Patent ID: 12241545

DESCRIPTION OF EMBODIMENTS

An embodiment of a hydraulic control system for a transmission according to the present disclosure will be explained below in detail with reference to the figures. The hydraulic control system for a transmission according to the present disclosure is mounted to a work vehicle provided with a plurality of drive wheels. The work vehicle may be, for example, a wheel loader, a dump truck, a bulldozer, a forklift, or the like but is not limited as such.

FIG.1is a side view of a work vehicle1according to the embodiment.FIG.2is a configuration view of a hydraulic control system100for a transmission according to the present embodiment.

The work vehicle1according to the present embodiment is a dump truck. The work vehicle1is provided with an engine2, an input shaft3, a differential device4, suspension cylinders5, drive wheels6, an output shaft7, a torque converter8, an auxiliary transmission9, and a main transmission10. The engine2is an example of a power source. A pair of left and right suspension cylinders5aand5bare included in the suspension cylinder5. A pair of left and right drive wheels6aand6bare included in the drive wheels6.

The work vehicle1is further provided with suspension pressure sensors44and drive wheel rotation speed sensors45. A pair of left and right suspension pressure sensors44aand44bare included in the suspension pressure sensors44. A pair of left and right drive wheel rotation speed sensors45aand45bare included in the drive wheel rotation speed sensors45.

The hydraulic control system100for a transmission illustrated inFIG.2is mounted to the work vehicle1.

The hydraulic control system100for a transmission is provided with the input shaft3connected to an output shaft of the engine2, and the output shaft7connected to the two drive wheels6aand6bvia the differential device4. The two drive wheels6aand6bare supported by the two suspension cylinders5aand5b. The suspension cylinders5aand5bare interposed between the drive wheels6aand6band a vehicle body frame (not illustrated). The drive wheels6aand6bare coupled to the differential device4via drive shafts15aand15b. The number of drive wheels may be two or more.

A “power transmission device” is provided between the input shaft3and the output shaft7. The power transmission device is configured by the torque converter8, the auxiliary transmission9, and the main transmission10disposed in said order from the input shaft3side. The power transmission device transmits driving power from the engine2to the two drive wheels6aand6b. Specifically, the driving power from the engine2is transmitted in the order of the input shaft3, the torque converter8, the auxiliary transmission9, the main transmission10, the output shaft7, the differential device4, and the drive shafts15aand15b, to the drive wheels6aand6b.

A hydraulic actuation-type lock-up clutch11is installed in the torque converter8. The lock-up clutch11connects and disconnects a pump and a turbine of the torque converter8.

The auxiliary transmission9is provided with a first gear train21and a second gear train22, and a No. 1 clutch (Hi)31and a No. 2 clutch (Low)32respectively corresponding to the gear trains21and22.

The main transmission10is provided with a third gear train23, a fourth gear train24, a fifth gear train25, a sixth gear train26, and a seventh gear train27, and a No. 3 clutch (1st)33, a No. 4 clutch (2nd)34, a No. 5 clutch (3rd)35, a No. 6 clutch (4th)36, and a No. 7 clutch (Rev)37respectively corresponding to the gear trains23to27.

The No. 1 clutch31to the No. 7 clutch37are all hydraulic actuation-type friction clutches. The gear trains corresponding to the clutches held in an engaged state among the No. 1 clutch31to the No. 7 clutch37, function as power transmission elements. As illustrated in Table 1, by selectively combining and holding the No. 1 clutch31to the No. 7 clutch37in an engaged state, the power transmission device can be set to speed stages comprising a forward 1-speed to a forward 7-speed and a reverse 1-speed to a reverse 2-speed. The power transmission device can be set to a plurality of speed stages but the number of speed stages is not limited.

