JPH0538958A - Power transmission control device for vehicle - Google Patents

Abstract

PURPOSE:To improve the fuel consumption performance at the coasting travel time and the stop time by setting plural differential limiting quantity decrease starting conditions, and changing a differential limiting quantity decrease state terminating condition according to these differential limiting quantity decrease starting conditions. CONSTITUTION:The throttle opening signal of an engine 1, brake on-off signal, clutch on-off signal, neutral signal, ABS operation signal, and the like are inputted into a differential limiting controller 20. In addition to these signals, the respective left-right and front-rear wheel rotating speeds detected by rotation sensors 25, 26, 27, 28 provided respectively for four wheels are inputted into the differential limiting controller 20. On the basis of the above-mentioned input signals, the differential limiting controller 20 performs current control, and electromagnetic type differential limiting mechanism (EMCD) is controlled by this control current. The respective differential limiting mechanisms of a center differential gear 3, a front differential gear 7 and a rear differential gear 12 are currentcontrolled, so that differential lock is not continued at the stop time, which results in improving the fuel consumption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission control device for a vehicle having a differential device having a differential limiting mechanism capable of changing a differential limiting amount.

[0002]

2. Description of the Related Art Output from a transmission is transmitted to a front wheel drive system and a rear wheel drive system via a center differential device (hereinafter referred to as "center differential"), and the front wheel drive system and the rear wheel drive system are selectively driven. There is known a four-wheel drive vehicle provided with a mechanism for locking the center differential so as to be directly connected to the vehicle.

By the way, in the above-described four-wheel drive vehicle, when the center differential is limited to the locked state while the vehicle is traveling, and the transmission is in the neutral state or the clutch is disengaged. When the vehicle turns by inertia, an excessive torque acts on the lock mechanism of the center differential. Therefore, from the viewpoint of durability and strength of the constituent members of the lock mechanism, it is necessary to make the constituent members particularly strong and sturdy, and there is a problem that the size, weight and cost of the locking mechanism are increased as a whole. ..

Therefore, in the four-wheel drive vehicle disclosed in Japanese Utility Model Laid-Open No. 62-36928, a state in which the drive force cannot be transmitted from the engine to the wheels such as the neutral state of the transmission or the state in which the clutch is disengaged. When making a turn with
The lock mechanism of the center differential is free.

[0005]

However, when the vehicle is coasting in a state where the driving force cannot be transmitted from the engine to the wheels even when the vehicle is traveling straight, if the center differential is locked, it becomes a traveling resistance and coasts. There is a problem that fuel efficiency is deteriorated because the distance does not increase. Further, there are various modes even if it is generally said that the driving force cannot be transmitted from the engine to the wheels, and it is necessary to reliably start and end (return) the differential limitation according to the various modes.

Particularly, when the diff lock is performed by the operation of the electromagnetic clutch, the differential limiting amount is substantially proportional to the supplied current until it becomes saturated, so that the vehicle is stopped or running at low speed coasting. Even if the diff lock is continued, the power consumption increases, which increases the load of the alternator and thus the load of the engine, which deteriorates fuel efficiency.

Therefore, an object of the present invention is to provide a power transmission control device for a vehicle, which solves the above-mentioned problems.

[0008]

SUMMARY OF THE INVENTION The present invention provides a power transmission control device having means for reducing the differential limiting amount of a differential device when a state in which drive power cannot be transmitted from an engine to wheels continues for a predetermined time. The above-mentioned problems are solved by. That is, in the present invention, a plurality of differential limiting amount reduction start conditions are set, and the ending condition of the differential limiting amount reduction state is changed according to these differential limiting amount reduction starting conditions.

[0009]

According to the present invention, it is possible to improve the fuel consumption performance during coasting and when the vehicle is stopped, and to reliably switch the differential limiting amount.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a four-wheel drive vehicle includes a power train P including an engine 1 and a transmission 2, and a transfer device 4 including a center differential 3 having an electromagnetic clutch type differential limiting mechanism (EMCD). The torque input to the center differential 3 is distributed and output to the front wheel side propeller shaft 5 and the rear wheel side propeller shaft 6.

