JP5940473B2 - Hydraulic drive unit for construction machinery - Google Patents

Description

  The present invention relates to a hydraulic drive device for a construction machine such as a hydraulic excavator, and in particular, a hydraulic drive that controls a discharge flow rate of the hydraulic pump so that a discharge pressure of the hydraulic pump is higher than a maximum load pressure of a plurality of actuators by a target differential pressure. Relates to the device.

  Some hydraulic drive devices for construction machines such as excavators control the discharge flow rate of the hydraulic pump so that the discharge pressure of the hydraulic pump is higher by the target differential pressure than the maximum load pressure of multiple actuators. This is called sensing control. A hydraulic drive device that performs this load sensing control is described in Patent Document 1, for example.

  The hydraulic drive device described in Patent Document 1 includes an engine, a variable displacement hydraulic pump driven by the engine, a plurality of actuators driven by pressure oil discharged from the hydraulic pump, and a plurality of hydraulic pumps. With multiple flow control valves that control the flow rate of pressure oil supplied to the actuator, the capacity of the hydraulic pump is reduced as the discharge pressure of the hydraulic pump increases, and the absorption torque of the hydraulic pump exceeds the preset maximum torque A pump regulator having a torque control unit that controls the hydraulic pump and a load sensing control unit that controls the capacity of the hydraulic pump so that the discharge pressure of the hydraulic pump is higher than the maximum load pressure of the plurality of actuators by a target differential pressure, It is provided in the oil passage that supplies the discharge oil to multiple flow control valves, and the discharge pressure of the hydraulic pump is released to the maximum load pressure. Return the oil discharged from the hydraulic pump to the tank becomes higher becomes the open state than the pressure obtained by adding over de set pressure, and a unloading valve to limit the rise in the delivery pressure of the hydraulic pump.

  Moreover, there exists a thing of patent document 2 as a hydraulic drive apparatus which performs load sensing control, and was equipped with the exhaust gas purification apparatus. In this device, an exhaust resistance sensor is provided in the exhaust gas purification device provided in the exhaust pipe, and when the detected value of the sensor exceeds a predetermined level, a signal is output from the control device, and the regulator and amplifier of the main pump are output. The load valve is controlled to increase the discharge amount and discharge pressure of the hydraulic pump at the same time and apply a hydraulic load to the engine. As a result, the engine output is increased to increase the exhaust gas temperature, the oxidation catalyst is activated, the filter deposits are burned, and the filter is regenerated.

JP 2001-193705 A Japanese Patent No. 3073380

  Construction machines such as hydraulic excavators are equipped with a diesel engine as a drive source. The amount of particulate matter (hereinafter referred to as PM) discharged from diesel engines is being regulated more and more year by year along with NOx, CO, HC, and the like. In response to such regulations, an exhaust gas purification device is provided in the engine, and PM is collected by a filter called a diesel particulate filter (DPF) in the engine exhaust gas purification device and discharged to the outside. It is common practice to reduce the amount of PM. In this exhaust gas purifying device, when the amount of PM supplemented by the filter increases, the filter becomes clogged, and as a result, the exhaust pressure of the engine increases, resulting in a decrease in engine output, deterioration in fuel consumption or engine life. Therefore, it is necessary to regenerate the filter by appropriately burning PM collected in the filter to remove clogging of the filter.

  For the regeneration of the filter, an oxidation catalyst is usually used. The oxidation catalyst may be disposed upstream of the filter, directly supported by the filter, or both. In either case, in order to activate the oxidation catalyst, the temperature of the exhaust gas Must be higher than the activation temperature of the oxidation catalyst, and for this purpose, it is necessary to forcibly raise the exhaust gas temperature to a temperature higher than the activation temperature of the oxidation catalyst.

  In the hydraulic drive device described in Patent Document 1, since the variable displacement main hydraulic pump is configured to perform load sensing control, for example, when all the operation levers are neutral, the tilt angle ( Capacity) is minimized and the discharge flow rate is also minimized. Further, the discharge pressure of the main pump is controlled by the unload valve, and when all the operation levers are neutral, the discharge pressure of the main pump becomes a minimum pressure that is substantially equal to the set pressure of the unload valve. As a result, the absorption torque of the main pump is also minimized. Similarly, when the operation amount of the operation lever is small, the discharge flow rate of the main pump is small, the discharge pressure is low, and the absorption torque is small.

  When an exhaust gas purifying device is provided in an engine of a hydraulic drive device that performs such load sensing control, the load on the engine is low when all the operating levers are neutral or when the operating amount of the operating lever is small. The exhaust gas temperature of the engine will be low. As a result, PM in the exhaust gas is not burned, clogging of the filter is not eliminated, engine exhaust pressure increases, and inconveniences such as a decrease in engine output, a deterioration in fuel consumption, or a decrease in engine life occur. There was a problem.

  In the hydraulic drive device described in Patent Document 2, when it is necessary to regenerate the filter of the exhaust gas purification device, this is detected by an exhaust resistance sensor, and control for simultaneously increasing the discharge flow rate and the discharge pressure of the main pump (hereinafter, referred to as the following) By performing pump output increase control), a hydraulic load is applied to the engine, the engine output is increased to increase the exhaust gas temperature, the oxidation catalyst is activated, and the filter deposit is combusted. For this reason, even when all the operation levers are neutral, the absorption horsepower of the main pump is not reduced, and the filter can be regenerated satisfactorily.

  However, in the hydraulic drive device described in Patent Document 2, the discharge flow rate of the hydraulic pump is returned to the tank via the unload valve, which is useless without using the energy of the pressure oil generated by the main pump. That is, the energy consumption efficiency of the entire hydraulic drive device is reduced.

  An object of the present invention is to efficiently remove the filter deposits of an exhaust gas purification device by increasing the absorption torque of a hydraulic pump and increasing the temperature of exhaust gas in a hydraulic drive device that performs load sensing control. Another object of the present invention is to provide a hydraulic drive device for a construction machine that can collect energy of pressure oil discharged from a hydraulic pump to a tank and can effectively use energy of pressure oil generated by the hydraulic pump.

  In order to solve the above problems, the present invention provides a prime mover, a variable displacement main pump driven by the prime mover, a plurality of actuators driven by pressure oil discharged from the main pump, and the main pump From a plurality of flow control valves that respectively control the flow of pressure oil supplied to the plurality of actuators, and the capacity of the main pump is reduced as the discharge pressure of the main pump increases, and the absorption torque of the main pump is reduced. A torque control unit for controlling so as not to exceed a preset maximum torque, and load sensing for controlling a capacity of the main pump so that a discharge pressure of the main pump is higher than a maximum load pressure of the plurality of actuators by a target differential pressure A hydraulic drive device for a construction machine comprising a pump control device having a control unit. A hydraulic motor that is disposed in a pressure oil supply oil passage that supplies pressure oil from the pump to the plurality of flow control valves and a control oil passage that connects a tank and that can be driven by the pressure oil discharged from the main pump, and the hydraulic pressure When the generator connected to the rotating shaft of the motor, the exhaust gas purification device for purifying the exhaust gas of the engine, and the discharge pressure of the main pump reach a target control pressure obtained by adding a predetermined value to the maximum load pressure A control device that controls the generator so that an increase in discharge pressure of the main pump is suppressed, the control device further determines whether or not regeneration processing of the exhaust gas purification device is necessary, and When regeneration processing of the exhaust gas purification device is necessary, the predetermined value is set to a value suitable for the regeneration processing and control is performed to increase the discharge pressure of the main pump, and And performs control for increasing the discharge flow rate of the main pump load sensing control over de sensing control unit as invalid.

  Control that increases the discharge pressure of the main pump by setting a predetermined value to a value suitable for the regeneration process when the exhaust gas purification device needs to be regenerated by providing the hydraulic motor, generator, and control device in this way When the exhaust gas purification device needs to be regenerated by performing the control to invalidate the load sensing control of the load sensing control unit and increase the discharge flow rate of the main pump, the absorption torque of the main pump 2 is increased. As the engine load increases and the exhaust temperature rises accordingly, the oxidation catalyst provided in the exhaust gas purification device is activated, and PM accumulated on the filter of the exhaust gas purification device is efficiently burned and removed can do.

