Device for effective lubrication of vehicle power transmission system upon starting of vehicle

Abstract: A lubricating device for a motor vehicle including (a) a power transmission system (16, 18, 38, 40) having rotating members which are all at rest upon stopping of the vehicle, (b) a casing (14) accommodating the power transmission system and storing a lubricating oil, and (c) an oil pump (46) which is driven by the power transmission system and which operates to deliver the oil from the bottom portion of the casing to lubricating points of the power transmission system, wherein an oil reservoir (52) is provided to store a predetermined amount of the oil delivered by the pump, when a delivery amount of the pump exceeds a predetermined value with an increase in the speed of the power transmission system, and the level (A) of the oil stored in the bottom portion of the casing when no oil is stored in the reservoir is determined such that a portion of the power transmission system is immersed in the bath of the lubricating oil, and the oil level (B) when the predetermined amount of the oil delivered by the pump is stored in the reservoir is determined such that the lower end of the power transmission system is located above the oil level (B).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates in general to a lubricating device for a power transmission system of a motor vehicle wherein all rotating members are at rest upon stopping of the vehicle, and more particularly to a lubricating device according to the preamble of the patent claim 1. Discussion of the Prior Art A power transmission system such as a transmission, a speed reducing device or a differential gear device used in a motor vehicle is equipped with a lubricating device for lubricating various rotating members of the power transmission system so as to protect bearing portions and mutually meshing portions of the rotating members from seizure and early wearing. There are proposed various types of such a lubricating device for the vehicle power transmission system. As one example of the lubricating device, so-called "oil bath lubrication" is known, wherein portions of the power transmission system are immersed in a lubricating oil stored in a suitable oil pan, and the lubricating oil is scattered by the rotating members within the power transmission system during operation. Another example of the lubricating device is known as so-called "forced-feed lubrication", wherein the lubricating oil stored in the oil pan is sucked and pressurized by a suitable oil pump, and the pressurized oil is delivered to the lubricating points such as the bearing and meshing portions of the rotating members. In a lubricating device as disclosed in laid-open Publication No. 5-89061 of unexamined Japanese Utility Model Application, the power transmission system is subject to the oil bath lubrication when the running speed of the vehicle is relatively low, while on the other hand, the power transmission system is subject to the forced-feed lubrication as well as the oil bath lubrication when the running speed of the vehicle is relatively high. Further, two types of the forced-feed lubrication are known, i.e., mechanical forced-feed lubrication in which the pump for delivering the lubricating oil is driven by a member of the power transmission system, and an electrically- operated forced-feed lubrication in which an electrically operated pump is employed to deliver the lubricating oil. In the oil-bath lubrication as described above, the stored lubricating oil is agitated and scattered by the rotating members of the power transmission system when these members are rotated. In this case, the vehicle undesirably suffers from an energy loss especially when the vehicle is running at a relatively high speed, that is, when the rotating members of the power transmission system are rotated at a relatively high speed. When the oil bath lubrication is used in an electric vehicle, for example, the travel distance of the vehicle per one battery charging is undesirably reduced. Further, since the lubricating oil is agitated intensively by the rotating members, the oil is apt to be overheated, leading to early deterioration of the oil. Moreover, as a result of the agitation of the oil by the rotating members, bubbles likely to be formed in the lubricating oil and the transmission system tends to suffer from an oil leakage. In some electric vehicle, the vehicle speed is controlled exclusively by the rotating speed of a drive motor of the vehicle. In this case, however, the rotating speed of the input shaft of the power transmission system is extremely high during running of the vehicle at a high speed, and the power transmission system cannot necessarily be lubricated to a satisfactory extent by the oil bath lubrication. In the lubricating device as disclosed in the above publication, the power transmission system is subject to the forced-feed lubrication in addition to the oil bath lubrication while the vehicle is running at a relatively high speed. This arrangement is capable of assuring a sufficient lubricating effect during running of the vehicle at a relatively high speed. Further, the amount of the lubricating oil used for the oil bath lubrication can be decreased, and the energy loss due to the agitation of the oil by the rotating members is accordingly reduced. However, as long as the power transmission system is subject to the oil bath lubrication while the vehicle is running at a high speed, the vehicle suffers from the energy loss due to the agitation of the oil by the rotating members of the power transmission system. Thus, the disclosed lubricating device is not necessarily satisfactory when used in the electric vehicle in which the rotating speed of the power transmission system is extremely high when the vehicle running speed is relatively high and in which an improvement of the travel distance per one battery charging is required. Unlike the oil bath lubrication, the above-described mechanical forced-feed lubrication is not likely to cause the energy loss. However, in the electric vehicle, all of the rotating members of the power transmission system are turned off when the vehicle is stopped. Accordingly, a mechanical oil pump which is adapted to be driven by the rotation of the power transmission system is also turned off, and therefore, the lubricating oil is no more supplied to the power transmission system. This means that the power transmission system cannot be adequately lubricated upon restarting of the vehicle after a stop. Described in detail, upon starting of the vehicle, the power transmission system starts to be rotated and accordingly, the lubricating oil is delivered by the mechanical pump and gradually supplied to the power transmission system. In the actual operating state of the vehicle, however, it takes some time before the delivered oil reaches the power transmission system. Furthermore, the rotating speed of the power transmission system is usually relatively low upon and immediately after starting of the vehicle, and accordingly, the amount of the lubricating oil delivered from the pump is small. However, a large amount of the lubricating oil is required to sufficiently lubricate the power transmission system upon and immediately after starting of the vehicle, since a comparatively large torque is transmitted to the power transmission system via the input shaft thereof and a relatively large amount of load acts on the bearing and meshing portions of the power transmission system. In case that the vehicle wheels slip on the road surface upon starting of the vehicle, the gears of the differential gear device are rotated at a high speed with a large amount of load applied thereto, and therefore a large amount of the lubricating oil is required to lubricate the gears. If the gears are not adequately lubricated, they would be damaged due to shortage of the lubricating oil. In the electrically-operated forced-feed lubrication, the electric pump is capable of delivering the lubricating oil to the power transmission system irrespective of the rotating speed of the power transmission system. Thus, the electrically-operated forced-feed lubrication is preferably employed in the electric vehicle wherein all of the rotating members of the power transmission system