Propulsion system for heavy vehicle, heavy vehicle and method for controlling propulsion system

Abstract

The present invention relates to a propulsion system (102, 202) for a heavy vehicle (100, 200), such as a truck, bus or construction equipment vehicle. The propulsion system includes an electric machine (EM), such as an electric motor and a generator, and a control device (126, 226) including a processor (128, 228) and a memory (130, 230). Each of the EM is either in an EM electrically connected state in which power is transmitted between the power source and the wheel and EM torque is applied to the wheel of the vehicle, or in an EM electrically disconnected state in which no power is transmitted between the power source and the wheel. Further, each of the EM is associated with EM power loss characteristics of the EM electrical connection state and the EM electrical disconnection state, respectively. The EM power loss characteristic of the EM electrically disconnected state is related to inertia and / or frictional loss caused by the EM when the power source does not supply power to the EM. The control means are arranged to: define a cost function dependent on EM states of the EM, where each of the EM states comprises either the EM electrical connection state or the EM electrical disconnection state, where the cost function further comprises a motion request associated with an expected value of global force; minimizing a cost function over a search space comprising the EM state such that it is determined to minimize the EM state; and controlling the EM in accordance with the minimized EM state.

Description

Technical Field

[0001] The present invention relates to propulsion systems for heavy vehicles. More particularly, the present invention relates to systems and methods for providing more efficient propulsion for heavy vehicles. Background Art

[0002] In recent years, the use of software-based vehicle motion management control systems has become increasingly popular in the heavy vehicle sector such as trucks, buses and construction equipment. For example, by being able to continuously collect parameter values ​​related to electric motors and friction brakes, more energy-efficient motion control can be provided, as well as more precise steering and improved driving dynamics.

[0003] A typical vehicle motion management control system comprises a plurality of actuators, such as steering, brakes, drives and shock absorbers, which are communicatively connected to a control device. In addition to the actuators, sensors are provided to feed sensor data to the control device. After processing the sensor data using software instructions held in the control device, the control data can be transmitted from the control device to the actuators so that, for example, more energy-efficient propulsion can be achieved.

[0004] More details can be found in the Master's thesis "Predictive Energy Management of Long-Haul Hybrid Trucks: Using Quadratic Programming and Branch-and-Bound" by Johnsson-Holm, Erik, Linköping University, 2021, which describes how to use mixed integer quadratic programming (MIQP) to reduce the fuel consumption of hybrid electric vehicles (HEVs) with electric propulsion systems and conventional internal combustion engines (ICEs). In addition, in the Master's thesis "Optimal torque split strategy for BEV powertrain considering thermal effects" by Yadav, Dhananjay, it is disclosed how to effectively control two or more electric machines in battery electric vehicles (BEVs).

[0005] Although different vehicle motion management control methods have been proposed, there is still room for further improvement. In particular, it would be of great benefit to be able to effectively reduce the power losses of vehicles consisting of one or a few electric motors. Summary of the invention

[0006] It is an object of the present invention to provide a propulsion system having a plurality of electric machines (EMs), such as electric motors, which can be controlled in such a way that power losses are reduced.

[0007] Generally, it has been recognized that additional degrees of freedom for controlling the propulsion system can be gained by allowing the EM to be mechanically connected to the drive train, but electrically disconnected (i.e., not powered). Although these states will generate power losses in the form of inertia and friction losses, these states may still be the best choice to reduce power losses. One reason for this is that the cost of changing states (e.g., from mechanical connection to mechanical disconnection) also results in power losses.

[0008] According to a first aspect of the invention, the object is achieved by a control system according to claim 1 .

[0009] According to one embodiment, the propulsion system may also include a mechanical actuator (MA) that may be mechanically connected or disconnected. By incorporating the state of the MA and the power loss characteristics of different MA states into the search space of the cost function used, a combination of states that minimizes the power loss of both the EM and the MA may be found. An advantage of evaluating both the EM and the MA simultaneously is that a combination of states may be found that would not be found when considering both types separately.

