JP5123927B2 - Differential gear protector - Google Patents

Description

  The present invention includes a driving wheel that is one of a front wheel and a rear wheel, a driven wheel that is the other of the front wheel and the rear wheel, a differential disposed between a driving source and the driving wheel, and the left and right driving. Left and right wheel speed difference calculating means for calculating the wheel speed difference between the wheels, and when the wheel speed difference between the left and right drive wheels calculated by the left and right wheel speed difference calculating means is equal to or greater than a first threshold value, The present invention relates to a protection device for a differential device, comprising an input rotation speed reduction means for protecting the differential device by reducing an input rotation speed.

  When the slip state determination means determines the slip state of the drive wheel when the vehicle starts on ice or the like having a low friction coefficient, the automatic transmission is held in the second speed shift stage to limit the shift up to the third speed shift stage. Thus, in order to prevent the durability of the differential gear from being adversely affected, when the time required for shifting up from the first gear to the second gear is shorter than a predetermined time, the second gear to the third gear. By limiting the shift-up to the speed gear, even if the slip state determination by the slip state determination means is not in time, an undesired shift-up can be avoided according to Patent Document 1 below. It is known.

  If the difference in wheel speed between the left and right drive wheels exceeds a specified value when the vehicle starts, it is determined that the vehicle is on ice with a low coefficient of friction and one of the left and right drive wheels is slipping. It is also known to protect the differential device by limiting the shift-up from the second gear to the third gear of the transmission.

JP-A-11-63210

  By the way, the slip state determination means of the invention described in Patent Document 1 compares the vehicle body acceleration calculated from the wheel speed of the driving wheel with the reference vehicle body acceleration calculated from the throttle opening and the gear position of the automatic transmission. Thus, the slip state of the drive wheel is determined, so that it is necessary to calculate many parameters, and there is a possibility that the determination time becomes longer or a determination omission occurs.

  If the difference between the wheel speeds of the left and right drive wheels exceeds a predetermined value, the vehicle speed difference between the left and right drive wheels is temporarily less than the predetermined value if it is determined that the vehicle is on ice with a low friction coefficient. Then, there is a problem that the restriction of upshifting is lifted and re-control becomes impossible. Furthermore, the method using the wheel speed difference between the left and right drive wheels achieves both the requirement not to erroneously determine the slip condition on a dry road surface with a high friction coefficient and the request to determine the slip condition on a low friction coefficient road surface as early as possible. When trying to do so, there is a problem that erroneous determination is likely to occur.

  The present invention has been made in view of the above circumstances, and an object thereof is to reliably determine a low friction coefficient road surface in a short time and to protect a differential device.

  To achieve the above object, according to the first aspect of the present invention, a drive wheel that is one of the front wheel and the rear wheel, a driven wheel that is the other of the front wheel and the rear wheel, a drive source, and the A differential device disposed between the drive wheels; a left and right wheel speed difference calculating means for calculating a wheel speed difference between the left and right drive wheels; and a wheel speed of the left and right drive wheels calculated by the left and right wheel speed difference calculating means. In the protection device for a differential device, comprising the input rotation speed reduction means for protecting the differential device by reducing the input rotation speed of the differential device when the difference is equal to or greater than a first threshold value. And a front-rear wheel speed difference calculating means for calculating a wheel speed difference of the driven wheel, wherein the input rotational speed reducing means is configured so that a wheel speed difference between the driving wheel and the driven wheel calculated by the front-rear wheel speed difference calculating means is When the second threshold value is exceeded, the first threshold value is Protection device of a differential device, characterized in that the lowering can is proposed.

  According to the invention described in claim 2, in addition to the configuration of claim 1, an automatic transmission disposed between the drive source and the differential device is provided, and the input rotation speed reducing means is A protection device for a differential device is proposed in which the differential device is protected by limiting upshifting of an automatic transmission.

  The engine E of the embodiment corresponds to the drive source of the present invention, and the upshift limiting means M5 of the embodiment corresponds to the input rotation speed reducing means of the present invention, and the left and right front wheels WFL, WFR of the embodiment. Corresponds to the drive wheel of the present invention, and the left and right rear wheels WRL, WRR of the embodiment correspond to the driven wheel of the present invention.