are turned off upon stopping of the vehicle. However, the electrically-operated forced-feed lubrication suffers from various problems as described below. For example, the electrically-operated forced-feed lubrication needs an electric motor for driving the electric pump, pushing up the cost of manufacture of the lubricating device as compared with the above-described mechanical forced feed-lubrication. Further, components of the electric motor such as a brush have a comparatively shorter service life than the vehicle itself, and they should be replaced or checked regularly. This regular replacement and checking make the vehicle maintenance cumbersome. To obtain a sufficient lubricating effect upon starting of the vehicle in the lubricating device employing the electric pump, the electric pump motor must be kept in the operating state for driving the electric pump so as to enable the lubricating oil to be continuously delivered to the power transmission system even while the vehicle is at a stop, since it is not possible to anticipate when the accelerator pedal is depressed by the vehicle driver for restarting the vehicle. In this case, the electric power consumed by the electric motor for continuously driving the electric pump is generally larger than the energy loss experienced in the mechanical forced-feed lubrication wherein the mechanical pump is driven by the rotation of the power transmission system. The preamble of the patent claim 1 starts out from a vehicle, especially a transmission for a vehicle, having a lubricating system as disclosed in the US 5,158,152. This lubricating system comprises an oil pan for storing lubricating oil in which rotating members of the transmission system are at least partly immersed in order to carry out the so-called oil bath lubrication. Furthermore, the lubrication system has an auxiliary oil reservoir which is connected to the oil pan via oil passages in which an oil pump is arranged for feeding oil from the oil pan to the auxiliary oil reservoir during a high-speed operation of the transmission system. It is disclosed that in the oil passages ejecting holes are provided for lubricating the rotating parts of the transmission system when the oil pump is in operation. That means that the lubricating system according to this document consists of a combination of an oil bath lubrication and a forced-feed lubrication wherein in the case that when the vehicle is traveling at a low vehicle speed, the amount of oil supplied by the oil pump is small so that the oil level in the oil pan is high and the portion of the gears of the transmission immersed in the lubricating oil is relatively large. The lubricating oil pumped by the oil pump is supplied to the ejecting holes for direct lubrication of rotating parts of the transmission and to the auxiliary oil reservoir. At a higher vehicle speed, the amount of lubricating oil pumped by the oil pump increases so that the part of the oil which is not ejected through the ejecting holes and which is therefore supplied to the auxiliary oil reservoir increases as well. It is, furthermore, disclosed that, since the oil pump is operatively connected to the transmission, the amount of oil transferred from the oil pan to the auxiliary oil reservoir is increased in accordance with any increases in the vehicle speed. On the other hand, the oil stored in the auxiliary oil reservoir is discharged to the transmission case through a small hole at a substantially constant flow rate. This means that during a high vehicle speed, the oil level in the oil pan falls so that the portion of the gears of the transmission immersed in the lubricating oil is relatively small. In other words, this document teaches that the oil pump supplies lubricating oil to the ejecting holes and the auxiliary oil reservoir in dependence on the transmission speed in order to increase or decrease the oil level in the oil pan in accordance with an increase or decrease in the vehicle speed. From the document DE 32 08 100 another transmission is known built-in a casing which forms oil accommodating zones. These zones are arranged separately from the transmission accomodating part of the casing and contain biasing means for applying pressure onto the oil stored therein. It is an object of the present invention to provide a lubricating device for lubricating a power transmission system of a motor vehicle wherein the rotating members are all at rest upon stopping of the vehicle, which assures an improved lubricating effect also upon starting of the vehicle. The above object is solved by a lubricting device having the technical features according to the patent claim 1. In the present lubricating device, the power transmission system is mainly forced-feed lubricated by the mechanical oil pump, while at the same time, the power transmission system is subject to the oil bath lubrication before the predetermined amount of the oil is accumulated in the oil reservoir with an increase in the rotating speed of the power transmission system. Thus, the lubricating device assures a satisfactory lubricating effect upon and immediately after starting of the vehicle, that is, when the rotating speed of the power transmission system is relatively low. As, for example the rotating speed of the power transmission system increases, the lubricating oil is accumulated in the oil reservoir. Consequently, the lubricating oil which has been stored in the bottom portion of the casing decreases to such an extent that the power transmission system is no more immersed in the oil bath. In this state, the oil bath lubrication is not effected, and therefore, the power transmission system is lubricated exclusively by the forced-feed lubrication by the mechanical oil pump, thereby to avoid the energy loss and the overheating of the lubricating oil which would result from the agitation of the oil by the rotating members of the power transmission system while the rotating speed of the power transmission system is relatively high. The present device assures effective lubrication when used in an electric vehicle wherein the rotating speed of the power transmission system is excessively high during high-speed running of the vehicle. The predetermined critical delivery amount of the mechanical oil pump at which the lubricating oil starts to be stored in the oil reservoir is an amount which ensures that the lubricating device exhibits a satisfactory lubricating effect only by the forced-feed lubrication effected by the mechanical oil pump. It is desirable that the critical delivery amount be set at a value as low as possible to minimize the energy loss due to the agitation of the oil by the rotating members of the power transmission system. The oil reservoir in the present lubricating device is actually an accumulator. In this case, when the delivery amount of the oil pump exceeds the predetermined critical value and the hydraulic pressure of the oil becomes higher than a predetermined value, the lubricating oil is gradually accumulated in the accumulator with a retracting movement of for example a piston in the accumulator as a moveable means in a direction to increase the volume of the accumulating chamber of the accumulator. The oil reservoir may be provided with flow regulating means for allowing the accumulated lubricating oil to be discharged at a controlled flow rate, such as an orifice or a flow restrictor having a suitable cross sectional area, or a flow control valve. In this case, the lubricating oil flowing into the oil reservoir is discharged without being accumulated therein while the delivery amount of the mechanical oil pump is small, and the lubricating oil starts to be accumulated in the oil reservoir when an amount of the oil flowing into the oil reservoir exceeds a predetermined value. The lubricating oil discharged from the oil reservoir may be returned directly into the oil bath at the bottom of the casing or directed to the lubricating points in the power transmission system. In the thus constructed lubricating device, the power transmission system is sufficiently lubricated over an entire range of its rotating speed from a relatively low speed to a relatively high speed while reducing the energy loss and avoiding the overheating of the lubricating oil. The present device is preferably employed in