JP2010074996A - Current limiting device, electromagnetic clutch device, and driving force distribution arrangement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current limiting device capable of stably executing overload driving, with a simple configuration, without rasing a current output up to a use limit for current output blocking. <P>SOLUTION: An ECU sets a cooling time for cooling an output element heated under execution of overload driving, by decreasing an upper limit value Ilim of current limitation to a first value I1 corresponding to a rated current value from a second value I2 corresponding to the limit conduction value for a predetermined time Tx after execution of the overload driving. The ECU measures a continuation time t of overload driving. Based on the continuation time t, it calculates the time period for the cooling time, i.e., the predetermined time Tx. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a current limiting device, an electromagnetic clutch device, and a driving force distribution device.

  Conventionally, a torque coupling that can arbitrarily change its torque capacity (torque transmission capacity) based on the engagement force of an electromagnetic clutch provided in the middle of the drive system that transmits engine driving force to each wheel has been provided. There is a driving force distribution device. Then, the adjustment of the engagement force, that is, the change of the torque transmission capacity is performed by controlling the energization amount to the electromagnetic clutch (see, for example, Patent Document 1).

  By the way, in recent years, as the adoption of a wide range of vehicles progresses, the performance required for such a driving force distribution device has become higher. For example, when mounted on a large vehicle or a vehicle with a large output, higher torque transmission performance is required. On the other hand, when mounted on a small vehicle, downsizing and cost reduction are required.

  However, if the clutch is reinforced (for example, an increase in the number of clutches, etc.) in accordance with the required increase in torque transmission performance, the size of the apparatus will be increased and the manufacturing cost will be increased. By setting a plurality of specifications according to the performance, a great management cost is generated.

  In view of this, it is conceivable to secure the required torque transmission performance by increasing the drive current output to the electromagnetic clutch, instead of such a method of mechanically strengthening the clutch. That is, the engaging force of the electromagnetic clutch depends on the magnitude of the input drive current. The so-called rated current value is the maximum value that allows continuous energization. In any vehicle, the time during which the required torque transmission capacity actually peaks continues for a relatively short time.

In other words, the current output to the electromagnetic clutch still has room for enhancement that can respond to the required increase in torque transmission performance, and is used as a standard in normal usage methods such as rated current values. It is possible to execute drive current output exceeding the value, that is, overload drive. And about the problem of heat_generation | fever of the current output element (FET) etc. accompanying the output of the increased drive current, for example, by aiming at fail safe promptly using the current output interruption | blocking function as shown in patent document 2, for example. It is possible to deal with this.
JP 2004-340345 A JP 2003-324841 A

  However, although fail safe is achieved by the above prior art, the operation of the torque coupling is stopped by the interruption of the current output. In other words, once the use limit is reached, the function as the driving force distribution device is lost until recovery. And in order to avoid such a use limit itself, physical heat countermeasures such as increasing the capacity of the current output element or providing a heat radiating member such as a heat sink are factors that increase the manufacturing cost. In this respect, there was still room for improvement.

  The present invention has been made to solve the above-described problems, and its object is to stably perform overload driving without reaching the use limit where the current output should be cut off with a simple configuration. An object of the present invention is to provide a current limiting device, an electromagnetic clutch device, and a driving force distribution device.

  In order to solve the above problem, the invention according to claim 1 limits the output current to a predetermined upper limit value or less, and sets the duration of the output current exceeding a predetermined reference value that is equal to or less than the upper limit value. The gist of the invention is that the current limiting device reduces the upper limit for a predetermined time based on the duration after the output current becomes equal to or lower than a predetermined set value.

  That is, as described above, after the overload drive is performed, the current output element is cooled by reducing the upper limit value of the current limit, and the current output is set by appropriately setting the cooling time for reducing the upper limit value. The current output exceeding the reference value can be executed more stably without reaching the limit of use of the element.