  According to the configuration of the first aspect, the input rotation speed reduction means is configured to input the input rotation speed of the differential when the wheel speed difference between the left and right drive wheels calculated by the left and right wheel speed difference calculation means is equal to or greater than the first threshold value. Therefore, it is possible to protect the differential device by preventing the input rotational speed of the differential device from increasing when the drive wheel is in the slip state. When the wheel speed difference between the driving wheel and the driven wheel calculated by the front-rear wheel speed difference calculating means becomes equal to or larger than the second threshold value, that is, when it is confirmed that the road surface friction coefficient is low, the input rotation speed reducing means lowers the first threshold value. Therefore, it is possible to reliably protect the differential device by limiting the increase in the input rotational speed of the differential device before the slip amount of the drive wheel increases. In addition, since the default value of the first threshold can be set higher by that amount, it is possible to prevent an unnecessary increase in the input rotational speed of the differential device from being restricted on the dry road surface. Can do.

  According to the second aspect of the present invention, when the wheel speed difference between the left and right drive wheels calculated by the left and right wheel speed difference calculating means is greater than or equal to the first threshold value, the input rotational speed reducing means limits the shift up of the automatic transmission. Therefore, it is possible to reliably prevent an increase in the input rotation speed of the differential device and protect the differential device.

The figure which shows the vehicle of a front engine front drive. The block diagram of an electronic control unit. The flowchart explaining an effect | action.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, a front engine / front drive vehicle is driven by an engine E via an automatic transmission T and a differential device D, and left and right front wheels WFL, WFR are driven wheels. And left and right rear wheels WRL, WRR, which are driven wheels that rotate.

  The electronic control unit U includes wheel speeds detected by wheel speed sensors SFL and SFR provided on the left and right front wheels WFL and WFR, and wheel speed sensors SRL and SRR provided on the left and right rear wheels WRL and WRR, respectively. The detected wheel speed and the accelerator opening detected by the accelerator opening sensor SA are input. The electronic control unit U controls the shift change of the automatic transmission T based on each signal, thereby establishing a desired gear stage in the automatic transmission T and protecting the differential device D.

  As shown in FIG. 2, the electronic control unit U includes vehicle speed calculation means M1, front and rear wheel speed difference calculation means M2, left and right wheel speed difference calculation means M3, shift change control means M4, and shift up restriction means M5. Is provided.

  The vehicle speed calculation means M1 and the front and rear wheel speed difference calculation means M2 are connected to the wheel speed sensors SFL, SFR of the left and right front wheels WFL, WFR and the wheel speed sensors SRL, SRR of the left and right rear wheels WRL, WRR. The vehicle speed calculation means M1 calculates the vehicle speed as an average value of the wheel speeds of the four wheels detected by the wheel speed sensors SFL, SFR; SRL, SRR. The vehicle speed calculation method is not limited to the above, and other appropriate methods such as calculating the average value of the wheel speeds of the left and right rear wheels WRL, WRR, which are driven wheels, can be employed.

  The front-rear wheel speed difference calculation means M2 calculates the front-rear wheel speed difference by subtracting the average value of the wheel speeds of the left and right rear wheels WRL, WRR from the average value of the wheel speeds of the left and right front wheels WFL, WFR. If the front wheels WFL and WFR, which are driving wheels, slip when the vehicle starts on a low friction coefficient road surface such as on ice, the wheel speed of the front wheels WFL and WFR increases rapidly, but the vehicle does not accelerate sufficiently. The wheel speed of a certain rear wheel WRL, WRR does not increase as much as the wheel speed of the front wheels WFL, WFR, and as a result, the front-rear wheel speed difference increases. Therefore, the front-rear wheel speed difference calculated by the front-rear wheel speed difference calculating means M2 serves as an index for determining the magnitude of the road surface friction coefficient.

  The left and right wheel speed difference calculating means M3 calculates the left and right wheel speed difference by subtracting the other from one of the wheel speeds of the left and right front wheels WFL and WFR. When one of the front wheels WFL, WFR slips due to a slight friction coefficient difference on the road surface on which the front wheels WFL, WFR, which are driving wheels, rides when the vehicle starts on a low friction coefficient road surface such as on ice, the function of the differential device D Since the driving force is distributed to the front wheels WFL and WFR on the slipped side, the difference between the left and right wheel speeds increases rapidly.

  The shift change control means M4 applies the vehicle speed calculated by the vehicle speed calculation means M1 and the accelerator opening detected by the accelerator opening sensor SA to the shift map, searches for the shift speed, and automatically establishes this shift speed. The upshift and downshift of the transmission T are controlled.

