JPH0814384A - Hydromechanical transmission and its method of changing speed - Google Patents

Abstract

PURPOSE:To provide a compact hydromechanical transmission whose machine parts, although of a sliding or constant type, can change speeds as efficiently as synchronization types and its method of changing speeds. CONSTITUTION:In a hydromechanical transmission which changes speeds by switching the engagement of an input gear 15 rotated by a fixed or variable displacment hydraulic motor 14 with an output gear 17 which transmits outputs to the outside, a closed-center type switching valve 9 whose open area A is freely variable is provided between the hydraulic motor 14 and a variable displacement hydraulic pump 7 that feeds oil to the motor 14. Also, the variable displacement hydraulic pump 7 is provided with a control mechanism 72 which, in response to the inputs of pressures Pp, Pr in front of and behind the switching valve 9, controls the quantity Qp of displacement of the variable displacement hydraulic pump Qp so that the differential pressure DELTAP between the pressures Pp, Pq is constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a wheel type construction vehicle,
The present invention relates to a hydromechanical transmission used for self-propelled vehicles such as agricultural vehicles and automobiles, and a transmission method thereof.

[0002]

2. Description of the Related Art Some hydraulic mechanical transmissions are capable of shifting by switching the meshing of an input gear rotated by a hydraulic motor and an output gear transmitting an output to the outside. A sliding type or a constant type is used for switching the mesh. Since the synchro type has a large number of parts and is fine, in order to transmit high torque at a low speed stage, it is necessary to strengthen each part, resulting in a large size and high cost. Therefore, the synchro type is usually not adopted in the hydromechanical transmission.

[0003]

However, since the mechanical portion of the hydraulic mechanical transmission is a sliding type or a constant type, it is necessary to temporarily stop the vehicle at each shift. As a result, the following problems occur.

(1) Frequent shift operations are required for traveling on a road where there are many ups and downs, traffic signals, and the like. Since it is necessary to stop the vehicle at each shift, it is difficult to maintain the optimum traveling speed and the vehicle travels for a long time. Under such circumstances, the operator is very tired and the satisfaction level cannot be obtained.

(2) As described above, since it is necessary to stop the vehicle at each shift, the starting traction force is required at all speed stages. For this reason, it is necessary to have a structure capable of withstanding the high torque at the time of starting not only in the low speed stage but also in all speed stages. Therefore, the strength and size of each component are increased.

The present invention focuses on the above-mentioned problems of the prior art, and even if the mechanical portion is a sliding type or a constant type, it is possible to shift gears in the same manner as a synchro type, and a compact hydraulic mechanical transmission and its shifting method. The purpose is to provide.

[0007]

In order to achieve the above object, a hydraulic mechanical transmission according to a first invention is a fixed displacement type or variable displacement type hydraulic motor 1 as described with reference to FIG.
In the hydromechanical transmission that achieves gear shifting by switching the meshing between the input gear 15 rotated in step 4 and the output gear 17 that transmits the output to the outside, the hydraulic motor 14 and oil are A closed center type switching valve 9 whose opening area A can be freely changed is provided between the variable displacement hydraulic pump 7 and the variable displacement hydraulic pump 7 to be supplied. A control mechanism 72 for inputting Pp and Pr and controlling the discharge amount Qp of the variable displacement hydraulic pump 7 so that the pressure difference ΔP between them becomes constant.
It is characterized by the provision of.

According to a second aspect of the present invention, there is provided a hydraulic mechanical transmission according to the first aspect of the present invention.
At the time of shifting, first, the opening area A of the switching valve 9 is changed to change the input gear 15b and the output gear 17 that are currently meshed.
The former input in the input gear 15a and the output gear 17a to be meshed next by minimizing the meshing torque with b, disengaging the meshing immediately after this minimization, and then changing the opening area A of the switching valve 9 again. The rotation speed of the gear 15a is synchronized with the rotation speed of the latter output gear 17a, and immediately after the synchronization, the gears are meshed with each other to change the speed.

