JPS62204052A - Speed-change control method for continuously variable transmission for vehicle - Google Patents

Abstract

PURPOSE:To prevent an engine in high speed operation from rotating with the speed over the design speed by holding the speed ratio immediately before switching into the neutral position as the speed ratio in neutral position in accordance with the switching into the neutral position. CONSTITUTION:In this hydraulic stepless speed changer T, a constant discharge type hydraulic pump 2 driven by engine E and a variable capacity hydraulic motor 4 coupled with a drive shaft 3 are connected with each other to constitute a hydraulic closed circuit 5. The inclination angle theta of a swash plate 104 of said variable capacity type hydraulic motor 4 is changed by a cylinder 101, which is so arranged as held in the position when a manual valve 78 is changed over to neutral position N through the action of a selector valve 118. That is, the speed ratio during neutral position is held at the ratio immediately before the switching.

Description

Detailed Description of the Invention A1 Objective of the Invention (1) Industrial Application Field The present invention provides an index indicating the driver's intention to accelerate or decelerate, an index indicating the engine output, and a choice between a forward position and a neutral position. The present invention relates to a speed change control method for a continuously variable transmission for a vehicle that changes the speed ratio steplessly in response to a cutting operation.

(2) Conventional technology Continuously variable transmissions for vehicles take into consideration the smooth start of a vehicle from a stopped state, and as disclosed in Japanese Patent Application Laid-open No. 58-191360, the speed at the neutral position is adjusted. Generally, the ratio is set to be the minimum.

(3) Problems to be solved by the invention Incidentally, while driving at high speed, the driver may operate from the forward position to the neutral position and then back to the forward position. If this is done, when the vehicle is operated from the neutral position to the forward position again, a sudden engine braking load will be applied and the engine may rotate at a speed higher than the design speed, which is undesirable.

Therefore, as disclosed in Japanese Patent Laid-Open No. 55-1292, it is conceivable to maximize the speed ratio at the same time as the switching operation to the neutral position. However, if such an operation is performed at a low speed with a small speed ratio, when the vehicle is returned to the forward position, the speed ratio may be too large and the vehicle may not be able to run smoothly, which is not desirable.

The present invention has been made in view of the above circumstances, and provides a vehicle that performs speed change control in order to eliminate the above-mentioned inconvenience when returning to the forward position again during a switching operation to the neutral position while traveling at high speed or low speed. An object of the present invention is to provide a method for controlling the speed change of a continuously variable transmission.

B0 Structure of the Invention fil Means for Solving the Problems According to the present invention, in response to a switching operation to the neutral position, the speed ratio immediately before the switching operation is held as the speed ratio at the neutral position.

(2) Effect When the vehicle is switched to the neutral position and returned to the forward position while driving at high speed, the speed ratio at the neutral position is maintained at a relatively large value, and no sudden engine braking load is applied. Further, when the vehicle is switched to the neutral position during low-speed running and then returned to the forward position, the speed ratio at the neutral position is maintained at a relatively small value, and smooth running is immediately possible.

(3) Examples Examples of the present invention will be explained below with reference to the drawings.
First, in FIG. 1 showing an embodiment of the present invention, a hydraulic continuously variable transmission T for an automobile includes a constant discharge hydraulic pump 2 having an input shaft 1 driven by an engine, and a drive shaft 3. The hydraulic pump 2 and a variable displacement hydraulic motor 4 disposed on the same axis are interconnected to form a hydraulic closed circuit 5. That is, the discharge port of the hydraulic pump 2 and the inlet of the hydraulic motor 4 are connected to each other by a high-pressure oil passage 5h, and the outlet of the hydraulic motor 4 and the suction port of the hydraulic pump 2 are connected to each other by a low-pressure oil passage 5! are interconnected by

A short-circuit path 6 is connected between the discharge port and the suction port of the hydraulic pump 2, that is, between the high-pressure and low-pressure oil paths 5h and 56, and a clutch valve 7 is provided in the middle of the short-circuit path 6.

Also, the discharge port of the replenishment pump 8 driven by the input shaft 1 is connected to a check valve 9. High pressure and low pressure oil lines 5h through to, 11
, 51, and hydraulic oil pumped up from the oil tank 12 is supplied to the hydraulic closed circuit 5 to replenish the shortage. Furthermore, a relief valve 13 is provided between the suction and discharge ports of the replenishment pump 8.

The output shaft 14 connected to the wheels W is arranged parallel to the drive shaft 3 of the hydraulic motor 4, and a forward/reverse switching device 15 is provided between the drive shaft 3 and the output shaft 14. This forward/reverse switching device 15 includes first and second drive gears 16 and 17 which are fixed to the drive shaft 3 with an interval in the axial direction, and a first drive gear which is rotatably supported by the output shaft 14. 16
a first driven gear 18 meshing with the second driven gear 18, a second driven gear 20 connected to the second drive gear 17 via an intermediate gear 19 and rotatably supported by the output shaft 14, and first and second driven gears. 18.20, and a clutch member 22 that selectively connects the driven clutch gear 21 and both driven gears 18.20. First and second driven gears 18.2
Driving clutch gears 18a and 20a are provided at the end portion of the driven clutch gear 21 of No. 0, and the clutch member 22 is located at a position where the driving clutch gear 18a and the driven clutch gear 21 are connected; It is movable between a position connecting the driven clutch gear 21 and the drive clutch gear 20a.

