RETARDER

Abstract: A retarder adapted for use on a vehicle comprises: a blower (6) connected to a crankshaft (2) of the vehicle; a clutch (4) provided between the blower (6) and the crankshaft (2) for selectively disconnecting the blower (6) from the crankshaft (2); a speed change mechanism (5) including a plurality of shafts, gears and bearings (13) and provided between the crankshaft (2) and the blower (6); an oil pump (7) driven by an energy transmitted from the clutch (4) and the blower (6) for supplying a lubrication oil to the speed change mechanism (5); a sensor (8) for detecting a pressure of the lubrication oil supplied to the bearing (13) of the speed change mechanism (5); and a control unit (9) for allowing the clutch (4) to disconnect the blower (6) from the crankshaft (2) when the lubrication oil pressure detected by the sensor (8) is below a certain value. The blower (6) consumes an energy of the engine which is transmitted from the crankshaft (2), thereby applying a brake force to the engine. When a trouble, such as a seize up of the bearings (13), occurs in the speed change mechanism (5), the rotation of the shafts of the speed change mechanism (5) is decelerated. Thereupon, the oil pressure from the oil pump (7) drops since the pump (7) is driven by an energy derived from the speed change mechanism (5). An excessive brake force is not applied to the crankshaft (2) since the blower (6) is disconnected from the crankshaft (2) promptly by the control unit (9).

Description: The present invention relates to a retarder according to the generic part of the main claim. A retarder of this kind is described in GB-A-746 681. Generally, large vehicles such as a large bus or truck are equipped with an auxiliary brake system in addition to a main brake system (foot brake) since they need a large brake force to stop. Fluid retarders and electrical retarders are well known in the art as the auxiliary brake system for the vehicle. However, these retarders generate a considerable amount of heat upon energy conversion during braking. Therefore, a device for cooling a working medium is required. The cooling device raises the cost of the auxiliary brake system and makes the arrangement complicated. On the other hand, a retarder of the kind mentioned above type of auxiliary brake system, namely "Turbo Retarder", which is disclosed in JP-A-63-302153 (Japanese Patent Application No. 62-136 476) published 9.12.1988, employs a blower which is connected to a crankshaft of the engine via a clutch and a speed change mechanism. The blower is driven by the crankshaft and consumes an eneryg of the engine, thereby applying a brake force to the engine. This arrangement does not require the device for cooling a working medium. However, if the gears of the speed change mechanism break or a seize occurs at the bearings of the speed change mechanism, a duly large force is applied to the crankshaft. This might result in a damage of the crankshaft or other members coupled with the crankshaft and further a breakdown of the vehicle. The problem of the present invention is to provide an auxiliary brake system which does not apply a brake force to the power transmission line of the vehicle when a trouble occurs in the speed change mechanism. The invention solves this problem by a retarder having the features described in the main claim. Advantageous further developments are described in the subclaims. When the blower is connected with the crankshaft of the engine via the clutch, and driven by the energy from the crankshaft, the blower consumes the energy of the engine, thereby applying a brake force to the engine. Also, at this situation, a lubrication oil supply device can be driven by the crankshaft and feeds the oil to the members of the speed change mechanism. During the deceleration by this brake system, if the gears of the speed change mechanism break or the bearings therein seize up, i. e., if the rotational speed of the gears or the shafts is lowered, the energy supplied to the oil supply device decreases since the oil supply device is driven by the energy transmitted between the clutch and the blower. When the oil pressure detected by the pressure sensor becomes lower than the predetermined value, the control unit demands the clutch to disconnect the blower from the crankshaft. If the blower would stay connected with the crankshaft, the speed change mechanism would apply a large brake force to the crankshaft. According to the invention, the blower of the brake system never applies an excessive brake force to the crankshaft and a safe deceleration is ensured by this brake system. A preferred embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 is a systematic diagram of the brake system according to the present invention; and Figure 2 is an enlarged sectional view of a clutch of Figure 1. Referring to Figure 1 of the accompanying drawings, numeral 1 designates an engine, and a crankshaft, i. e., a member of a power transmission line of a vehicle, 2, is connected to a retarder 3. The retarder 3 serves as an auxiliary brake system relative to a main brake system, i. e., a foot brake (not shown). The retarder 3 includes a blower 6 connected to the crankshaft 2 via a speed change mechanism 5 and a clutch 4 selectively connecting/disconnecting the blower 6 with/from the crankshaft 2, a lubrication oil supply device 7 driven by an energy transmitted between the clutch 4 and the blower 6 for supplying a lubrication oil to the speed change mechanism, a sensor 8 for detecting a pressure of the lubrication oil supplied to the speed change mechanism 5, and a control unit 9 for allowing the clutch 4 to disconnect the blower from the crankshaft when the detected oil pressure is