Determine the slip target of the vehicle engine speed controller

Abstract

The present inventive concept relates to a technique for determining a modified slip target for a vehicle engine speed controller. A method includes comparing a difference between a maximum wheel speed and a minimum wheel speed of wheels of an open differential and a drive axle controlled by a vehicle engine speed controller with a preconfigured wheel speed offset. The method includes setting a modified slip target to be lower than a requested slip target of the vehicle engine speed controller at least when the difference exceeds the preconfigured wheel speed offset.

Description

Technical Field

[0001] The embodiments presented herein relate to methods, systems, and computer programs for determining a modified slip target for a vehicle engine speed controller. The embodiments presented herein also relate to a vehicle including such a system. Background Art

[0002] Generally, split friction (or μ (mu)-split) is a road condition that occurs when the frictional forces between the left and right wheel paths of a vehicle are significantly different. Thus, when accelerating, cruising, or even gently braking, the road may not be considered dangerous. However, in the case of hard (emergency) braking, the vehicle will start to rotate along the wheel path that provides the highest grip. Split friction can cause an articulated truck to bend, while a truck towing a trailer may experience trailer swing. Split friction may be caused by improper road surface repairs, resulting in a large difference in texture and color across an entire section of the road (e.g., because thin ice on a newly paved black road surface melts faster than ice on an old gray asphalt surface).

[0003] More specifically, due to the mechanical function of an open differential, even when driving straight, the speeds of the left and right wheels may rotate at different speeds through the first or second drive axles due to traction loss caused by different normal loads, friction, conditions, tire wear, etc.

[0004] Once the rotational speed of one of the wheels exceeds the highest point of the tire curve, most of the propulsion torque may be transmitted to the most rotating wheel, thus becoming a system of "single-wheel drive for each drive axle". Since the output speed is mechanically ensured to be the average of the input speeds, the speed of the wheels will also be higher than the speed of the differential input cardan shaft. For a wheel slip controller that uses the output shaft speed to control slip, due to its advantages of fast signal response and resolution, problems will occur once the wheel speeds start to differ from left to right or between the first or second drive axles, which is caused by the mechanical characteristics described above. Summary of the Invention

[0005] The aim of the embodiments disclosed herein is to solve the above problems.

[0006] A specific aim of the embodiments disclosed herein is to provide techniques for adapting the requested slip target of a vehicle engine speed controller.

[0007] According to a first aspect, the object is achieved by a method for determining a modified slip target of a vehicle engine speed controller. The method includes comparing a difference between a maximum wheel speed and a minimum wheel speed of wheels of an open differential and a drive axle controlled by the vehicle engine speed controller with a preconfigured wheel speed offset. The method includes setting the modified slip target to be lower than a requested slip target of the vehicle engine speed controller at least when the difference exceeds the preconfigured wheel speed offset.

[0008] According to a second aspect, the object is achieved by a system for determining a modified slip target of a vehicle engine speed controller. The system includes a processing circuit. The processing circuit is configured to cause the system to compare a difference between a maximum wheel speed and a minimum wheel speed of wheels of an open differential and a drive axle controlled by the vehicle engine speed controller with a preconfigured wheel speed offset. The processing circuit is configured to cause the system to set the modified slip target to be lower than a requested slip target of the vehicle engine speed controller at least when the difference exceeds the preconfigured wheel speed offset.

[0009] According to a third aspect, the object is achieved by a vehicle including the system according to the second aspect.

[0010] According to a fourth aspect, the object is achieved by a computer program for determining a modified slip target of a vehicle engine speed controller, the computer program including computer program code which, when run on a system, causes the system to perform the method according to the first aspect.

[0011] According to a fifth aspect, a computer program product is proposed, the computer program product including the computer program according to the fourth aspect and a computer-readable storage medium storing the computer program. The computer-readable storage medium may be a non-transitory computer-readable storage medium.

[0012] Advantageously, these techniques can keep the wheel slip of all drive wheels below the peak.

[0013] Further advantageously, by ensuring that the wheel slip of all drive wheels is below the peak, not only can the traction of the most rotating wheels be increased, but also the slip of the slower wheels can potentially be increased. Furthermore, this can also increase the traction on the slower wheels.

[0014] Advantageously, these techniques can thus improve the safety of the vehicle in cases of traction loss due to road conditions and different normal loads, friction, tire wear, etc.

[0015] Advantageously, the techniques disclosed herein are robust for differential lock engagement by monitoring wheel slip.

[0016] According to an embodiment, when the difference is greater than the modified slip target is set lower than the requested slip target of the vehicle engine speed controller.

