Method for operating a coolant circuit for a vehicle air-conditioning system

Abstract

A method for operating a cooling circuit. It is provided that a) the actuation signal ST of the coolant compressor is provided so as to increase over time from a minimum value (ST.sub.min) in order to generate a start-up phase of the coolant compressor, b) a control signal maximum value (ST.sub.max) and a control signal threshold (ST.sub.SW) are provided, where ST.sub.SW<ST.sub.max, c) the actuation signal (ST) is limited to the control signal maximum value (ST.sub.max) if the actuation signal (ST) reaches the control signal threshold (ST.sub.SW) and the measured high and/or low-pressure value (PHD, P.sub.ND) satisfies a condition.

Claims

1. A method for operating a cooling circuit for a vehicle air-conditioning system with a coolant compressor which can be controlled by means of an actuation signal (ST) for controlling the compressor capacity, a condenser or gas cooler, an evaporator (3) with associated expansion device, and at least one pressure sensor means (pT1, pT3) for measuring the coolant pressure on a high-pressure and/or a low-pressure side of the cooling circuit, comprising: a) the actuation signal ST of the coolant compressor is provided so as to increase over time from a minimum value (ST.sub.min) in order to generate a start-up phase of the coolant compressor, b) a control signal maximum value (ST.sub.max) and a control signal threshold (ST.sub.SW) are provided, where ST.sub.SW<ST.sub.max, c) after the actuation signal ST of the coolant compressor is provided and after the control signal maximum value and control signal threshold are provided, the actuation signal (ST) is limited to the control signal maximum value (ST.sub.max) if the actuation signal (ST) reaches the control signal threshold (ST.sub.SW) and the measured high- and/or low-pressure pressure value (P.sub.HD, P.sub.ND) satisfies or satisfy one of the following conditions: (I) the high-pressure value (P.sub.HD) is less than a high-pressure threshold (S.sub.P_HD), (II) the low-pressure value (P.sub.ND) is greater than a low-pressure threshold (S.sub.P_ND), and/or (III) the difference (ΔP) between high-pressure value (P.sub.HD) and low-pressure value (P.sub.ND) is less than a differential pressure threshold (S.sub.ΔP), and d) after an expiration of a defined duration (t), the start-up phase of the coolant compressor is terminated if the measured high-pressure value (P.sub.HD) and/or the measured low-pressure value (P.sub.ND) still satisfy or satisfies one of the conditions (I) to (III).

2. The method according to claim 1, wherein e) the coolant compressor is designed with diagnosis means by means of which at least one capacity variable (L) of the coolant compressor is generated, and, instead of the method steps c and d, the following method steps are carried out: c1) the actuation signal (ST) is limited to the control signal maximum value (ST.sub.max) if the control signal (ST) reaches the control signal threshold (ST.sub.SW), the capacity variable (L) is less than a defined capacity threshold (S.sub.L), and the measured high- and/or low-pressure value (P.sub.HD, P.sub.ND) satisfy or satisfies one of the following conditions: (I) the high-pressure value (P.sub.HD) is less than a high-pressure threshold (S.sub.P_HD), (II) the low-pressure value (P.sub.ND) is greater than a low-pressure threshold (S.sub.P_NH), or (III) the difference (ΔP) between high-pressure value (P.sub.HD) and low-pressure value (P.sub.ND) is less than a differential pressure threshold (S.sub.ΔP), and d1) after expiration of a defined duration (t), the start-up phase of the coolant compressor is terminated if the measured high-pressure value (P.sub.HD) and/or the measured low-pressure value (P.sub.ND) satisfy or satisfies one of the conditions (I) to (III) as before, and the capacity variable (L) is less than the capacity threshold (S.sub.L).

3. The method according to claim 2, wherein the diagnosis means are designed to acquire the power consumption and/or the torque and/or the resulting output as capacity variable (L) of the coolant compressor.