  The hydraulic motor is driven by the discharge oil of the main pump, and the generator is driven by the hydraulic motor to generate electric energy, which is stored in the battery. Thereby, the energy of the pressure oil discharged from the main pump to the tank can be recovered, and the energy of the pressure oil generated by the main pump can be used effectively.

  The control device preferably sets the predetermined value to a value suitable for normal unload control when the regeneration process is not necessary.

  As a result, the discharge pressure of the main pump is controlled so as not to exceed the pressure obtained by adding a predetermined value (a value suitable for normal unload control) to the maximum load pressure. Can fulfill. In addition, when the hydraulic motor rotates and the discharge flow rate of the main pump is returned to the tank, the generator generates electrical energy, and the electrical energy is stored in the battery, so the pressure oil discharged from the main pump to the tank The energy of the pressure oil generated by the main pump can be effectively utilized.

  The hydraulic drive device is preferably a pilot pump driven by the engine, a pilot hydraulic source connected to the pilot pump and generating a pilot primary pressure based on discharge oil of the pilot pump, and the pilot pump And an engine speed detection valve that is located between the pilot hydraulic power source and generates a hydraulic signal that depends on the engine speed based on the discharge oil of the pilot pump. When processing is not required, the regeneration signal is required by setting the target differential pressure of the load sensing control by guiding the hydraulic signal generated by the engine speed detection valve to the load sensing control unit of the pump control device. When the discharge pressure of the pilot pump is transferred to the load sensing control unit of the pump control device There invalidates the load sensing control, performs control to increase the discharge flow rate of the main pump.

  Preferably, the torque control unit of the pump control device has a characteristic indicating a relationship between a discharge pressure and a capacity of the main pump, and a characteristic composed of a maximum capacity constant characteristic and a maximum absorption torque constant characteristic. When the discharge pressure of the main pump is lower than the pressure at the transition point from the maximum capacity constant characteristic to the maximum absorption torque constant characteristic, even if the discharge pressure of the main pump increases, When the discharge pressure of the main pump rises above the pressure at the transition point, the capacity of the main pump is reduced so that the maximum capacity of the main pump decreases according to the maximum absorption torque constant characteristic. A value suitable for the reproduction process that is set as the predetermined value when the control apparatus needs the reproduction process is a value that is suitable for the transfer process. Is the pressure above the value of the point.

  Thus, when performing the regeneration process, the pump output increase control using the constant absorption torque control of the torque control unit can be reliably performed, and the filter deposits in the exhaust gas purification device can be efficiently burned and removed. .

  According to the present invention, in a hydraulic drive device that performs load sensing control, the absorption torque of the hydraulic pump is increased to raise the temperature of the exhaust gas, thereby efficiently removing the filter deposits of the exhaust gas purification device. In addition, the energy of the pressure oil discharged from the hydraulic pump to the tank can be recovered, and the energy of the pressure oil generated by the hydraulic pump can be used effectively.

It is a figure which shows the hydraulic drive apparatus of the working machine concerning the 1st Embodiment of this invention. It is a figure which shows the external appearance of a hydraulic shovel. It is a figure which shows the relationship between the discharge pressure and capacity | capacitance (tilt angle) of a main pump by a torque control tilt actuator. It is a figure which shows the absorption torque characteristic of the main pump obtained as a result of the torque control of a torque control tilt actuator. It is a figure which shows the relationship between the amount of PM deposits in an exhaust-gas purification apparatus, and the exhaust resistance (differential pressure before and behind a filter) detected by an exhaust resistance sensor. It is a flowchart which shows the hydraulic motor control of a control apparatus. It is a flowchart which shows the reproduction | regeneration control of a control apparatus.

~Constitution~
FIG. 1 is a diagram showing a hydraulic drive device for a work machine according to an embodiment of the present invention.

  The hydraulic drive apparatus according to the present embodiment is driven by the engine 1 in conjunction with a diesel engine (hereinafter simply referred to as the engine) 1, a main hydraulic pump (hereinafter referred to as the main pump) 2 driven by the engine 1, and the main pump 2. Pilot pump 3, a plurality of actuators 5, 6, 7, 8, 9, 10, 11, 12 driven by pressure oil discharged from the main pump 2, the main pump 2 and a plurality of actuators 5, 6 , 7, 8, 9, 10, 11 and 12 and an engine speed detecting valve 30 connected to a pressure oil supply oil passage 3a to which the discharge oil of the pilot pump 3 is supplied. And a pilot relief valve 32 that is connected to the downstream side of the engine speed detection valve 30 and keeps the pressure in the pilot oil passage 31 constant. The control pilot pressures a, b, c, d, d, f, g, h, i, j, k, Operation lever devices 34a, 34b, 34c, 34d, 34e, 34f, 34g, and 34h having remote control valves for generating l, m, n, o, and p are provided.

  The work machine according to this embodiment is, for example, a hydraulic mini excavator, the actuator 5 is a swing motor of the hydraulic excavator, the actuators 6 and 8 are left and right traveling motors, the actuator 7 is a blade cylinder, and the actuator 9 is A swing cylinder, and the actuators 10, 11, and 12 are a boom cylinder, an arm cylinder, and a bucket cylinder, respectively.

  The control valve 4 is connected to a first pressure oil supply oil passage (pipe) 2a to which discharge oil of the main pump 2 is supplied via a second pressure oil supply oil passage (valve block passage) 4a. A plurality of valve sections 13, 14, 15, 16, 17, 18, 19, 20 for controlling the direction and flow rate of the pressure oil supplied to each actuator from A plurality of shuttle valves 22a, 22b, 22c, 22d, 22e, 22f that select the highest load pressure (hereinafter referred to as the maximum load pressure) PLmax from among the load pressures 10, 10, 11, and 12 and output it to the signal oil passage 21. , 22g, a main relief valve 23 as a safety valve connected to the second pressure oil supply oil passage 4a of the control valve 4 and limiting the maximum discharge pressure (maximum pump pressure) of the main pump 2, and a control A differential pressure reducing valve 24 is connected to the second pressure oil supply oil passage 4a of the lube 4 and detects and outputs a differential pressure PLS between the discharge pressure Pd of the main pump 2 and the maximum load pressure PLmax as an absolute pressure. ing. The discharge side of the main relief valve 23 is connected to a tank oil passage 29 in the control valve 2, and the tank oil passage 29 is connected to the tank T.

  The valve section 13 includes a flow control valve 26a and a pressure compensation valve 27a, the valve section 14 includes a flow control valve 26b and a pressure compensation valve 27b, and the valve section 15 includes a flow control valve 26c and a pressure compensation valve 27c. The valve section 16 is composed of a flow control valve 26d and a pressure compensation valve 27d, the valve section 17 is composed of a flow control valve 26e and a pressure compensation valve 27e, and the valve section 18 is composed of a flow control valve 26f and a pressure. The valve section 19 includes a flow rate control valve 26g and a pressure compensation valve 27g, and the valve section 20 includes a flow rate control valve 26h and a pressure compensation valve 27h.

  The flow rate control valves 26a to 26h respectively control the direction and flow rate of the pressure oil supplied from the main pump 2 to the respective actuators 5 to 12, and the pressure compensation valves 27a to 27h are differential pressures before and after the flow rate control valves 26a to 26h. To control each. The flow control valves 26a to 26h are controlled pilot pressures a, b, c, d, d, f, g, generated by remote control valves of the operating lever devices 34a, 34b, 34c, 34d, 34e, 34f, 34g, 34h. h, i, j, k, l, m, n, o, and p, respectively.