[0017] According to an embodiment, when the difference does not exceed the preconfigured wheel speed offset, the modified slip target is set to be at most equal to the requested slip target.

[0018] Further advantages and advantageous features of the inventive concept are disclosed in the following description and the dependent claims.

[0019] In general, unless otherwise clearly defined herein, all terms used in the claims should be interpreted according to their ordinary meaning in the relevant technical field. All references to "an / the element, apparatus, component, member, module, step, etc." are to be construed openly as referring to at least one instance of the element, apparatus, component, member, module, step, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless expressly stated. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The inventive concept will now be described by way of example with reference to the accompanying drawings, in which:

[0021] Figure 1 shows the results of a test according to an example;

[0022] Figure 2 is a high-level block diagram of a complete control loop of a vehicle engine speed controller according to an embodiment;

[0023] Figure 3 is a flowchart of a method according to an embodiment;

[0024] Figure 4 schematically shows according to an embodiment ;

[0025] Figure 5 shows the results of the application of the embodiments disclosed herein;

[0026] Figure 6 is a schematic view of a vehicle according to an embodiment;

[0027] Figure 7 is a schematic view showing the functional units of a system according to an embodiment; and

[0028] Figure 8Shows an example of a computer program product including a computer-readable storage medium according to an embodiment. Detailed Description

[0029] The present inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the present inventive concept are shown. However, the present inventive concept may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the present inventive concept to those skilled in the art. Throughout this specification, the same numerals refer to the same elements. Any step or feature shown in dashed lines should be considered optional.

[0030] The problems solved by the present disclosure relate to situations where wheel speeds are different, such as the above-mentioned separated friction (or μ (mu)-separated) road conditions, as well as other road conditions, loads, tire wear, etc. Due to the mechanical function of an open differential, the wheel speeds between the right and left wheels of the same axle may rotate at different speeds. For the same reason, even when driving straight, due to road conditions and traction loss caused by different normal loads, friction, tire wear, etc., the wheel speeds of the wheels of the first drive axle may also be different from those of the wheels of the second drive axle.

[0031] As an illustrative example, for a given same output shaft speed (e.g., given by the average of all drive wheels), the wheel slip of one axle may become zero while all the torque is transferred to the other axle, and thus finally has a rather high slip value. This not only reduces traction but also poses a safety hazard, especially at higher speeds, because excessive longitudinal slip greatly reduces the lateral force capability.

[0032] Now refer to Figure 1 , which shows the results of tests conducted in a basalt area. The results shown are for a vehicle with two drive rear axles. The slip of the second rear axle (rear axle 2) is zero, while the slip of the first rear axle (rear axle 1) is 25 - 30%. The target on the output shaft is 15% and is perfectly controlled. The phenomenon that occurs after about 57.5 seconds is due to an upshift.

[0033] According to the present disclosure, in order to ensure that a vehicle with an open differential and multiple drive axles has optimal starting performance and traction in case of traction loss caused by road conditions and different normal loads, friction, tire wear, etc., the requested slip target modified slip target is replaced.

[0034] Figure 2 An advanced block diagram 200 showing the complete control loop of average wheel slip and a vehicle engine speed controller is presented, where the vehicle engine speed controller is represented by the engine speed controller block 260. By providing an engine speed limit to the engine speed controller block 260 the engine / motor speed is controlled to control the wheel slip. Traditionally, the engine speed limit is calculated in the converter block 250 based on the requested slip target provided by the calculator block 210 and the reference wheel speed However, according to the embodiments disclosed herein, the requested slip target is replaced by a modified slip target Furthermore, the modified slip target is based on a reduction factor This reduction factor is used to at least temporarily reduce the actual average slip (reduce wheel slip) by reducing the target speed used by the closed-loop controller The functions of each block 220 - 250 will be disclosed in connection with the reference Figure 3 The engine / motor controlled by the vehicle engine speed controller is not shown in Figure 2 and may be located at different positions along the driveline depending on the embodiment.

[0035] Figure 3 is a flowchart showing an embodiment of a method for determining a modified slip target for a vehicle engine speed controller The method is executed in a system 700. The system 700 implements at least Figure 2 the blocks 220, 230, 240, but may also implement any one or all of the remaining blocks 210, 250, 260. The method is advantageously provided in the form of a computer program.

[0036] The method is based on using the difference between the maximum wheel speed and the minimum wheel speed of an open differential and a drive axle controlled by a vehicle engine speed controller. Generally, the maximum wheel speed is determined by the following formula:

[0037]

[0038] and the minimum wheel speed is determined as:

[0039]

[0040] where are the open differential of the vehicle and the wheels of the drive axle wheel speeds.