4. The method according to claim 1, wherein the control signal maximum value (ST.sub.max) is determined as a function of the extent of a control deviation between a target value of a control variable controlling the cooling circuit and its actual value.

5. The method according to claim 1, wherein the coolant compressor is an electrical coolant compressor with an electric motor, wherein, as control signal (ST), a rotational speed signal for the electric motor is used.

6. The method according to claim 1, wherein the coolant compressor is a mechanical coolant compressor with a proportional valve, wherein, as actuation signal (ST), a control current signal for the proportional valve is used.

7. The method according to claim 1, wherein the cooling circuit includes a heat pump function.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below, the invention is explained in greater detail on the basis of embodiment examples in reference to the appended figures.

(2) FIG. 1 shows a circuit diagram of a vehicle refrigeration system for carrying out the method according to the invention,

(3) FIG. 2 shows a flow chart for explaining the method according to the invention,

(4) FIG. 3 shows a detail of the flow chart according to FIG. 2 for explaining an alternative embodiment of the method according to the invention,

(5) FIG. 4 shows an additional detail of the flow chart according to FIG. 2 for explaining another alternative embodiment of the method according to the invention,

(6) FIG. 5 shows an additional detail of the flow chart according to FIG. 2 for explaining another alternative embodiment of the method according to the invention,

(7) FIG. 6 shows a temperature-rotational speed diagram with characteristic lines for determining a control signal maximum value ST.sub.max, and

(8) FIG. 7 shows an additional temperature-rotational speed diagram with characteristic lines for determining a control signal maximum value ST.sub.max.

DETAILED DESCRIPTION

(9) FIG. 1 shows a cooling circuit 1 of a vehicle air-conditioning system which is formed by an evaporator 2, a coolant compressor 3, a coolant condenser or gas cooler 4, an expansion device 5 upstream of the evaporator 2 in flow direction of the coolant, for example an R744 coolant, an inner heat exchanger 7, and a coolant collector 8.

(10) The closed loop control of the cooling circuit 1 occurs by means of a control device 6 as a function of parameters which are supplied to the control device 6 as input variables. As input variables, pressure and temperature values of pressure-temperature sensors pT1, pT2 and pT3 are acquired inter alia, wherein alternatively pure pressure sensors can also be used. The pressure-temperature sensor pT1 is arranged on the high-pressure side in flow direction of the coolant after the compressor 3, the pressure-temperature sensor pT2 is arranged in flow direction of the coolant after the condenser or gas cooler 4, and the pressure-temperature sensor pT3 is arranged in flow direction of the coolant after the coolant collector 8 in the cooling circuit 1. The pressure-temperature sensor pT1 acquires the high pressure and the hot gas temperature directly at the outlet of the compressor, the pressure-temperature sensor pT2 acquires the high pressure and the coolant temperature at the outlet of the condenser or gas cooler 4 for the implementation of a closed loop control of the optimal high pressure or of the supercooling of the coolant at the outlet of the condenser or gas cooler 4, and the pressure-temperature sensor pT3 acquires the low pressure of the cooling circuit 1. The environmental temperature is acquired by means of a temperature sensor T_Um and also supplied to the control device 6.

(11) When a coolant collector is used as low-pressure storage, it has been found to be advantageous to incorporate the pressure sensor pT3 directly after the coolant collector 8 in the pipe run, since a detection of underfilling can be implemented directly here. However, as a rule, it is conventional and state-of-the-art that the sensors pT1 and pT2 are built in directly in the inlet or outlet region of the coolant compressor 3 or in the inlet or outlet region of the condenser or gas cooler 4.

