JPS6357629B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a hydraulic system including a prime mover and a hydraulic pump, and more particularly to a control device for a hydraulic system that can prevent damage to the hydraulic pump at low temperatures.

In a hydraulic system that includes a prime mover and a hydraulic pump, if the temperature of the hydraulic oil flowing in this system is low and the viscosity is high, during normal operation, the suction port side of the hydraulic pump will Negative pressure is generated, causing problems such as insufficient discharge flow, abnormal fluctuations in discharge pressure, and abnormal noise, which can lead to pump damage.

In preparation for such a situation, conventional means have been proposed that detect the negative pressure at the suction port of the pump and display this or issue an alarm. In this case, the operator judges the operating status according to the display and alarm, and takes precautions such as not increasing the rotation of the prime mover or increasing the tilt angle of the variable displacement pump if it is equipped with a variable displacement pump. It is necessary to perform appropriate operations. However, operation using such conventional means is extremely troublesome for the operator, and there is a high risk that the pump may eventually be damaged due to continued forced operation due to the operator's carelessness. It is in.

The present invention was made in view of the above-mentioned problems in the prior art, and its purpose is to provide a control device for a hydraulic system that can reliably prevent damage to a hydraulic pump at low temperatures without relying on operator judgment. Our goal is to provide the following.

In order to achieve this objective, in the present invention,
In a control device for a hydraulic system including a prime mover and a hydraulic pump, a detector that detects a representative liquid temperature of hydraulic oil flowing through the hydraulic system or a pressure near a suction port of the hydraulic pump and generates a detection signal. a function generator that generates a control coefficient signal that becomes smaller as the detection signal becomes smaller when the detection signal becomes less than or equal to a predetermined value; calculation output means for calculating an operating state command value which becomes smaller as either the numerical signal or the target tilting angle signal of the hydraulic pump becomes smaller and outputting the operating state command value signal; The rotational speed of the prime mover or the tilt angle of the hydraulic pump is controlled in accordance with the operating state command value signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hydraulic system control device of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention. This first embodiment detects a typical fluid temperature in the hydraulic system, and if the fluid temperature is lower than a preset value, the prime mover is automatically operated at the lowest rotational speed. It is composed of In Figure 1, 1 is the prime mover, 2
3 is a hydraulic pump driven by the prime mover 1; 4 is a tank which is a hydraulic source; 5 is an operating state command value signal of the governor 2, that is, a target rotation speed N signal. It is an accelerator lever that gives. Reference numeral 6 denotes a detection means, ie, a liquid temperature detector, which detects a typical liquid temperature of the hydraulic oil flowing in the hydraulic system and issues a signal, and is arranged to detect, for example, the liquid temperature near the pump suction port. Reference numeral 7 denotes a function generating means, for example a function generator, which is connected to the liquid temperature detector 6 and generates a control coefficient K signal. A control coefficient K is set in this function generator 7 in relation to the liquid temperature θ detected by the liquid temperature detector 6. When the liquid temperature θ is lower than the set value θl, K is 0;
When the temperature is higher than θh, K is 1, and when it is higher than θl and lower than θh, K is a value between 0 and 1, and is proportional to the liquid temperature θ. Reference numeral 14 denotes a calculation output means, such as a calculation output device, connected to the function generator 7 and interposed between the accelerator lever 5 and the governor 2. This calculation output device 14 performs the following calculation based on the minimum rotation speed N0 of the prime mover given in advance, the target rotation speed N given from the accelerator lever 5, and the control coefficient K given from the function generator 7. Then, the operating state command value N' is obtained, and this operating state command value N' signal is output to the governor 2.

N'=N0+K(N-N0) (1) In the control device configured in this way, the representative liquid temperature is detected by the liquid temperature detector 6, and the function generator 7 A control coefficient K signal is sent to the calculation output device 14. At this time, if the liquid temperature θ is lower than the set value θl set in the function generator 7, K=0, and from the above equation (1), N'= N0
is calculated, and the operating state command value N' signal, which is the lowest rotational speed N0, is output from the calculation output device 14 to the governor 2. Therefore, in this case, the prime mover 1 is operated at the lowest rotational speed. Also, if the liquid temperature θ is higher than the set value θh set in the function generator 7, then K
= 1, and N' = N is calculated from the above formula (1),
An operating state command value N' signal, which is the target rotational speed N, is output from the calculation output device 14 to the governor 2. Therefore, in this case, the prime mover 1 is operated at the target rotation speed. Note that when the liquid temperature θ is higher than the set value θl and lower than the set value θh, the prime mover 1 is operated at a rotation speed intermediate between the minimum rotation speed and the target rotation speed according to the liquid temperature θ. In this way, even when the temperature θ of the hydraulic oil is low, the prime mover 1 can be completely automatically rotated at an appropriate rotation speed, and therefore the occurrence of cavitation can be effectively prevented.

FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention. This second embodiment exemplifies a case where a variable displacement pump is provided as the hydraulic pump,
The pressure on the suction port side of the pump is detected, and if the pressure is smaller than a preset value, the tilting angle of the pump is limited to a minimum. Note that in FIG. 2, the same members as those described above are designated by the same reference numerals. In the same figure 2, 10 is a variable displacement pump, 13 is a pump 1
0 and the tank 4, this filter 13 is provided to remove contaminants from the hydraulic fluid. Reference numeral 8 denotes a detection means, that is, a pressure detector, which detects the pressure of hydraulic oil flowing in the hydraulic system near the pump suction port and generates a signal.
Reference numeral 9 denotes a function generating means, such as a function generator, which is connected to the pressure detector 8 and generates a control coefficient K signal. A control coefficient K is set in this function generator 9 in relation to the pressure P detected by the pressure detector 8, and when the pressure P is lower than the set value Pl, K is 0, and the set value If higher than Ph, K is 1, Pl
When the pressure is higher and lower than Ph, K is a value between 0 and 1 and proportional to pressure P. 11 is a pump regulator that controls the tilt angle of the pump 10; 12 is a pump regulator 11;
This is a tilting angle command lever that provides an operating state command value signal, that is, a target tilting angle command value α signal. Reference numeral 15 denotes a calculation output means, such as a calculation output device, connected to the function generator 9 and interposed between the tilt angle command lever 12 and the pump regulator 11. In this calculation output device 15, the minimum tilting angle command value α ₀ of the pump given in advance and the target tilting angle α given from the tilting angle command lever 12 are calculated.
Then, the following calculation is performed based on the control coefficient K given from the function generator 9 to obtain the operating state command value α', and this operating state command value α' signal is output to the pump regulator 11.

α′=α ₀ +K(α−α ₀ ) (2) In the control device configured in this way, the pressure is detected by the pressure detector 8 near the pump suction port, and the function is generated according to the detection signal. The control coefficient K signal is sent from the function generator 9 to the calculation output device 15. At this time, if the pressure P is lower than the set value Pl set in the function generator 9, K=0, and from the above equation (2), α' =α ₀ is calculated, and the operational state command value α′ signal, which is the minimum tilt angle command value α ₀ , is output from the calculation output device 15 to the pump regulator 11 . Therefore, in this case, the pump 10 is controlled to the minimum tilt angle. Moreover, if the pressure P is higher than the set value Ph set in the function generator 9, K=1,
α′=α is calculated from the above equation (2), and the calculation output device 1
5 outputs an operating state command value α' signal, which is a target tilting angle command value α, to the pump regulator 11.
Therefore, in this case, the pump 10 is controlled to the target tilt angle. Note that if the pressure P is higher than the set value Pl,
If the pressure P is lower than the set value Ph, the pump 10 is controlled to a tilting angle intermediate between the minimum tilting angle and the minimum tilting angle. In this way, even when the pressure of the hydraulic oil on the suction port side of the pump 10 is low, the tilting angle of the pump 10 can be appropriately controlled, thereby effectively preventing the occurrence of cavitation. be able to. In this second embodiment, the structure is equipped with a filter 13, and the occurrence of cavitation due to clogging in this filter 13 is also detected by a pressure detector 8, and a function generator 9 and an arithmetic output device are used. This can be effectively prevented by controlling the tilt angle of the pump 10 via the pump 15.

Note that the first embodiment described above clearly shows the rotation speed control means of the prime mover based on liquid temperature detection, and the second embodiment clearly shows the pump tilting angle control means based on pressure detection. The second embodiment may be combined to provide a configuration in which both the prime mover rotation speed control means and the pump tilt angle control means are provided. Further, by detecting the pressure, it is also possible to perform both the rotational speed control of the prime mover and the pump tilt angle control. Furthermore, it is easily possible to configure the motor to stop or not start by detecting the liquid temperature. Note that the above-described function generation means, calculation output means, etc. may be included in a microcomputer.

As described above, the hydraulic system control device of the present invention includes a detection means for detecting the temperature of the hydraulic oil or the pressure near the pump suction port, and a control coefficient corresponding to the signal emitted by the detection means. A function generation means for generating a signal, and an arithmetic output means for calculating a predetermined operating state command value based on the control coefficient signal and an operating state command value signal of the prime mover or hydraulic pump inputted from the outside. The structure is such that the prime mover or hydraulic pump is controlled according to a predetermined operating condition command value signal calculated by calculation, so the prime mover can be operated at high speed or the variable displacement pump can be operated at a large tilt at low temperatures. If an attempt is made to do so, this will be prevented completely automatically, without any intervention from the operator.
Therefore, there is an effect of reliably preventing damage to the pump due to cavitation. If the temperature of the hydraulic oil flowing in the system rises due to continued work, normal operation can be automatically resumed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of a control device for a hydraulic system according to the present invention, and FIG. 2 is a schematic diagram showing a second embodiment of the same. 1... Prime mover, 2... Governor, 3... Hydraulic pump, 5... Accelerator lever, 6... Liquid temperature detector,
7, 9...Function generator, 8...Pressure detector, 10
... Variable displacement pump, 11 ... Pump regulator, 12 ... Tilt angle command lever, 14, 15 ...
Arithmetic output device.

Claims (1)

[Claims] 1. In a control device for a hydraulic system that includes a prime mover and a hydraulic pump, a detection signal is generated by detecting the representative liquid temperature of the hydraulic oil flowing through the hydraulic system or the pressure near the suction port of the hydraulic pump. a function generator that emits a control coefficient signal that becomes smaller as the detection signal becomes smaller when the detection signal becomes less than a predetermined value; and calculation output means for calculating an operating state command value that becomes smaller as either the rotational speed signal or the target tilting angle signal of the hydraulic pump becomes smaller, and outputting an operating state command value signal, A control device for a hydraulic system, characterized in that the rotational speed of the prime mover or the tilting angle of the hydraulic pump is controlled in accordance with the operating state command value signal.