GB2088009A

GB2088009A - Controlling Electromagnetic Clutch of Vehicle

Info

Publication number: GB2088009A
Application number: GB8130490A
Authority: GB
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1980-10-11
Filing date: 1981-10-08
Publication date: 1982-06-03
Also published as: NL8104610A; DE3140229A1; FR2492023A1; FR2492023B1; JPS5766031A; GB2088009B

Abstract

A control system for an electromagnetic clutch of an internal combustion engine mounted on a vehicle is capable of controlling the clutch current Ic to provide partial engagement of the clutch after a gear change. A negative pressure sensor is operated by the vacuum level in the induction passage of the engine. A shift lever signal (a) is supplied during operation of the shift lever of the transmission and a negative pressure signal (b) is provided by the negative pressure sensor according to acceleration of the vehicle. A control circuit includes a charging circuit (44) operated by the shift lever signal (a), a standard voltage circuit (49) responsive to the negative pressure signal (b), and a comparator (50) connected to the charging circuit (44) and the standard voltage circuit (49) and produces an output signal (e) for a period of time which is decided by the level of the negative pressure signal. A gate circuit (51, 52, 54, 55) under the control of the output signal (e) of the comparator controls the level of the clutch current Ic passing through the magnetizing coil (7). <IMAGE>

Description

SPECIFICATION Electromagnetic Clutch Control System The present invention relates to a system for controlling a vehicle electromagnetic clutch, and more particularly to such a system for an electromagnetic clutch of the type having a driven member connected to an internal combustion engine, a driven member connected to a transmission, which has multi-stage change gears and a shift lever for operating the transmission, and a magnetising coil for controlling the drive between the drive member and the driven member. Such a clutch will be referred to hereinafter as "a vehicle electromagnetic clutch of the type described".

Commonly, the shift lever is provided with a switch for the magnetizing coil, which is actuated during operation of the shift lever. When the shift lever is shifted to the gear engaging position, the switch is actuated, causing flow of electric current through the magnetizing coil to magnetize the drive member. As the accelerator pedal is depressed, the current applied to the coil increases. Magnetic powder is aggregated in the gap between the drive member and the driven member, bringing about a connection between drive member and driven member. The clutch current passing through the magnetizing coil is progressively increased according to the depression of the accelerator pedal, clutch slip occurring until the magnetizing current reaches a rated value.

Further, the system may be arranged to provide a small clutch current during the re-engaging period of the clutch after change-speed operation so as to transmit the power in a partial engagement clutch condition, thereby to abate the shock caused by abrupt engagement of the clutch. The circuit of the clutch coil is turned on and off by operation of the shift lever. The level of the clutch current is controlled by operation of an accelerator switch to cause clutch slippage. In Figure 7 of the accompanying drawings, reference A shows the full clutch engaging condition, during which clutch current Im flows to cause the fullengagement of clutch. When the shift lever is operated at the beginning of gear changing operation, the clutch coil circuit is cut off as shown by B and the clutch is disengaged.When the shift lever is released from the operator's hand after the completion of the gear changing, a clutch current In smaller than the current Im flows through the clutch coil as shown by C and keep it in a partial clutch engagement condition, i.e.

slipping condition, so that the shock of the clutch engagement is decreased. Controlling period t1 for the partial clutch engagement condition during acceleration is shorter than period t2 for deceleration. After the period t1 or t2, the rated current Im as shown by D or E in Figure 7 flows so that the clutch is fully engaged. The period of the partial clutch engagement due to the current In is determined by the actuation of accelerator switch which is closed during the depression of the accelerator pedal. Accordingly, in heavy load condition at the acceleration, the period of partial engagement is shortened to decrease the period of clutch slippage, and during deceleration, the period is lengthened.

Thus, in the conventional system when the accelerator pedal is not depressed, the clutch is in partial engagement condition during the longer period t2, to reduce the shock caused by clutch engagement during deceleration. However, when gear changes are frequently or rapidly made, closing of the accelerator switch will occur in spite of the deceleration condition. The partial engagement period then becomes short, i.e. t1, causing engagement to occur abruptly and thereby causing discomfort to the passenger.

Further, should the accelerator pedal be depressed, even though the vehicle is in deceleration condition and the depression is slight, the vehicle body is subject to shock because the accelerator switch is closed and the clutch is suddenly engaged.