  Each of the pressure compensation valves 27a to 27h has valve-opening side pressure receiving portions 28a, 28b, 28c, 28d, 28e, 28f, 28g, and 28h for setting a target differential pressure, and the pressure receiving portions 28a to 28h have differential pressures. The output pressure of the pressure reducing valve 24 is guided, and the target compensation differential pressure is set by the absolute pressure of the differential pressure PLS between the hydraulic pump pressure Pd and the maximum load pressure PLmax. As a result, the differential pressures before and after the flow control valves 26a to 26h are all controlled to be the same value (the differential pressure PLS between the hydraulic pump pressure Pd and the maximum load pressure PLmax), and at the time of combined operation for simultaneously driving a plurality of actuators. Regardless of the load pressure of the actuators 5 to 12, the discharge flow rate of the main pump 2 can be distributed according to the ratio of the opening areas of the flow control valves 26a to 26h, and the combined operability can be ensured. Further, when the discharge flow rate of the main pump 2 is in a saturation state where the required flow rate is less than the required flow rate, the differential pressure PLS decreases according to the degree of supply shortage, so that the pressure compensation valves 27a to 27h correspond to this. The differential pressure before and after the flow control valves 26a to 26h to be controlled decreases at the same rate, and the flow rate of the flow control valves 26a to 26h decreases. In this case as well, the main pump depends on the opening area ratio of the flow control valves 26a to 26h. Two discharge flow rates can be distributed to ensure composite operability.

  The engine speed detection valve 30 includes an oil passage 30e that connects the pressure oil supply oil passage 3a to which the discharge oil of the pilot pump 3 is supplied to the pilot oil passage 31, and a throttle element (fixed throttle) provided in the oil passage 30e. ) 30f, a flow rate detection valve 30a connected in parallel to the oil passage 30e and the throttle element 30f, and a differential pressure reducing valve 30b. The flow rate detection valve 30a has a variable throttle portion 30c that increases the opening area as the passing flow rate increases, and the discharge oil of the pilot pump 3 is supplied from the throttle element 30f of the oil passage 30e and the variable throttle portion 30c of the flow rate detection valve 30a. It passes through both and flows to the pilot oil passage 31 side. At this time, a differential pressure is increased in the throttle element 30f and the variable throttle portion 30c as the flow rate of the pressure oil flowing from the pressure oil supply oil passage 3a to the pilot oil passage 31 increases, and the differential pressure reducing valve 30b. Detects and outputs the differential pressure before and after as an absolute pressure Pa. Since the discharge flow rate of the pilot pump 3 varies depending on the rotation speed of the engine 1, the discharge flow rate of the pilot pump 3 can be detected by detecting the differential pressure across the throttle element 30f and the variable throttle portion 30c. The number of rotations can be detected. Further, the variable throttle portion 30c increases the opening area as the passing flow rate increases (as the front-rear differential pressure increases), so that the degree of increase in the front-rear differential pressure becomes milder as the passing flow rate increases. It is configured as follows.

  The main pump 2 is a variable displacement hydraulic pump, and includes a pump control device 35 for controlling the tilt angle (capacity) thereof. The pump control device 35 includes a torque control unit 35A including a torque control tilt actuator 35a, and a load sensing control unit 35B including an LS control valve 35b and an LS control tilt actuator 35c.

  The discharge pressure of the main pump 2 is guided to the torque control tilt actuator 35a. When the discharge pressure of the main pump 2 increases, the tilt angle of the main pump 2 is reduced, and the input torque of the main pump 2 is set to a preset maximum torque. Limit to not exceed. Accordingly, the torque control unit 35A limits the horsepower consumed by the main pump 2 and prevents the engine 1 from being stopped due to overload.

  The LS control valve 35b has pressure receiving portions 35d and 35e facing each other, and the pressure receiving portion 35d receives the absolute pressure Pa output from the differential pressure reducing valve 30b of the engine speed detection valve 30 via the oil passage 38 in the load sensing control. The absolute pressure of the differential pressure PLS output from the differential pressure reducing valve 24 to the pressure receiving portion 35e is guided as a feedback pressure via the oil passage 39, and the differential pressure PLS is calculated as the target differential pressure (target LS differential pressure). When the absolute pressure becomes higher than the absolute pressure Pa (PLS> Pa), the pressure of the pilot hydraulic source 33 is guided to the LS control tilt actuator 35c to reduce the tilt angle of the main pump 2, and the absolute pressure of the differential pressure PLS is absolute. When the pressure is lower than Pa (PLS <Pa), the tilt angle of the main pump 2 is increased by connecting the LS control tilt actuator 35c to the tank T. As a result, the amount of displacement (displacement volume) of the main pump 2 is controlled so that the discharge pressure Pd of the main pump 2 becomes higher than the maximum load pressure PLmax by the absolute pressure Pa (target LS differential pressure). The LS control valve 35b and the LS control tilting actuator 35c perform load sensing control in which the discharge pressure Pd of the main pump 2 is higher than the maximum load pressure PLmax of the plurality of actuators 5, 6, 7, 8, 9, 10, 11, 12. A load sensing type pump control device is configured to control the tilt of the main pump 2 so as to increase only by the target differential pressure (absolute pressure Pa).

  Here, since the absolute pressure Pa is a value that changes in accordance with the rotational speed of the engine 1, the absolute pressure Pa is used as the target differential pressure of the load sensing control, and the target compensated differential pressure of the pressure compensating valves 27a to 27h is used as the main pump. By setting the absolute pressure of the differential pressure PLS between the discharge pressure Pd of 2 and the maximum load pressure PLmax, the actuator speed can be controlled according to the rotational speed of the engine 1. Further, as described above, the variable throttle portion 30c of the flow rate detection valve 30a of the engine speed detection valve 30 is configured such that the degree of increase in the front-rear differential pressure becomes moderate as the passing flow rate increases. The saturation phenomenon according to the rotational speed of the engine 1 can be improved, and good fine operability can be obtained when the rotational speed of the engine 1 is set low.

  In addition, the hydraulic drive apparatus according to the present embodiment is arranged in a control oil passage 51 connecting the second pressure oil supply oil passage 4a and the tank T as a characteristic configuration, and the pressure oil discharged from the main pump 2 A fixed displacement hydraulic motor 52 that can be driven by the motor, a generator 53 coupled to the rotating shaft 52a of the hydraulic motor 52, a pressure sensor 54 that is connected to the signal oil path 21 and detects the maximum load pressure PLmax, When the discharge pressure of the main pump 2 reaches a pressure Pun (target control pressure) obtained by adding a predetermined value Pb to the maximum load pressure PLmax, the generator 53 is controlled so that an increase in the discharge pressure of the main pump 2 is suppressed (this embodiment). In this mode, the rotation of the hydraulic motor 52 is prevented until the discharge pressure of the main pump 2 becomes higher than the pressure Pun (target control pressure) obtained by adding a predetermined value Pb to the maximum load pressure PLmax, and the main pump 2 discharges. A control device 55 that controls the power generation torque of the generator 53 so that the hydraulic motor 52 rotates when the pressure becomes higher than the pressure Pun), a converter 56 that converts AC power generated by the generator 53 into DC power, A battery 57 (power storage device) that stores DC power generated by the machine 53 and converted by the converter 56. The control oil passage 51 in which the hydraulic motor 52 is disposed may be connected to the first pressure oil supply oil passage 2a.

  The hydraulic drive apparatus according to the present embodiment includes an exhaust gas purification device 62 disposed in an exhaust pipe 61 that constitutes an exhaust system of the engine 1, and an exhaust resistance sensor that detects exhaust resistance in the exhaust gas purification device 62. 63, a forced regeneration switch 64 that instructs to forcibly regenerate the exhaust gas purifying device 62, and an absolute pressure Pa that is an output pressure of the differential pressure reducing valve 30b of the engine speed detection valve 30 to the LS control valve 35b. It is arranged in the signal oil passage 38 leading to the pressure receiving portion 35d, and switches between the absolute pressure Pa and the pressure in the pilot oil passage 3a (the discharge pressure of the pilot pump 3), and one of the pressures is supplied to the pressure receiving portion 35d of the LS control valve 35b. And an electromagnetic switching valve 65 for outputting.

  The exhaust gas purification device 62 has a built-in filter that collects particulate matter (PM) contained in the exhaust gas. Further, the exhaust gas purification device 62 includes an oxidation catalyst. When the exhaust gas temperature reaches a predetermined temperature or higher, the oxidation catalyst is activated, and the activated oxidation catalyst burns unburned fuel added to the exhaust gas. As a result, the exhaust gas temperature is raised, and the PM collected and deposited on the filter is efficiently burned and removed.

  The exhaust resistance sensor 63 is, for example, a differential pressure detection device that detects a differential pressure across the upstream and downstream sides of the filter of the exhaust gas purification device 62 (exhaust resistance of the exhaust gas purification device 62).

