CONTROL SYSTEM FOR AN ELECTROMAGNETIC CLUTCH FOR A VEHICLE

Abstract: A system for controlling disengagement of an electro­ magnetic clutch of a vehicle during rapid deceleration of the vehicle. The rapid deceleration is detected by the rate of change of engine (or vehicle) speed and when the magnitude of deceleration is larger than a reference value, the electro­ magnetic clutch is disengaged at an engine speed which is above the idling speed, at which disengagement would otherwise take place.

Description: The present invention relates to a control system for an electromagnetic clutch for an automatic transmission of a motor vehicle as defined in the preamble of claim 1. An automobile provided with a continuously variable belt-drive transmission with such an electromagnetic clutch control system is disclosed in EP-A 151038. The electromagnetic clutch of the transmission is controlled by a control system to provide various operational modes for clutch torque (clutch current). One of the modes is selected in accordance with a position of a selector lever and driving conditions of the vehicle to control the electromagnetic clutch. On starting the vehicle, the clutch torque is increased in proportion to the engine speed or the opening degree of a throttle valve of the engine. When the vehicle speed reaches a predetermined speed, the clutch is completely engaged by a lock-up current. When the vehicle speed decreases below a predetermined speed, the clutch is disengaged to prevent stalling of the engine. Generaly, the vehicle speed is detected by counting pulses proportional to the speed. On the other hand, when the vehicle speed is braked by sudden heavy depression of the brake pedal, the deceleration of vehicle speed becomes very large. When the vehicle is decelerated, the separation of the pulses relative to the vehicle speed becomes long. As a result, there is a delay in detection of the predetermined speed for disengaging the clutch. Thus, the disengagement of the clutch is delayed, causing decrease of engine speed or stalling of the engine because of overload on the engine. Particularly, on a snowy road, the wheels are liable to be rapidly locked by braking, delaying the disengagement of the clutch. In order to solve the problem, it may be preferable to set the predetermined vehicle speed for disengaging the clutch at a high level. However, in such a system, since the clutch is disengaged at a high vehicle speed, the engine braking effect is reduced. The present invention seeks to provide a control system which operates to prevent the decrease of engine speed during rapid deceleration of the vehicle speed whilst maintaining a sufficient engine braking effect. According to the present invention there is provided a system for controlling an electromagnetic clutch for a vehicle as defined in claim 1. Some embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a system for controlling an electromagnetic clutch for a motor vehicle; Figures 2a and 2b show a block diagram of a control unit according to the present invention; Figure 3 is a graph showing regions of various modes; Figure 4 is a block diagram of a main part of the system according to the present invention; Figure 5 is a flow chart showing the operation of the system; Figure 6 is a graph showing regions of various modes of a system for another embodiment of the present invention; Fig. 7 is a block diagram of a main part of the system of the embodiment; Fig. 8 is a flow chart showing the operation of the system. Referring to Fig. 1, a crankshaft 10 of an engine 1 is operatively connected to an electromagnetic powder clutch 2 for transmitting the power of the engine 1 to a continuously variable belt-drive automatic transmission 4 through a selector mechanism 3. The output of the belt-drive transmission 4 is transmitted to axles 8 of vehicle driving wheels 9 through an output shaft 13, a pair of intermediate reduction gears 5, an intermediate shaft 6, and a differential 7. The electromagnetic powder clutch 2 comprises an annular drive member 2a connected to crankshaft 10 of the engine 1, a driven member 2b secured to an input shaft 11 of the transmission 4, and a magnetizing coil 2c provided in the driven member 2b. Magnetic powder is provided in a gap between the drive member 2a and driven member 2b. When the magnetizing coil 2c is excited by the clutch current, driven member 2b is magnetized to produce a magnetic flux passing through the drive member 2a. The magnetic powder is aggregated in the gap by the magnetic flux and the driven member 2b is engaged with the drive member 2a by the powder. On the other hand, when the clutch current is cut off, the drive and driven members 2a and 2b are disengaged from one another. In the belt-drive transmission 4, the selector mechanism 3 is provided between the input shaft 11 and a main shaft 12. The selector mechanism 3 is provided with a synchromesh mechanism comprising gears, hub, and sleeve for connecting the input shaft 11 and the main shaft 12 to selectively provide a driving position (D-range) and a reverse driving position (R-range). The continuously variable belt-drive automatic transmission 4 has the main shaft 12 and the output shaft 13 provided in parallel with the main shaft 12. A drive pulley 14 provided with a hydraulic cylinder 14a is mounted on the main shaft 12. A driven pulley 15 provided with a hydraulic cylinder 15a is mounted