JP3718405B2 - Hydraulic control device for continuously variable transmission - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a continuously variable transmission using a V-belt for a vehicle or the like, and more particularly to an improvement in a hydraulic control device thereof.
[0002]
[Prior art]
As a continuously variable transmission suitable for a vehicle, for example, there is a continuously variable transmission using a V-belt as disclosed in JP-A-11-82725.
In this method, a V-belt is stretched between a primary pulley connected to the engine side via a torque converter and a secondary pulley connected to the axle side, and the groove width of the primary pulley is variably controlled by hydraulic pressure.
That is, the primary pulley and the secondary pulley are respectively provided with the first and second cylinder chambers, the line pressure is always supplied to the second cylinder chamber of the secondary pulley, and the line pressure is supplied to the first cylinder chamber of the primary pulley. Hydraulic pressure obtained by adjusting the pressure with a shift control valve is supplied as pressure. And while driving | running | working, the groove ratio of a primary pulley is changed with the oil_pressure | hydraulic to a 1st cylinder chamber, and a gear ratio changes. During this time, the line pressure is changed within a predetermined range corresponding to the input torque, and the thrust (clamping pressure) for the V-belt is controlled.
[0003]
[Problems to be solved by the invention]
However, when a vehicle equipped with a continuously variable transmission as described above starts stalling on an uphill, for example, there is a problem that a phenomenon in which the engine speed is blown up and then a large shock occurs.
[0004]
This is because, as described above, the line pressure is controlled in accordance with the input torque during running and is set to a value that does not cause the belt to slip. The shock is due to the moment when the sliding belt is fastened to the pulley. Furthermore, the cause of the slip is that it is difficult to detect the input / output rotational speed at low speed, and as a result, the speed change control valve is opened. It is considered that the hydraulic pressure to the primary pulley supplied through the motor is unstable.
[0005]
Therefore, as a countermeasure, it is conceivable to set the line pressure to a value that is uniformly higher than the required value corresponding to the input torque during normal driving. However, this is possible even if the line pressure is low when the load is small. Therefore, the friction loss between the pulley and the belt is constantly increased. As a result, there is also a problem that the pump load is always increased.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hydraulic control device for a continuously variable transmission that does not cause a belt slip even at a stall start without causing a friction loss or an increase in pump load during normal running. And
[0006]
[Means for Solving the Problems]
Therefore, the present invention of claim 1 is directed to a transmission mechanism comprising a pair of variable pulleys capable of changing the groove width by being supplied with hydraulic pressure, and a belt spanned between the variable pulleys, and hydraulic pressure for supplying hydraulic pressure. A pump, a line pressure control means for adjusting the hydraulic pressure from the hydraulic pump to a predetermined line pressure, a shift control means for outputting a shift command based on the operating state, and the line pressure as the original pressure based on the shift command. In a hydraulic control device for a continuously variable transmission that includes a transmission control valve that supplies hydraulic pressure to a variable pulley of a transmission mechanism unit, the transmission control means uses a predetermined line pressure as a predetermined line pressure in a predetermined low vehicle speed region. A line pressure based on the line pressure characteristic at low speed is commanded to the line pressure control means .
Then, the line pressure characteristics during normal running and the low speed line pressure characteristic is represented by a linear function against each input torque, with up to a point corresponding to the creep torque value is set to the same, the higher the creep torque value It is assumed that the line pressure characteristic at low speed is set higher than the line pressure characteristic during normal driving with respect to the input torque.
[0007]
In the present invention, since the line pressure is increased at a low vehicle speed, the clamping pressure with respect to the belt is ensured, and even if the stall start is performed on the uphill, the belt does not slip.
In particular, since each line pressure characteristic is a linear function with respect to the input torque , the line pressure when the input torque is small is relatively lower than when the input torque is large, and is an appropriate value corresponding to the required amount. The load on the hydraulic pump is small.
In addition, the line pressure characteristic at low speed is set to the same as the line pressure characteristic during normal driving up to the point corresponding to the creep torque value, and the line pressure is increased from the normal value only at the creep torque value or higher. Sometimes there is no increase in rotation of the hydraulic pump, and noise can be suppressed.
[0008]
According to a second aspect of the present invention, the predetermined low vehicle speed region corresponds to the open control region of the shift control valve.
Since the line pressure is increased during open control where the hydraulic pressure to the variable pulley tends to become unstable, belt slippage is reliably prevented in the optimum region.
[0009]
According to a third aspect of the invention, when the shift control means shifts to a low line pressure based on a line pressure characteristic during normal driving when the vehicle speed exceeds a predetermined low vehicle speed region, a command is given for a line pressure with a limited degree of decrease. It is a thing.
