GB2263519A

GB2263519A - System for controlling a continuously-variable transmission for a motor vehicle

Info

Publication number: GB2263519A
Application number: GB9227164A
Authority: GB
Inventors: Hiroshi Tanaka; Maki Okayasu; Yasufumi Ideta
Original assignee: Nissan Motor Co Ltd; Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp; Nissan Motor Co Ltd
Priority date: 1992-01-22
Filing date: 1992-12-31
Publication date: 1993-07-28
Also published as: DE4301591A1; JPH05193402A; GB9227164D0

Description

1 2263519 1 SYSTEM FOR CONTROLLING A CONTINUOUSLY VARIABLE TRANSMISSION

FOR A MOTOR VEHICLE The present invention relates to a system f or controlling a continuously variable transmission (CVT) for a motor vehicle having an automatic clutch and an antilock brake system, and more particularly to a control system for properly controlling an automatic transmission in combination with the antilock brake system.

It has become popular to provide the antilock brake system (hereinafter called ABS) on the motor vehicle in order to prevent wheels from locking when the vehicle is braked on a road having a low friction coefficient thereby improving the directional stability and controllability of the vehicle. The ABS electronically controls the oil pressure supplied to the brakes to prevent the wheels from locking. However, in a vehicle provided with the continuously variable transmission where a transmission ratio and a line pressure are precisely controlled in accordance with wheel speed and other factors, the operation of the ABS influences largely the control of the transmission. Hence it is preferable to control both the ABS and the transmission when the ABS is operated.

Furthermore, in the operation of the ABS, the pressure of the brake oil supplied to a brake system is reduced to release the wheel, so that the wheel starts to rotate faster. However, the drive wheels are directly 1 q 1 2 connected to the engine through the automatic clutch and the transmission. Consequently, the rotation of the wheels is suppressed by the inertia mass of the engine. As a result, restoration of the wheel rotating speed may be delayed, thereby deteriorating the efficiency of the ABS.

Japanese Patent Application Laid-Open 62-247928 discloses an engine speed control system. In the system, when a driver selects an optimum transmission ratio, a throttle valve of the engine is controlled to maintain the engine speed to a set speed. However, the system is for controlling an engine speed while the clutch is engaged. Thus, as the system is not for controlling the ABS, the system cannot be applied to the engine speed control system with the ABS while the clutch is disengaged.

According to the present invention, there is provided a system for controlling a continuously variable transmission for a motor vehicle having an engine, an automatic clutch provided between the engine and the continuously variable transmission, hydraulic means for controlling the transmission, a wheel speed sensor for detecting a wheel speed of the vehicle, and an antilock brake system, the control system comprising:

determining means responsive to the wheel speed for producing an ABS signal for operating the antilock brake system; and clutch releasing means responsive to said ABS signal for releasing the automatic clutch.

3 Furthermore, there may be provided speed increasing means responsive to the ABS signal for increasing an idling speed of the engine, and stopping means responsive to the ABS signal for stopping an operation of an air conditioner mounted on the motor vehicle.

In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings in which:- 4 Fig. 1 shows a schematic diagram of a continuously variable belt-drive transmission and a hydraulic control circuit thereof according to the present invention; Fig. 2 shows a block diagram of a control unit of the present invention; Fig. 3a to 3f show operational characteristics of an ABS; Fig. 4 is a flowchart showing operation at a release of a clutch in accordance with the present invention; Fig. 5 is a schematic diagram of a second embodiment of the present invention; and Fig. 6 is a block diagram of a control unit of the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Fig. 1, a continuously variable belt-drive automatic transmission for a motor vehicle, to which the present invention is applied, comprises an automatics clutch 2 for transmitting power of an engine 1 to the continuously variable transmission 4 through a selector mechanism 3.