In such a forward/reverse switching device 15, when the driving clutch gear 18a is connected to the driven clutch gear 21 as shown in FIG. , the wheels W are rotatable in the forward direction. In addition, the driven clutch gear 21 and the drive clutch gear 2
When Oa is connected, the output shaft 14 is rotated in the same direction as the drive shaft 3, and the wheels W can be rotated in the reverse direction.

The clutch valve 7 is driven by a servo cylinder 23, and the switching operation of the forward/reverse switching device 15 is performed by a hydraulic cylinder 75.
The displacement of the hydraulic motor 4 is controlled by a hydraulic cylinder 1'')1.The operation of these cylinders 23, 75, 101 is controlled by a control device 24, which includes a The first one detects the engine rotation speed as an index indicating the output of the engine E.
The detection means SL is connected to a second detection means S2 that detects the throttle opening degree as an index indicating the driver's intention to accelerate or decelerate. The control device 24 detects these detection means SL, S2.
The servo cylinder 23 is controlled based on input signals from and the operation of the manual switching lever 100, and the hydraulic cylinder 75 is controlled based on the operation of the manual switching lever 100.

The first detection means S1 is, for example, a hydraulic governor that responds to the rotation of the input shaft l, and its input port 40 is connected to an oil passage 41 that can guide the discharge oil pressure PR of the replenishment pump 8.

The output boat 42 of the first detection means Sl outputs a governor oil pressure Pg proportional to the rotation speed of the engine E, and this governor oil pressure Pg is smaller than the discharge oil pressure PJ of the supply pump 8 (Pg<PN). It is set as follows.

The second detection means S2 is, for example, a throttle pressure-to-oil pressure converter, and outputs a throttle oil pressure pt corresponding to the operation of the throttle valve opening/closing device 43 from the output boat 44. On the other hand, the input port 45 of the second detection means S2 is connected to the oil passage 41, and the throttle oil pressure pt is determined to be smaller than the discharge oil pressure PIl (pt<Pz).

The servo cylinder 23 has a cylinder 34 and a cylinder 3.
a piston 37 that divides the inside of the cylinder 34 into a head chamber 35 and a rod chamber 36; a piston rod 38 that is integrated with the piston 37 and that penetrates the end wall of the cylinder 34 on the rod chamber 36 side in an oil-tight manner and that is movable; , and a spring 39 accommodated in the rod chamber 36 and urging the piston 37 toward the head chamber 35.

The tip of the piston rod 38 is connected to the clutch valve 7 via the link 31, and when the piston 37 is moved to the maximum right by the spring 39, the clutch valve 7 is fully opened.

Further, when the piston 37 moves to the left against the spring force of the spring 39, the opening degree of the clutch valve 7 becomes smaller, and the continuously variable transmission T becomes in a half-clutch state. Furthermore, it is pistoned against the spring force of the spring 39.

The hydraulic cylinder 75 includes a cylinder 83 and a cylinder 83.
a piston 86 which is slidably fitted within the cylinder 83 and divides the inside of the cylinder 83 into a head chamber 84 and a rod chamber 85;
6 and a piston rod 87 that oil-tightly and movably penetrates the end wall of the cylinder 83 on the rod chamber 85 side, and a spring 88 that is housed in the rod chamber 85 and biases the piston 86 toward the head chamber 84 side. It consists of

A connecting member 89 is fixed to the tip of the piston rod 87, and the clutch member 22 is fixed to this connecting member 89. Therefore, the clutch member 22 moves in response to the operations of the piston 86 and the piston rod 87, and the forward/reverse switching device 15 performs the switching operation. That is,
When the piston 86 and piston rod 87 move to the left limit position, the forward/reverse switching device i! At 15, a forward gear train is established, and when the piston 86 and piston loft 87 move to the right limit position, a reverse gear train is established in the forward/reverse switching device 15.

An oil passage 90 is connected to the head chamber 84, and an oil passage 91 is connected to the rod chamber 85.

In FIG. 2, the hydraulic motor 4 is, for example, a variable displacement axial piston motor, and a cylinder block 102 connected to the drive shaft 3 has a plurality of pistons 103 arranged annularly around the rotation axis of the drive shaft 3. A swash plate 104 that defines the reciprocating stroke of these pistons 103 is arranged with a variable inclination angle θ. Also, the cylinder chamber 1 corresponding to the piston 103 in the expansion stroke
05a communicates with the high pressure oil passage 5h, and the cylinder chamber 105b corresponding to the piston 103 in the contraction stroke communicates with the low pressure oil passage 5.
1.

Such a hydraulic motor 4 is conventionally known, and the high pressure oil discharged from the constant displacement hydraulic pump 2 flows into the cylinder chamber 1.
05a and discharged from the cylinder chamber 105b is returned to the hydraulic pump 2. During this period, the cylinder block 102 and the drive shaft 3 are rotationally driven by the reaction torque that the piston 103 receives from the swash plate 104 during the expansion stroke. Ru.

By the way, the capacity of the hydraulic motor 4 is determined by the stroke of the piston lO3, so by operating the tilt angle θ of the swash plate 104 from the maximum position shown by the solid line to the minimum position shown by the chain line, the speed ratio e can be changed from the minimum to the maximum. It can be controlled steplessly.

Here, the speed ratio e is expressed by the following equation.

Input rotation speed One end of the swinging link 106 is connected to the pin 1 at one end of the motor capacity swash plate 104.
07, and the other end of this link 106 is connected to a hydraulic cylinder lot via a pin 108 parallel to the pin 107.