It is, therefore, an object of the present invention to provide a vehicle electromagnetic clutch control system of the type described which operates to vary the period of the partial clutch engagement depending on the negative pressure or vacuum in the induction passage of the engine during gear changing, whereby the shock on engagement of the clutch is reduced.

According to the present invention, a system for controlling an electromagnetic clutch of the type described comprises a first detecting means responsive to the operation of the shift lever for providing a gear-changing output signal; a second detecting means responsive to vacuum pressure in the induction passage of the internal combustion engine for providing output signals according to the vacuum pressure; a control circuit responsive to output signals of the first detecting means and the second detecting means for producing an output signal for a period determined by the output signal of the second detecting means; gate means responsive to the output signal of the control circuit for producing an output signal; and switch means responsive to the output signal of the gate means for controlling the flow of current through the magnetizing coil.

The invention will be more readily understood by way of example from the following description of control systems for an electromagnetic clutch in accordance therewith, reference being made to the accompanying drawings, in which Figure 1 is a cross-sectional view of an electromagnetic powder clutch; Figure 2 is a cross-section taken along the line Z-Z of Figure 1; Figure 3 is an electronic circuit of the control system for the clutch; Figure 4 is a sectional view showing one form of negative pressure sensing device; Figure 5 is an enlarged sectional view of the sensing device of Figure 4; Figure 6 is a timing chart illustrating variation of signals located at specified parts of Figure 3; and Figure 7 is a graph illustrating the variation of clutch current.

In Figures 1 and 2, numeral 1 is an electromagnetic powder clutch, 2 is a four-speed transmission gear box and 3 is a final reduction device.

The electromagnetic powder clutch 1 is located in a clutch case and comprises a drive plate 6 attached to the end of a crankshaft 5 of an internal combustion engine, an annular drive member 8 secured to the drive plate 6, a magnetizing coil 7 provided in the drive member 8, and a driven member 10, which is secured by a spline engagement to an output shaft 9 of the transmission 2, and which is spaced from the drive member 8 by a gap 11. Powder of magnetic material is provided in a powder chamber 12 so that the gap 11 can be filled with the powder. A cap 13 is secured to the drive member 8. The cap 13 has a cylindrical portion coaxial with the input shaft 9, on which slip rings 14 are securely provided. Slip rings 14 are connected to thedrive member 8 by a lead X.Brushes 16 pressed against slip rings 14 are supported in a holder 1 7 and connected to a hereinafter described control means by a lead Y.

In such construction, the drive plate 6 and the drive member 8 rotate together with the crankshaft 5 and the magnetic powder sealed into the powder chamber 12 is driven on to the inner surface of the drive member 8 by centrifugal force. If the magnetizing coil 7 is excited by the current applied through the lead Y, brushes 16, slip rings 14 and lead X, the drive member 8 is magnetized to produce a magnetic flux passing through the driven member 10 as shown by arrows in Figure 1. Thus, the magnetic flux coheres the powder in the gap 11, so that the power of the engine is transmitted to the input shaft 9 through the clutch.

In the transmission 2, st to 4th speed drive gears 18 to 21 are integrally provided on the input shaft 9. The drive gears 18 to 21 are engaged with driven gears 23 to 26 respectively.

Driven gears 23 to 26 are rotatably mounted on the output shaft 22 parallel to the input shaft 9.

Each of driven gears 23 and 24 is adapted to be engaged with the output shaft 22 by operating a synchromesh mechanism 27 and each of driven gears 25 and 26 is engaged with the output shaft 22 by a synchromesh mechanism 28 in the well known manner. Further, a reverse driven gear means 29 is provided. Thus, by operating the shift lever (not shown) of the transmission, the driven gear 23 may be coupled to the output shaft 22 by the synchromesh mechanism 27 and the 1 st speed obtained on the output shaft 22 because the power of output shaft 9 is greatly decreased; the 2nd, 3rd and 4th speeds, or gear ratios may be similarly obtained.

Further provided on an end of the output shaft 22 is an output gear 30 which engages with a ring gear 32 of a differential 31 of the final reduction device 3. The output of the output shaft 22 of the transmission 2 is transmitted directly from ring gear 32 to spur gear 36 through a case 33, a spider 34 and a pinion 35, and thence to the driving wheels through wheel shafts 37.