an electric vehicle in which the rotating speed of the power transmission system is considerably high while the vehicle running speed is high. Further, the present device is effective to improve the travel distance per one battery charging of the electric vehicle. In the lubricating device according to the invention, the power transmission system which is principally forced-feed lubricated by the oil delivered from the mechanical pump is also oil-bath lubricated while the vehicle running speed is relatively low. This arrangement permits reduced cost of manufacture of the lubricating device and reduced electric power consumption of the vehicle, as compared with the electrically-operated forced-feed lubrication system wherein the pump for delivering the lubricating oil is driven by an electric motor. Furthermore, this arrangement assures a satisfactory lubricating effect with high reliability and permits easy maintenance of the vehicle, minimizing regular checking and replacement of a brush and other components of the electric pump motor. Furthermore, the inventive lubricating device comprises flow restricting means for restricting a rate of flow of the lubricating oil discharged from the oil reservoir through said discharge line. In the lubricating device constructed as described above, the lubricating oil is delivered by the mechanical oil pump to the lubricating points by the rotation of the power transmission system during running of the vehicle, while at the same time, a part of the lubricating oil is stored in the oil reservoir. The stored oil in the oil reservoir is discharged via the discharge line to the lubricating points at a flow rate determined by the flow restricting means. In this arrangement, therefore, even when the lubricating oil is not delivered by the oil pump upon or immediately after stopping of the vehicle, the lubricating points are adequately lubricated for a predetermined length of time by the oil which is supplied from the oil reservoir at the predetermined flow rate. Thus, the present lubricating device is free from an insufficient supply of the lubricating oil when the vehicle is restarted after stopping for a relatively short length of time, during which the lubricating oil continues to be delivered from the oil reservoir. The lubricating device is capable of assuring a satisfactory lubricating effect owing to the lubricating oil discharged from the oil reservoir, when the power transmission system is rotated at a relatively low speed, that is, when the lubricating points cannot be sufficiently lubricated by the lubricating oil delivered from the mechanical oil pump. The storage capacity of the oil reservoir and the rate of the discharge flow determined by the flow restricting means are predetermined such that the lubricating oil in the oil reservoir continues to be discharged therefrom for at least 3-5 minutes so as to ensure that the lubricating points can be sufficiently lubricated by the lubricating oil supplied from the oil reservoir when the vehicle is restarted after stopping at a traffic signal light, for instance. Upon an initial starting of the vehicle or restarting after stopping for a relatively long length of time, the power transmission system cannot be forced-feed lubricated by the lubricating oil stored in the oil reservoir, since the lubricating oil is not stored in the oil reservoir. However, the present device assures a satisfactory lubricating effect when the vehicle is restarted after stopping for a relatively short length of time during which the lubricating oil in the oil reservoir continues to be discharged therefrom and delivered to the lubricating points in the power transmission system. Thus, the device is capable of protecting the bearing portions and the power transmission gears from suffering from seizure, wearing, or damages due to the shortage of the lubricating oil, thereby to assure a considerably improved service life of the components of the power transmission system, as compared with a lubricating device in which the lubricating points are lubricated only by the oil delivered from the oil pump. Upon restarting of the vehicle after stopping for a relatively short length of time, the power transmission system is lubricated by the lubricating oil discharged from the oil reservoir. In the present lubricating device, accordingly, it is not always required to immerse the power transmission system in the lubricating oil bath at the bottom of the casing. Thus, the present device is effective to further reduce the energy loss due to the agitation of the lubricating oil by the power transmission system. The present device offers a satisfactory lubricating effect when used in an electric vehicle wherein the rotating speed of the power transmission system is considerably high during high-speed running of the vehicle. The lubricating device according to the invention is preferably constructed such that the lubricating oil delivered by the mechanical pump is supplied exclusively to the lubricating points while the power transmission system is rotating at a relatively low speed immediately after the starting of the vehicle, for instance, and such that the lubricating oil starts to be accumulated in the oil reservoir only after the delivery amount of the oil pump exceeds a predetermined value with a rise in the rotating speed of the power transmission system. In view of this, the oil reservoir takes the form of the accumulator which is adapted to accumulate the lubricating oil when the hydraulic pressure of the lubricating oil delivered from the oil pump is higher than a predetermined value. In the lubricating device employing the accumulator, the lubricating oil stored in the accumulator is forced to be discharged therefrom. Unlike the oil reservoir without the flow restricting means wherein the stored oil drops by gravity from the oil reservoir, the accumulator has a freedom in setting the rate of discharge flow of the oil from the accumulator. Further, there is less limitation in determining the location of the accumulator. Namely, the accumulator may be located beside or below the power transmission system. In the present lubricating device, a part of a forced-feed oil passage for supplying the lubricating oil delivered by the oil pump to the lubricating points may be utilized as the discharge line through which the lubricating oil discharged from the oil reservoir is fed so as to lubricate the lubricating points. However, it is possible to provide an exclusive discharge line independently of the forced-feed oil passage. The flow restricting means in the present device may be an orifice (or a flow restrictor) whose cross sectional area for the fluid flow is constant so as to obtain a desired flow rate. Alternatively, a flow control valve may be preferably employed, which is manually adjustable to change the flow rate as desired. It is to be understood from the above description that the present device according to the invention assures a satisfactory lubricating effect owing to the lubricating oil supplied from the oil reservoir as described above when the vehicle is restarted after stopping for a relatively short length of time or while the rotating speed of the power transmission system is relatively low. The lubricating device according to the invention further comprises a valve means which is selectively placed in an open position and a closed position for permitting and inhibiting a discharge flow of the lubricating oil from the oil reservoir through the discharge line, respectively; and valve control means for receiving information indicating whether an amount of the lubricating oil delivered to the lubricating points is insufficient, determining, on the basis of the information, whether or not the lubricating points suffer from shortage of the lubricating oil, and placing the valve means in the open position if the amount of the lubricating oil delivered to the lubricating points is insufficient. The lubricating device according to the invention is provided with the valve means in the discharge line through which the lubricating oil is discharged from the oil reservoir. The valve means is selectively placed in an open position and a closed position for permitting and inhibiting the discharge flow of the oil from the oil reservoir through the discharge