A third aspect of the present invention is a hydraulic mechanical transmission according to the first aspect of the present invention, wherein in the hydraulic mechanical transmission according to the first aspect of the present invention, when the hydraulic motor 14 is of a variable displacement type, when the gear is changed, the hydraulic motor is first The displacement volume of 14 is minimized and the opening area A of the switching valve 9 is reduced, thereby minimizing the meshing torque between the input gear 15b and the output gear 17b that are currently meshed, and immediately after this meshing, the meshing is performed. Then, by changing the opening area A of the switching valve 9 again, the rotation speed of the former input gear 15a in the next meshing input gear 15a and output gear 17a is synchronized with the rotation speed of the latter output gear 17a. Immediately after the synchronization, it was decided to shift gears by engaging them.

[0010]

The operation of the first invention will be described. The flow rate Q flowing through the opening area A of the switching valve 9 is calculated by the general formula “Q = C × A × (2
ΔP / ρ) ^1/2 ”, the differential pressure across the ΔP [= Pp−Pr (Pp is the upstream pump discharge pressure, Pp
r is a constant load pressure on the downstream side)], it is proportional to the opening area A regardless of the magnitude of the load pressure Pr (where C is the flow coefficient and ρ is the oil density). Therefore, the variable displacement hydraulic pump 7 (hereinafter simply referred to as a hydraulic pump) is provided with a control mechanism 72 capable of controlling the discharge amount Pp of the variable displacement hydraulic pump 7 so that the front-rear differential pressure ΔP becomes constant. That is, by simply adjusting the opening area A of the switching valve 9 as appropriate, the hydraulic motor 1
A flow rate proportional to the opening area A can be supplied to the hydraulic motor 14 regardless of the load pressure Pr of No. 4. Therefore, the rotation speed of the hydraulic motor 14 can be finely adjusted freely and accurately.

Utilization of the above-mentioned action in the first invention is second
It is a shift method according to the invention and a third invention.

That is, according to the second aspect of the present invention, at the time of gear shifting, first, the meshing torque of the gear currently meshed can be reduced only by appropriately changing the opening area A of the switching valve 9.
The gears can be disengaged immediately thereafter, and then the opening area A of the switching valve 9 can be appropriately changed again to synchronize the rotation between the gears to be meshed next time. It was decided to shift gears immediately thereafter.

According to the third aspect of the invention, when the hydraulic motor 14 is of a variable displacement type, the variable displacement control of the hydraulic motor 14 and the variable control of the opening area A of the switching valve 9 are performed only when the gear is disengaged during gear shifting. It was decided to remove the gear by carrying out. still,
It goes without saying that even if the hydraulic motor 14 is of a variable displacement type, the gear can be disengaged only by the variable control of the opening area A of the switching valve 9 (that is, only by the second invention). The operation of the other procedures in the third invention is the same as the operation in the second invention, and thus the description thereof will be omitted.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the hydromechanical transmission according to the present invention will be described with reference to FIG. FIG. 1 is a diagram of a wheel-type construction machine equipped with the hydraulic mechanical transmission according to the embodiment and using the gear shifting method according to the embodiment. In order to make the explanation easy to understand, the vehicle will first be described by dividing it into a hydraulic section, a mechanical section, and a control section, and then the characteristics of the embodiment will be described.

The hydraulic section will be described. The oil Qp sucked out from the oil sump 6 by the hydraulic pump 7 driven by the power source 5 such as an electric motor or an engine is transferred to the hydraulic actuator 8 for the working machine.
The oil is divided into oil Q1 flowing to the control oil device 8 for 1 and 82 and oil Q2 flowing to the switching valve 9 via the pressure compensating valve 74. still,
The working machine is rarely used during traveling, and it can be considered that the pump discharge amount Qp becomes Q2 during traveling. The switching valve 9 is a three-position switching valve having a reverse position R in the upper part of the drawing, a forward moving position F in the lower part of the drawing, and a neutral position N for stopping the vehicle in the center of the drawing, and switching signals S3R, S3F from the controller 1.
To switch. Further, proportional solenoids 9R and 9F are provided at the reverse position R and the forward position F, respectively, and the opening area A can be changed in proportion to the magnitude of the switching signals S3R and S3F. Oil Q2 switched by switching valve 9
Is a variable displacement hydraulic motor 14 (hereinafter simply referred to as the hydraulic motor 1
4), and this is rotated in the reverse direction or the forward direction, and then returned from the drain circuit 83 to the oil reservoir 6 via the two-stage back pressure valve 12. The hydraulic motor 14 is the servo mechanism 1
41, which receives the variable capacitance signal S2 from the controller 1,
For example, the displacement angle of the swash plate or the swash shaft is changed to change the displacement.

