle 10 comprises a friction brake and furthermore has the ability to motor brake. A well-known disadvantage with use of a friction brake to slow down the vehicle 10 is a risk of overheating. Therefore, using motor braking is preferred. Reliability in the braking systems of the vehicle 10 is crucial, not only for safe operation, but also because access to service and maintenance may be limited in parts of the mining environment.

[0035] Motor braking by means of regenerative braking brings about a charging operation performed by the electrical drive system, i.e., charging a battery 30 connected to the electrical drive system 20. When the mining vehicle 10 moves downhill, the electrical drive system 20 functions as a generator and generated electric power can be used to charge the vehicle battery. An important aspect to consider in relation to regenerative braking is that it is only available as long as the battery is not fully charged. [0036] The ability of the vehicle 10 to motor brake is dependent on a braking torque. A theoretical braking torque required for holding the vehicle 10 in standstill, stands in relation to an inclination a of the downhill slope. A greater inclination a implies a greater gravitational vector component and thus a greater gravitational force acting on the vehicle 10 and thereby a greater torque. A lesser inclination a implies a lesser torque.

[0037] Fig. 2 displays an electrical drive system 20 of the mining vehicle 10. The electrical drive system 20 generally comprises a traction motor 21 and an inverter 22. The electrical drive system 20 is connected to the battery 30 via the inverter 22 at one end, and to a gear box 40 at another end. The gearbox according to Fig. 2 comprises a first and second gear 42 and is in turn connected to at least one wheel axle 50 having two wheels 51 arranged thereon.

[0038] In alternative embodiment, the electrical drive system 20 is instead connected directly (or via suitable connecting means) to the at least one wheel axle 50, i.e., excluding the disclosed gear box 40.

[0039] The battery 30 is arranged to store electrical energy to drive the vehicle 10. The output electricity from the battery 30 is direct current (DC). The inverter 22 converts the DC to alternating current (AC) which drives the traction motor 21. The inverter 22 also controls the output frequency of the AC. A high output frequency leads to a high rotation speed of the traction motor 21. The rotation speed is the speed at which a rotor of the traction motor rotates. The rotation speed may be measured in revolutions per minute (rpm). When the rotation speed increases a traction speed of the vehicle 10 increases. The traction speed is defined as the speed at which the mining vehicle travels, for example on a road of the mining environment. The traction speed may be measured in for example kilometers per hour (km/h) or miles per hour. Conversely, a low output frequency leads to a low rotation speed and the vehicle 10 slows down. However, during downhill driving the rotation speed of the traction motor 21 is maintained or increases without energy input from the battery 30, due to the force of gravity. This causes the traction motor 21 to motor brake through regenerative braking. To this end, the inverter 22 is furthermore capable of converting input AC from the traction motor 21 into output DC to charge the battery 30. [0040] The traction speed affects how much electric power can be generated in the traction motor during downhill driving. The higher the traction speed of the mining vehicle 10 is, the more electric power needs to be generated in the traction motor in order to slow the vehicle down. It is therefore an advantage if the traction speed of the mining vehicle is maintained below a level where it would be impossible to slow the vehicle down without fully charging the battery.

[0041] A traction control system 60 is displayed with reference to Fig. 3. The traction control system 60 generally comprises communication means 61, processing circuitry 62 and a memory 63. In Fig. 3 there is furthermore displayed a computer program 70 comprising instructions which, when executed by a computer, cause a computer to carry out a method 80 according to the disclosure.

[0042] The traction control system 60 is arranged to control the traction speed of the vehicle 10. To this end, the traction control system 60 is arranged to control the amount of regenerated power charged to the battery 30, thus ensuring that a sufficient motor brake torque is always available.

[0043] Via the communication means 61, the traction control system 60 communicates with the electrical drive system 20. The traction control system 60 communicates with the inverter 22 to control the inverter 22. The traction control system 60 may control an output of the inverter 22. The traction control system 60 may control the output DC from the inverter 22 to the battery 30. The traction control system 60 may control the output frequency from the inverter 22 to the traction motor 21.

[0044] Via the communication means 61, the traction control system 60 furthermore communicates with a battery management system (BMS) of the vehicle 10. From the BMS, information relating to the battery 30 is obtainable by the traction control system 60. Such information may for example be the available charge power. The available charge power is defined as the ability of the battery 30 to receive charge power and depends both on a state of charge (SoC) of the battery 30 and a temperature of the battery 30. A higher SoC implies a lower available charge power. When the battery 30 has a temperature within an optimal temperature interval, a high available charge power is implied. When the temperature is outside the optimal temperature interval, a low available charge power is implied. Specifically, the available charge power is lower the further the temperature of the battery is from the optimal temperature interval. The optimal temperature interval may be between 20°C and 40°C. The optimal temperature interval may be between 25°C and 35°C. The optimal temperature interval may be between 27°C and 35°C.