  Here, in many cases, the function as the current limiting device is implemented in a current output device (ECU or the like) to which the current limitation is applied. However, the current output device must naturally execute a large number of high-immediate arithmetic processes related to the current function as its main function and the control of the object through the current output (for example, driving force distribution control). Don't be. Therefore, if the priority order is taken into consideration, it is desirable to make the calculation load related to the current limiting process, which can be called an additional function, as light as possible. Also, in an actual vehicle, the time during which the required torque transmission capacity reaches a peak is relatively short, so the setting of the cooling time is only a countermeasure when an exception occurs. Strong meaning. In other words, there is no particular advantage in strictly managing the predetermined time set as the cooling time. Although the duration of overload driving is extremely useful for estimating the degree of heat generated in the current output element due to the overload driving, the calculation load does not increase significantly.

  Therefore, according to the above configuration, it is possible to appropriately set the predetermined time as the cooling time to the extent that the calculation load is not increased. As a result, current output exceeding a predetermined reference value, that is, overload driving can be executed efficiently and stably.

The gist of the invention described in claim 2 is that, when the duration exceeds a set time, the upper limit value is reduced without waiting for the output current to fall below the set value. .
According to the above configuration, overheating of the current output element can be suppressed even in a situation where overload driving is sustained.

  The invention according to claim 3 monitors an average value of the values of the output current stored over a predetermined period, and reduces the upper limit value when the average value exceeds a predetermined threshold value. This is the gist.

  According to the above configuration, the current output element is limited to a state where heat generation is small, and the overload drive is allowed, so that the output of the drive current should be cut off due to overheating of the current output element, that is, the use limit. Without arriving, current output exceeding the reference value can be executed stably.

  According to a fourth aspect of the present invention, the reference value and the set value are values corresponding to a rated current value that allows continuous energization, and the upper limit value is reduced to the rated current value. The gist.

  That is, by setting the rated current at which continuous energization is allowed as the reference value and the set value, it is possible to accurately manage the heat generation and cooling of the current output element. As a result, it is possible to stably perform overload driving with a simple configuration without efficiently reaching the use limit of the current output element.

  The invention according to claim 5 is an electromagnetic clutch device capable of changing the engagement force generated by the clutch mechanism through the output of the drive current to the electromagnet, and the control means for outputting the drive current includes: The gist is that the current limiting device according to any one of Items 4 is provided.

  According to a sixth aspect of the present invention, there is provided a torque coupling in which a torque transmission capacity changes based on an engaging force of the electromagnetic clutch, and a control for controlling a driving force distribution through the torque coupling through an output of a driving current to the electromagnetic clutch. The control means is provided with the current limiting device according to any one of claims 1 to 4. The gist of the invention is a driving force distribution device.

  According to each of the above configurations, heat generation of the current output element can be efficiently managed without imposing an extra calculation load on the control means, and as a result, a current output exceeding a predetermined reference value more stably, That is, overload driving can be executed. In particular, the control means of the driving force distribution device is not only simple torque coupling control but also immediacy regarding control for realizing appropriate driving force distribution according to the running state of the vehicle, that is, driving force distribution control. A large number of high processing operations must be executed. Therefore, a more remarkable effect can be acquired by applying to such a thing.

  According to the present invention, there is provided a current limiting device, an electromagnetic clutch device, and a driving force distribution device capable of stably performing overload driving without reaching a use limit where current output should be cut off with a simple configuration. Can be provided.

Hereinafter, an embodiment in which the present invention is embodied in a driving force distribution device mounted on a four-wheel drive vehicle will be described with reference to the drawings.
As shown in FIG. 1, the vehicle 1 is a four-wheel drive vehicle based on a front wheel drive vehicle, and a pair of front axles 4 are connected to a transaxle 3 assembled on one side of the engine 2. Further, a propeller shaft 5 is connected to the transaxle 3 together with the front axles 4, and the propeller shaft 5 is connected to a pair of rear axles 8 via a rear differential 7. The driving force of the engine 2 is transmitted to the front wheels 6f through these front axles 4, and is also transmitted to the rear wheels 6r through the propeller shafts 5 and the respective rear axles 8.

  In other words, in the present embodiment, the transaxle 3, the front axle 4, the propeller shaft 5, the rear differential 7, and the rear axle 8 constitute a drive system that transmits the driving force of the engine 2 to each wheel (6f, 6r). Yes.