The reciprocating circuits 91R and 91F between the switching valve 9 and the hydraulic motor 14 and the check valves 10R and 10F and the relief valves 11R and 1R between the drain circuit 83 and the drain circuit 83, respectively.
1F and is installed. Relief valves 11R, 11F
Is the circuit (91R
Alternatively, it is a safety valve for releasing abnormal high pressure generated in 91F) to the drain circuit 83 to prevent damage to the oil container (mainly the hydraulic motor 14). On the other hand, the check valves 10R and 10F are valves (so-called vacuum prevention valves) for sucking oil from the drain circuit 83 into the circuit (91F or 91R) that has become negative pressure at the time of the above-mentioned runaway, and the negative pressure side circuit. Prevent the occurrence of cavitation. Further, the drain circuit 83 includes the check valve 1
A two-stage back pressure valve 12 for increasing the responsiveness of 0R and 10F is provided. The two-stage back pressure valve 12 is set to a low pressure side during traveling, and is set to a high pressure side during shifting and traveling while retarder braking is performed (hereinafter, simply referred to as retarder traveling).
The switching is performed by the switching signal S4 from the controller 1. In addition, this vehicle is a wheel-type construction machine in which a hydraulic motor and a machine part are mounted on a lower traveling body, and the others are mounted on an upper swing body. Therefore, the reciprocating circuits 91R and 91F are electrically connected by the hydraulic swivel 22.

The mechanical section will be described. The mechanical part was a constant speed transmission. The input gear 15 is connected to the rotary shaft 142 of the hydraulic motor 14 and rotates in the forward and reverse directions. The output gear 17 is connected to the external axle 20, and the input gear 1 is connected via the permanent gear 16.
5 is transmitted to the axle 20 (that is, the vehicle is moved forward and backward). In the figure, the left input gear 151 and the output gear 17 mesh with each other via the constant gear 16, and the meshing is a low speed running stage, while the right input gear 152 and the output gear 17 interpose with the constant gear 16. Engagement, which is the high speed stage. Permanent gear 1
The gear 6 is always meshed with the output gear 17 and is slidable on both the left and right input gears 151 and 152, so that the gear 6 can be selectively meshed with either one of them. In this vehicle, one reverse gear (reverse R),
Neutral (neutral N) and forward two steps (forward F1, forward F)
2)).

For shifting, the servo mechanism 19 receives the shift signal S1 from the controller 1 to move the shifter 18 from the center of the drawing to either the left or the right, and the end of the shifter 18 is rotatably slidably engaged. This is achieved by meshing the constant gear 16 with one of the left and right input gears 151, 152. Therefore, the stop of the vehicle is achieved by one or both of the neutral position N of the switching valve 9 and the central position of the shifter 18. Of course, the constant gear 16
Needless to say, the vehicle may be stopped only at the neutral position N of the switching valve 9 by always meshing with the input gear 151 on the low speed traveling side.

The control unit will be described. The operator operates the shift lever 2 to select the variable speed stage (reverse R, neutral N, forward F1, forward F2). The shift signal S5 from the shift lever 2 is once input to the controller 1 and adjusted, and then becomes the shift signal S1, the variable capacity signal S2, the switching signals S3R, S3F, and the switching signal S4. In addition, the acceleration / deceleration after the completion of the shift is performed by the controller 1 by the variable capacity signal S2 and the switching signals S3R and S3F.
Is performed in conjunction with the depression amount signal S7 from the accelerator pedal 4.