line. The valve control means is adapted to receive suitable information for determining whether or not the lubricating points suffer from shortage of the lubricating oil. The valve control means controls the valve means to be placed in the open position for permitting the discharge flow from the oil reservoir when the lubricating points suffer from shortage of the lubricating oil. For example, the valve control means can determine that the lubricating points suffer from the shortage of the oil when the delivery amount of the oil pump is small, in other words, when the vehicle speed or the rotating speed of the power transmission system is low. On the other hand, however, the oil amount required for the lubrication varies depending upon a load applied to the power transmission system, i.e., the rotating speed of the power transmission system, the torque transmitted to the power transmission system, or a rate of change in the transmitted torque. In view of this fact, it is desirable to effect the determination taking these parameters into consideration. The present device may be provided with detecting means as needed to obtain these parameters, such as means for detecting the speed of the transmission or means for detecting an electric current applied to the drive motor. In an electric vehicle, a command generated by a controller for controlling the torque of the electric drive motor may be used by the valve control means to control the valve means. Since the torque of the electric drive motor is usually controlled depending on an operating amount of the accelerator, the valve control means may use the operating amount of the accelerator or a rate of change in this operating amount as the information indicative of the load acting on to the power transmission system. The valve means in the present device is adapted to permit or inhibit the discharge flow of the lubricating oil from the oil reservoir through the discharge line. However, the valve means may be a flow regulating valve which regulates or restricts the flow rate of the lubricating oil discharged from the oil reservoir. In this case, the valve control means may adjust the discharge flow rate depending on a degree of the shortage of the lubricating oil at the lubricating points. In the lubricating device according to the invention, the lubricating oil accumulated in the oil reservoir is supplied to the lubricating points when these points suffer from the shortage of the oil, assuring similar advantages as already described above. In addition, the lubricating oil in the oil reservoir is more effectively utilized for lubricating the power transmission system, whereby the bearing portions and the gears of the power transmission system are protected against seizure, wearing or damages resulting from the shortage of the lubricating oil, so as to assure a further improved service life of the components of the power transmission system. As indicated above, the accumulator is used as the oil reservoir, which starts to store the lubricating oil when the hydraulic pressure of the oil exceeds a predetermined value. When the accumulator is used in the lubricating device as described above, the lubricating oil may start to be stored when the delivery amount of the oil pump becomes larger than a predetermined value and the hydraulic pressure of the oil delivered from the oil pump exceeds a predetermined value (a set pressure of the accumulator). In this arrangement, the set pressure of the accumulator may be adjusted by suitable pressure setting means such as a spring which biases the piston of the accumulator, so that the rotating speed of the power transmission system at which the oil bath lubrication is terminated can be easily adjusted as desired, by changing the biasing force of the spring, for example. When the above accumulator is employed in the lubricating devices according to the invention as described above, the lubricating oil delivered by the oil pump is supplied mainly to the lubricating points, when the hydraulic pressure of the delivered oil is lower than a predetermined value, namely, when the rotating speed of the power transmission system is relatively low (e.g., during starting of the vehicle). Thus, the device assures more effective lubrication while the rotating speed of the power transmission is low. The lubricating oil stored in the accumulator is forced to be discharged therefrom after the hydraulic pressure becomes higher than the predetermined value. Unlike the lubricating device wherein the accumulated oil drops by gravity, the accumulator of the present device has a high degree of freedom in setting the rate of discharge flow of the oil from the accumulator. Further, there is less limitation in determining the location of the accumulator. Namely, the accumulator may be located beside or below the power transmission system. The set pressure of the accumulator may be set at a constant value predetermined depending upon a biasing force of the spring and a load applied to the spring. Alternatively, the set pressure may be adjusted continuously by controlling a back pressure of the accumulator such as an air pressure. BRIEF DESCRIPTION OF THE DRAWINGS The above and optional objects, features and advantages of the present invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which: Fig. 1 is a schematic diagram showing a power transmission system for use in an electric vehicle, which is equipped with a lubricating device of general construction; Figs. 2A-2G are graphs showing oil levels and flow rates in the lubricating device of Fig. 1, which vary with running speed of the vehicle; Fig. 3 is a schematic diagram showing a power transmission system equipped with a lubricating device according to a first embodiment of the invention; Fig. 4 is a view showing another example of an accumulator employed in the lubricating device of Fig. 3; Fig. 5 is a schematic diagram showing a power transmission system with a lubricating device according to a further embodiment of the invention; Fig. 6 is a flow chart illustrating a control program for controlling a solenoid valve used in the lubricating device of Fig. 5; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to the schematic diagram of Fig. 1, there are illustrated an electric drive motor 10 and a transaxle 12 for an electric motor vehicle. The transaxle 12 includes a casing 14, a planetary gear type speed reducing device 16 and a bevel gear type differential gear device 18, which are accommodated within the casing 14 so as to be disposed coaxially with the electric drive motor 10. The speed reducing device 16 includes a sun gear 22 connected to a motor shaft 20 of the drive motor 10, a plurality of planetary gear pinions 24 meshing with the sun gear 22, a carrier 26 rotatably supporting the planetary gear pinions 24, and a ring gear 28 secured to the casing 14 and meshing with the planetary gear pinions 24. The differential gear device 18 includes a shaft 30 which is integrally fixed to the carrier 26 and which is rotated in a plane perpendicular to an axis of the speed reducing device 16, a pair of first bevel gears 32 rotatably mounted on the shaft 30, second bevel gears 34, 36 which are provided so as to be rotatable coaxially with the speed reducing device 16 and which mesh with the respective first bevel gears 32. The second bevel gears 34, 36 are splined to respective transmission shafts 38, 40 which are connected to respective left and right drive wheels of the vehicle, such that the second bevel gears 34, 36 are rotated together with the transmission shafts 38, 40. The rotation of the motor shaft 20 of the drive motor 10 is inputted to the sun gear 22, and outputted to the differential gear device 18 through the carrier 26, with the ring gear 28 functioning as a reaction element. The rotating speed of the carrier 26 is reduced with respect to the sun gear 22 at a predetermined suitable gear ratio of the speed reducing device 16. Thus, the rotation of the motor 10 is transmitted to the transmission shafts 38, 40 via the speed reducing device 16 and the differential gear device 18. The speed reducing device 16, differential gear device 18 and transmission shafts 38, 40 constitute a power transmission system. It is noted that the transaxle 12 as shown in Fig. 1 is made larger than the drive