(12) In the refrigeration system operation of the cooling circuit 1, the coolant compressed by the coolant compressor 3 is supplied to the coolant condenser 4 or gas cooler 4 arranged in the front region of the vehicle, where the coolant is condensed or cooled, before it is expanded by means of the expansion device 5 into the evaporator 2 after passage through the inner heat exchanger 7. A fresh air, environmental air or partial environmental air flow supplied to the evaporator 2 is cooled by same and supplied as incoming flow to the passenger compartment of the vehicle. The coolant evaporated in the evaporator 2 is supplied in turn to the compressor 3 on the low-pressure side via the coolant collector 8 and the inner heat exchanger 7.

(13) The coolant compressor 3 of the cooling circuit 1 is designed either as mechanical coolant compressor or as electrical coolant compressor. A mechanical coolant compressor is driven via a belt drive connected to the traction motor of the vehicle and controlled in terms of differential pressure, mass flow and suction pressure by means of a control current via a compressor control valve of the coolant compressor. An electrical coolant compressor comprises an internal electric motor as drive, so that a control of the rotational speed is enabled. In addition, it is also possible to use mechanical compressors via an electrically driven belt drive which can be uncoupled from the motor.

(14) If the control device 6 receives a request for the start-up of the coolant compressor 3, the method according to the invention explained on the basis of FIGS. 2 to 7, for monitoring the start-up behavior of the coolant compressor 3 designed as electrical or mechanical coolant compressor, is carried out with the method step Si according to FIG. 2.

(15) With the start of the method, the start-up phase of the coolant compressor 3 begins, in that an actuation signal ST is generated by the control device 6, which increases over time starting from a minimum value ST.sub.min as start value (compare method step S2). The increasing control signal ST is continuously compared, in accordance with the method step S3, with a control signal threshold ST.sub.SW, in that the condition:
ST≥ST.sub.SW
is verified. As long as this control signal threshold ST.sub.SW is not reached by the actuation signal ST, the actuation signal ST is increased continuously. Otherwise, if the control signal threshold ST.sub.SW is reached by the control signal ST, a monitoring of the high pressure P.sub.HD of the cooling circuit 1, which is sensed by the pressure-temperature sensor pT1, occurs with following condition (I):
P.sub.HD<S.sub.P_HD,  (I)
wherein S.sub.P_HD is a predetermined defined high-pressure threshold.

(16) If this condition (I) is not reached during the increase of the control signal ST to the point that the control signal threshold ST.sub.SW is reached, then the high pressure P.sub.HD does not increase, the actuation signal ST is limited to a maximum permissible value, namely the control signal maximum value ST.sub.max, and the coolant compressor 3 continues to be operated with such an actuation signal ST=ST.sub.max. If this condition (I) does not change during a subsequent defined duration t, that is to say if the high pressure P.sub.HD does not increase beyond the high-pressure threshold S.sub.P_HD (compare method step S7), the coolant compressor 3 is switched off in a subsequent method step S8, i.e., if the high pressure P.sub.HD thus does not increase even after the expiration of this defined duration t, this state of the coolant compressor 3 is interpreted as an unsuccessful start or unsuccessful start-up of the coolant compressor 3.

(17) However, if the condition (I) is not satisfied by the reaching of the control signal threshold ST.sub.SW or is not satisfied during the duration t, a branching occurs to a method step S5, by means of which the control signal ST is released and an air-conditioning control according to operating procedure is carried out by means of the control device 6.

(18) According to method step S8, the coolant compressor 3 can remain switched off and an error message can be generated or an error flag can be deposited in an error storage of the control device 6.

(19) According to FIG. 2, it is also possible to carry out a restart, in that, by means of a counter Z, the number N of restarts is counted (compare method step S9) and a branching off back to the method step S2 occurs. If the behavior of the coolant compressor, in that an unsuccessful start is identified, is repeated here during the start-up phase thereof, after the reaching of a predetermined number N, the method is terminated with a method step S 10, i.e., the coolant compressor 3 is definitively switched off.

