Patent Grant
8424298
The present invention relates to a pump torque control system for a hydraulic construction machine, and more particularly to a pump torque control system, which drives hydraulic actuators by means of a hydraulic fluid delivered from hydraulic pumps rotationally driven by a prime mover and is used for a hydraulic construction machine such as a hydraulic excavator to be used for necessary work.
A typical hydraulic construction machine such as a hydraulic excavator includes a pump torque control system having a regulator, which controls a displacement volume of a hydraulic pump and has a pump torque control function. The displacement volume of the hydraulic pump is controlled by the pump torque control system to ensure that an absorption torque of the hydraulic pump does not exceed a preset maximum absorption torque. This suppresses overload applied to a prime mover and prevents an engine stall.
In connection with such a pump torque control system for a hydraulic construction machine, Patent Document 1 discloses a control method titled “Method for controlling drive system including internal combustion and hydraulic pump”. The control method is to obtain the difference (engine speed deviation) between a target engine speed and an actual engine speed detected by an engine speed sensor and control an input torque of a hydraulic pump based on the engine speed deviation. The control method is an example of speed sensing control. This speed sensing control is capable of temporarily reducing the maximum absorption torque during the pump torque control, reliably preventing an engine stall due to overload applied to a prime mover, and quickly increasing an engine speed by controlling the amount of fuel to be injected.
In addition, in connection with such a pump torque control system, Patent Document 2 discloses a technique for controlling the maximum absorption torque of a hydraulic pump based on sensed environment related to a prime mover and the periphery of the prime mover, and suppressing a reduction in the engine speed of a prime mover even when power output from the prime mover is reduced due to a change in environment.
The abovementioned conventional techniques, however, encounter the following problems.
A typical hydraulic construction machine such as a hydraulic excavator is operated in outdoors. After the operation for the day is finished, the hydraulic construction machine is left in a workplace until the next operation starts. If the hydraulic construction machine is left in a workplace for a long time under such an environment as a cold region, in which the ambient temperature is low, the temperature of the entire hydraulic construction machine is reduced to the ambient temperature level. As a result, the temperature of a hydraulic fluid used by a hydraulic drive system of the hydraulic construction machine is also reduced. Since an operation of the hydraulic construction machine restarts under such conditions, the temperature of the hydraulic fluid is low until a warm-up operation for starting the operation of the hydraulic construction machine is sufficiently performed. The viscosity of the hydraulic fluid is high. The flow of the hydraulic fluid is therefore deteriorated.
When a hydraulic construction machine having a pump torque control system performing such speed sensing control as the technique described in Patent Document 1 is operated under the condition that the temperature of the hydraulic fluid is low and the viscosity of the hydraulic fluid is high, a response may be delayed in the speed sensing control due to the delay of output of control pressure, the delay of a pump tilting operation, or the like. When a fluctuating frequency of a pump torque due to the speed sensing control matches a fluctuating frequency of the engine speed due to control on the amount of fuel to be injected to a prime mover, the speed sensing control and the control of the engine speed due to control on the amount of the fuel to be injected to the prime mover interfere with each other. This may result in hunting.
In the technique described in Patent Document 2, even when power output from the prime mover is reduced due to a change in environment related to the prime mover and the periphery of the prime mover, the environment factors (atmospheric pressure, the temperature of the fuel, the temperature of cooling water, an intake temperature, intake pressure, an exhaust temperature, exhaust pressure, the temperature of engine oil) related to reduction in power output from the engine are detected and a reduction in the torque under the speed sensing control is modified in order to suppress a reduction in the engine speed of the prime mover. In the technique described in Patent Document 2, however, the temperature of a hydraulic fluid, which is not directly involved in the reduction in the power output from the prime mover, is not detected. Therefore, when the temperature of the hydraulic fluid is low and the viscosity of the hydraulic fluid is high, the technique described in Patent Document 2 encounters a similar problem to that of Patent Document 1.
An object of the present invention is to provide a pump torque control system for a hydraulic work machine. The pump torque control system is capable of preventing from hunting caused by interference between speed sensing control and control on an engine speed of a prime mover under the condition that the temperature of hydraulic fluid is low, and performing appropriate pump torque control.
(1) To accomplish the abovementioned object, a pump torque control system for a hydraulic construction machine, according to the present invention, includes: a prime mover; variable displacement hydraulic pumps that are rotationally driven by the prime mover; hydraulic actuators that are driven by means of a hydraulic fluid delivered from the hydraulic pumps; pump absorption torque control means for controlling displacement volumes of the hydraulic pumps to ensure that the total absorption torque of the hydraulic pumps does not exceed a set maximum absorption torque; and speed sensing control means for calculating a first torque reduction amount based on a deviation between a target engine speed of the prime mover and an actual engine speed of the prime mover and performing control to reduce the maximum absorption torque of the hydraulic pumps based on the first torque reduction amount, the maximum absorption torque of the hydraulic pump being set in the pump absorption torque control means based on the first torque reduction amount, wherein the speed sensing control means includes hydraulic fluid temperature detection means for detecting the temperature of the hydraulic fluid, and first hydraulic fluid temperature modification means for modifying a control gain to be used to calculate the first torque reduction amount in order to ensure that the first torque reduction amount is reduced as the temperature of the hydraulic fluid detected by the hydraulic fluid temperature detection means is reduced.
As described above, the speed sensing control means includes the hydraulic fluid temperature detection means and the first hydraulic fluid temperature modification means. The first hydraulic fluid temperature modification means modifies the control gain to be used to calculate the first torque reduction amount in order to ensure that the first torque reduction amount is reduced as the temperature of the hydraulic fluid is reduced. Due to the modification, the amount of a controlled pump torque under the speed sensing control is reduced when the construction machine is operated under the condition that the temperature of the hydraulic fluid is low and the viscosity of the hydraulic fluid is high. A response delay in the speed sensing control due to the delay of output of control pressure, the delay of the pump tilting operation or the like is suppressed. It is therefore possible to prevent a resonance between a fluctuating frequency of the pump torque due to the speed sensing control and a fluctuating frequency of the engine speed of the prime mover due to the control on the amount of the fuel to be injected. This prevents from hunting due to interference between the speed sensing control and the control of the engine speed of the prime mover and thereby makes it possible to perform appropriate pump torque control.