  The hydraulic drive device according to the present embodiment is further connected in parallel with the engine 1 via the power distributor 70 to the main pump 2 and the power distributor 70 disposed between the engine 1 and the main pump 2. Generated when the motor 71, the chopper 72 that boosts the DC power of the battery 57, the DC power boosted by the chopper 72 is converted into AC power and supplied to the motor 71, and the motor 71 functions as a generator. And an inverter 73 that converts AC power into DC power and stores it in the battery 57.

The control device 55 inputs the detection signal of the exhaust resistance sensor 63 and the command signal of the forced regeneration switch 64 in addition to the function of controlling the hydraulic motor 52 described above, and when the regeneration processing of the filter of the exhaust gas purification device 62 is necessary. In addition, it further has a function of performing regeneration control and a function of controlling the inverter 73.
~ Hydraulic excavator ~
FIG. 2 shows the external appearance of the hydraulic excavator.

In FIG. 2, a hydraulic excavator well known as a work machine includes an upper swing body 300, a lower traveling body 301, and a swing type front work machine 302. The front work machine 302 includes a boom 306, an arm 307, The bucket 308 is configured. The upper turning body 300 can turn with respect to the lower traveling body 301 by the rotation of the turning motor 5 shown in FIG. A swing post 303 is attached to the front portion of the upper swing body 300, and a front work machine 302 is attached to the swing post 303 so as to move up and down. The swing post 303 is rotatable in the horizontal direction with respect to the upper swing body 300 by expansion and contraction of the swing cylinder 9 shown in FIG. 1, and the boom 306, the arm 307, and the bucket 308 of the front work machine 302 are shown in FIG. The cylinder 10, the arm cylinder 11, and the bucket cylinder 12 can be rotated in the vertical direction by expansion and contraction. The lower traveling body 301 includes a central frame 304, and a blade 305 that moves up and down by the expansion and contraction of the blade cylinder 7 shown in FIG. The lower traveling body 301 travels by driving the left and right crawler belts 310 and 311 by the rotation of the traveling motors 6 and 8 shown in FIG.
~ Main pump torque control ~
Details of torque control of the torque control tilt actuator 35a of the torque control unit 35A will be described with reference to FIGS. 3A and 3B. FIG. 3A is a diagram showing the relationship between the discharge pressure and the capacity (tilt angle) of the main pump 2 by the torque control tilt actuator 35a (hereinafter referred to as Pq (pressure-pump capacity) characteristics), and FIG. 3B is the torque control. It is a figure which shows the absorption torque characteristic of the main pump 2 obtained as a result of the torque control of the inclination actuator 35a. The horizontal axis in FIGS. 3A and 3B indicates the discharge pressure P of the main pump 2. The vertical axis in FIG. 3A indicates the capacity (or tilt angle) q of the main pump 2, and the vertical axis in FIG. 3B indicates the absorption torque Tp of the main pump 2.

  In FIG. 3A, the Pq characteristic of the main pump 2 is composed of a maximum capacity constant characteristic TP0 and maximum absorption torque constant characteristics TP1, TP2.

A first value P0 (starting pressure of constant absorption torque control) that is the pressure at the break point (transition point) at which the discharge pressure P of the main pump 2 shifts from the maximum capacity constant characteristic TP0 to the maximum absorption torque constant characteristics TP1, TP2. When the pressure is below, the maximum capacity of the main pump 2 is constant at qmax even if the discharge pressure P of the main pump 2 increases. At this time, as shown in FIG. 3B, as the discharge pressure P of the main pump 2 increases, the maximum absorption torque of the main pump 2 that is the product of the pump discharge pressure and the pump capacity increases. When the discharge pressure P of the main pump 2 rises above the first value P0, the maximum capacity of the main pump 2 decreases along the characteristic line of the maximum absorption torque constant characteristics TP1 and TP2, and the absorption torque of the main pump 2 is The maximum torque Tmax determined by the characteristics of TP1 and TP2 is maintained. The characteristic lines of TP1 and TP2 are set by two springs (not shown) so as to approximate a constant absorption torque curve (hyperbola), and the maximum torque Tmax is substantially constant. Further, the maximum torque Tmax is set to be smaller than the limit torque TEL of the engine 1. As a result, when the discharge pressure P of the main pump 2 rises above the first value P0, the maximum capacity of the main pump 2 is reduced and the absorption torque (input torque) of the main pump 2 does not exceed the preset maximum torque Tmax. As a result, the absorption torque of the main pump 2 is controlled so as not to exceed the limit torque TEL of the engine 1. Control of the maximum absorption torque by these characteristics TP1 and TP2 is referred to as absorption torque constant control (absorption horsepower constant control when the vertical axis is expressed by pump discharge flow rate).
~ Relationship between PM accumulation amount and exhaust resistance (differential pressure across the filter) ~
FIG. 4 is a diagram showing the relationship between the amount of PM accumulated in the exhaust gas purification device 62 and the exhaust resistance (differential pressure across the filter) detected by the exhaust resistance sensor 63. As shown in FIG.

  In FIG. 4, the exhaust resistance of the exhaust gas purification device 62 increases as the PM deposition amount in the exhaust gas purification device 62 increases. In the figure, Wb is the PM deposition amount that requires automatic regeneration control, and ΔPb is the exhaust resistance when the PM deposition amount is Wb. Wa is a PM deposition amount that may terminate the regeneration control, and ΔPa is an exhaust resistance when the PM deposition amount is Wa.

In a storage device (not shown) of the control device 55, ΔPb is stored as a threshold value for starting automatic regeneration control, and ΔPa is stored as a threshold value for ending regeneration control.
~ Control flow ~
FIG. 5A is a flowchart showing control of the hydraulic motor 52 of the control device 55.

<Step S100>
First, the control device 55 determines whether or not the regeneration flag is ON (whether or not regeneration processing is necessary). If the reproduction flag is ON, it is determined that the reproduction process is being performed, and if the reproduction flag is OFF, it is determined that the reproduction process is not being performed. The reproduction flag will be described later.

<Step S110>
When the regeneration flag is not ON (when regeneration processing is not necessary), the control device 55 sets a predetermined value Pb (unload set pressure) to be added to the maximum load pressure PLmax in step S150A described later, to set the conventional unload valve. The same value as the pressure (that is, a value suitable for normal unload control) is set to P1 (Pb = P1). This value P1 is, for example, an absolute pressure Pa output from the differential pressure reducing valve 30b, that is, a pressure slightly higher than the target differential pressure of load sensing control. For example, when the absolute pressure Pa (target differential pressure for load sensing control) output from the differential pressure reducing valve 30b is 2 MPa, P1 is about 2.5 to 3 MPa. The predetermined value Pb may be a value lower than the absolute pressure Pa (target LS differential pressure) in consideration of the rotation delay due to the inertia of the hydraulic motor 52 and the generator 53.

<Step S120>
When the regeneration flag is ON (when regeneration processing is necessary), the control device 55 uses a predetermined value Pb to be added to the maximum load pressure PLmax in step S150A described later from a value P1 when the regeneration flag is not ON. Is set to a value P2 suitable for large reproduction processing (Pb = P2). This value P2 is set to, for example, a pressure (for example, a pressure equal to or slightly higher than P0) in the vicinity of the starting pressure P0 of the constant absorption torque control in the Pq (pressure-pump capacity) characteristic shown in FIG. 3A. Yes.

<Step S130>
Next, the control device 55 inputs the maximum load pressure PLmax detected by the pressure sensor 54.

<Step S140>
Next, the control device 55 determines whether or not the maximum load pressure PLmax has reached a predetermined pressure Pmro that is slightly lower than the main relief pressure Pmr (maximum pump pressure) that is the set pressure of the main relief valve 23.

<Step S150A>
When the maximum load pressure PLmax does not reach the predetermined pressure Pmro and is lower than that, the control device 55 sets the value obtained by adding the predetermined value Pb to the maximum load pressure PLmax at that time as the target control pressure for hydraulic motor control. Set as Pun.

That is, Pun = PLmax + Pb
<Step S150B>
When the maximum load pressure PLmax reaches a predetermined pressure Pmro, the control device 55 sets the maximum load pressure PLmax at that time as the target control pressure Pun.