[0010] According to further embodiments, the control means may be arranged to update the minimized MA state and the minimized EM state once per second or more frequently (e.g. once every 10 milliseconds). Switching from electrical disconnection to electrical connection and vice versa may be accomplished in a fraction of a second. Thus, allowing state changes that do not involve switching from mechanical connection to mechanical disconnection and vice versa is particularly beneficial for sub-second power loss optimization.

[0011] According to a second aspect of the invention, the object is achieved by a heavy vehicle according to claim 10 .

[0012] According to a third aspect of the present invention, the object is achieved by a method according to claim 11.

[0013] According to a fourth aspect of the invention, the object is achieved by a computer program according to claim 13.

[0014] According to a fifth aspect of the present invention, the object is achieved by a computer readable medium according to claim 14.

[0015] According to a sixth aspect of the present invention, the object is achieved by a control device according to claim 15.

[0016] Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the invention cited as examples will be described in more detail hereinafter with reference to the accompanying drawings.

[0018] In the attached picture:

[0019] Figure 1 By way of example, an example of a hybrid vehicle with two axles is shown.

[0020] Figure 2 By way of example, another hybrid vehicle with three axles is shown.

[0021] Figure 3 shows the power losses of the two electric motors and the brake,

[0022] Figure 4 The input and output of the motion coordination method are shown in general.

[0023] Figure 5 By way of example, it is shown that Figure 2 The relationship between the number of electric machines (EMs) used and the total longitudinal force request for a hybrid vehicle shown,

[0024] Figure 6 The example shows Figure 2 The torque distribution between the two EMs of the vehicle shown,

[0025] Figure 7 By way of example, the number of EMs used versus the total longitudinal force request for a vehicle having four EMs is shown,

[0026] Figure 8 The torque distribution between the four motors is shown by way of example,

[0027] Fig. 9 Shows by example how to select states when using the motion control method, and

[0028] Fig.10 is a flow chart illustrating a method of controlling a propulsion system. DETAILED DESCRIPTION

[0029] Figure 1 A propulsion system 102 of a vehicle 100, such as a truck, bus, or construction equipment vehicle, is generally shown by way of example. It should be understood herein that the propulsion system 102 includes any type of engine, such as an electric engine and / or an internal combustion (IC) engine, a transmission component, such as a gearbox, and other components arranged to provide positive momentum on wheels 104a-d of the vehicle. In addition to these components, the propulsion system 102 may also include components arranged to provide negative momentum on wheels 104a-d. For example, the propulsion system 102 may include mechanical brakes and an electric motor arranged to reduce the speed of the vehicle while generating electricity.

[0030] exist Figure 1In the example shown, the vehicle is a hybrid vehicle having an IC engine 106 (generally referred to herein as a mechanical actuator (MA)) connected via an MA clutch 108 to a transmission 110, which in turn is connected to a final drive 112. Figure 1 As shown, the final reducer 112 is connected to two of the wheels 104a, 104c, so that the power output from the IC engine 106 can provide the rotation of the two wheels 104a, 104c. The combination of components for driving the vehicle 100 (herein, the transmission 110 and the final reducer 112 are taken as examples) can generally be referred to as a transmission system 113.

[0031] In addition to the IC engine 106, in the example shown, an electric motor 114 is provided, generally referred to herein as an electric motor (EM). The electric motor 114 is connected to a battery 116 or other power source. A switch 118 may be placed between the battery 116 and the electric motor 114 so that the electric motor 114 can be electrically connected or disconnected from the battery 116. In addition, an EM clutch 120 may be provided between the electric motor 114 and the transmission 110. With the EM clutch 120, the electric motor 114 can be mechanically connected or disconnected from the transmission 110.

[0032] The steering systems 122a, 122b may form part of the vehicle 100. In the example shown, the steering systems 122a, 122b are coupled to the front axle, while the IC engine 106 and the electric motor 114 are coupled to the rear axle. Although shown in this manner, this is only one of several possible implementations.