TABLE 1ClutchesHiLow1st2nd3rd4thRevNo. 1No. 2No. 3No. 4No. 5No. 6No. 7Forward1-speed○○2-speed○○3-speed○○4-speed○○5-speed○○6-speed○○7-speed○○Reverse1-speed○○2-speed○○

Electronic control modulation valves (referred to below as “ECMV”)40are respectively connected to the lock-up clutch11and the No. 1 clutch31to the No. 7 clutch37. The ECMVs40are each provided with a pressure control valve connected to the clutches11and31to37, and an electromagnetic proportional valve for adjusting the size of the pilot pressure for actuating the pressure control valve. The ECMVs40perform incremental inflow control of the hydraulic fluid flowing into each of the clutches31to37, by controlling the electromagnetic proportional valve in response to a command current from the controller41.

A hydraulic pump50is driven by the engine2. The hydraulic fluid discharged by the hydraulic pump50is supplied to a main valve52through a filter51. The main valve52is disposed between the hydraulic pump50and the power transmission device. A portion of the hydraulic fluid supplied to the main valve52is supplied to the torque converter8, and the remainder is supplied to the power transmission device through the ECMVs40. The main valve52is controlled by the controller41.

The controller41is configured mainly as a microcomputer comprising a central arithmetic processing device (CPU), a memory storing predetermined programs and various types of data, and peripheral circuits and the like.

The controller41adjusts the main pressure of the hydraulic fluid supplied from the hydraulic pump50to the power transmission device by controlling the main valve52. The controller41corrects the “clutch holding pressure” of the set speed stage in the power transmission device, based on a “load” applied to the two drive wheels6aand6b, and sets the corrected clutch holding pressure as the main pressure.

The “clutch holding pressure” of the speed stage and the “load” applied to the two drive wheels6aand6bwill be explained below.

The controller41previously stores a unique clutch holding pressure for each speed stage of the power transmission device. The clutch holding pressures are the pressures required to hold, in an engaged state, each of the clutches used in each of the speed stages of the power transmission device. The clutch holding pressures are derived by dividing, by the friction surface area of the clutch used in each speed stage, a multiplied value derived by multiplying the torque input from the torque converter8or the lock-up clutch11to the auxiliary transmission9, by the speed reduction ratios of each speed stage.

The controller41is connected to an acceleration sensor42, an output shaft rotation speed sensor43, two suspension pressure sensors44aand44b, and two drive wheel rotation speed sensors45aand45b. The acceleration sensor42detects the acceleration of the work vehicle1and outputs the detection value to the controller41. The acceleration sensor42may be, for example, an inertia measurement device (IMU). The controller41derives the rate of change of the acceleration per unit of time based on the detection values from the acceleration sensor42. The output shaft rotation speed sensor43detects the rotation speed of the output shaft7and outputs the detection value to the controller41. The controller41detects the speed of the work vehicle1based on the detection values from the output shaft rotation speed sensor43and derives the rate of change of the speed of the work vehicle1per unit of time. The suspension pressure sensors44aand44bdetect the pressure (referred to below as “suspension pressure”) in the bottom chambers of the suspension cylinders5aand5b. The controller41derives the rate of change of the suspension pressure per unit of time based on the detection values from the suspension pressure sensors44aand44b. The controller41may use the greater rate of change among the suspension pressures of the suspension cylinders5aand5b, or may use an average value of the rate of change among the suspension pressures of the suspension cylinders5aand5b. The drive wheel rotation speed sensors45aand45bdetect the rotation speeds of the drive shafts15aand15band output the detection values to the controller41. The controller41derives the rate of change of the drive wheel rotation speed difference per unit of time based on the detection values from the drive wheel rotation speed sensors45aand45b.

When the work vehicle1is traveling over an irregular road surface, the acceleration, speed, and suspension pressures are likely to increase and decrease and large loads are applied to the drive wheels6aand6baccompanying the increase and decrease of the pressures. Therefore, when the work vehicle1is traveling over an irregular road surface, the loads applied to the drive wheels6aand6bare represented by the respective rates of change of the acceleration, the speed, and the suspension pressures.