(2) In the item (1), it is preferable that the speed sensing control means further have second hydraulic fluid temperature modification means for limiting a target value of the maximum absorption torque to ensure that the maximum absorption torque set in the pump absorption torque control means is reduced as the temperature of the hydraulic fluid detected by the hydraulic fluid temperature detection means is reduced.
Similarly to the item (1), this configuration makes it possible to prevent a stall of the prime mover and an increase in the number of temporal reductions in the engine speed due to a load rapidly applied to the prime mover, which is caused by insufficient effectiveness of the speed sensing control, since the maximum absorption torque of the hydraulic pumps is set to a relatively low level based on the temperature of the hydraulic fluid even under the condition that the amount of a controlled pump torque under the speed sensing control is reduced to reduce effectiveness of the speed sensing control when the temperature of the hydraulic fluid is low.
(3) In the item (1), it is preferable that the first hydraulic fluid temperature modification means include first means for calculating a hydraulic fluid temperature modification value that is reduced as the temperature of the hydraulic fluid is reduced, and second means for modifying the first torque reduction amount by using the hydraulic fluid temperature modification value and changing the control gain. It is preferable that the speed sensing control means further include third means for reducing the first torque reduction amount modified by the second means from a base torque of the hydraulic pumps and calculating a target value of the maximum absorption torque, and fourth means for setting the maximum absorption torque of the hydraulic pumps in the pump absorption torque control means based on the target value of the maximum absorption torque.
(4) In the item (3), it is preferable that the speed sensing control means further include fifth means for calculating a second torque reduction amount that is reduced as the temperature of the hydraulic fluid detected by the hydraulic fluid temperature detection means is reduced. It is preferable that the third means reduces the first and second torque reduction amounts from the base torque of the hydraulic pumps to calculate a target value of the maximum absorption torque.
According to the present invention, the pump torque control system is capable of preventing from hunting due to interference between the speed sensing control and the control on the engine speed of the prime mover and performing appropriate pump torque control, even when the temperature of the hydraulic fluid is low and the viscosity of the hydraulic fluid is high.
In addition, according to the present invention, the pump torque control system is capable of preventing a stall of the prime mover and an increase in the number of temporal reductions in the engine speed due to a load rapidly applied to the prime mover even under the condition that the amount of a controlled pump torque under the speed sensing control is reduced to reduce effectiveness of the speed sensing control when the temperature of the hydraulic fluid is low.
Embodiments of the present invention will be described below with reference to the accompanying drawings.
Referring to
The prime mover 1 is a diesel engine. A dial type engine speed instruction unit 21 and an engine control unit 22 are provided for the diesel engine (hereinafter merely referred to as the engine) 1. The engine speed instruction unit 21 is instruction means for instructing the engine 1 to set a target engine speed. The engine control unit 22 has a controller 23, a governor control motor 24, and a fuel injection unit (governor) 25. The controller 23 receives a command signal from the engine speed instruction unit 21 and performs predetermined arithmetic processing. The controller 23 then outputs a drive signal to the governor control motor 24. The governor control motor 24 is rotationally driven in accordance with the drive signal to control the amount of fuel to be injected by the fuel injection unit 25 in order to ensure that the target engine speed instructed by the engine speed instruction unit 21 is obtained.
Main relief valves 15 and 16 are provided in delivery lines 2a and 3a connected to the first and second hydraulic pumps 2 and 3, respectively. A pilot relief valve 18 is provided in a delivery line 5a connected to the pilot pump 5. The main relief valves 15 and 16 control delivery pressure of the first hydraulic pump 2 and delivery pressure of the second hydraulic pump 3, respectively, to set maximum pressure of a main circuit. The pilot relief valve 18 controls the maximum delivery pressure of the pilot pump 5 to set pressure of a pilot hydraulic source.
The control valve unit 6 has two valve groups 6a and 6b, which are provided for the first and second hydraulic pumps 2 and 3, respectively. The valve group 6a includes flow rate control valves 67, 68, and 69. The valve group 6b includes flow rate control valves 70, 71, and 72. The flow rate control valves 67 to 72 control the flows (directions and flow rates) of hydraulic fluids supplied from the first and second hydraulic pumps 2 and 3 to the hydraulic actuators 7, 8, 9, 10, 11, and 12. Control lever units 77, 78, 79, 80, 81, and 82 are provided for the hydraulic actuators 7, 8, 9, 10, 11 and 12, respectively. Each of the control lever units 77, 78, 79, 80, 81, and 82 generates control pilot pressure based on an operation direction and an operation amount of a control lever by using the delivery pressure of the pilot pump 5 as base pressure. The control pilot pressure is transmitted to a pressure receiver of each of the flow control valves 67, 68, 69, 70, 71, and 72. The flow control valves 67, 68, 69, 70, 71, and 72 are switched by means of the control pilot pressure transmitted from the control lever units 77, 78, 79, 80, 81, and 82, respectively. The flow control valves 67, 68, 69, 70, 71, and 72 are of center bypass type. When the control lever units 77, 78, 79, 80, 81, and 82 are not operated and the flow control valves 67, 68, 69, 70, 71, and 72 are set to neutral positions, the delivery lines 2a and 3a respectively connected to the first and second hydraulic pumps 2 and 3 are communicated with a tank. In this case, the delivery pressure of the first and second hydraulic pumps 2 and 3 is reduced to tank pressure.
The plurality of hydraulic actuators 7, 8, 9, 10, 11, and 12 are, for example, a swing motor of the hydraulic excavator, an arm cylinder, left and right traveling motors, a bucket cylinder, and a boom cylinder. For example, the hydraulic actuator 7 is the swing motor, the hydraulic actuator 8 is the arm cylinder, the hydraulic actuator 9 is the left traveling motor, the hydraulic actuator 10 is the right traveling motor, the hydraulic actuator 11 is the bucket cylinder, and the hydraulic actuator 12 is the boom cylinder.