  In the present embodiment, a torque capacity that can be transmitted, that is, a torque transmission capacity, is set between the propeller shaft 5 and the rear differential 7 constituting the drive system as described above based on the engagement force of the clutch mechanism. A changeable torque coupling 9 is interposed, and the operation of the torque coupling 9 is controlled by an ECU 10 as control means.

Specifically, the torque coupling 9 of the present embodiment includes an electromagnetic clutch 12 whose frictional engagement force changes according to the amount of current supplied to the electromagnetic coil, and the driving force based on the frictional engagement force is propeller. Transmission from the shaft 5 to the rear differential 7 is performed. Then, the ECU 10 adjusts the friction engagement force of the electromagnetic clutch 12 through the output of the drive current, that is, changes the torque transmission capacity of the torque coupling 9, thereby distributing the driving force transmitted through the torque coupling 9. It is configured to control,
That is, in the present embodiment, the torque coupling 9 and the ECU 10 constitute a driving force distribution device. And the vehicle 1 of this embodiment changes the driving force transmitted from the propeller shaft 5 to the rear differential 7 by this driving force distribution device, so that the driving force between the front wheel 6f and the rear wheel 6r is changed. The distribution can be changed continuously.

  More specifically, the ECU 10 of the present embodiment is connected to a number of sensors such as an accelerator opening sensor 13, a brake sensor 14, and wheel speed sensors 15a to 15d, and the ECU 10 receives output signals from these sensors. Based on various state quantities of the vehicle, for example, accelerator opening, brake state, vehicle speed, wheel speed difference, and the like are detected. Then, the ECU 10 controls the drive current output to the torque coupling 9 (electromagnetic clutch 12) based on the detected vehicle state quantity, that is, executes drive force distribution control.

  Specifically, as shown in the flowchart of FIG. 2, when the ECU 10 acquires various state quantities of the vehicle (step 101), the actual current value of the drive current that is subsequently output to the torque coupling 9 (electromagnetic clutch 12). I is detected (step 102). Next, the ECU 10 calculates a current command value I *, which is a control target value, based on the detected various state quantities (step 103). A restriction process is executed (step 104). Then, a current feedback calculation is executed so that the detected actual current value I follows the current command value I * calculated in step 103 (or the current command value I ** after the current limiting process in step 104). (Step 105) Based on the calculation result, a drive current output (Step 106) for the torque coupling 9 (electromagnetic clutch 12) is executed.

(Current limit processing)
Next, the aspect of the current limiting process in this embodiment will be described.
FIG. 3 is an explanatory diagram illustrating an example of a current limiting process performed by the ECU 10 of the present embodiment, FIG. 4 is a flowchart illustrating the current limiting process, and FIG. 5 is a cooling determination process in the current limiting process. It is a flowchart which shows. Each process shown in the flowcharts of FIGS. 4 and 5 and FIG. 2 is executed at a predetermined calculation cycle.

  As described above, in the ECU 10 of this embodiment, in order to suppress overheating of the current output element (FET) that outputs a drive current to the torque coupling 9 (electromagnetic clutch 12), the value of the output drive current is set. A current limiting process is performed to limit the current value to a predetermined upper limit value Ilim or less (see FIG. 2, step 104).

  Specifically, in the present embodiment, two values (I1, I2) are set as the upper limit value Ilim in the current limiting process. Specifically, a so-called rated current value that is a maximum value that allows continuous energization is set as the first value I1, and a limit that allows only short-time energization is set as the second value I2. The energization value is set. In this case, the “rated current value” is a value determined by the specifications of the current output element, whereas the “limit energization value” is a value determined by experiment or simulation (for example, the rated current value). (About 1.5 times the value). And ECU10 of this embodiment becomes a structure which selects either of these two values (I1, I2) as upper limit Ilim according to the output state of the drive current, and performs the said current limiting process. Yes.