[0045] With reference to Fig. 4, there is furthermore provided a method 80 according to the disclosure. The method 80 is a computer implemented method. The method 80 is preferably executed by the traction control system 60 according to the disclosure.

[0046] Executing the method 80 has the effect that the traction speed of the vehicle 10 may be controlled during downhill driving. As mentioned above, one purpose of controlling the traction speed during downhill driving is to control how much electric power is generated during regenerative braking. By controlling how much electric power is generated, it is possible to avoid charging the battery 30 to a level at which motor braking is unavailable.

[0047] The method 80 comprises a step of setting 81 a braking torque. The set braking torque may define a minimum level of braking torque, below which there is a risk of decreased motor brake availability. The set braking torque may define a minimum level of braking torque, below which motor braking is unavailable to the vehicle 10. The braking torque may be set to 500 Nm. The braking torque may be set to 200 Nm.

[0048] The method 80 comprises a step of determining 82 an available charge power of the battery 30. Determining the available charge power may comprise obtaining the available charge power. Determining the available charge power may comprise obtaining information relating to the available charge power. The information may be the SoC of the battery 30 and/or the temperature of the battery 30. Determining the available charge power may comprise calculating the available charge power based on the obtained information. The available charge power and/or related information may be obtained from the BMS. The available charge power and/or related information may be obtained by the traction control system 60 from the BMS. The available charge power and/or related information may be obtained by requesting it from the BMS. The available charge power and/or related information may be obtained from the BMS at scheduled and/or regular intervals. The available charge power and/or related information may be obtained from the BMS at predetermined time intervals when it is determined that the vehicle is in downhill driving. The method comprises determining if the available charge power is below a first predetermined value. The determining may be performed by the traction control system 60. The first predetermined value may relate to a minimum level of available charge power below which motor braking is unavailable to the vehicle 10. The first predetermined value may relate to a minimum level of available charge power below which there is a risk of decreased motor brake availability.

[0049] The method 80 comprises a step of calculating 83 a reference rotation speed of the traction motor 21. Calculating 83 a reference rotation speed may be performed by the traction control system 60. Calculating 83 a reference rotation speed may comprise obtaining the set braking torque. Calculating 83 a reference rotation speed may comprise obtaining the determined available charge power. Calculating 83 a reference rotation speed may be based on the available charge power and the set braking torque. Calculating 83 a reference rotation speed may comprise calculating which rotation speed of the traction motor is required to maintain the available charge power and maintain the set braking torque. Calculating 83 a reference rotation speed may comprise calculating which rotation speed of the traction motor is required to maintain the available charge power above the predetermined value and maintain. Calculating 83 a reference rotation speed may be performed when the available charge power is determined 82. Calculating 83 a reference rotation speed may be performed when the available charge power has changed more than a predetermined value. To this end, calculating 83 a reference rotation speed may comprise determining a change in the determined available charge power. Calculating 83 a reference rotation speed may be performed when setting 81 the braking torque. Calculating 83 a reference rotation speed may be performed when the set braking torque has changed. [0050] The reference rotation speed may be calculated by means of the following equation:

(P - B) * 1000 * 30

[0051] Wherein P is the available charge power in kW, B is a power margin in kW, M is the set braking torque in Nm and N is the reference rotation speed in km/h.

[0052] The power margin is a safety margin included in the equation to allow for uncertainties in the obtained available charge power. The power margin may be 10 kW. The power margin may be 20 kW. The power margin may be set depending on which gear is connected. The equation may furthermore be used without entering a power margin, that is setting the power margin to zero.

[0053] The method 80 comprises a step of controlling 84 the traction speed of the mining vehicle 10 by controlling the rotation speed of the traction motor 21 toward the reference rotation speed. Controlling the rotation speed of the traction motor 21 may comprise controlling the inverter 22. Controlling 84 the traction speed may comprise controlling the rotation speed of the traction motor 21 to not exceed the reference rotation speed.

