Patent Description:
Refrigerated transport vehicles such as refrigerated trucks or refrigerated railway wagons are equipped with cooling systems for transporting temperature-sensitive products. Usually, such a cooling system comprises a cooling chamber or several cooling chambers mounted on a chassis or integrated in the body of the vehicle in which temperature sensitive goods are stored during transport at a temperature of e.g. <NUM> to <NUM> or, in the case of frozen goods, at temperatures below <NUM>. For cooling the atmosphere in the cooling chamber mostly refrigeration units based on conventional compression refrigeration machines are used. However, the use of such conventional apparatuses use have increasingly been criticized due to their high noise emission and the high pollutant emissions of the diesel generators normally used for power generation of the compressor.

As an alternative, a cryogenic medium, e.g. liquid nitrogen or liquid CO<NUM>, can be used as a cooling agent for cooling the atmosphere in the cooling chamber. The cryogenic coolant is stored within a thermal insulated storage tank on board of the vehicle and is fed to the cooling chamber when needed. For chilling the cooling chamber the coolant either is sprayed into the chamber in gaseous or liquid form (direct cooling), or it is brought into indirect thermal contact with the atmosphere by means of a heat exchanger mounted inside the cooling chamber. Examples for such transport cooling systems are described e.g. in <CIT>, <CIT>, <CIT> or <CIT>. The filling of the coolant tank of a refrigerated truck is usually done from a stationary storage tank in which the coolant is stored in liquid form under cryogenic conditions.

Refrigerated trucks using liquid nitrogen or liquid C0<NUM> as coolant need an enlarged thermally well insulated tank mounted on the side or underneath the truck chassis. While they are increasingly being installed in larger vehicles their use in smaller refrigerated vehicles or delivery vans is hardly economically feasible due to the high dead weight of the tanks and safety considerations.

From <CIT> a cooling system for transport trucks based on carbon dioxide as coolant is known. The system comprises a cooling unit arranged in the roof space of a cooling chamber, which includes a storage for dry ice and a plate made of thermally conductive material with cooling fins on the underside, which acts as a heat exchanger at which the atmosphere of the cooling chamber is directly cooled. The disadvantage of this system is that it is difficult to control the temperature in the cooling chamber. For this reason, it is proposed in <CIT> to vary the cooling surface of the heat exchanging plate by means of a movable shutter. However, the installation of such a shutter is very laborious and increases the susceptibility of the cooling system to faults.

<CIT> discloses a transport vehicle according to the preamble of appended claim <NUM>.

Therefore, it is the aim of the present invention to provide a transport vehicle with a cooling system based on cryogenic cooling using carbon dioxide as coolant, which works reliably, is easy to install and is particularly suitable for installation in smaller refrigerated trucks or delivery vans.

This aim is achieved with a transport vehicle comprising the features of claim <NUM>.

Advantageous embodiments of the invention are claimed in the subclaims.

According to the invention, the cooling unit serves to cool the air in the cooling chamber using the cold content of carbon dioxide, without carbon dioxide entering the cooling chamber. It comprises two thermally, but not fluidly, connected sections, the carbon dioxide storage compartment on one hand and the air cooling compartment, which is not identical with the cooling chamber on the other. The air cooling compartment comprises a cooling channel or a plurality of cooling channels each of which is fluidly connected to the cooling chamber and thermally, but not fluidly, connected to the carbon dioxide storage compartment. The carbon dioxide storage compartment is filled with carbon dioxide snow by feeding liquid carbon dioxide having approximately ambient temperature and a pressure of more than <NUM> bar (e.g. <NUM>-<NUM> bar) via the supply line and expanding it within the carbon dioxide storage compartment. This leads to a mixture of carbon dioxide snow and carbon dioxide gas, the latter of which is exhausted via the exhaust pipe whereas the carbon dioxide snow is retained in the carbon dioxide storage compartment.

Cooling channel and cooling chamber are fluidly connected to each other via lines, which transport air from the cooling chamber into the cooling channel and back from the cooling channel into the cooling chamber. The flow of air through the cooling channel can easily be varied by means of fans, blowers, pumps or the like which may be installed in the cooling channel or in at least one of the lines leading thereto. On contact with the heat exchanger surface, heat from the air in the cooling channel is transferred to the carbon dioxide snow present in the carbon dioxide storage compartment. The heat transfer causes the carbon dioxide to sublimate gradually. The resulting gas is led to the outer atmosphere via the exhaust pipe. In this way, even walk-in cooling chambers, e.g. cooling chambers mounted on a transport vehicle, can be cooled without endangering the user due to sublimating carbon dioxide.