  More specifically, the ECU 10 of the present embodiment monitors the average value Iavr of the drive current output in the past, and calculates the moving average of the actual current value I detected in detail as needed. That is, the average value of the values stored in the past for the current value output in the past is monitored. When the average value Iavr exceeds a predetermined threshold value I0 (for example, about half of the rated current value), the first value I1 is set as the upper limit value Ilim, and the average value Iavr is equal to or less than the threshold value I0. The second value I2 is the upper limit value Ilim. That is, in this embodiment, when the average value Iavr of the drive current output in the past is equal to or less than the predetermined threshold value I0, the output of the drive current exceeding the rated current is allowed. Thus, the required torque transmission performance is ensured without increasing the size of the electromagnetic clutch 12 (the clutch mechanism).

  Specifically, for example, in the example shown in FIG. 3, during the period from time T0 to time T1, the average value Iavr of the drive current exceeds a predetermined threshold value I0 (Iavr> I0). The upper limit value Ilim is a first value I1 corresponding to the rated current value. That is, the section from time T0 to time T1 is an excess prohibition section in which the output of the drive current exceeding the rated current is prohibited.

  On the other hand, after the time T1, the average value Iavr of the drive current becomes equal to or less than the threshold value I0 (Iavr ≦ I0), and the current limit upper limit value Ilim is switched to the second value I2 corresponding to the limit energization value. It has been. That is, output of drive current exceeding the rated current is allowed in the section after time T1. In this example, from time T2 to time T3, calculation of the current command value I * exceeding the first value set as the reference value corresponding to the rated current value, that is, driving exceeding the rated current value Overload drive that outputs current is being executed.

  In addition, after such overload driving is performed, the ECU 10 of the present embodiment reduces the upper limit value Ilim of the current limit to the first value I1 for a predetermined time Tx. That is, in the present embodiment, the overload drive is executed by reducing the upper limit value Ilim of the current limit from the second value I2 corresponding to the limit energization value to the first value I1 corresponding to the rated current value. The cooling time for cooling the current output element that generates heat is set.

  Specifically, for example, in the example shown in FIG. 3, the current command value I * becomes the first value I1 corresponding to the rated current value at time T3, and overload driving is completed, so that time The predetermined time Tx up to T6 is a cooling section (cooling time) in which the upper limit value Ilim of the current limit is lowered to a first value I1 corresponding to the rated current value. Therefore, in this example, although the current command value I * exceeding the first value I1 is calculated in the section from time T4 to time T5, the current command value I ** limited by the current limit, that is, the above-mentioned Based on the first value I1, the output of drive current to the torque coupling 9 (electromagnetic clutch 12) is executed. In the section after the time T6 after the predetermined time Tx has elapsed, the upper limit value Ilim of the current limit is raised to the second value I2 on the condition that the average value Iavr of the drive current is not more than the threshold value I0. Thereafter, at time T7, the current command value I * exceeding the first value I1 corresponding to the standard current value is generated again, that is, overload driving is started.

  Here, in this embodiment, when the upper limit value Ilim of the current limit is raised to a second value I2 corresponding to the limit energization value, the ECU 10 corresponds to the rated current value set as the reference value. The duration t during which the output of the drive current exceeding the first value I1 is executed is measured. More specifically, the ECU 10 of the present embodiment first calculates the current command value I * from the time when the current command value I * exceeding the first value I1 is calculated (see FIG. 3, time T2). The time until the point of time when I1 or less (see the figure, time T3) is measured, and this is defined as the overload drive duration t during which the output of the drive current exceeding the first value I1 is executed. Then, based on the measured duration t, a predetermined time Tx set as the cooling time is determined. In the present embodiment, the correspondence between a plurality of times (for example, 10 seconds, 30 seconds, 50 seconds, etc.) preset as the predetermined time Tx and the duration t is specified, and the duration t is long. The predetermined time Tx is set so as to be longer. Then, the ECU 10 determines the predetermined time Tx based on the predetermined response. Here, the predetermined time Tx is a value that should be set in advance through experiments or the like in consideration of the cooling structure of the ECU 10 so that the current output element is not damaged by overheating.