on the output shaft 13. A drive belt 16 engages with the drive pulley 14 and the driven pulley 15. Hydraulic cylinders 14a and 15a are communicated with an oil hydraulic control circuit 17. The hydraulic control circuit 17 is responsive to vehicle speed, engine speed and throttle valve position for controlling the amount of oil supplied to the cylinders 14a and 15a. The pulleys 14 and 15 are operated by compressive forces of cylinders so that the running diameter of belt 16 is varied to continuously change the transmission ratio. An electronic control system for the clutch 2 and the belt-drive transmission 4 has an engine speed sensor 19, and rotating speed sensors 21 and 22 for respectively sensing speeds of drive pulley 14 and the driven pulley 15. A choke switch 24 produces an output signal when a choke valve of the engine 1 is closed, and an air conditioner switch 23 produces an output signal at the operation of an air conditioner. A selector lever 25 connected to the selector mechanism 3 is provided with a select position sensor 26 for sensing a drive position D and a reverse position R. An accelerator pedal switch 28 is provided for sensing the depression of an accelerator pedal 27, and a throttle position sensor 29 is provided. Output signals of the sensors and pulses of the switches are applied to an electronic control unit 20 which produces a clutch current control signal to the clutch 2 and a control signal for controlling the transmission ratio (i) and a line pressure control signal to the control circuit 17. Referring to Figs. 2a and 2b showing the control unit 20 of Fig. 1, a transmission ratio changing speed control section 30 is supplied with a drive pulley speed signal N P of the sensor 21, driven pulley speed signal N S of the sensor 22, and throttle position signal ϑ of the sensor 29 to produce the transmission ratio control signal dependent on a desired transmission ratio changing speed di/dt. A line pressure control section 31 is applied with an engine speed signal Ne of the sensor 19, throttle position signal ϑ of the sensor 29, actual transmission speed ratio signal i (N S /N P ) of the transmission ratio changing speed control section 30 to produce the line pressure control signal dependent on a desired line pressure. These control signals are applied to the control circuit 17 to control the transmission ratio and line pressure of the transmission 4. A reverse excitation mode deciding section 32 is applied with engine speed signal Ne of the sensor 19 and drive position signal of the select position sensor 26. When the engine speed Ne is below 300 rpm, or the selector lever 25 is at a neutral position (N-range) or a parking position (P-range), the reverse excitation mode deciding section 32 produces a reverse excitation signal which is applied to an output deciding section 33, so that a small reverse current flows in the clutch 2 to release the clutch completely. A clutch current mode deciding section 34 is supplied with signals from the reverse excitation mode deciding section 32 and accelerator pedal switch 28, and vehicle speed signal V from driven pulley speed sensor 22 for deciding driving conditions such as starting mode to produce output signals. The output signals are applied to a start mode providing section 35, drag mode providing section 36, and clutch lock-up engage mode providing section 37. The start mode providing section 35 decides clutch current of starting characteristic dependent on the engine speed Ne at ordinary start or at closing of the choke switch 24 or air conditioner switch 23. The starting characteristic is corrected by signals from the throttle valve opening degree ϑ, vehicle speed V, and driving positions of D-range and R-range. The drag mode providing section 36 decides a small drag current when the accelerator pedal 27 is released at a low speed in each drive position for providing a drag torque to the clutch 2 for the smooth start of the vehicle. The clutch lock-up engage mode providing section 37 decides a lock-up current in response to the vehicle speed V and throttle opening degree ϑ at each drive position for entirely engaging the clutch 2. Outputs of sections 35, 36 and 37 are applied to the output deciding section 33 to control the clutch current. A range of each mode is shown in Fig. 3. Output signals from throttle valve position sensor 29 and accelerator pedal switch 28 are applied to a throttle valve opening degree providing section 38 for operating an actuator 39 in accordance with the difference between both signals. Thus, the opening degree of a throttle valve is decided. Referring to Fig. 4, the clutch lock-up engage mode providing section 37 has a deceleration magnitude detecting section 40 which is applied with the engine speed signal Ne to make a calculation of the magnitude of deceleration G given by -dNe/dt. The deceleration magnitude G is compared with a predetermined reference deceleration G1. When the deceleration magnitude G is larger than or equal to the predetermined deceleration G1 (G≧ G1), the section 40 produces an output signal which is applied to a rapid deceleration deciding section 42. Further, in order to detect a lower limit engine speed for disengaging the clutch, an engine speed detector 41 is provided. The detector 41 is applied with the engine speed signal Ne and produces a lower limit signal when the engine speed decreases to or below a predetermined