In this vehicle, as shown as an option, oil pressure detectors 13R, 13F are provided in the reciprocating circuits 91R, 91F, respectively, and the detected oil pressure signals VR, VF are detected.
Can be output to the controller 1. A rotation detector 143 is provided near the rotation shaft 142 of the hydraulic motor 14 and outputs the detected input rotation signal Nm to the controller 1. Further, a rotation detector 21 is provided near the axle 20,
The detected output rotation signal Ns is output to the controller 1.

That is, as can be understood from the above description, the hydraulic mechanical transmission of the present vehicle has, if necessary, the input gear 15 rotated by the variable displacement hydraulic motor 14 and the output for transmitting the output to the outside. Shifting is achieved by switching the meshing with the gear 17.

The features of the embodiment are as follows. First, the switching valve 9 will be described. The switching valve 9 is a closed center type, and as described above, the switching signals S3R and S3 from the controller 1 are used.
The opening area A opens in proportion to the size of F. The opening area control is performed not only during acceleration / deceleration after completion of gear shift as described above but also during gear shift as described later.

Next, the hydraulic pump 7 will be described. The hydraulic pump 7 is a variable displacement type, and its displacement can be changed by the servo mechanism 71. The servo mechanism 71 is a control mechanism 72.
When the pressure oil is obtained from the hydraulic pump 7, the displacement volume of the hydraulic pump 7 is moved to the minimum side. Conversely, when the pressure oil is discharged from the servo mechanism 71 to the control mechanism 72, the displacement volume of the hydraulic pump 7 is moved to the maximum side.

The control mechanism 7 controls the oil pressure P on the upstream side of the switching valve 9.
The position b for inputting p (specifically, pump discharge pressure) and the hydraulic pressure Pr on the downstream side of the switching valve 9 (specifically, the hydraulic motor 14).
Is a two-position switching valve having a position for inputting the load pressure). Further, a spring 721 corresponding to ΔPs, which is biased in the relationship of “Pr + ΔPs = Pp”, is attached to the position a.

The operation of the control mechanism 72 will be described. When the opening area A of the switching valve 9 is widened by the switching signal S3F, a large amount of oil tends to flow in the switching valve 9. At this time, the differential pressure ΔP (= Pp-Pr) across the switching valve 9 becomes small (ΔPs
> ΔP), as a result, the control mechanism 72 is set to the a position, and the pressure oil of the servo mechanism 71 is distributed to the oil reservoir 6. Then, as described above, the hydraulic pump 7 is set to the maximum discharge amount side. That is, the large flow rate in the switching valve 9 is compensated. On the contrary, if the opening area A of the switching valve 9 is narrowed by the switching signal S3F, the oil flowing in the switching valve 9 decreases and the front-rear differential pressure ΔP of the switching valve 9 increases (ΔPs <ΔP). Mechanism 72
Becomes the b position, and pressure oil is supplied to the servo mechanism 71. Then, as described above, the hydraulic pump 7 is set to the minimum discharge amount side.
That is, the small flow rate in the switching valve 9 is compensated.

That is, the control mechanism 72 is always in the condition of "ΔP = ΔP".
The shuttle movement is performed so that the differential pressure Δ
Keep P constant. That is, the control mechanism 72 uses the general expression “Q = C × A × (2ΔP /
ΔP in ρ) ^1/2 ”is made constant, so that only the flow rate Q proportional to the opening area A of the switching valve 9 flows to the hydraulic motor 14. As can be seen from the above general formula, since ΔP is constant, even if the load pressure Pr of the hydraulic motor 14 changes, the load pressure Pr does not affect the flow rate of the switching valve 14.

The hydraulic section of this vehicle is provided with a shuttle valve 73 and a pressure compensating valve 74. These are irrelevant to the present subject matter of the present invention, but they are shown, and therefore only an outline will be described. The present vehicle is equipped with not only the hydraulic motor 14 for traveling but also various hydraulic actuators 81, 82 for working machines. The control mechanism 72 integrally controls the discharge amount of the hydraulic pump 7 while inputting the load pressure from each switching valve. In order to perform this integrated control, each switching valve has a shuttle valve 73.
A pressure compensation valve 74 is provided. The shuttle valve 73 is provided at each confluence point of the load pressures from the switching valves, and flows the larger load pressure to the control mechanism 72. Finally, the maximum load pressure ΔPrmax of each switching valve is set. Control mechanism 72
Is a valve that leads to. For example, the pressure compensation valve 74 has a function of integrating the control mechanism 72, the hydraulic pump 7 and the servo mechanism 71, and the maximum load pressure Δ
The Prmax switching valve is a valve for flowing a flow rate proportional to only the opening area A of the switching valve to the actuator without being affected by the load pressure of other switching valves.