In addition, when the work vehicle1moves off of a low-friction road and the tractive forces of the drive wheels6aand6brecover from a slipping state, the rate of change of the drive wheel rotation speed difference is likely to increase and decrease and large loads are applied to the drive wheels6aand6baccompanying the increase and decrease. Therefore, when the tractive force of the drive wheels6aand6brecovers from a slipping state, the loads applied to the drive wheels6aand6bare represented by the rate of change of the drive wheel rotation speed difference.

The controller41determines a “margin pressure” based on the greatest rate of change (referred to below as “maximum rate of change”) among the rates of change of the acceleration, the speed, the suspension pressures, and the drive wheel rotation speed difference. The margin pressure is the excess pressure required to suppress slipping of the clutches of each speed stage set in the power transmission device, caused by the loads (road surface resistance) applied to the drive wheels6aand6b. While the method for determining the margin pressure from the maximum rate of change is not limited in particular, a correspondence table or a relational expression of margin pressures and maximum rates of change is preferably stored in advance by the controller41.

The controller41corrects the clutch holding pressure based on the loads applied to the drive wheels6aand6b, by adding the margin pressure to the clutch holding pressure. The controller41sets the main pressure to the pressure value corrected based on the loads. The controller41controls the main valve52so that the main pressure of the hydraulic fluid supplied from the hydraulic pump50to the power transmission device becomes the set value.

In this way, because the main pressure of the main valve52is set to the pressure value derived by correcting the clutch holding pressure based on the loads applied to the drive wheels6aand6b, a necessary and sufficient margin pressure can be added to the clutch holding pressure only when there is a concern that the clutches may slip. Consequently, loss of the hydraulic pump is reduced in comparison to when the margin pressure is constantly included in the main pressure. As a result, fuel consumption of the work vehicle1can be improved.

(Hydraulic Control Method)

FIG.3is a flow chart for explaining a hydraulic control method of the hydraulic control system100for a transmission. In the following explanation, the work vehicle1is traveling.

In step S1, the controller41detects the speed stage set in the power transmission device.

In step S2, the controller41acquires the clutch holding pressure of the speed stage set in the power transmission device.

In step S3, the controller41acquires the respective rates of change of the acceleration, the speed, the suspension pressure, and the drive wheel rotation speed difference.

In step S4, the controller41determines the margin pressure based on the maximum rate of change which is the greatest rate of change among the respective rates of change of the acceleration, the speed, the suspension pressure, and the drive wheel rotation speed difference.

In step S5, the controller41sets the main pressure to the pressure value derived by adding the margin pressure to the clutch holding pressure.

In step S6, the controller41controls the main valve52so that the main pressure of the hydraulic fluid supplied from the hydraulic pump50to the power transmission device becomes the set value.

Modified Examples of the Embodiment

Although an embodiment of the present disclosure has been described so far, the present disclosure is not limited to the above embodiment and various modifications may be made within the scope of the disclosure.

Modified Example 1

While the controller41in the above embodiment determines the margin pressure based on the maximum rate of change which is the greatest rate of change among the respective rates of change of the acceleration, the speed, the suspension pressure, and the drive wheel rotation speed difference, the present disclosure is not limited in this way.

For example, one rate of change among the acceleration, the speed, the suspension pressure, and the drive wheel rotation speed difference may be used and fixed, or the use of any of the rates of change among the acceleration, the speed, the suspension pressure, and the drive wheel rotation speed difference may be changed as needed in response to the traveling state of the work vehicle1.

Modified Example 2

While the controller41in the above embodiment uses the rate of change of the drive wheel rotation speed difference separately from the rate of change of the acceleration, the present disclosure is not limited in this way. The controller may set the main pressure to a pressure value derived by adding the margin pressure and the clutch holding pressure determined based on the added value of the rates of change of the acceleration and the drive wheel rotation speed difference. Consequently, when the tractive force of the drive wheels6aand6brecovers from a slip state, slipping of the clutches of the speed stages due to the loads applied to the drive wheels6aand6bcan be suppressed.

Modified Example 3

While the controller in the above embodiment uses the speed of the work vehicle1to determine the margin pressure, the rotation speed of the output shaft7detected by the output shaft rotation speed sensor43may be used as the speed.