Referring back to
The regulator 31 has a control spool 31s, springs 31a and 31b, and pressure receivers 31c, 31d, and 31e. The control spool 31s is coupled with variable displacement volume mechanisms of the first and second hydraulic pumps 2 and 3 in an operable manner. The springs 31a and 31b act on the control spool 31s to increase the volumes of the first and second hydraulic pumps 2 and 3. The pressure receivers 31c, 31d, and 31e act on the control spool 31s to reduce the volumes of the first and second hydraulic pumps 2 and 3. The pressure receivers 31c and 31d receives the delivery pressure from the first and second hydraulic pumps 2 and 3 through pilot lines 37 and 38, respectively. The pressure receiver 31e receives control pressure from the solenoid proportional valve 35 through a control hydraulic line 39. The springs 31a and 31b and the pressure receiver 31e function as means for setting the maximum absorption torque that can be used by the first and second hydraulic pumps 2 and 3. The regulator 31 having the above-mentioned configuration controls the volumes of the first and second hydraulic pumps 2 and 3 to ensure that the total absorption torque of the first and second hydraulic pumps 2 and 3 does not exceed the maximum absorption torque set by biasing forces of the springs 31a and 31b and the control pressure introduced to the pressure receiver 31e.
The engine sensor 33 outputs a detection signal corresponding to the engine speed of the engine 1. The controller 23 receives the detection signal from the engine sensor 33. The hydraulic fluid temperature sensor 34 outputs a detection signal corresponding to the temperature of the hydraulic fluid. The controller 23 also receives the detection signal from the hydraulic fluid temperature sensor 34. The controller 23 performs predetermined arithmetic processing and outputs a drive signal to the solenoid proportional valve 35. The solenoid proportional valve 35 generates control pressure based on the drive signal output from the controller 23 by using the delivery pressure of the pilot pump 5 as base pressure. The control pressure is introduced to the pressure receiver 31e of the regulator 31 through the control hydraulic line 39. The regulator 31 having the abovementioned configuration adjusts the maximum absorption torque that can be used by the first and second hydraulic pumps 2 and 3 based on the control pressure introduced to the pressure receiver 31e.
When the maximum absorption torque of the first and second hydraulic pumps 2 and 3 is set to the base torque, the displacement volumes of the first and second hydraulic pumps 2 and 3 are changed as follows based on the total delivery pressure of the first and second hydraulic pumps 2 and 3.
When the total delivery pressure of the first and second hydraulic pumps 2 and 3 is in a range from a value P0 to a value P1A, the absorption torque control is not performed, and the displacement volumes of the first and second hydraulic pumps 2 and 3 are present on a maximum volume characteristic line L1 and are the maximum (constant). In this case, the absorption torques of the first and second hydraulic pumps 2 and 3 are increased as the delivery pressure of the first and second hydraulic pumps 2 and 3 is increased. When the total delivery pressure of the first and second hydraulic pumps 2 and 3 exceeds the value P1A, the absorption torque control is performed, and the displacement volumes of the first and second hydraulic pumps 2 and 3 are reduced in accordance with the characteristic line A. In this way, the absorption torques of the first and second hydraulic pumps 2 and 3 are controlled to ensure that the total absorption torque of the first and second hydraulic pumps 2 and 3 does not exceed the base torque Ta (=Tr0rated) indicated by a constant torque curved line TA. In this case, the pressure P1A is a value immediately before the absorption torque control is performed by the regulator 31. The range from the value P1A to a value Pmax is a range of the total delivery pressure of the first and second hydraulic pumps 2 and 3 when the absorption torque control is performed by the regulator 31. The value Pmax is the maximum value of the total delivery pressure of the first and second hydraulic pumps 2 and 3 and is a value corresponding to the total relief set pressure of the main relief valves 15 and 16. When the total delivery pressure of the first and second hydraulic pumps 2 and 3 reaches the value Pmax, the main relief valves 15 and 16 are operated to prevent a further increase in the total delivery pressure of the first and second hydraulic pumps 2 and 3.
When the maximum absorption torque of the first and second hydraulic pumps 2 and 3 is set to a value lower than the base torque by the speed sensing control (described later), the absorption torque control is performed in accordance with the characteristic line B instead of the characteristic line A. In accordance with the characteristic line B, the absorption torque control starts to be performed by the regulator 31 when the total delivery pressure of the first and second hydraulic pumps 2 and 3 is equal to a value P1B. In this case, the absorption torque control is performed by the regulator 31 under the condition that the total delivery pressure of the first and second hydraulic pumps 2 and 3 is in a range from the value P1B to the value Pmax. Therefore, the maximum absorption torque that can be used by the first and second hydraulic pumps 2 and 3 is reduced from Ta to Tb.
The engine sensor 33, the hydraulic fluid temperature sensor 34, the solenoid proportional valve 35, and processing functions (related to the pump torque control system) of the controller 23 constitute speed sensing control means for the pump absorption torque control.
The base torque calculating section 41 calculates the total maximum absorption torque that can be used by the first and second hydraulic pumps 2 and 3 as a base torque Tr0 based on a target engine speed Nr of the engine 1. This calculation is performed, for example, by the following operations: the controller 23 receives a command signal indicating the target engine speed Nr from the engine speed instruction unit 21; the received command signal is referenced by using a table stored in a memory; and the base torque calculating section 41 calculates a base torque Tr0 corresponding to the target engine speed Nr indicated by the command signal. The base torque Tr0 is set as a value falling within the range of a torque output from the engine 1. The relationship between the target engine speed Nr and the base torque Tr0 is set in the table stored in the memory. The relationship between the target engine speed Nr and the base torque Tr0 is established to ensure that the base torque Tr0 is reduced as the target engine speed Nr is reduced based on a change in the torque output from the engine 1.
