GB2129990A

GB2129990A - A system for temperature detection

Info

Publication number: GB2129990A
Application number: GB08306454A
Authority: GB
Inventors: Ryuzo Sakakiyama
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1982-03-19
Filing date: 1983-03-09
Publication date: 1984-05-23
Also published as: GB2129990B; DE3308605A1; JPS58163831A; NL186873C; FR2523675B1; DE3308605C2; NL8300969A; GB8306454D0; NL186873B; FR2523675A1

Abstract

For detecting the temperature of an electromagnetic clutch, the voltage applied to the clutch coil of the clutch is measured by a voltage measuring circuit (41) and the current passing through the clutch coil is measured by a current measuring circuit (42). A divider (43) divides the voltage by the current to give an output which represents the resistance of the clutch coil and which varies with the temperature of the coil. The output of the divider 43 is compared with a reference voltage by a comparator (45) and the output of the comparator controls an alarm (48). <IMAGE>

Description

SPECIFICATION System for detecting the temperature of an electromagnetic clutch for a vehicle The present invention relates to a system for detecting the temperature of a coil of a clutch for a vehicle.

Electromagnetic powder clutches are known.

Such an electromagnetic powder clutch comprises an annular drive member secured to a crankshaft of an engine, a clutch coil provided in the drive member, a driven member secured to an input shaft of a transmission and provided adjacent to the drive member with a small gap and magnetic powder provided in a chamber in the clutch.

Change speed gears in the transmission are operated by a shift lever, which includes a switch for the circuit of the clutch coil; when the shift lever is gripped by operator's hand, the switch is opened to cut off the clutch current and allow a change gear operation of the transmission to be performed. When the shift lever is shifted to the gear engaging position, and released by the hand, the switch is closed and electric current flows through the clutch coil to magnetize the drive member. The magnetic powder is aggregated in the gap between the drive member and the driven member, so that the driven member is coupled to the drive member.The clutch current passing the clutch coil progressively increases according to the degree of depression of the accelerator pedal, while the clutch slips between the drive member and driven member and gradually engages until full engagement is achieved when the clutch current reaches to the rated current. Thus, the vehicle may be started by depressing the accelerator pedal without operating a clutch pedal. Such a clutch control system is disclosed in U.S. patents 3,073,422 and 3,094,202.

In the electromagnetic clutch, the temperature of the coil increases with an increase of the clutch current and the friction between the drive member, driven member and electromagnetic powder. In a conventional clutch, in order to detect overheating of the coil, a thermistor or like thermo sensor is mounted on the clutch case.

Since the sensor detects the temperature of the coil indirectly, there is necessarily a delay between a change in coil temperature and the consequential change in sensor signal. As a result, compensating action cannot be taken immediately an overheating problem arises.

An object of the present invention is to provide a system which detects directly the temperature of the clutch coil. In accordance with the present invention, the resistance of the coil is determined from the current passing through the coil and the voltage applied thereto. Since the resistance of the coil varies with the temperature of the material of the coil, a temperature higher than a predetermined value can be detected by comparing the resistance with a reference value.

Thus, according to the present invention, a system for detecting the temperature of an electromagnetic clutch for a vehicle, the clutch having a clutch coil for magnetizing clutch element for the engagement of the clutch, comprises resistance determining means for giving an output in accordance with the resistance of the clutch coil by dividing the voltage applied to the clutch coil by the current passing through the clutch coil; a comparator for comparing the output of the resistance determining means with a reference value; and an alarm circuit for giving an output dependent on the output of the comparator.

The invention will be more readily understood by way of example from the following description of a clutch temperature in accordance therewith, reference being made to the accompanying drawings, in which Figure 1 is a sectional view of an electromagnetic powder clutch; Figure 2 is a section on the line Z-Z in Figure 1; Figure 3 is a block diagram illustrating the system for detecting the temperature of the clutch; and Figure 4 is a circuit of the system of Figure 3.

In the electromagnetic powder clutch of Figures 1 and 2, the clutch is provided between an internal combustion engine (not shown) and a four-speed transmission 2 which is connected to a final reduction device 3.

The electromagnetic powder clutch 1 is located in a clutch case 4, and comprises a drive plate 6 connected to the end of a crankshaft 5 of the internal combustion engine, an annular drive member 8 secured to the drive plate 6, a clutch coil 7 in the drive member 8, and a driven member 10 secured by spline engagement to an input shaft 9 of the transmission 2, leaving a gap 11 from the drive member 8. Magnetic powder is contained in a powder chamber 12. A cap 13 secured to the drive member 8 has a cylindrical portion 1 3a coaxial with the input shaft 9, on which slip rings 14 are secured. Slip rings 14 are electrically connected to the coil 7 by leads X, while brushes 1 6 pressed against slip rings 14 are supported in a holder 1 7 and connected to a hereinafter described control means by leads Y.

In such a construction, the drive plate 6 and the drive member 8 rotate together with the crankshaft 5 and the magnetic powder sealed in the powder chamber 12 is drawn on to the inner surface of the drive member 8 by centrifugal force.

When the clutch coil 7 is excited by a current supplied through the leads Y, brushes 16, slip rings 14 and leads 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 powder is aggregated in the gap 11, so that the output powder of the crankshaft 5 is transmitted to the input shaft 9 through the clutch.