The torque of the front wheel side propeller shaft 5 is input to a front differential 7 provided with an electromagnetic clutch type differential limiting mechanism (EMCD), further transmitted to a left front wheel 9 via a left front axle shaft 8, and It is adapted to be transmitted to the right front wheel 11 via the right front axle shaft 10. On the other hand, the torque of the rear wheel side propeller shaft 6 is the electromagnetic clutch differential limiting mechanism (EMC).
D) is input to the rear differential 12, and further transmitted to the left rear wheel 14 via the left rear axle shaft 13 and to the right rear wheel 16 via the right rear axle shaft 15. Center differential 3,
The electromagnetic clutch differential limiting mechanism (EMCD) provided in each of the front differential 7 and the rear differential 12 is configured to control each differential limiting amount by the current output from the differential limiting amount controller 20. ..

The differential limiting amount controller 20 is a digital controller composed of a microcomputer, and is detected by a throttle sensor 21 provided for a throttle valve (not shown) in the intake passage of the engine 1. Throttle opening signal TVO, brake ON / OFF signal generated by the brake switch 22 provided for the brake pedal, clutch ON / OFF signal generated by the clutch switch 30 provided for the clutch pedal, transmission 2 Neutral signal output from the neutral switch 23 provided in
An ABS operation signal or the like output from the ABS controller 24 for controlling the antilock brake system (ABS) is input to the differential limiting amount controller 20.

Further, the left front axle shaft 8
The front left wheel speed (rotational speed) NfL detected by the first rotation speed sensor 25 provided for the right front wheel speed (detected by the second rotation speed sensor 26 provided for the right front axle shaft 10 ( Rotation speed) NfR,
Third provided on the left rear axle shaft 13
The left rear wheel speed (rotation speed) NrL detected by the rotation speed sensor 27 and the right rear wheel speed (rotation speed) NrR detected by the fourth rotation speed sensor 28 provided for the right rear axle shaft 15 are respectively represented. The signal is AB
Differential limiting amount controller 2 via S controller 24
It is designed to be input to 0. The differential limiting amount controller 20 uses these signals as input information by a method described later, and uses the center differential 3, the front differential 7, and the rear differential 12.
The respective differential limiting mechanisms are current-controlled to improve the running stability, fuel efficiency, etc. of this four-wheel drive vehicle. The differential limiting force controller 20 is provided with an operating knob 29 capable of selecting four control modes of an auto mode Auto, a center differential lock mode C, a rear differential lock mode R, and a front differential lock mode F.

The control method of the differential limiting force control by the differential limiting amount controller 20 will be described below with reference to the flowcharts of FIG.

FIG. 2 shows a routine for calculating the vehicle body speed Vsp. In step S1, four wheel speeds (rotational speeds) Nf.
L, NfR, NrL and NrR are input. Then, in step S2, the minimum value of the four wheel speeds is defined as the vehicle body speed Vsp.

Next, FIG. 3 shows a calculation routine for the center differential differential rotation speed (the rotation speed difference between the front and rear wheels) ΔNc. In step S3, four wheel speeds NfL, NfR, NrL, Nr are shown.
R is input, and in step S4 the center differential differential rotation speed Δ
Nc is calculated by the following formula. ΔNc = | (NfL + NfR) / 2- (NrL + NrR) / 2 |

FIG. 4 shows a routine for calculating the rear differential differential rotational speed (rotational speed difference between the left and right rear wheels) ΔNr, and step S5.
The rear wheel speeds NrL and NrR are input at, and at the next step S26, the rear differential differential rotation speed ΔNr is calculated by the following equation. ΔNr = | NrL-NrR |

FIG. 5 shows a map control current value setting routine for the center differential 3. First, in step S7, the control current value Ic of the center differential 3 is set as a function of the center differential differential rotation speed ΔNc and the throttle opening TVO. Next, in step S8, it is determined whether or not the control current value Ic is greater than or equal to the maximum current value Imax (lock current value, Imax = 2.2 amperes). If this determination is “YES”, the timer Tc is set in step S9. After resetting, the map control current value Ica = Imax is set in the next step S10. And step S1
The timer is incremented by 1 and it is determined in step S12 whether or not the timer time is equal to or longer than the predetermined hold time Ta. If Tc <Ta, the process returns to step S11 to increment the timer time. And step S1
When the determination of 2 becomes "YES", the process returns to step S7. A map showing the relationship between the control current value Ica and the center differential rotation speed ΔNc is shown in FIG.

