Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on... – Fluid pressure actuator for adjustment of member
Reexamination Certificate
2000-08-21
2002-03-19
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
Fluid pressure actuator for adjustment of member
C474S018000, C477S039000
Reexamination Certificate
active
06358167
ABSTRACT:
The invention relates to a method of improving the efficiency of a continuously variable chain-belt transmission with two pairs of conically tapered disks and a chain belt transmitting torque of a variable magnitude from one to the other of the pairs of conically tapered disks. The chain belt is held tight by compressive contact with the conically tapered disks, with a belt-tightening contact pressure being applied to both pairs of disks dependent on the magnitude of the torque to be transmitted. A ratio-controlling pressure is applied to either one or the other of the pairs of conical disks dependent on a transmission ratio to be set. A pump pressure is generated by a pump and regulated to a pressure level that exceeds the ratio-controlling pressure by a preset amount and at least equals the belt-tightening contact pressure. A ratio-controlling valve device, responsive to a ratio-controlling current that is variable in a continuous range extending above and below a neutral value, directs the ratio-controlling pressure to one of the pairs of conical disks when the ratio-controlling current is above the neutral value and to the other of the pairs of conical disks when the ratio-controlling current is below the neutral value.
The invention further relates to a continuously variable chain-belt transmission with two pairs of conically tapered disks and a chain belt transmitting torque from one to the other of the pairs of conically tapered disks. The chain belt is held tight by compressive contact with the conically tapered disks. Each of the pairs of disks, has a first piston/cylinder unit energized by a belt-tightening contact pressure and a second piston/cylinder unit energized by a ratio-controlling pressure. A ratio-controlling valve device directs the ratio-controlling pressure to one or the other of the second piston/cylinder units in response to a ratio-controlling current, so that the ratio-controlling pressure is directed to one of the pairs of conical disks when the ratio-controlling current is above a neutral value and to the other of the pairs of conical disks when the ratio-controlling current is below the neutral value. The transmission also has a torque-sensor device controlling the belt-tightening pressure dependent on the magnitude of the torque to be transmitted. A pump generates a pump pressure, with an offset-pressure valve regulating the pump pressure to a pressure level that exceeds the ratio-controlling pressure by a preset amount and at least equals the belt-tightening contact pressure. An electronic control device equipped with sensors is used to monitor certain operational parameters of the transmission and to regulate the ratio-controlling current so that a transmission ratio is set according to a predetermined functional relationship between the operational parameters and the transmission ratio.
A continuously variable chain-belt transmission that fits the foregoing generic description is known, e.g., from DE 19546294 A1. As an important concept in this kind of a transmission, the conical disks of each disk pair are pushed against the chain belt by a force whose magnitude depends on the torque being transmitted by the transmission. The benefit derived from this concept is that the compressive forces gripping the chain belt are in each case only as large as is necessary for slip-free operation. This increases the useful lifetime of the transmission and cuts down on the power consumption of the pump that supplies the pressure required to generate the compressive belt-gripping forces. The transmission ratio is shifted by means of a ratio-controlling valve that selectively increases the pressure at one or the other of the disk pairs. The disks of the pair receiving the increased pressure will be pushed axially closer together while the disks of the other pair will be pushed farther apart by the chain belt, the result being a change of the transmission ratio.
The ratio-controlling valve is controlled by a ratio-controlling current which, in general, is the sum of a pre-biased component and a variable control component. The level of the ratio-controlling current where neither of the two pairs of conical disks is supplied with ratio-controlling pressure is of critical importance for the degree of efficiency or, expressed in another way, the power losses of the continuously variable chain-belt transmission. For example, when a vehicle equipped with a continuously variable chain-belt transmission is waiting at a traffic light, the disk pairs should be in their neutral position, i.e., no ratio-controlling pressure should be applied to either of the disk pairs. If this is not the case, the hydraulic system or, more specifically, the pressure-generating pump will consume more power than necessary. If furthermore the vehicle has a start-up clutch arranged on the output side of the continuously variable chain-belt transmission, the friction-based power losses in the idling transmission will cause an additional increase in fuel consumption.
The neutral value of the ratio-controlling current, i.e., the amount of current at which the ratio-controlling valve device is not directing any ratio-controlling pressure to either of the two disk pairs, is usually determined the first time the transmission is run in the test stand and stored in a memory of the electronic control unit of the transmission. However, due to manufacturing tolerances, wear, system drift and other changes affecting the operational parameters of the transmission and its control unit over the course of its operating life, the neutral value of the ratio-controlling current will change. As discussed above, the change in the neutral value of the ratio-controlling current over time has negative consequences for the efficiency of the transmission.
OBJECT OF THE INVENTION
Based on the observation that the change in the neutral value of the ratio-controlling current over time is a root cause of efficiency losses in the transmission, the present invention aims to solve the problem of the efficiency losses by eliminating the root cause.
SUMMARY OF THE INVENTION
To meet the objective just stated, the invention provides a method of improving the efficiency of a continuously variable chain-belt transmission with two pairs of conically tapered disks and a chain belt transmitting torque of a variable magnitude from one to the other of the pairs of conically tapered disks. The chain belt is held tight by compressive contact with the conically tapered disks, with a belt-tightening contact pressure being applied to both pairs of disks dependent on the magnitude of the torque to be transmitted. A ratio-controlling pressure is applied to either one or the other of the pairs of conical disks dependent on a transmission ratio to be set. A pump pressure is generated by a pump and regulated to a pressure level that exceeds the ratio-controlling pressure by a preset amount and at least equals the belt-tightening contact pressure. A ratio-controlling valve device, responsive to a ratio-controlling current that is variable in a continuous range extending above and below a neutral value of the ratio-controlling current, directs the ratio-controlling pressure to one of the pairs of conical disks when the ratio-controlling current is above the neutral value and to the other of the pairs of conical disks when the ratio-controlling current is below the neutral value. The method according to the invention has the following steps:
a) certain relevant operational parameters of the transmission are monitored while the transmission is in actual use;
b) the neutral value of the ratio-controlling current is updated based on the values of the monitored operational parameters.
According to the invention, the neutral value of the ratio-controlling current is updated during the actual use of the transmission. This assures that when the situation calls for a neutral operating mode of the transmission, the ratio-controlling valve does in fact receive a ratio-controlling current of the correct neutral value, so that neither of the two conical disk
Holtmann Ludger
Reuschel Michael
Bucci David A.
Charles Marcus
LuK Lamellen und Kupplungsbau GmbH
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