[0033] A mechanical brake 124a-d may be provided for each of the wheels 104a-d. The mechanical brakes 124a-d may be embodied in different ways, but the general purpose is to reduce the speed or completely stop the vehicle. Although not shown, a generator may be used as a supplement to the mechanical brakes 124a-d (which is an example of a mechanical actuator (MA)). The electricity generated by the generator may be used to charge the battery 116 while providing a braking effect.

[0034] In the context of this patent application, the IC engine 106 and the mechanical brakes 124a-d are generally referred to as MA. On the other hand, the electric motor 114 is referred to as EM. If a generator is added to charge the battery 116 while providing a braking effect, this can also be considered an electric machine (EM). In other words, in the context of this patent application, any non-electric machine is considered an MA. The difference between the two can also be described as the fact that the MA can be in two states: mechanically connected or mechanically disconnected, while the EM can be in a mechanically connected or disconnected state like the MA, and can also be in an electrically connected or disconnected state. Having this additional possibility can improve energy efficiency. For example, even though a mechanically connected but electrically disconnected motor (such as the electric motor 114) may have a negative impact on the propulsion of the vehicle 100 due to inertia and friction losses, putting the electric motor 114 in this state may still be the most energy-efficient option at a particular point in time, because the state change itself may incur energy costs. In particular, this is true when the state change is set to occur once per second or more frequently.

[0035] A control device 126 including a processor 128 and a memory 130 may be provided to control the states of EM and MA. In addition to adjusting EM and MA in accordance with a minimized MA state and a minimized EM state (i.e., states of MA and EM that result in the most energy-efficient propulsion of the vehicle 100), the control device 126 may also be arranged to set a force or torque applied by EM and / or MA.

[0036] Figure 2 Another example of a hybrid vehicle 200 is shown. Figure 1 Consistent with the example shown in , vehicle 200 includes a propulsion system 200 and wheels 204a-f. Figure 1 The example shown is different. Figure 2 The vehicle 200 shown is provided with three axles and six wheels. Figure 1 Consistent with the example shown, vehicle 200 includes IC engine 206, MA clutch 208, and transmission 210. Since there are two axles coupled to transmission 210, first and second final drives 112a-b may be used, one for each axle. Transmission 110 and final drives 112a-b together may be referred to as drive train 213.

[0037] The rearmost axle may be used as a starter axle (SA), and the middle axle may be used as a cruiser axle (CA). The first electric motor 214a, the first battery 216a, the first switch 218a, and the second EM clutch 220a may be coupled to the cruiser axle (CA), and the second electric motor 214b, the second battery 216b, the second switch 218b, and the second EM clutch 220b may be coupled to the starter axle (SA). Although the first and second electric motors 214a, b are shown as having separate batteries, they may also have the same battery or other power source shared between them.

[0038] and Figure 1 Similar to the example shown, a steering system 222a-b may be provided on the front axle. In addition, a mechanical brake 224a-f may be coupled to each of the wheels 204a-f. A control device 226 including a processor 228 and a memory 230 may be communicatively connected to the switches 218a-b, the EM clutches 220a-b, and the mechanical brakes 224a-f.

[0039] Apart from Figure 1 and Figure 2 In addition to the examples shown in , the vehicle may also be an electric vehicle (EV), ie, a vehicle whose propulsion system includes only an electric motor and no IC engine.

[0040] Furthermore, although only one axle is shown for each electric motor, it is also possible to connect an electric motor or more generally an electric machine to several axles. Furthermore, it is also possible to couple several electric motors or electric machines to the same axle.

[0041] For example, for Figure 1 and Figure 2 In the hybrid vehicle shown, in order to improve the energy efficiency of the propulsion system 102, 202, the forces of MA (such as service brakes) and EM can be selected to minimize power loss. For example, the optimal control problem design of motion coordination that minimizes power loss can be written as:

[0042] The u vector includes the forces of the devices to be controlled (in this case n electric machines and m service brakes), where the service brakes are mechanical brakes, but u can also include steering devices.