The slippage of the belt that may occur due to a sudden drop in the line pressure is also prevented.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described by way of examples.
First, FIG. 1 shows a schematic configuration of a continuously variable transmission in the embodiment, and FIG. 2 shows a hydraulic control circuit thereof.
A speed change mechanism 10 in which a V belt 24 is stretched between a primary pulley 16 and a secondary pulley 26 is connected to an engine (not shown) via a torque converter 12 including a lockup clutch 11.
The primary pulley 16 forms a V-shaped pulley groove with a fixed conical plate 18 that rotates integrally with the output shaft of the torque converter 12 and a movable conical plate 22 that faces the fixed conical plate 18. And a first cylinder chamber 20 that displaces the movable conical plate in the axial direction.
[0011]
The secondary pulley 26 forms a V-shaped pulley groove by a fixed conical plate 30 that rotates integrally with an output shaft toward the axle and a movable conical plate 34 that faces the fixed conical plate 30. The movable conical plate 34 is urged by a return spring (not shown) in the direction of narrowing the width of the pulley groove, and includes a second cylinder chamber 32 that applies hydraulic pressure to the back surface thereof to displace the movable conical plate 34 in the axial direction. .
[0012]
The transmission mechanism 10 is controlled by the hydraulic control valve 3 based on a signal from the CVT control unit 1.
Line pressure is always supplied from the hydraulic control valve 3 to the second cylinder chamber 32. The hydraulic control valve further includes a speed change control valve 63, and supplies the hydraulic pressure adjusted with the line pressure as the original pressure to the first cylinder chamber 20.
The pressure receiving area of the first cylinder chamber 20 is set larger than the pressure receiving area of the second cylinder chamber 32.
[0013]
The hydraulic pressure applied to the first cylinder chamber 20 is controlled by the shift control valve 63 to change the groove width of the primary pulley 16, while the line pressure is supplied to the second cylinder chamber 32 to control the clamping pressure with respect to the V belt 24. The speed is changed, and the driving force is transmitted according to the contact frictional force between the V belt 24 and the pulleys 16 and 26.
In terms of the rotational speed, the groove width of the primary pulley 16 is widened, and when the contact ratio of the V-belt 24 is small and the contact radius on the secondary pulley 26 side is large, the gear ratio becomes large and the engine ratio becomes large. The side rotation speed is decelerated and output to the axle side. With a reverse pulley ratio Hi, output is performed with a small gear ratio. During this time, the gear ratio changes continuously corresponding to the contact radius ratio between the primary pulley 16 and the secondary pulley 26.
[0014]
In the hydraulic control valve 3, the line pressure obtained by adjusting the hydraulic pressure from the hydraulic pump 80 driven by the electric motor 81 by the line pressure regulator 60 is constantly supplied to the second cylinder chamber 32 as described above, and the speed is changed. It is supplied to the control valve 63. The hydraulic pressure to the first cylinder chamber 20 is controlled by driving the speed change control valve 63 with a step motor 64 using the line pressure as a source pressure.
The hydraulic control valve 3 further includes a line pressure solenoid 4, a pressure modifier 62, and a pilot valve 61.
[0015]
The CVT control unit 1 feedback-controls the line pressure based on the normal line pressure characteristics during normal running.
That is, in addition to the select position signal from the inhibitor switch 8, in addition to the engine torque calculated based on the throttle opening (accelerator pedal opening) TV0 and the engine speed Ne from the throttle opening sensor 5 during traveling. Then, an input torque input to the speed change mechanism unit 10 through the torque converter 12 is obtained, and a necessary line pressure is obtained from the normal line pressure characteristics corresponding to the input torque.
A duty ratio signal corresponding to this is output to the line pressure solenoid 4 as a hydraulic pressure command, and a shift command is output to the step motor 64.
For example, the position of the step motor 64 in the range of 20 to 170 steps corresponding to the target gear ratio within a range of 200 steps is selected.
[0016]
The line pressure solenoid 4 supplies the hydraulic pressure from the pilot valve 61 to the pressure modifier 62 side according to the duty ratio signal from the CVT control unit 1, and the line pressure regulator 60 supplies the hydraulic pressure from the hydraulic pump 80 from the pressure modifier 62. Set the line pressure according to the output hydraulic pressure. Thus, the line pressure is changed within a predetermined range according to the required transmission driving force and is output.
Note that the rotation of the electric motor is also controlled by the CVT control unit 1 so that the necessary line pressure can be generated, and the output of the hydraulic pump is also variable.