The hydraulic cylinder 101 is slidably connected to a cylinder 110 and the head chamber 11 is inserted into the cylinder 110.
1 and a piston 113 partitioned into a rod chamber 112;
It is integrated into the screw I/n 113 and the cylinder 1.
It consists of a piston rod 114 that oil-tightly and movably penetrates the end wall on the rod chamber 112 side of No. 10.

One end of the swing link 106 is connected to the tip of the piston rod 114 via the pin 10B, and the piston 1
13 moves to the right as much as possible, the inclination angle θ of the swash plate 104 becomes maximum, the capacity of the hydraulic motor 4 becomes maximum, and the speed ratio e becomes minimum. Also, when the piston 113 moves to the left as much as possible,
The inclination angle θ of the swash plate 104 becomes the minimum as shown by the chain line,
The capacity of the hydraulic motor 4 becomes the minimum and the speed ratio e becomes the maximum.

Referring again to FIG. 1, the control device 24 controls the pilot valve 4
7,117, switching valve 48,118 and manual valve 7
8.

The pilot valve 47 is connected to the head chamber 3 of the servo cylinder 23.
5 and the rod chamber 36, respectively.
1, 52, and a supply oil path 5 connected to the discharge port of the replenishment pump 8.
3 and a release oil passage 54 that communicates with the oil tank 12, and includes a sleeve 55 and a spool 56 that is relatively movable within the sleeve 55.

The pilot valve 47 is provided with bows 57 and 58 that communicate with the oil passages 51 and 52, and bows 59 and 60 that communicate with the supply oil passage 53 and the release oil passage 54, respectively. Further, the piston loft 38 in the servo cylinder 23 is connected to the sleeve 55 via a link 61.
The action of the servo cylinder 23 is feedbanked to the pilot valve 47.

Spools 56 are connected to boats 58.59 and 57.
Left position connecting 60, baud) 57.58 and baud)
Neutral position that cuts off between 59 and 60, and boat 57
．． 59 and boats 58, 60 are moved relative to the sleeve 55 between three switching positions, the right position communicating with the boats 58 and 60. A spring 62 is brought into contact with the left end of the spool 56 to bias the spool 56 to the right.
A spring 63 for biasing the spool 6 to the left is brought into contact with the right end of the spool 56. The biloft valve 47 is also provided with a switching boat 64 for applying hydraulic pressure to the left end of the spool 56 and a switching port 65 for applying hydraulic pressure to the right end of the spool 56.

In such a pilot valve 47, the spool 56
The force Fl acting on the left end of the spring 62 is the sum of the load F11 of the spring 62 and the hydraulic pressure F12 acting on the left end of the spool 5G (F1=
F11+F12), and the force F2 acting on the right end of the spool 56 is the sum of the load F21 of the spring 63 and the hydraulic pressure F22 acting on the right end of the spool 56 (F2-F21 + F2
2), and the spool 56 is actuated by a change in the balance between these forces Fl and F2.

For example, when Fl<F2, the spool 56 moves leftward to the right position, the discharge hydraulic pressure PIl of the supply pump 8 is introduced into the head chamber 35 of the servo cylinder 23, and the rod chamber 36 is released to the oil tank 12. Ru. As a result, the piston 37 and the piston rod 38 move to the left, and the clutch valve 7 operates in the closing direction.

As the spool 56 moves to the left, the load F11 on the spring 62 increases, and conversely, the load F21 on the spring 63 decreases, causing F
When 1=F2, the spool 56 stops. Moreover, the sleeve 55 is moved to the left via the link 61 by the left movement of the piston rod 1'38. For this reason, when the positional relationship between the sleeve 55 and the spool 56 becomes a neutral position, the flow of hydraulic oil between the boats 57, 59; It also stops working. In addition, the sleeve 55 is also connected to the piston rod 38.
It stops in accordance with the action of.

When FL>F2, the spool 56 moves to the right, and the relative position of the spool 56 to the sleeve 55 becomes the left position.

As a result, the discharge oil pressure Pl of the replenishment pump 8 is delivered to the rod chamber 36 of the servo cylinder 23! is introduced, and the head chamber 35 is opened to the oil tank 12, so the piston 37 and the piston rod 38 move to the right. This causes the clutch valve 7 to operate in the valve opening direction.

Due to the rightward movement of the spool 56, the load F21 on the spring 63 increases and the load Fil on the spring 62 decreases, so that F1=
At F2, the spool 56 stops moving to the right. At this time, the sleeve 55 also moves to the right in response to the right movement of the piston rod 38, and when the positional relationship with the spool 56 becomes the neutral position,
The supply of hydraulic pressure to the iron chamber 36 is stopped, the rightward movement of the piston rod 38 is stopped, and the operation of the clutch valve 7 is also stopped.

Further, the rightward movement of the sleeve 55 also stops in accordance with the action of the piston rod 38.

Such a mechanism is a general servo mechanism, and by moving the piston 37 according to the amount of movement of the spool 56, the opening degree of the clutch valve 7, that is, the opening degree of the short circuit path 6 can be adjusted.

The switching valve 48 is a three-bottom, two-position switching valve, and has an oil passage 66 connected to the discharge port of the replenishment pump 8 and a second detection means S2.
An oil passage 67 connected to the output port 44 of the pilot valve 4
It is interposed between the pilot oil passage 68 connected to the switching port 64 of No. 7. This switching valve 48 can be switched between a left position where the oil passage 66 is communicated with the pilot oil passage 68 and a right position where the oil passage 67 is communicated with the pilot oil passage 68.
The right position is reached when the discharge oil passage Pl of the replenishment pump 8 is guided to the pilot oil passage 69 branched from the oil passage 41.