[0054] In one example, controlling 84 the traction speed of the mining vehicle 10 by controlling the rotation speed of the traction motor 21 may comprise controlling the output DC from the inverter 22 to the battery. Controlling the rotation speed of the traction motor 21 may comprise controlling the output DC from the inverter 22 to the battery which in turn controls the input AC to the inverter 22 from the traction motor 21 and which thereby controls the rotation speed of the traction motor 21. Controlling the rotation speed of the traction motor 21 may comprise limiting the output DC from the inverter 22 to the battery to limit the input AC to the inverter 22 from the traction motor 21 and thereby limit the rotation speed of the traction motor 21. [0055] In another example, controlling 84 the traction speed of the mining vehicle 10 by controlling the rotation speed of the traction motor 21 may comprise controlling the output frequency from the inverter to the traction motor 21. Controlling the rotation speed of the traction motor 21 may comprise limiting the output frequency from the inverter to the traction motor 21 and thereby limit the rotation speed of the traction motor 21.

[0056] Setting 81 the braking torque may comprise determining the inclination of the ground below the vehicle 10 or an inclination of a road segment lying ahead of the vehicle 10. Setting the braking torque may comprise determining that the inclination is above a predetermined inclination value. Setting the braking torque may comprise determining that the inclination is below a predetermined inclination value. Setting the braking torque may comprise setting a higher value of the braking torque if the inclination is above the predetermined inclination value and a lower braking torque is the inclination is below the predetermined inclination value. Determining the inclination may comprise a step of communicating with a means for determining the inclination arranged on the vehicle 10. Such a means may for example be a gyroscope. Determining the inclination may comprise obtaining the inclination from the means for determining the inclination by requesting the inclination. Obtaining the inclination from the means may be performed by the traction control system 60. Determining the inclination may also comprise a step of obtaining information relating to the inclination from a positioning system of the mining environment. The positioning system may be capable of determining a position of the vehicle 10 and transmitting information relating to said position to the vehicle 10. Said information may comprise the inclination at said position, or the inclination of a position lying ahead of the vehicle 10 on a travel route of the vehicle 10.

[0057] Setting 81 the braking torque may comprise determining a current gear of the vehicle 10. A higher braking torque may be set when it is determined that a higher gear is connected and a lower braking torque may be set when it is determined that a lower gear is connected. This is because a traction speed of the vehicle 10 is higher when a higher gear is connected, compared to when a lower gear is connected. When the traction speed is higher, the generated power may increase. Thus, a higher breaking torque may be set for a higher gear to control the reference rotation speed and in turn control the generated power to the battery 30. The higher gear may be the second gear and the lower gear may be the first gear. The braking torque may be set to 500 Nm. The braking torque may be set to 200 Nm. The braking torque may be set to 500 Nm when the vehicle 10 is in second gear 42. The braking torque may be set to 200 Nm when the vehicle 10 is in first gear 41. The method may also comprise determining if the available charge power is below a second predetermined value, being lower than the first predetermined value. When it is determined that the available charge power is below the second predetermined value, the method may comprise at least one of mechanically and/or electrically preventing shifting to a higher gear, communicating with a driver of the vehicle that shifting to a higher gear is not recommended, bringing the vehicle to a full stop, and communicating to a driver that motor brake is unavailable.

[0058] In one example the method comprises setting the braking torque to 500 Nm, obtaining an available charge power, wherein the obtained available charge power is 130 kW, calculating the reference rotation speed according to the equation with a power margin of 20 kW, wherein the resulting reference rotation speed is 2102 rpm, and controlling the rotation speed of the traction motor towards the reference rotation speed. According to this example, the resulting traction speed of the mining vehicle 10 is 10.0 km/h.

[0059] In one example the method comprises setting the braking torque to 500 Nm, obtaining an available charge power, wherein the obtained available charge power is 100 kW, calculating the reference rotation speed according to the equation with a power margin of 20 kW, wherein the resulting reference rotation speed is 1529 rpm, and controlling the rotation speed of the traction motor towards the reference rotation speed. According to this example, the resulting traction speed of the mining vehicle 10 is 7.3 km/h.

[0060] In one example the method comprises setting the braking torque to 200 Nm, obtaining an available charge power, wherein the obtained available charge power is 130 kW, calculating the reference rotation speed according to the equation with a power margin of 20 kW, wherein the resulting reference rotation speed is 5255 rpm, and controlling the rotation speed of the traction motor towards the reference rotation speed. According to this example, the resulting traction speed of the mining vehicle 10 is 25.0 km/h.

[0061] Preferred examples of a method 80 and a system have been disclosed above. However, a person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0062] All the described alternative embodiments above or parts of an embodiment can be freely combined or employed separately from each other without departing from the inventive idea as long as the combination is not contradictory.