motor 10 as shown in the figure. To the carrier 26, there is connected a pump drive gear 44 for driving a mechanical pump in the form of a gear type pump 46. When the gear 44 is rotated by rotation of the carrier 26 during running of the vehicle, the gear pump 46 sucks a lubricating oil from an oil pan 48 formed in the bottom portion of the casing 14, and delivers the lubricating oil, via a forced-feed oil passage 50 formed in the casing 14 and transaxle 12, to selected lubricating points of the power transmission system such as bearing portions of the motor shaft 20 of the drive motor 10, planetary gears 24, transmission shafts 38, 40, meshing portions of the gears of the speed reducing device 16 and the differential gear device 18. A delivery amount of the gear pump 46 changes proportionally with a change in the rotation speed of the carrier 26 and the vehicle speed V. As shown in the graph of Fig. 2A, the delivery amount of the gear pump 46 linearly changes with the vehicle speed V. The delivery amount of the gear pump 46 is zero when the vehicle speed V is zero, i.e., while the vehicle is stopped. The lubricating oil which has been supplied to the lubricating points of the power transmission system drops down from the lubricating points into the bottom portion of the casing 14 or is fed back to the same through a return passage not shown. The amount of lubricating oil stored within the casing 14 is predetermined so that the oil bath has an oil level A indicated by an upper broken line in Fig. 1, namely, so that the substantially lower half portions of the speed reducing device 16 and the differential gear device 18 are immersed in the oil bath when the transmission system is at rest. The gear pump 46 may be replaced by any other mechanical pump such as a vane pump or a Roots pump (a lobe-type rotary pump). To the forced-feed oil passage 50, there is connected, via a branch oil passage 53, an oil reservoir 52 which is disposed at an upper portion of the casing 14. The oil reservoir 52 is adapted to receive a part of the lubricating oil delivered by the gear pump 46. The lubricating oil flowing into the oil reservoir 52 is discharged therefrom by gravity at a predetermined flow rate through a drain port 54 formed at the bottom of the oil reservoir 52. The amount of the oil discharged from the drain port 54 before the vehicle speed V reaches a predetermined speed SPD1 is equal to an amount of the lubricating oil flowing into the oil reservoir 52. In other words, the lubricating oil flowing into the oil reservoir 52 is discharged through the drain port 54 without being accumulated in the oil reservoir 52 before the vehicle speed V reaches the speed SPD1. The amount of the lubricating oil flowing into the oil reservoir 52 exceeds the amount of discharge from the drain port 54 after the vehicle speed V reaches the speed SPD1 and before the oil reservoir 52 becomes full of the oil. As a result, the lubricating oil is accumulated in the oil reservoir 52. The oil capacity of the oil reservoir 52 is determined such that the lubricating oil stored within the casing 14 has an oil level B indicated by a lower broken line in Fig. 1 when the oil reservoir 52 is full of the lubricating oil. This oil level B is determined so that the speed reducing device 16 and the differential gear device 18 are positioned above the oil level B, i.e., these devices are no more immersed in the lubricating oil stored in the bottom portion of the casing 14. In this arrangement, therefore, while the vehicle running speed is lower than the predetermined speed SPD1, the power transmission system is subject to the oil bath lubrication, with the portions of the speed reducing device 16 and the differential gear device 18 being immersed in the lubricating oil stored in the bottom portion of the casing 14. At the same time, the power transmission system is subject to the forced-feed lubrication wherein the speed reducing device 16 and the differential gear device 18 are lubricated by the lubricating oil delivered by the gear pump 46 and fed through the forced-feed oil passage 50. After the vehicle speed reaches the predetermined speed SPD1, the oil level in the casing 14 is lowered to the level B as described above, at which it is impossible to effect the oil bath lubrication, since the oil level B is below the speed reducing device 16 and the differential gear device 18. Thus, these devices are subject to only the forced-feed lubrication. It is preferable that the predetermined speed SPD1 be set at a value low enough to reduce the energy loss due to agitation of the lubricating oil by the power transmission system while ensuring that the power transmission system is sufficiently forced-feed lubricated only by the lubricating oil delivered by the gear pump 46. For instance, the value SPD1 is determined to be equal to the vehicle speed at which the rotating speed of the motor shaft 20 of the drive motor 10 is about 1000rpm. However, the value SPD1 depends upon the gear ratio of the speed reducing device 16 and other parameters. The size of the drain port 54 is determined so that the lubricating oil starts to be accumulated in the oil reservoir 52 at the thus determined speed SPD1. The graphs of Figs. 2A-2G show oil levels and flow rates of the lubricating oil, which vary with the running speed of the vehicle. The oil levels and flow rates as shown are those which are established when the vehicle speed is held at each value (e.g., SPD1) for a long time. In this respect, it is noted for example that the oil reservoir 52 is filled with the oil if the vehicle speed is held at the predetermined critical speed SPD1. As shown in the graphs 2D and 2E, the rate of flow of the lubricating oil into the oil reservoir 52 is constantly equal to the rate of flow of the lubricating oil discharged out of the oil reservoir 52 through the drain port 54 except for the time period as described above. After the vehicle speed V exceeds the predetermined speed SPD1 and the lubricating oil is gradually accumulated in the oil reservoir 52, the rate of flow of the lubricating oil into the oil reservoir 52 continues to increase with a rise in the hydraulic pressure of the lubricating oil delivered from the gear pump 46, and the rate of discharge flow of the oil from the drain port 54 is accordingly increased. After the oil reservoir 52 is filled with the lubricating oil, the resistance of the lubricating oil to its flow into the oil reservoir 52 is made comparatively large, and the rate of increase of the amount of the lubricating oil used for the forced-feed lubrication of the lubricating points in the power transmission system is accordingly increased. To the forced-feed oil passage 50 is connected a pressure relief valve 56 for preventing an excessive rise of the pressure of the lubricating oil delivered by the gear pump 46, and reducing a load applied to the gear pump.46 so as to minimize the energy loss. The relief pressure of the valve 56 is preferably set at a value as low as possible while ensuring that the lubricating points in the power transmission system are adequately lubricated by the lubricating oil delivered from the gear pump 46. At the vehicle speed SPD1, the amount of the oil delivered by the gear pump 46 for the forced-feed lubrication is sufficient. In view of this, the relief pressure of the valve 56 may be set, for example, at a level slightly higher than a level which corresponds to the vehicle speed SPD1. In the thus constructed lubricating device, the power transmission system is principally forced-feed lubricated by the lubricating oil delivered from the gear pump 46. However, before the vehicle speed V reaches the predetermined speed SPD1, and therefore, before the lubricating oil is accumulated in the oil reservoir 52, the portions of the speed reducing device 16 and the differential gear device 18 are immersed in the lubricating oil bath in the bottom portion of the casing 14. Accordingly, the power transmission system is subject to both the oil bath lubrication and the forced-feed lubrication until the vehicle speed V reaches the predetermined speed SPD1. This arrangement assures a satisfactory lubricating effect even when the delivery amount of the gear pump 46 is relatively small, that is, even when the rate of flow of the oil used for the forced-feed