(20) Instead of the condition (I), the following condition (II) can be used:
P.sub.ND>S.sub.P_ND.  (II)
wherein S.sub.P_ND is a low-pressure threshold which is compared with the low pressure P.sub.ND acquired by means of the pressure-temperature sensor pT3. The start-up behavior of the coolant compressor 3 is monitored on the basis of the behavior of the low pressure P.sub.ND in the cooling circuit 1. The associated method corresponds to that according to FIG. 2, wherein the method step S4 according to FIG. 2 is replaced by the method step S4 according to FIG. 3.

(21) Moreover, it is also possible to monitor not only the high pressure P.sub.HD or the low pressure P.sub.ND in the cooling circuit 1 during a start-up phase of the coolant compressor 3, but also the difference ΔP (=P.sub.HD−P.sub.ND) of these two pressures P.sub.HD and P.sub.ND. For this purpose, a differential pressure threshold S.sub.ΔP is generated and compared according to the following condition (III) with the differential pressure ΔP:
ΔP<S.sub.ΔP.  (III)

(22) This condition (III) is carried out instead of the condition (I) or (II) for carrying out the method according to FIG. 2, wherein the method step S4 is replaced by the method steps S4 according to FIG. 4.

(23) Finally, it is also possible, in the method steps according to FIG. 2, to verify not only the condition (I), but at the same time also the conditions (II) and (III), and to continue the method with the method step S6 as soon as at least one of these conditions (I) to (III) is satisfied.

(24) If an electrical coolant compressor 3 which is itself designed to be capable of self-diagnosis is used, that is to say comprises diagnosis means, then these means generate at least one diagnosis signal which, for example, indicates the generated torque and/or the power consumption and/or the resulting output as capacity variable. Such a capacity variable L can also be used for monitoring the start-up behavior of the coolant compressor 3.

(25) For this purpose, the method step S4 according to FIG. 2 is extended by the method step S4′ according to FIG. 5. In such a method as well, the condition (I) is first verified with the method step S4, and if applicable, in the method step S4′, the condition
L<S.sub.L  (IV)
is verified, wherein L is the capacity variable, that is to say, for example, the torque or power consumption or the resulting output of the coolant compressor 3, and S.sub.L is a capacity threshold. Instead of the condition (I), in order to carry out the method according to FIG. 5, both the condition (II) or the condition (III) and any desired combination of these conditions (I) to (III) can be used.

(26) For all the load points of the cooling circuit 1, a single value for the control signal maximum value ST.sub.max can be determined. This means that, in the case of a mechanical coolant compressor 3, as control signal ST, a maximum value for the control current signal is determined, and, in the case of an electrical coolant compressor 3, as control signal ST, a maximum value for the rotational speed signal is determined. If, for all the load cases, a common control signal maximum value ST.sub.max is determined, a common control signal threshold ST.sub.SW can also be established for all the load cases.

(27) An optimization of the method according to the invention is achieved in that the control signal maximum value ST.sub.max is generated as a function of the load applied to the cooling circuit 1, which is dependent on the environmental temperature T_Um. Instead of this environmental temperature, the resting pressure of the coolant can also be used, since it directly depends on or is brought about by the environmental temperature. Its significance increases over the duration of the standstill time of a vehicle or of the resting state of a refrigeration system.

(28) Thus, FIGS. 6 and 7 each show, as curves K1 and K2, exemplary courses of the control signal maximum value ST.sub.max, wherein, as control signal ST, a rotational speed signal is generated, and therefore the control signal maximum value ST.sub.max is a maximum rotational speed value n.sub.max. According to these FIGS. 6 and 7, there are two operating ranges AB.sub.AC and AB.sub.AC_WP as a function of an environmental temperature interval. The operating range AB.sub.AC is used in the refrigeration system operation of the cooling circuit 1 (compare FIG. 1). If this cooling circuit 1 is provided with a heat pump function, the operating range AB.sub.AC_WP is used.