The engine speed deviation calculating section 42 reduces the target engine speed Nr from the engine speed (actual engine speed) Ne of the engine 1 detected by the engine sensor 33 to calculate an engine speed deviation ΔN.
ΔN=Ne−Nr (1)
The SS control torque calculating section 43 calculates, based on the engine speed deviation ΔN, a first order modification torque ΔTs1, which is a first order torque reduction amount (first torque reduction amount) for the speed sensing control. This calculation is performed, for example, by the following operations: the SS control torque calculating section 43 multiplies the engine speed deviation ΔN by a gain Ks of the speed sensing control; the SS control torque calculating section 43 performs upper limit processing and the lower limit processing; and the SS control torque calculating section 43 calculates the first order modification torque ΔTs1 for the speed sensing control.
The first modification factor calculating section 44 calculates, based on the target engine speed Nr, a first modification factor (engine speed modification value) Kn to be used to modify a torque reduction amount for the speed sensing control. This calculation is performed, for example, by the following operations: the target engine speed Nr is referenced by using the table stored in the memory; and the first modification factor calculating section 44 calculates the first modification factor Kn corresponding to the target engine speed Nr.
The second modification factor calculating section 45 calculates, based on the temperature Tf of the hydraulic fluid, a second modification factor (temperature modification value) Kt to be used to modify a torque reduction amount to be used for the speed sensing control. This calculation is performed, for example, by the following operations: the controller 23 receives a detection signal indicating the temperature Tf of the hydraulic fluid from the hydraulic fluid temperature sensor 34; the received detection signal is referenced by using the table stored in the memory; and the second modification factor calculating section 45 calculates the second modification factor Kt corresponding to the temperature Tf of the hydraulic fluid indicated by the detection signal.
The hydraulic fluid temperature sensor abnormality determination section 46 receives the detection signal indicating the temperature Tf of the hydraulic fluid from the hydraulic fluid temperature sensor 34 and determines whether or not the hydraulic fluid temperature sensor 34 normally functions. The determination is performed, for example, by the following operations: an allowable range of the maximum value of the detection signal transmitted by the hydraulic fluid temperature sensor 34 normally functioning is set; and the hydraulic fluid temperature sensor abnormality determination section 46 determines whether or not the detection signal indicates a value falling within the allowable range. When the detection signal indicates a value out of the allowable range, the hydraulic fluid temperature sensor abnormality determination section 46 determines that the hydraulic fluid temperature sensor 34 does not normally function (is in an abnormal state).
The first switch section 47 switches the value of the second modification factor Kt based on the result of the determination performed by the hydraulic fluid temperature sensor abnormality determination section 46. When the result of the determination performed by the hydraulic fluid temperature sensor abnormality determination section 46 indicates a “normal” condition, the first switch section 47 outputs the modification factor Kt calculated by the second modification factor calculating section 45 without changing the modification factor Kt. When the result of the determination performed by the hydraulic fluid temperature sensor abnormality determination section 46 indicates an “abnormal” condition, the first switch section 47 outputs a value of “1” as the second modification factor Kt.
The minimum value selecting section 48 selects a smaller one of the first modification factor Kn calculated by the first modification factor calculating section 44 and the second modification factor Kt output from the first switch section 47 and outputs the selected value as a modification factor Kc for control.
The control gain modifying section 49 is a multiplication section. The control gain modifying section 49 multiplies the modification factor Kc output from the minimum value selecting section 48 by the first order modification torque ΔTs1 (for the speed sensing control) calculated by the SS control torque calculating section 43 to calculate a second modification torque ΔTs2, which is a second order torque reduction amount (first torque reduction amount) for the speed sensing control. When the minimum value selecting section 48 selects the second modification factor Kt, the second modification torque ΔTs2 is equal to the first modification torque ΔTs1 modified based on the temperature of the hydraulic fluid.
As described above, the control gain modifying section 49 calculates the second modification torque ΔTs2 for the speed sensing control by multiplying the modification factor Kc output from the minimum value selecting section 48 by the first order modification torque ΔTs1 (for the speed sensing control) calculated by the SS control torque calculating section 43. The calculation performed by the control gain modifying section 49 means the modification of the gain Ks (of the speed sensing control) used by the SS control torque calculating section 43.
The low pass filter section 50 performs low pass filter processing on the second modification torque ΔTs2 for the speed sensing control to remove a high frequency component (noise) and calculates a modification torque ΔTs3, which is the final torque reduction amount (first torque reduction amount) for the speed sensing control.
The engine sensor abnormality determination section 51 receives a detection signal indicating the engine speed Nr of the engine from the engine sensor 33 and determines whether or not the engine sensor 33 normally functions. The determination is performed, for example, by the following operations: an allowable range of the maximum value of the detection signal transmitted by the engine sensor 33 normally functioning is set; and the engine sensor abnormality determination section 51 determines whether or not the detection signal indicates a value falling within the allowable range. When the detection signal indicates a value out of the allowable range, the engine sensor abnormality determination section 51 determines that the engine sensor 33 does not normally function (is in an abnormal state).
The second switch section 52 is adapted to switch the value of the modification torque ΔTs3 for the speed sensing control based on the result of the determination performed by the engine sensor abnormality determination section 51. When the result of the determination performed by the engine sensor abnormality determination section 51 indicates a “normal” condition, the second switch section 52 outputs the modification torque ΔTs3 calculated by the low pass filter section 50 without changing the modification torque ΔTs3. When the result of the determination performed by the engine sensor abnormality determination section 51 indicates an “abnormal” condition, the second switch section 52 outputs a value of “0” as the modification torque ΔTs3.
The hydraulic fluid temperature torque reduction calculating section 53 calculates, based on the temperature Tf of the hydraulic fluid, a torque reduction amount (second torque reduction amount) to be used to modify the degree of a target torque for the pump torque control. The calculation is performed, for example, by the following operations: the controller 23 receives a detection signal indicating the temperature Tf of the hydraulic fluid from the hydraulic fluid temperature sensor 34; the detection signal is referenced by using the table stored in the memory; the hydraulic fluid temperature torque reduction calculating section 53 calculates a torque reduction amount Td corresponding to the temperature Tf of the hydraulic fluid indicated by the detection signal.
