Patent Publication Number: US-2023158890-A1

Title: Vehicle control device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a vehicle control device configured to execute control for preventing burn-in of a differential device. 
     BACKGROUND ART 
     In the related art, a technique for preventing occurrence of burn-in due to an increase in a differential rotation speed in a vehicle in which a differential device is interposed between left and right wheels of the vehicle has been proposed. For example, there is known a technique of reducing the differential rotation speed by setting a supply current to a motor to zero or reversely rotating the motor when the differential rotation speed (a rotation speed difference) between left and right wheel shafts is equal to or higher than a predetermined value. By this control, burn-in of the differential device can be prevented (see Patent Literature  1 ). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP5379541B 
     SUMMARY OF INVENTION 
     Technical Problem 
     Generally, an average value of rotation speeds (the numbers of revolutions) of the left and right wheels distributed by the differential device coincides with a rotation speed (an input rotation speed) input to the differential device. Therefore, by measuring at least two types of rotation speeds among the rotation speed of the left wheel, the rotation speed of the right wheel, and the input rotation speed, the differential rotation speed of the differential device can be obtained. On the other hand, when wheel speed sensors that measure the rotation speeds of the left and right wheels fails, it is difficult to obtain an appropriate differential rotation speed, and it may not be possible to prevent the occurrence of burn-in. 
     The present disclosure is made in view of the above-described circumstances, and an object of the present disclosure is to provide a vehicle control device that can prevent burn-in of a differential device when a wheel speed sensor fails. The present disclosure is not limited to having this object, and can have another object of attaining functions and effects that are derived from configurations shown in the “description of embodiments” to be described later and that cannot be attained with a related-art technique. 
     Solution to Problem 
     A vehicle control device of the present disclosure includes: a drive source mounted on a vehicle; a differential device configured to distribute a driving force generated by the drive source to a right drive wheel and a left drive wheel; a speed sensor configured to detect a rotation speed of the drive source; and a pair of wheel speed sensors configured to detect rotation speeds of the right drive wheel and the left drive wheel. The vehicle control device further includes a control device configured to set an index value having a value obtained by multiplying the rotation speed of the drive source by a predetermined coefficient in a case that at least one of the pair of wheel speed sensors fails, and to control torque output from the drive source based on the index value. 
     Advantageous Effects of Invention 
     According to the technique of the present disclosure, it is possible to prevent burn-in of a differential device when a wheel speed sensor fails. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic view of a vehicle to which a vehicle control device according to an embodiment is applied. 
         FIG.  2    is a block diagram showing a configuration of a control device (ECU) in  FIG.  1   . 
         FIG.  3    is a block diagram showing a processing content of the control device in  FIG.  1   . 
         FIG.  4 A  is an example of a map stored in the control device in  FIG.  1   , and is a map that defines a relationship between a rotation speed difference (an index value) in a front wheel differential device and a torque limit value of a front wheel motor. 
         FIG.  4 B  is an example of a map stored in the control device in  FIG.  1   , and is a map that defines a relationship between a rotation speed difference (an index value) in a rear wheel differential device and a torque limit value of a rear wheel motor. 
         FIG.  5    is a flowchart showing a flow of control executed by the control device in  FIG.  1   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     [1. Configuration] 
     A vehicle  1  to which a vehicle control device according to an embodiment is applied will be described with reference to  FIGS.  1  to  5   . A motor  2  and a differential device  3  are mounted on the vehicle  1 . The motor  2  is a driving source of the vehicle  1  configured to generate a driving force of the vehicle  1  using electric power stored in a battery  6 . The motor  2  is, for example, a three-phase alternating current synchronous motor, and is connected to the battery  6  via an inverter  5 . A front wheel motor  2  (a front motor) and a rear wheel motor  2  (a rear motor) are separately mounted on the vehicle  1  shown in  FIG.  1   . However, either one of the front wheel motor  2  and the rear wheel motor  2  may be omitted, or a single motor  2  may drive four wheels. 
     The differential device  3  is a device configured to distribute a driving force generated by the motor  2  to left and right driving wheels, and is interposed between a left wheel shaft and a right wheel shaft. A transmission  4  is interposed in a transmission path of the driving force that connects the motor  2  and the differential device  3 . The transmission  4  is a device configured to change (decrease or increase) the driving force output from the motor  2 , and includes, for example, a plurality of gear trains, a planetary gear mechanism, and the like. A gear ratio (that is, input rotation speed÷output rotation speed), which is a ratio of an input rotation speed to an output rotation speed of the transmission  4 , may be a fixed value or a variable value. The information on the gear ratio of the transmission  4  is grasped by a control device  10  (ECU) to be described later. 