On the other hand, the switching port 65 of the pilot valve 47 has a first
The output port 42 of the detection means S1 is communicated via a pilot oil passage 70.

When the discharge oil pressure Pff of the replenishment pump 8 is supplied to the oil passage 41, the discharge oil pressure PR is also introduced into the pilot oil passage 69, and accordingly, the switching valve 48 moves to the right position, and the switching port of the pilot valve 47 Throttle oil pressure pt is supplied to 64. Further, the other switching port 65 is supplied with the governor hydraulic pressure Pg from the first detection means S1, and the hydraulic pressure F12. The balance between forces Fl and F2 including F22 causes the pilot valve 47 to operate, and the clutch valve 7 to open and close.

On the other hand, when the discharge oil pressure Pl is not supplied to the oil passage 41, that is, when the oil pressure of the oil passage 41 is rOJ, the switching valve 48 is in the left position, and the switching port 64 of the pilot valve 47 is supplied with the discharge oil pressure Pβ. be done. On the other hand, the governor oil pressure Pg from the first detection means S1 is
Since the oil pressure at zero is rOJ, it is rOJ, and no oil pressure acts on the right end of the spool 56. At times like this,
The force F1 that moves the spool 56 to the right is the force F2 that moves the spool 56 to the left.
(Fl>F2), the pilot valve 4
7 is determined, and the spool 56 moves until it reaches the right limit, ensuring that the clutch valve 7 is fully open.

The manual valve 78 is a six-point valve interposed between the oil passages 41, 90, 91, a pair of oil passages 92° 93 communicating with the supply oil passage 53, and a release oil passage 94 communicating with the oil tank 12. This is a 3-position switching valve that can be switched between forward, neutral, and reverse positions by manual operation. That is,
A manual switching lever 100 is connected to the manual valve 78, and depending on the operation of this manual switching lever 100,
It is possible to switch between three positions: forward position F (left position), neutral position N, and reverse position WH.

At the forward position F, the oil passages 92 and 41, between the oil passages 93 and 91, and between the oil passage 90 and the released oil passage 94 are in communication with each other, and at the neutral position N, the oil passages 41, 90, and 91 are all open oil passages. 9
4, and in the reverse position R, the oil passages 92 and 41, the oil passages 93 and 90, and the oil passage 91 and the release oil passage 94 communicate with each other.

The pilot valve 117 includes an oil passage 119 that can communicate with the head chamber 111 of the hydraulic cylinder 101 and a rod chamber 112.
and the discharge oil pressure P1 of the replenishment pump 8.
This is a four-port throttle switching valve interposed between an oil passage 121 branched from the supply oil passage 53 and a release oil passage 122 connected to the oil tank 12.

This pilot valve 117 includes boats 123 and 124 that communicate with oil passages 119 and 120 individually, boats 125 and 126 that communicate with oil passage 121 and release oil passage 122, and a spool 127.

Moreover, the spool 127 has two positions: a left position that communicates between the ports 123, 126 and ports 124, 125, a neutral position that blocks each port 123, 124, 125, 126, and ports 123, 125 and ports 124. ,1
It moves between three switching positions including the right position communicating between 26 and 26, with an intermediate position where the degree of aperture changes continuously.

A spring 128 is brought into contact with the left end of the spool 127 in order to bias the spool 127 in the right direction, and a spring 129 is brought into contact with the right end of the spool 127 in order to bias the spool 127 in the left direction. The pilot valve 117 is also provided with a switching port 130 for applying hydraulic pressure to the left end of the spool 127 and a switching port 131 for applying hydraulic pressure to the right end of the spool 127. Moreover, one switching port 130 is connected to a pilot oil passage 132 branched from an oil passage 67 connected to the output port 44 of the second detection means S2, and the other switching port 131 is connected to the first detection means S1. A pilot oil passage 133 branched from the pilot oil passage 70 connected to the output port 42 is connected.

In such a pilot valve 117, the spool 12
The force F3 acting on the left end of 7 is the load F31 of the spring 128,
The sum of the hydraulic pressure F32 acting on the left end of the spool 127 (
F3=F31+F32), and the force F4 acting on the right end of the spool 127 is the sum of the load F41 of the spring 129 and the hydraulic pressure F42 acting on the right end of the spool 127 (F4=F
41+F42), and these forces F3. The change in the balance of F4 causes the spool 127 to operate.

The switching valve 118 has an oil passage 119 connected to the port 123 of the pilot valve 117 and a head chamber 1 of the hydraulic cylinder 101.
It is a 2-point, 2-position switching valve that is interposed between the oil passage 134 connected to the oil passage 11, and has a left position that blocks off the oil passages 119 and 134, and a right position that communicates between the oil passages 119 and 134. It is in the right position when the discharge oil pressure Pl of the replenishment pump 8 is applied to the pilot oil passage 135 branched from the oil passage 41. That is, when the manual valve 78 is in the forward position F or the reverse position R, the switching valve 118 is in the right position, and when the manual valve 78 is in the neutral position, the switching valve 118 is in the left position.

When the switching valve 118 is in the right position and the oil passages 119 and 134 are in communication, the pilot valve 117 sets F3<F4.
Then, the spool 127 moves to the left, the load F31 of the spring 128 increases, and the load F41 of the spring 129 decreases, and when F3=F4, the spool 127 stops moving to the left. At this time, hydraulic oil with a flow rate corresponding to the opening degree between the boats 123 and 125 and the boats 124 and 126 is introduced into the head chamber 111 of the hydraulic cylinder Lot and discharged from the rod chamber 112, and is discharged from the rod chamber 112 and the piston 113 and piston rod. 114 moves to the left. Further, when F3>F4, the spool 127 moves to the right, the load F41 of the spring 129 increases, and the load F31 of the spring 128 increases.
decreases and when F3=F4, the spool 127 stops moving to the right.