engine speed n1 which is higher than an idling speed nId. The lower limit signal is applied to the rapid deceleration deciding section 42. In response to both the output signals, the rapid deceleration deciding section 42 produces a rapid deceleration signal. The clutch lock-up engage mode providing section 37 is further provided with a lock-up mode current deciding section 37a applied with signals of throttle valve opening degree ϑ, vehicle speed V, drive position R-range and D-range, and output signal of clutch current mode deciding section 34. A current setting section 37b is provided for determining various currents in responsive to input signals from sections 42 and 37a to produce a current signal I L which is applied to an output section 37c. The operation of the system will be described hereinafter. During ordinary deceleration in the drive range D, the lock-up current engage mode is changed to drag mode at a predetermined vehicle speed V4 set in the clutch current mode deciding section 34. The clutch current becomes zero to release the clutch 2. At rapid deceleration, the rapid deceleration deciding section 42 produces the rapid deceleration signal in accordance with output signals of the sections 40 and 41. Fig. 5 shows an interrupt routine at the deceleration magnitude detecting section 40 and the engine speed detector 41. The deceleration G is given by subtracting an engine speed Ne2 at the present program from an engine speed Ne1 at the last program. The present engine speed Ne2 is stored in a memory for the next program. When the deceleration G is larger than the predetermined reference deceleration G1, and engine speed Ne is lower than the set speed n1, the decision of rapid deceleration is made. The resultant signal of the section 42 is applied to the lock-up current providing section 37b, the lock-up current is cut off by the signal from the section 42 to disengage the clutch 2 at vehicle speed V₄. Thus, the engine 1 is prevented from reducing in speed. When the vehicle speed is decreased below V3, the cut off mode of the clutch is changed to the drag mode to keep the release of the clutch. Thus a drag torque is provided to the clutch 2. When the accelerator pedal is depressed, the mode of the clutch is changed to the start mode. Figs. 6 to 8 show another embodiment of the present invention. In this embodiment, a clutch release operation is operated in the clutch current mode deciding section 34. Referring to Fig. 7, a deceleration magnitude detecting section 45 is applied with the vehicle speed signal V from driven pulley speed sensor 22 (Fig. 2) and calculates a deceleration magnitude G (G = -dv/dt). The deceleration magnitude G is applied to a rapid deceleration deciding section 46 and compared with a predetermined deceleration G1. The rapid deceleration is decided, when the deceleration speed G is larger than or equal to the predetermined deceleration G1 (G ≧ G1). A clutch disengaging vehicle speed providing section 47 is applied with the vehicle speed V for providing a predetermined vehicle speed V5 which is higher than the ordinary disengaging speed V4. The output signal of the section 47 is applied to the rapid deceleration deciding section 46. At rapid deceleration, the vehicle speed V5 is applied from the section 46 to the clutch current mode deciding section 34 so as to cut off the clutch current at the speed. In response to the output signal of the section 34, the lock-up engage mode of the clutch is changed to the drag mode to cut off the clutch current. In operation, as shown in Fig. 8, the deceleration magnitude G is given by subtracting vehicle speed V2 at present program from a vehicle speed V1 at the last program. The present vehicle speed V2 is stored in a memory for the next program. When the magnitude G of deceleration is larger than the reference deceleration G1, the section 46 produces the output signal. The output signal is applied to the clutch current mode deciding section 34, so that as shown by the dotted line in Fig. 6, the clutch current is cut off at the vehicle speed V5 to disengage the clutch 2.

Claims: A system for controlling the current in an electromagnetic clutch for a vehicle of the kind in which the clutch is automatically disengaged at low engine or vehicle speeds, including means for producing an engine or vehicle speed signal, and means for setting a first level of engine or vehicle speed at which the clutch is disengaged when the engine or vehicle decelerates characterised by means for setting a second higher level at which the clutch is disengaged under rapid deceleration greater than a predetermined value, and a deceleration magnitude detection section (40) which is supplied with the speed signal to calculate deceleration from a previous value of the speed signal and a current value of the speed signal, means (42, 46) for detecting engine or vehicle deceleration greater than said predetermined value and for producing a rapid deceleration signal, and said clutch current control means (37b) being responsive to the rapid deceleration signal and so arranged that the clutch is disengaged at the second level under rapid deceleration. A sytem according to claim 1 wherein the first level is the idling speed of the engine.

Inventors: OHKUMO, HIROYA, SAKAKIYAMA, RYUZO
Applicants: FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1987
Main classification: B60K41
IPC codes: F16H59, F16D48