A preferred embodiment of the invention is characterized in that the expansion device is a nozzle arrangement, which is equipped with at least two nozzle heads each having nozzles pointing towards one another and arranged essentially horizontal, with an angle between <NUM>-<NUM>° towards to the horizontal, within the carbon dioxide storage compartment. The nozzles serve for expanding liquid carbon dioxide into a mixture of carbon dioxide gas and carbon dioxide snow. Due to the special arrangement of the nozzles the carbon dioxide snow is evenly distributed in the carbon dioxide storage compartment.

In another advantageous embodiment of the invention, the exhaust pipe is equipped with means for maintaining an overpressure in the carbon dioxide storage compartment. The overpressure in the carbon dioxide storage compartment prevents the entering of ambient air. Of course, it will be necessary in this case that the connection piece for connecting a liquid carbon dioxide filling device is also be designed in such a way that the ingress of ambient air is prevented. Thus, in each stage of operation of the cooling unit, an atmosphere essentially consisting of carbon dioxide prevails in the carbon dioxide storage compartment, which avoids clogging of the nozzles due to water ice and improves the cooling performance. The means for maintaining an overpressure in the carbon dioxide snow compartment comprise, e.g. a flap, a non-return-valve or a pressure retention valve.

In order to improve heat transfer from air in the cooling channel to the carbon dioxide snow it is advisable that the cooling channel, or at least one cooling channel, is equipped with baffles mounted perpendicular to the exchanger surface such that the air in the cooling channel is forced into an extended flow path along the heat exchanger surface. Also, the heat exchanger surface can be equipped with cooling fins in order to enhance the heat transfer.

Preferably, the, or each, cooling channel is equipped with means for conveying the cooling air through the cooling channel. Such means can be, e.g. a fan, a blower or an air pump mounted in the cooling channel or in at least one of the lines for feeding air to and/or from the cooling channel. In particular, such conveying means can also be used to regulate the flow of gas through the respective cooling channel and thus, to regulate the heat transfer from the cooling unit to the cooling chamber. For example, the power of the fan or blower can be varied depending on a temperature measured at suitable sensors in the cooling chamber and automatically controlled by a control unit.

Using the transport vehicle according to the invention, products can also be cooled at different temperatures during transport. For doing so, the cooling chamber is divided into a plurality of thermally separated compartments which can be each flow-connected to the cooling channel. Furthermore, means are provided for controlling the supply of cooling air into each of the compartments. Such means may be valves or flaps as well as separate fans for each compartment, which can be controlled automatically depending on the desired temperature in the respective compartment by a control unit. For example, a transport vehicle according to the invention can be used for cooling at the same time a first compartment filled with frozen products (at temperatures of about -<NUM>) and a second compartment filled with fresh products (at temperatures between <NUM> and <NUM>) both mounted on the same transport vehicle.

In order to facilitate maintenance, a particularly advantageous embodiment of the invention provides that the cooling unit is arranged outside the cooling chamber, with the cooling air lines to and from the air cooling compartment passing through the walls of both, the cooling unit and the cooling chamber. In the case of trucks, for example, the cooling unit is mounted above the cab of the truck on a front side of the cooling chamber, or on top of the cooling chamber. It is also possible to place the cooling unit at a distance from the cooling chamber and to provide only a flow connection via the cooling air lines mentioned above. For example, the cooling unit can be located in the chassis of a road or rail transport vehicle. However, it is also within the scope of the invention that the cooling unit, including carbon dioxide storage compartment and air cooling compartment, is mounted inside the cooling chamber.

In another preferred embodiment of the invention, the exhaust pipe is equipped with heat exchanger means mounted inside the cooling chamber. Thus, the sublimated carbon dioxide, which is still at a low temperature, contributes to the cooling of the atmosphere in the cooling chamber.

It is advantageous to provide a fan in the cooling chamber for homogenizing the temperature of the atmosphere in the cooling area.

Furthermore, the cooling chamber may be equipped with a safety device, e.g. a carbon dioxide detector, which, in the event that the carbon dioxide content exceeds a predetermined limit, emits an audible and/or visual warning signal.