The third switch section 54 is adapted to switch the value of the torque reduction amount Td based on the result of the determination performed by the hydraulic fluid temperature sensor abnormality determination section 46. When the result of the determination performed by the hydraulic fluid temperature abnormality determination section 46 indicates a “normal” condition, the third switch section 54 outputs the torque reduction amount Td calculated by the hydraulic fluid temperature torque reduction calculating section 53 without changing the torque reduction amount Td. When the result of the determination performed by the hydraulic fluid temperature sensor abnormality determination section 46 indicates an “abnormal” condition, the third switch section 54 outputs a value of “0” as the torque reduction amount Td.
The target torque calculating section 55 adds the base torque Tr0 calculated by the base torque calculating section 41 to the modification torque (first torque reduction amount) ΔTs3 (for the speed sensing control) selected by the second switch section 52 (the target torque calculating section 55 reduces an absolute value of the modification torque (first torque reduction amount) ΔTs3 from the base torque Tr0) to calculate a target torque Tr1 modified by the speed sensing control. In addition, the target torque calculating section 55 reduces the torque reduction amount (second torque reduction amount) Td selected by the third switch section 54 from the target torque Tr1 to calculate a target torque Tr2 for the pump torque control. That is, the target torque calculating section 55 performs the following calculations.
Tr1=Tr0+ΔTs3 (2)
Tr2=Tr1−Td (3)
The target torque calculating section 55 may obtain the target torque Tr2 through one calculation. In this case, the target torque calculating section 55 performs the following calculation.
Tr2=Tr0+ΔTs3−Td (4)
The solenoid valve output pressure calculating section 56 calculates control pressure to be used to set, in the regulator 31, the target torque Tr2 as the maximum absorption torque that can be used by the first and second hydraulic pumps 2 and 3. The target torque Tr2 calculated by the target torque calculating section 55 is referenced by using the table stored in the memory. The solenoid valve output pressure calculating section 56 calculates pressure Pc output from the solenoid proportional valve 35 and corresponding to the target torque Tr2. The relationship between the target torque Tr2 and the output pressure Pc is set in the table stored in the memory and is established to ensure that the output pressure Pc is reduced as the target torque Tr2 is increased.
The solenoid valve drive current calculating section 57 calculates a drive current Ic supplied to the solenoid proportional valve 35. The drive current Ic is used to obtain the pressure Pc, which is calculated by the solenoid valve output pressure calculating section 56 and output from the solenoid proportional valve 35. The pressure Pc calculated by the solenoid valve output pressure calculating section 56 and output from the solenoid proportional valve 35 is referenced by using the table stored in the memory. The solenoid valve drive current calculating section 57 then calculates the drive current Ic (supplied to the solenoid proportional valve 35) corresponding to the output pressure Pc. The relationship between the output pressure Pc and the drive current Ic is set in the table stored in the memory and is established to ensure that the drive current Ic is increased as the output pressure Pc is increased. The drive current Ic is amplified by an amplifier (not shown) and output to the solenoid proportional valve 35.
As described above, the regulator 31 constitutes pump absorption torque control means for controlling the displacement volumes of the hydraulic pumps 2 and 3 to ensure that the total absorption torque of the first and second hydraulic pumps 2 and 3 does not exceed the maximum absorption torque set in the regulator 31. The engine sensor 33, the hydraulic fluid temperature sensor 34, the solenoid proportional valve 35, and the functions (shown in
Next, operations of the pump torque control system having the abovementioned configuration according to the present embodiment will be described.
As an operation using a hydraulic excavator, there is a heavy load operation including an excavating operation. When such a heavy load operation is started, load pressure applied to any of the hydraulic actuators 7, 8, 9, 10, 11, and 12 is rapidly increased. The delivery pressure of at least one of the first and second hydraulic pumps 2 and 3 is also rapidly increased. In this case, a load applied to the engine 1 is temporarily increased, and the engine speed (actual engine speed) Ne of the engine 1 is reduced to a level lower than the target engine speed Nr (rated engine speed Nrated). When the engine speed Ne of the engine 1 is reduced, the controller 23 generates, based on the deviation between the actual engine speed Ne of the engine 1 and the target engine speed Nr, a drive signal to be used to increase the amount of fuel to be injected. The controller 23 transmits the drive signal to the governor control motor 24 to cause the governor control motor 24 to be rotationally driven. The governor control motor 24 increases the amount of the fuel to be injected by the fuel injection unit 25. The controller 23 performs control to increase an output torque of the engine 1.
On the other hand, in the pump torque control system according to the present embodiment, the regulator 31 is operated to control the displacement volumes of the first and second hydraulic pumps 2 and 3 in order to ensure that the total absorption torque of the first and second hydraulic pumps 2 and 3 does not exceed the maximum absorption torque (base torque) indicated by the constant torque curved line TA as shown in
In this case, the speed sensing control means functions to temporarily reduce the maximum absorption torque (along the broken line B shown in
In the present embodiment, when the temperature of the hydraulic fluid is low and the viscosity of the hydraulic fluid is high, the control gain (torque reduction amount ΔTs3) for the speed sensing control is modified based on the temperature of the hydraulic fluid. The amount of a controlled pump torque under the speed sensing control is reduced. This can suppress a response delay in the speed sensing control due to the delay of output of the control pressure output from the solenoid proportional valve 35, the delay of the pump tilting operation by means of the regulator 31 or the like and prevent a resonance between a fluctuating frequency of the pump torque due to the speed sensing control and a fluctuating frequency of the engine speed of the engine 1 due to the control on the amount of the fuel to be injected. This makes it possible to prevent from hunting due to interference between the speed sensing control and the control on the engine speed of the engine 1 and perform appropriate pump torque control.
The details will be described below.