[0043] B is called the control effectiveness matrix, is a virtual control input with the desired value of the global force, and the power losses of the n motors are approximated by a nonlinear function of the output torque or force, and in this example, a quadratic function that adds copper losses, iron losses, windage losses, and mechanical (friction / inertia) losses:

[0044] Where a3 is the moment of inertia loss due to the mechanical characteristics of the rotor when the current is turned off (ie, electrically disconnected), and a0 is the magnetic loss and inertia loss when current is supplied to the motor, .

[0045] The terms a0, a1, a2, and a3 are time-varying and depend on the operating conditions, such as the motor speed. :

[0046] although Figure 1 and Figure 2 The example provided in is a hybrid vehicle, but the method proposed above can also be used for electric vehicles (EV), ie vehicles without any ICE.

[0047] Furthermore, in the examples provided above, the power losses of the ICE were not considered. Although not part of the examples provided above, for hybrid vehicles, the power losses of the ICE may also be considered.

[0048] exist Figure 3 In Figure 1, the relationship between power losses and torque at the wheels is shown by way of example for an electric vehicle at 80 km / h. The electric vehicle in this particular example is provided with two different types of electric machines: one EM located at the cruising axle and one EM located at the starting axle, both with different designs. Furthermore, for clarity, the losses of the service brakes have been lumped into one item.

[0049] If the electric motors 214a-b are mechanically disconnected, or more generally the EM is disconnected, the losses can be assumed to be zero. However, by instead allowing the EM to be mechanically connected but electrically disconnected, additional degrees of freedom can be allowed, thereby increasing the potential for improved energy efficiency. However, a consequence of this approach is that the inertia-related losses of the EM are considered, as well as the friction losses. Therefore, when these additional degrees of freedom are allowed, the term a0 for the EM now depends on the torque.

[0050] Therefore, the optimization problem can be reformulated as follows. Unlike the problem posed above, this new approach includes a new output of the control algorithm, namely a binary variable, called , which considers whether different EMs should be electrically connected or electrically disconnected to reduce power loss.

[0051] The power loss of the EM is equal to:

[0052] And expand the vector u of optimization variables by including new binary variables:

[0053] The factor " ” is a parameter representing the cost of power loss. The optimization problem can be formulated as a standard mixed integer quadratic programming (MIQP) problem and solved using existing solvers in the literature.

[0054] The movement coordination methods described above are generally as follows Figure 4 As shown in Figure 2, the control effectiveness matrix B and the virtual control input V with the expected value of the global force can be input des In addition, you can enter the upper and lower limits of u. You can enter P 损耗 parameters, and cost c.

[0055] As shown, by using the motion coordination method, the force / torque of the EM, the connection / disconnection status of the EM (i.e., whether the different EMs should be electrically disconnected or electrically connected), and the force / torque of the service brake or more generally the MA can be output.

[0056] Consistent with the examples provided above, when the EM is electrically disconnected but mechanically connected, power losses will occur in the form of inertia and / or friction losses. When the EM is electrically connected but mechanically disconnected, power losses will occur in the form of inverter losses. When the EM is electrically disconnected and mechanically connected, power losses are close to zero.

[0057] By using the method proposed above, it is possible to provide Figure 2 The torque distribution between the first motor and the second motor 214a-b of the hybrid vehicle 200 is shown in FIG. Figure 5 In , the relationship between the number of electric motors and the total longitudinal force request for a vehicle speed point is shown. Figure 6 , a first electric motor and a second electric motor 214a-b (in Figure 6 As the vehicle's operating point changes during operation, and the motion global force targets and capabilities of devices such as electric motors change, motion control may be recalculated to meet these new conditions.

[0058] exist Figure 7 and Figure 8In the example shown, four identical EMs are used. These four EMs are of the same type as the second electric motor 214b that forms part of the example presented above. For four EMs, the maximum torque is 10500 Nm. When four EMs are provided and the above-described motion control method is used, it may result in the number of EMs in the on state (i.e. electrically connected) being proportional to the total longitudinal force request. Figure 7 The torque distribution of each machine can be as follows: Figure 8 shown.