[0041] The maximum wheel speed of the open differential and the wheels of the drive axle controlled by the vehicle engine speed controller and the minimum wheel speed between the difference and a preconfigured wheel speed offset are compared (step S102).

[0042] Based on the difference whether it exceeds the preconfigured wheel speed offset take different measures.

[0043] At least when the difference exceeds the preconfigured wheel speed offset the modified slip target is set (step S104) to be lower than the requested slip target of the vehicle engine speed controller .

[0044] Embodiments related to further details of determining the modified slip target of the vehicle engine speed controller will now be disclosed .

[0045] In some embodiments, when the difference is greater than the modified slip target is set (step S106) to be lower than the requested slip target of the vehicle engine speed controller .

[0046] In some embodiments, when the difference does not exceed the preconfigured wheel speed offset the modified slip target is set (step S108) to be at most equal to the requested slip target .

[0047] In some embodiments, relative to a reference wheel speed the modified slip target is converted (step S110) to an engine speed limit . In Figure 2 this operation is represented by the converter block 250.

[0048] In some embodiments, the wheel speeds of the open differential and the wheels of the drive axle are controlled (step S112) according to the engine speed limit . In Figure 2In this case, this operation is represented by the engine speed controller block 260.

[0049] Next, additional aspects of the modified slip target will be disclosed.

[0050] The modified slip target can be mathematically related to the requested slip target . Since , the modified slip target can thus be related to the requested slip target by using a reduction factor . Specifically, in some embodiments, the modified slip target is determined as:

[0051]

[0052] where is the reduction factor. In Figure 2 , this operation is represented by calculator block 240, where is the modified reduction factor, which, as will be disclosed below, has replaced .

[0053] The reduction factor is a function of the difference and a preconfigured wheel speed offset . In some examples, the reduction factor is determined according to:

[0054]

[0055] where is the offset value, where and are constants, and where . In Figure 2 , this operation is represented by calculator block 220.

[0056] In some examples, . In some examples, , and .

[0057] The offset value can be used for offset compensation to avoid the reduction factor from changing at very small speed differences .

[0058] Figure 4 is schematically shown, where: ​

[0059]

[0060] Next, the offset value will be disclosed for additional aspects.

[0061] In the case of the condition (as in S104) needs to be satisfied in order to make any compensation for the requested slip target That is to say, for an example where , where and where it can be obtained that:

[0062]

[0063] In the case of the condition needs to be satisfied in order to make any compensation for the requested slip target That is to say, for an example where , where and where it can be obtained that:

[0064]

[0065] On the other hand. In the case of the condition (as in S106) needs to be satisfied in order to make any compensation for the requested slip target That is to say, for an example where , where and where it can be obtained that:

[0066]

[0067] Therefore, the offset value acts as a hysteresis component or filter. It should be noted here that the offset value can take other values except .

[0068] In the case of no compensation will be made for the requested slip target for the speed change up to ). On the other hand, in the case of any very small change in the wheel speed (i.e. when ) will result in compensating for the requested slip target for compensation.

[0069] According to the first numerical example, assume , , , and [km / h]. Then, and the compensation factor are as disclosed in Table 1.

[0070]

[0071] Table 1: Values of the first numerical example

[0072] According to the second numerical example, assume , , , and [km / h]. Then, and the compensation factor are as disclosed in Table 2.

[0073]

[0074] Table 2: Values of the second numerical example

[0075] By monitoring the wheel speeds on the open differential and the drive axle , the reduction factor can be calculated based on the wheel speed offset . When the maximum speed difference between the wheels (given by ) reaches the value , the maximum reduction factor in the above formula becomes (assuming and ). This results in the modified slip target being equal to half of the requested slip target . That is:

[0076]

[0077] The modified slip target is sent to the wheel slip controller.

[0078] In some examples, the slip target is allowed to decrease immediately, but can only increase gradually. Specifically, in some embodiments, the reduction factor is restricted to vary differently over time, depending on whether the difference increases or decreases over time. In this regard, if the difference increases over time, then , where is a reduction factor is the time derivative of. Similarly, if the difference decreases over time, then . Specifically, in some examples, the reduction factor is limited to changing over time at most at a rate of change , and the rate of change is limited to:

[0079]

[0080] Thus, where describes the degree to which the reduction factor changes over time, and where is a constant. Thus, in some examples, the value used in calculating the modified slip target is replaced by , where depends on and . In Figure 2 , this operation is represented by the calculator block 230.