below a predetermined value. More specifically, the crankshaft 2 is connected with a first shaft or an input shaft 12 of the speed change mechanism 5 via gears 10 and 11, and the input shaft 12 is connected with a second shaft 14 via a first set of gears 15 and 16 of the speed change mechanism. The second shaft 14 is supported by a couple of first bearings 13 disposed in a casing of the speed change mechanism 5. The second shaft 14 is also connected with a third shaft or an output shaft 19 of the speed change mechanism 5 via a second set of gears 17 and 18 of the speed change mechanism 5. The blower 6 includes an impeller 21 fixed to one end of the output shaft 19. The impeller 20 is rotatably housed in an impeller casing 20. The gear 18 meshes with an oil pump gear 22 which drives a main pump 7. The main pump 7 is the oil supply device in this embodiment. The lubrication oil is fed to the above-mentioned gears of the speed change mechanism 5 and the bearings 13 as indicated by the broken line in Figure 1. One of the bearings 13 is provided with a pressure sensor 8 detecting the pressure of the oil fed to the bearing 13. In this embodiment, the sensor 8 includes a pressure switch which is turned off when the oil pressure is not more than the predetermined value. The gear 11 fixed to the input shaft 12 meshes with a gear 24 which drives an auxiliary pump 23 of a capacity smaller than the main pump 7. The auxiliary pump 23 also feeds the lubrication oil to the bearings 13 and other members in the speed change mechanism 5. The predetermined value to turn off the pressure switch 8 is greater than the oil pressure supplied from the auxiliary pump 23. The input shaft 12 has two segments 12a and 12b, and it is provided with a clutch 4 for selectively disconnecting these segments 12a and 12b from each other. As shown in Figure 2, the input shaft 12 includes a plurality of clutch plates 25, a pressing member 26 for engaging the clutch plates 25 with each other, a diaphragm 28 for pressing the member 26 (to the left in the drawing) to engage the clutch plates 25 with each other, and a spring 29 for biasing the member 26 toward the original position thereof (right in the drawing). The clutch 4 is also provided with a switch 30 which is turned on when the member 26 is moved against the spring 29 and engages the clutch plates 25 with each other. A pressure chamber 27 is defined in the clutch 4, and an air tank 32 (Figure 1) is connected to the pressure chamber 27 via an electromagnetic valve 31 (Figure 1). The pressurized air in the tank 32 is introduced to the pressure chamber 27 when the electromagnetic valve 31 is turned on, whereas the air in the pressure chamber 27 is expelled when the valve 31 is turned off. Between the electromagnetic valve 31 and a power source 33 for the control unit 9, there are provided a main switch 34 and the control unit 9. The control unit 9 performs a following control: when the vehicle needs an auxiliary brake force and the main switch 34 is turned on (At this situation, the pressure switch 8 is turned off), the control unit 9 turns on the electromagnetic valve 31, thereby engaging the clutch 4 and turning on the pressure switch 8. However, when the trouble occurs in the speed mechanism 5, the control unit 9 turns off the electromagnetic valve 31 upon turning off of the pressure switch 8, thereby disengaging the clutch 4, even if the main switch 34 is in the ON position. During a normal driving, the main switch 34 is turned off, so that the clutch 4 is not engaged and the blower 6 is not driven by the engine. During a long down hill driving, for example, or when the auxiliary brake force is required, the main switch 34 is turned on. (Before this situation, the pressure switch 8 is in the OFF position.) As the main switch 34 is turned on, the electromagnetic valve 31 is turned on by the control unit 9, whereby the pressurized air is supplied to the pressure chamber 27 of the clutch 4 from the tank 32. As the clutch 4 is engaged, the rotation power of the crankshafat 2 is transmitted to the speed change mechanism 5 and then the blower 6, thereby driving the blower 6. At the same time, the main pump 7 is driven, thereby feeding the lubrication oil to the bearing 13 and other elements of the speed change mechanism 5. If the main switch 34 is turned off at this situation, the electromagnetic valve 31 is turned off, whereby the clutch 4 is disengaged and the blower 6 stops. On the other hand, if a trouble occurs while the blower 6 is being driven, e. g., if the main pump 7 does not function, a clogging occurs in a lubrication line, the gears of the speed change mechanism 5 break or the bearings 13 seize up, the pressure of the lubrication oil drops. At this situation, when the lubrication oil pressure decreases below the predetermined value, the pressure switch 8 is turned off. Therefore, even if the main switch 34 is in the ON position, the electromagnetic valve 31 is turned off by the control unit 9, thereby disengaging the clutch 4. Therefore, an excessive brake force is never applied to the crankshaft 2. In other words, the power transmission line of the vehicle is not damaged by the auxiliary brake system and a safe deceleration is ensured. In the illustrated embodiment, the pressure switch is employed as the pressure sensor and the control unit 9 disengages the clutch 4 via the electromagnetic valve 31 upon the signal from the clutch switch 30 in addition to the singal from the pressure sensor. However, the clutch may be controlled by the signal from the pressure sensor 8 only. Also, the turbo retarder may be connected with the propeller shaft instead of the crankshaft. In addition, the auxiliary pump 23 is not necessarily provided.