The continuously variable transmission 4 has a main shaft 5 and an output shaft 6 provided in parallel with the main shaft 5. A drive pulley (primary pulley) 7 and a driven pulley (secondary pulley) 8 are mounted on the main shaft 5 and the output shaft 6, respectively. A fixed conical disc 7a of the drive pulley 7 is integral with the main shaft 5 and an axially movable conical disc 7b is axially slidably 5 mounted on the main shaft 5. 7b also slides in a cylinder 5 to provide a servo device.

A fixed conical disc Ba of the driven pulley 8 is formed on the output shaft 6 opposite to the movable conical disc 7b and a movable conical disc 8b is slidably mounted on the shaft 6 opposite to the disc 7a. The movable conical disc 8b has a cylindrical portion which is slidably engaged in a cylinder 10 of the output shaft 6 to form the servo device. A belt 11 engages wih the drive pulley 7 and the driven pulley 8.

The cylinder 9 of the drive pulley 7 has a pressure receiving area which is larger than that of the cylinder 10 of the driven pulley 8. Thus, a running diameter of the belt 11 on the pulleys 7 and 8 is varied dependent on driving conditions.

Secured to the output shaft 6 is a drive gear 12a which engages with an intermediate reduction gear 12 on an intermediate shaft 13. An intermediate gear 14a on the shaft 13 engages with a final reduction gear 14. A 25 rotation of the final reduction gear 14 is transmitted The movable conical disc 9 formed on the main shaft 6 to axles 17 of vehicle driving wheels 16 through a differential 15.

In a hydraulic control circuit, an oil in an oi reservoir 30 is supplied to a line pressure control valve 22 through a line pressure passage 21 by an oi pump 20. The oil pump 20 is further connected with the cylinder 10 of the driven pulley 8 through a passage 21b. The line pressure control valve 22 is communicated with a transmission ratio control valve 23 through a passage 21a. The cylinder 9 of the drive pulley 7 is applied with a pressurized oil through the passage 21, the line pressure control valve 22, the passage 21a, the transmission ratio control valve 23, and a passage 24. A passage 25 is connected between the line pressure control valve 22 and a solenoid operated on-off valve 27. A passage 26 is connected between the transmission ratio control valve 23 and a solenoid operated on-off valve 28. The solenoid operated valve 27 is connected with the pump 20 through a passage 21c having an orifice 27a, and the valve 28 is communicated with the passage 21a through a passage 21d having an orifice 28a.

The solenoid operated valve 27 is adapted to be operated by electric signals from a control unit 40 for producing control pressure. The control pressure is applied to the line pressure control valve 22. The 7 4 line pressure control valve 22 is connected with a sensor shoe 29 through a spr-ng retainer. The sensor shoe 29 is engaged with the movable disk 7b of the drive pulley 7 so as to detect an actual transmission ratio i. Thus, the line pressure PL is controlled in accordance with the transmission ratio i, and an engine torque Te.

The solenoid operated valve 28 is also operated by the electric signals and produces reducing pressure which is applied to the transmission ratio control valve 23 for shifting a spool of the valve 23 to an oil supply position and an oil drain position. Thus, the flow rate Q of the oil supplied to or drained from the cylinder 9 of the drive pulley 7 is controlled to provide an optimum transmission ratio i.

Describing a brake system having an ABS, a brake pedal 31 is connected to a master cylinder 32 for producing fluid pressure in accordance with a depression of the brake pedal. The master cylinder 32 is communicated with a pair of modulators 34 of the ABS through a pipe 33a. A pipe 33b from each modulator 34 is communicated with a brake device 35 of each driving wheel 16. The modulator 34 is further communicated with a brake device of the driven wheels (not shown) through a pipe 33c having a proportioning valve 36 for adjusting the pressure to the driven wheels. The 8 A modulator 34 has various solenoid valves for respectively reducing the pressure, increasing and holding the pressure, so as to control the brake fluid pressure when the antilock brake system is in operation 5 in accordance with a signal from the control unit 40.

Referring to Fig. 2 showing an electronic system of the control unit 40, the system is provided with a drive pulley speed sensor 41, a driven pulley speed sensor 42, a throttle position sensor 43, a shift position sensor 44, an accelerator pedal switch 45, an engine speed sensor 48, a front-wheel speed sensor 46 and a rear-wheel speed sensor 47.