The transport vehicle according to the invention is suited for cooling products like foods or pharmaceutical products during their transport. For this purpose, the cooling system may be mounted on or installed in a transport vehicle like a truck, a trailor, a delivery van, a railway wagon or within a ship. In the case of trucks, the cooling system is particularly suitable for smaller trucks, i.e. having a cooling chamber (in technical term also known as "refrigerating box body") with volume between <NUM><NUM> and <NUM><NUM>, preferably between <NUM><NUM> and <NUM><NUM>, most preferably between <NUM><NUM> and <NUM><NUM>, in which products can be transported at temperatures between -<NUM> and +<NUM>. Of course, this design of the invention is not limited to this configuration. For example, there can also be several compartments in which products can be transported at different temperatures, or compartments in which frozen products are stored or compartments in which products are only kept fresh can be arranged at the front or rear of the vehicle.

It is also useful to provide a drainage system for draining condensate water from the cooling chamber.

Preferably, a heating system is provided in the cooling chamber in order to manage temperature to be able to compensate for low outside temperatures in winter.

In another advantageous embodiment of the invention, the cooling unit is manufactured in a way that the expansion device and/or the filter means can easily be maintained. This can be done, for example, by that the cooling unit is equipped with a removable lid in the case of maintenance, ensures easy accessibility of the filter means and/or the injection system without removing the cooling unit from the cooling compartment or the truck.

Thus, the present invention seeks protection for refrigerated transport vehicles equipped with a cooling system according to the invention, like trucks, trailors, delivery vans, railway cooling wagons or ships, in which the cooling system is integrated in the vehicle body or mounted on the vehicle as a refrigerated box or as a container, and having in particular the ranges of volume and transport temperature mentioned above.

A preferred embodiment of the invention will be explained in more detail in the drawings. In schematic views the drawings show:.

The cooling system <NUM> shown in <FIG> is fixedly mounted on the chassis of a transport vehicle, in the example of a truck <NUM>. The cooling system <NUM> comprises a walk-in cooling chamber <NUM> having a volume of, e.g., <NUM><NUM>- <NUM><NUM> which is used for storing products needed to be cooled during transport, such as fresh or frozen foodstuffs, pharmaceuticals or other temperature-sensitive products. The cooling chamber <NUM> is equipped with thermally good insulating walls and is accessible via door <NUM>, which here is only indicated by a dotted line.

Optionally, the cooling chamber <NUM> can be divided into several compartments <NUM>, <NUM>, each separated by a partition wall <NUM>. For example, and shown in <FIG>, a front compartment <NUM> and a rear compartment <NUM> can be provided, the latter being accessible through a rear door <NUM>. By means of the separate compartments <NUM>, <NUM> products can be transported at different temperatures. For example, the atmosphere in the compartment <NUM> is cooled, in the way described in detail below, to a temperature of, e.g., -<NUM>, or <NUM>-<NUM>, while the atmosphere in compartment <NUM> is not or only slightly cooled due to the thermally insulated partition wall <NUM> and thus, is approximately at ambient temperature. It is, however, also within the framework of the present invention to provide several compartments within the cooling chamber, all of which are cooled in the manner described below, but at different temperatures. For example, there may be a first compartment in which products are cooled to freezing temperature (-<NUM>) and a second compartment in which the products are kept fresh at a temperature of e.g. <NUM>-<NUM>.

The cooling chamber <NUM> is cooled by means of a cooling unit <NUM> in which cold is produced by evaporating or sublimating carbon dioxide. The cooling unit <NUM> is divided vertically into two sections, namely, in its upper part, a carbon dioxide storage compartment <NUM> and a air cooling compartment <NUM> below, which are separated from each other by a gas-tight but thermally well-conducting separation plate <NUM> which may be, e.g., a metal plate.

The carbon dioxide storage compartment <NUM> comprises a space <NUM> for storing carbon dioxide snow. The feeding of carbon dioxide into space <NUM> is done by means of a carbon dioxide supply line <NUM>, which is fixedly connected to the carbon dioxide storage compartment <NUM>. The carbon dioxide supply line <NUM> is a pressure-resistant line for supplying liquid carbon dioxide. It begins at a connection piece <NUM> and ends inside the space <NUM> of the carbon dioxide storage compartment <NUM> at a nozzle arrangement <NUM>. For safety reasons, the connection piece <NUM> is preferably located on a lower section of the truck <NUM> chassis, even - and especially - if the cooling unit <NUM> is mounted on top of the cooling chamber <NUM> or above the cab of the truck <NUM>.