Next, FIG. 6 shows a map control current value setting routine for the rear differential 12. Similar to the case of FIG. 5, first in step S13, the control current value Ir of the rear differential 12 is set as a function of the rear differential differential rotation speed ΔNr and the throttle opening TVO. Next, in step S14, it is determined whether or not the control current value Ir is the maximum current value Imax (lock current value, Imax = 4.1 ampere) or more, and this determination is "YES".
If so, the timer Tr is reset in step S15,
In the next step S16, the map control current value Ira = Imax is set. Then, in step S17, the timer is incremented, and in step S18, it is determined whether or not the timer time has exceeded a predetermined hold time Ta, and Tr <Ta.
If so, the process returns to step S17 to increment the timer. When the determination in step S18 is "YES", the process returns to step S13. A map showing the relationship between the control current value Ira and the rear differential rotation speed ΔNr is shown in FIG. 11.

7 to 9 are flowcharts of a control current value determination routine for the front differential 7, the center differential 3, and the rear differential 12. First, in step S19, the map control current values Ica, Ira, AB set in FIGS. 5 and 6 are set.
The S signal, the brake signal, the control mode signal, and the vehicle speed Vsp calculated in FIG. 2 are input. And step S
At 20, it is determined whether the control mode is the auto mode. Then, if it is the automatic mode, the process proceeds to step S21, and it is determined whether or not the brake switch 22 is ON. If it is during the braking, if = 0, Ic in step S22.
= 0 and Ir = 0. If the vehicle is not being braked, the control current value If of the front differential is set to 0 in step S23, and the control current values Ic of the center differential 3 and the rear differential 7 are set.
Ir is the map control values Ica and Ira set in FIGS. 5 and 6, respectively.

If the determination in step S20 is "NO", it is determined in the next step S24 whether the control mode is the center lock mode. Then, in the center lock mode, the center differential lock mode control routine shown in FIG. 8 is executed. The determination in step S24 is "N
If "O", the process proceeds to step S25, it is determined whether the control mode is the rear differential lock mode, and if the control mode is the rear lock mode, the rear lock mode control routine shown in FIG. 9 is executed. If the determination in step S25 is also “NO”, it means the front lock mode, and thus step S2
The process proceeds to 6 or less, and the control current value is determined according to the vehicle body speed Vsp.

In steps S26, S27 and S28, the vehicle body speed Vsp is 100 km / h or more, less than 100 km / h 50 km / h or more, less than 50 km / h 30 km / h or more, 30 km / h It is determined whether or not each is less than. When the vehicle body speed Vsp is 100 km / h, the control current value If of the front differential is set to 0 in step S29, and the control current values Ic of the center differential 3 and the rear differential 7 are set.
Ir is the map control values Ica and Ira set in FIGS. 5 and 6, respectively. If the vehicle body speed Vsp is less than 100 km / h and 50 km / h or more, in step S30, If
= 0, Ic = 2.2 amperes (Imax), and Ir = Ira. Further, if the vehicle body speed Vsp is less than 50 km / h and 30 km / h or more, at step S31, If = 0, Ic = 2.2 amperes (Imax) and Ir = 4.1 amperes (Imax) are set.
Furthermore, when the vehicle body speed Vsp is 30 km / h or less, I
f = 2.1 amps (Imax), Ic = 2.2 amps (Ima
x), lock all differentials with Ir = 4.1 amps (Imax).

In the center differential lock mode of FIG. 8, it is first determined in step S33 whether or not the brake switch 22 is on, and if not in braking, then in step S34 it is determined whether or not the vehicle body speed Vsp is 100 km / h or more. Is determined. If it is 100 km / h or more, if = 0, Ic = Ica, and Ir = Ira are set in step S35. Again 10
If less than 0 km / h, If = 0, Ic = 2.2 amps
(Imax) and Ir = Ira.

On the other hand, if the brake switch 22 is on, the routine proceeds to step S37, where it is judged if the ABS has operated. If the ABS has not operated, step S3
At 8, If = 0, Ic = 0.8 amperes, and Ir = 0. When the ABS is operating, If = 0, Ic = 0 and Ir = 0 are set in step S39 so as not to hinder the ABS control.