In
<When the temperature of the hydraulic fluid detected by the hydraulic fluid temperature sensor 34 is in the range of the normal temperature (for example, 50° C. to 70° C.)>
Since the target engine speed of the engine 1 is equal to the rated engine speed Nrated, the base torque calculating section 41 included in the controller 23 calculates the torque Tr0rated corresponding to the rated engine speed Nrated as the base torque Tr0.
Since the operation point of the engine 1 is located at the point P1 present on the line of the regulation region R at the beginning, the engine speed Ne of the engine 1 is nearly equal to the target engine speed Nr (rated engine speed Nrated). The engine speed deviation calculating section 42 performs a calculation to obtain the engine speed deviation ΔN nearly equal to zero. As a result, the SS control torque calculating section 43 performs a calculation to obtain the first order modification torque ΔTs1 of the speed sensing control, which is nearly equal to zero. The modification torque (first torque reduction amount) ΔTs3 calculated by the low pass filter section 50 is therefore nearly equal to zero regardless of values calculated by the first and second modification factor calculating sections 44 and 45.
The hydraulic fluid temperature torque reduction calculating section 53 performs a calculation to obtain the torque reduction amount (second torque reduction amount) Td equal to zero since the temperature Tf of the hydraulic fluid is in the range of the normal temperature (for example, 50° C. to 70° C.).
Furthermore, the target torque calculating section 55 performs a calculation to obtain the target torque Tr2 equal to the base torque Tr0rated since both the modification torque ΔTs3 and the torque reduction amount Td are zero. The target torque Tr2 is processed by the solenoid valve output pressure calculating section 56 and the solenoid valve drive current calculating section 57, and the solenoid proportional valve 35 is driven to output control pressure corresponding to the pressure receiver 31e included in the regulator 31. In this way, the maximum absorption torque corresponding to the target torque Tr2 (=Tr0rated) is set in the regulator 31 by the biasing forces of the springs 31a and 31b and the control pressure introduced to the pressure receiver 31e.
The maximum absorption torque set in the regulator 31 in the abovementioned case is described above with reference to
When the load applied to the engine 1 is increased due to such a heavy load operation as described above from the abovementioned state, and the operation point of the engine 1 moves from the point P1 in
The control gain modifying section 49 performs a calculation to obtain the second order modification torque ΔTs2 equal to the first order modification torque ΔTs1 for the speed sensing control. The low pass filter section 50 calculates the modification torque ΔTs3 (for the speed sensing control) corresponding to the second order modification torque ΔTs2 (=ΔTs1).
The hydraulic fluid temperature torque reduction calculating section 53 performs a calculation to obtain the torque reduction amount Td equal to zero since the temperature Tf of the hydraulic fluid is in the range of the normal temperature (for example, 50° C. to 70° C.). The target torque calculating section 55 calculates the target torque Tr2 as follows.
Tr1=Tr0rated+ΔTs3
Tr2=Tr1−Td=Tr1=Tr0rated+ΔTs3
That is, the target torque Tr2 is reduced to a value lower by the modification torque ΔTs3 than the base torque Tr0rated. The target torque Tr2 is processed by the solenoid valve output pressure calculating section 56 and the solenoid valve drive current calculating section 57. The solenoid proportional valve 35 is driven to output control pressure corresponding to the target torque Tr2 to the pressure receiver 31e included in the regulator 31.
The output pressure Pc calculated by the solenoid valve output pressure calculating section 56 is in inverse proportion to the target torque Tr2. In the regulator 31, therefore, the control pressure introduced to the pressure receiver 31e is increased by the value ΔTs3, and the maximum absorption torque set by the biasing forces of the springs 31a and 31b and the control pressure introduced to the pressure receiver 31e is reduced based on the increase in the control pressure.
The change in the maximum absorption torque set by the regulator 31 corresponds to the change of the characteristic line for the absorption torque control from the broken line A to the broken line B. In
Since the characteristic line for the absorption torque control is shifted from the broken line A to the broken line B and the maximum absorption torque set in the regulator 31 is reduced, the load applied to the engine 1 is reduced. The engine 1 can quickly increase the engine speed thereof due to the control on the amount of the fuel to be injected by the fuel injection unit 25.
<The temperature of the hydraulic fluid detected by the hydraulic fluid temperature sensor 34 is lower than 25° C.>
When the operation point of the engine 1 is located at the point P1 present on the line of the regulation region R, the engine speed deviation calculating section 42 performs a calculation to obtain the engine speed deviation ΔN nearly equal to zero since the engine speed Ne of the engine 1 is nearly equal to the target engine speed Nr (rated engine speed Nrated). Similarly to the case where the temperature of the hydraulic fluid is in the range of the normal temperature, the modification torque ΔTs3 calculated by the low pass filter section 50 is nearly equal to zero regardless of values calculated by the first and second modification factor calculating sections 44 and 45.
The hydraulic fluid temperature torque reduction calculating section 53 performs a calculation to obtain the torque reduction amount Td corresponding to the temperature Tf of the hydraulic fluid, which is larger than zero since the temperature Tf of the hydraulic fluid is lower than 25° C. The target torque calculating section 55 calculates the target torque Tr2 as follows.
Tr1=Tr0rated+ΔTs3=Tr0rated
Tr2=Tr1−Td=Tr0rated−Td
That is, the target torque Tr2 is reduced to a value lower by the torque reduction amount Td than the base torque Tr0rated. The target torque Tr2 is processed by the solenoid valve output pressure calculating section 56 and the solenoid valve drive current calculating section 57. The solenoid proportional valve 35 is driven to output control pressure corresponding to the target torque Tr2 to the pressure receiver 31e included in the regulator 31.