Here, the CVT control unit 1 constitutes a shift control means, and the line pressure solenoid 4, the pressure modifier 62, the pilot valve 61 and the line pressure regulator 60 constitute a line pressure control means.
[0017]
The speed change control valve 63 is driven by the spool 63a according to the displacement of the speed change link 67 spanned between the movable conical plate 22 of the primary pulley 16 and the step motor 64, and adjusts the line pressure from the line pressure regulator 60 to adjust the line pressure. Supply to one cylinder chamber 20. When the groove width becomes a width corresponding to the position of the step motor 64, the hydraulic pressure supply to the first cylinder chamber 20 is stopped by the displacement of the speed change link 67 interlocked with the movable conical plate 22. Thereby, the groove width of the primary pulley 16 is variably controlled to obtain a predetermined gear ratio.
[0018]
The CVT control unit 1 is connected with a first rotation speed sensor 6 and a second rotation speed sensor 7 that detect the input and output rotation speeds Npri and Nsec of the primary pulley 16 and the secondary pulley 26, and detect these during normal driving. Based on the signal, an actual transmission ratio in the transmission mechanism unit 10 is obtained, and feedback control is performed.
[0019]
Here, in this embodiment, the line pressure characteristic with respect to the input torque is controlled to be switched according to the vehicle speed.
That is, the CVT control unit 1 has a low-speed line pressure characteristic in addition to the normal line pressure characteristic corresponding to the running state applied to the above-described normal feedback control.
FIG. 3 shows these line pressure characteristics. The line pressure characteristic B at low speed is a straight line of a linear function having a large slope with respect to the normal line pressure characteristic A. Basically, a higher line pressure than that based on the normal line pressure characteristic is set. The starting point X is a creep torque value.
[0020]
FIG. 4 is a flowchart showing a flow of line pressure control by the CVT control unit 1.
First, in step 101, the CVT control unit 1 clears an internal memory for storing a previous value, which will be described later, and then calculates an input torque in step 102.
In step 103, the required line pressure is calculated based on the normal line pressure characteristics.
[0021]
Subsequently, at step 104, it is checked whether or not the current vehicle speed is equal to or lower than the set vehicle speed V. The set vehicle speed V is a low vehicle speed of about 5 km / h belonging to the open control region of the shift control.
When the vehicle speed is equal to or lower than the set vehicle speed V, the line pressure characteristic at low speed is selected in step 105, and the line pressure corresponding to the input torque is calculated.
In step 106, the line pressure based on the low-speed line pressure characteristic is compared with the line pressure based on the normal line pressure characteristic obtained in the previous step 103, and the larger calculated value is selected. To do.
[0022]
Next, when the vehicle speed exceeds the set vehicle speed in the check in step 104, the process proceeds to step 107, where the difference between the previous value stored in the internal memory and the line pressure obtained in step 103 or 106 is the predetermined value ΔP. Check if it is within.
When the difference is within the predetermined value, the process proceeds to step 109.
When the difference exceeds the predetermined value, the process proceeds from step 107 to step 108, the hydraulic pressure command value is corrected to the previous value−Pd, and then the process proceeds to step 109.
In step 109, the line pressure obtained in step 107 or the value corrected in step 108 is output as a hydraulic pressure command value.
In step 110, the previous value in the internal memory is updated with the output hydraulic pressure command value.
[0023]
Thus, at low vehicle speeds near the start state, the line pressure based on the low-speed line pressure characteristic of a linear function with a large slope with respect to the normal line pressure characteristic is set, and after passing through the low vehicle speed region, the line pressure by the normal line pressure characteristic is set. Will be set.
Further, when shifting to the normal line pressure characteristic, the rate of decrease in the line pressure is limited by steps 107 and 108, and even if the set line pressure becomes extremely low, it does not rapidly decrease.
[0024]
The embodiment is configured as described above, and the line pressure with respect to the input torque is increased at a low vehicle speed including when starting, so that the hydraulic pressure to the primary pulley becomes unstable in the open control state of the shift control valve. However, since the clamping pressure with respect to the V-belt is secured, the belt does not slip even when the stall starts.
In addition, since the line pressure characteristic at low speed is a linear function, the increase in line pressure when the input torque is small is lower than when the input torque is large, and it is an appropriate value corresponding to the required amount. The load on the hydraulic pump is also small.
[0025]
Furthermore, since the starting point of the straight line of the linear function is the creep torque value, below that, the line pressure increases, so that the rotation of the hydraulic pump is not increased and noise can be suppressed.
In addition, when the drop to the line pressure due to the normal line pressure characteristic set after the vehicle speed is increased, the degree of decrease is limited, so there is also a belt slip that is a concern due to a sudden drop in the line pressure. Is prevented.