  In recent years, in vehicles, the calculation load of the ECU has become extremely high with the advancement of its electronic control, and the ECU 10 of the present embodiment also has a function other than the calculation related to the current limiting process, which is an additional function. A large number of highly-immediate arithmetic processes related to the driving force distribution control that is the main function must be executed. Therefore, if the priority order is taken into consideration, it is desirable to reduce the calculation load related to the current limiting process as much as possible.

  In consideration of this point, in the present embodiment, as described above, it is caused by the execution of the overload driving by measuring the duration t of the overload driving in which the output of the driving current exceeding the rated current value is executed. Instead of heat generation of the current output element and temperature estimation thereof.

  That is, in an actual vehicle, the time during which the required torque transmission capacity reaches a peak is relatively short, so the setting of the cooling time is only a countermeasure when an exception occurs. Strong meaning. Therefore, there is no particular advantage in performing strict management with respect to the predetermined time Tx set as the cooling time. Rather, it is desirable that the time is set appropriately to the extent that the calculation load is not increased. Since the output of the drive current exceeding the first value I1 corresponding to the rated current value is a direct factor causing the heat generation of the current output element, the duration t is the extent of the heat generated by the overload drive. In spite of being extremely useful for inferring, the calculation load does not increase much.

  As described above, in the present embodiment, as described above, the predetermined time Tx set as the cooling time is determined based on the overload driving duration t. As a result, the driving current exceeding the rated current can be output efficiently and stably without increasing the calculation load of the ECU 10, and the cost can be reduced without using a mechanically strengthening clutch. Thus, the required torque transmission capacity is ensured.

Next, a current limiting process procedure by the ECU 10 of the present embodiment will be described.
As shown in the flowchart of FIG. 4, in the current limiting process, the ECU 10 first calculates the average value Iavr of the drive current output in the past (step 201). Next, the ECU 10 determines whether or not it is within the cooling time (step 202). If it is not within the cooling time (step 202: NO), it is subsequently determined whether or not the overload driving is being performed. (Step 203). The determination within the cooling time in step 202 and the determination during overload driving in step 203 are performed based on a cooling flag and an overload flag, which will be described later, respectively.

  Next, if it is determined in step 203 that overload driving is not being performed (step 203: NO), is the average value Iavr of the drive current output in the past calculated in step 201 equal to or less than a predetermined threshold value I0? It is determined whether or not (step 204). When the average value Iavr is equal to or less than the threshold value I0 (step 204: YES), the second value I2 corresponding to the limit energization value is set as the upper limit value Ilim of the current limit (step 205), and the average value Iavr is the threshold value. If it exceeds I0 (step 204: NO), the first value I1 corresponding to the rated current value is set as the upper limit value Ilim (step 206).

  If it is determined in step 203 that overload driving has already been performed (step 203: YES), the ECU 10 does not execute the process of step 204, but sets the current limit upper limit value Ilim in step 205. The second value I2 is maintained. If it is determined in step 202 that it is within the cooling time (step 202: YES), the first step corresponding to the rated current value in step 207 is performed without executing the processing in steps 203 to 206. The value I1 is set as the upper limit value Ilim.

  Further, when the upper limit value Ilim is set to the second value I2 in step 205 or the upper limit value Ilim is set to the first value I1 in step 207, the ECU 10 subsequently sets and cancels the cooling time. A series of determination processes relating to cooling is executed (cooling determination, step 208). That is, both the cooling flag used for the determination within the cooling time in step 202 and the overload flag used for the determination during overload driving in step 203 are set and reset in this cooling determination process.

  When the upper limit value Ilim is set to the first value I1 in step 206, the cooling determination in step 208 is not executed. That is, if it is determined in step 204 that the average value Iavr exceeds the threshold value I0 (step 204: NO), the overload flag is not set.

  As shown in the flowchart of FIG. 5, in the cooling determination process (see FIG. 4, step 208), the ECU 10 first determines whether or not the cooling flag has already been set (step 301). If the cooling flag has not yet been set (step 301: NO), the current command value I * (see FIG. 2, step 103) calculated as the target value for current feedback control corresponds to the rated current value. It is determined whether or not it is larger than the first value I1 set as the reference value to be executed (step 302).