As can be seen from the above description, the hydromechanical transmission according to the above-described embodiment is, if necessary, "an input gear 15 rotated by a hydraulic motor 14 of a fixed displacement type or a variable displacement type,
In a hydraulic mechanical transmission in which gear shifting is achieved by switching meshing with an output gear 17 that transmits output to the outside, the hydraulic motor 14 and the variable displacement hydraulic pump 7 that supplies oil to the hydraulic motor 14 A closed center type switching valve 9 whose opening area A can be freely changed is provided between them, and the front and rear pressures Pp and Pr of the switching valve 9 are input to the variable displacement hydraulic pump 7 and the difference between them is provided. The discharge amount Qp of the variable displacement hydraulic pump 7 so that the pressure ΔP becomes constant.
A control mechanism 72 for controlling the

The operation and effect of the above-described structure is that the flow rate to the hydraulic motor 14 can be freely finely adjusted only by finely adjusting the opening area A of the switching valve 9, if necessary. That is, the rotational speed of the hydraulic motor 14 can be freely and finely adjusted.

Next, an embodiment of the shifting method of the hydraulic mechanical transmission according to the above embodiment will be described with reference to FIGS. 2 and 6 are upshifts during normal running according to the first embodiment, FIGS. 3 and 7 are upshifts during retarder running according to the second embodiment, and FIGS. 4 and 8 are during normal running according to the third embodiment. FIG. 5 and FIG. 9 are explanatory views of the shift down during the retarder traveling according to the fourth embodiment, FIGS. 2 to 5 are flowcharts, and FIGS. 6 to 9 are time charts.
6 to 9, each (a) is a displacement control of the hydraulic motor 14, each (b) is an opening area control of the switching valve 9, each (c) is a control of the shifter 18, and each (d) is a hydraulic motor 14. (E) shows the switching control of the two-stage back pressure valve 12.

The first embodiment is a shift-up method during normal driving, which will be described with reference to FIG. 2 and supplemented with FIG. That is, the mesh gear of the forward movement F1 (normal gear 1
151, which is the input gear 15b and the output gear 1
7b) (17b) and a forward F2 meshing gear (the input gear 15a 152 and the output gear 17a 17 are meshed via the normal gear 16).

As shown in FIG. 2, step (1a): traveling forward F1, step (2a): when the shift lever 2 is moved from the F1 position to the F2 position, the shift signal S5 from the shift lever 2 to the controller 1 is generated. Is output. Step (3a): When the shift signal S5 is input, the controller 1 receives the servo mechanism 141 as shown at t1 in FIG. 6A.
To the proportional solenoid 9F of the switching valve 9 as shown at t1 in FIG. 6B, while the displacement variable signal S2 is output to the hydraulic motor 14 to minimize the displacement of the hydraulic motor 14.
Is output to control the flow rate to the hydraulic motor 14 to maintain the input gear 151 at the current speed. By doing so, the meshing torque with the meshing gears 151, 16 becomes small, and the gears can be easily disengaged. In addition, in this vehicle, FIG.
As indicated by t1 to t4, during this period, the hydraulic motor 14 is easily rotated by the force from the axle 20 (hence, the circuit 9
Since cavitation is likely to occur at 1F), the controller 1 controls the switching signal S during this period as shown in FIG. 6 (e).
4 is output to switch the two-stage back pressure valve 12 to the high pressure side, thereby preventing the occurrence of cavitation in the circuit 9F. Step (4a): As shown at t2 in FIG. 6C, after a lapse of a predetermined time t1 to t2, the controller 1 outputs the first shift signal S1 to the servo mechanism 19 to drive the shifter 18 to perform a constant gear operation. The gear 16 is removed from the input gear 151. Step (5a): After that, the controller 1 sets t2 in FIG.
As shown at t3 to t3, the switching signal S3F is output to the switching valve 9 while being gradually reduced, and as shown at t2 to t3 in FIG.
The rotation speed of the hydraulic motor 14 is reduced. This is because it is necessary to reduce the rotation speed of the input gear 152 to the rotation speed of the constant gear 16 for synchronization in order to shift up. Step (6a): Next, as shown at t3 in FIG.
The rotation speed of the input gear 152 and the rotation speed of the constant gear 16 are in synchronization with each other, and the controller 1 sets t3 in FIG. 6 (c).
As shown in FIG. 3, the following gear change signal S1 is output to the servo mechanism 19, the shifter 18 is driven, and the constant gear 16 is moved to the input gear 1
Engage with 52. Step (7a): After the constant gear 16 meshes with the input gear 152, the controller 1 changes the time as shown at t3 in FIG.
The gradual increase of the switching signal S3F to the switching valve 9 is started, and
As shown at t4 in (a), the variable capacity signal S2 is output to the servo mechanism 141, and as shown in FIG. 6 (e),
By outputting the switching signal S4 and switching the two-stage back pressure valve 12 to the low pressure side, the vehicle travels forward F2.