Claims: A retarder adapted for use on a vehicle characterized in that the retarder comprises: a blower (6) connected to a member (2) of a power transmission line of the vehicle and applying a brake action to the vehicle; a clutch (4) provided between the blower (6) and the member (2) of the power transmission line and selectively connecting or disconnecting the blower (6) from the member (2) of the power transmission line; a speed change mechanism (5) provided between the blower (6) and the clutch (4), characterized by an oil supply device (7) driven by power transmitted between the clutch (4) and the blower (6) and supplying a lubrication oil to the speed change mechanism (5); a sensor (8) detecting a pressure of the lubrication oil supplied to the speed change mechanism (5); and a control unit (9) allowing the clutch (4) to disconnect the blower (6) from the member (2) of the power transmission line when the lubrication oil pressure detected by the sensor (8) is below a predetermined value to prevent an excessive brake action. A retarder as defined in claim 1, characterized in that the member of the power transmission line is a crankshaft (2) of the engine. A retarder as defined in claim 1 or 2, characterized in that the speed change mechanism (5) has an input shaft (12) which receives an energy from the member (2) of the power transmission line and an output shaft (19) which sends the energy to the blower (6), and the oil supply device includes a main pump (7) connected with the output shaft (19) of the speed change mechanism (5). A retarder as defined in claim 1, 2 or 3, characterized in that the pressure sensor includes a pressure switch (8) which is turned off when the lubrication oil pressure detected by the sensor (8) is below the predetermined value. A retarder as defined in claim 3, characterized in that the retarder further includes an auxiliary pump (23) of a capacity smaller than the main pump (7) which supplyies the lubrication oil to the speed change mechanism (5), the auxiliary pump (23) being provided between the member (2) of the power transmission line and the clutch (4) and being driven by energy transmitted between the member (2) of the power transmission line and the clutch (4). A retarder as defined in anyone of the forgoing claims, characterized in that the retarder further includes an electromagnetic valve (31) operating the clutch (4), wherein the control unit (9) is connected with the electromagnetic valve (31). A retarder as defined in anyone of the foregoing claims, characterized in that the retarder further includes a power source (33) and a main switch (34) for the clutch (4), wherein the control unit (9) is connected with the power source (33) via the main switch (34). A retarder as defined in anyone of the foregoing claims, characterized in that the clutch (4) includes a clutch switch (30) having an ON position, the clutch switch (30) being in the ON position when the clutch (4) connects the member (2) of the power transmission line with the blower (6), and the control unit (9) allows the clutch (4) to disconnect the blower (6) from the power transmission line when the clutch switch (30) has been in the ON position and then the pressure switch (8) is turned off. A retarder as defined in anyone of the foregoing claims, characterized in that the sensor (8): detects an oil pressure of at least one bearing (13) of the speed change mechanism (5).

Inventors: OKADA, MASAKI C/O FUJISAWA FACTORY
Applicants: ISUZU MOTORS LIMITED
Application year: 1989
Main classification: B60T1
IPC codes: B60T17, F16D57, F02B61, B60T1, F02D29