That is, Pun = PLmax
<Step S160>
Next, the control device 55 calculates a rotational torque Tm that is considered to act on the hydraulic motor 52 when the discharge pressure of the main pump 2 reaches the target control pressure Pun. This rotational torque Tm can be calculated by the following equation, where q is the capacity of the hydraulic motor 52.

Tm = Pun × q
In this specification, this rotational torque is called unload rotational torque.

<Step S170>
Next, the control device 55 calculates a power generation torque Tg having a magnitude that overcomes the unload rotation torque Tm of the hydraulic motor 52. The power generation torque Tg having a magnitude that overcomes the unload rotation torque Tm of the hydraulic motor 52 means a rotation torque that is the same as or slightly larger than the unload rotation torque Tm and that has a rotation direction opposite to that of the unload rotation torque Tm.

<Step S180>
Next, the control device 55 calculates the generated power for the generator 53 to generate the generated torque Tg.

<Step S190>
Next, the control device 55 outputs a control command corresponding to the generated power to the generator 53, and causes the generator 53 to generate a power generation torque Tg having a magnitude that overcomes the unload rotation torque Tm of the hydraulic motor 52.

  By controlling the generator 53 in this way, the rotation of the hydraulic motor 52 is prevented until the discharge pressure of the main pump 2 reaches a pressure Pun (target control pressure) obtained by adding a predetermined value Pb to the maximum load pressure PLmax. When the discharge pressure of the main pump 2 exceeds the pressure obtained by adding the predetermined value Pb to the maximum load pressure PLmax, the hydraulic motor 52 rotates and the discharge flow rate of the main pump 2 is returned to the tank T. As a result, when the predetermined value Pb is set to the same value P1 as the set pressure of the conventional unload valve, the discharge pressure of the main pump 2 is controlled so as not to exceed the pressure obtained by adding P1 to the maximum load pressure PLmax. Therefore, the function equivalent to the conventional unloading valve can be achieved. When the predetermined value Pb is set to a value P2 larger than P1, the discharge pressure of the main pump 2 is controlled so as not to exceed the pressure obtained by adding P2 to the maximum load pressure PLmax. The pressure can be increased to a value of PLmax + P2.

  When the maximum load pressure PLmax reaches a predetermined pressure Pmro that is slightly lower than the main relief pressure Pmr, before the discharge flow rate of the main pump 2 is returned to the tank via the main relief valve 23, the hydraulic motor 52 is turned on. It rotates and the discharge flow rate of the main pump 2 is returned to the tank T. This can prevent the discharge pressure of the main pump 2 from rising excessively.

  In any of the above cases, when the hydraulic motor 52 rotates and the discharge flow rate of the main pump 2 is returned to the tank T, the generator 53 generates electric energy (electric power), and the electric energy is supplied to the battery 57. Stored.

FIG. 5B is a flowchart showing the regeneration control of the control device 55.
<Step S200>
First, when the program starts, the control device 55 performs the following initial settings.

  (1a) The electrical signal output to the electromagnetic switching valve 65 is turned off.

  (2a) Turn off the regeneration flag.

  (3a) Turn off the control for supplying unburned fuel into the exhaust gas.

  By turning off the electrical signal output to the electromagnetic switching valve 65 as in (1a) above, the electromagnetic switching valve 65 is held at the illustrated position, and the pressure receiving portion 35d of the LS control valve 35b has a differential pressure reducing valve 30b. The absolute pressure Pa output from is derived. Accordingly, as in the case of the conventional load sensing control, the absolute pressure Pa is set as the target differential pressure of the load sensing control.

By turning off the regeneration flag as in (2a) above, the predetermined value Pb is set to the same value P1 as the set pressure of the conventional unload valve in the control of the hydraulic motor 52 as described above (Pb = P1). ), The hydraulic motor 52 can perform the same function as a conventional unloading valve.
<Step S210>
Next, based on the detection signal from the exhaust resistance sensor 63 and the command signal from the forced regeneration switch 64, the control device 55 and the threshold value for starting the automatic regeneration control in the exhaust gas purification device 62. It is compared with ΔPb to determine whether ΔP> ΔPb, and whether the forced regeneration switch 64 has been switched from OFF to ON. When ΔP> ΔPb, or when the forced regeneration switch 64 is ON, the process proceeds to the next process. If ΔP> ΔPb and the forced regeneration switch 64 is not ON, nothing is done and the determination process is repeated.
<Step S220>
When ΔP> ΔPb or when the forced regeneration switch 64 is ON, the control device 55 starts regeneration control as follows.

  (1b) The electric signal output to the electromagnetic switching valve 65 is turned ON, and the electromagnetic switching valve 65 is switched from the illustrated position.

  (2b) Turn on the regeneration flag.

  (3b) Turn on the control for supplying unburned fuel into the exhaust gas.

  By switching the electromagnetic switching valve 65 from the illustrated position as in (1b) above, the discharge pressure of the pilot pump 3 is guided to the pressure receiving portion 35d of the LS control valve 35b. Here, the discharge pressure of the pilot pump 3 is a pressure obtained by adding the pressure of the pilot hydraulic source 33 (pressure of the pilot oil passage 31) to the absolute pressure Pa output from the differential pressure reducing valve 30b. Higher pressure. Further, the absolute pressure of the differential pressure PLS output from the differential pressure reducing valve 24 guided to the pressure receiving portion 35e of the LS control valve 35b does not become higher than the pressure of the pilot hydraulic power source 33 that is the original pressure. Therefore, when the discharge pressure of the pilot pump 3 is guided to the pressure receiving portion 35d of the LS control valve 35b, the LS control valve 35b is switched to the left position in the drawing, the load sensing control becomes invalid, and the discharge flow rate of the main pump 2 increases. To do.

  By turning on the regeneration flag as in (2b) above, the predetermined value Pb is set to a value P2 suitable for regeneration processing larger than the value P1 in the control of the hydraulic motor 52 as described above (Pb = P2 ), The discharge pressure of the main pump 2 can be increased to a pressure obtained by adding the value of P2 to the maximum load pressure PLmax.

  Thus, by increasing the discharge flow rate of the main pump 2 and increasing the discharge pressure of the main pump 2, it is possible to perform pump absorption torque increase control in which the absorption torque of the main pump 2 is increased.

The control (3b) is performed, for example, by controlling an electronic governor (not shown) of the engine 1 and performing post injection (additional injection) in the expansion stroke after engine main injection. The unburned fuel may be supplied by providing a fuel injection device for regeneration control in the exhaust pipe and operating this fuel injection device.
<Step S230>
During the regeneration control, the control device 55 terminates the exhaust resistance ΔP in the exhaust gas purification device 62 and the automatic regeneration control based on the detection signal from the exhaust resistance sensor 63 provided in the exhaust gas purification device 62. The threshold value ΔPa is compared to determine whether or not ΔP <ΔPa. If ΔP <ΔPa is not satisfied, the determination is repeated and the regeneration control is continued.
<Step S240>
When ΔP <ΔPa, the control device 55 ends the regeneration control. That is,
(1c) The electrical signal output to the electromagnetic switching valve 65 is turned OFF, and the electromagnetic switching valve 65 is switched to the illustrated position.

  (2c) Turn off the regeneration flag.

(3c) Turn off the control for supplying unburned fuel into the exhaust gas.
~ Operation ~
Next, the operation of the hydraulic drive device according to the present embodiment will be described.

<When regeneration processing is not required and all control levers are neutral>
If the regeneration process is not necessary, the determination in step S210 of FIG. 5B is negative and the regeneration flag is OFF. In this case, an OFF electrical signal is output to the electromagnetic switching valve 65, and the electromagnetic switching valve 65 is turned off. Is in the position shown. When the electromagnetic switching valve 65 is in the illustrated position, the absolute pressure Pa output from the differential pressure reducing valve 30b of the engine speed detection valve 30 is supplied to the pressure receiving portion 35d of the LS control valve 35b as a target differential pressure for load sensing control. Led. Further, the control device 55 sets the predetermined value Pb to the same value P1 as the set pressure of the conventional unloading valve (Pb = P1), and sets PLmax + P1 as the target control pressure Pun for hydraulic motor control.