[0059] Since the four machines in this example are identical, the combinatorial problem of the MIQP can be reduced. Instead of just solving once for the four cases with only one EM on (electrically connected), once for the six cases with two EMs on (electrically connected), and once for the four cases with three EMs on (electrically connected), a total of five cases can be solved (equivalent to solving 5 QPs): {0,1,2,3,4} motors on. This also applies when we include knowledge about the preferred EM to use.

[0060] As described above, by using the methods described herein, the number of available states is increased, so more detailed settings can be made, thereby providing improved energy efficiency. Fig. 9 A state selection is shown, which may be selected as the most energy-efficient state combination, or in other words, the state combination with the lowest power loss. Fig. 9 The selected state is marked in bold.

[0061] Fig. 9 The specific example shown is similar to Figure 2 2 is related to the vehicle 200 shown. In this example, MA #1 - #4 (mechanical brakes) are mechanically disconnected. MA #5 (IC engine) is mechanically connected. The first electric motor EM #1 coupled to the starting axle is mechanically and electrically connected, while the second electric motor EM #2 coupled to the cruising axle is mechanically connected but electrically disconnected, i.e., inertia and friction losses are generated.

[0062] exist Fig.10 In the present invention, a flow chart showing a method 1000 for controlling a propulsion system 102, 202 of a vehicle 100, 200 is provided. In a first step 1002, a cost function that depends on a MA state and an EM state may be defined. In a second step 1004, the cost function may be minimized, which has the effect of determining a minimized MA state and a minimized EM state, or in other words an optimal MA state and an optimal EM state. In a third step, the MA and EM of the vehicle may be controlled by using the minimized MA state and the minimized EM state.

[0063] It should be understood that the present invention is not limited to the embodiments described above and shown in the drawings; rather, those skilled in the art will recognize that many changes and modifications are possible within the scope of the appended claims.

Claims

1. A propulsion system (102, 202) for a heavy vehicle (100, 200) such as a truck, bus or construction equipment vehicle, the propulsion system comprising Electric machines (EM), such as electric motors and generators, and A control device (126, 226), the control device comprising a processor (128, 228) and a memory (130, 230), wherein each of the EMs is either in an EM electrically connected state, wherein power is transferred between a power source and a wheel and EM torque is applied to the wheel of the vehicle, or in an EM electrically disconnected state, wherein no power is transferred between the power source and the wheel, wherein each of the EMs is associated with an EM power loss characteristic for the EM electrically connected state and the EM electrically disconnected state, respectively, wherein the EM power loss characteristics of the EM electrically disconnected state are related to inertia and / or friction losses caused by the EM when the power source is not supplying power to the EM, The control device is arranged as defining a cost function depending on an EM state of the EM, wherein each of the EM states comprises the EM electrically connected state or the EM electrically disconnected state, wherein the cost function further comprises a motion request associated with a desired value of a global force, minimizing a cost function over a search space including the EM state such that a minimizing EM state is determined, and The EM is controlled according to the minimized EM state.

2. The propulsion system of claim 1, wherein each of the EMs in the EM electrically disconnected state is mechanically connected to a drive train (113, 213) of the vehicle.

3. The propulsion system according to any one of claims 1 or 2, further comprising Mechanical actuators (MAs), such as mechanical brakes and internal combustion engines, wherein each of the MAs is either in a MA mechanically connected state, in which MA torque is applied to wheels of the vehicle, or in a MA mechanically disconnected state, in which MA torque is not applied, wherein each of the MAs is associated with an MA power loss characteristic for the MA mechanically connected state and the MA mechanically disconnected state, respectively, and wherein the cost function further depends on a MA state of the MA, wherein each of the MA states comprises the MA mechanically connected state or the MA mechanically disconnected state, wherein the search space also includes the MA state, so that the minimized MA state is also determined, The control device (126, 226) is further configured to control the MA according to the minimized MA state.