  Next, when the current command value I * is larger than the first value I1 in step 302 (step 302: YES), the ECU 10 determines whether or not the overload flag has already been set (step 303). ). If the overload flag has not yet been set (step 303: NO), the overload flag is set (step 304), and overload driving executed by setting the overload flag, that is, the rated current is set. The overload counter for measuring the duration t of the drive current output exceeding the first value I1 corresponding to the value is reset (t = 0, step 305). In addition, after resetting the overload counter by execution of step 305, the ECU 10 does not execute the processing after step 306 shown below in the calculation cycle.

  That is, when the cooling determination (see FIG. 4, step 208) is executed and the cooling flag is not yet set (step 301: NO), the average value Iavr of the drive current is equal to or less than the threshold value I0 (FIG. 4). (Refer to step 204: YES), only after the upper limit value Ilim of the current limit has been raised to the second value I2. In such a situation, although the current command value I * is larger than the first value I1 corresponding to the rated current (step 302: YES), the overload flag is not yet set (step 303: NO) means that the output of the drive current exceeding the rated current is generated for the first time after the permission, that is, the overload drive is started. Then, the ECU of the present embodiment starts measuring the duration t of overload driving from this point.

  If it is determined in step 303 that the overload flag has already been set (step 303: YES), that is, if overload driving has already started, the ECU 10 increments the overload counter (step 306), it is determined whether or not the count value, that is, the duration t exceeds a predetermined threshold t0 (step 307). When the duration t is equal to or less than the threshold value t0 (t ≦ t0, step 307: NO), the ECU 10 does not execute the processing after step 308 shown below in the calculation cycle.

  On the other hand, when it is determined in step 302 that the current command value I * is equal to or less than the first value I1 (step 302: NO), the ECU 10 determines whether or not the overload flag has already been set. (Step 308). If the overload flag has already been set (step 308: YES), the overload flag is reset (step 309), then the cooling flag is set (step 310) and the elapsed time of the cooling time. A cooling time counter for measuring T is reset (T = 0, step 311).

  That is, after the overload flag is set by the execution of step 304, the overload counter reset in the subsequent step 305 is incremented every calculation cycle until the overload flag is reset in step 309. Go. In the present embodiment, this allows the time from when the current command value I * exceeding the first value I1 is first calculated to the time when the current command value I * becomes equal to or less than the first value I1. The count value is calculated as the duration t of the overload drive.

  And as mentioned above, ECU10 of this embodiment calculates the predetermined time Tx set as the cooling time based on the continuation time t shown by the counter value of the overload counter (step 312).

  In step 308, if the overload flag has not yet been set (step 308: NO), the overload drive itself has not started, and of course, the processing after step 309 related to the setting of the cooling time. Is not executed.

  The ECU 10 according to the present embodiment also performs the above step even when it is determined in the above step 307 that the duration t indicated by the count value of the overload counter exceeds the threshold t0 (t> t0, step 307: YES). Processes 309 to 312 are executed.

  That is, in this embodiment, when the duration t of the overload drive exceeds the set time indicated by the predetermined threshold t0, the current command value I * decreases to the first value I1 or less ( Step 302: NO) The cooling time is forcibly set without waiting. As a result, even when a situation in which overload driving is sustained occurs, it is possible to suppress overheating of the current output elements constituting the ECU 10.

  On the other hand, when it is determined in step 301 that the cooling flag has already been set (step 301: YES), that is, in the calculation cycle after the cooling time is set by executing the processing in steps 309 to 312. The ECU 10 first increments the cooling counter (step 313), and determines whether or not the count value, that is, the elapsed time T exceeds the predetermined time Tx set in step 312 (step 314). If the elapsed time T exceeds the predetermined time Tx (T> Tx, Step 314: YES), the cooling flag is reset (Step 315). When the elapsed time T is equal to or shorter than the predetermined time Tx (T ≦ Tx, step 314: NO), the process of step 315 is not executed.