  When the operation levers of all the operation lever devices 34a to 34h are in the neutral position, all the flow control valves 26a to 26h are in the neutral position, and the maximum load pressure PLmax detected by the shuttle valves 22a to 22g is the tank pressure. The target control pressure Pun set by the control device 55 is P1, and the discharge pressure of the main pump 2 is controlled to increase to P1 by the control of the hydraulic motor 52 and the generator 53. This control is equivalent to the control of the conventional unload valve. The absolute pressure of the differential pressure PLS output from the differential pressure reducing valve 24 is the same as the discharge pressure of the main pump 2, and this pressure P1 is guided to the pressure receiving portion 35e of the LS control valve 35b. Since this pressure P1 is slightly higher than the absolute pressure Pa output from the differential pressure reducing valve 30b of the engine speed detection valve 30, the LS control valve 35b is switched to the right position in the figure. The operation of the hydraulic drive device at this time is the same as the conventional one, the tilt angle (capacity) of the main pump 2 is the minimum qmin, and the discharge flow rate is also the minimum Qmin.

  Further, the hydraulic motor 52 operates so as to perform the same function as a conventional unloading valve, and the absorption torque of the main pump 2 becomes the minimum Tmin. The operating point of the main pump 2 at this time is indicated by point A in FIGS. 3A and 3B.

  At this time, the hydraulic motor 52 is driven by the oil discharged from the main pump 2, and the generator 53 is driven by the hydraulic motor 52 to generate electric energy, which is stored in the battery 41 via the converter 56. The

<When playback is not required and the control lever is operated>
For example, when the operation lever of the boom operation lever device 34f is operated with a full stroke in the left direction (boom raising direction) in the drawing for the purpose of raising the boom, the boom flow control valve 26f is switched to the boom cylinder 10. Pressure oil is supplied and the boom cylinder 10 is driven.

  The flow rate through the flow control valve 26f is determined by the opening area of the meter-in throttle of the flow control valve 26f and the differential pressure across the meter-in throttle, and the differential pressure across the meter-in throttle is the output pressure of the differential pressure reducing valve 24 by the pressure compensation valve 27f. Since it is controlled to be equal to the absolute pressure of a certain differential pressure PLS, the flow rate (and hence the drive speed of the boom cylinder 10) flowing through the flow rate control valve 26f is controlled according to the operation amount of the operation lever.

  When the boom cylinder 10 starts to move, the discharge pressure of the main pump temporarily decreases. At this time, the load pressure of the boom cylinder 10 is detected as the maximum load pressure by the shuttle valves 22a to 22g, and the difference between the discharge pressure of the main pump and the load pressure of the boom cylinder 10 is output as the output pressure of the differential pressure reducing valve 24. Therefore, the absolute pressure of the differential pressure PLS output from the differential pressure reducing valve 24 is reduced, and the reduced absolute pressure of the differential pressure PLS is guided to the pressure receiving portion 35e of the LS control valve 35b. When the absolute pressure of the differential pressure PLS drops below the absolute pressure Pa, which is the output pressure of the differential pressure reducing valve 30b guided to the pressure receiving portion 35d of the LS control valve 35b, the LS control valve 35b is switched to the left position in the figure. Then, the pressure oil of the LS control tilt actuator 35c is returned to the tank so that the tilt angle of the main pump 2 is increased, and the discharge flow rate of the main pump 2 is increased. The increase in the discharge flow rate of the main pump 2 is continued until the absolute pressure of the differential pressure PLS becomes equal to the absolute pressure Pa, and the discharge pressure of the main pump 2 (the pressures of the first and second pressure oil supply oil passages 2a and 4a). ) Is controlled to be higher than the maximum load pressure PLmax by the absolute pressure Pa (target LS differential pressure) output from the engine speed detection valve 30, and the flow rate required by the boom flow control valve 26f is supplied to the boom cylinder 10. So-called load sensing control is performed.

  If the discharge pressure Pd of the main pump 2 transiently becomes higher than the pressure Pun obtained by adding a predetermined value Pb (= P1) to the maximum load pressure PLmax during this operation, the hydraulic motor 52 rotates ( The oil discharged from the main pump 2 is returned to the tank T, and the discharge pressure of the main pump 2 is controlled so as not to be higher than the pressure Pun obtained by adding a predetermined value Pb (= P1) to the maximum load pressure PLmax. That is, also in this case, the hydraulic motor 52 operates so as to perform the same function as a conventional unloading valve.

  At this time, the hydraulic motor 52 is driven by the oil discharged from the main pump 2, and the generator 53 is driven by the hydraulic motor 52 to generate electric energy, which is stored in the battery 41 via the converter 56. The

  When the operation lever devices of two or more actuators, for example, the operation lever device 34f for the boom and the operation lever device 34g for the arm are operated, the LS control valve 35b and the hydraulic motor are operated as in the case of the single operation. 52 operates to control the discharge flow rate and discharge pressure of the main pump 2. The generator 53 is driven by the hydraulic motor 52 to generate electric energy, and this electric energy is stored in the battery 41 via the converter 56.

  When the operation levers of the operation lever devices of two or more actuators are operated, the output pressure of the differential pressure reducing valve 24 is guided to the pressure compensating valves 27a to 27h as the target compensating differential pressure, and the pressure compensating valves 27f and 27g are In order to control the differential pressure across the flow control valves 26f, 26g to be equal to the differential pressure between the discharge pressure of the main pump 2 and the maximum load pressure PLmax, the load pressure of the boom cylinder 10 and the arm cylinder 11 is increased or decreased. Regardless, the pressure oil can be supplied to the boom cylinder 10 and the arm cylinder 11 at a ratio corresponding to the opening area of the meter-in throttle portions of the flow control valves 26f and 26g.

  At this time, when a saturation state occurs in which the discharge flow rate of the main pump 2 is less than the flow rate required by the flow control valves 26f and 26g, the output pressure of the differential pressure reducing valve 24 (the main pump 2 (The differential pressure between the discharge pressure and the maximum load pressure PLmax) is reduced, and the target compensation differential pressure of the pressure compensation valves 27a to 27h is accordingly reduced, so that the discharge flow rate of the main pump 2 is controlled by the flow control valves 26f and 26g. It can be redistributed to the required flow rate ratio, and a good combined operability can be obtained.

<When the control lever is returned to neutral>
For example, when the operation lever of the boom operation lever device 34f is returned from the full stroke to the neutral position with the intention of stopping the boom from the boom raising operation, the pressure oil in the pilot hydraulic source 33 is cut and the flow control valve 26f is operated. Therefore, the generation of the control pilot pressure k to stop is stopped, and the flow control valve 36f returns to the neutral position. The pressure oil discharged from the main pump 2 does not flow into the boom cylinder 10 because the flow control valve 26f has returned to the neutral position.

  At this time, the discharge pressure Pd of the main pump 2 temporarily increases, but when the discharge pressure Pd of the main pump 2 becomes higher than the pressure Pun obtained by adding a predetermined value Pb (= P1) to the maximum load pressure PLmax. The hydraulic motor 52 rotates and the discharge oil of the main pump 2 is returned to the tank T, and the discharge pressure of the main pump 2 does not become higher than the pressure Pun obtained by adding a predetermined value Pb (= P1) to the maximum load pressure PLmax. To be controlled. The generator 53 is driven by the hydraulic motor 52 to generate electric energy, and this electric energy is stored in the battery 41 via the converter 56.

<When regeneration is required and all control levers are neutral>
When the operation levers of all the operation lever devices 34a to 34h are in the neutral position, it is necessary to regenerate the exhaust gas purification device 62, and when the determination in step S210 of FIG. 5B is affirmed and the regeneration flag is turned ON. The electromagnetic switching valve 65 is switched from the position shown in the figure by an ON electrical signal, and the discharge pressure of the pilot pump 30 is guided to the pressure receiving portion 35d of the LS control valve 35b. Further, the control device 55 sets the predetermined value Pb to a value P2 suitable for the regeneration process (Pb = P2), and sets PLmax + P2 as the target control pressure Pun for hydraulic motor control.