[0026]
In the embodiment, the input torque to the transmission mechanism unit is calculated by the CVT control unit 1. However, for example, in a hybrid vehicle having a power train with an engine and a drive motor, the engine, the drive motor, and the continuously variable When the transmission is connected to the integrated control unit, the input torque can be received by the CVT control unit as an input torque command from the integrated control unit.
[0027]
【The invention's effect】
As described above, the present invention is provided with a speed change mechanism section in which a belt is stretched over a variable pulley that is supplied with hydraulic pressure and whose groove width can be changed, and the hydraulic pressure with the line pressure as the original pressure is supplied to the variable pulley by the speed change control valve In the continuously variable transmission hydraulic control device, the line pressure is set based on the low-speed line pressure characteristic in the predetermined low vehicle speed range, and the low-speed line pressure characteristic is the creep torque value. Up to the point corresponding to, the line pressure characteristic is set to be the same as that during normal driving, and a higher value than the line pressure characteristic during normal driving is set for input torque that is greater than the creep torque value . so it is secured clamped pressure on the belt, even if the stall start uphill without slippage of the belt occurs, therefore the shock subsequent rapid belt fastening is prevented together Has the effect that the lower pole low speed than creep torque value without rotation increase of the hydraulic pump, the noise is suppressed.
[0028]
Since the line pressure characteristic during normal traveling and the line pressure characteristic during low speed are expressed by linear functions with respect to the input torque , the line pressure is increased by an appropriate amount according to the input torque, and the load on the hydraulic pump is small.
[0029]
In addition, by making the predetermined low vehicle speed range to which the line pressure characteristic at low speed is applied correspond to the open control range of the shift control valve, the line pressure is increased during the open control where the hydraulic pressure to the variable pulley tends to become unstable, and optimal Slip of the belt is surely prevented in a limited area.
[0030]
Furthermore, by limiting the degree of decrease in the line pressure when the vehicle speed exceeds a predetermined low vehicle speed region and shifts to a low line pressure based on the line pressure characteristics during normal driving, the line pressure rapidly decreases. The belt slip which may occur is also prevented.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a continuously variable transmission according to an embodiment.
FIG. 2 is a diagram showing a hydraulic control circuit of a continuously variable transmission.
FIG. 3 is a diagram showing line pressure control characteristics;
FIG. 4 is a flowchart showing a flow of line pressure control.
[Explanation of symbols]
1 CVT Control Unit 3 Hydraulic Control Valve 4 Line Pressure Solenoid 6 First Revolution Sensor 7 Second Revolution Sensor 8 Inhibitor Switch 10 Transmission Mechanism 11 Lockup Clutch 12 Torque Converter 16 Primary Pulley 18 Fixed Conical Plate 20 First Cylinder Chamber 22 movable cone plate 24 V belt 26 secondary pulley 30 fixed cone plate 32 second cylinder chamber 34 movable cone plate 60 line pressure regulator 61 pilot valve 62 pressure modifier 63 shift control valve 63a spool 64 step motor 67 shift link 80 hydraulic pump 81 Electric motor

Claims (3)

A transmission mechanism comprising a pair of variable pulleys supplied with hydraulic pressure and capable of changing the groove width, and a belt stretched between the variable pulleys;
A hydraulic pump for supplying hydraulic pressure;
Line pressure control means for adjusting the hydraulic pressure from the hydraulic pump to a predetermined line pressure;
Shift control means for outputting a shift command based on the driving state ;
A hydraulic control device for a continuously variable transmission, comprising: a shift control valve that supplies a hydraulic pressure having a line pressure as a base pressure based on the shift command to a variable pulley of the shift mechanism unit;
The shift control means commands the line pressure control means as a predetermined line pressure based on a low-speed line pressure characteristic in a predetermined low vehicle speed range with respect to a normal running time .
The line pressure characteristic during normal driving and the line pressure characteristic at low speed are each expressed by a linear function with respect to the input torque, and are set to be the same up to the point corresponding to the creep torque value, and the input torque exceeds the creep torque value. On the other hand, a hydraulic control device for a continuously variable transmission, wherein the low-speed line pressure characteristic is set higher than the line pressure characteristic during normal running . 2. The hydraulic control device for a continuously variable transmission according to claim 1, wherein the predetermined low vehicle speed region corresponds to an open control region of the shift control valve . The shift control means commands a line pressure with a reduced degree of restriction when the vehicle speed exceeds the predetermined low vehicle speed region and shifts to a low line pressure based on a line pressure characteristic during normal running. Item 3. The hydraulic control device for a continuously variable transmission according to Item 1 or 2.

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