Output signals Np and NS of the sensors 41, 42 and an output signal e representing an opening degree of a throttle valve detected by the throttle position sensor 43 are fed to a transmission ratio control section 50. The control section 50 calculates the actual transmission ratio i and a desired transmission ratio id in accordance with the input signals. A transmission ratio changing speed di/dt is calculated in accordance with the difference between the actual transmission ratio i and the desired transmission ratio id. A duty ratio D determined in accordance with the transmission ratio changing speed (di/dt) is supplied to the solenoid operated on-off valve 28.

9 4 The engine speed signal Ne and the throttle valve opening degree e are applied to a line pressure control section 51. In the line pressure control section, the engine torque Te is estimated based on the engine speed Ne and the throttle opening degree e. A duty ratio DL which corresponds to a desired line pressure dependent on the engine torque Te is determined and supplied to the solenoid operated on-off valve 27.

The engine speed Ne, the driven pulley speed NS representing the vehicle speed, one of the output signals of the shift position sensor 44, and an output signal of the accelerator pedal switch 45 representing the depression of an accelerator pedal are fed to a clutch control section 52. The control section 52 determines an operational mode of the automatic clutch 2 in accordance with the driving conditions of the vehicle. When the vehicle is starting or under a condition where the complete engagement of the clutch 2 is preferable, the clutch current the level of which is appropriate for each operation mode is applied to the clutch 2. When the vehicle speed is lower than a predetermined reference speed, the clutch current is automatically cut off, thereby preventing the engine 1 from stalling.

For controlling the ABS, a vehicle speed calculator 53 is fed with a front-wheel speed NF from the front-wheel speed sensor 46 and a rear-wheel speed NR from the rear- wheel speed sensor 47. A vehicle speed V is calculated as an average of the wheel speeds NF and NR. A wheel lock determining section 54 is applied with the wheel speeds NF and NR for detecting the lock of the wheels. The wheels may be locked when the deceleration dN/dt of the wheel speed NF or NR is extremely large. A lock signal from the determining section 54, the vehicle speed V and wheel speeds NF and NR are applied to a hydraulic pressure controller 55 for controlling the modulator 34 through an output controller 56.

When the wheel speed NF or NR of the wheel is smaller than a pseudo vehicle speed Vc so that the wheel may be locked, the controller 55 produces a pressure reducing signal to reduce the hydraulic pressure for the brake device.

When the wheel speed restores, a signal to increase the hydraulic pressure is produced. The output controller 56 applies an ABS signal based on those signals to the solenoid valves in the modulator 34.

A system for preventing the efficiency of the ABS from deteriorating and for providing sufficient discharge of the pump 20 is described hereinafter. When the hydraulic pressure of the brake system 11 decreases at the operation of the ABS, the restoration of the wheel speed may be delayed caused by the inertia mass of the engine 1, thereby deteriorating efficiency of the ABS. On the other hand. when the automatic clutch 2 is released, the engine speed Ne decreases to an idle speed so that the discharge of the oil pump 20 driven by the engine rapidly reduces, which causes decrease of the line pressure. At the same time, oil pressure applied to a drive pulley of the continuously variable transmission decreases as well as the line pressure so that the belt 11 slips on the pulleys. Furthermore, if an air conditioner mounted on the vehicle is operated during the idling state of the engine, the load caused by a compresser (not shown) of the air conditioner is exerted on the engine. It may disturb or delay the increase of the engine speed Ne.

The control unit 40 is provided with a clutch release determining section 60 to which the ABS signal from the output controller 56 is fed. The clutch release determining section 60 produces a clutch release signal in accordance with the ABS signal which is fed to the clutch control section 52, thereby releasing the clutch 2.

The clutch release signal is further fed to an idle speed control section 61 which operates to actuate an actuator 62 mounted on the throttle valve la of the 12 engine-1 so as to increase engine speed Ne in the idling state.