In the step (3a), the input gear 15
There are various methods for maintaining the current speed of No. 1 as follows. First, the controller 1 uses the oil pressure detectors 13R and 13R.
While inputting the detected hydraulic pressures VR and VF from F, the switching signal S
This is a method in which 3F is gradually reduced and gears are disengaged during coasting in which the detected hydraulic pressures VR and VF are similar.

Second, the controller 1 uses the above equation [Q = C × A ×
(2ΔP / ρ) ^1/2 ] and the formula [Q = Ns × e1 × Dm
(Where Ns is the number of rotations of the axle 20 detected by the rotation detector 21, e1 is the gear ratio at F1, and Dm is the minimum displacement of the hydraulic motor 14)].
The switching valve 9 outputs the switching signal S3F that results in the opening area A.
Is output to the proportional solenoid 9F. In the above formula, all the indexes other than the rotation speed Ns are values that are known in advance, so only the rotation speed Ns is detected.

Third, the rotation shaft 142 of the hydraulic motor 14 in which the rotation detector 143 detects the index “Ns × e1” in the above equation.
It is a method of replacing with the rotation speed Nm.

A fourth method is to reduce the meshing torque of the meshing gears 152 and 16 by gradually decreasing the switching signal S3F, and forcefully shift the gears by the shifter 18 or after a predetermined time.

In step (3a), it is not necessary to minimize the displacement of the hydraulic motor 14 if the drive of the shifter 18 is accurate and the response is good. In this case, the hydraulic motor 14 may be a fixed displacement type.

As a method of gradually decreasing the opening area A of the switching valve 9 until the synchronous rotation in the step (5a), the above equation [Q = C
× A × (2ΔP / ρ) ^1/2 ] and the formula [Q = Ns × e2 ×
Dm (where Ns is the number of rotations of the axle 20 detected by the rotation detector 21, e2 is the gear ratio at F2, and Dm is the hydraulic motor 14).
Is the minimum displacement volume of the above)], and a switching signal S3F that produces the opening area A is output to the proportional solenoid 9F of the switching valve 9.
In the above formula, all the indexes other than the rotation speed Ns are values that are known in advance, so only the rotation speed Ns is detected.