lubrication is relatively low, immediately after starting of the vehicle, for instance. Thus, this arrangement is capable of protecting the bearing portions and the gears of the power transmission system against seizure, wearing and damages which result from shortage of the lubricating oil, thereby assuring considerably improved service life of the components of the power transmission system. In this arrangement, for instance, the gears of the differential gear device 18 are also protected with high reliability from being damaged due to the shortage of the lubricating oil even when the vehicle wheels are slipping on the road surface upon starting of the vehicle. After the vehicle speed V reaches the predetermined speed SPD1, the lubricating oil delivered from the gear pump 46 is gradually accumulated in the oil reservoir 52 via the branch oil passage 53. As a result, the level of the lubricating bath in the bottom portion of the casing 14 falls from the level A to the level B as shown in Fig. 1. In this state, the speed reducing device 16 and the differential gear device 18 are completely above the level B, making it impossible to lubricate these devices by the oil bath lubrication. Thus, the power transmission system is mainly forced-feed lubricated by the lubricating oil delivered by the gear pump 46 and fed through the forced-feed oil passage 50, effectively avoiding the energy loss and the overheating of the lubricating oil which would be caused by the agitation of the lubricating oil when the power transmission system is rotated at a relatively high speed. The forced-feed lubrication is capable of assuring a satisfactory lubricating effect when the motor shaft 20 of the drive motor 10 is rotated at a relatively high speed. In the thus constructed lubricating device, the power transmission system is sufficiently lubricated over an entire range of its rotating speed from a relatively low speed to a relatively high speed while reducing the energy loss and avoiding the overheating of the lubricating oil supplied to the lubricating points. Further, the travel distance of the present electric vehicle per one battery charging can be considerably increased as compared with that in the conventional electric vehicle wherein the power transmission system is lubricated only by the oil-bath lubrication. The power transmission system which is principally forced-feed lubricated is also oil-bath lubricated when the vehicle running speed is relatively low. This arrangement permits reduced cost of manufacture of the lubricating device and reduced electric power consumption of the vehicle, as compared with the electrically-operated forced-feed lubrication system wherein a pump for delivering the lubricating oil is driven by an exclusive electric motor. Further, this arrangement assures a satisfactory lubricating effect with high reliability and permits easy maintenance of the vehicle, eliminating regular checking and replacement of a brush and other components of the electric pump motor. Referring next to Fig. 3, there will be described a lubricating device according to a first embodiment of the present invention, wherein the same reference numerals as used in the preceding general device design are used to identify the corresponding components and detailed explanation thereof is dispensed with. In this first embodiment, the branch oil passage 53 is connected to an accumulator 60 in place of the oil reservoir 52 used in the general device design. The amount of the lubricating oil stored in the casing 14 is predetermined so as to establish an oil level C as indicated by a broken line in Fig. 3, so that the speed reducing device 16 and the differential gear device 18 are positioned above the lubricating oil bath. The accumulator 60 has a piston 64 which is biased by a spring 62. When the hydraulic pressure of the lubricating oil flowing through the branch oil passage 53 becomes higher than a predetermined level (i.e., a set pressure of the accumulator 60) corresponding to the biasing force of the spring 62, the lubricating oil flows into the accumulator 60 while pushing the piston 64 against the biasing force of the spring 62. The above-indicated set pressure of the accumulator 60 is determined so as to allow the lubricating oil to flow into the accumulator 60 only after a sufficient amount of the lubricating oil is supplied to the lubricating points of the power transmission system. In this arrangement, when the rotating speed of the power transmission system is relatively low, that is, when the amount of the lubricating oil delivered by the gear pump 46 is relatively small, the delivered oil is exclusively supplied to the lubricating points for forced-feed lubrication. After a sufficient amount of the oil is delivered to the lubricating points, the oil is allowed to flow into the accumulator 60 and is accumulated therein. The set pressure of the accumulator 60 is adjusted as desired by varying the biasing force of the spring 62 or a pre-load acting on the piston 64. The accumulator 60 used in this first embodiment may be replaced by any other types of accumulator. For instance, an accumulator 78 as shown in Fig. 4 may be employed in the present lubricating device. This accumulator 78 has a gas chamber 76 which is partially defined by a diaphragm 74. The set pressure of the accumulator 78 can be adjusted by varying the gas pressure in the chamber 76. In the thus constructed lubricating device, there is provided a check valve 66 between the branch oil passage 53 and the accumulator 60. The lubricating oil flows into the accumulator 60 through the check valve 66 when the pressure of the lubricating oil in the branch oil passage 53 is higher than the above-described set pressure of the accumulator 60. The present lubricating device is further provided with a discharge line 68 between the accumulator 60 and the branch oil passage 53 such that the discharge line 68 is disposed in parallel with the check valve 66. When the oil pressure in the branch oil passage 53 becomes lower than that in the accumulator 60, the piston 64 is moved in the biasing direction of the spring 62. As a result, the lubricating oil stored in the accumulator 60 is discharged therefrom into the branch oil passage 53 via the discharge line 68, and then supplied to the lubricating points. In the discharge line 68, there is provided with an orifice 70 as flow restricting means for restricting a flow rate of the lubricating oil discharged from the accumulator 60. In case that the gear pump 46 is turned off upon stopping of the vehicle, the lubricating oil stored in the accumulator 60 is supplied therefrom for a given length of time, i.e., about for 3-5 minutes, which is slightly longer than a usual stop time of the vehicle waiting for a traffic signal light. In this arrangement, even after the gear pump 46 is turned off when the vehicle stops, the lubricating points in the power transmission system are lubricated for a while by the lubricating oil discharged from the accumulator 60. The amount and set pressure of the accumulator 60 and the cross-sectional area for fluid flow of the orifice 70 are determined such that the lubricating oil is discharged from the accumulator 60 for a desired length of time after the gear pump 46 is turned off. In the present embodiment, the lubricating oil may flow into the accumulator 60 via the discharge line 68 when the pressure of the lubricating oil flowing through the branch oil passage 53 becomes higher than the set pressure of the accumulator 60. In the thus constructed lubricating device, a sufficient amount of the lubricating oil is delivered by the gear pump 46 to the lubricating points during running of the vehicle, while at the same time, a part of the lubricating oil flows into the accumulator 60 via the branch oil passage 53 and is stored therein. On the other hand, when the delivery amount of the gear pump 46 decreases with a decrease in the vehicle speed and the oil pressure in the branch oil passage 53 becomes lower than that in the accumulator 60, the lubricating oil in the accumulator 60 is discharged via the discharge line 68 to the lubricating points at a flow rate controlled by the orifice 70. In this arrangement, therefore, even when the lubricating oil is not delivered by the gear pump 46 upon stopping