  Here, the discharge pressure of the pilot pump 3 guided to the pressure receiving portion 35d of the LS control valve 35b is obtained by adding the pressure of the pilot hydraulic power source 33 (pressure of the pilot oil passage 31) to the absolute pressure Pa output from the differential pressure reducing valve 30b. The pressure is higher than the pressure of the pilot hydraulic power source 33. Further, the absolute pressure of the differential pressure PLS output from the differential pressure reducing valve 24 guided to the pressure receiving portion 35e of the LS control valve 35b does not become higher than the pressure of the pilot hydraulic power source 33 that is the original pressure. Therefore, when the discharge pressure of the pilot pump 3 is guided to the pressure receiving portion 35d of the LS control valve 35b, the LS control valve 35b is switched to the left position in the drawing, the load sensing control is disabled, and the capacity of the main pump 2 is the maximum capacity. qmax increases, and the discharge flow rate of the main pump 2 also increases to the maximum.

  Further, when the operation levers of all the operation lever devices 34a to 34h are in the neutral position, as described above, the maximum load pressure PLmax detected by the shuttle valves 22a to 22g is the tank pressure (approximately 0 MPa), and the control is performed. The target control pressure Pun set by the device 55 is P2, and the discharge pressure of the main pump 2 is controlled to increase to P2 by the control of the hydraulic motor 52 and the generator 53.

  In the Pq (pressure-pump capacity) characteristics of the main pump 2 shown in FIG. 3A, in general, in the case of a construction machine such as a hydraulic excavator, the starting pressure P0 for constant absorption torque control is often set to about 10 MPa. As described above, since P2 is set to a pressure in the vicinity of P0 (for example, a pressure equal to or slightly higher than P0), as a result, the main pump 2 when the electromagnetic switching valve 65 is switched from the illustrated position. The discharge pressure of the main pump 2 is a pressure near the break point of the Pq characteristic of the main pump 2, and the capacity of the main pump 2 is a value determined by the constant control of the absorption torque by the torque control tilt actuator 35a as shown by the point B in FIG. 3A. qb. Further, the absorption torque of the main pump 2 at this time becomes the maximum torque Tmax as indicated by a point B in FIG. 3B.

  Thus, by setting the target control pressure Pun of the hydraulic motor control to PLmax + P2 and switching the electromagnetic switching valve 65, the absorption torque of the main pump 2 increases to the maximum torque Tmax of the constant absorption torque control, and the torque control tilt actuator 35a. It is possible to perform pump absorption torque increase control at the maximum torque Tmax using the absorption torque constant control by.

  When the absorption torque of the main pump 2 increases in this way, the load on the engine 1 increases accordingly, and the exhaust temperature rises, so that the oxidation catalyst provided in the exhaust gas purification device 62 is activated, and such By supplying unburned fuel into the exhaust gas under circumstances, the unburnt fuel is burned by the activated oxidation catalyst to raise the temperature of the exhaust gas, and the PM accumulated on the filter by the high temperature exhaust gas is efficiently used. Can be removed by combustion.

  This pump absorption torque increase control is continued until the exhaust resistance ΔP in the exhaust gas purification device 42 detected by the exhaust resistance sensor 43 provided in the exhaust gas purification device 42 becomes smaller than the threshold value ΔPa.

  At this time, the hydraulic motor 52 is driven by the oil discharged from the main pump 2, and the generator 53 is driven by the hydraulic motor 52 to generate electric energy, which is stored in the battery 41 via the converter 56. The

<When playback processing is required and the control lever is operated>
For example, when the operation lever of the boom operation lever device 34f is operated with a full stroke in the left direction (boom raising direction) in the drawing for the purpose of raising the boom, the boom flow control valve 26f is switched to the boom cylinder 10. Pressure oil is supplied and the boom cylinder 10 is driven.

  At this time, the load pressure of the boom cylinder 10 is detected as the maximum load pressure PLmax by the shuttle valves 22a to 22g, the control device 55 sets PLmax + P2 as the target control pressure Pun of the hydraulic motor control, and the discharge pressure of the main pump 2 is The pressure is controlled to rise to PLmax + P2 by the control of the hydraulic motor 52 and the generator 53.

  Also at this time, as in the case where the operation lever is not operated, the electromagnetic switching valve 65 is switched from the illustrated position, and the discharge pressure of the pilot pump 30 is guided to the pressure receiving portion 35d of the LS control valve 35b. The control is disabled, and the discharge flow rate of the main pump 2 is controlled to increase within the limit range of the torque control unit 35A.

  The point C in FIGS. 3A and 3B shows an example of the operating point of the main pump 2 at this time. The discharge pressure of the main pump 2 is increased to Prc by the control of the hydraulic motor 52 and the generator 53, and the absorption torque of the main pump 2 does not exceed the maximum torque Tmax by the absorption torque constant control of the torque control tilt actuator 35a. Thus, the capacity of the main pump 2 becomes a value qc determined by the constant control of the absorption torque by the torque control tilt actuator 35a, and the discharge flow rate of the main pump 2 becomes a flow rate according to qc.

  Here, when the main pump 2 operates at the point B and when it operates at the point C, the magnitude of the pump absorption torque is substantially the same, and when the actuator is operated by operating the operation lever, the actuator operation is also performed. The pump absorption torque increase control similar to that before operating the actuator can be performed without being affected by the above.

  As described above, when the actuator is operated by operating the operation lever during the regeneration process of the exhaust gas purifying device 62, the pump absorption torque increase control using the constant absorption torque control is performed as in the case where the actuator is not operated. The exhaust temperature can be increased by increasing the load of the engine 1, and the PM accumulated on the filter can be efficiently burned and removed by the high-temperature exhaust gas.

  At this time, the hydraulic motor 52 is driven by the oil discharged from the main pump 2, and the generator 53 is driven by the hydraulic motor 52 to generate electric energy, which is stored in the battery 41 via the converter 56. The

When the load pressure (maximum load pressure) of the boom cylinder 10 reaches a predetermined pressure Pmro that is slightly lower than the relief pressure Pmr of the main relief valve 23, the discharge flow rate of the main pump 2 is tanked via the main relief valve 23. Before being returned to, the hydraulic motor 52 rotates to return the discharge flow rate of the main pump 2 to the tank. Thus, while preventing the discharge pressure of the main pump 2 from rising excessively, the hydraulic motor 52 rotates and the generator 53 generates electric energy, and the electric energy is stored in the battery 57. Thereby, the energy of the pressure oil discharged from the main pump 2 to the tank can be recovered, and the energy of the pressure oil generated by the main pump 2 can be used effectively.
~effect~
As described above, according to the present embodiment, when the regeneration processing of the exhaust gas purification device 62 is necessary in the hydraulic drive device that performs load sensing control, the absorption torque of the main pump 2 is increased to increase the exhaust gas. By raising the temperature, the filter deposits of the exhaust gas purifying device 62 can be efficiently burned and removed, and the hydraulic motor 52 rotates and the generator generates electric energy, which is stored in the battery 57. Therefore, the energy of the pressure oil discharged from the main pump 2 to the tank T can be recovered, and the energy of the pressure oil generated by the main pump 2 can be used effectively.

  Further, when the regeneration process of the exhaust gas purification device 62 is not necessary, the discharge pressure of the main pump 2 is set to a predetermined value (usually normal pressure) in order to set the predetermined value to a value suitable for normal unload control. It is controlled so as not to exceed a pressure obtained by adding a value suitable for unloading control), and can perform the same function as a conventional unloading valve. Further, since the hydraulic motor 52 rotates and the generator generates electric energy, and the electric energy is stored in the battery 57, the energy of the pressure oil discharged from the main pump 2 to the tank is recovered at this time as well. The energy of the pressure oil generated by the pump 2 can be used effectively.

  Further, when the maximum load pressure reaches a predetermined pressure Pmro that is slightly lower than the relief pressure Pmr of the main relief valve 23, the hydraulic motor before the discharge flow rate of the main pump 2 is returned to the tank via the main relief valve 23. 52 rotates and the discharge flow rate of the main pump 2 is returned to the tank. Therefore, the hydraulic motor 52 rotates and the generator 53 generates electric energy while preventing the discharge pressure of the main pump 2 from excessively rising. The electric energy is stored in the battery 57. At this time as well, the energy of the pressure oil discharged from the main pump to the tank can be recovered, and the energy of the pressure oil generated by the main pump can be used effectively.