     The battery  6  is, for example, a lithium ion battery or a nickel hydrogen battery, and is a secondary battery capable of supplying a high-voltage DC current of several hundred volts. The inverter  5  is a power conversion device configured to convert DC power on a battery  6  side and AC power on a motor  2  side, and is interposed on a power line that connects the battery  6  and the motor  2 . An inverter circuit including a switching element such as an Insulated Gate Bipolar Transistor (IGBT) or a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is provided in the inverter  5 . An output (torque) of the motor  2  is controlled by controlling an operating state (an on and off timing and a driving frequency) of the inverter  5 . 
     The operating state of the inverter  5  is controlled by the control device  10 . The control device  10  is an electronic control device (a computer) configured to control torque output from the motor  2  by managing on and off state of the switch element provided in the inverter  5 . As shown in  FIG.  2   , a processor (a central processing unit), a memory (a main memory), a storage device (a storage), an interface device, and the like are provided in the control device  10 , and are communicably connected to one another via an internal bus. A motor speed sensor  7 , a right wheel speed sensor  8 , and a left wheel speed sensor  9  are connected to the control device  10 , and a vehicle speed sensor and an accelerator opening degree sensor (not shown) are also connected to the control device  10 . 
     The motor speed sensor  7  is a speed sensor configured to detect a motor rotation speed (a rotation speed output from the motor  2 ). The right wheel speed sensor  8  is a wheel speed sensor configured to detect a rotation speed (a right wheel speed) of a drive wheel on a right side with respect to the differential device  3 , and the left wheel speed sensor  9  is a wheel speed sensor configured to detect a rotation speed (a left wheel speed) of a drive wheel on a left side with respect to the differential device  3 . Various types of information on the rotation speeds detected by these sensors  7  to  9  are input to the control device  10 . The vehicle speed sensor is a sensor configured to detect a traveling speed (a vehicle speed) of the vehicle  1 , and the accelerator opening degree sensor is a sensor configured to detect a depression amount (an accelerator opening degree) of an accelerator pedal. In  FIG.  1   , the sensors  7  to  9  are provided on a front side and a rear side, and any one of the sensors  7  to  9  may be omitted. 
     A magnitude of the torque output from the motor  2  is set according to the vehicle speed and the accelerator opening degree. On the other hand, depending on a traveling state of the vehicle  1 , the torque of the motor  2  may become excessive. For example, when a difference between the rotation speeds of the left and right drive wheels becomes large, burn-in may occur inside the differential device  3 . Therefore, the control device  10  sets a torque limit value of the motor  2 , and controls the inverter  5  such that the torque actually output from the motor  2  does not exceed the torque limit value. In the vehicle  1  shown in  FIG.  1   , the output of each of the front wheel motor  2  and the rear wheel motor  2  is controlled based on the torque limit value individually set for each of the front wheel motor  2  and the rear wheel motor  2 . 
       FIG.  3    is a block diagram showing a processing content for setting the torque limit value. The torque limit value is set using different methods depending on whether the wheel speed sensors  8 ,  9  fail or not. For example, in a case in which the pair of wheel speed sensors  8 ,  9  provided on left and right sides of the same differential device  3  do not fail, the torque limit value is set based on a rotation speed difference between the left and right drive wheels. On the other hand, in a case that at least one of the pair of wheel speed sensors  8 ,  9  provided on the left and right sides of the same differential device  3  has failed, the torque limit value is set based on the motor rotation speed. The former setting method corresponds to a processing content shown in a lower part in  FIG.  3   , and the latter setting method corresponds to a processing content shown in an upper part in  FIG.  3   . The presence or absence of a failure in the wheel speed sensors  8 ,  9  may be determined based on a signal transmitted from the wheel speed sensors  8 ,  9 , or a determination result obtained by a failure determination device (not shown) may be used. 
     Here, a setting method in a case that at least one of the pair of wheel speed sensors  8 ,  9  has failed will be described in detail. A divider  11  shown in  FIG.  3    calculates a value (a value obtained by multiplying a reciprocal of the gear ratio of the transmission  4 ) obtained by dividing the motor rotation speed by the gear ratio of the transmission  4 . The value calculated here corresponds to the rotation speed output from the transmission  4 , in other words, corresponds to the rotation speed input to the differential device  3 . The value calculated by the divider  11  is input to a multiplier  13  after a sign has been removed through an absolute value calculator  12 . The multiplier  13  calculates an index value obtained by multiplying the input value by a predetermined coefficient. A value of the coefficient is set to a value (for example, within a range of 1.9 to 2.1) close to 2. This value of the coefficient is preferably set to a value of 2 or more (for example, within a range of 2.0 to 2.1), and more preferably set to 2. The value calculated by the multiplier  13  is input to a multiplier  14 . 