Next, in the rear differential lock mode of FIG. 9, it is first determined in step S40 whether or not the brake switch 22 is on, and if no braking is being performed, step S41,
Whether the vehicle speed Vsp is 100 km / h or more in S42, 1
Less than 00km / h 50km / h or more, or 50km
/ H is determined. If the vehicle body speed Vsp is 100 km / h or more, If = 0 in step S43,
Ic = Ica and Ir = Ira. If the vehicle speed Vsp is less than 100 km / h and 50 km / h or more, step S44.
At If = 0, Ic = 2.2 Amps (Imax), Ir = Ira
It is said that. Further, if the vehicle body speed Vsp is less than 50 km / h, If = 0, Ic = 2.2 amps (Im
ax) and Ir = 4.1 ampere (Imax), and the center differential 3 and the rear differential 12 are locked.

On the other hand, if the brake switch 22 is on, the routine proceeds to step S46, where it is judged if the ABS has operated, and if the ABS has not operated, step S4.
At 7, If = 0, Ic = 0.8 amps and Ir = 1.2 amps. At the time of ABS operation, if = 0, Ic = 0, If = 0 in step S48 so as not to hinder the ABS control.
Ir = 0 is set.

FIG. 10 is a diagram showing the relationship between the center differential differential rotation speed (= | front wheel rotation speed−rear wheel rotation speed |) ΔNc and the map control current value Ica of the center differential 3, where the center differential differential rotation speed ΔNc is In the region of α or less, Ica = 0 is set to provide a dead zone on the front wheel high rotation side, and Δc is set in a region where the center differential differential rotation speed ΔNc is between α and A.
Ica increases linearly with an increase in Nc, and the upper limit value Ima
I'm trying to reach x. When Ica reaches Imax (2.2 amps), the center differential 3 is locked,
The differential between the front and rear wheels is completely stopped.

Next, FIG. 11 is a diagram showing the relationship between the rear differential differential rotation speed (the rotational speed difference between the left and right rear wheels) ΔNr and the map control current value Ira of the rear differential 12, where the rear differential differential rotation speed ΔNr is β. In the region below, Ira = 0 is set to provide a dead zone, and in the region where the rear differential differential rotation speed ΔNr is between β and B, Ira is increased with respect to ΔNr.
Is linearly increased to reach the upper limit value Imax (4.1 amperes). When Ira reaches Imax, the differential between the left and right rear wheels is completely stopped.

The characteristic operation of the vehicle power transmission control device according to the present invention is shown in the flow charts of FIGS. 12 and 13 and the timing chart of FIG.

In the flowchart of FIG. 12, first in step S51, the clutch ON / OFF signal generated by the clutch switch 30 provided for the clutch pedal in FIG. 1 and the neutral switch 23 provided in the transmission 2 are output. And the neutral signal to be input.

In the next step S52, the limiting current value I of the front differential 7, the center differential 3 and the rear differential 12 is set.
It is checked whether or not a flag F ₂ for setting f, Ic and Ir to zero is set. Initially, the determination in step S52 is "NO", so the process proceeds to step S53 in FIG.

Here, the clutch is engaged and the engine 1
The state in which power is transmitted from the vehicle to the transmission 2 is referred to as "clutch ON", and the state in which power transmission from the engine 1 to the transmission 2 is disabled due to clutch disengagement is referred to as "clutch OFF".

By the way, there are three modes in which the power cannot be transmitted from the engine 1 to the wheels. That is,

(1) When the clutch is ON, but the shift position of the transmission 2 is neutral. This is called mode A, and it is determined in step S53 in FIG. 13 whether or not this mode is A.

(2) When the clutch is OFF and the shift position of the transmission 2 is in neutral. This is called mode B, and it is determined in step S61 of FIG. 13 whether or not this mode B exists.

(3) The transmission 2 although the clutch is OFF
Shift position is other than neutral. This is called mode C, and whether or not this is mode C is determined in step S66 of FIG.

In step S53 of FIG. 13, the engine 1
It is checked whether or not the state in which power is not transmitted from the vehicle to the wheels is the mode A, and if this judgment is "YES", it is checked at step S54 whether or not the mode flag F ₁ = A.
If this determination is "NO", then in step S55 F ₁ =
A is set to A, and the timer T that measures, for example, 10 seconds is reset in step S56, and the time measurement is started from time t1 in FIG.