  When the cooling determination in step 208 shown in the flowchart of FIG. 4 is executed in this way, or when the upper limit value Ilim is set to the first value I1 in step 206, the ECU 10 next performs the current control. It is determined whether or not the current command value I * calculated as the target value (see FIG. 2, step 103) is larger than the upper limit value Ilim (step 209). When the current command value I * is larger than the upper limit value Ilim (step 209: YES), the upper limit value Ilim, that is, the second value I2 determined in step 205, or the first value determined in step 206. Is updated as a new current command value I ** (step 210). If the current command value I * is equal to or lower than the upper limit value Ilim (step 209: NO), the process of step 210 is not executed.

  Then, when current feedback control is executed based on the new current command value I ** (see FIG. 2), the drive current output to the torque coupling 9 (electromagnetic clutch 12) is equal to or less than the upper limit value Ilim. The configuration is limited to the above.

As described above, according to the present embodiment, the following operations and effects can be obtained.
(1) When the average value Iavr of the drive current output in the past is equal to or less than the predetermined threshold value I0, the ECU 10 corresponds to the upper limit value of the current limit as the limit energization value that allows only short-time energization. By switching to the second value I2 set as the value to be performed, the output of the drive current exceeding the first value I1 set as the reference value corresponding to the rated current value is allowed.

  According to the above configuration, the required torque transmission performance can be ensured without increasing the size of the electromagnetic clutch 12 (the clutch mechanism). Then, by limiting the current output element to a state where heat generation is small and allowing the overload drive, the output of the drive current should be cut off due to overheating of the current output element, that is, without reaching the use limit. Drive current that exceeds the rated current can be output stably.

  (2) After the overload drive is executed, the ECU 10 changes the current limit upper limit value Ilim from the second value I2 corresponding to the limit energization value to the rated current value from the first value I1 for the predetermined time Tx. By reducing to the corresponding first value I1, a cooling time for cooling the current output element that generates heat due to the overload drive is set. Further, the ECU 10 measures the duration t of overload driving. Based on the duration t, the length of the cooling time, that is, the predetermined time Tx is calculated.

  In other words, after executing overload driving, by setting an appropriate cooling time and cooling the current output element, the drive current exceeding the rated current can be output more stably without reaching the use limit. Is possible. However, the ECU 10 must execute a large number of highly immediate arithmetic processes related to the driving force distribution control which is the main function. Therefore, if the priority order is taken into consideration, it is desirable to make the calculation load related to the current limiting process, which can be called an additional function, as light as possible. Also, since the duration of the required peak torque transmission capacity in an actual vehicle is a relatively short time, the above cooling time setting is only a countermeasure when an exception occurs. The meaning as is strong. That is, there is no special advantage in performing strict management for the predetermined time Tx set as the cooling time. Then, the output of the drive current exceeding the first value I1 corresponding to the rated current value is a direct factor causing the heat generation of the current output element, and the duration t thereof estimates the degree of heat generated by the overload drive. In spite of being extremely useful for this purpose, the calculation load does not increase significantly.

  Therefore, according to the above configuration, it is possible to appropriately set the predetermined time Tx serving as the cooling time without causing an increase in the calculation load. As a result, the drive current exceeding the rated current can be output efficiently and stably.

  (3) When the duration t of the overload drive exceeds the set time indicated by the predetermined threshold t0, the ECU 10 determines that the current command value I * decreases to the first value I1 or less. Set the cooling time forcibly without waiting.

According to the above configuration, overheating of the current output element can be suppressed even in a situation where overload driving is sustained.
In addition, you may change this embodiment as follows.

  In the present embodiment, the present invention is embodied in a current limiting device mounted on the ECU 10 that outputs a driving current to the torque coupling 9 (the electromagnetic clutch 12 thereof) constituting the driving force distribution device of the vehicle. However, the present invention is not limited to this, and it may be embodied as a torque coupling used for applications other than the driving force distribution device or a current limit for limiting an output current to the electromagnetic clutch alone. Further, the present invention may be embodied in a current limiting device relating to an output current for electric parts other than the electromagnetic clutch.

  In the present embodiment, when overload driving is permitted, the upper limit value Ilim of the current limit is set to a second value I2 set as a value corresponding to a limit energization value in which only short-time energization is permitted. It was decided to use. However, the present invention is not limited to this, and the upper limit value Ilim of the current limit when overload driving is allowed may be arbitrarily set.