(29) The curves K1 according to FIGS. 6 and 7 each consist of straight curve sections. The course of these curves K1 can be designed to be as complex as desired. For example, the diagrams according to FIGS. 6 and 7 each show a polynomial function as curve K2. In such curves K2 as well, a start-up of the coolant compressor 3, both by means of a control current signal in a mechanical coolant compressor and also by means of a rotational speed signal in an electrical coolant compressor, is carried out.

(30) Below, the use of the curve K1 according to FIG. 6 in the heat pump operation and in the refrigeration system operation in the case of use of an electrical coolant compressor is explained. This also applied to the use of curve K2 according to FIG. 6.

(31) In the heat pump operation of the cooling circuit 1, according to curve K1 of FIG. 6, at a minimum permissible environmental temperature T.sub._UM_min which can be, for example, −20° C., the maximum rotational speed value n.sub.max is set to a rotational speed value of 1500 rpm. Subsequently, this maximum rotational speed value remains constant up to an environmental temperature T1.

(32) Subsequently, with increasing load, that is to say with increasing environmental temperature T_Um, the control signal maximum value ST.sub.ST increases from 1500 rpm to approximately 2750 rpm, and, starting at a load at an environmental temperature T2 of, for example, 50° C., it is limited to this maximum rotational speed value of 2750 rpm. Since electrical coolant compressors 3 according to the prior art have a minimum rotational speed of, for example, 800 rpm, a linear course up to a rotational speed value zero cannot be achieved. Therefore, for a start-up, an actuation with a minimum rotational speed increased by a certain rotational speed is carried out, in order to be able to overcome the internal resistances in the electrical coolant compressor 3 and to be able to set the associated electric motor in motion.

(33) Usually, in the case of starting, as start pulse, an exaggeratedly high rotational speed of, for example, 1500 rpm, is also necessary in order to be able to achieve a compressor start-up. After a successful compressor start-up, the operating rotational speed itself is then set, which, for example, can be below the start-up rotational speed, such as, for example, a minimum rotational speed of 800 rpm.

(34) If a start-up of the coolant compressor 3 in the AC operation occurs, at an environmental temperature T.sub._UM_AC in accordance with the curve K1 of FIG. 6, the maximum rotational speed value is set to the rotational speed value 1500 rpm. With increasing load, a linear increase occurs starting at the environmental temperature T1, which ends at the environmental temperature T2 with the rotational speed value 2750 rpm.

(35) In the case of a mechanical coolant compressor 3, for the maximum value of the control current signal, as control signal maximum value ST.sub.max, a course corresponding to the curves K1 and K2 of FIG. 6 results.

(36) At high loads, the control signal maximum value ST.sub.max is limited to a maximum value as represented, for example, in FIG. 6 on the basis of the curves K1 and K 2 and in FIG. 7 on the basis of the curve K1. It is also possible to dispense with such a limitation of the control signal maximum value ST.sub.max to a maximum value which remains constant, wherein, starting at the environmental temperature T1, a flatter rise is provided, in comparison to Figures K1 and K 2 according to FIG. 6 and to curve K1 according to FIG. 7.

(37) The curves K1 and K2 according to FIG. 7 show a course which differs from that of FIG. 6, in that the values of the control signal maximum value ST.sub.max do not increase continuously but instead decrease and subsequently increase again between the starting point T.sub._UM_min and the end point in a short temperature interval.

(38) The course of the n_max curve which in the end is expedient for the applied system load can deviate considerably from the curves K1 and K2 of FIGS. 6 and 7 and has to be newly determined for the respective vehicle air-conditioning system to be applied.

(39) The general start-up behavior of a coolant compressor 3 has no influence on the method according to the invention, since, in each case, the limitation of the control signal ST to the control signal maximum value ST.sub.max has to occur.

(40) If, in the end, a successful start-up of the compressor follows, the start-up curves from FIG. 6 and FIG. 7 are left, and, in accordance with the operating strategies of the flow charts of FIGS. 2 to 5, the rotational speed limits are allowed to reach the maximum value.