A filter <NUM> is arranged inside the space <NUM> above the nozzle arrangement <NUM>, which extends horizontally through the entire space <NUM> and thus separates an upper gas space <NUM> within the space <NUM>. From the gas space <NUM>, an exhaust pipe <NUM> is led through the outer wall, e.g. through the top or a sidewall, of the cooling compartment <NUM>. In order to prevent the ingress of ambient atmosphere into the space <NUM>, the exhaust pipe <NUM> is equipped with a non-return valve <NUM>, a flap or a pressure-maintaining valve, which guarantees a certain overpressure in the space <NUM> relative to the ambient atmosphere. The exhaust pipe <NUM> can optionally be passed through the cooling chamber <NUM> (as shown in the drawing) with a heat exchanger <NUM> where the cold sublimated carbon dioxide flowing through exhaust pipe <NUM> can absorb heat from the atmosphere inside the cooling chamber <NUM>. For safety reasons, the gas exhaust pipe <NUM> may also open out into a lower area of truck <NUM> (not shown here).

The nozzle arrangement <NUM> is shown in more detail in <FIG>. It extends within the space <NUM> and comprises two nozzle heads <NUM>, <NUM> arranged symmetrically to each other, each equipped with two nozzles <NUM> directed towards each other. The nozzles <NUM>, which are arranged approximately in a horizontal plane, are expansion nozzles, at which the liquid carbon dioxide, which is supplied via the carbon dioxide supply line <NUM>, is expanded and transforms into a mixture of carbon dioxide gas and carbon dioxide snow.

In <FIG>, the air cooling compartment <NUM> of the cooling unit <NUM> is shown in more detail. As mentioned above, the air cooling compartment <NUM> is arranged below the carbon dioxide storage compartment <NUM> and separated from the latter by a thermally well conducting but gas-tight separation plate <NUM>. The air cooling compartment <NUM> comprises - in the embodiment shown here - two cooling channels <NUM>, <NUM>, which extend through the air cooling compartment <NUM>. Each cooling channel <NUM>, <NUM> has an inlet opening <NUM>, <NUM>' and an outlet opening <NUM>, <NUM>' vertically spaced from each other. The inlet openings <NUM>, <NUM>' both are connected to a cooling air supply line <NUM> for feeding air to be cooled from the cooling chamber <NUM> into the air cooling compartment <NUM>, and the outlet openings <NUM>, <NUM>' both are connected to a cooling air outlet line <NUM> for supplying cooled air from the air cooling compartment <NUM> to the cooling chamber <NUM>. Both, the cooling air supply line <NUM> and the cooling air outlet line <NUM> lead to compartment <NUM> of cooling chamber <NUM> and exit there.

Each cooling channel <NUM>, <NUM> is equipped with a fan, <NUM>, <NUM> for conveying air through the respective cooling channel <NUM>, <NUM>. Within the cooling channel <NUM>, a number of flow deflectors such as baffles <NUM> are arranged which lead to an extended flow path of the air along the separation plate <NUM>. The fans <NUM>, <NUM> can be mounted in the cooling channel <NUM>, <NUM> within the air cooling compartment <NUM>. However, for maintenance reasons it is advisable to place the fans <NUM>, <NUM> outside the air cooling compartment <NUM> in front of the openings <NUM>, <NUM>', <NUM>, <NUM>', as shown in the <FIG> as an example in front of the openings <NUM>, <NUM>'. The fans <NUM>, <NUM> can be operated separately by means of a control device not shown here.

For maintenance reasons the cooling unit <NUM> is preferably located outside the cooling chamber <NUM> and preferably mounted on its outer wall by means of suitable securing means <NUM>. In the example shown in <FIG>, the cooling unit <NUM> is located just above the cab of the truck <NUM>. However, the cooling unit can also be mounted, for example, on the top of the cooling chamber <NUM> or in the area of the chassis of truck <NUM> and connected to cooling chamber <NUM> only via the lines <NUM>, <NUM>.

Furthermore, the cooling chamber <NUM> is equipped with a fan <NUM> working independently from the cooling unit <NUM> for homogenizing the temperature of the atmosphere in the cooling chamber <NUM>. The cooling chamber <NUM> is also equipped with a carbon dioxide detector <NUM> for monitoring the carbon dioxide content inside the cooling chamber <NUM>, which, in the event that the carbon dioxide content exceeds a predetermined limit, emits an audible and/or visual warning signal. The cooling chamber <NUM> further comprises a heater <NUM> for heating the cooling chamber, <NUM> if necessary, and a drainage system <NUM> for draining condensate water from the cooling chamber <NUM>.