In the control circuit of Figure 3, the input signals consist of a gear-changing signal a produced during operation of the shift lever, an acceleration signal b produced when the negative pressure or vacuum in the induction passage of the engine decreases, and a car speed signal c generated when the car speed exceeds a predetermined value. A clutch control signal k is produced from those signals a, b, e.. The gearchanging signal a is applied through an inverter 40 to the base of a transistor 41, the emitter of which is grounded and the collector of which is connected to a charging circuit 44 consisting of resistor 42 and capacitor 43.The acceleration signal b is similarly applied through an inverter 45 to a standard voltage circuit 49 consisting of resistors 46, 47, 48. The outputs b' orb" and d from the charging circuit 44 and the standard voltage circuit 49 are connected to inputs of a comparator 50. The output e of the comparator 50 is connected to an AND gate 51 and to a NAND gate 52. The other input of the AND gate 51 is supplied with the car speed signal c. The other input of NAND gate 52 is supplied with an output ffrom an oscillator circuit 53 which comprises inverters, resistors and a capacitor as shown. The outputs g, ifrom AND gate 51 and NAND gate 52 are connected to a NAND gate 54, the outputjof which is connected to an AND gate 55.The other input of AND gate 55 is supplied with the gear-changing signal a, and the output k of AND gate 55 is connected to the base of a transistor 56. The emitter of the transistor 56 is grounded and the collector is connected to one end of the coil 7. Further, both ends of the coil 7 are connected to a commutation circuit 57 comprising a diode and a resistor.

Figure 4 shows an example of the acceleration detecting means employing a vacuum switch 73 on an induction passage 72 of an engine 71. The vacuum switch 73 is operated by the negative pressure of the air-fuel mixture supplied by a carburettor 70. Numerai 74 designates an exhaust pipe of the engine 71. Figure 5 shows the interior of the vacuum switch 73. Switch 73 has a cylindrical hollow body 75 divided air-tightly by a diaphragm 76 into a pressure compartment 77 and a switch compartment 78. The pressure compartment 77 communicates with induction passage 72 and the switch compartment 78 communicates with atmosphere. Further, the pressure compartment 77 has a coil spring 79 acting on an actuating member 80 secured to the diaphragm 76, and the switch compartment 78 has a micro-switch 81 which is actuated by the diaphragm 76.

When the negative pressure in the induction passage 72 is low (when the accelerator pedal is depressed), the difference between the pressures in the pressure compartment 77 and in the switch compartment 78 is small. Accordingly, coil spring 79 biases the actuation member 80 to operate the micro-switch 81. When the negative pressure is high (when the accelerator pedal is released), the pressure difference is large, and the diaphragn 76 is deflected against the action of coil spring 79 causing the micro-switch 81 to tbe switched to the off position. The condition of the micro-switch 81 then represents acceleration or otherwise. The output signal from the micro-switch 81 is applied to input b of Figure 3.

The operation of the system will now be described with reference to timing chart of Figure 6.

The gear-changing signal a is at low level while the shift lever for the transmission is actuated; acceleration signal b becomes high level by the actuation of the micro-switch 81 only when the negative pressure in the induction passage is low; and the car speed signal c is at high level only when the car speed exceeds a predetermined speed, for example 1 5 km/h.

Gear-changing at a Speed Higher than the Predetermined Car Speed With Depression of the Accelerator Pedal and Consequential Low Negative Pressure.

The gear-changing signal a changes from high to low level and is inverted by the inverter 40 to high level, which turns on the transistor 41.

Consequently, the capacitor 43 of the charging circuit 44 is discharged and the output d of the charging circuit 44 is reduced to zero-level and is supplied to the comparator 50. The acceleration signal b, which is at high level, is inverted by the inverter 45 to low level and is applied to the resistor 46 to reduce the terminal voltage of the resistor 48. The reduced signal b' becomes a standard voltage for the comparator 50. The comparator 50 compares the signals b' and d, and produces a high level signal when the signal b' is higher than the signal d. When the high level signal e is applied to the AND gate 51, the AND gate 51 produces a high level signal g because the level of car speed signal c is high.Being supplied with the high level signal e from the comparator 50 and pulse waves ffrom the oscillator circuit 53, the NAND gate 52 produces pulse waves iwhich are inverted relative to pulse waves f. Therefore, only when signals g and i are at high level does the NAND gate 54 produce a low level signaljwhich is transmitted to the AND gate 55. At this time, as long as the other input of the AND gate 55 is applied with the low level gear-changing signal a, the level of the output of the AND gate 55 is low level and the transistor 56 is turned off.