  In addition, in the present embodiment, the first value I1 corresponding to the rated current value that is the criterion for overload driving is set as the reference value, but the driving current that always exceeds the rated current value strictly Is not defined as overload driving, and the reference value may be set arbitrarily.

  In addition, in the present embodiment, the upper limit value Ilim of the current limit is reduced to the first value I1 during the cooling time. However, for example, this may be arbitrarily set, for example, to a lower value. May be.

  Furthermore, in the present embodiment, a current value that is a reference for starting measurement of the duration t (“reference value” of the invention according to claim 1 of the present application) and a current value that is a reference for stopping the measurement (requested by the present application) The “setting value” of the invention according to item 1) is the same value (first value I1), but they are not necessarily the same. For example, the current value serving as a reference for stopping the measurement of the duration t may be made smaller than the current value at which the measurement is started.

  In addition, when the current limit upper limit value Ilim is switched, such as when overload driving is allowed or after the cooling time, the value may be gradually changed by performing a filter process or the like. As a result, it is possible to prevent the sudden current limit from being executed or released, and to smoothly shift the limit state.

  In the present embodiment, the duration t of overload driving is measured, and the length of the cooling time, that is, the predetermined time Tx is calculated based on the duration t. However, the present invention is not limited to this, and when there is a margin in the computing power of the information processing device, for example, the heat generation is estimated by integrating the excess value from the reference value and setting the cooling time based on the integrated value. The accuracy of the may be increased. Further, the cooling time setting method may be changed by varying the degree of reduction of the upper limit value Ilim of the current limit in accordance with the improvement in accuracy of heat generation estimation.

  In the present embodiment, the current limit is performed by correcting the current command value I *, which is the target value for current control. However, the output current itself may be limited. The overload drive determination may also be executed based on the detected actual current.

  In the present embodiment, the ECU 10 outputs the drive current by executing the current feedback control. However, the ECU 10 may be embodied in a configuration that executes the current output by open control.

The schematic block diagram of the vehicle by which a driving force distribution apparatus is mounted. The flowchart which shows the process sequence of the drive current output by ECU. Explanatory drawing which shows an example of the current limiting process of this embodiment. The flowchart which shows the process sequence of an electric current limitation. The flowchart which shows the process sequence of the cooling determination in an electric current limiting process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 9 ... Torque coupling, 10 ... ECU, 12 ... Electromagnetic clutch, I ... Actual current value, I *, I ** ... Current command value, I0 ... Threshold value, I1 ... First value, I2 ... First The value of 2, Iavr ... average value, Ilim ... upper limit value, t ... duration, t0 ... threshold, T ... elapsed time, Tx ... predetermined time.

Claims (6)

  The output current is limited to a predetermined upper limit value or less, the duration of the output current exceeding a predetermined reference value that is equal to or less than the upper limit value is measured, and after the output current becomes a predetermined set value or less, A current limiting device that reduces the upper limit for a predetermined time based on a duration. The current limiting device according to claim 1,
When the duration exceeds a set time, the upper limit value is reduced without waiting for a decrease in the output current below the set value. In the current limiting device according to claim 1 or 2,
A current limiting device that monitors an average value of values stored for a predetermined period of the current value of the output current and reduces the upper limit value when the average value exceeds a predetermined threshold value. . In the current limiting device according to any one of claims 1 to 3,
The reference value and the set value are values corresponding to a rated current value at which continuous energization is permitted, and the upper limit value is reduced to the rated current value. An electromagnetic clutch device capable of changing an engagement force generated by a clutch mechanism through an output of a drive current to an electromagnet,
An electromagnetic clutch device characterized in that the control means for outputting the drive current is provided with the current limiting device according to any one of claims 1 to 4. A driving force distribution device comprising: a torque coupling whose torque transmission capacity changes based on an engaging force of the electromagnetic clutch; and a control means for controlling the driving force distribution through the torque coupling through an output of a driving current to the electromagnetic clutch. Because
A driving force distribution device, wherein the control means is provided with the current limiting device according to any one of claims 1 to 4.

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