In the regulator 31, the control pressure introduced to the pressure receiver 31e is increased by the torque reduction amount Td, and the maximum absorption torque set by the biasing forces of the springs 31a and 31b and the control pressure introduced to the pressure receiver 31e is reduced based on the increase in the control pressure. In
The change in the maximum absorption torque set in the regulator 31 in the abovementioned case will be described with reference to
When the temperature of the hydraulic fluid is lower than 25° C., the target torque Tr2 is reduced to the value lower by the torque reduction amount Td than the base torque Tr0rated as described above. The characteristic line for the absorption torque control is shifted from the broken line A to the broken line C based on the reduction in the target torque Tr2. Since the torque output from the engine 1 in this case is equal to the value Te1 corresponding to the operation point P1, and the output torque Te1 is smaller than the value Te3, the first and second hydraulic pumps 2 and 3 are operated with the displacement volumes and the total delivery pressure which correspond to a range surrounded by the characteristic line C and the maximum volume characteristic line L1 and present on the constant torque curved line corresponding to the output torque Te1.
When the load applied to the engine 1 is increased due to a heavy load operation from the abovementioned state, and the operation point of the engine 1 moves from the point P1 in
The control gain modifying section 49 performs a calculation to obtain the second order modification torque ΔTs2 lower than the first order modification torque ΔTs1 for the speed sensing control since the modification factor Kc is equal to the modification factor Kt (<1). The low pass filter section 50 calculates the modification torque ΔTs3 (for the speed sensing control) corresponding to the second order modification torque ΔTs2 (<ΔTs1). Accordingly, the modification torque ΔTs3 is modified based on the temperature of the hydraulic fluid by means of the modification factor Kt (<1), and the low pass filter section 50 obtains a smaller value of the modification torque ΔTs3 than that in the case where the modification torque ΔTs3 is not modified based on the temperature of the hydraulic fluid.
The hydraulic fluid temperature torque reduction section 53 performs a calculation to obtain the torque reduction amount Td larger than 0 based on the temperature Tf of the hydraulic fluid since the temperature Tf of the hydraulic fluid is lower than 25° C. The target torque calculating section 55 calculates the Tr2 as follows.
Tr1=Tr0rated+ΔTs3
Tr2=Tr1−Td=Tr0rated+ΔTs3−Td
That is, the target torque Tr2 is reduced to a value lower by the torque reduction amount Td and the modification torque ΔTs3 than the base torque Tr0rated. The target torque Tr2 is processed by the solenoid valve output pressure calculating section 56 and the solenoid valve drive current calculating section 57. The solenoid proportional valve 35 is driven to output the corresponding control pressure to the pressure receiver 31e included in the regulator 31.
The output pressure Pc calculated by the solenoid valve output pressure calculating section 56 is in inverse proportion to the target torque Tr2. In the regulator 31, therefore, the control pressure introduced to the pressure receiver 31e is increased by the torque reduction amount Td and the modification torque ΔTs3, and the maximum absorption torque set by the biasing forces of the springs 31a and 31b and the control pressure introduced to the pressure receiver 31e is reduced based on the increase in the control pressure.
The change in the maximum absorption torque set in the regulator 31 in the abovementioned case corresponds to the change of the characteristic line obtained by the absorption torque control from the broken line C to a broken line D in
Since the characteristic line of the absorption torque control is shifted from the broken line C to the broken line D, and the maximum absorption torque set in the regulator 31 is reduced as described above, the load applied to the engine 1 is reduced. The engine 1 can quickly increase the engine speed due to the control on the amount of the fuel to be injected by the fuel injection unit 25.
In the present embodiment, the modification torque ΔTs3 is modified based on the temperature of the hydraulic fluid. Thus, the modification torque ΔTs3 is a smaller value than that in the case where the modification torque ΔTs3 is not modified based on the temperature of the hydraulic fluid. In
The modification based on the temperature of the hydraulic fluid of the modification torque ΔTs3 means that the amount of the controlled pump torque under the speed sensing control is reduced under the condition that the temperature of the hydraulic fluid is low in order to reduce the effectiveness of the speed sensing control. Under the condition that the effectiveness of the speed sensing control is reduced, if the target torque Tr2 is equal to the base torque Tr0, the engine 1 may be stalled due to the delay of an operation of the regulator 31 when a load is rapidly applied, or the number of temporal reductions in the engine speed of the engine 1 may be increased. In the present embodiment, a target value of the maximum absorption torque is set to a relatively low level based on the temperature of the hydraulic fluid, and the maximum absorption torque of the hydraulic pumps is controlled to be a relatively low level. This can prevent the stall of the engine 1 and the increase in the number of temporal reductions in the engine speed of the engine 1 due to the reduction in the effectiveness of the speed sensing control.
In the conventional technique as shown in
On the other hand, since the modification torque ΔTs3 is modified based on the temperature of the hydraulic fluid as shown in
The abovementioned operations are performed under the condition that the target engine speed of the engine 1, which is instructed by the engine speed instruction unit 21, is equal to the rated engine speed Nrated. When the target engine speed of the engine 1, which is instructed by the engine speed instruction unit 21, is lower than the rated engine speed Nrated, the base torque calculating section 41 and the first modification factor calculating section 44 perform calculations to respectively obtain the base torque Tr0 and the first modification factor Kn (i.e., the modification torque ΔTs3 of the speed sensing control), which are lower than those in the case where the target engine speed is equal to the rated engine speed Nrated. The speed sensing control is performed based on the target engine speed. In this case, when the reduction in the temperature of the hydraulic fluid is small and the first modification factor Kn is larger than the second modification factor Kt even under the condition that the temperature of the hydraulic fluid is low, the speed sensing control is performed giving priority to the reduction in the target engine speed. In this case, the modification torque ΔTs3 for the speed sensing control is reduced based on the reduction in the target engine speed. This makes it possible to suppress the response delay in the speed sensing control due to the delay of the output of the control pressure from the solenoid proportional valve 35 when the temperature of the hydraulic fluid is low and the viscosity of the hydraulic fluid is high, the delay of the pump tilting operation performed by the regulator 31 or the like and prevent the resonance between the fluctuating frequency of the pump torque due to the speed sensing control and the fluctuating frequency of the engine speed of the engine 1 due to the control on the amount of the fuel to be injected. When the reduction in the target engine speed is small, or when the reduction in the temperature of the hydraulic fluid is large and the first modification factor Kn is smaller than the second modification factor Kt, the modification torque ΔTs3 is modified based on the temperature of the hydraulic fluid, and the resonance between a fluctuating frequency of the pump torque due to the speed sensing control and a fluctuating frequency of the engine speed due to the control on the amount of the fuel to be injected to the engine 1 can be prevented in the same manner as the case where the target engine speed is equal to the rated engine speed Nrated.