[0081] Thus, the preconfigured wheel speed offset acts as a proportional control term, while the rate limit defined by the rate of change imitates human driver behavior. For example, when the slip suddenly increases, the driver may release the accelerator pedal and then carefully depress the accelerator pedal because the slip seems to be under control (since the actual friction level is rather unknown and has proven to be unreliably high because the wheel was just slipping).

[0082] Figure 5 shows the results of the application of the embodiments disclosed herein. Figure 5 (a) shows the wheel speed of the right rear wheel of a rear axle and the wheel speed of the left rear wheel of the same rear axle as well as the reference wheel speed Figure 5 (b) shows that the requested slip target is replaced by the modified slip target , and the modified slip target rather than the requested slip target is sent to the closed-loop vehicle engine speed controller. Given that one or more wheels (specifically the right rear wheel in this example) are slipping, the modified slip target differs from the requested slip target is reduced as compared with.

[0083] The system 700 disclosed herein is applicable to vehicles, such as heavy vehicles. Figure 6 Vehicle 600 including the system 700 disclosed herein is schematically shown. In some embodiments, vehicle 600 is a heavy vehicle. In this regard, the inventive concept is applicable to different types of heavy vehicles, such as but not limited to trucks, buses, and construction equipment. In addition, the present disclosure presents a method for controlling wheel speed by output shaft speed and is applicable to all types of powertrains, electric powertrains, or conventional powertrains with multiple drive axles.

[0084] Figure 7 The components of system 700 according to an embodiment are schematically shown in terms of several functional units. As described above, system 700 at least implements Figure 2 blocks 220, 230, 240 therein, but may also implement the remaining blocks 210, 250, 260. Processing circuitry 710 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc. capable of executing software instructions, the software instructions being stored in a computer program product 810 in the form of, for example, a storage medium 730 (such as Figure 8 as in). Processing circuitry 710 may further be provided as at least one application specific integrated circuit (ASIC) or field programmable gate array (FPGA).

[0085] In particular, processing circuitry 710 is configured to cause system 700 to perform a set of operations or steps disclosed as above. For example, storage medium 730 may store the set of operations, and processing circuitry 710 may be configured to retrieve the set of operations from storage medium 730 to cause system 700 to perform the set of operations. The set of operations may be provided as a set of executable instructions.

[0086] Thus, processing circuitry 710 is thereby arranged to perform the method as disclosed herein. Storage medium 730 may further include a persistent storage device, which may be, for example, any one or combination of a magnetic memory, an optical memory, a solid state memory, or even a remotely mounted memory. System 700 may further include an interface 720 at least configured to communicate with other functions, nodes, and devices. Processing circuitry 710 controls the general operation of system 700, for example, by sending data and control signals to interface 720 and storage medium 730, by receiving data and reports from interface 720, and by retrieving data and instructions from storage medium 730. Other components of system 700 and related functionality are omitted so as not to obscure the concepts presented herein.

[0087] Figure 8 An example of a computer program product 810 including a computer-readable storage medium 830 is shown. On the computer-readable storage medium 830, a computer program 820 can be stored, and the computer program 820 can cause a processing circuit 710 and entities and devices operatively coupled thereto, such as an interface 720 and a storage medium 730, to perform a method according to the embodiments described herein. Thus, the computer program 820 and / or the computer program product 810 can provide means for performing any of the steps disclosed herein.

[0088] In Figure 8 the example, the computer program product 810 is shown as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-ray disc. The computer program product 810 can also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM) or an electrically erasable programmable read-only memory (EEPROM), and more particularly embodied as a non-volatile storage medium in an external memory of a device, such as a USB (universal serial bus) memory or a flash memory, such as a compact flash memory. Thus, although the computer program 820 is schematically shown herein as tracks on the depicted optical disc, the computer program 820 can be stored in any manner suitable for the computer program product 810.

[0089] 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 can be made within the scope of the appended claims.

Claims

1. A method for determining a modified slip target μ of a vehicle engine speed controller trgt comprising: The difference between the maximum wheel speed ω of the open differential and the wheels of the drive axle controlled by the vehicle engine speed controller max and the minimum wheel speed ω min is compared with a preconfigured wheel speed offset ΔS (S102); and At least when the difference ω max -ω min exceeds the preconfigured wheel speed offset ΔS, the modified slip target μ trgt is set (S104) to be lower than the requested slip target μ of the vehicle engine speed controller req , where the modified slip target is determined as: μ trgt = μ req / K where K≥1 is a reduction factor, and where the reduction factor K is a function of the difference ω max -ω min and the preconfigured wheel speed offset ΔS.