     The multiplier  14  is configured to calculate a product of the value calculated by the multiplier  13  and an output of a failure determiner  15 . The failure determiner  15  is configured to output  1  in a case that at least one of the pair of wheel speed sensors  8 ,  9  has failed, and to output  0  in a case that neither of the pair of wheel speed sensors  8 ,  9  has failed. Therefore, in a case that neither of the pair of wheel speed sensors  8 ,  9  has failed, an output of the multiplier  14  becomes  0  regardless of a magnitude of an output of the multiplier  13 . Only in a case that at least one of the pair of wheel speed sensors  8 ,  9  has failed, the output of the multiplier  13  is output from the multiplier  14  as it is. In this way, in a case that at least one of the pair of wheel speed sensors  8 ,  9  has failed, the multiplier  14  functions to set an index value having a value obtained by multiplying the motor rotation speed by the predetermined coefficient. The value calculated by the multiplier  14  is transmitted to an adder  20 . 
     Next, a setting method in a case that neither of the pair of wheel speed sensors  8 ,  9  has failed will be described in detail. A subtractor  17  shown in  FIG.  3    is configured to calculate a value (a value obtained by adding a left wheel speed and a complement of a right wheel speed) obtained by subtracting the right wheel speed from the left wheel speed. The value calculated here corresponds to a rotation speed difference between left and right sides of the differential device  3 . The value calculated by the subtractor  17  is input to a multiplier  19  after a sign has been removed through an absolute value calculator  18 . The multiplier  19  is configured to output a product of an output of the absolute value calculator  18  and an output of a subtractor  16 . The subtractor  16  is configured to output a value obtained by inverting the output of the failure determiner  15 . 
     For example, the subtractor  16  outputs  1  when the failure determiner  15  outputs  0 , and outputs  0  when the failure determiner  15  outputs  1 . Therefore, in a case that at least one of the pair of wheel speed sensors  8 ,  9  has failed, an output of the multiplier  19  becomes  0  regardless of a magnitude of the output of the absolute value calculator  18 . Only in a case that neither of the pair of wheel speed sensors  8 ,  9  has failed, the output of the absolute value calculator  18  is output from the multiplier  19  as it is. In this way, the multiplier  19  functions to calculate the rotation speed difference between the left and right drive wheels in a case that the pair of wheel speed sensors  8 ,  9  do not fail. A value calculated by the multiplier  19  is transmitted to the adder  20 . 
     The adder  20  is configured to calculate a sum of the output of the multiplier  14  and the output of the multiplier  19 . The output of the multiplier  14  is 0 in a case that the pair of wheel speed sensors  8 ,  9  do not fail, and the output of the multiplier  19  is 0 in a case that the pair of wheel speed sensors  8 ,  9  have failed. Therefore, the adder  20  functions to receive one of the multipliers  14 ,  19  that outputs a value other than 0 as it is, and to transfer this information downstream. A value output from the adder  20  is input to a limit value setter  21 . The limit value setter  21  is configured to output a torque limit value corresponding to a value (an index value or a rotation speed difference) transmitted from the adder  20 . In the limit value setter  21 , at least a map or a mathematical formula that defines a correspondence relationship between the index value and the torque limit value set by the multiplier  14  is stored in advance. 
       FIG.  4 A  is a graph illustrating a relationship between a torque limit value and an index value in the front wheel motor  2 . A solid line in the graph represents the torque limit value, and a broken line represents torque at which burn-in may occur in the front wheel differential device  3 . The graph of the broken line shows a relationship in which the torque on a vertical axis is substantially inversely proportional to the index value on a horizontal axis.  FIG.  4 B  is a graph illustrating a relationship between a torque limit value and an index value in the rear wheel motor  2 . A solid line in the graph represents the torque limit value, and a broken line represents torque at which burn-in may occur in the rear wheel differential device  3 . 