If the hydraulic fluid temperature sensor 34 fails and does not normally functions, the hydraulic fluid temperature sensor abnormality determination section 46 detects the abnormality, and the first switch section 47 outputs a value of “1” as the second modification factor Kt, and the third switch section 54 outputs a value of “0” as the torque reduction amount Td. In this way, the modification based on the temperature of the hydraulic fluid in the speed sensing control is cancelled, and the pump torque control can be performed giving priority to safety. Similarly, if the engine sensor 33 fails and does not normally functions, the engine sensor abnormality determination section 51 detects the abnormality, and the second switch section 52 outputs a value of “0” as the modification torque ΔTs3. In this way, the speed sensing control itself is cancelled, and the pump torque control can be performed giving priority to safety.
In the present embodiment described above, the regulation region R (shown in
A description will be made of a second embodiment of the present invention with reference to
In
The regulator 131 has a tilting control actuator 112 for operating the swash plates 2b and 3b; a torque control servo valve 113 for controlling the tilting control actuator 112; and a position control valve 114. The tilting control actuator 112 is connected to the swash plates 2b and 3b. The tilting control actuator 112 has a pump tilting control spool 112a, a tilting control increasing torque pressure receiver chamber 112b, and a tilting control reducing torque pressure receiver chamber 112c. The pump tilting control spool 112a has pressure receiving sections at both edges thereof. The pressure receiving sections of the pump tilting control spool 112a have respective pressure receiving areas different from each other. The tilting control increasing torque pressure receiver chamber 112b is located on the side of the smaller one of the pressure receiving areas of the pump tilting control spool 112a. The tilting control reducing torque pressure receiver chamber 112c is located on the side of the larger one of the pressure receiving areas of the pump tilting control spool 112a. The tilting control increasing torque pressure receiver chamber 112b is connected to the delivery line 5a of the pilot pump 5 through a hydraulic line 135. The tilting control reducing torque pressure receiver chamber 112c is connected to the hydraulic line 135 through the torque control servo valve 113 and the position control valve 114.
The torque control servo valve 113 has a torque control spool 113a, a spring 113b, a PQ control pressure receiver chamber 113c and a torque reduction control pressure receiver chamber 113d. The spring 113b is located on the side of an edge of the torque control spool 113a. The PQ control pressure receiver chamber 113c is located on the side of the other edge of the torque control spool 113a. A shuttle valve 136 is connected to the delivery line 2a of the hydraulic pump 2 and to the delivery line 2b of the hydraulic pump 3 and adapted to detect delivery pressure applied from the high voltage side of the first and second hydraulic pumps 2 and 3. The PQ control pressure receiver chamber 113c is connected to an output port of the shuttle valve 136 through a signal line 115. The torque reduction control pressure receiver chamber 113d is connected to an output port of the solenoid proportional valve 35 through the control hydraulic line 39. The solenoid proportional valve 35 is operated by means of the drive signal (electrical signal) transmitted from the controller 23 (shown in
The position control valve 114 has a position control spool 114a, a spring 114b, and a control pressure receiver chamber 114c. The spring 114b is located on the side of an edge of the position control spool 114a and used to maintain the position. The spring 114b has a low elastic force. The control pressure receiver chamber 114c is located on the side of the other edge of the position control spool 114a. The control pressure receiver chamber 114c receives a hydraulic signal 116 corresponding to an operation amount (demanded flow rate) of an operation system related to the first and second hydraulic pumps 2 and 3. The hydraulic signal 116 can be generated through any of known various methods. For example, the control pilot pressure output from the control lever units 77, 78, 79, 80, 81, and 82 is introduced to a plurality of the shuttle valves. The control pilot pressure having the highest voltage is selected from the control pilot pressure output from the control lever units 77, 78, 79, 80, 81, and 82 shown in
The pump tilting control spool 112a controls the tilting angles (volumes) of the swash plates of the first and second hydraulic pumps 2 and 3 by means of a pressure balance of the hydraulic fluids present in the pressure receiver chambers 112b and 112c. The delivery pressure on the high voltage side of the first and second hydraulic pumps 2 and 3 is introduced to the PQ control pressure receiver chamber 113c of the torque control servo valve 13. The higher the delivery pressure introduced to the PQ control pressure receiver chamber 113c is, the more the torque control spool 113a moves to the left side of the
The characteristics of the absorption torque control performed by the torque control servo valve 113 for the first and second hydraulic pumps 2 and 3 are determined by the spring 113b and the control pressure introduced to the torque reduction pressure receiver chamber 113d. The characteristics of the absorption torque control is shifted (refer to
The configuration of parts other than the abovementioned parts in the second embodiment is essentially the same as that according to the first embodiment.
In the configuration according to the second embodiment described above, the regulator 131 has the function for controlling the volume (delivery flow rate) of the first and second hydraulic pumps 2 and 3 based on the demanded flow rate. The pump torque control system having the abovementioned configuration according to the second embodiment can obtain a similar effect to that in the first embodiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-31182 | Feb 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/051452 | 1/30/2008 | WO | 00 | 4/15/2009 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2008/096652 | 8/14/2008 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6183210 | Nakamura | Feb 2001 | B1 |
| 6655135 | Oka | Dec 2003 | B2 |
| 7020553 | Nakamura et al. | Mar 2006 | B2 |
| 20050071064 | Nakamura et al. | Mar 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 1 267 075 | Dec 2002 | EP |
| 62-8618 | Feb 1987 | JP |
| 11-101183 | Apr 1999 | JP |
| 2002-364603 | Dec 2002 | JP |
| 2004018877 | Mar 2004 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20100186402 A1 | Jul 2010 | US |