2. The method according to claim 1, wherein the method further comprises: When the difference ω max -ω min is greater than 0, set (S106) the modified slip target μ trgt to be lower than the requested slip target μ of the vehicle engine speed controller req .

3. The method according to claim 1 or 2, wherein the method further comprises: When the difference ω max -ω min does not exceed the preconfigured wheel speed offset ΔS, the modified slip target μ trgt is set (S108) to be at most equal to the requested slip target μ reg .

4. The method according to claim 1 or 2, wherein the reduction factor K is determined according to the following: where θ is an offset value, where c1 and c2 are constants, and where 1 ≤ c1 < c2.

5. The method according to claim 4, wherein c2 ≤ 2.

6. The method according to claim 1 or 2, wherein the reduction factor K is restricted to vary differently over time, depending on the difference ω max -ω min whether it increases or decreases over time.

7. The method according to claim 1 or 2, wherein the reduction factor K is restricted to change at most at a rate of change r over time, the rate of change being restricted to: Therefore, where the degree of change of the reduction factor K over time is described, and where K RtLim <0 is a constant.

8. The method according to claim 1 or 2, wherein the maximum wheel speed ω max is determined as: ω max = max(ω1, ω2, ω3,...) and said minimum wheel speed ω min is determined as: ω min = min(ω1, ω2, ω3,...) where ω i is the wheel speed of the open differential of the vehicle and wheel i of the drive axle.

9. The method according to claim 1 or 2, wherein the method further comprises: Relative to the reference wheel speed ω ref , convert the modified slip target μ trgt to the engine speed limit v (S110). lim .

10. The method according to claim 9, wherein the method further comprises: According to the engine speed limit v lim to control (S112) the wheel speeds of the wheels of the open differential and the drive axle.

11. A system (700) for determining a modified slip target μ for a vehicle engine speed controller, the system (700) including processing circuitry configured to cause the system (700) to: trgt ​ Compare the difference between the maximum wheel speed ω max and the minimum wheel speed ω min of the wheels of the open differential and the drive axle controlled by the vehicle engine speed controller with a pre-configured wheel speed offset ΔS; and At least when the difference ω max -ω min exceeds the preconfigured wheel speed offset ΔS, the modified slip target μ trgt is set lower than the requested slip target μ of the vehicle engine speed controller req , where the modified slip target is determined as: μ trgt = μ req / K where K≥1 is a reduction factor, and where said reduction factor K is a function of said difference ω max -ω min and said preconfigured wheel speed offset ΔS.

12. The system (700) according to claim 11, wherein the processing circuit is configured to cause the system (700) to: When the difference ω max -ω min is greater than 0, set the modified slip target μ trgt to be lower than the requested slip target μ of the vehicle engine speed controller req .

13. The system (700) according to claim 11 or 12, wherein the processing circuit is configured to cause the system (700) to: When the difference ω max -ω min does not exceed the preconfigured wheel speed offset ΔS, the modified slip target μ trgt is set to be at most equal to the requested slip target μ req .

14. The system (700) according to claim 11 or 12, wherein the processing circuit is configured to cause the system (700) to: Relative to the reference wheel speed ω ref , convert the modified slip target μ trgt to the engine speed limit v lim .

15. The system (700) according to claim 14, wherein the processing circuit is configured to cause the system (700) to: Based on the engine speed limit v lim to control the wheel speeds of the wheels of the open differential and the drive axle.

16. A vehicle comprising the system (700) according to any one of claims 11 to 15.

17. A computer program product for determining a modified slip target μ for a vehicle engine speed controller trgt comprising computer program code which, when run on a processing circuit of a system (700), causes the system (700) to: The difference between the maximum wheel speed ω of the open differential and the wheels of the drive axle controlled by the vehicle engine speed controller and the minimum wheel speed ω is compared with a preconfigured wheel speed offset ΔS (S102); and max and the minimum wheel speed ω min is compared with a preconfigured wheel speed offset ΔS (S102); and At least when the difference ω max -ω min exceeds the preconfigured wheel speed offset ΔS, the modified slip target μ trgt is set (S104) to be lower than the requested slip target μ of the vehicle engine speed controller req , where the modified slip target is determined as: μ trgt = μ req / K where K≥1 is a reduction factor, and where the reduction factor K is a function of the difference ω max -ω min and the preconfigured wheel speed offset ΔS.

18. A computer-readable storage medium storing computer program code of the computer program product according to claim 17.

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