At this time, port 123, 126 and port 124.
125 is discharged from the head chamber 111 of the hydraulic cylinder 101 and introduced into the rod chamber 112, causing the piston 113 and the piston rod 114 to move to the right.

Moreover, the pressure distribution between the head chamber 111 and the rod chamber 112 is determined by the degree of restriction in the pilot valve 117, and the pressure distribution between the piston 113 and the piston rod 114 is determined by the degree of restriction in the pilot valve 117.
operates at a speed corresponding to the pressure difference, thereby changing the capacity of the hydraulic motor 4.

Next, the operation of this embodiment will be explained. First, before starting the engine E, the replenishment pump 8 remains stopped and the discharge oil pressure PR=0.

Therefore, the governor oil pressure Pg and the throttle oil pressure pt are also zero. At this time, the position of the spool 56 in the pilot valve 47 is determined by the set load of the springs 62 and 63.
The set loads of the springs 62 and 63 are determined so that the spool 56 moves in the opening direction of the clutch valve 7, that is, moves rightward to the left position. Further, in the servo cylinder 23, the piston 37 and the piston rod 38 are moved to the right by the spring 39,
The clutch valve 7 is in the opening position, and the pilot valve 47
The sleeve 55 is also moved to the right via the link 61.

Next, after starting the engine E, the manual valve 78 is in the neutral position f.
Assume that there is a case in iN. In this state, oil passages 41, 9
0.91 is in communication with the oil tank 12, and the hydraulic pressure in the head chamber 84 and rod chamber 85 in the hydraulic cylinder 75 is released. Therefore, the piston 86 of the hydraulic cylinder 75 is pressed to the left limit position by the spring force of the spring 88, and the clutch member 22 is also located at the left limit according to the position of the piston 86, and the forward/reverse switching device 15 is Go to forward position. Further, the oil pressure in the oil passage 41 is "0", and the switching valve 48 is in the left position.

Therefore, in the pilot valve 47, the hydraulic pressure F12 is a value corresponding to the hydraulic pressure PR, and the hydraulic pressure F22 is O since Pg=0, and since Fl>F2 is always held, the spool 56
is the left position. Correspondingly, the piston 37 of the servo cylinder 23 is also stopped at the right limit position, and the clutch valve 7 is fully open.

In such a state, the hydraulic oil discharged from the hydraulic pump 2 according to the engine speed flows through the short circuit path 6, so the hydraulic motor 4 is not driven, and therefore no power is transmitted to the output shaft 14. The wheels W also remain stationary.

At this time, even if the engine speed increases due to the depression of the accelerator pedal in the throttle valve opening/closing device 43, F22=0 (Pg=0)' always holds, so the spool 56 of the pilot valve 47 is moved to the left. The clutch valve 7 does not move, and the opening degree of the clutch valve 7 is reliably maintained in the fully open state regardless of the throttle opening degree and the engine speed.

At this time, the switching valve 11B is in the left position because the oil passage 41 is open, and the pilot valve 117 is in the first position.
Since the governor oil pressure Pg from the detection means Sl is "0" and the throttle oil pressure pt from the second detection means S2 is also rOJ, F3=F31 and F4=F41.

In this state, springs 12B and 129 are set so that F3>F4.
A set load is determined, and the spool 127 is in the left position, in a state where the discharge hydraulic pressure PR of the replenishment pump 8 can be guided to the rod chamber 112 of the hydraulic cylinder 101. However, since the switching valve 118 is in the left position, the hydraulic cylinder 1
The head chamber 111 of No. 01 is in a sealed state. therefore,
Even if the discharge hydraulic pressure Pl is applied to the rod chamber 112, the piston 123 does not operate, and the inclination angle θ of the swash plate 104 in the hydraulic motor 4 remains constant. As a result, the inclination angle θ of the swash plate 104 at the neutral position N is fixed to the value at the forward position F or reverse position R immediately before switching the manual valve 78 to the neutral position N, and the speed ratio e is set at the neutral position. It will be held at the value immediately before switching to N.

Next, operate the manual switching lever 100 to open the manual valve 78.
When the is switched from the neutral position N to the forward position F, the oil passages 92,
41, between oil passages 93 and 91, and between oil passage 90 and release oil passage 94.

Therefore, the discharge hydraulic pressure Pβ is supplied to the rod chamber 85 of the hydraulic cylinder 75, the head chamber 84 remains open, and the piston 86 remains pressed to the left limit position.

As a result, the forward/reverse switching device 15 also remains set at the forward position. The oil pressure PIl is also supplied to the oil passage 41.

As a result, the switching valve 48 connects the pilot oil passage 69 with the hydraulic pressure P.
In response to the supply of R, the valve is placed in the right position, and the switching port 64 of the pilot valve 47 is supplied with the throttle oil pressure PL from the second detection means S2.

On the other hand, the governor oil pressure Pg from the first detection means Sl is transmitted from the pilot oil passage 70 to the switching port 65 of the pilot valve 47.
supplied to Therefore, the pilot valve 47 operates depending on the balance between the throttle oil pressure pt and the governor oil pressure Pg, and the clutch valve 7 also opens and closes accordingly.