In the next step S57, it is checked whether or not the timer T is in operation. Until the timer T times out, in step S58 the control current values If, Ic of the front differential 7, the center differential 3 and the rear differential 12 are set. Figure 7 for Ir
~ Return to step S51 as a current value according to the flow of Fig. 9.

Next, when the process goes to step S54 through steps S51 to S53, the determination in step S54 is "YE."
S ", the timer T is incremented in step S59 and the process proceeds to step S57. And since at time t2 has elapsed from the time point t1 in FIG. 14 10 seconds determination of step S57 becomes "NO", a flag F ₂ proceeds to step S60, If = 0, Ic = 0 at step S90,
With Ir = 0, the differential limiting amount of all differentials is set to zero. As shown in FIG. 14, the current change at this time is made relatively gentle so that the driver does not feel uncomfortable. (For example, the time t2-t3 is set to 1 second.)

On the other hand, when the determination in step S53 is "NO", the process proceeds to step S61, and it is checked whether or not the state in which power is not transmitted from the engine 1 to the wheels is the mode B, and this determination is "YES". , Then step S6
In 2 it is checked whether or not the mode flag F ₁ = B. If this determination is “NO”, then in step S62 F ₁ = B is set,
In addition, the timer T is reset in step S64, and
The time measurement is started from the time point t1 and the process proceeds to step S57,
As in the case of the mode A, the limit current values If, Ic, Ir are determined in step S58 until the timer T times out.
As a current value according to the flow of FIG. 7 to FIG.
Return to 51.

Next, steps S51 to S53 and S61.
When the process proceeds to step S62 through step S62, the determination in step S62 becomes "YES", so the timer T is incremented in step S65 and the process proceeds to step S57. Then, at the time point t2 when 10 seconds have elapsed from the time point t1 in FIG. 14, the judgment in the step S57 becomes “NO”, so that the step S60 is executed.
After that, the process proceeds to step S90, If = 0, Ic = 0, I
Let r = 0.

Furthermore, the determination in step S61 is "NO".
If so, the process proceeds to step S66, and it is determined whether or not the state in which power is not transmitted from the engine 1 to the wheels is the mode C. If this determination is "YES", step S66 is performed.
In 67, it is checked whether or not the mode flag F ₁ = C. If this determination is “NO”, F ₁ = C is set in step S68, and the timer T is reset in step S69. Time measurement is started from t1 and the process proceeds to step S57, and as in the modes A and B, the control current values If and I are controlled in step S58 until the timer T times up.
The values of c and Ir are set as current values according to the flow of FIGS. 7 to 9, and the process returns to step S51 of FIG.

Next, when the process goes to step S67 through steps S51 to S53 and steps S61 and S66, the determination at step S67 becomes "YES", so the timer T is incremented at step S70 and step S5 is performed.
Proceed to 7. Then, when 10 seconds have elapsed from the time point t1 in FIG. 14, the determination in step S57 becomes “NO”, and therefore, the process proceeds to step S90 via step S60 and If = 0,
Ic = 0 and Ir = 0.

Finally, the determination in step S66 is also "N
When it is "O", the process proceeds to step S58, and the control current values If, Ic, and Ir are set to current values according to the flows of FIGS. 7 to 9.

Next, regarding the control flow for returning from the control current cut state as described above to the control current value according to the flow of FIGS. 7 to 9, steps S71 to S of FIG.
A description will be given with reference to 82.

When the current cut state is started by the mode A, the restoration is performed at the time point t4 when the clutch is turned off. That is, in this case, step S7
Since the determination of 1 is "YES", the process proceeds to step S72 to check whether the clutch is off. Then, when the determination in step S72 is "YES", the process proceeds to step S73, and the control current values If, Ic, and Ir are shown in FIG.
Return to the current value according to the flow of FIG. 9, and step S74
Defeat flag F ₂ with. In this case, the driver is gently returned for one second so that the driver does not feel uncomfortable.