4. The method according to any one of the preceding claims, further comprising: an EM clutch (120, 220a-b) disposed between a subset of the EMs and the drive train (113, 213), wherein for each of the EMs in the subset, when in an EM mechanical connection state, the EM clutch (120, 220a-b) is engaged, wherein for each of the EMs in the subset, when in an EM mechanical disconnect state, the EM clutch (120, 220a-b) is disengaged, wherein for the subset, the EM state used in the search space also includes the EM mechanical disconnect state, Wherein for the subset, the EM electrical connection state and the EM electrical disconnection state are consistent with the EM mechanical connection state.

5. A propulsion system according to any preceding claim, wherein the control means is arranged to update the minimised MA state and the minimised EM state at a frequency of once per second or more, such as once every 10 milliseconds.

6. A propulsion system according to any of the preceding claims, wherein the control device is configured to provide control data to the drive train (113, 213) to cause at least one of the longitudinal motion, lateral motion, yaw moment, roll moment and pitch moment of the vehicle (100, 200) to change.

7. A propulsion system according to any one of the preceding claims, wherein a first electric machine (EM1) in the EM is arranged to propel a starting axle (SA) of the vehicle (200) and a second electric machine (EM2) in the EM is arranged to propel a cruising axle (CA) of the vehicle.

8. A propulsion system according to any one of the preceding claims, wherein the cost function comprises power losses of the EM, wherein a quadratic approximation of the power losses of the electric motor is provided as a function of the electric motor torque of the EM in the EM electrical connection state.

9. A propulsion system according to any one of the preceding claims, wherein the cost function comprises a cost term which adds an additional cost for switching between the EM electrically connected state and the EM electrically disconnected state of the EM.

10. A heavy vehicle, such as a truck, bus or construction equipment vehicle, comprising a propulsion system according to any one of claims 1 to 9.

11. A method (1000) for controlling a propulsion system of a heavy vehicle such as a truck, bus or construction equipment vehicle, The propulsion system comprises a mechanical actuator (MA), an electric motor (EM), and a control device (126, 226), wherein the control device comprises a processor (128, 228) and a memory (130, 230), wherein each of said MAs is either in a MA mechanically connected state, wherein MA torque is applied to the wheels of the vehicle, or in a MA mechanically disconnected state, wherein no negative torque is applied, wherein each of the electric motors is either in an electrically connected state, wherein power is transmitted between a power source and the wheels and EM torque is applied to the wheels of the vehicle, or in an electrically disconnected state, wherein no power is transmitted between the power source and the wheels, wherein each of the MAs is associated with a MA power loss characteristic of the MA mechanically connected state and the MA mechanically disconnected state, respectively, and each of the EMs is associated with an EM power loss characteristic of the EM electrically connected state and the EM electrically disconnected state, respectively, wherein the EM power loss characteristics of the EM electrically disconnected state are related to inertia and / or friction losses caused by the EM when no power is supplied to the EM, The method comprises: defining (1002) a cost function depending on a MA state of the MA and an EM state of the EM by using the control device, wherein each of the MA states comprises the MA mechanically connected state or the MA mechanically disconnected state, wherein each of the EM states comprises the EM electrically connected state or the EM electrically disconnected state, wherein the cost function further comprises a motion request associated with a desired value of a global force, By minimizing (1004) a cost function on a search space including the MA state and the EM state using the control device, a minimized MA state and a minimized EM state are determined, and The MA and the EM are controlled (1006) by using the control means according to the minimized MA state and the minimized EM state, respectively.

12. The method of claim 11, wherein each of the EMs in the EM electrically disconnected state is mechanically connected to a drive train (113, 213) of the vehicle.

13. A computer program comprising program code means for performing the steps of any one of claims 11 and 12 when said program is run on a computer.

14. A computer readable medium carrying a computer program, the computer program comprising program code means for executing the steps of any one of claims 11 to 12 when the program product is run on a computer.

15. A control device for controlling a vehicle propulsion system, the control device being configured to perform the steps of the method according to any one of claims 11 to 12.

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