When such an operation is performed with the engine idling when the vehicle is stopped and the throttle valve opening/closing device 43 is not operated, the first detection means S1 outputs the governor oil pressure Pg corresponding to the idling rotation of the engine E, and the second detection means Means S
In step 2, a throttle oil pressure pt corresponding to the throttle opening degree "0" is generated. At this time, by setting in advance so that F1=F2 at a position where the spool 56 of the pilot valve 47 has moved a predetermined amount to the left from the right limit position, the piston rod 38 of the servo cylinder 23 has also moved to the left by a predetermined amount. It will stop at the specified position. Thereby, the clutch valve 7 can be brought into a half-clutch state.

In addition, in this engine idling state, the governor oil pressure Pg corresponding to idling rotation acts on the switching boat 131 of the pilot valve 117, and the throttle oil pressure pt acting on the switching boat 130 is the oil pressure corresponding to the throttle opening "0". However, in this state, the loads F31. F41 and hydraulic pressure F32. Define F42. Then, the spool 127 is in the left position.

Moreover, since the discharge oil pressure is supplied to the oil passage 41, the switching valve 1
18 is in the right position in response to the introduction of the discharge oil pressure P1 into the pilot oil passage 135, and the oil passages 119 and 134 are in communication with each other.

Therefore, the head chamber l11 of the hydraulic cylinder 101 is opened to the oil tank 12, and the discharge oil pressure pz is released to the rod chamber 112.
acts, the piston 113 and the piston rod 114 move to the right and reach the rightmost position, the swash plate 104 maximizes its inclination angle θ, and the speed ratio e becomes the minimum state.

When the accelerator pedal is pressed to start from the engine idling state, the throttle valve opens and the throttle oil pressure pt increases, so the pilot valve 47
2 increases, resulting in an increase in F1. On the other hand, since the rotational speed of the engine E increases, the output of the first ridge means S1, that is, the governor oil pressure Pg also increases, and as a result, the pyro 7)
At valve 47, F2 increases. Here, when F2>Fl, the spool 56 moves to the left and discharges hydraulic pressure P to the head chamber 35.
1 is introduced, and the rod chamber 36 is opened to the atmosphere. As a result, the piston 37 and piston rod 38 of the servo cylinder 23 move to the left, the clutch valve 7 gradually operates in the closing direction, and the hydraulic pump 2 starts driving the hydraulic motor 4.

Spool 5 according to the balance of F l and F 2
6 further moves to the left, and finally the spool 56 stops at the left limit position. As a result, the clutch valve 7 becomes fully closed,
The hydraulic motor 4 will be driven by the hydraulic pump 2. Moreover, since the forward/reverse switching bag rf1.15 is in the forward position at this time, the vehicle starts in the forward direction in accordance with the rotation of the hydraulic motor 4.

At this time, in the pilot valve 117, the throttle oil pressure Pt generated in response to depression of the accelerator pedal acts on the switching boat 130, and F3 increases as the oil pressure F32 increases. In this state, it is preset so that F3>F4, and the speed ratio e is at its minimum as shown by curve A or curve E in FIG. 3, similar to when the engine is idling.

When the engine speed further increases, the governor oil pressure Pg increases, and F4 increases at the pilot valve 117, but F4 increases.
When 3>F4 or F3=F4, spool 12
7 is in the left position or neutral position, the piston 113 and piston rod 114 of the hydraulic cylinder 101 remain in the right limit position, and the speed ratio e is the minimum. However, as the engine speed increases, the curved line in FIG.

The vehicle speed increases as shown in .

Engine speed increases further to 1? 3 < F 4
When the spool 127 of the pilot valve 117 moves to the left and reaches the right position, the head chamber 111 of the hydraulic cylinder 101
The discharge hydraulic pressure Pffi is supplied to the rond chamber 11.
2 is released into the oil tank 12. Therefore piston 1
13 and screws) - the rotor 71'114 moves to the left, and the swash plate 1
04 operates in the direction of decreasing the inclination angle θ, that is, in the direction of increasing the speed ratio e, to increase the vehicle speed. Also at this time,
Since the increase in engine load is controlled to increase the engine speed, the engine speed is controlled to be approximately constant. This state is shown by curves C and G in FIG.

Even if the speed ratio e increases and reaches its maximum value, if you continue to press the accelerator pedal, the engine speed will increase until the engine output and load are balanced, and the vehicle speed will increase accordingly. It becomes a steady running state. This is shown by curves 2 and 1 in FIG.

The relationship between engine speed and vehicle speed from start to steady running is different between a slow start with a small amount of accelerator pedal depression and a sudden start with a large amount of accelerator pedal depression. That is, during a slow start, the order changes in the order of E-Lo Har Nich in FIG. 3, and in a sudden start, the order changes in the order of the Hohe Torch in FIG.

As is clear from FIG. 3, the engine speed at the time of gear shifting is set according to the amount of depression of the accelerator pedal, and gear change control is performed so that the engine speed is constant.

A case in which the manual valve 78 is set to the neutral position fiN while traveling with the manual valve 78 at the forward position F, and then returned to the forward position F will be described with reference to FIGS. 4 and 5. In FIGS. 4 and 5, the straight line eh indicates the line where the speed ratio C is maximum, and the straight line el shows the line where the speed ratio e is the minimum.