  By the way, when the vehicle starts on a low friction coefficient road surface such as on ice, only the front wheels WFL and WFR, which are drive wheels to which the driving force of the engine E is transmitted, may slip with respect to the road surface. At this time, as described above, if there is a slight difference in the coefficient of friction on a part of the road surface on which the left and right front wheels WFL and WFR ride, the function of the differential device D stops the rotation of one front wheel and only the other front wheel. If the automatic transmission T shifts up in this state, there is a possibility that the differential rotation on the left and right of the differential device D becomes excessive, and the durability may be adversely affected.

  In order to avoid such inconvenience, the shift-up limiting means M5, regardless of the shift speed searched in the shift map, when the left and right wheel speed difference calculated by the left and right wheel speed difference calculating means M3 is greater than or equal to the first threshold value. The above-described differential device D is protected by limiting the shift-up of the automatic transmission T from the second gear to the third gear. The first threshold value is a variable value, and its initial set value (default value) is a relatively large value suitable for a dry road surface (road surface having a large friction coefficient), and the value corrected in the decreasing direction is on ice (friction) A relatively small value suitable for a road surface having a small coefficient.

  That is, when the front-rear wheel speed difference calculated by the front-rear wheel speed difference calculating means M2 is equal to or greater than the second threshold value, that is, when the road surface friction coefficient is small, the shift-up limiting means M5 decreases the first threshold value from the default value. As a result, the shift-up from the second gear to the third gear is more strongly limited.

  The reason is as follows. The determination of the low friction coefficient road surface due to the difference between the left and right wheel speeds is based on a comparison of the wheel speed of the left front wheel WFL and the wheel speed of the right front wheel WFR, so that only the left and right front wheels WFL, WFR are locally low friction coefficients. When stepping on the road surface, there is a possibility that the entire road surface is erroneously determined to have a low coefficient of friction. On the other hand, the determination of the low friction coefficient road surface by the difference between the front and rear wheel speeds is based on the comparison of the average wheel speed of the left and right front wheels WFL and WFR and the average wheel speed of the left and right rear wheels WRL and WRR. When a typical low friction coefficient road surface is stepped on, the possibility of erroneous determination that the entire road surface has a low friction coefficient is reduced, and thus the low friction coefficient road surface can be accurately determined in a short time.

  Accordingly, when the front-rear wheel speed difference calculating means M2 accurately determines the low friction coefficient road surface, the shift-up limiting means M5 corrects the first threshold value in a direction to lower the first threshold based on the determination. The shift-up of the transmission T from the second gear to the third gear can be more strongly restricted, and the differential device D can be more reliably protected.

  If it is determined that the road surface friction coefficient is low, the first threshold value is lowered. Therefore, even if the default value of the first threshold value is set higher, the second speed gear stage to the third speed gear stage on the low friction coefficient road surface. It is possible to reliably limit the shift up to. On the other hand, since the default value of the first threshold value is set higher, the limitation on the upshifting from the second gear to the third gear is unnecessarily executed on a dry road surface with a large friction coefficient. Can be prevented.

  In the conventional system, when the difference between the front and rear wheel speeds is equal to or greater than the second threshold and the grip of the slipping front wheels WFL and WFR is slightly recovered and the front and rear wheel speed difference is less than the second threshold, The restriction on upshifting from the third gear to the third gear is released, and the upshifting to the third gear is executed. As a result, there has been a problem that it is impossible to limit the upshifting from the second gear to the third gear even if the difference between the front and rear wheel speeds becomes equal to or greater than the second threshold value.

  On the other hand, in the present embodiment, the slip of the front wheels WFL and WFR that are slipping is slightly recovered in a state where the front and rear wheel speed difference is equal to or larger than the second threshold, and the front and rear wheel speed difference becomes less than the second threshold. However, at that time, the limitation of the shift-up from the second gear to the third gear is not released, and when the front-rear wheel speed difference becomes less than the third threshold smaller than the second threshold, That is, when the road surface friction coefficient becomes high and the slip of the front wheels WFL and WFR is almost completely eliminated, the restriction on the upshifting from the second gear to the third gear is released.

  This prevents the restriction of upshifting from the second gear to the third gear when the grip of the slipping front wheels WFL and WFR is slightly recovered, and then prevents the front wheels from being inadvertently released. Even when WFL and WFR start slipping again, the upshifting to the third gear can be surely limited.

  The flowchart in FIG. 3 summarizes the above-described operation of the shift-up limiting unit M5.