In the transmission 2, 1 st to 4th speed drive gears 18 to 21 are integrally formed on the input shaft 9. The drive gears 1 8 to 21 are respectively engaged with driven gears 23 to 26. Driven gears 23 to 26 are rotatably mounted on the output shaft 22 which is parallel to the input shaft 9. Each of the driven gears 23 and 24 is adapted to be engaged with the output shaft 22 by operating a synchromesh mechanism 27 and each of the driven gears 25 ard 26 is adapted to be engaged with the output shaft 22 by a synchromesh mechanism 28 in a well-known manner. Further, a reverse drive gear 29 is formed on the input shaft 9. Thus, by operating a shift lever (not shown) of the transmission, the driven gear 23 is coupled with the output shaft 22 by the synchromesh mechanism 27 and the 1 st speed gear is obtained.

Similarly, the 2nd, 3rd and 4th speed gears may be respectively obtained by operating the shift lever.

Moreover, an output gear 30 is formed on an end of the output shaft 22, and is engaged with a ring gear 32 in a differential 31 of the final reduction device 3. Thus, the output of the output shaft 22 of the transmission 2 is transmitted to side gears 36 through a case 33, a spider 34 and pinions 35, and further to driving wheels through wheel shafts 37.

Referring to Figure 3 showing the temperature detection system, the clutch coil 7 is electrically connected to a voltage measuring circuit 41 and a current measuring circuit 42. The outputs of the two circuits 41 and 42 are connected to a divider 43. Output signals of divider 43 and a reference voltage generating circuit 44 are applied to a comparator 45 and the output of the comparator 45 is applied to an alarm circuit 48 through a holding circuit 46 which can be reset by a reset circuit 47.

The voltage across the clutch coil 7 and the current flowing through the coil are measured by circuits 41 and 42 and the outputs of those circuits are applied to the divider 43 in which the operation of R = V/I is performed, where the R is resistance, V is voltage and I is current. A measure of the resistance of the clutch coil 7 can be obtained. The resistance Rt which varies with the variation of temperature of the coil can be presented as Rt=R0(1 + try) where (z is the coefficient of the material of the coil and T is temperature. The output voltage of divider 43 corresponds to the resistance Rt and is compared with the reference voltage in the comparator 45. The reference voltage is slightly lower than a value which will cause overheating of the clutch.The comparator 45 produces an output signal when the input voltage from the divider is higher than the reference voltage, i.e. when the temperature of the clutch rises to a value approaching the overheating value. The output signal of the comparator 45 actuates the holding circuit 46 to produce an output which is held until a reset signal is applied thereto from the reset circuit 47. Thus, the alarm circuit 48 operates to produce alarm indication or sound until the reset signal is applied.

Figure 4 shows an example of a circuit for the system of Figure 3. The voltage applied to the coil is measured by an opamp OP1 with resistors R2, R3 and R4 and current is measured by an opamp OP2 with resistors R, and R5. Output K of the opamp OP, and output L of opamp OP2 are applied to the divider 43 to perform the calculation - K/L and to produce an output voltage M. The output voltage M is compared by comparator OP7 with a reference voltage applied by resistors R10 and R When the output M is higher than the reference voltage, the comparator OP7 produces an output signal which actuates a flip-flop circuit comprising NOR gates NOR, and NOR2 to change the output at the NOR gate NOR, to a high level. The high level output of the clip-flop circuit causes a transistor Tr to be turned on, so that an alarm lamp AL is turned on. If a switch SW is closed, a reset signal is applied to the flip-flop circuit to cause the output of the flip-flop circuit to go to a low level. Thus, the transistor Tr is cut off to turn off the lamp AL.

While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

1. A system for detecting the temperature of an electromagnetic clutch for a vehicle, said clutch having a clutch coil for magnetizing clutch elements for the engagement of the clutch comprising: resistance determining means for giving an output in accordance with the resistance of the clutch coil by dividing the voltage applied to the clutch coil by the current passing through the clutch coil; a comparator for comparing the output of the resistance determining means with a reference value; and an alarm circuit for giving an output dependent on the output of the comparator.

2. A system for detecting the temperature of an electromagnetic clutch for a vehicle, said clutch having a clutch coil for magnetizing clutch elements for the engagement of the clutch comprising: a first measuring circuit for measuring the voltage applied to the clutch coil; a second measuring circuit for measuring the current passing through the clutch coil; a divider for dividing the voltage measured with the first measuring circuit by the current measured with the second measuring circuit; a comparator for comparing the output of the divider with a reference value; and an alarm circuit actuated by the output of the comparator for giving an alarm indication.

3. A temperature detecting system according to claim 2, wherein the second measuring circuit is arranged to produce an output voltage corresponding to measured clutch current, and the comparator compares the output voltage of the divider with a reference voltage which is slightly lower than a critical voltage corresponding to overheating of the clutch.

4. A temperature detecting system according to claim 3, further comprising a holding circuit for holding the output of the comparator and for applying an output dependent on the holding state to the alarm circuit.

5. A temperature detecting system according to claim 3, wherein the holding circuit comprises a flip-flop circuit and a reset circuit therefor.

6. A system for detecting the temperature of an electromagnetic clutch for a vehicle, substantially as herein described with reference to the accompanying drawings.