First, in FIG. 4, while driving at a relatively large speed ratio e1 and a relatively high speed Vl, the manual valve 78
When the clutch valve 7 reaches the neutral position N, the clutch valve 7 becomes fully open as described above, power transmission is cut off, and the vehicle decelerates while coasting. At this time, according to the present invention, the speed ratio e is maintained at the speed ratio e1 immediately before switching to the neutral position N, as shown by the solid arrow. Therefore, when the vehicle speed reaches v2, which is lower than the vehicle speed V1, even if the vehicle returns to the forward position F, the engine speed due to engine braking will be reduced by the vehicle speed
The value n2 is lower than the value nl when 1, and the design value nm
It cannot be more than that. Shift control is then performed again in accordance with the throttle opening and engine speed.

On the other hand, in the conventional system, the speed ratio e becomes the minimum as shown by the broken line arrow in response to switching to the neutral position 1iN. Therefore, when the vehicle is returned to the forward position F at the vehicle speed v2, the engine rotational speed becomes N3, which exceeds the design value nm, which is not preferable.

In FIG. 5, while driving at a relatively small speed ratio e2, low vehicle speed ■3, and low engine speed n4, when switching from the forward position F to the neutral position N, the clutch valve 7 is fully opened. As a result, the vehicle decelerates while coasting. At this time, as shown by the solid line arrow, the speed ratio remains at e2, and even if the vehicle is decelerated to v4 and rotation speed n5 and then returned to the forward position F, an appropriate speed ratio is obtained and the throttle is opened. It is possible to restart the gear change control according to the engine speed and engine speed. On the other hand, when the speed ratio e is maximized at the neutral position N as shown by the dashed arrow, when the vehicle returns to the forward position F at a vehicle speed of 4, the engine speed is n6, which is lower than the value n5. Because it will drop to
This makes it difficult to drive smoothly.

When you take your foot off the accelerator pedal to stop during steady driving, the throttle oil pressure pt becomes a low value that corresponds to the throttle opening of "0", so the pilot valve 117 makes F3<F.
4, and the speed ratio e becomes maximum. Then, the hydraulic motor 4 is reversely driven by the inertia on the load side, and the hydraulic pump 2 rotates in accordance with the discharge of the motor 4. At the same time, the engine E connected to the pump 2 also rotates, and the engine brake is activated to decelerate the vehicle.

The changes in engine speed and vehicle speed at this time are shown in FIG. 3 as follows: chiniri→null→ruu→wo.

That is, a state in which the engine brake is applied and the speed ratio e is kept at the maximum and the vehicle is decelerated is shown by chineari in FIG.

As the engine speed decreases, F3>F4 in the pilot valve 117, and the speed ratio e decreases. Also, at this time, the engine braking load increases and the decrease in engine speed is suppressed, so that the engine speed becomes approximately constant as shown by the symbol N in FIG. Furthermore, when the speed ratio e becomes the minimum, the engine speed decreases as the vehicle speed decreases, as shown by R. When the engine speed further decreases, Fl>F2 at the pilot valve 47, and the clutch and valve 7
operates in the valve opening direction, as shown by w in Figure 3. As a result, power transmission between the hydraulic pump 2 and the hydraulic motor 4 is cut off, and the vehicle stops. At this time, the engine E is in an idling state, and the speed ratio e is at a minimum.

When the manual valve 78 is switched from the forward position F to the neutral position N after the vehicle has stopped, the hydraulic pressure in both oil chambers 84 and 85 in the hydraulic cylinder 75 is released, and the piston 8
6 remains pressed to the leftmost position by the spring 88. Therefore forward and backward movement.

The switching device 15 continues to be held in the forward position, and the oil passage 4
Since the oil pressure of the engine 1 becomes "O", the clutch valve 7 becomes fully open.

At this time, when the engine is in an idling state at the forward position F, the speed ratio e is at a minimum state, and when the engine is switched to the neutral position N in this state, the speed ratio e remains at the minimum state. Therefore, for the next start, the neutral position N
When the vehicle is switched from the forward position to the forward position F, the speed ratio e necessary for starting is immediately obtained, and smooth starting can be performed.

When the manual valve 78 is switched from the neutral position N to the reverse position R when the vehicle is stopped, between oil passages 92 and 41, oil passages 93 and 9
During the zero period, the oil passage 91 and the release oil passage 94 are in communication with each other, so in the hydraulic cylinder 75, the discharge oil pressure Pl is supplied to the head chamber 84, and the oil pressure in the rod chamber 85 is released. Therefore, the piston 86 moves to the right, and in the forward/reverse switching device 15, the clutch member 22 disconnects from the drive clutch gear 18a and moves to the right, causing the drive clutch gear 22 to move to the right.
Connect with 0a.

Further, since the discharge oil pressure pe is supplied to the oil passage 41, the clutch valve 7 operates according to the balance between the throttle oil pressure pt and the governor oil pressure Pg, and is in a half-clutch state particularly when the engine is idling.

At this time, the operation of the hydraulic cylinder 101 is the same as when switching from the neutral position IN to the forward position F, and the speed ratio e is the minimum.

Here, in order to start backward, the throttle valve opening/closing device 43 is operated to open the throttle valve (and the clutch valve 7 gradually closes, as in the case of forward movement described above, and the hydraulic motor 4 starts to drive, and the vehicle starts backward.Moreover, the pilot valve 117 operates in the same way as when moving forward.
The same speed change control as when moving forward is performed.