  In the present embodiment, the engine 1 and the electric motor 71 are provided as the prime mover for driving the main pump 2, and the electric motor 71 is driven by the electric energy stored in the battery 57 as described above. The recovered energy can be used as power for the hydraulic drive system, and energy saving of the entire system can be achieved.

<Others>
Various modifications can be made to the above embodiment within the spirit of the present invention.

  For example, in the above embodiment, the electromagnetic switching valve 65 is provided, and when the regeneration process is necessary, the electromagnetic switching valve 65 is switched to guide the discharge pressure of the pilot pump 3 of the pressure receiving portion 35d of the LS control valve 35b. However, when the LS control is invalidated, an electromagnetic switching valve is provided in the signal oil passage 21, and when the regeneration process is necessary, the switching valve is switched so that the pressure receiving portion 35e of the LS control valve 35b communicates with the tank. Thus, the load sensing control may be invalidated and the capacity of the main pump 2 may be controlled to increase.

  In the above embodiment, the output pressure of the differential pressure reducing valve 24 (the absolute pressure of the differential pressure between the discharge pressure of the main pump 2 and the maximum load pressure) is led to the pressure compensating valves 27a to 27h and the LS control valve 35b. However, the discharge pressure and the maximum load pressure of the main pump 2 may be individually led to the pressure compensation valves 27a to 27h and the LS control valve 35b.

  Further, in the above-described embodiment, the rotation speed of the engine 1 is detected hydraulically by the engine rotation speed detection valve 30, and the rotation speed signal of the engine 1 (the absolute pressure Pa output from the differential pressure reducing valve 30b) is obtained. The target LS differential pressure used was hydraulically set by the LS control valve 35d, but a rotation sensor for detecting the rotational speed of the engine 1 or the main pump 2 was provided, and the target differential pressure was calculated from the sensor signal to Load sensing control may be performed electrically by controlling the valve.

  In the above embodiment, the generator 53 is generated so that the hydraulic motor 52 does not rotate until the discharge pressure of the main pump 2 becomes higher than the target control pressure Pun obtained by adding a predetermined value Pb to the maximum load pressure PLmax. Even if the discharge pressure of the main pump 2 is not higher than the target control pressure Pun obtained by adding a predetermined value Pb to the maximum load pressure PLmax, the hydraulic motor 52 may be rotated as long as it is small. . As a result, when the discharge pressure of the main pump 2 becomes higher than the target control pressure Pun obtained by adding a predetermined value Pb to the maximum load pressure PLmax, the hydraulic motor 52 and the generator 53 are rotated without delay in response, and the discharge of the main pump 2 is performed. Control that suppresses a transient rise in pressure is possible. In addition, since the pressure oil always flows through the hydraulic motor 52, the hydraulic motor 52 can always be properly lubricated and the hydraulic motor 52 can be made to last longer.

  Furthermore, although the said embodiment demonstrated the case where a construction machine was a hydraulic excavator, even if it is construction machines (for example, a hydraulic crane, a wheeled shovel, etc.) other than a hydraulic excavator, a diesel engine and an exhaust gas purification apparatus are provided. And if it mounts the hydraulic drive system which performs load sensing control and torque control, this invention is applied similarly to the said embodiment, and the same effect is acquired.

DESCRIPTION OF SYMBOLS 1 Engine 2 Main pump 2a 1st pressure oil supply oil path 3 Pilot pump 3a Pressure oil supply oil path 4 Control valve 4a 2nd pressure oil supply oil path 5-12 Actuator 13-20 Valve section 21 Signal oil path 22a-22g Shuttle Valve 23 Main relief valve 24 Differential pressure reducing valve 26a-26h Flow control valve (main spool)
27a to 27h Pressure compensation valve 30 Engine speed detection valve 30a Flow rate detection valve 30b Differential pressure reducing valve 30c Variable throttle 30f Throttle element 31 Pilot oil passage 32 Pilot relief valve 33 Pilot hydraulic power source 34a to 34h Operation lever device 35 Pump control device 35A Torque control unit 35B Load sensing control unit 35a Torque control tilt actuator 35b LS control valve 35c LS control tilt actuators 35d, 35e Pressure receiving units 38, 39 Oil passage 51 Control oil passage 52 Hydraulic motor 53 Generator 54 Pressure sensor 55 Control Device 56 Converter 57 Battery 61 Exhaust pipe 62 Exhaust gas purification device 63 Exhaust resistance sensor 64 Forced regeneration switch 65 Electromagnetic switching valve 70 Power distributor 71 Electric motor 72 Chopper 300 Upper turning body 301 Lower traveling body 302 Front work machine 303 Swing post 304 central frame 305 blade 306 boom 307 arm 308 bucket 310 and 311 track

Claims (4)

Engine,
A variable displacement main pump driven by this engine;
A plurality of actuators driven by pressure oil discharged from the main pump;
A plurality of flow control valves that respectively control the flow of pressure oil supplied from the main pump to the plurality of actuators;
A torque control unit that reduces the capacity of the main pump as the discharge pressure of the main pump increases and controls the absorption torque of the main pump not to exceed a preset maximum torque; and a discharge pressure of the main pump A hydraulic drive device for a construction machine, comprising: a pump control device having a load sensing control unit that controls a capacity of the main pump so as to be higher by a target differential pressure than a maximum load pressure of the plurality of actuators;
A hydraulic motor that is disposed in a control oil passage that connects a tank with a pressure oil supply oil passage that supplies pressure oil from the main pump to the plurality of flow control valves, and that can be driven by the pressure oil discharged from the main pump;
A generator connected to the rotating shaft of the hydraulic motor;
An exhaust gas purification device for purifying the exhaust gas of the engine;
A controller for controlling the generator so that an increase in the discharge pressure of the main pump is suppressed when the discharge pressure of the main pump reaches a target control pressure obtained by adding a predetermined value to the maximum load pressure;
The control device further determines whether or not regeneration processing of the exhaust gas purification device is necessary, and when the regeneration processing of the exhaust gas purification device is necessary, the predetermined value is suitable for the regeneration processing. A construction machine that performs control to increase the discharge pressure of the main pump by setting the value to a value and disables the load sensing control of the load sensing control unit to increase the discharge flow rate of the main pump Hydraulic drive device. The hydraulic drive device for a construction machine according to claim 1,
The control device sets the predetermined value to a value suitable for normal unload control when the regeneration process is not necessary. The hydraulic drive device for a construction machine according to claim 1 or 2,
A pilot pump driven by the engine;
A pilot hydraulic power source connected to the pilot pump and generating a pilot primary pressure based on discharge oil of the pilot pump;
An engine speed detection valve that is located between the pilot pump and the pilot hydraulic power source and generates a hydraulic signal that depends on the engine speed based on the discharge oil of the pilot pump;
When the regeneration process is not required, the control device guides a hydraulic signal generated by the engine speed detection valve to a load sensing control unit of the pump control device to set a target differential pressure of the load sensing control, When the regeneration process is required, the discharge pressure of the pilot pump is led to the load sensing control unit of the pump control device to invalidate the load sensing control, and the discharge flow rate of the main pump is increased to perform control. A hydraulic drive device for a construction machine. The hydraulic drive device for a construction machine according to any one of claims 1 to 3,
The torque control unit of the pump control device is a characteristic indicating a relationship between the discharge pressure and the capacity of the main pump, and a characteristic constituted by a maximum capacity constant characteristic and a maximum absorption torque constant characteristic is preset, When the discharge pressure of the main pump is equal to or lower than the pressure at the transition point from the maximum capacity constant characteristic to the maximum absorption torque constant characteristic, the maximum capacity of the main pump is constant even if the discharge pressure of the main pump increases. And when the discharge pressure of the main pump rises above the pressure at the transition point, the capacity of the main pump is controlled so that the maximum capacity of the main pump decreases according to the constant maximum absorption torque characteristic. Configured,
A hydraulic drive device for a construction machine, wherein a value suitable for the regeneration processing set as the predetermined value when the control device requires the regeneration processing is a value equal to or higher than the pressure at the transition point .

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