The control unit 40 is further provided with an air conditioner controller 65 to which an output signal of the idle speed control section 61 is applied for controlling a clutch 63 of the air conditioner for operatively connecting the compresser of the air conditioner to the engine 1, and a condenser fan 64. In accordance with the input signal from the idle speed control section 61, the controller 65 is operated to release the clutch 63 and to stop the condenser fan 64.

The operation of the system will be described hereinafter.

When the accelerator pedal is depressed at the drive range, the clutch current increases progressively with an increase of the engine speed Ne. The automatic clutch 2 is gradually engaged, transmitting the engine power to the drive pulley 7. The power of the engine 1 is transmitted to the output shaft 6 at the largest transmission ratio by the drive belt 11 and the driven pulley 8, and further transmitted to the axles 17 of the driving wheels 16 through the intermediate shaft 13 and the differential 15. Thus, the vehicle is started. When the vehicle speed (output signal Ns) exceeds a predetermined value, the clutch 2 is entirely engaged.

13 t 9 1 The pump 20 driven by the engine 1 applies the oil to the line pressure control valve 22. When the engine torque Te is large in a low engine speed range, the desired line pressure is large. The solenoid operated on-off valve 27 is operated at the duty ratio DL corresponding to the desired line pressure, thus increasing the line pressure PL. As the engine torque Te decreases in a high engine speed range, the line pressure PL is reduced. Thus, the power is transmitted through the transmission without slipping the belt 11.

The line pressure PL is supplied to the cylinder 10 of the driven pulley 8 and the transmission ratio control valve 22. In the transmission control section 50 of the control unit 40, the desired transmission ratio id is determined in dependency on the respective driving conditions. The transmission ratio changing speed di/dt is calculated based on the actual transmission ratio i and the desired transmission ratio id so that the duty ratio D for the transmission control valve 23 is obtained.

The solenoid operated valve 28 is operated by the duty ratio D and produces reducing pressure which is applied to the transmission ratio control valve 23 for shifting the spool of the valve 23 to the oil supply position and the oil drain position. Thus, the flow rate of the oil supplied to or drained from the 14 1 I cylinder 9 of the drive pulley 7 is controlled in dependency on the transmission ratio changing speed di/dt to produce a primary pressure. Thus, the running diameter of the belt 11 changes by the drive pulley 7 for variable controlling the transmission.

When the brake pedal 31 is depressed during the driving condition, the master cylinder 32 produces the brake fluid pressure which is supplied to the brake devices 35to brake the wheels. As a result, the vehicle speed and the driven pulley speed NS are decreased, so that the transmission ratio control section 50 operates the transmission ratio control valve 23 to downshift the transmission ratio.

On the other hand, it is determined at the wheel lock determining section 54 if the wheels are going to be locked at a rapid deceleration of the wheel speed NF or NR. Namely, when the vehicle is braked on a road having a low friction coefficient as shown in Fig. 3a, the front-wheel speed NF or the rear-wheel speed NR rapidly decreases as shown in Fig. 3b. The hydraulic pressure controller 55 produces an ABS signal as shown in Fig. 3a, to increase. maintain or decrease the fluid pressure in accordance with the difference between the wheel speed NF or NR and the pseudo vehicle speed Vc. The ABS signal is applied to the modulator 34 through the output controller 56 for regulating the pressure.

Thus, the fluid pressure for the brake device 35 is modulated as shown in Fig. 3c. Hence the wheel speed NF or NR is decreased corresponding to the actual vehicle speed VB without causing the locking of the 5 wheels.

Thereafter, the program shown in the flowchart of Fig. 4 is executed. If the ABS is not operated, the idle speed of the engine is normally controlled. When the ABS is operated, the ABS signal is further applied to the clutch release determining section 60 which determines the release of the clutch 2 and produces the clutch release signal.