The cooling system <NUM> is operated as follows. Before using the cooling unit <NUM> for cooling products in the cooling chamber <NUM>, the carbon dioxide storage compartment <NUM> has to be filled with carbon dioxide snow. For this purpose, the connection piece <NUM> is connected to a filling device for liquid carbon dioxide (not shown here) at a pressure of more than <NUM> bar. The liquid carbon dioxide flows through the supply line <NUM> and exits at the nozzles <NUM> into the carbon dioxide storage compartment <NUM>, where it expands and passes into a mixture of carbon dioxide gas and carbon dioxide snow. During the feeding of the liquid carbon dioxide the filter <NUM> ensures that the carbon dioxide snow is retained within space <NUM>, while the carbon dioxide gas escapes into the surrounding atmosphere via the exhaust pipe <NUM>. Thereby, the non-return valve prevents moist ambient air from entering the carbon dioxide snow compartment <NUM>. The special design of the nozzle arrangement <NUM> shown here allows an even distribution of the carbon dioxide snow within the space <NUM>. After the carbon dioxide storage compartment <NUM> has been filled with a predetermined amount of carbon dioxide snow, the connection pipe <NUM> is separated from the filling device and is closed gas-tightly.

The carbon dioxide snow present in carbon dioxide storage compartment <NUM> cools the plate <NUM> and thus, also the air present in the air cooling compartment <NUM>. By means of the fans <NUM>, <NUM> air to be cooled is sucked or blown from the cooling chamber <NUM> into the air cooling compartment <NUM> via cooling air supply line <NUM>, while cooled air is fed from the air cooling compartment <NUM> into the cooling chamber <NUM> via air outlet line <NUM>. The Baffles <NUM> are arranged such that the air inside the cooling channel <NUM> is forced through an elongated flow path of the air inside the cooling channel <NUM>, thus leading to a relative long a contact time between the air passing through cooling channel <NUM> and the plate <NUM>.

In a first operational mode, which may be the usual operational mode for keeping the atmosphere in the compartment <NUM> at its (low) temperature, only fan <NUM> is in operation and air from the cooling chamber <NUM> is led only through the cooling channel <NUM>. In order to increase the efficiency of the cooling, e.g. for cooling down the atmosphere in the compartment <NUM> from ambient temperature to a preset temperature, the cooling channel <NUM> can be activated by switching on fan <NUM> in a second operational mode.

The operation of the fans <NUM>, <NUM> is preferably controlled by a control device not shown here in dependence on the temperature prevailing in the compartment <NUM>. In this way, the temperature in compartment <NUM> can be kept very precisely at a preset value during the whole transport.

Claim 1:
Transport vehicle equipped with a cooling system (<NUM>) for storing and cooling products during transport, the cooling system (<NUM>) comprising a cooling chamber (<NUM>) for receiving goods to be cooled and a cooling unit (<NUM>),
- said cooling unit (<NUM>) having a carbon dioxide storage compartment (<NUM>) equipped with thermally insulated walls,
- said cooling unit (<NUM>) further having an exhaust pipe (<NUM>) for removing gaseous carbon dioxide from the carbon dioxide storage compartment (<NUM>) and gas-permeable but particle-impermeable filter means (<NUM>) for preventing carbon dioxide snow particles in the carbon dioxide storage compartment (<NUM>) from entering the exhaust pipe (<NUM>),
- said cooling unit (<NUM>) further having an air cooling compartment (<NUM>), thermally but not fluidly connected to the carbon dioxide storage compartment (<NUM>), comprising at least one cooling channel (<NUM>, <NUM>) which has an inlet opening (<NUM>, <NUM>') into which a cooling air supply line (<NUM>) opens which is flow-connected to the cooling chamber (<NUM>) for feeding cooling air from the cooling chamber (<NUM>) into the cooling channel (<NUM>, <NUM>) and an outlet opening (<NUM>, <NUM>') at which an cooling air outlet line (<NUM>) opens which is flow-connected to the cooling chamber (<NUM>) for feeding cooling air from the cooling channel (<NUM>, <NUM>) into the cooling chamber (<NUM>), and
- said cooling unit (<NUM>) further having a heat exchanger surface (<NUM>) on which the carbon dioxide storage compartment (<NUM>) and the cooling channel/s (<NUM>, <NUM>) are thermally well-conductive but gas-tightly connected to each other, the transport vehicle being characterised in that the cooling unit (<NUM>) comprises a supply line (<NUM>) for feeding liquid carbon dioxide into the carbon dioxide storage compartment (<NUM>), said supply line (<NUM>) opening out inside the carbon dioxide storage compartment at an expansion device (<NUM>), and a connection piece (<NUM>) for detachably connecting a liquid carbon dioxide filling device, and in that the filter means (<NUM>) is configured to retain said carbon dioxide snow in the carbon dioxide storage compartment (<NUM>).