Next, when the current cut state is started by the mode B, the restoration is performed at the time t4 when the gear of the transmission 2 is shifted. That is, in this case, the determination in step S75 is “YES”,
In step S76, it is checked whether or not a gear shift has been performed. When the determination in step S76 is “YES”, the process proceeds to step S77, and the control current value If,
Ic and Ir are returned to the current values according to the flows of FIGS. 7 to 9, and the flag F ₂ is turned off in step S78. It should be noted that the time required for recovery in this case may be about 0.5 seconds, which is shorter than that in the case of mode A. (See Figure 14)

Further, when the current cut state is started by the mode C, the restoration is performed at the time point t4 when the clutch is turned on. That is, in this case, the determination in step S79 is “YES”, and thus step S8
0, and the control current values If, Ic, Ir are shown in FIGS.
The current value is returned according to the flow of, and the flag F ₂ is defeated in step S82. The time required for the recovery in this case may be a short time of about 0.3 seconds. (See Figure 14)

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a power transmission system of a four-wheel drive vehicle including a power transmission control device according to the present invention.

FIG. 2 is a flowchart of a vehicle body speed calculation routine.

FIG. 3 is a flowchart of a center differential differential rotation speed calculation routine.

FIG. 4 is a flowchart of a rear differential differential rotation speed calculation routine.

FIG. 5 is a flowchart of a center differential map control current value setting routine.

FIG. 6 is a flowchart of a rear differential map control current value setting routine.

FIG. 7 is a flowchart of a control current value determination routine.

8 is a flowchart of a control current value determination routine connected to FIG.

9 is a flowchart of a control current value determination routine connected to FIG.

FIG. 10 is a diagram showing a relationship between a center differential differential rotation speed and a center differential map control current value.

FIG. 11 is a diagram showing a relationship between a rear differential differential rotation speed and a rear differential map control current value.

FIG. 12 is a part of a flowchart showing a control current cut routine and a control current restoration routine in a state where the driving force cannot be transmitted from the engine to the wheels.

13 is a portion connected to the flowchart of FIG.

FIG. 14 is a timing chart for explaining a control current cut time point and a return time point.

[Explanation of symbols]

 1 Engine 2 Transmission 3 Center Diff 4 Transfer Device 7 Front Diff 9 Left Front Wheel 11 Right Front Wheel 12 Rear Diff 14 Left Rear Wheel 16 Right Rear Wheel 20 Differential Limit Controller 21 Throttle Sensor 22 Brake Switch 23 Neutral Switch 24 ABS Controller 25-28 Speed sensor

Claims (5)

[Claims] 1. A power transmission control device for a vehicle, comprising: a differential device having a differential limiting mechanism; and means for changing the differential limiting amount of the differential limiting mechanism, wherein a drive force is transmitted from an engine to wheels. A power transmission control device for a vehicle, comprising means for reducing the differential limiting amount when the disabled state continues for a predetermined time. 2. A plurality of differential limiting amount reduction start conditions are set, and the ending condition of the differential limiting amount reduction state is changed according to these differential limiting amount reduction starting conditions. Power transmission control device. 3. (a) A power transmission from the engine to the transmission is possible through a clutch interposed between the engine and the transmission, and the shift position of the transmission is neutral. If the above condition continues for a predetermined time, the reduction of the differential limiting amount is started, and then the differential limiting amount is reduced by the operation of interrupting the power transmission from the engine to the transmission by the clutch. (B) In the state where the power transmission is cut off by the clutch and the shift position of the transmission is in the neutral state for a predetermined time, the reduction of the differential limiting amount is started, By the subsequent shift operation of the transmission to a position other than the neutral position, the differential limiting amount reduction state is terminated, and (c) the power transmission is cut off by the clutch. When the transmission is being shifted to a position other than the neutral position for a predetermined period of time, the reduction of the differential limiting amount is started, and then the power transmission is connected by the clutch. The power transmission control device according to claim 2, wherein the differential limiting amount reduced state is ended by an operation. 4. When the differential limiting amount reduced state is terminated and the normal state is restored, the returning speed at the end of the differential limiting amount reducing state by the power transmission interruption operation of the clutch is the slowest, and the clutch 4. The power transmission control device according to claim 3, wherein the return speed at the end of the differential limiting amount reduction state by the power transmission connection operation is set to be the slowest. 5. The power transmission control device according to claim 1, wherein the differential limiting mechanism of the differential device is an electromagnetic clutch.