JPH0144552Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a speed control device for a hydraulically driven working machine.

[Prior Art] In hydraulically driven working machines such as cranes, there is a strong demand for slow speed control such as slow winding up and down of winches, and how to perform slow speed control has become one of the important issues.

In conventional slow speed control, the displacement amount to the hydraulic motor is changed by changing the tilt angle of the swash plate of the variable displacement pump through the operation of a solenoid valve, or
Alternatively, the discharge amount is changed by adjusting the rotation speed of the engine that drives the hydraulic pump.

[Problems to be solved by the invention] However, with the method of changing the tilting angle of a variable displacement pump, both normal speed work and slow speed work are constant speed work, which makes it difficult to perform delicate tasks such as positioning that require precision. It cannot be said that it is sufficient for carrying out such work. Furthermore, in the method of changing the engine speed, as shown in FIG. 3, the output torque of the engine decreases as the speed decreases, and below a certain speed, it becomes smaller than the required driving torque of the hydraulic pump. Therefore, when the load is large, the hydraulic pump cannot be driven below this rotation speed. In other words, a situation occurs in which the engine stops. Therefore, there is a limit to performing slow speed control by changing the engine speed, and using both of these methods in combination depends on the operator's skill level, as the degree of each operation varies depending on the work conditions and load. Strength is required.

In view of the above-mentioned circumstances, the present invention is intended to enable the operator to obtain any desired speed depending on the working conditions, and to reliably prevent engine stop even during slow-speed work.

[Means for Solving the Problems] The present invention changes the tilting angle of the swash plate of the variable displacement pump using a cylinder, and also operates the engine adjuster via the cylinder. The present invention is characterized in that a proportional reduction pressure valve operated by a speed change lever or the like is connected to a control pump connected to the pump, and the pressure reduction valve is connected to both the cylinders.

[Operation] The pilot pressure from the control pump acts on both cylinders via the proportional pressure reducing valve, and the tilting angle of the swash plate and the engine speed are determined according to the pilot pressure acting on the cylinders. Further, the pilot pressure acting on the cylinder is regulated by a proportional pressure reducing valve, and the proportional pressure reducing valve is operated via a speed change lever or the like operated by the driver.

[Example] Embodiments of the present invention will be described below based on the drawings.

In FIG. 1, 1 is an engine, 2 is a variable displacement pump driven by the engine, 3 is a control pump coaxially connected to the variable displacement pump, and 4 is an oil tank.

Adjustment cylinders 7 and 8 are connected to the speed governor 5 of the engine 1 and the swash plate 6 of the variable displacement pump 2, respectively, and return springs 9 and 8 are connected to both cylinders 7 and 8, respectively.
10 are provided. A proportional pressure reducing valve 11 is connected to the control pump 3, and the adjusting cylinders 7 and 8 are further connected to the proportional pressure reducing valve 11, respectively. This proportional pressure reducing valve 11 is a gear shift lever 1 installed in the driver's cab.
2 (or pedal).

Next, the adjustment operation will be explained.

When the shift lever 12 is operated, the shift lever 1
The proportional pressure reducing valve 11 operates in accordance with the manipulated variable 2, reducing the pilot pressure from the control pump 3 and supplying it to the adjusting cylinders 7 and 8. Each adjustment cylinder 7, 8
is the supplied pilot pressure and springs 9 and 10.
Based on this balance, the speed governor 5 is controlled to determine the rotational speed of the engine 1 and the tilt angle of the swash plate 6. Therefore, the discharge amount Q of the variable displacement pump 2 is adjusted by the interaction of the rotational speed change of the engine 1 and the tilt angle change of the swash plate 6.

Various modes of operation of the adjustment cylinders 7, 8 based on the pilot pressure can be considered, one example of which is shown in FIG.

In the case shown in Figure 2, only the swash plate of the pump is controlled when the engine is at its lowest speed (low idle), and the required torque of the pump is the torque at low engine speed. The engine rotation is increased just before it becomes equal to .

The change in the discharge amount Q when such speed adjustment is made is shown by the solid line in FIG.

[Effects of the invention] As described above, according to the invention, the speed can be changed steplessly from slow speed to maximum speed with one lever (or pedal), and the speed can be changed steplessly according to the amount of operation of the shift lever or pedal. Adjustments can be made and speed control performance can be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an embodiment according to the present invention, Fig. 2 is a diagram showing the speed control characteristics of the embodiment, and Fig. 3 is a diagram showing the relationship between the output torque of the engine and the driving torque of the pump. be. 1 is an engine, 2 is a variable displacement pump, 3 is a control pump, 6 is a swash plate, 7 and 8 are adjustment cylinders, 11
12 indicates a proportional pressure reducing valve, and 12 indicates a gear shift lever.

Claims (1)

[Scope of utility model registration request] The tilting angle of the swash plate of the variable displacement pump is changed by a cylinder, and the speed governor of the engine is operated via the cylinder, and the control pump connected to the variable displacement pump is operated by a speed change lever or the like. A speed control device for a hydraulically driven working machine, characterized in that a proportional pressure reducing valve is connected to the cylinder, and the pressure reducing valve is connected to both of the cylinders.