     The rear wheel motor  2  and the rear wheel differential device  3  are provided separately from the front wheel motor  2  and the front wheel differential device  3 , and do not necessarily have the same characteristics as those of the front wheel motor  2  and the front wheel differential device  3 . Therefore, the torque limit value of the rear wheel motor  2  can be set separately from the torque limit value of the front wheel motor  2 . Shapes of the solid line graph and the broken line graph in  FIG.  4 B  do not necessarily match shapes of the solid line graph and the broken line graph in  FIG.  4 A . A maximum value T 2  of the torque limit value in  FIG.  4 B  is different from a maximum value T 1  of the torque limit value in  FIG.  4 A . Similarly, a maximum value R 2  of the index value in  FIG.  4 B  is different from a maximum value R 1  of the index value in  FIG.  4 A . 
     In both  FIGS.  4 A and  4 B , the graph of the torque limit value indicated by the solid line is set to be lower (at a left side) with respect to at least the graph of the broken line. Therefore, when the rotation speed difference is input to the limit value setter  21 , the torque limit value corresponding to the rotation speed difference is set. Accordingly, a situation is prevented in which excessive torque is output from the motor  2 , and the occurrence of burn-in in the differential device  3  is prevented. When an index value is input to the limit value setter  21 , the index value has a value corresponding to a rotation speed approximately twice the rotation speed of the motor  2 . On the other hand, it is known that the rotation speed difference that may be generated in the differential device  3  is twice the input rotation speed at maximum. That is, the index value referred to here has a value corresponding to the maximum rotation speed difference that may be generated in the differential device  3 . Therefore, the torque limit value is set using the index value instead of the rotation speed difference, so that the situation is prevented in which the excessive torque is output from the motor  2 , and the occurrence of burn-in in the differential device  3  is prevented. 
     [2. Flowchart] 
       FIG.  5    is a flowchart showing a flow of control executed by the control device  10 . 
     In step A 1 , information on the motor rotation speed detected by the motor speed sensor  7  and information on the left and right wheel speeds detected by the pair of left and right wheel speed sensors  8 ,  9  are input to the control device  10 . When the gear ratio of the transmission  4  is variable, information on a value of the gear ratio is also input to the control device  10 . In the subsequent step A 2 , it is determined whether at least one of the pair of wheel speed sensors  8 ,  9  has failed. As shown in  FIG.  1   , when the pair of left and right wheel speed sensors  8 ,  9  are provided on a front wheel side and a rear wheel side, respectively, the front wheel side and the rear wheel side are distinguished from each other, and the presence or absence of a failure is determined independently of each other. 
     When it is determined in step A 2  that at least one of the wheel speed sensors  8 ,  9  has failed, the process proceeds to step A 3 , and the index value is set based on the motor rotation speed. The index value is calculated by, for example, multiplying an absolute value of a value obtained by dividing the motor rotation speed by the gear ratio of the transmission  4  by a predetermined coefficient. In the subsequent step A 4 , an index value is used as an argument of the map shown in  FIGS.  4 A and  4 B , and the torque limit value corresponding to the index value is acquired. Thereafter, in step A 5 , an operation state of the inverter  5  is controlled such that the torque of the motor  2  does not exceed the torque limit value. In this way, even if the wheel speed sensors  8 ,  9  have failed, since the torque of the motor  2  is appropriately limited, the occurrence of burn-in in the differential device  3  is prevented. 
     When it is determined in step A 2  that neither of the wheel speed sensors  8 ,  9  has failed, the process proceeds to step A 6 , and the actual rotation speed difference is calculated. The rotation speed difference is calculated as, for example, an absolute value of a value obtained by subtracting the right wheel speed from the left wheel speed. In the subsequent step A 7 , the rotation speed difference is used as the argument of the map shown in  FIGS.  4 A and  4 B , and the torque limit value corresponding to the rotation speed difference is acquired. Thereafter, in step A 5 , the operation state of the inverter  5  is controlled such that the torque of the motor  2  does not exceed the torque limit value. In this way, in a case that the wheel speed sensors  8 ,  9  do not fail, a value of the rotation speed difference is accurately calculated. Therefore, the torque of the motor  2  is appropriately limited, and the occurrence of burn-in in the differential device  3  is prevented. 
     [3. Operation and Effect] 
     (1) The above-described vehicle control device includes: a motor  2  mounted on a vehicle  1 ; a differential device  3  configured to distribute a driving force generated by the motor  2  to left and right drive wheels; a motor speed sensor  7  configured to detect a rotation speed of the motor  2 ; and a pair of wheel speed sensors  8 ,  9  configured to detect rotation speeds of the left and right drive wheels. Further, the above-described vehicle control device is provided with a control device  10  configured to set an index value having a value obtained by multiplying a rotation speed of the motor  2  by a predetermined coefficient in a case that at least one of the pair of wheel speed sensors  8 ,  9  has failed, and to control torque output from the motor  2  based on the index value. According to this configuration, the torque of the motor  2  can be limited without using information obtained by the wheel speed sensors  8 ,  9 , and burn-in of the differential device  3  during the failure of the wheel speed sensors  8 ,  9  can be prevented. 