The second embodiment is a method for shifting up during traveling of the retarder. Retarders, for example, on long downhills,
It is an auxiliary brake for continuously reducing or limiting the vehicle speed, and there are hydraulic type, exhaust type, electromagnetic type and the like. When the ON signal S6 of the retarder switch 3 operated by the operator is input to the controller 1, the retarder of the vehicle is controlled by the controller 1
Holds the displacement variable signal S2 at a constant value to fix the displacement of the hydraulic motor 14 and turns off the switching signal S3F to set the switching valve 9 to the neutral position N.
It is a hydraulic retarder that obtains retarder braking even when the retarder switch 3 is OFF, when the speed is faster than the target speed from the accelerator command. This retarder braking is performed by the relief valve 11
Since the abnormal pressure is relieved from R, the circuit 9F is connected to the drain circuit 8 via the vacuum prevention valve 10F.
It is necessary to suck a large amount of oil from 3. Therefore, during retarder braking, the two-stage back pressure valve 12 causes the switching signal S from the controller 1 to change.
The hydraulic pressure of the drain circuit 83 is made high by switching to the high pressure side by 4 to facilitate the supply of oil to the circuit 91F.

The second embodiment will be described in terms of differences from the first embodiment. As shown in FIG. 3 (3b) and t1 in FIG. 7 (b), the controller 1 controls the switching signal S3F to minimize the meshing torque when the gears 151 and 16 of F1 are disengaged.
Is output to switch the switching valve 9 from the neutral position N to the opening position F. Further, as shown in FIG. 3 (7b) and t3 in FIGS. 7 (a) and 7 (b), the engagement gear 152 of F2,
After the engagement of 16 is completed, the displacement of the hydraulic motor 14 is returned to the fixed position and the switching valve 9 is also returned to the neutral position N in order to return to the retarder traveling. There is no other big difference.

The third embodiment is a shift-down method during normal driving. That is, the forward F2 meshing gear (the mesh between the input gear 15b 152 and the output gear 17b 17 via the constant gear 16) is set to the forward F1 meshing gear (the input gear 15a via the normal gear 16). No. 151 and the output gear 17a 17).

The third embodiment will be described based on the differences from the first embodiment. In the upshift of the first embodiment, the rotational speed of the input gear 152 is lower than the rotational speed of the input gear 151 at the time of upshifting.
And (5c), and t1 to t3 of FIGS. 8B and 8D.
As shown in FIG.
It is necessary to increase the number of revolutions higher than 2. Others are almost the same as the first embodiment.

The fourth embodiment is a shift-down method during retarder running. In the fourth embodiment, as shown in FIG.
As shown in d) and t1 in FIG. 9B, the controller 1 outputs the switching signal S3F to switch the switching valve 9 to minimize the meshing torque when the gears 152, 16 of F2 are disengaged. This is performed by switching from the neutral position N to the opening position F. Further, as in the third embodiment, the rotation speed of the input gear 151 is set higher than the rotation speed of the input gear 152, as indicated by t1 to t3 in FIG. 5 (5b) and FIGS. 9 (b) and 9 (d). After the meshing of the F1 meshing gears 151 and 16 is completed, the switching valve 9 is returned to the neutral position N in order to return to the retarder traveling.

[0044]

As described above, the mechanical portion of the embodiment of the hydraulic mechanical transmission according to the present invention is of the constant type. Nevertheless, as is clear from the embodiment of the above-described gear shifting method, gear shifting can be performed without stopping the vehicle during gear shifting, that is, while the vehicle is traveling. Specifically, the following effects are achieved.

(1) Since it is possible to shift gears while traveling even on a road where there are many ups and downs, traffic signals, etc., an optimum traveling speed can be secured, operator fatigue is reduced, and operator satisfaction is obtained. This is the same even if the mechanical section of the above-mentioned embodiment is a sliding type.

(2) There are a wide variety of synchro types, from high-class gears capable of high-speed shifting to low-grade gears capable of only low-speed shifting. Therefore, if the mechanical section of the present invention is of a low-level synchro type, high-speed shifting is possible without using a high-grade synchro type.

(3) In the sliding type and constant type of the prior art and the ordinary synchronizing type of the prior art, it is necessary to provide a main clutch in order to shift gears.
However, according to the present invention, the gear can be disengaged with a low torque and the synchronization can be performed with high accuracy, so that a traveling shift similar to that of the synchro can be performed without mounting the main clutch unlike the prior art. Needless to say, the traveling speed can be changed (that is, the strength design for enabling the vehicle to start even at a high speed stage is not required unlike the related art), so that the cost and the size can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of a hydromechanical transmission.

FIG. 2 is a flow chart of shift-up during normal running according to the first embodiment of the present invention.