  First, if the front and rear wheel speed difference calculated by the front and rear wheel speed difference calculating means M2 in step S1 is equal to or greater than the second threshold value, it is determined in step S2 that the front wheels WFL and WFR have a large slip (the road surface friction coefficient is relatively small). In step S3, the first threshold value is corrected from the default value in a decreasing direction. If the difference between the front and rear wheel speeds is less than the second threshold value in step S1, it is determined in step S4 that the slip of the front wheels WFL and WFR is small (the road surface friction coefficient is relatively large), and the first threshold value is decreased in step S5. Keep the default value without correction.

  If the left and right wheel speed difference calculated by the left and right wheel speed difference calculating means M3 in step S6 is equal to or greater than the first threshold value (including both the default value and the decrease correction value of the default value), the front wheels are driven on the road surface having a low road surface friction coefficient. It is determined that WFL and WFR are slipping, and in step S7, the automatic transmission T is restricted from shifting up from the second gear to the third gear, and the differential rotation of the differential device D does not become excessive. To prevent damage. If it is determined in step S2 that the difference between the front and rear wheel speeds is less than the third threshold value, and it is determined in step S8 that the grip of the tire has recovered and the front wheels WFL and WFR have slipped, the shift from the second gear is performed in step S9. The restriction on the upshifting of the third gear is released, and the vehicle can be accelerated smoothly.

  The recovery of the tire grip means that the vehicle speed exceeds the predetermined value, the accelerator pedal opening exceeds the predetermined value, the throttle opening exceeds the predetermined value, and the slip ratio of the torque converter exceeds the predetermined value. Is determined by any of the following.

  As described above, the difference between the average wheel speed of the front wheels WFL and WFR calculated by the front and rear wheel speed difference calculation means M2 and the front and rear wheel speed difference which is the difference between the wheel speeds of the rear wheels WRL and WRR becomes equal to or greater than the second threshold value. If it is confirmed that the coefficient is low, the shift-up limiting means M5 lowers the first threshold value, so that the shift-up is limited before the slip amount of the front wheels WFL and WFR that are drive wheels increases, and the differential device D is It can be surely protected. Thereby, since the default value of the first threshold value can be set higher, it is possible to prevent an unnecessary restriction on upshifting from being performed on the dry road surface.

  The embodiments of the present invention have been described above, but various design changes can be made without departing from the scope of the present invention.

  For example, in the embodiment, the upshift limiting means M5 limits the upshift of the automatic transmission T to protect the differential device D. However, the throttle valve is closed to reduce the engine speed. The input rotational speed of the differential device D may be reduced by this means.

  In the embodiment, the front wheels WFL and WFR are driving wheels and the rear wheels WRL and WRR are driven wheels. However, the present invention is such that the front wheels WFL and WFR are driven wheels and the rear wheels WRL and WRR are driving wheels. It can also be applied to vehicles.

D Differential device E Engine (drive source)
M2 Front and rear wheel speed difference calculating means M3 Left and right wheel speed difference calculating means M5 Shift up limiting means (input rotation speed reducing means)
T Automatic transmission WFL Front left wheel (drive wheel)
WFR Right front wheel (drive wheel)
WRL Left rear wheel (driven wheel)
WRR Right rear wheel (driven wheel)

Claims (2)

Driving wheels (WFL, WFR) which are one of the front wheels and the rear wheels;
A driven wheel (WRL, WRR) which is the other of the front wheel and the rear wheel;
A differential device (D) disposed between the drive source (E) and the drive wheels (WFL, WFR), and a left / right wheel speed difference calculating means for calculating a wheel speed difference between the left and right drive wheels (WFL, WFR) (M3),
When the wheel speed difference between the left and right drive wheels (WFL, WFR) calculated by the left and right wheel speed difference calculating means (M3) is equal to or greater than a first threshold, the input rotational speed of the differential device (D) is reduced. In the protective device for the differential device, the input rotational speed reducing means (M5) for protecting the differential device (D).
Front and rear wheel speed difference calculating means (M2) for calculating a wheel speed difference between the driving wheel (WFL, WFR) and the driven wheel (WRL, WRR);
The input rotational speed reduction means (M5)
When the wheel speed difference between the driving wheel (WFL, WFR) and the driven wheel (WRL, WRR) calculated by the front / rear wheel speed difference calculating means (M2) is equal to or greater than a second threshold value, the first threshold value is set. A protective device for a differential device, characterized by being pulled down.   An automatic transmission (T) disposed between the drive source (E) and the differential device (D) is provided, and the input rotational speed reduction means (M5) shifts up the automatic transmission (T). The protection device of the differential device according to claim 1, wherein the differential device (D) is protected by limiting.

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