of the vehicle, the lubricating points are adequately lubricated for the predetermined length of time by the lubricating oil which is supplied from the accumulator 60 at the predetermined flow rate via the discharge line 68. Thus, this arrangement is free from an insufficient supply of the lubricating oil when the vehicle is restarted after stopping for a relatively short length of time, during which the lubricating oil continues to be delivered from the accumulator 60. The lubricating device according to the present embodiment is capable of assuring a satisfactory lubricating effect owing to the lubricating oil discharged from the accumulator 60, when the power transmission system is rotated at a relatively low speed, that is, when the lubricating points of the power transmission system cannot be sufficiently lubricated by the lubricating oil delivered from the gear pump 46. In the lubricating device according to the present embodiment, since the lubricating oil is not stored in the accumulator 60 upon an initial starting of the vehicle or restarting of the vehicle after stopping for a relatively long length of time, the lubricating points in the power transmission system cannot be forced-feed lubricated by the lubricating oil stored in the accumulator 60 as described above. However, this arrangement ensures a satisfactory lubricating effect when the vehicle is restarted after stopping for a relatively short length of time during which the lubricating oil in the accumulator 60 continues to be discharged via the discharge line 68 and delivered to the power transmission system. Thus, the present lubricating device is capable of protecting the bearing portions and the power transmission gears from suffering from seizure, wearing or damages due to the shortage of the lubricating oil, thereby to assure a considerably improved service life of the components of the power transmission system, as compared with a lubricating device in which the lubricating points are lubricated only by the oil delivered from the gear pump 46. In the lubricating device according to the present embodiment, the lubricating oil is allowed to flow into the accumulator 60 only after a sufficient amount of the oil is supplied to the lubricating points. Accordingly, upon initial starting of the vehicle or restarting of the vehicle after stopping for a relatively long length of time, a comparatively small amount of the lubricating oil can be efficiently utilized for forced-feed lubricating the lubricating points, since the lubricating oil delivered by the gear pump 46 is supplied exclusively to the lubricating points. Upon restarting of the vehicle after stopping for a relatively short length of time, the power transmission system is lubricated by the lubricating oil discharged from the accumulator 60. In the present lubricating device, accordingly, it is not always required to immerse the speed reducing device 16 and the differential gear device 18 in the lubricating oil bath in the bottom portion of the casing 14. In the present arrangement, the oil stored in the casing 14 upon initial starting of the vehicle is predetermined so as to have a level C as indicated by a broken line in Fig. 3, which is below the speed reducing device 16 and the differential gear device 18. This arrangement is effective to reduce the energy loss which would be caused by the agitation of the lubricating oil by the rotating members of the power transmission system, leading to a further increased travel distance of the vehicle per one battery charging. However, the present lubricating device may be modified such that portions of the speed reducing device 16 and the differential gear device 18 are subject to the oil bath lubrication, namely, such that these devices are partially immersed in the lubricating oil bath at the bottom of the casing 14 before the lubricating oil is partly accumulated in the accumulator 60. In the present lubricating device, the lubricating oil in the accumulator 60 is forced to be discharged due to the movement of the piston 64 in the biasing direction of the spring 62 when the oil pressure in the branch oil passage 53 becomes lower than that in the accumulator 60. Unlike the oil reservoir 52 in the lubricating device of the preceding general device design wherein the accumulated oil drops by gravity from the oil reservoir 52 through the drain port 54, the present accumulator 60 has a freedom in setting the rate of discharge flow of the oil from the accumulator 60 since the rate of the discharge flow is adjusted as desired by varying the cross-sectional area of the orifice 70. Further, there is less limitation in determining the location of the accumulator 60, as compared with the general lubricating device wherein the oil reservoir 52 is required to be located above the power transmission system. Referring next to Fig. 5, there is shown a lubricating device according to a second embodiment of the present invention. In the discharge line 68 of the lubricating device of Fig. 5, there is provided with a solenoid-operated valve 80 (hereinafter referred to as "solenoid valve") in place of the orifice 70 in the first embodiment of Fig. 3. The solenoid valve 80 is selectively placed in an open position and in a closed position under the control of a controller 82. When the solenoid valve 80 is placed in the open position, the lubricating oil stored in the accumulator 60 is allowed to be fed into the branch oil passage 53 via the discharge line 68 so as to lubricate the lubricating points in the power transmission system when the amount of oil delivered by the gear pump 46 is not sufficient to lubricate the lubricating points. The controller 82 is principally constituted by a microcomputer incorporating a CPU (central processing unit), a ROM (read-only memory) and a RAM (random-access memory). The controller 82 receives an output signal of a speed sensor 84, which indicates a rotating speed of the motor shaft 20 of the drive motor 10, and an output signal of an accelerator position sensor 86 such as a potentiometer, which indicates an operating amount  of an accelerator pedal provided on the vehicle. The detected rotating speed of the motor shaft 20 is used to obtain a running speed V of the vehicle. Based on the obtained vehicle speed V and the detected operating amount , the controller 82 determines whether the lubricating points suffer from the shortage of the lubricating oil. If it is determined that the lubricating points suffer from the shortage of the oil, the controller 82 outputs a drive signal SD for placing the solenoid valve 80 in the open position so as to permit the lubricating oil stored in the accumulator 60 to be discharged therefrom into the branch oil passage 53 via the discharge line 68 for lubricating the lubricating points. In the present embodiment, the solenoid valve 80 serves as valve means for permitting or inhibiting the discharge flow of the lubricating oil from the accumulator 60 while the controller 82 serves as valve control means for controlling the solenoid valve 80 to be selectively placed in the open and closed positions. Further, the vehicle speed V and the operating amount  of the accelerator pedal detected by the respective sensors are information necessary for determining whether the lubricating points suffer from the shortage of the oil. It is noted that the operating amount  of the accelerator pedal corresponds to a load applied to the power transmission system, since the torque of the drive motor 10 is controlled depending on the operating amount  of the accelerator pedal. Referring to a flow chart of Fig. 6, there is shown a routine executed by the controller 82 for controlling the solenoid valve 80 to be selectively placed in the open and closed positions. The routine is initiated with step S1 to determine whether or not the solenoid valve 80 is in the closed position, based on whether the drive signal SD is present or not. If the solenoid valve 80 is in the closed position, an affirmative decision (YES) is obtained and the control flow goes to step S2 to determine whether or not the vehicle speed V is lower than a first threshold VA. If an affirmative decision (YES) is obtained in step S2, step S3 is implemented to determine whether or not the operating amount  of the accelerator pedal is larger than a first