FIG. 3 is a flowchart of a shift-up operation during retarder traveling according to a second embodiment of the present invention.

FIG. 4 is a flowchart of downshifting during normal running according to a third embodiment of the present invention.

FIG. 5 is a flowchart for downshifting during retarder running, which is a fourth embodiment of the present invention.

FIG. 6 is a time chart of the first embodiment,
(A) is the displacement control of the hydraulic motor, (b) is the opening area control of the switching valve, (c) is the control of the shifter, (d) is the rotation speed of the hydraulic motor, and (e) is the switching control of the two-stage back pressure valve. Is.

FIG. 7 is a time chart of the second embodiment,
(A) is the displacement control of the hydraulic motor, (b) is the opening area control of the switching valve, (c) is the control of the shifter, (d) is the rotation speed of the hydraulic motor, and (e) is the switching control of the two-stage back pressure valve. Is.

FIG. 8 is a time chart of the third embodiment,
(A) is the displacement control of the hydraulic motor, (b) is the opening area control of the switching valve, (c) is the control of the shifter, (d) is the rotation speed of the hydraulic motor, and (e) is the switching control of the two-stage back pressure valve. Is.

FIG. 9 is a time chart of the fourth embodiment,
(A) is the displacement control of the hydraulic motor, (b) is the opening area control of the switching valve, (c) is the control of the shifter, (d) is the rotation speed of the hydraulic motor, and (e) is the switching control of the two-stage back pressure valve. Is.

[Explanation of symbols]

 7 ... Variable displacement hydraulic pump 9 ... Switching valve 14 ... Hydraulic motor 15 ... Input gear 15b ... Input gear 15a currently meshed ... Input gear 17 meshed next ... Output gear 17b ... Present Output gear 17a meshed with ... Output gear meshed with next 72 control mechanism A ... Opening area Pp ... Switching valve pomp pressure Pr ... Switching valve load pressure A / P pressure ΔP Differential pressure across valve Qp ... Pump discharge rate

Claims (3)

[Claims] 1. A hydraulic pressure achieved by shifting the input gear 15 rotated by a fixed displacement type or variable displacement type hydraulic motor 14 and an output gear 17 transmitting an output to the outside to change gears. In the mechanical transmission, a closed center type switching valve 9 whose opening area A is freely changeable is provided between the hydraulic motor 14 and a variable displacement hydraulic pump 7 which supplies oil to the hydraulic motor 14, and The variable displacement hydraulic pump 7 is provided with front and rear pressures Pp, Pr of the switching valve 9.
Is input to control the discharge amount Qp of the variable displacement hydraulic pump 7 so that the differential pressure ΔP becomes constant.
2. A hydromechanical transmission characterized by having two. 2. The method of shifting a hydraulic mechanical transmission according to claim 1, wherein at the time of shifting, the input gear 15b which is currently meshed by first changing the opening area A of the switching valve 9.
The meshing torque between the output gear 17b and the output gear 17b is minimized, the meshing is disengaged immediately after this minimization, and then the opening area A of the switching valve 9 is changed again to mesh the input gear 15a and the output gear 17a. Former input gear 15 in
A gear shifting method for a hydromechanical transmission characterized in that the rotation speed of a is synchronized with the rotation speed of the latter output gear 17a, and gear shifting is achieved by meshing these gears immediately after the synchronization. 3. A method of shifting a hydraulic mechanical transmission according to claim 1, wherein when the hydraulic motor 14 is of a variable displacement type, the displacement of the hydraulic motor 14 is first minimized and switched when shifting. The opening area A of the valve 9 is reduced so that the input gear 15b and the output gear 1 which are currently meshed with each other are reduced.
7b is minimized, the meshing is disengaged immediately after this minimization, and then the opening area A of the switching valve 9 is changed again, whereby the former input in the input gear 15a and the output gear 17a to be meshed next. A gear shifting method for a hydromechanical transmission, characterized in that the rotation speed of the gear 15a is synchronized with the rotation speed of the latter output gear 17a, and gear shifting is achieved by meshing these gears immediately after the synchronization.