After completion of the changespeed operation, the gear-changing signal a changes from low level to high level, so that the AND gate 55 generates high level signals k corresponding to high level parts of the signaljto thereby turn on and off the transistor 56. An alternating electric current then flows through the coil 7. The mean clutch coil current is smaller than the rated current and effects partial engagement of the clutch. Thus, the electromagnetic powder clutch 1 transmits the power of the engine with slippage.

When gear-changing signal a changes from low to high level, the output of the inverter 40 turns off the transistor 41,so that the capacitor 43 is charged through the resistor 42.

Accordingly, the signal dfrom the charging circuit 44 rises exponentially. When the voltage of the signal d exceeds the signal b' from the standard voltage circuit 49, the output e of the comparator 50 changes to a low level as indicated by m in Figure 6. Thus, the level of output g from the AND gate 51 becomes low; the outputj of the NAND gate 54 becomes high; AND gate 55, with high level gear-changing signal a, produces a high output so as to turn on the transistor 56, and to cause the rated current to flow through the coil 7 and effect full engagement of electromagnetic powder clutch 1.

Gear-changing at a Speed Higher than the Predetermined Speed Without Depression of the Accelerator Pedal and Consequential High Negative Pressure.

Because the accelerator signal b is at low level when the accelerator pedal is not depressed and a high level signal from the inverter 45 is applied to the resistor 46, the standard voltage circuit 49 supplies to the comparator 50 a signal b" as a standard voltage which is higher than the signal b' produced when the accelerator pedal is depressed. Then, when the gear-changing signal a changes from low to high level and the voltage of output signal dfrom the charging circuit 44 rises gradually, the change of the output signal e of the comparator 50 from high to low level occurs at a point n where both signals b' and d coincide at a same level. In this case, the point n comes later than the point m at which the levels of signals d and b' coincide when the accelerator pedal is depressed and the duration of the high level signal e is increased. Accordingly, the interval between the completion of change gear operation and the drop in the output signal e is elongated.

During this lengthened interval, the AND gate 55 generates pulse waves to make the partial clutch engagement period longer. The variations of signals by the output from the comparator 50 are indicated by dotted lines g, i, j, k, IC in Figure 6.

By the form of the control circuit described above, the period of partial clutch engagement condition can be varied depending on the acceleration condition of vehicle during a change gear operation, so that the shock caused by clutch engagement is abated.

Claims

1. A system for controlling a vehicle electromagnetic clutch of the type described, comprising a first detecting means responsive to the operation of the shift lever for providing a gear-changing output signal; a second detecting means responsive to vacuum pressure in the induction passage of the internal combustion engine for providing output signals according to the vacuum pressure; a control circuit responsive to output signals of the first detecting means and the second detecting means for producing an output signal for a period determined by the output signal of the second detecting means; gate means responsive to the output signal of the control circuit for producing an output signal; and switch means responsive to the output signal of the gate means for controlling the flow of current through the magnetizing coil.

2. A system for controlling a vehicle electromagnetic clutch according to claim 1, further comprising an oscillator circuit for generating alternating current and second gate means responsive to the alternating current of the oscillator circuit and the output signal from the control circuit for controlling the first gate means and for decreasing the mean current passing through the magnetizing coil.

3. A system for controlling a vehicle electromagnetic clutch according to claim 1 or claim 2, wherein the control circuit comprises a charging circuit under the control of the output signal of the first detecting means, a standard voltage circuit, and a comparator under the control of the output signal from the second detecting means for comparing the output signals of the charging circuit and the standard voltage circuit for producing an output signal for a period decided by the level of the output signal of said standard voltage circuit.

4. A system for controlling a vehicle electromagnetic clutch according to claim 1, wherein the gate means is arranged to be operated when the car speed exceeds a predetermined speed.

5. A system for controlling a vehicle electromagnetic clutch of the type described, substantially as herein described with reference to the accompanying drawings.