The clutch release signal is fed to the clutch control section 52 to compulsorily release the clutch 2 is as shown in Fig. 3d, thereby preventing the inertia mass of the engine from exerting on the wheels. On the other hand, the idle speed control section 61 is also applied with the clutch release signal and operated to produce the output signal which is applied to the air conditioner controller 65. The controller 65 is operated to release the clutch 63 of the air conditioner and stop the condenser fan 65, and hence stop the air conditioner as shown in Fig. 3f. Thus, the load on the engine 1 is reduced. In this state, the actuator 62 is actuated by the control section 61 so that the throttle valve la is opened wider to i 16 increase th e idling engine speed. Consequently, the idling speed, which may decrease as shown by a dotted line in Fig. 3e caused by the release of the automatic clutch 2, is prevented from decreasing. Thus, the engine speed Ne and hence the discharge of the pump 20 are maintained as shown by a solid line.

Accordingly, the line pressure control valve 22 can be operated to provide an optimum line pressure corresponding to the slow decreasing of the output of the pump 20. Thus, gripping the belt 11 by the pulleys 7 and 8 is ensured.

During the release of the clutch, the transmission ratio is controlled in the same manner as the conventional control unit.

Referring to Figs. 5 and 6 showing the second embodiment, the system has a hydraulic control unit 67 and a hydraulic circuit 68. The hydraulic circuit 68 is conventional as is disclosed in U.S. Patent 4,948,370. The hydraulic circuit 68 comprises a line pressure control valve and a transmission ratio control valve which are controlled by a pitot pressure from a pitot tube 69 which represents the engine speed, depression-degree of an accelerator pedal 70, and a select position of a selector lever 71 of the transmission. Thus, the transmission ratio and the 17 1 is line pressure are controlled in accordance with the driving conditions of the vehicle.

other construction and operation are the same as the first embodiment.

From the foregoing it will be understood that the present invention provides a continuously variable transmission for a vehicle having an ABS where the deterioration of the efficiency of the ABS is prevented by releasing the clutch during the operation of the ABS. At the same time, the idle speed is increased to prevent a rapid decline of the discharge of the pump, thereby preventing the belt from slipping.

Furthermore, since the load on the engine is reduced by stopping the operation of the air conditioner, the idle speed of the engine is increased without delay, thereby effectively preventing the line pressure from decreasing.

While the presently preferred embodiments of the present invention that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.

1 11 k is

Claims

CLAIMS:

1. A system for controlling a continuously variable transmission for a motor vehicle having an engine, an automatic clutch provided between the engine and the transmission, a wheel speed sensor for detecting a wheel speed of the vehicle, a hydraulic control system including an oil pump and a hydraulic circuit for controlling the transmission, and an antilock brake system responsive to an output of the wheel speed sensor for reducing a brake pressure, the system comprising: determining means responsive to the wheel speed for producing an ABS signal for operating the antilock brake system; and clutch releasing means responsive to said ABS signal for releasing the automatic clutch so as to efficiently operate said antilock brake system without belt slipping.

2. A system for controlling a continuously variable transmission for a motor vehicle having an engine, an automatic clutch provided between the engine and the continuously variable transmission, hydraulic means for controlling the transmission, a wheel speed sensor for detecting a wheel speed of the vehicle, and an antilock brake system, the control system comprising: determining means responsive to the wheel speed for producing an ABS signal for operating the antilock brake system; and clutch releasing means responsive to said ABS signal for releasing the automatic clutch.

3. The system according to claim 1 or 2, further comprising 1 4 19 speed increasing means responsive to said ABS signal for increasing the idling speed of the engine on release of the automatic clutch.

4. The system according to claim 3, further comprising stopping means responsive to the ABS signal for stopping operation of an air conditioner mounted on the motor vehicle and driven by the engine.

5. The system according to any preceding claim, wherein said determining means comprises wheel lock determining means responsive to the speed of the wheel detected by the wheel speed sensor for detecting a rapid deceleration of the wheel and for producing a wheel lock signal, and hydraulic pressure control means responsive to the wheel lock signal for producing the ABS signal.

6. A system for controlling a continuously variable belt drive transmission for a motor vehicle substantially as hereinbefore described with reference to the accompanying drawings.