threshold A. If the amount  is larger than the first threshold A, step S3 is followed by step S4 in which the controller outputs the drive signal SD so as to place the solenoid valve 80 in the open position. When the vehicle speed V is lower than the first threshold VA and the operating amount  of the accelerator pedal is larger than the first threshold A, in other words, when the vehicle is running at a relatively low speed with the accelerator pedal depressed by a considerable amount, the power transmission system is subject to a relatively large load. In this state, for example, immediately after starting of the vehicle, a large amount of the lubricating oil is required for lubricating the lubricating points while the delivery amount of the gear pump 46 is insufficient. Accordingly, the controller 82 operates the solenoid valve 80 to be placed in the open position, permitting the lubricating oil stored in the accumulator 60 to be discharged therefrom and supplied to the lubricating points via the discharge line 68 and the branch oil passage 53. On the other hand, if a negative decision (NO) is obtained in step S1, i.e., if the solenoid valve 80 is in the open position, the control flow goes to step S5 to determine whether or not the vehicle speed V is larger than a second threshold VB. If the vehicle speed V is larger than VB, this means that the power transmission system is adequately lubricated by the lubricating oil delivered by the gear pump 46, and therefore, the control flow goes to step S7 wherein the controller 82 terminates the output of the drive signal SD, to close the solenoid valve 82 for inhibiting the discharge flow of the lubricating oil from the accumulator 60. If a negative decision (NO) is obtained in step S5, i.e., if the vehicle speed V is not larger than the second threshold VB, step S5 is followed by step S6 to determine whether or not the operating amount  of the accelerator pedal is smaller than a second threshold B. If the amount  is smaller than B, it means that the load acting on the power transmission system is not large, and accordingly, the control flow goes to step S7 to place the solenoid valve 80 in the closed position to inhibit the discharge flow of the lubricating oil from the accumulator 60. It is noted that the second threshold VB is set at a value larger than the first threshold VA while the second threshold B is set at a value lower than the first threshold A. In the lubricating device according to the present embodiment, the solenoid valve 80 is opened for allowing the lubricating oil to be discharged from the accumulator 60 when the lubricating points suffer from the shortage of the lubricating oil. Thus, this arrangement permits more effective utilization of the lubricating oil stored in the accumulator 60 for lubricating the power transmission system, as compared with the lubricating device of the preceding embodiment of Fig. 3, whereby the bearing portions and the gears of the power transmission system are protected against seizure, wearing or damages resulting from the shortage of the lubricating oil, so as to assure a further prolonged service life of the components of the power transmission system. In the present embodiment, the solenoid valve 80 is opened when the vehicle speed V is smaller than the predetermined first threshold VA and the operating amount  of the accelerator pedal is larger than the predetermined first threshold A. However, the solenoid valve 80 may be opened according to a suitable data map for opening or closing the valve 80 depending upon the parameters V and , so as to permit highly accurate control of the solenoid valve 80. Alternatively, the solenoid valve 80 may be controlled by using suitable parameters other than V and .

Claims: A lubricating device for a motor vehicle including (a) a power transmission system (16, 18, 38, 40) having rotating members which are all at rest upon stopping of the vehicle, (b) a casing (14) which accommodates said power transmission system and which stores a lubricating oil in a bottom portion thereof, (c) a mechanical oil pump (46) which is driven by said power transmission system and which operates to deliver said lubricating oil from said bottom portion of said casing to lubricating points of said power transmission system, for effecting forced-feed lubrication of said power transmission system, (d) an oil reservoir (60, 78) having an oil chamber for storing said lubricating oil delivered by said mechanical pump, (e) a discharge line (68) through which said lubricating oil stored in said oil chamber of said oil reservoir is discharged to said lubricating points of said power transmission system, and (f) flow restricting means (70, 80) for restricting a flow of said lubricating oil discharged from said oil reservoir through said discharge line, said lubricating device being characterized in that said oil reservoir (60, 78) includes movable means (64, 74) for partially defining said oil chamber, and biasing means (62, 76) for biasing said movable means toward said oil chamber so that said lubricating oil is discharged from said oil chamber to said lubricating points through the flow-restricting means (70, 80), to effect forced-feed lubrication of said power transmission system (16, 18, 38, 40) even after said mechanical oil pump (46) has been turned off with said motor vehicle being stopped. A lubricating device for a motor vehicle according to claim 1, further comprising a forced-feed oil passage (50) connecting said mechanical oil pump (46) and said lubricating points, and wherein said discharge line (68) is connected to said forced-feed oil passage, to effect forced-feed lubrication of said power transmission system by the lubricating oil discharged from said oil reservoir (60, 78). A lubricating device for a motor vehicle according to claim 1 or 2, wherein said flow restricting means comprises an orifice (70) having a constant cross sectional area for restricting a rate of flow of said lubricating oil through said discharge line (68). A lubricating device for a motor vehicle according to any of claims 1 to 3, wherein said oil reservoir is an accumulator (60) having a piston (64) as said movable means which partially defines said oil chamber and which is biased by said biasing means toward said oil chamber. A lubricating device for a motor vehicle according to any of claims 1 to 3, wherein said oil reservoir is an accumulator (78) having a diaphragm (74) as said movable means which partially defines said oil chamber and a gas chamber (76) filled with a gas, said diaphragm being biased by a pressure of said gas toward said oil chamber, said pressure of said gas functioning as said biasing means. A lubricating device for a motor vehicle according to any of claims 1, 2 and 4, wherein said flow restricting means comprises valve means (80) which is selectively placed in an open position and a closed position for permitting and inhibiting a discharge flow of said lubricating oil from said oil reservoir (60) through said discharge line (68), respectively, said lubricating device further including: valve control means (82) for receiving information indicating whether an amount of said lubricating oil delivered to said lubricating point is insufficient, determining, on the basis of said information, whether or not said lubricating points suffer from shortage of said lubricating oil, and placing said valve means (80) in said open position if the amount of the lubricating oil delivered to said lubricating points is insufficient. A lubricating device for a motor vehicle according to claim 6, further comprising detector means (84, 86) for detecting at least one parameter which indicates a load acting on said power transmission system. A lubricating device for a motor vehicle according to claim 7, wherein said detector means comprises a sensor (84) for detecting an input speed of said power transmission system (16, 18, 38, 40). A lubricating device for a motor vehicle according to claim 7, wherein said detector means comprises a sensor (86) for detecting an operating amount of an accelerator pedal of said vehicle.

Inventors: INOUE DAISUKE, ITO HIROSHI, YASUE HIDEKI, INOUE, DAISUKE, ITO, HIROSHI, YASUE, HIDEKI
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1995
Main classification: F16H57
IPC codes: F16H57