During reverse movement, when switching operation is performed from reverse position R to neutral position N to reverse position R, the operation is the same as when switching from forward position F to neutral position N to forward position F, and the reverse position When the vehicle stops while traveling in R, the forward/reverse switching device 15 remains in the reverse position, and the clutch valve 7 and swash plate 104 operate in the same manner as when the vehicle stops during forward travel. Furthermore, when switching from the reverse position R to the neutral position N after the vehicle has stopped, both oil chambers 84°8 of the hydraulic cylinder 75
5 are both connected to the oil tank 12, so the piston 8
6 moves from the right limit position to the left limit position, and the setting of the reverse position in the forward/reverse switching device 15 is canceled. At this time, oil path 4
Since the oil pressure at No. 1 is "0" and the clutch valve 7 is fully open, the drive clutch gear 20a and the clutch member 22 are smoothly disconnected from each other. Also, the speed ratio e is
In the same way as when switching from forward positions W and F to neutral position'/iN,
It is minimum when the engine is idling at the reverse position R.

FIG. 6 shows another embodiment of the invention.

This example is similar to the previous example, but
Particularly noteworthy is that a four-point/two-position switching valve 118' is interposed between the hydraulic cylinder 101 and the pilot valve 117. This switching valve 118' has an oil passage 134 connected to the head chamber 111 of the hydraulic cylinder 101 and an oil passage 119 connected to the boat 123 of the pilot valve 117.
between the oil passage 120a connected to the rod chamber 112 of the hydraulic cylinder 101 and the port 1 of the pilot valve 117.
It is possible to switch between a right position where the oil passages 120b connected to 24 are communicated with each other, and a left position where they are blocked.
When the discharge oil pressure PI is supplied to the pilot oil passage 135 branched from the oil passage 41, the right position is reached.

According to this embodiment, when the manual valve 78 reaches the neutral position N, the hydraulic pressure is confined in the head chamber 111 and the rod chamber 112 of the hydraulic cylinder 101, and the piston rod 114
prevent the operation of Therefore, the hydraulic cylinder 101 is held in the state immediately before reaching the neutral position iN,
Even if an external force acts on the swash plate 104 of the hydraulic motor 4,
The operation of the swash plate 104 is prevented, and the inclination angle θ of the swash plate 104, that is, the speed ratio e, is maintained at the state immediately before reaching the neutral position N.

As yet another embodiment of the present invention, the control device 24 may be configured with a microcomputer or the like. That is, the engine speed, throttle opening, shift position, and setting position of the forward/reverse switching device 15 are electrically detected;
A microcomputer set with a program having a processing function similar to that of the above-mentioned embodiment is manually inputted, and a drive device that replaces the hydraulic cylinder 101 can be operated based on the calculation result. Furthermore, although the hydraulic cylinder 101 is a hydraulic actuator, it is also possible to use an electric actuator such as a pulse motor, linear pulse motor, DC motor, AC motor, etc. depending on the configuration of the control device 24. Also, pilot valve 117 and manual valve 7
8, it is also possible to use an electro-hydraulic servo valve or an electromagnetic proportional control valve.

Furthermore, the present invention is not limited to a hydraulic continuously variable transmission for a vehicle that is a combination of a constant displacement hydraulic pump 2 and a variable displacement hydraulic motor 4; It can also be implemented in connection with a transmission consisting of a combination with a hydraulic motor, or a transmission consisting of a combination of a variable displacement hydraulic pump and a variable displacement hydraulic motor.

Although the forward/reverse switching device 15 is of a dog type in the above embodiment, it may be a combination of a planetary gear and a wet clutch.

Furthermore, in the above embodiment, the discharge pressure P1 of the replenishment pump 8 was used as the working pressure of the hydraulic cylinder 101, but in order to obtain an even greater working force, the high oil pressure in the hydraulic closed circuit 5 is used as the working pressure. You can also do that.

Instead of detecting the degree of opening of the throttle or the amount of depression of the accelerator pedal as an index indicating the driver's intention to accelerate or decelerate, the negative pressure in the engine intake pipe or the amount of fuel supplied may be detected. Instead of the engine rotation speed, engine torque may be detected as an index indicating the engine output.

Furthermore, the present invention is not limited to hydraulic continuously variable transmissions, but can also be applied to other types of vehicle continuously variable transmissions, such as a belt drive type or a toroidal type.

C1 Effects of the invention As described above, according to the present invention, in response to the switching operation to the neutral position, the speed ratio immediately before the switching operation is maintained as the speed ratio of the neutral position, so that the engine reaches the design speed at high speeds. This prevents the vehicle from rotating, and at the same time ensures an appropriate speed ratio at low speeds, resulting in smooth running.

[Brief explanation of drawings]

1 to 5 show an embodiment of the present invention,
Fig. 1 is an overall hydraulic control circuit diagram, Fig. 2 is a schematic diagram showing the connection state of the hydraulic motor and hydraulic cylinder, Fig. 3 is a shift characteristic diagram, and Fig. 4 is a diagram showing changes due to switching operations during high-speed running. , FIG. 5 is a diagram showing changes caused by switching operations during low-speed running, and FIG. 6 is an overall hydraulic control circuit diagram of another embodiment of the present invention. T... Hydraulic continuously variable transmission Fig. 2 Fig. 3 Fig. 4 Vehicle speed Fig. 5 4 v3 car east

Claims (1)

[Claims] A continuously variable transmission for a vehicle that continuously changes a speed ratio according to an index indicating the driver's intention to accelerate or decelerate, an index indicating the engine output, and an alternative switching operation between a forward position and a neutral position. A speed change control method for a continuously variable transmission for a vehicle, characterized in that, in response to a switching operation to a neutral position, a speed ratio immediately before the switching operation is maintained as a speed ratio at the neutral position.