     (2) In the above-described vehicle control device, the index value set in a case that at least one of the pair of wheel speed sensors  8 ,  9  has failed is set to have, for example, a value twice or more a rotation speed input to the differential device  3 . Accordingly, the index value can be set to a value (or a value equal to or higher than the value) corresponding to the maximum rotation speed difference that may be generated in at least the differential device  3 . Therefore, it is possible to reliably prevent the occurrence of burn-in in the differential device  3 . 
     (3) As shown in  FIG.  3   , the predetermined coefficient is set to  2 , so that the index value is set to have a value twice a value obtained by dividing the motor rotation speed by a gear ratio. According to this setting, the index value is a value corresponding to the maximum rotation speed difference that may be generated in the differential device  3 , and the occurrence of burn-in in the differential device  3  can be prevented most efficiently and reliably. In consideration of the presence of a control error, a calculation error, or the like, it is also possible to recognize the technical significance of setting the value of the predetermined coefficient to be slightly shifted from  2 . 
     (4) In the above-described vehicle control device, as shown in  FIGS.  4 A and  4 B , a map that defines a relationship between the index value and the torque limit value is used. Torque output from the motor  2  is controlled in a manner of not exceeding the torque limit value of a magnitude corresponding to the index value using this map, so that a situation can be easily avoided in which excessive torque is input to the differential device  3 . Further, the relationship between the index value and the torque limit value is mapped, so that the value of the torque limit value can be obtained quickly and easily, and a calculation load can be reduced. Therefore, for example, it is possible to prevent the occurrence of burn-in due to a control delay of the motor  2 . 
     (5) In the above-described vehicle control device, in a case that the pair of wheel speed sensors  8 ,  9  do not fail, a rotation speed difference between the left and right drive wheels is calculated. Further, the torque limit value is acquired by substituting the rotation speed difference into the map instead of the index value. According to this control configuration, as shown in  FIGS.  4 A and  4 B , it is only necessary to prepare a single map for one motor  2 , and it is not necessary to add a new control map. Therefore, a control resource can be saved, and the occurrence of burn-in can be efficiently prevented. 
     [4. Modification] 
     The above-described embodiment is merely an example, and is not intended to exclude various modifications and application of techniques not explicitly described in the present embodiment. The configurations according to the present embodiment can be variously modified without departing from the gist thereof. Further, the configurations can be selected or discarded as necessary, or can be combined as appropriate. 
     For example, in the above-described embodiment, the motor  2  is used as a drive source of the vehicle  1 . Alternatively, the above-described vehicle control device may be applied to a hybrid vehicle in which the motor  2  and an engine (an internal combustion engine such as a gasoline engine or a diesel engine) are used in combination. The above-described vehicle control device may be applied to an automobile in which only the engine is used as a drive source of the vehicle  1 . Alternatively, the above-described vehicle control device may be applied to a vehicle in which a motor generator (a device having both a function of an electric motor and a function of a generator) is used as the drive source instead of the motor  2 . At least an index value having a value obtained by multiplying a rotation speed of the drive source by a predetermined coefficient is set, and torque output from the drive source is controlled based on the index value, so that the same effects as those according to the above-described embodiment are attained. 
     This application is based on Japanese Patent Application No. 2020-095235, filed on Jun. 1, 2020, the contents of which are incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     According to the vehicle control device in the present disclosure, it is possible to prevent burn-in of a differential device in a case that a wheel speed sensor fails. 
     REFERENCE SIGNS LIST 
       1  vehicle 
       2  motor (drive source) 
       3  differential device 
       4  transmission 
       5  inverter 
       6  battery 
       7  motor speed sensor (speed sensor) 
       8  right wheel speed sensor (wheel speed sensor) 
       9  left wheel speed sensor (wheel speed sensor) 
       10  control device (electronic control device) 
       11  divider 
       12  absolute value calculator 
       13  multiplier 
       14  multiplier 
       15  failure determiner 
       16  subtractor 
       17  subtractor 
       18  absolute value calculator 
       19  multiplier 
       20  adder 
       21  limit value setter